time retaining the lignin fragments thus maintaining the desired pulp yield after the post treatment stage the lignocellulosic pulp is advantageously washed in order to remove residual chemicals the pulp material may then be refined so as to further enhance fiber to fiber bonding one way of measuring the degree of refining is to measure the pulp 39 s drainage characteristics a measure of this drainage parameter is freeness and more particularly canadian standard freeness csf more 39 particularly for most commercial linerboard machines in operation today canadian standard freenesses typically range from about 150 csf to 700 csf in general pine freenesses preferably range from about 550 csf to 650 csf and this is the preferred freeness range obtained by refining the chemically treated pulp used in this invention the refined chemically treated high yield pulp may be combined with a conventional chemical pulp described above by simple admixture alternatively the chemically treated high yield pulp may be combined first with a chemical pulp and the mixture of pulps refined together the mixture of refined pulp may then be wet formed into a commercial grade linerboard web after forming the wet web is pressed to raise the solids content preferably to about 33 exiting solids but within the range of 30 to 40 exiting solids the pressed web is then subjected to an additional pressing operation at a press impulse of at least 7 5 psi second advantageously up to about 30 psi second at a temperature above 100 u00b0 f preferably below about 200 u00b0 f in order to develop the crush resistance of the sheet although the inventor is not to be bound by any theory of operation one possible explanation for the enhanced crush strength observed is that the chemical pulp serves to bond.