Torrefied sawdust gives PLA composites a 6% strength bump and 94% biodegradability in 90 days, Korea study finds
Low-temperature roast of forest residue turns cheap wood scrap into hydrophobic, micro-porous filler that speeds up composting while matching neat bioplastic’s water resistance
image: Torrefied Sawdust Gives PLA Composites a 6 % Strength Bump and 94 % Biodegradability in 90 Days, Korea Study Finds
Credit: Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, South Korea
Polylactic acid has become the flagship of biodegradable plastics, but its high price and stubbornly slow breakdown outside industrial composting plants keep it from displacing petro-polymers in disposable packaging. Now a Korea-based team has demonstrated that a low-temperature “roast” of otherwise worthless sawdust can flip those weaknesses into advantages: the treated wood flour not only strengthens PLA but also accelerates its ultimate disintegration to CO₂ and water.
The group, led by the Center for Bio-based Chemistry at KRICT, began with mixed hardwood residue collected from national forest operations. After drying, the chips were heated at 220, 250 or 280 °C for 50 min under nitrogen—a process known as torrefaction that drives off moisture and volatile acids while leaving a char-rich, micro-porous solid. Electron microscopy revealed that the gentle heat collapses the outer cell-wall sheath, exposing hair-like cellulose fibrils and creating nano-scale pits that act as mechanical anchors when the particles are melt-blended into PLA.
When 20 % of the 220 °C-treated filler was compounded with commercial PLA (Ingeo 4032D/4060D blend), tensile strength rose 6 % to 62.3 MPa while elongation at break stayed above 1.5 %. Higher roasting temperatures delivered diminishing returns; at 280 °C the cellulose backbone itself began to scorch, and tensile strength dipped below that of the untreated control. Differential scanning calorimetry showed that the optimal filler lowers cold-crystallisation temperature and reduces overall PLA crystallinity—an outcome that speeds up later hydrolysis.
That prediction was borne out in a 90-day compost test conducted under ISO 14855-1 conditions. Neat PLA achieved 88.8 % biodegradation, but the torrefied-wood composite hit 94.9 %, with CO₂ evolution detectable two weeks earlier. The authors attribute the faster onset to two factors: the micro-porous filler wicks water into the part, initiating hydrolysis of ester linkages, and the lower composite crystallinity leaves more amorphous zones exposed to microbial attack.
Life-cycle screening indicates that replacing one fifth of PLA with zero-value forest residue could cut raw-material cost by 12–15 % and reduce fossil-carbon content by roughly the same margin. Because torrefaction is exothermic once started, the energy demand is modest—about 0.8 MJ per kilogram of filler, or one-tenth of the calorific value of the volatiles recovered. Korea’s national forest service currently pays to landfill or burn slash; diverting just 5 % of annual residue could supply 30 000 t of filler, enough for 150 000 t of biocomposite.