Durez phenolic molding compounds

Durez Phenolic Molding Compounds

Product Description

Durez phenolic molding compounds were thermoset plastics manufactured by Durez Plastics Division — later operating under Hooker Chemical Company — from at least the 1950s through the mid-1970s. These compounds were engineered for applications demanding high heat resistance, dimensional stability, and electrical insulation properties. End users included manufacturers of circuit breakers, switchgear components, motor housings, electrical connectors, and industrial controls. The compounds were supplied as granular or pelletized resins that could be compression-molded or transfer-molded into finished components under heat and pressure.

Phenolic resins derived from formaldehyde-phenol chemistry had been a workhorse of the electrical manufacturing industry since the early twentieth century, and Durez was among the leading commercial suppliers of specialty formulations. The company developed product lines tailored to specific performance thresholds — arc resistance, flame retardancy, compressive strength — and asbestos-filled grades were positioned as premium offerings where thermal and mechanical demands were most severe. Hooker Chemical correspondence produced in litigation identifies active sales of asbestos-containing Durez formulations to industrial customers through at least 1976, when asbestos-filled phenolic grades were phased out of the product line.

Asbestos Content

Documentary evidence generated in product liability litigation identifies multiple specific Durez formulations containing asbestos at varying concentrations and fiber types. Hooker Chemical-to-Westinghouse correspondence dated between 1972 and 1976 provides the most granular product-level detail available in the public litigation record:

• Durez 1544 contained approximately 3.8% chrysotile asbestos by composition.
• Durez 160990 contained approximately 46% chrysotile asbestos by composition.
• Durez 18001 contained approximately 44% chrysotile asbestos by composition.
• Durez 23639 contained approximately 36% crocidolite asbestos by composition.

The range of asbestos content across these formulations — from roughly 4% to nearly half the total compound mass — reflects differing engineering objectives. Lower-filled grades used asbestos primarily as a processing or flow-control additive, while higher-filled compounds relied on asbestos fiber networks to achieve thermal insulation values and arc resistance ratings that competing fillers could not match at the time.

The presence of crocidolite (blue asbestos) in Durez 23639 is particularly significant from a health standpoint. Crocidolite fibers are considered among the most biopersistent asbestos fiber types and are associated with elevated risks of mesothelioma relative to chrysotile. Its documented use in a commercial molding compound sold to electrical manufacturers reflects industry practice that persisted into the mid-1970s despite growing regulatory and scientific attention to fiber type distinctions.

AHERA-recognized analytical methods — including polarized light microscopy and transmission electron microscopy — have been used in subsequent testing of archived product samples to confirm asbestos identity and fiber morphology consistent with these historically documented compositions.

How Workers Were Exposed

Workers at facilities that purchased, processed, or finished Durez asbestos-containing molding compounds encountered asbestos fibers at multiple stages of production. The nature and intensity of exposure varied by job task, but litigation records document that several distinct trades faced repeated and potentially significant contact with airborne asbestos.

Molding press operators loaded granular or pelletized compound into heated dies and operated compression or transfer presses. The loading process — scooping, measuring, and charging press cavities with raw compound — generated dust from the granular material. At the elevated temperatures used in phenolic molding (typically 300–375°F), some surface breakdown of the cured material also occurred, and mold release events could expel particulate matter into the work area.

Tumbling and deflashing workers processed freshly molded parts to remove flash — the thin fins of excess material squeezed out along parting lines during pressing. Tumbling barrels agitated batches of parts against each other or against abrasive media, breaking off flash mechanically. Plaintiffs alleged that this process released asbestos fibers embedded in the phenolic matrix as cured parts fractured and abraded, generating fine dust that remained suspended in poorly ventilated tumbling areas.

Grinding and buffing operators performed secondary finishing on molded electrical components, shaping gate stubs, smoothing mold marks, and achieving dimensional tolerances. Dry grinding of cured phenolic parts — particularly high-fill grades containing 36% to 46% asbestos — produced substantial quantities of fine particulate. Plaintiffs alleged that grinding and buffing stations operated without adequate local exhaust ventilation during much of the period when asbestos-filled compounds were in production use, and that workers in adjacent areas shared the same air handling zones.

Quality control inspectors at electrical equipment plants were documented as being present on production floors throughout shifts, moving between press areas, finishing stations, and inspection benches. Litigation records document allegations that inspectors received bystander-level exposures over sustained periods, including during deflashing and grinding operations, without being classified as primary production workers and therefore without access to whatever limited respiratory protection programs existed at individual facilities.

The 1972–1976 Hooker Chemical-to-Westinghouse correspondence referenced in litigation is notable because it reflects contemporaneous business communication between a major asbestos-containing compound supplier and one of the largest industrial users of molded electrical components — suggesting that knowledge of asbestos content was present at both the manufacturer and customer levels during the final years of asbestos-filled production.

Documented Product Identification

The following details are drawn from public asbestos litigation records, manufacturer catalog pages, technical manuals, and corporate history materials. Each item reflects the product as documented in those sources.

Documented asbestos-use period: 1972

Corporate context: Durez Division was a division of Hooker Chemical Company. Hooker Chemical Company later became part of Occidental Chemical Corporation (Occidental).

Documented asbestos components: Calidria RG-244 asbestos (thixotroping additive).

Documented asbestos-component suppliers: the public records lists the following external suppliers of asbestos-bearing packing, gaskets, and seals used in conjunction with this manufacturer’s equipment — Union Carbide (Calidria RG-244 asbestos).

Industries served: Structural resins, Polyester resin manufacturing.

Documented product lines:

• DRH-323 (Polyester Resin DRH-323) (1972). A structural vinyl resin made by thixotroping EPOCRYL Resin 21 with Union Carbide Calidria RG-244 asbestos and water for use as a thixotroped polyester resin. — asbestos components: Calidria RG-244 asbestos thixotroping agent.

Durez Division of Hooker Chemical Company purchased EPOCRYL Resin 21 from Shell Chemical Company and thixotroped it with Union Carbide Calidria RG-244 asbestos for resale as DRH-323. Shell Chemical Company manufactured the asbestos-containing resin under contract for Durez/Hooker.