SFG Analysis of Cellulose Polymorphs in Bleached, Mercerized, and l-NH3 Treated Cotton Fabrics

Sum frequency generation (SFG) is a non-linear spectroscopy which can take place only in a system lacking inversion symmetry. When a noncentrosymmetric medium material through which electromagnetic waves propagate is irradiated with high-intensity laser pulses with two different frequencies, a new photon can be emitted whose frequency is the sum of two input frequencies. The noncentrosymmetry constraint of the SFG process makes only the vibration modes with a net polar ordering in the cellulose crystal to be active in SFG vibration spectroscopy. All vibration modes that are arranged randomly or with inversion symmetry cannot generate SFG signal. Thus, SFG vibration spectroscopy is very sensitive to the structure of ordered cellulose in biomass. In this study, we report the detection and quantification of cellulose polymorphs (I, II, III) in cotton fabrics treated with bleaching, mercerizing, and liquid-NH3 processes.  The fabric treatments will be reviewed, and SFG analyses will be shown in comparison to traditional X-ray diffraction data.