Mechanical and Water Absorption Properties of Waterborne Polyurethane/Graphene Oxide Composites

Nanocomposites based on waterborne polyurethane (WPU) and graphene oxide (GO) have been synthesized and characterized. It was found that after the incorporation of GO, WPU films became mechanically more rigid, and the Young's modulus increased by almost six times. It is shown that the lateral size of GO sheets influences the mechanical properties of WPU/GO composites. In particular, composites with larger lateral size of GO sheets have higher values of Young's modulus. Additionally, if the mechanical properties are improved with the addition of GO additive, then water absorption decreases for WPU modified with small GO sheets whereas it increases for WPU modified with large GO sheets. Possible reasons for this behavior are discussed.

Property Modulation of Graphene Oxide Incorporated with TiO2 for Dye-Sensitized Solar Cells

Graphene oxide (GO) nano-powder is synthesized by the modified Hummer's method, and further thin films are deposited by using the water solution of GO through spin-coating. These films are thermally reduced along with the synthesized GO nano-powder at 50 to 200 °C in a high vacuum. Microstructural, electrical, and optical properties are expectedly controlled by thermal reduction. The electronic properties of GO are investigated by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. The reduction is confirmed by Raman spectroscopy. The work function and band gap of GO are tuned with the thermal reduction. The changes in properties of GO are not linear, and anomalous changes are observed for the reduction around 150 °C. Pristine and reduced GO nano-powder is incorporated into TiO₂ paste to be the photoanode for dye-sensitized solar cells (DSSCs). It is observed that the performance of the fabricated cells is significantly enhanced for the GO reduced at 150 °C, and the cell exhibited a significant increment of ∼23% for the power conversion efficiency in comparison to DSSC based on an unmodified TiO₂ photoanode.

Influence of Characteristics of Thermoplastic Polyurethane on Graphene-Thermoplastic Polyurethane Composite Film

Graphene-thermoplastic polyurethane (G-TPU) composite films were fabricated by traditional blending method and tape casting process with commercial graphene sheets as functional fillers and TPU masterbatches of four different melting points as matrix, respectively. The effects of matrix on the distribution of graphene, the electrical conductivity, and infrared (IR) light thermal properties of the G-TPU composite films were investigated. The experimental results reveal that the characteristics of TPU has little influence on the electrical conductivity of the G-TPU composite films, although the four TPU solutions have different viscosities. However, under the same graphene mass content, the thermal conductivity of four G-TPU composite films with different melting points is significantly different. The four kinds of G-TPU composite films have obvious infrared (IR) thermal effect. There is little difference in the temperatures between the composite films prepared by TPU with melting a point of 100 °C, 120 °C, and 140 °C, respectively; however, when the content of graphene is less than 5 wt%, the temperature of the composite film prepared by TPU with a melting point of 163 °C is obviously lower than that of the other three composite films. The possible reason for this phenomenon is related to the structure of TPU.

Using an Ionic Liquid to Reduce the Electrical Percolation Threshold in Biobased Thermoplastic Polyurethane/Graphene Nanocomposites

Biobased thermoplastic polyurethane (bTPU)/unmodified graphene (GR) nanocomposites (NCs) were obtained by melt-mixing in a lab-scaled conventional twin-screw extruder. Alternatively, GR was also modified with an ionic liquid (GR-IL) using a simple preparation method with the aim of improving the dispersion level. XRD diffractograms indicated a minor presence of well-ordered structures in both bTPU/GR and bTPU/GR-IL NCs, which also showed, as observed by TEM, nonuniform dispersion. Electrical conductivity measurements pointed to an improved dispersion level when GR was modified with the IL, because the bTPU/GR-IL NCs showed a significantly lower electrical percolation threshold (1.99 wt%) than the bTPU/GR NCs (3.21 wt%), as well as higher conductivity values. Young’s modulus increased upon the addition of the GR (by 65% with 4 wt%), as did the yield strength, while the ductile nature of the bTPU matrix maintained in all the compositions, with elongation at break values above 200%. This positive effect on the mechanical properties caused by the addition of GR maintained or slightly increased when GR-IL was used, pointing to the success of this method of modifying the nanofiller to obtain bTPU/GR NCs.

Morphology, Mechanical and Thermal Properties of Thermoplastic Polyurethane Containing Reduced Graphene Oxide and Graphene Nanoplatelets

Polyurethane/graphene nanocomposites were synthesized using commercial thermoplastic polyurethane (TPU, Apilon 52DE55), and two types of graphene derivatives: graphene nanoplatelets (GNP) and reduced graphene oxide (RGO). Fourier Transformation Infrared Spectroscopy Fourier Transformation Infrared Spectroscopy (FTIR) spectroscopy, TEM, and SEM microscopy and XRD techniques were used to chemically and structurally characterize GNP and RGO nanofillers. The properties of the new TPU nanocomposite materials were studied using thermal analysis techniques (Dynamical Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG)) to describe the influence of graphene nanofillers on polyurethane matrix. Our investigation describes the comparison of two types of graphene derivatives, commercial one (GNP) and synthesized (RGO) on thermoplastic polyurethanes. These nanofillers provides opportunities to achieve compatibility with the TPU matrix. The property enhancements are attributed commonly to high aspect ratio of graphene nanoplatelets and filler-polymer interactions at the interface. The obtained nanocomposites exhibit higher thermal and mechanical properties due to the good dispersion of both nanofillers into TPU matrix. It was found that the addition of 2 wt % of the nanofiller could lead to a significant reinforcement effect on the TPU matrix. Also, with high content of nanofiller (GNP and RGO), the Payne effect was observed.

FT-IR spectroscopic and thermal study of waterborne polyurethane-acrylate leather coatings using tartaric acid as an ionomer

Waterborne polyurethane (WDPU) comprising polycaprolactone diol and hexamethylene diisocyanate was prepared by using tartaric acid (TA) as an ionomer. WDPU was further modified with polymethyl methacrylate (PMMA). Hybrid WDPU-PMMA coatings were formed by using unsaturate end capping agents such as 2-hydroxyethylmethacrylate. WDPU-PMMA blend coatings were formed by using chain extenders such as ethylene glycol, ethylene diamine and mixed with PMMA. Thermal behavior and structural characterizations were investigated by means of thermogravimetric analysis and Fourier transformm infrared (FT-IR) spectroscopy, respectively. Chemical and solvent resistance was checked against various chemicals and solvents. Bio-stability was evaluated in CoCl2/H2O2 solution. Gloss, film flexibility, tackiness, abrasion resistance and adhesive prosperities of WDPU-PMMA coatings were also checked by applying these coatings on a leather sheet.