Abstract: Processes for increasing the strength of cellulosic fibers are carried out by contacting relatively dry cellulosic fibers with an agent in particulate or vapor form comprising a carboxylic acid cyclic anhydride at an elevated temperature for a time sufficient to significantly increase the bonding strength of the fibers. The treated fibers bond more readily to one another and they also hold wet and dry strength aids more strongly. Furthermore, the treatment does not significantly affect the internal chemical structure of the fibers so that paper made from the fibers exhibits overall improved dimensional stability.

Abstract: The specification discloses an improved method for drying a paper or paperboard web emerging from the press section of a papermaking machine as it traverses a dryer unit. The method comprises continuously rewetting the web across its width during the initial web drying stage when the web has a solids content of no more than about 65 wt. %. The method improves the water removal rate and decreases the shrinkage rate of the web during drying.

Abstract: The stiffness of multi-ply paper and board products is increased by dewatering the base ply on the papermaking machine to a consistency of at least about 8% prior to application of the next ply. The desired laminating consistency is more readily achieved through the use of pulp which has been subjected to a heat treatment process comprising heating the pulp at a temperature in the range of 170.degree. C. to 250.degree. in the presence of water for at least about 0.1 minutes, which reduces the water retention valve of the pulp. The heat treated pulp also produces a stiffer multi-ply product in its own right, which augments the stiffness advantage connected with attainment of higher laminating consistencies.

Abstract: A paper product having high stiffness, wet strength, and opacity, and good folding endurance is produced by subjecting a paper web containing a starch additive to high temperature heat treatment.

Abstract: The stiffness, wet strength and bursting strength of paper is improved by adding a latex such as milk to the paper and then subjecting the paper to steps of high temperature treatment and immediate rewetting.

Abstract: The stiffness and wet strength of paper products are improved by subjecting the products to high temperature treatment, immediately followed by rewetting. The resultant products have good folding endurance.