SMC (sheet molding compound) is a composite based on fibers‐reinforced unsaturated polyester (UP) resin molded usually at 140°C to 170°C under a pressure of 60 to 100 bars. In order to develop new SMC formulations that can be molded at lower temperature (100°C) for economic and environmental reasons, the formulation of the composite had to be completely modified, both to allow a rapid reaction at 100°C, but also to avoid a vitrification phenomenon due to the fact that the glass transition temperature (Tg) of the SMC parts becomes, during the molding process, higher than the mold temperature. In this paper, the relation between the molding temperature, the glass transition temperature, and the final conversion of UP resin/styrene formulations has been underlined. The Tg of the cured resin was decreased by two different ways. The first way involved the reduction of the crosslinking density of the UP resin by using a blend of two resins, a pure maleic and a more flexible one. This blend allows to adjust the Tg over a temperature range from 197°C (Tg of the pure UP resin) to 75°C (Tg of the pure flexible resin). The second way consisted in the addition of butyl methacrylate (BuMA), a reactive plasticizer, to the formulation, allowing a decrease of the final material's Tg from 197°C to 130°C by replacing 35 wt% of styrene by BuMA. These two methods allow to obtain a final conversion of 99% after 8 minutes of molding at 100°C.

中文翻译：

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交联的不饱和聚酯树脂/苯乙烯配方的玻璃化转变温度对100°C等温固化后最终转化率的影响

SMC（片状模塑料）是一种基于纤维增强的不饱和聚酯（UP）树脂的复合材料，通常在140°C至170°C的压力下于60至100 bar的压力下模制。为了开发可以出于经济和环境原因而在较低温度（100°C）下模塑的新SMC配方，必须对复合材料的配方进行完全改性，既可以在100°C下快速反应，又可以避免由于在成型过程中SMC零件的玻璃化转变温度（Tg）高于模具温度而导致的玻璃化现象。本文强调了模塑温度，玻璃化转变温度和UP树脂/苯乙烯配方的最终转化率之间的关系。固化树脂的Tg通过两种不同的方式降低。第一种方法涉及通过使用两种树脂的混合物来降低UP树脂的交联密度，这两种树脂是纯马来酸树脂和更柔软的树脂。这种共混物可以在197°C（纯UP树脂的Tg）至75°C（纯软性树脂的Tg）的温度范围内调节Tg。第二种方法是在配方中加入甲基丙烯酸丁酯（BuMA），一种反应性增塑剂，通过用BuMA代替35 wt％的苯乙烯，使最终材料的Tg从197°C降低到130°C。这两种方法允许在100°C模塑8分钟后获得99％的最终转化率。这种共混物可以在197°C（纯UP树脂的Tg）至75°C（纯软性树脂的Tg）的温度范围内调节Tg。第二种方法是在配方中加入甲基丙烯酸丁酯（BuMA），一种反应性增塑剂，通过用BuMA代替35 wt％的苯乙烯，使最终材料的Tg从197°C降低到130°C。这两种方法允许在100°C模塑8分钟后获得99％的最终转化率。这种共混物可以在197°C（纯UP树脂的Tg）至75°C（纯软性树脂的Tg）的温度范围内调节Tg。第二种方法是在配方中加入甲基丙烯酸丁酯（BuMA），一种反应性增塑剂，通过用BuMA代替35 wt％的苯乙烯，使最终材料的Tg从197°C降低到130°C。这两种方法允许在100°C模塑8分钟后获得99％的最终转化率。