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Why are newly made filaments stretched during fibre production?
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Figure 1: Three common polymer structures. The linear, branched, and network architectures are represented (from top), respectively, by high-density polyethylene (HDPE), low-density polyethylene (LDPE), and phenol formaldehyde (PF). The chemical structure and molecular structure of highlighted regions are also shown.
Newly made filaments are stretched, or drawn, during production primarily to align the long polymer chains along the longitudinal axis of the fibre. This process pulls the molecules into a more ordered arrangement, allowing them to pack closely together into crystallites.1
Stretching is essential for several reasons:
- Improved Strength and Stiffness: By aligning the molecules, the fibre develops greater breaking strength and rigidity, as the closely packed chains resist further movement.1
- Enhanced Physical Properties: The process transforms the appearance of the fibre, often providing the transparency and lustre characteristic of materials like nylon.1
- Chemical Stability: Increased molecular orientation reduces the ability of water and other foreign molecules to penetrate the fibre, which improves moisture resistance and general chemical stability.1
- Size Reduction: In the context of manufacturing, drawing also serves to attenuate the fibre, reducing its size to a uniform, usable strand.2
While some fibres can be cold-drawn, others require hot-drawing to achieve optimal strength or to prevent the material from becoming brittle.3