Biodegradable polymers protein-based plastics

Produced from renewable resources Living organisms—E. coli, yeast, plants, and animals—can be designed to produce protein-based polymers. Protein-based polymers can be produced with renewable resources. They can be prepared without resorting to toxic and noxious chemicals, and they can be programmed for a desired biodegradation. For example, they can mean food for the fishes rather than death to marine life, as occurs with present plastics. Thus, protein-based polymers can be environmentally friendly for their complete life cycle, from production to disposal. 

Soy protein-based plastics are another group of biodegradable, environmentally friendly, polymer materials from an abundantly renewable resource [29-31]. There are several types of soybean products that can potentially be utihzed for engineering structural applications [29],... 

Until recently, the ordy uses and apphcations for proteins were in food sciences [55]. The development of studies on non-food uses of agricultiual raw materials initiated an interest in protein-based plastics. A number of proteins of plant origin have received attention for the production of biodegradable polymers. These proteins are com zein, wheat gluten, soy protein, and sunflower protein. 

Edible films are arrother form of biodegradable polymer. These films act as moisture and aroma barriers arrd protect the food s mechanical integrity or handling characteristics. Emphasis is also being given for development and use of protein based plastics, polysaccharides, and wood derived plastics. The higher cost of the biodegradable plastics than petrolerrm-based polymers has been the major factor for their lirrtited rrse in food industry. 

Natural polymers such as starch and protein are potential alternatives to petroleum-based polymers for a number of applications. Unfortunately, their high solubility in water limit their use for water sensitive applications. To solve this problem thermoplastic starches have been laminated using water-resistant, biodegradable polymers. For example, polylactic acid and P(3HB-co-3HV) were utilised as the outer layers of the stratified polyester/PWS (plasticized wheat starch)/polyester film strucmre in order to improve the mechanical properties and water resistance of PWS which made it useful for food packaging and disposable articles [65]. Moreover, improved physic-chemical interactions between P(3HB-CO-3HV) and wheat straw fibres were achieved with high temperature treatment. It resulted in increased P(3HB-co-3HV) crystallization, increased Young s moduli and lowered values of stress and strain to break than the neat matrix of P(3HB-co-3HV). There was no difference in the biodegradation rate of the polymer [66]. 

The book addresses the most important biopolymer classes like polysaccharides, lignin, proteins and polyhydroxyalkanoates as raw materials for bio-based plastics, as well as materials derived from bio-based monomers like lipids, poly(lactic acid), polyesters, polyamides and polyolefines. Additional chapters on general topics - the market and availability of renewable raw materials, the importance of bio-based content and the issue of biodegradability - will provide important information related to all bio-based polymer classes. 

Figure 1.10. Ihermoplastics are polymers that melt at a temperature well below thermal decomposition such that they can be melted and formed into a desired shape as a melt. Shown are three thermoplastics, two are plastics of our daily use and a third is a designed protein-based thermoplastic that melts at 160°C and does not decompose until the temperature is raised above 250°C. The protein thermoplastic can be programmed to biodegrade with half-Uves ranging from days to decades when in an aqueous environment.

D.W. Urry, A. Pattanaik, M.A. Accavitti, C-X. Luan, D.T. McPherson, J. Xu, D.C. Gowda, T.M. Parker, C.M, Harris, and N. Jing, Tl-ansductional Elastic and Plastic Protein-based Polymers as Potential Medical Devices, in Handbook of Biodegradable Polymers, ed. by Domb, Kost, and Wiseman, Harwood Academic Publishers, Chur, Switzerland, pp. 367-386,1997. 

Proteins are natural, renewable, and biodegradable polymers which have attracted considerable attention in recent years in terms of advances in genetic engineering, eco-friendly materials, and novel composite materials based on renewable sources. This chapter reviews the protein structures, their physicochemical properties, their modification and their application, with particular emphasis on soy protein, zein, wheat protein, and casein. Firstly, it presents an overview of the structure, classification, hydration-dehydration, solubility, denaturation, and new concepts on proteins. Secondly, it concentrates on the physical and chemical properties of the four important kinds of proteins. Thirdly, the potential applications of proteins, including films and sheets, adhesives, plastics, blends, and composites, etc. are discussed. 

In this brief review of the elastic and plastic protein-based polymers, the chemical and microbial syntheses of these pohmers are noted several of the more commonly used physical characterizations of these polymers are described the important biological characterizations of biocompatibility (toxicity), immunogenicity, and biodegradability are considered, and the applications of drug delivery and tissue reconstruction are discussed. 

Of a rather long list of applications that are under consideration for these pohmers, only two will be discussed here. One is drug delivery because this application can take full advantage of the rich transitional properties of these transductional elastic and plastic protein-based poltmers (Urry et al, 1997), and the other is tissue reconstruction because this application can simidtaneously take advantage of the range of elastic moduli that are possible with these polymers, the capacity to introduce cell attachment sequences, and their ultimate biodegradability (Urr), 1993b). 

Urry, D.W. et al, Transductional elastic and plastic protein-based polymers as potential medical devices, in Drug Targeting and Delivery, Handbook of Biodegradable Polymers, Domb, A.)., Kost, and Wiseman, D.M. (Eds.), Harwood Academic Publ., Amsterdam, 1997, pp. 367-86. 

Guilbert, S. (2002) Protein-based Bio-Plastics formulation, thermoplastic processing and main applications International Congress Trade Show The Industrial Applications of Bioplastics, 3rd, 4th and 5th February Gunatillake P.A. and Adhikari R. (2003) Biodegradable synthetic polymers for tissue engineering , European Cells and Materials, 5, 1-16. 

The over growing environmental pressure caused by the wide spread consumption of petroleum based polymers and plastics has hastened the development of biodegradable and environmentally acceptable materials. Biopolymers derived from various natural resources such as proteins, cellulosics, starch and other polysaccharides are regarded as the alternate materials. Biodegradable polymeric materials derived from renewable sources are the most promising materials because of their easy availability and cost effectiveness. Biodegradable modified polysaccharides have been found to possess varied applications such as salt resistant absorption of water [109]. 

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