An integrated assessment of hemp (Cannabis sativa L.) and flax (Linum usitatissimum L.) as sources of fibre for newsprint production

The primary objective of the study reported in this thesis was to show whether fibre of value as a reinforcing agent in newsprint production could be produced economically from hemp and flax grown in Tasmania. This involved an integrated analysis of the whole potential industry, with studies into the key areas of crop production, pulp and paper manufacture and economic viability. Another objective of the study was to develop a computer model for simulating the growth, development and yield of hemp in response to climatic, soil and management inputs. This would enable the results of this project to be extrapolated to other suitable production areas and hence assist in the initial assessment of cropping potential and the identification of optimum site and management conditions. Of the nine hemp cultivars that were assessed, Kompolti and Futura 77 were the best performing, producing crops in excess of 2 m high and yielding up to 1500 g/m2of oven dry stem. The results from sowing date trials suggest that September is the optimum month for sowing hemp in Tasmania. Later sowings resulted in a reduction in stem yield associated with a shortening of the thermal time duration from sowing to flowering. Furthermore, van der Werf etal. (1996) reported yield declines from later sowings due to delays in canopy closure and a subsequent reduction in intercepted radiation. Sowings prior to September appear to be limited by premature flowering in response to short daylengths. In an irrigation trial conducted in north west Tasmania, significant stem yield differences were not apparent for irrigation regimes based on refill to field capacity at deficits down to 120 mm. Maximum bark yield was obtained from regimes based on a 60 mm deficit or less (water consumption of 535 mm). The stem yields under rainfed conditions were substantially below those of the irrigated treatments. Stem yield responded in a parabolic manner to plant densities ranging from 50 to 300 plants/m2, with maximum yields at about 110 plants/m 2. The results from a flax cultivar trial showed that stem yields of selected European cultivars were superior to a number of older Australian cultivars, developed for the Australian flax industry during the mid 1900's. The cultivar Ariane was selected for further field trials and produced crops with oven dry stem yields of up to 1000 g/m 2. Field studies with a range of sowing date and irrigation treatments demonstrated that flax could be sown from autumn through to spring, under either rainfed or irrigated conditions. Maximum stem and seed yields were from an autumn sowing with supplementary irrigation from flowering to late grain fill. The optimum seeding rate for autumn sown flax was found to involve a compromise between maximising yield and minimising the potential losses from lodging apparent at densities in excess of about 1000 plants/m2. Lodging was not a major problem at the optimum seeding rates for spring sowings of flax. Controlled environment studies were conducted into the response of pre-emergent development to temperature, and the flowering response of selected hemp cultivars to photoperiod. Parameters, constants and functions derived from these studies, the field trials and from selected references, were then used to develop a hemp simulation model. The model adequately predicted phenology, leaf area and biomass production for cv. Kompolti grown in north west Tasmania. The Australian newsprint industry currently uses a mixture of locally sourced eucalypt, radiata pine and recycled paper pulps, blended with an imported kraft (chemical) pulp. The purpose of the kraft pulp is to reinforce the newsprint. The primary aim of the pulping trials conducted in this study was to investigate the potential of using flax and hemp bark and whole stem pulps as alternative reinforcing agents in newsprint production. The existing cold caustic soda (CCS) and thermomechanical (TMP) processes were trialled with a view to harnessing the existing infrastructure and expertise. Cold caustic soda pulp made from the bark fraction formed paper of very high tear index, but with lower tensile index and tensile energy absorption than would be desirable from softwood kraft. This limitation might be overcome by using a higher proportion of non-wood pulp in the overall newsprint blend or through breeding improvements. The use of pulping (& pre-pulping) equipment more suited to non-woods may overcome handling difficulties associated with excessive fibre length. Pulps were also made from the core fraction to assess its suitability as a supplement to the short fibred component of the existing newsprint blend. Whilst potentially suited for use as a short fibred supplement in newsprint manufacture, the properties of the core pulps are not currently in demand within the industry. Interest from the newsprint industry in taking the financial risk of adopting hemp and flax based pulps as an alternative to kraft, would require that the total cost be somewhat less than the imported option. Similarly, interest from primary producers requires that the gross returns from these crops are at least comparable with a range of crop alternatives. The minimum bark price (mill gate) that is likely to attract farmers would vary between flax and hemp and between growing conditions. Dual purpose flax grown under dryland conditions would require a separated bark price in the vicinity of $400/t to $450/t. Irrigated hemp and flax crops grown in the more productive north west area of the state would require a price in excess of about $650/t. These minimum bark prices are not attractive to the newsprint industry at present. Future financial viability will depend on a number of factors, including: fibre yield and quality (eg bark proportion in the stem and fibre tensile strength properties) improvements, elevated kraft pulp prices, and the establishment of strong markets for the stem core fraction and the seed of flax.