Raman spectra of high‐density, low‐density, and linear low‐density polyethylene pellets and prediction of their physical properties by multivariate data analysis

Abstract

Raman spectra have been measured for pellets of five samples of high-density polyethylene (HDPE), seven samples of low-density polyethylene (LDPE), and six samples of linear low-density polyethylene (LLDPE). The obtained Raman spectra have been compared to find out characteristic Raman bands of HDPE, LDPE, and LLDPE. Principal component analysis (PCA) was applied to the Raman spectra in the 1600 -650 cm Ϫ1 region after multiplicative scatter correction (MSC) to discriminate the Raman spectra of the three different PE species. They are classified into three groups by a score plot of PCA factor 1 vs. 2. HDPE with high density and high crystallinity gives high scores on the factor 1 axis, while LDPE with low density and low crystallinity yields negative scores on the same axis. It seems that factor 1 reflects the density or crystallinity. A PC weight loadings plot for factor 1 shows six upward peaks corresponding to the bands arising from the crystalline parts or all-trans O(CH 2 ) n O groups and seven downward peaks ascribed to the bands of the amorphous or anisotropic regions and those arising from the short branches. Partial least-squares (PLS-1) regression was applied to the Raman spectra after MSC to propose calibration models that predict the density, crystallinity, and melting points of the polyethylenes. The correlation coefficient was calculated to be 0.9941, 0.9800, and 0.9709 for the density, crystallinity, and melting point, respectively, and their root-mean-square error of cross validation (RMSECV) was found to be 0.0015, 3.3707, and 2.3745, respectively. The loadings plot of factor 2 for the prediction of melting point is largely different from those for the prediction of density and crystallinity.

Advances in two-dimensional correlation spectroscopy

“…2D spectroscopy was mentioned in the NIR study of LLDPE [295]. Sato et al [296] mentioned 2D correlation in their Raman study of polyethylene. Zhang et al [297] carried out dielectric spectroscopy of the miscible blend of PVPh and PEMA.…”

Online monitoring of synthesis and curing of phenol–formaldehyde resol resins by Raman spectroscopy

“…However, the band at 1300-1296 cm À1 can probably be assigned to the twisting vibration of the CH 2 group which appears in the region [38,39]. For the aliphatic series of (CH 2 ) n , the intensity of the band at 1305-1295 cm À1 increases with n [38] and, in addition, the Raman spectra of polyethylenes show a strong peak in this area [42,43]. The signal at 1300-1296 cm À1 may thus mainly be due to methylene bridges formed between phenolic species in the condensation reactions.…”

Raman characterisation of conventional and cross‐linked polyethylene in acetabular cups run on a hip joint simulator

“…[34 -36] Actually, recent studies have demonstrated the usefulness of the Raman fingerprint region for the quantitative analysis of PE crystallinity. [29,31,33] All the spectra were recorded under back-scattering conditions with 5 cm −1 spectral resolution using the 488-nm line of an Ar laser (Innova Coherent 70) with a power of about 10 mW. The detector was a charge coupled device (CCD) from Princeton Instruments Inc. cooled to 160 K.…”