As a lubricant for processing

This also the function of ca- searate, so why we need zn stearate as well,sir?

Is this the only function for zn stearate?

better lubricating and processing of polyethylene than Ca stearate

Do not know especially this PE case but Ca is often recommendable to be used in combination with other, more active or more valuable carboxylates. The Ca salt contributes then ad a buffer against depletion of the primary carboxylate.

Dear Adel,

Although Ca and Zn stearate have a lubricating effect in PE, if there is need for lubrification at all, PE and PP waxes are the better internal lubricants, while amide wax and glycerol monostearate are typical external lubricants. The main function of Ca and Zn stearate in PE resins is that of an acid scavanger, i.e. they efficiently neutralize free acidity from catalyst residues. Zn stearate has a lower melt point (120°C) compared to Ca stearate (mp 155 °C). Certain blends of Ca and Zn stearate have even lower melt point ranges between 100 to 110 °C. However, Zn stearate has a lower tendency to cause turbidity and for that reason is preferred for transparent applications. For more info please refer to C Kröhnke, Polymer Additives, In: K. Matyjaszewski, M. Möller (eds.) Polymer Science: A Comprehensive Reference, Vol 8 Polymers for Advanced Functional Materials, K. Müllen, C. K. Ober (Vol. Edts.) Elsevier, Amsterdam, Oxford, Waltham (2012) pp. 349-375 and Technical Infos from suppliers such as Bärlocher, Faci or Ferro.

Best regards

Rainer

-----------------------------------------

Dr. Rainer Höfer

Editorial Ecosiris

Klever Str. 31

D- 40477 Düsseldorf

Tel.: +49 (0) 211 4920479

Fax: +49 (0) 211 4920477

Mobile: +49 (0) 172 2418861

E-Mail: [email protected]

www.ecosiris.eu

------------------------

Dear dr

many thanks.i really liked your answer.it is so helpful and knowledgeable. Now i have more specific question :

why we need the synergistic effect of both ca and zn stearate in pipe grade polymers where the turbidity is not a matter of concern??

Dear dr

actually the reference u mentioned seems to be fascinating. Unfortunately since i live in iran i cant pay for it through the internet. Anyway thanks a lot for being so kind and helpful.

Much obiged

adel mazraeh

process engineering head

Dear Adel,

I guess in PE pipes Ca stearate would do the job unless you like to take advantage of the better lubricity of Ca/Zn stearate. Eventually it does make sense to contact Battenfeld Extrusionstechnik GmbH for further details about hte extrusion of PE pipes. Ca/Zn stearates are also used as heat stabilizers for PVC having replaced Ba/Cd based stabilizers (ref. R. Höfer, Processing and Performance Additives for Plastics. In: K. Matyjaszewski, M. Möller (eds.) Polymer Science: A Comprehensive Reference, Vol 10, Polymers for a Sustainable Environment and Green Energy, J. E. McGrath, M. A. Hickner, R. Höfer (Vol. Edts.) Elsevier, Amsterdam, Oxford, Waltham (2012) pp. 369-381)

Best regards

Rainer