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At the request of another forum member, I looked into the reasons for carbon fiber pipes yellowing. I don’t own them but I understand that there is some question as to why the carbon fiber pipes (and any other carbon fiber parts for that matter) yellow over time. The yellowing is presumably due to some degradation over time. Here is what I found:
Carbon fiber parts are made by coating carbon fiber fabric with plastic. This composite is more accurately known as carbon fiber reinforced plastic, CFRP. The carbon fiber fabric doesn’t degrade; graphite is the lowest energy state for carbon (look out ladies, your diamonds will be nothing but graphite in mere millennia) and is very stable to heat, light, moisture, oxygen, etc. The plastic that is used to make the part yellows over time due to breaking of chemical bonds of the polymer. I knew that Travis, what causes these bonds to be broken?
Many plastics are used for CFRPs depending on the application but it appears as though the most popular plastic used for auto/cycle parts is epoxy resin. Please let me know if anyone happens to know what plastics are present in commercially available aftermarket pipes. Epoxy resins can be degraded by exposure to various factors: oxygen, moisture, heat, and UV light are the most common. Just sitting on a shelf they will degrade over time due to exposure to oxygen. This chemical reaction between the plastic and oxygen is called – surprise – oxidation, and is usually pretty slow with plastics, so nothing to worry about there…yet. Degradation due to moisture is mostly limited to marine applications where the epoxy is in constant contact with liquid water, so isn’t worth mentioning in this discussion.
Heat typically doesn’t degrade the plastic by itself (near room temperature), but it accelerates the oxidation process. In general, the rate of oxidation doubles for each 10°C (18°F) rise in temperature. This is a common way to accelerate the aging process for medical plastics to determine shelflife. So epoxy, as with any plastic, will degrade faster with an increase in heat. If room temperature is 20°C (68°F), when your pipes get to 60°C (140°F) they are being oxidized at approximately 16 times the rate as they do sitting on a shelf somewhere. Does anyone have CFRP pipes and access to an IR thermometer? I would be interested in the temperature of the shell after riding and after just sitting in the sun. We could come up with a ballpark number for how fast they age on a bike versus sitting on a shelf in a store.
UV light is probably the biggest cause of yellowing of CFRP parts. UV light breaks chemical bonds and creates radicals. Radicals are nasty creatures (except in my academic research where I use radicals for the good of mankind) that wreak havoc on plastics. The reason that radicals are nasty with respect to polymer degradation is that when a radical attacks a chemical bond, the reaction often produces another radical that can then go on to attack another chemical bond. It’s not a true chain reaction but the result is several chemical reactions from a single photon of UV light, making this a much more destructive pathway for a given energy input.
Nothing is that simple, there is a synergistic effect when all of the degradation factors are involved, but UV light and heat in that order likely cause the most damage. I would recommend protecting your CFRP parts from sunlight as much as possible. You can't protect them from the heat but you can protect them from the light anyway.
If anyone would like to donate a set of CF pipes I would be happy to conduct a thorough experiment and provide conclusive results.
My favorite are the M4s...
Carbon fiber parts are made by coating carbon fiber fabric with plastic. This composite is more accurately known as carbon fiber reinforced plastic, CFRP. The carbon fiber fabric doesn’t degrade; graphite is the lowest energy state for carbon (look out ladies, your diamonds will be nothing but graphite in mere millennia) and is very stable to heat, light, moisture, oxygen, etc. The plastic that is used to make the part yellows over time due to breaking of chemical bonds of the polymer. I knew that Travis, what causes these bonds to be broken?
Many plastics are used for CFRPs depending on the application but it appears as though the most popular plastic used for auto/cycle parts is epoxy resin. Please let me know if anyone happens to know what plastics are present in commercially available aftermarket pipes. Epoxy resins can be degraded by exposure to various factors: oxygen, moisture, heat, and UV light are the most common. Just sitting on a shelf they will degrade over time due to exposure to oxygen. This chemical reaction between the plastic and oxygen is called – surprise – oxidation, and is usually pretty slow with plastics, so nothing to worry about there…yet. Degradation due to moisture is mostly limited to marine applications where the epoxy is in constant contact with liquid water, so isn’t worth mentioning in this discussion.
Heat typically doesn’t degrade the plastic by itself (near room temperature), but it accelerates the oxidation process. In general, the rate of oxidation doubles for each 10°C (18°F) rise in temperature. This is a common way to accelerate the aging process for medical plastics to determine shelflife. So epoxy, as with any plastic, will degrade faster with an increase in heat. If room temperature is 20°C (68°F), when your pipes get to 60°C (140°F) they are being oxidized at approximately 16 times the rate as they do sitting on a shelf somewhere. Does anyone have CFRP pipes and access to an IR thermometer? I would be interested in the temperature of the shell after riding and after just sitting in the sun. We could come up with a ballpark number for how fast they age on a bike versus sitting on a shelf in a store.
UV light is probably the biggest cause of yellowing of CFRP parts. UV light breaks chemical bonds and creates radicals. Radicals are nasty creatures (except in my academic research where I use radicals for the good of mankind) that wreak havoc on plastics. The reason that radicals are nasty with respect to polymer degradation is that when a radical attacks a chemical bond, the reaction often produces another radical that can then go on to attack another chemical bond. It’s not a true chain reaction but the result is several chemical reactions from a single photon of UV light, making this a much more destructive pathway for a given energy input.
Nothing is that simple, there is a synergistic effect when all of the degradation factors are involved, but UV light and heat in that order likely cause the most damage. I would recommend protecting your CFRP parts from sunlight as much as possible. You can't protect them from the heat but you can protect them from the light anyway.
If anyone would like to donate a set of CF pipes I would be happy to conduct a thorough experiment and provide conclusive results.
My favorite are the M4s...
