Environmental and raw material concerns are pushing nonwood fibers into the limelight. Hemp could provide a useful alternative

By Mari Kane

Problems getting fiber¦ Hemp is at hand

Other advantages include hemp's high dry matter yield per hectare and the strength of its bast fibers. The low lignin content of hemp fibers also facilitates the use of totally chlorine-free (TCF) bleaching sequences in papermaking. Of course, the close kinship of hemp with marijuana - ie cannabis varieties with a high amount of psychoactive cannabinoids - has added much to the "media buzz" on hemp.

Growing up: a mature hemp field in Canada

From hemp to pulp

Industrial hemp grown on about 30,000 ha in the European Union (EU) and on 10,000 ha in Canada in 1999 is starting to develop new markets in nonwovens for automotive composites and insulation materials. Hemp seeds and oil products are also appearing in food products and retail stores in North America and Europe. Yet, despite all the conceivable benefits of hemp as a pulp source, and extensive research and design programs, hemp pulp consumption in western countries has not increased significantly in recent years beyond already established uses.

True hemp, like flax and abaca, has established niches in specialty paper production. Worldwide around 7,500 air dried tons of hemp pulp are produced annually. In western countries it is used almost exclusively for cigarette paper, with insignificant amounts used for other specialties, such as ultra-lightweight printing paper.

In recent years, pulps from bast fiber plants, such as flax and hemp, have come under increasing pressure though. With price tags of $2,200/air dried ton for this pulp compared to $700-900/ton for bleached softwood kraft pulp, cigarette manufacturers have been prompted to switch to mixed furnish sheets based primarily on softwood kraft pulp. This trend indicates that the global use of hemp and other bast fibers in specialty papers is not likely to increase significantly in the near future, if at all.

When looking for other potential markets for hemp pulp, it must be kept in mind that the stalks of the hemp plant provide two rather dissimilar sources of pulp. The outer bast fiber makes up 20-25% of the dry matter in hemp and consists of longer fibers, 2-55 mm in length. Early European papermakers recovered these bast fibers from rags and beat them into a paper furnish. Then, over the last century, alkaline pulping of tow or decorticated stalks has become essentially the sole source of hemp pulp.

The majority of the dry matter yield from hemp, however, is in the woody core and is commonly called hurds, ie the equivalent of flax shives. The core consists of very short, bulky fibers, typically 0.2-0.65 mm in length. Alkaline pulping of hurds produces a pulp with tensile and burst strength comparable to that of hardwood kraft pulp, but of a lower tear strength. Adding 10-30% of this pulp to softwood pulp was found to improve mass uniformity, paper formation and printability in fine paper and printing paper grades.

Producers of bast fiber pulps have traditionally accepted up to 30% of hurds in the bast fibers as a concession to the large-scale processors of hemp and flax stalks whose hammermill or roller-decorticator techniques do not easily achieve much higher purity. Fortunately, hurds even benefit the quality of some papers by acting as a filler, improving smoothness and printability. Yet, the difference in morphology and lignin content limits the amount of hurds that can be reasonably pulped with the bast fiber and some form of decortication is required. This need for mechanical processing of the stalks, the complex logistics of harvesting, transporting and storing a bulky, seasonal commodity, and the small size of existing nonwood fiber pulp mills has so far prevented the emergence of hemp as a source of cost competitive pulp for printing/writing paper.

Several novel technologies for more cost-effective pulping of hemp and other bast fibers have been proposed, bench and pilot-tested in recent years. They include several solvent extraction technologies with recovery of byproducts and a chemi-mechanical technology using twin screw extruders. More importantly, novel technologies such as thermal depolymerization (TDP) may also allow for more cost-effective recovery of cooking chemicals and organics from black liquor. All these emerging technologies still await implementation on the production scale.

Despite some experimenting, large industry players have so far shown little real interest in the use of bast fibers as their feedstock, while a lack of capital and the uncertainty of the markets has prevented the development of independent projects.

Building up the use of hemp

Nonwood numbers

World consumption of paper is expected to rise to over 400 million tons/yr by 2010. Much of this increase in fiber demand will be met by increased forestry production in tropical countries, but higher fiber recovery rates and the use of nonwood fibers will also play their part. Today, the use of nonwood fibers is common in wood-limited countries. For example, China and India are the two largest producers of nonwood pulp. In China, the nonwood pulping capacity is 80% of the country's total pulping capacity, while in India it is 60%.

Inadequate effluent treatment means that many of these mills are less than environmental showpieces though. Color, runability and printability of the paper are also often below western standards. Clearly, novel pulping and recovery technologies offer particular benefits in these applications.

In contrast, recycled fibers and nonwoods, such as hemp, have made their gradual re-entry into printing/writing papers in western countries via the market for "eco-friendly" papers. In 1996, North American supplies of printing/writing paper made with recycled content totaled more than 2.3 million tons. The market for purely "tree-free" printing/writing papers, ie those made entirely from the fibers of nonwood plants, is approximately 4,500 tons/yr. Early eco-papers with a high content of deinked pulp (DIP) from post-consumer recycled fiber and the use of ECF (elementary chlorine-free) or TCF (totally chlorine-free) bleaching soon became the rule.

At the same time, small, yet growing, niches have been developed for tree-free papers. The most popular fiber sources for these paper grades are kenaf, hemp, flax, bamboo, wheat straw and other grasses such as esparto. The emerging use of blends from nonwood and deinked fibers increasingly blurs the border between tree-free and other eco-friendly papers.

The higher cost of nonwood pulp, as well as the relatively higher papermaking and marketing costs, leaves the prices of most of these papers considerably higher than high-end wood furnished papers. This has limited their markets to ecologically motivated individuals and firms for use in high-end stationery and advertising. Expanding their share in the printing/writing paper market has been the main challenge for promoters of hemp-containing papers.

Many of the early publications printed on hemp paper were, perhaps unsurprisingly, about hemp. But in 1993, the German publishing company, 2001, began printing their bestseller "Hanf" on a 50/50 blend of hemp pulp and deinked fiber supplied by Schneidersöhne Papier. In the USA, Hemp Pages, a directory of the worldwide hemp companies has printed its 1999-2000 issues on several different brands and weights of hemp content papers. Such publication projects have been important showcases for hemp content papers. They also created good learning experiences for using hemp pulp in papermaking and printing. After all, despite their long history, such papers represent true novelties in the modern printing/writing paper sector. There are some drawbacks to using hemp though, notably the wrapping of long fibers on the paper machine and slower ink penetration and drying after printing.

Breaking through

Increasingly, paper with hemp content appeals to the growing number of environmentally aware companies, producers of natural foods and non-profit organizations who employ not only hemp's environmental attributes, but also its "mystique". The following examples show that this market has attracted paper suppliers from quite different backgrounds.

Since 1801, Crane of Dalton in the USA has produced cotton-based specialty paper for the US currency and high-end business applications. The growing interest in tree-free papers, and particularly the enthusiasm for hemp, encouraged the firm to take a closer look at this opportunity. After two years of pulping and papermaking trials, Crane added 50/50 hemp/cotton and 50/50 kenaf/cotton blends to their line of Continuum Papers. Pulped in Dalton from European hemp fiber and cotton rags, the pulp produces a strong sheet that runs well on offset presses. Crane plans to increase sales of this line to 500 tons/yr over the next few years. Target areas are both the existing market for high-end office papers, as well as direct sales to end-users and selected printers.

In Austria, Neusiedler has taken a different route to utilizing both the performance and the environmental attributes of hemp fibers. The company's Hemptec line uses a TCF bleached sulfite pulp that is cooked from a 30/70 blend of hemp hurds and spruce sawdust. The resulting paper shows a higher tensile strength compared to 100% sawdust paper, a smooth surface and good runability in high speed copying machines.

These products target customers looking for high-end papers with environmental attributes and who are willing to pay a premium. Another new route for expanding the use of hemp-based printing/writing papers is being tried by Living Tree Paper, based in Oregon, USA. The firm realized that tree-free papers will only have a real impact in the wood-dominated paper market if they become cost-competitive and find customers outside of the established distribution channels.

Sales of the company's Vanguard lines of hemp text and covers stock have been boosted by a combination of blending hemp with less costly deinked fiber, reaping the economies of scale offered by larger papermaking runs and using direct marketing to large users for products labels, company brochures and stationery. The paper is made from a 10% hemp and 90% post-consumer waste blend. According to the company, the line is currently the most cost-competitive eco-paper with nonwood content and has been successfully tested in offset and web presses. Paper sales are expected to increase to 3,000 tons in 2002.

Bigger players are also starting to take the market for eco-papers more seriously and are now positioning themselves in the so far tiny niche for eco-friendly nonwood printing/writing grades. Neenah Paper has released its Environment line, a printing paper made from a furnish containing 50% sugar cane bagasse. The Canadian paper company, Domtar, has recently developed a high-end printing grade made from a blend of bagasse and hemp named "weeds".

So, is there a future for hemp in printing/writing grade papers? The examples indicate that there might be. Yet, there are a few areas that need to be looked at if hemp, or other bast fibers, are to expand their use in printing/writing papers beyond the current niche markets.

For one, large scale, cost-effective pulping will be needed. The use of efficient, innovative recovery methods will be crucial to that process. Mastering the technical and logistical requirements of harvesting, storing and processing large quantities of bulky fibers will continue to be a challenge.

In the short term though, improving the economies of papermaking and developing an effective direct marketing system are the best ways to expand the option for hemp and other bast fibers in the future paper market.

Mari Kane is publisher of The International Hemp Journal (formerly known as HempWorld) and Hemp Pages - The Hemp Industry Source Book, as well as being a board member of the Hemp Industries Association (HIA). She can be contacted at: mari@marikane.com

This article was prepared with assistance from Gero Leson and Frank Riccio

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