This work aims to classify seven
common household plastic types
which include polyethylene terephthalate (PET), high density polyethylene
(HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE),
polypropylene (PP), polystyrene (PS), and polycarbonate (PC) utilizing
near-infrared (NIR) spectroscopy. Four methods including linear discriminant
analysis (LDA), partial least-squares discriminant analysis (PLS-DA),
spectral angle mapper (SAM), and support vector machine (SVM) were
tested for their classification performances, and principal component
analysis (PCA) was applied before LDA and SVM. All the classification
models were built based on virgin plastics. The results showed that
seven types of plastic could be classified excellently with all the
methods when the test sets were composed of virgin samples. When the
models were tested on waste plastics, most types could be well classified,
and all the misclassifications occurred between HDPE and LDPE and
PET and PC. Then for HDPE and LDPE and PET and PC that were prone
to be misidentified, some specific spectral bands were reselected
for further classification. To achieve the best result, an approach
combining PCA, SVM, LDA, and PLS-DA was presented. The validation
results showed significant improvement, with the F1 scores of LDPE
and HDPE increasing from 65.2% to 86.7% and 24.2% to 84.7%, respectively,
and 100% accuracy was achieved for the other five types.