Koextrusion

Koextrusion, also called coextrusion in English, is a polymer processing technique in which two or more polymers are extruded simultaneously to form a multilayer structure. Multiple extruders feed streams of different polymers into a single feedblock or multilayer die, which arranges the streams into a stack of layers. The finished product can be films, sheets, pipes, or profiles with laminated layers that retain distinct material properties.

Layer sequence and thickness are controlled by the feedblock design and die geometry. In film applications, total thickness typically ranges from tens to hundreds of micrometers, with individual layers spanning roughly 0.5 to 20 micrometers. Common materials include LDPE, LLDPE, HDPE, PP, PET, and PA, often paired with barrier layers such as EVOH or polyamides. Tie layers or compatibilizers are frequently used to promote adhesion between otherwise incompatible polymers.

Advantages of koextrusion include the ability to combine properties such as clarity, barrier performance, stiffness, and heat resistance in a single extruded structure, along with improved processing efficiency. Challenges involve achieving reliable interfacial adhesion, matching rheology among different polymers, and maintaining precise process control with specialized equipment.

Applications span packaging films, where barrier and strength are critical, to automotive components and medical products that benefit from tailored, multilayer material properties. Koextrusion enables multilayer products without the need for post-assembly lamination.