In situ FTIR and generalized 2D IR correlation spectroscopic studies on the crystallization behavior of solution-cast PHB film

The crystallization behavior of biosynthesized poly(3-hydroxybutyrate) film cast from 1,1,2,2-tetrachloromethane was studied by in situ FTIR spectroscopy and two-dimensional (2D) correlation analysis. Time-dependent in situ FTIR spectral variations in the C=O stretching region (1,780-1,700 cm(-1)) were monitored and analyzed by a series of data processing methods, including calculation of difference spectrum and second derivative spectrum, Fourier self-deconvolution, curve-fitting and 2D correlation analysis. Four bands have been resolved from the 2D correlation analysis, and the following overall sequential order among the intensity changes of the four bands has been obtained at 1,750 > 1,739 > 1,722 > 1,715 cm(-1). Combining with the other data processing methods, a curve-fitting approach has been employed to reveal that there are probably five component bands under the C=O band profile, centered at 1,746; 1,737; 1,728; 1,722; and 1,712 cm(-1). Detailed analysis on the in situ component band intensity variations in the C=O stretching region indicates that the crystalline and amorphous band intensities change simultaneously during the crystallization process, with no local sequential order. Further analysis on the relative area percentage changes of the five component bands suggests that the crystalline component only changes in a fully cooperative manner with part of the amorphous component at the initial crystallization period.