Dew-retting

Dew retting iuvolves the action of dew, sun, and fungi on the plants spread thinly on the ground. Dew retting takes 4—6 weeks, but the action is not uniform and it tends to yield a dark-colored fiber. However, it is far less labor iatensive and less expensive than water retting. It is commonly used iu regions of low water supply and accounts for 85% of the Western European crop, especially iu France, and also iu the former Soviet Union. 

Soil fungi, in dew-retting, 77 605-606 Soil heaping defined, 3 758t Soil heaps... 

The fact that the fungal population on dew-retted flax and hemp consists very largely of the same field fungi found on field-weathered cotton fiber was noted earlier Alternaria and Cladosporium herbarum are prominent (17). 

In contrast to the Russian method of production, Kentucky growers left the chopped cannabis stalks on the ground to become dew retted. Water retting was discouraged because Kentucky farmers believed that fish and livestock that drank from a pond in which hemp had been placed would be poisoned. Then, too, the water smelled like rotten eggs after hemp had been soaking in it, "which was considered unhealthy for slaves and twice as bad for whites."... 

Not only were the northern manufacturers reluctant to use dew-retted hemp, the United States Navy also refused to buy Kentucky hemp despite Congress s efforts to promote the industry. In 1824, Congress inquired as to the basis for this discrimination. The secretary of the navy s reply was that "cables and cordage manufactured from it [Kentucky hemp]... are inferior in color, strength and durability to those manufactured from imported hemp, and consequently are not safe or proper for use in the navy," An expert in rope making was quoted as... 

Dew retting is similar in action to water retting, but slower. The stalks are spread out on grass and allowed to ferment, the necessary moisture being supplied either by dew, rain, or occasional watering. Sometimes the fermentation is started by water retting and the stalks are then taken out and laid on grass to complete the process. In this way a better colour is obtained. 

To obtain fibers, stems are harvested and dew-retted, and the fibers are then mechanically processed to extract fibers from the nonfiber woody materials... 

All parts of fibrous plant stem must be removed for proper fiber separation. Bast fiber extraction is usually conducted using special processes such as water and dew retting, degumming, or decortication, in which the separation of bundles craitaining elementary fibers joined together by pectin and calcium ions is also performed. Fiber content in the stem of fibrous plants is shown in Table 4.1. 

Fig. 6.5 A comparison between not-treated flax fibre, dew-retted flax fibre and enzyme-retted fiax fibre reinforced HOPE composites. Adapted from [88]. Low indicates 0.05% enzyme and 5 mM chelator, medium indicates 0.1% enzyme and 10 mM chelator and high indicates 0.3% enzyme and 25 mM chelator...

Zafeiropoulos et al. [16] used four types of flax fiber when studying the crystallization of isotactic polypropylene in the presence of fibers unmodified, dew-retted (pectin removed), flax modified by esterificatirMi with stearic acid and flax modified by high temperature in autoclave. It was interesting to see that transcrystaUizatirHi occurred in both chemically and hydrothermafly modified fibers. Zafeiropoulos also fotmd that the rate of cooling may have an effect on the morphology of TCL. 

Morrison WH, Archibald DD, Sharma HSS et al (2000) Chemical and physical characterization of water- and dew-retted flax fibers. Ind Crops Prod 12 39-46 Mishra S, Misra M, Tripathy SS et al (2002) The infiuence of chemical surface modification on the performance of sisal- polyester bio composite. Polym Compos 23(2) 164-170 Bisanda ETN (2000) The effect of alkali treatment on the adhesitm characteristics of sisal fibers. Appl Compos Mater 7 331-339... 

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