How do i compression mould PET Plastic?
I am a Final Year Student doing my Final year project. The project I am working on is to make a composite of biowaste and PET plastic. Therefore, I have selected watermelon rind as my biowaste material. Therefore I have already grinded the watermelon into tiny particles.
The problem I am currently facing is due to the PET plastic, my matrix. I am currently using the compression moulder to make my specimen. I need to make 3 samples 50% PET 50% Dried watermelon rind, 70% PET 30% Dried watermelon rind and 100% PET plastic. I need to make a dogbone shaped specimen(ASTMD638) to carry out a degradation test on it. However, I am unable to find the best temperature and pressure parameters to properly form the PET plastic from PET pallets I have purchased. The specimens I have made so far have all cracked as shown in the images below and are also extremely hard and brittle and white in colour. The temperature I have used is 270*c with 5 ton increase in pressure, until 15 tons for 5 minute intervals.
I’d like to know if any of your good selves could help advise me on the best time, pressure and temperatures curve for heating as well as cooling and curing in order to produce good specimen for the PET pallets and PET watermelon composite using the compression moulder. Thank you very much.
I don’t have an answer for you. If you search the forum, there have been several attempts at working with PET. The only successes I remember are the finely shredded PET used in direct 3D printers. The general observation appears to be that PET is both moisture and temperature profile sensitive and may be too difficult for simple DIY recycling.
You didn’t say what discipline you are studying, If possible, I would consult with a polymer chemist to get a recommended process cycle and control tolerances.
There might be too much residual stress in your pallets which is why they’re breaking. When you heat the watermelon rind to 270C it will burn and produce a gas which will put pressure against the PET plastic surrounding it. The entrapped gas doesn’t have anywhere to go and will remain in the plastic after it cools and probably acts as a stress concentrator, meaning forces applied to the pallet can more easily break it, if the pressure from the press isn’t breaking it already. I’d recommend making sure you’re rind is completely dry (so put your rind in a furnace at something like 150C and weigh it on a micro scale every 4 hours, when you find that the mass hasn’t changed from the last time you weighed it then it’s dry). Also try using less rind and work your way up to what you need (you said percent rind in your post but do you mean weight percent or volume percent?).
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