Determining Bast Fibre Tex Values and Hackling Yield Correlates
Flax bundle tex governs hackling outturn: finer bundles yield over 50 percent long line sliver, cutting net sliver cost and unlocking counts above Nm 50.
Bundle
Technical bast strands arrive at the inspection table in scutched stricks measuring roughly one metre in length. Commercial buyers evaluate these parcels by pulling manual tufts, assessing colour uniformity, and flexing the middle stem to gauge cortical stiffness. Physical grading links raw strand thickness directly to the output of long line flax during mechanical combing.
When technical strands exhibit high linear density, middle lamella gums hold hundreds of elementary fibres in rigid groups. These coarse groupings resist pin penetration, causing transverse breakage along the stem rather than clean longitudinal splitting.
Coarse bundles reject fine drafting.
Laboratory determination of linear density relies on cut-and-weigh gravimetric sorting or pneumatic resistance instruments calibrated to specific surface areas. In industrial flax processing, the technical strand linear density spans from 1.8 tex to 4.5 tex. Elementary fibres enclosed within these aggregates possess individual linear densities between 0.18 tex and 0.38 tex, with individual lengths rarely exceeding forty millimetres.
The ratio between technical bundle fineness and elementary cell fineness establishes the ceiling for drafting attenuation during roving preparation.
Strands that split cleanly under thumb pressure yield long line sliver rather than short combings.
Spinning mills purchasing scutched straw demand precise linear density values to anticipate the split between hackled line sliver and hackled tow. Finer technical strands consistently translate into superior line recovery. Coarse strands generate excessive quantities of short, tangled combings that sell at a severe discount to long line material.
The financial return of a scutching lot depends almost entirely on this split.
Fibre mass dictates drafting limit.
| Bundle Linear Density (tex) | Mean Strand Diameter (microns) | Hackling Line Outturn (mass percent) | Hackled Tow Fraction (mass percent) | Maximum Achievable Wet Spun Count (Nm) |
|---|---|---|---|---|
| 1.8 to 2.2 | 45 to 65 | 52 to 56 | 34 to 38 | Nm 60 to Nm 80 |
| 2.3 to 2.8 | 66 to 85 | 46 to 51 | 39 to 44 | Nm 39 to Nm 50 |
| 2.9 to 3.5 | 86 to 110 | 40 to 45 | 45 to 50 | Nm 26 to Nm 36 |
| 3.6 to 4.5 | 111 to 145 | 32 to 39 | 51 to 58 | Nm 14 to Nm 24 |
Strands exhibiting linear densities above 3.5 tex undergo severe fragmentation when struck by the initial hackling bars. The mechanical shock shatters under-retted cortical tissues, transferring mass from the dressing table directly into the tow collection box. The resulting combed line sliver contains irregular clusters that jam drafting rollers during wet spinning.
Experienced graders verify bundle cleavability by splitting the base of the strick by hand before sending the lot to the feed table.
Strands showing low cohesion and thin cross sections survive the combing sheets intact, whereas thick, woody groupings break into low-value combings.
Airflow
Pneumatic resistance testing under ISO 2370 measures the specific surface area of a compacted test plug. Air driven through a compressed cylinder of parallelised flax encounters drag directly proportional to total fibre perimeter. Because finer strands present greater surface area per unit mass than coarse bundles, the pressure drop across the chamber indicates mean linear density.
Calibrating this pneumatic drop requires frequent verification against gravimetric cut-and-weigh standards derived from ISO 1973 procedures.
Moisture shifts the balance reading.
What Governs Fibre Bundle Tex Measurement?
Gravimetric cut-and-weigh procedures establish the baseline mass per unit length across conditioned test specimens. Technicians clamp parallel fibre arrays, cut a uniform central section of known length (typically 10 mm or 20 mm), and weigh the resulting mass on an analytical balance reading to six decimal places. The quotient of aggregate mass divided by aggregate cut length multiplied by bundle count yields the direct tex value.
Microscopic image analysis operates alongside this gravimetric route, measuring transverse cross-sectional areas across polarized optical fields.
Specimens tested below sixty percent relative humidity register an artificial fineness increase of three decitex.
Variations in moisture content alter the measured airflow value. Flax fibres absorb environmental water rapidly due to hygroscopic cellulose amorphicity and residual middle lamella hemicelluloses. A test plug tested at eight percent regain displays a smaller effective diameter and denser packing geometry than the same plug equalized to the official twelve percent commercial regain standard.
Laboratories correct pneumatic readings using empirical regain curves established by the International Confederation of Flax and Hemp.
Dew retting varies across stems.
Direct gravimetric methods reveal that a commercial lot delivered as 2.4 tex actually carries a coefficient of variation exceeding forty percent. Individual technical bundles within a single handful range from 1.2 tex to 5.8 tex. This internal heterogeneity stems from uneven fungal colonisation during field dew retting, where straw resting on the top of the windrow experiences stronger moisture cycles and enzymatic lysis than shaded lower stems.
Sourcing contracts specifying a single mean fineness number conceal this distribution, exposing downstream spinners to roving breakages.
- Under-retted cortical sheaths prevent uniform airflow penetration through the test plug, producing false readings of coarse bundle groupings.
- Residual shive fragments occupy volumetric space in the cylinder without contributing fibre surface area, skewing calculated specific area downward.
- Specimen crimp variations resist mechanical compression inside the measurement chamber, creating variable porosity channels that vent air prematurely.
- Environmental humidity drift alters cell wall swelling during continuous testing shifts, shifting apparent linear density by several tenths of a tex.
Controlled trials demonstrate that a 2.4 tex technical bundle fineness correlates with a 48.5 percent hackling line outturn on dew-retted Normandy straw. This baseline assumes an initial moisture regain of twelve percent and a combing pin progression starting at three pins per centimetre. If relative humidity in the mill drops below sixty percent, bundle brittleness accelerates pin-induced fractures, reducing the actual line yield to 45.5 percent on identical raw material.
The relationship between microscopic cell wall lumen dimensions and total pneumatic flow resistance remains unsettled across different regional cultivars, leaving technicians to debate whether airflow methods distinguish between hollow thin-walled bast cells and solid thick-walled technical groupings.
Comb
Mechanical pinned aprons advance stricks through graduated needle fields to split cortical bonds. The industrial hackling machine processes stricks clamped in moving steel holders, presenting the root end and the top end sequentially to rotating vertical belts. Coarse round pins on the opening sheets penetrate the fibre fringe to disentangle tangled strands.
Subsequent passages feature progressively higher pin densities, flattening the strick and tearing residual pectins apart.
Pins shatter brittle cell walls.
Where Does Stranded Pectin Depress Yield?
Incomplete microbial dissolution leaves intercellular gums cementing neighbouring cell walls. Polygalacturonase enzymes secreted during field dew retting target rhamnogalacturonan backbones within the middle lamella. When weather conditions turn dry during retting, fungal hyphae fail to colonise the inner bast ring.
The resulting technical strands retain tough calcium-pectate bridges that refuse to yield to the hackling pins. The pinned bars strike these stiff junctions, snapping the technical strand at the stem node instead of separating it into parallel elements.
Cohesion governs sliver consistency.
Combing pin dynamics mirror mechanical deformation mechanisms observed in wire-drawing dies, where frictional shear along metallic interfaces either burnishes the substrate or induces microscopic surface tearing depending on lubricant boundary conditions. Bast fibres moving past tempered steel pins generate localized friction that strips outer gummy layers while generating intense transverse tension. Excessive pin speed induces surface shear failure in dry fibres, multiplying micro-cracks along the secondary cell wall.
Short fibres migrate toward waste.
Testing reveals a mean bundle cleavage force of 18.2 centinewtons per tex under dry room ambient conditions. This cleavage force measures the resistance required to split technical aggregates into elementary units. Straw with a cleavage force above 24 centinewtons per tex generates heavy comb waste.
When cleavage resistance exceeds the transverse tensile strength of individual cell walls, the pins shear the stem completely, shedding thirty to forty percent of potential line flax into the hackled tow box.
Fine needle penetration converts unretted cortical bark into carding waste.
Secondary tow shaker screens recover short fibres shed between consecutive hackling sheets. Processing records indicate a secondary tow recovery rate of 34 percent on standard double-sided comb configurations. This figure represents an operational average subject to wide fluctuation, swinging between 26 percent and 41 percent across varied machine maintenance cycles.
Sourcing managers establish their financial pro formas using a conservative 28 percent floor when forecasting net line-and-tow value generation.
- Holder clamping locks the raw strick under pneumatic pressure, preventing root pullout during aggressive initial pin contact.
- Opening apron passage applies low-density round pins to disentangle twisted straw ends, shedding coarse woody shive and unbroken stem sections.
- Intermediate needle penetration drives medium-gauge flat pins through the central body, cleaving technical bundles along their natural pectin seams.
- Finishing sheet combing draws high-density fine needles through the fringe, removing short fibres under twenty centimetres and sizing the remaining line sliver.
Tow absorbs the mechanical impact.
Fibre suppliers frequently state that elevated tow yields during dry winter months stem entirely from ambient humidity variations on the factory floor rather than defective retting lots in the warehouse.
Conversion
Scutched flax valuation hinges on translating raw strick mass into usable line sliver. Commercial transactions value scutched flax per metric ton, but spinning profitability depends strictly on the cost per kilogram of combed line sliver delivered to the drawing frames. Material lost to hackled tow represents a severe economic downgrade, as tow sells on the open market at roughly one-quarter the price of hackled line sliver.
Clean separation preserves line margin.
Consider an industrial delivery scenario processing a 20-tonne commercial lot of scutched flax straw. Assume Grade A scutched flax arrives at 4,800 USD per metric ton, exhibiting an average technical bundle linear density of 2.2 tex. Processing this lot through modern hackling machinery yields 53 percent line sliver (10,600 kg) and 39 percent hackled tow (7,800 kg), with the remaining 8 percent accounted for as dust, shive, and invisible processing loss.
The hackled tow trades at an open valuation of 1,250 USD per metric ton, generating 9,750 USD in offset revenue.
Subtracting this tow credit from the initial raw material expenditure of 96,000 USD leaves a net raw material cost of 86,250 USD allocated across the 10,600 kg of long line sliver. The net fibre cost of the line sliver equals 8.14 USD per kilogram. Processing the combed sliver through wet spinning into a standard Nm 39 line yarn incurs a spinning conversion expenditure of 4.50 USD per kilogram, yielding an aggregate yarn manufacturing cost of 12.64 USD per kilogram.
Woven into plain apparel linen at 150 centimetres width and 180 grams per square metre, this yarn delivers finished fabric with a fibre-and-spinning raw input cost of 3.41 USD per linear metre.
Pectin content dictates roving softness.
Take an equivalent 20-tonne purchase of Grade C scutched flax at 3,600 USD per metric ton, carrying a coarse bundle linear density of 3.8 tex. Hackling yields fall to 35 percent line sliver (7,000 kg), while tow generation surges to 55 percent (11,000 kg). The raw material expenditure of 72,000 USD is offset by 13,750 USD in tow sales, leaving 58,250 USD resting against a mere 7,000 kg of combed line.
The net raw material cost per kilogram of line sliver climbs to 8.32 USD, exceeding the net sliver cost of the Grade A lot.
Fine yarns demand low variance.
| Lot Parameter | Grade A Parcel (2.2 tex) | Grade B Parcel (2.9 tex) | Grade C Parcel (3.8 tex) |
|---|---|---|---|
| Scutched Fibre Invoice (USD/tonne) | 4,800 | 4,200 | 3,600 |
| Combed Line Yield (mass percent) | 53.0 | 44.0 | 35.0 |
| Combed Tow Yield (mass percent) | 39.0 | 47.0 | 55.0 |
| Net Line Sliver Cost (USD/kg) | 8.14 | 8.23 | 8.32 |
| Maximum Target Yarn Count (Nm) | Nm 50 | Nm 36 | Nm 24 |
| Finished Fabric Cost (USD/linear metre) | 3.41 | 3.62 | 3.94 |
| Assumptions: 20-tonne input lot mass; hackled tow credit fixed at 1,250 USD/tonne; fabric specifications set at 150 cm width, plain weave, 180 grams per square metre; finished metres calculated at 92 percent weaving efficiency. | |||
Spinning trials expose lot variance.
Lower hackling yields alter the operational profile of the preparation room. Coarser line sliver requires double drawing passages to disperse remaining bundle thick spots, increasing energy consumption and maintenance overhead. The spinning frame experiences elevated end-breakage rates, forcing operators to reduce spindle speeds from 6,500 rpm down to 5,200 rpm to prevent excessive balloon collapses in the wet-spinning trough.
- Bundle fineness thresholds establish the ceiling on wet-spun yarn count, preventing low-grade raw material from entering fine yarn production lines.
- Moisture regain tolerances limit commercial weight adjustments, stopping mills from paying long-line prices for trapped water.
- Tow value credits buffer baseline input costs, providing a financial floor during periods of depressed yarn demand.
- Shive content ceilings prevent accelerated wear on drafting roll aprons and spinning frame pigtail guides.
Purchasing agents who commit capital to under-retted, coarse-bundle lots based entirely on an attractive initial price per metric ton find their savings erased by low combing yields, high machine downtime, and elevated cost per delivered metre of grey cloth.
Settlement
Commercial purchase contracts establish legal boundaries for moisture regain, line yield fractions, and mean linear density. Transactions governed by the standard terms of the International Flax and Hemp Federation define exact procedures for lot sampling and commercial mass determination. Certified testing laboratories extract representative cores from ten percent of unbroken bales across an incoming container.
If the conditioned weight falls below the declared invoice mass, the seller issues an immediate credit note for the missing dry substance.
Invoices settle on dry mass.
Settled standards protect the buyer.
Disputes regarding hackling yield outturn require standardized pilot combing trials conducted on calibrated laboratory hackling units. Standard contracts specify a tolerance limit of plus or minus 1.5 percentage points on declared line yield. When an independent test facility records a line outturn falling below this contractual threshold, the commercial valuation of the shipment resets automatically according to the verified ratio of long line sliver to hackled tow.
A verified line yield deficit exceeding two percentage points entitles the buyer to invoice deductions matching the tow price differential.
Flax contracts incorporating CELC Arbitration Rules stipulate that lots presenting bundle fineness values coarser than the agreed purchase specification by more than 0.4 tex permit the receiving mill to reject the shipment entirely or apply a mandatory five percent discount to the gross invoice value.