Why must fiber materials that are melt-spun and then drawn be thermoplastic? Cite two reasons.

1. Thermoplastic materials have the unique ability to melt when heated and solidify when cooled, which is essential for the melt-spinning process. This process involves heating a polymer material above its melting point, extruding it through a spinneret, and then cooling it to form fiber strands. The ability to undergo this process repeatedly without significant degradation of properties allows thermoplastic materials to be melt-spun efficiently and economically. 2. The ability to undergo deformation and drawing is another crucial property of thermoplastic materials. Drawing is the process of stretching the fiber after it has been spun, either in solid or semi-solid state, to align the molecular structure and improve mechanical properties, such as tensile strength and modulus. Thermoplastic materials, being capable of significant deformation without breaking, can undergo the drawing process, improving their properties as fibers. This property allows fiber materials to be strong and durable in their final applications, such as textiles and composite materials.