Fracture initiation and crack propagation of acrylonitrile-butadiene-styrene (ABS) in organic solvents

The effects of organic liquid environments on the fracture behaviour of acrylonitrile-butadiene-styrene (ABS) have been investigated. Fracture initiation experiments showed that K_i², (K_i being the stress intensity factor at crack/craze initiation), could be meaningfully correlated with the solvent solubility parameter (δ_s) of the different liquid environments and had a minimum value at δ_s=δ_p, where δ_p was the solubility parameter of ABS. For the range of organic liquids used, hydrogen bonding did not have any significant effects on the correlations. It was demonstrated that the K_i²-δ_s correlations could also be usefully extended to other materials such as plain and glass-filled polystyrenes. At a common crack speed (å), the fracture toughness (R) values in "crazing" liquids (i.e. alcohols) were greater than those in "cracking" solvents (i.e. acetone, benzene, toluene, etc.) which usually caused a "dissolution" effect on the plastic. From crack propagation experiments, and using fracture mechanics analyses, definite R(å) and K_c(å) relationships for ABS immersed in toluene, carbon tetrachloride and methanol were determined. These experimental results showed that crack propagation was relaxation controlled and agreed well with a recent theoretical analysis due to Williams and Marshall for environmental crack and craze growth in polymers. Finally, SEM pictures were presented to show the remarkable differences in the fracture morphologies of ABS in both "crazing" and "cracking" liquid environments.