Structure Of Polyurethanes Research Articles

Synthesis of Castor Oil‐Based Waterborne Polyurethane with Improved Properties via Adjusting PBA/CO Soft Segment Ratio

AbstractIn this study, dimethylol propionic acid (DMPA) and ethoxylated polymer diol (N120) are incorporated as composite hydrophilic groups to synthesize a series of castor oil‐based waterborne polyurethane (CWPU) nano‐emulsions. The properties of the nano‐emulsions with different ratio of polybutylene adipate (PBA) and castor oil (CO) soft segments as well as their film are investigated systematically. Fourier infrared spectroscopy (FTIR) confirms that CO was successfully introduced into the waterborne polyurethane (WPU) structure. The result indicates that the maximum contact angle of the film is 75.51° with a 7/3 molar ratio of PBA/CO. Thermal Gravimetric Analyzer (TGA) and Dynamic thermomechanical analysis (DMA) tests show that the thermal stability of the films has gradually improved with the increase of castor oil content. The content of castor oil in CWPU also affects the mechanical properties of the film. The tensile strength of the film reaches 23.2 MPa, and the elongation at break is 1460.7 %, when the molar ratio of PBA/CO is 9/1. Atomic force microscopy (AFM) is used to express the surface morphology of CWPU films. The films surface become rougher due to the introduction of CO. This work combines castor oil and water‐based systems to provide a relatively simple preparation method to synthesize CWPU nano‐emulsions, which can be used in environmental protection coatings and adhesives, and has broader application prospects.

Environmentally Benign and Self-Extinguishing Multilayer Nanocoating for Protection of Flammable Foam.

Most current flame-retardant nanocoatings for flexible polyurethane foam (PUF) consist of passive barriers, such as clay, graphene oxide, or metal hydroxide. In an effort to develop a polymeric and environmentally benign nanocoating for PUF, positively charged chitosan (CH) and anionic sodium hexametaphosphate (PSP) were deposited using layer-by-layer (LbL) assembly. Only six bilayers of CH/PSP film can withstand flame penetration during exposure to a butane torch (∼1400 °C) for 10 s and stop flame spread on the foam. Additionally, cone calorimetry reveals that the fire growth rate, peak heat release rate, and maximum average rate of heat emission are reduced by 55, 43, and 38%, respectively, compared with uncoated foam. This multilayer thin film quickly dehydrates to form an intumescent charred exoskeleton on the surface of the open-celled structure of polyurethane, inhibiting heat transfer and completely eliminating melt dripping. This entirely polymeric nanocoating provides a safe and effective alternative for reducing the fire hazard of polyurethane foam that is widely used for cushioning and insulation.

Effects of cyclic mechanical loads and thermal ageing on district heating pipes

The lifetime of pre-insulated district heating pipes is commonly evaluated by thermal ageing at elevated temperatures and is calculated using the Arrhenius equation. In this investigation, the effects of a repetitive shear stress during thermal ageing of pipes were studied. The degradation of polyurethane foam, especially at the interface with a steel pipe was evaluated from measurements of the adhesion strength and of alterations in the chemical structure of polyurethane by Fourier transform infrared spectroscopy. The main conclusion was that the thermal degradation of mechanically stressed district heating pipes was significantly faster than that of non-loaded pipes aged at the same temperature. It was also shown that the faster degradation of the mechanically loaded pipes is mainly due not to fatigue but to accelerated chemical degradation of the polyurethane foam. The results suggest that this methodology should be considered as an accelerated test method in order to avoid overestimation of the lifetime of district heating pipes and to show better ageing characteristics of mechanically stressed pipes, especially those intended for use in the fourth generation district heating networks

열가소성 폴리우레탄의 거시 구조가 초임계 이산화탄소 발포에 미치는 영향

열가소성 폴리우레탄의 거시 구조가 초임계 이산화탄소 발포에 미치는 영향

Experimental study on filtration effect of oilfield sewage based on new polyurethane modified materials.

In the process of oilfield wastewater treatment, the polymer-modified materials with special wettability have been recognized by many scholars for their high filtration efficiency and good adsorption effect. In this paper, we used micro-computed tomography scanning and infrared scanning technology to further explore the internal structure and surface chemistry of polyurethane modified materials and then established an experimental platform for the filtration performance of polyurethane modified materials. The change of suspended solids concentration and oil content in the sewage was tested under different filtration rate, filter layer thickness, and water quality. The results showed that the porosity of the filter material and the oil-absorbing material was 65.85% and 56.03% respectively, and the difference in the number of oxygen-containing functional groups on the surface of these two materials indicated different adsorption force for sewage impurities. And the polyurethane modified materials had good filtration performance. Through these experiments, we demonstrated that the quality of water filtrated by the polyurethane modified materials met the requirements of the 'National Comprehensive Wastewater Discharge Standards', and the filtration efficiency for suspended particles and oils in oily sewage was higher than 80%. These materials have important practical significance for the harmless treatment of oily sewage.

Formation of crystal-like structure and effective hard domain in a thermoplastic polyurethane

Traditionally, the hard domain of polyurethane was considered as the physical crosslinking point and has been studied for several decades. However, due to the hierarchical and metastable nature of the hard phase, its delicate structure hasn't been resolved thoroughly and its formation mechanism was unclear too. In this work, crystal-like structure in an amorphous polyurethane was discovered by conventional DSC experiments, and Flash DSC was used to study the thermodynamics and kinetics of such crystal-like structure by one-step and two-step temperature annealing experiment. It was found that the formation of crystal-like structure included nucleation and growth. However, its equilibrium melting point couldn't be obtained by Hoffman-Weeks’ method and its structural regularity was weaker than the crystal. Moreover, the nucleus had more compact structure than its outer layer and owned higher melting point. With the help of time dependent FTIR experiment, we proved that the hard domain formed much earlier than the crystal-like structure. Such result implied that the crystal-like structure was birthed inside the hard domain and its core was the reorganized hard segments, which acted as nucleus. After that, the reorganization of outer layer began, and was the growth process of crystal-like structure. Furthermore, time dependent oscillatory rheological experiment proved that the physical network in polyurethane formed much later than the formation of crystal-like structure, which meant the growth of hard domain was slow. In conclusion, the formation of effective hard domain, which could act as physical crosslinking point, experiences hydrogen bonding association, crystal-like structure formation and size expansion processes.

Research on structure and performance of polyurethane elastomer/superfine talcum powder composite

The structure and performance of polyurethane elastomer/superfine talcum powder composites were investigated by X ray diffraction ( XRD), FTIR spectra and thermogravimetric analysis ( TG - DTA, DSC ). The results showed that talcum powder and polyurethane elastomer formed com pound structure of heterogeneous nucleation when the content of superfine talcum powder was right(such as 15% ), which caused the soft segments, hard segments and talcum powder of polyurethane elastomer to form interactional congeries system and the integrated mechanical properties and thermostability of polyurethane elastomer were improved.

Investigation of the internal structure, combustion, and thermal resistance of the rigid polyurethane materials reinforced with vermiculite

In this study, 5%, 10%, and 15% vermiculite was added to the rigid polyurethane (PU) structure as a fire retardant. The scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), limiting oxygen index, thermal gravimetric analysis, differential scanning calorimetric (DSC) curves, and combustion behavior of the composite materials were investigated. When SEM/EDS analyses were examined, it was observed that surface morphology was affected by the amount of additive material. When XRD analyses were examined, peaks appeared in three different groups. Thermogravimetric analysis was used to determine the thermal stability of PU material with the addition of vermiculite. When the DSC analysis was examined, four temperature zones were obtained. The combustion behaviors of the vermiculite added PU samples with single-flame source and the flammability classes were determined with TS EN ISO 11925-2 standard. It can be said that the usage of inorganic mineral, which is harmless to the environment, can enhance the thermal stability of the material and also reduce the cost of production.

Obtaining and Characterization of a Polydisperse System Used as a Transmembrane Carrier for Isosorbide Derivatives.

Due to their effect of vasodilatation, isosorbide nitrates represent one of the most important and most used solutions for angina pectoris. Unfortunately, these compounds have multiple dose-related adverse drug reactions such as headache, weakness, mild dizziness, and occasionally heart rate changes, nausea, vomiting, and sweating. The main aims of this research were to obtain and to evaluate new polyurethane (PU) structures that can be used as a proper transmembrane carrier with an improved release kinetic. Chitosan-based PU structures were obtained by a polyaddition process between hexamethylene diisocyanate and a mixture of chitosan, butanediol, and polyethylene glycol in the presence of caffeine as a synthesis catalyst. The obtained samples (with and without isosorbide nitrates) were characterized regarding the encapsulation and release rate (UV-Vis spectra), chemical composition (FTIR), thermal stability (thermal analysis), morphology changes (SEM and SANS), and in vivo irritation tests. These methods revealed no significant differences between the two sample structures. Multipopulational structures with sizes between 73 and 310 nm, with an increased tendency to form clusters and a high resistance to heat (up to 280°C), were obtained. This study presents an alternative administration of isosorbide derivatives based on a PU carrier with a high biocompatibility and a prolonged release.

Shape memory thin films of polyurethane: Synthesis, characterization, and recovery behavior

AbstractPolyurethane thin films with inherent two phase segregated characters are exceptional candidates for the development of shape memory materials. However, controlling the phase behavior of such complex structures for decoding their recovery behavior still experiences its early stage of development. In this work, polyurethane thin films were synthesized based on two polyols, ester‐based polyols (ESP), and ether‐based polyols (ETP) together with diphenyl diisocyanate (MDI). The effects of ingredient ratio of PETP (ether‐based prepolymer)/PESP (ester‐based prepolymer) on the chemical structure and final properties of polyurethanes were studied by the Fourier‐transformed infrared spectroscopy (FTIR), the differential scanning calorimetry (DSC), the scanning electron microscopy (SEM), the dynamic mechanical thermal analysis (DMTA), a tensiometer, and the atomic force microscopy (AFM). The shape memory behaviors were explored by the thermomechanical cycles applied by a DMTA device in the controlled force mode. The PU films showed various properties compared with the bulk PU since they formed spherulitic textures with different structures. All the PU films except PU‐0 showed high shape recovery ca. 90% in the first cycle with a large glassy storage modulus in the range of 2,800–4,040MPa, and a recovery ratio enhanced by increasing the number of cycle to a maximum of 95%.

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.

Hydrothermal Synthesis of Polyoxometalate Containing Cobalt Ion, and Its Polyurethane Composites for Dielectric Material Applications

ABSTRACT Polyurethane (PU) composites were prepared with different diisocyanate and diol compounds by adding cobalt ion-based polyoxometalate (Co-POM) as reinforcement. For the determination of using potential in microelectronic applications, the dielectric behavior and dielectric constant of these PU composites were investigated and compared to pure polyurethane structures. For this aim, firstly, Co-POM with Keggin structure was obtained from ammonium heptamolybdate, 1,10-phenanthroline ligand and a cobalt (II) salt by hydrothermal synthesis technique. Then, polyurethane/Co-POM composites (PU/Co-POM) were prepared with ethylene glycol, nonaromatic diisocyanate and different amounts of Co-POM reinforcement (1%, 3%, 5% and 10%, w/w) by in situ polymerization and mix-blend technique. Obtained PU/Co-POM composites were characterized in detail by infrared spectroscopy, Elemental Mapping, Energy-dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) spectroscopy. The surface structure, morphology and roughness of PU/Co-POM composites were investigated by SEM and AFM analysis. The elemental maps of the PU/Co-POM surface were examined by EDX elemental mapping analysis methods. Thermal stability, Tg values and thermal decomposition temperatures of PU/Co-POM structures were determined by different thermal analysis techniques. Thermal analysis results showed that the PU/Co-POM composites are thermally stable up to approximately 200°C and Tg values of synthesized PU composites are seen between 54.72°C and 75.15°C. The dielectric properties and dielectric constants of the PU/Co-POM composites were determined in the frequency range 1 Hz to 1000 kHz at room temperature using impedance analyzer. Dielectric constants of these composites were ranged from 5.50 to 9.26 according to their polarizability and H-bonding ability of PU matrix structure. According to the dielectric measurements, the dielectric constants of the PU/Co-POM structures were significantly decreased compared to the pure PU structures.

Experimental investigation of mechanical and modal properties of Al2O3 nanoparticle reinforced polyurethane core sandwich structures

In this study, experimental mechanical and modal analyses of nano-Al2O3 ceramic powder reinforced polyurethane foam core sandwich composites was carried out along with the investigation of vibration, buckling and compression responses. The reinforcement ratio of Al2O3 ceramic powder was varied from 0 to 10 % by weight. The morphological effect of Al2O3 powder reinforcement on the polyurethane microstructure was also investigated by benefitting from an optical microscope. Significant improvements in the damping response and the buckling behavior of the Al2O3 sandwich specimens were observed. In this context, a 38.3 % increase in the damping ratio was observed for 2% Al2O3 reinforced specimens compared to the neat specimens and the specimens with 1% and 3% Al2O3 reinforcement showed 31.4 % and 26.8 % increase, respectively. Similarly, a 6% increase in the buckling peak load was observed for specimens with 5% reinforcement compared to the neat specimens. However, the compression peak load was observed to decrease linearly with an increase in the reinforcement ratio for all the reinforced specimens. TG-DTG, DSC and FTIR analysis of PUF cores with different reinforcement ratios were also performed within the scope of this study. It was observed in the TG graphs that the weight loss decreased with an increase in the reinforcement ratios. The glass transition temperatures of all the PUF core specimens were found by performing DSC analyses whereas, the structural bonds were detected by using the FTIR technique. Composite foam cores showed the existence of a dominant polyurethane structure.

Predicted Studies of Branched and Cross-Linked Polyurethanes Based on Polyhydroxybutyrate with Polycaprolactone Triol in Soft Segments.

The number of cross-links in the non-linear polyurethane structure is the basic factor affecting its properties. Selected properties of aliphatic polyurethanes with soft segments made of different amounts of polycaprolactonetriol, polycaprolactonediol and synthetic, telechelic poly([R,S]-3-hydroxybutyrate) were determined. On the basis of changes in polyurethane properties, the correlation between these properties and the construction of soft segments was found. The structure of polyurethanes, their morphology, hydrophilicity, thermal and mechanical properties were examined. These properties were changed linearly up to 15% content of polycaprolactonetriol in soft segments. A further increase in the amount of triol causes that these properties are mainly determined by the high number of cross-links.

The study of model reactions occurring in the synthesis of adaptive multiblock polyurethanes

In the paper a study of formation process of linear polyurethane on the basis of 4, 4′-diphenylmethane diisocyanate, poly(1, 4-butylene adipate) diol and 1, 4-butanediol is presented. The kinetics of the first stage of macrodiisocyanate formation reaction was studied by IR spectroscopy. Experimental and calculated values of the rate constant of the first reaction stage were obtained. The influence of the solvent on the polyurethane structure was defined. The conditions to fabricate polymer with a maximum crystallinity degree have been determined. Important results for the synthesis of the shape memory multiblock polyurethane thermoplastic elastomer have been obtained.

Polyvinylpyrrolidone (PVP) hydrogel coating for cylindrical polyurethane scaffolds

The presented study describes a method for the preparation and modification of cylindrical polyurethane structures with polyvinylpyrrolidone (PVP) hydrogel coating. The modified polyurethane scaffolds were fabricated using the phase-inversion technique and intended to be used as a vascular prosthesis. The proposed modification method involves a two-step Fenton-type reaction. Physicochemical analysis (Fourier transform infrared spectroscopy, scanning electron microscopy) confirmed the presence of the hydrogel coating. The influence of PVP and polymerization initiator (cumene hydroperoxide) concentrations on hydrogel’s properties were examined. The higher concentrations of reagent were used, the thicker coating was obtained. After modification, the material’s surface becomes more hydrophilic in comparison to pristine polyurethane. Cytotoxicity assay (MTT test) confirmed that PVP-coating is not toxic. The introduction of hydrogel coating resulted in a significant decrease in the fibrinogen adsorbed to the material’s surface as compared to a non-modified polymer. Platelet adhesion assay demonstrated almost no platelet adhesion to the modified surfaces.

Investigating the Properties and Structure of Polyurethane Elastomers with Monoethylene Glycol Chain Extender

The effect of monoethylene glycol (mEG) acting as chain extender in polypropylene glycol (PPG-4000) and 4,4ʹ-diphenylmethane diisocyanate (MDI) reaction was investigated. Polyurethane elastomers (PUR) were changed from flexible to rigid materials by varying the mEG content. Results show that Shore A and D hardness values trend to increase with increasing mEG content. It appears that increasing the chain extender content increases the hard segment content in the polyurethane structure. Moreover, increasing the mEG content increases Young’s modulus and the tensile strength of PUR, while elongation at break decreases. The chemical structure of the hard segment of PUR was characterized by Infrared (IR) spectroscopy. IR spectra exhibited the bands typical for PUR consisting of –NH, CH2– and C=O groups. The spectra reveal a few interactions between the polymeric chains that appear to be responsible for the shift of transmittance peak and decrease of some peak intensity. This may be due to the hard segment aggregating more to form domains in the PUR when mEG content was increased.

Fabrication of Aliphatic Water-Soluble Polyurethane Composites with Silane Treated CaCO3.

In the present study, composites of water-soluble polyurethane/calcium carbonate (CaCO3) were prepared from a soft segment of hydroxyl-terminated polybutadiene (HTPB) and polyethylene glycol (PEG, average molecular weight = 4000) with aliphatic diisocyanates. The functionality of CaCO3 particles was modified using aminopropyltriethoxysilane (APTES), and was confirmed by Fourier-transform infrared spectroscopy (FTIR). The solubility, hydrophilic properties, and chemical structures of the composites were analyzed by water-solubility tests, contact angle measurements, and FTIR, respectively, and the successful production of the hydrophilic water-soluble polyurethane (WSPU) structure was demonstrated. The adhesion of surface-modified CaCO3 particles to the WSPU matrix and the thermal degradation properties of the neat WSPU and WSPU/CaCO3 composites were studied using field emission scanning electron microscopy (FE-SEM) and thermogravimetric analysis (TGA). The results demonstrated good adhesion of the surface-modified CaCO3 particles along with an improved thermal degradation temperature with the addition of CaCO3 particles to the WSPU matrix.

Adjustment of Cell Adhesion on Polyurethane Structures via Control of the Hard/Soft Segment Ratio

AbstractCreating substrates with a similar composition that can either prevent or promote cell adhesion is still a challenging feat. Here, it is shown that a strikingly simple method of tuning the amount of hard segments or isocyanate index (NCOind) of a polyurethane (PU) film allows to modulate cell adhesiveness. PU films are synthesized with NCOind of 75, 100, 200, 300 and 400 corresponding to ratios of isocyanate to hydroxyl functions of 0.75, 1, 2, 3, 4, respectively. The adhesive capacity of NIH 3T3 fibroblasts (3T3) and Wharton's jelly mesenchymal stem cells (WJMSCs) are dependent on the NCOind. For NCOind below 300, no cell adhesion can be observed regardless of the cell type, whereas for NCOind of 300 and 400 cells adhere to the PU surface. WAXS and small angle X‐ray scattering (SAXS) studies reveal that variations of NCOind allows to modulate the phase separation in PU films. Porod's law shows that for NCOind of 300 and 400, the hard–soft segment interface is sharp. Conversely, samples with smaller NCOind present diffuse interfaces. Hence, the morphology of the interface between hard and soft domains appears to be a critical feature that correlates with the adhesion capacity of cells.

Preparation of hybrid PU/PCL fibers from steviol glycosides via electrospinning as a potential wound dressing materials

AbstractIn this study, the synthesis and application of biocompatible steviol glycosides based polyurethane/poly (ε‐caprolactone) (PU/PCL) fibers was performed by electrospinning as a potential wound dressing materials that can be used for the closure of nonhealing wounds. During electrospinning, steviol glycoside‐based polyurethane structures were used in blend formation with poly (ε‐caprolactone) for easy producibility. Steviol glycosides are a natural abundant and easily accessible source as the main component of the wound dressing material due to their free hydroxyl groups, high biocompatibility, and hydrophilicity. The structure of steviol glycosides is composed of saccharide units and the free OH groups. Thus, steviol glycosides act as a crosslinker within the polyurethane structure and provides mechanical strength. For the production of steviol glycosides based PU/PCL fibers first, the steviol glycosides as a monomer were isolated from the stevia rebudiana. Then, polyurethane structures containing stevia glycoside were synthesized with hexamethylene diisocyanate, lactose and PEG‐200 by solution polymerization technique. PCL was added to the prepared polyurethanes in a ratio of 1:2 and formation of nanofiber structure. The prepared wound dressing material was characterized by Fourier transform infrared, atomic force microscopy, and scanning electron microscope techniques. Swelling degree, water content and oxygen permeability assay of the steviol glycosides based PU/PCL wound dressing material was determined. In biocompatibility test, cell viability value of PU/PCL fibrous materials in indirect cytotoxicity test was determined as 86.9% and cell adhesion on hybrid PU/PCL fibers was showed as morphological. In accordance with this target, the steviol glycosides based PU/PCL wound dressing material can be produced easily and low cost. As a result, the wound dressing materials obtained with their high biocompatibility and low costs will be an effective and fast method for the healing of open wounds of diabetics.