Brittleness starch

The choice and combinations of different size components must take account of many factors if optimum results are to be obtained. Much has been published regarding the optimisation of size formulations in relation to desizing processes [177-183]. Cotton warp yarns sized with starch are normally woven at high humidity (80% and above) to keep yarn breakages low, as the starch film is brittle at low humidity. It has been shown [183], however, that improved weavability at moderate relative humidity (e.g. 65%) can be obtained using (a) starch/acrylamide or hydroxyethyl starch at not less than 15% add-on or (b) poly(vinyl alcohol), which gave excellent results even at a low add-on of 5-6%. 

The film-forming characteristics of starch have been used for many years. Numerous products can be protectively and decoratively coated with starch. Starch can be added to sugar solutions to provide a less brittle and moisture-sensitive surface. Starch coatings have the advantage of being oil and grease resistant. 

For a two-level factorial design, only two excipients can be selected for each factor. However, for the filler-binder, a combination of brittle and plastic materials is preferred for optimum compaction properties. Therefore, different combinations such as lactose with MCC or mannitol with starch can count as a single factor. Experimental responses can be powder blend flowability, compactibility, blend uniformity, uniformity of dose unit, dissolution, disintegration, and stability under stressed storage conditions. The major advantage of using a DOE to screen prototype formulations is that it allows evaluation of all potential factors simultaneously, systematically, and efficiently. It helps the scientist understand the effect of each formulation factor on each response, as well as potential interaction between factors. It also helps the scientist identify the critical factors based on statistical analysis. DOE results can define a prototype formulation that will meet the predefined requirements for product performance stability and manufacturing. 

One of the anticipated growth areas for industrial uses of plants is in development of non-brittle, durable polymers from renewable plant feedstocks (in both biodegradable and non-biodegradable forms). Starch and sugars are currently used commercially as feedstocks for polyester production utilising microbial monomer and polymer fermentation systems (see Chapter 5 for more information). 

Historically, chemical modification of starch was the first widely-investigated method for producing starch-based plastics. Attempts at forming cast films from starch or amy-lose showed that the properties were highly dependent on relative humidity the films became brittle at low humidities.4 Figure 19.2 shows data for films of various amylose/ amylopectin ratios conditioned at 50% relative humidity and 23°C. Efforts to overcome... 

---