Thermal state of tobacco materials in an electrically heated tobacco product (eHTP): Evaluation framework and experimental verification

Abstract

Electrically heated tobacco products (eHTPs) are novel products that could potentially reduce health risks relative to smoking. A series of thermal physico-chemical processes occur in tobacco materials while an eHTP is consumed under designed heating conditions. In order to establish a quantitative characterization of the thermal state of the tobacco materials in eHTPs, this study proposed a universal and systematic framework to evaluate the thermal state of eHTPs, irrespective of the heating technology used by the heating device (e.g., central vs. peripheral, radiation vs. induction, etc). For this purpose, a physical concept of thermal state $\hat{\eta }$of eHTPs was defined, which indicated the quantities and the compositions of the aerosol released, and a characteristic temperature $\hat{T}$ was also introduced. The framework uses the Pearson correlation to conduct dimensionless treatment on the thermal conversion efficiency of the working eHTPs, which took into account the effective migration of key aerosol components, the release of harmful or potentially harmful constituents (HPHCs), and the oxygen consumption of the thermal processing involved. The framework then defined a combination of datasets corresponding to $\hat{\eta }$, which involved 8 key thermophysical indicators, such as the tobacco's thermal mass loss, the oxygen consumption rate and carbon monoxide formation, the release of nicotine, glycerol and total particulate matter, and the release of acetaldehyde and toluene as markers of volatile HPHCs. Under the assumption of a unique relation between $\hat{\eta }$ and $\hat{T}$, the numerical function between volume average temperature$\bar{T}$ and $\hat{T}$ of the tobacco materials under different heating conditions was obtained by a modified factor method, and the function set f($\hat{T}$) was established. When $\hat{T}$ value of 240 ℃ was served as a key reference temperature, its corresponding ${\hat{\eta }}_W$ (substance) was 0.46, the corresponding $\hat{\eta }$ values for nicotine and glycerol are above 0.85, approaching full release for the two key aerosol substances, with a lower oxygen consumption and the release of HPHCs. Under the same heating temperature T or the $\bar{T}$, the $\hat{T}$and $\hat{\eta }$ of the tobacco materials under a peripherally heated condition were higher than those under a centrally heated one. In summary, the framework of the thermal state $\hat{\eta }$ defined as a function of f($\hat{T}$) could be used to quantitatively characterize the thermal state of eHTPs irrespective of their heating mechanisms.