Amphoteric starch

Like the natural gums, starches need to be cooked in water to form dispersions for addition to the papermaking system. Various techniques have been developed for cooking starches rapidly (see Starch). In general, anionic starches are used with alum, which aids in starch retention. The cationic and usually the amphoteric starches are self-retaining. 

Amphiphile-oil-water system, temperature of, 16 424-426 Amphiphiles, 16 420 Amphiphile strength, 6 424 Amphiphilic chemicals, 17 56 Amphiphilic copolymers, 20 482 behavior of, 20 483 well-defined, 20 485-490 Amphiphilic molecules, 15 99-101 Amphiphilic plasticizers, 14 480 Amphiphilic polymer blend, 23 720 Amphiphilic polymers statistical, 20 484-490 stimuli-responsive, 20 482-483 Ampholytes, 9 746-747 Amphoteric cyclocopolymers, water-soluble, 23 721 Amphoteric starches, 4 722 Amphoteric (zwitterionic) surfactants, 24 148... 

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... 

Further improvements in the retention of pigment in the paper and enhanced sheet formation are obtained when amphoteric starches are used. Phosphate groups have to be added to cationic cornstarch to produce amphoteric properties. Cationic potato starch has a natural source of anionic charge due to its phosphate content. In recent years, waxy com starches, which consist entirely of amylopectin, have been modified for use as cationic or amphoteric agents for papermaking and surface sizing. 

Cationic potato starch is actually an amphoteric starch due to the presence of phosphate groups. An increase in cationic charge results when phosphate groups pro-tonate or react with aluminum ions in an acid papermaking system. Anionic phosphate starch will adsorb on cellulose, depending on pH and concentration in solution.135,138... 

Cationic starch is a frequently-utilized retention aid, especially when paper strength improvement is a second objective.141,142 Low pH activates tertiary amino starch, but at pH 6 an amphoteric starch, and at pH above 7 a quartenary ammonium starch, will be needed. 

Chapter 9 provides a broad review of the evolution of starch use in paper to the present. The chemistry of starch components and their contents in starch from various sources is covered in detail. Although cationic starch is predominantly the product of use, the use of both anionic and amphoteric starch (which contains both anionic and cationic groups) is also mentioned. 

Cationic starch is the major wet-end starch. The phenomena involved in starch adsorption and the selection of cationic starch need careful consideration, as do the proper preparation and application of starch. The criteria for the use of native, anionic and amphoteric starches are also considered. 

Attempts were made to replicate potato starch performance with other starches and in 1965 National Starch filed their landmark patent application for amphoteric starch. 

Early amphoteric starches contained tertiary aminoethyl ether and phosphate ester groups in which the preferred molar ratios of anionic to cationic groups was from 0.07 to 0.18. Later patents cited phosphate ester and quaternary amine with ratios of 0.014 to 0.92. These derivatives provided synergistic effects and were effective filler retention aids and paper strengthening agents over the pH range from 4.0 to 10.0 [4]. 

Very early in the use of cationic starches, it was recognised that acidity from alnm in moderate to high levels can change the requirements for a cationic starch to those of an amphoteric starch. The highly cationic alnm at low pH competes for fibre and filler adsorption sites with the cationic starch [13]. It is postulated that interaction between the alum and the anionic phosphate affects starch retention. The anionic charge does not appear to provide an appreciable benefit in alkaline systems [14]. 

The presence of alnm is nsnally required for a successful result using amphoteric starch. Alum exhibits its maximum cationicity around pH 5.0 - corresponding to the maximum retention of amphoteric starch in Fig. 9.13. 

Fig. 9.13 Retention of cationic and amphoteric starches in handsheets (addition level of starch derivatives is 2% on dry weight of pulp) [15]...

Fig. 9.14 Effect of increased conductivity on cationic and amphoteric starch...

It is claimed that an amphoteric starch is more tolerant to changes in anionic or cationic materials in the system, acting as a charge buffer. It is also claimed that the anionic group on the starch complexes the soluble cationic materials and reduces system sensitivity to changes in pH and zeta potentials [16]. 

Size press starch may be non-ionic, from in-mill enzymatic conversion or thermo-chemical conversion of native starch. It may be anionie if an oxidised starch is used. (Note this refers to chemically modified oxidised starch. Many American texts wrongly refer to any viscosity-reduced starch - including enzyme-converted and thermo-chetnically converted stareh - as oxidised stareh. Such processes do not form any carboxyl or carbonyl groups on the starch.) Furthermore, cationic and amphoteric starches are frequently tpplied on multi-purpose office paper for improved ink-jet printability. 

J. Yoshizawa, A. Isogai and F. Onabe(1998), Cationic and amphoteric starches on hand-sheets, Journal of Pulp and Paper Science, 24(7), July. 

An amphoteric starch composed of a tertiary amino cationic starch witii a phosphate ester. 

Certain multiply substituted polysaccharides, such as amphoteric starches, have unique characteristics which provide benefits to industry. Why are multiply modified polysaccharides less commonly used than simple modifications ... 

Amphoteric starch - cationic starches which have had further derivatizations with anionic or neutral groups... 

Pasapane J, Ronco D. Novel amphoteric starch a naturally derived rheology modifer for skin care. Cosmet Toilet Manuf World 1996 175-179. 

Some major changes in starch usage in adhesives and related fields are the large increase of cationic and amphoteric starches in paper manufacture and the increased use of high amylose starches in the corrugating industry. 

Although starch is largely added at the wet end of the paper machine, it can be placed directly on the formed sheet. The starch can be sprayed onto the fibers, applied as foam directly on the wet web, or applied as a thin curtain to the wet web. These alternative methods have certain advantages, but they lose the flocculating ability of cationic or amphoteric starches. 

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