Pilling of fabrics

Definition: Pilling is a fabric-surface fault in which 'pills' of entangled fibres cling to the cloth
surface, giving a bad appearance to the garment. The entanglements of loose fibres that appear on
the fabric surface are called 'pills'.
The International Fabricare Institute's Education and Consumer Relations Departments defines
pilling as 'the formation of small tangles of fibres or balls on the surface of a fabric. The pills are
formed during wear and washing by the entanglement of loose fibres which protrude from the
fabric surface.

Mechanism of Pill formation

Pilling studies have shown that there are three distinct stages in the life span of a pill

a) Fuzz formation
b) Entanglement
c) Pill wear off.
Fuzz formation:

First, fibres are drawn to the fabric surface as a result of some mechanical action, and these form
Fuzz. But it was found that loose fiber ends which were present on the fabric surface did not grow
longer when the fabric was brushed or abraded. Rather, new fuzz was formed as contact was made
at some point along the fiber length, leading to a loop which finally pulled free at its looser end.
Entanglement: A pill formed quickly when the fuzz density reached a critical level. Pills are
formed by entanglement, interlacing, and rolling of the fibre tips projecting from the yarn.
Contaminants may adhere to the pills, which can facilitate their formation.
Pill wear off

The pills wear off under 'continued mechanical action, such as rubbing, laundering, drying, etc,
during wear and cleaning If at any time the external forces of bending or pulling exceed the total
breaking strength of the anchoring fibres, the pill is detached.

In a given fabric construction, the rate or extent at which these stages occur is determined by
the physical characteristics of the fibres that compose the fabric.
Fibre properties that affect the stage of pilling:

Fibre Properties that affect fuzz Formation:

Inter fibre Friction and Stiffness: For a fiber end to pull out of the yarn bundle, not only is it
necessary for interfiber frictional forces to be overcome. But The fiber must also bend as it works
its way under and over the cross-yarns of the fabric network. Thus, fibers which resist this bending
(stiff fibers) will have increased frictional restraining forces. High inter-fibre friction reduces the
pilling tendency [5]. Inter-fibre friction is effected through surface characteristics of the fibre.

Breaking Strength and abrasion resistance: When the restraining force exceeds the Fiber
breaking strength, the fiber will break rather than pull out. Therefore, the fiber breaking strength
determines the limit of the abrading force which can be applied-hence, the maximum length of
fibers which can be raised. On the other hand, the breaking of weak fibers during abrasion will
provide more ends leading to a shorter but denser fuzz.

Table 1: Fuzzy Tendency of various textile fibre.

Fibre Properties Fuzziness

Nylon high strength, a moderate inter fiber friction, and High
low stiffness.
Rayon a moderate strength, a high stiffness, and a low Intermediate
inter fiber friction.
 Polyester high strength, High inter fiber friction, high Intermediate
stiffness
Acrylic an intermediate strength, a high inter fiber Intermediate
friction, and a high stiffness.
Wool low tenacity fibers, so the fibers break instead of low
pulling out, resulting in short fuzz.
Acetate low tenacity fibers, so the fibers break instead of low
pulling out, resulting in short fuzz

Fibre properties that affect in entanglement tendency:

Fibre Shape: Fibres with a ribbon cross section are more effective in reducing the tendency of a
fabric to pill than round fibres. Research showed that the total fuzz level is the same for the round
and ribbon items while the pill level decreased to a level below that of the round fibres.

The difference in fuzz tendency between round and ribbon fibres depends on bending and frictional
effects. If the ribbon is bent across its minor axis, as it usually is, its bending stiffness would be
less than for round fibers. The friction between ribbon fibers is dependent on the transverse
loading. For high loadings, ribbons will line up with their flat sides in contact resulting in high
frictional values. Thus, the measured fuzz tendency represents a combination of these bending and
frictional force. The reduced pilling tendency of ribbon staple fibres was attributed to directional
bending, which reduced their entanglement tendency.

Stiffness and linear density:

The fibres with the highest stiffness at a given linear density show the greatest tendency to become
entangled. here only consider the anchor or projecting fibre whose stiffness is high with high
pilling tendency. Because if bending stiffness becomes low then it will not fulfill the critical height
of a pill as a result pill will not be visible. So in this case stiffness of fibres accelerate pill formation.
Comparatively large changes in linear density were required to effect significant changes in critical
height.

Fibre properties that affect in pill wear off

Abrasion resistance, breaking strength and flex life

Pills are removed during wear by the breakage of the anchoring fibres. There is a certain value
for the average breaking strength at break-off under given wearing conditions. Most synthetic
fibres are stronger than this required minimum, so the most important factor controlling the pill
wear-off becomes the amount of flexing necessary to reduce the fibre strength to the level of the
abrading forces. Above this minimum strength, flex-life is the controlling factor in pill wear-off.
The pill often contains other contaminants, and this accentuates the undesirable appearance. The
hydrophobic fibres (e.g. polyester fibre), because of their electrostatic properties, are more prone
to attract foreign matter than hydrophilic fibres (viscose, cotton, wool). The detached and
interlaced fibres are always shorter than the anchoring fibres. They are the finest and most flexible,
and the anchoring fibres are the strongest. As long as the materials or fibres consist mainly of wool,
cotton, or viscose, pills are removed by abrasion because the fibre has relatively low tensile
strength and abrasion-resistance, as compared with the synthetic fibres, which have high tensile
and flexural strength and abrasion-resistance.
This happens in the case of wool and synthetic fibres of low breaking strength and bending-
resistance. However, if the breaking strength and bending-resistance of anchoring fibres are higher
than the external forces, as in the case of synthetic fibres of high breaking strength, such as
polyester fibre, the pill will remain attached to the cloth

MEASUREMENT OF PILLS

There are more than twenty different test methods that have been developed to determine the
resistance of fabrics to pilling. The measurement of pills is in two stages, the formation of pills by
means of laboratory-test apparatus being followed by the evaluation of pills objectively or, more
popularly, subjectively.
Pilling test:
ICI BOX PILLING TEST:
1. For this test four specimens each 5 inch X 5 inch are cut from the fabric.
2. A seam allowance of 12mm is marked on the back of each square. In two of the samples the seam is
marked parallel to the warp direction and in the other two parallel to the weft direction.
3. The samples are then folded face to face and a seam is sewn on the marked line.
 4. This gives two specimens with the seam parallel to the warp and two with the seam parallel to the
weft.
5. Each specimen is turned inside out and 6mm cut off each end of it thus removing any sewing
distortion.
6. The fabric tubes made are then mounted on rubber tubes so that the length of tube showing at each
end is the same. Each of the loose ends is taped with poly (vinyl chloride) (PVC) tape so that 6mm
of the rubber tube is left exposed as shown in Figure.
7. All four specimens are then placed in one pilling box.
8. The samples are then tumbled together in a cork-lined box as shown in Figure.
9. The usual number of revolutions used in the test is 18,000 which take 5 hrs.
Assessment

The specimens are removed from the tubes and viewed using oblique lighting. The samples are then given
a rating of between 1 and 5 with the help of the descriptions in Table.
Factors affecting Pill Formation:

Yarn Parameter:

Yarn type:

The spinning technique used to make the component yarns has a significant impact on the pilling
tendency of a fabric. Ring-spun yarn is, in general, more resistant to pilling than open-end-spun
yarn [14]. Ring-spun and rotor-spun yarns are worse than air-jet-spun yams, which produce fabrics
with much-improved pilling control. Even when optional fibre properties are detennined, a fabric
constructed from air-jet-spun yam is the most pill-resistant, and a fabric constmcted from rotor-
spun yarn is the least pill-resistant.

In comparison, the ring-spun-yarn fabric was considerably more pill-resistant than the rotor-spun-
yarn fabric but still not as pill-resistant as the air-jet-spun-yam fabric.

This result is attributed to the slower rate of pill formation, due to the yarn's tightly wrapped
structure. this difference is attributed to the poorer fibre orientation of the rotor-spun yam, which
causes it to fuzz more initially.

Air-jet spinning provides a wrapper fibre that controls migration. Hence fabrics made from
air-jet-spun yams are superior to those made from yams produced by other spinning methods.
The most effective way to finish fabrics made from rotor- and ring-spun yams containing
low-flex-life fibres is to apply latex binders or durable-press resins and avoid the use of softeners

whenever possible

Pill resistant

Air jet spun yarn > ring spun yarn > rotor spun yarn

Yarn Count

Pilling is observed to be less for yarns of finer counts. This parameter is also found to be less for
a fabric produced with a higher machine gauge.

yarn became finer, pilling increased when all other yam and fabric parameters were kept constant.
Yarn twist

The higher the twist in the yam, the less is the pilling because of the compactness and because
there is less protruding fibre in the yam. Doubled yam gives less pilling than singles yam for the
same reasons. In singles yam, the pilling tendency is lower with an increase in the twist coefficient.
However, there is a maximum twist beyond which the pilling tendency is not further reduced. This
maximum is seldom reached in practice. In doubled yam, pilling is lower with an increase in
doubling twist in either ZZ or ZS twist. Highly twisted yams composed of short-staple fibres are
considered more secure than a loosely twisted yam composed of short-staple fibres. When a yarn
has a higher twist, the individual fibres are much more securely bound and do not tend to loosen
as easily. Doyle also stated that the pilling tendency decreased with an increase in the twist
coefficient.

Yam Hairiness

Pilling is less with less-hairy yam. The projecting loops or fibres causing the hairiness are very
important because pilling is less with fewer projecting fibres

Yam Plying

Fabrics made from singles yam are more prone to pilling than those produced from plied yams,
the reason being that the second twisting causes the fibres protruding on the surface of a singles
yam to be secured by being moved to some extent into the yarn.

Fabric Type

Knitted fabrics tend to pill more readily than woven fabrics. Since knitted constructions are
composed of a series of loops, a greater amount of yam surface area is exposed, making them more
susceptible to abrasion in wear. Moreover, knitted fabrics are more often constructed of low-twist
yarns made of staple fibres to give a soft, bulky feel and appearance.

Fabric Compactness

The construction of a fabric is very important in determining its susceptibility to pilling. A very
tight, compact construction, such as a denim, usually exhibits little or no pilhng during its life
expectancy. However, a loosely knitted or woven fabric will have more of a tendency to show such
damage when continually worn or cleaned. Furthermore, any fabric, with a soft, fuzzy surface,
known as 'nap', will have a good chance of pilling. The fibres are already brushed out of the yams
to achieve the desired appearance and may easily become tangled and pill. Over-all, the whole
fabric construction has a significant impact on the tendency to create fuzz and eventually pill; a
tighter fabric construction will have a decreased tendency for pill wear-off.

Fabric Structure

In spite of the slightly higher number of ends and picks per inch, the twill-woven fabric gives
substantially more pills than the plain-woven fabric in both the grey and finished conditions. The
greater number of inter lacings and short cross-lengths in the plain-woven fabric probably reduce
the opportunity for the free ends to emerge on the fabric surface and thus reduce pilling. The long
floats in a twill weave expose longer lengths of fibres to the abradant media, and, in addition"!
pilling of the fibres from the yarn is facilitated.

Fabric Weight

The pilling tendency falls with an increase in the weight per unit area of the fabric, which is in

a way influenced by the yarn count and fabric compactness.

Effect of relative humidity

Research shows that reducing the relative humidity from 80% to 11 % causes a marked decrease
in the pilling propensity. These results are consistent with the hypothesis that the mechanism for
these changes is that reducing relative humidity leads to a decrease in fibre mobility caused by an
increase in fibre-bending rigidity.

Control of Pilling:

The problem of pilling has plagued the textile industry for dozens of years. Controlling this
problem begins with selecting raw materials with pill avoidance in mind. The next step in
controlling pilling is to construct a yam through the proper pill-resistant steps. Finally, fabric can
be suitably constructed, and finishing and dyeing techniques can be adjusted to reduce a fabric's
pilling tendencies. The reduction of pills through controlling fibre, yarn, and fabric parameters
becomes difficult, since the controlling factors may affect other desirable characteristics of a
fabric.
Physical and chemical processes for reducing pilling in their study on methods and finishes for
reducing pilling under the following headings:

Physical processes for reducing pilling

(a) Shearing or cropping: Cropping and shearing reduce pilling by reducing the length of the
projecting fibres.
(b) Brushing: In the case of tighter-woven fabric made from highly twisted yam, loose fibres can
be brought to the surface of fabric by means of brushing, where they can be removed by a close
shearing. Such a procedure is not possible on loosely spun yams with a fluffy surface.
(c) Singeing: Sheared and cropped with brushing; this eliminates the surface fibres
and protmding fibres. singeing partly fuses the fibres. Thus the pilling tendency is reduced. For
very high-class finishes, the singed fabrics are again sheared and cropped to remove the nodes
formed by the melting of the surface fibres.
(d) Thermosetting: Heat-setting synthetic fibres to restrict fibre migration to the surface
(e) Hot-impregnation treatments applicable to synthetic fibres
(f) Steaming: steaming at temperatures above 100°C (generally 120°C or 130°C) also reduces the
pilling tendency as a result of increasing the coefficient of friction
(g) Treatment in soapy water
h) High-pressure heat treatment with liquid impregnation
(i) Careful selection of patterns and weaves
(/) Milling
(k) Thermal shock
(l) Random flattening of fibres (synthetic)
(m) Ultrasonic treatment
2. Chemical processes for reducing pilling
(a) Treatments based on silicic acid
(b) Latex treatment
(c) Easy-care finishes
id) Special treatments
(e) Shrink-resist treatments
(f) Treatments based on thermoplastic vinyl resin
(g) Treatments for blankets and melton fabrics
(h) Treatments for carpets and nonwoven fabrics
(/) Chemical treatments applicable to acrylic fibres
ij) Chemical treatments applicable to polyester fibres

Effect of enzyme treatment:

If the garments were constructed from cellulosic fibres or wool, these pills could effectively be
removed after the dyeing process by a treatment with an enzyme, Enzylon CM-30 for the
cellulosic-fibre garments and Enzylon ASN-30 for the wool garments.
Enzylon CM-30, a powder-grade product, is an enzyme based on cellulase that contains three
active ingredients: Exo-cellulase (Cx in Fig. 31), Endo-cellulase (C1, in Fig. 31), and |3-D
Glucosidease. Enzylon ASN-30 is an enzyme based on alkali protease, which is designed for
wool substrates. The action of the Enzylon CM-30 on the cellulose can be easily controlled by
regulating the temperature and pH value, thereby preventing loss in strength of the fabric or a
reduction in the seam strength of the garment
The enzyme treatment gives the fabric a soft handle. Furthermore, since the surface fibres have
been removed by the enzyme treatment, the garment surface will not pill during subsequent wear
or washing.