Thermoplastic polyurethane–urea elastomers with superior mechanical and thermal properties prepared from alicyclic diisocyanate and diamine

High-performance thermoplastic polyurethane (TPU) elastomers have long been the objective of numerous studies. In this work, thermoplastic polyurethane–urea (TPUU) elastomers with balanced superior mechanical and thermal properties, in comparison with the rare cases of high-performance TPU/TPUU elastomers with super-high tensile strength, were synthesized by the reaction of polycarbonate diols with excess alicyclic isophorone diisocyanate, followed by the chain extension of alicyclic isophorone diamine. When the content of hard segment was around 47%, the TPUU elastomer had super-high tensile strength of 51.7 MPa, initial elastic modulus of 698 MPa and elongation at break of 480%. The temperature range of this TPUU elastomer's rubbery state was up to 120°C with storage modulus above 200 MPa, and its rubbery flow state reached 200°C where the storage modulus was still as high as 100 MPa. Fourier transform infrared spectroscopy analysis indicated the presence of strongly hydrogen bonded urethane and urea groups in these TPUU elastomers. Atomic force microscopy and differential scanning calorimetry studies demonstrated significant and nearly perfect microphase separation in these TPUU elastomers when the hard segment content was around or below 47%. These noncrystalline TPUU elastomers could be thermally processed or processed in the form of a solution.     

Synthesis and properties of hybrid alkyd–acrylic dispersions and their use in VOC-free waterborne coatings

Hybrid waterborne alkyd–acrylic dispersions with solid content of 40%, free from any surfactant and exempt of any organic solvent, were successfully synthesized by a melt co-condensation reaction between an acrylic prepolymer bearing carboxylic groups and a long-oil alkyd resin. Spontaneous emulsification of the ensuing hybrid resin was achieved by the addition of an aqueous ammonia solution that neutralized the carboxylic functions. The key role of the carboxylic groups on the stabilization process and on the storage stability of the dispersion was assessed and it was shown that the insertion of anhydride moieties within the acrylic prepolymer ensured the efficient coupling between the acrylic and the alkyd resin and prevented the phase separation. These dispersions are easy to implement and might be used to prepare high quality zero VOC coatings in terms of drying time, stability and gloss. The most stable dispersion was also used in the formulation of air-drying waterborne lacquers and their coating properties were evaluated.     

Improved gas transport properties of polyurethane–urea membranes through incorporating a cadmium-based metal organic framework

The increasing need for more efficient separation processes has motivated the development of polymer membranes that can provide fast and selective transport. In this work, cadmium-based metal–organic framework (MOF) nanoparticles and a polyurethane–urea (PUU) elastomer were synthesized. New mixed-matrix membranes (MMMs) were then fabricated from the nanoparticles and the PUU. SEM images verified that embedding the nanoparticles changes the morphology of the PUU and the nanoparticles disperse well in the PUU due to satisfactory compatibility of the polymer and nanoparticles. Fourier transform infrared spectroscopy and X-ray diffraction analysis confirmed the dispersion of the nanoparticles in the soft segment of the PUU. With increased temperature, gas permeabilities of the MMMs improved but their sieving ability deteriorated. An MMM incorporating 2.5 wt % of the MOF showed a CO₂ permeability of ~140 barrer and a CO₂/N₂ selectivity of ~30, which are 89 and 38% higher than those of the pristine membrane. Gas permeation tests showed that the higher CO₂/N₂ selectivity of the MMMs was due to improved solubility selectivity and the higher CO₂ permeability was a result of improved CO₂ diffusivity and solubility coefficients. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48704.     

Thermomechanical and corrosion inhibition properties of graphene/epoxy ester–siloxane–urea hybrid polymer nanocomposites

The effect of graphene on the corrosion inhibition properties of a hybrid epoxy–ester–siloxane–urea polymer was investigated. The weight fraction of graphene was varied from 1 to 2 wt%. Direct current polarization (DCP) and electrochemical impedance spectroscopic (EIS) techniques were used to measure the polarization and coating resistance of the coated aluminum alloy substrate. The grapheme/hybrid polymer composite coatings showed much higher corrosion inhibition property when compared to the neat hybrid polymer coating. An increase in glass transition temperature and rubbery region modulus was also observed for composites containing 1–2 wt.% of graphene. A direct correlation between the rubbery plateau modulus of free standing composite thin films and corrosion resistance of the composite coatings was made, indicating that the corrosion protection mechanism is due to restriction of the polymer chain motion by graphene which causes a decrease in coating permeability.     

Preparation and properties of high viscosity and elasticity asphalt by styrene–butadiene–styrene/polyurethane prepolymer composite modification

The porous asphalt pavements is often used in important occasion for its special properties and performance which can be to a great extent attributed to the binder—high viscosity and elasticity asphalt (HVEA). To prepare high demanding binder for porous asphalt pavements, the polyurethane prepolymer (PUP) and styrene–butadiene–styrene (SBS) were used to modify the matrix asphalt compositely. First, based on a series of physical tests, the effects of binder composition on performance of SBS/PUP HVEA binder (SBS/PUP-HVEA) were investigated. Then the Fourier transform infrared (FTIR) test was conducted to investigate the reaction mechanism of SBS/PUP-HVEA binder. Last, the fluorescence microscopy, stability tests, multiple stress creep recovery test, and differential scanning calorimetry test were carried out to evaluate and compare the phase structure, storage, high-temperature performance, thermostability characteristics of several HVEA binders. It is found that the composite modification of SBS and PUP can produce high quality binder which possesses high viscosity and high elasticity. And the composition of SBS/PUP-HVEA were recommended as follows: Shell-70# can be chosen as matrix asphalt, the contents of SBS modifier (SBS1301:SBS4303 = 1:2), H2122A PUP, chain extender M-OEA, and crosslinker sulfur were suggested 4%, 5%, 0.5%, and 1‰, respectively. The new functional groups observed in FTIR confirmed the existence of physical and chemical reactions in the modification process, which were beneficial to improve the high temperature performance and storage stability of the binder. SBS/PUP-HVEA had good phase structure, storage stability, high temperature performance, and thermostability compared to other HVEA binders. This study demonstrated that the SBS/PUP compositely modified asphalt possessed high viscosity and high elasticity, which can be used in the porous asphalt mixture and other highly demanding working environment as well.     

Adhesion-to-fibers and film properties of etherified–oxidized cassava starch/polyvinyl alcohol blends

In our previous work, it was demonstrated that etherified–oxidized cassava starch (EOCS) showed greater adhesion and film properties than oxidized cassava starch (OCS). Therefore, the purpose of this paper is to reveal if blending EOCS with polyvinyl alcohol (PVA) could further enhance the adhesion of OCS to cotton and polylactic acid (PLA) fibers and toughen OCS film. The EOCS samples were synthesized through etherification of OCS with 3-chloro-2-hydroxypropyl sulfonic acid sodium in an aqueous medium, and were characterized by Fourier transform infrared spectroscopic technique. The apparent viscosity of cooked EOCS/PVA paste was measured, and the adhesion was evaluated by measuring the bonding forces of the blends to cotton and PLA fibers. Film properties were analyzed in terms of tensile strength, breaking elongation, bending endurance, scanning electron microscopy and X-ray diffraction. It was found that blending EOCS with PVA was able to further enhance the adhesion of OCS to both fibers and toughen OCS film. The enhancement in the adhesion and the film toughness was correlated with blending ratio of EOCS to PVA. With the decrease in the ratio, the breaking elongation and bending endurance of the blend films and bonding forces significantly increased. By increasing the degree of substitution (DS) of EOCS, the bonding forces of EOCS/PVA blends to both fibers gradually increased. In the adhesion, the positive influence performed by the ratio is more than that performed by the DS. The EOCS/PVA with a ratio of 50:50 and a DS of 0.031 could be adopted to further improve the adhesion and film toughness of OCS.

     

Structure–property correlation study of hyperbranched polyurethane–urea (HBPU) coatings

This paper deals with the structure–property relation of different HBPU coatings based on the variation of parameters like, NCO/OH ratio, generation number and type of diisocyanates used. For this, the NCO terminated HBPU prepolymers were synthesized first by reacting the different generation hyperbranched polyesters (HBPs) with excess diisocyanates. In the next step, these HBPU prepolymer coated films were completely moisture cured to get the desired HBPU coatings. The synthesized polymers were confirmed by ¹H, ¹³C NMR and FT-IR spectroscopy methods whereas structure–property relation was drawn from the FT-IR peak deconvolution technique. The degree of branching (DB) and percent composition of different structural units present in the HBPs were calculated from the ¹H and ¹³C NMR data by using Fretch equation. The melt viscosity study of different HBP samples suggests that most polyester sample showed Newtonian behavior. The coating film properties were studied by DMTA, TGA, UTM, and contact angle measurement instruments. DMTA and TGA data shows that the increase of NCO/OH ratio and generation number had a favorable impact on storage modulus (E′), glass transition temperature (T_g), onset degradation temperature (T_1ON) and char residue values of the coatings. The contact angle and UTM data suggest that the hydrophobicity and tensile strength increases but flexibility decreases with increasing the NCO/OH ratio.     

Effects of urea formaldehyde resin to film properties of alkyd–melamine formaldehyde resins containing organo clay

Organo clay modified alkyd resins were prepared and these modified alkyd resins were cured with different ratios of melamine formaldehyde and urea formaldehyde resins in this work. Alkyds formulated to have oil content 40% were prepared with phthalic anhydride (PA), glycerine (G), coconut oil fatty acid (COFA), dipropylene glycol (DPG) and organo clay. “K alkyd constant system” was used for the formulation calculations of the alkyd resins. Alkyd resins were blended with 40% of a commercial melamine formaldehyde. The films of the alkyd–amino resins were prepared from 60% solid content xylene solutions using 50 μm applicators. After the films were cured at 140 °C for 2 h in an oven, properties of the films were determined. The film properties of the alkyd–amino resins such as drying degree, hardness, adhesion strength, abrasion resistance, water, acid, alkaline, solvent resistance, and resistance to environmental conditions were investigated. The addition of the urea formaldehyde resin and organo clay has positive effect on the physical and chemical resistance of the alkyd–amino resins.     

Relationship on structure and properties of polyurethane modified Diels–Alder addition polymer

A series of linear and crosslinked polyurethane modified materials were prepared by Diels–Alder cycloaddition reaction. Based on raw materials, some novel equations were designed and effects of equation parameters on the mechanical properties of modified material were explored. It was demonstrated that tensile strength of modified materials and elongation at break were changed from 3.68 to 18.71 MPa, 200 to 866%, respectively. In addition, the optimal reaction temperature of retro-Diels–Alder (r-DA) reaction was determined by differential scanning calorimeter (DSC). Gel permeation chromatography (GPC) and tensile experiments were used to characterize the properties of repolymerized material after degradation. The results indicated the optimal temperature of r-DA for linear and crosslinked polyurethane modified materials is 127 and 150 °C. Moreover, after decomposed, the product was slowly repolymerized at 60 °C, and can more effectively restore material strength under the action of the solvent to achieve self-healing effect. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47355.     

Hierarchical mullite structures and their heat-insulation and compression–resilience properties

Near-net-shaped hierarchical structure-adjustable short mullite fibers/mullite whiskers frameworks (MF/MW frameworks) were prepared by slurry-filtration and heat-treating method. The main structure of MF/MW framework was constituted by lap-jointed mullite fibers. Every single fiber in the framework was densely covered by mullite whiskers which formed through fluorine-catalyzed gas-phase reaction, and the fibers actually served as curved substrates for the mullite whiskers' growth. The lap-jointing points of the fibers were served by movable intersected mullite whiskers. Moreover, the microstructure of the frameworks could be adjusted by tailoring the raw materials mass ratio. The volume densities, the apparent porosities and the thermal conductivities of the MF/MW frameworks in different raw materials mass ratios were 0.459–0.487 g/cm³, 79.7–82.8% and 0.1356–0.1965 W/k m, respectively. The compression–resilience property of the samples was tested under 0.4 MPa at room temperature. The compression ratio and resilience ratio of the MF/MW frameworks in different raw materials mass ratios were 1.63–2.25% and 92.67–98.16%, respectively. The MF/MW frameworks with advanced thermal and mechanical properties were considered to be promising high-temperature heat-insulation material.     

Synthesis and fluorescence properties of a waterborne polyurethane–acrylic hybrid polymeric dye

A waterborne polyurethane–acrylic hybrid polymeric dye was prepared depending on soap-free emulsion polymerization method. The resulting polymeric dye composed of methyl methacrylate (MMA) monomer which was polymerized into polymethyl methacrylate (PMMA) as cores and waterborne polyurethane-based dye was synthesized by anchoring dye monomers (6-amino-2-cyclohexyl-benz[de]isoquinone-1,3-dione) to polyurethane chains as shells. The average particle sizes of the hybrid polymeric dye emulsions were found to be increased with the increase in MMA contents for MMA monomers. Compared with dye monomers, the absorption intensities and fluorescence intensities of the hybrid polymeric dye were enhanced with the increase of particle sizes. This study revealed that enhanced fluorescence intensity of the hybrid polymeric dye was mainly attributed to the hindered formation of exciplexes among dye monomers and an augmented light absorption area. It was found that the fluorescence intensity of the hybrid polymeric dye was increased with increasing temperature and the trend first increased and then decreased with increase in concentration. Furthermore, the fluorescence of the hybrid polymeric dye emulsions was found to be very stable and not sensitive to the fluorescence quencher.     

Ternary Ti–Si–C alloy film formation on GaN and contact properties

Ternary Ti–Si–C alloy films were deposited on GaN substrates (n-type and p-type) by the radio- frequency magnetron sputtering method. The electrical properties of contact films with various chemical compositions were investigated. The microstructures were examined by X-ray diffractometry and transmission electron microscopy. The electrical properties of the contact films were improved after annealing at 873?K for 60?s. Ohmic contact characteristics were obtained for n-type GaN. The TiN phase plays an important role in obtaining the ohmic contact. The effect of deposition and annealing on the electrical properties between Ti–Si–C film and GaN are discussed based on the experimental results.     

Boron–hydrogen complexes in diamond and their vibrational properties

Diamond is a promising candidate material for high power, high temperature and high frequency electronics. Boron is well known as a shallow acceptor in diamond. Recently diamond has been successfully shallow n-type doped by introducing an excess of deuterium in high quality B doped diamond, enabling a reversible p-type to n-type conversion of B doped diamond. However, the nature of this new shallow donor has been the subject of debate. We calculate the properties of boron and its complexes with hydrogen in diamond, using accurate ab initio plane wave Density Functional Theory (DFT) methods, and show that BH₂ centres are stable with small binding energies of 0.23 to 0.71 eV, consistent with experimentally observed dissociation of the new donor at relatively low temperatures of 200 °C, and explain the two-step deuteration process in high quality boron doped diamond.Our ab initio Plane Wave periodic supercell DFT theory calculations confirm the existence of a BH induced level at E_c – 0.96 eV. We further show that the BH₂ centre possesses a very deep donor level, excluding the possibility of BH₂ doping the BH impurity band previously suggested.To facilitate experimental determination of the nature of the new shallow donor, we determine the Local Vibrational Modes of BH and BH₂ centres in different charge states, together with isotope shifts, which may be compared with experiment, towards establishing the nature of the new donor.     

Effects of pigmentation on siloxane–polyurethane coatings and their performance as fouling-release marine coatings

Siloxane–polyurethane paints were formulated and characterized for coating properties and performance as fouling-release (FR) marine coatings. Paints were formulated at 20 and 30 pigment volume concentrations with titanium dioxide, and aminopropyl-terminated poly(dimethylsiloxane) (APT-PDMS) loadings were varied from 0 to 30% based on binder mass. The coatings were characterized for water contact angle, surface energy (SE), gloss, and pseudobarnacle (PB) adhesion. The assessment of the FR performance compared with polyurethane (PU) and silicone standards through the use of laboratory biological assays was also performed. Biofilm retention and adhesion were conducted with the marine bacterium Cellulophaga lytica, and the microalgae diatom Navicula incerta. Live adult barnacle reattachment using Amphibalanus amphitrite was also performed. The pigmented coatings were found to have properties and FR performance similar to those prepared without pigment. However, a higher loading of PDMS was required, in some cases, to obtain the same properties as coatings prepared without pigment. These coatings rely on a self-stratification mechanism to bring the PDMS to the coating surface. The slight reduction in water contact angle (WCA) and increase in pseudobarnacle release force with pigmentation suggests that pigmentation slowed or interfered with the self-stratification mechanism. However, increasing the PDMS loading is an apparent method for overcoming this issue, allowing for coatings having similar properties as those of clear coatings and FR performance similar to those of silicone standard coatings.     

Hybrid peptide–carbon nanotube dispersions and hydrogels

Scanning probe microscopy (SPM) techniques based on nano-mechanical measurements (topography, adhesion, modulus) and electric force microscopy (EFM) have been used to examine mica surfaces modified with the ionic-complementary peptide EFK8 alone and with EFK8–single-walled carbon nanotube (SWNT) dispersions in water in order to gain a deeper understanding of the interaction between nanotubes and ionic-complementary peptides. Through the use of these techniques, it has been shown for the first time that peptide fibers can be distinguished from SWNTs and peptide-wrapped SWNTs. SPM images reveal features consistent with two types of helical structures: EFK8 fibers wrapped around each other during self-assembly and EFK8 fibers wrapped around SWNTs. In this second structure, EFK8 chains should be oriented with their hydrophobic sides oriented toward the SWNTs and their hydrophilic sides toward the water, thereby enabling the dispersion of the nanotubes in aqueous media. We have also demonstrated the formation of hybrid EFK8–SWNT hydrogels that have potentially superior physical and mechanical properties over those of other hydrogels and opens up new applications for this type of material. To the best of our knowledge, this is the first work reporting the formation of a composite hydrogel made of an ionic-complementary peptide and carbon nanotubes.     

Synthesis and properties of PDMS modified waterborne polyurethane–acrylic hybrid emulsion by solvent-free method

A new type of polysiloxane modified polyurethane–acrylic hybrid emulsion was synthesized by solvent-free method and the polysiloxane was introduced into the soft segment of polyurethane chains using dihydroxybutyl-terminated polydimethylsiloxane (PDMS). The formed film from the hybrid emulsion could provide obviously higher water-resistance property. The preparation technologies such as the content of carboxy group and acrylic monomer, the rate and the time of emulsification were discussed systematically. The chain structure and the particle size were confirmed by the analysis of Fourier transform infrared spectroscopy and transmission electron microscopy, respectively. The effect of PDMS content on the water resistance and the mechanical property were investigated by absorbed water ratio, water contact angle and dynamic mechanical measurement.     

Development of moisture cure polyurethane–urea coatings using 1,2,3-triazole core hyperbranched polyesters

This article reports the development of moisture cure polyurethane–urea coatings. The coating has been developed using different generations of novel 1,2,3-triazole core containing hyperbranched polyester polyols (THBP). For the synthesis of THBP, the core molecule, tetra hydroxyl-terminated di-triazole (THTD), has been synthesized by click reaction involving ethylene diazide and 2-butyne-1,4-diol. The polycondensation reaction between the core THTD and 2,2-bis (hydroxymethyl) propionic acid (Bis-MPA) at different mole ratios has been used to get first (THBPG-1), second (THBPG-2), and third (THBPG-3) generations of triazole core hyperbranched polyesters. The structural investigations of these THBPs have been carried out by ¹H NMR, ¹³C NMR, and FTIR spectroscopy. The different generations of THBPs were further reacted with 1-isocyanato-4-[(4-isocyanatocyclohexyl) methyl] cyclohexane (H₁₂-MDI) at OH:NCO ratio of 1:1.2 to get –NCO terminated triazole core hyperbranched polyurethanes. They were cured under atmospheric moisture to get hyperbranched polyurethane–urea coatings and were named as THBPUG-1, THBPUG-2, and THBPUG-3. FTIR has been used to confirm the formation of polyurethane coatings. The TGA and DMTA have been used to determine the thermal stability and dynamic mechanical properties of the coatings, respectively. The corrosion resistance properties of the coatings have been studied by salt spray and electrochemical test. The coatings were also evaluated for microbial resistance. The results indicate that the thermal stability, glass transition temperature, and corrosion resistance properties increase with an increase in generation number of THBPs used for coating development. All three generations of coating films show excellent antimicrobial activity. Based on overall combined structure–property relationship study, these types of coatings will be useful as multifunctional applications in marine and moist environments.     

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde and polyurethane adhesives

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde (MUF) and polyurethane (PUR) adhesives was monitored by measuring their rheological properties by means of a rheometer. Instead of the standard aluminium discs, wooden discs, made from heat-treated wood with different degrees of thermal modification and conditioned in different climates, were used. The wooden discs provided more realistic curing of the adhesives compared to the real-life bonding of wood, because of solvent absorption. The results of the rheological measurements suggested that the modified wood inhibited the curing of MUF and PUR adhesives. The curing of the MUF adhesive was slower because of the reduced absorption of water from the adhesive. The curing of the one-component PUR adhesive was affected by the lower moisture content (MC) of the modified wood.     

Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO₃)₃.9H₂O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al₂O₃). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.     

Preparation of waterborne phosphated acrylate–epoxy hybrid dispersions and their application as coil coating primer

In this paper, a series of waterborne acrylic-modified epoxy hybrid dispersions were synthesized and successfully used as primers for coil coatings. Epoxy was phosphated to improve its adhesion to the metal substrate. The grafting reaction of acrylate monomers onto the high molecular weight epoxy resins was studied with infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance. The structure and resin molecules were found to be as expected and the film had the best performance when the acrylate monomer made up less than 40 wt% of the epoxy resin. Modification of the epoxy with phosphoric acid could increase the adhesion to the metal substrate. Better adhesion was achieved with greater amounts of phosphoric acid. R578 urea resin was found to be the most suitable for crosslinking of the resin in this system, and a paint film based on the resulting resin had excellent overall performance.