Restore brittle plastic - Boil it
08-25-2016, 02:06 AM
#1
Rennlist Member
Thread Starter
Restore brittle plastic - Boil it
I was reading about restoring playability of old plastic parts and came across this article about boiling it.
http://classicoldsmobile.com/forums/...c-restore.html
Any thoughts or BTDT? Most other references say that plastic aging is a one way ticket. Just like us.
http://classicoldsmobile.com/forums/...c-restore.html
Any thoughts or BTDT? Most other references say that plastic aging is a one way ticket. Just like us.
08-25-2016, 03:25 AM
#2
Rennlist Member
Michael,
An interesting post and there may well be something in it given the qualifications made in the article. Heat can and does modify material properties and I see no reason why such should not happen with plastics albeit in a different heat range but interesting that I have never come across an article proposing such previously.
I did have a similar experience some years ago when I had a leak on the power steering input shaft seal on my Daimler Century. The main agents wanted something like $1k to replace the entire box stating that the seal was not available as a spare. I was somewhat pissed at this so removed the offending item to investigate possibilities. Took it to the main workshop of the national oil company who I worked for and the supervisor, a very experienced local chap took a look and told me that many years earlier he had a similar frequently occurring problem with the fleet vehicles that the company used in the desert. He advised me to boil the housing in a solution of washing powder [non detergent type] for 10 minutes- said it will soften the ring seal lip so that it can seal once more. He was right- it worked a treat!
So there are some solutions to some problems we might not expect if we do but know about them. Doubtless others will have had some experience of such examples.
Rgds
Fred
An interesting post and there may well be something in it given the qualifications made in the article. Heat can and does modify material properties and I see no reason why such should not happen with plastics albeit in a different heat range but interesting that I have never come across an article proposing such previously.
I did have a similar experience some years ago when I had a leak on the power steering input shaft seal on my Daimler Century. The main agents wanted something like $1k to replace the entire box stating that the seal was not available as a spare. I was somewhat pissed at this so removed the offending item to investigate possibilities. Took it to the main workshop of the national oil company who I worked for and the supervisor, a very experienced local chap took a look and told me that many years earlier he had a similar frequently occurring problem with the fleet vehicles that the company used in the desert. He advised me to boil the housing in a solution of washing powder [non detergent type] for 10 minutes- said it will soften the ring seal lip so that it can seal once more. He was right- it worked a treat!
So there are some solutions to some problems we might not expect if we do but know about them. Doubtless others will have had some experience of such examples.
Rgds
Fred
08-25-2016, 09:42 AM
#3
Drifting
When I started flying R/C in the '80s, Nylon propeller makers ssid that they had to be boiled for 30 min. before use. "to remove internal moulding stress". Always did, never broke a prop. I guess it works like heating metal to make it soft after it gets 'work hardened'. Only problem, the part breaks when you try to take it off. So now, how to boil the part while it's on the car??
08-25-2016, 10:02 AM
#4
Rennlist Member
fascinating. And Strikemaster is onto something - it is similar to annealing steal. I will try this.
08-25-2016, 10:53 AM
#7
Drifting
Well...maybe it can extend the life of aging plastic by a kind of annealing process. However, plastics do de-gas. New cars get the notorious film on the inside of the windshield because the petroleum-based vinyls and plastics in the car de gas "stuff" that winds up on the windshield. It makes sense that the light absorbing dash heats up, gasses are driven out of the dash, and then precipitate on the cooler windshield glass. I've noticed this happens less in older cars....with brittle vinyl dashes. I can't remember what the gas molecules actually are (it will probably have a long name)...but I'm guessing they are whatever makes plastics flexible - and I doubt it's H2O. This leads me to think the boiling is helpful, but not a complete rejuvenation of the plastics.
I was reading about restoring playability of old plastic parts and came across this article about boiling it.
http://classicoldsmobile.com/forums/...c-restore.html
Any thoughts or BTDT? Most other references say that plastic aging is a one way ticket. Just like us.
http://classicoldsmobile.com/forums/...c-restore.html
Any thoughts or BTDT? Most other references say that plastic aging is a one way ticket. Just like us.
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08-25-2016, 10:53 AM
#8
Nordschleife Master
08-25-2016, 12:20 PM
#9
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Metallurgist here, with just one polymer course in the 1970's. Speculating....
My best theory is that water penetrates the surface enough to cause some swelling, and therefore a compressive layer. A surface compressive layer is magic to brittle materials, such as tempered glass or Gorilla glass. For metals, peening does this, although that is for fatigue resistance. Either way, the surface defects that usually lead to failure are rendered impotent.
The water effect would be temporary, since the water will soon depart.
Another theory involves the added plasticizer that Jon mentioned. It becomes depleted at the surface from evaporation, but might be replenished by heating enough to move some internal plasticizer to the surface. Maybe it just evens out the tension in the surface layer that the missing plasticizer causes. Plasticizer is not always used.
I suppose an actual annealing sort of thing can happen. Plastics start off without any crystalline order - amorphous like glass - but crystallize partially during initial cooling, and may keep on crystallizing in service, reducing toughness. Heating to boiling water temperature probably isn't enough to reverse that process, but it might relax internal stresses the crystallization may cause.
For those nerdy enough for a lecture: Brittle fracture is interesting. It is nearly always caused by the extension of tiny surface flaws or cracks. The stress at an infinitely sharp crack tip is theoretically infinite; in practice, it is still very high. But the required energy is missing, the energy to create two new surfaces, the fracture surfaces. Until, that is, there is enough elastic energy in the piece to supply it. The relevant expression contains the term "2 times gamma", where gamma is surface energy. In liquids, surface energy has a more obvious effect: surface tension. They are actually the same. Atoms and molecules prefer to be inside, not hanging loose out the windows. If it's hot, though, they get jumpy and can no longer hang on. That's what sublimation, melting, evaporation and boiling is all about.
The other side of the expression is the elastic energy, not so easily stated. In the context of metals, the science of "Fracture Mechanics" is used to predict the life of components with defects. You assume a certain defect size from the limits of your inspection capability, and set up inspection intervals to catch cracks comfortably before they become critical. The sort of defect that put the Sioux City fan disk in a corn field was notoriously difficult to find. They still are, but the melting process was changed to be more certain that you don't get big ones.
Glass blowers will lick a glass rod before breaking it: this reduces the surface energy, lowering the fracture stress. Fiber glass and other composites are strong because small fibers cannot have large flaws. They are tough because of all the energy involved in creating a tortuous fracture path. There's a difference between being "strong" and being tough. There are many different kinds of "strong".
Fascinating!
My best theory is that water penetrates the surface enough to cause some swelling, and therefore a compressive layer. A surface compressive layer is magic to brittle materials, such as tempered glass or Gorilla glass. For metals, peening does this, although that is for fatigue resistance. Either way, the surface defects that usually lead to failure are rendered impotent.
The water effect would be temporary, since the water will soon depart.
Another theory involves the added plasticizer that Jon mentioned. It becomes depleted at the surface from evaporation, but might be replenished by heating enough to move some internal plasticizer to the surface. Maybe it just evens out the tension in the surface layer that the missing plasticizer causes. Plasticizer is not always used.
I suppose an actual annealing sort of thing can happen. Plastics start off without any crystalline order - amorphous like glass - but crystallize partially during initial cooling, and may keep on crystallizing in service, reducing toughness. Heating to boiling water temperature probably isn't enough to reverse that process, but it might relax internal stresses the crystallization may cause.
For those nerdy enough for a lecture: Brittle fracture is interesting. It is nearly always caused by the extension of tiny surface flaws or cracks. The stress at an infinitely sharp crack tip is theoretically infinite; in practice, it is still very high. But the required energy is missing, the energy to create two new surfaces, the fracture surfaces. Until, that is, there is enough elastic energy in the piece to supply it. The relevant expression contains the term "2 times gamma", where gamma is surface energy. In liquids, surface energy has a more obvious effect: surface tension. They are actually the same. Atoms and molecules prefer to be inside, not hanging loose out the windows. If it's hot, though, they get jumpy and can no longer hang on. That's what sublimation, melting, evaporation and boiling is all about.
The other side of the expression is the elastic energy, not so easily stated. In the context of metals, the science of "Fracture Mechanics" is used to predict the life of components with defects. You assume a certain defect size from the limits of your inspection capability, and set up inspection intervals to catch cracks comfortably before they become critical. The sort of defect that put the Sioux City fan disk in a corn field was notoriously difficult to find. They still are, but the melting process was changed to be more certain that you don't get big ones.
Glass blowers will lick a glass rod before breaking it: this reduces the surface energy, lowering the fracture stress. Fiber glass and other composites are strong because small fibers cannot have large flaws. They are tough because of all the energy involved in creating a tortuous fracture path. There's a difference between being "strong" and being tough. There are many different kinds of "strong".
Fascinating!
08-25-2016, 02:07 PM
#10
Not the sharpest tool in the shed
Rennlist Member
Rennlist Member
Is there risk of deformation of the plastic when you boil it? I haven't time to read the article as the moment.
08-25-2016, 05:35 PM
#11
Metallurgist here, with just one polymer course in the 1970's. Speculating....
My best theory is that water penetrates the surface enough to cause some swelling, and therefore a compressive layer. A surface compressive layer is magic to brittle materials, such as tempered glass or Gorilla glass. For metals, peening does this, although that is for fatigue resistance. Either way, the surface defects that usually lead to failure are rendered impotent.
The water effect would be temporary, since the water will soon depart.
Another theory involves the added plasticizer that Jon mentioned. It becomes depleted at the surface from evaporation, but might be replenished by heating enough to move some internal plasticizer to the surface. Maybe it just evens out the tension in the surface layer that the missing plasticizer causes. Plasticizer is not always used.
I suppose an actual annealing sort of thing can happen. Plastics start off without any crystalline order - amorphous like glass - but crystallize partially during initial cooling, and may keep on crystallizing in service, reducing toughness. Heating to boiling water temperature probably isn't enough to reverse that process, but it might relax internal stresses the crystallization may cause.
For those nerdy enough for a lecture: Brittle fracture is interesting. It is nearly always caused by the extension of tiny surface flaws or cracks. The stress at an infinitely sharp crack tip is theoretically infinite; in practice, it is still very high. But the required energy is missing, the energy to create two new surfaces, the fracture surfaces. Until, that is, there is enough elastic energy in the piece to supply it. The relevant expression contains the term "2 times gamma", where gamma is surface energy. In liquids, surface energy has a more obvious effect: surface tension. They are actually the same. Atoms and molecules prefer to be inside, not hanging loose out the windows. If it's hot, though, they get jumpy and can no longer hang on. That's what sublimation, melting, evaporation and boiling is all about.
The other side of the expression is the elastic energy, not so easily stated. In the context of metals, the science of "Fracture Mechanics" is used to predict the life of components with defects. You assume a certain defect size from the limits of your inspection capability, and set up inspection intervals to catch cracks comfortably before they become critical. The sort of defect that put the Sioux City fan disk in a corn field was notoriously difficult to find. They still are, but the melting process was changed to be more certain that you don't get big ones.
Glass blowers will lick a glass rod before breaking it: this reduces the surface energy, lowering the fracture stress. Fiber glass and other composites are strong because small fibers cannot have large flaws. They are tough because of all the energy involved in creating a tortuous fracture path. There's a difference between being "strong" and being tough. There are many different kinds of "strong".
Fascinating!
My best theory is that water penetrates the surface enough to cause some swelling, and therefore a compressive layer. A surface compressive layer is magic to brittle materials, such as tempered glass or Gorilla glass. For metals, peening does this, although that is for fatigue resistance. Either way, the surface defects that usually lead to failure are rendered impotent.
The water effect would be temporary, since the water will soon depart.
Another theory involves the added plasticizer that Jon mentioned. It becomes depleted at the surface from evaporation, but might be replenished by heating enough to move some internal plasticizer to the surface. Maybe it just evens out the tension in the surface layer that the missing plasticizer causes. Plasticizer is not always used.
I suppose an actual annealing sort of thing can happen. Plastics start off without any crystalline order - amorphous like glass - but crystallize partially during initial cooling, and may keep on crystallizing in service, reducing toughness. Heating to boiling water temperature probably isn't enough to reverse that process, but it might relax internal stresses the crystallization may cause.
For those nerdy enough for a lecture: Brittle fracture is interesting. It is nearly always caused by the extension of tiny surface flaws or cracks. The stress at an infinitely sharp crack tip is theoretically infinite; in practice, it is still very high. But the required energy is missing, the energy to create two new surfaces, the fracture surfaces. Until, that is, there is enough elastic energy in the piece to supply it. The relevant expression contains the term "2 times gamma", where gamma is surface energy. In liquids, surface energy has a more obvious effect: surface tension. They are actually the same. Atoms and molecules prefer to be inside, not hanging loose out the windows. If it's hot, though, they get jumpy and can no longer hang on. That's what sublimation, melting, evaporation and boiling is all about.
The other side of the expression is the elastic energy, not so easily stated. In the context of metals, the science of "Fracture Mechanics" is used to predict the life of components with defects. You assume a certain defect size from the limits of your inspection capability, and set up inspection intervals to catch cracks comfortably before they become critical. The sort of defect that put the Sioux City fan disk in a corn field was notoriously difficult to find. They still are, but the melting process was changed to be more certain that you don't get big ones.
Glass blowers will lick a glass rod before breaking it: this reduces the surface energy, lowering the fracture stress. Fiber glass and other composites are strong because small fibers cannot have large flaws. They are tough because of all the energy involved in creating a tortuous fracture path. There's a difference between being "strong" and being tough. There are many different kinds of "strong".
Fascinating!
08-26-2016, 01:11 AM
#12
Rennlist Member
Curt You are correct about the loss of plastizicer from the surface. I have found that multiple applications of "Armour All" will restore the condition. It however is not good on stitching. Leatherique has a product called "Rejuvenator" and is even better.
08-26-2016, 09:19 AM
#15
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The common test for a ductile material is to put a bar in a machine and pull on it, optionally with an "extensometer" to measure strain directly. You get a stress versus strain curve from which you can extract yield stress, ultimate tensile stress, ductility, and modulus (stiffness, the inherent spring rate).
You can also get a value for toughness – one flavor of toughness: the area under the stress-strain curve represents the energy required to break the bar. Energy is the controlling parameter in impact failure: a hammer must have this amount of kinetic energy in order to break something.
Something seriously brittle will break in the grips of such a machine, so they're tested in bending. Glass, ceramics, that sort of stuff. Or just compression, like concrete.
Most plastics are not ductile - you cannot bend a piece into a new shape. They have a low modulus, so they don't seem brittle – you don't fear them as you would a piece of glass – but strictly speaking, they are brittle. Rubber is brittle, too. They are tough, though, because the area under the stress-strain curve is large - it takes a lot of work to break them. Being compliant (the opposite of stiff), you can manhandle them without breaking them.
Toughness is often thought of as resistance to impact damage. Since a material can behave differently at high strain rates, you often need to test by impact. Steel is a huge example. The standard test uses notched bars at various temperatures. You whack them with a pendulum hammer; the rise of the pendulum after impact tells you how much energy was required. The rivets used for the Titanic may have had an unfortunate ductile-brittle transition temperature.
This is just the tip of the iceberg about "strength". You have hardness tests, high and low cycle fatigue tests, thermal fatigue resistance, corrosion fatigue tests, fatigue crack growth rate tests, fracture toughness (a crack is present), stress corrosion tests, creep rupture tests – tests for every sort of failure. I was involved in developing turbine blade alloys - the screening test was creep rupture - hang a weight on a bar to get about 20,000 psi, let it sit at 2000F, and see how long it lasts - about a week was good.
