Synthesis of reactive polyurethane adhesives and studying the effect of ketonic resins

Polyurethanes were first discovered by Otto Bayer and his colleagues at the end of the 1930s. It was soon learned that polyurethanes could adhere rubber to metal and so polyurethane adhesives containing polyester polyols have been developed rapidly. Many studies have been made to synthesize polyurethane adhesives until today and now it is widely used for bonding many materials such as rubber, plastic, metal, wood, glass and ceramics. Nowadays, polyurethane adhesives have very good hydrolytic stability, excellent low temperature performance as well as cost advantages. Although the performance at high temperatures is not sufficient, the application areas are narrowed to a certain extent, but recent developments are quite encouraging. The one-component reactive polyurethane adhesives subject to study are widely used especially in the furniture sector. One of the most important parameters affecting the productivity of the furniture producers is that the parts joined by bonding are waiting for long time and cannot be subjected to any processing during this period. In this case, the productivity of the production decreases. Ketonic resins are used as a resin in the ink and paint sector in an intensive adhesion. Many successful products that use ketonic resins in this direction are commercially available in our lives. However, their use in polyurethane adhesives has not been the subject to date due to the fact that ketonic resins are more difficult to access than polyols and the costs associated therewith are high. In this study, the effects of cyclohexanone formaldehyde ketonic resin (CFR) with different montmorillonite content on the viscosity, initial adhesion strength and temperature resistance of polyurethane one component adhesives were investigated. Two different blanks were synthesized with NCO/OH ratio 4.84. Polyether polyol and polymeric 4,4'-methylene diphenyl diisocyanate (p-MDI) were used only to synthesize the polyurethane pre-polymer/adhesive blanks. In the first case, plasticizer was used to adjust the viscosity and to reduce the fragile structure of the product. Montmorillonite clay containing (MM-CFR) and not containing CFR are synthesized like blanks with and without plasticizer. CFR and MM-CFR at a rate of 10% by weight of polyether polyol were used. In parallel with the reduction of the amount of polyether polyol used, the ratio of isocyanate groups (NCO) to hydroxyl groups (OH) was 5.38 (CFR and MM-CFR ketonic resins were not involved in calculation). The completion of reaction was followed by FT-IR device. Polyol has a characteristic peak corresponding to OH groups at 3400 cm-1. The peak disappears with the completion of reaction. The NCO % values of the synthesized products were measured with an automatic titrator and this value decreased with the use of CFR and MM-CFR. It has been found that the NCO % value tends to decrease with the increase in the amount of MM clay in the CFR. In fact, it is expected that the NCO % will increase with the increase of the MM clay amount. How the strength values are affected by the use of CFR and MM-CFR and the time-dependent variation of strength were investigated. It was observed that the build-up of green strength and the final strength are both better than blank samples. It was observed that the viscosity of the products synthesized increases in parallel with the increase of the MM ratio and CFR. Viscosity increase is an undesirable situation. The product viscosity remained at acceptable levels with incorporation of chloroparaffine. When TGA data were examined, it was found that the heat resistance of the product increased with the addition of CFR and MM-CFR. The increase in the amount of MM clay in the CFR appears to have a positive effect on the results. In this case, the use of CFR and MM-CFR may be appropriate in applications where temperature resistance is required. When DSC analyzes were examined, it was determined that the products which thermoset after curing were stable and did not decompose at the temperature range in which the analysis was carried out. The results were similar to TGA data. As a result of the experiments, adhesion properties and thermal stability of one component PU adhesives are found to be improved with incorporation of CFR and MM-CFR. In addition, the viscosity build-up of the adhesives with increasing amount of clay content in CFR can be overcome with plasticizer. The results encourage us that CFRs with increasing amount of montmorillonite clay can be a good alternative to improve adhesion properties and thermal stability without viscosity problems.