Performance Degradation of Highly Filled Cable Compounds – Compatibilizer Selection and Interfacial Anchoring Solutions

Driven by the "dual carbon" strategy and the continuous upgrading of fire safety standards, the wire and cable industry is shifting from traditional halogen-containing flame-retardant systems to low-smoke halogen-free (LSZH) flame-retardant technologies. Application scenarios are extending from rail transit and building wiring to emerging fields such as high-voltage wiring harnesses for new energy vehicles. However, a long-standing technical challenge has persistently troubled cable manufacturers—when the loading of inorganic flame-retardant fillers such as ATH and MDH reaches a relatively high proportion, the processing of cable compounds becomes extremely difficult, and mechanical properties drop sharply. The root cause of this issue must be understood from the fundamental principles of polymer composites.

I. Three Major Challenges in Highly Filled Systems
ATH and MDH are the most mainstream halogen-free flame retardants. They achieve flame retardancy and smoke suppression through endothermic decomposition, release of water vapor, dilution of combustible gases, and formation of a metal oxide protective layer on the material surface. The decomposition temperature of ATH is approximately 200–220°C, while that of MDH is about 330–340°C. To meet high flame-retardant grades such as B1, it is usually necessary to add a high proportion of ATH/MDH to the polyolefin matrix.

Although high loading ensures flame-retardant performance, it brings three core problems:

First, deterioration of rheological properties. A large amount of inorganic filler dramatically increases melt viscosity and severely reduces fluidity. Extrusion requires higher temperatures and shear forces, which increases energy consumption, accelerates equipment wear, and limits production efficiency.

Second, degradation of mechanical properties. Inorganic fillers dilute the polymer matrix and disrupt the continuous chain structure of the polyolefin. At high loadings, tensile strength decreases significantly, directly affecting the installation flexibility and long-term reliability of cables.

Third, dispersion difficulties and surface defects. ATH/MDH particles have polar surfaces, while the polyolefin matrix is non-polar—they are inherently incompatible. Fillers tend to agglomerate, forming stress concentration points, and cause surface defects such as shark-skin patterns, bubbles, and die buildup during extrusion.

II. Mechanism of Compatibilizers in Highly Filled Systems
The key to overcoming these challenges lies in compatibilizers. A compatibilizer is a chemically modified functionalized polyolefin, typically represented by maleic anhydride grafted polyolefins (POE-g-MAH, PE-g-MAH, EVA-g-MAH, etc.). One end of the molecule is a non-polar polyolefin backbone, which is compatible with the base resin; the other end is a polar maleic anhydride functional group, which bonds with the filler surface.

In highly filled systems, the compatibilizer performs three core functions:

First, interfacial anchoring. The maleic anhydride groups interact with the hydroxyl groups on the ATH/MDH filler surfaces through polar interactions, forming a stable interfacial anchoring layer under normal processing temperatures and significantly reducing interfacial tension.

Second, enforced dispersion. Filler particles coated with the compatibilizer have reduced surface polarity, leading to decreased interparticle cohesion and less agglomeration, enabling uniform and fine dispersion in the melt.

Third, stress transfer and dissipation. Good interfacial bonding allows effective transfer of matrix stress to the filler particles, avoiding localized stress concentration and improving both tensile strength and elongation at break.

III. Grafting Ratio: A Key Guarantee for Highly Filled Systems
The grafting ratio refers to the amount of maleic anhydride grafted onto the polyolefin backbone, which determines the number of anchoring sites that a unit mass of compatibilizer can provide. In highly filled systems, the total surface area of fillers increases dramatically, and the number of anchoring sites required rises exponentially. When the grafting ratio is insufficient, compatibilizer molecules cannot effectively coat every filler particle. Uncoated particles will still agglomerate and eventually appear as pitting or white spots on the cable surface.

The JP‑M13 cable compound compatibilizer from Shanghai Jiuju Polymer Materials Co., Ltd. is a POE‑based maleic anhydride grafted compatibilizer specially developed for highly filled low-smoke halogen‑free cable compound systems. The POE elastomer matrix has a low glass transition temperature (approximately –50°C) and excellent toughening efficiency, making it particularly suitable for cable sheath applications that require both low-temperature impact resistance and flexibility. Moreover, JP‑M13 employs a proprietary grafting process that maintains a consistently high grafting ratio, ensuring effective coating of filler particles in highly filled ATH/MDH systems, smooth processing, a glossy surface, and excellent mechanical properties in the final product.

If you are also struggling with the balance between processing and performance in highly filled cable compounds, please feel free to contact us. We have been stably serving a number of cable companies in their high‑loading LSZH cable compound systems. We can provide free samples for testing, with direct technical engineer support.