Starch networks as absorbent or superabsorbent materials and their preparation by extrusion
The present invention relates an absorbent material consisting of a molecular network of starch molecules, the starch molecules comprising an amylopectin content of at least 90% (w/w). The molecular network can either be comprised of self-entangled starches or cross-linked starches.
1. An absorbent material comprising: particles formed from an extruded network of either cross-linked or self-entangled starch molecules, containing, at least 90% (w/w) of amylopectin; said starch molecules are gelatinized during an extrusion; and said particles range in size from 89 μm to 589 μm, and exhibit a free swell capacity (FSC) of at least 13 g/g and a centrifuge retention capacity (CRC) of at least 10 g/g in a 0.9% saline solution.
2. The absorbent material according to claim 1 , wherein said starch network is produced from a waxy starch.
3. The absorbent material according to claim 2 , wherein said waxy starch is selected from the group consisting of; waxy maize starch, waxy wheat starch, waxy rice starch, waxy sorghum starch, waxy potato starch, waxy cassava starch, waxy barley starch and mixtures thereof.
4. The absorbent material of claim 2 , wherein said waxy starch is waxy maize starch.
5. A process for preparing the starch-based absorbent particle material of claim 1 , the process comprising: providing starch molecules which contain at least 90% (w/w) of amylopectin, a starch-based paste with a cohesive plasticity and having a moisture content in a range from about 25% to about 45% (w/w); introducing said starch-based paste into an extruder; performing an extrusion with an extruder temperature of at least 130° C. to gelatinize said starch molecules and to develop a starch molecular network in an extrudate; aging said extrudate; and grinding said extrudate into particles.
6. The process according to claim 5 , further comprises mixing said starch molecules with water, an alkali and a crosslinking agent.
7. The process according to claim 6 , wherein said starch molecules are cross-linked during extrusion.
8. The process according to claim 5 , wherein the paste includes from 0.001% to 02.0% (w/w on a dry starch basis) of said crosslinking agent.
9. The process according to claim 5 , wherein the paste includes from 0.001% to 02.0% (w/w on a dry starch basis) of said alkali.