Effect of melt vibration on mechanical properties of injection molding and rheology

A pulse pressure was superimposed on the melt flow in injection molding, called vibration injection molding (VIM); the mechanical properties of the resulting samples were compared with the values of conventional injection molding (CIM). A die (L/D = 17.5) was attached to this device to study rheology. Properties of an amorphous polymer (ABS) and a semicrystalline polymer (PP), prepared in the vibration field, were compared to each other. Applying VIM, the mechanical properties can be improved whether the material is amorphous or not. Increasing with vibration frequency, the tensile strengths of PP were improved. The processing parameters to obtain self-reinforcing and self-toughening moldings were found at high vibration frequency F-r (F-r > 1.2 Hz). For ABS, the improvement of tensile strength is very small. For both PP and ABS, the yield strength, Young's modulus, and impact strength are all improved by increased vibration pressure amplitude. The elongation at break of PP moldings, however, decreases sharply; but the corresponding value decreases little for ABS. So long as the pulse pressure is superimposed on the melt, the average apparent viscosity decreases sharply for both crystalline and amorphous polymers, and the decreases obtained at increased vibration pressure amplitude are bigger than are those obtained at increased vibration frequency. The changes in viscosities for the amorphous material, ABS, are smaller than the are values for the semicrystalline polymer, PP. The amounts of changes in the mechanical properties and rheology depend greatly on the melt temperature.