Plastic Biodegradable

Plastics, such as polyethylene, polypropylene, and polyethylene tere-phthalate, are synthetic polymers that are produced in very large amounts (see Chapters 6 and 8). A material that can be consumed by microorganisms and converted to compounds found in nature is called biodegradable. Plastics for all practical purposes are nonbiodegradable. When introduced in the ecosystem as industrial waste, they have adverse consequences. Therefore, for disposal of these polymers, methods such as recycling, incinerations, and burying in landfill are resorted to. 

Apart from these traditional methods, research directed toward the syntheses of biodegradable polymers has emerged as an important area. For polyolefins, metal complexes that initiate and catalyze oxidations are sometime added in the final polymer (see Section 8.3.1). Such additives hasten the biodegradation of polymers to some extent. In so far as polyesters are concerned, lactic acid can be produced on an industrial scale by the microbial fermentation of agricultural by-products. Therefore for medical and some other applications poly-lactide (PLA) as a material is preferred over nonbiodegradable polymers (see Section 8.4). 

Environmental awareness has led to the design and development of degradable plastics [271]. Biodegradable polymers are completely degraded via microbial attack. The term biodegradable has in recent years become part of the green vocabulary. 

New concepts are now known in material sciences and materials degradation such as [272]  

A degradable plastic undergoes disassembly that becomes part of the ecosystem carbon cycle in appropriate waste management infrastructures. For example, a biodegradable plastic would degrade into carbon dioxide and biomass (compost) in a composting infrastructure [275, 276]. 

Among biopolymers, in many cases polysaccharides are used, increasing attention is being given to more complex carbohydrate polymers produced by bacteria and fungi, especially to polysaccharides such as xanthan, curdlan, pullan and hyaluronic acid [277, 278]. 

Biodegradabie plastics can be categorized into severai major famiiies, which will be discussed next. Note that severai of these piastics are biobased, as well as being biodegradable, and were discussed in Section 4.18. 

When the solid waste crisis hit the United States in the 1980s, plastics were often attacked as particular problems because they are nonbiodegradable. There was a perception that biodegradation resulted in recovery of valuable landflll space. Some states even passed laws requiring that certain types of plastics (usually merchandise bags) be degradable. 

Biopol and licensed the production technology from Monsanto, with the intent to launch commercial products in late 2001. Other researchers and companies have developed similar bacteria-based polyesters, and there have also been successful efforts to transfer the plastics manufacturing genes to plants. However, so far none of these processes have achieved commercial success. 

Several companies are manufacturing synthetic biodegradable polyesters. DuPont s Biomax can be used in film or containers. Showa Highpolymer makes Bionolle for film and containers. Several other companies make similar materials. Prices are generally higher than for competitive nonbiodegradable plastics. 

In the waste disposal area, the environmental benefits of biodegradable plastics are limited to waste streams that will be composted, items that are associated with litter problems, and items that are apt to get into sewage treatment systems. If wastes will be disposed by landfill or incineration, biodegradability offers no real advantage. 

PCL -OCH CH CH CH CH CO-ln) is a partially-crystalline polyester that is biodegraded by microbial lipases and esterases. The plastic is made from petrochemical feedstocks. It has too low a melting point (60°C) to be useful in any packaging applications. Higher aliphatic polyesters such as poly(butylene succinate) (PBS) (-0(CH2) OC(CH2)2CO-)n and poly(ethylene succinate) (PES) (-OCCH l OOCCCH l CO-) are also biodegradable at a rate that depends on environmental factors (Kasuya et al., 1997). They have higher melting points of 112-114°C and 103-106°C, respectively, and the properties compare well to those of polyolefins. As succinic acid can be derived from plant sources, the polysuccinates can be potentially a bio-based polymer. 

FIGURE 6.12 Weight loss curves for PHB and PHBV (films and pellets) incubated in tropical garden soil at two exposure sites in Rnssia (a) Hoa Lac and (b) Dam Bai. Source Reproduced with permission from Boyandin et al. (2013). 

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Biodegradable Plastics and Polymers, Y. Doi and K. Eukuda, eds.. Studies in Poljmer Science, Vol. 12, Elsevier, Amsterdam, the Netherlands, 1994. 

Some 50 years later, in the 1990s Bayer produced their BAK polyesteramides by co-reacting either hexamethylene diamine or e-caprolactam with adipic acid and butane glycol. These materials do have sufficient regularity to be crystallisable and are of interest as biodegradable plastics and are discussed further in Chapter 31. 

Chapters 10 to 29 consisted of reviews of plastics materials available according to a chemical classification, whilst Chapter 30 rather more loosely looked at plastics derived from natural sources. It will have been obvious to the reader that for a given application plastics materials from quite different chemical classes may be in competition and attempts have been made to show this in the text. There have, however, been developments in three, quite unrelated, areas where the author has considered it more useful to review the different polymers together, namely thermoplastic elastomers, biodegradable plastics and electrically conductive polymers. 

A novel non-petroleum based biodegradable plastic produced from sugar based agricultural raw materials as sweet sorghum, sugarcane and molasses, having potential properties comparable with conventional or synthetic plastics, is under development and could lower the contribution of plastic wastes to municipal landfills at about 20% of the total waste by volume and 10% by weight and can achieve a satisfactory for the environmental imperative. 

Evan, J.D., Sikdar, S.K., 1990. Biodegradable plastic An idea whose time has come. 

Potts, J. E., Clendinning, R. A., and Cohen, S., Biodegradable plastic containers for seedling transplants, Soc. Plast. 

Yoon SC, Song JJ, Kim TU (1994) In Doi Y, Fukuda K (eds) Biodegradable plastics and polymers. Elsevier, Amsterdam London New York Tokyo, p 400... 

Although for many decades the primary interest in the production of PHAs has been as a source of biodegradable plastics and elastomers, PHA synthesis in plants has opened novel avenues for the use of these polymers in both plant biotechnology and basic research. 

One of the main barriers to the widespread use of biodegradable plastics is their higher production cost compared to petroleum plastics. For example, whereas the cost of most commodity plastics, such as polypropylene, is well below 1 US /kg, the costs of some of the cheapest biodegradable plastics on the... 

All of these factors mean that production of PHA in plants will likely be more expensive than starch. However, considering that starch costs about 0.25 US /kg, even tripling the production cost of PHA compared to starch would make PHA in plants at least five times cheaper than PHA obtained from bacterial fermentation and most likely the cheapest biodegradable plastic made from renewable resources. 

The most well known application of PHB and poly(3HB-co-3HV) is as substitute for conventional, non-biodegradable plastics used for packaging purposes and derived products [21, 115, 116]. Single-use bottles for shampoos, cosmetics and biodegradable motor-oil have been manufactured from these biopolyesters by common molding techniques. Containers and cups for food products were developed similarly, and bags have been produced from blown films of the material. 

Report by the study committee for the practical use of biodegradable plastics The age of new plastics March 1995... 

Although most of the polymeric objects are combustible, incineration is not always a feasible method of disposal because of attendant air pollution => Biodegradable plastics . 

Fig. 9.3 Degradation of a biodegradable plastic film after soil solarization in a field experiment in Southern Italy (courtesy of dr Donato Castronuovo)...

Castronuovo D, Candido V, Margiotta S, Manera C, Miccolis V, Basile M, D Addabbo T (2005) Potential of a corn starch-based biodegradable plastic film for soil solarization. Acta Hort (ISHS) 698 201-206... 

Russo G, Candura A, Scarascia-Mugnozza G (2005) Soil solarization with biodegradable plastic film two years of experimental tests. Acta Hort (ISHS) 691 717-724... 

Patel, M. (2005). Environmental life cycle comparisons of biodegradable plastics. Chapter 13. In Handbook of Biodegradable Polymers, ed. Bastioli, C. Shawbury, UK Rapra Technology Ltd. pp. 431 184. 

The ability of a degradable plastic to decay depends on the structure of its polymer chain. Biodegradable plastics are often manufactured from natural polymers, such as cornstarch and wheat gluten. Micro-organisms in the soil can break down these natural polymers. Ideally, a biodegradable plastic would break down completely into carbon dioxide, water, and biomass within six months, just like a natural material. 

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