The Research On Long-Glass-Fiber Reinforced Thermoplastic Composites Based On Polycarbonate/Poly (Butylene Terephthalate) Alloys

Long fiber reinforced thermoplastic resin (LFT), as the preparation technology for high performance composites, have a rapid development in recent years. This article investigated the mechanical, thermal performance and microstructures of long-fiber-reinforced thermoplastic (LFT) polycarbonate (PC)/poly (butylene terephthalate) (PBT) alloys through the joint processing of melt blending followed with a melt pultrusion. The mechanical evaluation demonstrated that the resulting composites achieved significant improvements in tensile strength, flexural strength and modulus, and notched impact strength. Such a prominent reinforcement effect is attributed to the feature that the residual fiber length within the injection-molded LFT composite specimens is much longer than that of the short-fiber-reinforced ones. This takes full advantage of the strength of the reinforcing fibers themselves. The improvement in impact toughness is due to the energy dissipation by both the fiber pull-out and fiber fracture as a result of the long-fiber-reinforcing effectiveness. The SEM investigation confirmed that the fiber pull-out and fiber breakage concurred on the impact and tensile fracture surfaces, and the former was more significant than the latter. Meanwhile, the coarse fiber surface also indicated a good interfacial adhesion between the thermoplastic matrix and fibers, so when the fiber debonding occurs, it could spread part of energy to enhance the mechanical properties of the composites. The residual fiber length and its distribution are important index to LFT composites, the article investigated effect to the residual fiber length with different content of fiber and PC. Results indicated that the mean fiber length ranging from 2 to 3 mm have a greater length than critical fiber length with a length of 0.65 mm, so the fiber could take full advantage of its strength. Moreover, the residual fiber length has a slighter reduce as the improvement of the content of fiber and PC. From the results of DSC, the introduction of PC evidently reduced the Tc of PBT phase due to the interference on the PBT crystallization from the PC macromolecules. However, glass fibers as nucleating agent seem to increase the Tc slightly, and thus enhance crystallization properties of the PBT phase. The load capacity under the high temperature is a very important indicator in engineering, the results of heat distortion temperature (HDT) indicated both glass fiber and PC could improve the HDT of PBT, but the former have greater efficiency. The HDT of alloy increased nearly 4 times as the content of fiber is 40%. The composites can maintain the stability of mechanical properties under 200 ℃. The study of dynamic mechanical analysis (DMA) revealed the LFT PC/PBT composites achieved a remarkable increase in storage modulus but presented a considerable decrease in loss-factor magnitude compared to the pristine alloys. The thermal stabilities and amount of residual carbon of the composites were also slightly improved in the presence of long glass fibers according to the results of thermogravimetric analysis.