Most of the marketed polypropylene –PP - is of the stereo-regular type (i.e. isotactic and then syndiotactic) . There is also the stereo-irregular atactic PP but it is not as widespread. Of course, a stereo-block is possible in PP (e.g. isotactic configurations linked with atactic configurations in the same main polymeric chain).

Polymers as PE & PET are much easier to recycle than PP & that is why most of it is dumped . This is because it has a higher crystallinity which rendered it to be insoluble in many common solvents. In fact, that is why researchers keep asking about solvents of PP as these examples show:

https://www.researchgate.net/post/What_solvent_can_be_used_for_the_dissolution_of_Polypropylene

(3 years ago)

I was honored to participate in answering this question:

https://www.researchgate.net/post/Which_solvents_can_dissolve_polypropylene_and_polyethylene_at_normal_room_temperature

(a year ago)

Thank you Nizar Matar . But I was more asking about mechanical recycling (melting the plastic) than chemical. I wanted to know if one could mix all kinds of PP together.

I disagree with Nizar Matar in the PP recycling, this is actually good on recycling. Lead-acid batteries cases and covers are made with it and the recycling stream is high. Another evidence are the antioxidant packages made just for recycled PP. Anyway, about the main question Abdelmalek Habchi : given your plastic stream is not stable then you will succeed sometimes when mixing all together and other times you won´t. A good idea is to add a compatibilizer, which will raise costs and success, it´s up to the use you will have with the product.

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Thank you Victor H Ponce ! However, I'm trying to get it done without adding anything, but what would cause it to succeed only sometimes? Are there any specific issues to be identified here? Thank you.

Abdelmalek Habchi : There is a lot of issues, more than can be discussed in written. My recommendation is to find somebody skilled and experienced near from you and willing to help, there is dozens of scenarios you can find and even more possible solutions.

@ Abdelmalek Habchi : Your question's title talked about miscibility "a physical property" & then you added recycling by heating "a physical action". When shredding is applied to a polymer, that will be recycled, then this is a mechanical action.

I did not rule out the possibility of recycling PP since I know that it is done but it is not as easy as the polymers I mentioned. Your research will work, for sure, if you keep trying. When you mix all the kinds of PP polymers in recycling attempts, the obtained product is better not used in articles that will be used for human foods. Scientists advise using recycled plastics for other purposes (such as flower pots).

Please see this question & the useful discussion which followed since it may help you:

https://www.researchgate.net/post/Bottle_but_not_textile_PET_recycling-why_not

Thank you very much Nizar Matar ! I said "mechanical recycling" as that is the way recycling plastic by extrusion is referred to in the industry. Of course, I'm not planning on making food containers with this, but I'm trying to innovate in what we can do with it.