Shout glass fibre reinforced poly(butylene terephthalate) - Part 2 - Effect of hygrothermal aging on mechanical properties

The mechanical properties of injection moulded poly(butylene terephthalate) (PBT) containing various loadings of short glass fibres (SGF) have been in vestigated. Properties studied include tensile, flexural, and impact. Effec t of hygrothermal aging on the mechanical properties was investigated by im mersing the respective specimens in distilled water at 30, 60, and 90 degre es C. All the materials tested showed poor retention in mechanical properti es upon exposure to hygrothermal aging. The effect became particularly pron ounced at an immersion temperature of 90 degrees C. Fractographic inspectio n of the fracture surfaces revealed that both PBT and SGF-PBT composites em brittled owing to a hydrolitic degradation process. Hydrolysis not only sup pressed the matrix ductility but also reduced the bonding quality between P BT and SGF. Poor interfacial bonding was indicated by the absence of polyme r matrix adhering to the fibre surfaces. The decrease in the impact strengt h of hygrothermally aged SGF PBT composites provided further evidence that hygrothermal aging at high temperature reduces the contribution of fibre re lated toughening mechanisms. The residual mechanical properties of both PBT and its composites were not fully recovered after redrying. The permanent damage to these materials was attributed to severe hydrolytic degradation o f PBT.