Some peculiarities of relaxation and structure-forming processes in polymer boundary layers

Abstract

The relaxation processes are retarded when the polymer interlayer in adhesive joints is diminished to a few microns. This retardation shifts the maximum on the temperature vs strength curve of such joints (under considerable overstresses) toward higher temperatures, and secondly, reduces the effectiveness of “rest” responsible for the partial strength recovery of the specimen in which rupturing crack propagates. In many systems the rate of polymer spherulite linear growth (G) diminishes with decreasing thickness of the polymer film (δ) from 15 to 30 μ. This was observed for isotactical polypropylene (PPr) and polystyrene, polyformaldehyde, cellulose tribenzoate, guttapercha, polypropyleneoxide (PPO), and polyethylenesebacynate (PES) on silica glass; PPr on copper, low-melting metal alloys (in crystalline or liquid state), various crystallo-graphic planes of NaCl, and planes (100) of CaF2 and LiF. The magnitude of G did not depend on δ in the crystallization of PPr, PPO, and PES on polyvinylacetate, polyvinylbutyral, crystalline and liquid low-melting mixtures of inorganic salts. Inhibition of spherulites growth in polymer boundary layers is strongly influenced by the surface energy irrespective of the phase or aggregate state of the substrate. The retarded growth of spherulites is probably due to the reduced density and lower mobility of polymer in the boundary layers.