Bioplastic films

An impartial criterion used to assess the plant yield is the commercial yield, i.e. the net amount of harvest really put on the market, expressed generally in kg/ ha or in kg/m. Products that are not commercial are destroyed. The commercial yields cultivated under bioplastic films have to be assessed to check if the behaviour of the bioplastic has affected yields compared to the yields obtained imder polyethylene films. One explanation is that the use of bioplastic does not induce more plant disease compared to plants grown under polyethylene. This is because, in some cases (e.g. melon), there is a reduction of humidity under the mulch and consequently the microclimate around the fruit is dryer than under polyethylene. 

It is demonstrated here that extrusion is an effective tool for texturing whey proteins to create new functions for dairy proteins and that thermally denatured WPl is a unique ingredient that can be used in large amounts in nontraditional applications for non-TWPl. This review covers the use of extrusion texturized dairy ingredients in foods however, there are other examples of fhe successful use of this technique along with the product, TWPl in different types of nonfood applications, such as in biodegradable films, and bioplastics. 

Biotec GmbH www.biotec.de/ensl/index ensl.htm Bioplast Thermoplastic starch bags, boxes, cups, cutlery, horticultural films, packaging films, planting pots, tableware, trays and wrap film... 

For the development of edible and biodegradable bioplastics, it is required solvents and a pH regulating agent, when necessary, in addition to the plasticizer and polymer. The pH adjustment in the case of proteins is necessary to control the solubility of the polymer. Some regulators of pH found in the literature [13] acetic acid and sodium hydroxide. The solvents commonly used to prepare these bioplastics are water, ethanol or a combination of both [14]. A crucial aspect in the preparation of films is the solubility of proteins and the ability to interact with the same solvent used, since the total solubility of the protein is required for films formation [15]. The dispersion of the protein molecule in water is possible due to the large number of amino acid residues that interact with the polar solvents. These interactions can be improved depending on the dielectric constant of the solvent, since this constant is inversely proportional to the strength of intermolecular attraction. Films can be simple, made with one type of macromolecule or composed by two or more types of macromolecules, and can be formed with two or... 

It is well established that the extrusion of proteins is a potential for obtaining edible films on a large scale [41]. For these authors, the incorporation of polysaccharides and inclusion of nanoparticles in these films tend to improve their mechanical properties. Park et al. [42] studied bioplastics made from extruded gelatin plasticized with glycerol, sorbitol or a mixture of both. In this study, they discard sorbitol as a plasticizer because of low flow in the extrusion of the material. 

Miller, M., Metabolix Wins Grant to Explore PHA Bioplastics for Packaging Film, Metabolix press release, March 2, 2004. 

As cited in Guilbert and Gontard, 2005 [3], agro-polymers that have been proposed to formulate edible films or coatings are numerous (Cuq et at, 1995 Guilbert and Cuq, 1998). Plant polysaccharides such as cellulose and derivatives are used in various forms (simple or composite materials, single-layer or multi-layer films). The formulation of bioplastic or edible films implies the use of at least one component able to form a matrix having sufficient cohesion and continuity. They are polymers, which under preparation conditions, have the property to form crystalline or amorphous continuous structures [3]. 

The market of destructurized and complexed starch-based bioplastics accoimts for about 25,000 ton/year, 75% of which is for packaging applications, including soluble foams for industrial packaging and films for bags and sacks. The market share of these products accoimts for about 75-80% of the global market of bioplastics (162). 

The main natural biomaterials for bioplastics are proteins, cellulose derivatives, alginates, pectins, starch and other polysaccharides. The solubility in water of the polysaccharide film is advantageous in situations where the film is consumed with the product, resulting in little change in the food s sensory properties. " Edible films based on proteins, polysaccharides or lipids minimize special care with the final package and increase food quality. ... 

Another way of generating biopolymers is the fermentation of starch, sugar and other commodities by various microorganisms. Typical examples are poly(hydroxyalkanoates) (especially poly(hydroxybuty-rate) (PHB)) and poly(lactic acid) (PLA). Due to the chirality of lactic acid (D- L-form), two distinct forms of poly(lactic acid) exist (poly(L-lactic acid) and poly(D-lactic acid)). PLA is used, e.g. in biomedical application (sutures, stents, drug-delivery, preparation of bioplastic), in agriculture (mulch-film), packaging, and in blends with synthetic polymers. 

In this scenario, compostable bioplastics can play a key role. Typical examples are waste bags for the collection of household waste, disposable catering items nsed in fast-food restaurants and agricultural mulch films. Bioplastics do not need separation but can be collected and treated in a homogeneous way with the other organic waste, making the system more efficient. 

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