shear strength of co-extruded PETG / PBT 1

[jvelliky]

I have a high shear force forming operation that is breaking the Admer Tie Layer used during experiments. That is to say 60% of the Admer remains on the surface, while 40% remains attached to the PBT bulk layer. I understand PETG / PET offers an excellent shear force bond, but want to understand if a PETG / PBT bond is fundamentally the same.

 

[Demon3]

See my answer at this location. It describes the factors infuencing strength in coextruded bonds.

http://www.eng-tips.com/viewthread.cfm?qid=238023&page=1

The shear strength between PET and PETG is expected to be better than that between PETG and PBT. The reason being that the first two materials are very similar whereas the latter pair are less similar in terms of polarity.

Bond strength comes from comingling of the polymer chains and that only happens when the two polymers are molecularly miscible. Hardly any polymer pairs are molecularly miscible so bond strength is limited.

One way to force adhesion is to make the two types of polyester react together for example using a transesterification catalyst or higher temperature. This forms a compatibilizer in-situ in the extruder. That approach works very well for blends of PET and polycarbonate.

Chris DeArmitt

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