Response of unsaturated polyester, vinyl ester, and acrylic resins to water exposure
The objective of this research is to understand the interaction of water with orthophthalic and isophthalic unsaturated polyesters, vinyl ester and acrylic resins. Water diffusion, nucleation of internal disk cracks and weight loss of samples were the major water-polymer interactions observed. The effects of initiator type, the amount of initiator, the post-curing treatment, the specimen thickness, relative humidity and temperature on water uptake were studied. A weight loss was observed during absorption. The true absorption characteristics of the polymer could not be obtained due to the weight loss. Absorption-desorption-reabsorption (ADR) experiments were conducted to find the true equilibrium water content and diffusion coefficient. The ADR experiments revealed that polymers lost continuously during long term water exposure. The weight loss was attributed to the loss of residual materials and polymer degradation. The water diffusion behavior with disk cracks inside the polymers were compared with those without disk cracks. The effect of pressure on water diffusion in orthophthalic polyester and vinyl ester resins was studied. The higher pressure did not change the water uptake behavior in cast resin. A mechanism for disk crack initiation was presented and the theory states that disk cracking is a phase separation event that is a result of nucleation of a second phase within a saturated polymer. In neat resin, disk cracking took place upon saturation of the polymer in a 100% relative humidity. The effect of initiator and post-curing on the initiation time, the growth rate and number of disk cracks was examined. The healing of disk cracks was observed in salt solutions which have less than 100% R.H at 65$\sp\circ$C and 90$\sp\circ$C. This disappearance of disk crack is caused by the removal of the second phase as the system shifts from a region in which two phases are thermodynamically stable, i.e. saturated polymer and liquid, to a single phase region.
"Response of unsaturated polyester, vinyl ester, and acrylic resins to water exposure"
Dissertations and Master's Theses (Campus Access).