Impact of Soybean Oil Epoxidation Degree on Hot-Melt Adhesives

Replacing mineral oil (MO) in Hot-melt pressure-sensitive adhesives (HM PSAs) with safer, greener, and more available plasticizerssuch as soybean oil (SO)is important given their broad consumption. Although vegetable oil (VO) exhibits no heat resistance, it can be chemically modified (e.g., epoxidized) to enhance this property (critical for HM PSAs). To this end, formulations containing MO and refined soybean oil (RSO) with epoxidation degrees (EDs) from 0 to 6.7% were compared. RSO in comparison to MO, reduced the adhesive's viscosity from 3998 ± 302 to 2580 ± 143 mPa.s and the softening point (SP) from 63.7 ± 0.8 to 45.6 ± 0.3 °C, which could optimize the applicability by reducing its melting/application temperature, with a positive impact on sustainability (reducing energy consumption). RSO and SO with 0, 2.0, and 3.7% EDs, in comparison to MO, showed characteristics compatible with freezer tapes and labels: higher tack (from 10.3 ± 1.3 to 11.4 ± 1.4, 11.8 ± 1.2, and 12.7 ± 0.9 N, respectively), reduced glass transitionT _g (from 22.0 ± 0.0 to 4.7 ± 1.8, 5.6 ± 0.0, and 9.7 ± 0.0 °C, respectively), and lower shear (from 1703.3 ± 88.1 to 36.1 ± 0.1, 55.2 ± 4.2, and 59.5 ± 7.0 min, respectively). The totally epoxidized soybean oil, in comparison to MO, showed characteristics compatible with removable tapes: lower tack (3.8 ± 1.7 N) and peeling strength reduction (from 3178 ± 302 to 1568 ± 193 gf.inch^-1). Finally, to validate these results and support formula adjustments, rheological results: T _g, tanδ, complex viscosity, and storage modulus were cross-checked with performance tests: SP, tack, and shear. Finally, this study supports the development of more sustainable HM PSAs by demonstrating shear performance adjustment through variation in raw material content (923.0 ± 174.3 min) and by introducing an end-block resin (1595.2 ± 117.0 min). In addition, a potential candidate for removable application was identified, exhibiting a shear value of 6351.4 ± 1465.1 min with a near zero tack/peeling strength.