Hi,
My name is Céeleste Robert and I am a master student at l'Université du Québec en Abitibi-Témiscamingue (UQAT). I am interested in your project as I am also working with PLA and natural fibers. I was wondering how your project is going. Have you encountered any difficulties while processing your composites? i am having some difficulties right now with the injection molding of my PLA. I started by practicing on the pure PLA, but they are giving me a lot of difficulties. The test specimen have defects in them and air bubbles. I tried tunnin many injection properties such as: the mold temp, the processing time and the time left in the mold before taking out the samples, the pressure, the injection time, and the injection temperature (nozzle and the different zones), but nothing seems to help.
Do you have any tips you could give me to make my injection adventure a little less chaotic? I am using a Haitian MA 600 II machine with a screw diameter of 24mm.
Thank you,
Céleste
Dear Celeste, I observed this problem also in the past in my lab. Maybe interesting to think for additives that can optimize the processing. KR, Nabyl
Dear Celeste:
What is the final goal/material - you'd like to receive by employing injection molding.
The Laboratory I am teaming up with - studies the bio-degradation of mixture of PLA with some other polymer. They also use injection molding for mixing the 2 polymers. From my viewpoint the formation of air bubbles in PLA after it is subjected injection molding - is quite natural and unavoidable - whichever regime you use.
After IM-mixing they obtain by hot pressing films. These films do not contain the air bubbles. The piec of extruded material they place between 2 Polyimide films
covered by Teflon (which, as you know, has a 0 adhesion). Polyimide like Kapton has a very high thermal resistance - over 350C you should use for hot-pressing the T 20-30C above melting point of PLA; the suspension of Teflon is sprayed over PI-film - in accord with instruction you should use an appropriate T to remove the solvent.
...It is how they get rid of bubbles.
Best Regards,
Leonid
Dear Nabyl Khenoussi,
Thank you for your response, and I agree. I already tried adding additives to help improve the ductility of the composite (improving the ductility is the main goal of my project). These additives I added seems to work with the PLA as the air bubbles and the deformation on the surface of the samples greatly decreased. I wanted to inject the PLA too (or use the same molding form for all), so I can have the PLA to compare my composites too.
Respectfully,
Céleste
Dear Leonid V Vladimirov ,
Thank you for your response. The main goal of my project is to improve the ductility of brittle biopolymers. I decided to use injection molding because we have the proper equipment to do so in our lab, and in theory, it's a bit faster than using a press (in my experience). I am using the press to make disks to use in the rheometer, and it's a bit of a pain. They are hard to remove from the mold (sometimes they just end up broken into pieces), and they take a while to make.
The lab technician and I tried various settings for the type of PLA I used and another type some students are using. For the injection, nothing seemed to be efficient. So we tried molding them by the intrusion and got some good results. The bubbles are gone which is a relief. It works with the PLA and the composites. The only problem is that for some composite, the mold doesn't fill up all the way if we try to mold many pieces at once, but by molding only one, the results are consistently good.
Respectfully,
Céleste
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