Injection molding of poly(ethylene terephthalate) reinforced with pregenerated thermotropic liquid crystalline polymer microfibrils

This work was concerned with the injection molding of poly(ethylene terepht halate) (PET) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) fibrils, where the TLCP had a higher melt processing tempera ture than PET, These composites, referred to as pregenerated microcomposite s, were produced using a two step processing scheme, First, a novel dual ex trusion process was used to spin strands of PET reinforced with nearly cont inuous TLCP fibrils. Second, these strands were subsequently chopped into p ellets and injection molded below the melt processing temperature of the TL CP but above that of PET. This allowed the high modulus TLCP fibrils genera ted in the spinning step to be retained in the injection molded samples. TL CP concentration and strand draw ratio were varied in the composite strands to determine how they affected mechanical properties. It was shown that th e best properties were obtained using strands containing 50 weight percent TLCP with draw ratios greater than 50, which were diluted to the desired lo ading level with a low viscosity injection molding grade of PET. Specifical ly, these composites had tensile moduli as high as 5.7 GPa when reinforced with 30 weight percent HX1000. Also, it was determined that pregenerated mi crocomposites had smoother surfaces than glass-filled PET.