Analyzing the influence of different synthetic talcs in waterborne polyurethane nanocomposites obtainment

Waterborne polyurethane (WPU) nanocomposites were produced utilizing synthetic talc in gel form in order to improve its physical–chemical properties. Synthetic talc manufactured in nano‐gel form are interesting because their interaction with water occurs through hydrogen bonding favoring fillers dispersion within the WPU matrix. WPUs are environmental friendly materials because no organic solvents are used in its production. The nanocomposites obtained with the three synthetic talc nano‐gel fillers presented a good dispersion even when higher amounts of fillers were added, as seen by X‐ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, and atomic force microscopy analyses. The addition of synthetic talcs improved WPU nanocomposites mechanical properties. Storage and loss modulus results proved fillers incorporation into the WPU matrix corroborating with Fourier transform infrared spectroscopy results. Results demonstrated that synthetic talcs in nano‐gel form are interesting to obtain WPU nanocomposites with superior mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46107.     

Improved corrosion resistance based on APTES-grafted reduced sulfonated graphene/waterborne polyurethane coatings

In this work, reduced sulfonated graphene (RSG) containing free amine groups was prepared and modified by 3-aminopropyltriethoxysilane (APTES) and reduction by diethanolamine (DEA). In addition, waterborne polyurethane (WPU) composite coatings were prepared by adding RSG as an anticorrosive filler to WPU. From the results of Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM), it can be found that sulfonated graphene was modified with APTES and successfully reduced by DEA. The SEM images illustrated that RSG was uniformly doped in the WPU. With increasing RSG content, the hydrophobicity of the RSG/WPU films increased due to the strong covalent interaction between RSG and WPU. Finally, the corrosion resistance of the coating was characterized by polarization curves and salt spray tests.     

Waterborne polyurethane/inorganic hybrid composites: preparation,morphology and properties

Abstract

A series of waterborne polyurethane/inorganic (WPU/TiO₂) hybrid composites were synthesised by a sol–gel process on the basis of isophorone diisocyanate, polyether polyol (GE-210), dimethylolpropionic acid, tetrabutyl titanate (TBT) and 3-glycidyloxypropyl trimethoxysilane as a coupling agent. The physical properties of the WPU and WPU/TiO₂ dispersions and hybrids were measured. Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction were used to assess the fracture surface morphology and the dispersions of the WPU/TiO₂ hybrids. The scanning electron microscopy, transmission electron microscopy and atomic force microscopy results showed that the TiO₂ particles were dispersed homogeneously in the WPU matrix in nanoscale. The prepared hybrids showed good thermal stability and mechanical properties in comparison with pure WPU and showed tunable transparence with the TBT fraction in the film. Through suitable adjustment of TBT content, some thin hybrids have potential applications, such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes.     

Fabrication of regenerated cellulose nanoparticles/waterborne polyurethane nanocomposites

Regenerated cellulose nanoparticles (RCNs) are ideal materials for new biomass polymer composites industries. RCNs and composites of RCNs and water‐borne polyurethane (RCN/WPU) were prepared using a facile and environmentally friendly approach without the use of any harmful chemicals. The morphological, thermal, and mechanical properties of the RCN/WPU nanocomposite were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), rheometer, wide‐angle X‐ray diffraction, and enzymatic hydrolysis. RCNs exhibited low crystallinity upon regeneration with an NaOH‐based aqueous solution, and were identified by SEM and TEM to consist of the more thermodynamically stable cellulose form. TGA showed that the thermal stability of RCN/WPU nanocomposites was increased by the addition of RCNs. Finally, enzymatic hydrolysis using cellulase indicated that the biodegradability of RCN/WPU nanocomposites was also improved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46633.     

Effect of octa(aminopropyl) polyhedral oligomeric silsesquioxane (OapPOSS) functionalized graphene oxide on the mechanical,thermal, and hydrophobic properties of waterborne polyurethane composites

A novel graphene nanomaterial functionalized by octa(aminopropyl) polyhedral oligomeric silsesquioxane (OapPOSS) was synthesized and then confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM EDX), atomic force microscopy, and X‐ray diffraction. The obtained functionalized graphene (OapPOSS‐GO) was used to reinforce waterborne polyurethane (WPU) to obtain OapPOSS‐GO/WPU nanocomposites by in situ polymerization. The thermal, mechanical, and hydrophobic properties of nanocomposites as well as the dispersion behavior of OapPOSS‐GO in the polymer were investigated by TGA, a tensile testing machine, water contact angle tests, and field emission SEM, respectively. Compared with GO/WPU and OapPOSS/WPU composites, the strong interfacial interaction between OapPOSS‐GO and the WPU matrix facilitates a much better dispersion and load transfer from the WPU matrix to the OapPOSS‐GO. It was found that the tensile strength of the OapPOSS‐GO/WPU composite film with 0.20 wt % OapPOSS‐GO exhibited a 2.5‐fold increase in tensile strength, compared with neat WPU. Better thermal stability and hydrophobicity of nanocomposites were also achieved by the addition of OapPOSS‐GO. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44440.     

A facile route for the synthesis of nanotubular composite of polyaniline with cobalt and its superparamagnetism below blocking temperature

We have prepared nanotubular composite of polyaniline with cobalt from the reverse micelle of sodium dioctyl sulfosuccinate and n‐hexane. Samples are characterized with characterized by X‐ray diffractometer (XRD), transmission electron microscopy, field emission scanning electron microscope, energy dispersive spectroscopy (EDS), Fourier transformed‐infrared spectrums (FTIR), thermo gravimetric analysis, differential scanning calorimeter, and vibrating sample magnetometer. XRD patterns shows metastable ε‐cobalt phase in the composite. Tube like morphology with average diameter of 25–35 nm and length up to 1 µm is obtained. Peak assignment of FTIR spectrum reveals that green solid material is polyaniline and incorporation of cobalt in polyaniline matrix leads structural change. EDS also indicates the presence of cobalt in the nanocomposite. Enhancement in thermal stability is obtained for nanocomposite. Superparamagnetism is obtained in the nanocomposite from dc magnetic measurement and ac susceptibility measurement. POLYM. COMPOS. 36:489–496, 2015. © 2014 Society of Plastics Engineers     

Preparation and characterization of water-based polyurethane–acrylic hybrid nanocomposite emulsion based on a new silane-containing acrylic macromonomer

A new silane-containing acrylic macromonomer, maleimidedoethoxybutoxydimethylsiloxy butyl acrylate (MEBDMSBA), based on maleic anhydride (MA), ethanolamine (EA), 1,4-butanediol (BDO), dichlorodimethylsilane (DCDMS), and acrylic acid (AA) has been synthesized for formulation of waterborne polyurethane (WPU). Also a series of new silane-containing WPU, methyl methacrylate (MMA), MEBDMSBA, and montmorillonite (MMT) with organically modified montmorillonite (OMMT) content (1.25 wt%) hybrid nanocomposites have been successfully prepared by the emulsion polymerization in the presence of a WPU dispersion, using ammonium peroxodisulfate (APS) as an initiator. The WPU dispersion has been synthesized by a polyaddition reaction of isophorone diisocyanate (IPDI) on polypropylene glycol (PPG-1000) and dimethylol propionic acid (DMPA) as chain extender. The monomer was characterized by Fourier transformer infrared spectroscopy (FTIR), elemental analysis, proton (¹H NMR), and carbon (¹³C NMR) nuclear magnetic resonance spectroscopes, respectively. The nanocomposite emulsions were also characterized using Fourier transform infrared spectroscopy (FTIR) and laser light scattering. Thermal properties of the copolymers were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The OMMT was characterized by FTIR and X-ray diffraction (XRD). The morphology of copolymers was investigated by scanning electron microscopy (SEM) and transition electron microscopy (TEM), and then the effects of silane concentrations on the water absorption ratio were examined. Results showed that OMMT could improve the properties of emulsion; in other words, the properties of nanocomposite emulsion were better when compared with those of the silane–acrylate emulsion.     

Effects of the reagent molar ratio on the phase separation and properties of waterborne polyurethane for application in a water‐based ink binder

Waterborne polyurethane (WPU) dispersions with a high solid content and low viscosity were prepared successfully by a two‐step polymerization with isophorone diisocyanate, poly(propylene glycol), and dimethylol propionic acid as the main raw materials. The molar ratio of hard segments to soft segments was controlled to investigate its influence on the particle size, particle morphology, stability of dispersions, and final properties of the WPU films. Measurements including attenuated total reflectance/Fourier transform infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, X‐ray diffraction, polarizing optical microscopy, and contact angle tests were used to characterize the bulk structures, phase separation, thermal stability, crystallinity, and wettability of the WPU dispersions. The results indicate that all of the WPU dispersions with a high solid content (ca. 40 wt %) and low viscosity (ca. 20–50 mPa s) displayed excellent stability. The prepared WPU dispersions with acetone contents of 5–7 wt % could be used directly as an ink binder without removing the acetone; this is beneficial to industrial applications of water‐based ink binders. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45406.     

Preparation of antibacterial temperature‐sensitive silver‐nanocomposite hydrogels from N‐isopropylacrylamide with green tea

This article reports the temperature‐sensitive, green tea (GT)‐based silver‐nanocomposite hydrogels for bacterial growth inactivation. The temperature‐sensitive hydrogels were prepared via free‐radical polymerization using temperature‐sensitive N‐isopropylacrylamide (NIPAM) monomer with GT as the hydrogel matrix. The nanocomposite hydrogels were encapsulated with silver ions via swelling method, which was later reduced to silver nanoparticles using Azadirachta indica leaf extract. The temperature‐sensitive silver nanocomposite hydrogels were analyzed by using Fourier transforms infrared, UV–visible spectroscopy, differential scanning calorimetry–thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The prepared hydrogels exhibited higher phase volume transition temperature than the NIPAM. The inhibition zone study of the inactivation of bacteria on the developed hydrogels was carried out against Gram negative (Escherichia coli) and Gram positive (Staphylococcus aureus), which revealed that the prepared hydrogels are helpful for the inactivation of these bacteria due to the high stabilization of antibacterial properties of the silver nanoparticles. The developed hydrogels are promising for biomedical applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45739.     

Compatibility effect of titanium dioxide nanofiber on reinforced biobased nanocomposites: Thermal,mechanical, and morphology characterization

Titanium dioxide nanofiber (TNF) was synthesized from the anatase phase of titanium dioxide by the hydrothermal process. The synthesized TNF was reinforced with poly(trimethylene terephthalate)/poly(butylene adipate‐co‐terephthalate) blend to enhance the compatibility and improve the mechanical properties of the blend. The nanocomposite blends were prepared by using a twin‐screw extrusion process with different percentages (2.5%, 5.0%, 7.5%, and 10%) of TNF. The synthesized TNF phase structure was investigated by X‐ray diffraction, scanning electron microscopy, and Fourier‐transform infrared characterization. Enhanced compatibility was observed between the nanofiber and the polymer matrix, which was further confirmed by X‐ray diffraction and scanning electron microscopy analysis. The synthesized nanocomposites exhibited higher thermal stability and enhanced mechanical properties compared with the neat poly(trimethylene terephthalate)/poly(butylene adipate‐co‐terephthalate) matrix. J. VINYL ADDIT. TECHNOL., 22:529–538, 2016. © 2015 Society of Plastics Engineers     

Novel LDPE/vermiculite/ciclopiroxolamine hybrid nanocomposites: Structure,surface properties,and antifungal activity

The increasing number of indwelling medical materials and devices are connected with infections caused by yeast, especially Candida albicans. This pathogen produces biofilms on synthetic materials, which facilitates adhesion of the organisms to devices and renders them relatively refractory to medical therapy. Since antimicrobial polymer nanocomposites present one of the promising possibilities, this study explores a new approach to achieving this goal by developing nanocomposite based on low density polyethylene (LDPE) with clay mineral vermiculite as an active carrier for antifungal compound. The set of LDPE/clay nanocomposite with increasing amount of antifungal nanofiller was prepared by melt compounding procedure. As antifungal agent was selected generally used active substance ciclopiroxolamine and this compound was loaded into natural vermiculite through ultrasound technique. The structure of all prepared samples was studied by X-ray diffraction analysis and Fourier transforms infrared spectroscopy. Further thermal properties of polyethylene/clay nanocomposites were investigated by thermogravimetric analysis and the surface properties were evaluated by light optical microscopy, scanning electron microscopy and atomic force microscopy. From mentioned characteristics, we conclude that presence of nanofiller in LDPE primarily causes shift of thermal degradation to higher temperatures and increasing of microhardness. All prepared LDPE nanocomposites possess an excellent and prolonged antifungal activity against Candida albicans.     

Synthesis of a phosphorus‐ and nitrogen‐containing flame retardant and evaluation of its application in waterborne polyurethane

A phosphorus‐ and nitrogen‐containing intumescent flame retardant, pentaerythritol di‐N‐hydroxyethyl phosphamide (PDNP), was synthesized with phosphorus oxychloride, pentaerythritol, and ethanolamine as raw materials. Using the prepared PDNP as a chain extender, a series of flame‐retardant waterborne polyurethanes (WPU) were prepared, and their structures were characterized using NMR and Fourier transform infrared spectroscopy (FTIR). Additionally, the thermal properties and flame retardancy of WPU films were investigated by thermogravimetric analysis, limiting oxygen index (LOI) tests, cone calorimeter tests, and thermogravimetry‐FTIR. These results indicated that PDNP materials exhibit good char‐forming ability at high temperature and that PDNP‐modified waterborne polyurethane obtained an LOI value of 26.0% for a PDNP content of 9 wt %. Finally, the morphology and the element distributions of char residues of WPU were analyzed by scanning electron microscopy and energy dispersive spectrometry after combustion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46093.     

Synergetic Effects of Graphene Oxide and Clay on the Microstructure and Properties of HIPS/Graphene Oxide/Clay Nanocomposites

In this paper, double-network structure nanocomposite with improved mechanical and thermal properties were prepared using high-impact polystyrene as a matrix phase, clay and graphene oxide as effective reinforcing fillers through a facile solution intercalation method. The structure and morphology of nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, and the synergetic effects of clay and graphene oxide on the final properties were investigated using tensile, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA) analysis. Mechanical analysis showed that the combination of graphene oxide and clay exerted a favorable synergistic effect on the tensile modulus and the yield strength of the ternary composite that are greatly improved as compared with neat high-impact polystyrene, high-impact polystyrene/graphene oxide, and high-impact polystyrene/clay binary composites due to the double-network structure formation between the nanofillers as confirmed by the direct morphological observations using transmission electron microscopy and scanning electron microscopy analysis. The viscoelastic behavior showed that storage modulus of ternary composite significantly improvement over than that of the pure matrix, high-impact polystyrene/graphene oxide and high-impact polystyrene/clay while network structure made. TGA and DMTA measurements also demonstrated that thermal stability of high-impact polystyrene matrix modified by graphene oxide and clay slightly enhanced during the creation of dual network structure of graphene oxide and clay. Our data suggest a potential application for the combination of graphene oxide and clay in graphene-based composite materials.     

A novel castor oil-based polyurethane/layered zirconium phosphonate nanocomposites: preparation,characterization, and properties

A new type of layered zirconium glycine-N,N-dimethylphosphonate (ZGDMP), with the functional groups –COOH, has been prepared and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Situ polymerization method was employed to prepare castor oil-based polyurethane/layered zirconium phosphonate (PU/ZGDMP-n) nanocomposite films. The structure and morphology of ZGDMP in PU matrix have been characterized by XRD, SEM, TEM, and Fourier transform infrared spectroscopy. The results show that the morphology and properties of PU-based nanocomposites greatly depend on the functional groups –COOH because of the chemical reactions and physical interactions involved. The tensile test shows that the tensile strength and elongation at break for the nanocomposite films increase with the loading of ZGDMP as compared to those of the virgin PU.     

Gelatin/montmorillonite hybrid nanocomposite. I. Preparation and properties

Gelatin/montmorillonite (MMT) hybrid nanocomposite was directly prepared with unmodified MMT and gelatin aqueous solution. Thermal and mechanical properties of the composite were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile tests. The results indicated that an intercalated or partially exfoliated nanocomposite could be achieved, and the properties of the composite were significantly improved. A T_g peak of high temperature disappeared in the DSC curve of the composite, and the thermogravity and thermally decomposed rate decreased obviously. The tensile strength and Young's modulus were also improved notably, which varied with MMT content, as well as the pH of gelatin matrix. Meanwhile, SEM photographs showed a plasticizing trend of gelatin fracture surface due to intercalation with MMT. Furthermore, the wet mechanical behavior was initially studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1189–1194, 2002     

Harmless hydrogels based on PVA/Na+‐MMT nanocomposites for biomedical applications: Fabrication and characterization

A series of nanocomposite hydrogels were prepared by a freeze‐thaw process, using polyvinyl alcohol (PVA) as polymer matrix and 0–10 wt% of hydrophilic natural Na‐montmorillonite (Na⁺‐MMT), free from any modification, as composite aggregates. The effect of nanoclay content and the sonication process on the nanocomposite microstructure and morphology as well as its properties (physical, mechanical, and thermal) were investigated. The microstructure and morphology were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X‐ray diffraction technique. The thermal stability and mechanical properties of nanocomposite hydrogels were examined using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis; moreover hardness and water vapor transmission rate measurements. It was concluded that the microstructure, morphology, physical (thermal) and mechanical properties of nanocomposite hydrogels have been modified followed by addition of nanoclay aggregates. The results showed that Na⁺‐MMT may act as a co‐crosslinker. Based on the results obtained, the nanocomposite hydrogel PVA/Na⁺‐MMT synthesized by a freeze‐thaw process, appeared to be a good candidate for biomedical applications. POLYM. COMPOS., 38:1135–1143, 2017. © 2015 Society of Plastics Engineers     

Electrospun polyvinyl alcohol/waterborne polyurethane composite nanofibers involving cellulose nanofibers

TEMPO‐oxidized cellulose nanofibers (TOCNs) were used as nanofillers in this work. Composite nanofibers of polyvinyl alcohol (PVA)/waterborne polyurethane (WPU) reinforced with TOCNs were produced by electrospinning. The reinforcing capability of TOCNs was investigated by tensile tests. Scanning electron microscopy (SEM), X‐ray diffraction, and thermogravimetry analyses were also carried out in order to characterize the appearance, crystallinity, and reinforcing effect of the cellulose nanofibers. SEM results showed that PVA/WPU/TOCNs composite nanofibers presented a highly homogeneous dispersion of TOCNs. The reinforced composites had about 44% increase in their mechanical properties with addition of only 5 wt % of TOCNs while about 42% decrease in elongation at break. The TOCNs reinforced composite nanofibers were more thermally stable than pure PVA/WPU nanofibers. The development of crystalline structure in the composite fibers was observed by XRD. Since PVA, WPU, and TOCNs are hydrophilic, non‐toxic, and biocompatible, and therefore, these nanocomposite nanofibers could be used for tissue scaffolding, filtration materials, and medical industries as wound dressing materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41051.     

Facile synthesis,characterization and material properties of a novel poly(vinyl cinnamate)/ nickel oxide nanocomposite

A poly(vinyl cinnamate) (PVCin) composite was synthesized by a simple one step in situ polymerization of vinyl cinnamate with nickel oxide (NiO) nanoparticles. The structural, morphological and thermal properties of the nanocomposite were characterized using Fourier transform (FT)‐Raman, FT infrared (FTIR) and UV spectroscopies, X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), differential scanning calorimetry and vibrating sample magnetometry (VSM) measurements. FT‐Raman, FTIR and UV spectroscopy results revealed the characteristic absorption and shifts of peaks of the polymer matrix, the shifts being attributed to the interaction of NiO nanoparticles with the polymer chains. The structural and morphological analysis using XRD, HRTEM and FESEM showed the uniform arrangement of nanoparticles within the polymer chains. VSM showed the ferromagnetic nature of the composite with an increasing saturation of magnetism. The glass transition temperature (T_g) of the composite was higher than that of pure PVCin and T_g of the composite increased with increasing nanoparticle content. The electrical resistivity of the nanocomposite was studied from AC and DC conductivity measurements. AC and dielectric properties were markedly enhanced in the whole range of frequency due to the presence of NiO nanoparticles. DC conductivity of the nanocomposite was much higher than that of PVCin and the conductivity of the nanocomposite increased with increasing content of NiO nanoparticles. © 2016 Society of Chemical Industry     

Conductive shape-memory polyurethane/multiwall carbon nanotube nanocomposite aerogels

Smart nanocomposite aerogels have promising applications. In this work, different percentages of multiwall carbon nanotube (MWCNT) added into synthesized polyurethane (PU) gel in the molten state, using a two-roll mill. By soaking the PU/MWCNT nanocomposite gel into the water, PU/MWCNT hydrogels containing more than 90 wt % of water were prepared. The obtained hydrogels were freeze-dried to produce aerogel counterparts. The aerogels were fully characterized using mercury porosimetry, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM). The electrical percolation threshold of conductive aerogel system was measured. The shape-memory behavior of PU/MWCNT nanocomposite aerogels was evaluated by dynamic mechanical thermal analysis (DMTA). The results of the DMTA showed that by adding 2.75 wt % of MWCNT, the recovery ratio and storage modulus of the PU/MWCNT nanocomposite aerogel increased 42 and 180%, respectively. The electrical conductivity of the system also increased three orders of magnitude at the percolation threshold. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48602.     

Influence of preparation method on adhesion and drying performances of polyurethane dispersion

Waterborne polyurethane (WPU) dispersions with a high solid content were prepared by one-step and two-step methods with polyester and polyether type macromolecular diols as the main raw materials. The effects of two synthesis methods on the properties of WPU of polyester and polyether were studied. Fourier transform infrared spectroscopy, particle size and distribution, and Thermogravimetric analysis (TGA) measurements were utilized to characterize the structure. The dryness test results showed that the WPU synthesized with polyester diol as the soft segment by the two-step method had the best drying. In addition, the microstructure of WPU was characterized by transmission electron microscopy, which confirmed that WPU was mainly spherical structure. TGA and scanning electron microscopy results showed that the microphase separation between the soft and hard segments of WPU prepared by the two-step method was weaker, the hydrogen bonding was stronger, the adhesion, and thermal stability of WPU was improved.