Flame Retardants: SEMITECH Halogen-Free Portfolio — ATH, MDH, Surface-Treated Mineral Fillers, and Zinc Borate Synergists

ATH is the highest-volume halogen-free flame retardant globally — over 1.2 million tonnes/year consumed in HFFR cable, EVA encapsulants, polyolefin compounds, and engineering thermoset cures. The flame retardancy mechanism combines three actions: endothermic decomposition at 180–200°C absorbs ~1.17 kJ/g of heat from the polymer matrix; release of 35% chemical water dilutes oxygen and combustible volatiles in the flame zone; and the residual alumina layer acts as a thermal barrier slowing further pyrolysis. SEMITECH supplies ATH at three particle-size cuts: ATH-1 (D50 1 µm) for premium HFFR EVA where mechanical retention is paramount; ATH-3 (D50 3 µm, the workhorse grade) for general PE/EVA cable jackets; and ATH-10 (D50 10 µm) for high-loading, mechanical-non-critical applications like rubber compounds. Loading levels run 50–65% in HFFR cable, 35–50% in epoxy potting, 25–40% in unsaturated polyester casting. The thermal cap at 200°C excludes ATH from nylon, PBT, and engineering polymer compounds where MDH is specified instead.

MDH uses the same endothermic-decomposition + water-release mechanism as ATH but with a 320–340°C decomposition window — 120–140°C higher than ATH, and crucially above the processing temperatures of nylon 6 (260°C), nylon 66 (290°C), PBT (250°C), and PPS (310°C). This makes MDH the only viable mineral flame retardant for engineering plastic compounding. Water release is 31% (vs 35% for ATH), and the heat absorption is similar at ~1.36 kJ/g. SEMITECH supplies MDH at MDH-1 (D50 1 µm) and MDH-3 (D50 3 µm) cuts, with surface area 8–12 m²/g and ≥99% purity. Industrial pricing runs 1.8–2.2× ATH per kilogram — the premium is justified only when ATH thermal stability fails. Common applications include nylon 66 cable connectors, PBT junction boxes, EVA cable jackets requiring extended thermal cycling, and EPDM rubber compounds for high-temperature gaskets.

ATH-Silane is ATH whose surface silanols have been pre-reacted with a functional silane coupling agent — typically vinyl trimethoxysilane (KH-171 / A-172) for peroxide-cure systems, or aminopropyl triethoxysilane (KH-550 / A-1100) for thermoplastic compounding. SEMITECH applies silane at 0.5–1.0% on filler weight via a fluidised-bed coating process; the silane’s alkoxy groups condense with surface Al-OH and the functional group (vinyl or amino) projects outward to bond with the polymer matrix during processing. The result for HFFR cable jackets is a 30–50% increase in tensile retention and a 50–80% increase in elongation at break versus untreated ATH at the same loading. For 60% ATH-Silane in EVA, typical mechanical performance is tensile ≥10 MPa, elongation ≥180%, LOI 32+ — directly qualifying for EN 50575 / IEC 60332-3 cable burn tests. Vinyl-silane grades require peroxide cure (DCP, DBPH) to lock the filler-polymer bond; amino-silane grades work directly in thermoplastic extrusion without cure step.

ATH-Zirconate uses neoalkoxy-zirconate chemistry (Kenrich NZ-44 / NZ-97 equivalent from SEMITECH’s own zirconate hub) at 0.3–0.5% on filler — half the loading of silane treatment for equivalent or better performance. The zirconate’s mono-alkoxy group reacts with surface Al-OH, while the chelate ligands provide steric shielding and lubrication during compounding. The downstream benefit is a 25–35% reduction in mixing torque on twin-screw extruders, allowing 15–20% higher throughput at the same 60–65% filler loading. For HFFR cable manufacturers competing on extrusion line productivity, this is the most consequential improvement available — and it is the application where SEMITECH’s vertically-integrated zirconate-plus-ATH supply chain delivers the strongest cost advantage. Premium pricing runs 3–5× untreated ATH; payback is rapid when extrusion productivity is the binding constraint.

MDH-Silane applies the same KH-550 aminopropyl silane chemistry to MDH at 0.5–1.0% surface loading. The application is exclusive to engineering plastic compounds — nylon 6, nylon 66, PBT — where ATH thermal cap excludes use and the buyer needs to maintain mechanical performance at 50–55% MDH loading. Typical performance: nylon 66 + 55% MDH-Silane achieves UL 94 V-0 at 1.6 mm with tensile strength ≥45 MPa and elongation ≥3.5% — qualifying for automotive electrical connector, high-voltage cable termination, and industrial control panel applications. SEMITECH MDH-Silane is the cost-rational alternative to Nabaltec Apyral grades for buyers in Asia, Europe and North America, with comparable surface-coating quality and 30% landed-cost savings.

Zinc borate (commercial grade ZB-2335, the industry standard composition) is a multifunctional halogen-free flame retardant additive with three concurrent mechanisms: char promotion (forms a glassy borate layer at 290–450°C that insulates the underlying polymer from heat); smoke suppression (reduces total smoke emission by 40–60% in HFFR cable EVA, measured via NBS smoke chamber per ASTM E662); and anti-tracking (raises CTI value by 30–50 points in electrical insulation applications). Loading is 5–15% in HFFR cable jacket, 3–8% in intumescent paint formulations, and 2–5% in epoxy electrical encapsulation. ZB is the most widely used synergist with ATH and MDH — typical compound design is 55% ATH + 5% ZB in EVA, achieving the LOI/smoke trade-off that pure ATH cannot reach. Note that ZB also functions as a 30–40% Sb₂O₃ replacement in legacy halogenated systems, allowing buyers to reduce antimony content in transition formulations.

Antimony trioxide is the classical halogen synergist — Sb₂O₃ reacts with brominated or chlorinated FRs in the flame zone to form volatile SbBr₃/SbCl₃ that scavenges hydrogen and hydroxyl radicals, breaking the combustion chain. Standard loading is 3–5 phr with 10–15 phr brominated FR. SEMITECH supplies Sb₂O₃ as a transitional inventory item for buyers maintaining legacy halogenated FR systems through market transition. Strategic note: Sb₂O₃ was added to the EU REACH SVHC candidate list in 2022 (categorised as suspected carcinogen via inhalation route) and is restricted in cosmetic and food-contact applications. We do not promote Sb₂O₃ as a growth grade and recommend buyers plan migration to halogen-free systems (ATH/MDH + ZB) over a 24–36 month horizon. SEMITECH’s role on Sb₂O₃ is supply continuity for existing qualified compounds, not formulation innovation.