NCO Groups Research Articles

Mối quan hệ giữa hàm lượng nhóm isocyanat trong prepolyme với một số tính chất của lớp phủ polyurea

Polyurea is prepared from a prepolymer based on isophorone isocyanate and a polyamine mixture, a volume ratio and molar ratio of NCO:NH2 = 1:1. The relationship between the content of NCO group in the prepolymer and some physicomechanical properties of polyurea has been studied; when the NCO group content decreases, the elongation increases, the hardness and tensile strength decrease, is caused the influence of the soft segment (PPG) in the prepolymer when the soft segment increases, the polyurea film becomes more flexible and elastic.

Synthesis and Characterization of Urethane Acrylate Resin Based on 1,3-Propanediol for Coating Applications

The significant development of industry and the growing demand for renewable fuels lead to the accumulation of massive amounts of glycerol as a by-product. Scientists have been trying to use this product as a raw material for several years. One of its uses is in the acquirement of 1,3-propanediol (PDO). This work presents studies on the synthesis of two new urethane acrylate resins obtained from 1,3-propanediol and urethane acrylate oligomers containing isocyanate groups in each molecule. The method for obtaining the resins was presented, considering various conditions of synthesis, i.e., the structure of the carbon chain of the oligomer used, the molar ratio of the reactants, or the use of solvents. The reactions were monitored in real time by FTIR until the disappearance of the NCO groups. Then, polymer films were prepared from the obtained products and cured using UV radiation or thermally. The obtained coatings were tested in terms of the photopolymerization kinetics and properties of the cured coatings. Resultantly, the obtained bio-sourced coatings were observed to be characterized by good functional properties and a short curing duration, both with the use of UV radiation-based or thermal curing. These types of resins obtained using a bioproduct can be employed as eco-friendly film-forming products in the coating industry for many applications. In particular, due to their potential for dual curing methods (UV or thermal), these resins can be used on three-dimensional surfaces, i.e., those in which there is a possibility of the insufficient availability of UV radiation.

Study on Preparation and Performances of the Triphenylmethane-4,4′,4″-Triisocyanate (TTI)/Epoxidized Soybean Oil Polyol (ESOP) Adhesives Modified by Vegetable Oil Polyol

First, epoxidized soybean oil polyol (ESOP) with high hydroxyl value and moderate viscosity was prepared by the ring-opening reaction of epoxidized soybean oil (ESO). Second, the triphenylmethane-4,4′,4″-triisocyanate (TTI)/ESOP adhesives were prepared by mixing the ESOP with the TTI for the purpose of chemically modifying the TTI. The results of FT-IR and SEM showed the -NCO groups in the TTI reacted with the -OH groups in the ESOP to form a cross-linked structure. In addition, the effects of the isocyanate index, R[n(-NCO)/n(-OH)], i.e., the molar ratio between the isocyanate groups (-NCO) and hydroxyl groups (-OH), on the curing properties, adhesion properties, water resistance, and thermal stability of the TTI adhesives were investigated by means of a digital viscometer, bonding tensile shear strength test, contact angle test, and thermo-gravimetric analysis (TGA), respectively. The results showed that at R = 1.25, the TTI/ESOP adhesives had the best overall performance; the viscosity of the TTI increased to 3190 mPa s after this modification, and the curing time significantly shortened, from 8 to 2.5 h, the solid content substantially increased, from 23.1% to 56% and the tensile shear strength of the metal–metal samples held together by the adhesives increased from 0.37 to 2.78 MPa. Compared with the TTI, the contact angle between the cured adhesive layer increased from 85.5° for TTI to 93.8° for the TTI/ESOP, and the thermal stability was also enhanced.

Investigation of the curing kinetics of polyurethane/nitrocellulose blends through FT‐IR measurements

AbstractPolyester (HTPS) based polyurethane (PU) elastomers were currently established to be effective binders for high‐energy composites with improved performances. Conventional PU binders are mostly non‐energetic materials, and consequently reduce the energy performance significantly. Nitrocellulose (NC), is an energetic polymer widely used as an ingredient in propellants, explosives, fireworks, and gas generators, it may be introduced in PU‐based compositions to overcome their performance drawback. Kinetic parameters must be specified in order to build PU binders with the most convenient and appropriate features. Therefore, the cure kinetics of polyester based polyurethane binder systems were investigated by Fourier transform infrared spectroscopy (FT‐IR) isothermal method. The polyester prepolymer (Desmophen® 1200) was cured with hexamethylene diisocyanate (HDI: Desmodur® N100) at various molar ratios (R[NCO]/[OH] = 0.6, 1, 1.25, and 1.5) and under different isothermal conditions (T = 60°C, 80°C, 100°C, and 120°C). In addition, the effect of the addition of nitrocellulose on the kinetics of polymerization of PU was investigated. The progression of the reaction was followed based on the decrease of the peak intensity of –NCO group at 2271 cm−1 as a function of the reaction time. The curing kinetic model and the apparent activation energy (Eα) were determined by the use of Kamal autocatalytic model and Friedman isoconversional method, respectively.

An Ab Initio Investigation on Relevant Oligomerization Reactions of Toluene Diisocyanate (TDI).

2,4- and 2,6-isomers of toluene diisocyanates (2,4-TDI and 2,6-TDI) are important raw materials in the polyurethane industry. These reactive compounds associate even under ambient conditions to form oligomers, changing the physicochemical properties of the raw material. Kinetically and thermodynamically relevant dimerization reactions were selected based on G3MP2B3 calculations from all possible dimers of phenyl isocyanate using these isocyanates as proxies. As it turned out, only the formation of the diazetidine-2,4-dione ring (11-dimer, uretdione) resulted in a species having an exothermic enthalpy of formation (−30.4 kJ/mol at 298.15 K). The oxazetidin-2-one ring product (1-2-dimer) had a slightly endothermic standard enthalpy of formation (37.2 kJ/mol at 298.15 K). The mechanism of the relevant cyclodimerization reactions was investigated further for 2,4-TDI and 2,6-TDI species using G3MP2B3 and SMD solvent model for diazetidine as well as oxazetidin-2-one ring formation. The formation of the uretdione ring structures, from the 2,4-TDI dimer with both NCO groups in the meta position for each phenyl ring and one methyl group in the para and one in the meta position, had the lowest-lying transition state (Δ#E0 = 94.4 kJ/mol) in the gas phase. The one- and two-step mechanisms of the TDI cyclotrimerization were also studied based on the quasi-G3MP2B3 (qG3MP2B3) computational protocol. The one-step mechanism had an activation barrier as high as 149.0 kJ/mol, while the relative energies in the two-step mechanism were significantly lower for both transition states in the gas phase (94.7 and 60.5 kJ/mol) and in ODCB (87.0 and 54.0 kJ/mol).

MODIFICATION OF CERAMIC MEMBRANES BY PYROCARBON FROM CARBONIZED POLY(URETHANE UREA)S

Modification of tubular ceramic membranes made of clay minerals, which were obtained by slip casting (produced by the Dumansky Institute of Colloid Chemistry and Water Chemistry of the National Academy of Sciences of Ukraine) was carried out. The membranes were modified with pyrocarbon, which was obtained by carbonization of a precursor – poly(urethane urea)s. The carbonization precursor was synthesized from polyisocyanate (average functionality 2.7) and laprol grade 5003, which was introduced into the membrane by impregnation of the corresponding solutions in ethylacetate. When laprol reacts with polyisocyanate, three-dimensional polyurethane is formed. Since undried reagents were used, water entered the pores of the membrane, which reacted with the NCO groups of the polyisocyanate to form polyurea. The parallel course of these reactions leads to the formation of poly(urethane urea)s in the pores of the membrane. Carbonization was carried at 800 °C in an argon flow. The apparent density and open porosity of the membranes were determined by CCl4 uptake. After modification, the open porosity of the membrane decreased from 29.9 to 27.3 %, the apparent density increased from 1.86 to 1.87 g/cm3. The composition and structure of the membranes were studied by X-ray diffraction analysis and SEM. It is shown that the obtained modifier is pyrocarbon - the relative intensity of reflexes increases at 26,0 - 26,4 and 41,3 and 44,2° 2Θ. Pyrocarbon covers the surface of the pores with a continuous layer, and there are also three-dimensional formations of various shapes and sizes from several nm to several microns. Testing of modified membranes was carried out by water purification from direct scarlet dye and from Ca2+ of calcium chloride using the baromembrane method at a working pressure of 0.7 MPa. The unmodified membrane does not retain direct scarlet dye and Ca2+ at all. Tests of modified membranes have shown that the membranes acquire ultrafiltration properties. The retention factor (R) for direct scarlet dye is 100 % and 25 % for Ca2+.

Engineering liquid pMDI into water-processable powder: Manufacture and application as waterborne additive

Petroleum-derived polyurethane using isocyanates by solvent-based processing causes undesired environmental pollution and health effects. Waterborne polyurethane is an alternative to solve this issue, however, they are inefficient as additives and inconvenient for transportation and usage owing to the large amount of water. Herein, water-processable polymethylene polyphenyl polyisocyanate (PAPI, referred as pMDI) powder modified by biobased castor oil is developed. The preparation of pMDI powder is characterized by its appearance, content of –NCO groups, and storage life. The protective mechanism of –NCO groups is explored by a battery of techniques, including microscopies, FTIR, TGA, DSC and reaction kinetics. The optimal formulation for powdered pMDI uses 0.6 wt% SDS prior to de-hydration, which retains a high level of residual –NCO groups up to two-week storage. The formation of polyurea shells covering pMDI powder upon water-processing minimizes contact and interaction between –NCO and moisture in air, blocking consumption of –NCO groups. The pMDI powder can be used as a crosslinking agent for waterborne wood adhesives, showing great bonding performances, particularly improving wet strength (0.84 MPa) at 18 wt% loading level. This strategy offers a simple, green, and cost-effective route to engineer hazardous, high-risk liquid isocyanates into environmentally-friendly, low-risk, and versatile water-processable materials that are suitable as waterborne additives.

Improved surface properties of a novel self-healing polyurethane-acrylate coating by in situ polymerizations of dihydroxy organo-montmorillonite on ancient wood

A novel polyurethane-acrylate (PUA) polymerized in situ with montmorillonite (MMT) was synthesized to improve the surface properties of self-healing coatings used for ancient wood. For better dispersion and interaction, natural MMT was initially modified to dihydroxy organo-montmorillonite (OMMT). The prepared self-healing PUA coatings were painted on ancient wood and the surface properties tested, characterized, and compared to pure PUA and natural MMT-added PUA. Those results showed that natural MMT was modified to dihydroxy OMMT by cation exchange. The dihydroxy OMMT was polymerized in situ during synthesis by reactions between OH and NCO groups. The PUA polymer incorporated within MMT to form an exfoliated structure. After painting ancient wood, the surface contained no obvious bulges and the roughness increased slightly. Due to OMMT addition, the adhesion and hardness of OMMT modified PUA increased to 1 class and 2H, respectively, which is acceptable for indoor woodenware. The abrasive resistance was also improved. Furthermore, dihydroxy OMMT promoted the self-healing of PUA. After 30 s of healing, damages disappeared.

Rhamnolipids Regulate Lipid Metabolism, Immune Response, and Gut Microbiota in Rats

ObjectivesGut microbes influence lipid metabolism and immune responses that are key features of metabolic disorders. This study examined effects of bacterial rhamnolipids (RLS) on lipid metabolism, immune response, and gut microbiota in rats.MethodsTwenty-four Sprague-Dawley rats were randomly divided into three groups and gavage-fed for seven weeks with normal saline (NCO group), 50 mg/kg bw RLS (RLS1 group), and 100 mg/kg bw RLS (RLS2 group).ResultsCompared with those of the NCO group, the RLS1 and RLS2 groups showed significantly decreased fat weight, relative fat weight, and adipocyte size (P < 0.05). Furthermore, RLS1 and RLS2 significantly decreased concentrations of triglycerides, low-density lipoprotein-cholesterol, and non-esterified fatty acids and increased high-density lipoprotein-cholesterol levels (P < 0.05). However, the total cholesterol content among the three groups (P > 0.05) were not significantly different. Serum concentrations of interleukin-1β, interleukin-6, and tumor necrosis factor-α were significantly lower in the RLS2 group than those in the NCO group (P < 0.05). The relative mRNA expression of fatty acid synthase was significantly decreased, while those of carnitine palmitoyltransferase-1, carnitine palmitoyltransferase-2, and peroxisome proliferator-activated receptor-gamma coactivator-1α were significantly increased in the RLS2 group compared with those in the NCO group (P < 0.05). Moreover, the relative abundances of Lactobacillus, Roseburia, Ruminococcus-1, and Parabacteroides were significantly higher in the RLS2 group than those in the NCO group (P < 0.05).ConclusionOur findings suggest that RLS reduces fat deposition, inhibits inflammation, regulates intestinal flora, and promotes the proliferation of beneficial bacteria in rats.

Role of Hydantoin Derivatives in Syntheses of Polyaspartates

Polyaspartates are industrially important resins formed by reactions of N-substituted 2‑aminosuccinates (or, synonymously, N-substituted aspartates) with isocyanates. To obtain sufficiently crosslinked networks, applicable as coatings, bis-aspartates with two secondary NH groups and isocyanates with more than two NCO groups in their molecules must be used. There are two major problems connected with these preparations: (i) bis-aspartates which are mostly synthesized by the aza-Michael addition of NH2 groups of a suitable diamine to C=C bonds of a maleate ester almost always contain a certain amount of a fumarate ester (usually a few percent) as a result of the Z→E isomerization, unavoidably accompanying the addition; this deteriorates the quality of the resulting product; (ii) during the reaction of bis-aspartate with isocyanate, hydantoin rings are often formed to some extent in addition to the desirable three dimensional structures; the presence of these rings decreases the attainable network density. In this review, those properties, syntheses, and reactions of hydantoin are summarized which could be useful for finding conditions to avoid the formation of hydantoin rings.&#x0D; Fulltext of this article is available on the website of this Journal.

Study on preparation and performance of a thermosetting polyurethane modified asphalt binder for bridge deck pavements

With the rapid development of traffic volume and loading, sustainable pavement materials are developing to improve the longevity of orthotropic bridge deck pavement structures. This paper aims to develop a new flexible binder with improved mechanical characteristics for bridge deck applications. This research studied the preparation process, microstructural morphology, and mechanical properties of a newly developed thermosetting polyurethane modified asphalt binder (TPUA). The results showed that the viscosity of TPUA was greatly affected by the preparation temperature and the viscosity growth rate increased with the increase of preparation temperature. The curing time was determined by the change in the absorption peak of the infrared spectra of the NCO groups. When the content of the PU modifier exceeded 30 wt%, the polyurethane (PU) resin formed a continuous polymeric network in asphalt binder, and the PU had relatively good compatibility with the asphalt binder. TPUA still showed the characteristics of a viscoelastic material at medium and low temperatures. When the content of PU exceeded 30 wt%, TPUA gradually showed the characteristics of an elastic material at high temperature and had excellent high-temperature deformation resistance and elastic recovery properties. In addition, the TPUA binder showed improved low-temperature flexibility with the increase of PU. Overall, the mechanical properties of the asphalt binder were substantially enhanced with the incorporation of PU resin, generating a flexible binder with favorable application prospects.

Performance of eco‐friendly particleboard from agro‐industrial residues bonded with formaldehyde‐free natural rubber latex adhesive for interior applications

AbstractIn this work, a novel way is proposed to produce an eco‐friendly and formaldehyde‐free particleboard (PB) panel from agro‐industrial residues bonded with natural rubber latex (NRL)‐based adhesive. Polyvinyl alcohol (PVOH) was added as an adhesion promoter and polymeric 4,4‐methylene diphenyl diisocyanate (pMDI) was used as cross‐linker. Different formulations of agro‐industrial residues (cassava stem, sengon wood waste, and rice husk) and different contents of NRL‐adhesive (10%, 15%, and 20%) were applied to prepare the PB panel. Several techniques were performed to characterize the properties of NRL‐based adhesive and to evaluate the performance of PB panels from agro‐industrial residues bonded with NRL‐based adhesive. The blending of NRL and PVOH resulted in weak hydrogen bonds in the polymer blends. Incorporation of pMDI provided NCO groups as the reactive site for cross‐linking with NRL‐PVOH via urethane linkages. The results showed that no remarkable differences in the physical properties of the PB panel, such as density, moisture content, water absorption, and thickness swelling, with different agro‐industrial residues formulations and NRL‐adhesive content. By contrast, greater NRL‐adhesive content affected the mechanical properties of the PB panel. The best mechanical properties of the PB panel were obtained using a formulation of 40% of cassava stem, 30% of sengon wood waste, 30% of rice husk, and bonded with 20% of NRL‐adhesive content, which resulted in 4.02 MPa of modulus of rupture (MOR), 441.00 MPa of modulus of elasticity (MOE), and 0.19 MPa of internal bonding (IB) strength. A combination of agro‐industrial residues particles and NRL‐based adhesive presented a high potential for application as an eco‐friendly, formaldehyde‐free, and non‐structural PB such as interior applications.

Optimization and design for the curing process of solid azide propellant: Influence of typical components on the curing reactions of PBT binders with TDI

AbstractThe effects of several typical ingredients on the thermal curing reactions of poly (3,3′‐bis‐azidomethyl oxetane)‐tetrahydrofuran (PBT) adhesive with curing agent toluene diisocyanate (TDI) were carried out using density functional theory. The results show that the most energetic favorable curing route is the reaction with the cured product with two urethane segments and its rate‐determining step is the nucleophilic addition reaction of TDI with triethanolamine (TEA). Compared to the reaction of TDI with PBT, the reaction with trimethylolpropane (TMP) shows relatively lower activation free energy mainly due to the weakening of N‐H bond in corresponding TS structures. After the pre‐modification of TDI by diethylene glycol (DEG), the reactivity of the remaining isocyanate group is significantly decreased, which is supported by the smallest absolute value of torsion angle when the electron density in NH and CO bond areas maintains locally concentrated. In contrast, the final curing reactions with PBT are remarkably facilitated as the participation of the intermediate structures formed through TEA. The stronger hindrance to the last step curing reaction of biuret molecule obtained through the continuous reaction stemming from H2O basically attributes to the reduction in the electrophilicity of relevant ‐NCO groups.

Polyurethane Nanofiber Artificial Leather with Improved Mechanical Properties and High Moisture Permeability Prepared by Electrospinning-in-situ Crosslinking

This paper reports a method for preparing artificial leather with high comfort and useful mechanical property. Blending thermoplastic polyurethane elastomer (TPU), Toluene diisocyanate (TDI) polyurethane prepolymer and 4,4-Methylene bis(2-chloroaniline) (MOCA), and a nanofiber artificial leather was obtained by using online reactive electrospinning technology and heat cross-linking. Compared with the commercial PU artificial leather, the tensile strength of nanofiber artificial leather from 3.2 MPa to 11.2 MPa, and the air permeability of nanofiber artificial leather from 0.25 to 2.974 mm/s, and the moisture permeability of nanofiber artificial leather from 981 to 4615 g/m2.24h. The NCO groups on the TPU and TDI prepolymer molecules, and the NH2 groups on the MOCA cross-linking agent were polymerized by heat treatment, and a cohesive structure was formed between fibers, which significantly improve the mechanical property of nanofiber artificial leather. It was close to sheep leather in mechanical property, and it was air permeability and moisture permeability were much higher than those of sheep leather and commercial PU artificial leather. The nanofiber artificial leather prepared in this study has excellent prospects for application in the fields of luggage, footwear, and clothing.

Effect of plasma-species to functionalize isocyanate-groups on multiwalled carbon nanotubes

This article reports our recent investigation of the relationship between the density of the active species in nitrogen-oxygen plasma and the degree of isocyanate (R-NCO) functionalization onto multiwalled carbon nanotubes. We first monitored the plasma active species with optical emission spectroscopy focusing on atomic nitrogen and oxygen species, which are the major components to form NCO groups. The optical emission intensity allowed us to find the density of atomic nitrogen and oxygen in plasma through the plasma optical actinometry method. The actinometry result showed that the density of atomic nitrogen and oxygen becomes as close as the nitrogen content in plasma increased to 90%. We then investigated the functionalization ratio with the fluorescent method and Raman spectroscopy to monitor the degree of NCO functionalization. The results suggested that NCO groups on carbon nanotubes should increase as the content ratio of atomic nitrogen and oxygen becomes equal in the plasma.

Influence of agitation methods of irrigants after methylene blue-mediated PDT on the bonding interface of a fiber post cementation system

BackgroundThis study evaluated the effects of final agitation methods of irrigants to remove methylene blue and sodium hypochlorite residues after PDT-assisted endodontic treatment on the bond strength of fiber posts cemented with etch-and-rinse adhesive and conventional resin cement. MethodsNinety bovine teeth were endodontically treated. In sequence, post space preparation followed by methylene blue-mediated PDT and sodium hypochlorite (NaOCl) irrigation were performed. Six final irrigations protocols for dye and NaOCl removal were performed prior to cementation with etch-and-rinse adhesive (Adper Scocthbond Multipurpose) and conventional dual resin cement (RelyX ARC): Conventional endodontic irrigation (CEI), passive ultrasonic irrigation (PUI), mechanical agitation with XP Endo Finisher (XPF), XP Clean (XPC) or Easy Clean (ECL) and distilled water (NCO - control). After fiber post cementation, push-out bond strength test was performed at different thirds of the post space. Failure mode was also analyzed. ANOVA and Tukey's post-hoc test was used for data analysis (α=5%). ResultsPUI, XPF e XPC protocols showed the highest bond strength values with no difference among them (p > 0.05), although they were similar to NCO, regardless of the post space third. CEI e ECL showed similar bond strength values, regardless of the third (p > 0.05). Adhesive failure was the most incident for CEI and ECL, while mixed and cohesive failures were predominant in PUI, XPF, XPC and NCO groups. ConclusionsMechanical agitation of distilled water with XPF, XPC and PUI after methylene blue-mediated PDT and irrigation with 2.5% sodium hypochlorite promoted bond strength of the resin cementation system in post space dentin comparable to control group.

Fully cross-linked UV-induced peelable acrylic PSA prepared from a dual curable castor oil based urethane acrylate oligomer for wafer dicing

For UV-induced peelable pressure sensitive adhesive (PSA) used in the wafer dicing process, improving the peel performance can effectively increase the process reliability and the yield of subsequent packaging process. In this work, a NCO-containing castor oil-based urethane acrylate oligomer called CO-PUB with dual curable functions (UV-induced polymerization and NCO/OH reaction) was obtained by partially sealing a castor oil-based urethane oligomer with hydroxyethyl acrylate. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectrometer (NMR) results indicated that CO-PUB was successfully prepared. CO-PUB, OH-containing acrylic copolymer, multifunctional acrylate monomer and photo-initiator were used to construct a UV-induced peelable adhesive for silicon wafer dicing. The results showed that NCO groups in CO-PUB underwent the NCO/OH reaction with the acrylic copolymer to obtain a vinyl pendant cross-linked acrylic copolymer. The peel strength of this peelable adhesive before UV irradiation could exceed 20 N/25 mm. After UV irradiation, the unsaturated vinyl bonds contained in it were copolymerized with the multifunctional acrylate monomer to form a fully cross-linked adhesive film and the peel strength could be reduced to below 1 N/25 mm. Compared with UV-induced peelable adhesives prepared by other reported curing agents, the adhesive prepared from CO-PUB reduced UV dose required for curing. The cross-linking degree of cured adhesive film was also increased and the gel content was up to 95%. The residual adhesive after peeling off could be reduced to about 0.32%. In addition, CO-PUB used renewable castor oil as polyol and did not need to add any organic solvent during the preparation process, providing a new idea for the green preparation of UV-induced peelable adhesive with excellent performances.

Enhancing Thermal and Mechanical Properties of Ramie Fiber via Impregnation by Lignin-Based Polyurethane Resin

In this study, lignin isolated and fractionated from black liquor was used as a pre-polymer to prepare bio-polyurethane (Bio-PU) resin, and the resin was impregnated into ramie fiber (Boehmeria nivea (L.) Gaudich) to improve its thermal and mechanical properties. The isolated lignin was fractionated by one-step fractionation using two different solvents, i.e., methanol (MeOH) and acetone (Ac). Each fractionated lignin was dissolved in NaOH and then reacted with a polymeric 4,4-methane diphenyl diisocyanate (pMDI) polymer at an NCO/OH mole ratio of 0.3. The resulting Bio-PU was then used in the impregnation of ramie fiber. The characterization of lignin, Bio-PU, and ramie fiber was carried out using several techniques, i.e., Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), pyrolysis-gas-chromatography-mass-spectroscopy (Py-GCMS), Micro Confocal Raman spectroscopy, and an evaluation of fiber mechanical properties (modulus of elasticity and tensile strength). Impregnation of Bio-PU into ramie fiber resulted in weight gain ranging from 6% to 15%, and the values increased when extending the impregnation time. The reaction between the NCO group on Bio-PU and the OH group on ramie fiber forms a C=O group of urethane as confirmed by FTIR and Micro Confocal Raman spectroscopies at a wavenumber of 1600 cm−1. Based on the TGA analysis, ramie fiber with lignin-based Bio-PU had better thermal properties than ramie fiber before impregnation with a greater weight residue of 21.7%. The mechanical properties of ramie fiber also increased after impregnation with lignin-based Bio-PU, resulting in a modulus of elasticity of 31 GPa for ramie-L-isolated and a tensile strength of 577 MPa for ramie-L-Ac. The enhanced thermal and mechanical properties of impregnated ramie fiber with lignin-based Bio-PU resins could increase the added value of ramie fiber and enhance its more comprehensive industrial application as a functional material.

Eco-Friendly Ether and Ester-Urethane Prepolymer: Structure, Processing and Properties.

This study concerns bio-based urethane prepolymers. The relationship between the chemical structure and the thermal and processing parameters of bio-based isocyanate-terminated ether and ester-urethane prepolymers was investigated. Bio-based prepolymers were obtained with the use of bio-monomers such as bio-based diisocyanate, bio-based polyether polyol or polyester polyols. In addition to their composition, the bio-based prepolymers were different in the content of iso-cyanate groups content (ca. 6 and 8%). The process of pre-polymerization and the obtained bio-based prepolymers were analyzed by determining the content of unreacted NCO groups, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, thermogravimetry, and rheological measurements. The research conducted facilitated the evaluation of the properties and processability of urethane prepolymers based on natural components. The results indicate that a significant impact on the processability has the origin the polyol ingredient as well as the NCO content. The thermal stability of all of the prepolymers is similar. A prepolymer based on a poly-ether polyol is characterized by a lower viscosity at a lower temperature than the prepolymer based on a polyester polyol. The viscosity value depends on the NCO content.

Continuous Blown Film Preparation of High Starch Content Composite Films with High Ultraviolet Aging Resistance and Excellent Mechanical Properties.

Starch/PBAT blown films with high ultraviolet aging resistance and excellent mechanical properties were prepared by introducing lignin with polyurethane prepolymer (PUP) as a starch modifier and physical compatibilizer and 4,4′–methylene diphenyl diisocyanate (MDI) as a crosslinker. Starch was modified by reacting the NCO groups of the PUP with the OH groups of the starch to form a carbamate bond. The mechanical properties, hydrophobic properties, ultraviolet barrier, ultraviolet aging properties and microscopic morphology of starch/PBAT films with different contents of lignin were investigated. The results showed that the starch/PBAT films were blown continuously. The addition of lignin did not decrease the mechanical properties. On the contrary, the film with 1% lignin possessed the excellent mechanical properties with longitudinal tensile strength of 15.87 MPa and the elongation at a break of 602.21%. In addition, the higher the lignin content, the better the UV blocking effect. The introduction of lignin did not affect the crystalline properties but improved the hydrophilic properties and sealing strength of the high starch content composite films.