Blend versus Non-blend 3

[nlj]

I have been reading through ASTM D2000 and corresponding standards, however I cannot find specific detail on how composition is controlled. I have field failures of a part specified to be polychloroprene (neoprene) per ASTM D2000 M2BC etc. I have been supplied with third party FTIR revealing the material to be a neoprene/SBR blend. The parts were subjected other testing specified such as hardness, tensile, heat aging, ozone, low temerature, etc and were found to meet all other parameters tested in accordance with the ASTM D2000 callout on the drawing.

For all practical purposes I think the parts meet the drawing, however I have been double guessing if a blend is sufficient for the specifications.

My question is; even if the parts meet all testing specified per ASTM is a blend considered polychloroprene? Are the specifics to what percentage of the material must be neoprene?

Thank you!

 

[Metten]

If you required a CR with certain ASTM detailed properties, you should receive a CR and not a CR/SBR. If you only specified the ASTM norm, people can offer you anything as long as it lives the tests. Fe cleaning products or chemical aids to put the part in place are often not mentioned, but some might influence SBR far more than CR.

There are many masterbatches with SBR as the matrix, but if I would see more than 5phr SBR, I would assume it was intentionally added and not originating from masterbatches.

 

[GrahamBennett]

I would suggest the compound used, whilst meeting the ASTM line call out requirements, has had SBR added to it for cost reduction purposes.

 

[stancom]

The various grade requirements for BC materials are written around the properties and expectations of chloroprene rubber but, as with other ASTM D2000 categories, the BC specification is open to any polymer - or blend - able to meet it, however unlikely. CR is just the rubber type normally used. The rubber type must always be specified and any compositional requirements given under the Z suffix letter. If CR is requested I certainly would not expect to be given a blend unless that was allowed in the contrast. How much second rubber can be tolerated before we use the word 'blend'? I am unaware of any figure but as a rule of thumb I have always considered a maximum of 10% of the total rubber content. Below that we are thinking of a rubber acting as a process aid or means of adding ingredients in masterbatch form. With this in mind, BS 3227 for butyl rubber compounds allows the addition of up to 10% of EPDM.

 

[tom1953]

If you feel you need a compound that's 100% CR, add to the ASTM D2000 callout: Z1: Rubber shall be 100% CR.