Reducing delamination in PS/PS foam coextruded profile

[Arcodes]

I'm currently trying to extrude a thin profile consisting of a low-density foamed PS core material with a coextruded PS layer (foamed or compact) on top to improve compressive strength.

Core is extruded at approx. 167°C, coextruded layer between 190 and 200°C.

What we see is that the top layer can easily be peeled off by hand. Since we are in a very subjective market we need to improve the interaction between both layers. My guess is the temperature of the foamed core is holding this back, plus the lack of cross-linking in polystyrene.

Are there additives that can improve the adhesion between the layers? Does anyone else have experience with a similar problem?

Thanks in advance

 

[Demon3]

Bonding of polymers depends on chain entanglement. In the real world that means you need both plastics to be warm and in contact long enough for the chains on each side to entangle and give a strong bond. So, you can't laminate one material onto the other one cold as the foam contains little heat and will lose it as soon as it contacts another surface.

Another problem may be a weak boundary layer. That's when low molecular weight additives migrate to the surface and prevent the chains from entangling. Effectively you can have for example a waxy layer there of calcium stearate, anti-static or other additive. Reduce that by minimizing such additives as much as possible.

Chris DeArmitt PhD FRSC CChem

 

[Arcodes]

Thank you for your reply.

Only additive used is a talcum-based nucleating agent which is distributed fairly evenly across the melt judging by the narrow cell size distribution we get.

I've played around with the composition of the coex layer without significant results.

Temperature might be the decisive factor but we tried coextrusion in a different extruder where the foam is fully formed before coextruding and the grafting was much better. Even though core temp was 150°C, coex temp around 175.

 

[patprimmer]

I don't mean to be disrespectful, But unless you compounded the material from barefoot polymer, or you have a very good relationship with the person doing the formulating at your polymer supplier, you are likely not aware of several additives it probably contains.

Regards
Pat
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[Arcodes]

Point taken Pat. I'll definitely try using different resins. Generally the same resin mixture is used for both core and coex layer.

 

[Demon3]

Polystyrene or HIPS contains mineral oil as delivered from the manufacturer.

In the case of HIPS you have lots of surfactant too.

Chris DeArmitt PhD FRSC CChem

 

[Arcodes]

Could a difference in velocity between both layers have a pronounced effect on the grafting?

Also, from our calculations the coextruded layer seems to be stretched elongationally due to shear forces.