Modelling of temperature-related phenomena in polymers

Abstract In comparison with metals, the characteristic temperatures at which polymers change their behaviour are significantly smaller. Temperature-related or temperature-driven phenomena in meltable thermoplastics, weakly crosslinked elastomers or highly crosslinked thermosets have their origin in physical or chemical changes on the microscale. On the macroscopic scale, the mechanical, thermal and caloric properties of polymers change. Some of these phenomena are reversible, others are irreversible. They take place when the temperature is changing due to heat supply from outside or energy dissipation caused by inelasticity and dynamic mechanical loads. As we know, growing temperature increases the mobility of the polymer molecules and changes the rates of chemical reactions. This review article addresses selected phenomena relevant for technical applications. As a reversible phenomenon, the process-dependent stiffening and softening of polymers around the glass transition is treated. Crystallisation, driven by deformation or temperature, is also a reversible phenomenon discussed in this article. Adhesives are applied in everyday life and change their material properties during curing. A phenomenon of high technical importance is ageing. Irreversible chemical ageing increases with the temperature or the environmental oxygen concentration, results from the generation of new crosslinks in combination with chain scission and modifies the mechanical material behaviour. Another characteristic, especially of thermoplastics, is physical ageing. It occurs below the glass transition, corresponds to a decrease in the free volume and leads to an increase in the relaxation times. If polymer parts are dynamically deformed over long times, dissipative heating takes place and leads to an increase in temperature. The focus of this review article is material modelling. Experimental investigations support the argumentation.