Influence of glycerol and water content on the structure and properties of extruded starch plastic sheets during aging

Abstract

ABSTRACT:The properties of starch plastic sheets were investigated by stress-strain measurements in relation with starch crystallinity. Granular potato starch was plasticized with different amounts of glycerol and water by extrusion. The materials were amorphous directly after processing. During aging above the glass transition temperature at various humidities single helical (V and E-type) and double helical (B-type) crystallinity was formed. The rate of crystallization is a function of water and glycerol content. The amorphous rubbery materials were soft and weak with high elongations. During aging the materials became less flexible with higher elastic modulus and tensile stress. The changes are related to changes in water content and glass transition temperature and to changes in B-type crystallinity. The changes in stress-strain properties are explained by the formation of helical structures and crystals, which results in a reinforcement of the starch network by physical crosslinking.

Extrusion Processing of Starch Film

“…A simple and common technique of producing sheet or film by extrusion is using a twin-screw extruder with a slit or flat film die followed by a take-off device for orientation and collection (van Soest and Knooren 1997;Fishman, Coffin et al 2000;Yu and Christie 2004;Dean, Yu et al 2007). During film or sheet extrusion, the viscoelastic starch-based materials are forced through the die to form sheet or film products (Chiang and Johnson 1977).…”

Starch Protective Loose-Fill Foams

“…Yu et al (1998) hold that TP maize starch with 10% moisture and 25-35% glycerol shows a T g running from 83 -71°C. Van Soest & Knooren (1997) proved that potato TPS with 11% moisture and 26% glycerol had a T g = 40 °C, whereas for the materials of higher moisture and glycerol content it fell below 20°C. Lourdin et al (1997) reported that potato starch of 13% moisture with 15% glycerol content had the T g around 25°C, while at 25% glycerol the T g dropped to around 0°C.…”

“…If the total thermal and mechanical energy provided to the starch is insufficient the product will show unmolten starch granules of clear crystallographic structure. Similarly, an insufficient amount of plasticizer may result in incomplete destruction of the crystallographic structure of starch (Souza & Andrade, 2002;Van Soest & Knooren, 1997). …”

“…Together with a longer storage period, and consequently TPS crystallinity, tensile strength increases and elongation at break decreases. The increase of moisture content of the starchy materials storage conditions brings about intensification of their mechanical properties changes (Van Soest & Knooren, 1997).…”

Mechanical properties and total hydroxycinnamic derivative release of starch/glycerol/Melissa officinalis extract films

“…The application of starch to obtain films is attributed to chemical, physical and functional properties of amylose. The amylose molecules in solution are arranged in parallel, forming hydrogen bonds among adjacent starch chains, reducing polymer water affinity and favoring the obtainment of opaque gels and reduced flexibility films (Lu, 2009;Shimazu, 2007;Jansson, Thuvander, 2004;Soest, Knooren, 1997). The mechanical properties of starch films can be changed by addition of plasticizing agents.…”