Biodegradation behavior of bacterial-based polyhydroxyalkanoate (PHA) and DDGS composites

Abstract

The extensive use of plastics in agriculture has increased the need for development and implementation of polymer materials that can degrade in soils under natural conditions. The biodegradation behavior in soil of polyhydroxyalkanoate (PHA) composites with 10 wt% distiller's dried grains with solubles (DDGS) was characterized and compared to pure PHA over 24 weeks. Injectionmolded samples were measured for degradation weight loss every 4 weeks, and the effects of degradation times on morphological, thermomechanical, and viscoelastic properties were evaluated by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and small-amplitude oscillatory shear flow experiments. Incorporation of DDGS had a strong effect on biodegradation rate, mechanical properties, and production cost. Material weight loss increased linearly with increasing biodegradation time for both neat PHA and the PHA/DDGS 90/10 composites. Weight loss after 24 weeks was approximately six times greater for the PHA/DDGS 90/10 composites than for unaltered PHA under identical conditions. Rough surface morphology was observed in early biodegradation stages (≥8 weeks). With increasing biodegradation time, the composite surface eroded and was covered with well-defined pits that were evenly distributed, giving an areolate structure. Zero shear viscosity, T g , gelation temperature, and cold crystallization temperature of the composites decreased linearly with increasing biodegradation time. Addition of DDGS to PHA establishes mechanical and biodegradation properties that can be utilized in sustainable plastics designed to end their lifecycle as organic matter in soil. Our results provide information that will guide development of PHA composites that fulfill application requirements then degrade harmlessly in soil.

Thermophysical properties and biodegradation behavior of green composites made from polyhydroxybutyrate and potato peel waste fermentation residue

“…Optical microscopy revealed that the high fiber content biocomposites readily biodegrade while the highly crystalline PHB was more resistant to biodegradation. This may be because the microorganisms will first produce schisms in the long chains of PHB and the process continues until all the polyester bonds are hydrolyzed and converted into CO 2 and H 2 O by aerobic biodegradation (Jandas et al, 2013;Madbouly et al, 2014). SEM supported these findings in that more apparent checking and pits were observed with biodegradation time (Fig.…”

“…This indicated that the introduction of PPW-FR into the PHB matrix lowers the T g 's, suggesting that large segments of the PHB chain within the biocomposites start to move at lower temperature. The higher relaxation appears at about 110 • C, which is contributed to the crystal-crystal slippage occurring in semicrystalline polymers just below melting transition temperature (Madbouly et al, 2014).…”

“…These residues are carbon rich waste sources, which are majorly composed of lignin and unreacted carbohydrates for producing value added biofuels and bioproducts (Liang et al, 2014a). More recently, dried distillers grains with solubles (DDGS), a major co-product of the corn ethanol industry, have been used for the production of "green" composites using biodegradable poly(butylene adipateco-terephthalate) (PBAT) and PHAs as polymer matrices (Madbouly et al, 2014;Muniyasamy et al, 2013). The addition of DDGS made the biocomposites easy to be bio-degraded in soil as compared with pure PHA, which makes these biocomposites commercially feasible for horticultural crop container (seedling tray).…”

Novel bio-based composites of polyhydroxyalkanoate (PHA)/distillers dried grains with solubles (DDGS)

“…Other studies have shown similar T g results. 20,21 The two endothermic peaks shown in Fig. 3a are related to the existence of two crystalline phases in PHA samples.…”

Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

“…Degradation occurs most rapidly in anaerobic sewage and slowest in seawater. Lee showed that P(HB-HV) completely degraded after 6, 75 and 350 weeks in anaerobic sewage, soil and sea water, respectively (107,191). Effective PHA destructors include various bacteria from widespread soil and water genera (Pseudomonas, Alcaligenes, Comamonas, Streptomyces, Ilyobacter) (192), as well as fungi (Ascomycetes, Basidiomycetes, Deuteromycetes, Mastigiomycetes and Myxomycetes) (180).…”