Polyurethane-silica Hybrid Research Articles

Polycaprolactone-based biodegradable acrylated polyurethanes: Influence of nanosilica amount on functional properties

A series of nontoxic acrylated waterborne polyurethane/silica hybrid composites were synthesized from 1,6-hexamethylene diisocyanate (HDI), polycaprolactone diol (PCL), dimethylolpropionic acid (DMPA), a mixture of 3-aminopropyltriethoxysilane (APTES) and 2-hydroxyethyl methacrylate (HEMA) as chain extender. To control crosslink density the mono-functional HEMA was incorporated into the biodegradable polyurethanes. Different amounts of nanosilica were incorporated into acrylic-based polyurethanes to prepare polyurethane/silica hybrid composites. The structures of the acrylated waterborne polyurethane/silica hybrid composites were characterized by Fourier-transform infrared spectroscopy (FTIR), 1H NMR,13C NMR analysis and scanning electron microscopy (SEM). The effect of the amount of nanosilica on the thermal properties of polyurethane nanocomposite films was investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Wide-angle X-ray scattering (WAXS) was used to investigate the degree of crystallinity of PCL as a soft segment into polyurethane hybrid composites.It is established that all samples containing PCL as a part soft segment with different silica loading are crystallisable polymers. The results from WAXS analysis have shown that the highest degree of crystallinity (37%) is reached in polyurethanes based on 1 wt% content of Aerosil OX50.The highest crystallization enthalpy (ΔHc) value for the sample with 1% nanosilica was 9.77 J/g confirmed by DSC analysis. The decrease of crystallinity of the PCL soft segment in polyurethanes indicates that the restriction of the crystallization of the PCL soft segment depends on the silica content. The incorporation of nanosilica into waterborne polyurethanes increases the thermal stability of the hybrid composite films. It was found that greater thermal and mechanical properties of waterborne polyurethane-silica hybrid composites were obtained due to a condensation process between triethoxysilane groups in the side chains of polyurethane molecules and silanols group on the surface of nanosilica.

Preparation and characterization of polyurethane–silica hybrid films

PurposeThe paper aims to provide a facile approach to the synthesis of polyurethane–silica nanocomposites by introducing self-made aqueous silica sols with different particle sizes into polyurethane materials. This paper investigates the effects of the silica nanoparticles on the polyester polyol, as well as the physical properties and transmittance of the hybrid polyurethane coatings.Design/methodology/approachColloidal silica particles of different sizes were obtained using a sol–gel process and were then embedded into polyester polyol by in-situ polymerization. These polyester polyol–silica resins were synthesized using an azeotrope process, using xylene to remove the water generated in the system and present in the dispersion medium for the colloidal silica. The polyester polyol–silica resins were further cured using isocyanate trimers to form polyurethane–silica hybrid films.FindingsThe paper observed that the viscosity of the polyester polyol–silica nanocomposite resins increased and their appearance changed from transparent to ivory white as the particle size of the added silica was increased. It was found that increasing the hydroxyl content of the silica improved the film transmittance in the visible light region. However, the transmittance decreased sharply once the diameter of the silica particles reached 100 nm.Research limitations/implicationsBecause of the limitation of experimental conditions, some performances have not been tested. Therefore, researchers are encouraged to conduct further tests.Practical implicationsThe paper provides a method of preparing hybrid polyurethane film by using silica; the results indicate that the introduction of nano-silica can improve the wear resistance and glass transition temperature of polyurethane coatings.Originality/valueThe results obtained in this study will be extremely useful to enhance the understanding of organic–inorganic hybrid materials.

Structure—Functional property relationship of aliphatic polyurethane-silica hybrid films

The novel aliphatic polyurethane-silica hybrid films were prepared using prepolymerization method in the presence of spherical, submicron amorphous SiO2 Sidistar T120 particles (0, 1, 2, 5 and 10 wt%). The study of the influence of silica distribution on the structure–functional property relationship of polyurethane (PU) composites was performed using FT-IR, SEM, AFM, TGA, DSC, DMTA, tensile testing and immersion test. It was found that the presence of low SiO2 content is acting as dispersing agent between soft- and hard-segments. Achieved uniform distribution of 1 and 2 wt% of silica caused the formation of additional hydrogen bonds between organic matrix and inorganic filler, and remarkably improved thermal stability, thermal and mechanical properties of obtained polyurethane composites. The agglomerates, formed at higher SiO2 loading (5 and 10 wt%), caused the change of thermal degradation mechanism as well as the change of physical crosslinking disruption mechanism. Despite significantly deteriorated mechanical properties of polyurethanes with heterogeneously incorporated silica particles, the onset temperature of elastomers and the starting of melting of hard domains were registered at higher temperature compared to pure PU. Optimal thermal characteristics (onset, decomposition and melting temperatures) and remarkable tensile properties (especially high elongation-at-break and tensile strength, and extraordinary energy-to-break) compared to pure polyurethane have been determined for the polycarbonate-based polyurethanes containing 1 wt% and especially 2 wt% of SiO2. It allows them to be utilized as mechanically strong and durable coatings or films in biomedical applications or as packaging materials. The solvent-resistance data are well described using novel proposed model covering two swelling and dissolution phenomena. The presence of silica decreased the rate and the amount of swelling in water, acetone, toluene and hexane. The rate and mass reduction of swollen sample in acetone, toluene and hexane also decreased by the addition of SiO2 particles.

Effect of the silica nanofiller on the properties of castor oil-based waterborne polyurethane hybrid dispersions based on recycled PET waste

The paper describes the chemical depolymerization of the polyethylene terephthalate (PET) waste from postconsumer soft drink bottles and a search for the way to use this product. The depolymerized oligoester obtained from glycolysis of PET waste using tiethylene glycol was transesterified with castor oil which resulted in the formation of hydroxyl-functional polyester polyol, with hydroxyl value of 391 mg KOH g−1. In the presented paper, series of castor oil-based waterborne polyurethane (CPU)/silica hybrid dispersions were prepared using dimethylolpropionic acid as an ionic center. The polyurethane prepolymers with pendent castor oil groups were prepared first, and then different concentrations of hydrophilic fumed silicas (0, 0.5, 0.75, 1.0 and 2.0 wt%) were added. For waterborne polyurethane dispersions of hydrophilic fumed silica with the surface area (50 ± 15 m2/g) and a primary particle size of 40 nm in the polymer matrix, ultrasound waves were used. The hybrid dispersions were prepared by adding the required amount of triethylamine and water. The molecular structures and mass of glycolyzed PET oligoesters, castor oil-based polyol and castor oil-based polyurethane–silica hybrid dispersions were estimated by FTIR method and gel permeation chromatography.The incorporation effect of SiO2 nanoparticles into the PU matrix on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis, differential scanning calorimetry (DSC), SEM microscope, and measurement of the coatings properties. The DSC data results suggest that hard segment glass temperature decreases, but mixed-phase glass transition temperature increases with increasing SiO2 content. The FTIR deconvolution result of the degree of phase separation between oxide nanoparticles and hard segment supports to the DSC analysis. The addition of silica oxide caused the increase in the thermal stability. The T10% and T50% of CPU films (the temperatures where 10 and 50% weight loss occurred) increased with increasing the SiO2 content. UV–Vis spectrophotometry showed that introduction of nanosilica particles into polyurethane enhanced the shielding property of obtained films for UV light. The hardness, adhesion, and gloss quality of the polyurethane films were also determined considering the effect of the phase separation and the SiO2 content, so this paper confirmed the suitability of using these castor oil-based waterborne polyurethane/silica hybrid dispersions as new materials with high-performance coatings materials.

Polyurethane-silica hybrid foams from a one-step foaming reaction, coupled with a sol-gel process, for enhanced wound healing

Polyurethane (PU)-based dressing foams have been widely used due to their excellent water absorption capability, optimal mechanical properties, and unequaled economic advantage. However, the low bioactivity and poor healing capability of PU limit the applications of PU dressings in complex wound healing cases. To resolve this problem, this study was carried out the hybridization of bioactive silica nanoparticles with PU through a one-step foaming reaction that is coupled with the sol-gel process. The hybridization with silica did not affect the intrinsically porous microstructure of PU foams with silica contents of up to 10wt% and where 5–60nm silica nanoparticles were well dispersed in the PU matrix, despite slight agglomerations. The incorporated silica enhanced the mechanical performance of PU by proffering better flexibility and durability as well as maintaining good water absorption capabilities and the WVTR characteristics of pure PU foam. The silica of PU-10wt% Si foams was gradually dissolved and released under physiological conditions during a 14-day immersion period. The in vitro cell attachment and proliferation tests showed significant improvements in terms of the biocompatibility of PU-Si hybrid foams and demonstrated the effects of silica on cell growth. More significantly, the superior healing capability of PU-Si as a wound dressing in comparison to PU-treated wounds was verified through in vivo animal tests. Full-thickness wounds treated with PU-Si foams exhibited faster wound closure rates as well as accelerated collagen and elastin fiber regeneration in newly formed dermis, which was ultimately completely covered by a new epithelial layer. It is clear that PU-Si hybrid foams have considerable potential as a wound dressing material geared for accelerated, superior wound healing.

Preparation and properties of waterborne bio-based polyurethane/siloxane cross-linked films by an in situ sol–gel process

Abstract Waterborne castor oil-based polyurethane-silica hybrid materials with chemically bonded polymer matrix and silica nanoparticles were designed and prepared. The formation of cross-linking structures in the waterborne polyurethane system was confirmed by Fourier transform infrared spectroscopy. Transmission electron microscopy images indicated that nano-silica was encapsulated by polyurethane and exhibited an apparent core–shell structure. The nano-silica in the polyurethane matrix was vital in improving both the hydrophobicity and thermal stability of the resulting hybrid polyurethane films. With increased silicone content, the roughness, hydrophobicity, and thermal stability of the films were enhanced, but the transparency of the films in the 300–800 nm region was decreased. These results can aid in the design of bio-based hydrophobic waterborne polyurethane films with favorable thermal stability and optical transmittance.

Polyurethane-silica hybrid foam by sol–gel approach: Chemical and functional properties

Hybrid foams based on polyurethane and polysiloxane-domains were designed in terms of chemical structure and hierarchical morphology to improve the thermal insulation capability of conventional polyurethane foams. Polysiloxane-domains by sol–gel approach reacted with polyols to produce a polysiloxane-reactive-adduct, which completed its formation into polysiloxane aerogel-like structure during the polyurethane foaming process. Hybrids with 5wt% of the polysiloxane-domains exhibited a 22% reduction in thermal conductivity in comparison with pristine PUR. The chemical structure and the hierarchical morphology were studied by means of SAXS/WAXS and 29Si and 13C NMR. In particular the hybrid structure consisted of coarse polysiloxane-fractal-aggregates composed of silica nanoparticles embedded in the polyurethane matrix. Morphological analysis revealed a decrease of the cell size with the increase of the siloxane content ascribed to the nucleation effect of polysiloxane-domains during the foaming. The cell size reduction and the formation of hybrid-aerogel-like structures within the cell-walls are considered the key factors to reduce the thermal conductivity of hybrid foams.

New high performance waterborne organic–inorganic hybrid materials from UV curing

The third generation glycerol based hyperbranched polyester (HBPE-3G) was synthesized by reacting glycerol and 2,2-bis(hydroxymethyl)propionic acid in a stoichiometric molar ratio. This polyester was used as preparation for waterborne hyperbranched UV cured polyurethane–silica hybrid coatings. The acrylic terminated waterborne coatings were prepared by modifying some of the hydroxyl groups HBPE-3G to acidic groups by reacting with maleic anhydride. The remaining hydroxyl groups were reacted with NCO terminated acrylate. Then the prepolymer was neutralized with triethyl amine and dispersed in water. The waterborne hybrid formulations were prepared by mixing 3, 5 and 10% of trimethoxysilylpropyl methacrylate (TMSPM) into the acrylic terminated waterborne coatings. The films were casted and cured under UV light. The various film properties were studied by XRD, AFM, TGA and DMTA instruments. TGA result suggests that the onset degradation temperature and final mass residue increase with increasing TMSPM concentration. DMTA results show that the storage modulus and glass transition temperature increase for the hybrid formulations with increasing TMSPM concentration. The structural characterization of the hybrid coatings was performed using FTIR spectroscopy. The tensile test demonstrated that the mechanical properties improve with the increasing TMSPM content. Surface morphology was studied by atomic force microscopy (AFM). AFM study revealed that TMSPM was crosslinked homogenously through the polymer matrix. The TGA and DMTA data suggest that higher thermal stability and glass transition temperature (Tg) for the TMSPM hybrid films compared to their pure counterparts were obtained with increasing the TMSPM content.

Sensing water in organic solvent using a polyurethane-silica hybrid membrane doped with a luminescent ruthenium complex

We have prepared an ~1.4 μm thin hybrid film from polyurethane (PU) hydrogel and tetraethylorthosilicate (TEOS) by a sol–gel method, and have incorporated the red-luminescent ruthenium-tris-bipyridyl complex. At an optimized ratio of PU/TEOS (1.5:1; w/w) and annealing temperature (60 °C), the membrane sensor exhibits good capability to extract water from organic solvents but also can well retain the ruthenium dye. If contacted with water-containing organic solvents such as acetone or THF, both the luminescence intensity and wavelength change significantly. The response of luminescence intensity to the water fraction in organics is sigmoidal, which can be well fitted with a modified Stern-Volmer equation. The sensor works in the ranges of 0–6 % and 0–12 % (v/v) of water in acetone and THF, respectively, with detection limits of 0.13 % and 0.486 % (v/v).