Summary of Responses - Polypro Shrinkage (1 of 2)
William Lifford
Description
Collection
Title:
Summary of Responses - Polypro Shrinkage (1 of 2)
Creator:
William Lifford
Date:
9/25/2003
Text:
Hello Colleagues....
Here are the responses for my post, Polypropylene shrinkage - Prosthetic Outer Sockets/Frames. I've included the original post in case some of you are interested. Thanks to all of who who replied... perhaps these responses will help a few of us out there!
Bill Lifford, C.P.
My original post read as follows:
Lately it seems as though many of our facility's polypropylene sockets shrink quite a bit. Sometimes, though, the shrinkage seems to be
circumferential and other times it seems to be longitudinal.
What are some methods we can use to control or reduce this shrinkage? I would rather not laminate everything, due to the dust created while
grinding laminated sockets; however, it frustrates me to have our technician pull a polypro frame for an AK socket and then have the thing
wind up being significantly shorter than the flexible inner socket. At least I know when I laminate a rigid frame, it's going to fit over the
flexible inner socket exactly when I'm done.
Also, with regards to circumferential shrinkage, is there a factor you can adjust for in fabrication, knowing that the shrinkage will occur? By
this I mean something along the lines of putting a sock (# of ply?) over the flexible inner socket before pulling the polypro over it. We use the
Fillauer shuttle lock a lot and so we often have BK sockets with a flexible inner socket and a polypro rigid outer socket. Once again, it's very
frustrating to have a check socket fit really well, then mold a socket over the exact same cast, and then have the definitive socket be too small to
the point where it's impossible to don!
Thanks for your help with this... any advice you can provide might help my professional life be far less stressful :)
Bill Lifford, C.P.
The responses were:
Our understanding is that the primary reason for plastic inconsistency is because material that contains re-ground material from edge trimmings is often put back in at the extruder to save costs. Mixing in material that has been through more than one heating and cooling cycle creates inconsistencies at the molecular level, making for stresses in the plastic that causes distortions such as shrinkage or spreading after cooling, as well as material waste from failed pulls. A little more about this topic may be found on page 464 of Knit-Rite catalog 14.
Mark Smith, CP
Knit-Rite, Inc.
--------------------------------------------------------------------------------
have you tried speaking with Gary Bedard at Becker? He's done lectures on material science directly relating to shrinking and machine direction of the
plastic. He'd be a good source to start out with.
good luck...
jose ignacio
--------------------------------------------------------------------------------
I suspect you are buying your polypro from a local source. If this is the case you may be getting to much reground i.e. recycled material in the plastic. The plastic is extruded which creates a grain like structure. This may account for the shrinkage orientation.
Try a premium source ($) and the shrinkage may reduce significantly. However you will always have some shrinkage with thermoplastics.
Dave Lindsey, C.O.
--------------------------------------------------------------------------------
I think Cascade is the one that told me, or taught me, that plastic has a direction to it. Even the Durrplex or Vivac shrinks in one direction, although it is very minimal. The copoly and polypro, and other plastics have a chemical characteristic that will shrink in one direction. There used to be some plastic sheets that had arrows on them signifying the shrinkage direction. I pull all the check sockets in one direction with the plastic. It sometimes wastes a significant amount of plastic, but my results are always consant, which is a good thing.
I don't ever make plastic sockets, I don't believe in them and don't trust them. I am a BK myself and in the past have had a few try to tell me how much better plastic sockets are than laminated sockets. I laugh at them. I actually had one person make me one to prove it. It might have been as strong, but it was 2 layers (2 pulls: inner socket and then a frame). It was very thick and weighed abuot 6 pounds just for the socket. I laughed at it. My laminated socket is very thin, 3 layers of carbon, and doesn't flex at all. It weighs just at one pound. I have yet to see the advantages of plastic, other than being a lot easier and cheaper and cleaner for the prosthetist to deal with. It poses no advantages to the amputee. Some say that it is better because they are easier to make adjustments to later. My belief is to get the check socket fitting correctly first, then laminate. With that process, you shouldn't need to make adjustments (unless it is a new amputee that is shrinking or changing.)
Sorry, but that is more of an answer than you probably wanted. But the plastic is uni-directional, and will always shrink at some unknown factor in one direction.
Jim DeWees, CP
--------------------------------------------------------------------------------
Check with Alan Finneston with Endolite of North America. I know they've given a lot of thought to that subject.
Randy McFarland, CPO
--------------------------------------------------------------------------------
Please post the replies. I too have become frustrated with the shrinkage of polypro/copoly sockets. It has forced me to go back to laminating, which of course, as you know, is more expensive, time-consuming, and unhealthy. In regards to plastic sockets, the best I've come up with is by adding (1) to (2) one-plys over the model prior to doing a pelite liner, or equivalent if there is no pelite liner. Other people's advice I've received is getting better quality plastic, but, as far as I understand, all polypro shrinks to some degree, and I've tried different plastic distributors. I used to think drape molding minimized the shrinking, but I'm no so sure about that. I had too many fitting problems that finally gave up, on the B/K's anyway. I still use plastic on A/K frames, because, in my humble opinion, the
shrinkage does not effect the fitting as much. Looking forward to the replies.
Best of luck,
Paul Rieth, CPO
Here are the responses for my post, Polypropylene shrinkage - Prosthetic Outer Sockets/Frames. I've included the original post in case some of you are interested. Thanks to all of who who replied... perhaps these responses will help a few of us out there!
Bill Lifford, C.P.
My original post read as follows:
Lately it seems as though many of our facility's polypropylene sockets shrink quite a bit. Sometimes, though, the shrinkage seems to be
circumferential and other times it seems to be longitudinal.
What are some methods we can use to control or reduce this shrinkage? I would rather not laminate everything, due to the dust created while
grinding laminated sockets; however, it frustrates me to have our technician pull a polypro frame for an AK socket and then have the thing
wind up being significantly shorter than the flexible inner socket. At least I know when I laminate a rigid frame, it's going to fit over the
flexible inner socket exactly when I'm done.
Also, with regards to circumferential shrinkage, is there a factor you can adjust for in fabrication, knowing that the shrinkage will occur? By
this I mean something along the lines of putting a sock (# of ply?) over the flexible inner socket before pulling the polypro over it. We use the
Fillauer shuttle lock a lot and so we often have BK sockets with a flexible inner socket and a polypro rigid outer socket. Once again, it's very
frustrating to have a check socket fit really well, then mold a socket over the exact same cast, and then have the definitive socket be too small to
the point where it's impossible to don!
Thanks for your help with this... any advice you can provide might help my professional life be far less stressful :)
Bill Lifford, C.P.
The responses were:
Our understanding is that the primary reason for plastic inconsistency is because material that contains re-ground material from edge trimmings is often put back in at the extruder to save costs. Mixing in material that has been through more than one heating and cooling cycle creates inconsistencies at the molecular level, making for stresses in the plastic that causes distortions such as shrinkage or spreading after cooling, as well as material waste from failed pulls. A little more about this topic may be found on page 464 of Knit-Rite catalog 14.
Mark Smith, CP
Knit-Rite, Inc.
--------------------------------------------------------------------------------
have you tried speaking with Gary Bedard at Becker? He's done lectures on material science directly relating to shrinking and machine direction of the
plastic. He'd be a good source to start out with.
good luck...
jose ignacio
--------------------------------------------------------------------------------
I suspect you are buying your polypro from a local source. If this is the case you may be getting to much reground i.e. recycled material in the plastic. The plastic is extruded which creates a grain like structure. This may account for the shrinkage orientation.
Try a premium source ($) and the shrinkage may reduce significantly. However you will always have some shrinkage with thermoplastics.
Dave Lindsey, C.O.
--------------------------------------------------------------------------------
I think Cascade is the one that told me, or taught me, that plastic has a direction to it. Even the Durrplex or Vivac shrinks in one direction, although it is very minimal. The copoly and polypro, and other plastics have a chemical characteristic that will shrink in one direction. There used to be some plastic sheets that had arrows on them signifying the shrinkage direction. I pull all the check sockets in one direction with the plastic. It sometimes wastes a significant amount of plastic, but my results are always consant, which is a good thing.
I don't ever make plastic sockets, I don't believe in them and don't trust them. I am a BK myself and in the past have had a few try to tell me how much better plastic sockets are than laminated sockets. I laugh at them. I actually had one person make me one to prove it. It might have been as strong, but it was 2 layers (2 pulls: inner socket and then a frame). It was very thick and weighed abuot 6 pounds just for the socket. I laughed at it. My laminated socket is very thin, 3 layers of carbon, and doesn't flex at all. It weighs just at one pound. I have yet to see the advantages of plastic, other than being a lot easier and cheaper and cleaner for the prosthetist to deal with. It poses no advantages to the amputee. Some say that it is better because they are easier to make adjustments to later. My belief is to get the check socket fitting correctly first, then laminate. With that process, you shouldn't need to make adjustments (unless it is a new amputee that is shrinking or changing.)
Sorry, but that is more of an answer than you probably wanted. But the plastic is uni-directional, and will always shrink at some unknown factor in one direction.
Jim DeWees, CP
--------------------------------------------------------------------------------
Check with Alan Finneston with Endolite of North America. I know they've given a lot of thought to that subject.
Randy McFarland, CPO
--------------------------------------------------------------------------------
Please post the replies. I too have become frustrated with the shrinkage of polypro/copoly sockets. It has forced me to go back to laminating, which of course, as you know, is more expensive, time-consuming, and unhealthy. In regards to plastic sockets, the best I've come up with is by adding (1) to (2) one-plys over the model prior to doing a pelite liner, or equivalent if there is no pelite liner. Other people's advice I've received is getting better quality plastic, but, as far as I understand, all polypro shrinks to some degree, and I've tried different plastic distributors. I used to think drape molding minimized the shrinking, but I'm no so sure about that. I had too many fitting problems that finally gave up, on the B/K's anyway. I still use plastic on A/K frames, because, in my humble opinion, the
shrinkage does not effect the fitting as much. Looking forward to the replies.
Best of luck,
Paul Rieth, CPO
Citation
William Lifford, “Summary of Responses - Polypro Shrinkage (1 of 2),” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 6, 2024, https://library.drfop.org/items/show/221816.
