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

Abstract

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, T deg : 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.

Quick and green toward conductive thermally‐stable biobasedstar‐shapedoligomers

“…It may imply two different structures with various chain mobilities and free volumes 67 . The T g at lower temperature can be attributed to the soft aliphatic ester backbone 18,62,68 and the higher one can be assigned to the stiff aromatic backbone; based on previous reports polyaniline has displayed T g about 100°C 69 and T g decreases by decrease in molecular weight 67…”

“…Compared to TA, the degradation offset temperature for SSB‐TA has visibly shifted to the higher temperatures (Figure 5G and H) while it has kept about 40% of its weight. Overall, SSB‐TA has experienced three steps of the degradation at 200, 330, and 430°C that can be assigned to dehydration, chain scission, and decarboxylation processes 18 . These outstanding results are attributed to capping with tetraaniline moiety if we compare them with the similar biobased analogous (T 10% = 237 °C, T50% = 302°C) 16 …”

“…This functional starshaped oligomer have been designed for incorporation in star‐shaped biobased resins and adhesives in order to boost the performance. In our previous study, 18 a high performance anaerobic biobased adhesive was fabricated using lactic acid‐based starshaped oligomer and HEMA. In this study, we simplified the system to biocompatible HEMA in order to easily track any changes in properties; HEMA was radically polymerized in presence of SSB‐TA.…”

“…Succinic acid and glycerol are biobased molecules, considered as members of the list of the 12 building block chemicals by the US department of Energy, which are producible from renewable raw resource via bioconversion or chemical production to deal with the shortage of petroleum‐based resource 21–23 . Glycerol is an inexpensive trifunctional alcohol capable of performing favorable polycondensation reactions in the presence of dicarboxylic acids to produce green hyperbranched polyesters without any solvent 24 with the possibility of the arms end‐capping with certain functional groups, such as vinyl‐groups 18 . Glycerol polyesters or oligoesters branched with pending hydroxyl groups appropriate for end‐functionalization with different structures for specific applications 25 …”

“…[11][12][13] The nature of core molecule, length of arms, architecture of the network, and method used for end-functionalization are directly affect properties of resin. 14 Hydrophilic multi-hydroxyl core molecules, including glycerol, xylitol, ethylene glycol, and erythritol were used for different applications, 15 whereas dicarboxylic acids, such as succinic acid, [15][16][17] lactic acid, 11,12,18,19 and itaconic acid, 13,20 were used as arms. Succinic acid and glycerol are biobased molecules, considered as members of the list of the 12 building block chemicals by the US department of Energy, which are producible from renewable raw resource via bioconversion or chemical production to deal with the shortage of petroleum-based resource.…”