HighlightsEnzymes are highly advantageous for consistent retting of flax aiming at composite applications.Pectinase enzymes play a major role in releasing fibers from the bast.Compromise between properties of enzymatically extracted fibers and composite performance.Recovery of enzymes important in view of overall process economy.

The application of enzymes as alternative to dew retting of flax was studied in correlation to the characteristics of composites reinforced with these natural fibers. Fiber fineness and mechanical properties of biocomposites were evaluated. Furthermore, moisture absorption by biocomposites was studied and fracture surfaces were investigated using Scanning Electron Microscopy. Compared to dew retted fiber composites, improvements in mechanical performance can be observed for composites impregnated with fibers extracted after enzymatic treatments. All enzymatic treatments resulted in finer fibers than green fibers and led to biocomposites with a reduced equilibrium moisture content and lower diffusion coefficient. This study illustrates the high potential of enzymatic retting, in particular with polygalacturonase. Also, the manual extraction procedure used, produced fibers with an E-modulus up to 84 GPa and strength up to 800 MPa, likely due to reduced fiber damage, which illustrates the hidden potential of flax fibers.

No abstract

The application of natural fibers as reinforcement material in composites can make an important contribution toward a more sustainable bio-based economy. To use these natural fibers, they need to be released from the stem. Traditionally, this is realized by dew retting. However, there are some disadvantages to this retting procedure. Due to changing weather conditions, it is quite difficult to guarantee a good and consistent fiber quality. Replacing the traditional retting process by a biocatalytic process may resolve these issues through application of a combination of pectinase and hemicellulase activities. In this context, several strategic pectinase and hemicellulase activities were blended. Flax fiber fineness and mechanical properties of resulting unidirectional fiber–epoxy composites were studied after treatment of flax stems with these strategic enzyme combinations. Characterization of fiber fineness showed a higher percentage of fiber widths smaller than 100 µm after combined treatment with two enzymes (44.7%), and the percentage was even higher after some combinations with three enzymes (51.2%). Assessment of mechanical properties of composites showed no significant differences in tensile or transverse properties for combined enzymatic treatments. Fiber properties were back-calculated from unidirectional flax fiber–epoxy composites and a Young’s modulus of 88 GPa and a tensile strength of 865 MPa were observed. Enzymatic extraction resulted in the achievement of similar results as dew retting concerning mechanical composite performance and fiber fineness.

Highlights Enzymatic treatment of flax offers a valuable alternative for dew retting. Polygalacturonase combined with xylanase activity leads to a markedly chemical refining of flax fibers. Enhanced fiber extraction efficiency reached by applying enzyme combinations. Extraction efficiencies twice as high compared to green fibers by combining polygalacturonase and pectinmethylesterase.