Mechanical and Insulation Performance of Rigid Polyurethane Foam Reinforced with Lignin-Containing Nanocellulose Fibrils.

Isocyanates are critical components that affect the crosslinking density and structure of polyurethane (PU) foams. However, due to the cost and hazardous nature of the precursor for isocyanate synthesis, there is growing interest in reducing their usage in polyurethane foam production-especially in rigid PU foams (RPUF) where isocyanate is used in excess of the stoichiometric ratio. In this study, lignin-containing nanocellulose fibrils (LCNF) were explored as mechanical reinforcements for RPUF with the goal of maintaining the mechanical performance of the foam while using less isocyanate. Different amounts of LCNF (0-0.2 wt.%) were added to the RPUF made using isocyanate indices of 1.1, 1.05, 1.0, and 0.95. Results showed that LCNF served as a nucleating agent, significantly reducing cell size and thermal conductivity. LCNF addition increased the crosslinking density of RPUF, leading to enhanced compressive properties at an optimal loading of 0.1 wt.% compared to unreinforced foams at the same isocyanate index. Furthermore, at the optimal loading, LCNF-reinforced foams made at lower isocyanate indices showed comparable stiffness and strength to unreinforced foams made at higher isocyanate indices. These results highlight the reinforcing potential of LCNF in rigid polyurethane foams to improve insulation and mechanical performance with lower isocyanate usage.

Extraction of lignin-containing nanocellulose fibrils from date palm waste using a green solvent.

Lignin-containing nanocellulose (LNC) is a compelling alternative to traditional nanocellulose (NC), it offers enhanced yields and a reduction in the demand for toxic chemicals. This research involves the isolation of LNC from date palm waste using a green hydrolysis process and its subsequent characterization. The potential of using ionic liquids (ILs) as green solvents to isolate LNC has not yet been explored. Our findings suggest that 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) can hydrolyze partially delignified and unbleached lignocellulose, achieving LNC synthesis. The obtained LNC showed a higher yield than its NC counterpart and exhibited rod-shaped fibers with nanoscale diameters and micrometer lengths, indicating a high aspect ratio. Dynamic Light Scattering (DLS) results indicate average particle sizes of 143.20 nm for NC and 282.30 nm for LNC, with a narrow particle size distribution conforming their monodisperse behavior. Thermogravimetric analysis and differential scanning calorimetry revealed high thermal stability (initial degradation temperature = 222.50 °C and glass transition temperature = 84.45°C) of LNC. Moreover, the obtained LNC fibers were crystalline (crystallinity index = 52.76 %). Their activation energy (124.95 kJ/mol) was determined using the Coats-Redfern method by employing eight solid-state diffusion models. Overall, this study motivates the use of ILs as green solvents to produce lignocellulose derivatives that are suitable for various applications.

Supramolecular structure of microwave treated bamboo for production of lignin-containing nanocellulose by oxalic acid dihydrate.

Supramolecular structure of cellulosic materials from microwave treatment were throughly investigated for production of lignin-containing nanocellulose. The results revealed that both the intermolecular and intramolecular hydrogen bonds were altered by microwave irradiation. Cellulose Iß was the main component in microwave treated bamboo (MTB) with smaller interplanar spacing, and the cellulose molecules were loosely connected resulting in a loose structure. Thereafter, MTB was used to produce lignin-containing nanocellulose by using oxalic acid dihydrate (OAD) to test the feasibility on its efficiency. The chemical consumed for the preparation of lignin-containing nanocellulose (LCN) with a comparable yield (68.08-82.33 %) from MTB was merely 1/10 that from conventional cellulosic materials, indicating the supramolecular structural changes of bamboo cellulose induced by microwave treatment provided suitable conditions for the subsequent hydrolysis of OAD to prepare LCN. The LCN was further added into the polyvinyl alcohol (PVA) matrix endowed excellent UV shielding property and thermal stability for the PVA/LCN films. This study was aimed to provide an environmentally friendly method on the production and application of LCN from bamboo by employing microwave treatment from the perspective of supramolecular level.

In Vitro Evaluation of Lignin-Containing Nanocellulose.

The increasing importance of environmental sustainability has led to the development of new materials that are environmentally friendly, functional, and cost-effective. Lignin-containing cellulose nanomaterials are a common example of these. The advantages of lignocelluloses include their renewability, sustainability, and functionality combined with molecular rigidity and enhanced hydrophobicity. In order to valorize these beneficial traits from lignin-containing nanocellulose, various approaches have been examined in industrial applications. However, the safety of these materials has not been tested or validated in humans. In this study, we tested 21 wt% lignin-containing nanocellulose (L-MFC) in vitro using the human lung and kidney cell lines, H460 and HEK293 cells, respectively. The cytotoxicity of cellulose, L-MFC, and lignin was compared using the water-soluble tetrazolium salt assays. In addition, the gene expressions of HSP70 and HSP90 as cellular stress markers treated with cellulose, L-MFC, and lignin were quantified using real-time polymerase chain reaction (PCR) and Western blotting. Our data indicated little cytotoxicity for cellulose and significant cytotoxicity for lignin and a relatively low level of cytotoxicity for L-MFC, providing the lethal median concentration (LC50) values of L-MFC and lignin. The gene expression of HSP70 and HSP90 was little affected by moderate concentrations of L-MFC. Interestingly, the lignin contained in L-MFC influenced the cell viability and the gene expression of HSP70 and HSP90 less than the same amount of lignin alone. These results indicate that L-MFC displays cell-type-dependent sensitivity and suggest that L-MFC could serve as a new eco-friendly material that is relatively safe for humans.

Production of lignin-containing cellulose nanofibers using deep eutectic solvents for UV-absorbing polymer reinforcement.

Lignin-containing cellulose nanofibers (LCNFs) from energy cane bagasse (ECB), were prepared using microwave assisted deep eutectic solvent (MV-DES) treatment in combination with ultrasonication. The yield of lignocellulose is up to 45.2 % with 81.0 % delignification under the optimal reaction condition (110 ℃, 30 min). The resulting LCNF exhibited a highly entangled network, which was caused by the binder role of lignin between cellulose nanofibers. The addition of LCNFs improved the stability of the polyanionic cellulose (PAC) film-forming suspension, which was confirmed by the increased zeta potential and viscosity values. The LCNF / PAC films showed tunable mechanical and UV-resistant properties, depending on the amount and type of LCNFs. PAC films with the addition of 5 % LCNFs (PEF-5 %) showed good mechanical properties (a tensile strength of 55.8 MPa with a 26.3 % strain to break) and high UV protection ability (a UV-transmittance of 2.9 %).

Acidic deep eutectic solvent assisted isolation of lignin containing nanocellulose from thermomechanical pulp.

Nanocellulose is a promising material but its isolation generally requires unrecyclable hazardous chemicals and high energy consumption and its overall yield is low due to the use of high purity cellulose as precursor. In order to overcome these shortcomings, in this study, thermomechanical pulp (TMP) was investigated as a precursor for isolating lignin containing nanocellulose (LNC) using an environmentally friendly acidic deep eutectic solvent (DES) pre-treatment. Flat "ribbon" like LNCs (around 7.1 nm wide, 3.7 nm thick) with uniformly distributed lignin nanoparticles of 20-50 nm in diameter were successfully obtained at 57 % yield under optimum pre-treatment conditions (90 °C, 6 h, 1:1 oxalic acid dihydrate to choline chloride ratio). The LNCs exhibit cellulose Iß structure, high lignin content (32.6 %), and high thermal stability (Tmax of 358 °C). In general, green acidic DES pre-treatment has shown high efficiency in converting high lignin content biomass into value-added LNC, which benefits both lignocellulose utilization and environmental protection.