Plasticized starch-based composites

Plasticized starch-based composites have also been the subject of an abnndant body of literature, particularly during the last decade, continuing on from the development of composites based on natural fibers. 

The literature in the domain has indeed shown improvements in performanee relating to the addition of this type of fibers. This evolution is conneeted to a strengthening of the matrix, becanse of exeellent fiber-matrix interactions. This results in  

On this topic, a large nnmber of patents have been published over the course of the past decade, with complex formulations, such as the introduction of proteins or of biodegradable polyesters. 

Mineral microfillers have been tested in a plasticized starch matrix [CAR 01]. For example, micrometric particles of kaolin have been incorporated by extrusion. Due to a significant compatibility between the matrix and the filler, we note an increase in the glass transition temperature, a reduction in water absorption and an increase in the rigidity of the material. However, with the corresponding filler contents, these composites no longer satisfy the standards of biodegradation (at least 90% of the material has to be degraded). 

There is a particular type of composites nanobiocomposites. Because of the significant discussion surrounding this type of material, the next section is given over to this topic. 

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Natural fillers used in this study are not water soluble (two of them contain significant amounts of cellulose in their chemical composition) and randomly disperse within the starch plasticized matrix, and appears as a discontinuous phase after composite films drying (as evidenced by the scanning electron microscopy SEM investigation presented below). Therefore, these natural fillers provide more interfacial area within the composite films stmcture. As a result, light diffusion is enhanced, thus generating a reduced transparency property for the composite films. Overall, plasticized starch-based composite films exhibit some relative transparency mainly at low amount values for natural fillers in composite formulations. 

The early research stage of thermoplastic starch-based composites was focused on the use of plasticized starch as matrix for EPN. The preparation of thermoplastic starch for EPN by melt intercalation in twin screw extrader was first reported by de Carvalho et al. (2001). The composites were prepared with regular com starch plasticized with glycerin and followed by reinforced with hydrated kaolin. The research result showed a significant incensement in the tensile strength from 5 to 7.5 MPa for the composite from matrix only up to 50 % clay composition. The result also indicates the maximum value of elasticity modulus and tensile strength incorporated in the matrix. 

De Carvalho et al. provided a first insight in the preparation and characterization of thermo plasticized starch-dtaohn composites by melt intercalation technique (2001). As films or bag, starch corrld be employed as packaging for fraits and vegetables, snacks, dry products, or as starch based adsorbent pads due to its hygroscopic nature for meat exudatiorr. 

A particular mention goes to Mater-Bi, produced by Novamont, who have revolutionised starch-based biomaterials for two decades. The commercial success of this biodegradable and biocompostable plastic relies on two main factors the scale economy that allows the reduction of costs, and the diversity of formulations to develop different end products (plastic bags, tableware, toys, etc.). More than 210 references in Chemical Abstracts are available on this (registered) keyword, and the number of patents related to different formulations and developments is also impressive. Mater-Bi can be essentially described as a blend of starch with a small amount of other biodegradable polymers and additives. The actual compositions are still known only by a very few people. 

These discoveries provided the technology base for commercialization efforts of starch-based plastics by the Novon division of the Warner-Lambert Company.157,158 The thermoplastic compositions were based on blends of destructurized starch and various hydrophilic polymers, such as ethylene-vinyl alcohol copolymers (EVOH). Hydrophobic polymers and additives, such as plasticizers and lubricants, could also... 

Surprisingly, the association between TPS and cellulose fibres (polysaccharide-based composites) has been little analysed. In the literature, cellulose fillers used in association with a plasticized starch matrix are commercial paper fibres,10 potato pulp microfibrils,11 12 tunicin whiskers and paper bleached pulp.13-14 The literature reports that these cellulose fillers improve the tensile strength. Besides, the composite water sorption seems to be decreased. This behaviour is related to the well known lower water uptake of cellulose compared to starch.10-14... 

The aim of this paper is to present the different properties of polysaccharide composites obtained by the introduction of cellulose fibres, varying in length and content, into plasticized wheat starch. We have used LDPE-based composites as reference, because without compatibilizer, the LDPE-fibres interactions are usually considered as very poor. To highlight the interactions developed between cellulose and starch, we have compared both kinds of composites. Finally, we have evaluated the post-processing ageing of TPS compared to some other systems. 

L. Averous, O. Martin and L. Moro, Plasticized Wheat Starch-based Biodegradable Blends and Composites, 6th 1SBP and 9th BEPS, Honolulu-Hawaii (USA), 12-16 December 2000. 

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