“LOW COBALT INITIATED SYSTEMS FOR SODIUM HYPOCHLORITE SERVICE”

摘要

Alkaline bleach is commonly used in the pulp and paper industry for the bleaching ofwood pulp. While some metal alloys can be used in these environments, their cost oftenlimits their commercial applicability. Lower-cost fiberglass reinforced plastic (FRP)composites have been successfully employed in bleach service for many years.Cobalt-initiated systems are the most common system used with epoxy vinyl ester resins(EVER) in the FRP industry. However, when used in bleach service, poor service lifehas often been found for systems utilizing cobalt in the cure system and thereforeBPO/amine cure systems are typically employed. While this eliminates the problemsfound with cobalt, many manufacturers find fabrication with BPO/amine more difficult.A comparison was made between a BPO/DMA system, a cobalt system at the levelsrequired for a new EVER (0.03% Cobalt 6%), and two “industry-standard” cobalt levelscommonly used with standard EVER resins (0.1% and 0.2% Cobalt 6%). The couponswere exposed to conditions of an accelerated corrosion test of 5.25% sodiumhypochlorite at 100 °C.Weight loss data at 3 months showed the corrosion performance of coupons was linear tothe amount of cobalt used. Therefore, as the level of cobalt becomes very small, theperformance of the coupon approximates that of BPO. The “very low” cobalt level of0.03% is only possible with the newly commercialized family of epoxy vinyl ester resinsand can provide an alternative to the more standard BPO/amine systems for sodiumhypochlorite services. These formulations provide superior performance as compared tocoupons made using the “industry-standard” cobalt levels.Additional data at 6 months and 12 months will provide the full picture of couponperformance over an extended period of time.