Formaldehyde-free adhesive resins

The use of formaldehyde-free adhesive resins from whey and whey byproducts for manufacturing construction-quality boards could resolve these problems simultaneously. The demand for formaldehyde-based thermosetting adhesive resins in the United States was estimated to be 1.9 billion pounds in 1983 (5). The anticipated requirement for resins and the potential availability of raw materials from whey are a fortuitous combination. 

Different phenoHc resins are used for different types of wood for example, plywood adhesives contain alkaline-catalyzed Hquid resole resins. Extension with a filler reduces cost, minimizes absorption, and increases bond strength. These resins have an alkaline content of 5—7% and are low in free phenol and formaldehyde. Because many resins have a high water content and limited storage stabiHty, they are frequently made at or near the mill producing the plywood product. The plywood veneers are dried, coated with resin, stacked for pressing, and cured at 140—150°C. 

Furfural has replaced formaldehyde in phenol-resorcinol-formaldehyde resins.These formaldehyde-containing resins have been used as cold-set, exterior grade structural wood adhesives for almost half a century. The use of furfural to prepare these resins has several advantages. In addition to longer resin shelf life, when furfural is used, the emission of formaldehyde is lowered. To enhance the reaction rate when furfural is used, a small amount of formaldehyde is added to the furfural system. Hence, the furfural system is not formaldehyde-free, but nearly so. Finally, furfural has a higher molecular weight than formaldehyde. This results in a smaller amount of the expensive resorcinol being required in the system. 

Lennox Polymers LTD USA Sulfate lignin (Lenox lignin) Formaldehyde-free resins Adhesives for wood products (chips, laminates, veneers) High-performance specialty resins urethane and polyester molding resins, thermoplastic resins Traction products winter tire traction product Lubricants... 

Chem. Descrip. Toluene sulfonamide/epoxy resin Uses Resin, gloss aid for nail enamels plasticizer for nitrocellulose food-contact paper/paperboard in resinous/polymeric food-contact coatings Features Patented formaldehyde-free provides superior clarity, brilliance, high gloss, adhesion... 

Within the scope of the project several new adhesive formulations were developed and tested. The formulations were based on DME (dimethoxyethanal) resin and the products derived from it to produce formaldehyde-free wood adhesives. The investigated adhesives were evaluated on laboratory scale in order to study their technical performances, their gluing parameters, their reactivity as well as their formaldehyde emissions. It was found that all formulations met the requirements of current standards EN 319 1993-08 and that for class P2 particleboards for general uses. From the technical point of view, major advantages of the tested systems were found to be colourless, low toxicity, easy handling, and high stability at room temperature (long shelf-life, pot-life and open-time). The formaldehyde emissions of the boards produced were found to be comparable with those of solid untreated wood (F JIS A 1460 2001 standard). 

Water-based dispersions or emulsions such as polyvinyl acetate, acrylics, polyvinyl chloride and polyvinyl alcohol with plasticizers and tackifiers. In addition, this range can include urea formaldehyde and phenolic adhesives, resins, natural adhesives produced from starch, dextrin, casein, animal glues (see Polyvinyl alcohol in adhesives, Phenolic adhesives single-stage resoles. Phenolic adhesives two-stage novolacs. Animal glues and technical gelatins) and rubber latex (see Emulsion and dispersion adhesives). Solvent-free 100% solids such as polyurethane. Hot melt adhesives include Ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyesters with tackifiers and waxes. More recent additions include cross-linkable systems. 

The conversion of low molecular weight urea-formaldehyde resins into high molecular weight network polymers is usually accomplished by heating under acidic conditions. Acidic compounds such as phthalic anhydride are incorporated into moulding powders whilst ammonium chloride is commonly added to adhesive resins prior to use. In the latter case the chloride reacts with free formaldehyde to form hydrochloric acid (which serves as catalyst) and hexamethylenetetramine ... 

The commercial method of preparation of trimethylbutylphenol [65, 66] or its calcium salt [67] has been reported. The process involves reacting slightly over 3.0 moles of formaldehyde with 1.0 mole of sodium phenate at low temperature. The salt-free product is obtained by neutralization with phosphoric acid and decantation from the salt solution. The product is mainly free of resinous material and has found use in laminates, adhesives [68], and foundry sand moWs [69]. 

The product can be used in adhesives to form flat or shaped laminated parts. The nature of the resin imparts the necessary performance to withstand bond stresses in the laminate along bends in the formed components. In addition, it exhibits good water and fatigue resistance properties. The product meets the standards of major flat-pack supplier regulations regarding formaldehyde-free and wood furniture construction performance. 

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... 

The lower cost of the urea-modified PF resins is a combination of PF solids extension by lower cost urea and improved adhesion and distribution capabilities. The improvements in storage stability stem from the thinning and dilution effects as well as from the formaldehyde scavenging. Liquid PF resoles with high free formaldehyde contents tend to be less stable in storage. 

MUF resin is widely used as an adhesive in wood industries, coating technology, paper industries and a main material in kitchenware production. In various applications, different resin properties are needed to suit its application. Important resin properties are for example higher resin solubility, low curing period with lower temperature and catalyst amount, good stability for longer shelf life, and lower free formaldehyde emission, as formaldehyde is very toxic, and can cause cancer [1]. One of the factors that affecting the MUF resin properties is the mole composition. The mole composition is a ratio of formaldehyde to amino compoimd... 

Formaldehyde has hundreds of uses. Its largest use is in the production of synthetic resins. Many formaldehyde resins are hard plastics used in molding and laminates. Formaldehyde resins are used to treat textiles to make them wrinkle-free. It is also used to produce adhesives, which are used extensively in the production of plywood and particleboard. Other common uses are as disinfectants, fungicides, and preservatives. Formalin has been the traditional embalming fluid used in the mortuary industry for the last century. Formaldehyde is also used in papermaking, textile production, and fertilizers. 

The chemical and physical characteristics of phenolic resins and adhesives made from them suggest that formaldehyde emissions should be very minor ( 1 ). One reason for predicting low emissions is that very little residual free formaldehyde is present in prepared phenolic resins. This low free formaldehyde content is due to both the use of low formaldehyde to phenol mole ratios in resin preparation and to the tendency of nearly all the formaldehyde to react irreversably with the phenol. 

The lack of reaction between methylolated phenol and cellulose reported by Allan and Neogi seems to contradict the findings of Chow and coworkers. One possible explanation for this disparity could be the difference In available free formaldehyde In their systems. Allan s model phenolic adhesive would have the equivalent of only one mole of formaldehyde per mole of phenol and would not be expected to have significant quantities of free formaldehyde. The resins used by Chow and coworkers had about 2 moles of combined formaldehyde per mole of phenol. Such resins are able to release formaldehyde during cure idien condensation occurs between two methylol groups. This formaldehyde ml t then add at the aliphatic hydroxyls on cellulose or lignin resulting In condensation, as proposed by Chow, between the methylolated wood components and the phenolic resins. 

Formaldehyde additions overcome the effect of phenolic extractives in certain hardwood species, which prevent proper cure or adhesion of PF resins. Free formaldehyde appears to react rapidly with these phenolic extractives before they can interfere with the phenolic resin curing mechanism. With certain wood species that are rich in extractives, this technique has been used to increase bond durability from interior-grade to true exterior-grade performance. 

The adhesive developed for the manufacture of damp-ply-resistant corrugated cardboard are based on the addition of spray-dried wattle extract, urea-formaldehyde resin, and formaldehyde to a typical Stein-Hall starch formula of 18 to 22% starch content [60,61]. The wattle tannin-urea-formaldehyde copolymer formed in situ, and any free... 

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