Biomedical Engineering Reference
In-Depth Information
In Australia, in the 10 years up to 2012, there was a substantial increase in fiber
length (0.16 mm per year), but fiber strength was constant at about 30.5 g/tex
through the same time and a trend for reduction in micronaire to more favored
values between 4.1 and 4.3 (Fig.
10.3
). The length and micronaire improvements
were the direct result of intensive breeding efforts over the previous 10 years
[
51
]. China reached 30 mm fiber length, while India has reached 28 mm fiber
length after great improvements since 2002 to reach the same levels as the USA.
China has improved fiber strength over a 10-year period to reach 30 g/tex by 2010.
Micronaire is usually influenced more by climate and management than cultivar
choice, so micronaire trends through time were variable in all countries.
Current Trait Targets and Breeding Goals
As a breeder, fiber quality improvement is seen as a way to maintain market
demand and price for cotton producers and a way for cotton to compete with
synthetic fibers in textile mills. Depending on the market, price premiums may be
applied for cotton fiber with higher values of length and strength, intermediate
micronaire values, and clean grade (as defined below), while conversely, price
discounts may apply to cotton fiber that is below industry-defined base levels for
key quality parameters. These parameters affect the efficiency of spinning, weav-
ing, and dying which ultimately influence the profitability of the textile industry and
in turn the profitability of cotton production.
After ginning, cotton fiber samples are tested for quality by standardized instru-
ments such as a High Volume Instrument (HVI) [
67
]. The HVI measures the length
by creating a “beard.” The beard is a clamped section of fiber that is combed to
remove any loose fibers; it is scanned from the clamp to the tip of the longest fiber.
The upper half mean length is determined by the average of the longest half of fibers
[
67
]. Fiber bundle strength is determined from this beard by using another clamp to
apply force. The amount of fibers in the beard and the force required to break them
determine the fiber strength.
Micronaire is a measure of fiber resistance to airflow, which is an indirect way to
estimate fiber fineness (linear density) and maturity. High micronaire vales (
5.0)
>
indicate a coarse fiber (less fine), while low values (
3.5) indicate immature fibers,
both undesirable for spinning. Assessment of fiber economic value based on
maturity and linear density separately are slowly being adopted as new instrumen-
tation is developed to measure them at a realistic speed to fit into a standard HVI
quality testing stream [
68
].
Grade currently encompasses color and trash content. Cotton is naturally white
and most desirable but due to environmental variables can turn yellow or even gray
in extreme situations. Leaf, dust, and other foreign material make up the trash
content. Excessive leaf hair is prone to adhere fragments to the cotton lint after
defoliation and during harvesting thus increasing trash content. Trash contaminates
the cotton and directly impacts the quality of
<
the yarn. Environment and
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