Impact modifiers are additives to engineering plastics including polyesters, polyamides, and polycarbonate blends that improve their impact resistance. They offer a remarkable balance of impact resistance, modulus, and viscosity, as well as exceptional heat distortion temperature retention.
Impact modifiers are added to plastic compounded materials to improve the durability and toughness of a variety of plastic resins. The amount of impact modifier that is added is determined by the level of impact resistance that is required for the end-use application in question.
What is the Need for Impact Modifiers?
To improve the durability and toughness of a range of plastic resins, impact modifiers are added to plastic compounded materials.
Formulators must achieve a wide range of impact resistance, from general-purpose to super toughness, depending on end-use applications and polymer intrinsic resistance.
General-purpose Impact Modification
General-purpose impact modification is a very low level of impact modification which is, for instance, applied to avoid conditioning of molded PA parts.
It translates to appropriate room temperature impact strength but ignores any low-temperature (below 0°C) impact strength needs.
For the majority of these applications, only minimal amounts of effect modifiers (less than 10%) are required, and the impact modifier does not have to contain reactive groups to be acceptable.
Low-temperature Impact Modification
For applications that demand a specific level of low-temperature flexibility and break resistance, the low-temperature impact strength is required.
Super Toughness
Super-tough impact strength will be required for applications that should not lead to a failure of the part even if hit at low temperatures (-30 to -40°C) under high speed. This requirement can only be fulfilled with high levels (20-25%) of reactive impact modifiers with low Tg.
In addition to the impact performance, impact modifiers can further help improve other characteristics of the material such as:
- Optical and tensile properties
- Weatherability
- Processability
- Flammability
- Heat distortion
How do Impact Modifiers Work?
The elastomeric and rubbery nature of impact modifiers absorbs or dissipates the energy of impact. Impact modifiers can be added as additives in the compounding step or incorporated during polymerization in the reactor. Below are the two processes via which effect modifiers work.
Craze Propagation
The principle is to disperse impact modifiers into the brittle matrix, a dampening phase capable to absorb energy and stop craze propagation.
Shear Band/Cavitation
The creation of shear bands surrounding the elastomeric particle absorbs deformation energy as a second mechanism. This mechanism is invariably accompanied by cavitation of the dampening particle (the appearance of voids), which absorbs the energy as well. The appearance of shear bands, on the other hand, absorbs the majority of the energy.
Industry-leading Impact Resistance Performance:
- Super-tough impact resistance
- Low-temperature toughness
- Intermediate toughness at a reduced cost
Additional Benefits:
- Improved flow for higher productivity
- Aesthetic properties (Class A surface finish, excellent colorability)
- Higher graft level to improve efficiency for cost reduction
- FDA compliance for direct food contact
Impact modification is a difficult problem for which there is only one solution dependent on the temperature required for general-purpose strength.
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