6: Polymer Additives

Overview of Polymer Additives

  • Polymer additives enhance properties of neat resins (pure polymers without fillers/additives).
  • Categories of additives discussed include plasticizers, fillers/reinforcements, and others serving various functions.

Plasticizers

  • Definition: Additives that lower the glass transition temperature (TG) and increase free volume in polymers.

  • Function:

    • Embed between polymer chains, increasing space for chains to slide over one another.
    • Ultimately makes polymers more flexible and less stiff.

  • Advantages of Plasticizers:

    • Improved flexibility of the polymer.
    • Increased elongation to failure.
    • Lower elastic modulus (where advantageous).
    • Significant increases in impact resistance.

  • Disadvantages of Plasticizers:

    • Reduced tensile strength.
    • Increased flammability.
    • Decreased heat distortion temperature and service temperatures.
    • Volatilization over time, leading to increased stiffness and brittleness.

  • Common Plasticizers: Phthalates are widely used; responsible for the "new car smell" due to volatilization.

  • Mechanical Properties Effects:

    • Increasing plasticizer amounts generally decreases melting point, hardness, and tensile strength.
    • Increases elongation to failure and impact strength.

Fillers and Reinforcements

  • Definition: Added to improve strength, modulus, and thermal stability of polymers.

  • Functions:

    • Decrease mold shrinkage and production costs (as fillers are typically cheaper).
    • Enhance overall polymer properties.

  • Common Fillers:

    • Minerals: mica, talc, calcium carbonate.
    • Glass fibers and other ceramic fibers.
    • Organic materials: wood flour, carbon fibers.

  • Filled Polymer Properties:

    • Conventional filled polymers: 20-50% filler volume.
    • Advanced composites can have up to 70% glass fiber volume.

  • Effects of Glass Fillers on Properties:

    • Increases tensile strength and elastic modulus.
    • Decreases impact strength and elongation to failure.
    • Decreases water absorption.
    • Increases heat distortion temperature.

Other Additive Types

  • Antioxidants and Heat Stabilizers: Improve temperature resistance.
  • UV Stabilizers: Enhance outdoor durability of plastics.
  • Flame Retardants and Smoke Suppressants: Increase safety of polymers.
  • Anti-static Additives: Reduce static charge on plastic surfaces.
  • Biocides, Fungicides, and Preservatives: Minimize microbial activity and prevent mildew.
  • Processing Modifiers: Plasticizers can lower polymer viscosity to improve processability.
  • Foaming and Blowing Agents: Reduce polymer density and create air spaces.
  • Aesthetic Modifiers: Include colorants, dyes, and fragrances to enhance appearance and odor.

Conclusion

  • Polymer additives significantly alter the physical and mechanical properties of neat resins, enhancing functionality and application versatility.