Updated: Dec 29, 2019
In November 2019 I began work on a 19th century mahogany bar back chair while a student at West Dean College. The initial assessment of the chair revealed that while most of the structure was stable, the front proper right joint (front right if you are sitting in the chair) where the leg and the front cross piece meet had split and broken in multiple places. An unknown adhesive had been used previously to repair the damage. The timber pieces were misaligned, leaving in some places a 2mm gap filled with the polymer adhesive. The adhesive itself was brittle and failing to adhere to the timber properly. These factors resulted in an unstable leg.
In furniture work, there are a number of adhesives that are used, and it is not always apparent to the general furniture owner or repairer as to what has been used previously, what can be done about it, and why adhesives behave the way they do.
Attached is a paper I wrote about this project which looks at the nature of polymer adhesives to better understand the science behind their behaviour. It discusses the basic structure of polymers, the theories of adhesion, and physical properties of polymer adhesives in their liquid and solid states. It then follows the process the student went through to analyse and remove the adhesive from the timber surface, exploring concepts of solvency, and glass transition temperature.
It was written as an introduction to complex topics of the chemistry of adhesives and polymers as understood in furniture conservation. I have posted it here in the hopes that it might help future conservators, or just curious people, better understand these materials. I am write a new version of it which is a lot more accessible to the average woodworker, and which discusses protein adhesives (such as hide glue) a bit more, but it will be some time before I get around to doing that.
In the meantime, you can find my original paper here