Understanding the effects of amine and morpholine adsorption on unglazed earthenware using density functional theory

Abstract

Recent efforts within the field of conservation science have focused on understanding how chemicals off-gassed from common storage materials impact museum objects. One source of particular concern is the identification of amines and morpholines as chemicals volatilized from polyester polyurethane foam, which is used extensively as crate padding for artwork storage and transport. Although a white-colored efflorescence on the surface of objects has been linked with amines off-gassed from these foams, little is known about the surface interactions that lead to these deposits. In the present work, periodic density functional theory (DFT) is used to investigate the molecular-level interactions that occur when clay mineral surfaces (such as those encountered in unglazed earthenware objects) are exposed to amines and alkylmorpholines. The data obtained here show that energetically favorable interactions are observed when kaolinite, partially dehydrated kaolinite, and metakaolin surfaces are exposed to different categories of amines including neutral amines, amine salts, morpholines, and morpholinium salts. Furthermore, it is demonstrated that surface dehydration is a key factor in how reactive a structure is toward these amine adsorbates. Special precautions are therefore recommended when storing unglazed earthenware in the presence of polyester polyurethane foam.