Progress in Making Paper
Because the timber industry is an important one in some of Alaska and neighboring parts of Canada, and since a fair bit of that industry is devoted to turning trees into pulp for paper, it seems worthwhile for northerners to keep an eye on what's going on in the paper-making trade.
Our transpolar neighbors in Sweden apparently have come up with something new: computer paper made by a more environmentally friendly method. The Swedish paper company Roffs Stralfors began selling the new paper in April of this year, but it is actually manufactured by the Holmen paper mill near Stockholm. That mill uses an unusual process to turn wood into pulp, and an even newer method of whitening the final paper.
The customary pulping method, known as the kraft or sulfate process, uses sodium hydroxide and sodium sulfide to dissolve out some of the lignin that binds wood fibers together. Enough lignin remains so the paper made from kraft-processed pulp has a fine finish, but the lignin is dark; that means the paper needs to be bleached before it can be used for anything other than plain brown wrappers.
The usual solution to the dark-paper problem involves removing more lignin with chlorine gas, then bleaching the pulp in up to eight steps with alternating acid and alkali treatments. The chemicals used in the bleaching are also based on chlorine compounds.
This standard treatment produces good paper but has some undesirable side effects. The kraft process yields unpleasant waste products, as people living downstream or downwind from pulp factories have long known. And the chlorine bleaching process has some really toxic, and possibly carcinogenic, byproducts: dioxins.
The Holmen mill's processes avoid most of the problems with noxious wastes. First, for pulping, the Swedes took a big step backward. Instead of relying on chemical treatment, they went for steam and brute force. This thermo-mechanical pulping softens wood fibers and extracts more lignin than does the kraft process, so the treated pulp needs less powerful bleaching before it can be milled into acceptably white paper. The Swedes are using hydrogen peroxide instead of chlorine and its compounds, and the bleaching by-products are only hydrogen and oxygen.
Naturally, with anything that seemed this good, there had to be drawbacks. The chief one was that the new paper had too little lignin, and thus its fibers were not very well bonded together. It was still strong--stronger than chemically pulped paper, in fact, because the fibers were less broken up--but its surface was flaky and dusty, and thus unsuitable for computer use. For fifteen years the Holmen people cranked out low-grade paper with their clean process, selling their output to newspapers while tinkering with quality control. Recently, they came up with the cure: they used a bigger hammer. For the Stralfors computer paper, they are effectively pressure-cooking the paper with very high temperatures and pressures. The fibers are so well bonded that none rub off. (They also add a bonding agent, which they aren't describing except to say it's "natural.)
Evidently the new paper is generating considerable interest internationally, and not just from firms seeking to improve their environmental image. Thermo-mechanical pulping uses more of a tree, so it needs only about half as much timber to produce the same weight of paper as does chemical pulping. That's especially important in Sweden, where paper companies are required by law to plant more trees than they harvest. Because the savings more than balance higher process costs, the Stalfors company is selling the new computer paper at a price five percent lower than that of their ordinary computer paper.
