Structure-activity relationship of antibacterial bio-based epoxy polymers made from phenolic branched fatty acids

Authors: Huang, Kun; Fan, Xuetong; Ashby, Richard - Rick; Ngo, Helen

Submitted to: Progress in Organic Coatings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2021
Publication Date: 3/2/2021
Citation: Huang, K., Fan, X., Ashby, R.D., Lew, H.N. 2021. Structure-activity relationship of antibacterial bio-based epoxy polymers made from phenolic branched fatty acids. Progress in Organic Coatings. 155:106228. https://doi.org/10.1016/j.porgcoat.2021.106228.
DOI: https://doi.org/10.1016/j.porgcoat.2021.106228

Interpretive Summary: Due to today’s growing health related concerns on harmful microbes, the search for innovative bio-based polymers for surface coatings that would actively and repeatedly kill bacteria is expected to increase. To design bio-based polymers that are applicable for this propose, it is important to understand the relationship between the polymer structure and its antimicrobial activity. For this research, new bio-based epoxy polymers have been produced from different sizes of phenolic fatty acid polyamine curing agents and then used to determine their relationship between the structure and antimicrobial activity. Exciting results reveal that two bio-epoxy polymers were active against both Gram-positive and Gram-negative bacteria. Based on the antimicrobial findings, these three factors (phenolics, polyamines and molecular weights) are concluded to play key roles in creating bioactive polymers. This information paves the way for developing more effective antimicrobial biopolymers.

Technical Abstract: In order to study the structure-activity relationship of antibacterial bio-based epoxy polymers made from phenolic branched fatty acids (phenolic BCFAs), a series of curing agents (i.e., phenolic BCFA-amides (phenolic BCFAAs)) were prepared from phenolic BCFAs and polyamines at 90 degree and 160 degree. Those phenolic BCFAs were made from phenol, thymol, carvacrol, and creosote, respectively, while the polyamines were ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and hexamethylenediamine (HDA). The prepared curing agents were then used to make different antimicrobial bio-epoxy polymers with a commercial epoxy resin, diglycidyl ether of bisphenol A (DGEBA). All the monomers were thoroughly characterized by Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). Two bio-epoxy polymers, phenol-BCFA (EDA) and creosote BCFA (EDA), were found to be most active against both Gram-positive and Gram-negative bacteria. The leaching experiments on the phenol-BCFA (EDA) showed no signs of small molecules (i.e., biocides) leaking out of the polymer to inactivate the bacteria. Most importantly, the reusability study indicated that the polymer was inherently antibacterial and maintained its efficacy for at least three uses. This study presents important findings on the antimicrobial activity of individual phenolics, polyamines and molecular weights of the curing agents, and the evidence demonstrates that the amphiphilicity contributes to the key impact of the antimicrobial activity of the bio-epoxy polymers.