(151b) Analysis of Spontaneous Ignition in Various Polymer Resin

Polymer resin in the form of powder or pellets are often put under thermal stress during storage, transportation and downstream processing such as extrusion and film productions. Thermal characteristics of polymer must be understood well and thermal conditions must be designed accordingly in order to avoid undesired combustion of the polymer. In this study, two types of polymer resins are put to thermal scanning test for characterization of the sample and self-ignition test to understand their behaviors when they are handled in bulk quantity.

In characterizing thermal behavior, scanning calorimetry such as SC-DSC and HP-DSC are useful tool. SC-DSC analysis can be performed under air atmosphere and under inert gas atmosphere such as nitrogen to test for any oxidation heat. If low temperature exotherm is observed only in the scan under air atmosphere, this exotherm can be assumed that it is due to oxidation reaction. However, such oxidation exotherm observed in SC-DSC analysis tend to be small due to lack of oxygen in the sealed cell and does not propagate to thermal degradation of the sample polymer. The true effect of oxidation can be seen using HP-DSC　analysis, in which excess oxygen is present in the pressure chamber. The on-set of the oxidative exotherm may be similar as in SC-DSC analysis, however due excess oxygen available in the system the exotherm is much greater then what was observed in SC-DSC and it continues into the temperature rage where thermal degradation occur.

When large amount of polymer resin is handled in commercial scale production, self-heating and spontaneous combustion must also be considered for safe handling. Non-agitated large amount of polymer resin may undergo slow oxidation to accumulate heat within the system. As described in the Frank-Kamenetskii theory, the balance between heat generation and heat dissipation are the key factors that determine self-heating of the material. Spontaneous Ignition Temperature test (SIT) and Wire Basket test (WB) have been performed to determine self-ignition temperature and induction time for safe handling condition.

By performing appropriate thermal scanning and bulk material testing, we were able to identify the potential dangers in the two types of polymer resin tested. From such limitations, process conditions for such polymers can be re-assessed for safer handling.