Structures and physical properties of rigid polyurethane foams with water as the sole blowing agent

Polyurethane rigid foams have been used for many applications such as pipelines insulation materials, automotive parts, solar water heater and construction materials[1,2], due to their desirable physical properties. Traditional rigid foam is made by the reaction of a polyol and 4,4′-diphenylmethane diisocyanate (MDI) with chlorofluorocarbons (CFCs), in particular tri- chlorofluoromethane (CFC-11) and/or HCFC-141b as blowing agents. However, the CFCs blowing agents contain halogens, whic…     

A conductive polymer composite derived from polyurethane and cathodically exfoliated graphene

Composite electrodes represent an important class of electromaterials, with enhanced functional properties tailored for targeted applications. Introduction of graphene as a conductive nanofiller into the thermoplastic polyurethane (PU) provides electrodes with interesting properties. In this study, a highly conductive cathodically exfoliated graphene (CEG) of ～2–8 μm lateral size was employed to prepare CEG-PU composites. The use of this larger graphene sheet requires loading of at least 20% w/w graphene to promote contact between the sheets, hence the conductivity. The CEG-PU composite electrodes were tested to determine their electrochemical capacitance and it was found that the 40% (w/w) CEG-PU composite shows areal capacitance, energy density, and power density of 2.51 mF/cm², 1.56 μW/h/cm², and 0.48 mW/cm², respectively, at a current density of 0.2 mA/cm² and an operating voltage of 1.0 V. In summary, the CEG-PU composite electrodes have excellent conductivity, chemical/mechanical properties, and capacitive performance.     

Direct observation of cellulose dissolution in subcritical and supercritical water over a wide range of water densities (550–1000 kg/m<Superscript>3</Superscript>)

Direct observations of the heating of microcrystalline cellulose (230 DP) in water at temperatures up to 410 °C and at pressures up to 700 MPa were made with a batch-type microreactor. Cellulose particles were found to dissolve with water over temperatures ranging from 315 to 355 °C at high pressures. Dissolution temperatures depended on water density and decreased from about 350 °C at a water density of 560 kg/m³ to a minimum of around 320 °C at a water density of 850 kg/m³. At densities greater than 850 kg/m³, the dissolution temperatures increased and reached a value of about 347 °C at 980 kg/m³. The cellulose dissolution temperatures were independent of heating rates for values ranging from 10 to 17 °C/s. The low dependence of dissolution temperatures on the heating rates is strong evidence for simultaneous dissolution and reaction of the cellulose. Different phenomena occurred depending on water density. At low densities, particles turned transparent and seemed to dissolve into the aqueous phase from the surface. From 670 to 850 kg/m³, the cellulose particles visibly swelled just before completely collapsing and dissolving into the aqueous phase. The swelling probably increased water accessibility and particle surface area and thus lead to the lower dissolution temperatures observed. From 850 to 1000 kg/m³, the particles required longer times to dissolve and many fine brown-like particles were generated as the particles dissolved. FT-IR spectra of the residues were analyzed. Residues formed from heating cellulose at high densities still retained some cellulose character whereas those as low densities had little cellulose character, especially in the O–H stretching vibration region.     

Glass transition and thermal degradation of rigid polyurethane foams derived from castor oil–molasses polyols

Rigid polyurethane (PU) foams having saccharide and castor oil structures in the molecular chain were prepared by reaction between reactive alcoholic hydroxyl group and isocyanate. The apparent density of PU foams was in a range from 0.05 to 0.15 g cm^?3. Thermal properties of the above polyurethane foams were studied by differential scanning calorimetry, thermogravimetry and thermal conductivity measurement. Glass transitions were observed in two steps. The low-temperature side glass transition was observed at around 220 K, regardless of castor oil content. This transition is attributed to the molecular motion of alkyl chain groups of castor oil. The high-temperature side glass transition observed in the temperature range from 350 to 390 K depends on the amount of molasses polyol content. The high-temperature side glass transition is attributed to the molecular motion of saccharides, such as sucrose, glucose, fructose as well as isocyanate phenyl rings, which act as rigid components. Thermal decomposition was observed in two steps at 570 and 620–670 K. Thermal conductivity was observed at around 0.032 J sec^?1 m^?1 K^?1. Compression strength and modulus of PU foams were obtained by mechanical test. It was confirmed that the thermal and mechanical properties of PU foams could be controlled by changing the mixing ratio of castor oil and molasses for suitable practical applications.     

Characterization of new cellulosic fiber from the stem of Sida rhombifolia

Natural fibers play a vital role in the field of composites mainly due to their environmental friendliness, the nature of their disposal, and low energy requirement for processing. Recently, research ideas have focused on exploration of promising natural fibers with superior mechanical properties. Sida rhombifolia is one such perennial shrub from which high stiffness natural fibers can be extracted. The physico-chemical properties of Sida rhombifolia fibers (SRFs), crystallinity index (56.6%), higher cellulose (75.09 wt.%) content, and lower density (1320.7 kg/m³) were revealed and compared to those properties of other natural fibers.     

Conversion of low density polyethylene foams into auxetic metamaterials

Cellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added-value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re-entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation-condensation leading to low density foams (77–200 kg/m³) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m³ were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment.     

Interrelationship between ultimate mechanical properties of variously structured polyurethanes and poly(urethane urea)s and stretching rate thereof

The ultimate mechanical properties of polyurethane determine their possible applications under various conditions of mechanical action. The mechanical properties of nine polyurethane and polyurethane urea samples were investigated in a range of stretching rates 0.56÷0.002 s⁻¹. A part of experiments was performed at several temperature values under conditions of stepwise variable stretching rates. The interrelationship between rate dependence of strength–strain properties of polyurethane compositions and the structure thereof was ascertained. The influence of molecular structure’s variations, of physical network density and of segmented polyurethane and polyurethane urea morphology on said interrelationship was examined on samples subjected to large strain values. The structure of some samples was radically distorted by plasticizers oppositely influencing micro-phase segregation of soft and hard segments. Multiple kinds of dependency (direct, inverse, moderate and strong) of elastomers’ strength versus stretching rate were demonstrated. Produced data and ascertained regularities are useful to perceive reasons for diversity of mechanical behavior of polyurethane materials and to control properties thereof.     

Design and Operating Characteristics of a Simple and Reliable DBD Reactor for Use with Atmospheric Air

The paper reports on the construction and operating characteristics of a planar dielectric barrier discharge (DBD) plasma generator. The generator was powered from a commercial frequency inverter at 400 Hz through a high voltage transformer. It could be operated up to a specific energy density (power per gas flow) of 20 Wh/m³. The corresponding power density was about 0.5 W per cubic centimeter of discharge volume. Special emphasis was given to a simple and reliable construction, which was easy to assemble and is based on a new, nonexpensive barrier material with excellent electrical, mechanical, and thermal properties. The modular reactor design allows simple plasma power scale-up. The reactor works with undried ambient air without additional cooling. In the range up to 10 Wh/m³ the ozone generation from ambient air was directly proportional to the energy density at a rate of 60 g O₃ per kWh or 30 ppm/Wh/m³. Thus the generator can serve as an effective source for chemically active radicals in plasma gas cleaning applications.     

Influence of dry density on HTO diffusion in GMZ bentonite

With the low permeability and high swelling property, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository. The diffusion behaviors of HTO in GMZ bentonite were studied to obtain effective diffusion coefficient (D _e) and accessible porosity (ε) by through- and out-diffusion experiments. A computer code named Fitting for diffusion coefficient (FDP) was used for the experimental data processing and theoretical modeling. The D _e and ε values were (5.2–11.2) × 10⁻¹¹ m²/s and 0.35–0.50 at dry density from 1,800 to 2,000 kg/m³, respectively. The D _e values at 1,800 kg/m³ was a little higher than that of at 2,000 kg/m³, whereas the D _e value at 1,600 kg/m³ was significantly higher (approximately twice) than that of at 1,800 and 2,000 kg/m³. It may be explained that the diffusion of HTO mainly occurred in the interlayer space for the highly compacted clay (dry density exceeding 1,300 kg/m³). 1,800 and 2,000 kg/m³ probably had similar interlayer space, whereas 1,600 kg/m³ had more. Both D _e and ε values decreased with increasing dry density. For compacted bentonite, the relationship of D _e and ε could be described by Archie’s law with exponent n = 4.5 ± 1.0.     

Preparation and characterization of silica aerogels from diatomite via ambient pressure drying

The silica aerogels were successfully fabricated under ambient pressure from diatomite. The influence of different dilution ratios of diatomite filtrate on physical properties of aerogels were studied. The microstructure, surface functional groups, thermal stability, morphology and mechanical properties of silica aerogels based on diatomite were investigated by BET adsorption, FT-IR, DTA-TG, FESEM, TEM, and nanoindentation methods. The results indicate that the filtrate diluted with distilled water in a proportion of 1: 2 could give silica aerogels in the largest size with highest transparency. The obtained aerogels with density of 0.122–0.203 g/m³ and specific surface area of 655.5–790.7 m²/g are crack free amorphous solids and exhibited a sponge-like structure. Moreover, the peak pore size resided at 9 nm. The initial aerogels were hydrophobic, when being heat-treated around 400°C, the aerogels were transformed into hydrophilic ones. The obtained aerogel has good mechanical properties.     

CONDUCTIVE COMPOSITES FROM POLYPYRROLE ELECTROPOLYMERIZED IN A POLYURETHANE MATRIX

In order to improve the mechanical properties of polypyrrole, composites were made by electropolymerizing polypyrrole in a polyurethane matrix. Polypyrrole/polyurethane (PPY/PU) composite films containing CLO_4~-, BF_4~- or CH_3-C_6H_4-SO_3~- counter ions were made in a variety of solvent systems and characterized by SEM, electronic conductivity, FTIR, and mechanical properties. Composite films showing much greater fiexibility than pure polypyrrole were obtained, but their electronic conductivities were substantially lower. Measured eonductivities ranged from 0.001 to 8 S/cm, tensile strengths from 44 to 592 psi, and elongation to failure from 3 to 70%.     

Preparation and properties of an efficient smoke suppressant and flame‐retardant agent for thermoplastic polyurethane

APP@ETA, as a new type of flame retardant, was prepared by chemically modifying ammonium polyphosphate (APP) with ethanolamine (ETA) and applied to thermoplastic polyurethane (TPU) in this study. Then, the smoke suppression properties and flame‐retardant effects of APP@ETA in TPU composites were evaluated using smoke density test, cone calorimeter test, etc. And, the thermal degradation properties of flame‐retardant TPU composites were investigated by thermogravimetric analysis/infrared spectrometry. The smoke density test results indicated that APP@ETA could obviously improve the luminous flux of TPU composites in the test with or without flame. The cone calorimeter test results showed that total smoke release, smoke production rate and smoke factor of the composites with APP@ETA were significantly decreased than those of the composites with APP. For example, when the loading of APP@ETA or APP was 12.5 wt%, the total smoke release of the sample with APP@ETA decreased to 3.5 m²/m² from 6.0 m²/m², which was much lower than that of the sample with APP, reduced by 41.7%. The thermogravimetric analysis results demonstrated that APP@ETA could decrease the initial decomposition temperature and improve the thermal stability at high temperature for TPU composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Covalent modification of temperature-sensitive breathable polyurethane with carbon nanotubes

Intelligent breathable polyurethane (PU) that is easily allowable for vapor transmission at critical temperature would have significant implication for numerous applications; however, fabrication of such materials has proven to be tremendously challenging. Herein, we reported novel breathable polyurethane material covalently modified with carbon nanotubes (CNTs). When an optimal amount of CNTs (0.5 wt%) was added, the resultant PU film presented high waterproofness with hydrostatic pressure up to 10.9 kPa, as well as enhanced mechanical properties with a tensile strength of 22.2 kPa and elongation at break of 990%. This smart PU film has a significant increase in water vapor transmission rate between 18°C (1400 g/(m²·d)) and 38°C (3440 g/(m²·d)). The type of intelligent polyurethane material is a promising candidate for applications in areas such as protective clothing, separator media, and wearable electronics.     

A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods

Microfibrillated celluloses (MFCs) with diameters predominantly in the range of 10–100 nm liberated from larger plant-based fibers have garnered much attention for the use in composites, coatings, and films due to large specific surface areas, renewability, and unique mechanical properties. Energy consumption during production is an important aspect in the determination of the “green” nature of these MFC-based materials. Bleached and unbleached hardwood pulp samples were processed by homogenization, microfluidization, and micro-grinding, to determine the effect of processing on microfibril and film properties, relative to energy consumption. Processing with these different methods affected the specific surface area of the MFCs, and the film characteristics such as opacity, roughness, density, water interaction properties, and tensile properties. Apparent film densities were approximately 900 kg/m³ for all samples and the specific surface area of the processed materials ranged from approximately 30 to 70 m²/g for bleached hardwood and 50 to 110 m²/g for unbleached hardwood. The microfluidizer resulted in films with higher tensile indices than both micro-grinding and homogenization (148 Nm/g vs. 105 Nm/g and 109 Nm/g, respectively for unbleached hardwood). Microfluidization and micro-grinding resulted in films with higher toughness values than homogenization and required less energy to obtain these properties, offering promise for producing MFC materials with lower energy input. It was also determined that a refining pretreatment required for microfluidization or homogenization can be reduced or eliminated when producing MFCs with the micro-grinder. A summary of the fiber and mechanical energy costs for different fibers and processing conditions with economic potential is presented.     

Synthesis of networked polymers by copolymerization of monoepoxy‐substituted lithium sulfonylimide and diepoxy‐substituted poly(ethylene glycol), and their properties

Networked polymers that had poly(ethylene glycol) (PEG) chains and lithium sulfonylimide salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3‐glycidyloxypropanesulfonyl‐trifluoromethanesulfonylimide with poly(ethylene glycol) bis(3‐aminopropyl) terminated. The obtained flexible self‐standing networked polymer films showed high thermal and mechanical stability with relatively high ionic conductivity. The room temperature ionic conductivity under a dry condition was in the range of 10^?5 ～ 10^?4 S m^?1, which is one order of magnitude higher than the corresponding networked polymers having lithium sulfonate salt structures (10^?6 ～ 10^?5 S m^?1). The film sample became swollen by immersing in propylene carbonate (PC) or PC solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The sample swollen in PC showed higher ionic conductivity (7.2 × 10^?3 S m^?1 at room temperature), and the sample swollen in 1.0 M LiTFSI/PC showed much higher ionic conductivity (8.2 × 10^?1 S m^?1 at room temperature). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Study of Aqueous Biomolecules with Magnetic Flux Using Density,Viscosity, and Surface Tension Probe at 304.15 K

Doses of 0.0150 weber m^?2 magnetic flux for 30 minutes are given to four series of biomolecules in aqueous medium, densities (ρ), viscosities (η), and surface tension (γ) were measured at 304.15 K. The vitamins and carbohydrates decrease densities and viscosities and the difference of density from magnet to aqueous solution in order of dextrose (? 0.00025 kg m^?3) > fructose (? 0.00021 kg m^?3) = B6 (? 0.00021 kg m^?3) > starch (? 0.00018 kg m^?3) > B1 (? 0.0018 kg m^?3), while viscosity in order of starch (? 0.0044 kg m^?1s^?1) > fructose (? 0.0037 kg m^?1s^?1) > B1(? 0.0018 kg m^?1s^?1) > dextrose (? 0.0016 kg m^?1s^?1) > B6 (? 0.0012 kg m^?1s^?1). The surface tension also decreases in vitamin and carbohydrate. The proteins show increase in ρ, η, and γ value hence casein decrease the density and viscosity. The glutamine show increase in density and surface tension while decrease in viscosity and vice versa to alanine. These orders of the data indicate the intermolecular force between water and bimolecules in magnetic flux.     

Preparation and properties of negative ion/polyurethane flexible foam composites

Abstract

In this study, negative ionpowder was modified with a silane coupling agent and then added to the polyurethane flexible foam to prepare NI/PU flexible foam composites by the one-step foaming method. The effects of the amount of negative ion powder on the mechanical properties, thermal properties and release of negative ions were investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and negative ion detectors. The SEM results showed that modified negative ion powder could be more uniformly distributed around the cell walls of the polyurethane flexible foam. The thermal stability, tensile strength and resilience of the NI/PU flexible foam composite were improved with the increase of the amount of modified negative ion powder. Increasing the amount of modified negative ion powder could also result in an increase in the release of negative ions, and it reached 5500/cm³ or higher at a negative ion content of 3%.     

Preparation of a chromatographic solid support on the basis of perlite and separation of uranium on a TBP-loaded perlite column

The possibilities of preparing a packing for reversed phase column chromatography from Menderes' perlite were studied. Its physical and chemical characteristics were compared with other solid supports prepared from rocks, such as perlite and volcanic slags. A series of chemical treatments were applied to improve the mechanical and chemical properties of perlite. The experimental work covers the strong acid treatment, the strong base treatment and the silanization with DMCS. The raw perlite containing 70–73% SiO₂ was treated with NaOH to make soluble silicates and to increase it. Thus the surface and mechanical characters of the modified perlite were determined. The mean surface OH group density and the specific surface area were 3.2 μmol/m² and 9.2 m²/g, respectively. The modified perlite was silanized and hydrophized to load organic complexing agents. The TBP was fixed successfully on perlite up to 20% w/w. The packing prepared was used to study the chromatographic behavior of UO₂ ²⁺ Fe³⁺.     

Phase equilibria of the 0.8H2O-0.2C5H12 system within the temperature range of 303–684 K at pressures up to 60 MPa

Thermodynamic properties of a binary system containing of 0.2 mass fractions of C₅H₁₂ and 0.8 mass fractions of H₂O over the density and temperature ranges 87–713.68 kg/m³ and 303–684 K at pressures up to 60 MPa were studied experimentally using the constant volume piezometer method. Phase equilibrium lines and critical points of the system were obtained.     

Determination of water density: limitations at the uncertainty level of 1 × 10<Superscript>−6</Superscript>

Absolute measurements of water density with very small uncertainties on the order of 0.001 kg/m³ have previously been a metrological challenge, as is shown by measurements of the density of pure water performed in recent decades with different methods. However, using water as a reference liquid with a well-known density, it is possible to perform density measurements relative to this reference liquid by means of an oscillation-type density meter. Using this so-called substitution method, it is possible to obtain uncertainties of about 0.002 kg/m³ or a relative uncertainty of 2 × 10⁻⁶. The conversion from relative to absolute measurements is performed using a water density table. The uncertainty of this absolute measurement is given by the combination of the uncertainty of the relative measurement and the uncertainty given for the density table. Presented at the PTB Seminar “Conductivity and Salinity”, September 2007, Braunschweig, Germany.