Organic peroxides are important tools for the composites industry. They can be used to make polymers (initiation), modify their rheological properties (visbreaking), alter polarity or attach pendant functional groups (grafting), and enhance high temperature performance (vulcanization). The utility of organic peroxides results from their ability to decompose and generate radicals when heated or promoted, but particular attention must be paid to ensure the safe storage and handling of these materials.
Guidance for the storage of organic peroxides is provided by the National Fire Protection Association’s Hazardous Materials Code (NFPA 400), as well as the International Fire Code. Organic peroxide formulations are differentiated into six classes (I, IIA, IIB, III, IV and V) according to their transportation type and available burn rate data. Of these, Class I has the most stringent storage requirements and allowed storage quantities.
These codes also provide guidance on other safety aspects such as signage, fire extinguishing systems and storage arrangements. In general, organic peroxides should be stored away from incompatible materials and within the temperature range specified by the manufacturer.
Each organic peroxide formulation is unique in its specific hazards, but the four main hazards of organic peroxides are thermal instability, flammability, reactivity to contaminants and shock sensitivity.
- Thermal instability is the property that makes these chemicals useful in the polymer industry because their decomposition yields radicals. If this decomposition occurs when the organic peroxide is in concentrated form a dangerous situation can result. The decomposition reaction is exothermic and can generate a large amount of heat. In addition, this decomposition may result in formation of lower molecular weight, flammable molecules. Vapors generated by peroxide decomposition could be vulnerable to ignition if an adequate energy source is available.
A benchmark metric for comparing peroxide stability is the self-accelerating decomposition temperature (SADT). This is the temperature at or above which the peroxide will undergo a self-accelerating decomposition generating heat at a faster rate than can be dissipated from the container to the environment. The SADT is typically determined using one of four methods specified by the United Nations’ Manual of Tests and Criteria and is shown in Section 9 of the Safety Data Sheet (SDS) for every organic peroxide.
Although the SADT provides guidance on the minimum temperature that would present a safety hazard, the maximum storage temperature provides more practical guidance for storage of organic peroxide formulations. This temperature specifies the maximum temperature that a formulation should be stored to ensure both safety and product quality. The maximum storage temperature for a peroxide formulation is listed in Section 7 of the SDS and is considerably lower than the SADT.