Carboxylic starch formation

Slow but significant progress is visible in this area. For example, potato starch (containing 27 % amylase and 73 % amylopectin) can be oxidized to superabsorbing biopolymers. The three-component system H202/HBr/CH3Re03 works in the formation of carboxylated starch according to the mechanism proposed in Scheme 10 [104],... 

The oxidation of starch leads to the formation of carbonyl and carboxyl groups in the polymer chain. Depolymerisation also occurs and starch turns yellowish. 

Like the simple formazans, the formazans of oxidized polysaccharides form complexes with heavy metal salts with ease. On warming the formazans of oxidized cellulose, starch, dextrin, dextran, or inulin with copper, cobalt, nickel, or uranium salt solutions, their characteristically-colored metal complexes are obtained. The presence of carboxyl groups in the polysaccharide formazans frequently facilitates complex formation. ... 

A separate group of metal starchates comprises metal salts of starches carrying carboxyl, xanthate, sulfate, phosphate, and similar groups. Oxidized, carboxyalkylated, sulfated, xanthated, and phosphorylated starches readily form corresponding salts by methatetical reactions between the sodium salts of the aforementioned derivatives and other water-soluble, metal salts. There are several patents on the formation of these salts for ion exchangers and the removal of... 

This includes reactions of the polymer groups with metallic sites on the particle surface that may result in the formation of stable or insoluble compounds through covalent, ionic or coordination bonding. Carboxyl flocculants such as polyacrylic acid and carboxyl-methyl cellulose can chemisorb on the surface of calcite and sphalerite which have calcium or zinc sites on them. Certain flocculants, such as cellulose and starch with xanthate and polyacrylamide with dithiocarbamate with high chemically active groups, have been found to exhibit selective reaction with sulfide minerals. Such complexing polymers have been investigated for their use in selective flocculation processes. 

Polyunsaturated compounds readily hydroperoxidize and the hydroperoxides so formed act as initiators for both thermal oxidation and photooxidation. The incorporation of unsaturated fats into polyethylene has been used [31] to induce the oxidation of polyethylene in starch-filled polyethylene. The potential limitation of the use of prooxidants is that oxidation commences during processing and could lead to the formation of low molecular weight aldehydes and carboxylic acids (food taints) particularly in the presence of transition metal ions. 

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