Meaning
Chemically modified polymers featuring highly polar functional groups grafted onto a non-polar polyolefin backbone enhance the compatibility between dissimilar materials. Formulators utilize maleic anhydride grafted polypropylene as a coupling agent to bind polar glass fibers or natural fillers to a polypropylene matrix. This additive bridges the interfacial energy gap, improving the distribution and adhesion of fillers within the polymer melt.
The compound is typically supplied in pellet form and is added in low percentages during the compounding step.
Chemical Bonding
Interfacial adhesion in composite materials requires a bridge between hydrophobic matrices and hydrophilic reinforcements. When maleic anhydride grafted polypropylene is blended into the compound, the anhydride groups react with the hydroxyl groups on the surface of glass fibers. This reaction creates strong covalent bonds that transfer mechanical stress from the polymer matrix to the reinforcing fibers.
Without this chemical link, the fibers would act as voids, reducing the strength of the part.
Composite Performance
Mechanical properties of filled thermoplastics depend heavily on the quality of the polymer-filler interface. Adding maleic anhydride grafted polypropylene increases the tensile and flexural strength of the composite, preventing premature failure under load. This improvement is especially pronounced in automotive under-the-hood components where high temperatures and mechanical stresses are present.
In addition, the coupling agent reduces moisture absorption, protecting the part from dimensional changes.
Processing Guide
Dispersion of additives during twin-screw compounding is enhanced by the presence of a compatibilizer. The addition of maleic anhydride grafted polypropylene reduces the melt viscosity, allowing for easier processing and better flow through the die. Moulders can operate at slightly lower temperatures and pressures when running compatibilized compounds, which helps to save energy and reduce cycle times.
Excessive levels of the grafted polymer must be avoided, as too much can plasticize the blend and reduce the heat deflection temperature. Achieving the optimal balance between the grafted polymer and filler loading is essential to maximizing both processing efficiency and mechanical performance.
