In vitro blood compatibility and bone mineralization aspects of polymeric scaffold laden with essential oil and metallic particles for bone tissue engineering

Bone tissue engineering scaffolds necessities appropriate physicochemical and mechanical properties to support its renewal. Electrospun scaffolds have been used unequivocally in bone tissue restoration. The main intention of this research is to develop electrospun polyurethane (PU) scaffold decorated with metallic particles and essential oil with advanced properties to make them as a putative candidate. The nanocomposite scaffold exhibited appropriate wettability and suitable fiber diameter compared to the polyurethane scaffold. Interaction of the added constituents with the polyurethane was corroborated through hydrogen bonding formation. Tensile strength of the composites was enhanced compared to the polyurethane scaffold. Thermal analysis depicted the lower weight loss of the composite scaffold than the pristine PU. Blood coagulation was significantly delayed and also the composite surface rendered safe interaction with red blood cells. In vitro toxicity testing using fibroblast cells portrayed the nontoxic behavior of the fabricated material. The above-said advanced properties of the composite scaffold can be warranted for bone tissue engineering application.     

The potential of biomimetic nanofibrous electrospun scaffold comprising dual component for bone tissue engineering

Oils play a putative choice for alleviating various symptoms associated with bone-related disorders. In this present study, polyurethane (PU) scaffold encompassing with Mahua oil (MO) and propolis (PP) were developed using the electrospinning technique. Morphological analysis showed the reduction in the diameter of the electrospun scaffold with blending of MO and MO/PP into the PU matrix. The strong interactions between PU, MO, and PP were evident through the infrared spectrum and thermal analysis. The wettability results showed the hydrophobic nature in electrospun PU/MO scaffold and hydrophilic behavior in electrospun PU/MO/PP scaffold. Mechanical testing indicated the enhancement in the strength of the PU due to the addition of MO and PP. Moreover, the fabricated scaffolds exhibited nontoxicity, low hemoglobin release and improved blood clotting time as evident in the coagulation studies. The cell proliferation studies showed the enhanced fibroblast cell adhesion in the developed nanocomposites than the pristine PU. Hence, the fabricated PU scaffolds blended with MO and PP having desirable properties can serve as a valuable candidate for bone tissue repair.     

Green synthesis of nickel oxide particles and its integration into polyurethane scaffold matrix ornamented with groundnut oil for bone tissue engineering

Physiochemical properties of the fabricated scaffolds play a crucial role in influencing the cellular response for the new tissue growth. In this study, electrospun polyurethane (PU) scaffolds incorporated with green synthesized nickel oxide nanoparticles and groundnut oil (GO) were fabricated using electrospinning technique. First, synthesis of nickel oxide (NiO) was done using leaf extract of Plectranthus amboinicus (PA) via microwave-assisted technique. Synthesized nanoparticles were confirmed through Energy-dispersive X-ray spectroscopy (EDX) analysis and size of the particles were in the range of 800–950?nm. Fiber morphology of the fabricated scaffolds was analyzed using scanning electron microscope (SEM) which showed decrease in fiber diameter for the fabricated composites compared to the pristine PU. The wettability studies showed an increase in contact angle for developed composites than the pure PU. Thermal analysis depicted an increase in thermal behavior for the PU/GO/NiO compared to the pristine PU. Surface roughness values were obtained through atomic force microscopy (AFM) which showed a decrease in roughness while adding GO and NiO to the PU. Finally, the fabricated composites showed enhanced deposition of calcium content than the pristine PU. These results corroborated that the developed composites have a significant effect on the fiber morphology, wettability, thermal behavior, surface roughness, and mineral deposition depicting its versatility for bone regeneration.     

Production,blood compatibility and cytotoxicity evaluation of a single stage non-woven multicomponent electrospun scaffold mixed with sesame oil,honey and propolis for skin tissue engineering

Scaffolds used in skin tissue engineering must mimic the native function of the extracellular matrix (ECM) and facilitate the fibroblast cell response for new tissue growth. In this study, a novel dressing scaffold based on polyurethane (PU) with sesame oil, honey, and propolis was fabricated by electrospinning. Scanning electron microscopy (SEM) images showed that the diameter of the electrospun scaffolds decreased by blending sesame oil (784?±?125.46?nm) and sesame oil/honey/propolis (576?±?133.72?nm) into the PU matrix (890?±?116.911?nm). Fourier infrared (FT-IR) and thermogravimetric (TGA) analysis demonstrated the formation of hydrogen bonds and interaction between PU and sesame oil, honey, and propolis. Contact-angle measurement indicated reduced wettability of PU/sesame oil scaffold (114?±?1.732) and improved wettability (54.33?±?1.528) in the PU/sesame oil/honey/propolis scaffold. Further, tensile tests and atomic force microscopy (AFM) analysis indicated that the fabricated composite membrane exhibited enhanced mechanical strength and reduced surface roughness compared to the pristine PU. The developed composite displayed less toxicity to the red blood cells (RBC’s) compared to the pristine PU. Cytotoxicity assay showed enhanced cell viability of HDF in electrospun scaffolds than pristine PU after 72?h culture. These enhanced properties of the developed scaffolds suggest the potential of utilizing them in skin tissue engineering.     

Synthesis and properties of conducting organic/inorganic polyurethane hybrids

A series of polyurethane/polyaniline/silica organic/inorganic hybrids were synthesized via the conventional polyurethane (PU) prepolymer technique. Amine-endcapped polyaniline (PANI) with low molecular weight and higher solubility was firstly synthesized. This PANI oligomer was then used together with nano-silica bearing silanol groups as chain extenders to prepare the conducting polyurethane hybrids. The polyurethane hybrids were designated as PU-xPANI-ySiO₂ (x + y = 1). For comparison, the urethane-aniline block copolymer and the PU/silica hybrid were designated as PU-PANI and PU-SiO₂, respectively.The structures of PU-PANI, PU-SiO₂ and conducting polyurethane hybrids were confirmed by FT-IR, solid-state ¹³C, and ²⁹Si NMR spectra. In nano-silica containing organic/inorganic conducting polyurethane hybrids, UV-vis spectra revealed the maximum absorption bands similar to that of PU-PANI. X-ray diffraction patterns indicated that these samples are typical of semicrystalline/amorphous materials. SEM image of PU-0.5PANI-0.5SiO₂ showed that PANI was dispersed homogeneously and interconnected continuously in the insulating PU-silica matrix. TGA results of the polymer hybrids exhibited higher thermal stabilities and lower decomposition rates than that of PU-PANI both in nitrogen and air. Differential scanning calorimetry (DSC) studies indicated that the polyurethane hybrids had higher glass-transition temperatures (T_g) with the increase of PANI, but lower than that of PU-PANI. Stress-strain curves for all of the polyurethane hybrids showed the elastomeric behavior of typical polyurethanes. The surface resistivity values of all hybrids were about 10⁸ ∼ 10¹⁰ Ω/sq. and might meet the requirement of the anti-electrostatic materials.     

Fabrication and characterization of polyurethane patch loaded with palmarosa and cobalt nitrate for cardiac tissue engineering

Cardiac patches are attractive option in overcoming the morbidities associated with cardiac disorders. Nanofibrous scaffolds were fabricated using polyurethane (PU) added with palmarosa (PR) and cobalt nitrate (CoNO₃) using an electrospinning technique. Several characterizations were employed namely field emission scanning electron microscopy, wettability measurement, attenuated total reflectance infrared spectroscopy, thermal analysis, surface roughness measurements, and tensile testing. Further, biological response of the electrospun nanofibers were tested through coagulation study and MTS assay. As-spun composite mats showed smaller fibers than pure PU as depicted in morphology analysis. The interaction of PU with PR and CoNO₃ was confirmed in infrared spectrum and thermal analysis. The incorporation of the PR decreased the wettability and while CoNO₃ addition resulted in the hydrophilic nature as depicted in the contact angle measurements. Mechanical properties testing showed that elongation at break for the pristine PU was increased with the addition of PR and CoNO_3. The surface measurements depicted that the incorporation of PR resulted in the improvement of the surface roughness while the addition of CoNO₃ reduced the surface roughness of the pristine PU. The electrospun nanocomposites showed delayed blood clotting time compared to the pristine PU as shown in coagulation study. Both composites supported the better proliferation of fibroblast cells than pure PU. Therefore, novel composites with smaller fiber diameter, hydrophilicity, better mechanical properties, improved blood compatibility parameters, and good cell viability rates would be a promising candidate for cardiac tissue engineering.     

Thermal,mechanical, and morphological properties of novolac‐type phenolic resin blended with fullerenol polyurethane and linear polyurethane

Fullerenol polyurethane (C₆₀‐PU) and linear polyurethane (linear‐PU) modified phenolic resins were prepared in this study. Phenolic resin/C₆₀‐PU and phenolic resin/linear‐PU blends show good miscibility as a result of the intermolecular hydrogen bonding existing between phenolic resin and PU modifiers. DSC and thermogravimetric analysis methods were used to study the thermal properties of phenolic resin blended with different types of PUs. The intermolecular hydrogen bonding that existed between phenolic resin and C₆₀‐PU was investigated by Fourier transform infrared spectroscopy. The morphology and mechanical properties of phenolic resin/C₆₀‐PU and phenolic resin/linear‐PU blends were also investigated. The char yield of the modified phenolic resins decreased with increasing PU modifier content. Significant improvement in the toughness of the modified phenolic resins was observed. The improvements of impact strength were 27.4% for the phenolic resin/linear‐PU system and 54.3% for the phenolic resin/C₆₀‐PU system, respectively, both with 3 phr linear‐PU and C₆₀‐PU content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2436–2443, 2001     

Polyurethane/polyethyl acrylate interpenetrating polymer networks

The thermal decomposition kinetics of polyurethane/polyethyl acrylate interpenetrating polymer networks (PU/PEA IPN) were studied by means of thermogravimetry and derivative thermogravimetry (TG-DTG), and compared with those of polyurethane (PU) and polyethyl acrylate (PEA). The decomposition temperature (T _i) of PU/PEA IPN was found to be higher thanT _i of PEA, but lower thanT _i of PU. Thermal decomposition kinetic parameters,n andE, estimated using Coats-Redfern method, are found for PU/PEA IPN, PU and PEA to be 1.6, 1.9 and 1.1, and 196.6, 258.6 and 139.2 kJ mol^–1, respectively. The results show that PU/PEA IPN is neither a simple mixture of PU and PEA nor a copolymer of them. The mechanism of thermal decomposition of PU/PEA IPN is different from those of PU and PEA. The special network in PU/PEA IPN effectually protects weak bonds in the molecular chain of PU and PEA.We express our thanks to Dr. Yaxiong Xie and Zhiyuong Ren for their help in this work,     

Incorporation of polydimethylsiloxane into polyurethanes and characterization of copolymers

Novel copolymers of polyurethane (PU) were prepared by direct transurethanetion reaction of a commercial PU with polydimethylsiloxanes (PDMS, MW 1000, 5000, and 10,000) containing hydroxyl end-groups. Transurethanetions with different mass ratios of hydrophobic PDMS to hydrophilic PU chains (PDMS1000–PU: 43:57, 67:33, 71:29, and 80:20; PDMS5000–PU: 37:63, and 51:49; PDMS10000–PU: 51:49) were carried out in solution at 65 and 100 °C. In catalyzed reactions, dibutyltin dilaurate (SnC₃₂H₆₄O₄) was used to promote bond breaking in the PU chain and accelerate the reaction between hydroxyl end-groups of PDMS and regenerated isocyanates of PU. The chemical structures of the prepared copolymers were comprehensively characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopies. According to elemental analysis, the content of PDMS varied between 3 wt.% and 16 wt.%, and results obtained from the ¹H NMR spectroscopy were in good agreement with the results of elemental analysis. Increased length of the hydrophobic chain increased the content of PDMS in the copolymer. The GPC results showed that molar masses of the PUPDMS copolymers were lower than the molar mass of the starting PU. The glass transitions (T_g) of the copolymers were shifted to lower temperature as compared with T_g of the starting polyurethane. ATR FTIR spectroscopy showed the surface of the copolymer films to be enriched with siloxane groups and, according to electron microscopy, it was textured with microspheres. The static contact angles for copolymer films measured with deionized water ranged from 94° to 117°. The different structural, thermal and surface properties of the PUPDMS copolymers as compared with PU indicated that transurethanetion had taken place.     

Polylactic acid-based polyurethane/polyamide 6,12 and graphene nanocomposite: Structure and physical property study for packaging application

This effort reports on novel polylactic acid-derived polyurethane (PU) and polyamide 6,12 (PA6,12)-based blends and graphene-reinforced nanocomposite. PU/PA6,12 (50:50) blend was opted as matrix based on molecular weight and shear stress performance. PU/PA6,12 with 5?wt% graphene (PU/PA6,12/graphene 3) showed improved T₀ and T_max of 515 and 541°C relative to neat blend. PU/PA6,12/graphene 3 also revealed significantly high tensile (53?MPa) and flexural strength (1,711?MPa). For Eschericia coli, Staphylococcus, and Pseudomonas bacterial strains, nanocomposite with higher graphene loading produced significant inhibitory effects. Novel nanocomposites displayed fine antimicrobial and barrier properties against O₂ and H₂O to be used as a packaging material.     

Calcification resistance of polyisobutylene and polyisobutylene‐based materials

Calcification of implanted biomaterials is highly undesirable and limits clinical applicability. Experiments were carried out to assess the calcification resistance of polyisobutylene (PIB), PIB‐based polyurethane (PIB‐PU), PIB‐PU reinforced with (CH₃)₃N⁺CH₂CH₂CH₂NH₂ I^?‐modified montmorillonite (PIB‐PU/nc), PIB‐based polyurethane urea (PIB‐PUU), PIB‐PU containing S atoms (PIB_S‐PU), PIB_S‐PU reinforced with (CH₃)₃N⁺CH₂CH₂CH₂NH₂ I^?‐modified montmorillonite (PIB_S‐PU/nc), and poly(isobutylene‐b‐styrene‐b‐isobutylene) (SIBS), relative to that of a clinically widely implanted polydimethylsiloxane (PDMS)–based PU, Elast‐Eon (the “control”). Samples were incubated in simulated body fluid for 28 days at 37°C, and the extent of surface calcification was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS), and Fourier‐transform‐infrared (FT‐IR) spectroscopy. Whereas the PDMS‐based PU showed extensive calcification, PIB and PIB‐PU containing 72.5% PIB, ie, a polyurethane whose surface is covered with PIB, were free of calcification. PIB_S‐PU and PIB‐PUU, ie, polyurethanes that contain S or urea groups, respectively, were slightly calcified. The amine‐modified montmorillonite‐reinforcing agent reduced the extent of calcification. SIBS was found slightly calcified. Evidently, PIB and materials fully coated with PIB are calcification resistant.     

Novel method for the preparation of poly(urethane–imide)s and their properties

A polymer blend consisting of polyimide (PI) and polyurethane (PU) was prepared by means of a novel approach. PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI) and then end-capped with phenol. Poly(amide acid) was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). A series of oligo(amide acid)s were also prepared by controlling the molar ratio of PMDA and ODA. The PU prepolymer and poly(amide acid) or oligo(amide acid) solution were blended at room temperature in various weight ratios. The cast films were obtained from the blend solution and treated at various temperatures. With the increase of polyurethane component, the films changed from plastic to brittle and then to elastic. The poly(urethane–imide) elastomers showed excellent mechanical properties and moderate thermal stability. The elongation of films with elasticity was more than 300%. The elongation set after the breaking of films was small. From the dynamic mechanical analysis, all the samples showed a glass transition temperature (T_g) at ca. −15°C, corresponding to T_g of the urethane component, suggesting that phase separation occurred between the two polymer components, irrespective of polyimide content. TGA and DSC studies indicated that the thermal degradation of poly(urethane–imide) was in the temperature range 250–270°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3745–3753, 1997     

Preparation of high‐temperature polyurethane by alloying with reactive polyamide

A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4‐tolylenediisocyanate and then was end‐capped with phenol. Soluble PA was prepared by the reaction of 1‐(m‐aminophenyl)‐2‐(p‐aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass‐transition temperatures (T_g's), a lower T_g due to the PU component and a higher T_g due to the PA component, suggesting that the two polymer components were phase‐separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high‐temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497–3503, 2002     

Effects of organophilic montmorillonite on hydrogen bonding, free volume and glass transition temperature of epoxy resin/polyurethane interpenetrating polymer networks

Epoxy resin nanocomposites containing organophilic montmorillonite (oM) and polyurethane were prepared by adding oM to interpenetrating polymer networks (IPNs) of epoxy resin and polyurethane (EP/PU). The dispersion degree of oM in EP/PU matrix was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectrometry (FT-IR) showed that strong interactions existed between oM and EP/PU matrix, and oM had some effect on hydrogen bonding of these EP/PU IPNs nanocomposites. Positron annihilation spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were used to investigate the effect of oM and PU contents on free volume and glass transition temperature (T_g) of these nanocomposites. The PALS and DSC results clearly showed that the presence of oM led to a decrease in the total fractional free volume, which was consistent with increasing T_g upon addition of oM, ascribed to increasing hydrogen bonding in interfacial regions of oM and EP/PU matrix and enhancing the miscibility between EP phase and PU phase. In addition, with increasing PU content, the total fractional free volume increased, corresponding to decreasing T_g.     

On the role of TiO<Subscript>2</Subscript> nanoparticles on thermal behavior of flexible polyurethane foam sandwich panels

A series of flexible polyurethane foam (FPUF) and monolithic polyurethane (PU) sandwich panels reinforced with different contents of TiO₂ nanoparticles (0, 0.5 and 1 mass%) have been successfully prepared by compression molding process at room temperature. The influence of TiO₂ nanoparticles on the thermal properties of PU matrix has been investigated by thermogravimetric and dynamic mechanical thermal analysis (DMTA). The morphology of porous structure of FPUF sandwich panels has been characterized by scanning electron microscopy. The presence of TiO₂ nanoparticles as reinforcement has improved the thermal properties of the FPUF and PU sandwich panel samples. It has been observed that FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles possessed the highest enhancement in thermal properties in all accomplished thermal tests. The DMTA results for the FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles indicated that the storage modulus and loss modulus have increased about 1.22 and 1.25 times, 1.5 and 1.55 times, respectively, compared to pure samples. Furthermore, the glass transition (T _g) obtained from the damping factor (tanδ) curves has increased 2 and 1 °C for FPUF and PU sandwich panels, respectively.     

Lanthanum phenylphosphonate–based multilayered coating for reducing flammability and smoke production of flexible polyurethane foam

In the present work, lanthanum phenylphosphonate (LaPP)–based multilayered film was fabricated on the surface of flexible polyurethane (PU) foam by layer‐by‐layer self‐assembled method. The successful deposition of the coating was confirmed by scanning electron microscopy (SEM) and energy‐dispersive X‐ray (EDX). Subsequently, the thermal decomposition and burning behavior of untreated and treated PU foams were investigated by thermogravimetric analysis (TGA) and cone calorimeter, respectively. The TGA results indicated that T_max2 of treated PU foams were increased by approximately 15°C to 20°C as compared with untreated PU foam. The peak heat release rate (PHRR) and total heat release (THR) of PU‐6 (with 19.5 wt% weight gain) were 188 kW/m² and 20.3 MJ/m², with reductions of 70% and 15% as compared with those of untreated PU foam, respectively. Meanwhile, the smoke production of treated PU foam was suppressed after the construction of LaPP‐based coating.     

Synthesis of NIPU by the carbonation of canola oil using highly efficient 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as novel catalyst

For the green synthesis of polyurethane (PU), non‐isocyanate routes are worthy alternatives. In the present work, we have explored 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as novel catalyst for coupling reaction between epoxidized canola oil and CO₂ (gaseous) to introduce cyclic carbonate moieties in the oil and further used it to obtain non‐isocyanate PU, generally abbreviated as NIPU, by curing with different diamines. The results obtained indicated a 1/4th of the reduction in reaction time with the use of 5,10,15‐tris(pentafluorophenyl)corrolato‐manganese(III) complex as catalyst as compared to the previously reported literature data. As per the reported studies, the corrole metal complex has not been used for this reaction earlier. The structure of products and intermediates were confirmed by using different characterization techniques like ¹H NMR and FTIR spectroscopies. The thermal and mechanical behavior of final product was analyzed by TGA and universal testing machine, respectively. The non‐isocyanate PU obtained showed a good thermal stability up to 200°C and a tensile strength of up to 8 MPa. The effect of structure of diamines on the properties of non‐isocyanate PU was also extensively studied.     

Graft copolymers of polyurethane with various vinyl monomers via radiation-induced miniemulsion polymerization: Influential factors to grafting efficiency and particle morphology

Graft copolymers of polyurethane (PU) with various vinyl monomers were synthesized through a one-pot but two-step miniemulsion polymerization process. Firstly, the polycondensation of isophorone diisocyanate (IPDI) with hydroxyl-terminated polybutadiene (HTPB) had been performed in aqueous miniemulsion at 40 °C in order to obtain PU dispersions. Consecutively, an in-situ graft copolymerization of the vinyl monomers with the synthesized PU was initiated by γ-ray radiation at room temperature. The grafting efficiency of PU with vinyl monomer (G_PU/monomer) was calculated from ¹H NMR spectra and the particle morphology of the final hybrid latex was observed by transmission electron microscopy (TEM). As there was no monomer transferring in miniemulsion system, homogenous hybrid particles would be synthesized provided that the monomer was miscible with PU, such as styrene. With the increase of the polarity of the monomer, the compatibility of PU with monomer decreased. G_PU/monomer varied as G_PU/styrene(37%)>G_{PU/butyl acrylate (BA)}(21%)>G_{PU/methyl methacrylate (MMA)}(12%). The proportion of homogeneous nucleation would increase as the hydrophilicity of the monomer increased. High temperature would destabilize the miniemulsion so as to result in a less grafting efficiency. Compared to the phase separation during the seeded emulsion polymerization, the miniemulsion polymerization method facilitated the preparation of homogeneous materials owing to its monomer droplet nucleation mechanism.     

Polyaniline-coated coconut fibers: Structure,properties and their use as conductive additives in matrix of polyurethane derived from castor oil

Electrically conducting fibers based on coconut fibers (CF) and polyaniline (PANI) were prepared through in situ oxidative polymerization of aniline (ANI) in the presence of CF using iron (III) chloride hexahydrate (FeCl_3.6H₂O) or ammonium persulfate (APS) as an oxidant. The PANI-coated coconut fibers (CF-PANI) displayed various morphologies, electrical conductivities and percentages of PANI on the CF surface. For both systems, a PANI conductive layer was present on the CF surface, which was responsible for an electrical conductivity of around 1.5 × 10⁻¹ and 1.9 × 10⁻² S cm⁻¹ for composites prepared with FeCl₃.6H₂O and APS, respectively; values that are similar to that of pure PANI. In order to modify the structure and properties of polyurethane derived from castor oil (PU) both CF-PANI and pure PANI were used as conductive additives. The PU/CF-PANI composites exhibited higher electrical conductivity than pure PU and PU/PANI blends. Additionally, the PU/CF-PANI composites showed a variation in electrical resistivity according to the compressive stress applied, indicating that these materials could be applied for pressure-sensitive applications.     

Tribological behavior of polyurethane-based composite coating reinforced with TiO2 nanotubes

The unmodified and hexamethylene diisocyanate (HDI) modified TiO₂ nanotubes, were used for fabricating TiO₂ nanotubes (TiNTs)/polyurethane (PU) composite coating. The effects of applied load and sliding speed on the tribological behavior of the composite coating were investigated using a block-on-ring wear tester. Compared to the TiO₂ nanotubes filled PU composite coating, the HDI modified TiO₂ nanotubes (TiNTs-HDI) filled one had the lower friction coefficient and higher wear life under various applied loads and sliding speed. Scanning electron microscope (SEM) investigation showed that the TiNTs-HDI filled PU coating had smooth worn surface under given applied load and sliding speed, and a continuous and uniform transfer film formed on the surface of the counterpart ring, which helped to reduce the wear of the coating. The improvement in the tribological properties of TiNTs-HDI/PU composite coating might due to an improvement in interfacial adhesion between TiNTs and PU after HDI treatment. The strong interfacial coupling of the composite coating made TiNTs-HDI not easy to detach from the PU matrix, and prevented the rubbing-off of PU composite coating, accordingly improved the friction and wear properties of the composite coating.