Knowledge You Can Build On — Est. 1998
Poly vs alcohol - question
John Crissman
>In reading the threads, one said poly is fine soaking overnight, while another said poly will dissolve with a two day soak.
It is my understanding that poly is actually activated by a small level of moisture content in the wood, hence the magazines recommend that you wet MDF prior to a poly glue-up.
Could it be that the two-day soak actually removes the amount of moisture necessary to sustain poly adherence?
Thanks,
John
Re: Poly vs alcohol - question
JL work
>Chemistry soapbox time.
Single part polyurethane adhesives require moisture for activation and curing. The isocyanate functionality reacts with hydroxyls. These can be in the form of water, polyols (two-part urethane adhesives) or alcohol. I would say that if the poly fell apart, an adequate time was not allowed for the moisture to complete the curing. Some of the poly also may have partially dissolved in the alcohol. Ideally, you want lots of long chain molecules building as the poly sets up. You don't want endcapping and chain termination of the growing poly molecule.
Allow the poly an adequate time to set before using alcohol.
Makes good sense to me - Thanks!
John Crissman
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