I would like to perform some Melt Flow Index (MFI) measurements on PA and ABS polymers.
I read the ISO 1133 and ASTM D1238 standard where it is written that hygroscopic materials (such as ABS or PA) need to be dried prior MFI test to avoid degradation and to obtain reproducible measurements.
What could you recommand as drying temperature for PA and ABS granulates prior MFI test ?
I am afraid that I can initiate degradation in the polymer and false the MFI measurement if I choose a too high drying temperature.
For example, for my particular PA, it is written on the commercial informations to dry it on a dessicant dryer at about 80°C between 4h to 12h before injection moulding. Would it be detrimental to dry it at 100°C for about 20 mn ?
And for ABS, what could be the good drying temperature and time ?
Thank you in advance !
Hi Fanny, Polyamides such as nylon can be dried between 80 - 120C, depending on their MW, but recommended to use vacuum drying at 104C for a couple of hours at least. Other places recommend 8 or 12 hours at lower temperatures. The drying condition could also be considered to relate to the dampening conditions the sample may have experience, for instance if exposed to atmospheric humidity for two hours, then only superficial absorption will have occurred and drying can be for just an hour or two. If the sample could be thoroughly wetted, then a longer slower drying would be necessary. The viscosity will be lower when the polymer is damp but will plateau when dry, so you could study this yourself as well if needed. Please also see:
http://www.plasticsgroup.com/pdfs/processing_guide_nylon.pdf
ABS is recommended 70-80C for 3-4 hours.
Hope this helps!
Fanny Bardot, I believe Philip Rolfe's views are correct. In addition, if you have access to a gravimetric moisture analyser, using it to determine the percentage moisture content prior to drying will help you decide if drying is needed at all, and if so, how much of it.
Kind regards
Dear Fanny,
You have received some helpfully answers from other RG colleagues regarding the drying of ABS and PA. Traditionally, the suppliers of PA and ABS recommend using a drying temperature of about 80°C and a time of up to 4 hours (NB: for granules with limited content of moisture):(http://iwww.plasticsportal.com/products/ultramidpa6.html; https://www.fostercomp.com/wp-content/uploads/2018/11/Foster_Lotte-PC-and-ABS-Processing-8-17-17.pdf )
Furthermore, the utilization of a vacuum oven can be beneficially, but is not obligatory (NB: PA is sensitive to oxidation when is exposed long time at high temperature).
Good luck and best regards,
Marius
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