Hi everyone, I haven't been around quite for a while. Now I am running some experiments on compounding of recycled bottle PET from flakes with other plastic materials and mineral fillers. The idea is to develop a compound which would have better properties like:
- wider "processing window";
- enhanced melt strength and thermal stability;
- lower polymer matrix sensibility towards water (hence pre-drying less critical) etc. It does not go well so far. And it doesn't seem there are many people around doing such things with recycled PET. Does anybody know anything about success stories in the area? Happy New Year! Ole
Candidly you are plowing old ground. Others are/have studied using recycle instead of virgin PET for many years. If you have never used PET, key is absolute dryness which means not only drying but conducting compounding in dry atmosphere. Frank
Most suppliers of PET plastics offer resins which are based 100% on recycled PET bottles, so you can use their resins as reference. Just go to their internet sites for more details ...
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Thanks Frank, The old ground has to be ploughed to get a new harvest anyway :-) The idea is not limited to use of recycled PET instead of virgin one - I have already done it (fully appreciating the importance of having it as dry as possible :-) Now the whole point is to develop a workable compound of recycled PET with other plastic materials (like PP for ex) and some mineral fillers. Target properties were outlined in the initial posting. It must be a different material, having wider processing window for extrusion, thermoforming and injection applications... Ole
Hi Rolf, Pls see my reply to Frank. I want a different stuff - a compound to extrude, thermoform, or inject. Not pure PET repro. Just a new material for not-bottle applications. Ole
sounds to be a rather complex task, since you are certainly talking about many different materials and not just one.
"recycled bottle PET from flakes with other plastic materials" means different blends, for each of which a different compatibilizer is needed! For blends with PP you ought to try MAn-g-PP, for blends with PE try MAn-g-PE.
"a compound to extrude, thermoform, or inject" also means at least 3 different types of resins, since melt viscosity and melt strength requirements vary between those 3 materials quite considerably, which in turn will require different measures! Melt viscosity can be enhanced by melt coupling additives, melt strength by additives which promote branching. For both you may want to try some suitably functionalized impact modifiers, for example. Injection molding resins need a suitable crystallization package.
"and some mineral fillers" means yet another resin; PET, due to its slow crystallization and low crystallinity, requires lengthy typ mineral fillers, i.e. with a high aspect ratio, otherwise you will not get any reinforcement and mechanical properties would be rather poor. Talc, kaolin, calcium carbonate are therefor not so good.
As long as the major portion of your resin is based on PET, you will always have some significant sensitivity towards moisture, just in order to get consistent material properties.
Last but not least, all modifications you apply to your recycled bottle PET, will depend on the enduse applications you have in mind ...
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Hi Rolf, Thnx for the exhaustive comments! Let me take it part by part.
Could you tell me who supplies maleic anhydride grafted polypropylene or polyethylene? I would probably order some small qties for the trials. Once we tried PET + PP with EVA as a compatibilizer (content of EVA 21%). The application was packaging strap. The result was more or less acceptable for the straps, but for thinner sheets it looked a bit problematic.
Oh yes, but I believe once we get a "workable" compound, we could well modify the properties making them fir for the specific applications.
reinforcement
I put some hopes on nano stuff, like wollastonite, but it is quite expensive so I doubt whether to go for this option. Can you recommend any of the fillers (having high aspect ratio) which you think might work?
One of the ideas is to choose mineral filler which would take up and bind some water thus making thorough PET-style drying less necessary.
Ideally, I am looking for a material suitable for thin (0.15 - 0.90 mm) sheet extrusion and thermoforming. But if a simple injectable resin for unexacting applications would be obtained, it should be already a success :-)
I'd try either FUSABOND* and/or POLYBOND*, to name just two brands:
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WOLLASTONITE is what I had in mind and you ought to ask your supplier for lower-cost grades, with a somewhat reduced aspect ratio.
I don't think that "mineral filler takes up and binds some water", the mineral filler just reduces the PET-volume, but the remaining PET matrix resin is still as moisture sensitive as pure PET is, so as long as your matrix resin contains mostly PET you will always have to dry it thorougly!
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