Comparative Thermo-Mechanical Properties of Sustainable Epoxy Polymer Networks Derived from Linseed Oil

Abstract

Considering its great industrial potential, epoxidized linseed oil (ELO) was crosslinked with different agents, both natural and synthetic: citric acid (CA, in the presence of water—W, or tetrahydrofuran—THF, as activator molecules) and Jeffamine D230, respectively, resulting bio-based polymeric matrices, studied further, comparatively, in terms of their properties, through different methods. Thermal curing parameters were established by means of Differential Scanning Calorimetry (DSC). Fourier transform Infrared Spectroscopy (FTIR) and DSC were used to identify the reactivity of each ELO-based formulation, discussing the influence of the employed curing systems under the conversion of the epoxy rings. Then, the obtained bio-based materials were characterized by different methods, establishing the structure–properties relation. Thermogravimetric analysis revealed higher thermal stability for the ELO_CA material when THF was used as an activator. Moreover, a higher glass transition temperature (Tg) with ~12 °C was registered for this material when compared with the one that resulted through the crosslinking of ELO with D230 conventional amine. Other important features, such as crosslink density, storage modulus, mechanical features, and water affinity, were discussed. Under the loop of a comprehensive approach, a set of remarkable properties were obtained for ELO_CA_THF material when compared with the one resulting from the crosslinking of ELO with the synthetic Jeffamine.

Investigating the Synthesis and Characteristics of UV-Cured Bio-Based Epoxy Vegetable Oil-Lignin Composites Mediated by Structure-Directing Agents

“…Oil derivative. Structural analysis of the ELALO monomer by 1 H-NMR revealed the success of the epoxidation reaction, with specific signals of those protons from the oxirane rings being noticed, as proven by Figure 2 : 3.04 ppm, 2.86 ppm, 1.70 ppm and 1.40 ppm in the Figure 2 b spectrum, as compared to spectrum from Figure 2 a, where the signal of the double bonds from the fatty acids can be observed at 5.33 ppm and 2.03 ppm [ 36 , 40 ].…”

Contribution of the Surface Treatment of Nanofibrillated Cellulose on the Properties of Bio-Based Epoxy Nanocomposites Intended for Flexible Electronics

“…The spectrum of neat ELO shows absorption bands at around 3500 cm −1 , which correspond to the stretching vibrations of the O-H groups, a band assigned to the carbonyl (C=O) stretching from the ester functionality (1736 cm −1 ), bands associated with the -CH asymmetric and symmetric bending vibrations from the CH 2 and CH 3 groups (1464 and 1385 cm −1 ), and the oxirane C-O twin bands at 823 cm −1 and 844 cm −1 [ 20 , 47 ] ( Figure 2 ).…”

“…Interestingly, the band at 1100 cm −1 assigned to the C-O stretching vibrations of O=C-O from ELO splits into two new bands (1092, 1067 cm −1 ) after the curing reaction as a consequence of the formation of new types of covalent C-O-C bonds. The newly emerged bands are typical of the ether C-O-C bands formed in accordance with the epoxy–acid curing mechanism [ 47 ]. These findings are valid for the neat epoxy system and the epoxy/NCs nanocomposites, regardless of the NCs type.…”

“…No separate degradation stage of NCs was observed in the TGA or DTG thermograms of the epoxy nanocomposites, regardless of the NCs type. The first degradation stage from 150 °C to 300 °C is probably due to the labile C-O type bonds from the molecular structures with higher mobility not being embedded within the epoxy network [ 47 , 48 , 52 ]. The main degradation step, which is placed between 330 °C and 480 °C, results from the chain cleavage of the ester groups in the ELO epoxy resin structure [ 53 , 54 ].…”

“…The main degradation step, which is placed between 330 °C and 480 °C, results from the chain cleavage of the ester groups in the ELO epoxy resin structure [ 53 , 54 ]. The breakage of the ester groups formed through the ring-opening reactions between the epoxy functional groups and the carboxyl ones occurred above 480 °C, and this is more evident in the matrix without NCs ( Figure 4 ) [ 47 , 48 ].…”