Flax (Linum usitatissimum
) is a fibrous plant and an important commercial crop grown all over the world. Flax plant is mainly grown for its seeds, which are used for various applications from cosmetic production to paint mixing [1
]. Flax stem contains natural fibers, which could be used in various applications like production of biocomposites, apparels, high quality papers etc.
]. Flax fibers are comparatively expensive and of high quality when compared to other fibers, which is due to the difficulty of it’s processing. Natural fibers are low in density, cheap, and biodegradable. However, the big disadvantage of natural fibers is that they do not have same consistency in quality as compared to synthetic fibers. This inconsistency is due to variety of reasons such as climate, crop variety, retting process, and processing equipment used for fibers [4
The processing of flax fiber from the stem is usually conducted by passing the straws through series of rollers under pressure exerted by the rollers. This action helps the outer skin, shives and other non-fibrous parts to detach from the fiber and the resultant product is a clean long fiber; the process is called decortication [3
]. In decortication of non-retted flax stems, the resultant fibers are of inferior quality with impurities on it, because flax fibers are attached to itself and to the stem with chemical bonds such as pectin bond, which cannot be broken completely by applying mechanical pressure. In order to release the fiber completely from the stem, these stems have to undergo a process called retting. The retting process employs the action of micro- organisms and moisture on plants to destroy the cellular tissues and pectin surrounding blast-fibers bundles, and hence facilitating separation of the fiber from the stem [3
]. Two primary methods for retting, namely water and dew retting have been used traditionally to extract fiber for textile and other commercial applications [5
]. According to available literature, dew retting is considered to be the oldest method of retting. The quality of dew-retted fiber is inferior than water retted fiber, but due to lower labor costs and high fiber yield, it remains as an attractive practice for the farmers. In dew retting, the stems are pulled and spread uniformly on the ground in a thin layer for 3–4 weeks. Changes in moisture and temperature result in the colonization and partial degradation of flax stems, mainly by saprophytic fungi. The main disadvantage of dew retted flax fiber is its poor and inconsistent qualities. The field use of 3–4 weeks is also another drawback of the process [6
]. In water retting, straw is submerged in water tanks, where a pectinolytic bacterial community develops [7
]. Bacillus species are dominant for 10 to 40 h after the start of the water retting process, and are followed by spore-forming anaerobic Clostridium spp. when oxygen concentration in water tanks becomes lower. Clostridia, the major group of bacteria, which shows pectin-degrading activity, are responsible for water retting [8
]. The sources of retting bacteria are suspected to be adhering soil particles, stem dust, air, and water. In water retting, consistent conditions for bacterial growth and activity exist, which results in the evenness of inoculum and colonization by bacteria and in turn the quality of the retted fiber [8
]. Though water retting produces the highest quality flax fiber, the environmental pollution caused by it forced the industries to regulate the procedure and find other alternatives like enzyme assisted retting, steam explosion and electromagnetic energy assisted retting [5
The objective of this study was to understand the effect of water retting at controlled temperature on physical properties of Polish flax variety Modran.