Ask Dr. Dave / Columns

Ask Dr. Dave

July 2007

Question: We are currently manufacturing a phosphoric acid-catalyzed phenolic primer to promote the adhesion of polyurethanes to metallic substrates. We have no problem with carbon steel, but we’re having problems bonding to aluminum surfaces. Do you have any suggestions that could improve our situation?

Answer: The traditional methods of improving adhesion to aluminum are abrasive treatment followed by caustic washing or a chromic/sulfuric acid etch. However, there has been a trend in recent years to find safer and faster treatments. A modern treatment, pioneered by aerospace companies, is commonly known as the sol-gel process, and uses a combination of a silane coupling agent and a metal alkoxide in an aqueous solution. These hydrolyze and condense with the hydroxyl groups on the aluminum surface to produce a thin film that is an organic/inorganic polymer network.

Question: We are considering manufacturing polyurethane sealants but are apprehensive about handling very moisture-sensitive raw materials. Can you tell us how difficult this is to do?

Answer: As you almost certainly already know, polyurethanes can either be single-component systems that are cured with atmospheric moisture or two-component systems that comprise an isocyanate component and a polyol component. It is relatively easy to make these products in a lab environment, but in manufacturing and packaging you have to ensure complete absence of moisture in your raw materials. This involves careful drying, such as applying heat and vacuum to your fillers. When you are packaging, complete sealing (to prevent ingress of moisture) is again essential. Failure to exclude moisture can lead to premature curing, reduced shelf life and foaming in the sealant. You might consider looking at the so-called MS or silane-modified polyether sealant technology as an alternative to conventional polyurethanes. These materials have a urethane-like backbone but cure via a silicone-type crosslinking reaction. Although they are still sensitive to moisture, they are easier to handle and package than polyurethanes.


Did you enjoy this article? Click here to subscribe to Adhesives & Sealants Industry Magazine.

Recent Articles by Dave Dunn

You must login or register in order to post a comment.



Image Galleries

ASI April 2014 Photo Gallery

Our April 2014 issue is now available!


ExxonMobil Tackifier Expansion

Dwight Tozer, vice president of ExxonMobil’s Adhesion Industry business, discusses the company’s latest tackifier expansion project with Editor-in-Chief Susan Sutton.

More Podcasts

Adhesives & Sealants Industry Magazine

ASI May 2015 cover

2015 May

You won't want to miss our May issue, with a special packaging-focused Adhesives at Work section, as well as coverage of pressure-sensitive adhesives (PSAs), biorenewable feedstocks, and more!

Table Of Contents Subscribe

Better Jobs

Is the economy prompting you to consider leaving your job for a better one?
View Results Poll Archive


Handbook of Sealant Technology

The Handbook of Sealant Technology provides an in-depth examination of sealants, reviewing their historical developments and fundamentals, adhesion theories and properties, and today’s wide range of applications.

More Products

ASI 2014 Buyers GuideASI's Buyers' Guide

Annual purchasing resource for equipment used in the manufacture/formulation of adhesives, sealants, pressure sensitives, tapes and labels and for application of finished adhesives. 


facebook_40px twitter_40  youtube_40pxlinkedin_40 google+ icon ASI 30px

Clear Seas Research

With access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.