Non-bleaching heather method for improved whiteness of greige cotton

Authors: Easson, Michael; Condon, Brian; Reynolds, Michael; FRANQUI, ROBERT - Tintoria Piana; Bland, John

Submitted to: Journal of Engineered Fibers and Fabrics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2016
Publication Date: 9/4/2017
Citation: Easson, M.W., Condon, B.D., Reynolds, M.L., Franqui, R., Bland, J.M. 2017. Non-bleaching heather method for improved whiteness of greige cotton. Journal of Engineered Fibers and Fabrics. 12(3):54-59.

Interpretive Summary: Greige cotton is typically off-white to slightly yellow in color. The majority of cotton spinning, weaving or knitting employs greige cotton which is subsequently scoured and bleached prior to use in white goods or prior to dyeing in an even and predictable manner before use in colored goods. However, some specialty end uses, such as nonwovens where dyeing is uncommon, could use greige cotton in the final product if not for the negative consumer perception of yellowness. Many nonwoven end uses such as wipes, diapers or personal care items have difficulty supporting increased fiber costs introduced by scouring and bleaching cotton, and thus incorporate synthetic fibers instead. As a potential alternative to wet chemical treatment of greige cotton to reduce yellowness such as bleaching, bluing, or optical brighteners, this study investigated a mainly mechanical approach, involving low level intimate blending of blue-dyed fiber into a slightly yellow greige cotton base fiber. In accordance with the color space theory known as additive light mixing (also called additive color mixing), close physical or overlapping association of yellow and blue sources of light will appear white to light grey to the observer, such as in an LED television monitor producing white from red, blue, and green LED pixels. This is different from the more intuitive observation of subtractive color mixing like mixing dyes or pigments where blue mixed with yellow appears green. In this study samples of one bale of off-white greige cotton which was mechanically cleaned of foreign matter were dyed with three different reactive blue dyes, each having a slightly different color spectrum. Guided by a statistically designed blending experiment, these three different blue-dyed fiber samples were then blended back into the original greige cotton in various ratios to each other and at varying levels up to 5% by mass of total blue-dyed fiber in the overall blend. L*a*b* color measurements and UV-Vis spectral analyses confirmed a variation of yellowness with the blended blue fiber and a low yellowness, high whiteness optimum was found.

Technical Abstract: In accordance with the color space theory known as additive light mixing, the presence of dispersed blue-dyed fiber reduced the overall yellowness of a blended greige fiber and they were perceived as “whiter”. Various intimate blends of blue-dyed cotton fiber in greige cotton fiber were analyzed for color properties using a L*a*b* color space chromameter and a Ultraviolet-Visible (UV-Vis) spectrophotometer. A design of experiments (DOE) matrix approach provided a statistically-based mathematical means to predict the color properties of the intimate blends. The predictive accuracy of the mathematical model was confirmed in a follow-up experiment, and the blend resulting in the lowest yellowness and highest whiteness was determined. For fiber end uses which are too cost sensitive to support comprehensive wet chemical treatment of all of the fiber, such as nonwovens, intimate blending with low amounts of dyed fiber could produce visible effects at lower cost.