Selection of PVC Heat Stabilizers

Created on Today

As one of the five general-purpose plastics, polyvinyl chloride (PVC) is widely used in construction materials, automobiles, wires, cables and packaging for its excellent flame retardancy, corrosion resistance and mechanical properties. However, PVC resin has an inherent flaw: extremely poor thermal stability.

Pure PVC starts to decompose at around 100°C, while its processing temperature is usually 160°C-220°C. This contradiction makes heat stabilizers indispensable in PVC processing. How to select them accurately? How to address failures like scorching, plate-out and zinc burning? This article provides an in-depth analysis.

I. Core Mechanism of Heat Stabilizers: What Do They Protect?

Before selection, we first understand their working principle. PVC decomposition mainly results from unstable allyl chloride or tertiary carbon chloride structures on the molecular chain, which undergo dehydrochlorination (HCl) when heated.

Once HCl is produced, it autocatalyzes further decomposition, forming conjugated double bonds and turning the product yellow → red → brown → black (i.e., scorching), with a sharp drop in mechanical properties.

Core functions of heat stabilizers:

1.HCl capture: Neutralize decomposed acidic substances to prevent autocatalysis.

2.Replacement of unstable chlorine atoms: Substitute unstable chlorine with stable ester groups or metal chlorides chemically.

3.Double bond addition: React with conjugated double bonds to avoid discoloration.

4.Antioxidation and lubrication: Inhibit oxidative degradation and provide internal/external lubrication during processing.

II. Selection Guide: Advantages & Disadvantages of Five Mainstream Heat Stabilizers

Mainstream PVC heat stabilizers fall into five categories. Selection should consider environmental regulations, processing technology, product transparency, weather resistance and cost.

1. Lead Salt Stabilizers

Features: Traditional dominant type with excellent thermal stability, good electrical insulation and ultra-low cost.

Disadvantages: Highly toxic heavy metal, non-compliant with RoHS, REACH and other environmental regulations; poor transparency and prone to sulfur contamination.

Status: Restricted by Europe, the US and China’s Guidance Catalogue for Industrial Restructuring, gradually phased out. Only a small amount is used in low-end, non-export fields such as water pipes and cables.

2. Calcium-Zinc Composite Stabilizers (Ca/Zn)

Features: Current eco-friendly mainstream, non-toxic and cost-effective.

Mechanism: Calcium stearate (long-term stabilizer) and zinc stearate (initial colorant) work synergistically.

Advantages: Non-toxic, heavy-metal-free, sulfur contamination-free and moderately priced.

Disadvantages: Zinc burning risk – excessive or improper zinc content causes sudden severe blackening in late processing; average transparency (lower than organotins).

Applications: Pipes, profiles, wires, cables, flexible films (with proper auxiliary stabilizers).

3. Organotin Stabilizers

Features: Top transparency and performance.

Advantages: Extremely high transparency, excellent thermal stability, good initial coloring and no zinc burning risk.

Disadvantages: High price, strong odor; some organotins (e.g., butyltin, octyltin) are eco-friendly but slightly biologically toxic, requiring careful handling.

Applications: High-transparency products (transparent sheets, crystal panels, mineral water bottles), food packaging, blow-molded products.

4. Liquid Composite Stabilizers

Features: Dedicated for flexible PVC.

Advantages: Excellent compatibility with PVC paste resins and plasticizers, easy to disperse.

Disadvantages: Low solid content, complex lubrication system; plate-out resistance requires special attention.

Applications: Flexible PVC products (artificial leather, films, drip molding, slush molding products).

5. Rare Earth Stabilizers

Features: China-specific resource-based product.

Advantages: Excellent thermal stability and coupling effect, improving product mechanical properties and weather resistance.

Disadvantages: Less formulation experience than traditional products; compatibility issues need targeted solutions.

Applications: High-end profiles, transparent products, eco-friendly pipes.

Disclaimer: This content is compiled from the internet for study and exchange only, without commercial purposes.

Contact

Leave your information and we will contact you.