CRACKING OF MONOLITHIC POLYCARBONATE SHEETS IN A STRESSED STATE

Abstract

The accelerated stress cracking of monolithic polycarbonate sheets was investigated. Cracking of polycarbonate organic glasses during operation leading to a drop in impact strength and transparency is their main disadvantage. The main role in the acceleration of the process of cracking is played by the stresses that arise when they are formed and mounted. The aim of this work was to investigate the dependence of the cracking start time on the stress applied to the sheet monolithic polycarbonate. This makes it possible to predict the lifetime of polycarbonate products. The experiments were carried out in air and in contact with an adsorption-active medium (a mixture of toluene and n-propanol). The stresses applied to the samples varied in the range from 25 to 55 MPa. It is shown that the dependence of the cracking start time of a polycarbonate on the applied stress can be described by Zhurkov exponential equation. The coefficients of this equation for the processes of cracking in air and in contact with the adsorption-active liquid are calculated. It is established that the activation energy of the polycarbonate cracking process (129.5 kJ/mol) is close in magnitude to the activation energy of the thermal-oxidative destruction (about 145-155 kJ/mol). In contact with the adsorption-active mixture of toluene (25% mass.) and n-propanol, the activation energy of the cracking is reduced to 98.5 kJ/mol. At the same time, the structural coefficient in the Zhurkov equation ("activation volume") increases from 1.45 to 2.45 nm3. The analysis of the obtained results made it possible to predict the lifetime of monolithic polycarbonate sheets and products made of them at various operating stresses