THE FRACTURE PROPERTIES OF GLASS POLYALKENOATE CEMENTS AS A FUNCTION OF CEMENT AGE

The fracture properties of two glass polyalkenoate cements based on a short chain-length and on a long chain-length poly(acrylic acid) have been studied as a function of the cement age. The stress intensity factor, K1, increases with cement age for both cements. The un-notched fracture strength sigma(f) increases with cement age, largely as a result of an increase in the Young's modulus accompanying crosslinking of the polyacrylate chains by metallic ions. The toughness G1 remains approximately constant for the short chain-length cement, but reduces with cement age for the long chain-length cement. Analysis of the toughness data using a chain pull-out model leads to the conclusion that chains distant from the fracture plane are involved in fracture, and that the number of chains that take part in chain pull-out decreases as the crack opening displacement reduces with cement age.