26 сентября, 2015 
Malyar The purposes of the addition of tannins are to accelerate the hardening reaction [110,116,176-178] and to replace phenol or a part of the PF resin [179-185].
2. Addition of Lignins
Lignins can be added to phenolic resins (i) as an extender, e. g., in order to increase the cold tack or to reduce costs, or (ii) to achieve a chemical modification of the resin, whereby the lignin is chemically incorporated into the phenolic resin [186-190]. The idea behind this is based on the chemical similarity between the phenolic resin and lignin or between phenol and the phenylpropane unit of the lignin. The lignin can be added at the beginning, during the cooking procedure, or at the end of the condensation reaction. It is not clear whether the lignin is really always incorporated into the phenolic resin or not. In practice lignin is used at present in just a few North American mills, only as a neutral filler/extender in adhesive resins. [30]
[192-194], on the marked curing acceleration of the PF resin by the isocyanate, and on the excellent results which were obtained industrially with these systems. Very recently this approach, due to its excellent performance, lower cost, and ease of preparation has received intense attention, and several other studies on the subject have been recently published [195-198].
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