Studying the mechanism of biodiesel acting as an environmental stress cracking agent with polyethylenes

This paper focuses on understanding the compatibility of biodiesel with different grades of polyethylene, specifically examining the environmental stress cracking ability of biodiesel. Traditional testing methods were coupled with a nondestructive ultrasonic testing method to investigate the modes of interaction by biodiesel with the polymer. The mechanism of failure was studied by gravimetric analysis and infrared spectroscopy to monitor fluid absorption in the notched and bent specimens while attenuation in the higher harmonics of an emitted acoustic pulse followed internal stresses. The ultrasonic technique offered a unique opportunity to link fuel penetration with microstructural changes prior to visible fracturing. Analysis of the mechanism was aided by the color of the fuel showing that cracking was preceded by highly localized absorption around the notch of the specimen, whereas resin grades with apparent immunity to cracking experienced uniform absorption over the whole body of a specimen.