Urea-formaldehyde resins, commercially available

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). 

Formaldehyde—Alcohol Solutions. These solutions are blends of concentrated aqueous formaldehyde, the alcohol, and the hemiacetal. Methanol decreases the average molecular weight of formaldehyde oligomers by formation of lower molecular weight hemiacetals. These solutions are used to produce urea and melamine resins the alcohol can act as the resin solvent and as a reactant. The low water content can improve reactivity and reduce waste disposal and losses. Typical specifications for commercially available products are shown in Table 7 (117). 

A wide selection of amino resin compositions is commercially available. They are all alkylated to some extent in order to provide compatibiUty with the other film formers, and formulation stabiUty. They vary not only in the type of amine (melamine, urea, ben2oguanamine, and glycolutil) used, but also in the concentration of combined formaldehyde, and the type and concentration of alkylation alcohol (/ -butanol, isobutyl alcohol, methanol). 

Currently, one of the most important commercially available materials today are the urea-formaldehyde (U-F) resins. Their applications include coatings, adhesives, castings, moulding compounds and textiles. Maciel et al. have produced a series of extensive papers in this area concentrating on both and CP/MAS [13-16]. 

The OPS veneers were then segregated by outer and inner layers. The adhesive mixture was composed of a commercially available urea-formaldehyde (UF) resin (42.5% solid) mixed with industrial wheat flour and hardener (ammonium chloride). The adhesive mixture was spread onto the veneers at different spread amounts 200 g/m and 250 g/m (double glueline). The assembled veneers were then cold pressed for 10 min and hot pressed at 130°C for 15 minutes. Two types (Type 1 comprised of 100% outer layer veneers and Type 2 comprised of 100% inner layer veneers) of 5-ply, 450 mm x 450 mm x 13 mm plywoods were produced. Then, the plywoods produced were conditioned at RH of 65% and temperature of 22°C for a week prior to cutting into test specimens. 

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