Curing and Degradation Kinetics of Phosphorus-Modified Eugenol-Based Epoxy Resin

Decreasing fossil fuel resources results in a growing demand for polymeric materials obtained from renewable raw materials, such as eugenol. Therefore, this work aimed to assess the kinetics of cross-linking and degradation of epoxy resin obtained from eugenol derivatives and cured with three types of amines: aliphatic: triethylenetetramine (TETA); aromatic: diaminodiphenylmethane (DDM), and cycloaliphatic isophorone diamine (IDA). The product was characterized by ¹H, ¹³C, and ³¹P NMR as well as ESI MS techniques. The curing kinetics of the biobased resin was studied using differential scanning calorimetry (DSC) at different heating rates. Fourier transform infrared (FTIR) spectroscopy was used to assess chemical changes in bioepoxy monomer after the curing process. The DSC method confirmed the occurrence of an exothermic curing reaction of the tested bioresin for all tested curing agents. The peak temperature <i>T_p</i> and enthalpy Δ<i>H</i> values determined during DSC analysis depended on the type of curing agent. The highest values of <i>T_p</i> (142.6-161.4 °C) and Δ<i>H</i> (28.5-38.3 J/g) were recorded for the TEEP + DDM composition. For the remaining compositions, the values were lower and were as follows: for TEEP + TETA, <i>T_p</i> = 115.0 to 129.9 °C and Δ<i>H</i> = 12.4-26.5 J/g and for TEEP + IDA, <i>T_p</i> = 118.0-137.1 °C and Δ<i>H</i> = 16.3 to 35.5 J/g. According to the Kissinger and Ozawa model, the activation energy of the resin cross-linking process was determined. The calculated activation energies according to Kissinger and Ozawa were 65.38 and 55.90 kJ/mol for TEEP + TETA, 60.09 and 63.84 kJ/mol for TEEP + DDM, and 57.36 and 60.85 kJ/mol for TEEP+IDA, respectively. The kinetics of thermal degradation of the eugenol-based resin were studied by thermogravimetric analysis (TGA) in a nitrogen atmosphere. Moreover, it should be emphasized that compared to commercial resins, bioresin has a much lower maximum degradation rate determined by DTG and a higher amount of char residue after thermal degradation, both in nitrogen and in air.