An overview of the recent developments in polylactide (PLA) research.

Biological degradation of plastics: a comprehensive review.

Environmental, economic, and safety challenges have provoked packaging scientists and producers to partially substitute petrochemical-based polymers with biodegradable ones. The general purpose of this review is to introduce poly-lactic acid (PLA), a compostable, biodegradable thermoplastic made from renewable sources. PLA properties and modifications via different methods, like using modifiers, blending, copolymerizing, and physical treatments, are mentioned; these are rarely discussed together in other reviews. Industrial processing methods for producing different PLA films, wrappings, laminates, containers (bottles and cups), are presented. The capabilities of PLA for being a strong active packaging material in different areas requiring antimicrobial and antioxidant characteristics are discussed. Consequently, applications of nanomaterials in combination with PLA structures for creating new PLA nanocomposites with greater abilities are also covered. These approaches may modify PLA weaknesses for some food packaging applications. Nanotechnology approaches are being broadened in food science, especially in packaging material science with high performances and low concentrations and prices, so this category of nano-research is estimated to be revolutionary in food packaging science in the near future. The linkage of a 100% bio-originated material and nanomaterials opens new windows for becoming independent, primarily, of petrochemical-based polymers and, secondarily, for answering environmental and health concerns will undoubtedly be growing with time.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2010.00126.x

Poly-Lactic Acid: Production, Applications, Nanocomposites, and Release Studies.

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

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Biodegradability of plastics.

The use of plastic mulch in agriculture has increased dramatically in the last 10 years throughout the world. This increase is due to benefits such as increase in soil temperature, reduced weed pressure, moisture conservation, reduction of certain insect pests, higher crop yields, and more efficient use of soil nutrients. However, disposing of used plastic films, which cause pollution, has led to development of photodegradable and biodegradable mulches. Here we review the use of plastic mulches in agriculture, with special reference to biodegradable mulches. Major topics discussed are (1) history of plastic mulch and impact on crop yield and pest management, (2) limitations of polyethylene mulches and potential alternatives, (3) biodegradable and photodegradable plastic mulches, (4) field performance of biodegradable mulches, and (5) use of biodegradable plastic mulches in organic production. We found that (1) despite multiple benefits, removal and disposal of conventional polyethylene mulches remains a major agronomic, economic, and environmental constraint; (2) early use of photodegradable plastic mulch during the 1970s and 1980s, wrongly named biodegradable mulch films, discouraged adoption of new biodegradable mulch films because they were too expensive and their breakdown was unpredictable; (3) biodegradable plastic films are converted through microbial activity in the soil to carbon dioxide, water, and natural substances; (4) polymers such as poly(lactic acid), poly(butylene adipate-coterephthalate), poly(e-caprolactone), and starch-based polymer blends or copolymers can degrade when exposed to bioactive environments such as soil and compost; (5) with truly biodegradable materials obtained from petroleum and natural resources, opportunity for using biodegradable polymers as agricultural mulch films has become more viable; and (6) the source of polymer and additives may limit use of some biodegradable mulches in organic production. More knowledge is needed on the effect of biodegradable mulches on crop growth, microclimate modifications, soil biota, soil fertility, and yields.

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Polyethylene and biodegradable mulches for agricultural applications: a review

Out of 25 Amycolatopsis strains, 15 formed clear zones on agar plate emulsified with poly(L-lactide) (PLA), suggesting a large distribution of PLA degraders within this genus. The clear zones were also observed with other polyesters and silk fibroin plates. In liquid cultures of PLA degraders, there were strains with and without ability to assimilate degradation products like L-lactic acid.

Degradation of poly(L-lactide) by strains belonging to genus Amycolatopsis

The poly(L-lactide) (PLA)-degrading ability of actinomycetes obtained from culture collections was examined by the formation of clear zones on PLA-emulsified agar plates. Using 41 genera. (105 strains) of actinomycetes with phylogenetic affiliations based on 16S rRNA sequences, PLA degraders were found to be limited to members of the family Pseudonocardiaceae and related genera. They included Amycolatopsis, saccharothrix, Lentzea, Kibdelosporangium, and Streptoalloteichus. A large number of PLA degraders were widely distributed within the genus Saccharothrix. Most strains forming clear zones on PLA-emulsified agar plates also formed clear zones on silk fibroin agar plates. Saccharothrix species showed an ability to degrade PLA films and assimilate degradation products in liquid cultures. No significant change of the molecular weight and polydispersity (M w /M n ) of the remaining film fragments was confirmed. After cultivation for two weeks, many irregular holes/pits on the surface of the film due to the colonization of microorganisms were observed by scanning electron microscopy.

Poly(L‐lactide)‐Degrading Activity in Various Actinomycetes

Full Paper: Poly (L-lactide), (PLLA)-degrading enzyme was produced in a liquid culture of Amycolatopsis sp. (strain 41). In comparison with polyester substrates, silk powder from silkworm cocoons was the most effective in inducing enzyme production within 5d. Application to DEAE and Superdex 75 columns resulted in a major protein with molecular weight estimated to be 42 kDa from size exclusion chromatography or 40 kDa from SDS-PAGE analysis. Optimum pH and temperature are 6.0 and 37-45°C, respectively. Besides PLLA, the enzyme degrades casein, silk powder and Suc-(Ala) 3 -pNA at an even lower level than Proteinase-K, but not Suc-(Gly) 3 -pNA, poly (e-caprolactone) and poly (β-hydroxybutyrate).

Poly (L‐lactide)‐Degrading Enzyme Produced by Amycolatopsis sp.

In order to assess feasibility of tropical starches (sago and cassava starches) as biodegradable plastic materials, blending with poly(e-caprolactone) (PCL), a biodegradable polymer, was carried out. It was confirmed that the physical properties (tensile strength and elongation) of PCL/sago and PCL/cassava blends were similar to those of PCL/corn blend, suggesting that sago and cassava starches can also be blended with PCL for production of biodegradable plastic. However, the properties of all PCL/starch blends were still low compared with those of polyethylene. Enzymatic degradability evaluation showed that lipase degradation of PCL andα-amylase degradation of starch increased as the starch content in the blend increased. Burial test of the blends for 1, 3, and 5 months was carried out and the rate of degradation of the PCL/sago blend was confirmed to be slower than those of PCL/corn and PCL/cassava blends. Observation of the film blends structure by scanning electron microscope revealed that the starch was dispersed in a PCL continuous phase. Furthermore, changes in the film surface before and after enyzme treatments were observed.

Physical properties and biodegradability of blends containing poly(ε-caprolactone) and tropical starches

Amycolatopsis sp. strain HT-6, a poly(tetramethylene succinate) (PTMS)-degrading actinomycete, was observed to degrade poly(tetramethylene carbonate) (PTMC). In a liquid culture with 150 mg of PTMC film, 59% degradation was achieved, but with a low yield of cell growth. On the other hand, PTMS copolymerized with a small amount of PTMC, forming a copolyester carbonate (PEC) that was completely and rapidly degraded with a high yield of cell growth.

Hardaning Pranamuda

Papers

Degradation of poly(L-lactide) by strains belonging to genus Amycolatopsis

Poly(L‐lactide)‐Degrading Activity in Various Actinomycetes

Poly (L‐lactide)‐Degrading Enzyme Produced by Amycolatopsis sp.

Physical properties and biodegradability of blends containing poly(ε-caprolactone) and tropical starches

Degradation of Polycarbonate by a Polyester-Degrading Strain, Amycolatopsis sp. Strain HT-6