Structural Defect
Microscopic disruptions in the cell walls of bast fibres represent areas where the parallel alignment of cellulose microfibrils has been permanently displaced. These localized disruptions are slip planes, which weaken the mechanical strength of the flax fibre.
Mechanical Cause
Processing of flax through heavy mechanical rollers during scutching and hackling introduces high compressive forces that can bend the stems too sharply. These forces generate slip planes along the fibre length, turning what should be a continuous crystalline structure into a series of weak points. Quality control technicians use polarized light microscopy to detect these defects, which appear as bright cross-markings on the fibre surface.
The frequency of these markings is logged in the processing report to evaluate whether the mechanical settings are too aggressive.
Product Failure
Yarn spun from flax fibres with high densities of these defects is prone to breaking during the high-tension stages of spinning and weaving. When the fibres contain numerous slip planes, they cannot withstand the wet spinning drafts, leading to frequent machine downtime. The resulting yarn has lower tensile strength and is more susceptible to acid damage during subsequent bleaching and dyeing.
Mills adjust their purchasing criteria to limit the acceptance of shipments that exhibit a high density of these structural defects.
