Evaluation of effective parameters on fiber separation from calotropis stems in mechanical methods

Calotropis is an evergreen and perennial shrub that grows in tropical areas of Iran and has valuable fibers in the bark of its stem. Fibers obtained from Calotropis stem have 75% cellulose. Tensile strength and modulus of the fibers is more than Cotton and elongation of the fibers is higher than Linen fibers. Calotropis stem fibers are researched for paper pulp applications and also has been evaluated for some applications such as their fiber characteristics for cloth making.
However, there are no more studies on Calotropis bark fibers and very limited information is available about fibers extraction methods. In traditional methods of extraction, the stems were wetted for a period of 8 days and then the fibers were separated manually. In another method that was common in south region of Iran, the dried stems were threshed by hand and the fibers were separated from the crushed stems manually. These methods need cumbersome works, and require long times for processing. Therefore the aim of this study is to develop an extraction method for Calotropis bark fibers based on mechanical ways. Investigation of some importance characteristics, e.g. moisture content and rotational speed on the performance of extraction machine is another objective of this study.
Considering that the fibers are in the bark of the stems, extracting principle is based on bark separation by pushing of stems against some pairs of sharp blades. Since diameter of stems is variable, it is essential that the designed system to be capable of auto-adjusting for different diameters. So the stems were fed through the blades, via two serrated rollers. The roller, blade and other parts of a separated unit were tightened to a yoke, so when thick stems are inserted, the roller compresses the spring and moves up, as a result, the blade was pulled up. The Yoke was connected to the frame through two long screws. For complete debarking and fibers extraction, three separation units were arranged in series at the final design. For complete debarking from all sides, the second unit was attached while 90o rotated in relation to the first unit.
To evaluate the machine performance, the test specimens were provided from the south region of Iran, Kerman. Approximated length of test specimens was 150 cm. Firstly, petioles and leaves were removed at the nodes of the stems. Extraction efficiency of the machine was evaluated with three moisture contents (75% w.b., 65% w.b. and 55% w.b.) and six rotational speeds (30, 35, 40, 45, 50 and 50 rpm). Stems with a moisture content higher than 75% w.b. and lower than 55% w.b. were not suitable for fiber extraction by the machine. Because latex flows from the stem at moisture content of higher than 75% w.b. and also the bark was being stuck on the stem at moisture content of lower than 55% w.b. The stem feeding capacity was evaluated at different moisture content and speeds as well. In order to investigate the power consumption due to moisture content and rotational speed, the consumed power per stem mass unit was calculated at three moisture contents and three speeds (35, 45 and 55 rpm).
Analysis of variance (ANOVA) technique was used to evaluate effect of different speeds and moisture contents. The study was planned as factorial experiments based on a completely randomized design and each treatment was replicated five times.
Based on the analysis of variance for extraction efficiency at different three moisture contents and six rotational speeds, it is obtained that the effect of moisture contents (at P≤0.01) and rotational speeds (at P≤0.05) were significant on the extraction efficiency. Comparison extraction efficiency at six speeds and three moisture content levels showed that the maximum extracting efficiency occurs at rotational speed of 40 rpm with the moisture content of 75% w.b. The average efficiency in this case was 95% approximately. Extraction efficiency at moisture contents of 65 and 55 % w.b. were 78-90% and 60-82% respectively. As the moisture content decreased, the bark was being bonded and stuck on the stem so the fibers were torn while debarking. It is found that the effect of speeds on the capacity was not significant. Average stem feeding capacity into the machine at rotational speed of 45 rpm and at three moisture contents of 75% w.b., 65% w.b. and 55%w.b. were respectively 46, 37 and 28 kg hr-1.
The effect of moisture content and rotational speed on the consumed power per stem mass unit was significant at 0.01 probability level. However, the consumed power per mass unit increased with decrease in moisture content and increase in rotational speed. The average of maximum consumed power per unit mass at moisture contents of 75%, 65% and 55% w.b. were 1.46, 1.70 and 1.85w g-1, respectively. Also 1 kg fibers were obtained from 22kg stems at a moisture content of 75% w.b. Finally, it is concluded that the fiber length varied from 10 cm to 80 cm by the mechanical method.
In this study, a machine that would be capable to extract fibers from stems of Calotropis was developed. Comparison of extracting efficiency at six speed levels and three moisture contents indicated that the maximum extracting efficiency (95%) is at rotational speed of 40 rpm with the moisture content of 75% w.b. Average stem feeding capacity into the machine at three moisture contents of 75% w.b., 65% w.b. and 55% w.b. were 46, 37 and 28 kg hr-1, respectively. Results showed that consumed power per unit mass is increased when moisture decreased. Also 1 kg fiber was obtained by 22kg stems at moisture content of 75% w.b.