ABS Outdoor Application

[toyman3]

Hi , First time post but have frequently browsed for help !. I need some advise regarding a suitable material for an outdoor application , which can also be overmoulded with a soft touch TPE material.The soft touch element must be "fused" to the base material as a safety requirment. Customer wants ABS + TPE -I think this is unsuitable and was thinking SAN + TPE but I know little about twin shot moulding or SAN. I know ABS can have problems with brittle faliure due to UV degradation and as part the will subject to tensile loading (circa 50kg) , I am worried about long term performace if they insist on ABS .
Any comments tips suggestions or background information greatly appreciated.

 

[Demon3]

ABS can be UV stabilized but will discolor and become brittle. The reason is that the impact modifier in ABS is polybutadiene, an inherently unstable polymer because it contains double bonds that oxidize.

PVC is very good outdoors. An alternative is ASA but that is double the price of ABS. Same mechanical properties and molding as ABS but the impact modifier is stable so it doesn't discolor and go brittle.

If it is an extruded part then you can add the ASA as a thin cap layer on ABS or PVC to save money. ASA as a cap on PVC is how they make high quality plastic siding in the USA.

Other polymers will work too but I have less experience with those and will let Pat and Harry suggest those. Also check the recent thread "Outdoor enclosure".

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

 

[patprimmer]

Other combinations that work as elastomer/rigid combinations are nylon/polyurethane and polypropylene/Santoprene. Polyester/Hytrel can also work but the softest Hytrel is still pretty hard for an elastomer. Sorry for the trade names Santoprene and Hytrel, but they are much more widely recognised than the the technical type names.

Regards
Pat
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[corrosionman]

I,ve discussed this subject with a leading UK manufacturer of ABS pipelines - - - they also make the "Double Material" coaxial type of pipe with a range that even includes an aluminium lining - - Their opinion is that uv will degrade the surface of ABS pipes but this degraded layer then protects the remainder of the pipe material.
Their additional comment is that although the pipes are lined, the fittings (bends, Flanges Tee pieces etc) are not lined due to impossibility of lining them.
I trust this is interesting info.
Corrosionman

 

[Pud]

All of the above - ABS is crap outdoors, even here in the UK where the sun don't shine! The surface "chalks" which reduces the impact strength dramatically (also any colour is quickly changed) - it's the butadiene rubber as Demon3 indicated. (Corrosionman: the outer surface degradation severely reduces impact strength due to micro crack initiation. Never believe sales' departments!!)

As Demon3 said, ASA is good outdoors but expensive and difficult to masterbatch as well due to high melt viscosity.

If PVC (uPVC and pPVC) is not possible to to processing considerations (i.e. stainless steel tooling and same for screw/barrel assemblies), then have a look at "Orgalloy" as a combination. It's a PP/PA alloy which is available in rigid and elastomeric versions. Good UV package in as well.

As a styrenic based material "Styrosun" is an impact modified PS but the impact modifier is EPDM which has very good UV stability and it has a very good UV package in as well. No idea what to overmould with though! Nice to mould though...

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Pud is absolutely correct. ABS is very poor to UV and the surface chalking DOES severely degrade impact strength due to microcrack formation. To sell you otherwise is at best a genuine error and at worst fraud.

Regards
Pat
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