PVC vs. HDPE

The PVC is much more resistant to degeneration in the underground environment and must be somewhat thinner to maintain the flexibility that you speak of, but the HDPE is much easier to process in the injection molding process and will flex at almost any thickness needed to meet your requirements. It is not as well resistant to that environment as PVC but does well if long time resistance is not important.

I'm also intrigued at riverpirate's submission. I'm not a chemical Engineer but have extensively used HDPE and PVC pipes for cable ductings.

From experience, HDPE pipes are more resistant to harsh (including undergroud) environment than PVC pipes.

Cheers,

ethobil

Thank you for the helpful info. Cost is an issue and useful life is about 8-10 years. If PVC is selected, is there a specific type/grade I should specify? Also, I have read that black HDPE is best for degradation (vs. colors). This design prefers the product to be red. Is color a problem for PVC?

Regards,

Michael

I am not familiar with the type and grade of the current best PVC for an application such as you speak but my knowledge of the work done for PVC by the housing and particularly the window manufacturing people lead me to give PVC a mark over HDPE for your application. HDPE is cheaper but has more flex than PVC and also exhibits creep where continueing load is present which may affect loading at attachments where PVC does not show that property. The cross-linked HDPE spoken of is a better grade of PE but costs more since it requires a secondary treatment with Pthalic Acid under high pressure and temperatures and becomes PET which is the common bottle forming plastic mentioned in an earlier response, and this also is a more difficult molding material. Is your product planned to be molded or extruded?

The warning made earlier about adding colorant is pertinant since it does reduce the polyethylene resistance to environmental features. Adding an ID could be done best by an attachment device when possible without degrading the product.

The material of choice in the UK for underground services (Natural Gas & water) is MDPE with electrofusion joints into fittings. PVC was never in the running underground but it is used extensivly above ground along with ABS pipe and fittings for potable water etc

As an injection molder of plastics, I know that many molders will not touch rigid PVC because it requires special equipment (screw, screw tip, and barrel), and can give off HCl acid while it is molded. Any molder can mold HDPE. It is one of the easiest plastics to mold. There are many variations in HDPE materials available, including High Molecular Weight and Ultra-High Molecular Weight if you need extra rigidity and strength. It is also very chemical resistant, which is why it is used for gasoline tanks. This is why the plastic milk bottles should be recycled, or archeologists will be digging them up 10,000 years from now.

HDPE is cheaper per pound than PVC

be very careful with your colorants and other additives. They will play a big role in the stability of your end product.