12.2 Film formation methods and properties

Polymer films are versatile materials used in packaging, construction, and more. Their formation involves methods like casting, extrusion, and blowing, each shaping the film's properties. Processing conditions, additives, and polymer type all play crucial roles in determining the final characteristics.

Film quality depends on factors like thickness uniformity, clarity, and mechanical properties. These are influenced by processing techniques, molecular structure, and additives. Understanding these elements is key to producing films with desired qualities for specific applications.

Film Formation Methods and Properties

Methods of film formation

Top images from around the web for Methods of film formation

• 

  Blow molding - Wikipedia View original

  Is this image relevant?

• 

  Frontiers | Engineering Biomaterials and Approaches for Mechanical Stretching of Cells in Three ... View original

  Is this image relevant?

• 

  File:Extruder section.jpg - Wikipedia View original

  Is this image relevant?

• 

  Blow molding - Wikipedia View original

  Is this image relevant?

• 

  Frontiers | Engineering Biomaterials and Approaches for Mechanical Stretching of Cells in Three ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Methods of film formation

• 

  Blow molding - Wikipedia View original

  Is this image relevant?

• 

  Frontiers | Engineering Biomaterials and Approaches for Mechanical Stretching of Cells in Three ... View original

  Is this image relevant?

• 

  File:Extruder section.jpg - Wikipedia View original

  Is this image relevant?

• 

  Blow molding - Wikipedia View original

  Is this image relevant?

• 

  Frontiers | Engineering Biomaterials and Approaches for Mechanical Stretching of Cells in Three ... View original

  Is this image relevant?

1 of 3

• Casting involves spreading a polymer solution or melt on a flat surface to form a film
  • Solution casting dissolves the polymer in a solvent, spreads the solution, and evaporates the solvent (water-based paints)
  • Melt casting spreads a molten polymer on a surface and cools it to form a film (hot melt adhesives)
• Extrusion forces molten polymer through a die to shape the film and cools it after exiting (plastic bags)
• Blowing involves extruding a tubular film and expanding it with air to form a thin film bubble
  • Tubular film extrusion pushes molten polymer through a circular die and blows air into the center (plastic wrap)
  • Biaxial stretching improves mechanical properties and clarity by stretching the film in both machine and transverse directions (shrink wrap)

Processing conditions and film properties

• Temperature affects polymer viscosity and molecular orientation, with higher temperatures leading to lower viscosity and less orientation (thermoforming)
• Cooling rate influences crystallization and molecular orientation, with rapid cooling resulting in less crystallinity and more amorphous regions (quenching)
• Draw ratio, the ratio of final to initial film dimensions, affects molecular orientation and mechanical properties, with higher ratios improving both (stretch blow molding)
• Additives like plasticizers, stabilizers, and fillers can modify film properties
  • Plasticizers increase flexibility and reduce brittleness (phthalates in PVC)
  • Stabilizers improve thermal and UV stability (antioxidants in polyolefins)
  • Fillers enhance mechanical properties or reduce cost (talc in polypropylene)

Characteristics of polymer films

• Polyethylene (PE) films are widely used for packaging and agricultural applications
  • Low-density polyethylene (LDPE) is flexible, tough, and transparent (cling wrap)
  • High-density polyethylene (HDPE) is stiffer, stronger, and more chemically resistant (grocery bags)
• Polypropylene (PP) films offer high clarity, strength, and heat resistance for packaging and labels (potato chip bags)
• Polyethylene terephthalate (PET) films have excellent mechanical properties, clarity, and gas barrier properties for packaging and insulation (mylar balloons)
• Polyvinyl chloride (PVC) films are durable, fire-resistant, and chemically resistant for construction and medical devices (blood bags)

Factors affecting film quality

• Film thickness uniformity is affected by die design, polymer flow, and processing conditions, with non-uniformity leading to variations in properties and appearance (uneven coating)
• Clarity is influenced by crystallinity, additives, and surface roughness, with higher crystallinity and roughness reducing clarity (frosted glass effect)
• Mechanical properties like tensile strength, elongation, and tear resistance are affected by molecular orientation, crystallinity, and additives
  • Increased orientation and crystallinity generally improve mechanical properties (biaxially oriented polypropylene)
  • Plasticizers can reduce strength but increase flexibility (soft PVC tubing)
• Residual stresses developed during processing can cause warping, curling, or poor dimensional stability, but can be minimized by optimizing processing conditions and post-treatment methods (annealing)