Polystyrene is an aromatic polymer made from an aromatic monomer (styrene) which is commercially manufactured from petroleum.107 High Impact Polystyrene (HIPS) is a type of polystyrene that is versatile, economical and easy to fabricate. HIPS is mostly used for low strength structural applications where impact resis­tance, machinability and low cost are needed. Polybutadiene is added during the polymerization of HIPS. This polybutadiene is generally known as rubber, which provides HIPS with the required toughness and impact resistance.57

9.4.1 MECHANICAL PROPERTIES

9.4.7.1 EFFECT OF FIBER LOADING

A study on the effect of SPF loading on the tensile properties of SPF/HIPS compos­ite was reported by Sapuan and Bachtiar57. Fiber contents of 0, 10, 20, 30, 40 and 50% by weight were incorporated in HIPS matrices. The tensile strength of short SPF/HIPS composites slightly decreased compared to the neat HIPS (0% loading) as the fiber content in them increased from 10 to 30%. The average tensile strength of the neat HIPS was 29.92 Mpa, which was approximately 12.4, 22.5 and 35.5% higher than SPF/HIPS composites with 10, 20 and 30% fiber contents, respectively (see Fig. 9.15). The decrease of tensile strength of the composites with fiber load­ings from 10 to 30% by weight emanated from the weak fiber-matrix interface as a result of differing polarities of the hydrophilic SPF and hydrophobic HIPS matrix. On the other hand, considerable increment in the tensile strength of the composites was realized as the fiber loadings increased from 40 to 50%. This may be attributed to the better interaction and improved dispersion of SPF in the HIPS matrix, which enhanced the interfacial bonding between fibers and matrix. Generally, good tensile strength depends more on effective and uniform stress distribution.96 The high ten­sile strength of composites at fiber content of 40 to 50% indicates the fibers were effectively capable of transfer the load to one another. This illustrates that the fibers (40 to 50% weight fraction) effectively participated in the stress transfer causing the effect of crack inhibition more dominant over the effect of crack initiators.96

The tensile moduli of short SPF/HIPS composites increased from 1516 to 1706 MPa with increase fiber loading from 10 to 30% by weight (see Fig. 9.16). The maximum tensile modulus value obtained at fiber content of 30% in HIPS matrix was 25.6% higher than neat HIPS (0% fiber loading). However, the addition of short SPF by 40 to 50% inflicted slight decrease on the tensile modulus of the compos­ites. The decrease of tensile modulus beyond SPF loading of 30% was due to the decrease of bond quality between the fibers and HIPS matrix. At high fiber contents, the extent of fiber wetting reduces because it is difficult to achieve good consolida­tion of the composites during fabrication process.107