Effects of coupling agent and morphology on the impact strength of high density polyethylene/CaCO₃composites

The effects of coupling agent, particle diameter (d), particle volume fraction (Vc), particle size distribution and average matrix ligament thickness (T̄) on the impact strength of high density polyethylene (HDPE)/CaCO3composites have been investigated. A coupling agent is required for dispersing the CaCO3particles (d ∼ 0.6-5.6 μm) without agglomeration in the HDPE matrix. The optimum weight ratio of coupling agent to CaCO3particles for achieving the highest toughening efficiency is about 0.05, which is independent of d, Vcand size distribution of CaCO3particles, HDPE/CaCO3composites undergo a brittle-ductile transition in the range Vc= 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 Vc. In general, a HDPE/CaCO3composite 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 T̄. Shear yielding of the polymer matrix induced by debonding at the interface between CaCO3and HDPE is shown to be the major toughening mechanism.