Fig. 2

Raman spectra (a, d), correlation matrix (b) and correlation values (c) of a typical spectrum collected from the released fibres. In (a), the collected sample’s spectrum is pre-treated towards identification, after intensity off-setting for presentation. Similarly, all the spectra including the sample and 14 items (13 common plastics and cotton) were subjected to the pre-treatment and then participate PCA to generate a correlation matrix in (b). The correlation value of the sample with 14 items is listed in (c). The direct comparison between the spectra of sample (after pre-treatment) and the standard spectrum of the assigned PA is presented in (d), after intensity off-setting for presentation. The assignment is indicated by circulating in (b, c)