Reactive processing and mechanical properties of cross-linked maize starch

There is a growing interest in non-food applications of starches mainly because of their total biodegradability, low cost and world-wide availability. In general, chemical modification reactions are performed on starches of several sources in order to expand their usefulness. Although cross-linking formation in the presence of sodium trimetaphosphate (STMP) and sodium hydroxide has been already addressed by many authors, the mechanical properties of the resulting products have not been reported. In the present work, maize starch was treated with varied concentrations of STMP and sodium hydroxide at 25% moisture content in an internal mixer. Processing was carried out at a constant rotors speed of 40 rpm for 15 min, at temperatures varying within a limited range. After processing, samples were compression-moulded, conditioned at 28 °C and 68% relative humidity for 20 days, and submitted to tensile tests. The effects of the independent variables, concentration of STMP expressed as phosphorous content, and temperature, on specific mechanical energy and mechanical properties of the cross-linked starch materials were analysed by the response surface methodology.