Synergistic effect of lignin and ethylene glycol crosslinked epoxy resin on enhancing thermal, mechanical and shape memory performance

Improvements in the Production of Isosorbide Monomethacrylate Using a Biobased Catalyst and Liquid-Liquid Extraction Isolation for Modifications of Oil-Based Resins

The improved production of a polar curable monomer, isosorbide monomethacrylate (MISD), with methacrylic anhydride (MAAH) as an acyl donor, was performed. A sustainable and cheap catalyst, potassium acetate (CH3COOK), was used for a solvent-free synthesis, requiring only the equimolar amount of reagents (no excess). The production included the quantitative separation of the secondary product, methacrylic acid (MAA), preventing the reaction batch from the purification process (neutralization of MAA), and gaining a usable reagent. The synthesis resulted in a sufficient yield of MISD (61.8%) obtained by the liquid-liquid extraction process (LLE), which is a significant improvement in the process, avoiding the flash chromatography step in the isolation of MISD. The purity of synthesized and isolated MISD via the LLE was confirmed by 1H NMR, MS, and FTIR analyses. The thermal analyses, namely, DSC and TGA, were used to characterize the curability and thermal stability of MISD. The activation energy of MISD's curing was calculated (E a = 94.6 kJ/mol) along with the heat-resistant index (T s = 136.8). The polar character of isosorbide monomethacrylate was investigated in a mixture with epoxidized acrylated soybean oil (EASO). It was found that MISD is entirely soluble in EASO and can modify the rheological behavior and surface energy of EASO-based resins. The apparent viscosity of EASO at 30 °C (ηapp = 3413 mPa·s) decreased with the 50% content of MISD significantly (ηapp = 500 mPa·s), and the free surface energy value of EASO (γS = 42.2 mJ/m2) also increased with the 50% content of MISD (γS = 48.7 mJ/m2). The produced MISD can be successfully used as a diluent and the polarity modifier of curable oil-based resins.

Fully bio-based epoxy resins from lignin and epoxidized soybean oil: Rigid-flexible, tunable properties and high lignin content

The application of epoxidized soybean oil (ESO) in thermosetting polymers is impeded by its unsatisfactory thermomechanical properties. Here, in order to address the limitation, technical lignin was modified by tung oil anhydride and then used as the hardener to compensate for the inherent flexibility defects of ESO thermosets (TLs). As the lignin content increased, a notable improvement in the activation energy of TLs was observed, attributed to the restraining effect of lignin's rigid structure on segmental relaxation. Concurrently, the tensile strength of TLs increased from 2.8 MPa to 34.0 MPa, concomitant with a decrease in elongation at break from 32.9 % to 8.0 %. Comparative analysis with TL-0 (devoid of lignin) demonstrated substantial enhancements in glass transition temperature, shape fixation ratio, and shape recovery ratio for TL-50 (comprising 50 wt% of lignin), elevating from 16.9 °C, 89.1 %, and 89.5 % to 118.6 °C, 94.0 %, and 99.3 %, respectively. These results unequivocally highlight the favorable dynamic mechanical and shape memory properties conferred upon TLs by lignin addition. While the introduction of lignin adversely affected thermal stability, a notable improvement in char yield (800 °C) was observed. Collectively, these findings underscore the potential of technical lignin as a promising bio-based curing agent for ESO.

New Approach to Shape Memory Polymer Composite Production Using Alkaline Lignin-Reinforced Epoxy-Based Shape Memory Polymers

In the past few decades, there has been continued interest in shape memory polymers (SMPs), and tremendous efforts have been made to develop multifunctional composites of these SMPs to enhance the existing properties of SMPs. Although fossil-based sources are widely used in the production of shape memory polymer composites (SMPCs), the depletion of fossil-based resources and associated environmental problems increase interest toward renewable biobased products synthesized from natural resources. This study aims to produce alkaline lignin-reinforced SMPCs by using alkaline lignin in the SMP matrix. Thermo-mechanical, morphological, and shape memory tests are performed in order to reveal the effect of alkaline lignin usage in the SMP matrix on SMPC production. Differential scanning calorimetry analysis results show that adding alkaline lignin into the SMP matrix with 1 and 3% ratios led to an increase in T _g values, while raising the alkaline lignin ratio to 5% decreased the T _g value. According to the DMA results, increasing the alkaline lignin ratios caused an increase in the storage modulus of SMPCs, and the best storage modulus value was obtained at the 5% alkaline lignin ratio. The results of the three-point bending test also confirmed the results obtained from the DMA analysis, showing that an increasing alkaline lignin ratio caused an increase in the bending modulus. Scanning electron microscopy analysis showed a rough structure in 1 and 3% alkaline lignin supplementation, while a smoother structure was observed in 5% alkaline lignin supplementation. The smoother structure of the sample containing 5% alkaline lignin indicates that alkaline lignin supplementation exhibits a smoother surface by showing a plasticizing effect. As a result, it was observed that increasing the lignin ratio increased the polymer/alkaline lignin interaction, resulting in a harder structure and an increase in the flexural modulus value.

Simultaneously reinforcing and toughening of shape-memory epoxy resin with carboxylated lignosulfonate: Facile preparation and effect mechanism

To improve the compatibility and reactivity of lignosulfonate (LS) with epoxy oligomers, the LS was firstly functionalized with anhydride via the carboxylation reaction. The carboxylated lignosulfonate (CLS) reinforced epoxy resin with excellent mechanical and shape memory performance was prepared facilely via distributing the CLS into the combined epoxy monomers of DGEBA and PEGDGE with the aid of water, rather than using the normal organic solvents. The incorporated CLS promoted the curing reaction of epoxy resin. A typical sea-island structure was formed in the cured sample at the CLS content of 5 phr, exhibiting the highest increases in tensile strength, modulus, elongation at break and toughness by 23.8 %, 18.2 %, 217 % and 113 %, respectively, relative to neat epoxy. Interestingly, the incorporation of CLS at a proper amount led to the simultaneous strengthening and toughing effects on cured epoxy resin, which could be attributed to the rigid structure of CLS covalently introduced in the epoxy resin network and the heterogeneous structure formed in the epoxy matrix. The rigid CLS component also restrained the movement of chain segments, consequently, the mechanical stability was enhanced and the fast shape recovery rate of epoxy resin network was slowed down to some extent.

A lignin-based epoxy/TiO2 hybrid nanoparticle for multifunctional bio-based epoxy with improved mechanical, UV absorption and antibacterial properties

Lignin, as a natural polymer material, has the advantages of green safety, renewable, and pollution-free. It has a wide application prospect in the field of thermosetting. However, it has been attractive but a huge challenge to design high performance and high added-value lignin-based epoxy resin. Herein, lignin-based epoxy (LEP) was synthesized from moso bamboo-derived lignin, and then lignin-based epoxy/titanium dioxide (LEP/TiO₂) hybrid nanoparticle was synthesized via liquid deposition method for modifying lignin-based epoxy resin to prepare multifunctional bio-based epoxy. The results show that the LEP/TiO₂ hybrid nanoparticle exhibits a stable topological surface shape and good dispersion and uniformity. By adding 10 wt% LEP/TiO₂ hybrid nanoparticles, the multifunctional bio-based epoxy exhibits good mechanical strength and toughness, and the tensile strength and fracture toughness reach 36 MPa and 1.26 MPa·m^1/2, respectively. In addition, the thermal stability, UV absorption and antibacterial properties of the multifunctional bio-based epoxy are further improved. This study provides a facile and efficient method for the preparation of high-performance multifunctional bio-based epoxy composite and a novel solution for the utilization of lignin.