Mechanical properties of woven glass fabric reinforced in situ polymerized poly(butylene terephthalate) composites

Cyclic butylene terephthalate (CBT) has been polymerized in situ at T = 190 °C in the presence and absence of woven glass fabric (WGF). The thermal properties of the in situ polymerized poly(butylene terephthalate) (ISP-PBT) were compared with those of a commercial injection molded PBT (IM-PBT). It was found that the crystallinity of IM-PBT is markedly lower than that of ISP-PBT rendering the latter more brittle. WGF-reinforced (ca. 50 vol.%) ISP-PBT composites were fabricated by compression molding at T = 190 °C using displacement and pressure-controls. Effects of the molding condition were investigated in tensile, three-point bending, short beam shear and dynamic mechanical thermal analysis tests. Both tensile and flexural properties (stiffness and strength), as well as inter-laminar shear strength, were enhanced when the molding occurred under pressure-controlled instead of displacement-controlled conditions. Scanning electron microscopic (SEM) inspection revealed excellent wet-out of the fibers and good interfacial bonding between the fibers and ISP-PBT.