Abstract
In order to reduce the dependency of resin synthesis on petroleum resources, vanillyl alcohol which is a renewable material that can be produced from lignin has been used to synthesize bioepoxy resin. Although it has been widely reported that the curing reaction and properties of the cured epoxies can be greatly affected by the molecular structure of the curing agents, the exact influence remains unknown for bioepoxies. In this study, four aliphatic amines with different molecular structures and amine functionalities, namely triethylenetetramine (TETA), Tris(2-aminoethyl)amine (TREN), diethylenetriamine (DETA), and ethylenediamine (EDA), were used to cure the synthesized vanillyl alcohol–based bioepoxy resin (VE). The curing reaction of VE and the physicochemical properties, especially the thermomechanical performance of the cured bioepoxies with different amine functionalities, were systematically investigated and compared using different characterization methods, such as DSC, ATR–FTIR, TGA, DMA, and tensile testing, etc. Despite a higher curing temperature needed in the VE–TETA resin system, the cured VE–TETA epoxy showed a better chemical resistance, particularly acidic resistance, as well as a lower swelling ratio than the others. The higher thermal decomposition temperature, storage modulus, and relaxation temperature of VE–TETA epoxy indicated its superior thermal stability and thermomechanical properties. Moreover, the tensile strength of VE cured by TETA was 1.4~2.6 times higher than those of other curing systems. In conclusion, TETA was shown to be the optimum epoxy curing agent for vanillyl alcohol–based bioepoxy resin.
Highlights
Nowadays, epoxy resin has become an indispensable thermosetting resin for many industrial fields and can be widely used as high–performance coatings, adhesives, and composites, etc., because of its premium physicochemical properties and excellent compatibility with most materials [1]
From the two obvious peaks appearing in the curves of every sample, the different polyaddition stages in the curing process can be observed, which were possibly attributable to the reaction between the epoxy group with primary amines and secondary amines
According to the differential scanning calorimetry (DSC) measurements, chemical resistance and swelling tests, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) analysis, and tensile tests, different curing agents had a significant influence on the curing behavior and properties of the cured bioepoxy resins
Summary
Epoxy resin has become an indispensable thermosetting resin for many industrial fields and can be widely used as high–performance coatings, adhesives, and composites, etc., because of its premium physicochemical properties and excellent compatibility with most materials [1]. Bioepoxies synthesized from natural renewable resources, such as plant oils, rosins, lignin, and lignin derivatives, have been explored [4,5,6,7,8,9]. Among these biomolecules, lignin, which makes up around 30% of woody biomass, was mostly used as a low–grade fuel by the traditional pulp and paper–making industries. The direct utilization of lignin in epoxy production is hindered by its large variability and complex chemical structures [14]
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