HDPE Wicker 1

[rjindal]

Hello
We are manufacturers of outdoor furniture and manufacture HDPE wicker (Plastic Cane) to be used in our furniture. Visit our website

http://www.loomcrafts.com

to see our products. We manufacture our wicker using HDPE (Bought from Reliance) and add UV in it. This wicker has to be very durable for outdoor conditions as this furniture is used all the time in outdoors. We are facing a problem of breakage of our wicker after some time of usage. Please suggest us if any kind of additive can be added so as to increase the tensile strength of the cane.

 

[tom1953]

It sounds like the UV protectants you're using are not adequate for your needs. Is this a new problem or a continuing one? If it's new, then maybe something has changed in the UV additives or the HDPE. If it's a continuing problem, then maybe looking at different types and/or amounts of UV stabilizers would be beneficial.

Suppliers of UV stabilizers like Ciba can provide assistance, if they're not already.

Good luck!

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[rjindal]

Is UV responsible for breakage also or is it the tensile strength we falling short off. This is a new problem after we changed our grade of HDPE from one company to another. The problem is not of fading of color in the sun but of breakage. Please suggest how to increase the tensile strength of the polymer, is there any filler which can be added.

 

[IRstuff]

Are they breakable when brand-new? If not, then it's UV damage.

TTFN

FAQ731-376

 

[tom1953]

UV exposure can definitely affect physical properties, as the effect is one of breaking polymer chains.
tom

 

[Demon3]

Yes, it sounds like UV is attacking the polymer so the tensile strength and elongation to break both decrease with time in the sun.

UV protection does is not the same thing from one supplier to another. There are lots of different additives, some better some worse and one supplier may use more UV stabilizer than the other. Your change to a cheaper material may cost you more than sticking with the old supplier.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Some people use UV opaque pigments as UV protection, but this does not protect the surface, just the matrix. If the surface degrades, it forms a powder like surface which is evidence of micro cracks. These cracks then propagate and cause breakage. You need a UV stabiliser that dissolves in the polymer and protects the surface by chemical action, not just by being an opaque particle.

Also, a good way to improve tensile in such a case is to improve elongation as that allows more load sharing between strands. An increase in molecular weight will improve both tensile and elongation and will also provide more in reserve to resist UV degradation.

UV degrades the polymer. Fading of pigments can be from UV or visible light so your comment re UV and fading is a bit off the mark.

A grade of HDPE with no nucleating agent present would help tensile and elongation. Many things like some pigments for instance can act as nucleating agents.

A small amount of vinyl acetate in the HDPE alos greatly improves elongation and stress crack formation. While it decreases tensile on lab test mouldings, it generally increases tensile of an unevenly loaded fabric as is the case in your outdoor furniture. Once again the effective tensile is improved by improved load sharing due to improved elongation.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[rjindal]

Yes, we are adding UV opaque pigments while extruding. As suggested we will contact CIBA and trial there UV stabilizers. Also someone else suggested us to use TPR (Thermoplast Rubber) around 3-5% to increase the tensile strength and elongation. What do you suggest. We have got our wicker made just of pure HDPE and no additives tested and got the below result:

1.tensile peak - 147.66 Kg/Cm Sq
2.tensile break - 142.68 Kg/Cm Sq
3.elogation peak - 23.86%
4.elogation Break - 760.57%

Now we need atleast 230 Kg/Cm Sq of tensile strength and the elongation is fine.

 

[Demon3]

The initial properties are meaningless. It's the degradation of properties after UV that is the problem. A meaningful test would be to expose your sample to UV e.g. Xenotest and then measure properties. The % loss of tensile strength and elongation to break tell you how well your UV stabilizers are working.

You said you use UV opaque pigments. The most popular is TiO2 (titanium dioxide) but that can actually attack your plastic when the sunlight hits unless you buy the right grade.

TiO2 when exposed to UV generates free radicals that rip your plastic to pieces. To prevent that, TiO2 is coated to shield the plastic from it. Some grades are well coated, others not.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[rjindal]

So maybe the UV pigments we are using might not be coated well which is resulting in the plastic degradation. Also let me know about the TPR, is it going to help in anyway.

 

[Demon3]

Does the part ever fail when new before it's been in the sun? If not, then adding elastomer to improve the initial properties won't help because the initial properties are not the issue.

If the new items fail then adding elastomer will increase the elongation to break but slightly reduce the yield strength. So, if the former is your problem then great, if the strength was the issue then the elastomer will harm your product.

It is most likely that the TiO2, other pigments or lack of proper UV stabilizer are the problem, not the new properties. We can't tell you for sure, you'll have to do tests to find out.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Chris

While elastomer decreases the strength of a single test bar, it can increase the strength of a woven fabric that has uneven load on a number of strands as the most heavily loaded strand yeilds more and allows the other strands to take a bigger portion of the total load. This is especially evident with higher MW but also shows up with elastomer.

The modifier of choice for PE manufacturers last time I was in the loop was VA. With up to 5% VA they don't even declare it as EVA, they simply call it high stress crack resistant PE.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Demon3]

Thanks for the explanation Pat. Makes complete sense. You can also add SBS like Styroflex at 3-5% as an elastomer in PE but in this case that would not be the right choice because it's not UV resistant.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry