To
understand the properties, performance and the durability of a denim fabric, it
is essential to understand the fibers within the fabric the yarn, the fabric
structure, and what processes and treatments that have been used to produce and
finish the fabric. Fibers contribute to fabric performance and influence
product aesthetic, comfort, durability, appearance retention and care. Fiber
properties are determined by their physical structure, chemical composition and
molecular arrangement. The type of yarn and its structure influence hand and
performance. The processes that are used also influence hand, performance,
appearance and the performance of the fabric During use and care
PROPERTIES
OF COTTON FIBRES
The
fibre length influences the properties of cotton and cotton denim fabric.
Longer fibers will give higher durability and quality .
Cotton
quality is classified considering staple length, grade and character. Only the two
first-named plays a role when purchasing cotton. In mass production and cotton synthetic
blends,
low-middling cotton is commonly used. For high quality products, longer staple fibers are preferred.
low-middling cotton is commonly used. For high quality products, longer staple fibers are preferred.
The
cotton fiber is a medium strength fiber with a dry breaking tenacity of 3,5 to
4,0 g/d. In contrast with other fibers, cotton will get stronger in wet
condition. Strength can increase by 30 % .
The
cotton fiber is easily harmed by acids but is not greatly harmed by alkalis.
Over all, the abrasion resistance of cotton is good, but heavy fabrics are more
resistant to abrasion in comparison with thinner cotton fabrics.
Due
to the higher strength in wet condition, cotton can be handled roughly during
laundering and in use. No special care needs to be taken when washing and
drying cotton and cotton jeans. Dyed cotton products that are washed in too hot
water, may lose color. For better retain of colour, warm water should be used.
Use of chlorine bleach will weaken the fibres and therefore it should not be
used on regular basis.
RING
SPUN YARNS
Ring
spun yarn is commonly used in denim fabrics. In ring spun yarns the entire
fibrous stand twisted. Ring spun yarns have fibres that are fairly well aligned
with the yarn axis. The longer the fibres are, the stronger the yarn will be.
Also, yarns with better-aligned fibres are stronger than yarns with less
well-aligned fibres.
Crease
retention is higher for those fabrics containing longer-fibers and
better-aligned fiber yarns.
DENIM
DYES
Indigo
is commonly used to dye blue jeans. There are different types of indigo dye,
both natural and synthetic. The synthetic indigo dye is commonly used in the
textile industry. Indigo is challenging to dye because it is not soluble in
water. To be dissolved, the indigo must undergo a reduction 11
.Generally
the indigo has a poor staining to the cotton fibre, which could cause dry- and
wet fade and colour loss. When dying dark, especially black denim jeans, Sulphur
dye is used. Like the indigo dye, the Sulphur dye is insoluble in water and a
reduction has to be made to make it attach to the fibre. Fibres, yarn, fabric
and garment can be dyed. For jeans, it is normal to dye the warp before weaving
and keep the weft undyed. Sometimes additional dying are made on the garment,
this is called garment dying. Dyes itself rarely cause damage on the fibres and
negative affect the durability of the jeans. The poor colour fastness to cotton
can sometime be a problem.
DENIM
FABRIC PROPERTIES
In
denim fabrics the woven structure called 2:1 twill is commonly used. In 2:1
twill warp yarn floats on the surface of the fabric. The twill weave have a
technical face and back, the technical face is the side of the fabric with most
pronounced wale. The technical face is usually more durable than the technical
back. High count woven fabric, i.e. high amount of interlacing, gives a strong,
compact, stable and durable fabric. Low count fabric, i.e. fewer amount interlaces,
gives a flexible and soft fabric that easily shrinks. To resist big dimensional
changes it is important with a good
balance
between warp and weft .
DIMENSIONAL
STABILITY
Dimensional
stability is the ability to resist shrinkage or stretching 15
.
As Mentioned earlier, fibre content has influence on properties of the fabric.
Three
factors that could cause dimensional changes are:
·
Tension
·
Swelling
·
(Felting, wool)
Tension,
and the degree of tension, is one important aspect that influences the dimensional
stability. Tensions generally occur during construction when yarns are held
stretched. When the fabric later on is exposed to moisture, this can result in
dimensional changes. The degree of dimensional change at relaxation depends on
weave type, both in warp, weft and on total shrinkage. Extremely compact
fabrics or high thread counts are more stable. Woven fabrics usually have a
tolerance of ± 3 % shrinkage. Studies show that for good dimensional stability,
woven fabrics must have a good number of interlacing in both weft and warp
direction. It is not enough to have good interlacing numbers in one direction,
since woven fabrics must have a stable structure. Also, studies show that
fabrics with low crimp values have good dimensional stability because it
restricts shrinkage, even at low number of interlacing’s.
Swelling
occurs when fibres are exposed to moisture and the fibre expands. Because of
hydrophilic properties, fibres like cotton, flax, silk and rami have great
abilities to swell. When fibres swell, their “way to walk” gets longer which
will lead to shrinkage. Due to friction, dimensional changes will retain after
drying. Swelling can also result in expansion, so called growth.
To
minimize the risk of having large dimensional changes, finishes can be done to
prevent this. Depending on type of dimensional change you want to fix,
finishing process is chosen.
A
connection could be stated between dimensional change and elastane in denim
fabrics. Cotton/elastane blends tended to shrink more, and easier than pure
cotton denim fabrics. The tension that is built up in fabric during weaving,
will relax after laundering, and cause the fabric to shrink. No conclusion
could be made that the amount of elastane in fabrics would have an impact on
the dimensional change.
TEAR
STRENGTH