Flow induced crystallization of HDPE 1

[happyam]

Hi all,

Recently, I hear about a process called "flow induced crystallization (FIC)".

After some preliminary study, it seems to me that FIC refers to the crystallization of polymer at temperature above its melting point due to the present of shear stress. And this kind of crystallization lead to the formation of Shish Kabab crystal structure.

However, I still have no idea in

1. What's the effect of the Shish Kabab structure on the mechanical properties of HDPE?

2. What's the shear stress (for HDPE) that lead to this kind of crystallization?

3. What's the temperature (for HDPE) for the crystallization to occur?

Could anyone please offer me some help in seeking for the answers for the above questions? (e.g. some books/reference?)

Many thanks,

 

[patprimmer]

I never really heard of this.

The only case of sheer induced crystallisation I am aware of is stretching during crystallisation at about the melting temperature like when spinning fibres or when flexing a live hinge where the molecules are drawn into a parallel and tight configuration to bring the intermolecular forces of attraction closer together so stronger tighter crystals quickly form.

Regards
Pat
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[btrueblood]

Using Pat's term "shear induced crystallization HDPE" returned a plethora of scholarly articles from a Google search.

 

[Demon3]

The Shish Kabab structure has a huge effect on properties. Look up Dyneema and Spectra properties and compare them to normal PE.

For example Google "Dyneema and Spectra shish kebab".

http://en.wikipedia.org/wiki/Ultra-high-molecular-weight_polyethylene

Chris DeArmitt - PhD FRSC CChem
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[patprimmer]

Chris

Even though I worked for DSM Engineering Plastics for a number of years, I had never seen the term Shish Kabab structure before with reference to a plastic so I learned something here.

The term I had seen was gel spun PE. I was of the opinion it was a second stage drawing down of the fibre in an autoclave where both the water and the temperature combined to assist in a more tightly packed more oriented crystal structure. I will now look up Shish Kabab structure on google.

Regards
Pat
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[Pud]

I had never seen the term Shish Kabab structure before with reference to a plastic so I learned something here.

Me too!

www.tynevalleyplastics.co.uk

Why be happy when you can be normal?

 

[happyam]

Thanks for replying. Now I realize that Shish structure improve the properties of polyethylene (i.e. in UHMWPE)

And I am now looking at the mechanical properties of the following polymer crystal micro-structures.

1. Spherulite of different sizes
2. Elongated spherulite
3. Columnar Crystal & Planar Crystal
4. Shishi Kabab

Hope that I could get a summary on the effect of these structures on the short term and long term behavior of polymer. Any tips for me?

Thanks.

 

[patprimmer]

Are you a student.

This is starting to sound like you would like us to write your thesis for you.

Regards
Pat
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[Demon3]

Don't forget to look at transcrystallinity (also known as epitaxial growth). That has a huge effect on properties.

Chris DeArmitt - PhD FRSC CChem
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