Physical properties of wax?

I have been working with a mixture of oleic acid and paraffin wax as a binder. The oleic acid is in the mix as a rheology modifier. I have
noticed something strange about the physical properties of the material and I hope someone can explain it to me. I am not an organic chemist.
I use a low melting (around 50 deg C) paraffin wax which is a mixture of C20 to C35 alkanes, mostly C23 - C26. I use lab grade (99.9%) oleic acid.
I melt the wax at 100 deg C and mix in the oleic acid very thoroughly then cool it to solidify.
I have tried 2 weight percent oleic acid and 5 weight percent oleic acid.
The strange effect is that the physical properties of the resulting solid material changes over time. Compared to the fresh mix, the low oleic acid mix becomes more brittle in 2 - 5 days and the high oleic acid mix becomes stronger and tougher in 2 - 5 days.
Why is this? Is there some sort of cross-linking reaction with the double bond? Can the oleic acid oxidise a little after a few days exposed to air?
Any comments?
Thanks
A
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I agree that this may be a crystallization effect. Normally the paraffin would crystallize rapidly on cooling, accompanied by significant shrinkage. The oleic acid may be inhibiting the crystallization and spreading it over a longer time.
RT
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Phase separation?
--
Dr. Lasse Murtomki
Helsinki University of Technology
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I can't fully explain what's happening but oleic acid and paraffin wax are probably not fully mutually soluble. You're getting a separation at some point which may lead to various hardening effects. Oleic acid will go rancid but I'm fairly sure it doesn't cross-link.
Barry Hunt
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