Textile Progress

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Cotton contamination

M. H. J. van der Sluijs & L. Hunter

To cite this article: M. H. J. van der Sluijs & L. Hunter (2017) Cotton contamination, Textile
Progress, 49:3, 137-171, DOI: 10.1080/00405167.2018.1437008

To link to this article: https://doi.org/10.1080/00405167.2018.1437008

Published online: 21 May 2018.

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TTPR_A_1437008.3d (Standard Sanserif) (174£248mm) 21-05-2018 9:8

TEXTILE PROGRESS, 2018

VOL. 49, NO. 3, 137–171
https://doi.org/10.1080/00405167.2018.1437008

Cotton contamination
M. H. J. van der Sluijsa and L. Hunterb,c
a
Commonwealth Scientific and Industrial Research Organization (CSIRO), Manufacturing, Waurn Ponds,
Geelong, Victoria, Australia; bCouncil for Scientific and Industrial Research (CSIR), Port Elizabeth, South Africa;
c
Nelson Mandela Metropolitan University, Port Elizabeth, South Africa

ABSTRACT KEYWORDS
This review focusses on physical forms of contaminant including the Cotton; contamination;
presence, prevention and/or removal of foreign bodies, stickiness and foreign fibres; seed-coat
seed-coat fragments rather than the type and quantity of chemical fragments; harvesting;
residues that might be present in cotton. Contamination in cotton, ginning; spinning; quality
even if it is a single foreign fibre, can lead to the downgrading of
yarn, fabric or garments, or even to the total rejection of an entire
batch and can cause irreparable harm to the relationship between
growers, ginners, merchants and textile and clothing mills.
Contamination thus continues to be a very important cotton fibre
quality parameter in the production pipeline, with countries and
cotton that are perceived to be contaminated heavily discounted. At
the same time, spinners are implementing various methods to detect
and eliminate contamination. Given the adverse effect on processing
and product quality arising from contamination, it was considered
important to compile a review of published work and knowledge
relating to the incidence, detection, measurement, consequences and
reduction of contamination.

1. Contamination
1.1. Introduction
Due to the increasing demands of modern spinning, in terms of speed, automation and
raw material cost and the increasingly competitive global textile market, cotton fibre qual-
ity, in terms of length and uniformity, strength, micronaire value, trash content, colour
grade and the presence of extraneous matter (any substance in the cotton, other than
plant material such as bark, grass, seed-coat fragments, dust and oil), is of the utmost
importance to the spinner. In addition, the presence of contaminants in the cotton, partic-
ularly foreign fibre, can greatly affect its perceived quality and value. Various contami-
nants, such as paper, plastic, feathers, etc., as described in Table 1, can be inadvertently
incorporated into the cotton bale often as a result of human interaction during harvesting,
ginning and baling, and even in the spinning mill itself [1,2]. Such contamination, even if it
is a single foreign fibre, can lead to the downgrading of yarn, fabric or garments, and/or
even to the total rejection of an entire batch, resulting in large financial claims and losses,

CONTACT M. H. J. van der Sluijs rene.vandersluijs@csiro.au

© 2018 The Textile Institute
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138 M. H. J. VAN DER SLUIJS AND L. HUNTER

Table 1. ITMF contamination sources [18].

S. no. General contaminant Specific contaminant
1 Fabrics made of Woven plastic
2 Plastic film
3 Jute/hessian
4 Cotton
5 Strings made of Woven plastic
6 Plastic film
7 Jute/hessian
8 Cotton
9 Organic matter Leaves, feathers, paper,
leather, etc.
10 Inorganic matter Sand, dust
11 Rust
12 Wire, metal
13 Oily substances/chemicals Grease/oil
14 Rubber
15 Stamp colour
16 Tar

which can cause irreparable harm to the relationship between growers, ginners, mer-
chants and textile and clothing manufacturers. Depending upon its nature, the spinning
and fabric processing method and route as well as the end use, contamination can
adversely affect textile processing efficiencies due to end breakages during yarn and fab-
ric formation, cause damage to processing equipment (such as beaters and wire) and
even cause fire in the mill. More generally, in terms of the textile being produced, contam-
ination can adversely affect the appearance of the yarn, fabric and final product [3–5],
especially in fine count yarns [6], resulting in such products having to be sold as seconds.
It has been stated that even though the levels of foreign-fibre contamination in cotton
have been drastically reduced due to the routine application of various corrective actions,
it still represented the number one problem for manufacturers of high-quality cotton
products [7,8]. Figures 1 and 2 show some examples of contaminated yarns and fabrics.
Contaminants have also even been found in classing samples which are collected at the
gin after bale formation – see Figure 3. It is also worth mentioning, that contamination

Figure 1. Examples of contaminants in cotton yarns (CSIRO and Cotton Incorporated).

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Figure 2. Examples of contaminants in cotton knitted fabrics (Cotton Incorporated and CSIRO).

can occur, and present a serious problem, in most other natural fibres, such as wool and
mohair, but seldom in man-made fibres.
In the light of the above, it is not surprising that there are serious penalties imposed on
the vendors for contamination in cotton [9]. In 2002, the International Textile Manufac-
turers Federation (ITMF) reported that claims, due to contamination in cotton, amounted
to between 1.4% and 3.2% of total cotton and blended yarn sales. Recognizing the slim
margins on which spinning mills operate, these figures illustrate the serious effect which

Figure 3. Examples of contaminants in classing samples (CSIRO).

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140 M. H. J. VAN DER SLUIJS AND L. HUNTER

contamination can have on spinning mill profit margins [10]. In fact, it was reported in
2015 that contamination related losses amounted to US$200 million per year worldwide
[11]. A study conducted by Ahmedabad Textile Industry’s Research Association (ATIRA)
showed that 70% of knitted fabric complaints produced from 20 tex combed yarns were
due to contamination, with 80% of the contamination due to human hair and jute and
14% due to coloured cotton fibre [12]. It has also been stated that the presence of col-
oured fibres in fabrics can result in bleeding during bleaching, requiring the now larger
affected sections of the finished fabric to be removed or the finished fabric to be replaced
or redyed with other colours [13]. It has also been reported that contamination-related
complaints and claims amount to approximately 15% of all yarn complaints [14]. It has
been stated that the more steps there are in the spinning process, the more difficult it is
for any foreign fibre to be detected as the distance between any such foreign fibres
increases with the number of stages, due to increased drafting ratios. For example, the
distance between foreign fibres is longer in combed ring-spun yarns than in rotor-spun
yarns [15].
The issue of contamination is nothing new, and spinning mills have for a long time
lodged complaints and produced evidence of contamination found in cotton bales they
have purchased, with the first recorded official complaint raised as far back as 1909 [16].
Indeed, there is a feeling amongst mills, which is borne out by the ITMF Contamination
Surveys, that contamination is increasing and that the cotton trade (growers through to
merchants) has not done enough to eliminate or reduce the incidence of contamination
[17,18]. There are, however, no established international or universal standards relating to
contamination size and frequency. As a consequence, the more quality-conscious spinners
have defined their own allowable levels of contamination, and developed a range of
screening protocols in order to assess the contamination risk associated with the various
sources or origins of cotton [19–21]. Most end-users even go so far as to demand a zero
level of contamination.
Levels of contamination are classifiable: the weight of contaminants in cotton bales can
range from 1 to 100 g/tonne with contamination rates of 1–4 g/tonne considered low, 5–
15 g/tonne moderate and above 20 g/tonne as high [9,22]. It has been suggested that, if
the level of contamination is <1 g/tonne, and all other remediation controls are in place,
the contamination in fabric and garment would be minimal. Although, at 0.001% by
weight, such level of contamination appears to be extremely small, it must be remem-
bered that contamination is quantified by the number and frequency of incidents, rather
than by their weight, and 0.001% by weight can equate to as many as 15,000 foreign
fibres [23–25].
To illustrate the serious losses which can be suffered as a result of contamination, it has
been calculated that, during processing, a 5-g piece of polypropylene twine in a cotton
bale could be fragmented into some 10,000 fibres and lead to financial losses exceeding
US$25,000 in the case of quality apparel and US$53,000 in the case of high-quality down-
proof covers [3,26]. Another case showed that a spinner, who purchased a bale of cotton
for US$600, made it into yarn and sold the yarn with foreign fibres that were only detected
after bleaching and dyeing, was required to pay US$7,320 in damages [27]. From the
above examples it is clear that contaminants remaining undetected until found in sewn
and finished goods result in the most costly penalties because of the number of process-
ing steps that have been undertaken and the value that is expected to have been added
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to the fibres by that stage. It has been stated that losses can be at least 1000 times greater
at the later stage than if the contaminants were detected and removed from the bale prior
to processing [28].
As blending of cotton lint from various parts of the world is a standard practice for spin-
ning mills, it is often difficult for a mill to pinpoint the origin of the contaminants, once an
incident has occurred or complaint has been received. Nevertheless, through the practical
experience of mill staff and from industry hearsay, cotton purchases from origins that are
known, or perceived, to be contaminated, are either avoided or the use of those growths
by the mill minimized. This is not always easy because the majority of cotton is produced
in Asia from which the most heavily-contaminated cottons originate [5]. Once an origin
has achieved a reputation for contamination, the likelihood of it achieving base world
market prices is slim, and cottons from that origin are usually heavily discounted, with dis-
counts ranging from 5% to 30%, even if the fibre quality is acceptable [19,22,23,29]. For
example, it has been stated that contamination is the biggest issue facing Indian cotton
[30,31] and that India and Pakistan are losing 10%–15% of the export value of their raw
cotton, totalling over US$500 million per year, due to contamination [20]. Another report
by the State Bank of Pakistan, estimated that contamination in the Pakistani cotton crop is
responsible for an annual loss of between US$1.4 and US$3 billion in export earnings, due
to discounted fibre, yarn, fabric and garments [32]. In order to minimize the effect of con-
tamination, the Pakistani government in 2002 introduced a ‘contamination-free cotton ini-
tiative’ which required textile mills to pay a premium of 63% for zero-contaminated fibre
[33]. Similarly, a large Indian vertically integrated textile and clothing manufacturer offers
Indian suppliers premiums of US$5 and US$2.4 per bale ‘for good and fair’ contaminated
cotton respectively, as judged by their contamination index [19]. Another large Indian
spinning company employs contract farming both to ensure supply and to reduce con-
taminants, resulting in a drop in the amount of contamination from a level of 18-20 g per
bale to <1g per bale [34]. Also, some mills will not, unless heavily discounted, purchase
hand-picked cotton due to the typically high incidence of contamination [9,13,22,35]
despite the fact that hand-picked cotton generally has fewer neps, fewer short fibres
and better length uniformity. This type of experience in India and Pakistan is in
contrast to that of Australia and the US, which continue to achieve premiums for their cot-
ton due to their reputation for having low contamination levels [1,2,35–38]. A survey con-
ducted in 2011 found that mills using such low-contamination cotton could demand a
premium of between 2 and 20 US cents/kg for their yarn due to the guarantee of being
able to deliver contaminant-free yarn for use in high-quality garments and light/pale
shades [37].

1.2. ITMF contamination surveys

Because of the global cotton industry’s growing concern about contamination, and in
order to quantify the type and level of contamination found in cotton, the ITMF has since
1983 conducted biennial contamination surveys of cotton users (mills) to obtain a mea-
sure of the level and type of contamination in world cotton crops. However, the ITMF sur-
vey has been conducted in its current format only since 1989, making comparisons with
the first three surveys conducted in 1983, 1985 and 1987 problematic; hence, this review
will concentrate on the results of the surveys conducted since 1989. This is somewhat
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142 M. H. J. VAN DER SLUIJS AND L. HUNTER

unfortunate as it has been stated that the type of contaminants have changed from the
late 1970s to 1990 [28].
The ITMF defines 16 categories of contamination, which are listed in Table 1. In the
ITMF survey, mills are asked to indicate the sources of contamination according to the 16
categories and to indicate in each category whether the contamination level was non-
existent/insignificant, moderate or serious. Essentially therefore, the survey records the
perception of spinners and should be regarded as akin to an ‘opinion poll’; whilst not
based on scientific evidence, even so it can still be considered a valuable source of infor-
mation and data for the industry [39,40]. It must be borne in mind that there are contami-
nants such as rocks, stones, human hair and other types of material that may be present
in bales of cotton that are not covered by the ITMF categories.
Across all growths, the incidence of contamination labelled ‘moderate’ or ‘serious’ (see
Table 2 and Figure 4) increased steadily from 14% of all bales surveyed in 1989 to 26% in
2003, followed by a decrease to 22%, stabilizing at this level between 2005 to 2009. This
was followed by a slight increase to 23% in 2011, a further increase to 26% in 2013 and
then a reduction to 23% again in 2016 – see Figure 4. What is notable in Figure 4 is the
steady increase in reported contamination worldwide after 1993, which is largely attrib-
uted to spinners becoming more aware of contamination as the number of complaints
received from fabric and garment manufacturers increased, as well as consumers becom-
ing more quality conscious [18]. Within this context, it is important to note that the instal-
lation of automatic detection systems in the spinning mills also began to provide more
accurate information on the type and frequency of contamination. A contributing factor
to the rise could also be that increasing automation and the subsequent reduction in

Table 2. Proportion (%) of particular contaminants found in cotton worldwide [18].

Contaminant 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2016
Fabrics
Woven plastic 13 15 16 16 19 20 23 29 25 23 25 28 29 31
Plastic film 11 12 11 14 14 16 21 24 25 30 26 24 31 38
Jute/hessian 15 18 19 22 20 25 24 30 21 27 25 23 25 27
Cotton 18 19 19 19 21 24 28 31 32 30 27 30 36 27
Strings
Woven plastic 15 14 17 20 31 25 24 32 29 25 29 29 36 31
Plastic film 14 13 12 18 18 22 22 28 26 29 23 28 31 30
Jute/hessian 22 21 24 30 25 30 30 38 25 29 32 27 34 29
Cotton 17 16 16 19 18 25 22 30 24 26 26 26 38 24
Organic matter
Leaves, feathers, paper 30 28 29 34 34 39 39 50 40 40 42 51 55 47
and leather
Inorganic matter
Sand/dust 16 20 19 25 23 30 28 37 29 25 26 31 33 31
Rust 10 13 12 13 13 18 15 20 15 13 15 16 15 14
Metal/wire 15 12 13 14 15 16 18 21 12 17 15 15 18 13
Oily substances/
chemicals
Grease/oil 14 14 15 20 18 23 22 23 16 17 16 13 14 11
Rubber 4 5 4 5 6 6 7 9 7 9 8 6 10 6
Stamp colour 12 15 12 14 14 14 16 17 15 11 11 8 9 10
Tar 3 3 2 4 4 4 6 6 5 5 4 5 7 5
Designation
Non-existent/ 86 85 85 82 82 79 78 73 78 78 78 77 73 77
insignificant
Moderate 9 11 11 13 13 15 16 18 15 15 16 16 18 18
Serious 5 4 4 5 5 6 6 8 7 7 6 7 8 5
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TEXTILE PROGRESS 143

30

25

% contaminated coon 20

15

10

Year

Figure 4. ITMF contamination survey results from 1989 to 2016 [18].

labour (i.e. human intervention) led to reduced human vigilance and fewer opportunities
for operatives to detect and eliminate contaminants, specifically in the ginning and spin-
ning mills [3,28,41,42].
Table 2 gives the worldwide averages per contamination category recorded during the
various surveys [18]. As can be seen in Table 2, the major type of contamination in all cot-
ton bales continues to be organic matter such as leaves, feathers, paper and leather,
whose contribution has steadily increased as a proportion of total contamination from
30% in 1989 to a high of 55% in 2013, then decreasing to 47% in 2016. The next most
prevalent contaminants are pieces of fabric and string made from woven plastic and plas-
tic film, followed by jute/hessian, which originate from bale covers and picking bags and
cotton both natural and coloured, mainly from bale covers but also from apparel, cleaning
rags and module ropes. The next highest contributor is inorganic matter such as sand/
dust, rust and metal wires, which is followed by oily chemical substances such as grease
and oil, contamination by which is mainly due to excess lubrication, worn seals and
hydraulic oil leaks during harvesting and ginning, stamp colour (mainly due to using per-
manent markers to identify modules or bales) rubber and tar. The incidence of oily chemi-
cal substances and inorganic matter, such as rust and metal, has remained fairly constant
since 1989.
Fabric and string contaminants mainly originate from module covers for both conven-
tional and round modules, plastic shopping bags and fertilizer bags, agricultural mulch
film, plastic twine, irrigation tubing and to a large extent from bale covers damaged dur-
ing warehousing and shipping [41,43–45]. The incidence of plastic contaminants has
become a major problem in the US as well as in other countries that have adopted the
new John Deere spindle and stripper harvesters; such equipment produces round mod-
ules covered with plastic wrap [46–48] with the potential to act as a contaminant source.
To improve bale covers and reduce potential contamination, certain countries such as the
US and Australia have changed their industry practices, with the US initiating the Joint Cotton
Industry Bale Packaging Committee to draw up specifications for bale covers and ties. Only
four types of bale covers are approved, namely 100% cotton (both woven and knitted),
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144 M. H. J. VAN DER SLUIJS AND L. HUNTER

Figure 5. Example of PET fragments on bale surface (USDA).

polyethylene film, polypropylene and woven polypropylene, and they are fully specified in
terms of their construction, yarn count, fabric weight, size, strength etc. [49]. Australia changed
their approved bale covers from jute/hessian to 100% cotton with the plastic known as PET
(polyethylene terephthalate) used in the strapping, in line with demands from international
spinning mills in various countries [37,50]. From an intensive study conducted by the United
States Department of Agriculture (USDA) in Clemson, it was concluded that PET fragments on
bale surfaces pose no risk of contamination (see Figure 5 for an example of PET fragments on
bale surface) [51].
The ITMF survey results are very similar to the results of a survey conducted on Austra-
lian cotton in 2005 and 2006, which showed that fabrics and strings were the largest con-
taminant category, followed by organic matter [1,2,35]. Another study, conducted on
ginners in Punjab, India, showed that organic matter, followed by inorganic matter, were
the two largest contaminant categories, followed by fabrics and strings composed of vari-
ous materials including woven plastic, plastic film, jute/hessian and cotton [52]. Details of
contaminants reported in US bales by the National Cotton Council in 1990 showed that
plastic was the largest contaminant followed by apparel fibres, rubber, grease and oil as
well as paint and metal [28]. Interestingly this listing was different to the contaminants
reported in the late 1970s which showed that plastic and rubber, mainly from rubber
doffers/moisture pads on harvesting machines, were the major contaminants followed by
grease and oil. Rubber contamination has been significantly reduced due to the fact that
the two harvesting machine manufacturers are using polyurethane instead of rubber to
produce the doffer pads.
As mentioned earlier, the degree of contamination varies widely from country to country
and region to region and is related to different farming, harvesting and ginning practices.
No particular cotton is completely contaminant free, with the least-contaminated cotton still
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TEXTILE PROGRESS 145

having contamination levels of around 4%–5%. According to the results of the ITMF surveys,
the most contaminated cottons continue to originate from India, Turkey and certain coun-
tries in Africa and Central Asia, with the least contaminated cotton continuing to originate
from the US, Israel, Australia and from certain countries in West Africa. The ITMF survey
results are very similar to the results of a survey conducted by the National Cotton Council
of America in 2008, which showed that cotton originating from the US, Australia, Israel, Bra-
zil and certain countries in Africa were perceived to be the least contaminated by US and
international mills [53]. Changes in contamination status have also occurred over time. For
example, cotton from Zimbabwe was once considered to be one of the least contaminated,
whereas it is now perceived as contaminated, demonstrating that continued industry vigi-
lance is required to maintain favourable perceptions by potential customers. It is also nota-
ble that mechanically-harvested cotton is generally less contaminated, probably due to the
lower level of interaction between humans and the cotton during mechanical harvesting
and the subsequent ginning processes; hand pickers, for example, use plastic bags to hold
the cotton, which can be a serious source of contaminants [6].

1.2.1. Limitations
It is important to note that there are a number of limitations associated with the ITMF Con-
tamination Survey, including the following:

(1) The number of companies participating in the ITMF Contamination Survey and the
number of evaluations have declined steadily since 2005, with only a small number
of spinning mills from Asia participating, despite the fact that when considered on a
worldwide basis, this is where the majority of cotton is consumed.
(2) Participating mills make a largely subjective assessment of the contamination found
in the cotton from a particular source, and this applies also as to whether they
regard the occurrence of the contamination as insignificant, moderate or serious.
The ITMF methodology states that the ‘basic statistical unit (the sample) of this sur-
vey is a spinners assessment of a given description of cotton which it had consumed
during the last 12 months’.
(3) The Survey is unable to quantify the number or proportion of bales actually affected
by contamination.
(4) Low overall levels of contamination can conceal the presence of higher levels of
particular contaminants, as each category is given equal weighting in determining
the average contamination level.

1.3. Methods to detect and eliminate contamination

1.3.1. General
Contamination represents a significant cost, the cost increasing as the cotton progresses
down the production pipeline and thus it is important to detect and eliminate it as early
in the process as possible. This has led to the development and implementation of a range
of methods and behaviours to detect and remove contamination from the processing
pipeline [54].
Cotton passes through a large number of processing stages in a spinning mill, each of
which can be affected differently by contaminants in the cotton, depending upon their
size and type. Nevertheless, the various stages can also present opportunities to detect
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146 M. H. J. VAN DER SLUIJS AND L. HUNTER

and eliminate contaminants. Contamination in cotton occurs in many types, shapes and
sizes and, while larger pieces of contaminants are more likely to be removed during proc-
essing, each mechanical process to which the cotton is subjected in opening, cleaning
carding and combing has the potential to reduce the size of the contaminants. The even-
tual result is a large number of fragments, particles or fibres, depending on the original
form of contamination, the latter being particularly problematic. Foreign fibres, when
present, tend not to be distributed uniformly across the contents of a bale or across bales;
generally, or initially at least, they form clusters which are very much dependent on the
particular process and machinery used, the type of raw material and the machine settings
[6]. It is worth noting that the vast majority of contaminants remain intact during the
opening and cleaning stages in the blowroom, but then become fragmented later. Fur-
thermore, although some contaminants are removed during the carding and combing
processes [55,56], the large majority are severely fragmented during carding, mainly due
to the action of the revolving flats [8,57–59]. The resulting smaller pieces and fragments
are difficult to remove and can remain largely undetected, only becoming noticeable in
subsequent processing stages and quite late in the conversion process. This type of con-
tamination can lead to drafting issues during drawing, roving and spinning, resulting in
end-breakages during the roving and spinning processes, or more costly and in the worst
case, it may only be detected once the finished fabric or garment is inspected before sale.
It has also been stated that some 20% of machine stops during sectional warping are
caused by foreign fibres [60].

1.3.2. Principles and techniques of detection

There are a variety of principles and techniques applied to the detection of contamination
in cotton, particularly the detection of dyed and undyed foreign fibres; these include the
following:

(1) Optical/acoustic/sonar [61]

(2) Infrared and near-infrared (NIR) [62–65].
(3) X-ray microtomographic image analysis [66]
(4) Attenuated total reflectance/Fourier transform infrared (ATR/FT-IR). In 2006, research-
ers from the US investigated the possibility of establishing a spectral database of
identified foreign matter in cotton. To this end, ATR/FT-IR spectra were identified for
various types of foreign matter including synthetic materials, organic materials and
inorganic materials in the 1800–650 cm¡1 or 5500–15,500 nm region, with the addition
of the X–H stretch region to the spectrum (3700–2700 cm¡1 or 2700–3700 nm) [67].
(5) Digital image processing [68] and texture feature extraction, using the grey level co-
occurrence matrix (GLCM) [69].
(6) Fluorescent imaging [70].
(7) Hyperspectral imaging [71].

The actual principles and techniques applied for the detection of contaminants in cotton
often differ according to the nature of the contaminants to be detected (e.g. dyed or
undyed polypropylene) and at what stage(s) in the processing pipeline detection and
removal are to take place. Some examples are as follows:
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TEXTILE PROGRESS 147

(1) Optical detection (in the blowroom).

(2) Image analysis detection (in the blowroom).
(3) Polarized transmitted light and high resolution 3-charge coupled device (CCD) col-
our line scan camera and ultraviolet (UV) illumination technologies (used in the
blowroom) [57,59,72].
(4) Optical and UV light (in the blowroom) [73,74].
(5) Triboelectric effect (used in yarn clearers) [60].

1.3.3. Pre-farm gate actions

The first and most logical step to address the problem of contamination is to prevent/
avoid or minimize the contamination entering the production process, particularly by tak-
ing steps to minimize the potential for contamination during growing and harvesting
through appropriate farm management, ensuring the transfer of good practices for main-
taining the integrity of the crop during growing and harvesting. This can be achieved by
appropriate educational programmes delivered to growers, harvesters and ginners that
provide information on preventing, or at least minimizing the contamination of seed-cot-
ton and lint in the field up to ginning. Such programmes need to be regularly presented
and updated to ensure high levels of awareness that contamination has cost implications,
that types of contaminant continue to change, the reasons why such changes may take
place and any links to farming/harvesting/processing equipment and methods; the pro-
grammes therefore need to include details about the latest developments in growing, har-
vesting and ginning technologies and practices. The key message in these campaigns
should be that negative reputations around contamination can lead to huge losses to the
country/region concerned [20,43–45,75].
A suggested method for reducing the potential for contamination at an early stage, but
which is perhaps less practical for large cotton fields, is the manual removal of plastic and
other contaminating debris prior to harvest [11,48]. The detection of plastics by either
infrared or UV light devices mounted on a mechanical harvester, has also been suggested
[46]. Other suggestions [4,13,25,76], perhaps more applicable to less-developed countries,
include the following:

(1) Selection of cotton in fields.

(2) Using picking bags made of grey or white cotton.
(3) Manual sorting of seed cotton for contaminants prior to ginning and during feeding
into the gin.
(4) Ginning under supervision.
(5) Avoiding HDPE and Hessian cloth for transportation of waste.
(6) Providing all workers with white cotton clothing as well as caps and gloves.
(7) Placing the picked cotton on cotton cloth while storing and/or transporting to the
gin.

1.3.4. Detection and removal at the gin

Examples of some the contaminants found in modules supplied to the gin are found in
Figure 6. In some instances, the upgrading and modernization of the gin, in terms of auto-
mation, the inclusion of modern cleaners and formulation and implementation of stan-
dard work practices, could contribute to the reduction of contamination. This is especially
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148 M. H. J. VAN DER SLUIJS AND L. HUNTER

Figure 6. Examples of contaminants found in modules supplied to the gin (CSIRO).

true for hand-picked cotton and in countries where labour costs are comparatively low,
with gins employing large numbers of people to feed and operate the gin [12,77,78].
Contamination detection-and-removal systems, developed originally for spinning mills,
have been applied in gins since the early 2000s. Nevertheless, despite their successful
application in Greece [79], the systems, or the sensors they employ, have not performed
well to date in high-volume and physically-harsh ginning environments (in terms of dust
and heat) [80]. Moreover, there is no immediate incentive, financial or otherwise, to the
grower or ginner, to cause them to take more precautions to avoid and minimize contami-
nation in baled cotton, despite the poor reputation and subsequent problems it causes in
the longer term [57,81]. Furthermore, there is a large cost associated with adapting the
particular systems originally designed for application in a spinning mill environment to
cope with the conditions that exist in a gin [80]. It has however been stated that cleaning
equipment installed in modern gins can potentially remove large contaminants that are
mixed in with seed-cotton [24,79] and this seems to be the case in India where a number
of gins have installed such systems with a 40–45% cleaning efficiency [82]; a typical layout
of such a modern saw gin is shown in Figure 7.
A number of studies were conducted in the US during 2015 and 2016, to determine the
efficiency of the ginning process in removing plastic sheet material of different types and
sizes. These studies showed that cylinder-type cleaners (rotating cylinders with spikes to
convey seed cotton across grid bars) removed some 10% of plastic contaminants, while
extractor-type cleaners (mainly the stick machine, where rotating saws hold the cotton
while centrifugal force removes larger foreign matter such as burrs and sticks), removed
56% of plastic with 17% found in the lint, the level of removal depending upon the type
and size of the plastic as well as on airflow and processing rates [47,83–85].
From the above, it is clear that it is preferable if not imperative to avoid contaminants
entering the ginning process in the first place, one solution being to install a camera in
the module feeder that automatically detects and alerts gin operators to the presence of
large pieces of contamination caught on the module beaters. The CSIRO Module Hood
Contamination Sensor, which alerts ginners and also provides a time stamp on
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Figure 7. Typical layout of a modern saw gin.

(Eagle 2013).

contamination as it enters the gin, has been installed in 27% of Australian gins since the
2012 ginning season [47], with a similar camera-based system being trialled in the US dur-
ing 2016 [46]. Further research in this area is continuing with various systems for the
detection of plastic in seed-cotton being investigated including using ion mobility, UV
fluorescence, visible and near-infrared and short-wave infrared [46,86–89]. The detection
of contamination is obviously an important part of the solution, but the question remains
as to whether the ginners would be willing to stop production to remove the contami-
nants once they have been detected.

1.3.5. Detection and removal prior to spinning

Equipment as well as the fibre being processed is vulnerable to contamination; Figure 8
shows examples of plastic contaminants wrapped on the module feeders of a cotton gin.

Figure 8. Examples of plastic contaminants wrapped on module feeder beaters (CSIRO).

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150 M. H. J. VAN DER SLUIJS AND L. HUNTER

As contamination represents a significant cost to spinning mills, various methods of elimi-

nating or minimizing contamination ranging from contract farming, to manual removal,
to detection and removal by instrument or machine, have been implemented, particularly
in mills using cotton of different origins. In countries where labour costs are comparatively
low, mills will often employ large numbers of people to patrol the bale laydown and
remove contamination from the bales before the cotton is fed into the blowroom line by
the bale opener/plucker. It has been stated that this manual and labour intensive, method
removes some 40%–45% of contaminants [55]. A number of spinning mills manually
inspect every bale of cotton and remove contamination before the bale is processed. This
manual sorting is either done directly from the bale, or the bale is first opened using a
bale opener with a spiked lattice prior to manual sorting. Manual sorting is, however, very
time-consuming and labour intensive and, depending on the cost of labour and level of
contamination, can add between 3.1 and 4.4 US cents/kg to the cost of the lint
[25,38,42,54,90] with the cleaning efficiency ranging from 55% to 70% [5,55,82]. Figures 9
and 10 show an example of a bale opener patrol and manual sorting, respectively.
Although manual intervention is helpful, spinning mills that employ staff to manually
remove contaminants have come to realize that in general only relatively large pieces of
contaminants, e.g. >1 cm2 are removed in this way [91]. Furthermore, the manual removal
of contaminants is costly, time consuming, tedious and prone to human error. The process
is also very harsh on the hands and eyes of the mostly female staff and in most cases the
work environment is uncomfortable with no, or very little, ergonomic considerations,
hence these types of mills also invest in systems to automatically detect and remove con-
taminants. The inclusion of metal detectors in blowrooms has been a standard feature for
many years and there are a number of foreign-matter detectors on the market which can
be installed at each of the different stages of the cotton-processing pipeline from bale to

Figure 9. Operators patrol a bale laydown to remove contamination from bales (CSIRO).
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Figure 10. Manual removal of contaminants from cotton prior to processing (CSIRO).

yarn. It was estimated that up to 2004, the installation of foreign matter detectors in spin-
ning mills cost the industry in excess of US$150 [10,19,21,44,92]. It has been stated that
excluding yarn clearers, spinning mills had, since 1990, invested over US$500 million on
systems to detect and remove contaminants in cotton [93]. At an average cost of
US$250,000 to US$500,000 per unit, such outlays would increase the cost per bale of cot-
ton by between US$5 and US$10 [5,11].
Careful control of waste recycling and of machine maintenance in the spinning mill are
also paramount to avoid the accidental introduction of contaminants into the process
[35,82]. Furthermore, spinning mills that produce yarns from various fibre types, blends
and even dyed material, either sequentially or simultaneously, need to have procedures in
place to ensure that all the machines are adequately cleaned prior to starting up a new
run, as well as to ensure that the different fibres are segregated to minimize contamina-
tion due to loose fly [82]. UV lights installed in the packing and inspection departments
can assist in detecting chemical/oily substances and foreign fibres, including synthetic
(man-made) fibres that fluoresce [35] – see Figure 11.
Contamination detection and removal systems installed in the blowroom prior to card-
ing are common and form a critical component of the blowroom, with these systems nor-
mally installed at the beginning of the blowroom line, after coarse cleaning and initial
opening of the fibre and before the final cleaning stage; however, a number of spinning
mills have also installed a second machine at the end of the blowroom line [74,92,94]. The
first contamination detection and removal system became available on the market in the
early 1990s and was based on the CSIRO Dark Lock Sorter patent, originally developed for
the wool industry. Current systems, such as those manufactured by UsterÒ Technologies
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152 M. H. J. VAN DER SLUIJS AND L. HUNTER

Figure 11. Inspecting cones of yarn for contaminants under UV lights (CSIRO).

AG (Uster, Switzerland), Tr€ utsczhler GmbH & Co. Kg (Mo€nchengladbach, Germany), Vetal
Textiles And Electronics Private Limited (Coimbatore, India), Loptex Italia S.r.L. (Montano
Lucino, Italy) and Barco NV (Kortrijk, Belgium), detect contaminants by means of using
acoustic, optical and colour sensors. These sensors can, depending on the particular sys-
tem, detect coloured, white, colourless and even transparent fibres as the material passes
through a viewing chamber after initial opening and before the final cleaning stage before
carding. When a contaminant is detected, it is measured (registered) and then pneumati-
cally removed via an alternative material-flow outlet [92]. Despite the fact that there are
estimated to be over 5000 contamination detection and removal systems installed world-
wide [35,57,59], they continue to be rather expensive and require highly-skilled techni-
cians for their operation. There are also issues with their capacity as well as with the
amount of good fibre that is extracted together with the contaminants being ejected
[5,9,41,91], with older systems removing 100–120 kg and newer systems 30–40 kg per day
of good fibre [95].
In 2004, it was reported that the equivalent of 25% of the global cotton consumption
was processed through contamination detection and removal systems installed in the
blowroom [21], with the present authors estimating that up to 80% of all cotton currently
consumed globally is processed through these systems. It has, however, been stated that
these systems remove only around 60%–75% of contaminants, their degree of effective-
ness being dependent on the positioning of the system (at the beginning or end of blow-
room line), the degree to which the fibre is opened prior to the attempt at detection, the
size and colour of the contaminants, the production rate and the possible number of air
blasts per hour (by pneumatic valves) that are able to be delivered by the equipment to
remove the contaminants [4,5,8,9,17,25,41,43,61,73,90,92].
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Figure 12. Blowroom equipped with UsterÒ Jossi Vision Shield (UsterÒ Technologies AG).

In addition to the foreign-matter detectors installed in the blowroom, there are devices
on the market that can be added to the creels of drawing and lapping machines, which
detect foreign fibres (of a different colour) and stop the machine for removal of the con-
taminant by the operator [42,48,76,82,96]. Figure 12 shows an example of a modern blow-
room contamination detection and removal system.

1.3.6. Detection and removal during spinning

Traditionally, electronic (optical- or capacitance-based) yarn clearers (installed on winding
and spinning machines, such as rotor- and air-jet machines) were used to detect and
remove unwanted and objectionable faults from yarn, such as slubs (long, raggedy thick
places), thin and thick places. Following on from the development of the Siroclear detec-
tor in 1990, modern clearers such as those manufactured by UsterÒ Technologies AG and
Loepfe Brothers Ltd (Wetzikon, Switzerland) are now also able to detect and remove for-
eign matter (e.g. foreign fibres) from yarn before it is wound onto packages. The clearers,
installed mainly on winding machines, are now sensitive enough to remove fibrous
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154 M. H. J. VAN DER SLUIJS AND L. HUNTER

material ranging from 1 cm2 down to 0.001 cm2 in size and are therefore considered to be
the most reliable for contamination detection and removal [8,76]. In 2006, 75% of yarn
clearers installed on winding machines worldwide (excluding China) had foreign-fibre
detectors fitted [91]. The actual number of such installations will be greater today, given
the modernization of the Chinese spinning industry. The types of contamination removed
and the efficiency of their removal depend on the sensors employed and also the specific
yarns they monitor. The disadvantage of these systems is their cost and sensitivity to a
large number of contaminants which, in extreme cases, can result in loss of production,
increased waste and increased processing and labour costs, as well as in a reduction in
yarn quality due to increases in the number of splices and in some instances, knots, due
to clearer cuts in spinning [5,8,17,41,42,55]. Clearers may also be installed on modern,
high-production spinning machines, such as air-jet and rotor (open-end) spinning
machines, but to avoid a dramatic drop in efficiency and yarn strength due to splicing
and piecings, these clearers need to be set to remove only the major contaminants [8,91].
It was estimated that in 2008, only 20% of the yarns spun on the rotor spinning machine
were cleared using yarn clearers designed to detect and remove foreign fibres [35], a
number that will be greater today given the modernization and installation of new rotor
spinning machines worldwide, an assertion highlighted by the fact that Schlafhorst
(Ubach-Palenberg, Germany) have sold >1 million Corolab clearers that can detect and
remove foreign fibres since 2005 [97]. A study conducted on rotor spinning showed that
high rotor speeds (>100, 000 rpm), smaller rotors (<36 mm) and low yarn counts (<25
tex) are more susceptible to being adversely affected by foreign fibres [98]. Figure 13
shows an example of a rotor spinning machine equipped with yarn clearers.
Spinners have also stated that yarn clearing systems only remove some 70%–85% of
contaminants [9,17,25,55,90]. From a commercial study, conducted by UsterÒ

Figure 13. Rotor spinning machine with Loepfe YarnMaster 1NI yarn clearers (Loepfe).
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Figure 14. Winding machine equipped with Loepfe Yarnmaster Zenit yarn clearers (Loepfe).

Technologies AG, it was concluded that a low degree of contamination in ring-spun

combed cotton yarns was 10 fibres/100 km, and for carded yarns 20 fibres/100 km; result-
ing from this, the first Uster Statistics for foreign-fibre levels were drawn up in 2006 [91].
Modern yarn clearing and monitoring systems on winding (Figure 14 shows an exam-
ple of a winding machine equipped with yarn clearers) and rotor spinning machines (see
Figure 13) and the UsterÒ Classimat yarn classification system, can together provide infor-
mation on the type and number of foreign fibres, providing data which assists in deter-
mining the clearer settings and also in determining the efficiency of foreign-fibre removal
[14,27].
In order to avoid or minimize any potential claims due to contamination, spinning mills,
especially those concerned to produce high-quality, fine combed yarns, will more often
than not install detection and removal systems in the blowroom and on their spinning
and winding machines, this being the most effective way to eliminate foreign fibres with-
out sacrificing production efficiencies [5]. One study showed that the installation of a
modern blowroom detection and removal system working in combination with yarn
clearers on winding machines led to a 54% reduction in polypropylene and foreign-fibre
cuts [95].

1.3.7. Detection and removal post spinning

Although there is a possibility of removing contaminants manually from the fabric, this is
both time-consuming and expensive. In 1995, it was estimated that the associated inspec-
tion and removal costs for fabrics were some US$4.00/100 metres, a similar cost being
arrived at in 2006 [91,99]. The difficulty of removing the contaminant without damaging
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156 M. H. J. VAN DER SLUIJS AND L. HUNTER

the fabric depends upon a number of factors such as fabric structure and compactness
and yarn twist. For example, contaminants cannot easily be removed from knitted cotton
fabrics, as this is likely to cause holes, while in a woven cotton fabric it is generally very dif-
ficult to remove contaminants present in the warp direction, due to the presence of size
[35].
UV lights can be installed in the yarn packing and inspection departments for the
detection of chemical/oily substances and foreign fibres such as polyester that fluoresce
[35]. Chemical treatments, such as bleaching/scouring in preparation for dyeing can some-
times reduce the problem of contamination, but that depends on the nature of the con-
taminants and adds further costs which are not always acceptable. The ‘chemical-
treatment’ option may, however, have to be phased out due to environmental legislation
prohibiting aggressive bleaching, for example with chlorine [17].
There is no doubt that all of the methods and approaches discussed above reduce the
risk of a yarn/fabric manufacturer receiving contamination-related claims but do not guar-
antee that the yarn or fabric produced will be totally free of contamination. Added to this
is the fact that there are no international standards for acceptable levels and sizes of con-
taminants in fabrics [91].

2. Cotton stickiness
Cotton stickiness, when it occurs, can present a major problem in terms of textile process-
ing performance, cost and product quality. The main problem related to cotton stickiness
is that of the sticky deposit or residue adhering to any machine part or surface encoun-
tered by the cotton along the processing pipeline, subsequently causing the build-up of
an accumulation of fibres on that part of the machine (together even with dust or grit)
during the ginning and spinning processes.
Cotton stickiness is a very wide field of investigation, with a large number of technical
and scientific publications; the main focus in the current review is on the various causes of
cotton stickiness and the consequences thereof in terms of textile processing and product
quality. For further detailed background information and list of references, the reader is
referred to the following excellent publications (also reviews) which deal in great detail
and depth with stickiness and also list a large number of relevant references, namely
Hequet and Abidi [100], Hequet, Henneberry and Nichols [101] as well as Gourlot [102]
and papers by Gourlot and co-workers presented at the ICCTM - ITMF Stickiness Working
Group meetings in 2012 [103], 2014 [104] and 2016 [105].

2.1. Stickiness as contamination

Stickiness represents a serious contamination problem worldwide, as illustrated by the
biennial ITMF Cotton Contamination Survey [18] compiled by spinners worldwide and
summarized in Figure 16 in terms of the industry perception of the average degree of
stickiness contamination over the past 27 years. A study conducted worldwide in 2016,
showed that 64% of the participants rated stickiness as a major defect of cotton that
affected yarn properties [106]. Because of a reputation for stickiness, some countries have
difficulty selling their cotton and incur discounts of between 5% and 30% for their raw
cotton [107], or US US$0.03–0.05/lb [108]. For example, it has been stated that stickiness is
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TEXTILE PROGRESS 157

the biggest issue facing Sudanese cotton, resulting in US$15–30 million loss which equa-
tes to a reduction of 23%–46% in the export value of their raw cotton per year [101,109].
Similarly, Arizona experienced major whitefly outbreaks in the 1980s and 1990s and the
resulting perception regarding susceptibility to stickiness continues to lead to a
US$0.0563/lb discount relative to Californian cotton [108].
In fact, sticky cottons, where the stickiness is caused by honeydew contamination for
example, are virtually impossible to process on their own into yarn of acceptable quality.
Furthermore, the costs for controlling stickiness in the field can be extremely high, with
insecticide treatment costs to control aphids and whitefly costing growers in Arizona up
to US$145/acre in 1995 [108].

2.2. Causes of stickiness

There are some 18 different sources or causes of stickiness in cotton, these generally being
divided into four main groups or categories according to origin, namely [100,101]:

(1) Insect (entomological),

(2) Physiological (plant),
(3) Fungal and bacterial (microorganisms), and
(4) Miscellaneous (e.g. oil grease, agricultural chemicals).

The most common and problematic causes of stickiness in practice, even today, are
those due to excess sugars related to insect secretions, notably aphids (Aphis gossypii
Glov.) and whitefly (Bemiesia tabaci Genn.); generally referred to as honeydew (insect
honeydew), these secretions are responsible for some 80%–90% of stickiness prob-
lems. Such stickiness caused by insects, mainly aphids, whiteflies and mealybugs, all
members of the insect order Homoptera, is the most problematic and common. In
general, a high percentage of melezitose (a tri-saccharide), along with a low percent-
age of trehalulose (an unusual disaccharide; an isomer of sucrose), indicates the pres-
ence of honeydew from aphids. Conversely, a dominance of trehalulose indicates
contamination by honeydew from whitefly. These insects ingest plant juices, extract
proteins and other nutrients from them and then expel honeydew (composed of sug-
ars and other carbohydrates) which falls onto the cotton plant leaves or lint after boll
opening, leaving a sticky, hygroscopic sugary deposit. Subequently a black sooty
mould can grow on the honeydew secretion on the cotton, darkening the lint and
adversely affecting its grade.
Physiological or plant-related stickiness mainly originates from highly immature cot-
tons (which can contain up to about 0.9% sugars) and plant sap, but can also arise from
crushed seeds, motes and seed fragments and fine leaf particles, as well as from the pro-
duction of excessive levels of cotton wax.

2.3. Detection and testing of stickiness

To be able to address the problem of stickiness, it is first of all necessary to detect and measure
the stickiness and to identify its source [100,101]. This is complicated by the often low levels
and isolated and random (spotty) nature of most forms of stickiness. Furthermore, since
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158 M. H. J. VAN DER SLUIJS AND L. HUNTER

stickiness has several possible causes, no one particular test can account for all causes; a com-
bination of chemical and physical/mechanical (e.g. mini-card) tests generally being required.
Most tests for sugar content fail to detect the random spotty honeydew contamination
from whiteflies and aphids, since just a few large drops of honeydew, each of which con-
tain only a few milligrams of sugars, are sufficient to create a stickiness problem, without
also generating any significant effect on the overall (average) sugar levels.
Stickiness arising physiologically from (plant) sugars however, is rare; under normal
conditions, any such stickiness should disappear quickly (within a few months) as bacteria
and fungi present on the lint readily metabolize any glucose, fructose and sucrose present.
Contamination due to lubricating oils show up as brilliant blue–white fluorescence
under UV light, whereas alcohol extractables give a good indication of the general level of
non-cellulosics present in cotton [101,102].
There are various tests for stickiness, some of which are listed below [100,110,111]:
Chemical tests:

A. Oxidation-reduction methods
Potassium ferricyanide (also known as the Perkins method)
Fehling/Follin test
Benedict test
Bremen honeydew test
B. Enzymatic tests
C. Chromatographic
Gas chromatography (GC)
High-performance liquid chromatography (HPLC)

pH

Indicator spray

Thermo-mechanical

Sticky Cotton Thermo-detector (SCT)

High Speed Stickiness Detector (H2SD)
Lintronics Fiber Contamination Tester (FCT/FQT)
Loepfe Labmaster Fibermap
Mesdan Contest

Mechanical

Mini-card (standard reference)

Rotor Ring (Quickspin method)
Shenkar Stickiness Tester (SST-1)

Other:

NIR
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TEXTILE PROGRESS 159

UV Fluorescence
Electrical Conductivity
Stickiness Tester (also known as the Stanley Anthony method)

Despite the large range of test methods listed here there is currently no recognized com-
mercial standard method for measuring stickiness in cotton lint on a high volume basis
[101]. From the various test methods listed above, the HPLC test is the only chemical test
method currently recognized by the research community as providing important informa-
tion on the source of the stickiness; it is however not feasible for mass testing as it is time
consuming and costly [100]. In terms of the thermo-mechanical test methods, the High
Speed Stickiness Detector (H2SD) and the Lintronics Fiber Contamination Tester (FCT).
FCT test methods offered the potential to become high-speed laboratory test methods;
the FCT instrument has now been superseded by the Loepfe and Mesdan instruments
[100,112].
In terms of the mechanical test methods, the mini-card test method relates well to the
conditions experienced by stickiness during yarn manufacturing. The mini-card test was
adopted by the ICCTM in 1988 as the reference method for assessing stickiness [110]. Nev-
ertheless, the test method is slow and time consuming, operator dependent and subjec-
tive, the results can be influenced by the condition, maintenance and level of cleaning
between tests and the relative humidity. Furthermore, the carding machines utilized are
no longer readily available and are expensive to purchase [100,110,111].
Some Classing facilities, merchants and mills use the pH indicator spray as a screening
tool to determine the incidence of stickiness if they suspect the presence of stickiness [110].
The various test methods produce different results and, as a consequence, the ITMF Inter-
national Committee on Cotton Testing Methods (ICCTM) was conducting Round Trials for
Stickiness in 2017 to determine if there are any relationships between the different methods.

2.4. Effect of stickiness on ginning

There are essentially two types of cotton gins, namely saw gins and roller gins. Saw gins
are generally used to process Upland-type cottons of short to medium staple length
(˂25.4–31.0 mm), and are consequently the most prevalent type of gin in the world. All
extra-long staple (ELS) cottons (35.0 mm) are ginned on roller gins and in addition, it is
estimated that currently 15%–20% of long staple upland (LS) and medium staple cottons
(27 mm) are also ginned on roller gins [113–118]. Roller-ginned cotton is adversely
affected by moderate levels of stickiness while saw-ginned cotton is less sensitive to mod-
erate levels of stickiness, and the problem is usually first detected in the textile mill [101].
Roller gins are more susceptible to stickiness due to their design, with the ginning process
reliant on friction, and a build-up of sticky spots on the ginning roller and the stationary
knife will result in a decrease in ginning efficiency. Saw ginning does not rely on friction
but on the mechanical pulling of fibre by saw teeth through two closely-spaced ribs and
thus moderate levels of stickiness will not affect production rates [101]. In terms of saw
ginning, sticky deposits can clog the saws in the saw gin and disrupt the baling process
due to accumulation of lint on the lint slide of the battery condenser. This disruption can
reduce gin production (usually expressed in bales/hour) by up to 25% [108], or up to 15
pounds per hour for roller ginning, which is about 50% of the normal output rate of roller
ginning [109]. These disruptions result in longer and more-expensive ginning seasons,
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160 M. H. J. VAN DER SLUIJS AND L. HUNTER

due to higher labour costs and additional spare parts as saws and blades need to be
replaced more regularly [119]. In extreme cases, stickiness can also affect harvesting with
the spindle-type harvesters, as sticky deposits will accumulate and clog the spindles caus-
ing blockages [101].

2.5. Effect of stickiness on textile processing

Cotton with a high incidence of stickiness will result in a gradual build-up of sticky deposits on
processing machinery which then disrupts, and/or interferes with, the smooth flow of the cot-
ton during processing, leading to machine stoppages (notably spinning ends down) and/or
poor quality products, particularly yarn. Sticky cotton will be first noticed on the calendar roll-
ers of a scutcher (picker) or carding machine and then during the drawing, roving and spin-
ning processes, where creel-drive deposits and (more typically) roller lapping is experienced –
see Figure 15. This results in frequent stoppages and requires thorough cleaning to correct.

Figure 15. Sticky cotton causing disruptions during processing on (a) the draw frame creel drive rolls
and (b) the drafting section of the draw frame [120].
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TEXTILE PROGRESS 161

2.6. Effect of stickiness on cotton classification

Sticky deposits can cause issues during cotton classification, with deposits on the combs
used in high-volume instruments resulting in incorrect and inaccurate fibre measurements.

2.7. ITMF surveys

As part of the ITMF surveys, the incidence of cotton stickiness has been included since
1989. Across all growths, the incidence of stickiness increased from 21% of all bales sur-
veyed in 1989 to 27% in 1991, followed by some fluctuations over the period from 1993
to 1997. This was followed by a steady decrease to 17% in 2005 but an increase to 21% in
2007, followed by a decrease to 16% in 2009. This was again followed by an increase to
23% in 2013 and then a reduction to 16% in 2016 – see Figure 16. It is clear from the
records that the incidence of stickiness varies considerably and is very much dependent
on the growing conditions (notably climatic) during a particular season as well as the farm
practices employed, specifically plant nutrition, farm hygiene, biosecurity, nitrogen fertil-
izer and late irrigation, timing of planting and field selection limiting availability of attrac-
tive crops, the integrated pest management practices adopted in terms of maintaining
beneficial numbers of pest control insects, harvest aid chemicals for mechanical harvest-
ing and variety selection [100,121,122]. Nevertheless, although there have been some fluc-
tuations from year to year the incidence of stickiness tended to decrease somewhat
slightly from 1991 to 2016.
As already mentioned, the degree of stickiness varies widely from region to region,
being related to the conditions and management practices applied during the growing
season and hence also can vary from year to year. According to the results of the ITMF sur-
veys, cottons affected the most by stickiness continue to originate from Sudan, the Far
West growing region of the US, certain countries in West Africa and Central Asia, with the
cottons affected the least by stickiness continuing to originate from the South East grow-
ing region of the US, China, Argentina, Australia, Egypt and certain countries in Africa.

Figure 16. ITMF stickiness survey results from 1989 to 2016 [18].
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162 M. H. J. VAN DER SLUIJS AND L. HUNTER

2.8. Prevention and treatment of stickiness problems

One of the major problems associated with the prevention and treatment of stickiness is
that due to its isolated and random nature, it is very difficult to effectively detect sticky
cottons until the problem manifests itself during the processing of the cotton. Some reme-
dial actions when it comes to cotton stickiness are listed below [100–102]:

 Eliminate problem at source, i.e. during cotton growing (insect management)

 Minimise seed-coat fragments (SCFs) during ginning and ensure efficient cleaning
during opening
 Avoid cottons with high levels of seed-coat (immature) fragments
 Avoid low micronaire value (immature) cottons
 Engage in the opening and extended storage (4–9 months) of cotton. (This is, how-
ever, not feasible for modern and automatic mills. It is also only really effective for
stickiness due to physiological sugars and not that due to entomological sugars, the
latter representing the main source of stickiness)
 Sun-dry for 3 or 4 days after ginning
 Apply chemical additives, e.g. hydrocarbon surfactant (costly and requires close
monitoring)
 Blend small proportions of sticky cottons with non-sticky cottons
 Process at low humidity (<50% RH) and temperature. It could, however, lead to
problems with static and excessive fibre breakage during mechanical processing
 Reduce pressure on card crush rollers
 Use tandem carding
 Clean rollers regularly
 Coat rollers with iodine or another suitable substance
 Apply a fungus or enzyme or bacteria to decompose the sugars, a procedure which
may prove effective but may lead to the growth of saprophytic micro-organisms and
adversely affect cotton quality. Bacteria may be better than fungi, but nevertheless,
most micro-organisms cannot metabolize insect sugars.

3. Seed-coat fragments
It has been stated that practically all ginned lint contains seed-coat fragments (SCFs) [123]
and that the main source is the chalazal end of the seed – see Figure 17 which is generally
not fully developed or is structurally-weak with fibres in this area (possibly immature due
to varietal and environmental factors) torn off together with a piece of seed instead of
being broken off [124,125]. This leads to the creation of SCFs when the fibre is eventually
separated from the seed, consisting mainly of pieces of the chalazal or rounded end of
the seed as well as motes (whole immature seeds) which broke during ginning [123].
Medium sized motes (1–3 mm in width and 3–5 mm in length), having fibres of medium
length attached, contribute to SCFs, due to them becoming fractured during ginning
[126].
The number of SCFs in ginned cotton can vary by as much as 50%, studies showing
that the major factors contributing to their occurrence were cotton variety, crop year and
timing of harvest [127–133]. It has further been stated that SCFs are becoming a bigger
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TEXTILE PROGRESS 163

Figure 17. Cotton seed illustrating the position of the Chalazal end (CSIRO).

issue, due to increased seed-cotton cleaning during ginning and the fact that spinners
require more uniform fibre which is free of foreign matter [134]. Not only do SCFs cause
spinning end breakages, but they also cause a deterioration in yarn appearance and
increase production costs, being virtually impossible to extract from the bulk of the raw
cotton, except at the combing process, because of the tuft of fibres attached to the seed-
coat. Hence they are generally incorporated into the yarns as a nep [129,134–136] – see
Figure 18. SCFs appear as dark specks on the surface of dyed fabrics, and are generally sur-
rounded by immature fibres of lighter colour, which reduce the quality of the final product
[135,137,138]. It is for this reason that spinners dread SCFs, with the ITMF Contamination
Surveys [18] highlighting the fact that there is a perception amongst spinners that SCFs
are a serious and increasing problem. A recent study conducted worldwide in 2016
showed that 58% of the participants rated SCFs as a major defect of cotton fibres that
affects yarn properties [106]. It has also been stated that cotton-seed oil from SCFs can be
associated with stickiness problems encountered during processing [139–142].
As would be expected, rotor-spun yarns tend to be less affected by SCFs than ring-spun
yarns, due to the fact that the opening roller of the rotor spinning machine removes a sig-
nificant amount of trash and SCFs from the input sliver prior to the formation of yarn, and
also the fact that the structure of the rotor-spun yarn has the tendency to hide SCFs within
the body of the yarn [143]. In one study it was found that the presence of SCFs had a sig-
nificant effect on yarn strength, the effect varying with fibre quality. In other words, the
presence of SCFs will only have a significant effect on yarn strength if the strength at the
point created by the SCFs is less than that at the weakest point, present elsewhere in that
yarn segment [144].
A study of thirteen cotton varieties from three production areas was undertaken to
determine the sources of imperfections in fabric, focussing on the three possible sources
suspected of giving rise to SCF contamination, namely pieces of the chalazal end, seed
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164 M. H. J. VAN DER SLUIJS AND L. HUNTER

Figure 18. Image of a seed-coat fragment in lint and yarn.

Obtained by means of a Wild Makroskop M420 microscope equipped with a Leica DFC290 digital camera (CSIRO).

damage and motes. It was found that the relationship between the three suspected areas
was poor. The only significant correlations were found between seed diameter and SCF
fabric imperfections (r = 0.86) and attachment force (r = 0.40) [145], it being concluded
that seeds smaller than 4 mm in diameter may be the major source of fabric SCF imperfec-
tions. Another study, involving the 1986 US Regional Cotton Variety Tests, and conducted
across the US cotton belt, showed that high nep counts and SCFs can be avoided by using
varieties with a low occurrence of immature cottonseed and which have seed diameters
greater than 3.73 mm [146]. This was confirmed by a study conducted in 2004, which
showed that, although no consistent relationship was found between SCFs and seed
diameter, there was a strong indication that cultivars with small seeds (measured in terms
of their seed diameter or seed index) did not produce ginned lint containing high levels
of SCFs [147–149].

3.1. ITMF surveys

Since 1991, the ITMF surveys include incidences of SCF. Across all growths, the incidence
of SCF contamination labelled ‘moderate’ or ‘serious’ increased steadily from 34% of all
bales surveyed in 1991 to 39% in 1995, followed by a decrease to 32% in 1997. This was
followed by a steady increase from 38% in 1999 to a record level of 44% in 2003, followed
by a steady decrease from 37% in 2005 to 27% in 2009. This was followed by yet another
steady increase from 38% in 2011 to 42% in 2013, and then a reduction to 32% in 2016 –
see Figure 19.
As mentioned earlier, the incidence of SCFs varies widely from region to region and is
related to the cotton varieties, growing conditions and management practices applied
during the growing season, and hence can also vary from year to year. According to the
results of the ITMF surveys, cottons affected the most by SCFs continue to originate from
Nigeria, India, Turkey and certain countries in West Africa and Central Asia, with the cot-
tons affected the least by SCFs continuing to originate from the US, Australia and certain
countries in West Africa.
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Figure 19. ITMF seed-coat fragment survey results from 1991 to 2016 [18].

3.2. Detection and testing of seed-coat fragments

There are various tests for SCFs, some of the more important of which are listed below.

3.2.1. Visual (manual) method

Despite the introduction of high-speed instruments, such as the High-Volume Instrument
(HVITM ), for monitoring the quality of cotton, and the undeniable value and significance of
the information provided by these instruments, cotton is largely still bought and sold world-
wide based on the cotton classer’s subjective assessment of colour (colour grade), visible
trash (leaf grade) and preparation against physical and descriptive grades, which are pre-
pared by the USDA on an annual basis. Besides the above, the classers will also call extrane-
ous that matter which is any substance in the cotton besides fibre and leaf. Examples
include bark, grass, dust, oil, SCFs and other. These extraneous matters are classified accord-
ing to the amount present in the sample and are identified as level 1 for light or level 2
for heavy. The code for identifying the incidences of SCF is 31 for level 1 and 32 for
level 2 [150].

3.2.2. Instrumental measurement

A number of instruments are available for testing for SCFs, the most popular of which,
with over 1000 instruments installed worldwide, is the UsterÒ Technologies AG, Advanced
Fiber Information System (AFIS). In the AFIS test, a 500mg specimen of cotton fibre (either
raw lint, sliver or roving) is weighed and hand-prepared into a sliver about 30–35cm long.
The sample is fed into a feed roller by an opening roller which passes the fibres through a
carding flat which combs and aligns the fibres and separates the non-fibrous components.
The fibre individualizer unit utilizes the principle of aero-mechanical separation to extract
trash particles, large SCFs and other types of foreign matter from the original fibre speci-
men, which are then conveyed through the trash channel. The individual fibres, neps, and
small SCFs pass through the fibre channel. Electro-optical sensors are installed in both the
trash and fibre channels and advanced signal processing technology is applied to identify
and characterize the several thousand individual cotton fibres, fibre entanglements, SCFs,
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166 M. H. J. VAN DER SLUIJS AND L. HUNTER

and foreign matter in the test specimen. Other such instruments include the Premier Evol-
vics Pvt. Ltd., aQura instrument which measures the number and size of contaminants
and SCFs, the FCT, the Loepfe Labmaster Fibermap and the Mesdan Contest which super-
seded the FCT in 2016. These instruments provide results on trash and dust, neps and
SCFs and are also used to detect stickiness.
The measurement of SCFs through the application of the test methods and instruments
referred to above is always carried out ‘off line’, with samples collected then transported
to and tested in the laboratory. Online detection and measurement is available, however,
to complement the laboratory data; most of the major machinery manufacturers produc-
ing carding machines now provide online nep sensors to detect and record the number
of neps and SCFs in the card sliver.

3.3. Standard or benchmark values for seed-coat fragments

The question remains as to what SCF levels the textile industry accepts or aspires to.
Zellweger UsterÒ (now UsterÒ Technologies) has been publishing The UsterÒ Statistics for
sliver, roving and yarn since 1957, and since 1964 for imperfections, including neps. These
UsterÒ Statistics have been updated a number of times since 1969 with the latest update
being released in 2016. Since the release of the first UsterÒ Statistics, they have become the
industry-accepted global standards for quality comparisons and benchmarking, and have
formed a basis for the trading and certification of textiles. Their progressive development
has taken place over a number of years; provisional UsterÒ Statistics for fibre properties, as
measured on the AFIS instrument, were first published in 1990 to provide a worldwide
guideline, but based on a limited number of samples. In 1997, more comprehensive statis-
tics were released on raw cotton fibre as measured by AFIS, which were updated a number
of times since 2001, with the latest update in 2016. UsterÒ Technologies classifies the SCF
content in short to medium staple raw cotton lint, as measured on an AFIS instrument as
per Table 3.

Table 3. Classification of SCFs according to UsterÒ Technologies [151].

SCFs/gram Classification
<10 Very low
11–20 Low
21–30 Medium
31–45 High
>46 Very high

This classification system allows growers and merchants to better describe and perhaps
obtain better premiums for their cotton, and helps spinning mills to establish standards
for the whole yarn manufacturing process.

4. Conclusion
It is clear that the problem of contamination in cotton has by no means been satisfactorily
resolved, and that it remains a serious issue. The negative economic, processing and qual-
ity impact of such contamination depends on the nature of the contaminant, with plastic
or fibrous contaminants currently proving particularly problematic. Although various
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TEXTILE PROGRESS 167

automatic detection and removal systems have been developed and installed at various
stages of the cotton pipeline, these tend to be expensive and are not 100% effective. Fur-
ther development in this area is certainly called for.
There can be little doubt that by far the most-effective and lasting way of dealing with
the problem of contamination in cotton is to prevent its occurrence at source. Prevention
will require regular, and continuously-updated instructional programmes to inform and
educate growers, harvesters (both hand and machine-assisted), ginners and cotton-mill
processing staff on the damaging effect of cotton contamination, how and where contam-
ination occurs and how to combat it, followed by a worldwide effort with a focus on
implementation of the necessary measures. The ‘second line of defence’ remains that of
detection and elimination of contaminants at the various stages of the cotton processing
pipeline; continual advancement in sensor and associated technologies will no doubt lead
to the development of new and more effective systems in this respect. Nevertheless,
because of the issues associated with actual contaminant removal such as associated loss
of fibre, it is unlikely that these alone will ever lead to a perfect solution to the problem;
avoiding or at least minimizing contamination at source will remain the most effective
and sustainable solution.

Acknowledgements
The authors thank everyone who has gathered and collected the numerous references used in this pub-
lication. The authors also thank everyone for their useful and insightful comments and suggestions.

Disclosure statement
Any trade names or commercial products mentioned in the publication are solely for the purpose of
providing specific information and do not imply recommendation or endorsement by the authors.

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