Picture lining adhesive

When voids are present in a bond line or when delamination occurs, the air that fills the voids has an acoustic impedance of 0 kg/m second and a large amplitude and total negative reflectance occurs. Most polymeric materials have acoustic impedances of 2.0-4.5 X 10 kg/m second compared to copper (42 x 10 kg/m second) and silicon (20 x 10 kg/m second). Examples of acoustic micrographs showing voids and delamination in an adhesive bond line are pictured in Figs. 6.6 and 6.7. 

The major use of EVA polymers in conservation is as additives to hot seal adhesives. Elvax 150 (Du Pont VAC 33%) and A-C Copolymer 400 (Allied VAC=15%) form the bulk of solids of BEVA 371 picture lining adhesive and consoUdant (Berger, 1976) (Figure A3.4), and has been widely applied for other types of objects (Kronthal et al., 2003 Karsten and Kerr, 2004). BEVA products... 

FIGURE A3.22 Solubility of a poly(dipentene) used as a tackifier in picture lining adhesives (Zonarez 7085 Arizona Chemicals, manufactured 1975) (Beardsley, 1978). Data kindly provided by Dr Greg Smith and Classes of 2009, 2010 and 2011 of the Art Conservation Department at Buffalo State College. 

We can see the comparative picture using two part epoxy and polyurethane adhesives. In this example, only the value of the modulus is changed. The results are shown in Fig. 26. This is a 25 mm square joint with 1.5 mm steel adherends and a glue line of 0.05 mm, with an applied load of 5000 N. 

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