Influence of poly(acrylic acid) content on the fracture behaviour of glass polyalkenoate cements

A linear elastic fracture mechanics approach (LEFM) was used to study glass polyalkenoate cements as a function of the poly(acrylic acid) content. Cement specimens were tested at three time intervals after mixing; one, seven and twenty eight days. Two series of cements were investigated one with a glass volume fraction of 0.4 and the other with a glass volume fraction of 0.5. The fracture toughness, toughness, Young's modulus and un-notched fracture strength increased significantly with the percentage polyacid content. The Young's modulus increased with time for all the cement samples studied. In many cases the moduli values at twenty eight days were twice the values at one day. This is consistent with increased ionic crosslinking of the polyacrylate matrix. The toughness increased with the polyacid content as predicted by the chain pull-out model for fracture and did not change significantly on increasing the glass volume fraction from 0.4 to 0.5. Fracture toughness and Young's modulus increased significantly with glass volume fraction consistent with the residual glass particles acting as a reinforcing filler.