Elaboration of Thermally Performing Polyurethane Foams, Based on Biopolyols, with Thermal Insulating Applications

In this work, biobased rigid polyurethane foams (PUFs) were developed with the aim of achieving thermal and fireproofing properties that can compete with those of the commercially available products. First, the synthesis of a biopolyol from a wood residue by means of a scaled-up process with suitable yield and reaction conditions was carried out. This biopolyol was able to substitute completely the synthetic polyols that are typically employed within a polyurethane formulation. Different formulations were developed to assess the effect of two flame retardants, namely, polyhedral oligomeric silsesquioxane (POSS) and amino polyphosphate (APP), in terms of their thermal properties and degradation and their fireproofing mechanism. The structure and the thermal degradation of the different formulations was evaluated via Fourier Transformed Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Likewise, the performance of the different PUF formulations was studied and compared to that of an industrial PUF. From these results, it can be highlighted that the addition of the flame retardants into the formulation showed an improvement in the results of the UL-94 vertical burning test and the LOI. Moreover, the fireproofing performance of the biobased formulations was comparable to that of the industrial one. In addition to that, it can be remarked that the biobased formulations displayed an excellent performance as thermal insulators (0.02371-0.02149 W·m-1·K-1), which was even slightly higher than that of the industrial one.

Fractionated lignin as a polyol in polyurethane fabrication

The main purpose of this paper was to systematically evaluate the effect of lignin, which was fractioned by green solvents into different molecular weights and used as polyol in the production of polyurethane foams (PUF). The results indicated that the foams prepared with the lower molecular weight lignin had uniform and complete pore structure and improved the mechanical strength. However, the higher molecular weight fraction lignin improved the density and thermal stability of the foam more significantly at the expense of inferior mechanical strength and pore structure deficiency. When the substitution degree of lignin in the PUF was 2 %-30 %, 99.13 % of the lowest molecular weight lignin was participated in the reaction to produce PUF, which improved the elongation at break (Eb) and tensile strength (Ts) of PUF to 834 % and 0.90 MPa, respectively. Also, thermal stability and the amount of unreacted lignin in PUF were increased at a higher substitution degree of lignin in PUF.

Biorenewable Oxypropylated Pentane-1,2,5-triol as a Source for Incorporation in Rigid Polyurethane Foams

In this study, as a product from the efficient Achmatowicz rearrangement and mild subsequent hydrogenation-reduction reactions of biorenewable C5 alcohols derived from lignocellulose, pentane-1,2,5-triol was successfully used after oxypropylation in the preparation of rigid polyurethane foams-one of the most important classes of polymeric materials. Despite the broad range of applications, the production of polyurethanes is still highly dependent on petrochemical materials considering the need of renewable raw materials and new process technologies for the production of polyol or isocyanate components as a key point for the sustainable development of polyurethane foams. The synthesized oxypropylated pentane-1,2,5-triol was analyzed using proton NMR spectroscopy, hydroxyl number, and viscosity, whereas the newly obtained foams incorporated with up to 30% biorenewable polyol were characterized using compressive stress, thermogravimetry, dynamic mechanical analysis, and scanning electron microscopy. The modified rigid polyurethanes showed better compressive strength (>400.0 kPa), a comparable thermal degradation range at 325-450 °C, and similar morphological properties to those of commercial polyurethane formulations.

New approach to recycle and valorize the first filtrate of the LignoForce system™: Lignin extraction and its use in rigid lignin-based polyurethane foams

In this work, we report on the fractionation, recovery and characterization of softwood kraft lignin from the first filtrate of the LignoForce™ process. It is estimated that the lignin content in this stream could be >20-30 % of the lignin present initially in the black liquor. The use of a membrane filtration system was experimentally validated as an effective method for fractionating the first filtrate. Two membranes with different nominal molecular weight cut-offs (4000 and 250 Da) were tested. Higher lignin retention and recovery was obtained using the 250-Da membrane. This lignin (lignin_250) was found also to have a lower molecular weight and a tighter molecular weight distribution compared to the lignin obtained using the 4000-Da membrane (lignin_4000). The lignin_250 was characterized for it's hydroxyl group content and used to produce polyurethane (PU) foams. Up to 30 wt% petroleum-based polyol replacement by lignin_250, the resulting lignin-based PU (LBPU) foams presented the same thermal conductivity as the control (0.0303 W/m.K (control) vs 0.029 W/m.K (30 wt%)), as well as comparable mechanical (max stress: 145.8 kPa (control) vs 222.7 KPa (30 wt%), modulus 64.3 kPa (control) vs 75.1 (30 wt%)) and morphological properties to the petroleum polyol-based PU foams.

Facile approach for nanoconfinement of multilayer graphene oxide with polyether polyurethane sponge as biological carrier for the establishment of microalgal-bacterial bioreactor

Physically precise and mechanically robust biocarrier is basic and urgent requirement of algal-bacterial wastewater treatment plants for homogenously biofilm growth. Herein, a highly efficient graphene oxide (GO) coordinated polyether polyurethane (PP) sponge was synthesized through GO incorporation into PP sponge to improve the GO coating, followed by UV-light treatment for industrial application. The resulted sponge showed remarkable physiochemical characteristics, excellent thermal (>0.02 Wm^-1 K^-1) and mechanical (>363.3 KPa) stability. To test the potential of sponge in real world scenarios, the activated sludge from real wastewater treatment plant was utilized. Interestingly, the GO-PP sponge enhanced the electron transfer between microorganisms and promoted the standardized microorganism's growth and biofilm formation (22.7 mg/d per gram sponge, 172.1 mg/g), providing the feasibility to accomplish a symbiotic system within specifically design upgraded algal-bacterial reactor. Furthermore, the continuous flow process by utilizing GO-PP sponge in algal-bacterial reactor demonstrated the effectiveness in treating low concentration antibiotic wastewater, presenting 86.7 % removal rate and >85 % after 20 cycles. Overall, this work illustrates an applicable strategy to develop a sophisticated modified pathway for the next-generation biological-based applications.

Studying the Suitability of Nineteen Lignins as Partial Polyol Replacement in Rigid Polyurethane/Polyisocyanurate Foam

In this study, nineteen unmodified lignins from various sources (hardwood, softwood, wheat straw, and corn stover) and isolation processes (kraft, soda, organosolv, sulfite, and enzymatic hydrolysis) were used to replace 30 wt.% of petroleum-based polyol in rigid polyurethane/polyisocyanurate (PUR/PIR) foam formulations. Lignin samples were characterized by measuring their ash content, hydroxyl content (Phosphorus Nuclear Magnetic Resonance Spectroscopy), impurities (Inductively Coupled Plasma), and pH. After foam formulation, properties of lignin-based foams were evaluated and compared with a control foam (with no lignin) via cell morphology, closed-cell content, compression strength, apparent density, thermal conductivity, and color analysis. Lignin-based foams passed all measured standard specifications required by ASTM International C1029-15 for type 1 rigid insulation foams, except for three foams. These three foams had poor compressive strengths, significantly larger cell sizes, darker color, lower closed-cell contents, and slower foaming times. The foam made with corn stover enzymatic hydrolysis lignin showed no significant difference from the control foam in terms of compressive strength and outperformed all other lignin-based foams due to its higher aliphatic and p-hydroxyphenyl hydroxyl contents. Lignin-based foams that passed all required performance testing were made with lignins having higher pH, potassium, sodium, calcium, magnesium, and aliphatic/p-hydroxyphenyl hydroxyl group contents than those that failed.

Bamboo-Based Biofoam Adsorbents for the Adsorption of Cationic Pollutants in Wastewater: Methylene Blue and Cu(II)

Human health is being threatened by cationic pollutants in wastewater, for example, methylene blue (MB) and Cu(II). Our research team successfully fabricated biofoam adsorbents from recycled bamboo waste that removed cationic pollutants via introducing bamboo fiber sources, i.e., bamboo fiber, bamboo α-cellulose fiber, and bamboo nanocellulose fiber, into a polyurethane (PU) foam matrix. The biofoam adsorbent with 1 g of nanocellulose (PUN1) presented high removal efficiencies for MB (95.52%) and Cu(II) (100%) in low cationic pollutant concentration aqueous solutions. The biofoam adsorbent with 1 g of bamboo fiber (PUB1) also displayed excellent removal efficiency for MB (98.61%) at pH 11. Meanwhile, 100% removal of Cu(II) was obtained by PUB1 at pH 7 (initial content = 15 mg/L). Furthermore, the PUN1 sample had excellent reusability, evidenced by 61.25% removal of MB after five adsorption-desorption cycles, suggesting that PUN1 is a promising renewable adsorbent for cationic pollutants. In addition, PUB1 is a low-cost adsorbent with good adsorption efficiencies for MB in weak alkaline solutions and Cu(II) in neutral aqueous solutions.

Flame Retardancy of Bio-Based Polyurethanes: Opportunities and Challenges

Sustainable polymers are emerging fast and have received much more attention in recent years compared to petro-sourced polymers. However, they inherently have low-quality properties, such as poor mechanical properties, and inadequate performance, such as high flammability. In general, two methods have been considered to tackle such drawbacks: (i) reinforcement of sustainable polymers with additives; and (ii) modification of chemical structure by architectural manipulation so as to modify polymers for advanced applications. Development and management of bio-based polyurethanes with flame-retardant properties have been at the core of attention in recent years. Bio-based polyurethanes are currently prepared from renewable, bio-based sources such as vegetable oils. They are used in a wide range of applications including coatings and foams. However, they are highly flammable, and their further development is dependent on their flame retardancy. The aim of the present review is to investigate recent advances in the development of flame-retardant bio-based polyurethanes. Chemical structures of bio-based flame-retardant polyurethanes have been studied and explained from the point of view of flame retardancy. Moreover, various strategies for improving the flame retardancy of bio-based polyurethanes as well as reactive and additive flame-retardant solutions are discussed.

Agricultural and Forest Residues towards Renewable Chemicals and Materials Using Microwave Liquefaction

Microwave-assisted liquefaction is regarded as a promising thermochemical approach to produce renewable and sustainable chemicals and materials from lignocellulosic biomass. Agricultural and forest residues as sources of lignocellulosic biomass have great potential in this regard. With process optimizations, several biomass types have been subjected to liquefaction in different solvents with various catalysts. The products from recent microwave liquefaction with and without further fractionation have been thoroughly analyzed and used for the synthesis of biomaterials. Renewable chemicals, polyurethane foams with partial use of renewable raw materials, and phenolic resins have been the main products from microwave-liquefied products. Further research on microwave liquefaction mechanisms and scalable production should be enhanced to fully evaluate the economic and environmental benefits. This work presents an overview on achievements using liquefaction in combination with microwave energy to convert lignocellulosic biomass into value-added products and chemicals.

Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives

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.

Preparation and Characterization of Rigid Polyurethane Foams with Different Loadings of Lignin-Derived Polycarboxylic Acids

Lignin was modified by oxidation to prepare lignin-derived polycarboxylic acids (LPCAs). LPCAs can be introduced into rigid polyurethane foams (RPUFs) via 1,4-dioxane. The expansion ratio and compressive strength of RPUFs were observed. When the loading of LPCAs was 0.67 wt% (based on polyol), the compressive strength of RPUF was the highest and was about 59.2% higher than that of the blank RPUF. The reinforcing mechanism of LPCAs was supposed that the interactions between LPCAs and RPUFs increased the strength of the cell walls. When the loading of LPCAs was less than 0.33 wt%, the expansion ratio of RPUFs increased slightly. The water resistance of RPUFs was not affected by LPCAs, suggesting that RPUFs with LPCAs could be used in a humid environment. Besides, the application of the oxidative modification products of lignin was broadened.

Ecofriendly Reduction of Methylene Blue with Polyurethane Catalyst

A number of physical, chemical, and biological technologies have been developed to address the issue of synthetic dyes in wastewater. One of the important chemical methods involves reduction of these stringent pollutants into less hazardous products. In this study, a cross-linked polyurethane foam (CPUF) was prepared from toluene diisocyanate (TDI), tetraethylenepentamine (TEPA), and polycaprolactone diol (PCL; Mw: 1000 g/mole). To avoid harmful reducing agents, ecofriendly reduction of methylene blue (MB) was executed with CPUF as catalyst where ascorbic acid and fresh juice extracts were applied as reducing agents. The FTIR and SEM analysis confirmed the chemical composition and porous morphology of CPUF, respectively. The 100% reduction of MB was recorded in just 15 minutes with ascorbic acid and CPUF, while similar result was obtained in 37 minutes in blank experiment composed of only MB and ascorbic acid. Thus, catalytic role of CPUF in reduction process was proved. Fresh fruit extracts also participated in the reduction process, but rate of reaction was accelerated in the presence of CPUF. The reusability study of the catalyst supported its stability and efficiency. All the successful reduction processes followed 1st-order kinetics with highest apparent rate constant for ascorbic acid. Furthermore, phytotoxicity evaluation proved safe reduction of MB with 60% germination index. Hence, it can be concluded that catalytic role of CPUF has been established with safe and biodegradable reducing agents which can be extended to other redox processes.

A Review of Microwave Assisted Liquefaction of Ligninin Hydrogen Donor Solvents: Effect of Solvents and Catalysts

Lignin, a renewable source of aromatic chemicals in nature, has attracted increasing attention due to its structure and application prospect. Catalytic solvolysis has developed as a promising method for the production of value-added products from lignin. The liquefaction process is closely associated with heating methods, catalysts and solvents. Microwave assisted lignin liquefaction in hydrogen donor solvent with the presence of catalysts has been confirmed to be effective to promote the production of liquid fuels or fine chemicals. A great number of researchers should be greatly appreciated on account of their contributions on the progress of microwave technology in lignin liquefaction. In this study, microwave assisted liquefaction of lignin in a hydrogen donor solvent is extensively overviewed, concerning the effect of different solvents and catalysts. This review concludes that microwave assisted liquefaction is a promising technology for the valorization of lignin, which could reduce the reaction time, decrease the reaction temperature, and finally fulfill the utilization of lignin in a relatively mild condition. In the future, heterogeneous catalysts with high catalytic activity and stability need to be prepared to achieve the need for large-scale production of high-quality fuels and value-added chemicals from lignin.

Effects of Surface Functionalization of Lignin on Synthesis and Properties of Rigid Bio-Based Polyurethanes Foams

We report the preparation of lignin-based rigid polyurethane (RPU) foams from surface functionalized kraft lignin via a simple and environmentally benign process. Lignin was functionalized with polyisocyanate at 80 °C for 1 h, the resulting lignin-polyisocyanate prepolymer was confirmed by increased viscosity and Fourier-transform infrared spectroscopy (FTIR). The RPU foams containing up to 30% surface functionalized lignin as a substitute for petroleum-based polyols exhibited comparable thermal and mechanical properties to conventional RPU foams. The lignin-based RPU foams prepared from surface functionalization outperformed RPU foams without the surface functionalization, showing up to 47% and 45% higher specific compressive strength and modulus, respectively, with a 40% lignin substitution ratio. Thermal insulation and temperature-stability of the two types of the foams were comparable. The results indicate that the surface functionalization of lignin increases reactivity and homogeneity of the lignin as a building block in RPU foams. The life cycle assessment for the lignin-based RPU foams shows that the surface functionalization process would have overall lesser environmental impacts when compared with the traditional manufacturing of RPU foams with synthetic polyols. These findings suggest the potential use of surface functionalized lignin as a sustainable core material replacement for synthetic polyols in building materials.