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Introduction to Low Smoke PVC Wire and Cable Compounds

Low smoke PVC (Polyvinyl Chloride) wire and cable compounds are specialized thermoplastic materials designed to minimize smoke and toxic gas emissions during combustion. This makes them an essential choice for applications where fire safety is a priority. Typically used for insulation and jacketing in electrical cables, these compounds offer several key features:

Composition: Low smoke PVC compounds are formulated with a combination of PVC resin, plasticizers (such as dioctyl phthalate and tri-2-ethylhexyl trimellitate), flame retardants (e.g., antimony trioxide, aluminum trihydrate, and zinc borate), stabilizers (calcium/zinc-based), fillers (calcium carbonate), and lubricants.

Low Smoke Properties: Unlike standard PVC, which can reduce visibility by up to 90% in just 30 minutes due to dense smoke, low smoke PVC compounds are engineered to meet safety standards such as BS EN 61034. These compounds allow at least 60% light transmittance during combustion, greatly improving safety.

Flame Retardancy: PVC inherently has flame-retardant properties due to its chlorine content, which is enhanced with additional flame retardant additives. These compounds meet stringent standards like IEC 60332-1-2, UL VW1, and E84 (flame spread index <25, smoke developed index <50).

 Applications: Commonly used in high-risk environments such as data centers, tunnels, aircraft, rail carriages, and public buildings, low smoke PVC wire and cable compounds are vital for minimizing the risks associated with smoke and toxic fumes in case of fire.

Common Processing Challenges and Solutions for Low Smoke PVC Wire and Cable Compounds

Processing low smoke PVC compounds involves managing a range of challenges, especially due to their complex formulation. Below, we discuss some of the most common processing issues and their solutions:

1. High Filler Content Leading to Poor Mobility and High Torque

Challenge: To achieve low smoke properties, PVC compounds often contain high levels of inorganic fillers like aluminum trihydrate (ATH) or magnesium hydroxide (Mg(OH)₂) — typically 20-60% by weight. While these fillers reduce smoke and flame, they can increase viscosity, reduce flowability, and cause equipment wear.

Solutions:

Incorporate processing aids like internal/external lubricants (e.g., calcium stearate, polyethylene waxes, or silicone additives) at 0.5-2.0 phr to lower viscosity and enhance flow.

Use high L/D ratio twin-screw extruders to improve mixing and filler dispersion.

Employ kneader systems with conical force feeding to ensure uniform compounding.

Choose fillers with controlled particle sizes and surface treatments to improve compatibility and reduce abrasion.

2. Thermal Stability

Challenge: PVC can degrade during processing, especially with high filler and flame-retardant loads, releasing hydrogen chloride (HCl) gas that leads to material degradation, discoloration, and equipment corrosion.

Solutions: 

Add heat stabilizers like calcium/zinc-based stabilizers at 2-4 phr to neutralize HCl and prevent degradation.

Use epoxidized soybean oil (ESO) as a co-stabilizer for improved thermal and photo-stability.

Control processing temperatures precisely (160-190°C) to avoid overheating.

Include phenolic antioxidants (e.g., Bisphenol A at 0.3-0.5%) to enhance aging resistance during processing.

3. Plasticizer Migration

Challenge: Plasticizers used to enhance flexibility can migrate under high heat (e.g., in data centers), leading to residue build-up that may interfere with signal transmission or reduce cable longevity.

Solutions:

Use non-migrating polymeric plasticizers instead of monomeric ones (e.g., DOP, DINP) to minimize migration.

Develop “no-liquid” plenum formulas, as pioneered by OTECH, to prevent plasticizer migration in high-temperature environments.

Opt for plasticizers like TOTM, which have lower volatility and are more suitable for high-temperature applications.

4. Balancing Flame Retardancy and Smoke Suppression

Challenge: Increasing flame retardancy through additives like antimony trioxide (3-5%) or brominated compounds (12-15%) can increase smoke emission, making it challenging to balance both properties. Similarly, fillers like calcium carbonate can reduce smoke but may lower the oxygen index, affecting flame retardancy.

Solutions:

Use synergistic flame retardant combinations (e.g., ATH with zinc borate) to optimize both flame retardancy and smoke suppression. ATH, for example, releases water vapor to disrupt combustion and form a protective char layer, which reduces smoke.

Limit the CaCO₃ loading to 20-40 phr to strike a balance between cost, smoke suppression, and flame retardancy, as excessive amounts can reduce the oxygen index.

Explore cross-linkable PVC formulations, such as radiation cross-linked PVC, to enhance flame retardancy without heavy reliance on halogenated additives.

5. Processability and Surface Quality

Challenge: High filler and additive content can lead to poor surface finish, die drool, and inconsistent extrusion, which affects the appearance and performance of the final cable product.

Solutions:Use SILIKE silicone Powder LYSI-100A. This silicone-based additive is widely used as an efficient lubricant processing additive for PVC-compatible resin systems to improve the processing properties and surface quality. Such as better resin flowability, mold filling & release, less extruder torque, and lower coefficient of friction, greater mar, and abrasion resistance…

Key Benefits of silicone Powder LYSI-100A for PVC compounds and final product applications :

1)  Low smoke PVC wire and cable compounds: stable extrusion, less die pressure, smooth surface of wire & cable.

2) Low friction PVC wire and cable: Low Coefficient of Friction, long-lasting smooth feeling.

3) Scratch-resistant PVC product: Anti-scratch, like in PVC shutters.

4) PVC profiles: better mold filling and mold release, no mold flash.

5)  PVC pipe: faster extrusion speed, reduced COF, improved surface smoothness, and saved cost.

If you’re facing challenges with PVC compound processing and surface defects, or struggling with low-smoke PVC wire and cable processing, try LYSI-100A Silicone Powder for smoother extrusion and higher efficiency.

For help locating specific information about a particular product, you can contact us at Tel: +86-28-83625089 / +86-15108280799, via email: amy.wang@silike.cn, or visit our website www.siliketech.com to discover how SILIKE can solve your PVC wire and cable production challenges related to processing properties and surface quality. We offer solutions including:

Enhance Surface Quality in Low-Smoke PVC Compounds

Improve PVC Cable Extrusion with Silicone Powder

Processing Aid for PVC Compounds to Reduce Friction

Boost PVC Wire and Cable Extrusion Efficiency

Improve PVC Compound Flowability for Faster Extrusion

Silicone Additives to Enhance PVC Processing Efficiency

Maximize PVC Cable Compound Performance with Silicone Masterbatch

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