Affects of cold temperature cycling on PolyCarbonate
Affects of cold temperature cycling on PolyCarbonate
(OP)
This comes from a Sport Fencing discussion group. Apparently there was a recent failure of a polycarbonate fencing mask in europe, and one of the possible claimed causes of this failure was the cyclical cooling and re-warming of the material from airline storage to room temperatures. This seemed to me rather counter-intuitive that a PC plate would become brittle due to what I would consider rather normal temperature cycles. While I understand that many thermoplastics do become more brittle at lower temperatures, it seems to me that their elasticity shuold return once the material has been allowed to return to 'room temperature' conditions. In this case there was a catastrophic failure of a (supposed) lexan (tm?) plate used as part of a fencing mask.
A picture of the shattered face plate can be seen on the fencing.se web site: ht tp://www.f encing.se/ nyheter/al lvarligt-t illbud-med -nya-maske n-i-odense
So to get to the point:
1: could exposure to cold temperatures found in aircraft baggage compartments cause lexan plates to become brittle and remain brittle after tehy have returned to normal room temperatures?
2: based soley on the picture on the web site, what would be the most likely explination of this kind of catastrophic failure of what is SUPPOSED to be a lexan (or PC) plate?
A picture of the shattered face plate can be seen on the fencing.se web site: ht
So to get to the point:
1: could exposure to cold temperatures found in aircraft baggage compartments cause lexan plates to become brittle and remain brittle after tehy have returned to normal room temperatures?
2: based soley on the picture on the web site, what would be the most likely explination of this kind of catastrophic failure of what is SUPPOSED to be a lexan (or PC) plate?





RE: Affects of cold temperature cycling on PolyCarbonate
1) No. The reason PC has a high impact strength is that it has a Tg of around 135ºC, so it is "rubbery" below this.
2) Are there silvery streaks which appear to be inside the material just above the hole? From what I can make our these look like environmental stress cracks (ESC). PC is very prone to this effect - virtually any fats/solvents (which may include polishes/cleaners/even natural grease off fingers) usually are a death knell. Any chance of a close-up of this area?
Micro scratches on the surface will also degrade the impact performance greatly.
The failure exhibits brittle fracture which leads me to the above hypotheses.
Just a thought - is the visor injection moulded or is it from a flat sheet that has been curved?
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: Affects of cold temperature cycling on PolyCarbonate
You mention that any kind of fats or solvents would degrade the material.. would that include animal fats and solvents normally present in perspiration?
Since this device is obviously used in a sport where the mask is constaly exposed to strikes with a metal object, sometimes at very high velocities, would that be counterindicated for use in this situation?
RE: Affects of cold temperature cycling on PolyCarbonate
It would indeed include bodily secretions.
Continued strikes will also cause scratches which will act as notches or stress raisers. PC is not good at notches.
I would guess that this sort of device needs to be changed on a regular basis. I recall reading somewhere that the cheaper PC motorcycle crash helmets should be changed at least every couple of years.
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: Affects of cold temperature cycling on PolyCarbonate
I have just enlarged the image with Photoshop and the visor is badly scratched all over. Some are deep gouges. Must have had difficulty seeing!
Harry
www.tynevalleyplastics.co.uk
RE: Affects of cold temperature cycling on PolyCarbonate
Some of these aromatics hydrocarbons are very common in in everyday items like aerosols, insecticides, cosmetics, food, body excretions, sun screen, detergents etc.
My recommendation for a tough RELIABLE reasonably scratch resistant reasonably clear plastic is cellulose propionate.
Regards
Pat
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RE: Affects of cold temperature cycling on PolyCarbonate
Chris DeArmitt
www.phantomplastics.com
Consulting to the plastics industry