Introduction: Solving High-Load ATH/MDH Flame-Retardant Polyolefin Compounds Processing Challenges
In the cable industry, stringent requirements for flame retardancy are essential to ensure the safety of personnel and equipment in the event of a fire. Aluminum hydroxide (ATH) and magnesium hydroxide (MDH), as halogen-free flame retardants, are widely used in polyolefin cable compounds due to their environmental friendliness, low smoke emission, and non-corrosive gas release. However, achieving the required flame-retardant performance often necessitates incorporating high loadings of ATH and MDH—typically 50–70 wt% or higher—into the polyolefin matrix.
While such high filler content significantly enhances flame retardancy, it also introduces severe processing challenges, including increased melt viscosity, reduced flowability, compromised mechanical properties, and poor surface quality. These issues can greatly limit production efficiency and product quality.
This article aims to systematically examine the processing challenges associated with high-load ATH/MDH flame-retardant polyolefin compounds in cable applications. Based on market feedback and practical experience, it identifies effective processing additives for addressing these challenges. The insights provided are intended to help wire and cable manufacturers optimize formulations and improve production processes when working with high-load ATH/MDH flame-retardant polyolefin compounds.
Understanding ATH and MDH Flame Retardants
ATH and MDH are two major inorganic, halogen-free flame retardants widely used in polymer materials, particularly in cable applications where safety and environmental standards are high. They act by endothermic decomposition and water release, diluting combustible gases and forming a protective oxide layer on the material surface, which suppresses combustion and reduces smoke. ATH decomposes at approximately 200–220°C, while MDH has a higher decomposition temperature of 330–340°C, making MDH more suitable for polymers processed at higher temperatures.
1. The flame-retardant mechanisms of ATH and MDH include:
1.1. Endothermic decomposition:
Upon heating, ATH (Al(OH)₃) and MDH (Mg(OH)₂) undergo endothermic decomposition, absorbing significant heat and lowering the polymer temperature to delay thermal degradation.
ATH: 2Al(OH)₃ → Al₂O₃ + 3H₂O, ΔH ≈ 1051 J/g
MDH: Mg(OH)₂ → MgO + H₂O, ΔH ≈ 1316 J/g
1.2. Water vapor release:
The released water vapor dilutes flammable gases around the polymer and restricts oxygen access, inhibiting combustion.
1.3. Formation of protective layers:
The resulting metal oxides (Al₂O₃ and MgO) combine with the polymer char layer to form a dense protective layer, which blocks heat and oxygen penetration and hinders the release of combustible gases.
1.4. Smoke suppression:
The protective layer also adsorbs smoke particles, reducing overall smoke density.
Despite their excellent flame-retardant performance and environmental benefits, achieving high flame-retardant ratings typically requires 50–70 wt% or more of ATH/MDH, which is the primary cause of subsequent processing challenges. 2. Key Processing Challenges of High-Load ATH/MDH Polyolefins in Cable Applications
2.1. Deteriorated rheological properties:
High filler loadings sharply increase melt viscosity and reduce flowability. This makes plasticization and flow during extrusion more difficult, requiring higher processing temperatures and shear forces, which increases energy consumption and accelerates equipment wear. Reduced melt flow also limits extrusion speed and production efficiency.
2.2. Reduced mechanical properties:
Large amounts of inorganic fillers dilute the polymer matrix, significantly decreasing tensile strength, elongation at break, and impact strength. For example, incorporating 50% or more ATH/MDH may reduce tensile strength by approximately 40% or more, posing a challenge for flexible and durable cable materials.
2.3. Dispersion issues:
ATH and MDH particles often aggregate in the polymer matrix, leading to stress concentration points, reduced mechanical performance, and extrusion defects such as surface roughness or bubbles.
2.4. Poor surface quality:
High melt viscosity, poor dispersion, and limited filler-polymer compatibility can cause extrudate surfaces to be rough or uneven, leading to “sharkskin” or die build-up. Accumulation at the die (die drool) affects both appearance and continuous production.
2.5. Electrical property impacts:
High filler content and uneven dispersion can affect dielectric properties, such as volume resistivity. Moreover, ATH/MDH has relatively high moisture absorption, which can potentially affect electrical performance and long-term stability in humid environments.
2.6. Narrow processing window:
The processing temperature range for high-load flame-retardant polyolefins is narrow. ATH begins decomposing around 200°C, while MDH decomposes around 330°C . Precise temperature control is required to prevent premature decomposition and ensure flame-retardant performance and material integrity.
These challenges make processing high-load ATH/MDH polyolefins complex and highlight the necessity of effective processing aids.
So, to address these challenges, various processing aids have been developed and applied in the cable industry. These aids improve polymer-filler interfacial compatibility, reduce melt viscosity, and enhance filler dispersion, optimizing both processing performance and final mechanical properties.
Which processing aids are most effective for solving processing and surface quality issues of high-load ATH/MDH flame-retardant polyolefin compounds in cable industry applications?
Silicone-based additives and production aids:
SILIKE offers versatile polysiloxane-based processing aids for both standard thermoplastics and engineering plastics, helping to optimize processing and enhance the performance of finished products. Our solutions range from the trusted silicone masterbatch LYSI-401 to the innovative SC920 additive—engineered to deliver greater efficiency and reliability in high-load, halogen-free LSZH and HFFR LSZH cable extrusion.
Specifically, SILIKE UHMW silicone-based lubricant processing additives have been proven beneficial for ATH/MDH flame-retardant polyolefin compounds in cables. Key effects include:
1. Reduced melt viscosity: Polysiloxanes migrate to the melt surface during processing, forming a lubricating film that reduces friction with equipment and improves flowability.
2. Enhanced dispersion: Silicon-based Additives promote uniform distribution of ATH/MDH in the polymer matrix, minimizing particle aggregation.
3. Improved surface quality: LYSI-401 silicone masterbatch reduces die build-up and melt fracture, producing smoother extrudate surfaces with fewer defects.
4. Faster line speed: Silicone Processing Aid SC920 is suitable for high-speed extrusion of cables. It can prevent wire diameter instability and screw slippage, and improve production efficiency. At the same energy consumption, extrusion volume increased by 10%.
5. Improved mechanical properties: By enhancing filler dispersion and interfacial adhesion, silicone masterbatch improves composite wear resistance and mechanical performance, such as impact property & elongation at break.
6. Flame-retardant synergism and smoke suppression: siloxane additives can slightly enhance flame-retardant performance (e.g., increasing LOI) and reduce smoke emission.
SILIKE is a leading producer of silicone-based additives, processing aids, and thermoplastic silicone elastomers in the Asia-Pacific region.
Our silicone processing aids are widely applied in the thermoplastics and cable industries to optimize processing, improve filler dispersion, reduce melt viscosity, and deliver smoother surfaces with higher efficiency.
Among them, the silicone masterbatch LYSI-401 and the innovative SC920 silicone processing aid are proven solutions for ATH/MDH flame-retardant polyolefin formulations, particularly in LSZH and HFFR cable extrusion. By integrating SILIKE’s silicone-based additives and production aids, manufacturers can achieve stable production and consistent quality.
If you are looking for silicone processing aids for ATH/MDH compounds, polysiloxane additives for flame-retardant polyolefins, silicone masterbatch for LSZH / HFFR cables, improve dispersion in ATH/MDH cable compounds, reduce melt viscosity flame-retardant polyolefin extrusion, cable extrusion processing additives, silicone-based extrusion aids for wires and cables, please visit www.siliketech.com or contact us at amy.wang@silike.cn to learn more.
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