How Do I Re-Polymerise Old Post-Consumer HDPE

I don't think there is a way .... I think limited amounts of regrind can be used with virgin material. If you find a way round the problem you will probably become very rich...
Maybe someone can offer some hope?

Del

Based on my experience, i think your problem is not de-polymerization but oxidation of certain properties of HDPE. You can try using paraffin wax or any lubricant suited for Ethylenes.

HTH.

Hi Guest!

It's an important question, so please be kind enough to report back when you find a suggestion that seems to work well, or a working solution to your problem.

Thanks,

Mark

I agree with Nelson, I don't think it is depolymerization. It is most probably oxidation and/or contamination with other scrap material. The only way to rework it is to blend it with virgin material but be careful, the product you are producing will have less tensile strenght than when using only virgin material.

I agreed with PADDLER. Polymerization is an irreversible reaction and several types of PE can be obtained. If you want to use again the used PE, be careful with the application to use. Actually, some companies are recycling most of the polymers to recover the monomer, which is hard to do it without the right technology, or re-use the polymer itself to make disposable containers.

I see your point. Since the thread starter and I are into recycling, could you enlighten us re recycling polymers to recover monomer? What is the right tech to do this?

I am unaware of any polymers that are being converted back to monomer. But I only know thermopplastices like PVC, PE, Poly propylene, ABS, Polystyrene, and Polybutadiene, acrylics and some acrylate. There are many more polymers I don't know about and would like to hear. Some of these are being stripped of monomer down to less than one part per million (monomer in polymer) and monomer cleaned and recycled. I am not as familiar with the thermosetting plastics.

I think what CHEMRICDO meant to say was that the value of the monomer is now in polymer form. The polymer waste, oversize sweeps, reactor cleanings can be collected and ground, blended, remelted and otherwise recovered.

Some heating value can be recovered by burning and (hopefully) scrubbing the stack to recover chlorine if it is PVC.

To undo the polymer chain and reform the double bond would not be practical. If anyone knows activity in this area, please respond.

The initial question was how to re-polymerize old HDPE. This means the polymerization must be carried out again from the ethylene monomer. The ethylene monomer can be obtained from the dehydration of ethanol, hydrogenation of acetylene, cracking of natural gas (ethane or propane) followed by purification process. As the polymer reaction is irreversible, a lot of energy must be used for cracking the polymer into small molecules (methane, ethane, propane). Once ethane or propane is obtained, a new cracking will be necessary to carry out to produce the ethylene monomer. This of course is more time consuming and expensive. Therefore, re-polymerization is not a cheap way to do using HDPE.

From EXXONMOBILE:

Barrier fuel tanks for automobiles may be built of incompatible polymeric layers, for example, virgin HDPE, an EVOH barrier layer, polyamide, and a regrind layer, attached with adhesive or tie layers. Blow molding or thermo-forming of fuel tanks can produce up to 60% trim waste. Manufacturers attempt to reuse this waste as an extra regrind layer. Unfortunately, these materials tend to form incompatible particles when reground, resulting in poor impact properties, and limiting the amount of regrind that can be used in the final structure to less than 35 wt%. Adding low-density metallocene polyethylenes to the regrind improves particle compatibility and enables an increase in the amount of regrind that can be used--up to 45 to 50 wt%. The low-density metallocene polyethylene has 50,000 to 200,000 number average molecular weight and low polydispersity. The amount of low-density metallocene resin added to the regrind layer is 3 to 20 wt%.

When i worked for a cable overmolder the most regrind we could use was 25% as it produced cosmetic blemishes. Mainly depends on what the finished product is.