Starch with melamine-formaldehyde resins

Materials from starch crosslinked with melamine-formaldehyde, methylated melamine-formaldehyde, and other amine-aldehyde resins were patented as binders for filter paper,1336 milk filter sheet materials,1338 and aqueous papercoating compositions containing clay, titanium(IV) oxide, butadiene-styrene latex, and calcium octadecanoate.1396,1397 Foams for filters were developed.1398 A heatsetting adhesive was one of the first applications reported for starch crosslinked by urea-formaldehyde and phenol-formaldehyde resins.1331,1340-1342,1347,1372,1399... 

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... 

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. 

Water molecules are so small and cellulose and so hydrophilic that this solution usually affords only temporary protection. Formaldehyde, glyoxal, polyethylen-imine, and, more recently, derivatized starch (50) and derivatized cationic polyacrylamide resins (51) have been used to provide temporary wet strength. The first two materials must be applied to the formed paper, but the other materials are substantive to the fiber and may be used as wet-end additives. Carboxymethylcellulose-calcium chloride and locust-bean gum-borax are examples of two-component systems applied separately to paper that were used to a limited extent before the advent of the amino resins. Today three major types of wet-strength resins are used in papermaking polyamide-polyamine resins cross-linked with epichlorohydrin (52) are used in neutral to alkaline papers cationic polyacrylamide resins cross-linked with glyoxal are used for acid to neutral papers and melamine-formaldehyde resins are used for acid papers. 

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... 

BERSET 2604 Is a melamine based resin with very low free formaldehyde content. It Is a very effective crosslinker and Insolublllzer for starch, protein, P.V.A., and latex In non-plgmented or pigmented coatings. When BERSET 2604 Is added to the coating color, good wet pick resistance and wet rub improvements are noticeable directly off the machine. 

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... 

The author has found the carbohydrate binders (e g. starch, dextrin) superior to phenol formaldehyde resins, maleic and phthalate type resins, polyester, glyptal resins, shellac, vegetable rosins, urea formaldehyde resin and melamine resin in all experiments to date. Dextrins and starches combine good binding properties and low cost with simple handling requirements. 

UF, urea-formaldehyde resin MUF, melamine fortified UF resin MF/MUF, melamine and melamine-urea resins (MF resins are only used mixed/coreacted with UF resins MUPF, melamine-urea-phenol-formaldehyde resin PF/PUF, phenol and phenol-urea-formaldehyde resin (P)RF, resoreinol-(phenol-)formaldehyde resin PMDI, polymeric methylenediisocyanate PVAc, polyvinylacetate adhesive old nat.adhesives, old (historic) natural adhesives (e.g., starch, glutin, casein adhesives) nat.adhesives, natural adhesives (e.g., tannins, lignins, carbohydrates) inorg.adhesives, inorganic adhesives (e.g., cement, gypsum) activation activation constituents of wood to function as adhesives (i.e., lignin). 

Mixed Glues. Starches and dextrins also are used in combination with other raw materials in adhesives. For example, the resistance to water of starch-based adhesives can be improved by the addition of melamine-formaldehyde or urea-formaldehyde resins. Mixtures of starch-based adhesives or dextrin-based adhesives with synthetic resin dispersions are also used. 

---