Acrylic Polymers 2 Conservation

Vinyl ester resins The vinyl ester resins are essentially epoxide resins, normally the digly-cidyl ether of bisphenol A, that have been reacted with acrylic acid or its derivatives. The unsaturation in the acid residues provides sites for a cross-linking mechanism based on free radical polymerization. The retention of the bisphenol A backbone in the chain of the cross-linked polymer conserves most of the mechanical and physical properties associated with the parent epoxy. The resins thus provide a combination of ease of processing with good chemical resistance and mechanical behaviour. 

Toniolo, L., Casadio, F., Cariati, F. (2004). OH radical degradation of acrylic polymers used as protective coatings for stone conservation. Science and Technology for Cultural Heritage, 13(1-2), 19-26. 

Brus J., Kotlik P. Consolidation of stone by mixtures of aLkoxysUane and acrylic polymer. Stud. Conserv. 1996 41(2) 109 119... 

The first synthetic polymers to be used as paint varnishes were acrylic and vinylic resins. Poly(vinyl acetate) (PVAc), commercialized under the name Mowilith by Hoechst and Vinylite by Union Carbide, has been used in conservation as an adhesive since 1932 and in 1937 it was proposed as a picture varnish by Stout and Cross [63]. PVAc was soon rejected as a varnish because, despite its light stability and good solubility in organic solvents, it demonstrated poor optical properties in terms of colour saturation and the tendency to pick up dirt due to its low glass transition temperature. 

Synthetic adhesives and acrylic paints are but two examples of synthetic polymers widely used in art and conservation. However, these products generally were not specifically developed for conservation purposes, and most manufacmrers, citing trade secrets, refuse to reveal the precise contents of their products. This is especially true of such additives as antioxidants, flocculants, antifoamers, emulsifiers, etc. Often companies have changed the contents of products, keeping the same name while not informing the customers about these changes. A weU-known example is that of ketone resin varnishes. An extensive review of the thermal analysis of polymers is given in Chapters 4 and 5 of this book. Here we note a few of the applications of pyrolysis in the area of art and conservation. 

Favaro, M., Mendichi, R., Ossola, E., Simon, S., et al. (2007). Evaluation of polyma-s for conservation treatments of outdoor exposed stone monuments. Part II Hioto-oxidative and salt-induced weathering of acrylic-silicone mixtures. Polymer Degradation and Stability, 92(3), 335-351. 

Primal N-560 has been nsed to form a temporary pressure-sensitive film where required (Notman and Tennent, 1980). PBA, with a small amount of dibutyl phthalate plasticizer probably applied from a dispersion, is the adhesive on a paper tape used for temporary attachment of paper (Archival Aids). A specially formulated acrylic/styrene polymer was made and its solution emulsified for textile conservation (Bengtsson, 1975). 

---