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Shore Hardness

Submitted by Fernando Angiolini on Thu, 12/10/2009 - 11:24am

I am currently manufacturing PVC flexible compounds using ESO (epoxidized soybean oil) as a plasticizer. I would like to know if there is some literature or work done on the evolution of shore A hardness of the PVC compounds as a function of time. I am seeing strange behaviours, shore A hardness begin to increase with time but after some time it decreases, but this only happens with some formulations. I would like to know if there is some standardized study done on this topic. Any help will be deeply appreciated

Comments

ESO Plasticizer and Shore, A hardness

Submitted by Leonard Horst on Tue, 01/19/2010 - 11:56am.

This is an old post, but in case you're still interested... here are some thoughts.

If ESO is your lone plasticizer, you're are probably seeing the result of incomplete compatibility. You see, ESO is not completely compatible, especially used at higher concentrations and if not used in combination w/ other more compatible plasticizers, over a long period of time. It will exude from the PVC surface. This could cause the Shore hardness to increase over time as plasticizer escapes from the bulk polymer. I suspect you are also seeing a temperature effect in this increase or decrease in Shore hardness. Higher temps will exacerbate exudation and increase hardness drift over time.

I hope this is helpful,
Len

I agree with Len about the

Submitted by Robert Brandes on Thu, 09/30/2010 - 10:16pm.

I agree with Len about the temperature affects on Shore A hardness. I was involved in a project with a color concentrate manufacturer who was measuring Shore A hardness too soon after the product was made so that the customer was getting a higher reading when it was tested in their facility. Typically a CC producer will wait 24 hours in a temperature controlled environment to avoid this from happening.

Another thing to consider is if you (and possibly another person) are using the same measuring equipment. I have heard of one person using a Shore B head and then doing a calculation to get the Shore A value. This is not a good way to do it. All testers should be doing it the same way, and the preferred way is with a Shore A head.