Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, we will review the current state of technology for utilizing lignin as a polyol replacement in different polyurethane products. This will include a discussion of lignin structure, diversity, and modification during chemical pulping and cellulosic biofuels processes, approaches for lignin extraction, recovery, fractionation, and modification/functionalization. We will discuss the potential of incorporation of lignins into polyurethane products that include rigid and flexible foams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating lignin in polyurethane formulations, potential solutions and approaches that have been taken to resolve those issues.

Despite several excellent properties including low shrinkage, good chemical resistance, curable at low temperatures and the absence of byproducts or volatiles, epoxy resins are susceptible to ultra violet (UV) damage and their durability is reduced substantially when exposed to outdoor environments. To overcome this drawback, UV absorbers have been usually used to decrease the rate of UV degradation. In this present study, the effects of UV light on the chemical, mechanical and physical properties of cured epoxy structure, as well as the effect of an organic UV absorber, Tinuvin 1130, on the epoxy properties were investigated. Chemical changes in a cured epoxy system as a result of the presence and absence of Tinuvin 1130 were determined using Fourier transform infrared spectroscopy (FT-IR) analyses. The effect of Tinuvin 1130 on the surface morphology of the epoxy systems was also investigated by scanning electron microscopy (SEM) imaging. Additionally, the glass transition temperatures (T_g) before and during UV radiation were measured. After an 800 h UV radiation, mechanical test results revealed that the lack of the UV absorber can lead to a ~30% reduction in tensile strength. However, in the presence of Tinuvin 1130, the tensile strength was reduced only by ~11%. It was hypothesized that the use of Tinuvin 1130, as an organic UV absorber in the epoxy-amine system, could decrease the undesirable effects, arising from exposure to UV light.

The aim of this study is to find a suitable substitution for diglycidyl ether bisphenol A (DGEBA) to avoid the devastating side effects of bisphenol A. Vanillin, an aromatic compound, was used as a renewable material to synthesize a bio-based epoxy resin. The structure of the vanillin-based epoxy resin was confirmed by Fourier transform infrared spectroscopy (FT-IR) analysis. The major drawback of bio-based epoxy resins is their poor mechanical properties preventing them from competing with petroleum based epoxy resins such as DGEBA. Herein, a prepared calcium nitrate solution as an inorganic accelerator was used to accelerate the curing reaction of bio-based epoxy resin which reduced curing times as well as improving significantly the mechanical properties e.g., tensile strength, pull-off strength, and Izod impact strength. Differential scanning calorimetry (DSC) analysis was used to investigate the curing process and thermal properties of the vanillin-based epoxy resin with and without inorganic accelerators and also DGEBA without accelerators. The results showed that in the presence of 2 wt% inorganic accelerator, the initial onset curing temperature of vanillin-based epoxy resin was reduced from 60.1 °C to 8.5 °C, while the initial onset curing temperature of DGEBA was 55.8 °C. In addition, tensile strength and Izod impact strength of the vanillin-based epoxy system in the presence of inorganic accelerators increased in comparison to the DGEBA system. Moreover, in order to study the effect of inorganic accelerators on the toughness of the synthesized vanillin-based epoxy resin, fracture surfaces from Izod impact strength tests were observed using scanning electron microscopy (SEM) which confirmed improving mechanical properties.

In this study, lignin, an aromatic compound from the forestry industry, was used as a renewable material to synthesize a new aromatic amine curing agent for epoxy resin. Firstly, lignin was separated from black liquor and hydroxyl groups were converted to tosyl groups as leaving groups. Then, primary amination was conducted using an ammonia solution at high pressure and temperature, in the presence of a nano-alumina-based catalyst. The structure of the nanocatalyst was confirmed by FT-IR, ICP, SEM, and XPS analyses. According to the FT-IR spectra, a demethylation reaction, the substitution of hydroxyl groups with tosyl groups, and then an amination reaction were successfully performed on lignin, which was further confirmed by the ¹³C NMR and CHNS analyses. The active hydrogen equivalent of aminated lignin was determined and three samples with 9.9 wt %, 12.9 wt %, and 15.9 wt % of aminated lignin, as curing agents, were prepared for curing the diglycidyl ether of bisphenol A (DGEBA). The thermal characteristics of the curing process of these epoxy samples were determined by DSC and TGA analyses. Moreover, the mechanical performance of the cured epoxy systems, e.g., the tensile strength and Izod impact strength, were measured, showing that in the presence of 12.9 wt % aminated lignin, the mechanical properties of the aminated lignin-epoxy system exhibited the best performance, which was competitive, compared to the epoxy systems cured by commercial aromatic curing agents.