Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET). Polyesters include naturally-occurring chemicals, such as in the cutin of plant cuticles, as well as synthetics such as polycarbonate and polybutyrate.

Polyesters may be produced in numerous forms such as fibers, sheets and three-dimensional shapes. Polyesters as thermoplastics may change shape after the application of heat. While combustible at high temperatures, polyesters tend to shrink away from flames and self-extinguish upon ignition. Polyester fibers have high tenacity and E-modulus as well as low water absorption and minimal shrinkage in comparison with other industrial fibers.
Applications

Polyesters are the most widely used man-made fiber in the world. Woven polyester fabrics are used in consumer apparel and home furnishings such as bed sheets, bedspreads, curtains and draperies. Similarly, industrial polyesters are used in tyre reinforcements, ropes, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high energy absorption. Polyester fiberfills are also used to stuff pillows, comforters and cushion padding.

Polyester fabrics are claimed to have a "less natural" feel when compared to similarly-woven fabrics made from natural fibers (i.e. cotton in textile uses). However, polyester fabrics may exhibit other advantages over natural fabrics, such as improved wrinkle resistance. As a result, polyester fibers are sometimes spun together with natural fibers to produce a cloth with blended properties.

Close-up of a polyester shirt
Polyesters are also used to make bottles, films, tarpaulin, canoes, liquid crystal displays, holograms, filters, dielectric film for capacitors, film insulation for wire and insulating tapes. Liquid crystalline polyesters are among the first industrially-used liquid crystalline polymers. They are used for their mechanical properties and heat-resistance. These traits also important in their application as an abradable seal in jet engines.

Thermosetting polyesters are used as casting materials, and chemosetting polyester resins are used as fiberglass laminating resins and non-metallic auto-body fillers. Fiberglass-reinforced unsaturated polyesters find wide application in bodies of yachts and as body parts of cars.

Polyesters are also widely used as a finish on high-quality wood products such as guitars, pianos and vehicle / yacht interiors. Burns Guitars, Rolls Royce and Sunseeker are a few companies that use polyesters to finish their products. Thixotropic properties of spray-applicable polyesters make them ideal for use on open-grain timbers, as they can quickly fill wood grain, with a high-build film thickness per coat. Cured polyesters can be sanded and polished to a high-gloss, durable finish.

Polyester fiber properties

Mechanical properties
Energy absorption of chemical fiber reinforced plastics (impact, bending and tensile tests) Investigation of the practical requirements for measuring the energy absorption of composite materials, and development of a suitable method for carrying out such measurements. A number of dynamic testing methods for measuring the energy absorption of laminates are reviewed, including animpact bending test, repeated-impact tests, an impact tensile test, and a ram bending test. Also discussed are impact tests on plate laminates. Particular emphasis is placed in these studies on composites with a chemical fiber reinforcement. It is established that a relation exists between the quasi-static energy absorption of the fibers and the dynamic energy absorption of the composite. Composites with commercial polyester and polyamide fibers lead to the highest energy absorptions, in which case the testing apparatus has a significant effect.

Chemical properties

The polyester industry

To get an idea about coverage, importance and complexity of the polyester industry, some basic information about polyester or polyethylene terephthalate (PET) at first:

What is polyester? Polyester is a synthetic polymer made of purified terephthalic acid (PTA) or its dimethyl ester dimethyl terephthalate (DMT) and monoethylene glycol (MEG). It ranges after polyethylene and polypropylene at the third place in terms of market size.
The main raw materials are described as follows:
• Purified Terephthalic Acid – PTA – CAS-No.: 100-21-0
Synonym: 1,4 Dibenzenedicarboxylic acid,
Sum formula; C6H4(COOH)2 , mol weight: 166,13
• Dimethylterephthalate – DMT- CAS-No: 120-61-6
Synonym: 1,4 Dibenzenedicarboxylic acid dimethyl ester
Sum formula C6H4(COOCH3)2 , mol weight: 194,19
• Mono Ethylene Glycol – MEG – CAS No.: 107-21-1
Synonym: 1,2 Ethanediol
Sum formula: C2H6O2 , mol weight: 62,07
More information about polyester raw materials one can find for PTA [1],DMT [2] and MEG [3], at the webpage INCHEM "Chemical Safety Information from Intergovernmental Organizations".
To make finally a polymer of high molecular weight one needs a catalyst. The most common catalyst is antimony trioxide (or antimony tri acetate)
Antimony trioxide – ATO – CAS-No.: 1309-64-4 Synonym: non, mol weight: 291,51 Sum formula: Sb2O3
In 2008 about 10 000 t Sb2O3 are used to produce around 49 Mio t polyethylene terephthalate.
Polyester is described as follows:
Polyethylene Terephthalate CAS-No.: 25038-59-9 Synonym / abbreviations: polyester, PET, PES Sum Formula: H-[C10H8O4]-n=60-120 OH, mol unit weight: 192,17
What are the success factors of the unbroken capacity growth of polyethylene terephthalate?
• The relatively easy accessible raw materials PTA or DMT and MEG
• The very well understood and described simple chemical process of polyester synthesis
• The low toxicity level of all raw materials and side products during production and processing
• The possibility to produce PET in a closed loop at low emissions to the environment
• The outstanding mechanical and chemical properties of polyester
• The recycle ability
• The wide variety of intermediate and final products made of polyester
All these facts are making this polymer one of the key elements of our daily life.
In table 1 we see the estimated world polyester production for textile polyester, bottle polyester resin, film polyester mainly for packaging and specialty polyesters for engineering plastics, which are the main fields of application. According to this table, the world's total polyester production might exceed 50 million tons per annum before the year 2010.

Table 1: World polyester production
Market size per year
Product Type 2002 [Mio t/a] 2008 [Mio t/a]
Textile-PET 20 39
Resin, Bottle/A-PET 9 16
Film-PET 1.2 1.5
Special Polyester 1 2.5
TOTAL 31.2 49

With its production volume and product diversity, polyester ranges after polyethylene (33.5%), polypropylene (19,5%) with a market share of about 18% in third position among all plastic materials produced worldwide. The polyester production chain, and the relative polyester industry chain, will now be explained in greater detail and step by step.

Raw material producer
The raw materials PTA, DMT and MEG are mainly produced by large chemical companies which are sometimes integrated down to the crude oil refinery where p-xylene is the base material to produce PTA and liquefied petroleum gas (LPG) is the base material to produce MEG.

Large PTA producers are for instance BP, Reliance, Sinopec, SK-Chemicals, Mitsui and Eastman Chemicals. MEG production is in the hand of about 10 global players which are headed by MEGlobal a JV of DOW and PIC Kuweit followed by Sabic.

Let us assume the average production capacity of a single polyester plant is about 200 t/day: we are talking about nearly 500 polyester plants around the globe. Adding to this figure the continuously-growing polyester recycling industry, which is estimated to have processed about 3 million t polyester waste in 2007 alone (5 million T/a in 2010 estimated) and where each plant produces on average about 10 000 t/a, we have another 500 plants. This is 1000 polyester production plants, all needing specific and polyester-dedicated engineering and equipment, machinery, process technology and know-how, producing, processing and recycling polyester.
Among the world's largest polyester producers are the following companies:

Artenius, Advansa, DAK, DuPont, Eastman/Voridian, Hyosung, Huvis, Indorama, Invista, Jiangsu Sanfangxian, M&G Group, Mitsui, Mitsubishi, NanYa Plastics,Reichhold, Reliance, Rongsheng, Sabic, Teijin, Toray, Tonkun, Tuntex, Wellman, Yizheng Sinopec and Sanfanxiang.

One should notice that China's capacity to produce and process polyester in more than 500 plants is nearly half that of the world's polyester capacity meanwhile. More information about polyester in China can be found under the web site of China Chemical Fiber Economic Information Network

Polyester processing
After the first stage of polymer production in the melt phase, the product stream divides into two different application areas which are mainly textile applications and packaging applications. In figure 2 the main applications of textile and packaging polyester are listed.
Table 2: Textile and packaging polyester application list

POLYESTER-BASED POLYMER (MELT or PELLETS)


Staple fiber (PSF) Bottles for CSD, Water, Beer, Juice, Detergents
Filaments POY, DTY, FDY A-PET Film
Technical yarn and tire cord Thermoforming
Non-woven and spunbond BO-PET Biaxial oriented Film
Mono-filament Strapping
Abbreviations: PSF = Polyester Staple Fiber; POY = Partially Oriented Yarn; DTY = Draw Textured Yarn; FDY = Fully Drawn Yarn; CSD = Carbonated Soft Drink; A-PET = Amorphous Polyester Film; BO-PET = Biaxial Oriented Polyester Film; A comparable small market segment (<<> benzene -> PX -> PTA -> PET melt -> fiber / filament or bottle-grade resin. Such integrated processes are meanwhile established in more or less interrupted processes at one production site. Eastman Chemicals introduced at first the idea to close the chain from PX to PET resin with their so-called INTEGREX® process. The capacity of such horizontal, integrated productions sites is >1000 t/d and can easily reach 2500 t/d.

Besides the above mentioned large processing units to produce staple fiber or yarns, there are ten thousands of small and very small processing plants, so that one can estimate that polyester is processed and recycled in more than 10 000 plants around the globe. This is without counting all the companies involved in the supply industry, beginning with engineering and processing machines and ending with special additives, stabilizers and colors. This is a gigantic industry complex and it is still growing by 4–8% per annum, depending on the world region. Useful information about the polyester industry can be found under where a “Who is Producing What in the Polyester Industry” is gradually being developed.

source : wikipedia.org

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Polyphenylethene

Polyphenylethene IPA (IUPAC Polyphenylethene) is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is a thermoplastic substance, normally existing in solid state at room temperature, but melting if heated (for molding or extrusion), and becoming solid again when cooling off.

Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colours. It is economical and is used for producing plastic model assembly kits, license plate frames, plastic cutlery, CD "jewel" cases, and many other objects where a fairly rigid, economical plastic is desired.

History
Polystyrene was discovered in 1839 by Eduard Simon,[3] an apothecary in Berlin. From storax, the resin of Liquidambar orientalis, he distilled an oily substance, a monomer which he named styrol. Several days later Simon found that the styrol had thickened, presumably from oxidation, into a jelly he dubbed styrol oxide ("Styroloxyd"). By 1845 English chemist John Blyth and German chemist August Wilhelm von Hofmann showed that the same transformation of styrol took place in the absence of oxygen. They called their substance metastyrol. Analysis later showed that it was chemically identical to Styroloxyd. In 1866 Marcelin Berthelot correctly identified the formation of metastyrol from styrol as a polymerization process. About 80 years went by before it was realized that heating of styrol starts a chain reaction which produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (1881–1965). This eventually led to the substance receiving its present name, polystyrene. The I. G. Farben company began manufacturing polystyrene in Ludwigshafen, Germany, about 1931, hoping it would be a suitable replacement for die cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form. Polystyrene is about as strong as unalloyed aluminium, but much more flexible.

Structure
The chemical makeup of polystyrene is a long chain hydrocarbon with every other carbon connected to a Phenyl group (the name given to the aromatic ring benzene, when bonded to complex carbon substituents).

A 3-D model would show that each of the chiral backbone carbons lies at the center of a tetrahedron, with its 4 bonds pointing toward the vertices. Say the -C-C- bonds are rotated so that the backbone chain lies entirely in the plane of the diagram. From this flat schematic, it is not evident which of the phenyl (benzene) groups are angled toward us from the plane of the diagram, and which ones are angled away. The isomer where all of them are on the same side is called isotactic polystyrene, which is not produced commercially. Ordinary atactic polystyrene has these large phenyl groups randomly distributed on both sides of the chain. This random positioning prevents the chains from ever aligning with sufficient regularity to achieve any crystallinity, so the plastic has no melting temperature, Tm. But metallocene-catalyzed polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups on alternating sides. This form is highly crystalline with a Tm of 270 °C.

Solid foam

Expanded polysterene tray with tomato seedlings

Expanded polystyrene packaging material
Polystyrene's most common use is as expanded polystyrene (EPS). Expanded polystyrene is produced from a mixture of about 90-95% polystyrene and 5-10% gaseous blowing agent, most commonly pentane or carbon dioxide[4]. The solid plastic is expanded into a foam through the use of heat, usually steam.

Extruded polystyrene (XPS), which is different from expanded polystyrene (EPS), is commonly known by the trade name Styrofoam. The voids filled with trapped air give it low thermal conductivity. This makes it ideal as a construction material and it is therefore sometimes used in structural insulated panel building systems. It is also used as insulation in building structures, as molded packing material for cushioning fragile equipment inside boxes, as packing "peanuts", as non-weight-bearing architectural structures (such as pillars), and also in crafts and model building, particularly architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for corrugated cardboard, tradenamed Foamcore. A more unexpected use for the material is as a lightweight fill for embankments in the civil engineering industry.
Expanded polystyrene used to contain CFCs, but other, more environmentally-safe blowing agents are now used. Because it is an aromatic hydrocarbon, it burns with an orange-yellow flame, giving off soot, as opposed to non-aromatic hydrocarbon polymers such as polyethylene, which burn with a light yellow flame (often with a blue tinge) and no soot.

Production methods include sheet stamping (PS) and injection molding (both PS and HIPS).
The density of expanded polystyrene varies greatly from around 25 kg/m³ to 200 kg/m³ depending on how much gas was admixed to create the foam. A density of 200 kg/m³ is typical for the expanded polystyrene used in surfboards.

Standard markings
The resin identification code symbol for polystyrene, developed by the Society of the Plastics Industry so that items can be labeled for easy recycling, is . However, the majority of polystyrene products are currently not recycled because of a lack of suitable recycling facilities. Furthermore, when it is "recycled," it is not a closed loop — polystyrene cups and other packaging materials are usually recycled into fillers in other plastics, or other items that cannot themselves be recycled and are thrown away.

Copolymers

Structure of expanded polystyrene (microscope)
Pure polystyrene is brittle, but hard enough that a fairly high-performance product can be made by giving it some of the properties of a stretchier material, such as polybutadiene rubber. The two such materials can never normally be mixed because of the amplified effect of intermolecular forces on polymer insolubility (see plastic recycling), but if polybutadiene is added during polymerization it can become chemically bonded to the polystyrene, forming a graft copolymer which helps to incorporate normal polybutadiene into the final mix, resulting in high-impact polystyrene or HIPS, often called "high-impact plastic" in advertisements. One commercial name for HIPS is Bextrene. Common applications include use in toys and product casings. HIPS is usually injection molded in production. Autoclaving polystyrene can compress and harden the material.

Acrylonitrile butadiene styrene or ABS plastic is similar to HIPS: a copolymer of acrylonitrile and styrene, toughened with polybutadiene. Most electronics cases are made of this form of polystyrene, as are many sewer pipes. ABS pipes may become brittle over time. SAN is a copolymer of styrene with acrylonitrile and SMA one with maleic anhydride. Styrene can be copolymerized with other monomers; for example, divinylbenzene for cross-linking the polystyrene chains.

Cutting and shaping

Expanded polystyrene
Expanded polystyrene is very easily cut with a hot-wire foam cutter, which is easily made by a heated taut length of wire, usually nichrome because of nichrome's resistance to oxidation at high temperatures and its suitable electrical conductivity. The hot wire foam cutter works by heating the wire to the point where it can vaporize foam immediately adjacent to it. The foam gets vaporized before actually touching the heated wire, which yields exceptionally smooth cuts.

Polystyrene, shaped and cut with hot wire foam cutters, is used in architecture models, actual signage, amusement parks, movie sets, airplane construction, and much more. Such cutters may cost just a few dollars (for a completely manual cutter) to tens of thousands of dollars for large CNC machines that can be used in high-volume industrial production.

Polystyrene can also be cut with a traditional cutter. In order to do this without ruining the sides of the blade one must first dip the blade in water and cut with the blade at an angle of about 30º. The procedure has to be repeated multiple times for best results.

Polystyrene can also be cut on 3 and 5-axis routers, enabling large-scale prototyping and model-making. Special polystyrene cutters are available that look more like large cylindrical rasps.

Use in biology
Petri dishes and other containers such as test tubes, made of polystyrene, play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post molding, either by irradiation or treatment with ethylene oxide. Post mold surface modification, usually with oxygen rich plasmas, is often done to introduce polar groups. Much of modern biomedical research relies on the use of such products; they therefore play a critical role in pharmaceutical research.

Finishing
In the United States, environmental protection regulations prohibit the use of solvents on polystyrene (which would dissolve the polystyrene and de-foam most of foams anyway).
Some acceptable finishing materials are
• Water-based paint (artists have created paintings on polystyrene with gouache)
• Mortar or acrylic/cement render, often used in the building industry as a weather-hard overcoat that hides the foam completely after finishing the objects.
• Cotton wool or other fabrics used in conjunction with a stapling implement.
[edit] Dangers and fire hazard
Benzene, a material used in the production of polystyrene, is a known human carcinogen. Moreover, butadiene and styrene (in ABS), when combined, become benzene-like in both form and function.[citation needed]

The EPA claims
"Styrene is primarily used in the production of polystyrene plastics and resins. Acute (short-term) exposure to styrene in humans results in mucous membrane and eye irritation, and gastrointestinal effects. Chronic (long-term) exposure to styrene in humans results in effects on the central nervous system (CNS), such as headache, fatigue, weakness, and depression, CSN dysfunction, hearing loss, and peripheral neuropathy. Human studies are inconclusive on the reproductive and developmental effects of styrene; several studies did not report an increase in developmental effects in women who worked in the plastics industry, while an increased frequency of spontaneous abortions and decreased frequency of births were reported in another study. Several epidemiologic studies suggest there may be an association between styrene exposure and an increased risk of leukemia and lymphoma. However, the evidence is inconclusive due to confounding factors. EPA has not given a formal carcinogen classification to styrene."

Polystyrene is classified according to DIN4102 as a "B3" product, meaning highly flammable or "easily ignited". Consequently, though it is an efficient insulator at low temperatures, it is prohibited from being used in any exposed installations in building construction as long the material is not flame retarded e.g. with hexabromocyclododecane. It must be concealed behind drywall, sheet metal or concrete. Foamed plastic materials have been accidentally ignited and caused huge fires and losses. Examples include the Düsseldorf International Airport, the Channel tunnel, where it was inside a railcar and caught on fire, and the Browns Ferry Nuclear Power Plant, where fire reached through a fire retardant, reached the foamed plastic underneath, inside a firestop that had not been tested and certified in accordance with the final installation. In addition to fire hazard, substances that contain acetone (such as most aerosol paint sprays), and cyanoacrylate glues can dissolve polystyrene.

Environmental concerns and bans
Expanded polystyrene is not easily recyclable because of its light weight and low scrap value. It is generally not accepted in curbside programs. Expanded polystyrene foam takes 900 years to decompose in the environment[citation needed] and has been documented to cause starvation in birds and other marine wildlife.[citation needed] According to the California Coastal Commission, it is a principal component of marine debris. Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste environmentalist organizations, like Californians Against Waste.

The city of Berkeley, California was one of the first cities in the world to ban polystyrene food packaging (called Styrofoam in the media announcements). It was also banned in Portland, OR, and Suffolk County, NY in 1990. Now, over 20 US cities have banned polystyrene food packaging, including Oakland, CA on Jan 1st 2007. San Francisco introduced a ban on the packaging on June 1 2007

"This is a long time coming. Polystyrene foam products rely on nonrenewable sources for production, are nearly indestructible and leave a legacy of pollution on our urban and natural environments. If McDonald's could see the light and phase out polystyrene foam more than a decade ago, it's about time San Francisco got with the program." Board of Supervisors President, Aaron Peskin

The overall benefits of the ban in Portland have been questioned,as have the general environmental concepts of the use of paper versus polystyrene. A campaign to achieve the first ban of polystyrene foam from the food & beverage industry in Canada has been launched in Toronto as of January 2007, by local non-profit organization NaturoPack.

The California and New York legislatures are currently considering bills which would effectively ban expanded polystyrene in all takeout food packaging state-wide.

Explosives
Polystyrene is used in some polymer-bonded explosives:
Some Polystyrene PBX Examples
Name Explosive Ingredients Binder Ingredients Usage
PBX-9205 RDX 92%
Polystyrene 6%; DOP 2%
PBX-9007 RDX 90%
Polystyrene 9.1%; DOP 0.5%; resin 0.4%
It is also a component of Napalm and a component of most designs of hydrogen bombs.
[edit] Cleaning
Polystyrene can be dishwashed at 70 °C without deformation since it has a glass transition temperature of 95 °C

References
1. ^ International Labour Organisation chemical safety card for polystyrene
2. ^ A.K. van der Vegt & L.E. Govaert, Polymeren, van keten tot kunstof, ISBN 90-407-2388-5
3. ^ The history of plastics
4. ^ process plastics Moulding Expanded Polystyrene
5. ^ Expanded polystyrene civil engineering products for roads, bridges and culverts: Vencel Resil
6. ^ Jed Norton. "Blue Foam, Pink Foam and Foam Board". Antenociti's Workshop. Retrieved on 2008-01-29.
7. ^ Styrene | Technology Transfer Network Air Toxics Web site | US EPA
8. ^ "Business Gives Styrofoam a Rare Redemption.", Stockton Record (21 September 2007). Retrieved on 2007-10-09.
9. ^ The Berkeley Daily Planet
10. ^ Styrofoam food packaging banned in Oakland
11. ^ Californians Against Waste website
12. ^ San Francisco Chronical article, June 28, 2006
13. ^ San Francisco Chronical article, November 7, 2006
14. ^ San Francisco Chronical Article, June 27, 2006
15. ^ Eckhardt, Angela (November, 1998). "Paper Waste: Why Portland's Ban on Polystyrene Foam Products Has Been a Costly Failure". Cascade Policy Institute. Retrieved on 2007-10-23.
16. ^ Thomas, Robert A. (March 8, 2005). "Where Might We Look for Environmental Heroes?". Center for Environmental Communications, Loyola University, New Orleans. Retrieved on 2007-10-23.
17. ^ Naturopack Campaign Page
18. ^ AB 904

source : wikipedia.org

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Soal dan Jawaban UAS Karet dan Plastik

1. Natural polymers are available in nature. Could you write several examples of natural polymers and their applications (UAS no 1 090824)

Jawab:

Silk: is applied mainly for expensive textiles
Natural rubber: is applied for many different industrial application such as tires, gaskets, belts etc
Wool: is applied mainly for textiles, jackets and winter clothes
Wood: is applied for furniture, timber and construction
Celluloses: are applied for paper, food etc
Starches: are applied for food and recently it is used for fuel as well
Proteins: are mainly for food
etc

2. When thermal energy is applied on polymer materials, they will show two different effects that are thermoplastic and thermosetting polymers. Could you explain what thermoplastic and thermosetting are and what is the different between them? (UAS no 2 090824)
Thermoplastic polymers: They can be softened or plasticized repeatedly on application of thermal energy, without much change in properties if treated with certain precautions, e.g. polyolefins, polystyrene, nylons, linear polyesters and polyethers, poly vinyl chloride, etc. They normally remain soluble and fusible after many cycles of heating and cooling. Thermoplastic polymers can normally be recycled.

Thermosetting polymers: They can be obtained in soluble and fusible forms in early or intermediate stages of theirs synthesis, but they get set or cured and become insoluble and infusible when further heated or thermally treated, the curing or setting process involves chemical reactions leading to further growth and cross linking of the polymer chain molecules and producing giant molecules, e.g. phenolic resins, urea/melamine resins, epoxy resins, diene rubbers, unsaturated polyesthers, etc.. Thermosetting polymers cannot normally be recycled.


3. Could you explain different kind of plastics and their application in the daily life? (UAS no 3 090824)
Polyethylene: is widely used in daily life such as moulded or formed objects, films, sheets, bottles and containers, pipes and tubes, and in wire insulation and cables.
Polypropylene: is used in the form of moulded and formed objects, sheets and films, bristles, monofilaments and fibres, covering such items as luggage, frames containers and different packaging items, ropes, textiles, tows and nets, pipes and tubes, etc
Polystyrene is used in packaging and shock absorbing application, in thermal insulation, and as acoustic improvers in hall and auditoria
Polymethil methacrylate is used for automotive tail lamp and signal light lenses, jewellery, lense of optical equipment and contact lenses
Polyvinylchloride is used in chemical plants and equipments, storage tanks, building items, pipes, sheets, specific moulded objects and containers
Dst


4. Could you explain advantages and disadvantages of both natural and synthetic rubbers? Please, write down several examples of synthetic rubbers? (UAS no 4 090824)
Natural rubber:
Advantages:
• Flexible
• Elastic
• Environmental friendly (biodegradable)
• Raw material is easy to get
Disadvantages:
• Normally weaker then synthetic rubber
• Less consistent due to the season and place
• More expensive
• Easy to react

Synthetic rubber:

Advantages:
• Strong
• Large range of synthetic material
• Consistent
• Cheaper

Disadvantages:
• Less flexible
• less elastic
• Fracture
• Not environmental friendly (non biodegradable material)

Examples of synthetic rubbers:
Styrene Butadiene Rubber (SBR), Polychloroprene Rubber (CR), Nitrile Butadiene Rubber (NBR), Isobutyl rubber (IIR), Ethylene Propylene Diene Terpolymer (EPDM), Polysulphide rubber (PSR) dst

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Polyethylene

Polyethylene or polythene (IUPAC name poly(ethene)) is a thermoplastic commodity heavily used in consumer products (notably the plastic shopping bag). Over 60 million tons of the material are produced worldwide every year.

Description

Polyethylene is a polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer. In certain circumstances it is useful to use a structure–based nomenclature. In such cases IUPAC recommends poly(methylene). The difference is due to the opening up of the monomer's double bond upon polymerisation.

In the polymer industry the name is sometimes shortened to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognised scientifically. The ethene molecule (known almost universally by its common name ethylene) C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:

Polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.

Classification

Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight.
• Ultra high molecular weight polyethylene (UHMWPE)
• Ultra low molecular weight polyethylene (ULMWPE - PE-WAX)
• High molecular weight polyethylene (HMWPE)
• High density polyethylene (HDPE)
• High density cross-linked polyethylene (HDXLPE)
• Cross-linked polyethylene (PEX)
• Medium density polyethylene (MDPE)
• Low density polyethylene (LDPE)
• Linear low density polyethylene (LLDPE)
• Very low density polyethylene (VLDPE)

UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high density polyethylene (for example, 0.930–0.935 g/cm3). The high molecular weight results in a very tough material. UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, UHMWPE is used in a wide diversity of applications. These include can and bottle handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks and butchers' chopping boards. It competes with Aramid in bulletproof vests, under the tradenames Spectra and Dyneema, and is commonly used for the construction of articular portions of implants used for hip and knee replacements.

HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.

PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high-temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight, connection.

MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.

LLDPE is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). LLDPE has higher tensile strength than LDPE, it exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown, compared with LDPE, with better environmental stress cracking resistance but is not as easy to process. LLDPE is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. Cable covering, toys, lids, buckets, containers and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency.

LDPE is defined by a density range of 0.910–0.940 g/cm3. LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.

VLDPE is defined by a density range of 0.880–0.915 g/cm3. VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers.

Recently much research activity has focused on the nature and distribution of long chain branches in polyethylene. In HDPE a relatively small number of these branches, perhaps 1 in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.

Ethylene copolymers

In addition to copolymerization with alpha-olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product is ethylene-vinyl acetate copolymer, or EVA, widely used in athletic-shoe sole foams) and a variety of acrylates (applications include packaging and sporting goods).

History

Polyethylene was first synthesized by the German chemist Hans von Pechmann who prepared it by accident in 1898 while heating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy, substance that he had created they recognized that it contained long -CH2- chains and termed it polymethylene.

The first industrially practical polyethylene synthesis was discovered (again by accident) in 1933 by Eric Fawcett and Reginald Gibson at the ICI works in Northwich, England. Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde they again produced a white, waxy, material. Because the reaction had been initiated by trace oxygen contamination in their apparatus the experiment was, at first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939.

Subsequent landmarks in polyethylene synthesis have revolved around the development of several types of catalyst that promote ethylene polymerization at more mild temperatures and pressures. The first of these was a chromium trioxide-based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are used in industrial practice.

By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for HDPE production. Phillips initially had difficulties producing a HDPE product of uniform quality and filled warehouses with off-specification plastic. However, financial ruin was unexpectedly averted in 1957 when the hula hoop, a toy consisting of a circular polyethylene tube, became a fad among youth in the United States.

A third type of catalytic system, one based on metallocenes, was discovered in 1976 in Germany by Walter Kaminsky and Hansjörg Sinn. The Ziegler and metallocene catalyst families have since proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low-density polyethylene and linear low-density polyethylene. Such resins, in the form of fibers like Dyneema, have (as of 2005) begun to replace aramids in many high-strength applications.

Until recently the metallocenes were the most active single-site catalysts for ethylene polymerisation known—new catalysts are typically compared to zirconocene dichloride. Much effort is currently being exerted on developing new, single-site (so-called post-metallocene) catalysts that may allow greater tuning of the polymer structure than is possible with metallocenes. Recently work by Fujita at the Mitsui corporation (amongst others) has demonstrated that certain salicylaldimine complexes of Group 4 metals show substantially higher activity than the metallocenes.

Physical properties

Depending on the crystallinity and molecular weight, a melting point and glass transition may or may not be observable. The temperature at which these occur varies strongly with the type of polyethylene. For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 130 °C ((250 to 265 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (220 to 240 °F).

Most LDPE, MDPE and HDPE grades have excellent chemical resistance and do not dissolve at room temperature because of their crystallinity. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene.

Environmental issues

The wide use of polyethylene makes it an important environmental issue. Though it can be recycled, most of the commercial polyethylene ends up in landfills and in the oceans (notably the Great Pacific Garbage Patch). Polyethylene is not considered biodegradable, as it takes several centuries until it is efficiently degraded. Recently (May 2008) Daniel Burd, a 16 year old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Sphingomonas, a type of bacteria, can degrade over 40% of the weight of plastic bags in less than three months. The applicability of this finding is still a matter for the future.


References
1. ^ A Guide to IUPAC Nomenclature of Organic Compounds, Blackwell Scientific Publications, Oxford (1993).
2. ^ a b J. KAHOVEC, R. B. FOX and K. HATADA; “Nomenclature of regular single-strand organic polymers (IUPAC Recommendations 2002);” Pure and Applied Chemistry; IUPAC; 2002; 74 (10): pp. 1921–1956.
3. ^ "Winnington history in the making". This is Cheshire. Retrieved on 2006-12-05.

source : wikipedia.org

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Natural Rubber

Natural rubber is an elastic hydrocarbon polymer that naturally occurs as a milky colloidal suspension, or latex, in the sap of some plants. It can also be synthesized. The entropy model of rubber was developed in 1934 by Werner Kuhn. The scientific name for the rubber tree is Hevea brasiliensis.
Explanation

The major commercial source of natural rubber latex is the Para rubber tree, Hevea brasiliensis (Euphorbiaceae). This is largely because it responds to wounding by producing more latex. Henry Wickham gathered thousands of seeds from Brazil in 1876 and they were germinated in Kew Gardens, England. The seedlings were sent to Ceylon (Sri Lanka), Indonesia, Singapore and British Malaya. Malaya(now Malaysia) was later to become the biggest producer of rubber. Liberia and Nigeria are examples of African rubber-producing countries.

Other plants containing latex include figs (Ficus elastica), Castilla (Panama rubber tree), euphorbias, lettuce, the common dandelion and specially Taraxacum kok-saghyz (Russian dandelion) contains good quantities, Scorzonera tau-saghyz and Guayule. Although these have not been major sources of rubber, Germany attempted to use some of these sources during World War II when it was cut off from rubber supplies[citation needed]. These attempts were later supplanted by the development of synthetic rubber.

Synthetic rubbers are made by the polymerization of a single monomer or a mixture of monomers to produce polymers. These form part of a broad range of products extensively studied by polymer science and rubber technology. Examples are SBR, or styrene-butadiene rubber, BR or butadiene rubber, CR or chloroprene rubber and EPDM (ethylene-propylene-diene rubber).

History

Charles Marie de La Condamine is credited with introducing samples of rubber to the Académie Royale des Sciences of France in 1736.[1] In 1751 he presented a paper by François Fresneau to the Académie (eventually published in 1755) which described many of the properties of rubber. This has been referred to as the first scientific paper on rubber.

The first European to return to Portugal from Brazil with samples of such water-repellent rubberized cloth so shocked people that he was brought to court on the charge of witchcraft.
When samples of rubber first arrived in England, it was observed by Joseph Priestley, in 1770, that a piece of the material was extremely good for rubbing out pencil marks on paper, hence the name "rubber".

The para rubber tree initially grew in South America, where it was the main source of what limited amount of latex rubber was consumed during much of the 19th century. About 100 years ago, the Congo Free State in Africa was a significant source of natural rubber latex, mostly gathered by forced labor. After repeated efforts (see Henry Wickham) rubber was successfully cultivated in Southeast Asia, where it is now widely grown.

In India commercial cultivation of natural rubber was introduced by the British Planters, although the experimental efforts to grow rubber on a commercial scale in India were initiated as early as 1873 at the Botanical Gardens, Kolkata. The first commercial Hevea plantations in India were established at Thattekadu in Kerala in 1902.

Rubber latex.

Rubber exhibits unique physical and chemical properties. Rubber's stress-strain behavior exhibits the Mullins effect, the Payne effect and is often modeled as hyperelastic. Rubber strain crystallizes. Owing to the presence of a double bond in each and every repeat unit, natural rubber is sensitive to ozone cracking

Chemical makeup

Aside from a few natural product impurities, natural rubber is essentially a polymer of isoprene units, a hydrocarbon diene monomer. Synthetic rubber can be made as a polymer of isoprene or various other monomers. The material properties of natural rubber make it an elastomer and a thermoplastic. However it should be noted that as the rubber is vulcanized it will turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both; i.e., if it is heated and cooled, it is degraded but not destroyed.

Elasticity

In most elastic materials, such as metals used in springs, the elastic behavior is caused by bond distortions. When force is applied, bond lengths deviate from the (minimum energy) equilibrium and strain energy is stored electrostatically. Rubber is often assumed to behave in the same way, but it turns out this is a poor description. Rubber is a curious material because, unlike metals, strain energy is stored thermally.

In its relaxed state rubber consists of long, coiled-up polymer chains that are interlinked at a few points. Between a pair of links each monomer can rotate freely about its neighbour. This gives each section of chain leeway to assume a large number of geometries, like a very loose rope attached to a pair of fixed points. At room temperature rubber stores enough kinetic energy so that each section of chain oscillates chaotically, like the above piece of rope being shaken violently.

When rubber is stretched the "loose pieces of rope" are taut and thus no longer able to oscillate. Their kinetic energy is given off as excess heat. Therefore, the entropy decreases when going from the relaxed to the stretched state, and it increases during relaxation. This change in entropy can also be explained by the fact that a tight section of chain can fold in fewer ways (W) than a loose section of chain, at a given temperature (nb. entropy is defined as S=k*ln(W)). Relaxation of a stretched rubber band is thus driven by an increase in entropy, and the force experienced is not electrostatic, rather it is a result of the thermal energy of the material being converted to kinetic energy. Rubber relaxation is endothermic, and for this reason the force exerted by a stretched piece of rubber increases with temperature (metals, for example, become softer as temperature increases). The material undergoes adiabatic cooling during contraction. This property of rubber can easily be verified by holding a stretched rubber band to your lips and relaxing it.

Stretching of a rubber band is in some ways equivalent to the compression of an ideal gas, and relaxation in equivalent to its expansion. Note that a compressed gas also exhibits "elastic" properties, for instance inside an inflated car tire. The fact that stretching is equivalent to compression may seem somewhat counter-intuitive, but it makes sense if rubber is viewed as a one-dimensional gas. Stretching reduces the "space" available to each section of chain.

Vulcanization of rubber creates more disulfide bonds between chains so it makes each free section of chain shorter. The result is that the chains tighten more quickly for a given length of strain. This increases the elastic force constant and makes rubber harder and less extendable.

When cooled below the glass transition temperature, the quasi-fluid chain segments "freeze" into fixed geometries and the rubber abruptly loses its elastic properties, though the process is reversible. This is a property it shares with most elastomers. At very cold temperatures rubber is actually rather brittle; it will break into shards when struck or stretched. This critical temperature is the reason that winter tires use a softer version of rubber than normal tires. The failing rubber o-ring seals that contributed to the cause of the Challenger disaster were thought to have cooled below their critical temperature. The disaster happened on an unusually cold day.

Current sources

Close to 21 million tons of rubber were produced in 2005 of which around 42% was natural. Since the bulk of the rubber produced is the synthetic variety which is derived from petroleum, the price of even natural rubber is determined to a very large extent by the prevailing global price of crude oil[citation needed]. Today Asia is the main source of natural rubber, accounting for around 94% of output in 2005. The three largest producing countries (Indonesia, Malaysia and Thailand) together account for around 72% of all natural rubber production.

Cultivation

Rubber is generally cultivated in large plantations. See the coconut shell used in collecting latex, in plantations in Kerala. Rubber latex is extracted from Rubber trees. The economic life period of rubber trees in plantations is around 32 years – 7 years of immature phase and about 25 years of productive phase.

The soil requirement of the plant is generally well-drained weathered soil consisting of laterite, lateritic types, sedimentary types, nonlateritic red or alluvial soils.
The climatic conditions for optimum growth of Rubber tree consist of (a) Rainfall of around 250 cm evenly distributed without any marked dry season and with at least 100 rainy days per annum (b) Temperature range of about 20°C to 34°C with a monthly mean of 25°C to 28°C (c) High atmospheric humidity of around 80% (d) Bright sunshine amounting to about 2000 hours per annum at the rate of 6 hours per day throughout the year and (e) Absence of strong winds.
Many high-yielding clones have been developed for commercial planting. These clones yield more than 1,500 Kilogrammes of dry Rubber per hectare (or, over 4 tons per acre), per annum, when grown under ideal conditions

Collection

A tree woman in Sri Lanka in the process of harvesting rubber. In places like Kerala, where coconuts are in abundance, the shell of half a coconut is used as the collection container for the latex. The shells are attached to the tree via a short sharp stick and the latex drips down into it overnight. This usually produces latex up to a level of half to three quarters of the shell.

The latex can be either collected in its liquid state, in which case ammonia solution can be added to the collecting cup prior to tapping in order to prevent natural coagulation, or it can be left in the field to coagulate into a cup lump.

Latex is generally processed into either latex concentrate for manufacture of dipped goods or it can be coagulated under controlled, clean conditions using formic acid. The coagulated latex can then be processed into the higher grade technically specified block rubbers such as TSR3L or TSRCV or used to produce Ribbed Smoke Sheet grades.

Naturally coagulated rubber (cup lump) is used in the manufacture of TSR10 and TSR20 grade rubbers. The processing of the rubber for these grades is basically a size reduction and cleaning process in order to remove contamination and prepare the material for the final stage drying. The dried material is then baled and palletized for shipment.

Uses

The use of rubber is widespread, ranging from household to industrial products, entering the production stream at the intermediate stage or as final products. Tires and tubes are the largest consumers of rubber, accounting for around 56% total consumption in 2005. The remaining 44% are taken up by the general rubber goods (GRG) sector, which includes all products except tires and tubes.

Other significant uses of rubber are door and window profiles, hoses, belts, matting, flooring and dampeners (anti-vibration mounts) for the automotive industry in what is known as the "under the bonnet" products. Gloves (medical, household and industrial) are also large consumers of rubber and toy balloons, although the type of rubber used is that of the concentrated latex. Significant tonnage of rubber is used as adhesives in many manufacturing industries and products, although the two most noticeable are the paper and the carpet industry. Rubber is also commonly used to make rubber bands and pencil erasers.

Additionally, rubber produced as a fiber sometimes called elastic, has significant value for use in the textile industry because of its excellent elongation and recovery properties. For these purposes, manufactured rubber fiber is made as either an extruded round fiber or rectangular fibers that are cut into strips from extruded film. Because of its low dye acceptance, feel and appearance, the rubber fiber is either covered by yarn of another fiber or directly woven with other yarns into the fabric. In the early 1900’s, for example, rubber yarns were used in foundation garments. While rubber is still used in textile manufacturing, its low tenacity limits its use in lightweight garments because latex lacks resistance to oxidizing agents and is damaged by aging, sunlight, oil, and perspiration. Seeking a way to address these shortcomings, the textile industry has turned to Neoprene (polymer form of Chloroprene), a type of synthetic rubber as well as another more commonly used elastomer fiber, spandex (also known as elastane), because of their superiority to rubber in both strength and durability.
Hypoallergenic rubber can be made from Guayule.

Early experiments in the development of synthetic rubber also led to the invention of Silly Putty.
Natural rubber is often vulcanized, a process by which the rubber is heated and sulfur, peroxide or bisphenol are added to improve resilience and elasticity, and to prevent it from perishing. Vulcanization greatly improved the durability and utility of rubber from the 1830s on. The successful development of vulcanization is most closely associated with Charles Goodyear. Carbon black is often used as an additive to rubber to improve its strength, especially in vehicle tires.

References

1. ^ a b http://www.bouncing-balls.com/timeline/people/nr_condamine.htm
• Rubbery Materials and their Compounds by J.A Brydson
• Rubber Technology by Maurice Morton

source : wikipedia.org

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Latex

Latex refers generically to a stable dispersion (emulsion) of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic. Latex as found in nature is a milky sap-like fluid within many plants that coagulates on exposure to air. It is a complex emulsion in which proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums are found. In most plants, latex is white, but some have yellow, orange, or scarlet latex.

The word is also used to refer to natural latex rubber; particularly for non-vulcanized rubber. Such is the case in products like latex gloves, latex condoms and latex clothing. It can also be made synthetically by polymerizing a monomer that has been emulsified with surfactants.
The term latex is attributed to Charles Marie de la Condamine, who derived it from Latin latex, fluid.

Sources

The cells or vessels in which latex is found make up the laticiferous system, which forms in two very different ways. In many plants, the laticiferous system is formed from rows of cells laid down in the meristem of the stem or root. The cell walls between these cells are dissolved so that continuous tubes, called latex vessels, are formed. This method of formation is found in the poppy family, in the rubber trees (Para rubber tree and Castilla elastica), and in the Cichorieae, a section of the Family Asteraceae distinguished by the presence of latex in its members. Dandelion, lettuce, hawkweed, and salsify are members of the Cichorieae. It is also present in another member of the Asteraceae, the guayule plant.

In the milkweed and spurge families, on the other hand, the laticiferous system is formed quite differently. Early in the development of the seedling latex cells differentiate, and as the plant grows these latex cells grow into a branching system extending throughout the plant. In the mature plant, the entire laticiferous system is descended from a single cell or group of cells present in the embryo.

The laticiferous system is present in all parts of the mature plant, including roots, stems, leaves, and sometimes the fruits. It is particularly noticeable in the cortical tissues.
Several members of the fungal kingdom also produce latex upon injury. Notable are the milk-caps such as Lactarius deliciosus.

Natural function of latex

This article is missing citations or needs footnotes. Please help add inline citations to guard against copyright violations and factual inaccuracies. (May 2008)

Rubber latex

Many plant functions have been attributed to latex. Some regard it as a form of stored food, while others consider it an excretory product in which waste products of the plant are deposited. Still others believe it functions to protect the plant in case of injuries; drying to form a protective layer that prevents the entry of fungi and bacteria. Similarly, it may provide some protection against browsing animals, since in some plants latex is very bitter or even poisonous. It may be that latex fulfills all of these functions to varying degrees in the numerous plant species in which it occurs.

Uses of latex

The latex of many species can be processed to produce other materials. Natural rubber is the most important product obtained from latex; more than 12,000 plant species yield latex containing rubber, though in the vast majority of those species the rubber is not suitable for commercial use.

Balatá and gutta percha latex contain an inelastic polymer related to rubber. Latex from the chicle and jelutong trees is used in chewing gum. Poppy latex is a source of opium and its many derivatives. Latex is also used to make gloves, catheters, condoms, balloons, and many other products as well.

Latex clothing

Main article: Latex clothing. Latex is used in many types of clothing. Worn on the body (or applied directly by painting) it tends to be skin-tight, producing a "second skin" effect.

Allergic reactions

Main article: Latex allergy. Some people have a serious latex allergy, and exposure to latex products such as latex gloves can cause anaphylactic shock. Guayule latex is hypoallergenic and is being researched as a substitute to the allergy-inducing Hevea latexes. Many people with spina bifida are also allergic to natural latex rubber, as well as people who have had multiple surgeries, and people who have had prolonged exposure to natural latex.

source : wikipedia.org

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Epoxy Resin

In chemistry, epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or "hardener". Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin were made in 1927 in the United States. Credit for the first synthesis of bisphenol-A-based epoxy resins is shared by Dr. Pierre Castan of Switzerland and Dr. S.O. Greenlee of the United States in 1936. Dr. Castan's work was licensed by Ciba, Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. Ciba's epoxy business was spun off and later sold in the late 1990s and is now the advanced materials business unit of Huntsman Corporation of the United States. Dr. Greenlee's work was for the firm of Devoe-Reynolds of the United States. Devoe-Reynolds, which was active in the early days of the epoxy resin industry, was sold to Shell Chemical (now Hexion, formerly Resolution Polymers and others).

Industry

As of 2006, the epoxy industry amounts to more than US$5 billion in North America and about US$15 billion world-wide. The Chinese market has been growing rapidly, and the market size is more than 30% of the total worldwide market. It is made up of approximately 50–100 manufacturers of basic or commodity epoxy resins and hardeners of which the three largest are Hexion (formerly Resolution Performance Products, formerly Shell Development Company; whose epoxy tradename is "Epon"), The Dow Chemical Company (tradename "D.E.R."), and Huntsman Corporation's Advanced Materials business unit (formerly Vantico, formerly Ciba Specialty Chemical; tradename "Araldite"). In 2007 Huntsman Corporation agreed to merge with Hexion (owned by the Apollo Group)[1][2]. KUKDO Chemical is one of the largest epoxy manufacturers in Asia, and recently their capacity has been increased up to 210,000 MT/Y (Korea 150,000 MT/Y, China 60,000 MT/Y and will be increased totally 300,000 MT/Y by 2009). Nanya Plastic also has the capacity of over 250,000 MT/Y (Taiwan and China), which is mostly for captive use. There are over 50 smaller epoxy manufacturers primarily producing epoxies only regionally, epoxy hardeners only, specialty epoxies, or epoxy modifiers.

These commodity epoxy manufacturers mentioned above typically do not sell epoxy resins in a form usable to smaller end users, so there is another group of companies that purchase epoxy raw materials from the major producers and then compounds (blends, modifies, or otherwise customizes) epoxy systems from these raw materials. These companies are known as "formulators". The majority of the epoxy systems sold are produced by these formulators and they comprise over 60% of the dollar value of the epoxy market. There are hundreds of ways that these formulators can modify epoxies—by adding mineral fillers (talc, silica, alumina, etc.), by adding flexibilizers, viscosity reducers, colorants, thickeners, accelerators, adhesion promoters, etc. These modifications are made to reduce costs, to improve performance, and to improve processing convenience. As a result a typical formulator sells dozens or even thousands of formulations—each tailored to the requirements of a particular application or market.

The applications for epoxy-based materials are extensive and include coatings, adhesives and composite materials such as those using carbon fiber and fiberglass reinforcements (although polyester, vinyl ester, and other thermosetting resins are also used for glass-reinforced plastic). The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Many properties of epoxies can be modified (for example silver-filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating).
Epoxies find significant use in many applications which are described in following sections.

Paints and coatings

"2 part waterborne epoxy coatings" are used as ambient cure epoxy coatings. These non-HAP, two-part epoxy coatings are developed for heavy duty service on metal substrates and use less energy than heat cured powder coatings. These systems use a more attractive 4:1 by volume mixing ratio. The coating dries quickly providing a tough, UV resistant, protective coating with excellent ultimate hardness, and good mar and abrasion resistance. They are designed for rapid dry protective coating applications. Ambient cure 2 Part waterborne epoxy coatings provide excellent physical properties in exterior applications. These products have excellent adhesion to various metal substrates. Their low VOC and water clean up makes them a natural choice for factory cast iron, cast steel, cast aluminum applications and reduces exposure and flammability issues associated with solventborne coatings. They are usually used for industrial and automotive uses as they are high heat resistant (as latex-based and alkyd-based paints usually burn, thus peel, with slight high heat temperatures).

Polyester Epoxies are used as powder coatings for washers, driers and other "white goods". Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in the oil and gas industry, potable water transmission pipelines (steel), concrete reinforcing rebar, et cetera. Epoxy coatings are also widely used as primers to improve the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Metal cans and containers are often coated with epoxy to prevent rusting, especially for foods like tomatoes that are acidic. Epoxy resins are also used for high performance and decorative flooring applications especially terrazzo flooring, chip flooring and colored aggregate flooring.

Adhesives

Special epoxy is strong enough to withstand the extreme force transferred from a surfboard fin to the fin mount. This epoxy is waterproof and capable of curing underwater. The blue-coloured epoxy on the left is still undergoing curing.

Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" (which also includes polyurethane, acrylic, cyanoacrylate, and other chemistries.) These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snow boards, and other applications where high strength bonds are required. Epoxy adhesives can be developed to suit almost any application. They are exceptional adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or opaque/colored, fast setting or extremely slow setting. Epoxy adhesives are almost unmatched in heat and chemical resistance among common adhesives. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature.

Some epoxies are cured by exposure to ultraviolet light. Such epoxies are commonly used in optics, fiber optics, optoelectronics and dentistry.

Industrial tooling and composites

Epoxy systems are used in industrial tooling applications to produce molds, master models, laminates, castings, fixtures, and other industrial production aids. This "plastic tooling" replaces metal, wood and other traditional materials, and generally improves the efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. Epoxies are also used in producing fiber-reinforced or composite parts. They are more expensive than polyester resins and vinyl ester resins, but usually produce stronger and more temperature-resistant composite parts.

Electrical systems and electronics

An epoxy encapsulated hybrid circuit on a printed circuit board. Epoxy resin formulations are important in the electronics industry, and are employed in motors, generators, transformers, switchgear, bushings, and insulators. Epoxy resins are excellent electrical insulators and protect electrical components from short circuiting, dust and moisture. In the electronics industry epoxy resins are the primary resin used in overmolding integrated circuits, transistors and hybrid circuits, and making printed circuit boards. The largest volume type of circuit board — an "FR-4 board" — is a sandwich of layers of glass cloth bonded into a composite by an epoxy resin. Epoxy resins are used to bond copper foil to circuit board substrates, and are a component of the solder mask on many circuit boards.

Flexible epoxy resins are used for potting transformers and inductors. By using vacuum impregnation on uncured epoxy, winding-to-winding, winding-to-core, and winding-to-insulator air voids are eliminated. The cured epoxy is an electrical insulator and a much better conductor of heat than air. Transformer and inductor hot spots are greatly reduced, giving the component a stable and longer life than unpotted product.

Epoxy resins are applied using the technology of resin casting.

Consumer and marine applications

Epoxies are sold in hardware stores, typically as a pack containing separate resin and hardener, which must be mixed immediately before use. They are also sold in boat shops as repair resins for marine applications. Epoxies typically are not used in the outer layer of a boat because they deteriorate by exposure to UV light. They are often used during boat repair and assembly, and then over-coated with conventional or two-part polyurethane paint or marine-varnishes that provide UV protection.

There are two main areas of marine use. Because of the better mechanical properties relative to the more common polyester resins, epoxies are used for commercial manufacture of components where a high strength/weight ratio is required. The second area is that their strength, gap filling properties and excellent adhesion to many materials including timber have created a boom in amateur building projects including aircraft and boats.

Normal gelcoat formulated for use with polyester resins and polyester resins does not adhere to epoxy surfaces, though epoxy adheres very well if applied to polyester resin surfaces. "Flocoat" that is normally used to coat the interior of polyester fibreglass yachts is also compatible with epoxies.

Polyester thermosets typically use a ratio of at least 10:1 of resin to hardener (or "catalyst"), while epoxy materials typically use a lower ratio of between 5:1 and 1:1. Epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden quickly.

The classic epoxy reference guide is the Handbook of epoxy resins by Henry Lee and Kris Neville. Originally issued in 1967, it has been reissued repeatedly and still gives an excellent overview of the technology. Some basic tips are given here:www.epoxy.com/install.htm.

Aerospace applications

In the aerospace industry, epoxy is used as a structural matrix material which is then reinforced by fiber. Typical fiber reinforcements include glass, carbon, Kevlar, and boron. Epoxies are also used as a structural glue. Materials like wood, and others that are 'low-tech' are glued with epoxy resin. One example, a homebuilt aircraft, would be the RJ.03 IBIS. This design is based on a classic wooden lattice structured fuselage and a classic wooden spar, internally stiffened with foam and completely covered with plywood. Except for the plywood covering the wings, everything is glued with epoxy resin.

Wind Energy applications

Epoxy resin is used in manufacturing rotor blades of wind turbine. The resin is infused in the core material like Balsa, foam & reinforcing media glass fabric. The process is called VARTM i.e. vacuum assisted resin transfer moulding. Due to excellent properties & good finish, epoxy is most favoured resin for composites.

Chemistry

Structure of unmodified epoxy prepolymer. n denotes the number of polymerized subunits and is in the range from 0 to about 25. When epoxies are mixed with the appropriate catalyst, the resulting reaction is exothermic, and the oxygen on the epoxy monomers is "flipped." This occurs throughout the epoxy, and a matrix with a high stress tolerance is formed, and "glues" the materials together.

Cleanup

When using epoxy resin and hardener, vinegar is an effective and safe solvent to clean up tools, brushes, skin, and most surfaces. Acetone can also be used, but it is very volatile and flammable, unlike vinegar. Vinegar is safer for cleaning epoxy resin from human skin than acetone: both liquids will dissolve the resin, but the resin/acetone solution can easily pass through the skin into the bloodstream, unlike vinegar. White vinegar can even clean up epoxy resin that is beginning to cure/harden. DME (Dimethoxyethane) is also a good solvent for epoxy resin and hardener that gives off very little vapor. However, none of these substances is an effective solvent for epoxy that has cured.

Health risks

The primary risk associated with epoxy use is sensitization to the hardener, which, over time, can induce an allergic reaction. Both epichlorohydrin and bisphenol A are suspected endocrine disruptors.
According to some reports Bisphenol A is linked to the following effects in humans:
• oestrogenic activity;
• alteration of male reproductive organs;
• early puberty induction;
• shortened duration of breast feeding;
• pancreatic cancer


References

1. Steve Gelsi, "Huntsman OK's $10.6 bln takeover offer from Apollo's Hexion", Market Watch, July 12, 2007.
2. Market Participant, "Hexion IPO Creates Way Too Much Debt", June 22, 2006.
3. Chips Flooring
4. Quartz Flooring
5. Greenpeace 2006 April Report "Our reproductive health and chemical exposure"

source : wikipedia.org

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Pembuatan Nata dari Mata Buah Nenas

BAB I
PENDAHULUAN

1. Latar Belakang
Banyak sekali makanan yang dapat dihasilkan dari fermentasi bakteri Acetobacter xylinum salah satu yang banyak digunakan saat ini adalah untuk pembuatan nata. Nata adalah biomassa yang sebagian besar terdiri dari sellulosa, berbentuk agar dan berwarna putih seperti gel. Massa ini berasal dari pertumbuhan bakteri Acetobacter xylinum pada permukaan media cair yang asam dan mengandung gula (http://warintek.progressio.or.id).
Nata yang biasa kita kenal dan temui adalah nata yang terbuat dari air kelapa atau yang sering disebut dengan nata de coco. Ada pula nata de soya yang terbuat dari limbah cair pengolahan tahu (whey tahu) sebagai bahan baku utama pembuatan nata ini. Dalam bahan yang dipakai dalam pembuatan nata sendiri adalah dari kulit buah atau limbah-limbah organik yang bisa disebut sebagai sampah.
Ketika kita mengupas nenas dan mata nenas itu kita buang begitu saja, tanpa memperoleh nilai guna. Dari dasar itulah, kita ingin membuat nata dengan memanfaatkan limbah mata nenas, yang jarang sekali bermanfaat terutama untuk dikonsumsi dan hanya di buang begitu saja.
Selain sangat mudah dalam mendapatkan limbah ini, kandungan gula yang terdapat dalam mata nenas cukup tinggi,


BAB II
LANDASAN TEORI
2.1 Pengertian Nata
Kata nata berasal dari bahasa Spanyol yang berarti krim. Nata diterjemahkan ke dalam bahasa Latin sebagai 'natare' yang berarti terapung-apung. Nata dapat dibuat dari air kelapa, santan kelapa, tetes tebu (molases), limbah cair tebu, atau sari buah (nanas, melon, pisang, jeruk, jambu biji, strawberry dan lain-lain). Nata yang dibuat dari air kelapa disebut nata de coco. Di Indonesia, nata de coco sering disebut sari air kelapa atau sari kelapa. Nata de coco pertama kali berasal dari Filipina. Di Indonesia, nata de coco mulai dicoba pada tahun 1973 dan mulai diperkenalkan pada tahun 1975. Namun demikian, nata de coco mulai dikenal luas di pasaran pada tahun 1981 (Sutarminingsih, 2004).
Nata diambil dari nama tuan Nata yang berhasil menemukan nata de coco. Dari tangan tuan Nata, teknologi pembuatan nata mulai diperkenalkan kepada masyarakat luas di Philiphina. Pada saat ini, Filiphina menjadi negara nomer satu di dunia penghasil nata. Nat de coco dari Filiphina banyak diekspor ke Jepang (Warisno, 2006).
Nata de coco merupakan produk makanan yang dihasilkan dari air kelapa yang mengalami proses fermentasi dengan melibatkan bakteri Acetobacter xylinum, sehingga membentuk kumpulan biomassa yang terdiri dari selulosa dan memiliki bentuk padat, berwarna putih seperti kolang-kaling sehingga sering dikenal sebagai kolang-kaling imitasi.
(diakses dari http://jatim.litbang.deptan.go.id/).
Pemberian nama untuk nata tergantung dari bahan baku yang digunakan. Nata de pinna untuk yang berasal dari nanas, nata de tomato untuk tomat, serta nata de soya yang dibuat dari limbah tahu (diakses dari http://www.kompas.com/).


2.2 Kandungan Gizi Nata
Menurut penelitian dari Balai Mikrobiologi, Puslitbang Biologi LIPI, di dalam 100 gram nata de coco terkandung nutrisi, antara lain : kalori 146 kal; lemak 20 g; karbohidrat 36,1 mg; Ca 12 mg; Fosfor 2 mg; dan Fe 0,5 mg. Nata juga mengandung air yang cukup banyak (sekitar 80%), namun tetap dapat disimpan lama (diakses dari http://jatim.litbang.deptan.go.id).
Kandungan gizi nata yang dihidangkan dengan sirup adalah sebagai berikut: 67,7 persen air, 0,2 persen lemak, 12 mg kalsium, 5 mg zat besi, 2 mg fosfor, vitamin B1, protein, serta hanya 0,01 mikrogram riboflavin per 100 gramnya.
Beberapa tindakan fortifikasi dengan vitamin (niasin, riboflavin, vitamin B1, dan vitamin C) dan mineral (kalsium dan fosfor), telah dilakukan untuk meningkatkan nilai gizinya. Bahan-bahan tambahan ini stabil pada suhu kamar selama 11 bulan atau lebih.
Karena kandungan gizi (khususnya energi) yang sangat rendah, produk ini aman untuk dimakan oleh siapa saja. Produk ini tidak akan menyebabkan gemuk, sehingga sangat dianjurkan bagi mereka yang sedang diet rendah kalori untuk menurunkan berat badan. Keunggulan lain dari nata de coco adalah kandungan serat (dietary fiber)-nya yang cukup tinggi, terutama selulosa.
Tanpa adanya serat dalam makanan, kita akan mudah mengalami gejala sembelit atau konstipasi (susah buang air besar), wasir, penyakit divertikulosis, kanker usus besar, radang apendiks, kencing manis, jantung koroner, dan kegemukan (obesitas). Dengan adanya serat dari nata de coco atau bahan pangan lainnya, proses buang air besar menjadi teratur dan berbagai penyakit tersebut dapat dihindari.
Walaupun nata de coco rendah kandungan gizinya, cara mengonsumsi yang salah dapat menyebabkan kita menjadi gemuk. Proses menjadi gemuk tersebut tidak disebabkan oleh nata de coco itu sendiri. Penyebabnya adalah sirup yang terlalu manis atau bahan pencampur lainnya. Oleh karena itu, hindari mengonsumsi nata de coco dengan campuran sirup yang terlalu manis atau bahan-bahan lain yang kaya kalori (diakses dari http://www.kompas.com/).
2.3 Tinjauan tentang Nenas
Nanas, nenas, atau ananas (Ananas comosus (L.) Merr.) adalah sejenis tumbuhan tropis yang berasal dari Brazil, Bolivia, dan Paraguay. Tumbuhan ini termasuk dalam familia nanas-nanasan (Famili Bromeliaceae). Perawakan (habitus) tumbuhannya rendah, herba (menahun) dengan 30 atau lebih daun yang panjang, berujung tajam, tersusun dalam bentuk roset mengelilingi batang yang tebal. Buahnya dalam bahasa Inggris disebut sebagai pineapple karena bentuknya yang seperti pohon pinus. Nama 'nanas' berasal dari sebutan orang Tupi untuk buah ini: anana, yang bermakna "buah yang sangat baik". Burung penghisap madu (hummingbird) merupakan penyerbuk alamiah dari buah ini, meskipun berbagai serangga juga memiliki peran yang sama.
Buah nanas sebagaimana yang dijual orang bukanlah buah sejati, melainkan gabungan buah-buah sejati (bekasnya terlihat dari setiap 'sisik' pada kulit buahnya) yang dalam perkembangannya tergabung -- bersama-sama dengan tongkol (spadix) bunga majemuk -- menjadi satu 'buah' besar. Nanas yang dibudidayakan orang sudah kehilangan kemampuan memperbanyak secara seksual, namun ia mengembangkan tanaman muda (bagian 'mahkota' buah) yang merupakan sarana perbanyakan secara vegetatif. Di Indonesia, propinsi Lampung merupakan daerah penanaman nanas utama, dengan beberapa pabrik pengolahan nanas juga terdapat di sana.
Nenas adalah buah tropis dengan daging buah berwarna kuning memiliki kandungan air 90% dan kaya akan Kalium, Kalsium, lodium, Sulfur, dan Khlor. Selain itu juga kaya Asam, Biotin, Vitamin B12, Vitamin E serta Enzim Bromelin. Salah satu wilayah di Indonesia yang memiliki hasil agroindustri nanas yang cukup populer adalah Sumatera Selatan. Nanas merupakan komoditas unggulan di Sumatera Selatan. Nanas dihasilkan dari sekitar Palembang, yang paling terkenal adalah nanas Prabumulih yang terkenal dengan rasa manisnya, konon nanas termanis di Indonesia berasal dari daerah ini. Pada tahun 2006 produksi panen nanas di Sumatera Selatan mencapai 141.542 ton/tahun, peringkat ke tiga setelah Jawa Barat dan Lampung. Permintaan pasar dalam negeri terhadap buah nanas cenderung meningkat sejalan dengan pertumbuhan jumlah penduduk, semakin baik pendapatan masyarakat, dan semakin tinggi kesadaran penduduk tentang nilai gizi dari buah-buahan.
Nanas termasuk komoditas buah yang mudah rusak, susut, dan cepat busuk. Oleh karena itu, seusai panen memerlukan penanganan pasca panen, salah satunya dengan pengolahan. Gagasan ini terbukti menguntungkan, sebab dengan menjadi produk olahan akan diperoleh banyak keuntungan. Selain menyelamatkan hasil panen, pengolahan buah nanas juga dapat memperpanjang umur simpan, diversifikasi pangan dan meningkatkan kualitas maupun nilai ekonomis buah tersebut. Produk olahan nanas dapat berupa makanan dan minuman, seperti selai, cocktail, sirup, sari buah, keripik hingga manisan buah kering. Sari buah nanas adalah cairan yang diperoleh dari proses ekstraksi buah nanas. Sari buah tersebut terbagi dua, ada yang dapat diminum langsung dan ada yang difermentasi menjadi minuman kesehatan.
Buah nanas mengandung vitamin (A dan C), Kalsium, Fosfor, Magnesium, Besi, Natrium, Kalium, Dekstrosa, Sukrosa (gula tebu), dan Enzim Bromelain. Bromelain berkhasiat antiradang, membantu melunakkan makanan di lambung, mengganggu pertumbuhan sel kanker, menghambat agregasi platelet, dan mempunyai aktivitas fibrinolitik. Kandungan seratnya dapat mempermudah buang air besar pada penderita sembelit (konstipasi). Daun mengandung kalsium oksalat dan pectic substances.
2.4 Tinjauan tentang Mata Nenas

Nanas termasuk buah yang banyak digunakan pada beberapa industri olahan pangan seperti jam, sirup, sari buah, nektar serta buah dalam botol atau kaleng. Berbagai macam pengolahan tersebut, akan membutuhkan buah nanas dalam jumlah yang cukup besar dan selanjutnya tentu akan menghasilkan limbah dalam jumlah besar juga. Limbah buah nenas tersebut terdiri dari : limbah kulit, limbah mata, dan limbah hati. Kalau diamati bagian limbah yang terbuang ini masih memiliki bagian yang mirip dengan bagian daging buah, hanya saja bercampur dengan bagian yang tidak diinginkan. Limbah atau hasil ikutan (side product) nenas relatif hanya dibuang begitu saja. Sebenarnya peluang untuk dimanfaatkan lebih lanjut sangat mungkin.
Salah satu alternatif pemanfaatan limbah nenas yang dapat dilakukan adalah dengan pemanfaatannya menjadi produk nata de pina. Nata merupakan produk fermentasi dengan bantuan bakteri Acetobacter xylinum. Dilihat dari namanya bakteri ini termasuk kelompok bakteri asam asetat (aceto : asetat, bacter : bakteri). Jika ditumbuhkan di media cair yang mengandung gula, bakteri ini akan menghasilkan asam cuka atau asam asetat dan padatan putih yang terapung di permukaan media cair tersebut. Lapisan putih itulah yang dikenal sebagai nata. Pada dasarnya produksi nata dengan media sari buah nenas telah banyak dilakukan yakni dikenal sebagai nata de pina, tetapi dengan mencoba produksi nata dengan menumbuhkan bakteri A. xylinum pada media limbah buah nenas belum dilakukan.
Pada umumnya buah nenas memiliki bagian-bagian yang bersifat buangan, bagian-bagian tersebut yaitu tunas daun, kulit luar, mata dan hati. Untuk tunas daun tidak mungkin dimanfaatkan sebagai media nata. Pada bagian kulit yang merupakan bagian terluar, memiliki tekstur yang tidak rata, dan banyak terdapat duri-duri kecil pada permukaan luarnya. Biasanya pada bagian ini merupakan bagian yang pertama dibuang oleh masyarakat karena bagian ini tergolong bagian yang tidak dapat dikonsumsi langsung sebagai buah segar. Bagian mata merupakan bagian ke dua setelah kulit yang dibuang oleh masyarakat. Mata memiliki bentuk yang agak rata dan banyak terdapat lubang-lubang kecil menyerupai mata. Bagian terakhir yang juga merupakan bagian buangan adalah hati. Hati merupakan bagian tengah dari buah nenas, memiliki bentuk memanjang sepanjang buah nenas, memiliki tekstur yang agak keras dan rasanya agak manis. Hati nenas dapat juga dimanfaatkan dengan mengambil tepungnya. Kadar tepung hati nenas yang sudah tua berkisar antara 10% - 15% dari berat segar.
Nanas termasuk buah yang banyak digunakan pada beberapa industri olahan pangan seperti jam, sirup, sari buah, nektar serta buah dalam botol atau kaleng. Berbagai macam pengolahan tersebut, akan membutuhkan buah nanas dalam jumlah yang cukup besar dan selanjutnya tentu akan menghasilkan limbah dalam jumlah besar juga. Limbah buah nenas tersebut terdiri dari : limbah kulit, limbah mata, dan limbah hati. Kalau diamati bagian limbah yang terbuang ini masih memiliki bagian yang mirip dengan bagian daging buah, hanya saja bercampur dengan bagian yang tidak diinginkan. Limbah atau hasil ikutan (side product) nenas relatif hanya dibuang begitu saja. Sebenarnya peluang untuk dimanfaatkan lebih lanjut sangat mungkin.
Salah satu alternatif pemanfaatan limbah nenas yang dapat dilakukan adalah dengan pemanfaatannya menjadi produk nata de pina. Nata merupakan produk fermentasi dengan bantuan bakteri Acetobacter xylinum. Dilihat dari namanya bakteri ini termasuk kelompok bakteri asam asetat (aceto : asetat, bacter : bakteri). Jika ditumbuhkan di media cair yang mengandung gula, bakteri ini akan menghasilkan asam cuka atau asam asetat dan padatan putih yang terapung di permukaan media cair tersebut. Lapisan putih itulah yang dikenal sebagai nata. Pada dasarnya produksi nata dengan media sari buah nenas telah banyak dilakukan yakni dikenal sebagai nata de pina, tetapi dengan mencoba produksi nata dengan menumbuhkan bakteri A. xylinum pada media limbah buah nenas belum dilakukan.
Pada umumnya buah nenas memiliki bagian-bagian yang bersifat buangan, bagian-bagian tersebut yaitu tunas daun, kulit luar, mata dan hati. Untuk tunas daun tidak mungkin dimanfaatkan sebagai media nata. Pada bagian kulit yang merupakan bagian terluar, memiliki tekstur yang tidak rata, dan banyak terdapat duri-duri kecil pada permukaan luarnya. Biasanya pada bagian ini merupakan bagian yang pertama dibuang oleh masyarakat karena bagian ini tergolong bagian yang tidak dapat dikonsumsi langsung sebagai buah segar. Bagian mata merupakan bagian ke dua setelah kulit yang dibuang oleh masyarakat. Mata memiliki bentuk yang agak rata dan banyak terdapat lubang-lubang kecil menyerupai mata. Bagian terakhir yang juga merupakan bagian buangan adalah hati. Hati merupakan bagian tengah dari buah nenas, memiliki bentuk memanjang sepanjang buah nenas, memiliki tekstur yang agak keras dan rasanya agak manis. Hati nenas dapat juga dimanfaatkan dengan mengambil tepungnya. Kadar tepung hati nenas yang sudah tua berkisar antara 10% - 15% dari berat segar.
2.5 Bakteri Pembentuk Nata
Nata de coco merupakan hasil fermentasi air kelapa dengan bantuan mikroba Acetobacter xylinum. Gula pada air kelapa diubah menjadi asam asetat dan benang-benang selulosa. Massa ini berasal dari pertumbuhan Acetobacter xylinum pada permukaan media cair yang asam dan mengandung gula. Lama-kelamaan akan terbentuk suatu massa yang kokoh dan mencapai ketebalan beberapa sentimeter. Dengan demikian, nata de coco dapat juga dianggap sebagai selulosa bakteri yang berbentuk padat, berwarna putih, transparan, berasa manis, bertekstur kenyal, dan umumnya dikonsumsi sebagai makanan ringan
(diakses dari http://shantybio.transdigit.com/).
Acetobacter xylinum adalah genus schizomycetes dari famili pseudomonadaceae, ordo pseudomonadales, sebagai sel berbentuk elips sampai berbentuk batang, sendiri-sendiri atau berpasangan, berantai pendek atau panjang, penting karena perannya pada penyelesaian siklus karbon dan pembuatan cuka. (kamus kedokteran Dorland, 1996)
Dalam bakteri tersebut tumbuh dan berkembang dengan derajat keasaman atau pH 3-4. Mikroba yang aktif dalam pembuatan nata adalah bakteri pembentuk asam asetat yaitu Acetobacter xylinum. Mikroba ini dapat merubah gula menjadi selulosa. Jalinan selulosa inilah yang membuat nata terlihat putih. Tahap-tahap yang perlu dilakukan dalam pembuatan nata adalah persiapan media, starter, inokulasi, fermentasi atau pengeraman, pemanenan, penghilangan asam dan pengawetan. Komposisi media yang digunakan untuk pengawetan. Komposisi media yang digunakan untuk starter adalah sama dengan media untuk pemeliharaan kultur tetapi tanpa media agar (Warisno, 2005)
Pertumbuhan bakteri Acetobacter Xylinum dipengaruhi oleh berbagai factor, misalnya tingkat keasaman medium, suhu fermentasi, lama fermentasi, sumber nitrogen, sumber karbon, konsentrasi starter (bibit). Aktivitas pembentukan nata hanya terjadi pada kisaran pH 3,5-7,5. Asam asetat glacial yang ditambahkan ke dalam medium dapat berfungsi menurunkan pH medium hingga tercapai pH optimal, yaitu sekitar 4. Sementara, suhu yang memungkinkan nata dapat terbentuk dengan baik adalah suhu kamar, yang berkisar antara 280C-320C.
Bibit merupakan salah satu factor yang menentukan jeberhasilan dalam pembuatan nata. Penggunaan bibit terutama dimaksudkan untuk mengurangi pencemaran yang dapat disebabkan oleh adanya bakteri pembusuk serta untuk mempercepat pembentukan nata. (Sutarminingsih, 2006).
2.6 Mekanisme Pembentukan Nata
Nata de fina merupakan hasil fermentasi mata nenas dengan bantuan mikroba Acetobacter xylinum. Gula pada mata nenas diubah menjadi asam asetat dan benang-benang selulosa. Lama-kelamaan akan terbentuk suatu massa yang kokoh dan mencapai ketebalan beberapa sentimeter. Dengan demikian, nata de fina dapat juga dianggap sebagai selulosa bakteri yang berbentuk padat, berwarna putih, transparan, berasa manis, bertekstur kenyal, dan umumnya dikonsumsi sebagai makanan ringan.
Starter atau biakan mikroba merupakan suatu bahan yang paling penting dalam pembentukan nata. Sebagai starter, digunakan biakan murni dari Acetobacter xylinum. Bakteri ini secara alami dapat ditemukan pada sari tanaman bergula yang telah mengalami fermentasi atau pada sayuran dan buah-buahan bergula yang sudah membusuk.
Bila mikroba ini ditumbuhkan pada media yang mengandung gula, organisme ini dapat mengubah 19 persen gula menjadi selulosa. Selulosa yang dikeluarkan ke dalam media itu berupa benang-benang yang bersama-sama dengan polisakarida berlendir membentuk jalinan yang terus menebal menjadi lapisan nata.

2.7 Penentuan Kadar Sukrosa Dengan Metode “ LUFF SCHOORL ”
Volume Na2S2O3 0,1 N yang diperlukan untuk :kan table, untuk volume
Titrasi Blanko = 10,2 mL
Titrasi Sampel =4,1 mL
Selisih volume ( AV ) =10,2 - 4,1 = 6,1 mL
Berdasarkan table pada lampiran , untuk volume 6 Ml Na2S2O3, maka kadar sukrosa sebesar 14,7 mg.
Volume sampel = 5 ml
Sehingga kadar sukrosa = 14,7 mg / 5 mL
= 2,94 mg/ml
Kadar Sukrosa dalam 100 ml sampel 2940 mg / 100 ml atau 0,2940 g / 100ml = 0,294 % b/v


BAB III
METODE PENELITIAN
3.1 Waktu dan Tempat
Percobaan ini akan dilaksanakan di laboratorium Teknik kimia pada tanggal 24 Maret sampai jam 11:00 W.I.B
3.2 Alat dan Bahan
3.4.1 Bahan
1. Mata nenas
2. Biakan Murni Acetobacter Xylinum
3. Gula Pasir
4. Pupuk ZA
5. Asam Cuka
6. Garam Inggris
7. Air
8. Sirup
3.4.2 Peralatan
1. Kompor
2. Panci
3. Pengaduk
4. Botol
5. Corong Plastik
6. Baki atau Loyang Plastik
7. Gayung plastik
8. Gelas Ukur
9. Kertas Koran Bekas
10. Karet Gelang
3.3. Cara Kerja
1. Persiapan Media Stater
Starter atau biakan mikroba merupakan suatu bahan yang paling penting dalam pembentukan nata. Sebagai starter, digunakan biakan murni dari Acetobacter xylinum. Bakteri ini dapat dihasilkan dari ampas nenas yang telah diinkubasi (diperam) selama 2-3 minggu. Starter yang digunakan dalam pembuatan nata sebanyak 170 ml
2. Pencucian
Untuk menghilangkan kotoran yang bercampur pada mata nenas dilakukan pencucian mata nenas dan dipisahkan antara kulit dan mata nenas nya.
3. Penghalusan
Mata nenas ditambahkan air 1: 2 lalu diblender hingga halus dan kemudian disaring dengan kain saring hingga diperoleh filtrate ( Cairan hasil penyaringan ).
4. Pendidihan
Masukan kedalam panci lalu panaskan diatas kompor. Setelah mendidih, tambahkan gula pasir 10%b/v, asam cuka 0,8%b/v ( bila yang digunakan asam cuka dipasaran 4-5% v/v), pupuk ZA 0,125%b/v ( 1 pucuk sendok the ), dan Garam inggris 0,01%b/v. Aduk sampai larut lalu angkat.

3. Inokulasi ( Pencampuran Dengan Strater )
Filtrat mata nenas yang dingin, Kemudian diinokulasi dengan menambahkan starter (Acetobacter xylinum) ± 10-20 % filtrat.
4. Fermentasi
Masukkan campuran tersebut ke dalam wadah fermentasi (baskom berukuran 34 x 25 x 5 cm). Wadah ditutup dengan kain saring dan diletakkan ditempat yang bersih dan aman. Dilakukan pemeraman selama 8-14 hari hingga lapisan mencapai ketebalan yang maksimum.
5. Pemanenan
Setelah pemeraman selesai 10 hari dengan terbentuk lapisan nata siap dipanen, lapisan nata diangkat secara hati-hati dengan menggunakan garpu atau penjepit yang bersih supaya cairan dibawah lapisan tidak tercemar. Kemudian cuci lalu peras dengan kain saring ( agar tidak licin ), Iris dengan ukuran sesuai selera, lalu masak dengan air sampai mendidih. Tiriskan dan peras lagi dengan kain saring, lalu dimask lagi. Pemasakan dilakukan sampai bau asam cuka hilang. Nata siap dihidangkan dengan larutan syrup.


BAB III
HASIL DAN PEMBAHASAN
3.1 Hasil
Hasil dari nata yang diperoleh mempunyai warna agak kekuningan dibanding nata yang terbuat dari air kelapa murni. Nata yang terbuat dari mata nenas ini memiliki kekenyalan yang hampir sama dengan nata yang dibuat dari bahan baku air kelapa.
3.2 Pembahasan
Nenas mengandung kadar asam yang lebih tinggi dibandingkan dengan air kelapa. Pada percobaan kmren, kita terlalu banyak menambahkan asam cuka nya, sehingga pada saat pemanenan, hanya terbentuk nata dibeberapa lapisan atas saja sedangkan yang bagian bawahnya tidak terbentuk nata. Ini dikarenakan terlalu banyak penambahkan asam pada saat pencampuran filtrate di proses atas. Tetapi nata yang dihasilkan cukup kenyal juga bila dibandingkan dengan nata air kelapa.


BAB V
KESIMPULAN DAN SARAN
5.1 Kesimpulan
Dari hasil yang didapat, ternyata mata nenas dapat dimanfaatkan sebagai nata karena dapat terbentuk jaringan-jaringan selulosa sehingga nata yang dihasilkan dapat padat, putih dan kenyal.
5.2 Saran
1. Dalam pembuatan nata, maka kebersihan alat dan bahan serta kemurnian media perlu diperhatikan untuk hasil yang lebih optimal
2. Bahan-bahan dasar nata juga perlu diperhatikan kemurnian dan kebersihannya untuk memperoleh hasil yang optimal.
3. Penambahan asam cuka harus benar – benar diperhitungkan..
4. Pendinginan adonan nata sebaiknya dengan ditutupi kertas Koran bekas yang telah disetrika.
5. Pembaca bisa melakukan percobaan yang sama dengan perbandingan yang diubah-ubah

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