Tensile and fatigue properties of long glass fibre-reinforced polypropylene immersed in hot water

Abstract

Tensile tests and pulsating-tension fatigue tests have been carried out using smooth specimens of two materials of long glass fibre-reinforced polypropylene (LGF/PP), with and without acid modified polypropylene (APP). Specimens were immersed in distilled water at 80°C up to 6666 h. In both materials, the weight increased rapidly and reached the maximum, then decreased gradually with immersion time. The material without APP showed initially larger weight increase, but after immersion for over 2500 h more remarkable decrease was seen, indicating that the addition of APP was effective in improving water absorption characteristics of LGF/PP. Water entered along the fibre/resin interface and the weight loss of LGF/PP was attributed to leaching of surface treatment agents and dissolution of glass fibres, because the weight gain of the resin itself was negligible. Tensile and fatigue strengths were considerably decreased after hot water immersion because of the degradation of glass fibres, i.e. the reduction of fibre strength. The material with APP still exhibited higher strengths than the material without APP, also showing a beneficial effect of the addition of APP. Fracture mechanisms are discussed on the basis of close examination of fractured specimens.