Dissolving pulp

Dissolving pulp (also called dissolving cellulose) is a bleached wood pulp that has a high cellulose content (> 90%). It is produced chemically from the pulpwood, in a process that has a low yield (30 - 35% of the wood). This pulp has special properties, such as a high level of brightness and uniform molecular-weight distribution.^[1]

Manufacture

Dissolving pulp is made from the sulfite process or the kraft process with an acid prehydrolysis step to remove hemicelluloses.

The sulfite process produces pulp with a cellulose content up to 92 percent. It can use ammonium, calcium, magnesium or sodium as a base. The prehydrolysis sulfate process produces pulp with a cellulose content up to 96 %.

Special alkaline purification treatments can yield even higher cellulose levels: up to 96 percent for the sulfite process and up to 98 percent for the sulfate process.

Applications

Dissolving pulp is used in production of regenerated cellulose. The cellulose is dissolved in an organic solvent and processed to regenerate the cellulose fibres in different forms.

The 90-92 % cellulose content sulfite pulps are used mostly to make textiles (like rayon) and cellophane. The 96-% cellulose content sulfate pulps are used to make rayon yarn for industrial products such as tire cord, rayon staple for high-quality fabrics, and various acetate and other specialty products.

As a raw material of cellulose derivatives, dissolving pulp is used in carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), etc.

Since dissolving pulp is highly refined, it is a product of high whiteness with few impurities making it suitable in specialty paper-related products such as filter paper and vulcanized fibre.

Cellulose powder is dissolving pulp that has undergone acid hydrolysis, been mechanically disintegrated and made into fine powder.

This pulp is used as a filler for urea-formaldehyde resins and melamine resin products.

References

1. ^ Biermann, Christpher J. (1996). "3". Handbook of Pulping and Papermaking (2nd ed.). pp. 72–73. ISBN 0-12-097362-6.