Sizing Agent Selection for Fine Spun Bast Yarns

Bath

Fine-spun flax yarns finer than Nm 60/1 are naturally stiff and have low ultimate elongation. Managing the sizing bath for these high-count bast strands requires tight control over polymer dispersion, liquid temperature, and concentration. Standard starch formulations built for coarse cotton or tow linen fail on fine wet-spun yarns; their high viscosity keeps the size from penetrating to the bundle core, forming a weak outer shell that flakes off during warp preparation.

Fluid penetration into a fine bast bundle depends on capillary action and squeeze-roll pressure. Because fine wet-spun flax contains residual natural waxes and pectins, it resists liquid uptake below eighty degrees Celsius. Maintaining the size liquor between eighty-five and ninety degrees Celsius lowers dynamic surface tension, letting polymer molecules move between individual ultimates before the squeeze rollers fix the film depth.

For fine bast warps, target pick-up ranges from ten to twelve percent dry add-on by unsized yarn weight.

Setting dry substance ratios in warp preparation comes down to matching film mass against thread surface area. Fine yarns present far more surface area per unit mass than coarse counts do. Raising bath concentration while keeping viscosity low deposits high solids without encasing the thread in a thick shell.

Formulations maintain low viscosity through low-molecular-weight synthetic binders or chemically modified starches that resist shear breakdown during high-speed pumping.

Keeping temperatures consistently between eighty-five and ninety degrees Celsius stops native starch components from gelling prematurely. A temperature drop inside the size box triggers immediate viscosity spikes, causing uneven pick-up, warp beam streakiness, and heavy resistance at the lease rods. Automated controls offset thermal losses by running liquor through jacketed heat exchangers and tracking concentration via inline refractometers.

Viscosity directly governs liquor pick-up, while higher solids content reduces overall drying energy and cold liquor impedes size penetration into the yarn core.

When size flaking occurs at the lease rods, improper binder plasticization is usually the cause rather than yarn moisture variation.

Adhesion

Coat durability depends on chemical affinity between the binder polymer and the cellulosic substrate. Bast fibers have a highly crystalline structure with cellulose-rich secondary walls wrapped in an amorphous hemicellulose and lignin matrix. Sizing agents need to form hydrogen bonds with accessible hydroxyl groups on these crystalline zones while anchoring mechanically inside inter-fiber voids.

Unbleached bast fibers hold residual pectin, lignin, and natural fats that disrupt film attachment. Native starches bond poorly to unbleached flax because hydrophobic waxes prevent uniform wetting. Carboxymethyl cellulose (CMC) and partially hydrolyzed polyvinyl alcohol (PVA) adhere far better to bast substrates, thanks to high ionic affinity and flexible polymer chains that conform to surface irregularities.

Size films on bast fibers require sufficient elasticity to accommodate high warp tension without cracking before the shed opens.

Blending synthetic binders with modified starches gives rigid yarns the elongation they lack. Unsized flax breaks at under two point five percent elongation. If a size coating is too stiff to stretch alongside the yarn during shedding, it fractures, dropping size powder into the reed and leaving raw fiber bundles exposed to abrasive wear.

Adding glycerol or polyoxyethylene keeps size coatings from shattering under shedding stress. Plasticizers lower the glass transition temperature of PVA and starch blends, preserving ductility in dry mill environments. Too much plasticizer, however, reduces film tenacity, bringing on binder migration and tacky surfaces that cling as the shed opens.

• Brittle film fracture occurs when the ratio of starch to plasticizer exceeds twelve to one, causing heavy size dusting under drop wires.
• Inter-fiber slippage develops when binder adhesion falls below the tensile yield point of the raw bast fiber bundle.
• Warp end cling happens when trapped moisture or excessive tallow content creates surface tackiness between adjacent beam ends.
• Fibril shedding results from incomplete hairiness encapsulation when binder molecules fail to penetrate surface fiber crossovers.

A size film that binds tightly to individual flax fibrils without bridging across adjacent yarn wraps ensures smooth shedding without warp cling.

Abrasion

Friction during shedding subjects single bast strands to severe mechanical stress. Rapier insertion tapes, drop wires, heddle eyes, and reed dents strike the warp repeatedly in every loom cycle. Lacking continuous filaments, fine-spun bast yarns suffer from fibril peeling, where surface fibers strip back into dense neps that stop the loom.

How Does Size Film Toughness Prevent Fibril Splitting?

A cohesive surface film binds loose fiber ends against the main thread core during reed contact. On rapier looms running at six hundred picks per minute, high contact frequencies break down weak size films within thousands of cycles. Blending medium-viscosity PVA with carboxymethyl cellulose creates a tough film that resists cyclic friction while preserving thread roundness at high harness lift angles.

Hairiness Encapsulation Metrics

An eighty percent drop in projecting fiber count indicates adequate lay-down before mounting the warp on the loom. Optical hairiness testers measuring hair counts per hundred metres verify binder performance. On Nm 80/1 wet-spun flax, hairs over three millimetres long must drop from a baseline of four hundred per hundred metres to under thirty after sizing.

Worked Calculation for Warp Break Dynamics

Efficiency forecasting uses baseline parameters from an eight hundred metre warp beam of Nm 80/1 wet-spun linen running at five hundred picks per minute. The beam carries six thousand four hundred ends on a four-shaft rapier loom operating at ninety-two percent nominal shed efficiency. Unsized flax shows a baseline break rate of six point five breaks per hundred thousand picks from reed abrasion.

Applying a standard oxidized starch size at ten percent add-on cuts the warp break rate to two point four breaks per hundred thousand picks. Upgrading to a high-performance formulation of sixty percent PVA, thirty percent CMC, and ten percent plasticized synthetic ester at eleven percent add-on brings breaks down to zero point seven per hundred thousand picks. Over a twenty-four-hour production run, these figures translate to the following performance levels:

A loom running at five hundred picks per minute completes seven hundred twenty thousand picks in twenty-four hours. At six point five breaks per hundred thousand picks, an unsized warp causes forty-six point eight stops per day. At two point four breaks per hundred thousand picks, starch sizing reduces stops to seventeen point two.

At zero point seven breaks, the polymer blend reduces stoppages to five point zero per day.

At an average repair time of three minutes per break, daily downtime drops from one hundred forty-point-four minutes unsized, to fifty-one-point-six minutes with starch, and to fifteen minutes with the polymer blend. Net loom efficiency climbs from ninety point two percent to ninety-six point five percent, adding eighty-four linear metres of woven greige linen per machine day.

Warp end break rates on Nm 80/1 wet-spun linen drop below 0.8 per hundred thousand picks when size add-on reaches eleven percent with a PVA to carboxymethyl cellulose ratio of three to two.

1. Prepare size cooking vessel by metering demineralized water to prevent calcium cross-linking with carboxyl groups on modified polymers.
2. Slurry raw binder materials under high-shear agitation for fifteen minutes before introducing thermal steam injection.
3. Elevate liquor temperature to ninety-five degrees Celsius and hold for thirty minutes to ensure complete starch gelatinization and polymer dissolution.
4. Pump prepared size to the supply reservoir through a one hundred mesh stainless steel filter screen to trap undissolved gel particles.
5. Verify refractometer solids reading against laboratory calibration curves before committing warp beams to the size box.

Inadequate hairiness lay-down leads to warp end entanglement, pushing loom stoppage rates high enough to undermine weaving margins.

Desizing

Removing protective films after weaving prepares grey fabric for bleaching and dyeing. Thorough desizing is essential on fine linen, as residual polymers block even dye penetration, cause blotchy spots, and leave finished fabrics stiff and harsh.

Polymer Wash out Dynamics

Solubility profiles determine how quickly synthetic binders disperse in wash baths. Fully hydrolyzed PVA requires wash water above eighty-five degrees Celsius to dissolve fully, while partially hydrolyzed PVA dissolves quickly in cold or warm water. Carboxymethyl cellulose washes out readily in warm alkaline baths without enzymes, fitting cleanly into standard linen scouring routines.

Effluent Loading and Chemical Recovery

Discharging starches into wastewater streams drives up biological oxygen demand. Because mills face strict regulatory limits on chemical oxygen demand (COD) and biological oxygen demand (BOD), synthetic sizes like PVA offer distinct advantages. They can be recovered from wash water via ultrafiltration, reclaiming up to eighty percent of size polymers and lowering effluent surcharges.

Residual Size Testing Standards

Quantitative iodine spot testing alongside Soxhlet extraction measures residual binder mass. ISO 20743 protocols set specific limits for organic matter on greige goods before wet processing. Starch levels above zero point two percent by dry weight cause severe dye resist during reactive or vat dyeing.

Fabric rejection under ISO 20743 grey goods standards occurs when residual starch content exceeds zero point five percent by dry weight after finishing wash cycles.

Enzyme baths break down and clear residual starch, whereas unwashed size leaves greige goods stiff and rigid.

1. Sample greige fabric by cutting three ten-gram specimens across the full usable cloth width.
2. Dry specimens in a vacuum oven at one hundred five degrees Celsius until a constant weight is recorded.
3. Perform Soxhlet extraction using solvent to remove added tallow, lubricants, and waxes.
4. Immerse extracted samples in an enzymatic alpha-amylase bath at sixty-five degrees Celsius for forty-five minutes to hydrolyze starch compounds.
5. Rinse thoroughly in boiling water followed by cold distilled water, then dry and re-weigh to calculate mass loss from size removal.

Whether low-temperature enzymatic formulations can fully clear synthetic acrylic binders from fine wet-spun flax without degrading natural pectin networks remains disputed.

Contract

Commercial agreements for warp sizing set target pick-up ranges and mandatory testing protocols. Contracts that omit strict size chemistry limits leave room for mill substitutions ~ replacing synthetic polymers with cheap native starches and shifting costs from sizing preparation onto loom downtime.

Size Add on Verification Terms

Measuring dry chemical mass added to raw yarn requires comparing oven-dry weights before and after processing. Sizing specifications should clearly state that add-on percentages are based on dry fiber weight at standard moisture regain. For flax, standard moisture regain is fixed at twelve percent under ISO 139 baseline conditions.

Loom Hour Economics in Fine Linen Weaving

Financial losses from warp-related loom stoppages directly drive up the cost per finished metre. Operating a high-speed rapier or air-jet loom carries fixed hourly overheads including power, labor, depreciation, and floor space. When poor size selection drops loom efficiency from ninety-five percent to eighty-two percent, the landed cost per metre of fine linen rises by up to fifteen percent.

Loom efficiency directly influences finished metre pricing, while excessive add-on leads to severe size flaking during weaving.

Including a size add-on tolerance clause that caps moisture regain variance at two percent obligates the mill to absorb re-sizing costs whenever film cracking exceeds agreed thresholds.