Development of Low Moisture Absorbing SMC

Abstract

In this work, the role of SMC constituent components in controlling the moisture absorption of the final molded panels is discussed. A variety of polyester resins, low profile additives, and fillers were exposed to high humidity, defined as 90% relative humidity at 40°C, for extended hours. It was concluded that calcium carbonate, which is the most common filler for SMC, at a 0.12 wt% moisture absorption level, is the second lowest in moisture absorption. The comparison of the calculated and measured moisture absorption numbers indicated that rule of mixtures can be used to accurately predict the behavior of SMC based on the polymeric matrix. However, the polymeric matrix moisture uptake has to be measured experimentally and cannot be predicted using the mixing rule for its constituent ingredients due to the complexity of the interactions in the mixture. It was also identified that MgO, which is the most commonly used thickening agent, has a significant impact on moisture uptake of SMC. Based on the generated information, two low moisture absorbing SMC formulations were developed and their properties were measured.