Cold-setting phenolic resins

Conifer Bark and Related Tannins in Cold-Setting Phenolic Resins... 

With the exception of the early work by Herrick and Conca (95) there has, until recently, been surprisingly little research directed to the use of conifer bark tannins in cold-setting wood-laminating adhesives. Current prices for the resorcinol that generally makes up about 25% of the weight of cold-setting phenolic resins are about 1.80 to 1.85/lb. Therefore, comparatively expensive reactions and processing costs can be economically feasible in the development of these types of... 

Cold-Setting Synthetic Resin Adhesives for Constructional Work in Wood (Phenolic and Aminoplastic), 1945. Amendment PD 1090, September 1950. (Bound with 1203.)... 

Laminated beams (glulam), parallam (or LSL) and fingerjoints a flat pressed multilayer wood beam, thiek wood planks constituting the layers, used for structural exterior applications and bonded with PRF (phenol-resorcinol-formaldehyde) cold-setting resins, or MUF cold-setting resins, or even with certain types of polurethanes (although the use of these latter ones is only established in one country and can show creep and temperature-induced creep problems). The indi-... 

More recently, a modification of the system described by Kreibich has been used extensively in industry with good success. Part A of the adhesive is again a standard phenol-resorcinol-formaldehyde (PRF) cold-setting adhesive, with powder hardener added at its standard pH. Part B can be either the same PRF adhesive with no hardener and the pH adjusted to 12, or a 50 to 55% tannin extract solution at a pH of 12-13, provided that the tannin is of the condensed or flavonoid type, such as mimosa, quebracho, or pine bark extract, with no hardener [118,135-137], The results obtained with these two systems are good and the resin not only has all the advantages desired but also the use of vegetable tannins and the halving of the resorcinol content makes the system considerably cheaper [118,135-137]. 

Alkaline phenolic resin, ester hardened. The binder is a low viscosity, highly alkaline phenolic resole resin (1.2 to 1.7%). The hardener is a liquid organic ester (18 to 25%). Sand is mixed with hardener and resin, usually in a continuous mixer. The speed of setting is controlled by the type of ester used. Low sand temperature slows the cure rate, but special hardeners are available for cold and warm sand. In 24 h compression strength can reach 4000 kPa (600 psi). 

Subsequent work was, therefore, directed to substitution of resorcinol, a much more expensive phenol, in cold-setting, waterproof adhesives (38). Formulations based on 30 to 60% of extract mixed with a resorcinol-formaldehyde condensate and additional formaldehyde met pot-life and assembly time requirements for timber lamination. Test bonds passed requirements of the major performance standards in the United States, but competition from lower cost, phenol-modified resorcinol resins and the lack of longterm commercial perfor-... 

Applications for cold-setting, wood-laminating adhesives initially followed the same approach (47) used for laminating resins from western hemlock (38) (i.e., reaction of tannin with phenol-resorcinol-formaldehyde prepolymers). Improvements resulted through the application of Kreibich s Honeymoon technique (48) wherein one side of the material to be bonded is treated with resin and the other with catalyst. One of the preferred systems (49) was phenol-resorcinol-formaldehyde or tannin-resorcinol-formaldehyde at pH 8 with extra paraformaldehyde on the A-side and tannin at 53% solids or tannin-resorcinol-formaldehyde at pH 12 on the B-side. Such resin systems are currently used to laminate eucalyptus or pine in most South African timber-laminating plants. 

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. 

This approach was then extended by Pizzi s group to other phenolic type adhesives such as phenol-resorcinol-formaldehyde networks [19], In this work, it was shown that the addition of 1 gave cold setting resins with performances and costs comparable to those made using formaldehyde alone. Thus, the phenol-resorcinol-furfural-formaldehyde cold sets obtained appeared to have a lower bulk shrinkage compared to those prepared without 1. Moreover, it was established that the presence of furfural did not slow down the curing rate of the resins. 

ALKALINE PHENOLIC Resol - Alkaline phenol-formaldehyde resin 1. Gas hardened (alkaline phenohc cold- box) 2. Self-setting (alkaline phenohc no bake) Gas hardened with methyl formate vapour - low Cold-set with esters - low Formaldehyde Phenol Methyl formate Formaldehyde Phenol Esters ... 

FURAN Combination resins of Phenol Urea Furfuryl alcohol Formaldehyde Cold-set with acids - low Formaldehyde Phenol Furfuryl alcohol Hydrogen sulphide Acid mists Resins and acids must be kept apart (unless sand is present) as they are vigorously exoAermic when in contact... 

Xylenols (all six isomers) are now also in conunon use to form alkali-resistant grades of phenohc resins. High 3,5-xylenol mixtures are preferred. Also, resorcinol, which forms very reactive phenohc resins, is used in preparations of cold-setting adhesives. Higher homologs of phenol, like bisphenol A, are used to prepare special phenol-formaldehyde condensates. 

Acid catalysts n. Acids which may be either organic or inorganic, or salts from these acids which exhibit acidic characteristics. They are used to promote or accelerate chemical reactions, and find special applications in the manufacture and subsequent hardening of synthetic resins. Acid catalysts have been employed in the manufacture of polymerized drying oils, coumarone, urea, phenol-and melamine-formaldehyde resins, and in the cold-setting of compositions containing the last three named resins. Odian GC... 

Foundry resin n. A thermosetting resin used as a binder for sand in metals founding. The types most commonly used as water-soluble phenol-formaldehyde resins that become insoluble when cured, and cold-setting furfuryl alcohol resins that cure in the presence of an acid catalyst. 

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