Abstract: PP/PA6 blends were prepared at four blending ratios using PP as a continuous phase and PA6 as a disperse phase, and the effect of PP/PA6 blending ratio on the tensile strength and microstructure of the pipes obtained by WAIM with PP/PA6 blends was investigated. The tensile experimental results indicated that the tensile strength of the pipes increased at first and then tended to decrease with an increase of PA6 content. The scanning electron microscopic observation showed that the PA6 phase was dispersed in both the near-wall and the near-water layers in a long strip or long slice shape with a large length/thick ratio, but it was dispersed in the middle layer as ellipsoids. There is an increase trend in the aggregation and growth of the dispersed phases in each layer with an increase of PA6 content. Polarizing microscopic observation showed that some small and dense crystals were formed along the flow direction at the near-wall and near-water layers, whereas the relatively larger crystals were distributed at the middle layer. Moreover, PP was found to only form one crystal form during the WAIM process, but two crystal forms were generated in the PA6 phase. The degree of crystallinity of PP domain at the near-water and near-wall layers was higher than that at the middle layer. The degree of crystallinity of PA6 phase increased with its weight fraction in the blends, while a high degree of crystallinity was maintained for the PA6 phase at the near-wall layer.

Key words: polyprogylene, blend, waterassisted injection molding, tensile strength, morphology