Fibre Analysis Flashcards
History
- Silk was being spun and worn by the Chinese for well over 5000 years and at the same time the Egyptians were wearing both cotton and wool
- I20th Century man-made or semi-synthetic fibres began to be introduced starting with acetate in 1904
- first commercially viable fibres was Rayon 1905
- The following 30 years saw the introduction of cellulose diacetate and cellulose triacetate and many others
- 1935 when Wallace Carothers (DuPont) first synthesized Nylon – The first true synthetic
- Next came acrylic in 1940
- The end of the 20th century
Nomex – Fire resistant, high strength, tear resistant fibre
Kevlar – Extremely strong material used in body armour
Various other technical fibres such as modacrylic and low drag PU continues the quest for the ideal fibre
Fibre properties
tenacity
Overall structural strength of a fibre (both wet and dry)
fibre properties durability
The ability of a fibre to withstand rubbing or friction
fibre properties dimensional stability
The ability of a fibre to maintain its original shape, neither shrinking nor stretching
fibre properties pilling properties
The formation of balls of loose fibres on the surface of a fabric resulting from abrasion
fibre properties elastic recovery
The ability of a fibre to return to its original length after it is stretched
fibre properties creep
How a fibre responds to a constant stretching force
fibre properties flexibility
The ease by which fibres can be bent or folded which affects the overall drape
fibre properties resilience
How easily a fibres returns to original state after creasing
fibre properties absorbency
The ability of a fibre to take in moisture
fibre properties thermal properties
– How well the fibre insulates the wearer
fibre properties effects of heat
Clearly an important property… Consider the effects of a hot iron on plastics!
fibre properties synthetics
– Often thermoplastic and may readily melt!
fibre properties cellulosic
may scorch or burn
fibre properties flammability
wool is flammable
fibre properties stability
Stability with respect to insect attack, light, chemical attack etc.
2 main categories of fibres
Natural – derived from animal, vegetable or mineral
Synthetic or man-made- semi- synthetic, derived from regenerated natural materials such as cellulose in the form of wood pulp. Synthetic, often derived from petrochemicals
3 classes of natural fibres
Animal fibres- proteinaceous materials
Sub divided in to 3 further groups depending on structure- silks (fibroin), wool (keratin and hair (keratin)
Vegetable fibres
Again subdivided into 3 groups depending on derivation- seed fibres, bast (stem) fibres and leaf fibres
Mineral fibres
Very few examples other than asbestos which itself present itself in 3 common forms
silk
- A material obtained from the larvae of the silk moth
- Silk is spun from 2 glands in the mouthparts of the creature
- This produces two individual strands which are then encased in a protein known as sericin
- the sericin casing is degummed by dissolving in dilute alkaline revealing two translucent fibres of triangular cross section
- Composed of the protein fibroin, which is rich in alanine, glycine and serine and contains no sulphur containing amino-acids
- Forensically not very common
wool and animal fur/hair
Animal fibres of this type are primarily composed of the protein keratin made of sulphur rich amino acids but varies by species
Ovine (sheep) Wool is hugely common
Soft, strong, elastic, warm, breathable and comparatively inexpensive
Wool can be easily identified microscopically and shows considerable variation according to sheep breed
All wools will show obvious signs of scaly morphology and the number of will again vary by breed of sheep
A cross section shows a round/ovoid morphology
3 types of cells that make up hair
– Medulla cells – Where present often dead and air filled
– Cortical cells – Spindle shaped cells packed together
– Cuticle cells – Forming a tough outer sheath of tip facing overlapping scales which vary between species and hence can be fairly discriminating
vegetable fibres - cotton
most common vegetable fibres
A seed fibre obtained from Gossypium hirsutum and other species
Soft, strong, elastic, warm and breathable
Represents >50% of annual fibre usage
Composed of ~95% cellulose
After maturation, the fibre walls shrink and the central hollow lumen becomes smaller and flattens which evokes convolutions or twist which improves flexibility and allows better interlocking in yarn
- The fibre is easily dyed with a range of materials
- Can be treated in a process called mercerisation in which the fibre is treated with NaOH and elongated causing the fibre to swell
- This produces a more lustrous, softer, stronger fibre that takes up dye better
vegetable fibres hemp
Hemp fibres were once much more commonly used in than today
- A bast fibre obtained from Cannabis sativa and species low in THC
- Used in a variety of objects from clothing to bags to cordage and bedding although often blended with other materials e.g. Jute, cotton, flax etc.
- Most commonly a technical fibre
- As a material, its cheap and considered to be quite ecologically sound… Each plant can yield a significant quantity of fibres and rarely requires the use of pesticides
- Composed of ~75% cellulose, 17% hemi-cellulose, pectins, lignin and fats and waxes
- Identified microscopically
mineral fibres asbestos
- Asbestos is a naturally mineral fibres
- A generic term for a number of silicate fibre types with high elasticity and high resistance to corrosion, wear and tear and heat
- Mined in a variety of countries
- Used industrially where it was once mixed with concrete and other materials to produce fire resistant board, insulation etc.
- used in some friction materials and some fireproofing
- Four major varieties
• Chrysotile (White) – Mg3(Si2O5)(OH)4
• Crocidolite (Blue) - Na2Fe2+3Fe3+2Si8O22(OH)2
• Cummingtononite-grunerite or Amosite (Brown) – Fe7Si8O22(OH)2
• Anthophyllite – Various forms - Identification by complex microscopy
man made fibres
Either synthetic or semi-synthetic
- The former is derived from petrochemicals – e.g polyamides (nylons), polyesters, acrylics and polyurethanes
- The latter are derived from natural materials but are ‘regenerated’ to produce novel properties – e.g viscose, rayon and acetate
synthetic fibres
- The aim is to produce something that replicates natural fibres, a cheaper version or improves limitations of natural fibre
- Improvements may include greater tolerance to chemical action, heat, shrinkage, greater strength, greater absorbency or less practically, improved appearance, texture or the greater ability to be permanently coloured
semi synthetic fibres
Regenerated fibres from one of two sources
Biological sources: Most commonly cellulose which is used in the manufacture of viscose, rayon and various cellulose ester or alternatively a protein source such as casein or seaweeds!
Mineral Source: Glass fibres and metallised yarns
Cellulosic fibres By far the most common class of regenerated fibres Various sub-classes of regenerated cellulosic fibre each with very different mechanical and structural properties Despite this cellulosic fibres appear very similar with uniform diameter, longitudinal striations and irregular cross section
semi synthetic fibres- rayon
Semi-Synthetic Fibres – Rayon
Viscose Rayon
- The most important regenerated fibre in terms of volume
- Inexpensive to manufacture and versatile producing fibres of silk, wool or cotton like feel, lustre or appearance!
- A very soft, comfortable fibre ideal for warm climates
- The cheapest man-made fibre and therefore often used in clothing made to a budget or commonly seen in furnishings and medical and hygiene products due to absorptiveness
– Weak with poor abrasion resistance and low wet strength (50% dry) meaning dry cleaning is a necessity
rayon manufacture
- The process begins with cellulose material in the form of wood pulp
- This is treated with sodium hydroxide which causes a chemical change
- The material is then treated with CS2 forming Sodium Cellulose Xanthate!
- This when a little water and sodium hydroxide is added, will form a viscous liquid of honey like consistency and this is then extruded in a hardening bath
- Hardening bath consists of H2SO4 (which converts Xanthate to cellulose), sodium and zinc sulphates (which precipitate the xanthate and add structural strength
semi synthetic fibreslyocell- tencel
A modern variant of viscose with superior properties (1991)
- Performs well with a soft, strong, wrinkle resistant fibre with strong water absorption properties
- Similar applications to viscose rayon including medical and personal products, clothing, conveyor belts and cigarette filters!
- Novel manufacture process in which the fibre is obtained direct from a solvent without derivative formation
- Raw bleached cellulose dissolved in N-methylmorpholine N-oxide
- This material is then extruded and drawn in air after which they are set in dilute amine oxide which hardens the fibres
- From this point they can be washed and dried and undergo any post-processing
semi synthetic fibres cellulose esters (dictate and triacetate)
- semi-synthetic fibre type derived from cellulose
- Soft smooth fibres, which dries quickly and has a lustrous appearance and is colourfast under most circumstances
- distorts and wrinkles very easily, has poor thermal properties and is a comparatively weak fibre especially when wet making it dry clean only
- Raw bleached cellulose reacts with acetic anhydride, acetic acid and sulphuric acid which acetylates the hydroxyl groups
- This then undergoes controlled hydrolysis to produce diacetate or triacetate
- This is then dissolved in acetone or other solvent and extruded into fibres
synthetic fibres
- All are organic polymeric fibres
- Manufactured by chemical synthesis
- The first example (Nylon) was developed in about 1935 by Wallace Carothers
- Most polymers are manufactured from simple precursors generally by one of two methods of polymerisation
- Condensation polymerisation
- Chemical condensation reaction in which water or acid is produced as a by-product
- Addition polymerisation
- Produced by joining molecules using a double bond or free radical reaction
synthetic fibres polyamides- nylon 6,6 and nylon 6
- Soft, smooth fibres, with controllable lustre characteristics and able to be set allowing early non-iron
- High strength fibres with good abrasion resistance and elastic recovery
- used for manufacture of seatbelts, tirecord, ropes and other high strength materials including gun parts!
- Resists attack by some chemicals, molds and mildew
- A fibre derived from simple pre-cursor organic materials
- Produced in two forms: Nylon 6,6 and Nylon 6
- Nylon 6 is slightly inferior in its properties particularly in regard to its melting point
- Nylon 6,6 is produced from a condensation reaction between adipic acid and hexamethylene diamine - The 6,6 comes from the use of two 6C precursors
- The reaction is a simple condensation
- Nylon 6 is produced from a ring opening reaction between molecules of caprolactam - The 6 comes from the use of a single 6C precursor
- The reaction is a ring opening forming a linear chain polymeric molecule
synthetic fibres polyamides- Nome and kevlar
- Aromatic polyamides having at least 85% of their amide linkage directly attached to two aromatic rings
- By comparison to traditional fibres, aramids lack the properties required to produce soft, comfortable fashionable clothing
- Both fibres are extremely strong with good abrasion resistance
- Nomex has excellent thermal resistance properties and is used in flame retardant clothing for pilots, firefighters and racing drivers
- Kevlar has incredible strength being on a weight for weight basis five times stronger than steel!
- It is used far ballistic protection, stab resistance gloves, tyre ply and for top end racing sails
- Nomex is produced from a condensation reaction between meta-phenylenediamine and isophthaloyl chloride producing HCl condensate
- Kevlar is produced from para-phenylenediamine and terphthaloyl chloride producing very linear polymer chain of high strength
synthetic fibres- polyacrylonitrile- acrylic
- Smooth, soft warm fibres comparable to wool
- Moderate strength fibres with fair abrasion resistance
- May be seen in jumpers, hats rugs, curtains and various plastic items such as garden furniture
- Light and chemical resistant but flammable and ‘staticky’
- A fibre derived from acrylonitrile (>85%) and a copolymer (such as methyl acrylate) which are polymerised and dissolved in a solvent
- The material produced then undergoes dry spinning or wet spinning in a bath of dilute solvent
synthetic fibres polyavrylonitrile- modacrylic
- Many of the same properties as acrylic and similar uses
- modacrylic is somewhat flame retardant and will self extinguish
- Modacrylic is as the name suggests a modified acrylic fibre where between 35% and 85% of the fibre consists of polyacrlonitrile monomer units and the remainder consists of some other sub-unit
- This is normally vinyl chloride, vinylidene chloride or vinyl bromide
- Once polymerised, the fibre is dissolved in solvent and dry spun
man-made fibres- spinning
- Both semi and synthetic fibres are produced using similar principles
- Polymer prepared in conc. Viscous form in solvent or in molten state
- This is the extruded through tiny holes in a spinneret
- The spinneret can produce fibres of various shapes
3 principle types of spinning process
- Wet spinning
- Dry spinning
- Melt spinning
wet spinning
- may be used for polymers which need to be dissolved in a solvent for spinning such as acrylic, rayon, aramid and modacrylic
- The spinneret is submerged in a bath containing a solution with causes the emerging fibres to precipitate and solidify to strands
- The strands are then taken up and are normally drawn to increase their strength and align the polymers chain in the same direction thereby increasing fibre tenacity
- Setting solution varies according to the fibre being manufactured and is normally sulphuric acid for rayon and DMF or thiocyanate for acrylic
dry spinning
- used for polymers which need to be dissolved in a solvent for spinning such as acetate and triacetate and acrylic
- Instead of the spinneret being submerged in a chemical bath, it lies at the top of a warmed chamber
- As the material emerges from the spinneret, the solvent evaporates causing the polymer to coagulate and form individual fibres
- Hot air of warmed inert gases carry the solvent away where it can be recovered and reused
- The strands are then taken up and are normally drawn
melt spinning
- used for polymers which can be melted such as nylons, polyester and various others
- The polymer, normally in pellet form is melted in an inert atmosphere and then forced through the spinneret into a cooling chamber
- The strands are then taken up and are normally drawn to increase overall strength
- Cross sectional shape is easily controlled using melt spinning which is a very useful point for fibre identification
cross section shape
- Fibre cross sectional shape may be a result of the spinning process
- With melt spun fibres it is possible to engineer the fibre cross section to produce certain specific properties such as greater softness of wicking
Examples
- Round – No major longitudinal striations uniform diameter
- Bilobal – Kidney or dog-bone shaped single or double striation
- Trilobal – Parallel striations that appear to move
- Hollow – Single continuous hollow forming a black core
- Complex – Multiple striation appearing irregular
- Natural fibre may have their own distinct shape… e.g. silk
delustrant
for many applications, lustre within man-made fibre can be problematic
- Engineering fibre shape and cross section can help to alleviate the problem to some extent but may not always lead to favourable ‘hand’
- In such cases, it is possible to include materials that help dampen the lustre of fibres and in most cases this is Anatase (Titanium Dioxide)
- Not only does Anatase help prevent light reflection, but its inclusion may also roughen the fibre surface dampening reflectivity
- Delustrant appears as dark coloured ‘dots’ (0.1-1μm) within the fibre matrix and the size, shape, appearance, abundance and general distribution are useful for comparative purposes
- Although the presence of delustrant does not serve to identify a specific fibre type, it is a useful indicator of man-made fibre and may be use as a comparison tool
fibres dye
• The dyeing process can be completed after spinning or part of the spinning process
• dyes and pigments all can be designated by one or all of the following:
• CI number
– All dyes are given a 5 digit colour index number or CI number
– Dyes which comes as multiple salts may include a sixth
• Generic Name
– All dyes are also given a generic name which may indicate use
• Commercial Name
man-made fibres- different forms of dye
- Acid Dyes – Polyamides, wools, silk and polypropylene
- Azo Dyes – Cellulosic fibres
- Basic Dyes – Acrylics, polyester and polypropylene
- Direct Dyes e.g Dylon – Cellulosic fibres
- Disperse Dyes – Commonly polyester and acetate
- Metallized Dyes – Wool
- Sulphur Dyes – Cellulosic fibres
- Vat Dyes – Cellulosic fibres – Principally denim
- Pigment – Polypropylene, viscose, acrylic, polyamide and polyester
(pigments are different to dyes as they are insoluable)
