| HS Code | 113735 |
| Material | Polypropylene |
| Fibertype | Staple fiber |
| Fineness | 1.5-15 dtex |
| Length | 38-90 mm |
| Tenacity | 3.0-7.0 cN/dtex |
| Elongationatbreak | 20-60% |
| Density | 0.90-0.91 g/cm³ |
| Meltingpoint | 160-170 °C |
| Softeningpoint | 150-160 °C |
| Continuousservicetemperature | 90-100 °C |
| Shorttermheatresistance | 130 °C |
| Chemicalresistance | Good to acids and alkalis; excellent to most organic solvents; poor to oxidizing agents and chlorinated hydrocarbons |
| Waterabsorption | <0.1% |
| Moistureregain | 0.01-0.1% |
| Hydrophobicity | Hydrophobic |
| Microorganismresistance | Excellent |
| Uvresistance | Poor unless UV stabilized |
| Crimp | 8-20 crimps/25 mm |
| Crimpelasticity | >90% |
| Oilcontent | 0.5-1.5% |
| Thermalshrinkage | <5% at 100 °C |
| Abrasionresistance | Good |
| Electricalconductivity | Insulating; antistatic variants available |
| Color | White, natural, black, or custom |
As an accredited PP Staple Fiber for Filtration Bags & Liquid-Solid Separation factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | PP staple fiber is packed in 20 kg woven bags or 250 kg compressed bales, wrapped and palletized for shipping. |
| Container Loading (20′ FCL) | 20′ FCL containing PP staple fiber for filtration bags and liquid-solid separation, palletized, shrink-wrapped, and securely loaded for chemical export. |
| Shipping | PP staple fiber for filtration bags and liquid-solid separation is shipped in moisture-resistant bales or woven bags, palletized and shrink-wrapped. It is non-hazardous, requiring no UN classification. Transport in clean, dry containers or trucks. Store in a dry, ventilated area away from heat, moisture, and contamination. |
| Storage | Store PP staple fiber in a dry, clean, well-ventilated warehouse, away from direct sunlight, moisture, heat, and ignition sources. Keep in original packaging on pallets, off the floor and away from walls. Avoid contact with oils, acids, alkalis, and strong chemicals. Maintain moderate temperature and humidity, and use first-in, first-out stock rotation. Protect from UV degradation and physical damage. |
| Shelf Life | Shelf Life: 24 months in original packaging when stored dry, cool, ventilated, away from direct sunlight, moisture, heat, and contamination. |
Liquid process filtration in plating, phosphating, acid transfer, and alkali transfer lines uses needlepunched polypropylene staple felt because the fiber network provides a tortuous depth-filtration path that retains particles below the surface while maintaining cake-release properties. The compliance set includes ISO 16889:2022 for multipass filter performance evaluation, ISO 9073-1 for mass per unit area of nonwovens, ISO 9073-3 for breaking strength, ISO 9073-4 for tear resistance, and, where the filter bag contacts food-processing streams, FDA 21 CFR 177.1520 for olefin polymers. The PP staple addition ratio is commonly specified at 100 wt% virgin homopolymer staple, or 85–100 wt% PP staple with 0–15 wt% polyethylene/polypropylene bicomponent binder fiber when low-temperature thermal bonding is required alongside needlepunch consolidation. Raw fiber linear density is selected from 2.2 dtex to 6.7 dtex because higher denier increases void volume but lowers particle retention uniformity; crimp count is set at 12–16 crimps per 25 mm to maintain card cohesion. Downstream bag manufacturing begins with bale opening, coarse carding on a single-cylinder card at 2.5–3.5 m working width, cross-lapping to a basis weight of 500–650 g/m², needle punching at 200–350 punches/cm², and heat setting at 130–140 °C for 3–5 min to stabilise the pore structure. The felt is then rotary die-cut and ultrasonically welded into standard #1 and #2 filter bag sleeves with polypropylene collar rings. Terminal product types include needlefelt liquid filter bags for acids, caustic, plating solutions, and water-based coatings with retention ratings from 1 μm to 100 μm. Operational boundaries are set by polypropylene chemical resistance: the fiber is not specified for strong oxidising acids above 10% concentration at temperatures above 40 °C, for chlorinated solvents above 25 °C, or for continuous UV exposure exceeding 6 months without UV-stabilised grades.
In dredged sediment and municipal sludge dewatering, the tube filler contract specification often requires a nonwoven geotextile fabric with an apparent opening size small enough to retain fine solids under hydraulic pressure but large enough to allow drainage within a contract dewatering cycle. For these geotextile tubes, the PP staple addition ratio is typically 100 wt% UV-stabilised polypropylene staple, with fabric mass per unit area between 500 g/m² and 800 g/m². Conformity assessment follows ISO 10319:2015 for wide-width tensile testing, ISO 11058:2010 for water permeability characteristics normal to the plane, and ASTM D4533-11 for trapezoidal tear resistance. Where the fabric is placed on European civil engineering projects, the product falls under EU Construction Products Regulation (EU) No 305/2011. Downstream production converts carded and cross-lapped staple webs through needlepunch lines operating at 180–300 punches/cm², followed by heat setting at 130–145 °C to control shrinkage during tube filling. The finished fabric is cut into panels and sewn with high-tenacity polyester or polypropylene thread into tube lengths of 5–50 m, with fill ports spaced according to pump discharge design. Terminal finished product types include geotextile dewatering tubes, sludge consolidation bags, dredge spoil containment cells, and filter container bags for cement slurry. Field failure experience shows that sewn seam integrity is the primary processing bottleneck: geotextile tube ruptures commonly initiate at seams when stitch density drops below 2.5 stitches per 25 mm, so fabricators specify seam efficiency of at least 50% of fabric tensile strength under ISO 10319. Published data for site-specific dewatering performance is limited because slurry particle-size distribution and pump head vary; fabric selection therefore requires bench-scale cone tests or full-scale geotextile tube fills rather than reliance on nominal AOS values alone.
Beverage clarification, juice pre-filtration, and edible oil polishing lines specify polypropylene staple needlefelt as a substitute for cellulose sheet media where wet strength loss and fiber sloughing are unacceptable. The applicable food-contact compliance regime is FDA 21 CFR 177.1520 for PP homopolymer plus EU Regulation 10/2011 and EC 1935/2004 for overall food-contact material safety; extractive testing is conducted according to the EN 1186-1 series or specified migration limits in EU 10/2011. The PP staple addition ratio is maintained at 100 wt% virgin PP staple, with no post-consumer or regrind content, because batch-to-batch traceability is required under food-contact declarations. Production of the filtration medium uses carded staple webs cross-lapped to 300–500 g/m², needle punched at 150–250 punches/cm², and calendered at 120–140 °C under a linear load of 60–120 N/mm to reduce surface fiber release. The calendered roll is die-cut into discs, sheet packs, or bag sleeves depending on downstream module design. Terminal finished product types include lenticular filter modules, plate-and-frame sheet filter pads, filter bag inserts for wine and juice clarification, and pre-filter media in edible oil polishing housings. The operational boundary is wet processing only; dry exposure to peroxides or strong oxidising cleaners above 50 °C can embrittle the PP fiber surface and should be avoided.
When a plate-and-frame filter press is fitted with woven polypropylene monofilament cloth, the fine-particle retention ceiling is often limited by the open area of the weave, and process operators add needled PP staple fiber media as a precoat or support layer to capture fines that would otherwise pass through the cloth. In this configuration, the PP staple addition ratio in the media layer is 100 wt% PP staple, with fabric mass per unit area specified between 450 g/m² and 650 g/m². Mechanical integrity compliance includes ISO 9073-3 for breaking strength, ISO 9073-4 for tear resistance, ASTM D5034-21 for grab tensile, and ISO 12956 for wet-sieve apparent opening size. Downstream processing consists of carding, cross-lapping, needle punching at 200–300 punches/cm², and heat setting at 135–145 °C; the fabric is then slit to belt widths from 1.2 m to 2.2 m and fitted with welded or clipper seams. Terminal finished product types include vacuum belt filter media, plate-and-frame filter press support media, drum filter panels, and mining tailings dewatering cloths. The operational ceiling for PP staple media is 90 °C in water-based slurries; aromatic solvents, strong oxidising agents, and high-chlorine liquors require alternative fiber chemistry.
Oil spill recovery sorbents and oil-water separator coalescing media require a hydrophobic, oleophilic fiber matrix that retains buoyancy after prolonged contact with water. The relevant industry compliance standard for sorbent performance is ASTM F726-17, and physical property controls include ISO 9073-1 for mass per unit area and ISO 9073-2 for thickness. The PP staple addition ratio is held at 100 wt% PP staple, with no water-absorbing cellulosic fiber and no hydrophilic binder, because water uptake reduces oil capacity and floatability. Downstream production uses carded staple webs consolidated by needle punching at 80–150 punches/cm² to a basis weight of 200–450 g/m², followed by cutting into pads, filling sewn polypropylene skins, or spiral-winding into coalescing cartridges. Terminal finished product types include oil-only sorbent pads, booms, socks, sweeps, and coalescing media inserts for industrial oil-water separators. The operational boundary is that PP staple sorbents are designed for free-phase oil and not for dissolved or emulsified oil fractions; recovery efficiency for emulsified oil requires a downstream coalescer with sufficient residence time and pressure drop.
In vacuum belt filtration of machine tool coolant, the media roll width is matched to the belt index of the filter unit, and the PP staple felt must resist mineral oil, water-miscible cutting fluid, and tramp oil while maintaining a stable pressure drop. Coolant filtration lines specify a PP staple addition ratio of 100 wt% PP staple, with fabric basis weight from 300 g/m² to 500 g/m² measured under ISO 9073-1 and thickness from 1.5 mm to 2.5 mm measured under ISO 9073-2. Filtration efficiency can be assessed using ISO 16889:2022 multipass testing for hydraulic fluids, while system cleanliness is expressed using ISO 4406:2017 particle size classes. Downstream media production utilises carded web cross-lapping, needle punching at 100–180 punches/cm², and optional calendering to produce a smooth surface for filter cake release; the roll is slit to widths of 500–1500 mm for belt filter installations. Terminal finished product types include vacuum belt filter rolls, gravity bed filter media, pressure belt filter media, and coolant filter bag sleeves. The primary operational boundary is media blinding when tramp oil and fine metal particles form a viscous cake; media selection requires laboratory filtration trials because published data for this specific configuration is limited.
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Polypropylene staple fiber for filtration bags and liquid-solid separation is manufactured in linear densities from 2.2 dtex to 15 dtex and cut lengths from 38 mm to 110 mm. The fibre is circular in cross-section, with a density of 0.90–0.91 g/cm³ (ISO 1183) and a melting point of 160–165 °C. Moisture regain remains below 0.1 % at 20 °C and 65 % RH. Available configurations include PP-SF-2.2/51, PP-SF-3.3/64, PP-SF-6.7/76 and PP-SF-15/90, each differentiated by linear density, staple length and crimp frequency. The product is used in needlepunched filter bags, cartridge support layers and filter press cloths in chemical clarification, wastewater treatment, pharmaceutical intermediate recovery and food and beverage processing. The main functional difference from polyester and polyamide is the combination of low density, broad acid and alkali tolerance and very low moisture absorption, with the stated limitation of a lower thermal service ceiling.
Representative physical properties are tested per ISO 1973 for linear density, ISO 5079 for tenacity and elongation, ISO 4912 for crimp frequency and ISO 1183 for density. The base resin melt flow rate is controlled at 14–18 g/10 min at 230 °C/2.16 kg (ISO 1133-1). Spin finish content is maintained at 0.15–0.35 % by mass to balance carding performance against extractables. Batch-to-batch variation in crimp frequency beyond ±1 crimp/cm can shift card web density and final felt basis weight; mill trials therefore specify crimp frequency rather than staple length alone.
| Configuration | Linear density (ISO 1973) | Staple length | Crimp frequency (ISO 4912) | Tenacity (ISO 5079) | Elongation at break (ISO 5079) | Typical felt basis weight (ISO 9073-1) |
|---|---|---|---|---|---|---|
| PP-SF-2.2/51 | 2.2 dtex | 51 mm | 11–13 crimps/cm | 4.0–5.0 cN/dtex | 35–55 % | 250–450 g/m² |
| PP-SF-3.3/64 | 3.3 dtex | 64 mm | 10–12 crimps/cm | 3.8–4.8 cN/dtex | 40–60 % | 300–500 g/m² |
| PP-SF-6.7/76 | 6.7 dtex | 76 mm | 9–11 crimps/cm | 3.5–4.5 cN/dtex | 45–65 % | 350–600 g/m² |
| PP-SF-15/90 | 15 dtex | 90 mm | 8–10 crimps/cm | 3.2–4.2 cN/dtex | 50–70 % | 500–800 g/m² |
For fine-particle retention, the 2.2 dtex/51 mm grade gives a denser card web and smaller mean flow pore diameter after needlepunching; the 15 dtex/90 mm grade is limited to coarse filtration and precoat support layers where strength and cake release dominate. The values in the table are not absolute; felt properties also depend on needling density, calender gap and upstream carding quality.
Below 40 % RH, hydrophobic PP generates static charge during carding. An antistatic spin finish of 0.10–0.20 % by mass is available for dry processing conditions; the standard hydrophobic finish is preferred for food-contact media because of lower extractables.
In needlefelt production, the thermal bonding step imposes a narrow processing window because polypropylene begins to soften at about 155 °C and melts at 160–165 °C. Oil-heated calender rolls are typically operated at surface temperatures of 145–158 °C, with a nip pressure of 40–80 N/mm and a gap of 0.15–0.30 mm. At roll temperatures below 142 °C, fibre-to-fibre fusion remains incomplete, and the felt delaminates during backpulsing or cake discharge. At temperatures above 160 °C, the web can adhere to the roll, creating pinholes and hard spots that reduce filtration efficiency. Production lines therefore require calender roll surface temperature control of ±1 °C and infrared pyrometry across the roll face. When 3.3 dtex/64 mm fibre is needled at 120–160 punches/cm², the felt before calendering typically shows a mean flow pore diameter of 15–25 µm by capillary flow porometry (ASTM F316-03). After calendering under the conditions above, the mean flow pore diameter shifts to 8–15 µm, and air permeability at 200 Pa falls from 120–180 L/m²/s to 60–110 L/m²/s (ISO 9237). These changes are used to set the nominal retention rating of the filter bag. A processing conflict exists between achieving low pore size and preserving the loft needed for high flow; excess calendering closes the surface and produces a dense, low-permeability skin that increases pressure drop without improving particle retention.
Static charge generation during carding of hydrophobic PP below 40 % RH causes web wrap on the doffer and uneven batt laydown. Conditioning to 50–60 % RH and using antistatic finish reduce the effect, but pre-drying is not required because PP absorbs no bulk moisture. Card clothing with 6–8 points/cm² and cylinder speeds below 120 m/min are used for fibre below 3.3 dtex to limit nep formation. These process constraints are observed on production-scale carding lines with working widths from 1.5 m to 3.0 m.
Unlike PET and PA66, polypropylene does not absorb process water and does not hydrolyse in wet service. Its density is approximately 34 % lower than PET and 20 % lower than PA66, which reduces filter element mass at equal fabric thickness. PET can operate at higher temperatures but is susceptible to alkaline hydrolysis above pH 9, while PA66 swells in humid environments and is attacked by mineral acids. The comparative table below summarises the main fibre properties relevant to filter bag design.
| Property | PP staple fiber | PET staple fiber | PA66 staple fiber |
|---|---|---|---|
| Density (ISO 1183) | 0.90–0.91 g/cm³ | 1.38 g/cm³ | 1.14 g/cm³ |
| Melting point | 160–165 °C | 250–260 °C | 255–265 °C |
| Moisture regain at 20 °C/65 % RH | <0.1 % | 0.4 % | 4.0–4.5 % |
| Wet continuous service limit | 80–90 °C | 120–140 °C | 100–120 °C |
| Acid resistance | pH 1–14 stable at 25 °C | good at pH 4–8 | poor below pH 3 |
| Alkali resistance | good | hydrolyses above pH 9 | good at ambient |
| Hydrolytic stability in wet service | excellent | susceptible | moderate |
Selection of PP over PET in pharmaceutical filtration is sometimes made on extractables grounds. Some PET grades contain antimony trioxide as a polycondensation catalyst; PP produced with Ziegler-Natta or metallocene catalysts may show lower extractable metal content, but published data for specific catalyst residues is limited and should be verified lot-specific.
Polypropylene staple fiber is not compatible with strong oxidizing agents. In immersion tests, PP staple fiber exposed to 5 % sodium hypochlorite at 40 °C shows surface crazing and tensile strength loss of 40–60 % within 72 h when measured by ISO 5079. At 10 % hypochlorite and 60 °C, significant embrittlement is observed within 24 h. Ozone-containing streams cause chain scission and embrittlement; published data for specific ozone concentrations in filter bags is limited. Aromatic and chlorinated solvents swell polypropylene significantly above 60 °C, and continuous exposure to toluene at 80 °C can soften the fibre and collapse the needlefelt pore structure. For these conditions, fluoropolymer or polyamide fibre may be required. Concentrated sulfuric acid at 98 % and 25 °C can slowly sulfonate the surface, whereas 10 % sulfuric acid at 40 °C is generally acceptable for continuous service. The operational boundary of PP staple fiber is therefore defined not by a single pH value but by oxidant concentration, temperature and solvent type.
In non-oxidizing mineral acid and alkali service, PP staple fiber retains sufficient strength for filtration. It is widely used in spent caustic clarification, acid mine drainage lime precipitation and metal hydroxide slurries at pH values from 2 to 12 and temperatures below 60 °C. At higher pH with calcium hydroxide, calcium scaling on fibres can reduce flux; surface modification or regular acid cleaning is required. Published data for long-term exposure in these systems is limited.
Compliance for food contact is generally established under FDA 21 CFR 177.1520 for olefin polymers when the base resin and additives meet the prescribed extractable limits. In the European Union, final filter media must comply with Regulation (EU) No 10/2011 on plastic materials intended to come into contact with food, including overall migration limits of 10 mg/dm². Filter bags used in potable water and food processing may also be required to meet NSF/ANSI 42 or NSF/ANSI 61; these certifications are product-specific, not fibre-specific. PP staple fiber can be supplied with low-finish or food-grade finishes to reduce total extractables, but the final article must be tested after needlepunching, calendering and welding because process heat and lubricants can add extractable material.
Under REACH, suppliers must provide SVHC declarations for substances of very high concern. The fibre is also typically supplied free of APEO surfactants and phthalate plasticisers, but these are supplier-specific. The user should verify final filter bag compliance against ISO 10993 if the application extends to bioprocessing, because the fibre itself is not a medical device and final sterilisation validation is required.
For filter bag fabrication, the choice of sewn or welded seams changes the effective filtration area and bypass risk. Sewn seams using PP thread can introduce needle holes, so high-purity liquid-solid separation frequently uses hot-wedge welded seams or ultrasonic welds. Fabricated bags operate in housing differential pressures up to 1.5–2.0 bar depending on bag size and support basket design. Standard PP felt is not recommended for direct steam sterilisation above 100 °C because softening and shrinkage can exceed 3 %; for steam sterilisation cycles, a higher-temperature fibre or autoclavable design is required. The product is compatible with cake discharge by reverse air or mechanical shaking, but long-term cycle life depends on the stiffness loss caused by repeated flexing. Published data for cycle life of specific PP filter bags is limited; qualification trials should be run on the actual slurry and cleaning sequence.
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