Adhesives for Use Inside Exhibit Cases

Category:Exhibition
Category: Exhibit Technical Notes
Category: Exhibit Case Design
Category: Exhibit Fabrication
Category: Standards & Guidelines
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Contributors: Members of the MWG's Materials Fact Sheet Working group, Jenifer Bosworth, Anne Ennes, Lisa Goldberg, Jamie Gleason, Jennifer Herrmann, Nancy Lev-Alexander, Patricia Silence, Catherine H. Stephens, and Theresa Voellinger
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=== How are adhesives used in exhibits? ===
Adhesives are used to secure case liners, graphics and other elements to the case interior and must meet conservation standards for stability and low offgassing, while continuing to function well over time. If suﬃcient surface area is covered, adhesive systems can be used in a variety of case applications including adhering wood veneer, fabrics, and boards. 
=== Why are adhesives a preservation concern? ===
The selection of adhesives used in exhibit cases is an important conservation decision because most adhesives emit large quantities of solvents and unreacted monomers that are volatile substances during their drying or setting phase. Even after the initial period, lower levels of offgassing can continue indefinitely. In the past, a wide variety of glues, adhesives, and tapes were used indiscriminately in exhibit assembly. Today a myriad of new and complex formulations are available on the market making the selection of a conservation appropriate adhesive a difficult process. Components of adhesives and tapes may also migrate or creep causing issues with nearby materials or objects.  
Specific materials of concern include:
* Rubber-based adhesives, either vulcanized or synthetic: Avoid any adhesive that is based on or contains natural or synthetic rubber because of its poor aging characteristics due to sulfur and chloride content.
* Animal glues: This adhesive type contains residual sulfur and is therefore not a good choice for use in enclosed spaces.
* Vinyl emulsions: Emulsion-type adhesives in which a resin is dispersed in water, include polyvinyl acetate emulsions. These "white glues" do outgas, especially once the shelf life has expired.
* Two-part adhesive systems: these include epoxy and polyester types, can be unstable if not mixed and cured properly.
=== What types of adhesives can be recommended for use inside exhibit cases? ===
Adhesive types considered acceptable:
* Acrylics: Acrylic adhesives are a stable class of adhesives that can be chosen for most museum applications. Acrylics are used in many types of solvent adhesives, adhesive tapes, pressure sensitive tapes, hot-melt adhesives, and stick formulations. For more specific information on products that have been investigated by the museum field, go to Double-sided tape or see references in additional resources below.
* Hot melt: Acrylic hot-melt adhesive sticks used in heat guns are approved for exhibit use; these are usually clear sticks. Opaque sticks with a yellow cast often contain waxes and other additives that make them a less desirable choice. For more specific information on products that have been investigated by the museum field, go to 3M Hot-melt glue sticks.
Check the AIC Wiki for the most recent Adhesives and Tapes Oddy test results.
=== Preservation strategies ===
Careful design of exhibits can lessen the need to use adhesives; exhibit cases can be designed so that adhesives do not interface with the display chamber. Unfamiliar adhesive systems require investigation and careful scrutiny; the key guidelines for selection are:
* Use mechanical fastening techniques to limit adhesive use within the case interior. Whenever feasible, use a mechanical attachment method, such as staples, pins or construction overlap. In particular, attaching fabric case liners mechanically greatly reduces the amount of adhesive exposure within a case.
* Use barrier films to limit infiltration of volatile adhesive components into the object chamber. Use tested laminates, such as a barrier film, and caulks to create eﬀective barriers at joints to prevent inﬁltration of volatile adhesive components.
* Use conservation-quality adhesive. Use adhesive systems which have a track record and include acceptable chemical components, such as acrylic resins and high-temperature, hot-melt adhesives.
* Aerate the adhesive. Allow suﬃcient time for the curing and setting of adhesives before objects are enclosed in the exhibit case. A minimum period of four weeks is recommended during which time the case doors should be open and bonnets left oﬀ. 
There are two types of tapes that have applications in case construction: 
* Adhesive transfer systems use paper backings to support the deposition of a layer of adhesive onto a surface. 
* Double-sided ﬁlm tapes have two surfaces of adhesive with a carrier sandwiched between. 
These adhesive systems are usually based on rubber or acrylic formulations, and the acrylic adhesive formulation should be chosen for any exhibit use. Carrier films for double sided tapes can be made from a variety of materials; an acrylic carrier is preferable to polyurethane.
=== Additional Resources ===
* Stephens, C. H. and E. M. Breitung. 2021. "Impact of volatile organic compounds (VOCs) acrylic double-sided pressure-sensitive adhesives (PSAs) on metals found in cultural heritage environments." Polymer Degradation and Stability 193. 
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