Biorenewable nanocomposites
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Introduction The vast number of biodegradable polymers is chemically synthesized or biosynthesized during the growth cycles of organisms. Some micro-organisms and enzymes capable of degrading these have also been identified. Depending on the synthesis process, classification of polymers into four different categories can be proposed:1 (1) polymers from a biomass, such as agro-polymers from agro-resources (e.g., starch, cellulose) and their derivatives (e.g., modified starch or cellulose), (2) polymers through microbial production (e.g., the polyhydroxyalkanoates), (3) polymers chemically synthesized using monomers obtained from agro-resources (e.g., poly(lactic acid)), and (4) polymers whose monomers and polymers are both obtained by chemical synthesis from fossil resources. Only the first three categories are obtained from renewable resources. We can sort these biodegradable and bio-based polymers into two main families: the agro-polymers (category 1) and biodegradable polyesters (categories 2 to 4), also called biopolyesters. They represent an interesting alternative route to common non-degradable polymers for short-life-range applications (packaging, agriculture). Compared to conventional thermoplastics, their properties are sometimes too weak for certain end applications. Therefore, it is necessary to improve the properties of these polymers to make them fully competitive with common thermoplastics.
Nanocomposites are novel materials with significantly improved properties due to the incorporation of small amounts (less than 10 wt%) of nano-sized fillers into a polymer matrix. The different types of nanofillers can be classified according to their morphologies such as (1) layered (e.g., clays), (2) spherical (e.g., silica), or (3) acicular particles (e.g., whiskers, carbon nanotubes). Their specific geometrical dimensions, and thus aspect ratios, partly affect the final material properties. The layered silicate clays offer high surface areas, up to 700 m2/g (i.e., a huge interface with the polymer matrix, which governs the global material properties). The final behavior can be considerably improved thanks to strong polymer-nanofiller interactions as well as good particle dispersion. Nano-biocomposites, a novel class of polymer-based material, are obtained by adding nanofillers to these biodegradable and bio-based polymers, resulting in promising bio-based materials that show improved properties while preserving final material biodegradability without causing toxic effects to the constituents of ecosystems. These are mainly destined for short-term applications (e.g., packaging, agriculture or hygiene devices, and biomedical applications). Until the end of the 20th century, very few articles had been printed on these materials, but this has increased over the last few years. This article aims to present a brief report on the state-of-theart of nano-biocomposites, including some recent results. Since this field is fairly broad, this article is limited to describing, as
Luc Avérous, Laboratory of Engineering Polymers for High Tec
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