Protein-based plastics and composites

Protein-Based Plastics and Composites as Smart Green Materials... 

Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity. 

Several proteins have been extensively studied for their materials applications. Among them, soy protein is one of the most popular. Indeed, since the early 1930s it was used in phenol-formaldehyde blends for automotive applications. However, soy protein is sensitive to moisture and exhibits relatively low strength properties. Thus stabilization by plasticization, compatibilization or crosslinkage is required to maintain long-term performance of soy protein-based plastic materials. Also, several studies on soy protein-based blends with other natural polymers or their reinforcement by natural fibres have been performed. More recently studies on soy protein-nanoclay composites and polyfbutylene adipate-co-terephthalate) (PBAT) blends were also performed. 

Lodha, R, Fundamental approaches to improving performance of soy protein isolate based green plastics and composites, PhD Thesis, Cornell University, 2004. Lai, H.M., Padua, G.W. and Wei, L.S., Cereal Chem., 74, 49-59, 1995. 

Protein-based polymers have the potential to surpass the polyesters and other polymers because they can be directly produced in microorganisms and plants by recombinant DNA technology resulting in the capacity for diverse and precisely controlled composition and sequence. This is not possible with any other polymer, and it increases range of properties and the numbers of applications. Remarkably, with the proper design of composition, protein-based materials can be thermoplastics, melting at temperatures as much as 100°C below their decomposition temperatures. Therefore, they can be molded, extruded, or drawn into shapes as desired. Aspects of protein-based materials as plastics is also considered below. 

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. 

Soy protein-based green composites are not only applied as an environmental friendly material in the fields of adhesives (Kumar et al. 2002), plastics (Kumar et al. 2011), and textile fibers (Kobayashi et al. 2014), but also as biodegradable membranes (Mamthi et al. 2014). Furthermore, the nutritional and health benefits of soy protein draw attention to the application in the field of biomedical materials (Silva et al. 2014), such as tissue engineering scaffolds (Chien and Shah 2012),... 

The mechanical properties of protein-based materials closely depend on the plasticizer content, temperature and ambient relative humidity (16,34,35). At constant temperature and composition, an increase in relative humidity leads to a major change in the material properties, with a sharp drop in mechanical strength and a concomitant sharp rise in distortion. These modifications occur when the Tg of the material is surpassed (Figure 1). These variations can be reduced by implementing crosslinking treatments (physical or chemical) or using high cellulose or mineral loads (22). 

Use Water-soluble lubricants solvents for dyes, resins, proteins plasticizers for casein and gelatin compositions, glues, zein, cork, and special printing inks solvent and ointment bases for cosmetics and pharmaceuticals intermediates for nonionic surfactants and alkyd resins. 

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