LDPE-based thermoplastic elastomers containing ground tire rubber with and without dynamic curing

Abstract

Attempts were made to use a ground tire rubber (GTR) fraction (particle size: 0.4–0.7 mm) to produce thermoplastic elastomers (TPEs) composed of low-density polyethylene (LDPE), fresh rubber and GTR with and without dynamic curing. GTR has been thermomechanically decomposed in the presence (GTR PM) and absence of processing oil (GTR M) and its decomposition was followed by the increase in the acetone-soluble fraction. The composition of the TPEs was constant, viz. LDPE: rubber:GTR=50:25:25 wt.%. As fresh gums styrene/butadiene (SBR), natural (NR) and ethylene/propylene/diene (EPDM) rubbers were used in blends with GTR R (reference, not treated), GTR M and GTR PM at 1:1 ratio. Dynamic vulcanisation occurred either by sulfur or by peroxide curatives. Based on the thermomechanical and mechanical properties of the resulting TPEs, the best performance was achieved by recipes containing GTR M and EPDM after dynamic vulcanisation with sulfur. This was traced to the dual compatibilizer effect of the EPDM. The ethylene segments of the EPDM are compatible with the LDPE, whereas the surface of the partially decomposed GTR may be involved in both molecular entangling and interphase sulfur crosslinking mechanisms which all yield a better interfacial bonding between the GTR particle and the matrix. The phase structure of the TPEs were assessed by dynamic-mechanical thermal analysis (DMTA) and fractography (etched cryogenic fracture surface) and discussed.