Amnat Jarerat

Biodegradation of poly(L-lactide).

The biodegradation of poly(l-lactide) (PLA) is reviewed. The important role of actinomycetes in PLA degradation is emphasized. These PLA-degrading actinomycetes belong phylogenetically to the Pseudonocardiaceae family and related genera, including Amycolatopsis, Lentzea, Streptoalloteichus, Kibdelosporangium and Saccharothrix. A PLA-degrading enzyme purified from an isolated Amycolatopsis strain-41 has substrate specificity on PLA higher than proteinase K. The application of these strains and their enzymes can be effectively used for biological treatment of plastic wastes containing PLA.

Degradation of poly(l-lactide) by a fungus

Fungal degradation of poly(L-lactide) (PLA) was studied using Tritirachium album ATCC 22563. In liquid culture using basal medium and PLA film, no film degradation was observed. However, by the addition of 0.1% gelatin, about 76% of the PLA film was degraded after 14 days of cultivation at 30°C. Furthermore, the culture filtrate showed degradation activity against PLA, silk fibroin and elastin, but not against poly(β-hydroxybuty rate), poly(butylene succinate) and poly(e-caprolactone). The PLA-degrading enzyme produced is likely to be protease rather than lipase or poly(β-hydroxybutyrate)-depolymerase.

A modified method for isolating poly(vinyl alcohol)-degrading bacteria and study of their degradation patterns

An addition of catalase or peroxidase into an agar plate containing poly(vinyl alcohol) (PVA), was effective for the isolation of PVA-degrading microorganisms. A Gram-negative bacterium, strain TK-2 (γ-group of proteobacteria), rapidly degraded a high molecular weight PVA to low molecular weight material after 1 day thereby producing oligomers of PVA as shown by gel permeation chromatography. Conversely, Sphingomonas strain TJ-7 did not produce any PVA oligomers, suggesting that the strain TJ-7 degraded PVA from the terminal ends of the molecules, whereas the strain TK-2 cleaved PVA at random.

Degradation of poly(tetramethylene succinate) by thermophilic actinomycetes

Various thermophilic actinomycetes were screened for their ability to degrade a high melting point, aliphatic polyester, poly(tetramethylene succinate) (PTMS), at 50 °C. By using the clear zone method, Microbispora rosea, Excellospora japonica and E. viridilutea were found to have PTMS-degrading activity. In a liquid culture with 100 mg PTMS film, M. rosea subsp. aerata IFO 14046 degraded about 50 mg film sample after 8 days. Degradation at the amorphous regions of the PTMS film was observed by scanning electron microscopy. This strain was also able to completely degrade poly(ε-caprolactone).

Preparation and Characterization of Enzymatically-Treated Granular Cassava Starch and Poly(butylene adipate-co-terephthalate) Blends

Raw cassava starch was treated with α-amylase and amyloglucosidase in aqueous solution under annealing condition to obtain starch granules with rough and porous surfaces. Many different pits and pores formed by the activity of the enzymes on the surface granules and were observed by scanning electron microscopy (SEM). The obtained starch granules with rough surfaces were mechanically blended with poly(butylenes adipate-co-terephthalate)(PBAT) at different ratios by using a single screw extruder. The results showed that the samples comprised of enzymatically treated starch blends had higher elongation than those comprised of untreated starch blends. At 10% starch content, the treated starch/PBAT blend had about 37.55% more elongation than the untreated starch/PBAT blend. This resulted in the improved compatibility of the starch granules and PBAT matrix in the blends as confirmed by SEM.

Degradation of Porous Starch Granules and Poly(Butylene Adipate-co-Terephthalate)(PBAT) Blends: Soil Burial and Enzymatic Tests

In order to confirm the feasibility of porous rice starch granules and PBAT blends as biodegradable composites, their degradability were carried out. Enzymatic degradability evaluation showed that α-amylase degradation of starch increased as the starch content in the blend increased. Burial test of the blends for 1-4 months was carried out and the rate of degradation of the PBAT/porous starch blend was confirmed to be slower than those of PBAT/native rice starch blend. Observation of the film blends structure by scanning electron microscope revealed that the starch was dispersed in a PBAT matrix. Furthermore, changes in the film surface after enzyme treatments were observed. The results obtained from the degradability of the porous starch granules and PBAT blends showed that this bio-composite was relatively slow, regarding as controllable degradation material.

Production and Characterization of Porous Starch Granule and Poly(butylene adipate-co-terephthalate) Blend as a Bio-Composite

To improve the miscibility of native rice starch granules and poly(butylene adipate-co-terephthalate)(PBAT), rice starch was hydrolyzed by a mixture of α-amylase and amyloglucosidase. The obtained porous rice granular starch was then mechanically blended with PBAT by single screw extruder. Many pits and holes on the surface of starch granules were observed by scanning electron microscopy (SEM). The rough surface of the rice starch granules improved the compatibility of the polymers in the blends, which consequently increased the tensile strength and the elongation at break. In addition, SEM also revealed that the porous granules were homogeneously distributed in the polymer matrix with no appearance of gaps.