Polyolefin composites or POC’s are generally defined as materials that contain two or more phases and have a distinct boundary between the two phases. The careful combination of different and unique systems can result in improved structures and functions over the individual components alone.
The properties of POC’s can be enhanced through the appropriate engineering techniques.
Some of the current applications for POC’s include their use in automotive parts. Specifically, one area where there has been a great deal of interest is in automotive bumper beams. In addition, polyolefin composites are also presently used in construction applications. For many of the described uses, natural-filled polyolefin composites are the desired material of choice.
Despite of multiple applications of POC, there’s something that restricts its performance. Let’s see what that is and how could it be overcome…
What Limits the Use of Polyolefin Composites?
One of the primary issues with POC’s that has limited their use in more applications is the incompatibility between the polyolefin matrix polymer and the reinforcing fiber or filler. That incompatibility at the interface results in reduced adhesion between the two materials in the composite structure.
This factor limits the stress transfer via the interface, meaning that the reinforcement potential of the fibers or particles cannot be exploited to the full extent, especially for short fibers and particles.
The incompatibility can also lead to the fibers or particles forming aggregates rather than being uniformly dispersed in the polymer matrix. This fact leads to either an optimum property profile not being realized or the presence of very non-uniform properties in the final composite.
| NOTE:Incompatibility between the polyolefin matrix polymer and the reinforcing fibers or fillers results in reduced adhesion between the two materials & aggregation of fillers inside the polymer matrix |
Related Read: Solutions to Optimize Matrix Fiber Interface in Thermoplastic Composites »
Overcoming Polymer Composites Incompatibilities
In composites that are based on polymers other than polyolefins, there are several well established approaches for addressing these incompatibility issues. Among the techniques that have been utilized are:
- Use of coupling agents
- Use of compatibilizing agents, and
- Treatment of fibers using peroxide, permanganate and plasma
Each of these technologies has had varying degrees of success when used with a variety of matrix polymer / reinforcement combinations.
In general, these approaches are based on the establishment of an interaction, either chemical or physical, between the matrix polymer and the reinforcing material in the composite. That interaction leads to an improved interface being present compared to the material that does not have such an interaction.
The interaction is often due to the presence of specific chemical functionalities or groups that exist in the structure of both the polymer matrix and the reinforcing material. The chemical group in the matrix polymer has an interaction with the chemical group in the reinforcement and this leads to a favorable interface in the resulting composite structure.
However, the issue with the use of polyolefins as the matrix polymer is that there are limited possibilities for interactions with the reinforcement in the composite. With there are no polar chemical groups in the polyolefin polymers generally present. It is the presence of such polar functional groups that usually leads to the type of interactions that are required to have good interfacial properties in composites.