Mixing of two polymer particles heated above Tg

[Excom]

TL;DR

Can two polymer particles heated above Tg be mixed? Mixed, meaning that the two particles in the end will share the same surface.

I am wondering if two polymer particles, of same kind, heated above Tg can be mixed, over time, if they are squeezed together. By mixing I mean that the surfaces of the two particles will mix into one after they are squeezed together.

For simplicity let's assume that the polymer particles are 100% amorphous.

 

[ChemAir]

Can you clarify what you mean by"two polymer particles" and "of same kind"? Do you mean the same polymer, the same type of polymer, polymers with similar glass transition, or something else?

 

[Excom]

Same polymer, same glass transition temperature, same size, same everything.

Regarding the size: >10 um to avoid strange effects at the nanoscale.

 

[ChemAir]

Is there a particular reason for your question?, i.e. why you would think it not possible?

Normally when making stuff out of plastic, resins or pellets are combined (melting, extruding, molding), so manufacturers are doing exactly what you are asking--combining many single pellets into a larger piece by heat application. Plastics are also commonly compounded (heated and mixed with other polymers and additives) above their glass transition to make compositions with unique properties.

In PVC manufacture (not pipe) "color concentrates" are manufactured for PVC compounders that don't have the ability or desire to handle raw pigments. A color concentrate is just PVC plastic with a very high pigment load. These are added to white (virgin) PVC to adjust color for consumer products. Also, scrap material is regularly recycled and incorporated into certain grades. This doesn't mean there is a new chemical bond or chain lengthening when the blending occurs. Just that you have a larger amount of amorphous polymer after combination. So yes, compatible plastics can be mixed at temperature, and are, often.

Also, in underground piping, it's very common to do a heat fusion weld on thermoplastic piping to repair, connect or extend it.

Two "pieces" of the same polymer that can undergo reversible glass transition/melting should be compatible.

Did I miss the point of the question (I'm prone to)?

 

[Excom]

Thanks for the reply.

I get that mixing is possible when heated above the melting temperature but is it also possible when heated above the glass transition temperature but below the melting point?

In real life the polymer will have some degree of crystallinity. In this case, is it necessary to go above the melting temperature before mixing/merging of the polymer particles becomes possible?

 

[ChemAir]

Thanks for the reply.

I get that mixing is possible when heated above the melting temperature but is it also possible when heated above the glass transition temperature but below the melting point?

In real life the polymer will have some degree of crystallinity. In this case, is it necessary to go above the melting temperature before mixing/merging of the polymer particles becomes possible?

I don't know that, specifically, but plastics are generally difficult to transfer heat to, and it takes a good deal of mechanical energy to mix them, which also adds heat. I don't believe the temperature in an extruder is remotely uniform on a micro-scale, so it seems possible there is at least some portion of the material that is in the area above glass transition, but below melting, but it may be academic. As difficult as it is to mix polymers, it is harder to measure an accurate temperature profile on material being mixed, so I'm not sure how you would be sure.

Mostly, I believe factories will blend and extrude with the following in mind:
-Makes desired quality--No thermal decomposition, or insufficient mixing
-Fastest/easiest processing
-Most energy efficient

If the conditions required to meet the above, happen to create a situation that is near the margin between TG and melting point, that's just what it is.

My plastics experience is with PVC compounds and nylon, and I'd hesitate to speak on all polymers with that limited experience. I'd expect, however, that money, energy, and quality will still be just as important.

 

[Excom]

Thanks for the reply.

My question is more driven by getting an understanding on what does it mean when a polymer is above Tg and below Tm. Money, processing time etc. is not important for now.

When read about it, polymers heated above Tg are no longer brittle and they can now be plastic deformed. However, is the above Tg behavior sufficient for mixing/fusing of polymer particles? I don't think so but then again, if I read about sintering of materials I am no longer so sure.