Sodium Sulfate Filler Masterbatch in Blown Film

2025/02/19 16:41

Introduction: Our "Filler Choice" in LDPE Blown Film

We were originally attempting to optimize cost and physical properties in blown film production, aiming to make trash bags, shopping bags, and industrial packaging films both stronger and more affordable. Initially, we used calcium carbonate filler masterbatch. However, as order complexity increased—particularly with lightweight films (<10μm) and high-speed blown film lines—we discovered some issues.

So we began exploring a relatively unpopular but promising alternative: Sodium Sulfate Filler Masterbatch. This experiment changed our traditional view of filler materials. It taught us that not all fillers are created equal—and more suitable options may lie hidden in unassuming raw materials.

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What is a Filler Masterbatch?

Filler masterbatch refers to a functional plastic additive made by granulating an inorganic mineral core (such as CaCO₃, Na₂SO₄) with a polymer carrier (like PE or PP) and additives. In LDPE blown film, its benefits include:

Reducing raw material costs
Increasing stiffness and rigidity
Reducing shrinkage
Improving printing and heat-sealing
Enhancing film thickness uniformity

Calcium Carbonate vs Sodium Sulfate: What's the Difference?

Physical Property Comparison

Property	Calcium Carbonate (CaCO₃)	Sodium Sulfate (Na₂SO₄)
Appearance	White powder, fine particles	White crystals, harder particles
Density	~2.7 g/cm³	~2.6 g/cm³
Thermal Conductivity	Medium	Slightly higher
Hardness	Low (brittle)	Slightly higher (semi-hard)
Reactivity	Weakly alkaline, stable	Neutral, soluble (stabilized after granulation)
Cost	Low	Slightly higher

Performance Comparison in LDPE Film

1. Blown Film Stability

Calcium carbonate often causes instability at high concentrations. Sodium sulfate provides excellent bubble stability for thin and high-speed blown films.

2. Touch and Hardness

Calcium carbonate results in stiffer films. Sodium sulfate offers elasticity and a smoother surface feel—ideal for thinner, flexible bags.

3. Transparency

Calcium carbonate decreases transparency. Sodium sulfate maintains excellent clarity, even with high filler ratios.

4. Thickness Uniformity

Calcium carbonate may agglomerate and cause uneven film. Sodium sulfate ensures uniform dispersion and smoother extrusion.

5. Recycled Material Compatibility

Both are suitable, but sodium sulfate shows better adaptability in recycled LDPE/LLDPE blends.

Application Recommendations

End Product	Recommended Filler	Dosage
Supermarket Shopping Bags	Calcium Carbonate	10–30%
Trash Bags	Sodium Sulfate	15–40%
Industrial Films	Mixed Fillers	25–35%
Colored Printed Roll Bags	Sodium Sulfate	20–30%
Courier/Parcel Bags	Calcium Carbonate	15–40%
Aquaculture Bags	Calcium Carbonate	20–45%

Cost Analysis

Although sodium sulfate masterbatch costs slightly more per ton, it reduces scrap rate, enhances film processability, and supports higher production speeds—leading to better ROI. In thin films, its benefits are most noticeable:

Less bubble rupture → lower production waste
Improved brightness and touch → higher end-user satisfaction
Compatibility with high-speed machines → fewer stoppages

Environmental Impact: Which Is Greener?

Both are non-toxic and widely available. Calcium carbonate is mined naturally, while sodium sulfate is often recovered from industrial byproducts (e.g., chemical salts), contributing to industrial waste recycling.

In recycled plastics, sodium sulfate's better dispersibility improves recyclability and helps promote circular economy practices.

Conclusion: Not “Expensive,” But “Appropriate”

Choosing the right filler is not about price alone. It’s about selecting what fits your process, film thickness, and application.

Calcium carbonate offers stability and strength; sodium sulfate provides finesse, clarity, and flexibility. For LDPE blown film manufacturers seeking next-level performance—especially in high-speed and thin-gauge lines—sodium sulfate masterbatch deserves a serious look.