Properties of Natural and Synthetic Adhesives

This research seeks to quantify the mechanical and physical properties of natural and synthetic adhesives and how they are affected by, primarily, climatic conditions (relative humidity and temperature), time, chemical aging, and manufacturing process.

Animal glues have been used for centuries as adhesives, coatings, and binders by craftsmen and artists and are present in virtually any museum or ethnological collection. They are also commonly used in conservation practice due to their compatibility with the original materials used by artists as well as their excellent workability, stability, and re-treatability.

Gathering knowledge about animal glues’ properties and stability over time is crucial to long-term preservation of art collections and to make informed choices about treatments. How do factors such as the source, glue preparation, or thermal history of collagen, influence the glue’s response to moisture and temperature? The current move among museums toward more relaxed climate conditions to reduce energy consumption necessitates a better understanding of these glues’ mechanical and adhesive behavior under changing relative humidity and temperature conditions.

With the use of thermal techniques of analysis, (differential scanning calorimetry [DSC] and thermal gravimetric analysis [TGA]), dynamic moisture content measurements (DVS), and mechanical testing apparatus such as universal testing machine (UTM), dynamic mechanical analysis (DMA), and nanoindentation, we aim to bringing answers to these questions.

The applied experimental protocol enables the identification of phase transitions between the glassy and rubbery states and the evaluation in those states of the stiffness, viscoelasticity, strength, and strain at break of each tested adhesive. It allows for the prediction of environmental conditions at which specific glues may fail and may help to select the most appropriate adhesive, from a mechanical point of view, for particular applications.

Synthetic adhesives form a big part of the adhesives currently used in conservation. Several studies have investigated and listed their chemical and physical properties, in particular their solubility, appearance, adhesive power, and stability over aging.

Mechanical properties studies are not as widely available as studies for chemical and physical properties. The mechanical characterization of synthetic adhesives is one of our research priorities, given both the current knowledge gap as well as the challenges posed by climate change on museum collection environments, especially in the case of highly responsive hygroscopic materials.

Studies conducted on adhesives include the comparison of the adhesive strength of a range of synthetic adhesives (epoxies, acrylics) for poly(methyl methacrylate) joint repair.