Polymeric Capstocks – A Primer

Compounding Creativity with Technology

Polymer capstocks are compounds that are extruded to form the protective layer or “cap” over a variety of plastic base materials. 

The capstock layer is co-extruded over the base material in a single process which provides the option to adjust the thickness to meet the functional needs and performance criteria in applications like decking, fencing, railings, window and door profiles and other outdoor applications where durability is required.

Composition and Compatibility

Teknor Apex supplies rigid and flexible materials made from a variety of different polymer families – the most common plastics being PVC and polyolefin-based. In the selection process for a capstock, job one is to determine compatibility to the substrate. In other words, if the substrate (profile) is made from PVC, then the capstock must be compatible with PVC to get proper adhesion.  As these capstocks are typically extruded, processability is critical to ensure the desired surface appearance and gloss are obtained. 

Functionality and Performance

As capstocks are typically used in outdoor applications, they can be formulated with UV inhibitors, pigments, polymer modifiers, adhesion promoters, impact modifiers and other chemical components to meet the demands of the environment. Each of these components can be tailored to meet the various functional and performance needs of the end use product to provide benefits such as: 

• UV and whitening resistance – Providing a finish and hue that will not fade or discolor over time.

• Scratch and abrasion resistance – Limiting scratches from patio furniture, foot traffic, grills, etc. 
• Chemical resistance – Avoiding staining from food, drinks or commonly used outdoor sprays. 
• Color and aesthetic performance – Capstocks can be produced in highly weatherable white (as a siding or window frame) or in a traditional decking application where they’re required to have a more wood-like (variegated) appearance. 

All of these benefits become critical as OEMs/specifiers continue to extend their warranties. 

Our History in Capstocks

As a custom compounder of plastic materials with a long-standing history in building and construction, Teknor Apex understands these requirements and serves the industry with a diverse product line, supported by ongoing development for ever-changing needs. Let us know how we can help in your selection process.