Mitsui Chemicals, Inc.(MCI) is a major petrochemical company worldwide. They produce polymeric materials resulting in high value-added products covering a wide range of industries. Normally, polymeric materials are polymerized under controlled radical polymerization, which releases a large amount of energy and increases temperature. Uncontrolled radical polymerization can occur, resulting in serious accidents. In the worst case, secondary reactions such as the decomposition of the polymer can occur, leading to more energy, pressure, and temperature increases. These secondary reactions can cause serious fires and explosions.
To avoid these major accidents, many studies about the stabilization of polymeric materials have been undertaken 1,2). For example, the addition of effective inhibitors and modeling of the inhibition mechanism have been reported 3,4).
Acrylic acid is one of the most reactive of polymeric substances. An example of an accident with an acrylic acid tank occurred in 2012 5), after which, we re-evaluated how to treat acrylic materials safely from storage to disposal within our plants. But it's difficult to judge the optimum conditions. Therefore, MCI undertook to reveal the influential factors and their impact behind the thermal behavior of acrylic materials.
Commercially, acrylic acid is stabilized with p-methoxyphenol (MEHQ). It's known that the presence of dissolved oxygen is necessary for MEHQ to function effectively. Polymerization reaction is prevented by the consumption of oxygen and MEHQ (called the polymerization induction period). During polymerization induction periods, thermally produced radicals react with oxygen to form peroxide which can work as a radical initiator.
This paper reports on the thermal behavior of acrylic acid and its esters as a result of using a differential scanning calorimeter (DSC) and an accelerating rate calorimeter (ARC) under different conditions involving oxygen and inhibitor concentration. The unique thermal behavior involving acrylic acid and its esters were found.