Effect of mixed silanes on the hydrolytic stability of composites

A filler for a urethanedimethacrylate composite was silanated with mixtures of fluoroalkyl-, aminoalkyl-, phenyl-, vinyl-, bis silyl ethane- and 3-methacryloxypropyltrimethoxysilane (MAOP) in an attempt to increase the hydrophobicity of the coupling agent layer. Diametral tensile strength was used to evaluate composites stored for (1) 24 h in 23 degrees C (RT) air; (2) 24 h in RT air plus 24 h in 100 degrees C air; (3) 24 h in RT air plus 24 h in 100 degrees C water; and (4) 24 h in RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. Water sorption and solubility of composites was also determined on samples stored for 24 h in RT air. Heating composites for 24 h in 100 degrees C air increased the tensile strength in eight of 13 silane treatments, while heating in 100 degrees C water for 24 h caused decreases for five silane treatments, no change for six and increases in tensile strength for two silane treatments. When composites that had been stored for 24 h at RT plus heated for 24 h in 100 degrees C air were then heated for 24 h in 100 degrees C water, only one silane treatment, the vinyltriethoxysilane at 25% (25% V), showed no significant decrease in tensile strength. Also, the composite silanated with 25% V had the highest value for tensile strength after storing for 24 h at RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. These data indicate that the use of vinyltriethoxysilane increases the hydrolytic stability of the composite. Water sorption and solubility of the silanated composites were not satisfactory tests for evaluating hydrolytic stability of composites.