Industrial hardboard and other panels binder from waste lignocellulosic liquors/phenol-formaldehyde resins [Kleber für industrielle Hartfaserplatten und andere Platten aus Lignocellulose-Ablaugen mit Phenol-Formaldehyd]

The use of a waste chestnut-wood lignocellulosic black liquor composed in almost equal parts of carbohydrates coming from partially degraded hemicelluloses, of non-sulphited lignin and of low reactivity hydrolysable chestnut tannin, produced as waste from the humid-type binderless hardboard manufacturing process has been shown to be very useful at industrial level for coreaction with simple, unsophisticated PF resins and flocculation on fibers for the production of water resistant hardboard without any drop of performance, and this under industrial conditions. In the case of other panel products which rely on greater proportions of adhesive, exterior grade plywood of excellent performance, satisfying well the relevant exterior grade specification of the European Norm EN314, and of pressing time comparable to currently industrial PF and MUF resins, is obtained once triacetin ester accelerator is added to the glue-mix. In the case of particleboard the results obtained are encouraging as regards exterior performance, but at pressing times still at the longer acceptable limits for synthetic phenolic resins, even when considerably aided by addition to the glue mix of the same accelerator. Use of esters accelerators is again proven as essential in the application of low reactivity natural and synthetic phenolic resins. Coreaction and partecipation in the final hardened network of all the three types of phenolic species present, namely synthetic phenol, gallic acid structures from the chestnut tannin and guaiacyl units of lignin has been shown to occur by liquid and solid state 13C NMR.