ABSTRACT:The effect of the filler volume fraction on the tensile behavior of injectionmolded rice husk-filled polypropylene (RH-PP) composites was studied. Hygrothermal aging behavior was also investigated by immersing the specimens in distilled water at 30 and 90°C. The kinetics of moisture absorption was studied from the amount of water uptake by specimens at regular interval times. It was found that the diffusion coefficient and the maximum moisture content are dependent on the filler volume fraction and the immersion temperatures. Incorporation of RH into the PP matrix has led to a significant improvement in the tensile modulus and a moderate improvement in the tensile strength. Elongation at break and energy at break, on the other hand, decreased drastically with the incorporation of the RH filler. The extent of deterioration incurred by hygrothermal aging was dependent on the immersion temperature. Both the tensile strength and tensile modulus deteriorated as a result of the combined effect of thermal aging and moisture attack. Furthermore, the tensile properties were not recovered upon redrying of the specimens. Scanning electron microscopy was used to investigate the mode of failure of the RH-PP composites.

Fracture behavior of poly(butylene terephthalate) (PBT) and its rubbertoughened (RT) 10 wt %) grades; ethylene-co-glycidyl methacrylate-co-methacrylate terpolymer-toughened poly(butylene terephthalate) PBT/AX8900 (90/10), and Paraloid acrylic-based rubber-toughened poly(butylene terephthalate) PBT/EX2314 (90/10) was investigated using the fracture mechanics approach. The effects of controlling parameters such as type of impact modifier and deformation rate on fracture behavior of PBT and RT-PBT were investigated. Fracture tests were carried out on notched compact tension (CT) specimens. Fracture toughness, K c , and fracture energy, G c , of PBT decreased as the test speed increased from 1 to 500 mm/min. An opposite trend was observed in PBT/AX8900 and PBT/EXL2314. The fracture properties of 30 wt % short glass fiber-reinforced PBT (SGF-PBT) and 10 wt % impact-modified PBT composite (SGF-RT-PBT) were also studied. Incorporation of SGF into PBT has profoundly increased the fracture properties both at high and low speed. However, inclusion of 10 wt % of AX8900 into the reinforced PBT (PBT/AX8900/SGF) (60/10/30) adversely affected the fracture properties. EXL2314, on the other hand, showed a different effect, especially at high testing speed. Both types of impact modifiers were able to retain the flexural strength and flexural modulus of PBT. However, PBT/EXL2314 showed a better retention of flexural properties than PBT/AX8900. Incorporation of SGF in the EXL2314-toughened PBT, i.e., PBT/EXL2314/SGF (60/10/30) also gave a better balance of flexural properties compared to PBT/AX8900/SGF (60/10/30). Both PBT/AX8900 and PBT/EXL2314 showed enhancement of impact strength on the unnotched specimens. The failure modes of CT and impact specimens of PBT, RT-PBTs, and SGF-RT-PBTs were assessed using a scanning electron microscope (SEM). Brittle failure was observed for CT specimens of PBT at high testing speed, while incorporation of the impact modifier AX8900 and EXL2314 resulted in a shift of failure mode from brittle to ductile. SEM micrographs also revealed extensive fiber pull out in SGF-PBT and SGF-RT-PBT.

ABSTRACT:The objectives of this paper were to investigate the water absorption and hygrothermal aging behavior of rubber-toughened poly(butylenes terephthalate) (RT-PBT) with and without short glass fiber (SGF) reinforcement. The rubbers used in the study were AX8900 and EXL2314, both of which are acrylate-based terpolymer. The effect of the hygrothermal aging on its fracture properties was also studied. The kinetics of the water absorption study were carried out on the injection-molded samples of the RT-PBTs and the SGF-reinforced rubber-toughened PBT (SGF-RT-PBT) at three immersion temperatures, 30, 60 and 90°C, for a total of 450 h. The study of the deterioration caused by the hygrothermal aging was conducted by investigating the fracture parameters and flexural properties of all the materials as both hygrothermally aged (HA) and redried state (RD). The modes of the failure of HA and RD samples were studied using the scanning electron microscopy (SEM) technique. It was found that all the samples conformed to Fickian behavior and the kinetics of absorption exhibited a strong dependency on the rubber types, presence of SGF, as well as the immersion temperature. Generally, SGF-RT-PBT showed a better resistance to hygrothermal aging than that of RT-PBT and PBT, though a declining trend was observed in the fracture parameters, K c and G c . However, an opposite observation was exhibited in the flexural properties in some, but not all cases. Finally, the results obtained from SEM micrographs showed that permanent damage occurred in the materials and the hygrothermal aging had suppressed the plastic deformation ability of the PBT matrix and both types of impact modifiers where brittle failure was observed. Fiber pull-out was apparently the failure mode of the SGF-reinforced materials.

The kinetics of moisture absorption have been studied by immersing poly-( butylene terephthalate) (PBT) and its short glass fibre reinforced composites (SGF-PBT) in water at 30, 60, and 90°C. A single free phase model of absorption was applied to the kinetics data and the diffusion coefficient or diffusivity D was evaluated. The value of D was found to be strongly dependent on the water immersion temperatures and to a limited extent on the volume fraction of fibres. The incorporation of fibres resulted in a reduction of the equilibrium moisture content M m . The nature of the interaction of water molecules with PBT and SGF-PBT was investigated by immersing both materials in water at 90°C for a prolonged period. Variation of the pH of the water with immersion time, FTIR spectra taken on the water extract, and SEM examination of the specimen surface, revealed the occurrence of hydrolysis.

The mechanical properties of injection moulded poly( butylene terephthalate) (PBT) containing various loadings of short glass fibres (SGF) have been investigated. Properties studied include tensile, flexural, and impact. Effect of hygrothermal aging on the mechanical properties was investigated by immersing the respective specimens in distilled water at 30, 60, and 90°C. All the materials tested showed poor retention in mechanical properties upon exposure to hygrothermal aging. The effect became particularly pronounced at an immersion temperature of 90°C. Fractographic inspection of the fracture surfaces revealed that both PBT and SGF-PBT composites embrittled owing to a hydrolitic degradation process. Hydrolysis not only suppressed the matrix ductility but also reduced the bonding quality between PBT and SGF. Poor interfacial bonding was indicated by the absence of polymer matrix adhering to the fibre surfaces. The decrease in the impact strength of hygrothermally aged SGF-PBT composites provided further evidence that hygrothermal aging at high temperature reduces the contribution of fibre related 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 of PBT.