Mechanical decomposition of isotactic polypropylene subjected to plastic flow under high pressure

The molecular mass distribution (MMD) of isotactic PP subjected to shear deformation under a pressure of 1 GPa in the Bridgman anvils was investigated. The M w and M n values decrease with increasing shear strain (angle). Three regions with different extent of the mechanical decomposition and type of plastic flow can be distinguished. In the central and middle regions of the sample the polymer is deformed in azimuthal direction, the M w and M n values change in phase depending on the deformation only, and the MMD width remains constant. In the peripheral region, the plastic flow is biaxial and the pressure is smaller than that in the central region. At large shear angles, M n does not change and, therefore, the MMD is narrowing. The kinetics and mechanisms of mechanical decomposition in PP subjected to plastic flow under high pressure are discussed. Kinetic equations, describing the change of M n depending on deformation, are proposed.