Which material is more effected by UV rays?

[MechEng92]

We currently use a material that has been known to become brittle over time in sunlight. I have been given the material properties for the material and another material that could be a potential alternative. But I'm not sure which property to be interested in to determine it's capability in sunlight to be come brittle over time.

The properties I have been given for both of the materials are as follows:

- Melt Flow Rate (Melt Flow Index)
- Nominal Density
- Flexural Modulus
- Tensile Strength
- Heat Distortion Temperature

Other properties I have been given for just one of the materials or the other:

- Vicat Softening Point
- Flammability Resistance
- Moulding Shrinkage

Would any of these properties help determine the better material for outdoor use in sunlight? If so, which property/properties and would I be looking for a high or low value?

Thanks in advance.

 

[Pud]

None of those will give you a clue as to UV stability. What is the current and proposed material? UV additives can be used but they are not as good as using an inherently UV stable material. (e.g. Acrylic, PBT or PVC)

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[MechEng92]

The current material is H200TF40/2 - a Polypropylene Homopolymer containing 40% Talc Filler. The suggestive alternative is CA200TF30-2 - a Polypropylene Copolymer containing 30% mineral filler.

 

[Pud]

Polypropylene is pretty poor in UV. The talc and/or mineral filler is of course unaffected.
I don't quite grasp how two grades are different for UV stability. They are both PP.
The copolymer will be higher impact strength which may offset UV degradation, but I would like to hear the rationale behind the choices?

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[Demon3]

Pud is giving good advice (as usual). PP is inherently unstable to UV light. Additives make a huge difference. Particulate pigments like carbon black and certain types of TiO2 can block the UV or you can use organic additives to vastly improve the UV stability. How UV stable does it need to be? If it needs to be extremely stable then you have have to choose another polymer.

Chris DeArmitt PhD FRSC
President

Plastic materials consultant to the Fortune 100

http://www.phantomplastics.com

 

[MechEng92]

Thank you both for your input, sorry my late reply I've been out of office from Friday midday.

We buy in moulded parts of the Homopolymer from a supplier currently to fit to our units which sit outside, and we have heard reports that over time the parts are becoming brittle sitting in the sun. We heard from the supplier that this other material (Copolymer) may be better against UV rays but to be honest, I've tried asking all sorts of questions to the supplier about the properties and they never really answer my questions so I'm not sure how good their knowledge is.

 

[btrueblood]

"We buy in moulded parts of the Homopolymer from a supplier currently to fit to our units which sit outside, and we have heard reports that over time the parts are becoming brittle sitting in the sun."

So, thought about putting a tarp over them? Or are they also sitting outside when in use?

 

[MechEng92]

They're always sat outside and in use so can't be covered.

 

[Pud]

There are materials which have similar shrinkage to PP so you could use the same tooling. The problem is they are all more expensive. ( e.g. Nylon 6 - much better that PP, but not as good as PBT which is excellent). If size not important, there is always ASA, or PVC.

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[Demon3]

As mentioned, you need to add carbon black plus UV stabilizer to the PP.

Chris DeArmitt PhD FRSC
President

Plastic materials consultant to the Fortune 100

http://www.phantomplastics.com