UV Protection 1

[rmainer]

Polypropylene lasts about 2 weeks in the sun without any UV protection. About how long would it last with carbon black, HALS or other UV absorbers beside carbon black? How much longer would nylon last with UV protection?

 

[plasticsguru]

I would reccomend that you contact a UV additive supplier as they would have data on most polymers and how they react in terms of physical property retention.

 

[patprimmer]

There are many variables in UV degradation, not the least of which is the weather.

Section thickness can have a marked effect, as can the changes that constitute a failure, ie is it a failure if it breaks, or simply if it looks bad.

Even if only the surface is degraded, breakages can occur as the powdered surface is covered with tiny notches. Also, if crosslinking occurs (as it is prone to do) the surface becomes more brittle, and cracks start easier.

Carbon black only protects the polymer below the surface,as the carbon black simply blocks the UV light that hits it. Any polymer between the partical of black and the surace will be damaged. The smaller the partical size and the better dispersed the carbon is, the better the protection. The carbon is not sacrificial, so if surface degradation is acceptable, the carbon can protect for a very long time.

Carbon black can affect both the processing and the physical properties, by influencing the formation of crystals

Chemical stabilisers protect the surface, but they are normally sacrificial, so they have a finite life.

Nylon has substantially better resistance to UV degradation then PP. My experience has been with roof racks and external rear veiw mirrors on cars in Australia.

Australia is probably the most hostile place on earth re UV due to our latitude, lack of cloud cover, lack of polution in the uper atmosphere, and holes in the ozone layer in the southern hemisphere.

Permantly exposed roofracks in non stabilised, 25% GF nylon 6, with 0.5% fine dispersed carbon black, last 1 summer, at which time, they show a noticable whitening or powdering of the surface, but no significant loss of properties, as the GF reduces the notch sensitivity.

With a copper salt heat stabiliser (anti oxidant) the racks stand 5 summers before any noticable degradation occurs.

These are thick mouldings, that are occasionally exposed to high loads.

Bottom line, nylon is substantially better than PP re UV resistance, but there are many variables to consider. Regards
pat

 

[Soupcat]

Any opinions/experiences on my door panel job entitled PVC/ABS/ASA for exterior doors Pat?

Kieran

http://www.moulddesigner.com

 

[patprimmer]

Kieran
Sorry, but I stayed away from that one, as I lacked knowledge in significant areas, ie the severity (or lack thereof) of exposure to UV in the UK, and only a limited knowledge of the UV properties of PVC.

ASA is much better than ABS and I expect a little better than PVC re delta factor, which is only a measure of discolouration. It is not a measure of loss of properties, and I think it is a bit naughty of ASA suppliers to infer it is. It all depends on the application, the environment and the additive package, as well as the resin.

My experiences with ASA in a full on outdoor envoronment, under cyclic load and chemical attack in Australia, is that even though it did not discolour much, it did stress crack, where glass filled, UV stabilised ABS survived, admitedly, much to my surprise.

My experience lays mainly with nylons, polyesters, acetal, polycarbonate, acrylic, and TPX Regards
pat

 

[Soupcat]

Thanks Pat,

My application doesn't really have a mechanical function other than the fact that there are snap features holding it in place. PVC is probably the ideal material for me as resistance to discolouration is my primary concern and because of it's relatively low cost. But as you know most moulders tend to steer away from PVC and my job whilst having a relatively low shot weight is a large frame in a large tool hence a large press so the material will be residing in the barrel for a time before being injected. This is why I'm looking into alternatives and ASA seems to be the fore-runner at this stage. There doesn't seem to be a huge difference in price between ASA and UV stabilised ABS so ASA is the obvious choice between the two. As always thanks for your input.

Kieran

http://www.moulddesigner.com