Sunday 25 November 2012

Practical Polysaccharides (Part 8) Starch-based Nonwovens and Superabsorbents

Part 8 of the paper by Jacek K. Dutkiewicz of Buckeye Technologies Inc given at this years Insight Conference organised by MTS in Norfolk Virginia. (Click here for Part 1)

From the cost point of view, starch may seem even more attractive as a raw material compared to cellulose for a superabsorbent polymer because of its high-molecular weight and abundance of reactive hydroxyl groups.  Indeed, relatively high-capacity products have been commercialized and there were even some attempts to use them for personal care applications.  So far the performance of synthetic SAP is far more superior and it may be hard to replace it in the disposable hygiene area with a starch-based polymer.  Still it is worth mentioning at least one simple technical solution which involved an approach similar to the one referenced above with regard to cellulose [8]. In this case, carboxymethylstarch was cross-linked also by heat treatment to achieve a decent, but not permanent absorbency capacity (Fig.13).  One can speculate that, over a period of time, polysaccharides may undergo morphological changes due to relaxation and reorientation of polymeric chains, which affect the physical crosslink density in the material.   Therefore, the absorbency properties may gradually decline.

Even though natural starch was not designed by the nature to be a fiber as it is in the case of cellulose, certain grades of soluble starches can be spun into fibers.  Relatively low cost of the raw material and use  of water as a solvent seem to be strong enough arguments for putting up resources to develop natural, environmentally friendly fibrous materials.  The solution to a problem of making the product with useful properties is not that simple because of poor mechanical properties of the starch polymer which is inherently amorphous.   So, rather than dealing with a pure starch fiber the challenge has been focused on finding the right plasticizers and on the method of spinning the fibers with minimum amount of water (Fig. 14). Much progress has been made in the area of so-called thermoplastic starches (TPS) by a number of researchers [9].   However, there is still a significant gap between the mechanical characteristics of traditional man-made fibers and starch-based fibrous materials.

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