水辅助注塑PP/EVOH共混物制品的相形态与阻渗性能

Phase morphology and barrier performance of water-assisted injection-molded PP/EVOH blend parts

选择3种不同黏度的聚丙烯(PP)与聚乙烯醇(EVOH)共混制备质量比为90/10的共混物,并采用水辅助注塑(WAIM)将这3种共混物成型为中空制品。从WAIM制品靠近浇口(1#)和末端(2#)两个位置取出样品,通过扫描电镜观察样品壁厚上3个位置的相形态,并测试所取样品的甲苯渗透率。借助WAIM中高压水作用下模腔内熔体的流场对样品中3个位置的相形态进行了分析。对WAIM的高黏度比共混物制品2#样品,在外表层和内表层分散相呈粗纤维状,芯层主要呈液滴状,其阻渗性能与相应的WAIM PP样品比有适度提高(约2.4倍);对WAIM的2种低黏度比共混物制品2#样品,外表层和内表层分散相呈细纤维状,芯层呈粗长纤维状,其阻渗性能与相应的WAIM PP样品比提高幅度较大(其中对黏度比最小的共混物达9.8倍)。1#位置所取3种WAIM PP/EVOH样品中分散相纤维的平均直径比2#位置的大,导致1#位置所取样品的阻渗性能比2#位置的低。

Three kinds of polypropylene （PP） with different viscosities were blended with poly（vinyl alcohol） （EVOH） to prepare 90/10 PP/EVOH blends, and the blends were then molded into hollow partsvia water-assisted injection molding （WAIM）. Samples were cut from locations near the gate （marked as 1#） and the end of flow channel （marked as 2#） of the WAIM blend parts, and the phase morphologies at three regions across the residual wall of the samples were observed with scanning electron microscope. The toluene permeabilities of the samples cut from the WAIM blend parts were measured. The phase morphologies at the three regions in the samples were interpreted with the aid of flow fields within the mold cavity under high-pressure water penetration during WAIM. Coarse fibers appeared in both outer and inner layers and droplets in the core layer for the sample taken from location 2# of the WAIM blend with high viscosity ratio, which resulted in modestly improved barrier performance of the sample compared with the WAIM corresponding PP sample （about 2.4 times）. Slim fibers existed in the outer and inner layers and coarse and long fibers in the core layer for the samples taken from location 2# of the WAIM blends with low viscosity ratios, which resulted in greatly improved barrier performance of the samples compared with the WAIM correponding PP sample （about 9.8 times for the blend with the lowest viscosity ratio）. Average diameters of dispersed fibers for the samples taken from location 1# of three WAIM parts were larger than those taken from location 2#, which resulted in lower barrier performance for the former samples.