Processing, thermoplastics homopolymer

PTFE Teflon Politef Tetrafluoroethylene Resin Fluor Tetran. Versatile, chemically inert thermoplastic homopolymer. Used as tubing or sheeting for chemical laboratory and process work gaskets and pump packings as electrical insulators especially in high frequency applications, filtration fabrics, protective clothing, prosthetic aids. White solid usable between -270° and 265°. DuPont Janssen Chimica. 

Because of the difficulty of melt processing the homopolymer, acrylonitrile is usually copolymerized to achieve a desirable thermal stability, melt flow, and physical properities. As a comonomer, acrylonitrile contributes hardness, rigidity, solvent and light resistance, gas impermeability, and the ability to orient. These properties have led to many copol5mier application developments since 1950. The utility of acrylonitrile [107-13-1] in thermoplastics was first realized in its copolymer with styrene (CsHs) [100-42-5], in the late 1950s. Styrene is the largest volume of comonomer for acrylonitrile in thermoplastic applications. Styrene—acrylonitrile copolymers [9003-54-7] are inherently transparent plastics with high heat... 

Polypropylene (PP) is a family of thermoplastic polymers based on the polymerization of the propylene monomer. They are commercially available as PP homopolymers and PP random copolymers. The latter are produced by the addition of small amount of ethylene (2 to 5 percent) during the polymerization process. Thermoplastic PP polymers are characterized by their low density as compared with the rest of polymers (0.89 to 0.92 g/cm ), by their resistance to chemicals, and by their endurance to mechanical fatigue. PP resins are frequently employed in films and rigid containers. 

Polystyrene is one of the oldest commercially produced thermoplastic polymers. The homopolymer, frequently referred to as GPPS, is a highly versatile product that has found acceptance in widely diverse applications. The strengths of this brilliant, clear, noncrystalline plastic are processing ease, rigidity, dimensional stability and clarity. However, the low impact strength of polystyrene limits its use. 

During the past four years, linear low-density polyethylene (LLDPE) has probably become the most important of the thermoplastic copolymers. In contrast to the customary practice of producing branched ethylene homopolymer in a high-pressure reaction, a system of copolymerizing ethylene with a-C g olefins at low pressure is used to make LLPDE copolymer. This random copolymerization is commercially carried out in gas-phase, slurry, and solution processes in the presence of a transition metal catalyst 1-butene, 1-hexene, 4-methyl-l-pentene, or 1-octene are choices of comonomer. In the face of plant overcapacity and idle equipment existing at this time, LLDPE can also be made in high-pressure autoclaves and tubular reactors. 

EVA copolymers represent the largest-volume segment of ethylene copolymer market and are the products of low-density polyethylene (LDPE) technology. Commercial preparation of EVA copolymer is based on the same process as LDPE with the addition of controlled comonomer stream into the reactor. EVA copolymers are thermoplastic materials consisting of an ethylene chain incorporating 5-20 mol% vinyl acetate (VA), in general. The VA produces a copolymer with lower crystallinity than conventional ethylene homopolymer. 

As stated previously, styrene-diene triblock copolymers are the most important category of thermoplastic elastomers. Unlike most other TPEs, they can be blended with large quantities of additives without a drastic effect on properties. In almost all applications, the actual triblock copolymer content is less than 50%. Oils are used as a processing aid and do not result in a significant loss of properties if the polystyrene domains are not plasticized. For this reason, naphthalenic oils are preferred. The use of inert fillers such as clays or chalks reduces the cost of the final material. Unlike conventional rubbers, inert fillers do not have a substantial effect on the mechanical properties of TPEs. Thermoplastics such as polyethylene or polypropylene are also used to improve the solvent resistance and can increase the upper service temperature. Polystyrene homopolymer is used as a processing aid, which also increases the hard phase weight fraction and causes the material to stiffen. 

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