SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Biodegradable plastic

28

We developed a rapid and simple method for evaluating the degradation of solid biodegradable plastics (BPs). Dye-containing BP films were used as substrates and the release of dye caused by the degradation of BPs was confirmed by a color change in the enzyme solution after a reaction time of 24 h.

Concepts: Enzyme, Catalysis, Starch, Plastic, Biodegradation, Recyclable materials, Bioplastic, Biodegradable plastic

28

Society is fundamentally ambivalent to the use of plastics. On the one hand, plastics are uniquely flexible materials that have seen them occupy a huge range of functions, from simple packing materials to complex engineering components. On the other, their durability has raised concerns about their end-of-life disposal. When that disposal route is landfill, their invulnerability to microbial decomposition, combined with relatively low density and high bulk, means that plastics will occupy increasing amounts of landfill space in a world where available suitable landfill sites is shrinking. The search for biodegradable plastics and their introduction to the marketplace would appear to be a suitable amelioration strategy for such a problem. And yet the uptake of biodegradable plastics has been slow. The term biodegradable itself has entered public controversy, with accidental and intended misuse of the term; the intended misuse has led to accusations and instances of “greenwashing”. For this and other reasons standards for biodegradability and compostability testing of plastics have been sought. An environmental dilemma with more far-reaching implications is climate change. The need for rapid and deep greenhouse gas (GHG) emissions cuts is one of the drivers for the resurgence of industrial biotechnology generally, and the search for bio-based plastics more specifically. Bio-based has come to mean plastics based on renewable resources, but this need not necessarily imply biodegradability. If the primary purpose is GHG emissions savings, then once again plastics durability can be a virtue, if the end-of-life solution can be energy recovery during incineration or recycling. The pattern of production is shifting from the true biodegradable plastics to the bio-based plastics, and that trend is likely to persist into the future. This paper looks at aspects of the science of biodegradable and bio-based plastics from the perspective of policy advisers and makers. It is often said that the bioplastics suffer from a lack of a favourable policy regime when compared to the wide-ranging set of policy instruments that are available on both the supply and demand side of biofuels production. Some possible policy measures are discussed.

Concepts: Climate change, Biodegradation, Methane, Greenhouse gas, Bioplastic, Landfill, Biodegradable plastic, Biodegradable waste management

28

To improve the biodegradation of biodegradable plastic (BP) mulch films, 1227 fungal strains were isolated from plant surface (phylloplane) and evaluated for BP-degrading ability. Among them, B47-9 a strain isolated from the leaf surface of barley showed the strongest ability to degrade poly-(butylene succinate-co-butylene adipate) (PBSA) and poly-(butylene succinate) (PBS) films. The strain grew on the surface of soil-mounted BP films, produced breaks along the direction of hyphal growth indicated that it secreted a BP-degrading enzyme, and has directly contributing to accelerating the degradation of film. Treatment with the culture filtrate decomposed 91.2 wt%, 23.7 wt%, and 14.6 wt% of PBSA, PBS, and commercially available BP polymer blended mulch film, respectively, on unsterlized soil within 6 days. The PCR-DGGE analysis of the transition of soil microbial community during film degradation revealed that the process was accompanied with drastic changes in the population of soil fungi and Acantamoeba spp., as well as the growth of inoculated strain B47-9. It has a potential for application in the development of an effective method for accelerating degradation of used plastics under actual field conditions.

Concepts: Microbiology, Plant, Fungus, Hypha, Plastic, Biodegradation, Bioplastic, Biodegradable plastic

22

The increasing significance of non-degradable plastic wastes is an emerging concern. As a substitute, researches are being endeavoured from existing reserve to yield bioplastics based on their properties of biodegradability. Owing to their cost, now the experts are quest for a substitute source like bacteria, microalgae, actinomycetes, cyanobacteria and plants. PHB is biodegradable, environmental friendly and biocompatible thermoplastics. Varying in toughness and flexibility, depending on their formulation, they are used in various ways similar to many non-biodegradable petrochemical plastics currently in use. Promising strategies contain genetic engineering of microorganisms to introduce production pathways examined for the past two decades. Such kind of researches focusing on the use of unconventional substrates, novel extraction methods, and genetically enhanced species with assessment to make PHB from marine microbes are commercially attractive field. Hence, this biopolymer synthesis may displayed as one of the survival mechanisms of endosymbiotic, macroalgae, or sponge-associated bacteria, which exist in a highly competitive and stressful marine microenvironment. This review throws light on the promising and growing awareness of using marine microbes as PHB source, along with their applications in different fields of aquaculture, medicine, antifouling and tissue engineering.

Concepts: Algae, Photosynthesis, Archaea, Bacteria, Organism, Biotechnology, Microorganism, Biodegradable plastic

3

Growing concerns regarding the impact of the accumulation of plastic waste over several decades on the environmental have led to the development of biodegradable plastic. These plastics can be degraded by microorganisms and absorbed by the environment and are therefore gaining public support as a possible alternative to petroleum-derived plastics. Among the developed biodegradable plastics, oxo-biodegradable polymers have been used to produce plastic bags. Exposure of this waste plastic to ultraviolet light (UV) or heat can lead to breakage of the polymer chains in the plastic, and the resulting compounds are easily degraded by microorganisms. However, few studies have characterized the microbial degradation of oxo-biodegradable plastics. In this study, we tested the capability of Pleurotus ostreatus to degrade oxo-biodegradable (D2W) plastic without prior physical treatment, such as exposure to UV or thermal heating. After 45 d of incubation in substrate-containing plastic bags, the oxo-biodegradable plastic, which is commonly used in supermarkets, developed cracks and small holes in the plastic surface as a result of the formation of hydroxyl groups and carbon-oxygen bonds. These alterations may be due to laccase activity. Furthermore, we observed the degradation of the dye found in these bags as well as mushroom formation. Thus, P. ostreatus degrades oxo-biodegradable plastics and produces mushrooms using this plastic as substrate.

Concepts: Ionizing radiation, Ultraviolet, Polymer, Plastic, Biodegradation, Land degradation, Polycarbonate, Biodegradable plastic

2

The accumulation of plastic debris is a global environmental problem due to its durability, persistence and abundance. Although effects of plastic debris on individual marine organisms, particularly mammals and birds have been extensively documented (e.g. entanglement, choking), very little is known about effects on assemblages, and consequences for ecosystem functioning. In Europe, around 40% of plastic items produced are utilised as single-use packaging, which rapidly accumulate in waste management facilities and as litter in the environment. A range of biodegradable plastics have been developed with the aspiration of reducing the persistence of litter, however their impacts on marine assemblages or ecosystem functioning have never been evaluated. A field experiment was conducted to assess the impact of conventional and biodegradable plastic carrier bags as litter on benthic macro- and meio-faunal assemblages and biogeochemical processes (primary productivity, redox condition, organic matter content and pore-water nutrients) on an intertidal shore near Dublin, Ireland. After nine weeks, the presence of either type of bag created anoxic conditions within the sediment along with reduced primary productivity and organic matter and significantly lower abundances of infaunal invertebrates. This indicates that both conventional and biodegradable bags can rapidly alter marine assemblages and the ecosystem services they provide.

Concepts: Photosynthesis, Ecology, Carbon, Plastic, Biodegradation, Waste, Biodegradable plastic, Plastic shopping bag

1

The concept of materials coming from nature with environmental advantages of being biodegradable and/or biobased (often referred to as bioplastics) is very attractive to the industry and to the consumers. Bioplastics already play an important role in the fields of packaging, agriculture, gastronomy, consumer electronics and automotive, but still they have a very low share in the total production of plastics (currently about 1% of the about 300 million tonnes of plastic produced annually). Biodegradable plastics are often perceived as the possible solution for the waste problem, but biodegradability is just an additional feature of the material to be exploited at the end of its life in specific terms, in the specific disposal environment and in a specific time, which is often forgotten. They should be used as a favoured choice for the applications that demand a cheap way to dispose of the item after it has fulfilled its job (e.g. for food packaging, agriculture or medical products). The mini-review presents the opportunities and future challenges of biodegradable plastics, regarding processing, properties and waste management options.

Concepts: Time, Plastic, Anaerobic digestion, Biodegradation, Bioplastic, Consumer protection, Biodegradable plastic, Biodegradable waste management

1

To date, the longevity of plastic litter at the sea floor is poorly constrained. The present study compares colonization and biodegradation of plastic bags by aerobic and anaerobic benthic microbes in temperate fine-grained organic-rich marine sediments. Samples of polyethylene and biodegradable plastic carrier bags were incubated in natural oxic and anoxic sediments from Eckernförde Bay (Western Baltic Sea) for 98days. Analyses included (1) microbial colonization rates on the bags, (2) examination of the surface structure, wettability, and chemistry, and (3) mass loss of the samples during incubation. On average, biodegradable plastic bags were colonized five times higher by aerobic and eight times higher by anaerobic microbes than polyethylene bags. Both types of bags showed no sign of biodegradation during this study. Therefore, marine sediment in temperate coastal zones may represent a long-term sink for plastic litter and also supposedly compostable material.

Concepts: Sediment, Oceanography, Biodegradation, Polyethylene, Bioplastic, Biodegradable plastic, Biodegradable waste management, Plastic shopping bag

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Polyethylene mulch films used in agriculture are a major source of plastic pollution in soils. Biodegradable plastics have been introduced as alternative to commonly-used polyethylene. Here we studied the interaction of earthworms (Lumbricus terrestris) with polyethylene and biodegradable plastic mulches. The objective was to assess whether earthworms would select between different types of mulches when foraging for food, and whether they drag macroscopic plastic mulch into the soil. Laboratory experiments were carried out with earthworms in Petri dishes and mesocosms. The treatments were standard polyethylene mulch, four biodegradable plastic mulches (PLA/PHA [polylactic acid/polyhydroxy alkanoate], Organix, BioAgri, Naturecycle), a biodegradable paper mulch (WeedGuardPlus), and poplar litter, which served as control. Four and three replicates for the Petri dish and mesocosm experiments were used, respectively. Macroscopic plastic and paper mulch pieces (1.5 cm × 1.5 cm and 2 cm × 2 cm) were collected from an agricultural field after a growing season, after being buried in the soil for 6 and 12 months, and after being composted for 2 weeks. We found that earthworms did not ingest polyethylene. Field-weathered biodegradable plastic mulches were not ingested either, however, after soil burial and composting, some biodegradable plastics were eaten and could not be recovered from soil any longer. Earthworms, when foraging for food, dragged plastic mulch, including polyethylene and biodegradable plastic, and poplar leaves into their burrows. The burial of macroscopic plastic mulch underground led to a redistribution of plastics in the soil profile, and likely enhances the degradation of biodegradable mulches in soil, but also can lead to leaching of plastic fragments by macropore flow.

Concepts: Agriculture, Soil, Plastic, Recyclable materials, Bioplastic, Lumbricus terrestris, Biodegradable plastic, Mulch

0

Three biodegradable plastics materials, namely pure poly(l-lactide) (PLA), PLA with plasticizer triacetine (TAC) and the mixture PLA/polyhydroxybutyrate (PHB) and TAC were investigated concerning changes of physical properties due to biodegradation in compost at 58 °C up to 16 days. With rising time of degradation in compost, both number and weight molecular masses were decreasing progressively, but only marginal change of the polydispersity index was observed which indicates that biodegradation is not random process. FTIR spectroscopy revealed that in spite of the extensive decrease of molecular weight, no substantial change in chemical composition was found. The most significant modification of the spectra consisted in an appearing of the broad band in region 3100-3300 cm-1, which was assigned to a formation of biofilm on the sample surfaces. This effect appeared for all three materials, however, it was much more pronounced for samples containing also triacetine. Measurement of changes in crystalline portion confirmed that amorphous phase degrades substantially faster compared to crystalline part. The plasticizer triacetine is disappearing also rather fast from the sample resulting besides other effect also in a temporary increase of Tg, which at the beginning grows almost to the value typical for PLA without plasticizer but later the Tg is decreasing due to substantial changes in molecular weight. Generally during composting, the samples keep shape for up to 8 days, after that time the material disintegrates to rough powder.

Concepts: Chemistry, Mass, Polymer, Chemical substance, Materials science, Biodegradation, Molecular mass, Biodegradable plastic