Effect of dew retting and maceration on fibre properties of hemp and flax in Manitoba

Abstract

Hemp (Cannabis sativa L.) and flax (Linum Usitatissimum L.) are both bast fibre plants and have historically been used in paper, rope, thread, yarns and other materials. Recently, companies like the Composites Innovation Center (CIC) Inc. of Winnipeg, Manitoba have explored the use of hemp and flax as environmentally sustainable alternatives to glass/carbon fibres in biocomposites. In order to easily extract fibres from hemp and flax stalks, the stalks must first go through a process known as “retting” in which the cellulosic fibres are separated from the outer cuticle and woody core. Various retting methods exist and have an impact on fibre quality and ease of extraction. Dew or field retting is an environmentally appealing retting method that has regained popularity, particularly in Europe, but has not been rigorously studied in Manitoba. During dew retting, bast fibre straw is permitted to lay in the field in swathes and the rain and morning dew grants the necessary moisture while micro-organisms secrete the necessary enzymes to degrade the pectinaceous matrix encasing the natural fibres. As the retting process greatly influences the quality of the end product, methods such as maceration have been applied to bast fibre straw in an attempt to increase retting efficiency. The goal of this research was to determine the effects of dew retting in Manitoba and maceration using flat rollers on flax and hemp fibre properties. The properties investigated were fibre yield, quality of pectin matrix degradation using scanning electron microscopy and single fibre tensile stress. Water retted and unretted hemp and flax were used as means for comparison. Results indicate that dew retting is possible in Manitoba climate and requires further optimization, and maceration using flat rollers has no significant effect on retting efficiency.