Posts: 15
From:milton keynes england
Registered: Aug 2005

posted January 23, 2006 09:58 AM               

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Has anyone suffered these problems with off grade material
I purchased some off grade ldpe mi 1 to 3
which should have possed no problem in extruding material as we use a mi of 2
however after running a few tonnes of this material we started to get an affect as if water was in the material quite drastic
infact it was totaly unusable even as low as 5 % of our blend.We sent this for analysis which came back saying it had a percentage of Silica master batch. would this cause the affect I have described ? any input would be appreciated as the company I purchased this from are being quite unreasonable I shall not
mention their name at present but if this is
not resolved I shall to preworn anyone else
from the troubles I am having.

5%

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Posts: 36
From:bethesda MD USA
Registered: Sep 2001

posted January 30, 2006 12:26 AM            

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Silica won't absorb water but silicates will. Do you have a clear number for the percent of silica? A small amount of fine silica particles is used as an antiblock for film, but a lot of silica will give you a sandy surface (it is, after all, sand), not the bubbles and holes typical of moisture.
Are you sure there isn't anything else in it (e.g., foaming agent)?
Is it in pellet form? If not, it may be trapping air. Slow down and if it disappears suddenly, that's it. Your only recourse then is to pelletize it, or run it in a vented extruder.
The baffling part of your post is that it runs OK for a few tonnes, then does this moisture-like thing. If it is due to an additive or its particle form, that should show up right away.
I hope this helps.
Allan Griff
Consulting Engineer
algriff@griffex.com

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Posts: 15
From:milton keynes england
Registered: Aug 2005

posted January 30, 2006 04:37 AM               

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Hi Alan
Thanks for your reply
What has happened the first few tonnes of material did not have this in
Whan we started another batch we had this problem,when we had it anylised what should have been a off spec PE MI 1 to 3 actualy
had 5 different Type of PE including a silica masterbatch all in granule form
when I informed the supplier they said they have had no other complaints.But it is just impossible to run on our machines we run a cast film line and the material coming out is if you like pebble dashed
John Green

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