A. Ariffin

Effects of hygrothermal aging and a silane coupling agent on the tensile properties of injection molded short glass fiber reinforced poly(butylene terephthalate) composites

Abstract The hygrothermal and mechanical properties of injection molded poly(butylene terephthalate) (PBT) composites containing 10, 20 and 30 wt.% short glass fiber (SGF) has been investigated. The kinetics of moisture absorption was investigated by immersion of PBT and SGF–PBT specimens in water at three different temperatures, i.e. 60°C, 80°C and 100°C. A single free-phase model of diffusion, which assumed Fickian diffusion and utilized Ficks second law of diffusion was used in analysing the data. A good agreement was observed between the experimental and theoretical values. The equilibrium moisture content, Mm and the apparent diffusivity, D, were found to be dependent on the volume fraction of the fibers. DSC measurements revealed that the thermal behavior, viz. the melting point and the degree of crystallinity of PBT and SGF–PBT composites were affected by hygrothermal aging process. This was attributed to the changes in the microstructure of PBT due to its interactions with water molecules. Hygrothermal aging reduced the tensile properties of PBT, the effect of which is strongly dependant on factors such as water immersion temperatures, volume fractions of fibers and also the chemical treatment of SGF. The presence of 3-aminopropyltriethoxysilane (3-APE) coupling agent has improved the retention of tensile properties of SGF–PBT composites, especially under adverse hygrothermal condition. Failure modes of both the matrix and the composites, assessed by fractographic studies in a scanning electron microscope (SEM) are discussed.

Filler treatment effects on the weathering of talc-, CaCO3- and kaolin-filled polypropylene hybrid composites

Talc, calcium carbonate (CaCO3), and kaolin hold considerable promise in the development of polymer composites for good mechanical properties and stability. Comparative studies on the usage of these minerals as single fillers in polypropylene (PP) have shown varying degrees of reinforcement due to their differences in terms of particle geometry, surface energy and affinity towards the matrix polymer. In this study, comparisons were made in terms of mechanical, thermal and weatherability properties between hybrid-filler PP composites (i.e. PP filled with either talc–CaCO3 or talc–kaolin hybrid filler combinations), with particular attention directed towards the effect of surface modification of the fillers. The talc/CaCO3 hybrid composites have shown exceptional performance in terms of flexural and impact properties. The contribution of talc in the talc–kaolin hybrid composite system has been significant in terms of enhancing the overall tensile and flexural properties. The ability of silane and titanate coupling agents in boosting the resistance of the composites to severe damage and degradation due to natural weathering has been shown.

Evaluation on extrudate swell and melt fracture of polypropylene/kaolin composites at high shear stress:

Kaolin-filled PP composites were compounded using a heated two-roll mill prior to extrusion process in order to improve the rheological properties of the samples. The extrudate swell and flow instability (melt fracture) behavior of kaolin-filled PP composite melts were investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 165°C to 220°C. The extrudate swell studies demonstrate that the die swell ratio decreases with an increase in the processing temperature and filler loading at fixed shear stress. Nonetheless, the study on the effect of shear stress and shear rate showed that the die swell ratio (B) of the melts decreases linearly with increasing apparent shear stresses and shear rates for both systems, unfilled and filled PP only up to one point above the critical shear rate (1.8 × 10 s-1). The B values remained almost constant when the shear rate is greater than 1.8 × 10 s -1 at a constant temperature. Kaolin-filled PP composites exhibit a characteristic of flow instability and extrudate distortions upon exiting from extrusion dies at low filler loading and at low processing temperature of 165°C. This type of defect is characterized by highly rough, fractured, and distorted extrudate surface. It was also found that decreasing the shear stress improved the surface appearance of all samples. Finally, the melt fracture tended to be suppressed when a capillary die with a high L/D ratio, which is 10 was used.

Evaluation of hybridizing talc and surface-treated kaolin on the properties of PP hybrid composites:

In this article, the effects of kaolin surface treatment on mechanical, morphological, and thermal behavior of PP/talc/ kaolin hybrid composites with different filler ratio were studied. Kaolin was pre-treated with QAC and SHMP, in order to eradicate the attraction of kaolin interparticle forces. It was found that both types of treatments enhanced the toughness of the composite remarkably. Although the tensile and flexural strength of the treated composites reduced with increasing amount of kaolin, it was still acceptably higher than the untreated composite. The enhancement of flexural modulus of the treated composites was attributed to the improvement of filler dispersion as observed by SEM results. In the light of the results achieved, the QAC proved to be more effective as dispersant for kaolin filler. This finding was further confirmed by thermal analysis and MFI study which shows that the properties of QAC-treated kaolin composites were comparable to the properties of talc-filled PP composite.

Effects of kaolin and maleic anhydride contents on melt elasticity and flexural behaviour of polypropylene/kaolin and unplasticised poly(vinyl chloride)/kaolin composites

Abstract Polypropylene/kaolin and unplasticised poly(vinyl chloride)/kaolin composites were prepared by directly melt mixing polypropylene (PP) and unplasticised poly(vinyl chloride) (UPVC) with maleic anhydride (MAH) and low cost kaolin via in situ extrusion process. The influences of kaolin particles and MAH in PP and UPVC matrix were discussed through investigating the flexural and morphological properties of filled PP and UPVC composites. The extrudates obtained from the extrusion process were carefully collected in order to investigate the elastic properties (extrudate swell and melt fracture). Results revealed that the above mentioned properties are strongly dependent on the presences of kaolin and MAH in both composite systems. Observation on scanning electron microscopy (SEM) analysis showed that the kaolin books (stacks of kaolin particles) were successfully delaminated thus lead to a well dispersed of kaolin particles in PP and UPVC matrix.