Exploiting Urazole’s Acidity for Fabrication of Hydrogels and Ion-Exchange Materials

In this study, the acidity of urazole (pKa 5–6) was exploited to fabricate a hydrogel in two simple and scalable steps. Commercially available poly(hexamethylene)diisocyanate was used as a precursor to synthesize an urazole containing gel. The formation of urazole was confirmed by FT-IR and 1H-NMR spectroscopy. The hydrogel was characterized by microscopy imaging as well as spectroscopic and thermo-gravimetric analyses. Mechanical analysis and cell viability tests were performed for its initial biocompatibility evaluation. The prepared hydrogel is a highly porous hydrogel with a Young’s modulus of 0.91 MPa, has a swelling ratio of 87%, and is capable of exchanging ions in a medium. Finally, a general strategy was demonstrated to embed urazole groups directly into a crosslinked material.

Synthesis of Biobased and Hybrid Polyurethane Xerogels from Bacterial Polyester for Potential Biomedical Applications

Organic–inorganic xerogel networks were synthesized from bacterial poly (3-hydroxybutyrate) (PHB) for potential biomedical applications. Since silane-based networks usually demonstrate increased biocompatibility and mechanical properties, siloxane groups have been added onto polyurethane (PU) architectures. In this work, a diol oligomer (oligoPHB-diol) was first prepared from bacterial poly(3-hydroxybutyrate) (PHB) with an environmentally friendly method. Then, hexamethylene diisocyanate or biobased dimeryl diisocyanate was used as diisocyanate to react with the short oligoPHB-diol for the synthesis of different NCO-terminated PU systems in a bulk process and without catalyst. Various PU systems containing increasing NCO/OH molar ratios were prepared. Siloxane precursors were then obtained after reaction of the NCO-terminated PUs with (3-aminopropyl)triethoxysilane, resulting in silane-terminated polymers. These structures were confirmed by different analytical techniques. Finally, four series of xerogels were prepared via a sol–gel process from the siloxane precursors, and their properties were evaluated depending on varying parameters such as the inorganic network crosslinking density. The final xerogels exhibited adequate properties in connection with biomedical applications such as a high in vitro degradation up to 15 wt% after 12 weeks.

PREPARATION, CHARACTERIZATION AND UTILIZATION OF A NOVEL TRIFLUOROACETIC ACID SUPPORTED STARCH/GRAPHENE OXIDE GREEN NANOCOMPOSITE FOR EFFICIENT SYNTHESIS OF 2,4,5-TRISUBSTITUTED IMIDAZOLES

This study reports on the production, characterization, and application of a novel starch/graphene oxide nanocomposite for rapid synthesis of 2,4,5-trisubstituted imidazoles. To this end, graphene oxide was first functionalized by 1,8-diamino-3,5-dioxaoctane under appropriate conditions. Starch, functionalized graphene oxide, and 3-aminopyridine nanocomposite were then prepared from the reaction of starch with graphene oxide functionalized with 1,8-diamino-3,5-dioxaoctane in the presence of hexamethylene diisocyanate (HDMI) as a binding agent and 3-aminopyridine. Then, trifluoroacetic acid was added, giving rise to an acid-supported starch and graphene oxide nanocomposite. To examine the efficiency of the nanocomposite, 2,4,5-trisubstituted imidazoles were efficiently synthesized in the presence of the nanocomposite using benzil, aryl aldehyde, and ammonium acetate under solvent-free condition within a short reaction time. The moderate conditions, fast reaction rates, ease of purification, solvent-free condition, use of a green catalyst (nanocomposite), and environmental friendliness are among the advantages of the proposed synthesis method. The recoverability and durability of the catalyst were confirmed after five runs with no significant loss of activity. Thus, this research presents a novel nanocomposite based on starch and graphene oxide with superior properties.

Viability of cultured human skin cells treated with 1,6-hexamethylene diisocyanate monomer and its oligomer isocyanurate in different culture media

The isocyanate monomer 1,6-hexamethylene diisocyanate (HDI) and one of its trimers, HDI isocyanurate, are airway and skin sensitizers contained in polyurethane paint. The toxic response of cultured skin cells to these compounds was measured by evaluating the isocyanate concentrations at which 50% of the cells die (i.e., lethal concentration 50%, LC50) because the relative toxicity of each form of HDI should be considered when exposure limits of HDI-based paints are set. By using a luminescent ATP-viability assay, we compared the cytotoxic effects of HDI monomer and HDI isocyanurate on cultured human skin cells (keratinocytes, fibroblasts, and melanocytes) after 4-h isocyanate exposures using culture media with varying levels of nutrients in order to also determine the effects of media composition on isocyanate toxicity. Before analysis, experimental wells were normalized to controls containing cells that were cultured with the same vehicle and media. The measured mean LC50 values ranged from 5 to 200 µM across the experimental conditions, in which HDI isocyanurate in protein-devoid media was the most toxic to cells, producing the lowest LC50 values. For HDI monomer, keratinocytes were the most resistant to its toxicity and melanocytes were the most susceptible. However, when exposed to HDI isocyanurate, the opposite was observed, with melanocytes being the most resilient and the keratinocytes and fibroblasts were more susceptible. Depending on the type of skin cells, dose–response data indicated that HDI isocyanurate was 2–6 times more toxic than HDI monomer when using protein-devoid media whereas HDI isocyanurate was 4–13 times more toxic than HDI monomer when protein-rich media was used. Therefore, if the protein-devoid saline medium alone were used for these experiments, then a significant under-estimation of their relative toxicities in protein-rich environments would have resulted. This difference is because HDI monomer toxicity was more attenuated by the presence of protein in the culture media than HDI isocyanurate toxicity. Thus, conclusions based on comparative toxicity studies and consequent inference applied to potential human toxicity can be affected by in vitro culture media conditions. The physiochemical difference in reactivity of the two forms of HDI to biological molecules most likely explains the observed toxicity differences and may have implications for skin penetration, adverse effects like skin sensitization, and systemic responses like asthma. Future studies are warranted to investigate differences in the biological availability, cellular toxicity, and immunologic sensitization mechanisms for HDI monomer and HDI isocyanurate.

Rearranged Copolyurea Networks for Selective Carbon Dioxide Adsorption at Room Temperature

Copolyurea networks (co-UNs) were synthesized via crosslinking polymerization of a mixture of tetrakis(4-aminophenyl)methane (TAPM) and melamine with hexamethylene diisocyanate (HDI) using the organic sol-gel polymerization method. The subsequent thermal treatment of between 200 and 400 °C induced the sintering of the powdery polyurea networks to form porous frameworks via urea bond rearrangement and the removal of volatile hexamethylene moieties. Incorporating melamine into the networks resulted in a higher nitrogen content and micropore ratio, whereas the overall porosity decreased with the melamine composition. The rearranged network composed of the tetraamine/melamine units in an 80:20 ratio showed the highest carbon dioxide adsorption quantity at room temperature. The results show that optimizing the chemical structure and porosity of polyurea-based networks can lead to carbon dioxide adsorbents working at elevated temperatures.

Syntheses and Characteristics of Urushiol-Based Waterborne UV-Cured Wood Coatings

The manufacture and properties of waterborne UV-cured coatings (WUV coatings) by acetone process based on urushiol for wood finishing were investigated. Firstly, epoxide urushiol (EU) was prepared by reacting urushiol with epichlorohydrin. Secondly, the EU was reacted with acrylic acid to obtain acrylic epoxide urushiol (AEU). Next, the prepolymers were synthesized by the reaction of AEU, 2,2-Bis(hydroxymethyl)propionic acid (DMPA), and isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), respectively, using acetone as a solvent. The prepolymers were further neutralized by triethylamine (TEA) to obtain ionomers and dispersed in the water. After removing the acetone by vacuum distillation, the polyurethane dispersions (PUDs) were obtained. Finally, the WUV coatings were performed by adding a photoinitiator (Irgacure 2959). The products in the synthesized processes and the properties of the WUV coatings were examined. The results showed that the EU, AEU, prepolymers, and ionomers could be synthesized stably. The PUDs synthesized by the IPDI and HDI had a similar solid content of 25.2% and 26.2%, and similar pH values of 7.8 and 7.6. However, the IPDI-containing PUD displayed lower viscosity, smaller particle size, and a more even polydispersity index. The IPDI-containing WUV film displayed a higher hardness, gloss, and lightfastness. The HDI-containing WUV film possessed superior impact resistance. Both IPDI-containing and HDI-containing WUV films showed excellent adhesion, bending resistance, and mass retention, and demonstrated a potential for wood finishing.

Segmented bio-based polyurethane composites containing powdered cellulose obtained from novel bio-based diisocyanate mixtures

A considerable number of research works focus on the positive influence of cellulose on the properties of polymer-based composites and their wide range of application possibilities. The present work is focused on the synthesis of novel bio-based polyurethane (bio-PU) composites filled with powdered cellulose (microcellulose, MC) in an amount of 5 wt.%. Bio-PU composites were synthesized via a non-solvent prepolymer method. First, the prepolymer was synthesized from diisocyanate mixture based on hexamethylene diisocyanate and bio-based polyisocyanate Tolonate™ X Flo 100 and α,ω-oligo(ethylene-butylene adipate)diol which contained cellulose. Then, resulted prepolymer was extended by bio-based 1,4 butanediol (bio-BDO). Bio-PU composites were obtained with the different [NCO]/[OH] molar ratios: 0.95, 1.0, 105 and 1.1. Special attention was paid to the influence of MC on the phase separation between soft and hard segments of bio-PU by studying the chemical structure, morphology and thermal and mechanical properties of the prepared cellulose-based composites.

Urazole as an unorthodox functional group for fabrication of anionic hydrogels and ion-exchange materials

In this study, highly ionazable protons (pKa 5-6) of urazole were exploited to obtain an anionic hydrogel in two simple and scalable steps. Commercially available multiisocyanate, poly(hexamethylene)diisocyanate, was used to prepare urazole containing gel. Urazole formation was confirmed by FT-IR and 1H-NMR spectroscopy. The hydrogel were characterized by microscopy imaging, spectroscopic and gravimetric analysis. Mechanical analysis and cell viability test were performed for its initial biocompatibility evaluation. The prepared hydrogel is a highly porous hydrogel with a Young’s modulus of 0.91MPa, has swelling ratio of 87% and capable of exchanging ions in a medium. In this report, we demonstrated a strategy to overcome synthetic challenge of incorporating urazole into a material via precursor path rather than attempting to embeding urazole groups directly.

Preparation and Application of Polyurethane Coating Material Based on Epoxycyclohexane-Tetrahydrofuran in Paper Conservation

Paper cultural heritages are valuable historical records and also abound in cultural resources. Due to its organic property, paper is susceptible to aging, destruction by environmental pollution and human factors. At present, many countries in the world are facing the problem of paper conservation. Coating reinforcement is one of the methods for paper conservation, in which the choice of reinforcing resin is key. A transparent polyurethane, based on epoxycyclohexane (CHO)-tetrahydrofuran (THF) copolyether, was adopted in this study. The ring-opening polymerization for generating the CHO-THF copolyether took place by the reactants CHO and THF, in the catalysis of boron trifluoride diethyl etherate, initiation of glycerol. Characterizations of the synthetic copolyether were conducted by infrared (IR) spectroscopy and proton nuclear magnetic resonance (1HNMR) spectroscopy. The transparent polyurethane was then produced by the CHO-THF copolyether and hexamethylene diisocyanate (HDI) trimer. The influences of different concentrations of polyurethane solution upon the paper tensile strength, elongation, folding endurance, tearing strength, gloss, and brightness were studied. These findings suggest that 10% polyurethane solution is optimal, not only for greatly improving the paper performance, but also for keeping with the principle of “repair as old”. The applied results demonstrate that the polyurethane based on the CHO-THF copolyether has the characteristics of copolyether along with polyurethane, displaying good mechanical properties in paper reinforcement.