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

The effects of coupling agent, particle diameter (d), particle volume fraction (V_c), particle size distribution and average matrix ligament thickness (T̄) on the impact strength of high density polyethylene (HDPE)/CaCO₃ composites have been investigated. A coupling agent is required for dispersing the CaCO₃ particles (d ∼ 0.6-5.6 μm) without agglomeration in the HDPE matrix. The optimum weight ratio of coupling agent to CaCO₃ particles for achieving the highest toughening efficiency is about 0.05, which is independent of d, V_c and size distribution of CaCO₃ particles, HDPE/CaCO₃ 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/CaCO₃ composite 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 CaCO₃ and HDPE is shown to be the major toughening mechanism. © 2002 Elsevier Science Ltd. All rights reserved.