Kraft process, a paper maker’s craft

Subject :Science and Tech

Section: MSC

It is a technique that accepts wood chips as input to produce cellulose fibres, which are then used to make paper and other materials used in everyday objects.
Paper is most commonly produced by the kraft process today.
Process:
- The process is chemical in nature. The chips are treated with water, sodium hydroxide, and sodium sulphide – the last two forming a highly alkaline mixture called white liquor – at a relatively high temperature.
- This breaks the bonds between lignin (an organic polymer and important constituent of cell walls), hemicellulose (cellulose-like fibres that are shorter), and cellulose.
- The steps are followed by those to obtain the wood pulp, wash off and recover the reaction chemicals, bleaching, and processing.
Advantage:
- Kraft-process paper has higher sulphidity (a measure of strength) than that produced by other processes.
Drawbacks:
- The process is not environmentally friendly. It requires a large volume of water; the process of removing lignin from the wood chips also discharges the lignin through water along with dissolved carbon, alcohol ions, and heavy metals.