Design and production of a new adhesion testing device and its utilization with testing of wood varnishes

In this dissertation, a pneumatic adhesion device that is intended to be utilized in testing of organic coatings (paint/varnish) was designed and produced with project support (TOGTAG no:2741) of Turkish Scientific and Technical research Council (TÜBİTAK). After that, for the sample of study specimens were cut from pine (Pinus sitvestris L.), fir (Abies sp), beech (Fagus orientalis L.)" and oak (Quercus petreae L.). Cellulose, poh/urethane, acrylic and water based varnishes were applied to specimens. Preparation and adhesion testing were made according to the principles of ASTM D 4541 and TS EN 24624. In order to confirm the results and ensure the calibration of the designed testing device, same tests were carried out with Erichsen Adhesion-Master 525 MC testing device. Afterwards, the results from both devices were statistically compared. Following the tests, wood-finish interface of each specimen was set to a stereo- microscope in order to observe and analyze the failures. Each failure was also photographed and recorded. Results of the study indicated that the effect of wood species and varnish type in adhesion are statistically significant, while the effect of testing device and thickness of the varnish layer are not significant. In addition, it was deduced that the strength of adhesion is higher in hardwood specimens than that of softwood specimens. Furthermore, it was concluded that the designed adhesion device is reliable. The highest strength was measured with acrylic and polyurethane since these varnishes complete the polymerization on the surface of the wood after application. Tests also showed that failures mostly occur on the interface of first coat to wood surface. Thus, it can be concluded that the final coat does not have effect on the strength of adhesion. In conclusion, on such applications that require high adhesion it is suggested to utilize hardwoods such as beech and avoid use of porous materials such as fir. It should be kept in mind that highest adhesion was measured with polyurethane based varnish while the lowest was cellulose based one. It is also recommended to apply one layer of first coat and two layers of final coats in order to ensure surface smoothness and durability. Science Code : 6001013Key Words : Adhesion, adhesion testers, pull-off strength, paint and varnishes, organic coatings