Phenol formaldehyde resol resins with plant-based tannin for composite laminate applications

The use of phenol and formaldehyde in preparing resole resins had sparked some environmental concerns. This study investigated the feasibility of substituting or minimising the use of phenols and formaldehyde in the preparation of phenol formaldehyde resins by adding dissolved tannin into the formulations. The objectives of the research include assessing the effects of varying the molar ratio of phenol and formaldehyde in the preparation of phenol formaldehyde resins, evaluating the effects of minimising the use of phenol and formaldehyde and replacing it with dissolved tannin in the resins’ formulation, and analysing the curing kinetics of resins and profiling the heat transfer behaviour of the composite laminate using a computational fluid dynamics software. The analyses performed in this research cover the rheological, physical, thermal, chemical and mechanical properties as well as the microscopic imaging of the produced resins and the composite laminates. The phenol formaldehyde (PF) resin shows a shear thickening behaviour at all temperature sets, i.e., 40oC, 60oC, 80oC and 100oC. Water in formalin reduces the flexural and tensile properties of the PF composite laminates by 97.0% and 67.8%, respectively. The dissolved tannin reduces the amount of PF used by 20.0 % and improves the flexural and tensile properties of the PF composite laminates by 26.0% and 8.8%, respectively. Some reduction in the thermal properties of the resins were noted whilst the Ea values for both formulations were similar. Autocatalytic model can be used to represent the curing kinetics when the degree of cure is lower than 0.4 and 0.5 whilst the nth order model can be used to represent the curing kinetics when the degree of cure is higher than or equal to 0.4 and 0.5 for PF and dissolved tannin phenol formaldehyde (DTPF) resin, respectively. During curing the laminate, the heat was dissipated from the edges of the composite to the centre, while, during post curing, the heat was dispersed from the centre to the edges of the composite laminate. This study shows the feasibility of reducing the content of PF in the formulation of PF by adding dissolved tannin to the formulations. It is good to note that with the addition of dissolved tannin, the mechanical integrity of the composite laminate was improved