Flame-Retardant Pressure-Sensitive Adhesives Derived from Epoxidized Soybean Oil and Phosphorus-Containing Dicarboxylic Acids

In this study, novel biobased pressure-sensitive adhesives (PSAs) derived from epoxidized soybean oils and carboxylic acid-terminated polyesters were developed with flame retardance, thermal stability, and peel strength comparable to those of current PSAs. The dynamic mechanical analysis indicated that the PSAs exhibited a dynamic mechanical response consistent with related high-performance PSAs. The thermal properties of the PSAs were investigated by thermogravimetric analysis, and the results suggested that the onset decomposition temperatures in both nitrogen and air atmospheres were improved by incorporating both 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP) and 2-(6-oxido-6H-dibenz<1,2>oxaphosphorin-6-yl)-1,4-hydroxyethoxyphenylene (DOPO-HQ-HE) as the flame-retardant monomer. Microscale combustion calorimetry, the limiting oxygen index test, UL-94, and the test method for flame resistance of PSA tapes were used to evaluate the flame retardance of the PSAs. With an increase in the content of the flame-retardant monomers, the flame retardance of two phosphorus-containing PSAs improved. The PSAs were based on renewable materials without any volatile organic compound, thus being environmentally friendly together with having the expected thermal stability and flame retardance. If we take advantage of these features, the PSAs can provide more opportunities for versatile applications.