Effects of coupling agent and morphology on the impact strength of high density polyethylene/CaCO3 composites

Abstract The effects of coupling agent, particle diameter ( d ), particle volume fraction ( V c ), particle size distribution and average matrix ligament thickness ( T ) on the impact strength of high density polyethylene (HDPE)/CaCO 3 composites have been investigated. A coupling agent is required for dispersing the CaCO 3 particles ( d ∼0.6–5.6 μm) without agglomeration in the HDPE matrix. The optimum weight ratio of coupling agent to CaCO 3 particles for achieving the highest toughening efficiency is about 0.05, which is independent of d , V c and size distribution of CaCO 3 particles. HDPE/CaCO 3 composites undergo a brittle–ductile transition in the range V c =0.1–0.3, and the maximum impact strength achieved depends on d and size distribution. Above the transition, the impact strength of the composite decreases with increasing V c . In general, a HDPE/CaCO 3 composite with smaller d and broader size distribution has a higher toughness. A single brittle–ductile transition curve is not obtained when the impact strength is plotted against T . Shear yielding of the polymer matrix induced by debonding at the interface between CaCO 3 and HDPE is shown to be the major toughening mechanism.