The Effects of Resin Content, Initiator, and Mix Temperature on the Rate of Linear Shrinkage of Unsaturated Polyester Resins Used in Cast Polymer Applications

摘要

Shrinkage during cure is an important characteristic of unsaturated polyester resins. In the cast polymer industry, shrinkage may lead to warping, cracking, or delamination of the gel coat. In order to better understand the relationship between shrinkage, temperature during cure, and the onset of BARCOL hardness, a method to measure shrinkage throughout the curing process was developed. A laser was used to measure linear shrinkage during the cure of a resin/filler mixture as a function of time. Simultaneously, a second container of the same mix was used to measure the temperature profile and onset of BARCOL hardness. A designed experiment was carried out to investigate the effects of initiator, resin/filler ratio and mix temperature on the relationship between shrinkage, temperature and the onset of BARCOL hardness. The rate of shrinkage was quantified by evaluating the slope of the displacement as a function of time. In all of the tests, the rate of shrinkage was found to be greatest during the first three hours after gelation. After four hours, the rate of shrinkage diminished significantly, although after 100 hours measurable shrinkage continued. The rate of shrinkage was greater for systems with higher initiator content and higher resin content. The systems with the higher mix temperatures also had higher rates of shrinkage. Quantifying the shrinkage rate and correlating this with onset of BARCOL hardness provides insights to factors that affect cast polymer manufacturing.