Definitions of Plastic Resins; Part 3
Thursday, November 19th, 2009by Frank Hild
Polyethylene
A family of thermoplastic resins obtained by polymerizing the gas ethylene [C2H4]. Low molecular weight polymers of ethylene are fluids used as lubricants; medium weight polymers are waxes miscible with paraffin; and the high molecular weight polymers (i.e., over 6000) are the materials used in the plastics industry. Polymers with densities ranging from about .910 to .925 are called low density; those of densities from .926 to .940 are called medium density; and those from .941 to .965 and over are called high density. The low density types are polymerized at very high pressures and temperatures, and the high density types at relatively low temperatures and pressures. A relatively new type called linear low density polyethylene is manufactured through a variety of processes: gas phase, solution, slurry, or high pressure conversion. A high efficiency catalyst system aids in the polymerization of ethylene and allows for lower temperatures and pressures than those required in making conventional low density polyethylene. Copolymers of ethylene with vinyl acetate, ethyl acrylate, and acrylic acid are commercially important. Major polyethylene applications can be found in packaging, housewares, toys and communications equipment. Can be bonded effectively after plasma treatments or by using our UltraFlon Bond-X 1606.
Polyimides
A family of thermoset and thermoplastic resins characterized by repeating imide linkages: There are four types of aromatic polyimides: (1) condensation products made by the reaction pyromellitic dianhydride (PMDA) [C6H2(C2O3)2] and aromatic diamines such as 4,4′-diaminodiphenyl ether [(C6H4NH2)2O]; (2) condensation products of 3,4,3′,4′-benzophenone tetracarboxylic dianhydride (BTDA) [(C6H5)2CO(C2O3)2] and aromatic amines;(3) the reaction of BTDA and a diisocyanate such as 4,4′-methylene-bis(phenylisocyanate) [OCNC6H4CH2C6H4NCO]; and (4) a polyimide based on diaminophenylindane and a dicarboxylic anhydride such as carbonyldiphthalic anhydride [OC6H4(CO)2COC6H4(CO)2]. Thermoset polyimides are produced in condensation polymers that possess reactive terminal groups capable of subsequent cross-linking through an addition reaction. Typical applications for thermoplastic and thermosetting polyimides are transportation and electronics. Can be bonded after plasma treatment using most epoxies.
Polyphenylene Oxide, Modified
Engineering thermoplastic resins produced by the oxidative coupling of 2, 6-dimethylphenol [(CH3)2C6H3OH] (xylenol), then blended with impact polystyrene. Typical applications are found in electrical/electronic uses, business machine parts, appliances, and automotive parts. Can be bonded with solvents or epoxies. Adhesion can be enhanced greatly after plasma treatments.
Polyphenylene Sulfide
Engineering thermoplastic resins produced by the reaction of p-dichlorobenzene [C6H4CI2] with sodium sulfide [Na2S]. The major use for polyphenylene sulfide is in electrical/ electronic parts and automotive parts. After plasma treatments, this material bonds effectively with most epoxies.
Polypropylene
Thermoplastic resins made by polymerizing propylene [CH3CHCH2] and in the case of copolymers with monomers, with suitable catalysts, generally aluminum alkyl and titanium tetrachloride mixed with solvents. The monomer unit in polypropylene is asymmetric and can assume two regular geometric arrangements: isotactic, with all methyl groups aligned on the same side of the chain, or syndiotactic, with the methyl groups alternating. All other forms, where this positioning is random, are called atactic. Commercial polypropylene contains 90-97% crystalline or isotactic PP with the remainder being atactic. Most processes remove excess atactic PP. This by-product is used in adhesives, caulks, and cablefilling compounds. Major applications of commercial PP are found in packaging, automotive, appliance and carpeting markets. This material can be bonded effectively using UtraFlon Bond-X 1606.
Polystyrene
High molecular weight thermoplastic resins produced generally by the free-radical polymerization of styrene monomer [C6H5CHCH2] which can be initiated by heating alone but more effectively by heating in the presence of free-radical initiator (such as benzoyl peroxide [(C6H5CO)2O2]. Typical processing techniques are modified mass polymerization or solution polymerization, suspension polymerization, and expandable beads. Major markets for polystyrene are in consumer and institutional products, electrical/electronic uses, and building/ construction. Typically there are no issues bonding this material. But, plasma treatments have been used to enhance wettability of the material.
Polyurethanes
A large family of polymers based on the reaction product of an organic isocyanate with compounds containing a hydroxyl group. The commonly used isocyanates are toluene diisocyanate (TDI) [CH3C6H3(NCO)2], methylene diphenyl isocyanate (MDI) [OCNC6H4CH2C6H4NCO], and polymeric isocyanates (PMDI), obtained by the phosgenation of polyamines derived from the condensation of aniline [C6H5NH2] with formaldehyde (HCHO]. Polyols (with hydroxyl groups) are macroglycols which are either polyester or polyether based. Polyurethane elastomers and resins take the form of liquid castings systems thermoplastic elastomers and resins, microcellular products, and millible gums. Typical applications are found in the automotive industry. Polyurethane foams are widely used in transportation, furniture, and construction markets. Can be bonded effectively using acrylic adhesive or urethane adhesive. Adhesion can be improved greatly after plasma treatment.
If you have any questions about the materials above, Ask The Experts – or visit TriStar.
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