Waxy maize starch cationic

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Potato starch is inherently anionic, since it contains phosphate groups. The presence of both anionic and cationic groups in cationized potato starch enhances its flocculation power and renders it active over a wider pH range. Com starch has to be rendered amphoteric by the introduction of phosphate groups. Charge modification has also been applied to waxy maize starch. 

Cationic starch must be thermally dispersed before it is added to the papermaking furnish. In batch cooking, a slurry with up to 4% starch content is heated to a temperature of 93-96°C (200-205°F) for 20-30 minutes. In jet cooking, the solids can be raised to 6% and the temperature to 102-116°C (215-240°F) with short retention. For waxy maize starch, the cooking temperature should not exceed 107°C (225°F). The starch cook must be diluted to <1% solids before addition to the paper stock. 

Eliasson and Ljunger (33) reported that the cationic surfactant cetyl trimethyl-ammonium bromide (CTAB) slowed down the rate of formation of amylopectin crystallites in gelatinized waxy maize starch, as measured by differential scanning calorimetry (DSC). 

Cationization of waxy maize, corn and barley starches in aqueous alcohol slurries is most effective at 35-65% ethanol for all starch types a 1 1 starch to water ratio gave highest DS values.51 A process for making cationic or amphoteric starches in aqueous, alkaline alcoholic solvents has also been described.52... 

Controlled crosslinking of cationic starches improves performance in microparticle-containing papermaking systems.84-86 Superior performance over cationic potato starch was achieved with crosslinked cationic or amphoteric waxy maize, tapioca or potato starch in microparticle systems when the starch cooking was optimized to produce the proper colloidal dispersions.86... 

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