Lecture 09 - Sheet and Films, Foams, Fiber and Filaments

Polymer Sheet and Film

• Film: thickness below 0.7 mm, used for packaging.
• Sheet: thickness 0.5 mm to 12.5 mm, used for window glazing and thermoforming.
• Materials: PE, PP, PVC, cellophane (thermoplastics).

Processes

• Calendering: Uses rollers to reduce thickness, provides good surface finish and gage accuracy. Used for PVC products.
• Slit-Die Extrusion: Extrusion through a narrow slit die, can produce wide sheets/films.
• Blown-Film Extrusion: Combines extrusion and air blowing to form a thin film tube.

Calendering

• Feedstock is passed through a series of rolls to reduce thickness.
• Materials: PVC, rubbery thermoplastics (plasticized PVC, ABS).
• Additives include resins, stabilizers, lubricants, colorants, and plasticizers.

Slit-Die Extrusion

• Uses a narrow slit as die opening.
• Issue: Maintaining thickness uniformity.

Blown-Film Extrusion

• Combines extrusion and blowing to produce thin film tubes.
• Process involves extrusion, upward drawing, and air inflation.

Polymer Foam

• Polymer-and-gas mixture creating a porous structure.
• Common foams: Polystyrene (Styrofoam), Polyurethane.
• Other foams: Natural rubber, PVC.
• Types: Elastomeric, Flexible, Rigid.

Applications of Polymer Foams

• Insulation (hot beverage cups, structural materials).
• Packaging.
• Cushioning (furniture, dashboards).
• Buoyancy.

Fiber and Filaments

• Fiber: Long, thin strand (length >= 100 times cross-section).
• Filament: Continuous length fiber.

Applications

• Textiles (most important).
• Reinforcement in polymer composites.
• Natural fibers (~25%): Cotton, wool.
• Synthetic fibers (~75%): Polyester, nylon, acrylics, rayon.

Fiber and Filament Production - Spinning

• Extrusion through a spinneret, followed by drawing and winding.
• Spinneret: Die with multiple small holes.
• Variations: Melt spinning, dry spinning, wet spinning.

Melt Spinning

• Polymer is heated to molten state and pumped through spinneret.
• Filaments are drawn and air-cooled.
• Used for polyester and nylon filaments.

Dry Spinning

• Polymer is in solution; solvent is removed via evaporation in a heated chamber.
• Used for cellulose acetate and acrylic filaments.

Wet Spinning

• Polymer is in solution; extrudate is passed through a chemical to precipitate the polymer.
• Used for rayon filaments.