24 Questions
What is a characteristic of the POY process that allows for greater flexibility in subsequent processing?
Long length of the cooling unit
What is a key difference between FOY yarns and POY yarns?
Level of orientation
What is the primary purpose of the cooling unit in the POY process?
To cool the individual filaments
What is a characteristic of isotactic PP chains?
Methyl side-groups are situated uniformly on the same side of the chain
What is a key benefit of the FOY process?
Production of yarns with a wide range of mechanical properties
What is the primary difference between the FOY and BCF processes?
Texturing of filaments
What is a characteristic of BCF yarns?
They are textured after drawing
What is a key advantage of FOY yarns over POY yarns?
Greater strength even after drawing
What is the arrangement of –CH3 groups in the isotactic form of PP?
On one side of the chain
What is the most stable crystalline form of PP?
α form
What is the advantage of using non-circular cross-sections in PP fibres?
Reduced waxy feel
What is the characteristic of syndiotactic PP chains?
All –CH3 groups alternate between the two sides of the chain
What is the characteristic of atactic PP?
All –CH3 groups are randomly arranged on the chain
What is the main advantage of the α crystalline form of PP?
Superior mechanical properties
What is the characteristic of PP fibres with non-circular cross-sections?
Improved resilience
What is the arrangement of crystalline regions in PP fibres?
Well-defined lattice structures
Why do fibres with exotic cross-sectional shapes pack more loosely than those with circular cross-sections?
They have a larger fibre bulk
What is the main reason PP fibres are not commonly used in clothing?
They cannot be readily dyed
What is a benefit of PP fibres in sportswear and activewear?
They transport water easily and do not absorb moisture
What can weaken PP fibres and cause discolouration?
Strong oxidants
What is a key feature of PP fibres that makes them suitable for outdoor activities?
They have high abrasion resistance
Why do PP fibres retain thermal insulation when worn?
They do not become wet
What is a characteristic of PP fibres that makes them suitable for sportswear?
They possess almost no moisture absorbency
Why are commercial PP fibres treated with light stabilisers?
To protect them from UV radiation
Study Notes
Multifilament Yarns of PP
- Multifilament yarns of PP are produced in three forms: partially oriented (POY) yarns, fully oriented (FOY) yarns, and bulked continuous filament (BCF)
- POY process is low-cost and allows for greater flexibility in subsequent processing such as drawing, twisting, and texturing
- POY process has a long cooling unit to ensure sufficient cooling of individual filaments before winding
Fully Oriented (FOY) Yarns
- FOY process combines spinning and drawing in a continuous process
- FOY process is highly versatile, producing yarns with a wide range of mechanical properties
- FOY yarns are generally stronger than POY yarns, even after POY yarns have been drawn
Bulked Continuous Filament (BCF)
- BCF process combines spinning, drawing, and texturing in one process
- BCF process resembles the FOY process, except that the filaments are textured after drawing
Fibre Structure
- PP chains can adopt several molecular configurations: isotactic, syndiotactic, and atactic
- Isotactic PP chains have all methyl groups projecting from the main chain on one side, conferring superior mechanical properties
- Syndiotactic PP chains have methyl groups alternating between the two sides of each chain
- Atactic PP chains have methyl groups arranged randomly on the two sides of the chain
Fibre Properties
- PP fibres are highly resistant to chemical attack by acids, alkalis, and most organic liquids
- PP fibres are susceptible to strong oxidants, such as hydrogen peroxide, which can reduce fibre strength and cause discolouration
- PP fibres are weakened by ultra-violet radiation, but not degraded by micro-organisms
- Tenacity: 30-80 (cN/tex)
- Elongation at break: 15-35 (%)
- High abrasion resistance
Applications
- PP fibres have a wide range of applications due to their good technological performance and low production cost
- PP fibres are used in sportswear and activewear, such as walking socks, cycle shorts, swimwear, and diving suits, due to their low moisture absorbency and ability to transport water easily
- PP fibres provide good thermal insulation and retain their comfort next to the skin
The production process of multifilament yarns of polypropylene in various forms, including partially oriented yarns, fully oriented yarns, and bulked continuous filament.
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