Monday, April 16, 2012
Hemp's future in Chinese fabrics
Zhang Jianchun, Director General of China's Hemp Research Centre in Beijing has a dream: to see lush green plantations of Cannabis sativa growing across 1.3 million hectares of the country's farmland. That would be sufficient, Zhang calculates, to produce up to 10 million tonnes of hemp plants a year and, with it, around two million tonnes of hemp fibre.
Expanded production of hemp, he says, offers enormous benefits for China. First, it would provide a major new source of fibre for the textile industry, reduce dependency on cotton and, in the process, free large areas of cotton-growing land for food production. In addition, hemp cultivation would generate extra income for millions of small-scale farmers in some of the country's poorest rural areas.
China currently cultivates industrial hemp over an area of around 20 000 ha. That is just a fraction of the 5.6 million ha dedicated to cotton (China is the world's biggest cotton grower, with a harvest of some 6.6 million tonnes in 2006). Among natural fibres processed for use in Chinese textiles, hemp output ranks far behind that of wool and silk and of other bast sources such as flax, jute, kenaf and ramie.
"Performance properties". The Hemp Research Centre is working to change that - and restore hemp to its once important place in Chinese agriculture and textiles. Zhang points out that China is the birthplace of industrial hemp: archaeological evidence shows that the plant was grown for fibre some 4 000 years ago, and it was not overtaken by cotton in clothing until early last century.
Today, a small quantity of pure hemp fashion fabric is produced in China for high-value niche markets. But, Zhang says, the fibre's future lies in its integration into the production of cotton, wool, cashmere and silk textiles, and blending with synthetic fibres. "The inherent and special performance properties of hemp are very important in the market because they are attractive to consumers," he says. "Compared with cotton, hemp fibre has greater heat resistance and better moisture absorption and dispersion, while its high rate of absorption of toxic gases makes it excellent for use in household textiles."
The key to hemp's future in fabrics is "cottonization": removing the lignin that binds the hemp fibres (and gives stalks their rigidity), but prevents them from being spun and finished on slightly modified cotton or wool processing equipment.
Using specially developed machines and an array of de-gumming technologies, Chinese scientists say they have successfully reduced the lignin content in hemp fibres from 8-10% to as little as 0.2%. Result: "We can now cottonize hemp fibre into quite fine, soft and workable textile fibres for cotton and wool systems and for blending with man-made fibres," says Zhang. "One kilogram of textile fibres can be produced from 2 kgs of hemp bark."
Technologies developed by the centre are now being used in China's first commercial-scale hemp processing mill, in Xishuangbana,Yunnan Province, which has the capacity to process 50 000 tonnes of hemp fibres a year, mainly for use in cotton-hemp blends.
Food security. Zhang says hemp agriculture could play an important role in guaranteeing China's food security, protecting the environment and contributing to farmers' incomes. "Hemp production is best suited to hilly areas and uplands, as well as semi-arid regions and areas with poor soils," he says.
"It can also be grown with little need for pesticides, unlike cotton. If 1.3 million ha of hemp were grown, China could reduce its cotton area by the same amount and use it for growing food crops."
The centre has identified large areas in northern and northwest China and in Yunnan Province suitable for hemp. "In these regions, hemp will not displace food crop production," says Zhang Jianchun. "In some cases, they are not major food growing areas. In others, such as the northern plains, hemp would be ideal as a rotation crop with soybean and wheat, allowing farmers to make better use of their land and generate extra income." For the large-scale soybean farms of northern China, the centre recommends its newly developed "combine harvester + decorticator" for hemp operations.