Bio-Based Alternative to the Diglycidyl Ether of Bisphenol A with Controlled Materials Properties

Abstract

A series of biobased epoxy monomers were prepared from diphenolic acid (DPA) by transforming the free acid into n-alkyl esters and the phenolic hydroxyl groups into diglycidyl ethers. NMR experiments confirmed that the diglycidyl ethers of diphenolates (DGEDP) with methyl and ethyl esters have 6 and 3 mol % of glycidyl ester. Increasing the chain length of DGEDP n-alkyl esters from methyl to n-pentyl resulted in large decreases in epoxy resin viscosity (700-to-11 Pa•s). Storage modulus of DPA epoxy resins, cured with isophorone diamine, also varied with n-alkyl ester chain length (e.g., 3300 and 2100 MPa for the methyl and n-pentyl esters). The alpha transition temperature of the cured materials showed a linear decrease from 158 to 86 °C as the ester length increases. The Young's modulus and tensile strengths were about 1150 and 40 MPa, respectively, for all the cured resins tested (including DGEBA) and varied little as a function of ester length. Degree of cure for the different epoxy resins, determined by FTIR and DSC, closely approached the theoretical maximum. The result of this work demonstrates that diglycidyl ethers of n-alkyl diphenolates represent a new family of biobased liquid epoxy resins that, when cured, have similar properties to those from DGEBA.

Bio-based epoxy resin toughening with cashew nut shell liquid-derived resin

“…This indicates that the origin of neat DGEDP-Me's high viscosity is primarily weak intermolecular interactions as had previously been postulated. 32 Likewise, neat DGEDP-Me viscosity at 40 and 50°C decreased by 94 and 99%, respectively, relative to the viscosity at 25°C. Resin viscosities were repeatable after being tested at 60°C indicating that, under these conditions, the epoxy resins are chemically stable.…”

“…Epoxide equivalent weights of the neat resins were taken from previously reported results 32 or the manufacture's specification. Weights of reaction components were calculated by using the epoxide equivalent weight (EEW) and the amine hydrogen equivalent weight (AHEW), which were calculated by Equations 1 and 2, respectively.…”

“…The average molecular weight between cross-links was determined using a TA Instruments AR-G2 rheometer by a literature method. 32 For chemorheology, dynamic shear experiments were performed using a TA Instruments AR-G2 rheometer equipped with 8-mm-diameter parallel plates. Temperatures were ramped at 5°C/min at a frequency of 1 rad/s to the isothermal time sweep.…”

“…This decrease is attributed to the increasing aliphatic content of the thermoset, and its significant deviation from a linear trend is most likely due to the presence in DGEDP-Me of 6 mol% DGEDP-glycidyl ester coproduct. 32 In other words, the three epoxy functionalities of DGEDP-glycidyl ester that result in relatively higher cross-link densities in cured resins skew the storage modulus to higher values. As the NC-514 content in the epoxy resins increases, DGEDP-glycidyl ester is diluted to values that have no substantial effects on cured resin properties.…”

“…A series of thermoset resins were prepared from different ratios of diglycidyl ether diphenolate methyl ester (DGEDP-Me), a high-viscosity bio-based epoxy resin recently reported by some of the present authors, 32 and a flexible lowerviscosity epoxy cardanol resin prepared from cashew nut shell liquid (NC-514) (Scheme 1). 16 Studies are described that provide an understanding of how the DGEDP-Me/NC-514 composition and temperature influence resin viscosity and gelation.…”