Fiber Manufacturing And Properties

Step 1: Understand the property being explained. Acrylic is called "artificial wool" because it is bulky, lightweight, and has good warmth/insulation properties, similar to wool.

Step 2: Analyze the manufacturing process of acrylic. Acrylic is typically wet or dry spun. During these processes, the polymer is dissolved in a solvent, extruded, and then the solvent is removed. When the solvent is removed rapidly from the fiber, it can leave behind microscopic, empty spaces or pores within the fiber structure.

Step 3: Relate these structural features to the wool-like properties. These microscopic voids trap air inside the fiber. Trapped air is an excellent thermal insulator. This trapped air gives the acrylic fiber its low density (making it lightweight), bulkiness, and excellent insulation (warmth), which are the key characteristics that make it resemble wool.

Conclusion: The formation of voids during solvent removal is responsible for the wool-like properties of acrylic fiber.

Step 1: Define the "drawing" process. Drawing is a post-spinning process where newly formed synthetic filaments are stretched to several times their original length.

Step 2: Understand what happens at a molecular level during drawing. In the as-spun state, the long polymer chains in the fiber are randomly coiled and arranged. The drawing process pulls these chains, causing them to uncoil and align themselves parallel to the fiber axis. This alignment is called "molecular orientation."

Step 3: Analyze the consequences of molecular orientation. When the molecules are oriented, they can pack more closely together and exert stronger intermolecular forces on each other. This leads to a significant increase in the fiber's strength (tenacity) and stiffness (modulus), which are the primary goals of drawing. While crystallinity (A) may also increase as a result of the better packing (a phenomenon called stress-induced crystallization), the fundamental objective and direct change is the improvement in molecular orientation. Density (C) will increase slightly and thickness (D) will decrease, but these are consequences, not the primary objective.

Conclusion: The main objective of drawing is to align the polymer chains along the fiber axis, i.e., to improve molecular orientation, which in turn increases strength.