Evaluation of quantitative and qualitative characteristics of stem fibers and pulp obtained from seed flax (Linum usititassimum L.)

Background and objectives: Although the main goal of seed flax (Linum usititassimum L.) cultivation is to produce seeds and extract oil from it, significant amounts of long bast fibers of this plant can be a very suitable source of long fibers used in papermaking industries. The objectives of this study were to examine the quantitative, qualitative and pulping characteristics of seed flax and to investigate the effect of planting distance on these characteristics.

Materials and methods: This study was conducted from May to August 2015 at the UPark farm of the University of Maine, USA. The experiments were carried out using split Plot with a randomized complete block design. The main factors included 4 planting distances (9.0, 5.1, 2.2, and 4.4 cm) and the secondary factors included 3 harvest times (50, 75, and 100 days after planting). The distance between the planting rows was 4.25 cm and each plot consisted of 5 rows, each 2 meters long. At 50, 75, and 100 days after planting, the diameter and length of the stems were measured for 30 samples from each of the three middle rows of each plot. After harvesting the samples, various plant components (core, stem bast, leaves, roots, and fruit capsules) were measured and their weights and weight percentages per hectare were calculated in the laboratory. Additionally, fiber biometrics of the stem bast and core were also performed. Pulping experiments were also conducted using the bast and the whole stem with two methods: SO2-ethanol-water (SEW) and soda. All statistical analyses were performed using the SPSS software, and the comparison of means was conducted using the Duncan test at the 1% and 5% levels.

Results: The ANOVA results showed that the individual effects of different factors on the length and diameter of seed flax stem were significant at the 1% level, while their interaction was not significant. Increasing planting distance resulted in higher yields of stem, root, leaf, and fruit capsule. Despite a decrease in the percentage of seed flax stem bast from 33 to 25.4% when the planting distance increased from 0.9 cm to 4.4 cm, the overall stem yield increased significantly. The longest bast and core fibers (4700 and 608 µm, respectively) were observed at a planting distance of 0.9 cm, while the shortest (4080 and 510 µm, respectively) were at 4.4 cm. Pulping experiments from the whole stem using soda and SEW methods showed that the highest and lowest yields were 62.9% and 48.57%, respectively, at cooking times of 30 and 90 minutes in the SEW process. The ANOVA results showed that the independent effects of planting distance and stem components on the Kappa number of the resulting SEW pulps were significant at the 5% and 1% levels, respectively. The highest Kappa number (62.12) was associated with the pulp obtained from the core of seed flax planted at a distance of 4.4 cm, while the lowest (14.88) was associated with the bast of seed flax at a planting distance of 0.9 cm. According to the Duncan grouping test, no significant difference was observed between the Kappa values of the pulp obtained from the core of seed flax planted at distances of 0.9 and 4.4 cm.

Conclusion: By increasing the planting distance of seed flax, the yield of bast and core of stem increases. Qualitatively, the length of bast and core fibers decreases; so that the length of bast fibers is always about 8 times the length of core fibers. In terms of pulping, the Kappa and the yield of SEW pulp obtained from the bast and the core of the stem increases.