Thermomechanical Characterization of an Unsaturated Polyester Vitrimer Synthesized Using a Titanium Transesterification Catalyst

Abstract

Unsaturated polyester resins (UPRs) are widely applied thermosets characterized by good thermo-mechanical properties and excellent chemical resistivity. However, the nonreprocessability of UPRs once cured, together with the increasing amount of their waste, has recently urged research and industries to develop more sustainable substituents. In this work, an unsaturated polyester vitrimer was synthesized and characterized by exploiting titanium (IV) butoxide as the transesterification catalyst. This simple approach demonstrated how the design of a covalent adaptable network could solve the issues related to reprocessability, self-healing, and the recyclability of unsaturated polyester thermosets. Here, an intramolecular transesterification exchange was exploited to confer reparability, reshaping, and thermoforming abilities to commercial polyester. Furthermore, the mechanical properties, the glass transition, and the chemical stability of the polyester resin were preserved despite the conversion of the thermoset matrix into a vitrimeric network.

Converting Unrefined Birch Suberin Monomers into Vitrimer

“…Several different catalysts have been reported for polyester vitrimers, including zinc, titanium, tin, and organic catalysts. − We have chosen a set of catalysts that include Zn­(OAc) 2 , Zn­(acac) 2 , DBTDL, Sn­(Oct) 2 , Ti­(iOPr) 4 , and TBD to test whether they can promote both esterification and transesterification reactions in suberin. Our preliminary studies on model fatty alcohols, acids, and esters (data not presented) indicated that all of the above-mentioned metal-containing catalysts promote both reactions to some extent.…”

Enhancing Sustainability in Unsaturated Polyester Resin: A Way to Use Biobased Curing Agents for Reduced Styrene Content and Improved Recyclability Properties

“…Thermomechanical and Chemical Characterization. In our previous work, 25 the addition of titanium butoxide allows the conversion of commercial UPR into a vitrimeric resin, able to reshape, repair, and reprocess under thermal stimulus. The exploitation of vitrimeric chemistry for UPR provides therefore the manufacturing of environmentally friendly thermosets, facilitating the potential reuse of the endof-life products.…”

“…Furthermore, due to the already enriched esters groups, the transesterification process in UPR can be easily exploited for exchange mechanisms, as described in our previous work. 25 On this scenario, this work investigates the synthesis and characterization of a UPR thermoset cured with a blend of methyl acrylate, functionalized vegetable oil, and styrene, to improve mechanical properties and implement exchange mechanisms. Acetyl acetonate of zinc was used as transesterification catalyst to promote both transesterification 26,27 and cross-linking 28 processes.…”

“…Similarly, a strategic combination between renewable and nonrenewable feedstocks, along with the implementation of exchange mechanisms, can provide the manufacturing of greener UPR thermoset as well. Furthermore, due to the already enriched esters groups, the transesterification process in UPR can be easily exploited for exchange mechanisms, as described in our previous work . On this scenario, this work investigates the synthesis and characterization of a UPR thermoset cured with a blend of methyl acrylate, functionalized vegetable oil, and styrene, to improve mechanical properties and implement exchange mechanisms.…”

Evaluation of 2,5‐Furandicarboxylic Acid as Building Block for Unsaturated Polyester Resins

“…Following the general trend towards a more sustainable production of industrial chemicals and materials [4][5][6][7][8], there have also been efforts to integrate renewable resources as a sustainable raw material basis into UPR manufacturing processes [9][10][11][12][13][14], to evaluate chemical recycling as a means to handle UPR post-consumer waste [15][16][17][18][19], and, more recently, to install dynamic networks (i.e. vitrimers) which render re-processable thermosets possible [20][21][22] (for general readings on thermosets composed of dynamic networks see [23][24][25][26]). We will not review the literature on bio-based UPR here in detail, but we note that while all efforts remain as an excellent proof of concept, the detailed inspection of the accounts revealed only a handful contributions [27][28][29][30][31][32][33][34][35][36][37] which reported mechanical properties in agreement with industrial standards [38,39] (For a comprehensive overview of bio-based UPR see Supporting Information).…”