Page 295 - Handbook of Properties of Textile and Technical Fibres

Tensile properties of cotton fibers: importance, research, and limitations 269

After the introduction of HVI in the early 1980s, it was realized that the speed of
testing of fiber properties began to match the speed of testing of yarn properties,
perhaps faster. Thus, researchers around the world became more interested in
developing empirical relationships between fiber properties and yarn properties.
This interest was largely prompted by the introduction of many analytical tools and
computation software programs. Numerous studies were made by many cotton and
textile researchers, including the authors of this chapter, to establish such relationships.
The main analysis used to develop these relationships was multiple regression
analysis. This has made the relationships largely localized; in other words, they could
not be generalized or used in other situations except for the processes in which they
were developed. Nevertheless, empirical fiber-to-yarn relationships have served the
industry in addressing many questions. In the context of fiber-to-yarn strength relation-
ship, empirical analysis is still far from being reliable. This is largely due to the high
variability in the strength parameters and the mismatch of the testing principles of fiber
strength and yarn strength, or what can be termed “geometrical conflict.” For instance,
testing the yarn strength in a skein geometry at a constant rate of traverse, by winding a
120-yard (w110 m) skein on a wrap reel, may be useful for predicting the tensile
behavior of yarn during weaving or knitting, but it certainly has little physical
correspondence with a fiber beard strength or a single-fiber strength.

7.17.3 Cotton tensile behavior in end products
Perhaps, the ultimate benefit of understanding the tensile behavior of cotton fibers is to
be able to establish a fingerprint of a particular cotton type or variety in the end
product. This fingerprint is more critical today than ever before, as evident from a
recent study by Dr. Elmogahzy (2009b) sponsored by the Supima Cotton Association.
This study revealed a very serious issue regarding cotton fiber identity theft. It was
found through an extensive survey and testing of many cotton textile products (e.g.,
knit shirts, towels, and bedsheets) that there are numerous cotton textile products
available in the market that carry the labels of 100% ELS cotton (Supima or Egyptian
cotton), yet the percent of ELS cotton in these products did not exceed 20%, and more
than 80% of the fibers in these products were of the short- to medium-staple fibers. The
products inspected in this study consisted of many well-known textile brands in the
market. Many of these products were enhanced in both appearance and feel via
different methods of dyeing and finishing. However, inspection of the performance
of some of these products under repeated washing and drying, abrasive testing, and
random-tumbling pilling tests revealed that the initial appearance and feel has deteri-
orated after few washing and drying cycles, and the fabric suffered poor dimensional
stability and low durability. Unfortunately, the only valid way to discover the causes of
these problems was through tedious analysis involving extraction of the fibers from the
end products and testing them. It is true that superior tensile characteristics can be
masked temporarily in some products. However, when these products are put to
durability tests during repeated use and repeated washing and drying, poor fiber tensile
behavior will manifest itself in the performance of these products. These effects are
even clearer when products such as towels and bedsheets are used at high frequency
in hotel and hospital applications.