Plastic Information

Polymethyl methacrylate

2012-04-29T08:44:00.005-07:00

Acrylic glass

Chemical name	poly(methyl 2-methylpropenoate)
Chemical formula	(C₅O₂H₈)_n
Synonyms	polymethylmethacrylate PMMA poly(methyl methacrylate) methyl methacrylate resin
Molecular mass	varies
CAS number	9011-14-7
Density	1.19 g/cm³
Melting point	n/a (amorphous polymer)
[Glass transition tempreture]	~118 °C
[Beta transition tempreture]	~60 °C
Boiling point	200.0 °C
Refractive index	1.492 (λ=589.3 nm)
V-number	55.3
SMILES	C[C](C)C(=O)OC

Polymethyl methacrylate (PMMA) or poly(methyl 2-methylpropenoate) is thesynthetic polymer of methyl methacrylate. This thermoplastic and transparentplastic is sold by the tradenames Plexiglas, Perspex, Plazcryl,Acrylite,Acrylplast, Altuglas, and Lucite and is commonly called acrylic glass or simplyacrylic. The material was developed in 1928 in various laboratories and was brought to market in 1933 by the German Company Rohm and Haas (GmbH & Co. KG).

Properties

The material is often used as an alternative to glass. Differences in the properties of the two materials include:

§ PMMA is lighter: its density (1190 kg/m³) is about half that of glass.

§ PMMA does not shatter

§ PMMA is softer and more easily scratched than glass. This can be overcome with scratch-resistant coatings.

§ PMMA can be easily formed, by heating it to 100 degrees Celsius.

§ PMMA transmits more light (92% of visible light) than glass.

§ Unlike glass, PMMA does not filter UV (ultraviolet) light. PMMA transmits UV light, at best intensity, down to 300 nm. Some manufacturers coat their PMMA with UV films to add this property. On the other hand, PMMA molecules have great UV stability compared to polycarbonate.

§ PMMA allows infrared light of up to 2800 nm wavelength to pass. IR of longer wavelengths, up to 25,000 nm, are essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).

PMMA can be joined using cyanoacrylate cement (so-called "Superglue"), or by using liquid di- or trichloromethane to dissolve the plastic at the joint which then fuses and sets, forming an almost invisible weld. PMMA can also be easily polished to restore cut edges to full transparency.

To produce 1 kg of PMMA, about 2 kg of petroleum is needed. In the presence of air, PMMA ignites at 460° C and burns completely to form only carbon dioxide and water.

If hydrogen atoms are substituted for the methyl groups (CH₃) attached to the C atoms, poly(methyl acrylate) is produced. This soft white rubbery material is softer than PMMA because its long polymer chains are thinner and smoother and can more easily slide past each other.

Grades

§ Injection moulding grade

Molar Mass ~ 60,000

§ Cast grade

Molar Mass ~ 10^6 Production: monomer + initiator are heated together forming a syrup-----> syrup is poured in a mould(low temp for long duration)eg: 50 degrees C for few hours method used to make sheets and rods.(simple shapes)

Uses

PMMA is used for instance in the lenses of automobile running-lights. The spectator protection in ice hockey stadiums is made of PMMA, as are the largest windows and aquariums in the world. The material is used to produce laserdiscs, and sometimes also for DVDs, but the more expensive polycarbonate (also used for CDs) has better properties when exposed to moisture.

Acrylic paint essentially consists of PMMA suspended in water; however since PMMA is hydrophobic, a substance with both hydrophobic and hydrophilic groups needs to be added to facilitate the suspension.

PMMA has a good degree of compatibilty with human tissue, and can be used for replacement intraocular lenses in the eye when the original lens has been removed in the treatment of cataracts. Hard contact lenses are frequently made of this material; soft contact lenses are often made of a related polymer, in which acrylate monomers are used that contain one or more hydroxyl groups to make them hydrophilic.

In orthopaedics, PMMA bone cement is used to affix implants and to remodel lost bone. It is supplied as a powder with liquid methyl methacrylate (MMA); when mixed together these yield a dough-like cement that gradually hardens in the body. Surgeons can judge the curing of the PMMA bone cement by the smell of MMA in the patient's breath. Athough PMMA is biologically compatible, MMA is considered to be an irritant and a possible carcinogen. PMMA has also been linked to cardiopulmonary events in the operating room due to hypotension. <ref>American Journal of Neuroradiology, 23:601-604, April 2002.</ref> Bone cement acts like a grout and not so much like a glue in arthroplasty. Although sticky, it primarily fills the spaces between the prosthesis and the bone preventing motion. It has a young's modulus between cancellous bone and cortical bone. Thus, it is a load sharing entity in the body not causing bone resorption. <ref>Miller, Review of Orthopaedics, 4th Edition, p 129.</ref>

Dentures are often made of PMMA. In cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid are injected under the skin to reduce wrinkles or scars permanently.

Artificial nails are made of acrylic too.

Modern furniture makers, especially in the 1960s and 1970s, looking to give their products a space age feel also incorporated Lucite and other PMMA products into their designs, especially in office chairs. Many other products (for example, guitars) are sometimes made with acrylic glass, giving otherwise-ordinary objects a transparent or futuristic look.

Recently, a blacklight-reactive tattoo ink using PMMA microcapsules has surfaced. The technical name is BIOMETRIX System-1000, and it is marketed under the name "Chameleon Tattoo Ink". This ink is reportedly quite safe for use, and claims to be Food and Drug Administration approved for use on wildlife that may enter the food supply.

In semiconductor research and industry, PMMA aids as a resist in the electron beam lithography process. A solution consisting of the polymer in a solvent is used to spin coat silicon wafers with a thin film. Patterns on this can be made by an electron beam (using an electron microscope), deep UV light (shorter wavelength than the standard photolithography process), or X-rays. Exposure to these creates chain scission or (cross-linking) within the PMMA, allowing for the selective removal of exposed areas by a chemical developer. PMMA's advantage lies in that it allows for extremely high resolution (nanoscale) patterns to be made. It is an invaluable tool in nanotechnology.

Acrylonitrile Butadine Styrene

2012-04-29T08:29:00.001-07:00

Acrylonitrile butadiene styrene, or ABS, (chemical formula (C₈H₈· C₄H₆·C₃H₃N)_x) is a common thermoplastic used to make light, rigid, molded products such as pipes, golf club heads (used for its good shock absorbance), automotive body parts, wheel covers, enclosures, protective head gear, and toys including LEGO bricks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. ABS can be used between −25 °C and 60 °C.

Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy. It can also be recycled.

Synthesis

Acrylonitrile butadiene styrene can be found as a graft copolymer, in which styrene-acrylonitrile polymer is formed in a polymerization system in the presence of polybutadiene rubber latex; the final product is a complex mixture consisting of styrene-acrylonitrile copolymer, a graft polymer of styrene-acrylonitrile and polybutadiene and some unchanged polybutadiene rubber. There are, therefore, many variables to the process besides the different positions of the starting materials, so this technique is capable of producing polymers with a much wider range of properties. [Brighton et al. 1979] ABS can be made by blending, the technique involved mechanical blending by mixing a butadiene-acrylonitrile rubber with styrene-acrylonitrile resins, the process is being carried out under such conditions that the two polymers underwent some grafting. This technique is rather limited and has been largely suppressed by chemical process. [Brighton et al. 1979]

Properties

ABS is derived from acrylonitrile, butadiene, and styrene. Where acrylonitrile are synthetic monomers produced from propylene and ammonia; butadiene is a petroleum hydrocarbon obtained from butane; and styrene monomers, derived from coal, are commercially obtained from benzene and ethylene from coal. The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. The most amazing mechanical properties of ABS are resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. For instance, the impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and acrylonitrile although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads. Even though ABS plastics are used largely for mechanical purposes, they also have good electrical properties that are fairly constant over a wide range of frequencies. These properties are little affected by temperature and atmospheric humidity in the acceptable operating range of temperatures. [Harper, 1975] The final properties will be influenced to some extent by the conditions under which the material is processed to the final product; for example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature. ABS polymers are resistant to aqueous acids, alkalis, concentrated hydrochloric and phosphoric acids, alcohols and animal, vegetable and mineral oils, but they are swollen by glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons and are attacked by concentrated sulfuric and nitric acids. They are soluble in esters, ketones and ethylene dichloride. The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. [Brighton et al. 1979] On the other hand, the cost of producing ABS is roughly twice the cost of producing polystyrene, ABS is considered superior for its hardness, gloss, toughness, and electrical insulation properties. However, it will be degraded when exposed to acetone.

Trivia

§ Acrylonitrile butadiene styrene is the plastic from which Lego bricks are made.

Thermosetting polymer

2012-04-29T08:06:00.002-07:00

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing.

Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuit (IC). Once hardened a thermoset resin cannot be reheated and melted back to a liquid form.

According to IUPAC recommendation: A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of heat or suitable radiation, or both. A cured thermosetting polymer is called a thermoset.

Process

The curing process transforms the resin into a plastic or rubber by a crosslinking process. Energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example), linking into a rigid, 3-D structure. The cross-linking process forms a molecule with a larger molecular weight, resulting in a material with a higher melting point. During the reaction, the molecular weight has increased to a point so that the melting point is higher than the surrounding ambient temperature, the material forms into a solid material.

Uncontrolled reheating of the material results in reaching the decomposition temperature before the melting point is obtained. Therefore, a thermoset material cannot be melted and re-shaped after it is cured. This implies that thermosets cannot be recycled, except as filler material.

Properties

Thermoset materials are generally stronger than thermoplastic materials due to this three dimensional network of bonds (cross-linking), and are also better suited to high-temperature applications up to the decomposition temperature. However, they are more brittle. Many thermosetting polymers are difficult to recycle.

Examples

Some examples of thermosets are given below:

§ Polyester fibreglass systems: sheet molding compounds and bulk molding compounds)

§ Vulcanized rubber

§ Duroplast, light but strong material, similar to bakelite used for making car parts

§ Urea-formaldehyde foam used in plywood, particleboard and medium-density fiberboard

§ Melamine resin used on worktop surfaces

§ Epoxy resin used as the matrix component in many fiber reinforced plastics such as glass reinforced plastic and graphite-reinforced plastic)

§ Polyimides used in printed circuit boards and in body parts of modern airplanes

§ Cyanate esters or polycyanurates for electronics applications with high demands on dielectric properties and high glass temperature requirements in composites

§ Mold or mold runners (the black plastic part in integrated circuits or semiconductors)

Some methods of molding thermosets are:

§ Reactive injection molding (used for objects such as milk bottle crates)

§ Extrusion molding (used for making pipes, threads of fabric and insulation for electrical cables)

§ Compression molding (used to shape most thermosetting plastics)

§ Spin casting (used for producing fishing lures and jigs, gaming miniatures, figurines, emblems as well as production and replacement parts)

MATERIALS

Thermosets

Natural Rubber

Bakelite, a Phenol Formaldehyde Resin (used in electrical insulators and plastic wear)

Duroplast

Urea-Formaldehyde Foam (used in plywood, particleboard and medium-density fibreboard)

Melamine (used on worktop surfaces)

Polyester Resin (used in glass-reinforced plastics/Fibreglass (GRP)

Epoxy Resin

Thermoplastic

2012-04-23T07:42:00.000-07:00

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a rigid state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak van der waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding(nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers(e.g phenolics, epoxies) in that they can be remelted and remoulded. Many thermoplastic materials are additionpolymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene; others are productions of condensation or other forms of polyaddition polymerisation, such as the polyamides or polyesters

Theory

Thermoplastics are elastic and flexible above a glass transition temperature T_g, specific for each one — the midpoint of a temperature range in contrast to the sharp melting point of a pure crystalline substance like water. Below a second, higher melting temperature, T_m, also the midpoint of a range, some thermoplastics have crystalline regions alternating with amorphous regions in which the chains approximate random coils. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity, as is also the case for non-thermoplastic fibrous protenis such as silk. (Elasticity does not mean they are particularly stretchy; e.g., polyamides/Nylons rope and fishing line.) Above T_m all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above T_m, viscosity gradually decreases without any distinct phasechange.

Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the T_g. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS, and PC. Generally, amorphous thermoplastics are less chemically resistant and can be subject to environmental stress cracking. Thermoplastics will crystallize to a certain extent and are called "semi-crystalline" for this reason. Typical semi-crystalline thermoplastics are PE,PP,PBT andPET. The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque.

Semi-crystalline thermoplastics become less brittle above 'T'_g. If a plastic with otherwise desirable properties has too high a T_g, it can often be lowered by adding a relatively low molecular weight plasticizer to the melt before forming (plastics extrusion; moulding) and cooling. A similar result can sometimes be achieved by adding non-reactive side chains to the monomers before polymeriztion. Both methods make the polymer chains stand off a bit from one another. Before the introduction of plasticizers, plastic automobile parts often cracked in cold winter weather. Another method of lowering T_g (or raising T_m) is to incorporate the original plastic into a copolymer, as with graft copolymer of polystyrene, or into a composite material. Lowering T_g is not the only way to reduce brittleness. Drawing (and similar processes that stretch or orient the molecules) or increasing the length of the polymer chains also decrease brittleness.

Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. This quality makes thermoplastics recyclable. The processes required for recycling vary with the thermoplastic. The plastics used for soda bottles are a common example of thermoplastics that can be and are widely recycled. Animal horn, made of the protein keratene, softens on heating, is somewhat reshapable, and may be regarded as a natural, quasi-thermoplastic material.

Although modestly vulcanized natural and synthetic rubbers are stretchy, they are elastomeric thermosets, not thermoplastics. Each has its own T_g, and will crack and shatter when cold enough so that the crosslinked polymer chains can no longer move relative to one another. But they have no T_m and will decompose at high temperatures rather than melt. Recently, thermoplastic elastomers have become available.

Melting point and glass transition temperature of various thermoplastics
Polymer	T_m	T_g
Acrylonitrile butadiene styrene (ABS)
Acrylic (PMMA)	130–140 °C
Celluloid
Cellulose acetate
Cyclic Olefin Copolymer (COC)
Ethylene-Vinyl Acetate (EVA)
Ethylene vinyl alcohol (EVOH)
Fluoroplastics (PTFE, alongside with FEP, PFA,CTFE, ECTFE, ETFE)
Ionomers
Kydex, a trademarked acrylic/PVC alloy
Liquid Crystal Polymer (LCP)
Polyoxymethylene (POM or Acetal)	175°C
Polyacrylates (Acrylic)
Polyacrylonitrile (PAN or Acrylonitrile)
Polyamide (PA or Nylon)
Polyamide-imide (PAI)
Polyaryletherketone (PAEK or Ketone)
Polybutadiene (PBD)
Polybutylene (PB)
Polybutylene terephthalate (PBT)	225°C	40°C
Polycaprolactone (PCL)	62 °C
Polychlorotrifluoroethylene (PCTFE)
Polyethylene terephthalate (PET)	255 °C	75 °C
Polycyclohexylene dimethylene terephthalate (PCT)
Polycarbonate (PC)	267 °C
Polyhydroxyalkanoates (PHAs)	145\|
Polyketone (PK)
Polyester	260 C	75 C
Polyethylene (PE)	105–130 °C	-127 °C
Polyetheretherketone (PEEK)	343 °C	143 °C
Polyetherketoneketone (PEKK)
Polyetherimide (PEI)
Polyethersulfone (PES)- see Polysulfone
Chlorinated Polyethylene (CPE)
Polyimide (PI)
Polylactic acid (PLA)	50–80 °C
Polymethylpentene (PMP)
Polyphenylene oxide (PPO)
Polyphenylene sulfide (PPS)
Polyphthalamide (PPA)
Polypropylene (PP)	160 °C
Polystyrene (PS)	240 °C
Polysulfone (PSU)
Polytrimethylene terephthalate (PTT)
Polyurethane (PU)
Polyvinyl acetate (PVA)		32 °C
Polyvinyl chloride (PVC)		80 °C
Polyvinylidene chloride (PVDC)	185 °C	40 °C
Styrene-acrylonitrile (SAN)	115\|

Terminology

The literature on thermoplastics is huge, and can be quite confusing, as the same chemical can be available in many different forms (for example, at different molecular weight), which might have quite different physical properties. The same chemical can be referred to by many different tradenames, by different abbreviations; two chemical compounds can share the same name; a good example of the latter is the word "Teflon" which is used to refer to a specific polymer (PTFE); to related polymers such as PFA, and generically to fluoropolymer

Testing

Testing of thermoplastics can take various forms.

Tensile tests—ISO 527 -1/-2 and ASTM D 638 set out the standardized test methods. These standards are technically equivalent. However they are not fully comparable because of the difference in testing speeds. The modulus determination requires a high accuracy of ± 1 micrometer for the diameter.

Flexural tests—3-points flexural tests are among the most common and classic methods for semi rigid and rigid plastics.

Pendulum impact tests—impact tests are used to measure the behavior of materials at higher deformation speeds. Pendulum impact testers are used to determine the energy required to break a standardized specimen by measuring the height to which the pendulum hammer rises after impacting the test piece.

About Plastic

2012-04-21T04:04:00.000-07:00

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids that are mold able. Plastics are typically organic polymers of high molecular mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural.

Composition

Almost invariably, organic polymers mainly comprise plastics. The vast majority of these polymers are based on chains of carbon atoms alone or with oxygen, sulfur, or nitrogen as well. The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To customize the properties of a plastic, different molecular groups "hang" from the backbone (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). The structure of these "side chains" influence the properties of the polymer. This fine tuning of the properties of the polymer by repeating unit's molecular structure has allowed plastics to become an indispensable part of the twenty-first century world.

Additives

Most plastics contain other organic or inorganic compounds blended in. The amount of additives ranges from zero percentage for polymers used to wrap foods to more than 50% for certain electronic applications. The average content of additives is 20% by weight of the polymer. Fillers improve performance and/or reduce production costs. Stabilizing additives include fire retardants to lower the flammability of the material. Many plastics contain fillers, relatively inert and inexpensive materials that make the product cheaper by weight. Typically fillers are mineral in origin, e.g., chalk. Some fillers are more chemically active and are called reinforcing agents. Since many organic polymers are too rigid for particular applications, they are blended with plasticizers, oily compounds that confer improved rheology. Colourants are of course common additives, although their weight contribution is small. Many of the controversies associated with plastics are associated with the additives.

Classification

Plastics are usually classified by their chemical structure of the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking.

Thermoplastics and thermosetting polymers

There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be moulded again and again. Examples include polyethylene, polypropylene, polystyrene,polyvinyl chloride, and polytetrafluoroethylene (PTFE). Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived frommonomers; each polymer chain will have several thousand repeating units.

Thermosets can melt and take shape once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Before heating with sulfur, the polyisoprene is a tacky, slightly runny material, but after vulcanization the product is rigid and non-tacky.

Other classifications

Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, and electrically conductive. Plastics can also be classified by variousphysical properties, such as density, tensile strength, glass transition temperature, and resistance to various chemical products.

Biodegradability

Main article: Biodegradable plastic

Biodegradable plastics break down (degrade) upon exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion, and in some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. Some modes of degradation require that the plastic be exposed at the surface, whereas other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present. The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications.

Natural vs synthetic

Main article: Bioplastic

Most plastics are produced from petrochemicals. Motivated by the finiteness of petrochemical reserves and possibility of global warming, bioplastics are being developed. Bioplastics are made substantially from renewable plant materials such as cellulose and starch.

In comparison to the global consumption of all flexible packaging, estimated at 12.3 million tonnes, estimates put global production capacity at 327,000 tonnes for related bio-derived materials.

Crystalline vs amorphous

Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). The so-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets.

History

Early plastics were bio-derived materials such as egg and blood proteins, which are organic polymers. Treated cattle horns were used as windows for lanterns in the Middle Ages. Materials that mimicked the properties of horns were developed by treating milk-proteins (casein) with lye. In the 1800s the development of plastics accelerated with Charles Goodyear's discovery of vulcanization as a route to thermoset materials derived from natural rubber. Many storied materials were reported as industrial chemistry was developed in the 1800s. In the early 1900s, Bakelite, the first fully synthetic thermoset was reported by Belgian chemist Leo Baekeland. After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new polymers were polystyrene (PS) and polyvinyl chloride (PVC). The development of plastics has come from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., rubber,nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, polyvinyl chloride).

Parkesine

The plastic material, parkesine, was patented by Alexander Parkes, In Birmingham, UK in 1856. It was unveiled at the 1862 Great International Exhibition in London. Parkesine won a bronze medal at the 1862 World's fair in London. Parkesine was made from cellulose (the major component of plant cell walls) treated with nitric acid as a solvent. The output of the process (commonly known as cellulose nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic material that could be molded when heated. By incorporating pigments into the product, it could be made to resemble ivory.

Bakelite

Main article: Bakelite

The first so called plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in 1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state. Baekeland was looking for an insulating shellac to coat wires in electric motors and generators. He found that combining phenol (C₆H₅OH) and formaldehyde (HCOH) formed a sticky mass and later found that the material could be mixed with wood flour, asbestos, or slate dust to create strong and fire resistant "composite" materials. The new material tended to foam during synthesis, requiring that Baekeland build pressure vessels to force out the bubbles and provide a smooth, uniform product, as announced his in 1909, in a meeting of the American Chemical Society.Bakelite was originally used for electrical and mechanical parts, coming into widespread use in consumer goods in the 1920s. Bakelite was a purely synthetic material, not derived from living matter. It was also an early thermosetting plastic

Representative polymers

Polystyrene

Plastic piping and firestops being installed in Ontario. Certain plastic pipes can be used in some non-combustible buildings, provided they are firestopped properly and that the flame spread ratings comply with the localbuilding code.

Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and similar knick-knacks. It would also be the basis for one of the most popular "foamed" plastics, under the name styrene foam or Styrofoam. Foam plastics can be synthesized in an "open cell" form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell", in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and flotation devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much current use as the substance of toy figurines and novelties.

Polyvinyl chloride

Polyvinyl chloride (PVC, commonly called "vinyl")^[13]incorporates chlorine atoms. The C-Cl bonds in the backbone are hydrophobic and resist oxidation (and burning). PVC is stiff, strong, heat and weather resistant, properties that
Styrene polymerization

recommend its use in devices for plumbing, gutters, house siding, enclosures for computers and other electronics gear. PVC can also be softened with chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear.

All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is released into the atmosphere and oxidation of the compound

Vinylchloride polymerization
occurs.^[14] Because hydrogen chloride readily combines with water vapor in the air to form hydrochloric acid,^[15] polyvinyl chloride is not recommended for long-term archival storage of silver, photographic film or paper (mylar is preferable).^[16]

Nylon

Main article: Nylon

The plastics industry was revolutionized in the 1930s with the announcement of polyamide (PA), far better known by its trade name nylon. Nylon was the first purely synthetic fiber, introduced by DuPont Corporation at the 1939 World's Fair in New York City.

In 1927, DuPont had begun a secret development project designated Fiber66, under the direction of Harvard chemist Wallace Carothers and chemistry department director Elmer Keiser Bolton. Carothers had been hired to perform pure research, and he worked to understand the new materials' molecular structure and physical properties. He took some of the first steps in the molecular design of the materials.

His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. The first application was for bristles fortoothbrushes. However, Du Pont's real target was silk, particularly silk stockings. Carothers and his team synthesized a number of different polyamides including polyamide 6.6 and 4.6, as well as polyesters.

General condensation polymerization reaction for nylon

It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the industrial processes for bulk manufacture. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation, or "nylon mania".

Nylon mania came to an abrupt stop at the end of 1941 when the USA entered World War II. The production capacity that had been built up to produce nylon stockings, or just nylons, for American women was taken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so called nylon riots.

Subsequently polyamides 6, 10, 11, and 12 have been developed based on monomers which are ring compounds; e.g. caprolactam. Nylon 66 is a material manufactured by condensation polymerization.

Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, and because of good heat-resistance, increasingly for under-the-hood applications in cars, and other mechanical parts.

Rubber

Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloidal suspension found in the sap of some plants. It is useful directly in this form (indeed, the first appearance of rubber in Europe was cloth waterproofed with unvulcanized latex from Brazil) but, later, in 1839, Charles Goodyear invented vulcanized rubber; this a form of natural rubber heated with, mostly, sulfur forming cross-links between polymer chains (vulcanization), improving elasticity and durability.

Synthetic rubber

Main article: Synthetic rubber

The first fully synthetic rubber was synthesized by Sergei Lebedev in 1910. In World War II, supply blockades of natural rubber from South East Asia caused a boom in development of synthetic rubber, notably styrene-butadiene rubber. In 1941, annual production of synthetic rubber in the U.S. was only 231 tonnes which increased to 840,000 tonnes in 1945. In the space race and nuclear arms race, Caltechresearchers experimented with using synthetic rubbers for solid fuel for rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort.

Properties of plastics

The properties of plastics is defined chiefly by the organic chemistry of the polymer. such as hardness, density, and resistance to heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt upon heating to a few hundred degrees celsius.^[18]While plastics can be made electrically conductive, with the conductivity of up to 80 kS/cm in stretch-oriented polyacetylene, they are still no match for most metals like copper which have conductivities of several hundreds kS/cm.

Toxicity

Due to their insolubility in water and relative chemical inertness, pure plastics generally have low toxicity. Some plastic products contain a variety of additives, some of which can be toxic. For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride to make them pliable enough for use in food packaging, toys, and many other items. Traces of these compounds can leach out of the product. Owing to concerns over the effects of such leachates, the European Union has restricted the use of DEHP (di-2-ethylhexyl phthalate)and other phthalates in some applications. Some compounds leaching from polystyrene food containers have been proposed to interfere with hormone functions and are suspected human carcinogens.

Whereas the finished plastic may be non-toxic, the monomers used in the manufacture of the parent polymers may be toxic. In some cases, small amounts of those chemicals can remain trapped in the product unless suitable processing is employed. For example, the World Health Organization's International Agency for Research on Cancer (IARC) has recognized that vinyl chloride, the precursor to PVC, as a humancarcinogen.

BPA controversy

Some polymers may also decompose into the monomers or other toxic substances when heated. In 2011, it was reported that "almost all plastic products" sampled released chemicals with estrogenic activity, although the researchers identified plastics which did not leach chemicals with estrogenic activity.

The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food.Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring. A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease.

As of January 2010, the LA Times newspaper reports that the United States FDA is spending $30 million to investigate indications of BPA being linked to cancer.

Bis(2-ethylhexyl) adipate, present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present in new car smell.

The European Union has a permanent ban on the use of phthalates in toys. In 2009, the United States government banned certain types of phthalates commonly used in plastic.

Environmental issues

Further information: Marine debris and Great Pacific Garbage Patch

Plastics are durable and degrade very slowly; the chemical bonds that make plastic so durable make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of plastic have been discarded and may persist for hundreds or even thousands of years.Perhaps the biggest environmental threat from plastic comes from nurdles, which are the raw material from which all plastics are made. They are tiny pre-plastic pellets that kill large numbers of fish and birds that mistake them for food.

Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in life-critical fire suppression systems; seeMontreal Protocol), the production of polystyrene contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process.

Incineration of plastics

Plastic can be converted as a fuel since they are usually hydrocarbon-based and can be broken down into liquid hydrocarbon. One kilogram of waste plastic produces a liter of hydrocarbon. In some cases, burning plastic can release toxic fumes. Burning the plastic polyvinyl chloride (PVC) may create dioxin.

Recycling

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, although the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken back down to a feedstock state.

The greatest challenge to the recycling of plastics is the difficulty of automating the sorting of plastic wastes, making it labor intensive. Typically, workers sort the plastic by looking at the resin identification code, although common containers like soda bottles can be sorted from memory. Typically, the caps for PETE bottles are made from a different kind of plastic which is not recyclable, which presents additional problems to the automated sorting process. Other recyclable materials such as metals are easier to process mechanically. However, new processes of mechanical sorting are being developed to increase capacity and efficiency of plastic recycling.

While containers are usually made from a single type and color of plastic, making them relatively easy to be sorted, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types and colors of plastics. In such cases, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field ofactive disassembly, which may result in more consumer product components being re-used or recycled. Recycling certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows"

Plastics type marks: the resin identification code

1. PET (PETE), polyethylene terephthalate

2. HDPE, high-density polyethylene

3. PVC, polyvinyl chloride

4. LDPE, low-density polyethylene,

5. PP, polypropylene

6. PS, polystyrene

7. Other types of plastics

Common plastics and uses

Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood, stone,horn and bone, leather, paper, metal, glass, and ceramic, in most of their former uses.

§ Polyester (PES) – Fibers, textiles.

§ Polyethylene terephthalate (PET) – Carbonated drinks bottles, peanut butter jars, plastic film, microwavable packaging.

§ Polyethylene (PE) – Wide range of inexpensive uses including supermarket bags, plastic bottles.

§ High-density polyethylene (HDPE) – Detergent bottles, milk jugs, and molded plastic cases.

§ Polyvinyl chloride (PVC) – Plumbing pipes and guttering, shower curtains, window frames, flooring.

§ Polyvinylidene chloride (PVDC) (Saran) – Food packaging.

§ Low-density polyethylene (LDPE) – Outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.

§ Polypropylene (PP) – Bottle caps, drinking straws, yogurt containers, appliances, car fenders (bumpers), plastic pressure pipe systems.
A chair made with a polypropylene seat

§ Polystyrene (PS) – Packaging foam/"peanuts", food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes.

§ High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups.

§ Polyamides (PA) (Nylons) – Fibers, toothbrush bristles, fishing line, under-the-hood car engine moldings.

§ Acrylonitrile butadiene styrene (ABS) – Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.

§ Polycarbonate (PC) – Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.

§ Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) – A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.

§ Polyurethanes (PU) – Cushioning foams, thermal insulation foams, surface coatings, printing rollers (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).

Special purpose plastics

§ Melamine formaldehyde (MF) – One of the aminoplasts, and used as a multi-colorable alternative to phenolics, for instance in moldings (e.g., break-resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g., Formica).

§ Plastarch material – Biodegradable and heat resistant, thermoplastic composed of modified corn starch.

§ Phenolics (PF) or (phenol formaldehydes) – High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be molded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam (e.g., Oasis). Problems include the probability of moldings naturally being dark colors (red, green, brown), and as thermoset it is difficult to recycle.

§ Polyetheretherketone (PEEK) – Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implantapplications, aerospace moldings. One of the most expensive commercial polymers.

§ Polyetherimide (PEI) (Ultem) – A high temperature, chemically stable polymer that does not crystallize.

§ Polylactic acid (PLA) – A biodegradable, thermoplastic found converted into a variety of aliphatic polyesters derived from lactic acid which in turn can be made by fermentation of various agricultural products such as corn starch, once made from dairy products.

§ Polymethyl methacrylate (PMMA) – Contact lenses, glazing (best known in this form by its various trade names around the world; e.g., Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for vehicles. It forms the basis of artistic and commercialacrylic paints when suspended in water with the use of other agents.

§ Polytetrafluoroethylene (PTFE) – Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly known as Teflon.

§ Urea-formaldehyde (UF) – One of the aminoplasts and used as a multi-colorable alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings.

Material properties of some thermoplastics

Properties of some thermoplastic materials
name	Symbol	Density [g/cm³]	Tensile strength [MPa]	Flexural strength [MPa]	Elastic modulus [GPa]	Elongation at rupture [%]	Thermal stability [°C]	Expansion at 20°C [10⁻⁶/°C]
High DensityPolyethylene	HDPE	0.95	31	40	1.86	100	120	126	^[32]
Low DensityPolyethylene	LDPE	0.92	17	14	0.29	500	90	160
Polyvinyl Chloride	PVC	1.44	47	91	3.32	60	80	75
Polypropylene	PP	0.91	37	49	1.36	350	150	90
Polyethylene terephthalate	PET	1.35	61	105	1.35	170	120	70
Polymethylmethacrylate	PMMA	1.19	61	103	2.77	4	100	65
Polycarbonate	PC	1.2	68	95	2.3	130	120	66
Acrylonitrile butadiene styrene	ABS	1.05	45	70	2.45	33	70	90
Polyamide	Nylon 6	1.13	60	91	2.95	60	110	66
Polyimide	PI	1.38	96	143	3.1	7	380	43
Polysulfone	PSF	1.25	68	115	2.61	75	160	56
Polyamide-imide, electrical grade	PAI	1.41	138	193	4.1	12	260	30
Polyamide-imide, bearing grade	PAI	1.46	103	159	5.5	6	260	25
Polytetrafluoroethylene	PTFE	2.17	24	33	0.49	300	260	95
Polyetherimide	PEI	1.27	105	151	2.9	60	210	31	^[33]
Polyether ether ketone	PEEK	1.32	100		3.6	50	343
Polyaryletherketone(strong)	PEAK	1.46	136	213	12.4	2.1	267
Polyaryletherketone(tough)	PEAK	1.29	87	124	3	40	190
Self-reinforcedpolyphenylene	SRP	1.19	152	234	5.52	10	151
Polyamide-imide	PAI	1.42	152	241	4.9	15	278

NOTE: Bulk properties of pure cast or hot formed materials. Properties could change considerably by mechanical treatment and cold forming. Fiber and foils are not considered