Correlation between UV Masterbatch and Melt Flow Index

1.Melt Flow Index Definition

Melt Flow Index (MFI) is a core indicator for measuring the fluidity of thermoplastic melts. It is defined as "the mass of the melt passing through a 2.095mm diameter die in 10 minutes under standard temperature and load (unit: g/10min)."

2. Melt Flow Index Test Principle

The test follows ASTM D1238 or ISO 1133 standards and has three steps:

1) Heat the plastic particles to a specified temperature (e.g., 230°C for PP and 190°C for PE);

2) Apply a standard weight (commonly 2.16 kg );

3) Measure the weight of the melt extruded within 10 minutes. This requires a regularly calibrated melt indexer.

3. Correlation between UV Masterbatch and Melt Flow Index

The core function of Ultraviolet stabilizer masterbatch: By adding UV absorbers (such as benzotriazoles) or light stabilizers (such as hindered amines), it extends the outdoor service life of plastic products (e.g., passing the QUV 1000-hour weathering test).

MFI Requirements:

High MFI substrates (e.g., 8-15 g/10 min): Tailored to lightweight injection/blown film fabrication (such as PET film), compensating for the loss of flowability caused by additives.

Medium-low MFI substrates (2-6 g/10 min):Utilized in extrusion operations such as woven bags and shade nets, ensuring tensile strength.

4. Mechanisms of the Impact of Melt Flow Index on UV Blocking Masterbatch Performance

1)Impact of Additive Content

When the dosage of UV absorbers or light stabilizers exceeds 5%, the MFI of the substrate resin must be increased by 10%-20% to compensate for the melt fluidity reduction caused by additives. For example: If pure PP resin has an MFI of 10 g/10min, after adding 6% benzotriazole-based absorber, a substrate with MFI ≥12 g/10min should be selected.

2) Processing Temperature Sensitivity

High-temperature-resistant additives (such as hindered amine light stabilizers) should be used to ensure stable performance at an MFI test temperature ≤ 240°C. For example, a UV-resistant masterbatch (MFI = 5g/10min) for a certain car bumper must withstand injection molding temperatures of 220-240°C.

3) Dispersion Requirements

If the additive has good compatibility with the resin, conventional dispersion can meet the requirements. However, attention should still be paid to melt flow uniformity (e.g., MFI fluctuation ≤ 5%).

Industrial Example: Uniform dispersion of HDPE Anti-UV masterbatch for sunshade netting is achieved through twin-screw extrusion.