appearance of fibres Flashcards
longitudinal appearance
Smooth, striated
Inclusive e.g. dye, wax
Texturing e.g. crimping process
cross sections
Manufacturing process
Engineered for reason
spinning
Specialised form of extrusion that uses a spinneret to form multiple continuous filaments
Polymer must be in fluid form either by melting or dissolving in a solvent and then forces through the spinneret
wet spinning
Oldest process and the polymer is dissolved in a solvent and the spinneret submerges in a chemical bath which precipitates the fibre as it comes out of the spinneret e.g. acrylic, rayon etc
dry-jet spinning
Extrudes solution in air, dry’s it and then submerges it in liquid bath e.g. lyocell spinning of dissolved cellulose
dry spinning
With hot air on spinneret solidifying fibres by evaporation of solvent
extrusion spinning
Pellets of solid polymer are melted by an extrusion screw then fed via pump to spinneret
melt spinning
Fibres solidify by cooling on exiting spinneret e.g. nylon, polyester, saran
gel spinning
Of high strength fibres uses a polymer gel where polymer chains are orientated so large intermolecular forces e.g. polythene, Aramis
electrospinning
Uses electrical charge to draw very fine fibres from polymer liquid
modification ratio
Industry recognised
The size of the outer circles circumference of the fibre is compared to the size of the inner circle circumference
see powerpoint for
circumferences
modification ration =
x/y
a fibre with a round cross section has what MR
1
what does modification ratio affect
flexibility and soil accumulation/hiding of the fibre
see powerpoint for
method of determining the modification ratio
the larger the modification ratio..
- The more likely the fibre shape can trap and hold soil
- More likely have premature crushing and matting
MR of <2.2 is recommended for what
medium to high soil area
MR of <1.5 is recommended for what
high to very high soil area
trilobal shapes hold soil
Fibred with four holes, diffuse the light and provide soil hiding
The smooth outer surface with no grooves enhances soil release with vacuuming
Dirt cannot get into the holes of the hollow filament fibre. The holes are one ten thousandth of an inch, dirt particles are much, much larger
The best basis for discrimination of trilobal fibres is the modification ratio
Very discriminating
Wayne Williams murder investigation
America serial killer “Atlanta child murders” 1979-1981 killed 11 young men
Prosecutors matched 19 different sources of fibres from William’s home and car to the victims including an unusual trilobal carpet fibre
Chemists from Du Pont testified about fibre manufacture
Fibre traced to Wellman Inc. a Boston textile company who designed fibre of a particular shape to get around Du Pont patent
see powerpoint for
fibre cross sections
see powerpoint for
methods used for analysis of automobile carpet fibres
galaxy
Trilobal Viscose Fibre with High Absorbency
Y design increases the absorption capability of nonwoven structures.
main application in the manufacture of tampons, the global market leader.
Also used in standard nonwoven processes such as dry laying or spunlacing.
poseidon
Viscose fibre with an ion exchange functionality which can be fully regenerated.
Much higher active surface area, than traditional bead resins permitting an increased rate of ion exchange.
Can be exchanged with silver or copper ions
verdi
Anionic Viscose Fibre with a Defined Core-Sheath Structure results in an increased absorbency of water vapour: moisture management in textiles.
Non-sticking fibre surface in wet state allows use in wound-dressings.
Exhibits self extinguishing properties.
outlast
Viscose Fibre with benefits of viscose, e.g. soft, fine feel – similar to cotton or silk, absorbtion of moisture, hygienicic while also providing temperature-buffering
Fibres contain micro-encapsulated phase-change materials,‘Thermocules’, which store, absorb and release heat.
Used for clothing and beadspreads,blankets or mattress covers.
UV/VIS spectra vs fluorescence spectroscopy
• Morgan et al.together with the FBI May 2004 showed that UV/VIS spectra could not distinguish between 3 red polyester fibres but that fluorescence spectroscopy could.
ring vs exhaustive dying
Confocal laser scanning microscopy cross sections of polyethylene terphthalate (PET) fibres dyed with 8% of dye BzDF1 as a function of increasing temperature and time in the dyebath
- 80°C (ii) 90°C (iii) 100°C (iv) 110°C (v) 120°C (vi) 130°C
Then at different times (mins) at 130°C
- (vii) 20min (ix) 40min (x) 60min (xi) 80min (xii) 100min (xiii) 120min
what are spherulites
• Spherical semi crystalline regions inside non-branched linear polymers
formulation of spherulites
• Their formation is associated with crystallisation of polymers from the melt and is controlled by several parameters such as the number of nucleation sites, structure of the polymer molecules, cooling rate etc
what are spherulites composed of
highly ordered lamellae, which result in higher density, hardness, but also brittleness of the spherulites as compared to disordered polymer
lamellae in spherulites are connected by
amorphous regions which provide certain elasticity and impact resistance.
birefringence
Alignment of the polymer molecules within the lamellae results in birefringence producing a variety of coloured patterns
birefringence is dependent on
Refractive index on the polarisation and direction of light)
see powerpoint for
diagrams of spherulites
size of spherulites
varies in a wide range, from micrometres up to 1 centimetre
• Mechanical properties
mechanical properties of spherulites
- Formation of spherulites affects many properties of the polymer material; in particular crystallinity, density, tensile strength and Young’s modulus of polymers increase during spherization. This increase is due to the lamellae fraction within the spherulites, where the molecules are more densely packed than in the amorphous phase
see powerpoint for
graph os isotopic polyporylene
optical properties of spherulites
- Spherulites can scatter light rays and hence the transparency of a given material decreases as the size of the spherulites increases. Alignment of the polymer molecules within the lamellae results in birefringence producing a variety of coloured patterns when spherulites are viewed between crossed polarisers in optical microscope
Polyacrylonitrile (PAN) fiber spun at high coagulation bath temperature (60 °C), containing macrovoids.
Coagulation bath hardens viscous polymer strands into solid fibers after extrusion through spinneret in wet spinning
circular cross section determined by relative diffusion of solvent out and non-solvent in the filaments during coagulation.
When the flux of solvent outward is less than the inward flux, the filament swells and a circular cross-section can be expected.
occurs at high coagulation bath temperatures and high solvent content in the coagulating bath. Cross sections are round at 50 °C or above.
However, high bath temperatures give an increase in void content and subsequent decrease in fiber density, resulting in poor fiber properties.
what is yarn
Group of fibers or filaments that are interlocked together to form a long continuous strand
Either natural or man-made
natural yarn
wool, silk . . (animal – slightly elastic, breathable, warm)
cotton . . . . . (less elastic, stronger),
hemp . . . . . .(plant) – can shrink, stain, etc. but also easy to dye
man made yarn
polyester, nylon . . – can be stronger than natural yarns. – May be finished with wax or alternative coatings allowing for durability during sewing process and during its’ wear and tear in garment
see powerpoint for
S and Z twist yarn
