LDPE process question

I'm using an extrusion of LDPE, 640i. ID .032" Wall .005". I have a process where I re-flow the extrusion, using a mandrel,FEP heatshrink and hotair. I have noticed that my pre reflow process tensile strength is about 2x of what my post reflow process strength is. Also, post process elongation is about 3x what the pre process elongation is. I believe that is telling me that the material is being annealed, and becomes more amorphous during the process.
The ID and OD do not change significantly during the process step. I used a thermal couple under the FEP heatshrink to measure the actual temperature that the material is exposed to during process, and the temperature was 425F. I tried lowering the temperature to see if that had an effect on the tensile strength of the post process material, and there was no difference. Still about half of pre process material strength.
Can someone explain what is happening? Why does the material loose half of it's tensile strength, and can I do some post processing to gain the tensile strength back? ?( Maybe irradiate the parts to recross link?)
Thanks in advanced.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I'm using an extrusion of LDPE, 640i. ID .032" Wall .005". I have a process where I re-flow the extrusion, using a mandrel,FEP heatshrink and hotair. I have noticed that my pre reflow process tensile strength is about 2x of what my post reflow process strength is. Also, post process elongation is about 3x what the pre process elongation is. I believe that is telling me that the material is being annealed, and becomes more amorphous during the process.
The ID and OD do not change significantly during the process step. I used a thermal couple under the FEP heatshrink to measure the actual temperature that the material is exposed to during process, and the temperature was 425F. I tried lowering the temperature to see if that had an effect on the tensile strength of the post process material, and there was no difference. Still about half of pre process material strength.
Can someone explain what is happening? Why does the material loose half of it's tensile strength, and can I do some post processing to gain the tensile strength back? ?( Maybe irradiate the parts to recross link?)
Thanks in advanced. ------ During your reprocessing you seem to be losing the orientation of the polymer in the extrusion direction. If high stresses are induced during the extrusion process, you could be seeing an exaggerated effect.
Crosslinking should increase your tensile substantially (with a loss of elongation), as well as increase resistance to abrasion.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

E-beamed five sets of pre and post processed material (low tensile) to 150, 170, 190, 210 and 230kGy, The tensile testing results did not have a substantial increase in post process tensile strength. The extruded suggested that I should try annealing the post process parts at 165F (74C) for 30 minutes. I tried this at both 74C and 84C for 30 minutes, and still no increase in the tensile strength. Does anyone have additional thoughts or ideas?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

E-beamed five sets of pre and post processed material (low tensile) to 150, 170, 190, 210 and 230kGy, The tensile testing results did not have a substantial increase in post process tensile strength. The extruded suggested that I should try annealing the post process parts at 165F (74C) for 30 minutes. I tried this at both 74C and 84C for 30 minutes, and still no increase in the tensile strength. Does anyone have additional thoughts or ideas?
--
If you're aiming to add tensile strength to the raw extrusion, you
could ask whoever is making your tubing to maximize crystallinity of
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.