Xinghai Liu

Waterborne UV-curable polyurethane acrylate/silica nanocomposites for thermochromic coatings

Waterborne UV-curable polyurethane acrylate/silica (PUA/SiO2) nanocomposites were prepared by a sol–gel method. SiO2 nanoparticles were modified by γ-methacryloxypropyltrimethoxysilane (KH-570) and then introduced to the ends of the PUA main chains through radical polymerization. According to the transmission electron microscopy (TEM) results, the size of the PUA/SiO2 nanocomposite particles was approximately 70–100 nm. It was easier to get a uniform emulsion by the sol–gel method than by the physical blending method. Surface tension and contact angle tests both demonstrated the good wettability of the nanocomposites. Besides, the kinetics of the curing process of the PUA/SiO2 films were analyzed by ATR-FTIR and gel content. This revealed that the modified SiO2 could accelerate the curing speed of PUA coatings. Scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) indicated that the nanosilica were well dispersed in the PUA matrix and the soft and hard segments of PUA/SiO2 were well phase mixed. Furthermore, the nanocomposite films displayed enhanced rigidity, hardness, abrasion resistance and good weather resistance. Finally, waterborne UV-curable PUA/SiO2 nanocomposites were applied to thermochromic coatings, showing excellent temperature sensitivity and reversibility.

UV-curable coating crosslinked by a novel hyperbranched polyurethane acrylate with excellent mechanical properties and hardness

A novel hyperbranched polyurethane acrylate (HBPUA), successfully synthesized based on a reaction of hyperbranched polyether (HBP-OH) with toluene diisocyanate (TDI) and hydroxy-ethyl acrylate (HEA), was incorporated into photosensitive polyurethane acrylate (PUA) as crosslinker to prepare a series of high-performance UV-curable coatings. The structure of HBPUA was characterized by Fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (1H NMR). The kinetics of the curing process was monitored using real-time IR. The results indicated that the final double bond conversion was associated with acrylate double bond concentration and the initial viscosity of the curing system. The properties of cured films were investigated by tensile tests, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The hardness, abrasion resistance, adhesion on plastics and transparency of the cured coatings were also tested. The results revealed that tensile strength and storage modulus of the cured film could be improved by 148% and 74%, respectively, by adding HBPUA, and that the hardness of the cured coating could reach 9H. Furthermore, the cured coatings also showed excellent adhesion on PC and PVC sheets, enhanced abrasion resistance and thermal properties as well as outstanding transparency.

Novel Waterborne UV-Curable Hyperbranched Polyurethane Acrylate/Silica with Good Printability and Rheological Properties Applicable to Flexographic Ink

Novel waterborne UV-curable hyperbranched polyurethane acrylate/silica (HBWPUA/SiO2) nanocomposites were prepared by a three-step procedure and sol–gel method. 1H NMR and 13C NMR results indicate that HBWPU is successfully synthesized. Surface tension and contact angle tests both demonstrate the good wettability of the nanocomposites. Besides, the kinetics of photopolymerization of HBWPUA/SiO2 films were analyzed by attenuated total reflection-Fourier transform infrared spectroscopy, which reveals that the modified SiO2 could accelerate the curing speed of HBWPUA coatings. Thermal gravity analysis indicates that the HBWPUA/SiO2 hybrid films have a better thermal stability than the pure HBWPUA cured films. Furthermore, the hybrid films show enhanced pencil hardness, abrasion resistance, and adhesion. On the basis of the above, HBWPUA/SiO2 nanocomposites were finally applied to waterborne UV-curing flexographic printing ink, which is printed on poly(ethylene terephthalate) and glass. The nanocomposite presents good rheological behavior because the ink has a lower Z0, a higher Z∞, and the viscosity rebuild time is 375 s. Three colors (red, yellow, and blue) of ink were used to test its printing quality, the curing time was below 30 s, and the adhesion was excellent without being stripped. All of the inks show good water resistance and abrasion resistance. Moreover, the red and blue inks possess better solid densities than the value of 1.07 of yellow ink, and are 1.83 and 1.84, respectively. The current study suggests that the process has promise in applications of food packages.

Monitoring of oxygen using colorimetric indicator based on graphene/TiO2 composite with first-order kinetics of methylene blue for modified atmosphere packaging

Oxygen is crucial in food preservation and food spoilage. For the purpose of monitoring intact of modified atmosphere packaging (MAP) by nondestructive testing and controlling the reaction rate during recovery stage, we report a convenient and visual colorimetric oxygen indicator based on a graphene /titanium oxide composite, incorporating glycerol, methylene blue (MB), hydroxyethyl cellulose (HEC) and poly (vinyl alcohol) (PVA). The graphene/titanium oxide (GNT) composite was synthesized through a modified Hummers synthesis of graphene oxide, followed by the hydro-thermal treatment with butyl titanate without using any reducing agent, then the morphology and structure characteristics were analyzed by XRD, FT-IR, Raman spectra, UV-vis, SEM and TEM. According to the performance tests using UV-vis and CIElab, the indicator demonstrated the pseudo first-order kinetics of MB for modified atmosphere packaging in detecting stage. It is confirmed with the results that the prepared colorimetric indicator can actually detect the intact of MAP without destruction. Additionally, the reaction time of indicator in recovery stage can be controlled by changing the concentration of MB, because of pseudo first-order kinetics.