Gravimetric and Optical Quantification Protocols for Bast Defect Content
Gravimetric digestion provides absolute mass baseline proof for bast defects, while optical scanning provides fast surface area sorting requiring lot calibration.
Unretted Fiber Bundles
Biological Residue
Sections of flax stalks where the biological breakdown of the woody core and the pectin binders remained incomplete appear as stiff, greenish clumps in the raw stock. Presence of unretted fiber bundles creates major problems during the drafting and spinning stages. These bundles do not separate into individual fibers.
Processing Failure
Mechanical rollers cannot thin these thick clusters, which leads to large slubs and thick spots in the finished yarn. Because unretted fiber bundles are harder and less flexible than properly processed flax, they often break the fine needles used in knitting or the delicate components of a spinning frame. The lack of retting means the bacteria did not consume the lignin that glues the fibers to the stem.
This defect usually occurs when the straw is baled while still wet or when the weather conditions during field retting are too cold.
Finished Quality
Removing these defects requires intensive combing or carding, which increases the amount of waste and lowers the overall yield. If they reach the weaving stage, the resulting fabric will have a rough, uneven texture that is generally considered a second-grade product. Mills reject lots with high counts of unretted fiber bundles to maintain their quality reputation.