Influence Of Polymer Composition Research Articles

The flow of solid polymers under high pressure

The deformation and flow properties of solid polymers under uniaxial tensile and compressive loading have been determined for a variety of both crystalline and amorphous polymers at hydrostatic pressures to about 7 , kb. For some polymers, like polytetrafluoroethylene, cold drawing is inhibited by increasing pressure, and scanning electron micrographs show that local plastic deformation is greatly reduced. However, the true flow stress and the true fracture stress both increase with pressure, as does, also, the elastic modulus. The increase is greatest in the low-pressure range below 2 kb. This behavior is attributed to the pressure-induced shifting of a lowtemperatureβ′-transition. The influence of polymer composition and of the initial elastic constants on the pressure dependence of the elastic modulus and the yield stress is discussed. The observed behavior can be analyzed in terms of finite strain effects and a pressure-dependent yield criterion. It is shown that some amorphous polymers undergo a pressure-induced brittle-ductile transition, and these findings are used to explore the hydrostatic extrusion of polyimide and polysulfone at room temperature.

Temperature dependence of polymer viscosity. The influence of polymer composition

AbstractThe change of viscosity with temperature has been reported in the literature for a variety of linear, amorphous polymers. These data in terms of the flow activation energy, E*, indicate a wide variation among polymers with each exhibiting an essentially constant and characteristic E* at high temperature and high polymer molecular weight. These characteristic values of E* have been evaluated in terms of chemical composition and structure of individual polymer coils. The value of E* increases as a regular function of the molar volume of pendant groups along the polymer chain. More generally, a relation is shown between E* and the steric or conformational factor σ. For polyolefins, E* also increases regularly with the molar volume per monomer unit and with the mean‐square displacement length per chain unit.

Adhesion. III. Adhesion of polymers to cellulose and alumina

AbstractA relationship between tack temperature and molecular weight has been deduced and illustrated with polyvinyl acetate polymers. Provided the molecular weight is high enough to prevent cohesive failure, the adhesion of polyvinyl acetate to cellulose and aluminum is independent of molecular weight. The influence of humidity on adhesion of polymers to cellulose is shown. The influence of polymer composition on adhesion is illustrated with copolymers of vinyl acetate and methyl vinyl ketone and with styrene and methyl vinyl ketone. Above a mole fraction of ketone of 0.8, adhesion increases rapidly. The interdependence of tack temperature and composition on adhesion is exemplified with ethylene ‐ vinyl chloride copolymers. A temperature dependence of adhesion is cited for copolymers containing maleic acid.