Environmental stress cracking (ESC) refers to a phenomenon causing the failure of polymeric materials such as thermoplastics. Although the precise mechanism is not fully understood, a few key incidents are known to be involved in the full failure process. Adsorbed fluid molecules on the polymer surface and their migration into the bulk material cause craze initiation and growth as well as eventually parts breakdown.The diffusion of the media inside the polymer, causing plasticization, is accepted to be one of the key incidents involved. Such materials degradation is a self-sustained aging mechanism: local defects creating more free volume for fluid molecules to migrate into, causing more degradation until critical failure. Molecular modelling (MM) simulation techniques have been used in the present study for the first time in the ESC research to scrutinize the applicability of these techniques to the description of molecular events responsible for the various degradation steps. Molecular cross section, polymer-fluid compatibility (as measured by the fluid solvation free energy), adsorption energies, etc, are possible descriptors to build up a quantitative structure-activity relationship (QSAR) model to allow the prediction of the ESC risk presented by a fluid for a given polymer. Three amorphous polymers, namely, polystyrene (PS), polymethylmethacrylate (PMMA), and polycarbonate (PC), and various fluids (such as water and ethanol) have been modelled, using the above-mentioned MM techniques.

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Plastic components in use are often exposed to a large number of influences which strongly affect the functionality of the component and are often the main cause of their failure. Here, the environmental stress cracking (ESC) is considered as the main cause for the failure of plastics. Until now, there are only a few possibilities on how to predict the ESC resistance of a plastics component in use and the engineer is often confronted with this failure after the product development process is already completed. This investigations deal with that problem and it is shown how the stress cracking resistance of plastics can be influenced according to the already completed product development by the example of polycarbonate under the influence of water. The focus is on the targeted influencing of the internal part properties, the influence of additional fiber reinforcement and as a last option the selection of a new material under the elimination of elaborate experiments using molecular dynamics simulations. POLYM. ENG. SCI., 59:E361–E366, 2019. © 2018 Society of Plastics Engineers

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