[Measurement of ethylene content in polypropylene by Raman spectrum]

Ethylene content in polypropylene was studied by Raman spectrum, combined with partial least squares (PLS) method. The comparison between Raman spectra for polyethylene and polypropylene was carried out, and the spectra between 50 and 600, 600 and 1600, and 2700 and 3100 cm(-1) were analyzed respectively. The models for ethylene content prediction were built, while the model based on 50-3600 cm(-1) spectra gave the best performance. The experiment indicated that Raman spectrum gave the similar predictive results as the near infrared (NIR) spectrum; the values of correlation coefficient (r), relative average deviation (RAD) and root mean square error (RMSE) between predictive results and actual values were 0.995, 2.65% and 0.319, respectively. According to PLS analysis, the loadings of factor 1 could reflect the relationship between the composition of polypropylene molecular chain and ethylene content, and ethylene content had a positive correlation with CH2 content, but a negative correlation with content of CH3, C-H, and C-C. The results indicated that it was feasible to detect the ethylene content in polypropylene by Raman spectrum.