A Study of Influential Factors on Thermal Stability of Polymeric Materials

Mitsui Chemicals, Inc. is one of the major petrochemical companies in Japan. We use avariety of polymeric materials which provide high value-added products to a wide range of industries. Nowadays, polymeric materials are necessary for industries to produce commodities. Therefore, large amounts of polymeric materials are used in chemical plants every day. On the other hand, they have caused several serious accidents in recent years because radical polymerization reactions can release a large amount of energy. If uncontrolled polymerization occurs, it will be rapid and can be violent, generating large amounts of heat which increases the pressure. In addition, second reactions such as decomposition of products lead to more temperature and pressure rises which cause explosions. To avoid these accidents, many studies about stabilization of polymeric materials have been done. For example, the addition of effective inhibitors and modeling of the inhibition mechanism have been reported.

Acrylic acid is one of the most reactive polymeric substances, once a runaway reaction, it can’t be stopped. In 2012, an explosion and fire involving acrylic acid occurred at Nippon Shokubai and the accidents damaged not only the plants but also the surroundings. In our plants, we also use acrylic materials such as acrylic acid and its esters. So after this accident, we have re-evaluated how to treat acrylic materials safety from storage to disposal.

But it’s difficult to judge whether it is the optimum condition or not. Therefore we tried to reveal the influential factors and their impact on thermal behavior of acrylic materials.

Commercially, acrylic acid is stabilized with p-methoxyphenol (MEHQ) or phenothiazine (PTZ). It’s known that the presence of dissolved oxygen is necessary for MEHQ to function effectively. A polymerization reaction is prevented by the consumption of the oxygen and MEHQ (here, we call it polymerization induction periods). During polymerization induction periods, thermally produced radicals react with oxygen to form peroxide which can work as a radical initiator. So the forming peroxide has a potential hazard.

In this work, we compare the thermal behavior of acrylic acid and its esters under different conditions of oxygen and inhibitor concentration.

Keywords: polymeric materials, acrylic acid, thermal stability, polymerization, inhibitor,

MEHQ, oxygen, peroxide