fibers

Fibers

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Slide 1

Fibers

In this section, we will discuss the basic building block of all textile materials, the fiber. We’ll learn basic properties common to all fibers as well as properties that can vary for specific fibers. We’ll learn how fibers are classified and see how their chemical composition and structure can affect their behavior. We’ll also see how fiber properties can affect yarn, fabric, and end-use products. Before we can learn about specific fiber types, we need to spend some time discussing information that can be applied to all fiber types, including fiber definitions and classifications, general textile nomenclature, and yes, even a little bit of chemistry. After all, fibers are chemicals! But don’t worry, it will be fun!

Fibers


Slide 2

Basic structural material of clothing, domestic, and industrial textile products

Sources of fibers:

• Naturally occurring

• Man-made from naturally existing materials

• Man-made from basic organic or inorganic components

Fiber Characteristics:

• High length to diameter ratio (at least 1000:1)

• Low bending rigidity

• Small diameter (10 to 200 microns)

What Is a Fiber?

Think about the following questions: • Can you visualize a fiber? • What size is it? • Where do fibers come from? Before we consider how to define and characterize a fiber, let’s consider the nomenclature of textile processing. Let’s call the final product a fabric. If we start to break down a knitted or woven fabric into its components, we call those components yarns. Now let’s break down the yarn into its components, which are fibers. Let’s now complicate matters by considering a type of fabric that is not woven or knitted and that we will call a nonwoven material. If we break down a nonwoven fabric into its direct components, we have fibers. A nonwoven material is made by converting fibers directly into fabric and bypassing the intermediate yarn step. You will learn much more about nonwovens, as well as yarn manufacturing, weaving, and knitting, in other modules of the Textile Fundamentals course. We will consider a fiber to be the basic building block of all textile materials. But what are the building blocks of fibers? If you said polymers, you are correct. We are now delving into the range beyond which our eyes can see. Polymers are actually very large, chain-like molecules. They are considered large by molecular standards but are still very small by our visual standards. We can’t really even see them with the most powerful microscopes available! We’ll talk more about polymers a little later. Let’s talk about the sources of fibers, of which there are three categories. Fibers can be naturally occurring, meaning that Mother Nature provides them to us in fiber form. Think of some examples of these fibers. The most abundant fiber in this category is cotton. Cotton is a seed-hair fiber from the cotton plant. Other examples of natural fibers would be the animal hair fibers – wool, cashmere, mohair, and camel, to name a few. The second category of fibers would be those that require processing to convert them to fiber form even though the raw materials come from nature. These fibers are thus considered to be man-made from natural sources. A good example of a fiber in this category is rayon. Rayon is derived from wood pulp, but the wood pulp must be processed and extruded into fiber form. Other examples of this category would be acetate, triacetate, and PLA fibers. As with rayon, acetate and triacetate are derived from wood pulp, while PLA, which stands for poly (lactic acid), is made from corn starch. The final category of fibers is the truly synthetic fibers. These fibers are made from polymers than can be synthesized from basic chemical components. Examples here would be polyester and nylon. Now that we know the sources of fibers, we need to determine the properties that a material must possess in order to be called a fiber. A material should possess all three of the characteristics listed to meet the requirements. Many materials meet the first two requirements – they’re long and

Fibers


skinny and can bend without breaking – but the third requirement eliminates many candidates. Fibers are very small objects, with a typical diameter of 20 to 30 microns. A typical cotton fiber would be slightly longer than one inch (or 25 millimeters) long, and it would be much, much finer than your own hair. One micron is one one-thousandth of a millimeter. 25 microns is just about the minimum limit of what the human eye can see, so a fiber of this diameter would be just barely visible to most people. Rather than defining fiber size by diameter, we typically use the term denier. Denier has units of mass per length, also called linear density, and is defined as the number of grams per 9,000 meters of fiber. A polyester fiber with a diameter of 25 microns would have a denier value of around 4. This means that 9,000 meters of this fiber would weigh a total of four grams! On the next slide, we will look at the relative sizes of several types of fibers and see what the term microfiber tells us about a fiber’s size.

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Slide 3

Microfibers are generally defined as fibers of less than one denier per filament (dpf). Microfibers can generally be produced by direct spinning methods but may require bi-component technology (e.g. – segmented pie) for production.

Comparisons:Human Hair 30 – 50 dpfWool 4 – 6 dpfCotton 1.4 – 1.6 dpfSilk 1.1 – 1.2 dpfMicrofiber less than 1.0 dpfUltra Microfiber less than 0.2 dpf

Microfibers

Have you ever bought a garment that had a label advertising it as being made from microfibers? Think of the characteristics claimed by the garment label or that you observed in the garment. While you’re thinking, let’s look at the sizes of some typical fibers. Your own hair, with a diameter of 30 to 50 denier per filament, is considered very coarse by fiber standards. By extension, wool fibers are somewhat coarse compared to other fibers. Cotton and silk are some of the finest naturally occurring fibers, both approaching one denier per filament. We define the term microfiber to mean a fiber less than one denier per filament. When you hear that term used, that will tell you that you are dealing with synthetic fibers, generally polyester or nylon. These fibers can be engineered during the extrusion process to be very small in diameter. The smaller the diameter of the fiber, the lower the denier. These smaller fibers are sometimes difficult to produce by conventional extrusion methods, in which a liquid (either a solution or a molten polymer) is forced through tiny holes in a spinneret to form filaments. (We’ll discuss the extrusion process in more detail later.) Special processes, examples of which are segmented pie and islands-in the-sea technology, may be needed to produce microfibers. In these processes, the target fiber is extruded within a matrix of another polymer, followed by removal of the matrix by dissolution or other means. Here we see an illustration of the segmented pie technology, in which the pie-shaped microfibers can be seen pulling away from the star-shaped matrix polymer. Now let’s return to the question of the characteristics of products made from microfibers. The fabrics generally have a much softer hand and are more breathable and comfortable to wear than fabrics made from larger fibers of the same type. Fabrics that resemble suede can be made from microfibers. One reason for the soft hand is, that for a given weight of fabric, a microfiber fabric would have more exposed surface area than a conventional fabric.

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Slide 4

Microfibers vs. Conventional Fibers

Look at this photograph of two fabrics, both made of nylon and dyed in the same dyebath. By the way, these fabrics are nonwoven, and their weights are comparable. One of the fabrics is made from microfibers, and the other is not. Can you predict which fabric is made from microfibers based on the color of the fabrics? If you were able to hold these fabrics in your hand, you would easily know which side was made from microfibers because of the soft, suede-like hand, but can you guess just from the shade appearance? If you said the lighter side was made from microfibers, you are correct. Because both fabrics were dyed in the same dyebath at the same time and are of comparable weights, we can assume that each fabric has the same percentage of dye per unit weight of fabric. The microfiber side appears lighter to your eyes because the finer fibers create more surface area and therefore more scattering of reflected light, resulting in a lighter shade.

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Slide 5

Mono: One

Mer: Unit

Poly: Many

Polymerization is the linking of many small molecules (monomers) to form a long, chain-like molecule (polymer).

Polymerization

Now it’s time for our chemistry lesson. We mentioned the word polymer earlier. Polymers are the molecular building blocks of fibers. Polymers are long, chain-like molecules, and their structure is the chemical composition of the fiber. The word polymer literally means “many units.” Polymers are formed when many monomers react with each other to create a very long molecule.

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Slide 6

Polymerization Animation

For example, in the making of polyester, two starting chemicals that we’ll call A and B react with each other to form an AB unit. This AB monomer unit can react with other AB units over and over again until we have a long chain of AB units connected to each other. This process is called polymerization. AB is called the repeat unit, and the number of times it repeats is called the degree of polymerization. The degree of polymerization could be several thousand or more.

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Slide 7

In the diagram shown on the slide, each tiny circle represents a repeat unit of the polymer. These drawings represent how a polymer chain may be arranged inside the fiber. Consider one fiber, which is very small itself, and think about how many polymer chains are inside that fiber. The answer is billions! The arrangement of these chains inside the fiber plays an important role in determining the properties of that fiber. To visualize the behavior of the polymer chains, let’s think of them as spaghetti strands. In some regions of the fiber, the polymers behave as uncooked spaghetti. Imagine holding a bunch of uncooked spaghetti in your fist. The strands are straight and rigid and can pack tightly together. In the fiber, these regions are called crystallinity. We can see these crystalline regions in the diagram. Think of some fiber properties that would be enhanced or determined by crystallinity. Some possible answers here would be strength, stiffness or modulus, toughness, and melting point. Returning to our spaghetti analogy, let’s imagine the behavior of cooked spaghetti. The strands are now soft and flexible and can move around, leaving space between each strand. The regions in the fiber where the polymer chains behave this way, especially at higher temperatures, are called amorphous regions. Note the amorphous regions in the fiber diagrams. Some fiber properties enhanced by the amorphous regions are flexibility, extension, and dyeability. Dye molecules can not penetrate crystalline regions of a fiber. This is why Kevlar®, a highly crystalline fiber, can’t be dyed by conventional means. Also note in the diagram how the same polymer chain can wind through several crystalline and amorphous regions. This in part explains why fibers can be at the same time both strong and flexible. Another important property related to the arrangement of polymer chains is orientation. Orientation refers to the alignment of the crystalline regions in the fiber. In the diagram on the left, the crystalline regions are all aligned parallel to the fiber axis, resulting in a high degree of orientation. The fiber on the right exhibits low orientation. In general, higher orientation contributes to higher strength in the fiber.

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Slide 8

Fiber Properties Depend On:

• Chemical composition of the polymer

• Arrangement of polymer molecules

To summarize, we can say that the properties of a fiber will be influenced primarily by two factors: (1) its chemical composition, in other words, what is the chemical composition of the polymer? and (2) the arrangement of the polymer chains inside the fiber. We’ll cover typical fiber properties and how they are influenced by these factors in the following slides.

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Slide 9

Polymer Terms Related to Fiber Properties

• Homopolymer

• Copolymer

• Degree of polymerization

• Molecular weight

• Orientation

• Crystalline

• Amorphous

Here we see a list of terms relating to polymers. We have already covered some of these such as crystalline and amorphous. Let’s give a brief definition of each of these terms, including those we have already covered. A homopolymer is one in which all the repeat units are the same and made from the same monomer unit. Most of the fibers commonly used in textiles are considered to be composed of homopolymers. Examples would be cotton, made from cellulose, and polyester, typically made from a polymer called poly(ethylene terephthalate). A copolymer is made up of repeat units of two or more types of monomers. The copolymers can be classified as alternating, random, block, or branched, depending on their structure. Examples of textile fibers that would be considered copolymers are acrylics, modacrylics, and spandex. The degree of polymerization is the number of times the monomer unit repeats in the polymer chain. Thus, a high degree of polymerization results in a longer chain and also in a higher polymer molecular weight, which is defined as the molecular weight of the monomer unit multiplied by the degree of polymerization. In general, for a given polymer type, a higher molecular weight results in a stronger fiber. Orientation refers to the alignment of the polymer chains along the direction of the length of the fiber, which also contributes to fiber strength. Crystalline regions of the fiber are those in which the polymer chains are aligned and packed tightly together, whereas amorphous regions are those where the chains are non-crystalline and more randomly distributed, resulting in a more open structure. Orientation and crystallinity also contribute to fiber strength.

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Slide 10

Textile Product CharacterThe character or personality of any textile structure or end-use product, i.e., its appearance, texture, hand, wear performance, mechanical properties, etc., is generally influenced by four factors:

• The fiber or blend of fibers used

• Yarn structure or structures – size, twist, etc.

• Fabric structure – weave, knit, non-woven

• Type of finish or finishes – color added, chemical and/or mechanical finish

We have talked in very technical terms about fiber structure, but these considerations also have very practical applications. Let’s consider, for example, two fibers that have the same chemical composition but have different physical properties – cotton and rayon. Both are made of the polymer cellulose. However, clothing made from 100% rayon will typically have a care label advising dry-clean only, whereas 100% cotton is most always machine washable. Why the difference? The reason rayon should be dry-cleaned is because its tensile strength is less than half that of cotton, and it becomes even weaker in the wet state. Why would two fibers made of the same polymer have such different strength properties? The reason is the internal structure and arrangement of the polymer molecules! Cotton is approximately 80% crystalline, whereas conventional rayon is around 30% crystalline. We know that higher crystallinity generally translates to a stronger fiber. Now can you predict which of these two fibers (in comparable constructions and weights) would dye to a darker shade if placed in the same dyebath? Because both fibers are chemically the same, they are dyed with the same classes of dyes, but rayon would dye to a darker shade than cotton because of its amorphous, more open structure. This is but one example of how fiber properties are an important contributor to the properties of the end-use textile product. Those fiber properties influence yarn properties which then influence fabric properties. Fabric is dyed to give color and finished to give other desired properties. Any problems or defects in the finished goods could therefore have originated at one or more or many steps of the manufacturing process. For example, in the production of a man-made fiber, problems with the control of the crystallinity level in the fiber could lead to variability of the dye uptake in that fiber. This would show up in the final fabric as streakiness. When diagnosing problems in a textile product, it’s always good to have as much information as possible about all of the manufacturing history of that product.

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Slide 11

Yarn Examples

Although this is a topic that is covered in great detail in another module, here is a photograph of different types of yarns illustrating the difference between staple fibers and continuous filaments. The top yarn is a spun yarn, made of short lengths of fiber, or staple fiber. These fibers must be twisted together to form a yarn structure that will hold together and have acceptable strength. Note the many fibers protruding from the yarn structure. This is called “hairiness” and is a characteristic of spun yarns. The lower two yarns are filament yarns and are bundles of long, continuous strands of fiber, or filaments. The middle yarn is called a flat filament yarn. The bottom yarn is a filament yarn that has been through a process called texturing, in which crimp and bulk have been imparted. Non-textured filament yarns are smoother and have a more lustrous appearance than spun yarns, and the texturing process makes a filament yarn behave more like a spun yarn. A comparison of the properties of spun versus flat filament yarns is shown on the slide. The properties of textured yarns would fall somewhere in between spun and flat filament yarns. In general, spun yarns are softer, bulkier, and more absorbent than filament yarns. You will learn much more about yarns in a separate module.

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Slide 12

Fiber Usefulness

The following factors influence the use of a particular fiber in a textile:

• Ability of a fiber to be converted to a yarn and then to a finished product

• Availability of the fiber

• Cost or economics of production

• Public acceptability and demand

Here we see factors that must be considered when trying to introduce a new fiber to the marketplace. To be a useful textile fiber, all four factors must be considered. The fiber must be able to withstand the mechanical and thermal rigors of textile processing, it must come from a readily available source, it must be economically feasible to produce, and it must be something that people will want to buy. A good example of a fiber that, at one time or another, did not meet one or more of these criteria is colored cotton. Naturally-colored cotton varieties, in shades of green and brown, have been in existence for centuries, but the fibers from these plants were too short and too weak to be spun into yarns. In the early nineteen eighties, a scientist named Sally Fox was able to breed colored cotton varieties with longer, stronger fibers that could be processed into yarns. However, the cost per pound of these fibers was approximately ten times that of conventional cream-colored cotton fibers. Even given the cost savings of eliminating the dyeing step, this fiber just was not an economically viable product and today is targeted only to a niche market.

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Slide 13

Important Fiber Properties (primary)Fibrous materials should possess certain properties for them to be useful as textile raw materials. Those properties which are essential for acceptance as a suitable raw material may be classified as “primary properties,” while those which add specific desirable character or aesthetics to the end product and its use may be classified as “secondary properties.”

Primary Properties• Length and length distribution

• Tensile properties (tenacity, elongation, modulus)

• Flexibility (pliability)

• Cohesion

• Uniformity of properties

Secondary Properties• Appearance (shape, cross section, birefringence)

• Crimp

• Dyeability

• Fineness (linear density)

• Flammability

• Luster

• Moisture regain (comfort, static, etc.)

• Solubility and chemical resistance

• Specific gravity (influences weight, cover, etc.)

• Thermal properties (Tg, Tm) and flammability

On this slide, we have listed some of the more important fiber properties that can be measured in a suitably equipped laboratory. Later in the discussion, you will be given values for some of these properties for specific fiber types, but for now we would just like to discuss how these properties are defined and how they are generally applied to all fibers. We have separated the properties into two groups: the primary properties are those that are essential for a textile fiber to possess, and the secondary properties are those that enhance the performance or aesthetics of a product made from the fiber. The primary properties, such as length, strength, flexibility, and cohesion relate to a fiber’s ability to be processed into a yarn. It is especially important to know the distribution of lengths in a natural fiber sample such as cotton. Nature does not provide us with fibers from the cotton plant that are all uniform in length. For American Upland cotton, the fibers will range from less than one-half inch to over 1-1/4 inches. The average length and the distribution of lengths will affect the strength and evenness of a staple yarn spun from those fibers. In general, longer staple lengths will produce better quality yarns. For cotton, staple length is measured on a machine called an HVI, or High Volume Instrument. Let’s also define the tensile properties of tenacity, elongation, and modulus. These properties are all measured by a machine that can grip each end of the fiber and pull it lengthwise until it breaks. In doing this, the machine will generate a graph plotting the force needed to pull the fiber versus the actual extension of the fiber. You may sometimes hear this referred to as a load-elongation curve or a stress-strain curve. Each type of fiber will have a characteristic shape to its stress-strain curve. The tenacity of a fiber is a measure of its strength and it is defined as the load or the force, usually expressed in grams, to break the fiber divided by the linear density of the fiber. Earlier, we said that denier was a typical way to express linear density, so typical units of tenacity would be grams per denier. Recall that denier is the number of grams per 9,000 meters. Sometimes, particularly for cotton fibers, tenacity is expressed as grams per tex. Tex is defined as the number of grams per 1,000 meters. Elongation of the fiber would be the distance the fiber extends, or stretches, divided by the original gauge length of the fiber. Modulus is a term for the stiffness of the fiber as measured by the initial slope of the stress strain curve. A very stiff fiber would require a high force to cause very low elongation, which would be represented by a steep slope. Can you think of an example of a high modulus fiber? Examples would be Kevlar® or fiberglass. An example of a very low modulus fiber would be spandex, which requires very little force to extend quite a bit.

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Slide 14

Secondary Fiber Properties

Secondary Properties• Appearance (shape, cross section, birefringence)

• Crimp

• Dyeability

• Fineness (linear density)

• Flammability

• Luster

• Moisture regain (comfort, static, etc.)

• Solubility and chemical resistance

• Specific gravity (influences weight, cover, etc.)

• Thermal properties (Tg, Tm) and flammability

You can see the secondary properties listed here, of which we will mention a couple. The luster of a fiber refers to its ability to reflect, absorb, or transmit light. We have very little control over the luster of natural fibers, although we can do a process called mercerization of cotton to affect its luster. You will learn about mercerization in another module. For man-made fibers, however, we can control fiber luster by the addition of a white pigment called titanium dioxide, which is sometimes referred to as a delustrant. The delustrant is responsible for the speckled appearance of the polyester fiber in the following photograph. Man-made fibers can be described as bright, semi-dull, or dull, depending upon the amount of delustrant that has been added. Bright fibers have no delustrant added and have an appearance similar to monofilament fishing line. Fibers are, after all, plastics in filament form. Dull fibers would have up to two percent delustrant on the weight of the fiber and would appear white. Finally, moisture regain is an important fiber property that determines whether a fiber is classified as hydrophilic (water-loving) or hydrophobic (water-hating). This property is largely dependent on the chemical nature of the fiber, or in other words, the polymer of which it is made. Moisture regain of a fiber has a large influence on the comfort properties of that fiber. In general, hydrophilic fibers are more comfortable to wear. Cotton is a hydrophilic fiber whose moisture regain is around 8.5%. In order to define moisture regain, we need to define standard conditions of temperature and humidity for a textile testing laboratory. A testing lab should be 70 degrees Fahrenheit plus or minus two degrees and 65 percent relative humidity plus or minus two percent. These standard conditions ensure consistency in testing between labs and within the same lab over time because test results could vary with the moisture level in a sample. Moisture regain is defined as the amount of moisture in a fiber sample expressed as a percentage of its bone-dry weight. Moisture regain is always measured under standard conditions of temperature and humidity. Hydrophilic fibers have higher values of moisture regain. For example the moisture regain of cotton is around 8.5% and of rayon is anywhere from 11 to 16%. Based on what you have learned about the structure of cotton and rayon, think about possible reasons that the moisture regain of rayon is higher than that of cotton even though the two fibers are made of the same polymer – cellulose. A hydrophobic fiber such as polyester has a moisture regain of less than one percent. Polyester is hydrophobic because its polymer molecules have little or no chemical attraction to water molecules.

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Slide 15

Fibers can have various shapes and configurations, some of which you see pictured here. Most fibers have a round cross-sectional shape, but there are also triangular and multilobal fibers. Some fibers have smooth edges and others are serrated. Fibers can sometimes, but not always, be identified by their shape and appearance under a microscope. Cotton can usually be identified by looking at the twists or convolutions that are characteristic only of cotton. These can be observed in a longitudinal view of the fiber under a microscope. Cotton also has a unique kidney-shaped cross-section. Most animal hair fibers are characterized by scales that are visible in a longitudinal view, but an experienced observer would be required to differentiate between different types of animal hair fibers, for example, wool and cashmere. Most synthetic fibers are difficult to positively identify under a microscope based on their shape alone because most are round. Other optical techniques such as measurement of birefringence must be used. The shape of a fiber can affect the luster, appearance, and stiffness of the end-use fabric.

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Slide 16

Textile Fibers

Natural Man-Made

Cellulose Protein Mineral Organic Inorganic

NaturalPolymer

SyntheticPolymer

BastFlax

HempJute

Ramie

LeafManila

Sisal

Seed HairCottonKapok

Asbestos

StapleAlpacaCamel

CashmereLlama

MohairVicunaWool

FilamentSilk

Glass*Metallic*

Cellulose BaseRayon*Lyocell*Acetate*

Triacetate*

Protein BaseAzlon*

Rubber*

Natural Sugars BasePLA*

Acrylic*Anidex*Aramid*

Elastoester*Fluoropolymer*

Lastrile*Melamine*Modacrylic*Novoloid*

Nylon*Nytril*Olefin*

PBI*Polyester*

Rubber* (Synthetic)Saran*

Spandex*Sulfar*Vinal*

Vinyon*

*Generic classification based on chemical composition as defined by theTextile Fiber Products Identification Act.

Textile Fibers Classification

The organizational chart that you see here shows textile fibers categorized by the three sources that we discussed earlier: natural, man-made from natural sources, and man-made from basic chemicals. This chart shows natural fibers as well as all the generic classes of man-made fibers as defined by the Federal Trade Commission under the Textile Fiber Products Identification Act. Each generic fiber class is defined by the chemical composition of the fiber. The names of the generic fiber types are denoted on the chart by an asterisk (*). No registered trademarks appear on the chart. The most recent fiber class to be recognized by the FTC is PLA, which stands for poly(lactic acid) that is derived from naturally-occurring sugars such as corn starch. It was recognized in 2002. Let’s look at the breakdown of the chart. The first division is between natural and man-made fibers. All the fibers under the “Natural” category appear in nature in fiber form. The sources of these natural fibers can be plant (cellulose-based fibers), animal (protein-based fibers, generally from animal hair), or mineral (asbestos). Focusing on the plant fibers, we see that they can come from the stem, leaf, or seed hair of the plant. Fibers that come from the stem of the plant are called bast fibers. Regardless of their origination on the plant, all these fibers are composed of cellulose. The most important of the cellulose fibers is, of course, cotton, but other fibers in this category include flax, hemp, jute, and ramie. Moving now to the protein-based fibers, we see that they are divided into categories of “Staple” and “Filament.” Silk is the only naturally-occurring fiber that is produced in continuous filament form. The fiber is obtained by unwinding the cocoon of the silkworm in a process called reeling. Continuous lengths of up to 600 meters can be recovered, although shorter, staple fibers are obtained as well. Silk is processed into both continuous filament and spun yarns. Under the staple fiber category, we see all the animal hair fibers, including wool, alpaca, and cashmere. Depending on the length of the hair on the animal, the staple lengths could be up to ten to fifteen inches, but all the animal hair fibers must be processed into spun yarns. The term worsted describes a spinning system for wool that can accommodate longer staple fibers of two to nine inches. Now let’s examine the man-made categories. Note that all the fiber names listed under the man-made heading are followed by an asterisk, which as you recall denotes recognition by the Federal Trade Commission as a generic fiber class. In a subsequent slide, you will see abbreviated definitions of each fiber class, which are based on chemical composition. The first division under man-made is between organic and inorganic fibers. Here we define the word organic to mean that the polymer contains the element carbon in its structure. In this sense of the word, most fibers are organic, with the exceptions being fiberglass and metallic fibers, which are considered inorganic. Under the organic classification, we find the other two categories of our three sources of fibers: the natural-based man-made fibers and the truly synthetic fibers. Do you recall the naturally-occurring raw material from which rayon is made? It is wood pulp, which is composed of cellulose. Man-made fibers made or derived from wood pulp include rayon, lyocell (which you may know by its trade name - Tencel®), acetate, and triacetate. Earlier, we

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mentioned PLA fiber, which is derived from corn starch. Neither wood pulp nor corn starch are fibrous in their naturally-occurring state, so we must process them and extrude them into fiber form, which is why these fibers are categorized as man-made. Finally, there are twenty generic fiber classes under the synthetic polymer category. These include such familiar names as acrylic, nylon, olefin, and polyester. Each generic fiber name can have one or more registered trademark names. For categories such as nylon or polyester, there may be hundreds of trade names and types.

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Slide 17

Natural Fiber Properties

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Slide 18

We have covered a lot of general fiber information that can be applied to all fibers. Now we will look at some specific fibers and their properties, starting with the natural fibers of cotton, flax, wool, and silk. Cotton is a seed hair fiber. Here we see the stages of development of the cotton fibers on the plant from full bloom through the opening of the cotton boll. One boll of cotton produces from 24 to 45 seeds, with each seed producing 10,000 to 20,000 fibers. A bale of cotton, which weighs about 500 pounds, contains approximately 145,000 bolls. As the fiber develops before opening of the boll, it first forms an outer, primary wall, followed by development of an inner, secondary wall that is composed of cellulose. In a mature cotton fiber, the secondary wall should be well-developed. After the boll opens, the fibers die and dry out. The round cross section becomes flatter and kidney shaped, and the fiber twists into its characteristic convoluted shape. Immature fibers are caused by drying of the fiber before the secondary wall is fully developed. Immature fibers have very flat cross-sections and appear ribbon-like when viewed under a microscope. Once the boll has opened and dried, the cotton is ready for harvesting.

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Slide 19

Cotton Harvesting

Cotton is harvested mechanically by one of two kinds of machines: cotton pickers or cotton strippers. A cotton picker is pictured here. The picker heads contain a series of spindles covered with barbs that remove the cotton fibers from the boll. The fibers, called seed cotton because they still contain the seeds, are conveyed pneumatically into a basket for collection. In the photograph, there are four picker heads on the lower front of the machine. The second type of harvester is a cotton stripper. For this type, the plants are killed by frost or chemical defoliant before harvesting, and the stripper removes the boll and fibers by two counter-rotating rolls. Only the dry stalks remain in the field. Augers and pneumatic conveyors transfer the seed cotton to the collection baskets. The trash content, which refers primarily to residual pieces of the cotton plant, of the seed cotton is higher for cotton strippers than for cotton pickers. The baskets of seed cotton are transferred to a module builder, a metal box that allows the packing of an eight- to twelve-bale module in the field. Once full, the module builder is removed, and the module is picked up by a truck and transported to the gin for removal of seeds. In some parts of the world, cotton is still harvested by hand, resulting in a very low trash content, but this represents a small percentage of worldwide cotton production.

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Slide 20

Cotton Ginning

The ginning process separates the seeds from the cotton fibers, cleans the fibers, and allows for the recovery and sale of both commodities. The seeds can be used for cattle feed, production of cottonseed oil, or for planting next year’s cotton crop. The fibers from the gin are pressed into 500-pound bales for textile production. Ideally, the gin will cause minimal damage to the cotton fibers. Pictured here are two gin stands, where seed and fiber separation is accomplished by rotating saw blades and doffer brushes. Seed cotton enters the top of the machine, and separated seeds and fibers are conveyed from the bottom.

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Slide 21

Instrumental Classification of Cotton

High Volume Instrument (HVI) measures the following properties:

•Grade–Trash Content

–Color

•Fineness (Micronaire)

•Strength

•Staple Length and Length Uniformity

After ginning, samples of fiber are taken from each bale of cotton for classification. The samples are tested on an instrument called an HVI, which stands for High Volume Instrument. In the United States, samples from every bale of cotton produced are sent to one of 12 cotton classing facilities operated by the US Department of Agriculture for HVI classification. The cotton is assigned a grade based on trash content and fiber color. The grade is a two-digit number, in which the first digit represents trash content, sometimes called leaf content, and the second digit represents color. The first number ranges from 1 to 8, and the second number can range from 1 to 6. The USDA maintains and provides physical standards for 15 of the 25 possible color grades for American Upland Cotton. We will see illustrations of some of these boxes in the next slide. Before the advent of HVI equipment, color grade was assigned by visual assessment, but modern equipment uses optical sensors to measure values for yellowness and reflectance of the cotton sample, which are then converted to the two-digit color grade. For each digit, the lower the number, the better the grade and the higher cost per pound. In addition to the color grade, the HVI measures fineness, length, and strength of the cotton sample. The fineness of the cotton is measured in micronaire, which stands for micrograms per inch. The micronaire value for cotton is determined by fiber size and maturity. The measurement of micronaire by an HVI is based on the resistance to air flow of a known mass of cotton fibers compressed to a constant volume. The measurement of length by the HVI is based on the array principle. Here we see a picture of a cotton fiber array, in which the fibers in a sample have been arranged from longest to shortest. The HVI scans a randomly-distributed sampling of fibers that have been straightened and made to lie parallel to each other. This is called a sample beard. The HVI can detect the various lengths of fibers in the sample and can generate an array curve without having to physically rearrange the fibers. Based on this array curve, the HVI reports average fiber length as the upper half mean length, which is the average length of the longest 50% of the fibers in the sample. It also reports uniformity index, which is a measure of the distribution of lengths and is the mean length expressed as a percentage of the upper half mean length. The higher the uniformity index, the better the uniformity in the sample. Uniformity index would never exceed 100%, and its average value is around 80%. Finally, after the length scan is made, the HVI will clamp both sides of the sample beard and determine the force to break the fibers. Strength is reported in tenacity units of grams per tex. Tex is a unit of linear density and is the number of grams of fiber per 1,000 meters. Recall that denier is the number of grams per 9,000 meters. In general, stronger fibers will produce stronger yarns. Newer models of HVI will also measure maturity of the cotton. Immature cotton, which is a result of poor development of the secondary wall of the fiber, can often go undetected until the fiber has been made into fabric and dyed. It will then show up as white, undyed spots on the fabric. Thus, it is very useful to know whether a cotton fiber sample has a high percentage of immature fibers before it is processed.

Fibers


Slide 22

Cotton Grade Boxes

Here we see an illustration of three of the USDA Color Grade standards for American Upland cotton. American Upland is the variety of cotton most commonly grown in the United States. Pima is another cotton variety that has different standards. The color grade for Pima is still determined visually by highly trained observers. Pima fibers are generally longer and finer that Upland cotton fibers. Illustrated here are standards for 11 (pronounced one-one), 41 (pronounced four-one), and 44 (four-four) cotton. Recall that the first digit represents trash content and the second digit represents fiber color. The 11 box is high quality cotton with low trash and creamy white colored fibers. Trash content is primarily affected by the harvesting method (hand-picked vs. automated), whereas fiber color is affected by growing conditions such as moisture, temperature levels, and insect damage. If we increase the first digit to four and leave the second digit one, the trash content will increase while the color is constant. The last illustration shows high trash content as well as discolored cotton. The 44 grade would require more opening and cleaning to remove trash and more bleaching to remove the discoloration. Yarn producers will generally buy a range of color grades and blend them together during the first steps of yarn processing in order to give the best product at the lowest cost.

Fibers


Slide 23

Cotton PropertiesComposition

• 87 to 90% cellulose

• 5 to 8% water

• Remainder is natural impurities

Thermal Properties

• Does not melt

• Decomposes slowly upon exposure to dry heat above 300 °F

• Decomposes rapidly above 475 °F

Chemical Properties

• Easily damaged by strong acids

• Good resistance to alkalis

• Loses strength under prolonged exposure to sunlight

Strength – Dry (grams/denier) 3.0 – 5.0

Strength – Wet (grams/denier) 3.3 – 6.0

Extensibility 3 - 10%

Elasticity 75% recovery at 2% extension

Resiliency low

Moisture Regain @ 70° F, 65% rh 8.5%

Specific Gravity 1.54

Physical Properties

This page summarizes physical, thermal, and chemical properties of cotton fibers, as well as shows a photograph of the fiber and describes its chemical composition. This format will be used for various fibers throughout the remainder of this fiber module, and the information on these pages will be useful as reference material. In the photograph of cotton, note the twist, or convolutions, along the length of the fiber. The appearance of cotton is unique among fibers. The chemical composition of cotton is the polymer cellulose. In the physical property summary, values are given for tensile properties, moisture regain, and specific gravity. Specific gravity is the density of the fiber compared to that of water, which is one gram per cubic centimeter. Recall that moisture regain is an indication of the hydrophilicity of the fiber, or its affinity for water. Cotton is classified as a hydrophilic fiber. As with most of the natural fibers, cotton does not have a melting point, but decomposes at high temperatures. With regard to chemical properties, cotton is susceptible to damage by acids. Acidic chemicals are characterized by a pH value between 1 and 7, with a lower number indicating a stronger acid. A pH of 7 is neutral, while a pH between 7 and 14 indicates alkalinity, with a higher number indicating stronger alkalinity. Cotton has good resistance to alkaline chemicals, which is fortunate because textile processes such as scouring and bleaching are generally carried out at a pH of between 10 and 11. Finally, cotton is susceptible to damage and weakening by exposure to sunlight, as are most fibers. Based on our earlier discussion, can you predict the reason for this? The ultraviolet radiation in sunlight breaks the chemical bonds in the polymer chain, resulting in shorter chains with lower molecular weight, thus reducing fiber strength.

Fibers


Slide 24

The photographs here are useful for illustrating the cross-sectional shape of cotton. The photograph on the left shows untreated cotton fibers, which are kidney-shaped. The flatter fibers in the picture could be immature. Note also the hollow strip in the center of the fibers – this is called the lumen. The portion of the fiber between the lumen and the outer wall is called the secondary wall, and this is the part of the fiber that is composed of cellulose. The photograph on the right shows the effect of mercerization on cotton fibers. Mercerization is an optional preparation step that is generally done to fabric but can also be done to yarn. Mercerization is the immersion of cotton in sodium hydroxide (sometimes called caustic soda), causing the fibers to swell and the polymer chains to rearrange. The process improves luster, strength, absorbency, and dye uptake. Note the rounder, more uniform cross-sections in the photograph on the right. In some cases, the lumen disappears. Mercerization will be discussed in much more detail in another section.

Fibers


Slide 25

Flax Properties

Composition

• Cellulose (from stem of plant)

• water

• natural impurities

Thermal Properties

• Does not melt

• Prolonged exposure above 300 °F will cause discoloration

• Withstands ironing temperatures up to 500 °F

Chemical Properties

• Strong acids cause deterioration


• Loses strength under prolonged exposure to sunlight



Extensibility 2.7 – 3.3%


Resiliency poor

Moisture Regain @ 70° F, 65% rh 12%


Physical Properties

The flax fiber is made of cellulose, just like cotton, so those fiber properties affected by chemical composition should be similar for flax and cotton. The flax fiber is used in making linen fabric. Flax is a bast fiber obtained from the stem of the plant. The fibers are removed from the stalk by a process called retting, in which the stalks are soaked in water to cause the outer woody portion to rot away. After retting, the flax is rinsed and dried and combed to remove the fiber. The typical staple length of flax is ten to fifteen inches, but the fibers are generally not as fine as cotton fibers. Linen fabrics are used in table coverings, draperies, upholstery, and apparel.

Fibers


Slide 26

Wool Properties

Composition

• Protein fiber

Thermal Properties

• Becomes weak when heated in boiling water for prolonged times

• In dry heat above 266 °F begins to decompose and yellow

Chemical Properties

• Not easily damaged by acids

• Very easily attacked by alkalis

• Weakened by sunlight



Extensibility 20 -40%


Resiliency high

Moisture Regain @ 70° F, 65% rh 13 - 16%


Physical Properties

Sheep’s wool is the most important and plentiful of the animal hair fibers, which are composed of amino acids that are formed into high molecular weight polypeptide chains. These fibers are called natural protein fibers. In addition to the animal hair fibers, this group includes fibers such as silk that are secreted by worms or insects. As with the cellulosic fibers, these fibers have high affinity for water and are considered to be hydrophilic. Compared to cotton, wool fibers are much weaker but much more extensible. Wool fibers can range from coarse to fine, and the finer fibers are preferred for better quality yarn. The staple length of wool can range from 1.5 to 15 inches. Fabrics made from wool fibers are known for their resilience and good cover and insulation properties. The fibers are light in weight, as characterized by a specific gravity lower than that of cotton. Wool fibers are susceptible to damage by alkaline chemicals, so care must be taken not to damage the fiber during the preparation steps of scouring and bleaching. Wool and other animal hair fibers are characterized by a scaly appearance, as noted in the scanning electron photomicrograph here. These scales are responsible for an effect called felting, in which a fabric made of wool shrinks excessively when the fabric is washed in hot water. As the fibers move past each other during washing, the scales lock together and immobilize the fibers. Wool fibers are used primarily in apparel but can also be used in carpeting, blankets, upholstery, and industrial textiles.

Fibers


Slide 27

Silk Properties

Composition

• Protein fiber

Thermal Properties

• Degrades rapidly at temperatures above 350 °F

• Scorches easily at temperatures above 300 °F

Chemical Properties

• Good resistance to most acids except strong mineral acids

• Slightly more resistant to alkalis than wool

• Weakened by sunlight





Resiliency medium

Moisture Regain @ 70° F, 65% rh 11%

Specific Gravity 1.25 – 1.34

Physical Properties

Silk is a protein fiber obtained from the cocoon of various insects, but the commercial silk used in textiles is produced by the silkworm. Silk can be cultivated or wild. Wild silk is also known as Tussah silk. As discussed earlier, silk is the only natural fiber available in continuous filament form, so it can be processed into both filament and staple yarns. Cultivated silk filaments are somewhat triangular in cross-sectional shape. The silk strand reeled from the cocoon consists of two filaments held together by a gum called sericin. The photograph on this slide shows the two filaments held together. In this form the fiber produces yarns and fabrics that are very stiff. To soften the fibers, the sericin is dissolved in a process called degumming, in which the yarns or fabrics are boiled in soapy water. Because silk is a protein fiber, its properties are similar to those of wool. Silk is a more crystalline fiber than wool, so it is slightly stronger but less extensible. It also has a lower moisture regain than wool, but it is still considered to be a hydrophilic fiber. Silk fibers are used primarily for apparel but can be used in draperies and upholstery as well.

Fibers


Slide 28

Man-Made Fiber Properties

In this section, we’ll look at how man-made fibers are produced by a process called extrusion. All man-made fibers, whether they are from natural sources or are synthesized from basic chemicals, must be extruded into fiber form. The extrusion occurs when a polymer solution or melt is forced through a spinneret, which is a metal plate with tiny holes. Each hole produces one filament. Here is a photograph of the bottom view of a spinneret. The actual size of this spinneret is approximately 76 mm in diameter. It contains 1276 holes, each with a diameter of 0.28 mm. After we’ve discussed extrusion, we’ll look at some specific man-made fibers and their properties.

Fibers


Slide 29

Man-Made Fiber CompositionsGeneric Name Textile Fiber Products Identification Act Definition

Acetate cellulose acetate; triacetate where not less than 92% of the cellulose is acetylated

Acrylic at least 85% by weight acrylonitrile units

Anidex at least 50% by weight of one or more esters of a monohydric alcohol and acrylic acid

Aramid polyamide in which at least 85% of the amide linkages are directly attached to two aromatic rings

Azlon regenerated naturally occurring proteins

Elastoester at least 50% by weight of aliphatic polyether and at least 35% by weight of polyester

Fluoropolymer at least 95% by weight of a polymer synthesized from aliphatic fluorocarbon monomers

Glass glass

Melamine at least 50% by weight of a cross-linked melamine polymer

Metallic metal, plastic-coated metal, metal-coated plastic, or a core completely covered by metal

Modacrylic less than 85% but at least 35% by weight acrylonitrile units

Novoloid at least 85% cross-linked novolac

Nylon polyamide in which less than 85% of the amide linkages are directly attached to two aromatic rings

Nytril at least 85% long chain polymer of vinylidene dinitrile where the vinylidene dinitrile content represents not less than every other unit in the chain

Olefin at least 85% ethylene, propylene, or other olefin units

PBI aromatic polymer having reoccurring imidazole groups as an integral part of the polymer chain

PLA at least 85% by weight of lactic acid ester units derived from naturally occurring sugars

Polyester at least 85% by weight ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalate units and para-substituted hydroxy-benzoate units

Rayon regenerated cellulose in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. Lycocell is cellulose precipitated from an organic solution in which no substitution of the hydroxyl groups takes place and no chemical intermediates are formed.

Rubber natural or synthetic rubber

Saran at least 80% by weight of vinylidene chloride

Spandex elastomer of at least 85% of a segmented polyurethane

Sulfar polysulfide in which at least 85% of the sulfide linkages are attached directly to two aromatic rings

Vinal at least 50% by weight vinyl alcohol units and at least 85% total vinyl alcohol and other acetal units

Vinyon at least 85% by weight vinyl chloride units

This page shows how generic fiber classes are defined under the Textile Fiber Products Identification Act. These represent all the man-made fiber classifications recognized by the Federal Trade Commission as of early 2008. You will probably see both familiar and unfamiliar fibers in the list. You will not see any registered trademarks such as Dacron, Spectra, or Nomex in this list. The definitions are based on the chemical composition of the fiber, or in other words, the polymer it’s made of. Recall that chemical composition is one of the two primary factors that influence the properties of a fiber. Properties that are greatly influenced by chemical composition include moisture regain, melting temperature, solubility, and resistance to various chemicals.

Fibers


Slide 30

Extrusion Processes

• Wet Spinning

• Dry Spinning

• Melt Spinning

• Gel Spinning

• Reaction Spinning

• Emulsion or Dispersion Spinning

Now let’s talk about the process by which man-made fibers are produced. Here we see a list of various extrusion methods. The type of fiber being produced generally dictates the method by which it is extruded. Let’s also discuss the use of the word “spinning.” This word can be used to mean the conversion of staple fibers to yarn as well as to mean the production of man-made filaments by extrusion. For our discussion here, we are using the second meaning. All the processes listed on this page are extrusion processes. The first three listed (wet, dry, and melt spinning) are conventional processes that have been used for many years and are still used today to produce the bulk of man-made fibers from either a polymer solution or a polymer melt. We’ll cover each of these processes in a separate slide. The last three processes (gel, reaction, and emulsion spinning) are specialized processes that have come into existence in recent years to accommodate newer fibers that could not be produced by conventional methods. For example, gel spinning is used to produce very high molecular weight fibers such as ultra high molecular weight polyethylene. The trade name for this high-strength fiber is Spectra®. After passing through the spinneret, the polymer solution cools to form a gel consisting of the polymer and its solvent. The polymer solidifies upon removal of the solvent by washing. In reaction spinning, polymerization occurs during extrusion. Some spandex fibers are produced by this method. Emulsion or dispersion spinning is used to produce fluorocarbon fibers, which have an extremely high melting point. Particles of the polymer are dispersed in a carrier, which is generally another polymer material. After extrusion, heat or a solvent is used to remove the carrier. Other specialized extrusion processes include bicomponent technology, including islands-in-the-sea and segmented pie microfiber production.

Fibers


Slide 31

Here we see a diagram of the wet spinning process, so-called because the filaments are extruded into a liquid medium called a coagulation or spin bath. A solution of the polymer is pumped through a spinneret that is immersed in a coagulation bath, where the chemicals in the bath cause the polymer to solidify and form fibers. The godet wheel controls the speed at which the filaments are pulled from the bath. The filaments are then washed and are either combined to form filament yarns or cut into staple fibers. The winding process imparts sufficient twist for the filament yarns to hold together. Rayon and lyocell fibers are produced by wet spinning. Both are made of cellulose, and the Federal Trade Commission considers lyocell to be a special type of rayon. Rayon is sometimes referred to as regenerated cellulose, and lyocell is called solvent-spun cellulose. Rayon was the very first man-made fiber. Production of rayon in the United States began in 1910. It is called regenerated cellulose because the cellulose must be converted into a chemical derivative in order to go into solution for extrusion. In the coagulation bath, the derivative is converted (or regenerated) back to cellulose. There are two types of rayon, depending on the nature of the chemical derivative. The most common type of rayon is called viscose rayon, and the second type is called cuprammonium rayon. Commercial production of lyocell (trade name: Tencel®) began in the early 1990’s. During the 1980’s the solvent spinning technique for cellulose was researched and developed. The solvent used is an amine oxide. In this process, the cellulose can be dissolved without being converted to a chemical derivative, resulting in lyocell fibers being much stronger than rayon fibers.

Fibers


Slide 32

Wet Spinning Animation

Here we see an animation of the wet spinning process. The polymer feed tank contains the solution of the polymer to be extruded. For production of viscose rayon, this aqueous solution would actually contain a chemical derivative of cellulose called cellulose xanthate. Making the derivative is necessary in order to solubilize the cellulose. The polymer should be in liquid form in order to be extruded. The viscous, honey-colored solution is filtered and pumped from the feed tank to the spinneret, which is immersed in a spin bath, also called a coagulation bath. As the liquid is pumped through the tiny holes in the spinneret, filaments are formed. The chemicals in the spin bath cause coagulation, regeneration, and solidification of the filaments into cellulose. For production of rayon, these chemicals would typically include sulfuric acid and sodium sulfate in water. Godet wheels pull the solidified filaments from the spin bath. The amount of stretch imparted to the filaments in this step influences the tenacity and modulus of the fibers. After regeneration, the filaments must be thoroughly washed to remove impurities before being wound as filament yarns or cut into staple fibers.

Fibers


Slide 33

The dry spinning process is used to produce acetate, triacetate, and some spandex fibers. In this process a solvent is required to make a solution of the polymer, which is then pumped through the spinneret. Solid fibers form when the solvent evaporates.

Fibers


Slide 34

Dry Spinning Animation

As it was for wet spinning, the liquid polymer to be extruded through a spinneret in dry spinning is in the form of a solution. However, the dry spinning solutions generally use organic solvents rather than the aqueous solutions used in wet spinning. The solution is filtered and pumped through the spinneret that is contained in a heated chamber that causes evaporation of the solvent, leaving purified solid filaments. The evaporated solvents are recovered for re-use. The solid filaments are generally stretched or drawn while still hot to impart orientation and fineness to the fibers before they are wound.

Fibers


Slide 35

Polymers whose melting temperature is easily controllable and does not degrade the material can be produced by the melt spinning process. These would include nylon, polyester, and olefin fibers. More recently, PLA fibers have been added to this list. No solvent is required for this process; the pure polymer is melted from chips or pellets as seen in the lower left of the screen. These chips are made of the same polymer as that found in two-liter plastic soft drink bottles. Your recycled drink bottles can be melted and extruded into polyester fiber! It takes approximately ten two-liter bottles to make one pound of recycled polyester fiber. The molten polymer is pumped through the spinneret, and the solid fiber forms upon cooling. The cross-sectional shape of the fiber can be determined by the shape of the hole in the spinneret. The internal structural factors such as crystallinity and orientation that we discussed earlier are greatly influenced by the process controls in melt spinning. They are affected by viscosity and purity of the polymer melt, temperature and pressure of the melt, rate of cooling of the extruded fibers, and the rate of uptake and drawing of the solid fiber, among others. The drawing step, which increases orientation, can be a part of the extrusion process, or it can be a separate step. Fully drawn filaments can then be cut into staple fibers or used as untextured filament yarns. POY, or partially oriented yarns, are yarns that are only partially drawn. These generally will be textured in a separate step for use as textured filament yarns.

Fibers


Slide 36

Melt Spinning Animation

No solvents are necessary for melt spinning; chips or pellets of the pure polymer are heated and melted into a viscous liquid. In this illustration, the liquid is filtered and channeled to the spinneret by a threaded shaft called a screw extruder. The viscous polymer melt is forced through the spinneret holes, and the resulting filaments solidify in a cooling chamber, followed by stretching and take-up. No solvents are necessary for melt spinning; chips or pellets of the pure polymer are heated and melted into a viscous liquid. In this illustration, the liquid is filtered and channeled to the spinneret by a threaded shaft called a screw extruder. The viscous polymer melt is forced through the spinneret holes, and the resulting filaments solidify in a cooling chamber, followed by stretching and take-up.

Fibers


Slide 37

Melt Spinning Video

This is a video of a melt spinning machine. Chips or pellets of pure polymer are delivered to the extruder from a hopper, then they are heated and melted into a viscous liquid. In this video the liquid is filtered and channeled to the spinneret by a threaded shaft called a screw extruder. The viscous polymer melt is forced through the spinneret holes , and the resulting filaments solidify in a cooling chamber ,followed by the application of a spin finish and subsequent stretching and take up. These machines are monitored and controlled by computers.

Fibers


Slide 38

Rayon Properties

Composition

• Regenerated Cellulose

Thermal Properties

• Loses strength above 300 °F

• Decomposes above 350 °F

Chemical Properties


• Good resistance to most alkalis; loses strength in strong alkalis

• Lengthy exposure to sunlight weakens the fabric

• Greater affinity for dyes than cotton

Strength – Dry (grams/denier) regular rayon: 2.4 – 3.0; high wet modulus: 4.0 – 5.0

Strength – Wet (grams/denier) regular rayon: 1.1 – 1.5; high wet modulus: 2.2 – 3.0

Extensibility 15 – 24%

Elasticity 82% recovery at 2% extension (95% for HWM)

Resiliency low

Moisture Regain @ 70° F, 65% rh 11 – 16%


Physical Properties

As discussed earlier, rayon fiber is made of regenerated cellulose, so those fiber properties affected by chemical composition, such as hydrophilicity, should be similar for rayon and cotton. Without looking at the properties table, would you predict the moisture regain of rayon to be higher, lower, or about the same as that of cotton and why? The correct response would be higher. Even though the two fibers are made of the same polymer, which is the primary influence on their affinity for water, recall that rayon fibers have much lower crystallinity than cotton. These amorphous regions allow for more penetration by water into the rayon fiber’s internal structure. The lower crystallinity level in rayon also makes it a very weak fiber, although certain types of rayon, known as high-wet-modulus rayons, are stronger than traditional rayon due to the increased molecular weight or crystallinity. The terms Polynosic and Modal refer to high-wet-modulus rayon. Bamboo fibers, in most cases, are actually regenerated cellulose made from the wood pulp of bamboo, so they would be classified as a type of rayon fiber. Rayon is a very absorbent fiber whose primary use is in medical textiles, but it is also used in apparel and household textiles.

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Slide 39

Lyocell Properties

Composition

• Solvent-spun Cellulose

Thermal Properties

• Loses strength above 300 °F• Begins to decompose on

extended exposure to 350 °F and above

Chemical Properties


• Strong alkalis cause swelling and reduce strength

• Can be mercerized

• Loses strength under prolonged exposure to ultraviolet rays of sunlight




Resiliency low



Physical Properties

Better known by its trade name, Tencel®, lyocell is made of solvent-spun cellulose, so it has all the desirable comfort properties of cotton and rayon, while at the same time having strength comparable to polyester. Whereas rayon is made from wood pulp from pine and spruce trees, the pulp for the production of lyocell generally comes from hardwood trees like oak and birch. The major use for lyocell is for apparel, particularly high-end designer goods, but because of its strength and absorbency, it can also be used in industrial textiles and in bandages and other medical textiles.

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Slide 40

Acetate Properties

Composition

• Acetate ester of cellulose

Thermal Properties

• Acetate softens and begins to melt at 347 °F

• Triacetate softens and begins to melt at 455 °F

Chemical Properties

• Poor resistance to concentrated acids

• Poor resistance to concentrated alkalis

• Acetate susceptible to damage by long exposure to sunlight; triacetate has better resistance

Strength – Dry (grams/denier) acetate: 1.2 – 1.4; triacetate: 1.1 – 1.4

Strength – Wet (grams/denier) acetate: 0.9 – 1.0; triacetate: 0.8 – 1.0

Extensibility 25 – 35%

Elasticity 48 - 75% recovery at 4% extension (80% for triacetate)

Resiliency acetate: low; triacetate: good

Moisture Regain @ 70° F, 65% rh acetate: 6.5%;triacetate: 3.2 – 3.5%


Physical Properties

As with rayon and lyocell, acetate fibers are derived from cellulose, but the cellulose is chemically modified by treatment with acetic acid to form cellulose acetate. This polymer is not as hydrophilic in nature as cellulose because hydroxyl groups along the polymer chain have been replaced by acetate groups. When more than 92% of the hydroxyl groups have been converted to acetate groups, the fiber is called triacetate. A major use of acetate fibers is in cigarette filters. The fiber is also used to make garment linings and lingerie. Acetate fibers are soluble in acetone, so fingernail polish remover will easily dissolve garments containing acetate!

Fibers


Slide 41

Acrylic Properties

Composition

• Polyacrylonitrile and small

amounts of other monomers

Thermal Properties

• Does not melt

• Sticks at 450 °F

Chemical Properties

• Resistance to most acids; strong concentrated acids can cause strength loss

• Damaged by concentrated alkalis

• Excellent resistance to ultraviolet light





Resiliency good

Moisture Regain @ 70° F, 65% rh 1.0 – 1.5%


Physical Properties

The polymer in acrylic fibers is poly(acrylonitrile). A homopolymer of 100% poly(acrylonitrile), however, could not be dyed, so most acrylic fibers are copolymers, with a second monomer, such as vinyl acetate, introduced to provide dyeability. Acrylic fibers decompose before melting, so they must be extruded by the wet or dry spinning processes. The properties of acrylic fiber are similar to many of the properties of wool. The fiber is lightweight and can be made into bulky yarns with good cover and warmth, so it is used in such items as sweaters, socks, and blankets. Acrylic fibers can be modified in many ways to affect their dyeability, flame resistance, bulk and comfort properties, and anti-microbial properties. The term modacrylic describes a fiber composed of between 35% and 85% acrylonitrile, and these fibers are known for their flame-resistance properties.

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Slide 42

Nylon Properties

Composition

• Nylon 6,6:

polyhexamethylene adipamide

• Nylon 6:

polycaprolactam

Thermal Properties

• Nylon 6,6 softens at 445 °F and melts at 480-500 °F

• Nylon 6 melts at 419 – 430 °F

Chemical Properties

• Dissolves in mineral and formic acids


• Loses strength on prolonged exposure to sunlight





Resiliency good

Moisture Regain @ 70° F, 65% rh 2.8 – 5.0%


Physical Properties

Nylon was the first truly synthetic fiber and was first produced in the United States in 1938. It was first used in toothbrush bristles but quickly became popular for use in women’s hosiery, which were known as nylons. Soon after this popularity boost, World War II necessitated that the production of nylon be diverted to tents and parachutes for the military, so nylon hosiery was unavailable until the end of the war. Nylon is a polyamide fiber, which means that it is formed from the reaction of an amine group with an acid group to form an amide chemical group. Nylon fibers are named based on the number of carbon atoms in the diamine and diacid starting chemicals. For example, Nylon 6,6 is a polymer formed from the reaction of hexamethylene diamine with adipic acid. Each of these starting compounds contains 6 carbon atoms. Nylon 6 polymer is formed from a cyclic compound called caprolactam (an amino acid), which contains six carbons. The cyclic compound opens up and joins with itself from end-to-end to form the nylon 6 polymer. Other nylons on the market include nylon 6,10; nylon 6,12; and nylon 11; but nylon 6 and nylon 6,6 are by far the most commonly-used nylon fibers. Physical properties vary with the type of nylon. For example, the melting point of nylon 6 is lower than that of nylon 6,6. Aramid fibers, such as Kevlar and Nomex, are a separate class of polyamides that contain aromatic structures in their polymer chains. Nylon is used for all kinds of apparel, including hosiery, lingerie, bathing suits, sportswear, and outerwear. It is also found in floor coverings, tire cords, and various industrial uses.

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Slide 43

Polyester PropertiesComposition

• Polyethylene terephthalate:

(Combination of terephthalicacid or dimethyl terephthalate

and ethylene glycol)

Thermal Properties

• Softens or sticks at 440 - 465 °F

• Melts at 478 – 495 °F

Chemical Properties

• Good resistance to most acids

• Good resistance to most alkalis

• Good resistance to sunlight




Elasticity 97 - 100% recovery at 2% extension

Resiliency excellent



Physical Properties

The first polyester fibers were produced in 1951. Polyester is now used more than any other synthetic fiber and is very close to cotton in the amount of fiber produced per year. It is an extremely versatile fiber used in all kinds of apparel and industrial products. It is used as fiberfill in such items as quilts, pillows, comforters, and furniture. It is a strong yet flexible fiber with very low moisture regain, so fabrics made of polyester are quick-drying. The fiber can also be set by high temperature approximately 350 to 400 degrees Fahrenheit to impart a “memory,” resulting in fabrics with good wrinkle resistance and dimensional stability. Because of its hydrophobic nature, polyester can be uncomfortable when worn under conditions that cause the wearer to perspire. Hydrophobic fibers will not absorb perspiration and can trap the moisture against the skin. The comfort of a hydrophobic fiber such as polyester can be improved by enhancing the wickability of the fiber, that is, its ability to transport moisture away from the skin’s surface. Wickability can be improved by increasing the surface area of the fiber and providing channels for transporting the moisture to the outer surfaces of the garment, where it can evaporate. This is the mechanism used by Coolmax® polyester, which was developed by DuPont. Note the cross-sectional shape in the lower right hand corner of the slide. The hydrophobic nature of polyester can also make it very difficult to remove oily stains from a polyester fabric. Polyester is sometimes treated with a soil release finish to make the fiber surfaces more hydrophilic so that they have less affinity for oil.

Fibers


Slide 44

Spandex PropertiesComposition

• Copolymer of segmented polyurethane with polyester, polyether, polycarbonate, or others

Thermal Properties

• Short exposure times between 200 and 300 °F do not damage the fiber

• Melts at 446 °F

Chemical Properties

• Good resistance to mild acids and alkalis

• Sensitive to chlorine; yellowed by hypochlorite bleach

• Prolonged exposure to sunlight causes strength loss


Extensibility 400 – 800 %


Resiliency very high



Physical Properties

The generic fiber class spandex is a derivative of the word “expand,” which describes what spandex fiber does very well! Note in the physical properties table that spandex can extend from 400% to 800% of its original length before breaking. Spandex is a block copolymer composed of hard and soft segments. The soft segments can extend and then snap back to their original configuration, which gives the polymer its elasticity. The hard, rigid segments are a polyurethane polymer, and the soft segments are either a polyether or a polyester. Spandex filaments can be produced in deniers from 20 up to 5400, so they are much larger than typical apparel fibers. The photographs show a bundle of coalesced spandex filaments that are fused together. This is typical of spandex. Spandex is always blended with other fibers in a fabric. The percentage of spandex can be anywhere from 2% for apparel up to 40% for medical garments. The elasticity of the fabric increases with the amount of spandex. Spandex can be incorporated as a bare filament, which is knitted or woven alongside the other yarns in the fabric, or as a core-spun yarn, in which the spandex filaments are the core of the yarn with the other fiber components spun around the outside. Spandex fibers are particularly sensitive to damage by chlorine bleach, so garments containing spandex should not be bleached. Spandex is, however, fairly resistant to the concentration of chlorine typically in swimming pools. Spandex fibers are used in a variety of applications, including swimwear, sportswear, foundation garments and underwear, hosiery, medical stockings, bandages, and athletic shoes.

Fibers


Slide 45

Specific Gravity

Tenacity-dry

(g/d)

Tenacity-wet

(g/d)

Moisture Regain (%)

Elongation (%) Softening/

Melting Point

(ºF)

Acetate 1.32 1.2 – 1.4 0.9 – 1.0 6.5 25 – 35 (s) 400 – 445

(m) 500

Acrylic 1.17 2.0 – 2.7 1.6 – 2.2 1.0 – 1.5 34 – 50 (s) 450

Cotton 1.54 3.0 – 5.0 3.3 – 6.0 8.5 3 – 10 None

Glass 2.50 – 2.55 9.6 – 19.9 6.7 – 19.9 0 3.1 – 5.3 (s) 1350 – 1560

Lyocell 1.56 4.8 – 5.0 3.8 – 4.2 11.5 14 – 16 Does not melt

Decomposes 350 – 400

Nylon 6,6 1.14 3.5 – 9.0 3.2 – 8.0 2.8 – 5.0 16 – 50 (s) 445

(m) 480 – 500

Polyester 1.38 2.8 – 6.3 2.8 – 6.3 0.4 19 – 50 (s) 440 – 465

(m) 478 – 495

Rayon, Regular 1.51 2.4 – 3.0 1.1 – 1.5 11 – 16 15 – 24 Does not melt


Rayon, HWM 1.51 4.0 – 5.0 2.2 – 3.0 11 – 16 15 - 24 Does not melt


Silk 1.25 – 1.34 2.4 – 5.1 2.0 – 4.3 11 10 – 25 Does not melt


Spandex 1.2 0.7 – 1.0 1.3 400 – 800 (m) 446

Wool 1.30 1.0 – 1.7 0.8 – 1.6 13 – 16 20 – 40 Does not melt


Summary of Conventional Textile Fiber Properties

This table summarizes various physical properties for commonly-used fibers and is suitable as a reference.

Fibers


Slide 46

Melting Point(ºF)

Melting Point(ºC)

Softening Sticking Point

(ºF)

Softening Sticking Point(ºC)

Safe Ironing (ºF)

Safe Ironing (ºC)

Natural Fibers

Cotton Non-melting Non-melting 425 218

Flax Non-melting Non-melting 450 232

Silk Non-melting Non-melting 300 149

Wool Non-melting Non-melting 300 149

Man-made Fibers

Acetate 446 230 364 184 350 177

Triacetate 575 302 482 250 464 240

Acrylic 400 – 490 204 – 254 300 – 350 149 – 176

Aramid Non-melting

Glass 1400 – 3033

Modacrylic 410 210 300 149 200 – 250 93 – 121

Nylon 6 414 212 340 171 300 149

Nylon 6,6 482 250 445 229 350 177

Olefin 338 170 260 127 150 66

Polyester 480 249 460 238 325 163

Rayon Non-melting 375 191

Saran 350 177 300 149 Do not iron Do not iron

Spandex 446 230 347 175 300 149

Vinyon 285 140 200 93 Do not iron Do not iron

Thermal Properties of Conventional Fibers

This table summarizes various thermal properties for commonly-used fibers and is also suitable for reference.

Fibers


Slide 47

Apparel and Domestic Requirements

•Tenacity: 3 - 5 grams/denier•Elongation at break: 10 – 35%•Recovery from elongation: 100% at strains up to 5%•Modulus of elasticity: 30 – 60 grams/denier•Moisture absorbency: 2 – 5%•Zero strength temperature (excessive creep and softening point): above 215 ºC•High abrasion resistance (varies with type fabric structure)•Dyeable•Low flammability•Insoluble with low swelling in water, in moderately strong acids and bases, and in conventional organic solvents from room temperature to 100 ºC•Ease of care

Industrial Requirements

•Tenacity: 7 – 8 grams/denier•Elongation at break: 8 – 15%•Modulus of elasticity: > 80 grams/denier conditioned; > 50 g/d wet•Zero strength temperature: 250 ºC or above

Properties Desired for Textile Fibers

This slide gives values for various fiber properties that we would expect to see for apparel and domestic uses compared to industrial uses. Fibers for industrial uses are expected to be stronger and show higher modulus values than apparel fibers. The temperature requirements for industrial fibers are generally higher as well.

Fibers


Slide 48

• To facilitate processing

• To improve properties

• Abrasion resistance

• Strength

• Absorbency

• Bulk and warmth

• Hand

• Dimensional stability

• Resistance to wrinkling

• To produce multi-color fabrics

• To reduce costs

Fiber Blends

Lastly, we see that various fibers can be blended to produce yarns and fabrics with improved properties that take advantage of the desirable properties of both fiber components while many times lowering the cost. In some cases, more than two fiber types can be blended. The most uniform way to blend fibers is in what is referred to as an intimate blend. In this type of blend, two or more different kinds of staple fibers are blended before being spun into a yarn. Cotton and polyester are often blended in this manner. Another way to blend would be to have a warp yarn of one fiber type and a filling yarn of a second fiber type woven into a fabric. Think about a fabric made from a cotton/polyester blend. Can you name some desirable properties of cotton? Now think of some undesirable properties of cotton. Desirable properties would be comfort due to its hydrophilic nature, hand, and softness. Going hand in hand with its hydrophilic nature and high absorbency, however, would also be a tendency to wrinkle and shrink after laundering. Thus, we can blend polyester into the fabric for stabilization. When polyester is heat-set, it has much lower tendency to wrinkle or shrink. Thus, a blend of cotton and polyester gives us the comfort and softness of cotton combined with the stability of polyester. Now if we could just reduce its pilling tendency!

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