Quite often we find plastic items of different rigidity which belong to same type. For instance, LDPE is used mostly for films and bags, but sometimes thick and rigid containers are also made.

Can we (after shredding) extrude together two items of same type but different rigidity? Will the rigidity of output material be uniform?

  • $\begingroup$ Your "rigidity" isn't really a property of substance itself. $\endgroup$
    – Mithoron
    Jan 6 at 15:22
  • $\begingroup$ Mechanical properties are (not only) a property of the substance. A plastic bag is so flexible because of the blowing process that creates the film, of course. But then you don't use the same PE type for film blowing than for other uses. $\endgroup$
    – Karl
    Jan 6 at 16:46

1 Answer 1


Yes, certainly.

If it's all LDPE, you get a uniform LDPE afterwards.

During extrusion, large extensional deformations are applied to the melt, which will completely homogenise the material.

Of course you don't get a defined quality ("grade"), unless you have very good control over the relative proportions of different LDPE grades that go into your recycling.

I assume you know that no two LDPEs are quite the same, on a molecular level and also in the resulting mechanical properties. Although they're not nearly as diverse as HDPE or LLDPE.

And please note, film blowing (plastic bags etc.) creates a frozen-in two dimensional orientation of polymer chains in the material. The mechanical properties are totally different then.


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