Spunbound nonwoven production is one of the most demanding applications for polypropylene resin. A single line may run at 400–600 meters per minute, spinning thousands of filaments simultaneously, with no tolerance for breaks or web defects. Over 15 years of supplying fiber grades to nonwoven manufacturers across Southeast Asia, the Middle East, and beyond, we have seen the same resin-selection questions repeat themselves. This guide distills that field experience into a practical framework for choosing the right PP grade for your spunbound line.
1. What Spunbound Nonwoven Demands from PP Resin
A spunbound line extrudes molten PP through a spinneret, draws the filaments with high-velocity air, lays them onto a moving conveyor, and bonds them thermally. Every stage places specific demands on the resin. The melt must be homogeneous enough to spin without breaks, the filaments must be uniform in denier, the web must lay down evenly, and the final fabric must meet tensile and basis-weight specifications. Resin choice is the single largest variable a plant controls — and it is where most production problems begin.
2. Melt Flow Rate: Why 25–35 g/10min Is the Sweet Spot
Melt Flow Rate (MFR) is the first parameter every nonwoven buyer checks, and for good reason. It governs how easily the polymer flows through the spinneret and how readily it can be drawn into fine filaments. For spunbound applications, the optimal MFR window is 25–35 g/10min (230 °C / 2.16 kg).
Below 25, the melt is too viscous: drawing resistance rises, filament denier increases, and the line cannot reach target speeds without overstressing the polymer. Above 35, the melt flows too easily: melt strength drops, filaments become fragile and prone to breakage under draw air, and fabric tensile strength suffers because the molecular chains are too short to develop adequate orientation. Within the 25–35 window, the polymer balances flowability and melt strength — the foundation of stable high-speed spinning.
3. Molecular Weight Distribution: The Hidden Driver of Uniformity
MFR alone does not tell the whole story. Two resins with identical MFR can behave very differently on the line if their molecular weight distributions (MWD) differ. For spunbound nonwoven, a narrow MWD is essential.
A narrow distribution means the polymer chains are more similar in length. This translates directly into uniform rheological behavior across the spinneret: every filament draws at the same rate, solidifies at the same point, and lands on the conveyor at the same denier. The result is even web formation, consistent basis weight, and balanced machine-direction/cross-direction (MD/CD) tensile strength. Broad-MWD resins, by contrast, produce a mix of long and short chains that draw unevenly — causing denier variation, weak spots, and patchy fabric. Modern metallocenecatalyzed and advanced Ziegler-Natta fiber grades from leading Chinese mills are engineered specifically to deliver this narrow distribution.
4. Matching the Grade to Your Line Speed
Line speed is the deciding factor once MFR and MWD are in range. Different spinneret geometries and draw systems — Reicofil, Oerlikon Neumag, and domestic Chinese lines — impose different shear and draw histories on the melt. The table below maps typical line speeds to recommended MFR targets:
| Line Speed | Recommended MFR | Typical Filament Denier | Notes |
|---|---|---|---|
| 300–400 m/min | 25–28 g/10min | 1.8–2.5 dpf | Lower-speed lines favor slightly higher melt strength |
| 400–500 m/min | 28–32 g/10min | 1.5–2.0 dpf | Balanced window for most general-purpose nonwoven |
| 500–600 m/min | 32–35 g/10min | 1.2–1.7 dpf | Higher MFR eases drawing at high take-up speeds |
| 600+ m/min (SMS lines) | 35–40 g/10min | 1.0–1.5 dpf | Specialty fine-denier; tight die-temp control essential |
The rule of thumb: as line speed increases, push toward the upper end of the MFR window to reduce draw resistance — but never at the cost of melt strength. If breaks rise when you shift to a higher-MFR grade, the distribution has likely widened and a different lot or grade is needed.
5. HP565S: Our Flagship Fiber Grade in Detail
HP565S is the PP fiber grade we ship in the highest volume to spunbound manufacturers worldwide. Produced by leading Chinese mills, it is purpose-built for spunbound and SMS nonwoven applications.
Key Characteristics
- MFR: 25–35 g/10min — squarely in the spunbound sweet spot
- MWD: Narrow, controlled distribution for uniform filament denier
- Low extractables: Suitable for skin-contact hygiene products (diaper top sheets, feminine care) and medical nonwoven
- Lot-to-lot consistency: Tight MFR tolerance keeps spinning parameters stable across shipments
Typical Applications
- Hygiene nonwoven: baby diaper top sheets, acquisition/distribution layers, feminine hygiene
- Medical nonwoven: surgical gowns, drapes, masks (SMS structures)
- Agricultural and industrial: crop cover, geotextiles, furniture backing
- Wipes and disposables: dry and wet wipes, cleaning substrates
Recommended Processing Parameters
| Parameter | Starting Value |
|---|---|
| Extruder melt temperature | 230–250 °C |
| Die temperature | 235–245 °C (maintain within ±2 °C) |
| Draw air temperature | 150–200 °C |
| Calender bonding temperature | 140–150 °C |
| Calender pressure | 80–120 N/mm |
| Drying (optional) | 80 °C, 2–3 hours (removes surface moisture) |
Although PP is non-hygroscopic, a short drying pass is worthwhile on high-speed lines: surface moisture on pellets can flash to steam at the die and cause micro-breaks that do not appear until the fabric is inspected.
6. Troubleshooting Common Spunbound Defects
Even with the right grade, processing issues arise. The table below links the most frequent defects to their likely resin-related causes and the first corrective steps:
| Defect | Likely Resin Cause | First Corrective Step |
|---|---|---|
| Filament breakage / line stops | MFR too high (low melt strength) or contamination | Verify MFR against spec; inspect melt filter for gels/contaminants |
| Fly / dripping at die | MFR too low for line speed, or die temperature too low | Raise die temperature 5 °C; confirm MFR is in the 25–35 window |
| Uneven fabric / basis-weight variation | Broad MWD, or MFR drift between lots | Request MWD data; quarantine lot; switch to consistent supplier |
| Low MD tensile strength | Insufficient draw / molecular orientation | Increase draw air velocity; verify MFR is not too high |
| Weak CD strength / poor bonding | Calender temperature or pressure too low for resin crystallinity | Raise calender temperature 5–10 °C; check bonding pressure |
7. Conclusion: A Simple Selection Checklist
Choosing a PP grade for spunbound nonwoven comes down to four questions. Is the MFR in the 25–35 g/10min window? Is the molecular weight distribution narrow and consistent lot-to-lot? Does the MFR target match your line speed? And does the grade meet the extractables and compliance requirements of your end-use? When all four answers are yes, the line will run clean. HP565S is our recommendation for the majority of spunbound and SMS applications because it answers yes to all four — and because we have validated it across hundreds of shipments to nonwoven plants worldwide.
If you are running a Reicofil, Oerlikon, or domestic Chinese line and want to benchmark your current grade against HP565S, share your line type, target gsm, and monthly volume. We will provide tuned starting parameters drawn from comparable installations.