In-line monitoring of thermal degradation of PHA during melt-processing by Near-Infrared spectroscopy

Polyhydroxyalkanoate (PHA) biopolymer processing is often challenged by low thermal stability, meaning that the temperatures and time for which these polymers can be processed is restrictive. Considering the sensitivity of PHA to processing conditions, there is a demand for in-line monitoring of the material behaviour in the melt. This paper investigates the application of Near-Infrared (NIR) spectroscopy for monitoring the thermal degradation of PHAs during melt-processing. Two types of materials were tested: two mixed culture PHAs extracted from biomass produced in laboratory and pilot scale after an acidic pre-treatment, and two commercially available materials derived from pure culture production systems. Thermal degradation studies were carried out in a laboratory scale extruder with conical twin screws connected to a NIR spectrometer by a fibre optic to allow in situ monitoring. Multivariate data analysis methods were applied for assessing thermal degradation kinetics and predicted the degree of degradation as measured by H-1 NMR (proton nuclear magnetic resonance spectroscopy). The pre-treated mixed culture PHAs were found to be more thermally stable when compared with the commercial pure culture PHAs as demonstrated by NIR, H-1 NMR and GPC (gel permeation chromatography).