1. Commonly Used Elastomer Toughening Materials
Elastomer materials can be categorized in several ways:
A. Classification by Glass Transition Temperature:
High-Impact Resins: Common examples include CPE (Chlorinated Polyethylene), MBS (Methyl Methacrylate-Butadiene-Styrene Copolymer), ACR (Acrylate Copolymer), ABS (Acrylonitrile Butadiene Styrene), EVA (Ethylene-Vinyl Acetate), and MPR (Modified Petroleum Resin). These materials are generally easier to process and disperse.
High-Impact Rubbers: Common examples include EPDM (Ethylene Propylene Diene Monomer), NBR (Nitrile Butadiene Rubber), SBR (Styrene Butadiene Rubber), and natural rubber. These typically require more careful compatibility design with the base plastic.
B. Classification by Molecular Structure:
Pre-designed Elastomers (Core-Shell Structure):
Structure: Similar to an egg, they have a soft elastomer "core" that absorbs impact energy, encapsulated by a hard polymer "shell" that aids dispersion and prevents particle agglomeration.
Characteristics: High toughening efficiency with minimal reduction in the base material's strength.
Common Types: MBS (offers good transparency), ACR (offers good weather resistance).
Non-Pre-designed Elastomers:
Structure: They toughen the plastic through a solvation (plasticizing) mechanism, forming a network within the base polymer.
Common Types: CPE (offers good flame retardancy), EVA
Transitional Elastomers:
Characteristics: Their structure is intermediate between the two types above.
Common Types: ABS is a typical example, offering a balanced set of properties.
2. Selection of Common Elastomer Toughening Materials
Method 1: Follow the Compatibility Principle – "Like Dissolves Like"
For effective toughening, the elastomer must be compatible with the base plastic.
Polarity Matching Principle: Plastics with high polarity (e.g., PA, PVC) should be matched with highly polar elastomers (e.g., NBR). Plastics with low polarity (e.g., PP, PE) should be matched with low-polarity elastomers (e.g., EPDM).
Solubility Parameter Matching Principle: The difference in solubility parameters between the plastic and elastomer should generally be less than 1.5 to ensure good compatibility and dispersion.
Method 2: Synergistic Blending for 1+1>2 Effects
Using a combination of two or more elastomers often creates a synergistic effect, enhancing performance beyond what either could achieve alone.
Classic Example: Adding both EPDM and ABS to PP (Polypropylene) results in better toughening than using either one individually.
Method 3: Select Based on Product Functional Requirements
The choice of elastomer can be driven by the specific end-use application of the product:
Flame Retardancy Required: Choose CPE
Transparency Required: Choose MBS
Weather Resistance (Aging Resistance) Required: Choose ACR and EVA (Avoid MBS and ABS for outdoor use)
Low Cost Required: Choose MPR, CPE, and EVA
Method 4: Balance Toughness and Rigidity via Combination with Rigid Materials
Toughening often reduces the stiffness, strength, and heat resistance of the plastic. To mitigate this:
Combine with Rigid Materials: For example, adding talc to a PP/EPDM blend, or adding AS resin (Acrylonitrile-Styrene) to MBS/CPE blends. This approach helps maintain sufficient rigidity and heat resistance while achieving high toughness.