Final Exam Flashcards
What is the flow chart of filament yarn processing?
Polymerization → Dissolving → Extrusion → Drawing → Texturing
What are the reasons for mixing polymers in filament yarn processing?
- Polymers that cannot be dyed are mixed
- Blending fibers to get desired properties
- Enhances brightness
- Reduces degradation
- Increases conductivity
What are the three primary spinning methods for filament yarn processing?
Melt spinning, Dry spinning, Wet spinning
What is melt spinning?
A process where polymers are melted, extruded through a spinneret, solidified by cold air, and then collected.
What are some examples of thermoplastic fibers used in melt spinning?
PET, Nylon, Polypropylene
What are the advantages of melt spinning?
- High productivity
- No solvents required
- Ability to combine two or more materials
What are the disadvantages of melt spinning?
Low tenacity (strength) and modulus (stiffness) of fibers.
What is dry spinning used for?
Polymers that need to be dissolved in a solvent because they cannot be melted.
What is the dry spinning process?
- Polymer dissolved in volatile solvent
- Solution is purified and extruded through a spinneret
- Fibers solidify as solvent evaporates in a warm chamber
What are examples of fibers produced by dry spinning?
Acetate, Triacetate, Acrylic, Modacrylic, Spandex, Vinyon
What are the advantages of dry spinning?
- High productivity
- Yarn does not need purification
What are the disadvantages of dry spinning?
- More complex compared to melt spinning
- Flammable due to the use of volatile solvents
What is wet spinning used for?
Polymers that do not melt and only dissolve in non-volatile or thermally unstable solvents.
What is the wet spinning process?
- Polymer solution is extruded into a spinning bath
- Fibers coagulate in the bath and are collected
What are examples of fibers produced by wet spinning?
Lycocell, PVC, Vinyon, Kevlar, Nomex, Spandex, Acrylic, Modacrylic, Zylon
What are the advantages of wet spinning?
Can produce large tows (fiber bundles).
What are the disadvantages of wet spinning?
- Low productivity
- Solvent needs to be washed out, making it resource-intensive
What is gel spinning used for?
Producing high-strength and high-modulus fibers.
What is the gel spinning process?
- Polymer is kept in a liquid state with a high degree of orientation
- Solution is extruded through spinnerets and cooled in solvent or water
- Yarn is then stretched
What are examples of fibers produced by gel spinning?
Ultra-high molecular weight polyethylene, Polyvinyl alcohol, Polyacrylonitrile
What are the characteristics of non-round cross-section fibers?
High surface area
High cover
Higher filtration efficacy
Higher liquid wicking
Higher sound insulation
Higher thermal insulation
High bend rigidity
Higher friction
What is the purpose of drawing in filament yarn processing?
- Increases fiber strength
- Removes permanent elongation
What factors affect the drawing process?
- Material type
- Spinning conditions
- Spinning take-up speed
What is fiber tenacity?
Fiber tenacity is the normalized value used to compare fiber strengths, measured by dividing the breaking force by the fiber denier.
What materials use high draw ratios for producing high-tenacity yarns?
Nylon, Polyester, Polypropylene, Gel-spun yarns
What happens when the draw ratio increases?
Increases molecular orientation
Increases yarn tenacity
Decreases breaking elongation
What are the end uses of high-performance fibers?
Protective clothing
Aerospace
Sports
Industrial materials
What are the advantages of synthetic yarns?
High strength
High elongation and recovery
Uniformity
Resistance to mildew
Easy care
What are the disadvantages of synthetic yarns?
Too smooth
Sticky
Do not wick moisture
Poor insulators
What is texturing?
A post-extrusion process applied to flat continuous filament yarns to modify their structure for specific end uses like apparel.
What does texturing improve in yarns?
Stretch
Bulkiness
Thermal insulation
Wicking ability
What modifications does texturing introduce to yarn?
Crimps
Loops
Knots
What are the texturing methods?
False twist
Stuffer box
Knit-de-knit
Air jet
What is the false twist texturing process?
Flat thermoplastic yarn moves through a heating zone and is false twisted
The yarn is cooled, the false twist is removed
Yarn is overfed and wound into a package
What is the stuffer box texturing process?
Filaments are stuffed into a heating box and crimped
Heat is applied and then cooled to maintain the crimp
What is stuffer box texturing used for?
Carpeting yarns
What is the knit-de-knit texturing process?
Filaments are knitted into fabric
A wavy configuration is created
Knitting gauge and loop length determine the size and frequency of yarn waves
What is air-jet texturing?
A process that creates crimps or loops through mechanical interlocking using an air jet.
What types of yarns can use air-jet texturing?
: Any continuous filament yarns.
Which texturing methods are used for thermoplastic continuous filament yarns?
False twist, Stuffer box, and Knit-de-knit.
