Mastication Behavior of cis-1,4-Polyisoprene as a Model for NaturalRubber

The mastication behavior of synthetic cis-1,4-polyisoprene (IR), deproteinized natural rubber (DPNR), and natural rubber (NR) in an internal mixer has been investigated at mixing temperatures from 88 to 186°C and different levels of mechanical energy, using Mooney viscosity and size exclusion chromatography (SEC). An envelope-shaped mastication efficiency curve and high similarity in the mastication behavior can be observed for IR and NR but not for DPNR. The minimum of the envelope-shaped curve shifts to lower temperatures when the mechanical energy is increased. Based on these findings, a mathematical description for the contribution of mechanical and thermo-oxidative mastication mechanisms has been established. Distinct statistical distribution of thermo-oxidative scission can only be observed in SEC measurements of materials masticated at high temperatures over 170°C.