USING HEMP FOR MAKING PAPER
USING HEMP FOR MAKING PAPER
Wood pulp paper makers have complained that hemp is an impractical fiber source because it is so different from wood fiber (Judt, 1994). In order to make hemp paper commercially competitive with wood paper, processes are being developed to use hemp fiber to best advantage. For existing mills, this can involve prohibitively expensive re-tooling to accommodate the different fiber.
Hemps long, strong fibers can get tangled up in the beating stage and cause uneven sheet formation. Problems with slow drainage on the paper machine have been reported too, perhaps due to the waxy, water-repellent resins naturally occurring in the fiber. Slow drainage is a significant problem to the paper industry since it affects production times.
The fact that hemp has two different kinds of fiber also poses some difficulties. The fiber types can be separated and used to make various qualities of paper, or combined into one hybrid pulp. This is a situation that calls for thorough testing to find the best mixtures and techniques.
Yet another challenge to paper makers, one offered by any annual plant, is harvesting and transport. Trees may be harvested at almost any time of the year, ensuring a steady supply. The harvest time for a crop of hemp is quite specific, however. Storing adequate fiber supplies without spoilage is a big stumbling block when production is on a scale of 1000 tons per day and is expected to continue year-round.
Novel Technologies
Two new pulping methods which have been successfully used with hemp fiber are organosolv pulping and biopulping. Both promise environmental sustainability, but have yet to be implemented on a widespread industrial scale. The high technology approaches of biochemistry and microbiology are slowly changing paper science; increasingly sophisticated processes are being developed which demand greater process control than most mills are presently set up to do. As research of this sort continues we can expect to see more subtle and high-tech methods emerge that use advanced bio-organic technology to degrade lignin as nature does, yet at the accelerated pace we humans seem to prefer.
Organosolv Pulping
Organosolv pulping uses concentrated acetic acid or ethanol to delignify fiber by breaking off pieces of the lignin molecule to render it soluble (McDonough, 1993). It is a fairly new technology, and only a few industrial-scale organosolv process mills have been constructed to date. The first one was built in Newcastle, New Brunswick, Canada in 1989. So far, the reports are good (PPI, 1991). The use of ethanol is particularly attractive both ecologically and economically, since the ethanol solvent can be distilled and reused, leaving behind a powder rich in lignin and other organics, which can then be sold to make fertilizer or binding agents. Unlike the traditional sulfite and Kraft processes, non-chlorine bleaching is easily accomplished with organosolv pulps. Organosolv mills can be economically vital with a smaller ton-per-day capacity as little as 300 tons per day, compared with 1000 tons per day for a Kraft mill. Since some expensive pieces of hardware used in traditional processes are unnecessary for organosolv pulping, a lower start-up cost is an added plus.
Hemp has been pulped using an organosolv process (Tjeerdsma and Zomers, 1993, Tjeerdsma et al, 1993). The researchers, working as collaborators on the Dutch Hemp Project from 19901994, came to the conclusion that organosolv pulping would be appropriate as a nationally endorsed pulping process for hemp due to its small-scale potential, lack of toxicity, and pulping effectiveness. Additionally, these researchers were able to make good pulp and paper from the hurd of the hemp stalk, which tends to be more difficult than paper making with the long outer bast fibers.
Biopulping
Lignin molecules share some structural similarities with dioxin, TNT, and petroleum. Some paper scientists are using fungi to take the place of synthetic chemicals in the pulping process and are also isolating the chemical secretions of fungi and using them in a concentrated form (Grant, 1994).
Biopulping is the cultivation of fungi on fiber in order to let the fungi decompose the lignin (Kirk and Chang, 1990, Kuwahara and Shimada, 1992). Fungi, which are chemoheterotrophs, obtain nourishment by secreting enzymes which break down complex organic polymers into simpler compounds which the fungi can then absorb and metabolize. The fungi used in biopulping secrete enzymes which degrade lignin.
Very little commercial scale biopulping has been done so far; instead, the industry seems to be waiting for faster-working, more industrial applications of this technology. Advanced biotechnology is turning this into a very high-tech area of pursuit.
Conclusion
Hemp is a very good source material for paper making, and it is only a matter of time until industrial-scale manufacturing will go into full swing. Hemp being such a different fiber than wood, and current wood paper manufacturing techniques being far from ideal, there are indeed numerous challenges to be met.
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