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UV stabilized plastic reccomendation
5

UV stabilized plastic reccomendation

UV stabilized plastic reccomendation

(OP)
I have a thermoformed HDPE cover that is used outdoors as a machine guard.  After a few months in service the part becomes brittle and fails. Can anyone reccomend a material that has similar mechanical poperties with enhanced UV stability? The color must be white or a carbon black would be substituted. Also the production volume is fairly low so a higher priced stocked material would be preffered to an X ton minimum order. Would a TiO2 additive help?  

RE: UV stabilized plastic reccomendation

There are plenty of options.

Firstly, the HDPE would work with carbon black and proper UV stabilizers. Other alternatives are PP and ASA (the latter much more expensive).

Chris DeArmitt PhD FRSC CChem

www.phantomplastics.com
Consultant to the plastics industry

RE: UV stabilized plastic reccomendation

PVC is another great choice for outdoors and has the advantage that it's intrinsically flame retardant and cheap.

Chris DeArmitt PhD FRSC CChem

www.phantomplastics.com
Consultant to the plastics industry

RE: UV stabilized plastic reccomendation

I like Pud's suggestion best, but then I like Royalex too, makes great watercraft hulls.  For the outdoor machine guard application of the OP, it would save weight for the same stiffness, and has a gentler failure (i.e, a ductile yield rather than a brittle snap like PVC can give).

But, I also think the OP owes three stars for the prior posters, all of whom gave quite good info., as usual.

RE: UV stabilized plastic reccomendation

(OP)
Thanks for the replies.  Does white PVC have better UV properties than a white PP or HDPE?  

RE: UV stabilized plastic reccomendation

Yes, presuming the same pigment formulation.

Not all pigments of the same colour offer the same UV protection.

eg, Carbon black is impervious to UV light while Nigroseine has no effect at all. Both are black.

Also particle size and quality of dispersion of the pigment has a significant effect om results.

Regards
Pat
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RE: UV stabilized plastic reccomendation

A weatherable sign grade of PC could work but it is not as easy to mold and the shrinkage may not match up with HDPE. However, it will make a nice strong guard. Look through the Spartech catalog for other options.

RE: UV stabilized plastic reccomendation

Good point Pat. I have seen PC guards self destruct because of exposure to brake clean.

RE: UV stabilized plastic reccomendation

(OP)
I have found a UV resistant HDPE called Marine Board.  Would it have the same processing capacbilitites as a standard HDPE?

RE: UV stabilized plastic reccomendation

Check the MFI to see if the viscosity is the same as the PE you are used to.

UV stable PE should process the same as all you need is 1 % carbon black and the right UV stabilizer, e.g. HAS (also known as HALS in the old literature).

Chris DeArmitt PhD FRSC CChem

www.phantomplastics.com
Consultant to the plastics industry

RE: UV stabilized plastic reccomendation

If they are both extruded sheet with about the same dimensions and form, I would expect they are both probably fractional MFI and would process the same, however that is not a guarantee and as Chris states you should check.

If the supplier gives you a blank look when you ask what is the MFI, you can get a real rough idea by placing small offcuts of both, side by side in an oven and test them as they start to melt. If they are both about as bendy or malleable as each other you are probably OK. It is a real rough test, but might be all you have available.

Regards
Pat
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RE: UV stabilized plastic reccomendation

You can give it a try. Send the data sheet to your thermoformer.

MFI isn't as important with thermoforming like it is with injection molding. There is a hot strength test which is more relevant (but I forget it's name).

I would worry more about forming temperature and shrinkage. The orientation of PE sheet is important and can make a big difference in the sag of the sheet and the shrinkage. However, if you ordering small lots you won't get to specify this.

RE: UV stabilized plastic reccomendation

Attempts to describe viscosity of melted plastics getts a lot of different approaches and terminology depending of whos telling for what reason.

MFI is used to attempt to describe how easy a plastic will flow in the mould It is used by pretty much injection moulders. It is a poor method but is easy to do and comprehend.

Molecular Weight is used by polymer chemists.

Melt viscosity is used by physicists.

Melt strength is used by blow moulders and extruders in a descriptive manner, but they still use MFI for a quantitative measure.

You want high melt strength which is low MFI. Fractional MFI is less than or a fraction of 1.

Regards
Pat
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RE: UV stabilized plastic reccomendation

Great post Pat.

Chris DeArmitt PhD FRSC CChem

www.phantomplastics.com
Consultant to the plastics industry

RE: UV stabilized plastic reccomendation

Extruded millions of feet of vinyl siding, and I can tell you that PVC has poor UV characteristics unless it specificallay has an inhibitor blended in.

RE: UV stabilized plastic reccomendation

Same for many plastics. Even ASA which is extruded onto PVC siding to improve weatherability needs UV stabilizers and titanium dioxide to withstand UV.

Chris DeArmitt PhD FRSC CChem

www.phantomplastics.com
Consultant to the plastics industry

RE: UV stabilized plastic reccomendation

(OP)
So TiO2 is used as a UV stabilizer?  One material manufacturer said it was an antioxidant and didn't specifically serve as a UV blocker.  My thermoformer thinks the Marine board will form the same as regular HDPE.

RE: UV stabilized plastic reccomendation

TiO2 is a white pigment. It has at least 2 crystal forms. The rutile form blocks UV light but a lot depends on particle size and distribution. Carbon black also blocks UV light. Same deal re size and distribution.

It can only protect what is behind it, not what is in front of it.

Stabilisers that dissolve at a molecular level are required to protect the surface. There are numerous types and different modes of action. Different formulations are used for each polymer. To explain it in full detail would be a few hundred pages.

Grey "outdoor PVC normally contains TiO2 and carbon black to get the grey colour. It also contains some antioxidants (previously lead compounds, but now more likely tin compounds) and cheap mineral fillers.

 

Regards
Pat
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RE: UV stabilized plastic reccomendation

TiO2 was the primary UV blocker in our siding. Tin was a heat stabilizer and various waxes where lubricants. Yesteryear lubricants did have lead content.

RE: UV stabilized plastic reccomendation

2 questions
1. Anyone have recommendations on a UV blocking PP that is FDA compliant (injection moldable)?
2. If I wanted to spec a resin that blocks 90% of UV light from passing through how would I do so? Is there an ASTM spec? As I understand ASTM D1003 Haze isn't the right thing.  

RE: UV stabilized plastic reccomendation


qtg836b: suggest you start a new thread rather than hijacking this one - you will get a better response.

You will also need to define your requirements much more than you have done...

H

www.tynevalleyplastics.co.uk

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