Hemp or wood: potential substitutes

V.S. Krotov

The Ukranian Pulp and Paper Research Institute

18/7 Kutuzovstreet, Kiev 252133, Ukraine

Introduction

Three major factors are restraining the development of the pulp and paper industry of Ukraine:

• 1. The capital costs for the construction of new production facilities are high, with payback time often exceeding the normative service life of the main process equipment.
• 2. The current obsolete equipment causes environmental problems, as it has a high consumption of raw materials, water and energy and a relatively low yield of finished products. Over 10 % of the raw materials, the pulping chemicals, and almost all bleaching agents are discharged into the environment.
• 3. Ukraine is sparsely wooded, and a lack of traditional raw materials hampers the development of its pulp and paper industry. Forests take up only 13.2 % of its territory, and logging covers about one third of its pulp requirements. At the same time, Ukraine's agriculture generates millions of tons of fibrous products: cereal straw, sunflower and corn stems, flax, hemp and others. In this paper fibre hemp as a raw material for paper pulp will be compared to poplar.

Pulping of non-wood raw materials

In principle, all fibre-containing by-products can be used for pulping, but their processing in the pulp and paper industry is more expensive than the processing of wood. Agricultural by-products are more bulky and dispersed over larger territories than wood, making their transport and storage more costly. Other factors increasing the costs of pulping of non-wood raw materials using existing technologies are:

• -heterogenous morphology of the raw material containing stems, leaves, spikes, seeds etcetera, and the presence of non-fibrous impurities (e. g. soil),
• -high ash content of raw materials and especially the presence of silicon compounds,
• -lower pulp yield as compared to wood pulping.

The negative effect of these factors on production and environmental safety can be minimized by additional expenses for the preparation of raw materials, the removal of silicon and the disposal of wastes. However, the extra costs involved would make non-wood pulp more expensive than wood pulp.

Poplar or hemp?

The development of a competitive pulp industry in sparsely wooded countries requires:

• 1. Setting up plantations of fast-growing plants with a high yield of fibrous raw materials,
• 2. The development of a new technology adapted to the specific characteristics of local raw materials, including agricultural by-products.

For the conditions of Ukraine, the choice of plants to be grown on plantations and to be used for pulp and paper is limited to fast-growing poplars or hemp. The technology for growing poplar in short rotation (12 years) plantations has been developed by one of the Ukrainian Research Stations. In the south of Ukraine, Toropogritsky's poplar is recommended for growing. The annual increment of such poplar plantations on irrigation areas of the Kherson Region varies from 20 to 40 m3/ha, depending on fertility, planting pattern and irrigation practice. Taking an average annual increment of 30 m3/ha, and a poplar wood density of 420 kg/m3, we obtain an amount of wood of 12.6 ton per ha per year. A feasibility study for such poplar plantations has shown that the costs of the wood were four to five times higher than those of aspen wood logged and delivered to the Kherson Pulp and Paper Mill from Central European regions of Russia.

Hemp is promising as a raw material for pulp and paper. Southern hemp is most suitable for growing under the conditions of Ukraine, since it is hardy, suffers little damage from pests and diseases, and can be grown in monoculture for many years. At present its yield of dry stems is 8-10 ton/ha in many areas, which is four to five times more than the average annual increment in Ukranian forests and approaches the increment of the most productive plantations of fast growing poplars.

Perspectives

The Ukranian Institute of Bast Crops (UIBC) at Glukhov, Sumy Region, has bred hemp cultivars containing practically no psycho-active components. Until the present the hemp selection was aimed at breeding varieties for the textile industry, i.e. the selection work took into account the bast portion of the stem, as well as the content of THC. In the pulp and paper industry, the entire stem can be used. Based on its large experience, the UIBC expects it can breed cultivars yielding 12-14 ton/ha of dry stems. In this case the stem yield is comparable to the wood yield of the best polar hybrids. As opposed to hardwoods such as poplar, hemp can meet all the requirements of the paper industry for short- and long-fibred pulps for practically any paper or board grade. In 1992, UIBC compared the labour costs of growing and harvesting hemp to those of poplar. Proceeding from the present average yield of 6 ton/ha for hemp and from an annual increment of poplar of 12.6 ton/ha, the costs were comparable. Thus, hemp plantations are more efficient than poplar plantations as a source of raw materials for the pulp and paper industry. However, the advantages of hemp can be realized only if a new technology allowing pulping of the entire stem is developed. Such a technology has been developed at the Ukrainian Pulp and Paper Research Institute. Its basic concepts are summarized in a research proposal (page 28) and will be presented more in detail in a future paper.

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