Evolution of physical and mechanical properties during phase transformation in poly(1-butene)

Abstract

The work is focused on study of evolution of the physical and mechanical properties of poly(1-butene) (PB-1). This evolution was observed during the phase transformation from the metastable form II to the thermodynamically more stable form I. Three different commercially-available grades of PB-1 were used in this work; two homopolymers and one ethylene copolymer. Specimens were prepared by compression molding with three various thickness and by extrusion This specimens were annealed at five various temperatures of -22, 5, 22, 40, and 60 degrees C during a time. Content of the form I in specimens was calculated by wide angle X-ray scattering during the phase transformation. Physical properties were measured via density changes of specimens and changes of mechanical properties were measured via tensile testing. From density measurements, it is obvious that the different thicknesses of compression-molded specimens do not influence the evolution of rate of the phase transformation. Densities of compression-molded and extrudates posses virtually the same values after the phase transformation. The evolution of the Form 1 content was confirmed by the trends, which were observed, via density measurements and by tensile testing in the evolution of tensile modulus. The evolution of tensile properties was carried out on extrudates and the results were consequently compared with the evolution of injection-molded specimens. From this observation it was found that values of moduli in extrudates are remarkably higher than in the injection-molded specimens. This is a consequence of different morphological structures, which have direct impact on mechanical properties and the phase transformation in PB-1. It is evident that processing is a key parameter influencing mechanical properties and together with annealing temperature significantly influences the rate of the phase transformation of PB-1.