Polymers melting temperature, factors affecting

POLYMER FIBERS Processing Polymerization, additives, melting, fiber forming Y Melting temperature, factors that affect Y ... 

Chemical structure factors affect the melting point and glass transition temperature in much the same manner. A good empirical rale for many polymers is (142-144)... 

A variety of relaxation time studies have been performed on toluene. The choice of deuterated toluene avoids certain complicating factors which affect proton NMR studies, such as, dipolar or spin-spin couplings. The dominant relaxation mechanism is quadrupolar and the relaxation times are determined by the reorientation of the C-D bond vector. Relaxation times such as T, are sensitive to the motions of the solvent around the larmor frequency, which is on the order of 14 MHz in this study. T2 measurements may probe slower motions if the molecule undergoes slow and/or anisotropic motion. The relaxation time results presented in Figure 3 are significantly shorter than those found in bulk toluene solutions (18.19). In bulk toluene, the T and T2 values are equal above the melting temperature (1.2.). In this polymer system T2 < T indicative of slow and/or anisotropic reorientation. 

Effect of Temperature and Water. Thermal oxidation of plastics and rubbers can occur at all stages of their lifecycle but is most pronounced during melt processing. The combined effects of temperature (180-330°C) and shear lead to mechanical rupture of polymer chains and formation of reactive mechano-alkyl radical (R). The thermal history of a polymer, therefore, has major consequences on its subsequent in-service performance. Table 1 summarizes the factors affecting polymer degradation at different stages of its lifecycle. 

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