聚丙烯-聚乙烯消光膜体系织态结构形成机理

Mechanism of the Surface Texture Formation in the Polypropylene and Polyethylene Blends

采用偏光显微镜和热台联用的方法,研究了聚丙烯(PP)-聚乙烯(PE)共混体系降温过程中的相分离和结晶行为。在此共混体系中,PE质量分数为10%~60%,随着PE质量分数增加,结果呈现2种不同的分相形貌特征:PE质量分数为10%~30%时,PE相区分散在连续相PP中,当PE质量分数为40%~60%时,PE/PP共存,为双连续相。通过对结晶过程形貌特征的转变以及相畴尺寸的定量分析,发现了2种控制表面粗糙程度的机理:在PP为单连续相时,粗糙度主要取决于分散相相畴大小;在PE/PP双连续相的情况下,在互穿网络结构中主要为骨架相互挤压控制。通过比对各拉伸比下的形貌特征,发现静态结晶形成的织态结构在拉伸过程中发生与宏观应变相关的等比放大,表明消光膜表面形貌主要取决于静态结晶过程。为了建立静态结晶形成结构和消光膜雾度的关系,通过共混-挤出-流延-双向拉伸的方法制备了不同PE含量所对应的消光膜样品,通过雾度测试,证明表面粗糙的织态结构为决定雾度的关键,同时证明了静态结晶实验对于消光膜加工过程中雾度控制的指导意义。

The phase separation and crystallization during constant rate cooling of polyethylene(PE)and polypropylene(PP)were investigated through combination of polarized microscopy characterization and heat stage.The blend ratio of PE in PP ranges from 10%to 60%,exhibiting two distinct morphological features,i.e.isolated island PE phase dispersed in PP matrix and two interpenetrating networks for 10%~30%and 40%~60%,respectively.Through quantitative analysis,size of dispersed phase is the dominating factor determining the surface morphological features at PE from 10%~30%while the internal stress imbalance between interpenetrating networks is responsible for 40%~60%.The features of surface morphology keep similar by the comparison of samplesat different biaxial draw ratios.Consequently,phase separation and crystallization are the most critical factors determining the surface morphology.In order to establish the relationship between microstructure formed after crystallization and haze of matt film,samples are prepared with different PE contents by blending,coextrusion,film casting and biaxial stretching.The surface texture is validated to be the key factor deciding haze.Moreover,the investigation of phase separation and crystallization under static condition can be adopted to guide processing of matt film.