DCBP Peroxide

Overview

DCBP — bis(2,4-dichlorobenzoyl) peroxide, CAS 133-14-2 — is the lowest-decomposition-temperature aromatic diacyl peroxide widely used in HTV silicone rubber. With a 1-minute half-life at 124°C and 10-minute half-life at 95°C, DCBP is far below DCP (dicumyl peroxide, t½ 1 min at 175°C) and DBPH (t½ 1 min at 196°C) on the peroxide-decomposition curve, making it the standard cure agent for thin-section extruded profiles where short cycles in continuous hot-air vulcanisation tunnels demand fast onset. Molecular formula C₁₄H₆Cl₄O₄, molecular weight 380.0 g/mol.

The compound is shipped as a 50 wt% paste dispersion in non-reactive silicone fluid (typically methyl-silicone fluid 100–500 cP) to suppress decomposition risk during shipping and to provide uniform mill-mix dispersion in HTV silicone gum. Pure DCBP solid melts at 137–139°C with decomposition. SEMITECH issues a Self-Accelerating Decomposition Temperature (SADT) certificate of 50°C with every shipment in compliance with UN transport regulations for organic peroxides; UN classification 3106 / Class 5.2 (Organic Peroxide Type C, solid). Tropical-climate transport requires reefer-container shipping above 5°C and below 25°C ambient.

DCBP cures HTV silicone rubber by classical free-radical chemistry: thermal homolysis of the weak O–O peroxide bond at processing temperature (120–170°C) generates two 2,4-dichlorobenzoyloxy radicals, which decarboxylate to 2,4-dichlorophenyl radicals plus CO₂. These aryl radicals abstract methyl-H from the methyl groups on PDMS gum, producing methylene radicals on the polymer chain. Two such methylene radicals on adjacent chains recombine to form a Si–CH₂–CH₂–Si crosslink — the only crosslink in pure peroxide-cured silicone. Typical crosslink density at 1.0 phr DCBP loading is 50–80 mol/m³, giving Shore A 50–70 in standard methyl-silicone gum compounds.

The dominant operational issue is transport and storage. SADT 50°C — the temperature above which a 50 kg package will undergo runaway decomposition within 7 days. Storage must be 25°C below SADT minimum; transport temperature must never exceed SADT minus 10°C. Hot spots in warehouse are the early warning of self-accelerating decomposition. Avoid DCBP for medical, food-contact, or optical silicone — peroxide-derived 2,4-dichlorobenzoic acid byproduct (~0.5% residual after cure) and the non-zero halogen content fail toxicology and migration limits for those applications.

Technical Specifications

Applications

HTV Silicone Cable Insulation and Jackets

Solid silicone insulation for high-voltage power cables (10–35 kV class), motor lead wire (Class H 180°C), railway and aerospace wiring, and fire-survival circuit integrity cables. DCBP at 1.0–1.5 phr in methyl-silicone HTV gum gives a curing window of 4–8 minutes at 200°C continuous vulcanisation tunnel temperature, with line speeds of 5–10 m/min for typical 5 mm wall thickness.

Extruded Silicone Profiles

Sealing profiles, gaskets, food-contact tubing (without medical-grade qualification — Karstedt-cured silicone is required for that) use DCBP at 0.5–1.0 phr.

Calendered Silicone Sheet and Mat

Thermal insulation pads, gasket sheet stock, silicone-coated fabric use DCBP at 1.5–2.0 phr to achieve Shore A 70+ hardness.

Compression-Moulded Silicone Parts

Automotive boot covers, oven seals, kitchenware use DCBP at 0.8–1.5 phr with cure cycles of 3–10 minutes at 170–180°C platen temperature.

Selection Guide vs Other Peroxides

DCBP is the lowest-temperature peroxide — choose for thin-section extrusion in continuous vulcanisation tunnels where fast onset matters. For higher-temperature cures (above 130°C) where DCBP would be over-active, specify DCP (dicumyl peroxide) or DBPH. For medical, food-contact, or optical silicone, switch entirely to Karstedt platinum addition cure to eliminate peroxide byproduct and halogen content.

Equivalent Grades

• Akzo Nobel Perkadox PD-50S — primary commercial DCBP paste
• Arkema Luperox CDB — alternative European supply
• Pergan PD 50 — alternative supplier
• Generic DCBP 50% paste — Chinese commodity grade with SADT certificate