Melt Flow Rate (MFR) is a core indicator of thermoplastic melt fluidity, measured in g/10min (typically at 230℃ and 2.16kg load). Its value directly impacts plastic wire drawing stability, finished product mechanical properties, and production cost control. As two main polypropylene (PP) woven product types, ordinary woven bags (50kg class) and Flexible Intermediate Bulk Containers (FIBCs, 500~2000kg class) vary greatly in MFR selection, control range, and formula adaptability due to their distinct load-bearing and application needs. This article analyzes their core differences and technical logic professionally.

MFR indirectly reflects polypropylene molecular chain length and entanglement: lower MFR means longer chains, tighter entanglement, higher molecular weight, and better tensile strength, impact resistance, weather resistance, and fatigue resistance, but poorer melt fluidity and higher processing demands. Higher MFR improves fluidity and eases processing but reduces mechanical properties.

For PP woven products, wire drawing is MFR-critical: melt fluidity must match the wire drawing machine’s screw speed, die temperature, and cooling speed to ensure uniform flat wire (no breakage or crystal points) and stable weaving/heat sealing. Load-bearing differences between the two products determine their MFR priorities: ordinary woven bags focus on efficiency and cost, while FIBCs prioritize strength and safety.

Ordinary woven bags are used for short-distance bulk packaging (grain, fertilizers, building materials) with a 20~50kg load. They have moderate tensile strength and weather resistance requirements, prioritizing low cost and easy processing, so MFR selection is flexible.

• Typical MFR Range: 2.5~4.0 g/10min, with mainstream grades including T30S (≈3.0 g/10min), 1102K (≈3.4 g/10min), and HP550K (≈4.0 g/10min). These materials balance fluidity and flat wire tensile strength (≥1500N/5cm) to meet 50kg load requirements.
• Recycled Material Adaptability: 10%~40% PP recycled material (e.g., crushed waste woven bags) can be blended, slightly raising MFR to 3.0~5.0 g/10min. This slightly reduces strength but still meets basic needs, lowering costs.
• Processing Adaptability: Simple wire drawing processes allow wide adjustments of screw speed and die temperature. Higher MFR materials reduce processing difficulty, improve efficiency, and cut energy consumption, suitable for small and medium enterprises.

FIBCs transport bulk goods (chemicals, ores, grain) with a 500~2000kg load, requiring a 5:1~6:1 safety factor. They must withstand hoisting, stacking, and transportation impacts, demanding high PP mechanical properties and strict medium-low MFR control.

• Typical MFR Range: Base cloth flat wire uses 2.0~3.5 g/10min (preferably 2.5~3.0 g/10min); slings/webbings (core load-bearing parts) use 2.0~3.0 g/10min. Mainstream grades are low-melt T30S (2.8~3.0 g/10min) and 504PT (≈3.0 g/10min) (high-purity wire drawing PP). MFR＞3.5 g/10min is prohibited due to insufficient strength and fatigue resistance.
• Recycled Material Adaptability: Few or no recycled materials (≤10%, only for non-load-bearing parts) are used to ensure MFR stability, avoid performance fluctuations from impurities or molecular chain breakage, and prevent FIBC tearing.
• Processing Adaptability: Precision wire drawing (strict control of screw speed, die temperature, and cooling) is required for medium-low MFR materials. Despite higher processing difficulty, formed flat wires have tight molecular chains, with tensile strength ≥1800~2000N/5cm and sling breaking strength ≥15000N, meeting high load-bearing needs.

Ordinary woven bags (≤50kg load) have low strength requirements, allowing relaxed MFR and recycled material blending to reduce costs. FIBCs (10~40 times heavier) require low-MFR, high-molecular-weight, high-purity PP to ensure strength and avoid safety accidents.

Ordinary woven bags are for short-term, one-time use in mild environments. FIBCs are for long-term, repeated outdoor use, requiring low-MFR materials (stable molecular chains, strong weather/aging resistance) to extend service life. High-MFR materials embrittle easily outdoors.

Ordinary woven bags prioritize cost, using wide MFR ranges and recycled materials. FIBCs prioritize safety, sacrificing some efficiency and cost for low-MFR, high-purity materials to avoid bulk goods leakage and economic losses.

1. Core Principles and Measured Performance (Test Standards: GB/T 8946-2013 for woven bags; GB/T 10454-2000 for FIBCs):

   Product Type	MFR (g/10min)	Flat Wire Performance			Sling Breaking Strength (N)	Notes
   		Tensile Strength (N/5cm)	Elongation (%)	Modulus (N/5cm)
   Ordinary Woven Bags	2.5	≈1800	≈25	≈7500	-	Recycled materials optional
   	3.0	≈1650	≈23	≈7000	-
   	4.0	≈1500	≈20	≈6500	-
   FIBCs (Base Cloth)	2.5	≥1950	≈22	≈8000	-	High-purity PP
   	3.0	≥1900	≈21	≈7800	-
   	3.5	1580	≈18	≈6200	-	Insufficient strength, MFR＞3.5 g/10min prohibited
   FIBCs (Slings/Webbings)	2.0	-	-	-	≥16500	Meeting 5:1~6:1 safety factor
   	3.0	-	-	-	≥15000

   Supplementary Note: Measured data are based on standard conditions (23℃, 50%RH), conventional wire drawing (die temperature 230~240℃, cooling water 25~30℃), and mainstream PP (T30S, 504PT). Adjustments are required for different materials, processes, and environments.

2. MFR Fluctuation Control: Maintain fluctuation within ±0.5 g/10min for both products. Excessive fluctuation causes uneven flat wire thickness/strength, leading to breakage (woven bags) or tearing (FIBCs).
3. Process Adjustment: For low-MFR FIBC materials, increase die temperature and reduce screw speed for sufficient plasticization. For high-MFR woven bag materials, lower die temperature and increase screw speed to boost efficiency and avoid over-plasticization.

MFR is critical for PP woven products, directly determining performance, safety, and cost. Ordinary woven bags use a wide MFR range (2.5~4.0 g/10min) and recycled materials for cost optimization; FIBCs use stable, medium-low MFR (2.5~3.0 g/10min) and high-purity PP for safe load-bearing. Accurate MFR selection based on load, scenario, and process achieves the best performance-cost balance and promotes industry development.