Types of Fibres.pptx

This lecture is about the different types of fibres and their classification

1. Types of fibres

2. What is a fibre ? a slender and greatly elongated substance capable of being spun into yarn. Fibres are deemed the fourth most important evidence when DNA, fingerprints, and footwear are available.

3. Fibre evidence used for 3 reasons: Intelligence information Associative evidence To reconstruct a crime scene.

4. When fibres are brought in from a case study, they are analysed using microscopy to recognize characteristics to compare to a suspect sample However, the first thing that will be done will be to identify what type of fibre it is .

5. The transfer of fibres from article to article lends itself to identify who has come in with contact these objects. The transfer of fibres depends on the shedding ability of the fabric and the persistence of these fibres on other types of fabric. The easier these fibres are shed, the more chance there will be for secondary, tertiary or even quaternary transfer.

6. Classification of Fibres

7. Classifying fibres Fibres are divided into two main categories: 'Natural fibres' are fibres that occur in nature: wool, cotton, asbestos, etc. 'Man-made fibres' is the term applied to fibres that have been manufactured by humans from either naturally occurring fibre -forming polymers (for example viscose, acetate and rayon) or synthetic fibre -forming polymers (for example polyester).

8. Manmade fibres Man-made fibres can be divided into three subdivisions: Synthetic fibres' are man-made fibres spun from synthesized fibre-forming polymers. 'Regenerated fibres' are man-made fibres that have been produced from naturally occurring polymers by a technique that includes the regeneration of the polymer structure (casein, viscose, acetate, etc.)

9. other fibres (carbon, glass, metal, etc ).

10. Subdivisions of Natural fibres animal (protein) vegetable (cellulose) and mineral (asbestos)

11. Subdivisions of animal fibres Divisions based on protein composition and utilization. silk (fibroin) wool (keratin) hair fibres (also keratin).

12. Vegetable fibres Groups of vegetable or cellulosic fibres : based on the part of the plant that is the source of the fibre ( i ) seed fibres (cotton, kapok, and coir) (ii) bast (stem) fibres (flax, hemp,jute,ramie ) (iii) leaf fibres (manila, sisal, etc.).

13. Characteristics of fiber polymers linear molecular chains which possess some degree of extension to the fibre axis- making it stronger longitudinally than transversely streamlined molecular chains- allowing for close packing of the polymer chains

14. Characteristics of fiber polymers the molecular chains should be flexible and hence impart extensibility to the fibres . a high molecular weight-imparting both a high melting point and low solubility in most solvents

15. Natural fibres -Silk Silk is obtained from a class of insects called Lepidoptera (scaled winged insects). The principal species cultivated for the commercial production of silk is Bombyx mori or mulberry silkworm.

16. The production of silk can be divided into two areas – sericulture and silk reeling. Sericulture is the production of cocoons from eggs Silk reeling is where the cocoon is converted into the thread .

17. Cocoon of Bombyx mori

18. Silk is composed of the proteins fibroin and sericin Has crystalline regions where the protein chains are fully extended in the B-sheet structure with maximized hydrogen bonding . has a markedly different amino acid composition than other animal fibres.

19. Silk Fibres

20. SEM silk fibres

21. No Cysteine, and therefore disulphide crosslinks are not present in silk. Consequently, silk will dissolve in powerful hydrogen bond-breaking solvents such as cuprammonium hydroxide , in which other animal fibres will not dissolve.

22. Silk is extensible and elastic Silk has a reversible extension of up to 4%, beyond which recovery is slow with some permanent set. Silk almost equals nylon in resistance to abrasion and toughness (the ability to absorb work) – as a result of crystalline structure .

23. Raw silk has a regain of 11%, but that of de-gummed silk is about 10%, the sericin having a higher water-absorbing capacity than the fibroin. Silk more susceptible to acids than wool, but is more resistant to alkalis, though low concentrations at high temperatures will cause some tendering . Still silk is not readily attacked by warm dilute acids, but dissolves in strong acids.

24. Silk is very resistan t to all organic solvents , but is soluble in cuprammonium hydroxide and cupriethylene diamine , the latter solvent being used for fluidity tests . Silk is more susceptible to oxidizing agents and exposure to sunlight than cellulosic or synthetic fibres More resistant to biological attack than other natural fibres Easily dyed with a wide range of dyestuffs including acid, basic, and metal complex dyes.

25. Summary Properties of silk Strong Tough high regain Resistant to creasing Good draping properties Luxurious appearance.

26. Draping silk textile

27. Used in apparel and drapery industries High cost restricts use of silk Since silk is a continuous filament fibre , with a smooth surface, fibre transfer during contact is unlikely-poor shedder

28. Wool Wool is made of the protein called keratin. hair, feathers, beaks, claws, hooves, horn, and even certain types of skin tumour are also made of keratin. Arguably the most common hair fibre used in textiles. The fineness, quality, and properties of wool depend on the sheep breed

29. Merino wool is soft, fine and strong Leicester, Cheviot and Corriedale are medium wools used in knitting yarns, blankets etc . Even within the same breed, differences in diet, health, climate make wool show considerable variation in physical and chemical properties: For example, one expects considerable variation in physical properties such as fibre diameter, length, and crimp as well as the chemical constitution of the fibres . Wool can be difficult to analyse and interpret due to differences in hair over the whole body of the sheep .

30. Wool, like other hair fibres , contains a substantial quantity of the amino acid cysteine. Cysteine residues in wool play a very important role in the stabilization of the fibre structure owing to the crosslinking action of their disulphide bonds

31. Since wool is a staple fibre , with a rough 'scaly' fibre surface, wool fibres may transfer readily during contact, especially from loosely constructed fabrics. Wool sheds more readily than man-made fibres .

32. SEM wool Fibres

33. Specialty hair fibres The hair fibres , sometimes referred to as 'specialty' hair fibres , can be divided roughly into three groups : fibres from the goat family (mohair, cashmere) fibres from the camel family (camel hair, alpaca, vicuna) fibres from other fur-bearing animals, in particular the rabbit (angora).

34. Goat Hair fibres Mohair is from the angora goat . Fibres are between 20-30 cm for a full year’s growth. Identification of mohair can be difficult as similar to wool Cashmere is from the Asiatic goat and is chemically identical to wool . The extra softness is due to cashmere fibres being finer . There have been many cases of Cashmere fraud over the years.

35. Camel (family) hair fibres Alpaca fibres are from Lama pacos species inhabiting South America Alpaca fibres are more easily identified as they have a distinct scale structure and medullation . Fibres vary from alpaca to alpaca and in some alpacas there may be a higher incidence of medullated fibers, compared to wool and mohair. Medullated fibers can take less dye , standing out in the finished garment, and are weaker

36. Strands of alpaca fiber are smooth and therefore feel less prickly or itchy next to the skin than wool Alpaca insulates from cool and warm temperatures and is comfortable for any season- hollowness of fibre . Most people who have wool-based allergies will not be allergic to alpaca- no lanolin

37. Rabbit fibres Rabbit fibres are usually from the angora species of rabbit. These rabbits are bred primarily for their fur. Angora fibres are retrieved by shaving the pelts of the rabbits and then separated by blowing. Often used in hats or jumpers but mixed with wool or nylon .

38. SEM of various fibre types

39. Vegetable fibres Vegetable fibres are spilt into 3 categories: Seed fibres Bast fibres Leaf fibres The chemical constituents can vary dramatically. The main constituents to note are cellulose, pectins , fats, waxes and lignins .

40. Seed Fibres Cotton is retrieved from the seed of the species Gossypium which is found in subtropical countries. A boll is formed on the plant which bursts into sections. Fibres are formed inside and mature as cellulose is deposited on the interior surface of the boll. The convoluted shape is due to the shrinking of the fibre as it dries .

41. This convoluted staple fibre may transfer readily during contact. Since a very high proportion of cotton is marketed in 'white' products , colourless cotton fibres have little, if any, value as evidence.

42. Bolls of cotton

43. Convoluted cotton fibres

44. Kapok Fibres obtained from the kapok tree, native to Mexico Central America and the Caribbean Pods are picked from the tree and broken open and dried in the sun. Kapok fibres can be identified by their low density. Fibres are resistant to water . Buoyant but highly flammable . Used to make lifebuoys and mattresses

45. Pod

46. Coir A fruit fibre from coconuts Husks are soaked for a week, dried and passed through a crusher. The best coir is from unripe husks. This is used for ropes, matting. Coir from mature husks is coarser and so used for brushes, brooms . Has great tensile strength

47. Coconut fruit

48. Bast Fibres Bast fibres are from the stems of plants which are bundled under the bark. Flax Scientific name Linum usitatissimum . Has been cultivated for over 6000 years Flax is stronger than other natural fibres but is much less pliable and elastic . Also absorbs and desorbs water rapidly smooth fibre surface makes it very easy to launder , hence linen found great use in the manufacture of table cloths and bandages.

49. Linum usitatissimum

50. Flax grown for the fibre which is linen and the seed which is linseed Flax strength due to its compact structure Hemp Scientific name Cannabis sativa Used mainly for ropes and twine .

51. Flax

52. Leaf Fibres Also known as ‘hard’ fibres: thicker and harder than bast Obtained from certain tropical and subtropical plants Sisal Scientific name Agava sisalana Leaves are removed and crushed and the fibres scraped away. Usually easy to identify as are polygonal in cross-section. Used in ropes and twines . Other leaf fibres are Abaca and New Zealand hemp . These are not widely used and commercial quantities have dramatically decreased

53. Agava sisalana

54. Abaca/ manila Leaf fibre , Abaca Plant and fibre produced.

55. New Zealand Hemp: Plant and fibres

56. Mineral fibres

57. Analysis of natural fibres Differs from man-made fibres Primarily use of compound microscopes Can include the following: Overall morphology Length Cross-sectional shape Thickness of lumen Determination of refractive index Lignification – Phloroglucinol reagent https://www.youtube.com/watch?v=HHNeoefK1ow Herzog test- plant fibres molecular orientation https://www.youtube.com/watch?v=sC9GlUKjBDE

58. Herzog test can be used to differentiate between flax, hemp and cotton. Cotton looks multi-coloured Hemp is look purple horizontally and blue vertically Flax looks blue horizontally and purple vertically Used to tell the type of twist a fibre has.

59. Herzog test results A Z-twist fibre is said to turn yellow when parallel to the polarizer and blue when parallel to the analyser, while for a S-twist fibre the situation is exactly opposite. Hemp and jute have Z-twist and flax and ramie have S-twist. The modified Herzog test can also be used to distinguish between bast fibres and other plant fibres. For example, in cotton, a seed fibre, the microfibrils change their twist directions at short intervals

60. Man-Made Fibres There are two types of Man-made fibres : Regenerated fibres : made from natural polymers Eg . Rubber and viscose Synthetic Fibres : made from synthetic polymers Eg . Polyamide and polyester

61. Manufacture of Man-Made fibres Process is called spinning or extrusion The concentrated, viscous polymer, either in solution or in a molten state, is forced through the tiny holes of a spinneret The emerging filaments are immediately precipitated or cooled to form the solid-state fibre .

62. Types of spinning: Wet spinning : concentrated solution of polymer dissolved in aqueous or organic solvents . The extruded filaments are immediately precipitated in a coagulation bath. Dry spinning: concentrated solution of polymer dissolved in volatile solvent systems which allow rapid evaporation of the solvent, effecting fibre solidification after extrusion. Melt spinning: The molten polymer is extruded and the filaments are solidified by simple cooling ( applies to thermoplastics only) Type used determined by physical and chemical property of polymer

63. Effects of Spinning Spinning causes the polymer chains to become more aligned (or oriented) in the direction of the longitudinal axis of the fibre . maximizes the inter-polymer forces of attraction between polymer chains, leading to an increase in polymer crystallinity and fibre strength. Parts of the fibre will be crystalline and others amorphous - influencing the property of the fibre

64. Extrusion method ( eg . Shape of spinnerets or rate of cooling) determine the longitudinal and cross-sectional appearance of man-made fibres

65. Types of synthetic polymers Condensation polymers: Monomers bearing two reactive or functional groups from one or more compound(s) condense by normal chemical reaction to produce a linear polymer . Repeating units are joined by inter-unit functional groups (ester, amide, urethanes) The linkages are susceptible to hydrolysis – acids and alkalis Eg . polyamides and aramids, polyesters, and polyurethanes.

66. Condensation polymerization

67. https://youtu.be/-d14DmSBuAQ

68. Addition polymers Occur when monomers containing double bonds from one or more compounds add together at the double bond to form a polymer confined to an aliphatic carbon chain. Results in no loss of atom or molecule Has strong C-C bonds in polymer backbone Not susceptible to cleavage hence more stable than condensation polymers- non-biodegradable Eg . Polyolefins and polyvinyl derivatives.

69. Addition polymerization

70. Eg . Addition polymers

71. The degree of polymerization attained for addition polymers is usually much higher than that for condensation polymers because of the nature of their respective polymerization reactions. https://www.youtube.com/watch?v=sk6h4oaArE0

72. Polyamides Polyamides may be synthesized via the condensation of diamine (H2N–R1–NH2) and dicarboxylic acid (HOOC-R2-COOH) monomers, or by the polymerization of an - amino acid R group may be either aliphatic (straight carbon chain), alicyclic (ring), or aromatic (benzene ring) Polymer has the amide functional group: (–CONH–)

73. Naming polyamide fibres Aliphatic polyamide fibres : named according to the number of carbon atoms in the repeating unit. eg if the repeating unit is derived from a diamine and a di-acid, the polymer is designated by two numerals: the first indicating the number of carbon atoms in the diamine and the second the number of carbon atoms in the dicarboxylic acid Eg . Nylon 6.6

74. Nylons synthesized from an -amino acid are designated by a single numeral denoting the number of carbon atoms in the amino acid. Eg . Nylon 6

75. Nylon Most common polyamides Smooth, regular longitudinal appearance results in a highly lustrous and translucent fibre Requires the addition of a delustring agent (for example titanium dioxide) Nylon fibres are melt spun- can be texturized by heat treatment( improves appearance and resilience) Many hydrogen bonds between polymer chains -Polar amide linkages along backbone plus absence of bulky side groups

76. Hydrogen bonds : Crystalline makes it strong with good elastic recovery Wetting causes nylon to increase in fibre extensibility and decrease in elasticity and tensile strength . Crystalline structure: cause it to exhibit outstanding resistance to abrasion Has low moisture regain- the crystalline structure prevents water entering Not very conductive – develops static electricity

77. Amide linkages: Nylon is relatively stable in alkalis. Hydrolyzed by acids . Nylon fibres are soluble in phenols and concentrated acid oxidation by sunlight- weakening the fibre ideal for the carpet and hosiery industries, Eg.Nylon 6.6: Antron , Rhodiastar , Tactel , Ultron Nylon 6: Anso , Enkalon , Patina, Perlon , Zeftron

78. Aramids Aramids are aromatic polyamides defined as having at least 85% of their amide linkages attached directly to two aromatic rings. Eg. Kermel , Kevlar, Nomex , Teijin Conex , Twaron Nomex and Kevlar are the most commonly encountered aramids,

79. Kevlar Nomex

80. The molecular chain linearity (due to aromatic ring) and hydrogen bonding- results in almost perfect molecular orientation of polymer chains better alignment of polymer chains than seen in aliphatic polyamides: Higher specific gravity higher tensile strength, higher modulus (resistance to stretching), and extremely high chemical and heat resistance (up to 300°C). insoluble in most common solvents and therefore require the use of special solvent systems for extrusion into filaments .

81. The fibres char and decompose rather than melt at temperatures above 300°C. Expense to manufacture aramid fibre - limits applications to high-performance products.

82. Applications Nomex is principally used for fire/heat retardant purposes such as in heat protective clothing Applications of Kevlar include high-performance tyres and conveyor belts , and reinforcement fibres in sporting goods and in the aerospace industry, bullet proof vests. (Kevlar is 5 times and 10 times stronger than steel and aluminum respectively)

83. Polyester Eg. Dacron, Diolen , Fortrel , Grilene , Tergal, Terital , Terlenka , Terylene, Teteron , Trevira Polyesters are synthesized by the condensation of a diol (for example ethylene glycol) and a dicarboxylic acid (for example adipic acid) with formation of an ester linkage (–COO–) along the polymer chain backbone. The most common polyester manufactured is based on the polymer polyethylene terephthalate (PET) Polyesters are melt-spun: The fibres are fine, regular, and translucent, and are usually textured, as is nylon, by a heat treatment.

84. Carbonyl groups present are weakly polar: hydrophobic interactions such as weak van der Waals' forces holds adjacent polymer chains together The para-substituted benzene rings reinforce the linearity of the polymer , thus maximizing the van der Waals' attractive forces. Making fibre very crystalline Resistant to abrasion strong

85. No loss of strength on wetting because of the hydrophobic nature of the polymer chains . Para-substituted benzene ring makes polyester textiles stiff (not elastic) requiring twice the force required by nylon to produce similar extension.

86. Wrinkle resistant Low moisture regain- due to high crystallinity and hydrophobic properties (produces static ) Polyester is insoluble in most organic solvents, including 90% o-phosphoric acid, which will digest most other textile fibres derived from organic polymers . Dissolves in chlorophenol and hot 90% phenol.

87. Unlike nylon, the ester linkage in polyester is hydrolyzed by alkalis (surface damage mostly) but stable even in concentrated acids (dissolving only in hot sulphuric acid) More resistant to sunlight degradation than nylon. Difficult to dye Static electricity

88. Both nylon and polyester fibres have: strength abrasion resistance thermal stability ability to hold a heat-setting treatment Polyester has more applications than nylon- due to higher modulus and lower production cost

89. Overcoming the limitations of polyester Increase moisture absorbency by blending with absorbent fibres to increase wear comfort. Treatment with antistatic agents serves to dissipate static charge Dyeing with carriers swells the fibre , facilitating the penetration of disperse dyes e.g. Orthophenylphenol , Benzyl benzoate

90. Applications Apparel: Staple fibre blending with wool or cotton for making apparel. Easy care and toughness of polyester render it very suitable for apparel Continuous filament polyester suitable for industrial applications such as: ropes, conveyor belts, seat belts, and tarpaulins.

91. Polyurethane ( elastane ) Eg . Acelan , Dorlastan , Cleerspan , Glospan , Lycra, Opelon Contain at least 85% of organic units joined by urethane linkages (–NH–COO–). Reacting a diisocyanate ( two isocyanate functional groups) with a long chain polygycol monomer ( two hydroxyl or alcohol groups ). Properties vary depending on monomers. Polyurethane fibres commonly used in textile industry are very complex polymers combining a flexible segment (provides lots of stretch and rapid recovery of an elastomer), with a rigid segment (confers strength of a fibre ).

92. The flexible segments can be one of two types, a long polyether or polyester chain rigid segments are composed of a diphenyl methyl group attached to a urethane group. Polyurethane elastomers are usually solution spun Thermoset plastic-excessive amounts of heat can disrupt the elastic properties of the fibre .

93. Polyurethane

94. The polymer network of polyurethanes is largely amorphous as a result of the long, flexible polyether or polyester chains which are folded on themselves. The interconnecting hard segments tend to be more aligned, with hydrogen bonding between the urethane groups of adjacent chains contributing to polymer strength and crystallinity . distinctive highly extensible , 'snap-back' property of elastomeric fibres - due to the inter-chain region between the crystalline region.

95. hydrophobic nature of the flexible region and the crystalline nature of the rigid region. Low moisture regain Prone to static electricity Difficult to dye not susceptible to attack by corrosive although alkalis will readily attack the ester linkages of the polyester type of polyurethanes Usually combined with fibres like nylon that dye more readily.

96. Applications Used in apparel where stretch and recovery are important swim wear and active wear

97. Polyolefins Polyethylene: Dyneema , Polysteen , Spectra, Vestolan Polypropylene: Asota , Danaklon , Downspun , Gymlene , Herculon , Meraklon , Novatron , Vegon

98. Polyethylene and polypropylene polymers are polymerized from the petroleum-based products ethylene and propylene, respectively (addition polymerization). Both polypropylene (PP) and polyethylene (PE) are melt-extruded (thermoplastics)

99. High degree of polymerization/The dense packing of linear polymer chains/ - maximize the van der Waals' inter-chain forces: Very crystalline Lower modulus than polyester highly crystalline and hydrophobic nature extremely difficult to dye fibre with high tenacity (similar to nylon and polyester). High performance PE as strong and stiff as aramids. Zero moisture regain very resistant to attack by corrosive chemicals. abrasive resistant but less so than nylon

100. highly resistant to chemical degradation by acids and alkalis but soluble in hot hydrocarbon solvents and cannot be dry-cleaned . 'wicking', which allows moisture to be transferred rapidly between fibres without actually being absorbed by the fibres . Pigmentation is achieved by dying before melt spinning or addition of modifying chemicals to the spinning dope (act as light stabilizer and mordant) Use limited by low melting points ( PE( 135°C) and PP (165°C). The fibre is flammable , although self-extinguishing.

101. Degraded by sunlight- need to be treated with ultra violet stabilizers for some indoor and out door applications inert material that is also resistant to bacterial growth

102. Applications next-to-skin active wear furnishings PP Backing for carpets Carpet face yarns PP Fishing nets and cordage (replacing sisal and jute)

103. Polyvinyl Derivatives Acrylics (85% by weight of acrylonitrile units) : Acrilan , Beslon , Cashmilon , Courtelle, Dolan, Dralon, Leacril , Vonnel , Orlon, Dynel Modacrylics (at least 35% but not more than 85% of acrylonitrile units) : Kanecaron , Kanekalon , Nonbur , SEF, Velicren FR polyacrylonitrile Velicren FR Polyacrylonitrile is the commonest addition polymer

104. Acrylic and modacrylic fibres are solution spun (either wet or dry spun) acrylonitrile units are largely non-polar, and the polymer system is therefore held together predominantly by van der Waals' forces.

105. High polymerization results in long chains-maximize van der Waals' forces and results in high crystallinity . Polyacrylonitrile (100%) is extremely difficult to dye, being non-polar and highly crystalline . low moisture regain , as a result of the predominantly hydrophobic character and highly crystalline nature Acrylic fibres have only moderate tensile strength compared to nylon and polyester

106. Static charge Little penetration of acids and alkalis , with only hot concentrated alkalis causing surface hydrolysis. Acrylic fibres are insoluble in most organic solvents, but will dissolve in boiling dimethylformamide and dimethylsulphoxide

107. Acrylic polymers are generally copolymerized with up to 15% of different monomers Comonomers open up the polymer structure and/or to incorporate anionic or cationic groups within the polymer system- attracting and allowing dyes to penetrate Basic dyes are commonly used on acrylic fibres , producing bright shades with good light fastness. often delustred processed into staple fibre

108. loss in strength when wet Wrinkles : indicating slippage of polymer chains due to weak inter-chain forces Resistant to degradation by sunlight ( most, of all textile fibres )

109. Acrylics very heat-sensitive Acrylics are readily flammable on close approach to a flame; they burn with a characteristic smoky flame . Flammability retarded by copolymerization with vinylidene chloride monomers - produce flame-resistant polymers- degradation of C-Cl bond is endothermic. shrink when subjected to steam (more than other textiles) chlorine-containing modacrylics have lower heat stability than acrylics in that they soften more readily from heat application (150°C) and shrink markedly in boiling water.

110. Applications Acrylic fibres are most commonly blended with other fibres in: Knitted outerwear, furnishings, carpet, and fabrics for outdoor use (awnings etc.). These applications make use of their high bulk characteristics, bright colours , Modacrylics: Hair in wigs Apparel lining Furlike outerwear

111. Modacrylics are also usually blended with other fibres to impart flame retardancy in apparel and furnishings.