Engineered Green Adhesives Based on Demands: Star-Shaped Glycerol–Lactic Acid Oligomers in Anaerobic Adhesives

Solvent-resistant, biobased anaerobic adhesives have been engineered, employing star-shaped glycerol-lactic acid oligomers (SLAOs). For optimization of the performance, first, the best combination set of the comonomer and accelerators were achieved (i.e., amidosulfunic acid and methylmethacrylate); second, the effect of the arm length of SLAO on the adhesive properties was evaluated; and; finally, the impacts of SLAO content on the performance of the adhesives were assessed. Adhesives containing oligomers with 4 and 6 lactic units showed maximum adhesion; and the best performance was achieved on the steel substrates. The adhesives were evaluated by differential scanning calorimetry, thermogravimetric analyses, rotational viscometer, single lap shear (LSS), and breakaway torque tests. Heat of the curing reaction, a function of arm lengths of the employed SLAOs, reduced from 238 J·g–1 for oligomers with two lactic units, to 74 J·g–1 for oligomers with ten lactic units. In an attempt to reduce the nonrenewable portion of the adhesives, up to 95 wt % of the adhesives was substituted by SLAO. These green adhesives present tunable viscosities (in the range of 20–510 cP), along with promising thermal–mechanical properties (LSS: 8.62 MPa, Tdeg: 370 °C); moreover, they outperformed in various aspects, including providing a higher breakaway torque strength (∼7–27 N·m), better solvent resistance, and lower environmental impacts.