Monte Carlo simulations of methanol absorption and clustering in polyvinylchloride and high density polyethylene

A pertinent issue facing the materials industry is that of the lifespan of materials when exposed to certain solvents/ environments. Limitations to the applications of materials require further research into understanding their failure mechanisms and how such problems can be addressed in terms of re-engineering such materials to be more durable. PVC and HDPE are two common polymers used extensively in industrial applications. Gibbs ensemble Monte Carlo simulations were used to simulate systems of PVC and HDPE with methanol, respectively. The temperatures used in this work were 25, 30 and 40 oC and all systems were at atmospheric pressure. Laboratory tests were used to complement simulations for analysis purposes. Results showed an increase in temperature resulted in a decrease in the overall clustering in both polymers although PVC displayed a greater decrease than HDPE. Linear clustering dominated over other forms of clustering with increases in temperature, with dimers being the most prevalent topology type. The results of this study suggest that the presence of chlorine atoms in PVC may not directly affect clustering of absorbed methanol, and their effect may instead be indirect by means of altering the accessible free volume within the polymer. Swelling was also investigated in the simulated systems and it was found that PVC displayed a greater degree of swelling than HDPE despite its lower rate of clustering. The effect of cluster radius on the cluster analysis was also considered.

The degradation of mechanical properties in halloysite nanoclay–polyester nanocomposites exposed to diluted methanol

The degradation of mechanical properties in halloysite nanoclay–polyester nanocomposites was studied after an exposure of 24 h in diluted methanol system by clamping test specimens across steel templates. The glass transition temperature ( Tg) and storage modulus increased steadily with the increase of halloysite nanoclays before and after diluted methanol exposure. The addition of nano-fillers was found to reduce liquid uptake by 0.6% in case of 1 wt% reinforcement compared to monolithic polyester. The mechanical properties of polyester-based nanocomposites were found to decrease as a result of diluted methanol absorption. After diluted methanol exposure, the maximum microhardness, tensile, flexural and impact toughness values were observed at 1 wt% of halloysite nanoclay. The microhardness increased from 203 to 294 HV (45% increase). The Young’s modulus increased from 0.49 to 0.83 GPa (70% increase) and the tensile strength increased from 23 to 27 MPa (17.4% increase). The impact toughness increased from 0.19 to 0.54 kJ/m2 in diluted methanol system (184% increase). Surprisingly, the fracture toughness of all types of nanocomposites was found to increase after exposing to diluted methanol due to plasticization effect. Scanning electron microscope images of the fractured surfaces of tensile specimens revealed that the methanol increased the ductility of the matrix and reduced the mechanical properties of the nanocomposites.