Fast cure and pre-cure resistant cross-linked phenol-formaldehyde

Abstract

Fast cure and 'pre-cure' resistance thermosetting adhesives and methods for their production useful for binding lignocellulosic materials together, are disclosed. A fast curing adhesive is obtained by cross-linking binary phenol-formaldehyde consisting of high average molecular weight phenolformaldehyde (PF) resin and low average molecular weight PF resin with lignin. A 'pre-cure' resistant adhesive is obtained by cross-linking a PF resin, such as binary phenol-formaldehyde, with a lignin with the addition of ammonia preferably in the form of an ammonium salt. The lignin may be obtained from different wood pulping waste materials including that recovered from the sulphite, kraft, organosolv or steam hydrolysed wood pulping processes. The adhesive can be produced as an aqueous solution of dispersion, and used in either a basic or acidic environment. The quick setting and 'pre-cure' resistant adhesive are inexpensive to produce and both display improved adhesion characteristics when compared with existing adhesives prepared from wood waste products. The adhesives also compare advantageously to a variety of existing commercial phenolic resin presently being used in the manufacture of wood composite products such as waferboards. These adhesives are capable of being spray dried more easily and produce higher yields, when compared with existing wood waste products which have been cross-linked with commercial PF resin or to a variety of existing commercial phenolic resins.