Patent ID: 6254722
Filing Date: 2001-07-03
Classification: D21C,Y02W

Abstract:
A method for making dissolving pulp from a cellulosic fiber source consisting essentially of:treating the cellulosic fiber source with a 3-stage sequence of a first alkali extraction stage, a xylanase treatment stage, and a second alkali extraction stage,(a) wherein the cellulosic fiber source is selected from the group consisting of recycled paper products made from hardwood fiber, recycled paper products made from a mixture of hardwood fiber and softwood fiber, and combinations thereof, and wherein the recycled paper products are selected from the group consisting of waste paper from unprinted envelopes, waste paper from de-inked envelopes, waste paper from unprinted ledger paper, waste paper from de-inked ledger paper, and combinations thereof, and(b) wherein each of the first and the second alkali extraction stages is conducted with aqueous sodium hydroxide at a temperature from about 0.degree. C. to about 23.degree. C. and the xylanase stage is conducted at a temperature from about 40.degree. C. to about 70.degree. C., and wherein each of the 3 stages is conducted for a sufficient time and the xylanase stage is conducted with a charge of sufficient unties of activity of xylanase per gram of cellulosic fiber source to obtain dissolving pulp having selected properties of:(i) a resistance of about 97.0% or greater to extraction with 10% sodium hydroxide in water,(ii) a xylan content of about 2.6% or less by weight,(iii) a mannan content of about 1.5% or less by weight, and(iv) a cuene viscosity of about 7.5 or greater centipoise.