New foaming formulations for production of bio-phenol formaldehyde foams using raw kraft lignin

Synthesis of a reactive lignin-based flame retardant and its application in phenolic foam

To improve the flame retardancy of phenolic foam from the perspective of sustainable development, it is a feasible way to add bio-based flame retardants into phenolic foam. Lignin has a similar structure to phenol, which provides a possibility to replace part of phenol. In this paper, we prepared a kind of reactive bio-based flame retardant based on enzymatic hydrolyzed lignin, in which side chain was chemically grafted with phosphorus and nitrogen and benzene ring would participate in the phenolic condensation reaction. According to elemental analysis and ICP-OES data, the content of nitrogen and phosphorus in modified lignin (NP-L) increased to 2.95% and 3.55% respectively. Compared with original lignin, the carbon residue rate of NP-L increased from 3.25% to 12.13% because of the presence of flame retardant elements N and P. Then lignin-based flame retardant was used to replace phenol for modifying phenolic foams (NPLPFX). The limited oxygen index (LOI) and compressive strength of phenolic foam were improved effectively by adding modified lignin when the substitution rate was less than 25%. The LOI and compressive strength of the modified phenolic foam with 5% replacement amount (NPLPF5) are 55.6% and 0.24 MPa, which increased by 88% and 60% compared with pure phenolic foam. The cone calorimetric data also showed that NPLPF5 had good flame retardancy, and the peak heat release rate and total heat release were significantly lower than PF. This work suggests a novel green strategy for improving the flame retardancy performance of phenolic foam and promoting the utilization of lignin.

Insights into the Relationship between the Microstructure and the Catalytic Behavior of Fe2(MoO4)3 during the Ethanolysis of Naomaohu Coal

Ethanolysis is an effective method to depolymerize weak bonds in lignite under mild conditions, which can result in the production of high-value-added chemicals. However, improving ethanolysis yield and regulating its resulting product distribution is a big challenge. Hence, exploiting highly active catalysts is vital. In this work, Fe2(MoO4)3 catalysts with zero-dimensional nanoparticles, one-dimensional (1D) nanorods, two-dimensional (2D) nanosheets, and three-dimensional (3D) nanoflower structures were successfully prepared and applied in the ethanolysis of Naomaohu coal. The results showed that for all samples, the yield of ethanol-soluble portions (ESP) was significantly improved. The highest yield was obtained for the Fe2(MoO4)3 nanorods, with an increase from 28.84% to 47.68%, and could be attributed to the fact that the Fe2(MoO4)3 nanorods had a higher number of exposed active (100) facets. In addition, the amounts of oxygen-containing compounds, such as ethers, esters, and phenols, increased significantly. The mechanism of ethanolysis catalyzed by the Fe2(MoO4)3 nanorods was also studied using phenylbenzyl ether (BOB) as a model compound. BOB was completely converted at 260 °C after 2 h. It is suggested that Fe2(MoO4)3 nanorods can effectively break the C-O bonds of coal macromolecules, thus promoting the conversion of coal.

Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process

Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a "green" levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.

Improved flame retardancy and smoke suppression properties of phenolic resin by incorporating MoO3 particles

Phenolic resin (PF) is widely used in aerospace, composite materials, and other fields. However, large amount of heat and smoke are produced during its combustion process, which is an important factor limiting its usage. To solve this problem, additive flame retardant MoO3 has been incorporated into PF for improving its flame retardancy and smoke suppression properties. Thermogravimetric analyses results show that the T5% of PF composites was gradually decreased from 264°C to 184°C and the char yield of PF-10% MoO3 is 57 wt.%, higher than that of neat PF (50 wt.%). The PF composites with 10 wt.% MoO3 passed UL-94 V-0 rating with a limiting oxygen index value of 29.8%. Meanwhile, the total heat release and total smoke production of PF-10% MoO3 are 37.60 MJ/m2 and 5.79 m2 respectively, which are reduced by 30.5% and 24.8% compared with neat PF. Only 10 wt.% MoO3 provide a 56.5% reduction (from 255 to 111) in maximal smoke density, meaning the good smoke suppression properties of MoO3. The pyrolysis products components are determined by thermogravimetric analysis combined with Fourier transform infrared spectroscopy. Furthermore, the micromorphology and chemical structure of char residue are also investigated by scanning electron microscopy, x-ray diffraction and Raman spectroscopy techniques. The promoting carbonization effect of MoO3 significantly reduces the heat release and toxic smoke production of PF composites.

On the Development of Phenol-Formaldehyde Resins Using a New Type of Lignin Extracted from Pine Wood with a Levulinic-Acid Based Solvent

Resole resins have many applications, especially for foam production. However, the use of phenol, a key ingredient in resoles, has serious environmental and economic disadvantages. In this work, lignin extracted from pine wood using a "green" solvent, levulinic acid, was used to partially replace the non-sustainable phenol. The physicochemical properties of this novel resin were compared with resins composed of different types of commercial lignins. All resins were optimized to keep their free formaldehyde content below 1 wt%, by carefully adjusting the pH of the mixture. Substitution of phenol with lignin generally increases the viscosity of the resins, which is further increased with the lignin mass fraction. The addition of lignin decreases the kinetics of gelification of the resin. The type and amount of lignin also affect the thermal stability of the resins. It was possible to obtain resins with higher thermal stability than the standard phenol-formaldehyde resins without lignin. This work provides new insights regarding the development of lignin-based resoles as a very promising sustainable alternative to petrol-based resins.

Effect of Impregnated Phenolic Resins on the Cellulose Membrane for Polymeric Insulator

In this study, a cellulose membrane (CM) was chemically treated with phenolic (PF) resin to improve its performance as a polymeric insulator. The CM was prepared from kenaf pulp, and the PF was synthesized from oil palm empty fruit (EFB) fibre. Four different concentrations of synthesized PF resin (5, 10, 15, and 20 wt.%) were impregnated under wet or dry conditions. Thermal analysis of the phenolic cellulose membrane (PCM) showed that the samples had good chemical interaction and compatibility. The PF uptake in the wet phenolic cellulose membrane (PCMW) was higher than in the dry phenolic cellulose membrane (PCMD). During the PF uptake, the CM underwent solvent exchange and absorption in wet and dry membranes, respectively. This difference also affected the crosslinking of PCM samples via the formation of methylene bridges. Due to the PF treatment, the PCM showed lower water absorption than CM. The PF concentrations also affect the surface roughness and electrical properties of PCM samples. These findings prove that PCM can be used as a renewable and green polymer electrical insulator.

Comparison of dehydration methods for untreated lignin resole by hot air oven and vacuum rotary evaporator to synthesize lignin-based phenolic foam

We investigate two different dehydration methods to determine their suitability for preparing resoles for foam synthesis. A simplified process for synthesizing lignin foam (LF) from lignin resole (LR) dehydrated in a hot air oven (HAO) is compared with that dehydrated using a vacuum rotary evaporator (VRE). First, the LR formulation is prepared by mixing phenol with untreated lignin (0%–15% by weight), and subsequently, the prepared LRs are dehydrated using an HAO and a VRE. We find that for the same dehydration time, both techniques yield LRs with the same chemical compositions; however, the HAO technique affords a moisture removal of 13–17% by weight, whereas the VRE technique removes 9–12% moisture by weight. The LR obtained by the HAO is more viscous and maintains a circular shape after being dropped on a plate. In our experimental synthesis of LF containing VRE resole, biofoam is not formed owing to insufficient viscosity, whereas biofoam is obtained with the HAO resole. The synthesized LF exhibits a density range of 44.96–85.68 kg/m³ and a compressive strength of 103.28–152.27 kPa. Scanning electron microscopy investigations show that the morphology of the foam is a closed-cell structure. The simplified synthesis of LF from the HAO-treated resole offers significant advantages over the complexity of the conventional VRE approach in terms of equipment cost and energy consumption. The resulting foam exhibits a thermal stability and thermal performance comparable with the counterpart properties of phenolic foam.

Revisiting lignin: a tour through its structural features, characterization methods and applications

A pedagogical overview of the main extraction procedures and structural features, characterization methods and state-of-the-art applications.

Lignin Particles for Multifunctional Membranes, Antioxidative Microfiltration, Patterning, and 3D Structuring

We introduce a new type of particle-based membrane based on the combination of lignin particles (LPs) and cellulose nanofibrils (CNF), the latter of which are introduced in small volume fractions to act as networking and adhesive agents. The synergies that are inherent to lignin and cellulose in plants are re-engineered to render materials with low surface energy (contact angle measurements) and can be rendered water-resistant with the aid of wet-strength agents (WSAs). Importantly, they are most suitable for antioxidative separation (ABTS^•+ radical inhibition): membranes with uniform porous structures (air permeability and capillary flow porosimetry) allow effluent oxidation at 95 mL/cm², demonstrating, for the first time, the use of unmodified lignin particles in flexible membranes for active microfiltration. Moreover, the membranes are found to be nonfouling (protein adhesion and activity rate). The inherent properties of lignin, including UV radiation blocking capacity (UV transmittance analysis) and reduced surface energy, are further exploited in the development of tailorable and self-standing architectures that are almost entirely comprised of nonbonding LP (solids content as high as 92 w/w%). Despite such composition, the materials develop high toughness (oscillatory dynamic mechanical analysis), owing to the addition of minor amounts of CNF. Multifunctional materials based on thin films (casting), 3D structures (molding), and patterned geometries (extrusion deposition) are developed as a demonstration of the potential use of lignin particles as precursors of new material generation. Remarkably, our observations hold for spherical LPs since a much poorer performance was observed after using amorphous powder, indicating the role of size and shape in related applications.

Novel Synthesis of Nitrogen-Containing Bio-Phenol Resin and Its Molten Salt Activation of Porous Carbon for Supercapacitor Electrode

Nitrogen hybridization is an attractive way to enhance the wettability and electric conductivity of porous carbon, which increases the capacitance of carbon-based supercapacitor, however, there is lack of low-cost methods to prepare the nitrogen-doped porous carbon materials. Herein, a novel facile nitrogen-containing bio-phenolic resin was synthesized by polymerization of the carbamate bio-oil, Phenol and paraformaldehyde. As a precursor of nitrogen-doped porous carbon, the nitrogen-containing bio-phenol resin was activated by the one-step molten-salt method. The resultant nitrogen-doped porous carbon showed a high specific surface area up to 1401 m²·g⁻¹. As a supercapacitor electrode, the nitrogen-doped porous carbons showed specific capacitance of 159 F·g⁻¹ at 0.5 A·g⁻¹. It also exhibited high cyclic stability with 94.8% retention of the initial specific capacitance over 1000 charge-discharge cycles at 1.0 A·g⁻¹. The results suggest that these nitrogen-containing bio-phenol resin provide a new source of nitrogen-doped porous carbon for high-performance supercapacitor electrodes.

Recent Trends of Foaming in Polymer Processing: A Review

Polymer foams have low density, good heat insulation, good sound insulation effects, high specific strength, and high corrosion resistance, and are widely used in civil and industrial applications. In this paper, the classification of polymer foams, principles of the foaming process, types of blowing agents, and raw materials of polymer foams are reviewed. The research progress of various foaming methods and the current problems and possible solutions are discussed in detail.