Cotton Contamination - Its Sources & Remedial Measures
By: Ms. Madhuri V. Kakde & Prof. H. R. Shah





















ABSTRACT

According to recent survey by ITMF, Indian cottons are amongst the most contaminated cottons in the world due to the lack of availability of systematic instruments to judge the level of contamination. Contaminations present in the fabric not only deteriorate the quality and appearance of fabric, but also affect on the profits of the organization. Here, we have tried to highlight the sources and remedial measures for contamination, practiced in the cotton cultivation to yarn manufacturing industry.

INTRODUCTION

As prevention is better than cure, it is always more desirable not to generate contamination at all than to have to clean it at different stages of processing. To achieve this, all concerned industries have to work together. According to recent survey by ITMF, Indian cottons are amongst the most contaminated cottons in the world so; producing yarns of world class quality from Indian cottons is a greater challenge. This challenge can be met with selection of suitable cottons, appropriate work practices and proper use of modern machines and technologies. Contamination represents a significant threat and element of cost to spinning mills and this led them to implement a range of costly methods to remove the contamination. On analysis it was found that amongst all the areas of textile sectors, "Fiber cultivation to Yarn spinning stage" remains major source of contamination. Therefore, we have highlighted certain facts and few recent developmental steps, which are being taken to reduce or minimize the contamination level in this area.

NATURE OF CONTAMINATION

Before finding any measures for elimination of contamination first of all let us understand the possible sources of contamination and necessity for contamination removal. Once these sources are sorted out, elimination process becomes effective and easier. Contamination is "the presence of extraneous and undesirable substance in yarn which leads to impure the quality of final textile product". Contaminations at yarn stage are mainly categorized in three types:
1. Removal contaminations like dust, rust, mud and washable finish stains.
2. Partially removable contaminations like loose fly spun, oil stain and grease stain.
3. Irremovable contaminations like bleached fiber, fibers having optical brightening agent and dyed fiber contaminations which get spun with the yarn.
According to International Textile Manufacturers Federation (ITMF), the major contaminant found in cotton bales were pieces of cloth from either woven or knitted clothing in various colors made from either cotton or polyester or blends.
For India the need for the removal of contamination is felt much more since currently India is a topmost exporter of the cotton yarn. Contamination is one of the most serious problems affecting the cotton fibers. The whole product is rejected due to contamination, even though the basic material has been from the best of cottons and the product was made using the latest machines, which causes the serious problem in cotton spinning industry worldwide. Contamination is one of the critical issues for spinners to maintain first grade yarn quality because it causes the breakages in the warping, sizing, and weaving results in tile defective packages as well as faults in the fabric thus lowering the efficiency means increased cost of production.

                                                        Table 1: Types of contaminant

White contaminants    Alien fibers    Colored objects         Oily substances        Dense objects
White plastic fabric                Hair                    Colored cotton fabric   Sticks/twigs                Metal pieces
White plastic strings             Feather               Colored cotton yarn     Leaves                        Paper

White/transparent                 Colored cotton     Jute fabric                   Oily/Rusty/Black         Sand, stones
 Plastic film                             fibers                                                       cotton clumps 
                                                 Coir fibers            Jute yarn                     Stamp colored/            Leather bits          
                                                                                                                Yellow cotton lumps 
                                                 Colored plastic      Coir yarn                    Tar/Grease-affected     Wooden pieces   
                                                 fibres                                                        cotton clumps
                                                                          Colored plastic fabric   Colored plastic string, film    


SOURCES OF CONTAMINATION


Contaminations are not being grown with cotton balls in the tree. These are mostly "added" in fresh cotton during picking. Contaminations to raw cotton take place at every step i.e. from the farm picking to the ginning stage. Since cotton is picked manually by ruler woman so human hair, contamination caused by cloth pieces and fabric sheets are the biggest source of contamination.
International Textile Manufactures Federation (ITMF), Zurich, which conducts a survey on cotton contamination every two years, has identified five major sources of contamination:

1. Strings made of jute.
2. Strings made of hessian.
3. Fabric made of jute.
4. Fabric made of hessian.
5. Organic matter such as leaves, feather, paper, leather etc.
Contamination within raw material

There are the two possibilities of contamination. As the natural fiber cultivation, ginning, and packing process are mostly manual, chances of oil/grease/rust stain on fiber after the stoppages, or the maintenance activities of spinning machines exist.

Handling of packing material during raw material opening

Due to poor wrapper quality, wrapper stripe is passing with fiber mixing and converting in small fiber/strip during carding and finally, gets spun with fiber and creates contamination in yarn.

Cleaning of mixing and conditioning bin

To create difference between product and lot, different chemicals like antistatic, lubricant, optical brightening agent and tint apply on the fiber gets stick on wall and floor and apply on next chemical free mixing will results in contamination if the cleaning is not followed properly.

Frequent product change and loose fly spun

Running gray and dyed material in the same department causes fibers floating from dyed material, getting contaminated with gray material and vice versa. The starting of dyed material after run out of gray material on the same machine produce contaminated yarn. When two or more different products are running in same department, then contamination is mainly caused due to lose fly.

Oil and grease stain after machine maintenance

In case of some machine parts getting oil or grease stains during its maintenance and are not properly cleaned then it results in contamination.
                       Table 2: Various sources of contamination, their effect and remedial stages

Source of contamination                   Effect                                                 Remedies

Strings/fabrics of                  Increased end breakage rate at ring/rotor.                    Avoid use of hessian for jute/hessian                          Poor yarn appearance           differential dye pick-up.                                                   transport use cotton cloth  

Strings/fabrics of cotton        Poor quality yarn/cloth                                                Manual picking, automatic 

                                                                                                                                             transportation, training

Strings/fabrics of woven      Differential dye pick-up Very Poor quality yarn/       Avoid use of plastic,      

plastics/plastic film               cloth. Damaged to machinery                                        better hose keeping 

Organic matter - Leaves,     Increased waste, machinery damage                           Use of pre-cleaner at ginning, use .

feather, paper, leather etc                                                                                             of gravity trap, better housekeeping

Inorganic matter                              ,,                                                                              Use of pre-cleaner at ginning,metal 

1 . sand dust                                                                                                                    detector, better house keeping                                                                        

2. metal/wire

Oily matter                          Mars yarn/fabric appearance                                     Avoid use of stamp color, hosue keeping   
1. Stamp color
2. Grease/oil

Hair- human                       Increased end breaks at ring rotor                                 Use of caps, automatic transportation          
                                          Poor yarn/fabric appearance                                             continuous training

Stones                                Damaged to machinery                                                   Better housekeeping and practices

Seed coats                         Increased waste at spinning Poor                                 Use pre-cleaner and post cleaner at ginning    

                                         yarn/fabric appearance

Pouches - Gutkha             Damaged to machinery part                                             Bet ter practices, education/ training

CONTAMINATION DETECTION SYSTEM

Manual process

Contaminants like jute, chindies, HDPE, gutkha packs, etc. can be removed by the workers. It is difficult to detect the contamination -due to their unpredictable size, shape, material and position as some of the contaminants get inside the cotton fiber layer and become invisible. This system is costly, time consuming and chances of human error are more. The accuracy of this system is also very poor.
Gravimetric method
In this system the contaminated material is removed because of gravity only. In this method of detection of cotton contaminants, a mechanical model is used. For the vision system and the sorting system, synchronized with the movement of cotton on the conveyor, an encoder is installed at the shift of the conveyor and driven by the belt. In this system only heavy contamination can be removed. Efficiency of this system is less due to lot of mechanical parts.
Electro-optical method
Electro-optical method used for cotton contaminant is based on the High Volume Instrument (HVI). This system is suitable for the extensive quality control of all the bale proceeds in a spinning mill. In this system Digital Image Process Technique is used, and this is the one of most efficient method of removal of contaminations.

WORKING PRINCIPLE

Contamination detection by optical means
All systems detect contamination by optical means. Yarn clearers and the" sorter of Loptex use photo sensors and detect the contamination as being darker than the cotton. Optical sensor can only see what visible means is, it cannot detect the contamination which is hidden within the cotton tufts. This permit detection of colorless contamination namely, packing material in polypropylene.
Contamination ejection by ultrasonic means
The degree of reflectance of acoustic waves depends on the surface structure of the object in their path. The sensor consists of a number of emitters of ultrasonic therefore not hearable waves. The receiver will receive waves which are reflected by the contamination contained in the lose cotton. If no contamination is present, the ultrasonic wave will be absorbed in the absorber box located on the other side of the system.
Contamination ejection by pneumatic valves
In case of the detection of a contamination by the optical or the acoustic system, the electronic control will activate pneumatic valves which are variable. It depends on the  size of contamination. It takes into account the transportation speed of the raw material and releases the air blow after the necessary delay. The air blow will be targeted since only the valves are activated, which are located in front of the passing contamination.

CONTAMINATION REMOVAL AT VARIOUS STAGES OF SPINNING

Contamination can be detected at any stage of the processing, from bale to yarn. From the point of view of contamination removal, however each stage has its own advantage and disadvantage in terms efficiency, reliability and impact.

Contamination removal at ginning stage

It is more beneficial to remove the contamination in earlier processing stage because of two reasons, first, the early removal enables to prevent the contamination from spreading to a large extent and second, it also helps to avoid more numerous interventions in later stage.
Figure shows, the manual picking of cotton contaminant before feeding to the blow room. In many ginning factories, electronic contamination control system like Vision shield of Reiter, have been installed in the transportation line between ginning and storing, before putting the cotton fiber into Bale press. Average efficiency of this contamination control system is around 40-45% at this stage. The sorting efficiency is 55-70% with a sorting load of 165 kgs/person/8 hr.

Contamination removal on Blow room

Blow room equipped with different kinds of contamination detection equipment available from different manufacturers like Premier Fibre Eye, Uster Optiscan, and Barco Vision cotton Sorter, Loptex Sorter, and Vision Shield detects and removes the contaminants that can be distinguished by color immediately following the initial stages of opening in the blow room. Any contaminants that are completely masked by the bulk fiber are not detected. The working principle is optical based from all manufacturers. Optimum illumination with combined incident and transmitted light enables both light and dark contaminants to be detected.

Contamination removal on carding and comber

Foreign fibers and cotton contaminants are detected by using intensity and hue properties, they give the Cotton Contamination Analyzer for Micro Cards which convert the raw cotton into thin uniform web without removing any impurities scanned by the CCD camera. Imaging system is used to classify particles in terms of size and number and detect the contamination from the cotton. In case of carding, contaminants are removed with flat and licker-in waste and most of the hair contamination is removed through noil in comber.

Contamination removal on draw frame and lappers

BMS Vision Sliver watch system is installed in the creel of the draw frame for the purpose that it stops the draw frame if the contaminated sliver is detected. Any foreign fibers as well as the fibers of colors other than the cotton are detected. Short and intensive contaminants can also be detected by filter settings.
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On lappers up to 24 sensors can be installed in the creel to monitor the sliver and the lapper is stopped if the contaminants are detected.

Contamination removal on ring frame

In the ring frame no direct contamination removal procedure is available but many times yarn breaks where contamination is present. These contaminants go into pnumafit waste, although it does not occur most of the time for very fine fiber shaped plastic contaminations that are longer than cotton fiber and is spun into the yarn.

Contamination removal on winding

Winding is the last process in the spinning mill where the maximum contaminations are removed from the yarn. The procedures are as described below:
By using Electronic contamination channel (foreign matter detection) channel:
Such kind of electronic contamination clearing channels are available from different manufactures like Uster, Loepfe, Keissoki, and Premiere. The working principle is almost same and optical based for all manufactures. During yarn winding this channel measures the color intensity of the yarn and compares the portion every 2mm continuously against the base white yarn. In case of variation in color intensity, it detects and actuates the cutter assembly to cut the contamination portion.
By using PP (polypropylene) contamination detection channel:
The device like Loepfe, Zen it, Uster, Keissoki detect white colored polypropylene contaminants by using UV light. Polypropylene and other synthetic contaminants cannot be detected with conventional optical foreign fiber clearers as contaminants are transparent or look like cotton. The detection is based on the Tribo-electric effect is an electrical phenomenon in which fibers exchange electrons with the sensor, the so called Tribo-electric effect, where certain materials become electrically charged after coming into contact with another different material.

Contamination detection during inspection and packing

Ultra violet lights are installed in the packing and inspection department to detect chemical/oily substances and foreign fibers and other synthetic manmade fibers.

CONCLUSION

Contamination is one of the critical issues for spinners to maintain first grade yarn quality. Contamination comes from raw material, handling of material, ancillary products and work practices. Different methods to reduce contamination are now practiced in cotton ginning to yarn manufacturing processes, which have been reviewed. More and more involvement will definitely improve the contamination removal
efficiency of the industry and as a result such a burning issue of contamination may be solved with ease.

This article was originally published in the textile Review magazine, March, 2013 issue, published by Saket Projects Limited, Ahmedabad.
About the Authors:
Ms. Madhuri V. Kakde and Prof. H.R. Shah are associated with the D.K.T.E. Society’s Textile and Engineering Institue, Ichalkaranji.

COTTON FIBRE GROWTH

COTTON FIBRE GROWTH:
Improvements in cotton fiber properties for textiles depend on changes in the growth and development of the fiber.
Manipulation of fiber perimeter has a potential to impact the length, micronaire, and strength of cotton fibers. The perimeter of the fiber is regulated by biological mechanisms that control the expansion characteristic of the cell wall and establish cell diameter.
mprovements in fiber quality can take many different forms. Changes in length, strength, uniformity, and fineness In one recent analysis, fiber perimeter was shown to be the single quantitative trait of the fiber that affects all other traits . Fiber perimeter is the variable that has the greatest affect on fiber elongation and strength properties. While mature dead fibers have an elliptical morphology, living fibers have a cylindrical morphology during growth and development. Geometrically, perimeter is directly determined by diameter (perimeter = diameter × p). Thus, fiber diameter is the only variable that directly affects perimeter. For this reason, understanding the biological mechanisms that regulate fiber diameter is important for the long-term improvement of cotton.
A review of the literature indicates that many researchers believe diameter is established at fiber initiation and is maintained throughout the duration of fiber development . A few studies have examined, either directly or indirectly, changes in fiber diameter during development. Some studies indicate that diameter remains constant ; while others indicate that fiber diameter increases as the fiber develops.
The first three stages occur while the fiber is alive and actively growing. Fiber initiation involves the initial isodiametric expansion of the epidermal cell above the surface of the ovule. This stage may last only a day or so for each fiber. Because there are several waves of fiber initiation across the surface of the ovule , one may find fiber initials at any time during the first 5 or 6 d post anthesis. The elongation phase encompasses the major expansion growth phase of the fiber. Depending on genotype, this stage may last for several weeks post anthesis. During this stage of development the fiber deposits a thin, expandable primary cell wall composed of a variety of carbohydrate polymers . As the fiber approaches the end of elongation, the major phase of secondary wall synthesis starts. In cotton fiber, the secondary cell wall is composed almost exclusively of cellulose. During this stage, which lasts until the boll opens (50 to 60 d post anthesis), the cell wall becomes progressively thicker and the living protoplast decreases in volume. There is a significant overlap in the timing of the elongation and secondary wall synthesis stages. Thus, fibers are simultaneously elongating and depositing secondary cell wall.
The establishment of fiber diameter is a complex process that is governed, to a certain extent, by the overall mechanism by which fibers expand. The expansion of fiber cells is governed by the same related mechanisms occurring in other walled plant cells. Most cells exhibit diffuse cell growth, in which new wall and membrane materials are added throughout the surface area of the cell. Specialized, highly elongated cells, such as root hairs and pollen tubes, expand via tip synthesis where new wall and membrane materials are added only at a specific location that becomes the growing tip of the cell. While the growth mechanisms for cotton fiber have not been fully documented, recent evidence indicates that throughout the initiation and early elongation phases of development, cotton fiber expands primarily via diffuse growth . Later in fiber development, late in cell elongation, and well into secondary cell wall synthesis (35 d post anthesis), the organization of cellular organelles is consistent with continued diffuse growth . Many cells that expand via diffuse growth exhibit increases in both cell length and diameter; but cells that exhibit tip synthesis do not exhibit increases in cell diameter . If cotton fiber expands by diffuse growth, then it is reasonable to suggest that cell diameter might increase during the cell elongation phase of development.
Cell expansion is also regulated by the extensibility of the cell wall. For this reason, cell expansion most commonly occurs in cells that have only a primary cell wall . Primary cell walls contain low levels of cellulose. Production of the more rigid secondary cell wall usually signals the cessation of cell expansion. Secondary cell wall formation is often indicated by the development of wall birefringence.
Analyses of fiber diameter and cell wall birefringence show that fiber diameter significantly increased as fibers grew and developed secondary cell walls. Both cotton species and all the genotypes tested exhibited similar increases in diameter; however, the specific rates of change differed. Fibers continued to increase in diameter during the secondary wall synthesis stage of development, indicating that the synthesis of secondary cell wall does not coincide with the cessation of cell expansion.

GINNING
The generally recommended machinery sequence at gins for spindle-picked cotton is rock and green-boll trap, feed control, tower drier, cylinder cleaner, stick machine, tower drier, cylinder cleaner, extractor feeder, gin stand, lint cleaner, lint cleaner, and press. 
Cylinder cleaners use rotating spiked drums that open and clean the seedcotton by scrubbing it across a grid-rod or wire mesh screen that allows the trash to sift through. The stick machine utilizes the sling-off action of channel-type saw cylinders to extract foreign matter from the seedcotton by centrifugal force. In addition to feeding seedcotton to the gin stand, the extractor feeder cleans the cotton using the stick machine's sling-off principle. 
In some cases the extractor-feeder is a combination of a cylinder cleaner and an extractor. Sometimes an impact or revolving screen cleaner is used in addition to the second cylinder cleaner. In the impact cleaner, seedcotton is conveyed across a series of revolving, serrated disks instead of the grid-rod or wire mesh screen.
Lint cleaners at gins are mostly of the controlled-batt, saw type. In this cleaner a saw cylinder combs the fibers and extracts trash from the lint cotton by a combination of centrifugal force, scrubbing action between saw cylinder and grid bars, and gravity assisted by an air current 
Seedcotton-type cleaners extract the large trash components from cotton. However, they have only a small influence on the cotton's grade index, visible liint foreign-matter content, and fiber length distribution when compared with the lint cleaning effects. Also, the number of neps created by the entire seedcotton cleaning process is about the same as the increase caused by one saw-cylinder lint cleaner. 
Most cotton gins today use one or two stages of saw-type lint cleaners. The use of too many stages of lint cleaning can reduce the market value of the bale, because the weight loss may offset any gain from grade improvement. Increasing the number of saw lint cleaners at gins, in addition to increasing the nep count and short-fiber content of the raw lint, causes problems at the spinning mill. These show up as more neps in the card web and reduced yarn strength and appearance .
Pima cotton, extra-long-staple cotton, is roller ginned to preserve its length and to minimize neps. To maintain the highest possible quality bale of pima cotton, mill-type lint cleaners were for a long time the predominant cleaner used by the roller-ginning industry. Today, various combinations of impacts, incline, and pneumatic cleaners are used in most roller-ginning plants to increase lint-cleaning capacity. 
COTTON FIBER QUALITY:
Two simple words, fiber quality, mean quite different things to cotton growers and to cotton processors. No after-harvest mechanisms are available to either growers or processors that can improve intrinsic fiber quality. Most cotton production research by physiologists and agronomists has been directed toward improving yields, so the few cultural-input strategies suggested for improving fiber quality during the production season are of limited validity. Thus, producers have limited alternatives in production practices that might result in fibers of acceptable quality and yield without increased production costs. Fiber processors seek to acquire the highest quality cotton at the lowest price, and attempt to meet processing requirements by blending bales with different average fiber properties. Of course, bale averages for fiber properties do not describe the fiber-quality ranges that can occur within the bales or the resulting blends. Further, the natural variability among cotton fibers unpredictably reduces the processing success for blends made up of low-priced, lower-quality fibers and high-priced, higher-quality fibers. Blends that fail to meet processing specifications show marked increases in processing disruptions and product defects that cut into the profits of the yarn and textile manufacturers. Mill owners do not have sufficient knowledge of the role classing-office fiber properties play in determining the outcome of cotton spinning and dyeing processes. Even when a processor is able to make the connection between yarn and fabric defects and increased proportions of low-quality fibers, producers have no way of explaining why the rejected bales failed to meet processing specifications when the bale averages for important fiber properties fell within the acceptable ranges. If, on the other hand, the causes of a processing defect are unknown, neither the producer nor the processor will be able to prevent or avoid that defect in the future. Any future research that is designed to predict, prevent, or avoid low-quality cotton fibers that cause processing defects in yarn and fabric must address the interface between cotton production and cotton processing. Every bale of cotton produced in the USA crosses that interface via the USDA-AMS classing offices, which report bale averages of quantified fiber properties. Indeed, fiber-quality data reports from classing offices are designed as a common quantitative language that can be interpreted and understood by both producers and processors. But the meaning and utility of classing-office reports can vary, depending on the instrument used to evaluate.

Fiber maturity is a composite of factors, including inherent genetic fineness compared with the perimeter or cross section achieved under prevailing growing conditions and the relative fiber cell-wall thickness and the primary -to- secondary fiber cell-wall ratio, and the time elapsed between flowering and boll opening or harvest. While all the above traits are important to varying degrees in determining processing success, none of them appear in classing-office reports.
Micronaire, which is often treated as the fiber maturity measurement in classing-office data, provides an empirical composite of fiber cross section and relative wall thickening. But laydown blends that are based solely on bale-average micronaire will vary greatly in processing properties and outcomes. Cotton physiologists who follow fiber development can discuss fiber chronological maturity in terms of days after floral anthesis. But, they must quantify the corresponding fiber physical maturity as micronaire readings for samples pooled across several plants, because valid micronaire determinations require at least 10 g of individualized fiber.

Some fiber properties, like length and single fiber strength, appear to be simple and easily understood terms. But the bale average length reported by the classing office does not describe the range or variability of fiber lengths that must be handled by the spinning equipment processing each individual fiber from the highly variable fiber population found in that bale. Even when a processing problem can be linked directly to a substandard fiber property, surprisingly little is known about the causes of variability in fiber shape and maturity. For example:
Spinners can see the results of excessive variability in fiber length or strength when manifested as yarn breaks and production halts.Knitters and weavers can see the knots and slubs or holes that reduce the value of fabrics made from defective yarns that were spun from poor-quality fibre
Inspectors of dyed fabrics can see the unacceptable color streaks and specks associated with variations in fiber maturity and the relative dye-uptake success.
The grower, ginner, and buyer can see variations in color or trash content of ginned and baled cotton.
But there are no inspectors or instruments that can see or predict any of the above quality traits of fibers while they are developing in the boll. There is no definitive reference source, model, or database to which a producer can turn for information on how cultural inputs could be adapted to the prevailing growth conditions of soil fertility, water availability, and weather (temperature, for example) to produce higher quality fiber.
The scattered research publications that address fiber quality, usually in conjunction with yield improvement, are confusing because their measurement protocols are not standardized and results are not reported in terms that are meaningful to either producers or processors. Thus, physiological and agronomic studies of fiber quality frequently widen, rather than bridge, the communication gap between cotton producers and processors.
This overview assembles and assesses current literature citations regarding the quantitation of fiber quality and the manner in which irrigation, soil fertility, weather, and cotton genetic potential interact to modulate fiber quality. The ultimate goal is to provide access to the best answers currently available to the question of what causes the annual and regional fiber quality variations 
From the physiologist's perspective, the fiber quality of a specific cotton genotype is a composite of fiber shape and maturity properties that depend on complex interactions among the genetics and physiology of the plants producing the fibers and the growth environment prevailing during the cotton production season.
Fiber shape properties, particularly length and diameter, are largely dependent on genetics. Fiber maturity properties, which are dependent on deposition of photosynthate in the fiber cell wall, are more sensitive to changes in the growth environment. The effects of the growth environment on the genetic potential of a genotype modulate both shape and maturity properties to varying degrees.
Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell arising from the protodermal cells of the outer integument layer of the seed coat. Like all living plant cells, developing cotton fibers respond individually to fluctuations in the macro- and microenvironments. Thus, the fibers on a single seed constitute continua of fiber length, shape, cell-wall thickness, and physical maturity .
Environmental variations within the plant canopy, among the individual plants, and within and among fields ensure that the fiber population in each boll, indeed on each seed, encompasses a broad range of fiber properties and that every bale of cotton contains a highly variable population of fibers.
Successful processing of cotton lint depends on appropriate management during and after harvest of those highly variable fiber properties that have been shown to affect finished-product quality and manufacturing efficiency . If fiber-blending strategies and subsequent spinning and dyeing processes are to be optimized for specific end-uses and profitability, production managers in textile mills need accurate and effective descriptive and predictive quantitative measures of both the means and the ranges of these highly variable fiber properties .
In the USA, the components of cotton fiber quality are usually defined as those properties reported for every bale by the classing offices of the USDA-AMS, which currently include length, length uniformity index, strength, micronaire, color as reflectance (Rd) and yellowness (+b), and trash content, all quantified by the High Volume Instrument (HVI) line. The classing offices also provide each bale with the more qualitative classers' color and leaf grades and with estimates of preparation (degree of roughness of ginned lint) and content of extraneous matter.
The naturally wide variations in fiber quality, in combination with differences in end-use requirements, result in significant variability in the value of the cotton lint to the processor. Therefore, a system of premiums and discounts has been established to denote a specified base quality. In general, cotton fiber value increases as the bulk-averaged fibers increase in whiteness (+Rd), length, strength, and micronaire; and discounts are made for both low mike (micronaire less than 3.5) and high mike (micronaire more than 4.9). 
Ideal fiber-quality specifications favored by processors traditionally have been summarized thusly: "as white as snow, as long as wool, as strong as steel, as fine as silk, and as cheap as hell." These specifications are extremely difficult to incorporate into a breeding program or to set as goals for cotton producers. Fiber-classing technologies in use and being tested allow quantitation of fiber properties, improvement of standards for end-product quality, and, perhaps most importantly, creation of a fiber-quality language and system of fiber-quality measurements that can be meaningful and useful to producers and processors alike.GENE AND ENVIRONMENTAL VARIABILITY:
Improvements in textile processing, particularly advances in spinning technology, have led to increased emphasis on breeding cotton for both improved yield and improved fiber properties Studies of gene action suggest that, within upland cotton genotypes there is little non-additive gene action in fiber length, strength, and fineness ; that is, genes determine those fiber properties. However, large interactions between combined annual environmental factors (primarily weather) and fiber strength suggest that environmental variability can prevent full realization of the fiber-quality potential of a cotton genotype. More recently, statistical comparisons of the relative genetic and environmental influences upon fiber strength suggest that fiber strength is determined by a few major genes, rather than by variations in the growth environment . Indeed, spatial variations of single fertility factors in the edaphic environment were found to be unrelated to fiber strength and only weakly correlated with fiber length .
Genetic potential of a specific genotype is defined as the level of fiber yield or quality that could be attained under optimal growing conditions. The degree to which genetic potential is realized changes in response to environmental fluctuations such as application of water or fertilizer and the inevitable seasonal shifts such as temperature, day length, and insolation.In addition to environment-related modulations of fiber quality at the crop and whole-plant levels, significant differences in fiber properties also can be traced to variations among the shapes and maturities of fibers on a single seed and, consequently, within a given boll.
EFFECT ON FIBER LENGTH:
Comparisons of the fiber-length arrays from different regions on a single seed have revealed that markedly different patterns in fiber length can be found in the micropylar, middle, and chalazal regions of a cotton seed - at either end and around the middle . Mean fiber lengths were shortest at the micropylar (upper, pointed end of the seed) . The most mature fibers and the fibers having the largest perimeters also were found in the micropylar region of the seed. After hand ginning, the percentage of short fibers less than 0.5 inch or 12.7 mm long on a cotton seed was extremely low.
It has been reported that, in ginned and baled cotton, the short fibers with small perimeters did not originate in the micropylar region of the seed . MEasurements of fibers from micropylar and chalazal regions of seeds revealed that the location of a seed within the boll was related to the magnitude of the differences in the properties of fibers from the micropylar and chalazal regions. Significant variations in fiber maturity also can be related to the seed position (apical, medial, or due to the variability inherent in cotton fiber, there is no absolute value for fiber length within a genotype or within a test sample . Even on a single seed, fiber lengths vary significantly because the longer fibers occur at the chalazal (cup-shaped, lower) end of the seed and the shorter fibers are found at the micropylar (pointed) end. Coefficients of fiber-length variation, which also vary significantly from sample to sample, are on the order of 40% for upland cotton. Variations in fiber length attributable to genotype and fiber location on the seed are modulated by factors in the micro- and macroenvironment . Environmental changes occurring around the time of floral anthesis may limit fiber initiation or retard the onset of fiber elongation. Suboptimal environmental conditions during the fiber elongation phase may decrease the rate of elongation or shorten the elongation period so that the genotypic potential for fiber length is not fully realized . Further, the results of environmental stresses and the corresponding physiological responses to the growth environment may become evident at a stage in fiber development that is offset in time from the occurrence of the stressful conditions. Fiber lengths on individual seeds can be determined while the fibers are still attached to the seed , by hand stapling or by photoelectric measurement after ginning. Traditionally, staple lengths have been measured and reported to the nearest 32nd of an inch or to the nearest millimeter. The four upland staple classes are: short (<21>34 mm). Additionally, short fiber content is defined as the percentage of fiber less than 12.7 mm.
Cotton buyers and processors used the term staple length long before development of quantitative methods for measuring fiber properties. Consequently, staple length has never been formally defined in terms of a statistically valid length distribution. In Fibrograph testing, fibers are randomly caught on combs, and the beard formed by the captured fibers is scanned photoelectrically from base to tip . The amount of light passing through the beard is a measure of the number of fibers that extend various distances from the combs. Data are recorded as span length (the distance spanned by a specific percentage of fibers in the test beard). Span lengths are usually reported as 2.5 and 50%. The 2.5% span length is the basis for machine settings at various stages during fiber processing.
The uniformity ratio is the ratio between the two span lengths expressed as a percentage of the longer length. The Fibrograph provides a relatively fast method for reproducibility in measuring the length and length uniformity of fiber samples. Fibrograph test data are used in research studies, in qualitative surveys such as those checking commercial staple-length classifications, and in assembling cotton bales into uniform lots. Since 1980, USDA-AMS classing offices have relied almost entirely on high-volume instrumentation (HVI) for measuring fiber length and other fiber properties (Moore, 1996). The HVI length analyzer determines length parameters by photoelectrically scanning a test beard that is selected by a specimen loader and prepared by a comber/brusher attachment
The fibers in the test beard are assumed to be uniform in cross-section, but this is a false assumption because the cross section of each individual fiber in the beard varies significantly from tip to tip. The HVI fiber-length data are converted into the percentage of the total number of fibers present at each length value and into other length parameters, such as mean length, upper-half mean length, and length uniformity . This test method for determining cotton fiber length is considered acceptable for testing commercial shipments when the testing services use the same reference standard cotton samples.
All fiber-length methods discussed above require a minimum of 5 g of ginned fibers and were developed for rapid classing of relatively large, bulk fiber samples. For analyses of small fiber samples , fiber property measurements with an electron-optical particle-sizer, the Zellweger Uster AFIS-A2 have been found to be acceptably sensitive, rapid, and reproducible. The AFIS-A2 Length and Diameter module generates values for mean fiber length by weight and mean fiber length by number, fiber length histograms, and values for upper quartile length, and for short-fiber contents by weight and by number (the percentages of fibers shorter than 12.7 mm). The AFIS-A2 Length and Diameter module also quantifies mean fiber diameter by number .
Although short-fiber content is not currently included in official USDA-AMS classing office reports, short-fiber content is increasingly recognized as a fiber property comparable in importance to fiber fineness, strength, and length . The importance of short-fiber content in determining fiber-processing success, yarn properties, and fabric performance has led the post-harvest sector of the U.S. cotton industry to assign top priority to minimizing short-fiber content, whatever the causes . The perceived importance of short-fiber content to processors has led to increased demands for development and approval of a standard short-fiber content measurement that would be added to classing office HVI systems . This accepted classing office-measurement would allow inclusion of short-fiber content in the cotton valuation system. Documentation of post-ginning short-fiber content at the bale level is expected to reduce the cost of textile processing and to increase the value of the raw fiber . However, modulation of short-fiber content before harvest cannot be accomplished until the causes of increased short-fiber content are better understood.
Fiber length is primarily a genetic trait, but short-fiber content is dependent upon genotype, growing conditions, and harvesting, ginning, and processing methods. Further, little is known about the levels or sources of pre-harvest short-fiber content . 
It is essential that geneticists and physiologists understand the underlying concepts and the practical limitations of the methods for measuring fiber length and short-fiber content so that the strong genetic component in fiber length can be separated from environmental components introduced by excessive temperatures and water or nutrient deficiencies. Genetic improvement of fiber length is fruitless if the responses of the new genotypes to the growth environment prevent full realization of the enhanced genetic potential or if the fibers produced by the new genotypes break more easily during harvesting or processing. The reported effects of several environmental factors on fiber length and short-fiber content, which are assumed to be primarily genotype-dependent, are discussed in the subsections that follow.FIBER LENGTH AND TEMPERATURE:
Maximum cotton fiber lengths were reached when night temperatures were around 19 to 20 °C, depending on the genotype . Early-stage fiber elongation was highly temperature dependent; late fiber elongation was temperature independent . Fiber length (upper-half mean length) was negatively correlated with the difference between maximum and minimum temperature.
Modifications of fiber length by growth temperatures also have been observed in planting-date studies in which the later planting dates were associated with small increases in 2.5 and 50% span lengths . If the growing season is long enough and other inhibitory factors do not interfere with fiber development, early-season delays in fiber initiation and elongation may be counteracted by an extension of the elongation period .
Variations in fiber length and the elongation period also were associated with relative heat-unit accumulations. Regression analyses showed that genotypes that produced longer fibers were more responsive to heat-unit accumulation levels than were genotypes that produced shorter fibers . However, the earliness of the genotype was also a factor in the relationship between fiber length (and short-fiber content by weight) and accumulated heat units . 
As temperature increased, the number of small motes per boll also increased. Fertilization efficiency, which was negatively correlated with small-mote frequency, also decreased. Although fiber length did not change significantly with increasing temperature, the percentage of short-fibers was lower when temperatures were higher. The apparent improvement in fiber length uniformity may be related to increased assimilate availability to the fibers because there were fewer seeds per boll.FIBER LENGTH AND WATER:
Cotton water relationships and irrigation traditionally have been studied with respect to yield . Fiber length was not affected unless the water deficit was great enough to lower the yield to 700 kg ha-1. Fiber elongation was inhibited when the midday water potential was -2.5 to -2.8 mPa. Occurrence of moisture deficits during the early flowering period did not alter fiber length. However, when drought occurred later in the flowering period, fiber length was decreased .
Severe water deficits during the fiber elongation stage reduce fiber length , apparently due simply to the direct mechanical and physiological processes of cell expansion. However, water availability and the duration and timing of flowering and boll set can result in complex physiological interactions between water deficits and fiber properties including length.
FIBRE LENGTH AND LIGHT:
Changes in the growth environment also alter canopy structure and the photon flux environment within the canopy. For example, loss of leaves and bolls from unfavorable weather (wind, hail), disease, or herbivory and compensatory regrowth can greatly affect both fiber yield and quality . The amount of light within the crop canopy is an important determinant of photosynthetic activity and, therefore, of the source-to-sink relationships that allocate photoassimilate within the canopy . Eaton and Ergle (1954) observed that reduced-light treatments increased fiber length. Shading during the first 7 d after floral anthesis resulted in a 2% increase in the 2.5% span length .
Shading (or prolonged periods of cloudy weather) and seasonal shifts in day length also modulate temperature, which modifies fiber properties, including length.
Commercial cotton genotypes are considered to be day-length neutral with respect to both flowering and fruiting . However, incorporation of day-length data in upland and pima fiber-quality models, based on accumulated heat units, increased the coefficients of determination for the length predictors from 30 to 54% for the upland model and from 44 to 57% for the pima model .
It was found that the light wavelengths reflected from red and green mulches increased fiber length, even though plants grown under those mulches received less reflected photosynthetic flux than did plants grown with white mulches. The longest fiber was harvested from plants that received the highest far red/red ratios.