A woven sack tape line runs on a polypropylene homopolymer with a melt flow rate near 3 g/10 min (230 °C / 2.16 kg) and an isotactic index above 95%. That single sentence narrows thousands of commercial PP grades to a handful.
The melt-flow number is the easy part. Every certificate prints it. The harder question is what the certificate does not print, and why two grades quoting the same melt flow can behave differently at the draw stand.
What Qualifies a Homopolymer as a Raffia Grade
Homopolymer, not a random or impact copolymer, is the resin family because the tape needs crystallinity for draw strength. Copolymer ethylene units dilute that crystallinity, so copolymer grades belong in pipe or packaging film, not in a tape line.
Melt flow is the gatekeeper. Trader pages publish a 2 to 5 g/10 min band, but real certificates cluster tighter:
| Grade | Producer group | Melt flow spec | Method |
|---|---|---|---|
| S1003 | CHN Energy / China Shenhua | 3.0 +/- 0.5 g/10 min | printed on TDS |
| L5E89 | Datang Inner Mongolia Duolun | 3.5 +/- 0.5 (lot 3.4) | GB/T 3682.1-2008 |
| T30S | Sinopec | 2.5 to 3.7 | GB/T 36820 |
The recovered certificates centre on 3.0 to 3.5 g/10 min. A grade quoting 5 g/10 min is still inside the published band, but no recovered certificate sits that high.
Isotactic index is the second row. Specs range from 95.0% (L5E89) to 97.6% or higher (T30S), all tested by GB/T 2412.
Higher isotacticity raises crystallinity and draw strength, but it also stiffens the melt. The right figure depends on where inside the draw-ratio range the line operates.
Ash content is the third row, measured by GB/T 9345.1. Specs run from 115 mg/kg to 500 mg/kg across the grades in this set.
Higher ash means more catalyst residue, which shows up as “hold-up particles in film” on a tape-plant fault table. That residue feeds breakage or gel defects at the slitter.
Why Two Grades at the Same Melt Flow Draw Differently
Molecular-weight distribution (MWD) is what separates two same-melt-flow grades, and it does not appear on any of the certificates above. A resin producer’s own patent (US11845816B2, TotalEnergies, 2023) states that its polypropylenes differ in MWD, xylene solubles, and molecular weight “at similar MFI.” The patent specifies the MWD window as Mw/Mn between 2.0 and 2.9.
MFI alone does not tell you whether a grade will draw clean. You also need molecular-weight distribution data.
How Tenacity Responds to Draw Ratio
Tenacity peaks near a 7:1 draw ratio. Patent examples (EP2084316A1, Fina Technology, 2009) report 8.1 g/denier at 7:1, 7.9 at 8:1, and 7.8 at 9:1, against a stated commercial baseline of 4 to 6 g/denier.
More draw is not monotonically more strength. A second patent (US11845816B2) claims at least 45 cN/tex (roughly 5.1 g/denier) at draw ratios of 2 to 12, and at least 50 cN/tex at 5 to 7. These are patent-example figures, not production-line data.
Which MWD direction the line wants depends on what it optimises. The high-tenacity patents use metallocene and specialty compositions with narrow MWD.
Producer-side raffia guidance lists “moderately broad molecular-weight distribution” as a desirable characteristic for Ziegler-Natta grades. The breadth trades some tenacity for melt strength and stable die running.
When the Tape Splits
On the tape-plant fault table, “very stiff film” and “too soft film” are the two resin-side handles for tape breakage and low tenacity. Both map back to where inside the MWD and melt-flow window the grade sits.
Denier variation has no resin-side cause listed at all. Attribute the splitting to the resin only after the orientation oven profile, godet speed ratio, and stretch ratio have been checked.
A tape line trying to run a PP-R pipe grade would not extrude a castable film. The specification axis for pipe is hydrostatic pressure class, not tape tenacity.
How to Verify a Quoted Polypropylene Raffia Grade Before Ordering
A grade code on a quote is a producer namespace, not a property guarantee. The published S1003 technical data sheet is headed CHN Energy / China Shenhua and cites INEOS horizontal-kettle gas-phase technology.
The same sheet carries a standardised designation, PP-H,T,130-45-030, whose trailing 030 tracks the 3.0 g/10 min melt flow. PP S1003 in the PetroChina KUNLUN channel is the same grade code from a different producer. One trade code, at least two producers.
Grade Code vs Property Claim
T30S is another example: Sinopec sells it as a raffia grade, and marketplace listings from other regions describe it the same way. The code tells you a producer’s catalogue slot. The certificate tells you the lot.
The “why not this one” question answers itself with a number. PP grade S2025, also PetroChina KUNLUN brand, quotes a melt flow of 22.4 g/10 min at a near-identical isotactic index of 97.7%.
Isotacticity alone does not make a raffia grade. S2025 is a BCF yarn grade for carpet, designed for spinneret extrusion at high throughput.
What the Certificate Confirms and What It Misses
Chinese certificates carry isotactic index by GB/T 2412, not xylene solubles. Xylene solubles (0.5 to 0.8 wt%) and mmmm pentad content appear on Western datasheets and patents. These are three metrics for the same underlying property.
Before comparing two isotacticity figures from different documents, confirm whether both cite the same edition of GB/T 2412. The 1980 and 2008 editions appear on real paperwork.
The certificate does not measure molecular-weight distribution, draw ratio, or tape tenacity. A buyer holding two certificates at the same melt flow cannot tell from the paper which grade draws better.
Ask the supplier for MWD data, or at minimum ask what tenacity other tape lines have achieved on the same lot. When swapping to a second source at the same nominal melt flow, run a trial spool at the target draw ratio before committing the lot to production.
What This Means in Practice
Start with the melt-flow band, not the grade code. Any homopolymer quoting 2.5 to 4.0 g/10 min at 230 °C / 2.16 kg with an isotactic index above 95% is in the raffia window.
The grade code tells you which producer made it. The certificate tells you which lot you are buying. Neither tells you how the tape will draw.
The COA gives you four numbers; the spec sheet gives you the window; the application tells you which corner of the window you actually need. Ask the supplier for the MWD data before releasing a container-load order.