NBR compound for MBB application 1

[TBR29]

Hello

I'm having problems to get MBB standard like DBL 5563-21 just in elongation at break like the results below:

1000h@100°C ageing in air
change in Hardness (+18 Shore A max) - +16 Shore A
Tensile at break (7 MPa min) - 13,5 MPa
Change in tensile (30% max) - -7,3%
Elongation at break (160 % min) - 120%
Change in elongation (50 % max) - -62,4%

This is the compound formulation i'm already using:
NBR with medium ACN - 100
ZnO - 4,0
Stearic Acid - 1,5
Antiozonant Wax - 2,0
IPPD - 2,0
TMQ - 1,0
ZMTI - 2,0
Carbon black N762 - 52
Carbon black N330 - 10
TP 759 plasticizer - 4,0
Sulphur - 0,3
TMTD - 1,0
CBS - 2,0
ZDBC - 1,5
DTDM - 2,2
WB 16 - 2,0

the MBB normally tests the final part laminated too and this is a problem.
If anybody can help me i will appreciate so much.

Thanks in advance

 

[stancom]

I presume the test resulta beneath the heading are all aged ones, in which case the EB non compliance stems from the ageing. Stiffening is normal in butadiene based rubbers, but in this case the increase in hardness is higher than I'd expect, given the use of a low sulphur EV system. Two things come in mind. One is that hardness/modulus increase in aged SBR has been reported to be higher when a reinforcing black like N33O is present. Admittedly 10 phr is not much to play with but is it really necessary? The other thing is that the antioxidant synergist zinc 2-mercaptotolumidazole (ZMTI), however benefit to aged tensile strength, can sometimes cause a an additional increase in aged modulus. There may be scope for reducing or indeed omitting it because the change in strength is well within specification.

One hopes that reduced stiffening will be accompanied by a smaller change in EB.

 

[TBR29]

First of all thanks stancom !!
I will make this changes and do some tests...
What do you think about the ACN content ?? With higher teor its better for heat ageing is that all rigth ?! what do you think about blends ?
My problem is that the customer tests in the final test piece (laminated) and normally the results is always worse than in the test specimens.

 

[stancom]

Heat ageing resistance should increase with ACN content simply because there are fewer butadiene units susceptible to oxidation and oxidative crosslinking. That is borne out by the following recently published paper : Richard J. Pazur, J. G. Cormier, K. Korhan-Taymaz (2014) THE EFFECT OF ACRYLONITRILE CONTENT ON THE THERMO-OXIDATIVE AGING OF NITRILE RUBBER. Rubber Chemistry and Technology: March 2014, Vol. 87, No. 1, pp. 53-69. The lower permeability to air should also be beneficial. I am not familiar with the MBB specification but if NBR is being used for properties such as fluid resistance or damping, a change in grade might cause more problems than it solves. The same applies to blends. I think you have to consult an NBR supplier on that one.

It goes almost without saying that the compound should be fully cured ( ie 95%) to ensure no additional crosslinking during ageing.

Happy New Year