PHA/PBAT biocomposites reinforced with rice straw lignocellulosic macromolecules: Decoding structure-property relationships through filler size and concentration

The environmental crisis caused by the accumulation of conventional plastics requires the development of sustainable alternatives. This study introduced a novel approach to valorize agricultural waste by engineering composite materials based on blends of poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and polybutylene adipate terephthalate (PBAT) reinforced with rice straw (RS) as a possible alternative to conventional plastics. Composites were produced by melt compounding and compression molding, varying PHBV:PBAT mass ratios (80:20, 50:50, 20:80), RS particle sizes (≤250 μm and ≤ 500 μm), and RS concentration (20, 30 and 40 w/w %). Results showed that the polymer ratio and RS particle size significantly affected filler dispersion and film properties. Smaller RS particles and higher PHBV content (80:20) led to better homogenization, improved interfacial adhesion, and enhanced water vapor barrier properties, while 50:50 blends showed poor dispersion and higher permeability. Colorimetric analysis highlighted the role of RS size in composite coloration. FTIR confirmed that RS interacts physically with the polymers, not chemically. RS addition increased rigidity and water contact angle but reduced ductility, thermal stability, and crystallinity (depending on the concentration and particle size), and increased water vapor permeability. Disintegration tests revealed that only 80:20 blends met ISO 20200:2016 standards, while biodegradation, under industrial composting, was lower for RS-containing blends than controls, highlighting the role of environmental conditions and microbial communities. Life cycle assessment showed the composites had a cradle-to-grave climate change impact of 7.89-8.28 kg CO₂-eq·kg^-1, which is lower than commercial plastics. These findings demonstrate the potential of rice straw as a sustainable filler for biodegradable PHBV/PBAT composites, offering promising alternatives for eco-friendly packaging applications.