Wet strength, paper

During the next 15 years the urea resins were also developed for use as adhesives, as textile finishing agents and in the production of surface coatings and wet-strength paper. Since World War II the development of chipboard has resulted in a large new outlet for urea-based resins which have also found other uses, such as in firelighters and foams. 

Uses. Hardener/cross-linker for epoxy resins metal chelator constituent of wet-strength paper resins copolymer with fatty acids in metal spray coatings constituent of synthetic elastomer formulations... 

Melamine and its polymers have uses in many industrial fields. The commercial importance of the compounds is shown by the fact that 34 x 106 kg of melamine was produced in the USA in 1970. The chemistry of the melamine resins has been discussed already (see Chapter 1.11). The major uses of the resins are in the formation of high-pressure laminates for home furniture, and as moldings for crockery. In addition the resins are used in finishing textiles, to improve crease resistance, and as coatings for wet strength paper. 

The largest use is for binding fibrous and granulated wood into indoor composition board. Smaller uses are for wet-strength paper and permanent-crease textiles. About 4 percent of urea-formaldehyde resin is combined with alpha-cellulose to make molding powders (Table 15.18). These find use mainly in electrical parts such as switches, wall plates and receptacles, circuit breakers, electric blankets, handles and knobs. 

Use Adhesives for particle board, plywood, various wood-gluing applications, wet-strength paper. 

Use With alkyd resins in coatings, industrial finishes on appliances, automobiles, etc adhesives for paperboard boxes, paper coatings, wet-strength paper, textile pigment binding. 

Developments since 1920 include multistage bleaching of kraft bleaching with peroxides, chlorine dioxide, and sodium hypochlorite use of synthetic resins for wet-strength paper for bags, maps, etc. and use of soluble bases for sulfite pulping, which allow the use of more species of wood. 

These polymers are mostly applied in the paper industry for wet-strength papers usable in neutral of alkaline systems instead of the urea-formaldehyde resins requiring acid conditions for crosslinking. PolyEI increases retention of dyes, pigments and fillers. PolyEI is known as a powerful flocculant used in the clarification of fruit juices and in water treatment. It removes effectively clays, colloidal acids, pectines and tannines from water. Commercially available polyEI have molecular weights in the range Mn = 600 to 100000 60). 

Flirt et al. [51] have published an effective and rapid method for the detection of melamine by ultraviolet spectrophotometry. This method can be used for products containing MF. It makes use of the strong absorption of the melamine ion at 235 nm. The resin is extracted from comminuted MF samples by hydrolyzing to melamine by boiling under reflux in 0.1 N hydrochloric acid. Stafford [52] also gives a method for the identification of melamine in wet-strength paper. 

Uses Emulsifier, lubricant, dye leveling agent, antistat, dispersant for textiles emulsifier for cosmetics, PU foams softener, rewetting agent for wet-strength paper in food-pkg. adhesives, resinous/polymeric coatings in food-contact textiles... 

Ethyl methacrylate Isobutyl methacrylate resin, wet strength paper Adipic acid Bis-hexamethylenetriamine resin, wood coatings Tetrachioronaphthaiene resin-bonded fiiters, food-contact Vinyi acetate resinous product mfg. Triethyienemeiamine resinous products Fiuorene... 

The bottles are inspected for fill-height and then are conveyed to the labeller (Fig. 20.29). Bottle labels are made of (/) sized machine-coated paper, ( ) wet-strength paper, Hi) foil, or (/v) metallized paper. The first is cheapest and the range of grades is 70-85 g/m. Wet-strength paper is paper treated with either melamine-formaldehyde or urea-formaldehyde resins. Compared with the machine-coated paper it is marginally more expensive and is less likely to be pulped in modern bottle washers. Aluminium foil is 4-5-fold more expensive... 

The -OH groups in wood cellulose copolymerize with the methylol -CH2OH groups in urea, melamine, and phenolic resins (Fig. 3.74) in plywood, composition board, connter-tops, cabinets, and furniture. Similarly, the -OH groups in ceUulose copolymerize with the methylol groups in urea-formaldehyde to produce wet-strength paper and crease-resistant permanent-press cotton fabrics. 

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