Using Foaming Agents in PVC Dryblends – Which One to Choose and Why?

PVC dryblend manufacturers often receive specific customer requests regarding material properties. One common request is the addition of foaming agents to reduce the density of PVC and lower the amount of raw material used in pipe production.

However, adding the right foaming agent requires precise selection, as it affects PVC processability, foaming quality, and mechanical properties. This article discusses the best available options on the market and key factors in choosing the right foaming agent.

1️⃣ Why Add Foaming Agents to PVC Dryblends?

Foaming agents are chemical additives that decompose thermally during processing, releasing gases (such as CO₂ or nitrogen), which creates a porous structure in the polymer. The benefits include:

✔️ Lower material density – reducing the amount of raw material needed to produce the same volume of pipe.
✔️ Lower PVC consumption – foamed PVC saves raw material without compromising structural integrity.
✔️ Improved thermal insulation – the porous structure enhances insulation properties.

Key note: Foaming PVC does not change the pipe’s volume, so it does not directly affect transportation costs. The primary savings come from reducing material consumption, making production more cost-effective.

2️⃣ Challenges in Using Foaming Agents in PVC Dryblends

Adding foaming agents to recycled PVC dryblends involves several technological challenges:

• Homogenization of the mixture – foaming agents must be evenly distributed throughout the material.
• Impact on PVC thermal stability – some foaming agents can accelerate polymer degradation.
• Optimal activation temperature – each foaming agent decomposes at a different temperature range.

3️⃣ Types of Foaming Agents for PVC – Which One to Choose?

Various foaming agents are available on the market for PVC dryblends, categorized into chemical and physical agents.

Chemical Foaming Agents

🔹 Azodicarbonamide (ADC)

• The most commonly used foaming agent for PVC.
• Decomposes at 190–210°C, releasing nitrogen and CO₂.
• Creates medium-sized pores – a balance between weight reduction and strength.
• Activation can be adjusted using activators (e.g., metal oxides).

🔹 Oxobisbenzenosulfonylhydrazid (OBS)

• Activates at lower temperatures (150–180°C), making it suitable for PVC with lower thermal resistance.
  
• Produces smaller pores than ADC, improving surface quality.
  
• Less thermal degradation than ADC.

🔹 Carbonates and bicarbonates (e.g., sodium bicarbonate, NaHCO₃)

• Decompose into CO₂ and water for foaming.
• Less aggressive than ADC but may require higher activation temperatures
•  Suitable for less demanding applications.

🔬 Physical Foaming Agents

Less commonly used in PVC dryblends but applied in extrusion processes.

🔹 Nitrogen (N₂), carbon dioxide (CO₂) – require high-pressure systems for gas injection into molten PVC.
🔹 Fluorinated hydrocarbons (e.g., pentane, isobutane) – mainly used for foaming polyolefins.

4️⃣ How to Choose the Best Foaming Agent?

Choosing the right foaming agent depends on several key factors:

Activation Temperature

✔️ Rigid PVC (pipes, profiles): ADC (190–210°C) or OBS (150–180°C).
✔️ Foamed PVC (e.g., panels, sheets): OBS or sodium bicarbonates.

Impact on PVC Thermal Stability

✔️ For recycled PVC, avoiding high ADC content is advisable – OBS may be a better choice.

Pore Size and Distribution

✔️ ADC – medium pores → a good balance between weight and strength.
✔️ OBS – smaller pores → smoother surface, less mechanical weakening.
✔️ Sodium bicarbonate – larger pores → for less demanding applications.

Ease of Mixing with Dryblend

✔️ ADC and OBS require intensive mixing, preferably in high-speed mixers (e.g., Henschel).

5️⃣ How to Ensure Effective Homogenization of Dryblend?

To avoid processing issues:

✔️ Use high-performance high-speed mixers (e.g., Henschel) for even distribution of foaming agents.
✔️ Optimize mixing time and temperature – excessive heating may activate foaming agents too early.
✔️ Apply compatible thermal stabilizers to prevent PVC degradation during processing.

Summary – Which Foaming Agent to Choose for PVC Dryblends?

✔️ ADC is the most commonly used foaming agent but requires careful thermal stability control.
✔️ OBS is better suited for recycled PVC due to its lower activation temperature.
✔️ Sodium bicarbonate is a simple alternative for less demanding applications.
✔️ Proper mixing and activation temperature control are crucial for effective foaming.

If you manufacture PVC dryblends and are considering foaming agents, choosing the right additive for your customer's process is key

Processing and Decomposition Temperatures of PVC

If we talk about processing temperatures, it is worth considering:

PVC Processing Temperature:

• Rigid PVC (uPVC): 160–200°C
• Plasticized PVC (Soft PVC): 140–180°C

PVC Decomposition Temperature:

• PVC starts thermally degrading at around 200–220°C, but significant decomposition occurs above 250°C.
• During decomposition, hydrogen chloride (HCl) is released, which accelerates degradation and causes yellowing of the material.

Thermal stabilizers (e.g., calcium-zinc, organotin compounds) allow PVC to be processed at higher temperatures, delaying degradation.

In industrial applications, maintaining the proper processing window is crucial to prevent PVC damage during extrusion or molding.