The principal objective in the treatment
of e-waste is to capture
the bromine released from the brominated flame retardants (BFRs) added
to the polymeric constituents of printed circuits boards (PCBs) and
to produce pure bromine-free hydrocarbons. Metal oxides such as calcium
hydroxide (Ca(OH)2) have been shown to exhibit high debromination
capacity when added to BFRs in e-waste and capturing the released
HBr. Tetrabromobisphenol A (TBBA) is the most commonly utilized model
compound as a representative for BFRs. Our coauthors had previously
studied the pyrolytic and oxidative decomposition of the TBBA:Ca(OH)2 mixture at four different heating rates, 5, 10, 15, and 20
°C/min, using a thermogravimetric (TGA) analyzer and reported
the mass loss data between room temperature and 800 °C. However,
in the current work, we applied different machine learning (ML) and
chemometric techniques involving regression models to predict the
TGA data at different heating rates. The motivation of this work was
to reproduce the TGA data with high accuracy in order to eliminate
the physical need of the instrument itself, so that this could save
significant experimental time involving sample preparation and subsequently
minimizing human errors. The novelty of our work lies in the application
of ML techniques to predict the TGA data from e-waste pyrolysis since
this has not been conducted previously. The significance of our work
lies in the fact that e-waste is ever increasing, and predicting the
mass loss curves faster will enable better compositional analysis
of the e-waste samples in the industry. Three ML models were employed
in our work, namely Linear, random forest (RF), and support vector
regression (SVR), out of which the RF method exhibited the highest
coefficient of determination (R
2) of 0.999
and least error of prediction as estimated by the root mean squared
error (RMSEP) at all 4 heating rates for both pyrolysis and oxidation
conditions. An 80:20 split was used for calibration and validation
data sets. Furthermore, for showing versatility and robustness of
the best-predicting RF model, it was also trained using all the data
points in the lower heating rates of 5 and 10 °C/min and predicted
on all the data points for the higher heating rates of 15 and 20 °C/min
to again obtain a high R
2 of 0.999. The
excellent performance of the RF model showed that ML techniques can
be used to eliminate the physical use of TGA equipment, thus saving
experimental time and potential human errors, and can further be applied
in other real-time e-waste recycling scenarios.