Polymer nanocomposites reinforced with polysaccharide nanocrystals

Abstract

Aqueous suspensions of polysaccharide nanocrystals can be prepared by acid hydrolysis of natural resources, such as cellulose, chitin and starch. The object of this treatment is to dissolve away regions of low lateral order so that the water–insoluble, highly crystalline residue may be converted into a stable suspensoid by subsequent vigorous mechanical shearing action. When using cellulose or chitin, the resulting nanocrystals occur as rod–like particles or whiskers, which dimensions depend on the nature of the substrate, while in the case of starch the nanocrystals appear as platelet–like nanoparticles. During the last decade we have attempted to mimic biocomposite by blending polysaccharide nanocrystals from different sources with polymer matrices, including synthetic and natural ones. Casting mixtures of polysaccharide nanocrystals and lattices led to composites with drastically enhanced mechanical properties, especially at T ? Tg of the matrix, by virtue of the formation of a whiskers network, even when the whisker volume fraction was only a few percent. The formation of this rigid network, resulting from strong interactions between whiskers was assumed to be governed by a percolation mechanism. This hydrogen–bonded network induced a thermal stabilisation of the composite up to 500 K, the temperature at which polysaccharides start to decompose. A new and promising way of nanocomposite processing consists in transforming polysaccharide nanocrystals into a co–continuous material through long chain surface chemical modification. It consists in submitting polysaccharide nanocrystals to surface chemical modification based on the use of grafting agents bearing a reactive end group and a long compatibilising tail.