Starch with formaldehyde

The effect of microwave radiation on maize, potato, and cassava starch (all either air-dried, in slurry, or pregelatinized) has been studied by Muzimbaranda and Tomasik.295a Starch readily dextrinized under such treatment. The sensitivity to microwaves increased in the order com > cassava >> potato starch. Micro-wave radiation also allowed facile cross-linking of starch with formaldehyde. The reaction took place for 5-15 min. and did not require any catalyst. Extended periods of reaction led to dextrins. In the presence of hydrogen peroxide, starch could be cross-linked with acetylene.2953... 

Since aldehydes behave as bifunctional reagents, crosslinking of starch occurs. For example, Syniewski1275 reported the reaction of starch with formaldehyde. 

Modification of carbamoylated and carbaminated starches by oxidation and crosslinking with formaldehyde was reported.2623 Crosslinking was used to produce fire-resistant construction boards.1360 A size for cellulose fabrics was produced by crosslinking poly(carbamoylethyl)ethers of starch with formaldehyde.1351... 

It was reported that the reaction of starch with phenol in the presence of a Lewis acid such as AICI3 resulted in resins of controlled melt viscosity.252 Probably, the product results from the hydrolysis of starch to glucose with conbversion of the latter into 5-(hydroxymethyl)-2-furaldehyde, which subsequently condensed with phenol.253 The reaction of starch with phenol without any catalyst required temperatures between 200 and 260 °C, and the resultant resinous product was then hardened by condensation with formaldehyde.254 Mastication of either glycerol or phenol with starch and water was said not to involve alcoholysis, but instead results in the formation of polymeric products.255 Reactions with gossypol256,257 and propylene glycol258 that were performed in the presence of a basic catalyst were in fact polymerization reactions and not alcoholyses. 

Several copolymers and condensates of oxidized starches with polymers have been developed. For example, products of starch dialdehyde condensation with acrylamide were prepared for further copolymerization with various monomers to form resins for coatings, molding powders,585 and materials for immobilization of enzymes, for instance, alpha amylase.586 Hypochlorite-oxidized starches were also reacted with acrylonitrile.507,521 Hypochlorite-oxidized starches were allowed to react with allylated starch dialdehyde,587 polycondensates of ammonia-dimethylamine-epichlorohydrin,588 polycondensates of starch dialdehyde with melamine,589 urea433,541,590 capable of precipitation of tannin591, carboxyamides,411 urea and formaldehyde,592 proteins,524,593,594 polyfyinyl alcohol),595 alkylammonium salts,519,596 alkoxyalkylamines,597... 

There are also patents for solid, water-insoluble products resulting from such a reaction.1276,1277 In addition there are reports of the strengthening of artificial silk, starches, and cellulose after contact with formaldehyde.1278 On the other hand model studies carried out by Tomasik and Schilling1279 on the reaction of maltodextrins with formaldehyde and pyruvaldehyde suggested that neither of these, in contrast to glyoxal and glutaraldehyde, acted as crosslinker. 

A wide variety of reaction conditions have been proposed for the reaction of starch with aldehydes. Early studies entailed use of alkaline solutions, perhaps in order to gelatinize starch.1276 Because of the known behavior of aldehydes in alkaline media (Cannizzaro disproportionation and aldol condensations of aldehydes with active active a-methylene groups), this reaction has no simple outcome. However, a process of acetalation in alkaline solutions was subsequendy patented.1293 An exothermic reaction was observed within 3 4 min using an excess of formaldehyde. It was also reported that a,(3-unsaturated aldehydes reacted readily in slightly basic media.1294... 

Early patents reported formation of acetals with formaldehyde at pH < 2.1295,1296 Interestingly, even when starch was pretreated with alkali,1295 the reaction is complete within 3-28 h at pH 1.6-2.5 and at a temperature below gelation. The concentration of either formaldehyde or acetaldehyde was 0.075-0.5 wt.% of starch in suspension. It was reported that this reaction carried out in acidic media could be shortened to 1 h and that the viscosity of the final product depended on the... 

A cationic starch can be prepared by blending a condensate of formaldehyde plus an inorganic ammonium salt with starch and heating at 80 °C for up to 1 h.1316 A great interest was developed with urea-formaldehyde resins that were made to react with such polyalcohols as starch.1317-1319 It was reported that the reaction of starch with urea-formaldehyde resin required an acidic catalyst592,1320-1325 and the use of such dispersants as polyphosphates.1326 Ammonium metaphosphate catalyzed the reaction without the addition of any other acid catalyst.1327 A product that formed a paste was produced by controlling the proportion of starch to aldehyde (either up to 20% of formaldehyde or up to 30% of acetaldehyde) and urea (up to 15%) at pH 2 1.1328... 

A thixotropic starch was produced in reactions of POCl3-crosslinked starch with unsaturated aliphatic aldehydes.1361 Starch phosphates have been crosslinked by various aliphatic and aromatic aldehydes in the presence of urea, melamine, and similar compounds. Among several aldehydes tested[formaldehyde, propanal (propionaldehyde), glyoxal, glutaraldehyde, 2-hydroxyadipaldehyde (2-hydroxy -1,6-hexanedial), and some aromatic aldehydes], only those products that had reacted with glyoxal were insoluble in water.1322 Significant increases in viscosity occurred after starch phosphates having a low DS were treated with urea.1590... 

Borax has frequently been used in conjunction with such reagents as (3-chloro-2-hydroxypropyl)trimethylammonium salts,1853 epichlorohydrin or formaldehyde,1401185318541855 melamine-formaldehyde resins,1856 (carboxymethyl) starch, oxidized (carboxymethyl)starch, (carboxymethyl)starch-acrylamide copolymer,1857 and oxidized starch.1858 Boric acid was also used jointly with formaldehyde,1859 and starch dialdehyde has been crosslinked with boric acid.526... 

Various aminoalkyl and alkylaminoalkyl halides react with starch in alkaline media and are readily available by the reaction of epichlorohydrin with primary, secondary, and tertiary amines and even aqueous ammonia. Prior to the reaction with starch, the quaternary ammonium compounds were either decomposed to free amines, or they reacted as amminium compounds to give cationic aminium starches. Cationic starches were produced by the reaction of starch with arylalky-laminoalkyl epoxides. In the presence of formaldehyde, inorganic ammonium salts provided the source of amino groups.1316... 

Starch and urea were combined under pressure in order to produce an adhesive for corrugated paperboard2616 and a thickener for frozen food.2660 Carbamoylated starch could also be further reacted with formaldehyde and amines2661 or with... 

The presence of numerous hydroxyl groups able to react with formaldehyde makes starch-derived products suitable chemicals for formaldehyde-based resins. Research on this subject started many years ago and showed that in a number of applications it is possible to partially replace or extend urea formaldehyde, phenol formaldehyde and melamine formaldehyde resins without significantly affecting the finished product s performance. In many applications, adhesive systems based on formaldehyde resins incorporate a polysaccharide component. More than 4.5 Mio mto of formaldehyde-based resins have been produced in Western Europe alone. The use of carbohydrates allows lower consumption of oil-based resins and, consequently, reduced release of formaldehyde in the environment. 

For detecting small amounts of this antibiotic on silica gel plates an N-chlorination of the amide group of chloramphenicol with chlorine vapor, evolving from the decomposition of calcium hypochlorite, followed by selective reduction of the excess chlorine with formaldehyde vapor, has been worked out (60). The solvent was ethyl acetate, the plate was dried, placed for 2 min into a tank with Ca(OCI)2, transferred to a tank with formalin (30-45 s), and sprayed with a solution containing 1% starch, 1% Kl, nd 0.05% Triton X-100. The purplish-blue spots (/ /= 0.61) give a low detection limit of 60 ng. 

Starch Is modified with formaldehA de to give pastes or pow ders w hich can be. solidified to produce water-resistant products. Such materials may be employed as siang agents, coating compounds, and adhesives. Procedures inroh-e heating with formaldehyde under various conditions alone and in the presence of acid catalysts -. Production of a mbber-like product from stai ch is also claimed by one investigator (page 143). 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

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