Apparently very cold temperatures make PVC even more brittle.... Why is this so ?
Last edited by Ari Ben Canaan; 19-04-2012 at 16:44.
OK - from a materials chemist - PVC is a brittle material, most of the PVC we see in use appears more plastic becase it has small molecules called pastisisers in them.
(Original post by Ari Ben Canaan)
My textbook states that PVC is brittle because :
"...the larger Cl atoms tend to catch on each other when the polymer chains are pulled apart."
To be honest, I am not too satisfied with this explanation nor do I fully understand what the size of the Cl atom has to with the material being brittle.
In terms of chemical bonds what are the pre-requisites for a brittle material ?
Most polymers have a degree of randomness to them, like spagetti in a bowl. this mean that there is extra space between the molecules. If a polymer/plastic is too be maluble - not brittle, then the chains need to be able to move past each other and therefore there needs to be sufficient space for this to happen. As we warm a plastic the chains move more and have more fee space, at some point there is enought space for the chains to pass eachother and the material goes from being brittle to being plastic.
If we compare polyethylene and PVC they are similar polymers but PE is plastic at room temp and PVC is not, this is because the chlorines on the PVC chain are large and inflexable and therefore require more free space in the polymer for the chains to pass eachother, therefore a higher temperature before it becomes plastic.
The pasticisers help this process by acting to increase the free volume in the polymer and therefore lowering the temperature at which the material becomes plastic.
To learn more about this try reading up on glass transision temperatures.
Last edited by Illusionary; 20-04-2012 at 22:37.