Unravelling biodegradation and toxin release kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-based biocomposites in a simulated rumen environment: A preliminary study

The development of completely digestible rumino-reticulum devices (RRDs) able to slowly release natural toxins in bovine rumen has been proposed to be a sustainable strategy to control Pimelea poisoning among graving cattle caused by toxic grasses endemic in Australia. Three pioneer biocomposites were extruded from the plant particles of the toxic plant Pimelea trichostachya and the biodegradable biopolymer poly-3-hydroxybutyrate-co-1 mol% 3-hydroxyvalerate (PHBV), with or without sucrose and starch as pore forming agents. To understand the biodegradation and toxin release mechanisms of these emerging materials in a rumen environment, these biocomposites were incubated, along with pristine PHBV as reference, in an in vitro anaerobic bioreactor simulating the rumen fermentation process. It was shown that surface erosion was the dominant pattern of biodegradation for all the biocomposites, through a series of comprehensive analyses on micro- and macroscopic scales. X-ray computed tomography scanning (μ-CT) observations and the biodegradation kinetic modelling results confirmed that porogen leaching introduced more interior surface areas but did not accelerate the biodegradation rate significantly. Competing phenomena of toxin adsorption and release from the biocomposites were also revealed. This study not only provided guidance in further tailoring the toxin release behaviours and assessing the end-of-life of these biocomposites, but could also be beneficial for constructing PHBV based-RRDs with other purposes.