Thesis Details

Thesis Title: Evaluation of near-infrared reflectance spectroscopy to estimate the dye uptake of cotton
Thesis Author: Barbara Wall
Abstract: There are a large number of variables which will cause structural and property variations in cotton, resulting in differential dye uptake between cottons. This work concentrated on determining how different properties influence the dye uptake of cotton, and on using NIRA to estimate the effect of these variations on dye uptake. It is difficult for a dyer to asses the dye uptake characteristics of cotton prior to dyeing, as no plant-useable methods are available to accomplish this. The lack of predictability in the cotton dyeing process often results in costly reworks or dye adds. A method of determining the dyeing characteristics of cotton would be a tremendous aid to dyers. The speed 'and reliability of NIR techniques for measuring other textile materials has already been established. A recent study which evaluated the application of NIRA to analyze the internal structure and predict the dye uptake of polyester fibers was successful, indicating the potential of NIRA to estimate the dye uptake of cotton. The first part of this work was to identify those cotton properties that were influencing dye uptake. A number of variables believed to be related to dye uptake were evaluated to determine which properties had the greatest impact on dye uptake. It was determined that the 60% of the dye uptake of cotton is dependent upon a combination of fineness and maturity. The second part of this work was to relate the dye uptake values of the samples to NIRA measurements, in order to determine if NIRA was detecting these same changes in properties which were influencing dye uptake. The wavelengths selected by the InfraAlyzer as being the significant wavelengths for determining dye uptake were all wavelengths associated with cellulose bonds. Based on the results obtained in this study, the following conclusions were made: 1. A combination of cotton maturity as determined by NIRA, and fiber fineness account for 60% of changes in dye uptake of cotton, as measured by the K/S values for the dyed fibers. Micronaire was also determined to have a significant effect on dye uptake equal to that of NIRA maturity and fineness values combined. In this thesis, 100% of the dyeing behavior of cotton could not be explained. 2. NIR can detect the same changes in cellulosic content that are influencing dye uptake. The four wavelengths indicated by the regression analysis as having a significant affect on dye uptake were associated with absorption bands resulting from first overtone and combination bands of O-H as well as C=OjC-H combination bands of the bonds in the cellulose molecule. To further examine the mechanism by which NIR was measuring dye uptake, spectral analysis was completed on two samples exhibiting high and low dye uptake. The plot of second derivative scans of the two samples further sUbstantiated these observations. 3. with a correlation of 0.85, NIRA estimated the dye uptake of the 43 samples used in creating the original calibration equation. For ten unknown samples not used in the calibration equation, NIRA estimated the dye uptake with a correlation of 0.54. These results indicate that further research is needed to identify the remaining 40% of the variations influencing the dye uptake of cotton, before NIRA can successfully be applied in a production situation. However, the potential for NIRA to determine dye uptake of cotton exists, as is evidenced by successful detection of those changes in the cellulose bond vibrations that are indicative of changes in dye uptake. The potential use of the InfraAlyzer as a production tool would enable quick detection of cottons with critical differences in dye uptake. However at the present time, further research is necessary to fully understand the mechanism of dye uptake in cotton. An understanding of the properties influencing the remaining 40% of the variations in dye uptake would enable a more effective calibration equation to be developed.