Technical Info South Africa

Plastic Material Classifications

Plastic Materials Classification

Plastics Classification

Plastics are usually classified by their chemical structure of the polymer's backbone and side chains. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking.


About Polyurethanes


Thermoplastics and thermosetting polymers



Polyethylene (abbreviated PE) or polythene (IUPAC name polyethene or poly(methylene)) is the most common plastic. The annual production is approximately 80 million metric tons. Its primary use is within packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, but they almost always have the chemical formula (C2H4)nH2. Thus PE is usually a mixture of similar organic compound that differ in terms of the value of n.


  • Ultra-high-molecular-weight polyethylene (UHMWPE)
  • Ultra-low-molecular-weight polyethylene (ULMWPE or PE-WAX)
  • High-molecular-weight polyethylene (HMWPE)
  • High-density polyethylene (HDPE)
  • High-density cross-linked polyethylene (HDXLPE)
  • Cross-linked polyethylene (PEX or XLPE)
  • Medium-density polyethylene (MDPE)
  • Linear low-density polyethylene (LLDPE)
  • Low-density polyethylene (LDPE)
  • Very-low-density polyethylene (VLDPE)
  • Chlorinated polyethylene (CPE)
Ultra-high-molecular-weight polyethylene (UHMWPE)

UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.1 and 5.67 million. The high molecular weight makes it a very tough material, but 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). 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 diverse range 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.

High-density polyethylene (HDPE)


Cross-linked polyethylene (PEX or XLPE)


Medium-density polyethylene (MDPE)


Linear low-density polyethylene (LLDPE)

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. Product examples range from agricultural films, saran wrap, and bubble wrap, to multilayer and composite films. In 2009 the world LLDPE market reached a volume of almost US$24 billion (€17 billion).

Low-density polyethylene (LDPE)

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 ducility. 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. In 2009 the global LDPE market had a volume of circa US$22.2 billion (€15.9 billion).

Very-low-density polyethylene (VLDPE)


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.






PET Applications:


When filled with glass particles or fibers, it becomes significantly stiffer and more durable. This glass-filled plastic, in a semi-crystalline formulation, is sold under the tradename Rynite, Arnite, Hostadur& Crastin.

Sails are usually made of Dacron, a brand of PET fiber; colorful lightweight spinnakers are usually made of nylon.While all thermoplastics are technically recyclable, PET bottle recycling is more practical than many other plastic applications. The primary reason is that plastic carbonated soft drink bottles and water bottles are almost exclusively PET which makes them more easily identifiable in a recycle stream. PET has a resin identification code of 1. PET, as with many plastics, is also an excellent candidate for thermal recycling (incineration) as it is composed of carbon, hydrogen and oxygen with only trace amounts of catalyst elements (no sulfur) and has the energy content of soft coal. PET was patented in 1941 by the Calico Printers' Association of Manchester. The PET bottle was patented in 1973. Copolymers
In addition to pure (homopolymer) PET, PET modified by copolymerization is also available. In some cases, the modified properties of copolymer are more desirable for a particular application. For example, cyclohexane dimethanol (CHDM) can be added to the polymer backbone in place of ethylene glycol. Since this building block is much larger (6 additional carbon atoms) than the ethylene glycol unit it replaces, it does not fit in with the neighboring chains the way an ethylene glycol unit would. This interferes with crystallization and lowers the polymer's melting temperature. Such PET is generally known as PETG (EastmanChemical and SKchemicals are the only two manufacturers).
Replacing terephthalic acid (right) with isophthalic acid (center) creates a kink in the PET chain, interfering with crystallization and lowering the polymer's melting point.Another common modifier is isophthalic acid, replacing some of the 1,4- (para-) linked terephthalate units. The 1,2- (ortho-) or 1,3- (meta-) linkage produces an angle in the chain, which also disturbs crystallinity. Such copolymers are advantageous for certain molding applications, such as thermoforming, which is used to make tray or blister packages from PET sheet (sometimes called APET, for "amorphous PET"). On the other hand, crystallization is important in other applications where mechanical and dimensional stability are important, such as seat belts. For PET bottles, the use of small amounts of CHDM or other comonomers can be useful: if only small amounts of comonomers are used, crystallization is slowed but not prevented entirely. As a result, bottles are obtainable via stretch blow molding ("SBM"), which are both clear and crystalline enough to be an adequate barrier to aromas and even gasses, such as the carbon dioxide in carbonated beverages.
Low-density polyethylene (LDPE) is a thermoplastic made from oil. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerisation [1]. Its manufacture employs the same method today.
Other products made from it include:
Trays & general purpose containers
Food storage and laboratory containers
Corrosion-resistant work surfaces
Parts that need to be weldable and machinable
Parts that require flexibility, for which it serves very well
Very soft and pliable parts
Six-pack soda can rings
Extrusion coating on paperboard and aluminum laminated for beverage cartons.
Computer components, such as hard drives, screen cards and disk-drives.

Acrylonitrile butadiene styrene
Monomers in ABS polymerAcrylonitrile butadiene styrene, or ABS, (chemical formula (C8H8· C4H6·C3H3N)n) is a common thermoplastic used to make light, rigid, molded products such as piping, musical instruments (most notably recorders), golf club heads (used for its good shock absorbance), automotive body parts, wheel covers, enclosures, protective head gear, vballs [reusable paintballs], and toys including LEGO bricks[1]. In plumbing, ABS pipes are the black pipes (PVC pipes are white) and also in Plastic Pressure Pipe Systems. ABS plastic ground down to an average diameter of less than 1 micrometre is used as the colorant in some tattoo inks. Tattoo inks that use ABS are extremely vivid. This vividness is the most obvious indicator that the ink contains ABS, as tattoo inks rarely list their ingredients. 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 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.



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