Polyhydroxybutyrate rice hull and torrefied rice hull biocomposites

Authors: McCaffrey, Zachariah - Zach; CAL, ANDREW - Mango Materials; Torres, Lennard; Chiou, Bor-Sen; Wood, Delilah - De; Williams, Tina; Orts, William

Submitted to: Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2022
Publication Date: 9/17/2022
Citation: McCaffrey, Z., Cal, A., Torres, L.F., Chiou, B., Wood, D.F., Williams, T.G., Orts, W.J. 2022. Polyhydroxybutyrate rice hull and torrefied rice hull biocomposites. Polymers. 14(18). Article 3882. https://doi.org/10.3390/polym14183882.
DOI: https://doi.org/10.3390/polym14183882

Interpretive Summary: Plastics are a huge source of environmental pollution. To address this problem, we are taking advantage of poly 3-hydroxybutyrate (PHB), a naturally existing biodegradable bio-based polymer produced from renewable resources. PHB can be produced industrially by bacterial fermentation and has material property advantages over petroleum-based polymers. PHB is highly crystalline and not fully compatible with existing production processes. Blending with fillers improves functionality of PHB composites thereby reducing manufacturing costs. A filler made from rice hulls; an underutilized, readily available byproduct of the rice industry was used in this study. Blending of heat-treated rice hulls with PHB improved the properties of the resulting composites resulting in useful plastic composites that have potential to reduce the negative environmental impact of plastic products and reduce impact of rice production by using rice hulls, a byproducts of rice production.

Technical Abstract: Raw and torrefied rice hulls (RRH and TRH) were incorporated into polyhydroxybutyrate (PHB) as fillers using extrusion and injection molding to produce biomass-polymer composites. Filler and composite materials were characterized by particle size analysis, thermomechanical analysis, thermogravimetric analysis, differential scanning calorimetry, FTIR analysis, CHNSO analysis, and mechanical testing. Heat distortion temperature of the RRH composites were 16-22 °C higher than TRH composites. The RRH composite samples showed a 50-60% increase in flexural modulus and 5% increase in stress at yield compared to neat PHB while TRH showed nearly equal flexural modulus and 24% decrease in stress at yield. The improved mechanical properties of the RRH composites in comparison to TRH composites were due to better particle-matrix adhesion. FTIR analysis showed RRH particles contained more oxygen containing surface functional groups than TRH particles, indicating that RRHs should be more compatible with the polar PHB plastic. SEM images showed space between filler and plastic in TRH composites and better wetted filler particles in the RRH composites.