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Topic Tag: gas

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Hi everyone, I'm Marius. I currently have a problem with creating High Impact Polystyrene (HIPS) samples without bubbles forming in the polymer structure. I work at a university project that tries to recycle HIPS from different stuff like laptop cases. In the university I stay, they organized a heated press  and an aluminium moulde to make some tests (pictures following). It is the first time we are working with the machines and the material and so no one has much experience.. The Problem: Every sample has a lot of bubbles inside and we don't exactly know why. The material is  clean and the size is about 3x3,5mm. We also dry the material over night at ~70 °C and preheat the moulde to ~ 100 °C. After heating up the moulde, I use some silicone spray to remove the plastic after the compression melting. Then I fill the moulde with the HDPE pellets as close as possible and heat up the open moulde to 220°C - 280°C (best try was around 230°C). After one hour I close the moulde and compress it to 9 Ton, wich is the maximum of the press. Then I continue heating for ~2 hours while holding the pressure. After that, I turn off the heating and hold the pressure over night. When checking in the next day, the plastic is full of air bubbles. I found some information in the forum and I think in general we have 3 main problems: 1. Air between the pellets after filling Maybe our pellets are too big and it would help to get some powder? We also tried to melt the material outside the moulde in a separate oven at ~260°C for 5 hours and put it in the moulde afterwards. This also gave us a lot of bubbles and the plastic did also not melt into a homogeneous mass. 2. Gas is created It can also be, that Gas is created while the procedure, wich forms the bubbles. Therfore, we tried at Temperatures between 210 °C and 280 °C and with/without silicon spray. Like I said, the polymer is also dryed and cleand before. Maybe it is also a problem that the gas can't escape. 3. Polymer is reducing its size when cooling down While cooling down the plastic is shrinking down, so we keep the pressure the whole night. But I am not sure if this solves the problem of shrinking completely. I also tested to increase the pressure stepwise, like +1Ton every 15 mins. Sadly, none of the ideas I had or found here in the forum helped to get a solid plastic. Maybe some of you have already more experience in compression melting of HIPS and can help :) I am happy about any idea and help! :) Best wishes, Marius
Viewing 3 topics - 1 through 3 (of 3 total)
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