Introduction

Yellowing of textile fabrics is one of the oldest and most widespread quality problems known. The yellowing can be seen directly in the case of market whites, pastel shades or even after-washed denims. However, shade change noticed in darker colored fabrics can often be attributed to chemical change or degradation of the fiber or some chemical agent either purposely applied to the fabric in finishing or inadvertently absorbed by the fabric in its storage and shipment to market or during its end use. As a general statement, yellowing of textile materials is an indication of unanticipated chemical degradation. Very often, as colorless chemicals decompose, they form light to moderate yellowish colors. Of course, if this chemical is a textile finish or additive or has been absorbed by a textile product, this color formation is noted as fabric or garment yellowing. It should also be noted that continued chemical decomposition could form moderate to dark brown colors or, in some extreme cases, even black colors.


It has been suggested by many investigators in the textile, retail, and consumer protection areas that the frequency of occurrence of yellowing of fabrics is actually on the increase. This is understandable because of the wide variety of fibers and fiber blends that compose textile fabrics available in todays market.


Additionally, textile finishing chemicals are more numerous and chemically complex than ever before. They often show yellowing tendencies as they age or are subjected to improper storage and cleaning techniques. Also, investigators have suggested that the high concentration of various atmospheric pollutants present today in many parts of the world resulting from a variety of industrial and natural sources are the major reason for the observed fabric yellowing increase.


Causes of Yellowing


All types of textile products have been subject to yellowing including those made from natural fibers such as cotton wool or silk, as well as those composed of synthetic fibers such as polyester, nylon, or spandex. It should also be noted that in the cases of blended fabrics, at times only one fiber in the blend may be affected by the yellowing. However, at other times several or all fibers in the blend are affected. Specifically, the cause of the yellowing often determines which fiber(s) in the blend exhibit the yellowing. This fact can be used as a diagnostic tool to help determine the source of the observed yellowing and aid in the development of a strategy to prevent future problems.


In recent years, the various causes of these yellowing issues have been studied extensively with the subsequent publication of numerous technical papers and reports. Generally, the causes can be grouped into the following broad categories with the understanding that there can be crossover or combinations of causes that yield observed fabric yellowing:


1. Fiber Degradation Destruction, decomposition, internal change of the fiber structure due to chemical or biological degradation, exposure to excessive heat, intensive or long term exposure to light radiation and/or fiber aging are all primary causes of fabric yellowing. Additionally, specific fiber blends may actually increase the occurrence of these problems.


2. Chemical Additives or Auxiliaries It is well known that the overuse or misuse of chemical finishes such as softeners, lubricating oils, resins, optical brightening agents, or metallic salts can lead to unwanted fabric color change including fabric yellowing.


3. Atmospheric Pollutants As was stated previously, atmospheric contaminants from both natural and industrial sources can lead to pronounced fabric yellowing. The specific pollutants include, but are not limited to oxides of nitrogen, sulfur dioxide, and ozone. The mechanisms for the actual fabric contamination are numerous and varied but are normally directly related to specific fiber or fiber blend content along with fabric finishing processes.


4. Transferred Contaminants The contaminants often are contained in cardboard boxes or dividers, plastic sheets, films, or bags and in auxiliary materials such as pumice stones used for garment after-washing processes. In recent years this type of yellowing has been both frequent and also difficult to minimize.