Amino Acids as Bio-Based Curing Agents for Epoxy Resin: Correlation of Network Structure and Mechanical Properties

Bio-based alternatives for petroleum-based thermosets are crucial for implementing sustainable practices in fiber-reinforced polymer composites. Therefore, the mechanical properties of diglycidyl ether of bisphenol a (DGEBA) cured with either l-arginine, l-citrulline, [Formula: see text]-aminobutyric acid, l-glutamine, l-tryptophan, or l-tyrosine were investigated to determine the potential of amino acids as bio-based curing agents for epoxy resins. Depending on the curing agent, the glass transition temperature, Young’s modulus, tensile strength, and critical stress intensity factor range from [Formula: see text] [Formula: see text] to [Formula: see text] [Formula: see text] , [Formula: see text] [Formula: see text] [Formula: see text] to [Formula: see text] [Formula: see text] [Formula: see text] , [Formula: see text] [Formula: see text] [Formula: see text] to [Formula: see text] [Formula: see text] [Formula: see text] , and [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] to [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] , respectively. This shows that amino acids as curing agents for epoxy resins result in thermosets with a wide range of thermo-mechanical properties and that the choice of curing agent has significant influence on the thermoset’s properties. After collecting the results of dynamic mechanical analysis (DMA), tensile, flexural, compression, and compact tension tests, the functionality f, cross-link density [Formula: see text] , glass transition temperature [Formula: see text] , Young’s modulus [Formula: see text] , compression yield strength [Formula: see text] , critical stress intensity factor in mode I [Formula: see text] , fracture energy [Formula: see text] , and diameter of the plastic zone [Formula: see text] are correlated with one another to analyze their inter-dependencies. Here, the cross-link density correlates strongly positively with [Formula: see text] , [Formula: see text] , and [Formula: see text] , and strongly negatively with [Formula: see text] , [Formula: see text] , and [Formula: see text]. This shows that the cross-link density of DGEBA cured with amino acids has a crucial influence on their thermo-mechanical properties and that the thermosets considered may either be stiff and strong or tough, but hardly both at the same time.