Improving adhesion of LLDPE to steel during rotational lining of pipes 1

[rotoliner]

We are currently using an imported LLDPE powder (ICORENE 1869) for the rotational lining of pipes that seems to perform well. Unfortunately the lead time to obtain is very long. We are refurbishing pipes where we burn off the old coating in a cleaning oven, make welding repairs if required, grit blast to white metal and then line the interior of the pipe including flanges with LLDPE to about 4-6mm in thickness. The pipes are used in seawater applications for ships like cooling systems and ballast systems. Temp range about 2 to 40 degrees celsius for the seawater. Most pipes are DN250 to DN600 in diameter. We turn the pipes in two axis and put in a 3.5 meter coating oven to melt the PE powder to the pipe.

We are importing and using the ICORENE 1869 because it is sold as a rotolining grade of LLDPE with the characteristics of superior adhesion to steel and it is a proven product. Is anyone aware of any other LLDPE rotolining grades of LLDPE that are available in China?

Is anyone able to explain how LLDPE is modified to improve the adhesion to steel?

 

[CoryPad]

I am not certain about China availability, but LyondellBasell offers Microthene resins for rotational lining applications.

One method for improving the adhesion is to add reactive functional groups to the polymer chain, as described in this document:

http://www.lyondellbasell.com/techlit/techlit/Brochures/Guide to Rotational Molding 5717.pdf

 

[rotoliner]

Thank you for the advice. I met the Lyondonbasel sales rep at the Chinaplas trade show last week. Apparently the microtherm product you mentioned is not sold in China. I took a look at the link you included and it to me to a Rotomoulding guide. I read it and did not see anything about the additives you mentioned to improve adhesion to steel substrates. Would be appreciated if you could check the link and repost. Thanks

 

[Demon3]

The reason PE doesn't stick to metal, or anything else, is that it's non-polar. Silicones and Teflon are also non-polar, i.e. have a low surface energy and don't stick to anything. There are no chemical groups on the PE chain that can attach and form bonds to the metal.

The way to solve that is to add some reactive chemical groups in the PE chain. This forms a so-called coupling agent. An example would be maleated PE or PE with acrylic acid groups added to it. These reactive groups can dock on the metal and attach the PE more strongly. Several companies make such modified PE products. One well-known brand is Epolene. This chap seems to be a good person to ask:

http://www.westlake.com/fw/main/epolene----ask-dr--stuart--378.html

One adds some of that product to the normal PE resin to improve adhesion.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world

http://www.phantomplastics.com

 

[rotoliner]

Thanks, I have reached out to Dr. Stewart.

 

[rotoliner]

I just received an additive which the China supplier is calling MAPL and also using a code 7701-2 as a description. The directions say to add 1% to the PE powder to improve the adhesion to steel. It improves the adhesion although it turns the White Lldpe powder a bit yellowish in the finished product. The Color does not matter since it is inside a pipe. Does anyone have any idea if this product changes any of the properties of the PE and does anyone have a data sheet or technical description? A MSDS would also be nice since unsure if any safety issues.

Everything you get in China is top secret!

 

[Demon3]

Check the safety datasheet and see what it is. Probably the same maleic anhydride grafeted PE I suggested.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world

http://www.phantomplastics.com

 

[Demon3]

They have to provide one...

Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world

http://www.phantomplastics.com

 

[rotoliner]

Chris, in Europe and the USA, they have to give a MSDS, in China it is not uncommon for there to be no data sheet for the product. This is especially the case of the additive is compounded in a small lab.

 

[Demon3]

You can do FTIR on it to see if it's maleated PE. Look for the carbonyl peak around 1800cm-1. Any decent lab can do it cheaply. Or contact a reliable supplier like Eastman or Cray Valley and get it from a source who will tell you what you're buying. Plus at only 1% loading the effect on cost will be low no matter who you buy from.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world

http://www.phantomplastics.com

 

[Demon3]

By the way, there is a second type of additive that should improve the adhesion. Moisture cross linking polyethylene is made by putting organosilane groups on the PE. Those react with moisture and bond to silane groups on other nearby PE chains. It's described here:

http://www.plasticstoday.com/articles/one-step-process-extrudes-crosslinked-pe-pipe

and here

http://iwcs.omnibooksonline.com/data/papers/2011/5-4.pdf

If you were to add 1-3% of that silane derivatized PE to your normal PE, the silane should bond to the metal and improve your adhesion. It works the same way as the maleic anhydride but uses different chemistry to make the bond.



Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world

http://www.phantomplastics.com