The material properties between cast and extruded PMMA differ enough at the molecular level to make a difference in highly specialized applications—but the surprising truth is that in most industrial applications, the differences between the two types of PMMA don’t really matter.
Therefore, the choice of PMMA depends much more on factors such as availability – especially when it comes to specifications such as:
Cast PMMA usually excels in available colors, thin thicknesses, and lower volumes. Lead times are also generally shorter for non-stock colors and thicknesses for cast PMMA. Therefore, casting is a flexible option where the customer can pick and choose thickness, volume, and color as needed. However, if the desired color and thickness are readily available as an extruded material, choosing the extruded solution is often more cost-efficient.
Extruded PMMA is a less flexible manufacturing process than casting PMMA sheets because extrusion is a continuous process by nature. This means that any changes in thickness or color produce a lot of scrap material and take considerable time and energy compared to manufacturing cast PMMA.
For this reason, the choice between extruded and cast PMMA isn’t as important as the abovementioned considerations. Even though extruded PMMA is generally considered the more cost-efficient manufacturing solution, the factors mentioned above might exclude the choice of extruded PMMA.
PMMA is made by polymerizing methyl methacrylate monomers into long strands through cell-casting or a reactor process.
The two polymerization methods give the finished PMMA different mechanical properties:
Acrylic manufacturing processes don’t just involve casting or extrusion. Once the PMMA has been cast or extruded, you can improve its mechanical and optical properties with coatings that add unique qualities to the PMMA. Examples include coatings that enhance wear-, cleaning- and chemical resistance or coatings that reduce glare and reflections.
This type of processing is suitable for both cast and extruded PMMA, and in many cases, adding the right coating or other treatment is more important than choosing between cast and extruded PMMA. The reason is simple: While the material properties of cast and extruded PMMA are very similar, the right coating can significantly improve the material properties of the PMMA in certain areas and add value to your application.
Before you decide on a PMMA type, you need to know the technical requirements of your application to choose the most efficient way of meeting those requirements.
Here are some considerations you should make when choosing the base material:
If you have an application utilizing circularly polarized light (CPL), cast PMMA is the better option because it is 100% amorphous by nature. As mentioned above, this means there is no risk of optical distortions of the CPL passing forth and back through the material. Extruded acrylic is unsuited for this type of application because of the retardation in the material. This distorts the CPL when passing through the material.
Imagine, for example, that you are developing a high-end barcode reader utilizing embedded CPL illumination for hard-to-read information, i.e., laser-etched markings on highly polished stainless steel parts. The distortions from extruded material will significantly reduce the scanning system’s signal quality or signal-to-noise ratio, making cast acrylic the only viable option.
In conclusion, the choice between cast and extruded PMMA is about availability or cost considerations in most cases, not mechanical or optical properties. There are a few cases where cast acrylic is the only option, but these cases are definitely few and far between.
At PSC, we have decades of experience developing and manufacturing PMMA to our customer´s exact specifications, using casting and extrusion processes, and applying various coatings and other special treatments. We use that experience to give you a PMMA solution engineered precisely for your application—no more and no less.
Contact us to discuss your requirements and options, no matter if you are gearing up for a highly specialized development project or cost-sensitive and high-volume serial production.