Experimental Study On Application Of Radio Frequency And Microwave Heating Into Retting Of Flax Straws

Flax fiber is largely used in textile and composites industries. Retting of flax straws, which is the very first step to manufacture fibers, is vital to determine fibers quality. In order to improve retting efficiency while guaranteeing fibers properties, radio frequency (RF) and microwave (MW) heating technology were applied into flax water and enzymatic retting respectively in this work. By evaluating the retting quality which included retting efficiency of flax straws and properties of fibers obtained, it was concluded that the application of RF and MW into retting improved the retting efficiency significantly and obtained flax fibers with reasonable apparent and mechanical properties. This work could provide some information for future work into improving retting quality and shortening retting period by using dielectric heating.Firstly, RF was introduced to assist flax water retting of different stages. The retting qualities of pure water retting and RF assisted water retting were studied. The conclusion shows that RF treatment at 40℃ and 90℃ for 60 minutes should be the optimal condition for the flax which had undertaken 2 days and 6 and 10 days of water retting, respectively, to get maximum improvement in retting efficiency and better apparent and mechanical properties of fibers. Considering both retting quality and retting period, six-day was appropriate water-retting duration and 90℃-60min would be its best RF treatment.RF and MW were then used respectively as the pretreatment for flax enzymatic retting. Based on the retting efficiency, flax straws presoaked for 8 hours then RF or MW treated for 30 minutes got larger weight loss, retting degree and improvement in retting efficiency compared to just enzymatic retting, and the resulting flax fibers yielded better whiteness, linear density and reasonable tensile properties. RF or MW pretreatment could improve the retting efficiency of enzymatic retting, however, this treatment tended to impair the tensile properties of flax fibers at same time. Compared with RF, MW pretreatment seemed to prevail a little bit to obtain better enzymatic retting efficiency.It was found that the way RF or MW functioning in retting was a combined effect on either polar pectin or cellulose molecules. RF or MW treatment was a "double-edged sword", which helped degradation of pectin therefore improved the retting efficiency, but impaired fibers tensile properties due to weakening the chains of cellulose molecules through their polarization under dielectric heating treatment.