Research on Stress Whitening Phenomenon of Polypropylene and Its Modified Materials

The stress whitening phenomenon refers to the fact that when insulating materials are subjected to external stress, the microstructure inside the material changes, resulting in enhanced light scattering in certain areas and thus presenting a phenomenon of changing from transparent to white. Polypropylene (PP), as a commonly used insulating material for power cables in recent years, has the advantages of hightemperature resistance, great toughness, easy processing and environmental friendliness. However, during the cable laying process, stress concentration occurs in the bent parts of the cable, and the cable insulation material polypropylene may experience stress whitening. Based on the cavity theory, this paper uses the constant extension retainer to apply a 10 % strain corresponding to the yield point of each of the two polypropylenes, and adds the same content of polyolefin elastomer (POE). Through experiments such as polarizing microscopy and electro-acoustic pulse method, the following conclusions are drawn. Under the same strain, copolymer polypropylene is more prone to stress whitening than homopolymer polypropylene. After polypropylene undergoes the stress whitening phenomenon, its dielectric properties decline. The addition of polyolefin elastomer (POE) can effectively suppress the stress whitening phenomenon. However, adding too much POE will also reduce the dielectric performance of the material. Therefore, it is necessary to add an appropriate amount of POE to suppress stress whitening without affecting the dielectric performance of polypropylene itself.