Thermoplastic polymers characteristics

All materials belong to the class of semi-crystalline thermoplastic polymers. Characteristic appearances of spherulitic microstructures of the polymers are shown in Figures 4 and 5 for the examples of POM and PA66. 

The next major commodity plastic worth discussing is polypropylene. Polypropylene is a thermoplastic, crystalline resin. Its production technology is based on Ziegler s discovery in 1953 of metal alkyl-transition metal halide olefin polymerization catalysts. These are heterogeneous coordination systems that produce resin by stereo specific polymerization of propylene. Stereoregular polymers characteristically have monomeric units arranged in orderly periodic steric configuration. 

Articles made from polypropylene have good electrical and chemical resistance and low water absorption. Its other useful characteristics are its light weight (lowest thermoplastic polymer density), high abrasion resistance, dimensional stability, high impact strength, and no toxicity. Table 12-3 shows the properties of polypropylene. 

Tetrazole, DNA synthesis and, 1115 Thermal cracking, 173-174 Thermodynamic control, 491 Thermoplastic polymer, 1216 characteristics of, 1216 examples of. 1216 Tg of, 1216 uses of, 1216... 

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

The importance of the use of mineral fillers to the growth of applications for thermoplastic polymers has already been described. The addition of such materials affects most of the significant properties of the matrix, some beneficially, others detrimentally. Only some of these altered properties are important to the use of thermoplastics, and an appreciation of what these are is critical to identifying those filler characteristics that are important and in understanding how certain filler types and production methods have come to dominate the market. 

The most common advanced composites are made of thermosetting resins, such as epoxy polymers (the most popular singlematrix material), polyesters, vinyl esters, polyurethanes, polyimids, cianamids, bismaleimides, silicones, and melamine. Some of the most widely used thermoplastic polymers are polyvinyl chloride (PVC), PPE (poly[phenylene ether]), polypropylene, PEEK (poly [etheretherketone]), and ABS (acrylonitrile-butadiene-styrene). The precise matrix selected for any given product depends primarily on the physical properties desired for that product. Each type of resin has its own characteristic thermal properties (such as melting point... 

As seen from Fig. 1, theory and practice coincide. The methods and equations, given in Sect. 3.1-3.3 allow us to calculate the head and consumption characteristics of the melted thermoplast, filled with a disperse inert filler, in particular, a mineralorganic one, at various pre-set temperatures and concentrations by using a single known head and consumption basic polymer characteristic, measured at any fixed temperature. The authors of this review have developed appropriate algorithms and programs for carrying out these calculations. 

The selected scenario comprises the conceptual design of a polymerization process for the production of Polyamide-6 (PA6) from caprolactam [99, 104]. PA6 is a thermoplastic polymer with a world production capacity of more than 4 million tons per year (as of 2006). The most frequent use of PA6 is the production of fibers, which are used in home textiles, bath clothing and for carpet production. In addition, PA6 is used as an engineering construction material if high abrasion resistance, firmness, and solvent stability are required. Glass-fiber reinforced and mineral material-filled PA6 is a preferred construction material if a combination of rigidity, elasticity and refractory quality characteristics are required. 

Figure 13.17 compares inorganic nanoplatelets with single-wall carbon nanotubes, dispersed in a typical thermoplastic polymer melt at given and Af values, including the effects of shear rate and particle flexibility. The fact that the nanotube dispersion shows much higher viscosity than the nanoplatelet dispersion at low shear rates is a result of the superposition of two effects. Firstly, there is the effect of the difference between the geometrical characteristics of fibers and platelets, as was also shown in Figure 13.15. Secondly, there is the effect of the much greater stiffness of single-wall carbon nanotubes (E=5000 GPa [45]) compared to nanoplatelets (E-100 GPa), which results in the effects of particle flexibility becoming very small for the nanotubes.

The most widely used thermoplastic polymer is the ethylene—vinyl acetate copolymer, which is obtainable in a wide range of molecular weights as well as in a variety of compositions. Often flexibilizers or plasticizers are added in order to improve both the mechanical shock resistance and the thermal properties of the adhesive. Polybutenes, phthalates, and tricresyl phosphate have been used as plasticizers. Tackifying agents can also be added. Because hot-melt adhesives are frequendy ethylene-based, they are subject to oxidation if, as in a typical situation, the adhesive sits in an applicator for long periods before use. Thus, antioxidants such as hindered phenols are often used, as are fillers. Fillers are added to opacify or to modify the adhesive s flow characteristics, as well as to reduce cost. Wax is also a very important component. Wax alters surface characteristics by decreasing both the liquid adhesive s surface tension and its viscosity in the melt. Upon solidification, however, the wax acts to increase the strength of the adhesive. Both paraffin and microcrystalline wax are used (see Waxes). 

Melt Properties. Block polymers may display thermoplasticlike processability in the melt state as exemplified by the A-B-A thermoplastic elastomers. However, various characteristic features distinguish the melt behavior of block polymers from that of conventional thermoplastic polymers (21. 86). These can be summarized as follows ... 

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