Light Stabilizers 119 Mixing Issues: A Real Case Study from a South African Customer

Light Stabilizers 119 Mixing Issues: A Real Case Study from a South African Customer

Light stabilizers play a critical role in extending the service life of plastic products by protecting polymers from UV degradation and thermal aging. Among them, Light Stabilizer 119 (LS 119) is widely used in polyolefins and engineering plastics due to its excellent long-term heat stability and low migration behavior.

However, even high-performance light stabilizers can present processing challenges if the mixing equipment or operating conditions are not well matched to their physical properties.

In this article, we share a real application case from our South African customer, Ricc, who encountered compaction and caking issues when mixing Light Stabilizers 119 in a high-speed mixer. We will analyze the root cause of the problem and explain the solution recommended by our technical team.

Customer Background and Problem Description

Ricc is a plastics manufacturer based in South Africa, producing polyolefin compounds and masterbatches for industrial applications. During routine production, Ricc used a high-speed mixer to premix resin, additives, and Light Stabilizer 119.

During one production run, Ricc noticed abnormal material buildup inside the mixer and contacted us with photos and the following description:

“Please see how the product has compacted on the blades and sides at the bottom of the mixer.
This is due to the pulverizing of the 119 and the compaction is quite tight, which we have to scrape off.
Heat is up to around 35–40°C.
We know this is the norm as the 119 is very brittle, but perhaps you have some recommendations.”

Compaction of Light Stabilizer 119 on mixer blades and walls 

Key issues observed:

• Severe compaction on mixing blades

• Tight caking on the bottom and side walls of the mixer

• Manual scraping required after mixing

• Mixing temperature reaching 35–40°C

• Reduced production efficiency and cleaning difficulties

Why Does Light Stabilizer 119 Cake in High-Speed Mixers?

After receiving the photos, we consulted our technical department and reviewed the case based on our experience with light stabilizers in various processing environments.

1. Physical Characteristics of Light Stabilizer 119

Light Stabilizer 119 has several inherent physical properties that must be considered during processing:

• Relatively brittle structure

• Low softening point compared with inorganic additives

• Sensitive to mechanical shear and friction

• Tendency to pulverize under high-impact mixing

When exposed to excessive shear forces, LS 119 particles can fracture into fine powder, increasing surface area and heat sensitivity.

2. Characteristics of High-Speed Mixing Equipment

High-speed mixers are designed to:

• Operate at high rotational speeds

• Generate strong shear and friction

• Achieve rapid dispersion of materials

However, these conditions also result in:

• Continuous mechanical impact on additives

• Significant frictional heat generation

• Local hot spots at the mixing blades, often higher than the measured bulk temperature

Although the average material temperature was reported at 35–40°C, the actual blade surface temperature can be considerably higher during operation.

For low-melting, brittle light stabilizers like LS 119, this environment is not ideal.

Root Cause Analysis

Based on our assessment, the issue was not related to product quality, but rather to equipment suitability.

The combination of:

• High rotational speed

• Strong shear forces

• Elevated local temperatures

led to:

1. Pulverization of Light Stabilizer 119

2. Partial softening of fine particles

3. Adhesion to hot blade surfaces

4. Progressive compaction and caking on blades and mixer walls

This phenomenon is quite common when LS 119 is processed in high-speed mixers and is consistent with observations at other customer sites.

Our Technical Recommendation

After internal discussion, we provided Ricc with the following professional recommendation.

Avoid High-Speed Mixing for LS 119

For Light Stabilizer 119 and similar organic light stabilizers, we do not recommend high-speed mixers, especially when:

• Mixing times are long

• Batch temperatures increase

• Cleaning efficiency is critical

Recommended Solution: Low-Speed Ribbon Blender

Based on site visits to multiple customers using light stabilizers, we have found that ribbon blenders perform exceptionally well in this application.

Ribbon blender recommended for Light Stabilizers mixing

Why Ribbon Blenders Work Better

A ribbon blender features:

• Horizontal mixing chamber

• Inner and outer ribbon agitators

• Low rotational speed

• Gentle axial and radial material movement

Key advantages include:

• Low shear force

• Minimal frictional heat generation

• Uniform dry blending

• Significantly reduced caking and compaction

• Improved cleaning efficiency

Ribbon blenders are widely used for:

• Plastic additives

• Masterbatch premixing

• Light stabilizers and antioxidant additives

• Dry blending of temperature-sensitive materials

Customer Response and Industry Insight

Ricc acknowledged that the explanation matched their on-site observations and expressed interest in adjusting their mixing process accordingly.

This case highlights an important lesson for the plastics industry:

Even high-quality light stabilizers require the right processing conditions to perform optimally.

Selecting the correct mixing equipment is just as important as choosing the right additive.

Practical Recommendations for Light Stabilizers Users

If you are experiencing similar issues when processing Light Stabilizers 119 or other HALS products, consider the following:

1. Review mixer type and operating speed

2. Monitor not only bulk temperature, but also localized heat generation

3. Avoid excessive shear for brittle organic additives

4. Consider low-speed mixing solutions for dry blending

Our technical team is always available to evaluate your specific application and provide tailored recommendations.

Conclusion

This real case from South Africa demonstrates that mixing problems with Light Stabilizer 119 are often process-related rather than product-related.

By matching light stabilizers with appropriate equipment—such as low-speed ribbon blenders—manufacturers can:

• Improve production efficiency

• Reduce downtime

• Minimize cleaning effort

• Achieve more stable and consistent results

If you are working with Light Stabilizers 119 or other polymer additives and need technical support, please feel free to contact us for professional guidance.