Variety and growing condition effect on the yield and tensile strength of flax fibers

Flax (Linum Usitatissimum L.) fiber composites serve as sustainable replacement for glass fiber composites. Given that these composites are based on natural sources, their performance is susceptible to variation induced by several factors. Hence, ten flax fiber varieties cultivated in two different regions of Belgium in 2017 and 2018 are compared in terms of their yield and their tensile strength. Statistical analyses are carried out to determine the varietal difference in terms of tensile strength of bundles and of composites. The mechanical tests of flax fibers are carried out in two ways, i.e. dry fiber bundle tests and impregnated fiber bundle tests (IFBT). The results from the two consecutive growth years show their significant influence on the yield of the flax fibers, which are highly dependent on the weather conditions, in particular the precipitation during the growing season. The influence of the date of pulling and the retting degree on the yield of flax fibers and the tensile strength of fiber bundles is also investigated. The early pulling and lower retting degree result in a detrimental effect on the fiber strength whereas the late pulling shows little to no effect on the fiber strength. The difference of flax fiber strength among ten flax varieties over two years can be easily identified using IFBT and a couple of flax varieties exhibit a good tensile strength with low variation. This methodology can be used to select good flax varieties which have high mechanical properties with a small variation, which are suitable for a fiber reinforcement of high performance natural fiber  reinforced composites.