Developing the Best Resin for the Particular Process

The wide range of composition board products requires “tailored” resins. The factors to be considered in formulating these special purpose resins have to do with long lists of characteristics of the board and wood raw materials, resin characteristics, and resin manufacturing variables. Interrelations among these factors have been worked out so that resins can be tailored to specific processes, that is, the resin characteristics are precisely adjusted such that, when combined with the wood variables, they will result in a board with desired properties. For example, condensation or advancement of a phenol-formaldehyde resin may be varied in a number of ways. High advancement can be obtained by long, high temperature processing, usually in the presence of an excess of some alkaline catalyst such as sodium hydroxide. The use of high formaldehyde to phenol molar ratios also tends to give high resin advancement. Specific degrees of condensation, high or low, are achieved through exact control of these and many other factors. With respect to the use of caustic, interactions with factors other than advancement come into play. For example, the use of a high caustic content resin in dry-process hardboard would produce a board with both high water absorption and thickness swell values. The resin must be tailored to give optimum results with respect to all of these factors. Another example of resin processing to meet certain conditions is the use of modifiers to minimize the odor of formaldehyde in urea resins. Formaldehyde odor may also he controlled by proper control of the time-temperature cycle in resin processing. As a result of this trend to tailored resins, many new and specific resins are continually being developed.

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