Process for producing a pulp having a low degree of polymerization

A pulp having a low degree of polymerization is produced by a process which comprises irradiating a dried pulp sheet with electron beams in the energy range between 300 and 600 keV, using a material for electron back scattering consisting of a simple substance, compound or mixture of element(s) with an atomic number of 13 or more. The process makes the distribution of polymerization degree uniform and improves the efficiency of electron beam utilization. In one embodiment, irradiation was carried out at an acceleration voltage of 500 kV, an electron current of 4.1 mA, an electron scanning width of 400 mm, a distance of 2-0 mm from a window of titanium foil 43 μ thick, and a pulp running speed of 10 m/min. The absorption dose given to the maximum energy absorption section of the pulpsheet was 1.1 x 106 rad. A plate of aluminum-13 and lead-82 were fixed to the back of the pulp sheet. After irradiation, the pulp sheet was divided in the direction of its thickness into 13 sections, each of which was 0.0006 g/cm2, and the degree of polymerization was derived. The calculated absorption dose was 1.13 x 106 rad maximum and 1.00 x 106 rad minimum for lead, and the utilization efficiency of the electron beams was approximately 90%. In another embodiment, a purified linter pulp sheet was irradiated under different conditions, using an alloy consisting of iron-26, nickel-28 and chromium-24 as the back scattering material. The mean degree of polymerization at intervals from the irradiation surface was for example 446 as compared with 599 without the back scattering. (Iwakiri, K.)