Effect of filler content and surface treatment on the tensile properties of glass-bead-filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A-glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus Ec of the composites increases non-linearly with increasing volume fraction of glass beads ϕf, while the tensile yield strength σyc and tensile stress at break σbc of the composites decrease with an increase of ϕf, in the ϕf range 0–30%. Furthermore, the values of Ec and σbc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break εbc and tensile fracture energy Ebc, especially at higher ϕf values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, εbc and Ebc reach maximum values at ϕf = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry