Differences between production of paper grade pulp and dissolving pulp
The majority of paper pulp factories use the kraft or sulphate pulp process. It is an alkaline process. There are few industrial units which use the magnesium bisulphite process to produce pulp, although there are some mills in Europe which use this method. In Portugal only Caima uses this process.
It is not only the production processes which are different.
When producing pulp for paper market, one of the aims is to remove the lignin and the extractables from the wood, whilst endeavouring to preserve the cellulose and hemicelluloses. As well as looking out for specific aspects such as whiteness, a paper producer will also seek a pulp which will result in a paper with certain physical and mechanical characteristics, such as resistance. This is what allows a sheet of paper to pass through a photocopier or printer which prints or copies 50 sheets a minute without any of them folding or tearing, and without clogging up the machine.
Meanwhile, what the chemical industry looks for in dissolving pulp is characteristics such as high levels of alpha-cellulose, and very low ash and calcium contents. These chemical characteristics are important in the production of viscose, which is currently the main market for Caima’s pulp.
The dissolving pulp produced by Caima is, at first glance, identical to the paper grade pulp. The end product is much whiter than paper pulp and this can be clearly seen, but in fact the fundamental differences lie in the pulp’s chemical make-up.
It is called dissolving pulp because the first stage of the processes which use this pulp is to dissolve it in a vat of caustic soda.