Coextrusion, bonding strentgh
Coextrusion, bonding strentgh
(OP)
Hi,
I have a question regarding the bonding strentgh between 2 polymeric materials in coextrusion. I would like to know how the bond strength varies with temperature? Does it decreases until Tg, Tm? or it just drop once reaching them? or combination of both?
Thanks
Manu
I have a question regarding the bonding strentgh between 2 polymeric materials in coextrusion. I would like to know how the bond strength varies with temperature? Does it decreases until Tg, Tm? or it just drop once reaching them? or combination of both?
Thanks
Manu





RE: Coextrusion, bonding strentgh
1. Time of contact, longer contact time in the melt gives time for entanglement and improves bond strength
2. Compatibility of the polymers. As a crude estimation look at the polarity or better the solubility parameters for each polymer (available on the web or in the Polymer Handbook). Polymers of similar polarity will mix and give good bond strength.
3. Molecular weight. High molecular weight will give better bond strength if you give it enough time for entanglement. Lower molecular weigh can diffuse faster so it may give better bond strength for short melt contact times.
4. Temperature. High temperature increases polymer mobility, allowing entanglements to form and thereby improving strength.
5. Impurities. Low molecular weight additives like antioxidants and stearates can decrease strength by collecting at the interface and forming a weak boundary layer (low molecular weight additives cannot entangle and have no strength).
6. Compatibilizer. You can add a block copolmer where each of the two blocks is soluble in one of the polymers to be co-extruded. The compatibilizer can span the boundary and entangle with each phase, improving strength.
7. Use a tie-layer, i.e. a polymer of intermediate polarity co-extruded in a thin layer between the two other polymers to be bonded.
For a book that explains this very well, with data, see...
Polymer Interface and Adhesion by Souheng WU
ISBN 0-8247-1533-0
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
RE: Coextrusion, bonding strentgh
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
RE: Coextrusion, bonding strentgh
That's the sort of information that makes this site a great place
With your permission I will print it off and use it for my plastics trades students.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
RE: Coextrusion, bonding strentgh
Nice one Chris - star indeed for an informative and concise "over the top" post.
I assume similar criteria apply for overmoulding applications?
I hope the OP does the same - star for you!
You have too much time on your hands....
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: Coextrusion, bonding strentgh
I know few things that you say. The problem is that so far i have to deal with the material we have, which is i think already well engineered (on a bond strentgh point of view). The only problem is that i have a different application ( ie on temperature). According to what you say the bond strength decreases above Tg. One of my material is PP whose Tg is about -10C. Therefore i have to expect the bond strength to decreases. How weaker will it be at 90C? Does the bond strength decrease lineary up to Tm?
Thanks again
Emmanuel
RE: Coextrusion, bonding strentgh
Cheers
RE: Coextrusion, bonding strentgh
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
RE: Coextrusion, bonding strentgh
Corona treatment would only affect bonding if you had treated the interface to be bonded so a post treatment on an already bonded specimen should have no effect.
If PP is one of the two materials then what is the other? Knowing that may allow us to help you better.
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
RE: Coextrusion, bonding strentgh
RE: Coextrusion, bonding strentgh
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
RE: Coextrusion, bonding strentgh
Cheers,
manu
RE: Coextrusion, bonding strentgh
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