class-notes-4-纺织材料学

1、Chapter 11 Silk Fibers,Yiping Qiu,Introduction,The larva of certain insects for use in their building webs, climbing ropes and cocoons Commercial silk industry: use larva of silkworm Spiders Application: mostly apparel, also used for parachutes.,Life of a Silkworm,Chrysalis,Butterfly,Silkworm,Cocoon

2、,Tussah: “wild” silk,Spider,Structure,Macrostructure: Length: 915-1190 m (1000-1300 yds )/cocoon Max 2750 m (3000yds)/cocoon, 1 fiber/cocoon. Thickness: 9-11 mm or 1.2-1.5 denier. Varies: thickest in the middle thinnest inside.,Structure,Microstructure Cross-section: 2 triangular filaments co-extrud

3、ed by a worm. The two are called brins held together by sericin (gum or silk glue). Wild silk worms produce ribbon-like silk fibers,Structure,Submicrostructure Silk from cultivated worm: no identifiable submicrostructure. Wild silk or Tussah silk has internal fibrillar structure.,Structure,Fibroin p

4、rotein polymer A chain of amino acids forming a protein called fibroin composed of 15-18 different amino acids. Glycine, alanine and serine occupy 86% of the polymer The side groups of the above 3 amino acids are small compared with those in wool: glycine: R = H alanine: R = -CH3 Serine: R = -CH2OH

5、Crystallize readily: 70-75%,Amino Acidsin wool,Structure,Fibroin protein polymer Pack well: lots of H-bonds, small number of ionic bonds No cystine: no S-S bonds Configuration: pleated b-sheet Degree of polymerization of silk DPsilk DPwool,Spinning of silk by silkworm,Asakura et al ：birefringence in

6、creases as silk fiber is spun out,Spinning of silk,Silkworm and spider spin the fibers started with liquid crystals, resulting in good molecular orientation and high crystallinity,Asakura et al,Properties,For silk producers, i.e. silk worm, spider etc., silk fibers are for protection, transport and

7、food capture Mechanical properties Medium tenacity but higher than wool resulted from molecular structure: zigzag b-sheet of silk vs a-helix of wool extruded instead of grown as a cell higher crystallinity than wool,Tensile behavior of natural fibers,Properties,Mechanical properties Medium elongatio

8、n at break High elastic recovery at low elongation When elongated 2%, 90% elastic recovery Medium modulus Medium abrasion resistance Medium resilience: (cotton silk wool) pleated sheets can slide over one-another.,Properties,Comfort High heat of wetting: lots of polar groups available High water abs

9、orption: up to 1/3 of its weight Smooth and soft High luster: high crystallinity and triangular cross-sectional shape. Scroop: rustling sound due to an acid treatment that hardens fiber surface.,Properties,Other properties Ignites and burns but sometimes selfextinguishing Dry-cleaning preferred due

10、to: lower tenacity and initial modulus when wet degraded by alkaline solutions may be hand-washed using mild detergents Lowest UV light resistance: avoid prolonged exposure to sunshine,Production,Moth: Bombyx fed on mulberry tree leaves World production: 70 million kg/yr Originally from China Types:

11、 Raw silk: silk with gum,Production,Silk yarn spinning: Filament yarn, 7 8 ends (cocoons) per yarn, total linear density 20 22 denier Staple yarns Duppioni: 2 silk worm spin their cocoons together: having special appearance (irregular thickness) similar to wild silk but better color,Regular cocoon,D

12、uppioni cocoon,Chapter 12 Cotton Fibers,Introduction,Cotton: seed hair obtained from the boll of the cotton plant 4000 fibers/seed, max 20,000 fibers/seed 250,000 fibers/boll,Cotton,Ginning mill,Types:,Commodity: Upland Long staple: Pima cotton: extra-long staple (ELS) cotton grown in the U.S., Aust

13、ralia, Peru etc. Sea island Egyptian,Types,Other: naturally colored: Mostly brown or green Eventually all brown Inconsistency Poor properties,Application,55% of apparel fibers are cotton 70% of mens apparels made of cotton 40% of womens apparels made of cotton 65% of all cotton fibers were used for

14、apparels in 1990 Additional 27% of cotton for sheets and towels or other non-apparel household applications 7% for industrial use,Structure,Cotton fiber: single plant cell Macrostructure Staple length: 1/8 - 2.5 inch (0.32 - 6.35 cm) Cotton fibers used in textile yarns: 7/8 - 1.25 inch (2 3 cm) Diam

15、eters: 16 - 20 mm but varies from fiber to fiber: longer fibers are finer,Structure,Macrostructure Length to breadth ratio: 6000:1 to 350:1 Relatively uniform along its length Color: never truly white but creamy white to gray,Structure,Microstructure Flat, twisted ribbon 50 twists/cm (convolutions)

16、The twists reverse in direction along the length Cross-section: kidney-bean shaped with a lumen,Cotton fiber,Structure,Submicrostructure 5 distinctive regions: Cuticle: out layer of wax, a few molecules thick to protect seeds but can be removed by wet processing and laundering.,Structure,Submicrostr

17、ucture 5 distinctive regions: Primary wall: composed of fibrils: a sheath of spiraling fibrils 20 - 30 degree to the fiber axis Mature fibers - thicker primary walls; immature fibers thinner primary walls and entangles: forming clumps called neps: leading to nonuniform dye properties and irregular s

18、urface of fabrics,Structure,Submicrostructure 5 distinctive regions: Secondary wall: bulk of the fiber concentric layer of spiraling fibrils similar to rings of trees 20 rings and each corresponding to 1 days growth. outmost layer of secondary wall: winding layer Lumen: hollow canal running through

19、the length of the fiber,Structure,Polymer system Linear cellulose Average Degree of Polymerization 6,000 to 10,000 Functional side group: -OH,Hydrogen bonds in cellulose,Structure,Polymer system Crystallinity: 65 - 70% but depends on how to define. H-bonding sites: not necessarily just -OH to -OH bu

20、t also OH to the O- group between the neighboring two rings: confers strength and additional rigidity to the fiber. -OH: reacting with a variety of chemicals: thus finish can be applied easily, also attract and hold water. -C-O-C- bonds are more susceptible to oxidation than C-C-C bonds 20 41% unocc

21、upied space, 1/3 by lumen,Properties,Mechanical Properties Tenacity and initial modulus: medium Elongation at break: low: spiral fibrils: makes it relatively brittle Elastic recovery: low, only 75% at 2% extension: due to H-bond,Mechanical Properties,Properties,Comfort Fiber ends and convolutions: c

22、omfortable to touch Hydrophilic: max water absorption: 25-27% regain due to -OH group and fibrils Upon water absorption, fibers become softer and collapses on to skin, dries slowly When it is dry: comfortable because of water absorption, water vapor transfer and no static charge,Properties,Comfort W

23、ater resistant fabric possible: swelling of fibers in water: no liquid water penetration Maintenance Soiling: easy to be soiled and desoiled due to -OH groups Launderability: dimensionally stable and tenacity increases when wet (10-20%) due to improvement of fibril orientation and thus molecular ori

24、entation.,Properties,Maintenance No special precautions for laundering, high temperature, any detergents, and bleaches can be used. Shrinkage likely due to relaxation of yarn tension induced by processing,Properties,Other properties acids cause degradation of cotton or cellulose: acid free paper for

25、 long lasting items not affected by most of organic solvents damaged by fungi and bacteria prolonged exposure to sunlight: yellow heat resistant low luster high cover power,Properties,Other properties no pill but lint highly flammable and can smolder without fire for hours: need flame-retardant trea

26、tment for many end uses biodegradable can be boiled and sterilized: good for hospital use,Mercerized cotton,Process:(applied to either fibers or yarns) cold bath of 18-27% NaOH for 1 minute or less rinsed and neutralized by a cold acid bath tension applied to break H-bonds polymer rearranged and reo

27、riented: untwist rounder cross-section and the convolutions are nearly gone Stronger, more lustrous and easier to dye,Chapter 14 Rayon,Introduction,Rayon: ray of light on Invented 1884 Definition: manufactured fibers composed of 100% regenerated cellulose, as well as manufactured fibers of regenerat

28、ed cellulose in which substituents have replaced not more than 15% of the hydrogens of the -OH groups.,Introduction,Made from 4 processes: Nitro cellulose: made in U.S. during 20s-40s and easy to explode. Viscose: 95% today Cuprammonium: use cuprammonium hydroxide solvent as spinning solution Lyocel

29、l：environmentally friendly process,Introduction, 4% of total fiber consumed in the U.S. Usage: 52.4% apparels 26.8% nonwovens 20.8% households,Structures,Macrostructure Continuous filaments or staple: 1.5-15 denier Microstructure: Surface: striated Cross-section: serrated,Cross sectional shapes of f

30、ibers,Structures,Submicrostructure Skin-core structure: caused by spinning process Skin: small crystal, imperfect, darker Core: large, more perfect crystal,Structures,Molecular Regular viscose rayon: DP400 (cotton 6k-10k) 35 - 40% amorphous,Properties,Mechanical Medium tenacity and elongation Low in

31、itial modulus Low elastic recovery Low bending rigidity Tenacity and modulus drops drastically upon water absorption: -50%. Elongation to failure +20%.,Properties,Comfort Hydrophilic and high moisture regain: 13% at 70% RH: more absorbent than cotton due to more amorphous region. High heat of wettin

32、g High cross-sectional swelling Irregular surface next to skin: comfortable No static charge build up,Properties,Maintenance Easy to deform in laundering due to mechanical property change in water Degrades in medium acids, strong alkalies, bleaches and sunlight more than any other cellulosic fibers

33、Highly flammable with afterglow,Production,Viscose process: purified cellulose in sheet form viscose solution pumped through spinnerets into a coagulation bath solid cellulose,Production,Preparation of spinning solution cellulose extracted from wood (sheet form steeped in NaOH cellulose swell and co

34、nverted to alkali cellulose the alkalied pulp sheets are pressed and shredded into crumbs crumbs are aged (chemical reaction occurs between cellulose and O2 to reduce DP of cellulose),Wet spinning,Solvent is extracted in nonsolvent coagulation bath due to diffusion Skin “dry” first while core still contains large amount of solvent, resulting in a large skin with small core serrated structure,Nonsolvent,Production,Prepa