Polypropylene (PP) raffia grade for woven bags, FIBC & ropes is a high-stiffness, controlled-crystallinity resin formulated specifically for flat-tape extrusion and subsequent uniaxial orientation. The melt mass-flow rate is generally held between 2.5 g/10 min and 4.0 g/10 min when tested in accordance with ISO 1133-1:2022 at 230°C/2.16 kg. Supplier technical datasheets commonly report a density of 0.905–0.910 g/cm³ under ISO 1183-1, tensile yield stress of 33–37 MPa under ISO 527-2, flexural modulus of 1,450–1,650 MPa under ISO 178, notched Charpy impact strength of 4.0–6.0 kJ/m² under ISO 179-1/1eA, and Vicat softening temperature of 152–155°C under ISO 306/A50. The raffia variant differs from general-purpose injection-molding PP by its higher melt strength and narrower molecular weight distribution, both of which reduce draw resonance and improve tape gauge uniformity during stretching. Antioxidant packages based on hindered phenol and phosphite chemistries are typically added in the range of 0.05–0.15 wt% to stabilise the melt during multiple heat histories and to limit chain scission in high-shear extrusion.

Why Does Narrow Molecular Weight Distribution Control Tape Draw Stability?

Draw stability in raffia tape orientation is governed by extensional viscosity, molecular weight distribution, and quench-induced crystallinity. On a single-screw extruder with a 90 mm screw and 32:1 L/D ratio, melt temperature is normally maintained between 240°C and 260°C. The water bath quench is held at 30–40°C; a higher quench temperature reduces crystallinity and lowers orientation-induced tensile strength, while a lower bath temperature can generate skin-core morphology differences and surface roughness. The orientation ratio is maintained between 6.0:1 and 8.0:1. At draw ratios below 5.5:1, tape tensile strength frequently falls below 25 MPa, whereas ratios above 8.5:1 increase fibrillation and web splitting. A narrow molecular weight distribution, typically described by a polydispersity index below 4.0, supports stable drawing because low-molecular-weight fractions do not plasticise the oriented web and high-molecular-weight fractions do not form excessive gel particles. Converter records from high-output tape lines describe draw resonance as cyclic variation in tape width exceeding ±0.2 mm on a target width of 2.5 mm. Once draw resonance begins, it propagates into circular loom warping as tension variability and increases end breaks.

In woven sack manufacturing, flat tape is slit from an oriented film web and wound onto beams for circular looms. A typical tape width for cement, fertiliser, or petrochemical sacks is 2.5–3.5 mm in warp and 2.0–3.0 mm in weft, with fabric areal weight between 55 g/m² and 90 g/m². Tape tensile strength is specified at 30–38 MPa according to ISO 527-3, with elongation at break between 15% and 25%. Warp tension must be controlled within narrow limits because PP tape exhibits viscoelastic creep at ambient temperature; excessive creel tension causes permanent elongation before weaving and reduces fabric dimensional stability. Fabric strip tensile properties are verified under ISO 13934-1, and seam strength of bottom and top closures is tested under ISO 13935-1. When woven sacks require moisture resistance, extrusion coating with low-density polyethylene at 15–25 g/m² is applied after corona treatment above 38 mN/m measured by ASTM D2578. The coating process exerts additional thermal load on the PP substrate, making stabiliser selection and regrind control critical to prevent delamination and seam failure.

When a Flexible Intermediate Bulk Container Is Designed for a Safe Working Load of 1,250 kg

FIBC fabric requires a heavier denier tape than commodity woven sacks. Base fabric weight commonly falls between 160 g/m² and 220 g/m², with tape width in the range of 3.5–4.5 mm. Safe working load certification to ISO 21898 requires top-lift testing at a safety factor of 5:1 for single-trip designs and 6:1 for reusable designs. Under such loading, stress concentrates in the lifting loops and seam junctions; therefore PP raffia grade for FIBC must retain impact strength after multiple extrusion and weaving heat histories. Notched Charpy impact values below 4.0 kJ/m² at 23°C under ISO 179-1/1eA are considered insufficient for cold-climate FIBC handling because loop attachment zones become crack-sensitive during drop testing.

For outdoor exposure, UV stabilisation packages for FIBC are based on hindered amine light stabilisers at 0.15–0.40 wt%, combined with an ultraviolet absorber at 0.05–0.20 wt%. Xenon-arc aging per ISO 4892-2 method A for 1,500 h typically requires retained tape tensile strength of at least 70%. Incompatibilities arise when low-quality carbon black masterbatch containing acidic residues is used with hindered amine stabilisers because the acidic sites can deactivate the amine chemistry. PP raffia grade for FIBC must therefore be certified with a defined antioxidant and HALS package, and regrind from UV-exposed fabric should be limited because partially consumed stabiliser systems do not provide the same protection as virgin resin.

Rope-grade raffia PP is processed into fibrillated tape, split-film yarn, or monofilament depending on rope construction. Twisted and braided constructions are evaluated for breaking force and elongation under ISO 2307:2019. Marine and agricultural ropes use a tape tenacity of 5.0–6.5 gf/denier after orientation, with free shrinkage at 130°C below 3.0% measured by ASTM D2732. Carbon black masterbatch is added at 2.0–2.5 wt% for ultraviolet protection in long-service outdoor ropes, but agglomerate size must remain below 20 µm to avoid surface fissures under repeated bending. Rope-grade formulations typically require a slightly lower melt mass-flow rate than woven-tape grades because the fibrillation step demands higher melt strength and controlled molecular orientation. Braided PP rope shows lower knot strength than straight tensile breaking force; stress concentration at the knot reduces retained strength to approximately 45–60% of the straight value, and this reduction is accounted for in working-load ratings.

On high-output tape lines producing 500 kg/h of 2.5 mm tape on a 1,600 mm slot die, melt temperature and quench stability dictate production yield. Surface moisture on pellets above 0.10 wt% after outdoor storage in high-humidity conditions causes pinholes and local die-lip build-up; hopper drying at 80°C for 2–4 h is recommended before extrusion. Melt temperature above 280°C accelerates thermo-oxidative degradation, resulting in yellowing, gel formation, and cross-direction tape splitting. Melt temperature below 235°C increases orientation stress and draw breaks. Recycled raffia PP regrind can be used up to 20 wt% after dust removal and screen filtration through 250 mesh, but higher regrind fractions reduce tape tenacity by 4–8% and increase gauge variation. Published data for this specific line configuration is limited; converter qualification is required before regrind levels exceed the stated boundary.

Physical Property and Compliance Matrix for Oriented PP Tape

The following tables summarise typical property windows and compliance designations used in converting-equipment qualification. Values are drawn from supplier datasheets and converter acceptance protocols; variations occur with additive package, draw ratio, and tape denier.

Compliance for the three application classes is structured around the following test designations and acceptance parameters.

Converter failure records show three recurring process faults: tape width variation from draw resonance, web splitting from excessive orientation or gel contamination, and seam strength loss from low-molecular-weight additive exudation. In a six-shuttle circular loom running at 700 rpm, warp tape tension variation above ±10% increases end breaks by approximately 2–3 per 10,000 picks and creates visible stop marks in the fabric. For FIBC, inconsistent tape denier causes local weak points that fail cyclic top-lift testing under ISO 21898 at 70% of minimum break force. For rope, inadequate dispersion of carbon black below 20 µm agglomerate size can reduce abrasion resistance and initiate surface fissures under repeated bending.