you could try to add elongation in your process. e.g. by adding one of several harsh compression zones and to speed up the screws as much as possible.

So pre-mixing in a co-rotating twin screw extruder is ceretainly a good start, especially when you design the screws to above standards.

Careful: high pressures could overload your motor or pressure transducers.

For PA, I know that it was found that injecting water into the extruder helps a lot as they form a supercrical mixture. That effectively exfoliates montmorillonites. For PE this won't work, so you would have to go for organic solvents, which is dangerous!

What about making kind of preproduct/concentrate ??? I mean you can add earlier premixed polymer granulate.

Hello dear, your trouble is common in polymer processing, because usually occur particle-particle interaction. Therefore, sometimes is required a modifier for increasing particle -polymer interaction. An amount of stearic acid (modifier) can improve the dispersion of your nanoparticles.

The dodecanethiol is a liquid material, but when you use this compound is possible that your nanoparticles are doing aglomerate for this liquid. Therefore produce a low dispersion of the nanoparticles.

Another recommendation is that you use a masterbatch.

Best regards

Try coating the PE pellets with a suspension of your nanoparticles in a voltatile solvent (methanol, for instance) then evaporate the solvent with an air flux, leaving a thin layer of your nanofiller in each pellet. Then try to process a masterbatch starting from the coated pellets.

Kind regards.

You can try liquid assisted extrusion. In this method, nanoparticles are dispersed in some solvent such as ethanol or water which results in better dispersion in polymer after extrusion.

Here are some papers.

Article Functionalized blown films of plasticized polylactic acid/ch...

Article Water-assisted extrusion as a novel processing route to prep...

Good Luck!