PBT degradation question 1

[metFTIR]

Wanting to determine if a particular lot of PBT (15% glass-filled) has had any degradation occur. Melt flow index, melt point (DSC), and TGA show no major difference btwn suspect material and ok material. FTIR shows very minor differences at 1470, 1264, and 917 cm-1. Processing is likely the source of the differences the engineers are seeing, but any suggestions to completely rule out material differences would be greatly appreciated! Thanks in advance for your help!

 

[patprimmer]

Mould test bars and do izod impact, and elongation at break tests

Regards
pat

 

[smltwnboy]

Pay special attention to the pre-mold drying process... I've seen inattention to this detail result in nearly 50% reduction in some mechanical properties.

 

[patprimmer]

yes, and the real danger is that the mouldings can look perfect and still be substantally down on some physicals due to hydrolysis

Regards
pat

 

[Chris1001]

Other contibutors are right. In addition, I'd suggest an intrinsic viscosity test of the suspect material against standard granulate or suppliers literature. Like nylons, PBT can have sharp melt transitions which can make MVR measurements less useful. I would try this before going down the DSC / FTIR route.

 

[sean01]

metFTIR,

Can only agree with smltwnboy here !!! Moisture absorption of PBT can be a real headache - definately worth considering looking at this. One of the simplest tests I've ever done for this is to take a moulding straight from the machine, then drop it onto a concrete floor from about a metre, listening for the sound it makes. Then, take one from stores thats been hanging around for a while (1 week to 2 weeks) and do the same. The one from the stores should give a dull thud - the one just moulded a crisp well defined noise. If you get this you can fairly safely assume moisture is the problem - proceed directly to processing and the drying option in particular !!