CRYSTALLINITY DETERMINATION OF POLYLACTIDE BY FT-RAMAN SPECTROMETRY

The complete Raman spectra of isotropically crystalline and amorphous polylactide (PLA) have been successfully obtained with the use of a Fo urier transform instrument equipped with a near-IR laser source. The R aman spectra of PLA were recorded at a resolution of 4 cm(-1) from a b ackscattering sampling geometry. The changes in band intensity and sha pe of Raman spectra in the crystalline PLA samples facilitated the qua ntification of the crystallinity, which was primarily determined by th e change in enthalpy via differential scanning calorimetry (DSC). A co mparison of quantitative analysis of crystallinity by a multivariate t echnique, partial least-squares (PLS), and a univariate method at the carbonyl stretching band is described. Quantitative analysis of PLA cr ystallinity was performed after the data preprocessing with the standa rd normal variate (SNV) method in the combined spectral regions 3100-2 800 cm(-1) and 2000-200 cm(-1) that were determined by the analysis of the correlation spectrum. The use of the calibration model containing mostly 1% D-PLA samples to separately analyze the samples with 1% and 5% D-PLA is discussed. Superior results obtained from the multivariat e over the univariate method make PLS the preferred method of choice i n quantification of crystallinity. The standard error of prediction (S EP) for the analysis of 1% D-PLA samples with the use of the calibrati on model described is 0.85 (-J/g), and the SEP for 5% D-PLA samples is 1.35 (-J/g) with the outliers excluded. The discrepancy in analyzing these two types of PLA samples with the use of the same calibration mo del is also discussed.