Bio-based epoxy resins with low molecular weight kraft lignin and pyrogallol

Abstract

A low-molecular lignin fraction (L) was extracted for the preparation of bio-based epoxy resins. Various compositions with the "green" 1,3-glycerol diglycidyl ether (1) and the co-component pyrogallol (2) were tested. In a first series of experiments, thermosets consisting of 1 and L, were studied with respect to variable lignin contents between 20 and 50%. The best thermoset has a tensile strength of 37 MPa and a Young's modulus of 2.2 GPa at 40% lignin input. Secondly, lignin-free compositions of 1 and 2 were prepared. For a molar fraction of the functional groups (n(OH) n(Epoxy)(-1)) of 130%, the tensile strength could be enhanced to 93 MPa and the modulus reached 3.7 GPa. Finally, systems with all three components were examined. The best mechanical performance of the corresponding neat thermosets was reached at n(OH) n(Epoxy)(-1) of 130%. Tensile strength decreases slightly to 86 MPa and Young's modulus remains nearly unchanged at 3.2 GPa. Two resin compositions, L+ 1 and L+ 1+ 2, were tested for the preparation of unidirectional composites reinforced with man-made cellulosic fibers (50% by vol.). The bending strength was 208 MPa in combination with a bending modulus of 12.5 GPa

Bio-Based Aromatic Epoxy Monomers for Thermoset Materials

“…Lignin functionalized by a dicarboxylic acid prepared by dimerizing unsaturated fatty acids was considered as a phenolic aldehyde amine curing agent by Fang et al [ 191 ]. Similarly, Engelmann et Ganster [ 192 ] blended a low molecular weight lignin fraction with the bio-based tri-glycidylated glycerol for the preparation of composites reinforced with cellulosic fibers.…”

Pyrolysis oil substituted epoxy resin: Improved ratio optimization and crosslinking efficiency

“…As illustrated in Figure 1, PO contains a significant number of hydroxyl groups as indicated by a peak at 3400 cm 21 . However, POBER resin exhibited a weak hydroxyl peak at 3400 cm 21 . The peak area at 3400 cm 21 of the PO and POBER resin was calculated to be 26.0458 and 4.5802 A cm 21 , respectively, which clearly indicates that OH groups in the PO was consumed during the curing.…”

“…However, POBER resin exhibited a weak hydroxyl peak at 3400 cm 21 . The peak area at 3400 cm 21 of the PO and POBER resin was calculated to be 26.0458 and 4.5802 A cm 21 , respectively, which clearly indicates that OH groups in the PO was consumed during the curing. On the other hand, the epoxide groups within the EPON828 ARTICLE WILEYONLINELIBRARY.COM/APP are indicated by the sharp peak at the 910 cm 21 .…”

“…Another change in the IR spectra was observed at the carbonyl peak (1725 cm 21 ). As the PO was consumed by EPON828, the peak at 1725 cm 21 was not observed in the POBER resin suggesting that carbonyl groups within the PO contributed the curing of EPON828 resin along with the hydroxyl groups.…”

Fully Biobased Epoxy Resins from Fatty Acids and Lignin

“…The quest for a lignin-epoxy resin goes decades back [15,16]. There is an extensive body of literature showing that the hydroxyl groups in the lignin can react with terminal epoxy groups in molecules such as (polyethelene) glycerol digylicidy ether [17][18][19][20][21]. However, EVO such as ESO or ELO did not yield a fully cured product, probably due to the lower reactivity of internal epoxy groups.…”