In the production of plastic products, the selection and application of additives play a decisive role in the quality of the final product. Among these, silicone oil and defoamers are two essential functional additives that serve indispensable roles in plastic processing. They not only improve processing performance but also significantly enhance the appearance and mechanical properties of the finished product. This article delves into the principles, specific functions, and selection criteria of silicone oil and defoamers in the plastics industry, providing valuable insights for plastic manufacturers.

Applications of Silicone Oil in Plastic Processing

Silicone oil, chemically known as polydimethylsiloxane (PDMS), is a linear polymer composed of silicon-oxygen bonds. This unique structure gives silicone oil exceptional properties, including low surface tension, high thermal stability, excellent lubricity, and chemical inertness. In plastic processing, silicone oil primarily serves four key functions:

First, as a highly effective release agent, silicone oil significantly reduces adhesion between plastic and molds. In injection molding, spraying a solution containing 0.5–2% silicone oil onto the mold surface can decrease demolding force by 40–60%, reducing surface defects and improving production efficiency. This is particularly crucial for complex-shaped products, where silicone oil ensures complete demolding and lowers rejection rates.

Second, silicone oil acts as an outstanding surface modifier. Adding 0.1–0.5% silicone oil can dramatically improve the surface characteristics of plastic products, imparting a smooth, silky feel while reducing friction. This is especially important for plastic films and packaging materials, enhancing tactile quality and minimizing wear during use.

Third, silicone oil functions as an internal lubricant in plastics. When processing PVC, PP, and other plastics, adding 0.3–1% silicone oil reduces melt viscosity by 15–30%, improving flow properties and ensuring complete mold filling while lowering energy consumption. Experimental data show that appropriate silicone oil addition can reduce extruder torque by 10–15%, significantly boosting production efficiency.

Finally, silicone oil enhances weather resistance. By incorporating 1–3% functionalized silicone oil (such as amino- or epoxy-modified silicone), plastic materials gain superior UV resistance, extending their outdoor lifespan. Studies indicate that modified silicone oil can increase PP’s weather resistance by 2–3 times.

The Importance of Defoamers in Plastic Processing

Bubbles formed during plastic processing directly impact product quality and production efficiency. These bubbles originate from three main sources: volatile substances in raw materials, trapped air during processing, and gases released from additive decomposition. Bubbles can cause surface defects, reduced mechanical strength, and even rejection rates of 5–15%.

Defoamers work by altering bubble surface tension through three mechanisms: reducing local surface tension to rupture bubble films, preventing bubble stabilization, and promoting bubble coalescence and escape. In the plastics industry, defoamers are mainly categorized into silicone-based and non-silicone types. Silicone defoamers (e.g., polydimethylsiloxane) are highly effective but may affect transparency, while non-silicone defoamers (e.g., mineral oil or polyether-based) are better suited for transparent products.

In PVC calendaring film production, adding 0.1–0.3% silicone defoamer can reduce bubble defects by over 70%. In PU foam plastics, composite defoamers precisely control cell structure, maintaining density deviation within ±3%. For PET injection molding, specialized polyether defoamers eliminate micro-bubbles caused by moisture evaporation without compromising transparency.

Synergistic Effects of Silicone Oil and Defoamers

In practical applications, silicone oil and defoamers often exhibit significant synergistic effects, primarily in three areas:

1. Process Optimization: Silicone oil improves melt flow, while defoamers eliminate bubbles, resulting in more stable extrusion or injection molding. For example, in PE pipe production, combining 0.2% silicone oil and 0.1% defoamer increases line speed by 15% while reducing bubble defects by 60%.

2. Product Quality Enhancement: The synergy is even more pronounced in improving product quality. In transparent PP products, carefully balancing silicone oil and defoamer ratios yields bubble-free surfaces with gloss levels exceeding 95 GU. Tests show that optimal formulations can boost impact strength by 10–20%.

3. Cost Efficiency: Smart formulation design minimizes additive usage. One case study showed that reducing silicone oil from 0.5% to 0.3% while adding 0.05% high-efficiency defoamer maintained product quality while saving ¥120,000 annually in additive costs.

Selection and Usage Guidelines

Choosing the right silicone oil and defoamer requires considering multiple factors:

• Silicone Oil Selection:

  • PP/PE: Dimethyl silicone oil (100–1000 cSt viscosity)

  • PVC: Amino-modified silicone oil

  • Engineering Plastics: High-temperature-resistant phenyl silicone oil

  • Typical dosage: 0.1–1%, added via masterbatch or direct mixing

• Defoamer Selection:

  • Depends on processing method (injection molding, extrusion, etc.), temperature, and transparency requirements.

  • General rules:

    • High-temperature processing: Use thermally stable types

    • Transparent products: Polyether-based

    • Foamed plastics: Specialized foam-control agents

  • Dosage: Usually 0.05–0.3% (excessive amounts may cause defects)

Key Usage Tips:

• Conduct small-scale trials before full production

• Add defoamers at later mixing stages

• Store in dry, cool conditions

• Regularly check additive effectiveness

Troubleshooting Common Issues:

• Fish eyes/surface defects: Try switching silicone oil type or reducing dosage

• Poor defoaming: Increase processing temperature or switch to a stronger defoamer

Industry Trends and Innovations

As the plastics industry shifts toward high-performance and eco-friendly solutions, silicone oil and defoamer technologies continue to evolve. Key trends include:

1. Eco-Friendly Additives:

   • Bio-based silicone oils (e.g., derived from castor oil) and biodegradable defoamers are emerging to meet regulations like EU REACH.

   • Some manufacturers have developed green silicone oils with a 40% lower carbon footprint.

2. Nanotechnology Applications:

   • Nano-silicone oils (<100 nm particle size) improve dispersion, reducing usage by 30% without sacrificing performance.

   • Nano-composite defoamers enable precise micro-bubble control, ideal for high-precision injection molding.

3. Smart Additive Systems:

   • Real-time monitoring and automated dosing systems optimize silicone oil and defoamer levels, ensuring consistent quality.

   • Data shows smart systems reduce additive consumption by 15–20% while minimizing quality fluctuations.

4. Multifunctional Additives:

   • New composite additives combine lubrication, defoaming, and antistatic properties, simplifying formulations.

   • Example: One additive can replace traditional silicone oil, defoamer, and antistatic agents.

Silicone oil and defoamers are indispensable additives in plastic processing, crucial for enhancing product quality and production efficiency. As technology advances, these additives are becoming more efficient, sustainable, and intelligent. Plastic manufacturers should recognize their importance, select the right additives for their products, and continuously optimize formulations.

Looking ahead, emerging additive technologies and smart manufacturing will enable even more precise and efficient applications. Companies that stay updated on industry innovations and adopt cutting-edge solutions will maintain a competitive edge in the evolving plastics market.