Chemical and strength differences in dewretted hemp fiber
1945
Hessler, L.E.
Retted hemp fiber is composed of about 80% cellulose and lignin, while the remaining 20% or partially soluble fraction is made up of nitrogen compounds, pectic substances, pentosans, ash, and other extractable substances. Unretted hemp fiber consists of about 30% of the partially soluble fraction. By retting, part of it is removed in order to free the fiber. When the fiber is exposed to microbiological action, it is weakened and, as a result, the breaking strength varies inversely with the length of the retting period. Exposure to the sun shortens the time of retting. Damage to hemp fiber during retting may occur to a greater extent when the fresh green plants are retted than if the plants are allowed to cure by shocking; further, the younger top part of the plant may readily result in weaker fiber. Winter retting compared with fall retting usually has been observed in practice, and substantiated by the experiment reported here, to result in a better color but weaker fiber. This condition is probably due to the slower, longer retting period. The chemical composition of winter-retted fiber was lower in the more soluble fractions, which indicates more retting. Fiber grown from Kentucky hemp seed had a different level of constituents and greater strength than fiber from Chilean hemp. In general, the breaking-strength tests were related to commercial fiber grades; however, the lower grade had some of the strongest fibers, which can be attributed to under-retting.
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