Controlling Cavitation of Semicrystalline Polymers during Tensile Drawing

Abstract

A common belief is that liquids have no strength. An example is tap water. However, liquids devoid of dissolved gases and impurities exhibit strength. By analogy, it was expected that purification would reduce cavitation and would increase polymer strength. In contrast to expectation, purified polymers exhibited surprisingly more intense cavitation during tensile deformation than pristine ones. It was concluded that cavitation is initiated in amorphous phase from homogeneous nuclei that are fluctuations of free volume. It seems that introducing a liquid penetrant into interlamellar regions should lead to filling free volume pores and to a decrease of intensity of cavitation. Polyethylene, polypropylene, and polyamide were selected for experiments. Modification of amorphous phases of polymers was conducted by introduction chloroform and hexane for polyolefins and water for polyamide. Chosen liquids penetrate amorphous phase of polymers but do not influence their crystalline phase. Samples whose amorphous phase had been filled with low molecular weight molecules remained transparent up to rupture without evidencing cavitation during tensile drawing. It appears that blocking cavitation in crystallizing polymers is possible by removing homogeneous cavitation nuclei by filling the free volume of amorphous phase of the material with low molecular weight liquids. The type of liquid is not relevant, except that it should not dissolve polymer crystals. The above observation is valid for polyethylene, polypropylene, and polyamide; however, it seems that other crystallizing polymers should also reflect similar dependencies. By infusing low molecular weight penetrants, one may control cavitation. Moreover, liquids that can be used are not limited to the ones described in the paper.