Wood adhesive

Table 1. Chemical Structures of Constituents of Principal Wood Adhesives...

The main uses of resorcinol are in the manufacture of mbber and wood adhesives. Manufacturing capacity is about 30,000 t/yr worldwide. World average prices in November 1993 are reported for the main derivatives in Table 2. 

Applications. These materials are stiU in developmental infancy. Current production is limited to one commercial process in Europe and a demonstration-scale process in North America. The lignins produced in these processes have potential appHcation in wood adhesives, as flame retardants (qv), as slow-release agents for agricultural and pharmaceutical products, as surfactants (qv), as antioxidants (qv), as asphalt extenders, and as a raw material source for lignin-derived chemicals. 

Benzenedisulfonic acid [831-59-4] (disodium salt), produced by the neutralization of the disulfonic acid with sodium sulfite [7757-83-7] is used in the manufacture of resorcinol [108-46-3] (1,3-benzenediol) (2), a chemical component found in mbber products and wood adhesives (72). The disodium salt is fused with sodium hydroxide, dissolved in water, and acidified to produce resorcinol, which is isolated via extraction (73). 

A variety of applications exist for liquid, 100% solid adhesives, (An adhesive is considered 100% solid if there is no solvent in the adhesive.) Some of the largest uses include structural wood adhesives and adhesives used for the transportation industry, such as windshield adhesives and those used for bonding composite sidewalls of a recreational vehicle (RV). Structural wood adhesives are often made of a polymeric MDI with functionality of approximately 2.7 or higher. Rigid assemblies often utilize polymeric MDI, whereas flexible adhesive assemblies will more often utilize pure MDI, a solid waxy material that melts at around 37°C, or a modified MDI , i.e., MDI that has been modified to make it a liquid at room temperature. Prepolymers are made with ratios of anywhere from NCO/OH = 1.6 to 3.0 or higher. 

In 1932, the first plywood hot press was installed in the United States. This marked the advent of the large market for phenolic wood adhesives [51]. By 1962, the volume of phenolic wood adhesives had reached about 33 kt (solids) in the U.S. Growth was accelerated in 1962 with the development of Southern pine plywood. By 1979, the consumption of phenolic plywood adhesives exceeded 220 kt or about 25% of phenolic resin production [51]. Phenolic adhesive demand for wood products took another jump in 1964 with the commencement of waferboard production. The first oriented strandboard (OSB) plants were built in 1981 [52]. OSB soon replaced most of the waferboard production and began a period of... 

The consumption of resins for wood adhesives in North America and Europe in 1997 and 1999, respectively, based on resin solids, were as shown in Table 2. 

Estimated consumption of wood adhesives solids in North America and Western Europe (in 1(K)0 metric tons)... 

Acid-induced gelling reactions of PF resins can cause severe deterioration of the wood substrate and therefore have lost any importance in the wood adhesives field. Pizzi et al. [85] describe a procedure for the neutralization of acid-hardened PF glue lines by partly using as hardener a mix of p-toluene sulfonic acid with a... 

Where resorcinol adhesives are not suitable, resins can be prepared from modified resorcinol [128], Characteristic of these types of resins arc those used for tyre cord adhesives, in which a pure resorcinol-formaldehyde resin is used, or alternatively, alkyl resorcinol or oil-soluble resins suitable for rubber compounding are obtained by prereaction of resorcinol with fatty acids in the presence of sulfuric acid at high temperature followed by reaction with formaldehyde. Worldwide more than 90% of resorcinol adhesives are used as cold-setting wood adhesives. The other most notable application is as tyre cord adhesives, which constitutes less than 5% of the total use. 

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