Wet strength resins

Application of Wet-Strength Resins. Wet-strength resins seldom are appHed to the surface of paper for enhancing wet strength because the commercially available, cationic wet-strength resins are retained so effectively internally. However, wet-strength resins are appHed frequendy to the surface of towels and tissues as creping aids. 

Fiba-Bond. [CNCInt l.] Urea-tomalde-hyde resins wet strength resins topa-per industry. 

Fiba-Bond. [CNC Int l.] Urea-formaldehyde resins wet strength resins for papa industry. 

Farley, C.E. (1994), Glyoxalated polyacrylamide wet strength resin, Wet-Strength Resins and Their Applications, Tappi. 

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... 

Urea—formaldehyde resins are also used as mol ding compounds and as wet strength additives for paper products. Melamine—formaldehyde resins find use in decorative laminates, thermoset surface coatings, and mol ding compounds such as dinnerware. 

The most commonly used reinforcement for high pressure decorative and industrial laminates is paper (qv). The strong substrate layers, or filler, are kraft paper. Kraft is a brown paper made from a sulfate pulp process (8). It consists of both short cellulose fibers from hardwoods and long fibers from conifers. The long fibers impart most of the wet strength required for resin saturation processes. 

Analysis of certain papers requires special treatment before they can be disintegrated properly. Papers containing synthetics, tars, asphalt, mbber, viscose, or wet-strength resins must be analyzed individually (see TAPPI T401) (20). Dyes or colors must be removed from highly colored papers before examination. The method of dye removal depends on the type of dye. 

Combinations of anionic and cationic resins are used. Some of the eady systems involved the use of a cationic wet-strength resin with an anionic dry-strength additive to provide both increased wet and dry strength (63). Combinations of anionic and cationic dry-strength additives also are used to provide strength effects which cannot be achieved by using either polymer alone (64). The ratio of the two polymers must be optimized to achieve maximum performance (see Acrylamide polymers). 

The recovery of fiber from broke (off-specification paper or trim produced in the paper mill) is compHcated by high levels of urea—formaldehyde and melamine—formaldehyde wet-strength resin. The urea resins present a lesser problem than the melamine resins because they cure slower and are not as resistant to hydrolysis. Broke from either resin treatment may be reclaimed by hot acidic repulping. Even the melamine resin is hydrolyzed rapidly under acidic conditions at high temperature. The cellulose is far more resistant and is not harmed if the acid is neutralized as soon as repulping is complete. 

Another significant end-use for polyamines is in preparation of paper wet-strength resins. These are polyamide, modified formaldehyde, and polyamine resins used to improve the physical strength of tissue, toweling, and packaging paper products. The cationic formaldehyde resins include both urea—formaldehyde and melamine—formaldehyde types (248,249). Cationic functionaHty is imparted by incorporation of DETA, TETA, and/or TEPA in... 

The metering and addition of dyestuff solutions is critical to successhil operation of continuous dyeing. It is also just as critical to meter other components of the process including pulp, broke, fiUers, size, alum, fixing agents, retention aids, wet-strength resins, and other additions that affect dyeing. 

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. 

These resins are referred to as cationic resins . Paper with improved wet strength may be obtained by adding an ionic resin at the beater stage of a papermaking operation. For the best results a high molecular weight resin is required. 

Paper with enhanced wet-strength may be obtained by incorporating melamine resin acid colloid into the pulp. Melamine resin acid colloid is obtained by dissolving a lightly condensed melamine resin or trihydroxymethylmelamine, which are both normally basic in nature, in dilute hydrochloric acid. Further condensation occurs in solution and eventually a colloidal solution is formed in which the particles have a positive charge. Careful control over the constitution of the colloidal solution must be exercised in order to obtain products of maximum stability. 

In the literature, various other types of resin preparation procedures are described, e.g. yielding uron structures [20-22] or triazinone rings in the resins [23,24]. The last ones are formed by the reaction of urea and an excess of formaldehyde under basic conditions in the presence of ammonia or an amine, respectively. These resins are used to enhance the wet strength of paper. 

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