Re: PVC vs PE

In general, PVC is much better suited to outdoor exposure than PE. It's >used
>> for vinyl siding, electrical conduit and pool liners to name a few. > > Is this really true? I thought PVC itself is not stable against >UV, but has to be stabilised with certain additives. Judging from >practical experience with PVC-covered aluminium windows the >reason to use PVC is not its stability in outdoor environments. > > Oliver

My comments refer to formulated plastics in the actual outdoor applications described. I didn't intend to comment on UV resistance of unmodified polymer samples.

PVC condiut and pipe are known to have service lives measured in decades for outdoor exposure. No similar examples come to mind for PE even though this might be possilbe for with the right additive package.

Typically, the only UV additive in a weatherable PVC formulation is a rutile grade of TiO2. The level of TiO2 depends somewhat on the heat stabilization system used. Pb based and Ca-Zn based stabilized formulation use about 4-5 phr of TiO2, while Sn stabilized formulations use 9-10 phr. The level of heat stabilizer is also typically increased for weatherable formulations. This is done to minimize the number of ayllic CHCl groups formed during processing that can then act later as UV degradation sites. However, to boost performance in harsh evironments such as Arizona, many PVC build products are being coated with an acrylic top coat.

PE and PP typically need an additional boost from hindered amine light stabilizer (HALS).

Is one more weatherable than the other? Well, PVC is used in siding, window profiles and roofing membranes with service lifes of 15-20 years and of course for years in automotive applications.. On the other hand HDPE is used in blow molded outdoor toys and storage sheds that have similar life spans. TPOs based on PP are used in many automotive applications including bumpers and side panels and soon might be making inroads on conventional f-PVC interior applications such as door panels and perhaps instrument panel skins.

So, I think the conclusion is that any polymer with a saturated chain can be used in weatherable applications if the appropriate stabilizer package for its chemistry is employed.

Larry Effler

applications