Toughening Anhydride-Cured Epoxy Resins Using Fatty Alkyl-Anhydride-Grafted Epoxidized Soybean Oil

Chitosan toughened epoxy resin by chemical cross-linking: Enabling excellent mechanical properties and corrosion resistance

There is a growing demand for the development of epoxy resin modified with biomaterials, aiming to achieve high toughness. Herein, chitosan crosslinked epoxy resin (CE) was synthesized by diisocyanate as a bridge. With 4,4'-diamino-diphenylmethane (DDM) as the curing agent, thanks to the unique cross-linking structure of the CE resin and the presence of carbamate groups, the cured CE/DDM exhibited superior properties compared to commercially available epoxy resin (E51). The tensile strength of the cured CE-3/DDM reached 90.17 MPa, the elongation at break was 11.2 %, and the critical stress intensity factor (KIC) measured 1.78 MPa m1/2. These values were 21.4 %, 151.6 %, and 81.6 % higher than those of the cured E51/DDM, respectively. It is worth noting that the addition of biomass material chitosan did not reduce the thermal stability of the resin. Additionally, the CE coatings on the metal substrate exhibited exceptional corrosion resistance, as evidenced by higher impedance values in electrochemical impedance spectroscopy (EIS) and polarization voltages in the Tafel curve compared to those of the E51 coating. This study opens up a novel approach to modifying epoxy resin with biomass materials with high toughness and corrosion resistance, without sacrificing other performance.

Impact- and Thermal-Resistant Epoxy Resin Toughened with Acacia Honey

High performance polymers with bio-based modifiers are promising materials in terms of applications and environmental impact. In this work, raw acacia honey was used as a bio-modifier for epoxy resin, as a rich source of functional groups. The addition of honey resulted in the formation of highly stable structures that were observed in scanning electron microscopy images as separate phases at the fracture surface, which were involved in the toughening of the resin. Structural changes were investigated, revealing the formation of a new aldehyde carbonyl group. Thermal analysis confirmed the formation of products that were stable up to 600 °C, with a glass transition temperature of 228 °C. An energy-controlled impact test was performed to compare the absorbed impact energy of bio-modified epoxy containing different amounts of honey with unmodified epoxy resin. The results showed that bio-modified epoxy resin with 3 wt% of acacia honey could withstand several impacts with full recovery, while unmodified epoxy resin broke at first impact. The absorbed energy at first impact was 2.5 times higher for bio-modified epoxy resin than it was for unmodified epoxy resin. In this manner, by using simple preparation and a raw material that is abundant in nature, a novel epoxy with high thermal and impact resistance was obtained, opening a path for further research in this field.

Bio-Based Coating Materials Derived from Acetoacetylated Soybean Oil and Aromatic Dicarboxaldehydes

Bio-based coating materials were prepared from epoxidized soybean oil as a renewable source. Acetoacetylated soybean oil was synthesized by the ring-opened and transesterification reaction of epoxidized soybean oil, and its chemical structure was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and rheometric viscosity analyses. On the basis of acetoacetylated soybean oil, several bio-based coating materials were prepared using different aromatic dicarboxaldehydes (1,2-benzenedialdehyde, 1,3-benzenedialdehyde, 1,4-phthalaldehyde, 4,4'-biphenyldicarboxaldehyde) and characterized. The resulting films possess good performance, including the highest glass transition temperature of 54 °C, a Young's modulus of 24.91 MPa, tensile strength of 5.65 MPa, and an elongation at break of 286%. Thus, this work demonstrates the Knoevenagel condensation reaction, which is based on soybean oil as a potential newer eco-friendly raw material.

Synthesis and Properties of Organosilicon-Grafted Cardanol Novolac Epoxy Resin as a Novel Biobased Reactive Diluent and Toughening Agent

The aim of this work is to develop a biobased functional reactive diluent for thermosetting epoxy resins suitable for high-performance applications. An advanced organosilicon-grafted cardanol novolac epoxy resin (SCNER) was synthesized from cardanol novolac epoxy resin and heptamethyltrisiloxane. After the chemical structure of SCNER was identified by Fourier transform infrared, ¹H NMR, and ¹³C NMR, it was used to modify the diglycidyl ether of the bisphenol A (DGEBA)/methylhexahydrophthalic anhydride system. The SCNER showed unique advantages, reducing the viscosity of DGEBA and improving the properties of the cured resin. With 10 wt % SCNER, the cured resin exhibited a higher tensile strength (78.84 MPa) and impact strength (32.36 kJ·m^-2). The single glass transition temperature (T _g) step proved the homogeneous phase structure of the cured resin. Inevitably, the T _g of the cured resin decreased for the addition of SCNER. The dynamic mechanical analysis results indicated that the storage modulus of the cured resin decreased with the increasing content of SCNER. The morphology showing the ductile fracture of the cured resin was testified by scanning electron microscopy. The dilution and toughening properties of SCNER paves the way to a wide range of possible "eco-friendly" applications, especially in the fields of coatings, paintings, and adhesives.