A process for manufacturing heat-sealable packaging materials which are permeable to air, from a paper, cardboard, pasteboard, or corrugated cardboard base material comprising the steps of applying to the said base material an organic solvent solution consisting essentially of (1) from 10 percent to 50 percent by weight based upon the total solution weight of a thermoplastic material, (2) from 10 percent to 80 percent by weight based upon the weight of solid matter in the solution of an organic low molecular weight acicularly crystallizable compound having a melting point in excess of 130.degree.C and at least 30.degree.C in excess of the activation temperature for sealing purposes of the thermoplastic material, (3) from 0 percent to 20 percent by weight based upon the total solution weight of auxiliary substances, and (4) from 20 percent to 85 percent by weight based upon the total solution weight of an organic solvent, and evaporating the solvent from the solution to form a coating on the base material containing acicular crystals of the low molecular weight compound.
A method of preparing a sheet of a lignocellulosic material such as paper for the manufacture of a finished product, includes the steps of impregnating the sheet with an impregnating composition comprising a composition for the chemical modification of the lignocellulosic material containing a dicarboxylic anhydride or a tricarboxylic anhydride dissolved in a suitable non-aqueous solvent, and a composition for resinating the lignocellulosic material containing an isocyanate thermosetting resin dissolved in a suitable non-aqueous solvent. Thereafter any excess of the impregnating composition is removed from the impregnated lignocellulosic material and the non-aqueous solvent or solvents are removed. Subsequently the sheet of lignocellulosic material so treated may be used in a method of forming an article by adhering a sheet so treated to a second sheet optionally so treated, with a suitable adhesive material. The result is a product which may be used as a building board or the like.
