Self-heating evaluation on thermal analysis of polymethyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE)

Abstract

Thermal analysis has been proven to be an efficiently technique to analyse thermal decomposition reactions of different type of materials. This technique is widely used in different fields. Among them, fire science, where polymeric materials are very common, has a particular issue, being the combustion reactions recurrent on these analyses. Thermal analysis has different particularities depending on the studied material. For instance, polymeric materials could undergo different decomposition reactions that are highly dependent on definition of the thermal analysis boundary conditions. The International Confederation for Thermal Analysis and Calorimetry (ICTAC) (Vyazovkin et al. in Thermochim Acta 590:1–23, 2014) and standards (ISO 11358-1. Plastics—Thermogravimetry (TG) of polymers—Part 1: General principles. ISO. 2014; https://www.iso.org/standard/59710.html. Accessed 31 Jan 2022), (ISO 11357-1. Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles. ISO. 2016; https://www.iso.org/standard/70024.html. Accessed 31 Jan 2022) stablish how to set-up these boundary conditions in the thermogravimetric (TG) and differential scanning calorimetry (DSC) standards. As far as initial amount of sample mass is concern, some discrepancies can be found between the standards. For instance, the standards suggest a sample mass between 10 and 100 mg for TG and between 2 and 40 mg for DSC, whereas the ICTAC recommendations suggests that the sample mass times the heating rate should not exceed 100 mg K·min−1 in thermo-oxidative decomposition analysis, which is equivalent to samples masses lower than 10 mg for heating rates of 10 K·min−1, or lower than 5 mg for heating rates of 20 K·min−1. This discrepancy may lead to obtain different results from the tests. Additionally, according to the thermal and thermo-oxidative decomposition of polymers, the ICTAC remarks the influence on the results of the sample thicknesses, carrier gas and heating rates, but it does not analyse the influence of self-heating as it does for the hazardous materials. This work presents a study of the self-heating influence in the thermal decomposition processes of two widely used polymers as poly methyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE). TG/DSC tests are used to evaluate the thermal decomposition processes. Boundary conditions of the tests definition as sample mass, atmospheres, and heating rate are considered to evaluate its influence on the polymers self-heating effect on the thermal decomposition. It also includes how to check if TG/DSC tests follows the theoretical principles of the thermal analysis, or if the results are affected by the self-heating. In the present study, a series of 32 experimental tests has been performed, analysing 16 boundary conditions. These experimental tests allow evaluating the influence of selected boundary conditions on the mass loss, the heat flux, and the materials decomposition reactions. Additionally, we analyse the effect of the boundary conditions on the temperature of the sample. Results show the impact of each different boundary conditions of the self-heating effect, and its influence in the final thermal decomposition measured and they represent an aid to define the suitable conditions to perform TG/DSC test on PMMA and LLDPE, or similar polymer materials. This is done by the evaluation of the influence of the self-heating in parameters as the sample temperature lags defined in [1], the reactions heat fluxes, and the difference between the sample and the programmed temperature. It is also analysed the influence of the auto-ignition temperature in the thermal analysis. It is remarkable the PMMA auto-ignition temperature effect on the TG/DSC results. Finally, some useful recommendations have been defined.

Depolymerization of PMMA-Based Dental Resin Scraps on Different Production Scales

“…Indeed, the reported decomposition heat of PMMA is in the range of 820 J/g [81]. The heat of gasification obtained in PMMAW DSC is in accord with other numbers reported for the thermal decomposition of PMMA [81][82][83].…”

“…Most studies focused on transitions below 200 °C, such as glass transition temperatures for composites prepared using PMMA and other plastics [68,[72][73][74][75][76][77], or assessed the mechanical and thermal properties of the polymer [78][79][80]. Reports of DSC analysis of the thermal decomposition of PMMA performed under higher temperature conditions are scarce [81][82][83]. Fiola et al [81] analyzed the thermal properties of extruded and cast PMMA by DSC, finding an endothermic peak between 327 and 427 °C for both samples with values of integrated heat flow (measure of the process enthalpy) An analysis of Figure 5 reveals the presence of one large endothermic peak between 370 and 433 • C. It is difficult to accurately describe energy trades in pyrolysis such as the heat of pyrolysis and vaporization enthalpies of products since many processes are coupled and happening at the same time.…”

“…Most studies focused on transitions below 200 • C, such as glass transition temperatures for composites prepared using PMMA and other plastics [68,[72][73][74][75][76][77], or assessed the mechanical and thermal properties of the polymer [78][79][80]. Reports of DSC analysis of the thermal decomposition of PMMA performed under higher temperature conditions are scarce [81][82][83]. Fiola et al [81] analyzed the thermal properties of extruded and cast PMMA by DSC, finding an endothermic peak between 327 and 427 • C for both samples with values of integrated heat flow (measure of the process enthalpy) of 1.5 J/g [81].…”

“…Wang et al [83] tested PMMA composites through DSC under a nitrogen atmosphere and different heating rates (10-30 • C/min) and found three stages of decomposition with three endothermic peaks [83]. Alonso et al [82] used DSC to analyze the thermal decomposition of PMMA under different mass quantities and different atmospheres, observing endothermic peaks in a nitrogen atmosphere [82].…”

Experimental and analytical study of the influence of the incident heat flux in cables heat release

“…This is the unique cable studied in the present work that does not have XLPE. As shown in the thermal analysis collected in [18,19], the PE is much more energetic than the PVC.…”