Fiber orientation propelled by high-pressure water penetration in water-assisted injection molded fiber-reinforced thermoplastics part

Abstract

Fiber orientation pattern across the thickness of water-assisted injection molded (WAIM) fiber-reinforced polypropylene part was investigated and its formation mechanism was interpreted with the aid of unique shear rate and cooling rate fields within mold cavity under melt filling and high-pressure water penetration. It was found that the relative thickness of ordered region in WAIM part is much larger than that in conventional injection molded part. At the position near water inlet, less and less fibers arrange along flow direction from the area near mold wall to the one near water channel; whereas at the position near the end of water channel, almost no disordered region exists. Higher water pressure and lower melt temperature result in more fibers orienting along flow direction. More importantly, high-pressure water penetration can remarkably propel the fiber orientation in WAIM fiber-reinforced parts, which may improve their mechanical properties.