Liquid Polyol Research Articles

Tuning of molecular weight and chemical composition of polyols obtained from Poly(ethylene terephthalate) waste recycling through the application of organocatalysts in an upcycling route

High molecular weight liquid polyols were produced from complex Poly (ethylene terephthalate) (PET) waste (low molecular weight PET waste, monolayer compounds, and coloured PET bottles) in one-step synthesis using mild reaction conditions. For the first time, a wide range of upcycled polyols were obtained by modulating the reaction conditions to control the chemical composition and molecular weight, in order to revalorize the same PET waste in different polyols.A new versatile, efficient, selective and sustainable chemical recycling method was developed, employing cheap reagents (ethylene carbonate) and basic organocatalysts, under mild reaction conditions (moderate temperatures and atmospheric pressure). Chemically, the polyols showed a singular composition, consisting of three types of repeating units, two coming from PET and one belonging to the ethylene carbonate ring-opening. Depending on the depolymerisation conditions of the PET waste and the catalyst used, the ratio between these moieties varied considerably, giving rise to a wide portfolio of liquid polyols. In addition, the ability of the organocatalyst to introduce the carbonate unit into the polyol chain was analysed as a function of the number of ethylene carbonate units used.As a proof of concept, these new liquid secondary raw materials served as a starting point for the synthesis of polyurethanes under standard conditions. Ultimately, the final objective of this upcycling process will be the application of a wide range of high-quality polyols as soft segments to produce more sustainable and high-performance polyurethanes (flexible foams, coatings, sealants, adhesives, elastomers).

From Lignins to Renewable Aromatic Vitrimers based on Vinylogous Urethane.

During the last decades, Covalent Adaptable Networks (CANs) have proven to be an important new class of polymer materials combining the main advantages of thermoplastics and thermosets. For instance, materials can undergo reprocessing cycles by incorporating dynamic covalent bonds within cross-linked network. Due to their versatility, renewable resources can be easily integrated into these innovative systems to develop sustainable materials, which can be related to the context of the recent development of circular bioeconomy. Lignins, the main renewable sources of aromatic structures, is a major candidate in the design of novel and biobased stimuli-responsive materials such as vitrimers due to their high functionality and specific chemical architectures. In the aim of developing recyclable lignin-based vinylogous urethane (VU) networks, an innovative strategy was elaborated in which lignin was first modified into liquid polyols, and then into polyacetoacetates. Resulting macromonomers were integrated into aromatic VU networks and fully characterized through thermal, mechanical, and rheological experiments. Viscoelastic behaviors of the different aromatic vitrimers exhibited fast stress-relaxations (e.g., 39s at 130°C) allowing easy and fast mechanical reprocessing. A thermomechanical recycling study was successfully performed. Then, the developed strategy enabled the fabrication of healing biobased aromatic vitrimers with tunable structural design and properties.

Scale-Up for the Conversion of Corn Stover-Derived Levulinic Acid into 2-Methyltetrahydrofuran

Previous research has identified attractive chemical pathways to form levulinic–lactic acid mixtures from corn stover. Unfortunately, there is little market demand for levulinic acid, so conversion into more useful chemicals is needed. Presented herein are the results from a study to translate and optimize two lab-scale reactions that can be used to transform levulinic acid into a useful platform chemical, 2-methyltetrahydrofuran (2-MeTHF), to the continuous bench-scale. 2-MeTHF is an important monomer for the production of liquid polyols, which are used in polymer foam products. First, a hydrogenation reaction takes place, transforming levulinic acid into γ-valerolactone (GVL) by reaction with isopropanol using a Zr-β-zeolite catalyst. Next, the GVL is reacted with hydrogen to form 2-MeTHF utilizing a CuO/Al2O3 catalyst. Both reactions were optimized in bench-scale continuous flow reactors designed to produce 0.613 kg/h of 2-MeTHF from an initial feed of 1.02 kg/h of levulinic acid with a single pass conversion of 81 mol%.

Preparation and Application of Ultrafine Copper Powder

Ultrafine copper powder has the excellent characteristics of both copper and ultrafine particles and has been widely used in industry. Different fields have different requirements for ultrafine copper powder, so various preparation methods have been derived. In this paper, the characteristics of electrolysis, liquid phase reduction, hydrothermal method and polyol method are analyzed. Some new preparation methods with novel ideas are also enumerated. Also, the applications of ultrafine copper powder are described. In electronic industry, ultrafine copper powder can be used in preparing conductive paste of multilayer ceramic capacitor (MLCC) and conductive ink. In catalysts, copper powder can catalyze the reaction alone, can be loaded on other substances and form alloys with other metals for catalysis. In antibacterial materials, copper nanoparticles can distort the DNA of bacteria and interrupt its biochemical process. Finally, the application trend of ultrafine copper powder is prospected, which is helpful to develop new synthesizing methods and applications of ultrafine copper powder.

Direct conversion of waste polyesters to low molecular weight polyols for polyurethane production

An effective process for synthesizing liquid dihydroxyl group-ended oligomers directly from waste polyethylene terephthalate (PET) using a metal chelating agent, ethylenediaminetetraacetic acid (EDTA), is described in this study. The deactivation of transesterification catalyst was confirmed by a model process that involves the reaction of bis(2-hydroxyethyl) terephthalate with diethylene glycol under different catalytic conditions. The depolymerization of PET was performed with an excess amount of diethylene glycol and Zn2+ catalysts to form intermediates. The chelating agent was then introduced as a catalytic defunctionalizer, after which the residual glycols were distilled and recovered under reduced pressure. The obtained polyols were characterized by 1H and 13C nuclear magnetic resonance, gel permeation chromatography, and viscometry. Utilizing EDTA showed high efficiency in blocking catalysts during high-temperature distillation, resulting in maximum trimer chain-length sized and low-viscosity liquid polyols. Subsequently, thermoplastic polyurethanes (TPUs) were prepared using synthesized polyols as the soft segment, with 4,4’-methylene-bis(phenyl isocyanate) and 1,4-butanediol as the isocyanate and chain extender, respectively. The final TPUs were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, and mechanical testing.

Lignin as a Renewable Building Block for Sustainable Polyurethanes.

Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed.

Toughness Improvement of Epoxy Composites Using a Kind of Environment-Friendly Bio-Based Polyester Polyol

Epoxy resin (EP) is a thermosetting resin with prominent performances and wide applications. However, the inherent brittleness limits its development in the engineering materials area. A liquid bio-based polyester polyol (LLP) with flexible long chains was synthesized in this study by melt polycondensation of corn straw lignin. After being compounded with EP (LLP/EP), the mechanical property, micromorphology and thermal behavior of the composite were evaluated. The experimental result indicated that the fracture brittleness of EP composite was decreased by importing the LLP. The bending and impact strength were up to 113.67 MPa and 51.29 kJ/m2 for 10%-LLP/EP, which were 5.25% and 27% higher than those of unmodified EP. The results of this work build new avenues for the efficient utilization of lignin and the development of low-cost, high-performance and well environmentally adaptable EP composite by renewable resources.Graphical Abstract

Science and Business Developments

Science and Business Developments

Oxyalkylation of Lignoboost™ Kraft Lignin with Propylene Carbonate: Design of Experiments towards Synthesis Optimization.

Oxyalkylation with propylene carbonate (PC) is a safe process to convert lignin into a reactive liquid polyol to be used in polyurethane formulations. In this study, the effect of operating conditions of oxyalkylation (temperature, time and quantify of PC) on the quality of lignin-based polyol in terms hydroxyl number (IOH) and viscosity was studied. Full factorial modeling and response surface methodology (RSM) were applied to study the effect and interaction of process variables on the IOH and viscosity of lignin-based polyols. The results revealed that the IOH is highly affected by the reaction time, while the viscosity is affected by the amount of PC. Validation experiments confirmed the model is reliable. Furthermore, RSM optimization allowed to reduce the amount of PC by about 50% and to increase the lignin content in the polyol from 12.5% to 25% (w/w) depending on the temperature and time of the process and also on the purpose of the polyol produced (i.e., application in rigid foams or adhesives).

Scalable single-step synthesis of lignin-based liquid polyols with ethylene carbonate for polyurethane foams

A new method for the synthesis of lignin-based liquid polyols was developed. Organosolv lignin was reacted with ethylene carbonate in polyethylene glycol as solvent, leading to a full conversion of the phenolic OH into primary aliphatic OH groups. These aromatic polyols are obtained in a single step, without any purification. Upon modification of the polyethylene glycol molar mass, a wide range of hydroxyl values (IOH) can be covered. The polyols with up to 30%wt lignin have a viscosity suitable for the direct elaboration of polyurethane (PUR) foams. The method presents significant advantages over oxypropylation, the most common method for producing lignin-based polyols since it is performed at ambient pressure, without any toxic chemicals, does not require purification or post treatment, and allows to produce polyols with tunable properties. Four different aromatic polyols were then synthesized to produce rigid PUR foams, with substitution of up to 100% of a standard polyether polyol. The developed polyols showed very high reactivity, allowing to reduce the catalyst content in the PUR formulation by 75%. Rigid PUR foams prepared with 25% substitution of the standard polyol showed properties in the range of commercial PUR foams, with more than 90% closed cells and thermal conductivity of about 25 mW m−1/K, perfectly adequate for thermal insulation applications.

Instant catapult steam explosion pretreatment of wheat straw liquefied polyols to prolong the slow-release longevity of bio-based polyurethane-coated fertilizers

The direct liquefaction product of crop straws for bio-based polyurethane-coated fertilizers (BPCFs) has low hydroxyl values and complicated composition types, resulting in poor crosslinking degree, high hydrophilicity, and short release longevity. This study created an efficient physicochemical instant catapult steam explosion pretreatment wheat straw (SEWS) technology to remove small molecular hemicellulose and difficult-to-film-forming ions, improve straw liquefied polyol quality, and extend the release longevity of BPCFs. The results revealed that the steam explosion process (2.0 MPa for 5 min) broken the straw cell wall, hydrolyzed hemicellulose, and significantly decreased the difficult-to-film-forming ions (K+, Ca2+, and Mg2+). The SEWS liquefied residue rate dropped 38.1% to 5.5%, while the hydroxyl value increased 36.51% to 125.32 mg KOH g−1. The liquid polyol of SEWS and diphenyl-methane-diisocyanate formed a tightly cross-linked, homogenous bio-based membrane with no visible holes. Under the condition of 3% weight of the core fertilizer, the release longevity of SEWS increased from 14 to 32 days. The use of instant catapult steam explosion technology for high-efficiency pretreatment of biomass materials is conducive to improving the quality of bio-based polyols and the industrial production of bio-based controlled-release fertilizers. Furthermore, the pretreatment technology promotes the use of biomass for sustainable agriculture.

Dependence of the mechanical properties of rigid PU foam on density

Density is an important parameter that influences the properties and performances of rigid polyurethane foam. In this study, a systematic engineering approach is presented for determining the effect of density on mechanical properties of rigid/crushable PU foam for design applications. To this end, several mechanical performance parameters, that is, mean load and strength, secant modulus, energy absorption efficiency and densification strain are at first identified for the PU foam. Foam samples of different densities are obtained by varying the amount of liquid polyol–isocyanate of a desired mixing ratio in a constant-volume cubical mould and letting the blow and gelation reactions progress to completion. By conducting compression tests on cubic specimens of foam obtained, it is shown that various mechanical parameters of interest increase monotonically with respect to density. An SEM-based study on the effect of density on foam microstructure has also been carried out.

Insights into the growth of nanoparticles in liquid polyol by thermal annealing.

We report on the growth of metal- and metal-oxide based nanoparticles (NPs) in heated polyol solutions. For this purpose, NPs are produced by the sputtering of a silver, gold, or a copper target to produce either silver, gold, or copper oxide NPs in pentaerythritol ethoxylate (PEEL) which has been annealed up to 200 °C. The objective of the annealing step is the fine modulation of their size. Thus, the evolution of the NP size and shape after thermal annealing is explained according to collision/coalescence kinetics and the affinity between the metal-/metal-oxide and PEEL molecule. Moreover, highlights of few phenomena arising from the annealing step are described such as (i) the reduction of copper oxide into copper by the polyol process and (ii) the effective formation of carbon dots after annealing at 200 °C.

Synthesis of waterborne polyurethane ink binder with high T‐peel strength and its application in biaxially oriented polypropylene film printing

AbstractIn order to improve adhesion properties of waterborne polyurethane (WPU) inks on biaxially oriented polypropylene (BOPP) films, herein, a liquid polyester polyol BY3003 with long‐branched aliphatic chains was used to prepare WPU latexes suitable for BOPP films printing. The application of BY3003 made the surface tension of the prepared latexes not more than 43 mN/m, while that of traditional WPU latex exceeded 55 mN/m. Accordingly, the T‐peel strength of the inks made from these latexes was all above 0.8 N/15 mm. In addition, post chain extension degree, dimethylol butyric acid content, and NCO/OH molar ratio also had significantly effect on latex and film properties of WPU, especially on the T‐peel strength of the corresponding inks. By optimizing these factors, a WPU latex with surface tension as low as 39.6 mN/m and adhesion fastness over 95% on BOPP film were obtained, and the T‐peel strength of its corresponding ink was up to 2.05 N/15 mm, which is the highest value recorded in the literature as far as we know.

A Novel, Nontoxic and Scalable Process to Produce Lipidic Vehicles.

Lipidic vehicles are novel industrial products, utilized as components for pharmaceutical, cosmeceutical and nutraceutical formulations. The present study concerns a newly invented method to produce lipidic vehicles in the nanoscale that is simple, nontoxic, versatile, time-efficient, low-cost and easy to scale up. The process is a modification of the heating method (MHM) and comprises (i) providing a mixture of an amphiphilic lipid and a charged lipid and/or a fluidity regulator in a liquid medium composed of water and a liquid polyol, (ii) stirring and heating the mixture in two heating steps, wherein the temperature of the second step is higher than the temperature of the first step and (iii) allowing the mixture to cool down to room temperature. The process leads to the self-assembly of nanoparticles of small size and good homogeneity, compared with conventional approaches that require additional size reduction steps. In addition, the incorporation of bioactive molecules, such as drugs, inside the nanoparticles is possible, while lyophilization of the products provides long-term stability. Most importantly, the absence of toxic solvents and the simplicity guarantee the safety and scalability of the process, distinguishing it from most prior art processes to produce lipidic vehicles.

Effect of different catalysts on the oxyalkylation of eucalyptus Lignoboost® kraft lignin

Abstract Lignin obtained by Lignoboost® procedure from black liquor after kraft pulping of Eucalyptus globulus wood was characterized and converted into liquid polyols via an innovative and safe procedure using base catalyzed oxyalkylation with propylene carbonate (PC). The effect of four catalysts, Potassium carbonate (K2CO3), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU), dicyanodiamide (DICY), and 1,4-diazabicyclo [2.2.2] octane (DABCO) was evaluated in terms of lignin polyol yield and weight gain. The ensuing polyols were also characterized by fourier transform infrared (FTIR), 1H NMR, 13C NMR, and size exclusion chromatography (SEC) to determine the degree of the substitution (DS), degree of polymerization (DP), and the molecular weight, respectively. Only a minor proportion of PC (ca. 3–15%) was converted to propylene glycol/homooligomers as revealed by high performance liquid chromatography (HPLC). All catalysts promoted preferential derivatization of lignin phenolic OH groups by oxypropyl moieties. The maximum average DP of propylene oxide chains in oxyalkylated Lignoboost® kraft lignin (oKL) was 1.85 per one phenylpropane unit (PPU) using DBU. Conversely, the DP of oKL using DICY was very low (0.27/PPU). DICY’s catalytic activity seems to be jeopardized due to the formation of unreactive adducts with lignin. The oKL obtained using DBU, DABCO, and K2CO3 have potential to be used as polyols in the production of polyurethanes as the corresponding hydroxyl number (IOH) is in the range of 198–410 mg KOH g−1.

One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation.

The one-step seed-mediated synthesis is widely used for the preparation of ferromagnetic metal nanoparticles (NPs) since it offers a good control of particle morphology. Nevertheless, this approach suffers from a lack of mechanistic studies because of the difficulties of following in real time the heterogeneous nucleation and predicting structure effects with seeds that are generated in situ. Here, we propose a complete scheme of the heteronucleation process involved in one-pot seed-mediated syntheses of cobalt nanoparticles in liquid polyols, relying on geometrical phase analysis (GPA) of high-resolution high-angle annular dark field (HAADF)-STEM images and in situ measurements of the molecular hydrogen evolution. Cobalt particles of different shapes (rods, platelets, or hourglass-like particles) were grown by reducing cobalt carboxylate in liquid polyols in the presence of iridium or ruthenium chloride as the nucleating agent. A reaction scheme was established by monitoring the H2 evolution resulting from the decomposition of metal hydrides, formed in situ by β-elimination of metal alkoxides, and from the polyol dehydrogenation, catalytically activated by the metal particles. This is a very good probe for both the noble metal nucleation and the heterogeneous nucleation of cobalt, showing a good separation of these two steps. Ir and Ru seeds with a size in the range 1-2 nm were found exactly in the center of the cobalt particles, whatever the cobalt particle shape, and high-resolution images revealed an epitaxial growth of the hcp Co on fcc Ir or hcp Ru seeds. The microstructure analysis around the seeds made evident two different ways of relaxing the lattice mismatch between the seeds and the cobalt, with the presence of dislocations around the Ir seeds and compression zones of the cobalt lattice near the Ru seeds. The relationship between the nature of the nucleating agent, the reaction steps, and the microstructure is discussed.

Synthesis and properties of flame-retardant reactive hot melt polyurethane adhesive

A novel liquid polyphosphonate polyol (DMDP) was synthesized from dimethyl methylphosphonate and 1,6-hexanediol. Reactive hot melt polyurethane adhesives with high flame retardancy (HMPURs) were prepared from poly(tetramethylene ether glycol) (PTMG-2000), two kinds of poly(1,4-butylene adipate) (PBA-2000 and PBA-3000) and DMDP or dimethyl methylphosphonate as well as tetrahydrofuran acrylate. Five specimens of flame-retardant HMPURs with different weight percent of DMDP (0, 2, 4 and 6 wt%) and dimethyl methylphosphonate (4 wt%) were obtained. The mechanical properties, thermal stability, flammability, and bonding strength of the specimens were investigated. The results show that with the increase of DMDP content, the elongation at break and tensile strength decrease slightly, and the flame retardancy of HMPURs is significantly improved with the limiting oxygen index (LOI) value increasing from 17.2 to 28.2. The incorporation of DMDP leads to a higher thermal stability of HMPURs at high temperature and more char yield at 650 °C. With the increase of DMDP content, the final bond strength of HMPURs on the same substrate changes little, but the green strength of HMPUR-6 on the same substrate is observably less than other samples. The performance of HMPUR with the reactive flame retardant is superior to that of HMPUR with the additive flame retardant. In addition, the corresponding flame-retardant mechanism of DMDP-containing HMPURs was investigated by pyrolysis-gas chromatography coupled to mass spectrometry (Py-GC/MS). The results indicate that the pyrolysis of the HMPURs releases phosphorus-containing fragments to play a flame retardant role.

Tweaking the Interplay among Galvanic Exchange, Oxidative Etching, and Seed-Mediated Deposition toward Architectural Control of Multimetallic Nanoelectrocatalysts.

Nanoscale galvanic exchange confined by metallic nanoparticles is an intriguing structure-remodeling process that transforms geometrically simple solid nanoparticles into multimetallic hollow nanoparticles with increased structural complexity and compositional diversity. Using liquid polyols with intrinsic reducing capabilities as the reaction medium for nanoparticle-templated galvanic exchange represents an interesting paradigm shift, allowing us to interface galvanic exchange with oxidative etching and seed-mediated deposition without introducing any additional oxidizing or reducing agents. By kinetically maneuvering the interplay among galvanic Cu-Pt exchange, oxidative Cu etching, and seed-mediated Pt deposition, we have been able to selectively transform AuCu3 alloy nanoparticles into two architecturally distinct multimetallic heteronanostructures, namely, Au-Pt alloy skin-covered spongy nanoparticles and Pt nanodendrite-covered hollow nanoparticles, both of which exhibit unique structural features highly desirable for high-performance electrocatalysis. Using the formic acid oxidation and hydrogen evolution reactions in acidic electrolytes as model electrocatalytic reactions, we show that the multimetallic nanoparticles derived from AuCu3 alloy nanoparticles through polyol-mediated galvanic exchange reactions markedly outperform the commercial Pt/C benchmark catalysts in terms of both activity and durability. This work not only provides important mechanistic insights on how galvanic exchange dynamically interplays with other redox processes to rigorously dictate the versatile structural transformations of multimetallic nanoparticles but also sheds light on the detailed structure-property relationships underpinning the intriguing electrocatalytic behaviors of architecturally complex multimetallic heteronanostructures.

Synthesis of trifunctional graft polymer polyether polyols employing a silica based gel as non-aqueous dispersant

Currently, the PU industry is developing new products with enhanced physical, mechanical and structural properties. One of the specialties that is attracting more and more attention from managers and enterprises all over the world are the PUs based on polymer polyether polyols (graft polyols).In this work, the synthesis of graft polyols was developed employing a non-aqueous dispersant (NAD) based on silica gel, which contains in its chemical structure segments with a great affinity for the solid polymeric particles and other segment having a strong affinity for the hydroxyl groups of the liquid polyol. The combination of both polar and non-polar characteristics ensures the stability of the resulting polymer dispersion and prevent the sedimentation and the coalescence of the polymer particles. By using this NAD it was possible to synthesize trifunctional polymer polyether polyol (PPP) from Styrene and containing up to 38.69 wt% of solids. The optimal reaction conditions have been stablished using a concentration of 1.5 wt% NAD, 4 wt% of initiator respect to the monomer amount and a polymerization temperature of 80 °C. The viscosity of the optimal PPP (1930 mPa·s) and the particle size (dv0.5 of 5.427 μm and dn0.5 of 1.711 μm) were in the range of graft polyols available in the market for similar solids content, with the additional advantage of employing a lower quantity of NAD and a softer reaction temperature than those employed in the industrial process (110 °C).