INVESTIGATING THE COMPATIBILITY OF BIODIESEL ON POLYETHYLENE THROUGH NONDESTRUCTIVE AND TRADITIONAL METHODS

Abstract

Being the most abundant cause of unexpected brittle failures of polymers, environmental stress cracking (ESC) is a major issue for the plastics industry, accounting for approximately 15-40% of all plastic part failures in service. ESC is an intriguing phenomenon that is not yet well understood, which relates to the accelerated failure of a stressed polymer whilst the presence of an active medium, such as biodiesel. Unexpected failures of polyethylene parts in tanks aboard marine vessels that were operated with biodiesel has generated concerns in the polymer industry over the compatibility of this relatively new fuel, making investigations into these failures both urgent and essential for the process of change towards renewable fuel standards. Experimental trials carried out for a two-stage project investigating the compatibility of fresh and degraded biodiesel with polyethylene were used to suggest a plasticization mechanism targeting tie molecules (often related to micellular contaminants in a contacting medium) as the probable pathway for ESC of polyethylene with biodiesel. Preliminary analysis was done using the Bell Test (ASTM D1693) showing evidence of pure biodiesel as a stress cracking agent with an aggressiveness similar to a 10% biodiesel in water solution for which the majority of trials used. Results from the first stage of this study revealed evidence of differing modes of interaction for biodiesel and toluene (a known plasticizing agent) with the semi-crystalline polymer structure. The second stage utilized acoustic analysis to monitor internal stresses during long-term aging to better explain the theory of ESC for polyethylene with biodiesel, showing that both plasticization and ESC behaviors occurred.