The technology to make paper by retting hemp was known to man nearly 2000 years back, and much until the 19th century books were printed from paper made from hemp. Paper making then was considered an art although it had more to do with biotechnology, but then biotechnology itself borders on art that in modern times has to do with genes and genetic modification.
Making paper from wood entails four different steps namely wood processing: pulping, bleaching and sheet formation, and today biotechnology plays a stellar role in some of these processes.
To understand how biotechnology plays a role in the making of paper, one has to have a basic understanding of the conventional steps involved in manufacturing paper.
Conventional way of making paper pulp
At first the bark of the wood is removed and the logs so obtained are cut into smaller pieces called chips. The stripped bark is used as fuel for running the pulping mill power plant. The chips are heated under pressure along with caustic soda and sulfur so that lignin that binds the cellulose fibers are removed. This is called the chemical pulping process that gives 30% yield lesser than what is obtained by mechanical pulping.
Now the other way of pulping, that is, mechanical pulping process (gives more yield than chemical process) means forcing the debarked logs through rotating toothed steel discs that tear the logs and remove the lignin. Paper made this way has a brownish tinge because of the degradation of the lignin, as for example in the paper used for printing newspapers.
Let's now look at how biotechnology enhances the functionality of these processes.
Making pulp using enzymes
Fungi that can degrade lignin such as O. piliferum is used in a fermentation process before carrying out the normal mechanical or chemical pulping, so that it reduces the overall energy requirements when mechanical process is used or reduce the quantum of chemicals if chemical pulping is adopted.
Pulp bleaching using enzymes
Pulp is usually tinged with brown color due to lignin content and the conventional method has been to bleach pulp with chlorine to remove the color. Now there are two specific ways to enhance this bleaching process using enzymes. Xylase isolated from a fungus can successfully break down the carbohydrate xylan (this entraps pulp lignin). This can help reduce the need for chlorine in bleaching, but this does not solve the problem of chlorination such as the byproducts dioxins and PCBs. Therefore the re-engineered enzyme made by modification of three of the amino acid components of xylanase is used which is known as BiobriteĀ® that helps in saving production costs and prevents formation of unwanted products during pulp bleaching process. Use of BiobriteĀ® leads to substantial savings in chlorine which means lower chemical costs and reduction in toxic effluents as well.
The pulp bleaching process can also be augmented by using other enzymes such as laccase and manganese peroxidase
Enzymes used for de-inking
When recycled paper fibers are used as feedstock to make paper, it has to undergo a cumbersome deinking process to remove whatever ink that gets fused on to the paper during printing. Now, different cellulase enzymes from Novozymes are used to facilitate this deinking process and what this means is, the use of recycled paper becomes a viable proposition and which means reduction in the number of trees that need to be cut to make paper.
GM trees with less of lignin
As the pulping process in paper manufacturing involves getting rid of the lignin (chain of galacturonic acid) that binds the cellulosic fibers, the idea has been to make GM trees with less of lignin so as to take advantage of the reduced lignin at the pulping stage and save on energy costs. But such trees have drawback, in that; lesser lignin content makes them susceptible to disease and attack by pests. Moreover, there are environmental concerns as well. For example, wood with less of lignin degrades quickly releasing more carbon dioxide into the atmosphere whereas wood with more lignin takes time to degrade and hence is a sort of carbon sink. Supporters of GM trees with less of lignin argue that in any case these trees will be cultivated for captive use by paper factories and hence may not cause environmental issues.
Paper from bagasse
Dwindling forest cover worldwide is a matter of concern for both the environmentalists and the paper industry, but for different reasons. As wood (which is fast depleting) is their principal feedstock, paper manufacturers are now switching to sugarcane bagasse. Sugarcane bagasse is sugar factory waste. But the process of delignification and bleaching is necessary even if bagasse is used to make paper. But biotechnology plays a role here.
Scientists have succeeded in using laccase (a delignifying enzyme) from the fungus Pycnoporus cinnabarinus to break down the lignin in the fibers of bagasse, and this makes it possible to refine it further to paper pulp. As the lignin gets removed gradually, the pulp gets bleached and it can be used to make cardboard.
When wood is used as the feedstock and biotechnological processes are used, this means a more than 25% increase in the efficiency of pulp production and with the annual production of wood pulp world wide expected to touch 260 million tonnes this year, you can well imagine how much biotechnology can help lessen the requirement of wood feedstock. Besides, the obvious advantage with the enzymatic route for pulp making is of course the cost factor including lesser costs for effluent disposal.
It is obvious that biotechnology through enzymatic processes confers economic and environmental benefits in the making of paper. For example the uses of White rot fungus to break down the lignin which is impregnated in the wood's cellulose walls during the preprocess step in paper making saves the European paper industry 250,000 tonnes of carbon dioxide emissions annually.
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