Effect of Field Retting in Manitoba and Maceration on Fibre Yield of Hemp (Cannabis sativa L.) Stalks

Abstract. Hemp (Cannabis sativa L.) has historically been cultivated for fibre to be used for various applications such as textiles, and other materials. In recent years, interest has risen in using hemp as an alternative to glass/carbon fibres in biocomposites. In order to easily extract fibres from hemp stalks they must first go through a process known as “retting” in which the fibres are separated from the hurd. Field or dew retting is a low cost and eco-friendly method commonly used in Europe. The goal of the present study is to determine the effects of dew retting in Manitoba climate and stalk “maceration” (i.e., crushing) on fibre yield using raw and water retted hemp from the same crops as a basis for comparison. Hemp stalks were cut down with a conventional swather and half the material was passed through a macerator machine to crush the stalks. Fresh hemp stalks from two separate locations, both macerated and non-macerated were collected immediately after harvest. Dew retted hemp stalks (macerated and non-macerated) remained in the field undisturbed for the following 24 to 33 days and were allowed to ret naturally. The fibre extraction was accomplished using a custom setup based on previous literature and traditional methods consisting of manually passing straw samples through a roller crusher followed by separation using two hackles (coarse and fine), first to scutch out hurd and then to separate short from long fibres. Hemp stalks were conditioned at 21^οC and 65% RH for 48 hours prior to fibre extraction. Six 50 g samples of each treatment combination were processed and weighed after crushing, after scutching and finally short and long fibres were weighed separately. Results indicate that brittle fibres were produced by the dew retted hemp due to significantly high post-crusher hurd yields and low long fibre yields with averages of 36.81±3.23% and 6.29±0.74% respectively in the case of non-macerated material. The brittle fibres are suspected of being a sign of over retting, which implies that proper retting is possible in future works with more careful monitoring. Maceration using local agriculture equipment which employs flat rollers did not have a significant effect on whole or long fibre yield. Based on these results, dew retting in Manitoba shows promise in terms of fibre separation and extraction but maceration using fluted instead of flat rollers requires investigation.