Functionalisation of paper with polyhydroxybutyrate-Cyrene™ coating for enhanced barrier properties
摘要
The poor barrier properties of paper restrict its use in packaging, particularly for applications requiring resistance to moisture and vapor. Polyhydroxybutyrate (PHB) is a microbial bio-polyester with excellent biodegradability, biocompatibility and hydrophobicity, offering a renewable alternative to petrochemical-based polymers. However, PHB’s insolubility in most solvents, with chloroform being the most effective, is a barrier to application. In this study we assess Cyrene™, a biodegradable green solvent, as an alternative to chloroform for dissolving and solvent-casting PHB onto paper. PHB (3% w/v) dissolved in chloroform at 50 °C formed a visually viscous, homogenous solution but at higher concentrations, solubility was reduced and coating lacked uniformity. In Cyrene™, PHB solubility was temperature-dependent: at 90 °C, it formed a cloudy but homogeneous solution while at 140 °C it was fully dissolved producing a clear, viscous solution, even at 5% (w/v). PHB-Cyrene™ solutions were compared with PHB-chloroform for casting onto Whatman filter paper 1. Optical profilometry and SEM showed smoother, more uniform PHB-Cyrene™ coatings, while FTIR confirmed PHB presence through the characteristic C=O (1720 cm−1) peak. PHB coating imparted some oil resistance to papers. The water contact angle was highest for 3% PHB-Cyrene coated papers at 118° indicating excellent hydrophobicity. The water vapour permeability (WVP) performance of the 5% PHB-Cyrene™ coated paper (7.30 × 10−11 g/Pa.s.m) was significantly (p = 0.0086) better than 5% PHB-chloroform (2.81 × 10−10 g/Pa.s.m), most likely due to more uniform coating, which also contributed to enhanced tensile strength. Cyrene™ is an effective and sustainable solvent for dissolving PHB and casting onto paper surfaces for sustainable packaging applications.