SELF-REINFORCEMENT OF POLYPROPYLENE BY FLOW-INDUCED CRYSTALLIZATION DURING CONTINUOUS EXTRUSION

Self-reinforced polypropylene (PP) sheets have been prepared from melt flow-induced crystallization through a conical slit die fed by a conv entional extruder. Their structure and properties, influenced by the d ie pressure ranging from 20 to 50 MPa and die outlet temperature, are studied by scanning electron microscopy observation, differential scan ning calorimetry analyses, tensile strength, and light transmittance m easurements. At a die outlet temperature of 162 degrees C and a pressu re above 30 MPa, conspicuous increases in the melting peak, tensile st rength, and light transmittance (they can be used to characterize the self-reinforcement degree of sheet) are observed. The self-reinforceme nt degree, however, increases only slightly with increasing pressure a s it exceeds 40 MPa. Raising the die outlet temperature from 162 to 17 2 degrees C results in a further increase in the self-reinforcement de gree (for example, a highest tensile strength of 288 MPa) while keepin g the pressure at 40 MPa, so bulk PP materials with high properties ca n be produced from continuous melt extrusion under pressures lower tha n 40 MPa. Furthermore, the melt temperature plays an important role in determining the properties of self-reinforced polymeric materials. (C ) 1998 John Wiley & Sons, Inc.