2.2 dtex (2.0D)×38/51mm PP Staple Fiber for Thermal Bonded Nonwoven

Calendered Coverstock in Disposable Hygiene Lines

On high-speed carded lines producing hydrophobic coverstock at 2400–3600 mm working width, the 2.2 dtex (2.0 D) × 38 mm PP staple fibre is selected when the converter prioritizes lower web defects over maximum softness. Compared with 1.7 dtex fibre, the 2.2 dtex filament cross-section reduces card cylinder wrap and fly, but it also lowers fibre count per gram and increases mean pore diameter. When the 51 mm cut is substituted onto the same card, machine-direction tensile rises but card loading increases; the measurable outcome on a double-doffer card at ≥650 m/min cylinder surface speed is a higher nep count and greater web weight variability across the cross-machine profile. Compliance baseline for hygiene coverstock supplied into the EU market is OEKO-TEX Standard 100 Annex 6 product class I, with additional converter audits requiring nonwoven lot release against ISO 9073-2:1995 for tensile and ISO 9073-1:1989 for basis weight. REACH Annex XVII restrictions on PAH content apply when post-industrial recycled PP is introduced into the blend; virgin polymer with documented supplier declaration is preferred for skin-contact layers. The fibre addition ratio in final web is either 100 % by fibre mass for standard 18–28 g/m² thermal-bonded coverstock, or 25–35 wt% of the 2.2 dtex grade blended with 65–75 wt% of 1.3 dtex soft-touch fibre. In the blend, the 2.2 dtex fraction functions as the thermal bonding backbone because its higher melt mass per filament creates larger bond sites at equivalent calender pressure; lowering the 2.2 dtex share below 20 wt% produces a measurable decline in web tear strength and increases pinhole defects after embossing. Downstream production is carding, crosslapping where specified, and heated calender point bonding. Calender roll surface temperature is maintained at 148–153 °C with engraved bond area 16–19 % and linear pressure 60–90 N/mm. Finished forms include urine acquisition layer carrier tissue, leg-cuff nonwoven, femcare pad coverstock, and ADL support scrim; the 38 mm grade is typically not used for 3D embossed top sheets because the coarser filament diameter reduces emboss pattern sharpness.

In medical face-mask outer-ply and isolation gown lamination lines, the 2.2 dtex × 38 mm PP staple fibre web is calendered as a reinforcing facing against a meltblown polypropylene mid-layer rather than used as an exposed absorbent structure. The outer ply is typically run at 22–28 g/m² and 100 % PP by fibre mass. When the same fibre is used as one layer in a three-layer SMS composite, the staple facing is reduced to 40–55 wt% of the final laminate, with spunbond and meltblown layers contributing the remainder. Compliance is evaluated under EN 14683:2019 for bacterial filtration efficiency and differential pressure; for gowns, EN 13795:2019 and AAMI PB70:2012 liquid-barrier classification govern the laminate rather than the fibre alone. Cytotoxicity testing is performed according to ISO 10993-5:2009, skin irritation to ISO 10993-10:2010, and latex-free verification is recorded because calender roll release agents can introduce trace contamination. A conformance matrix is provided below.

Downstream production on standard carded lines includes web formation at 60–100 m/min, two-roll heated calender point bonding at 143–150 °C, inline corona treatment to raise surface energy to 38–44 mN/m, and rotary ultrasonic edge sealing at 30–35 kHz. A documented failure mode on high-humidity shifts is web wrapping at the calender entry due to condensation on the fibre finish; conditioned fibre moisture above 0.35 % by weight reduces splice strength and increases static decay time. Finished products include surgical mask outer shells, procedure mask facings, isolation gown back panels, disposable cap base layers, and emergency-use respirator outer covers where the staple fibre layer is not the primary filter medium.

Why Does the 38 mm Staple Grade Outperform 51 mm in Automotive Air-Laid Preforms?

Automotive nonwoven converters run air-laid or carded crosslapped preforms for acoustic insulation where staple length directly controls loft retention. The 2.2 dtex × 38 mm PP fibre is favoured over 51 mm in air-laid preforms because the shorter cut length reduces fibre roping during silo discharge and improves density distribution in high-loft mats. On a production-scale air-lay machine, the 51 mm cut gives higher tensile strength but also a wider basis-weight coefficient of variation; the 38 mm cut typically narrows cross-direction basis-weight variation to ±3 % at 800 g/m² when fibre finish is held above 0.10 % by mass. Formulation addition ratio in firewall and wheel-arch insulation is commonly 65–80 wt% 2.2 dtex PP staple fibre blended with 20–35 wt% 6.7 dtex hollow or recycled PET. In luggage compartment high-loft panels, PP content falls to 50 wt%, with bicomponent binder fibre added to maintain thermal bond integrity and PET filler to increase recoverable compression. The 2.2 dtex PP fibre remains the carrier because of its elongation before break, which permits the preform to be compressed in heated tooling without tearing. Compliance requirements are set by vehicle manufacturers rather than a single global standard; baseline flammability is evaluated under FMVSS 302 and ISO 3795:1989, where the burn rate must be <100 mm/min on a 100 mm mark. VOC and FOG emissions are assessed by VDA 278:2011, with individual OEM limits applied; odour testing follows VDA 270:2018 because PP fibre can carry thermal oxidation by-products from upstream compounding. REACH Annex XVII applies to any recycled PET fraction introduced. Downstream processing starts with bale opening, carding, crosslapping into 300–800 g/m² batts, and through-air oven bonding at 158–165 °C for 45–90 s. The web is then compression-moulded at 170–190 °C into automotive preforms, die-cut, and finished with polyamide scrim if required. Finished part types include wheel arch liners, trunk side trims, engine bay firewall insulators, under-dash pads, A/B/C pillar insulation, and under-carpet acoustic backboards.

Where the production line is configured for pleated panel filters and cabin air prefilter media, the 2.2 dtex × 51 mm PP staple fibre is not used as the high-efficiency layer; its role is to form a low-pressure-drop prefilter that protects the meltblown or electrospun layer from dust cake impaction. On a commercial filter converting line, the carded PP web is calendered at low bond area to preserve tortuosity, because overbonding above 14 % bond area creates film-like zones that raise pressure drop without improving dust-holding capacity. Formulation addition ratio for the prefilter is 100 % PP staple fibre at 100–180 g/m²; when pleat stiffness is required, 60–70 wt% PP is blended with 30–40 wt% recycled PET fibre. The 51 mm length is selected when pleat retention after scoring is a parameter, whereas 38 mm is used for thin, flexible prefilter layers. Filter media compliance is classified under ISO 16890:2016 as coarse to ePM10, not as high-efficiency; automotive cabin filter test methods follow ISO 11155-1:2001 for particle removal and differential pressure. REACH Annex XVII limits apply to any recycled PET input. Downstream production includes carding, crosslap or inline feed, belt calendering at 145–155 °C, belt preheating to 120–130 °C before calender entry, and then pleating at 25–35 mm pleat pitch. A production-scale bottleneck occurs when web moisture exceeds 0.3 %, causing steam blowholes at the calender nip and variable pleat geometry. Finished product types include cabin air filter prefilters, commercial HVAC coarse panels, paint booth intake mats, and respirator prefilter wraps.

When Thermal Calendering Replaces Latex Bonding in Mattress Insulation Nonwovens

In mattress border wrap and upholstery cushion interliner programmes, latex binder removal is driven by VOC control and by the need to avoid cellulose degradation in humid storage. The 2.2 dtex × 51 mm PP staple fibre enters the formulation as the melt-fusion component, but it is not a flame barrier. The fibre is dosed at 20–35 wt% of total fibre mass, combined with 40–60 wt% flame-retardant rayon, 10–25 wt% polyester, and 0–5 wt% bicomponent fibre. Exceeding 35 wt% PP raises the fibre-melt drip area during open-flame testing and reduces char integrity; dropping below 20 wt% produces weak sheet integrity and delamination after mattress compression cycles. Compliance for the finished interliner is tested to 16 CFR 1633 for full-mattress open-flame performance, 16 CFR 1632 for cigarette smoulder, and BS 5852:2006 ignition source scheduling where the product is exported to the UK. Upholstery applications are additionally assessed under California TB 117-2013 smoulder criteria. The nonwoven sheet itself is tested for tensile loss after heat ageing at 70 °C for 96 h, but published data for this specific PP grade in FR rayon blends is limited; converter trials typically establish lot-specific retention values before full production. Downstream processing uses a carded crosslapper to build 200–400 g/m² batts, followed by through-air oven bonding at 155–162 °C with a dwell of 60–90 s. The web is then cooled below 45 °C before rotary-knife cutting to prevent deformation. A process conflict on mixed-fibre lines is finish dilution: FR rayon can strip lubrication from PP fibre, so inline static control and monitoring of finish-on-fibre below 0.08 % are necessary to prevent card wrap. Terminal forms include mattress border wrap, spring insulator felt, upholstery cushion wrap, furniture deck pad, and bed base dust cover.

For bituminous roofing carrier web production, the 51 mm cut is normally selected because the longer staple increases cross-machine tensile after needle-and-thermal prebonding, while the 2.2 dtex filament diameter preserves enough closed area to limit bitumen bleed-through during coating. The carded carrier is run at 120–200 g/m²; 100 % PP staple fibre is used when low water absorption is required, but in high-tear self-adhesive membranes the PP fraction is reduced to 60–75 wt% with 25–40 wt% polyester fibre, with the PP function shifting to thermal matrix and dimensional stabiliser. Compliance is structured around EN 13707:2018 for flexible sheets for roofing waterproofing, supported by EN 12311-1:1999 for tensile properties, EN 1849-1:1999 for thickness, and EN 1109:2013 for cold bend temperature. When the membrane is intended for contact with drinking water in some civil structures, additional member-state approvals apply; published data for this specific fibre grade in potable-water contact roofing systems is limited and must be verified at the converter level. Downstream processing includes bale opening, carding, crosslapping, pre-needling at 80–120 punches/cm², then inline thermal bonding at 150–160 °C. The bonded carrier is coated with oxidised bitumen at 170–180 °C; prolonged exposure above 180 °C induces shrinkage in the PP fibre and must be controlled by line speed interlock. Finished products include bituminous roof underlayment, SG tinned roofing membrane carrier, self-adhesive waterproofing membrane reinforcement, and bridge tunnel waterproofing base sheet.