Molecular weight, tensile properties

We first briefly review the effects of M on physical properties under monotonic loading conditions. Some properties, such as density and low temperature dynamic mechanical behavior, are essentially unaffected by changes in molecular weight. Other properties, such as the glass transition temperature, T, and the tensile strength, increase appreciably with M in the low molecular weight region but tend to approach an asymptotic value as M is further increased. Fox and Flory have shown that for PS the dependence of T on M can be expressed as... 

Equivalency can be established through a series of data. Replacement materials can be compared with the original material in terms of chemical (structure, molecular weight, thermal properties, etc.) and mechanical properties (strength, tensile modulus, endurance, etc.). Data from actual devices fabricated from the new material should be compared with those from the original device. Biocompatibility data may be available from the material manufacturer, although the agency will request that additional data be supplied if the process used to fabricate the test samples differs from the process used to fabricate the device. 

Tensile properties of rigid-rod fibers, especially tensile strength, generally depend on molecular weight. With increasing molecular weight, tensile strength and... 

Table 7.8 The effect of irradiation dose on changes in average number Mn and molecular Mv, weights, tensile properties (strength (a), elongation (e), modulus (E)) and relative change of M after in vitro degradation...

The deterioration influences the physical and chemical properties, such as morphology, molecular weight, tensile strength, elongation at break and colour. 

Tensile Properties. Tensile properties of nylon-6 and nylon-6,6 yams shown in Table 1 are a function of polymer molecular weight, fiber spinning speed, quenching rate, and draw ratio. The degree of crystallinity and crystal and amorphous orientation obtained by modifying elements of the melt-spinning process have been related to the tenacity of nylon fiber (23,27). 

Desirable properties of elastomers include elasticity, abrasion resistance, tensile strength, elongation, modulus, and processibiUty. These properties are related to and dependent on the average molecular weight and mol wt distribution, polymer macro- and microstmcture, branching, gel (cross-linking), and... 

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