Effect of hemicellulose content on the solution properties of cellulose carbamates in NaOH/ZnO aqueous system.

Hemicellulose removal from bleached bamboo pulp is key to produce qualified dissolving pulps. In this work, alkali/urea aqueous solution was firstly applied to remove hemicellulose in bleached bamboo pulp (BP). The effect of urea usage, time and temperature on the hemicellulose content of BP was studied. The reduction of hemicellulose content from 15.9 to 5.7 % was achieved in 6 wt% NaOH/1 wt% urea aqueous solution at 40 °C for 30 min. Cellulose carbamates (CCs) were obtained from the esterification of BP with urea. The dissolution behavior of CCs in NaOH/ZnO aqueous solutions with different degree of polymerization (DP), hemicellulose and nitrogen contents were studied by using optical microscope and rheology. The highest solubility was up to 97.7 % when the hemicellulose was 5.7 % and Mη was 6.5 × 104 (g/mol). With the decrease of hemicellulose content from 15.9 % to 8.60 % and 5.70 %, the gel temperature increased from 59.0, 69.0 to 73.4 °C. The apparent gelation time increased from 5640 to 12,120 s with the hemicellulose content increased from 8.60 % to 15.9 %. CC solution with 5.70 % hemicellulose always keeps a liquid-state (G" > G') until the test time reached 17,000 s. The results showed that the removal of hemicellulose, the decrease of DP and the increase of esterification endowed CC with higher solubility and solution stability.

One-Step Treatment for Upgrading Bleached Bamboo Pulp to Dissolving Pulp High Solvency in Green Alkali/Urea Aqueous Solution.

Bleached bamboo pulp, as a kind of natural cellulose, has received significant attention in the field of biomass materials due to its advantages of environmental protection and the abundance of raw materials. Low-temperature alkali/urea aqueous system is a green dissolution technology for cellulose, which has promising application prospects in the field of regenerated cellulose materials. However, bleached bamboo pulp, with high viscosity average molecular weight (Mη) and high crystallinity, is difficult to dissolve in an alkaline urea solvent system, restraining its practical application in the textile field. Herein, based on commercial bleached bamboo pulp with high Mη, a series of dissolvable bamboo pulps with suitable Mη was prepared using a method of adjusting the ratio of sodium hydroxide and hydrogen peroxide in the pulping process. Due to the hydroxyl radicals being able to react with hydroxyls of cellulose, molecular chains are cut down. Moreover, several regenerated cellulose hydrogels and films were fabricated in an ethanol coagulation bath or a citric acid coagulation bath, and the relationship between the properties of the regenerated materials and the Mη of the bamboo cellulose was systematically studied. The results showed that hydrogel/film had good mechanical properties, as the Mη is 8.3 × 104 and the tensile strength of a regenerated film and the film have values up to 101 MPa and 3.19 MPa, respectively. In this contribution, a simple method of a one-step oxidation of hydroxyl radicals to prepare bamboo cellulose with diversified Mη is presented, providing an avenue for a preparation of dissolving pulp with different Mη in an alkali/urea dissolution system and expanding the practical applications of bamboo pulp in biomass-based materials, textiles, and biomedical materials.

Bioinspired Superhydrophobic/Superhydrophilic Janus Copper Foam for On-Demand Oil/Water Separation.

Superwettable Janus membranes with unique interfacial characteristics have versatile applications in oil/water separation, microfluid transportation, and membrane distillation. However, it remains a significant challenge to simply fabricate three-dimensional (3D) metallic foams with Janus superwettability using a facile and environment-friendly method. In this study, a novel method is present to construct a Janus copper foam (CF) by combining superhydrophobicity and superhydrophilicity into CF. Based on gravity, the water in the light oil (LO)/water mixture can be transported from the superhydrophilic (SHL) side to the superhydrophobic (SHB) side, while the heavy oil (HO) in the HO/water/mixture can be transported from the SHB side to the SHL side. Therefore, cylindrical Janus oil/water separation devices with superior separation efficiency and excellent repeatability can achieve on-demand oil/water separation effortlessly. This design and fabrication method offers a novel avenue for the preparation of Janus interface materials for practical applications in liquid transportation, sensor devices, energy materials, and oil spills.

Fabrication of Superhydrophobic/Superoleophilic Bamboo Cellulose Foam for Oil/Water Separation.

Water is an indispensable strategic resource for biological and social development. The problem of oily wastewater pollution originating from oil spillages, industrial discharge and domestic oil pollution has become an extremely serious international challenge. At present, numerous superwetting materials have been applied to effectively separate oil and water. However, most of these materials are difficult to scale and their large-scale application is limited by cost and environmental protection. Herein, a simple, environmentally friendly strategy including sol-gel, freeze-drying and surface hydrophobic modification is presented to fabricate a bamboo cellulose foam with special wetting characteristics. The bamboo cellulose foam is superhydrophobic, with a water contact angle of 160°, and it has the superoleophilic property of instantaneous oil absorption. Owing to the synergistic effect of the three-dimensional network structure of the superhydrophobic bamboo cellulose foam and its hydrophobic composition, it has an excellent oil-absorption performance of 11.5 g/g~37.5 g/g for various types of oil, as well as good recyclability, with an oil (1,2-dichloroethane) absorption capacity of up to 31.5 g/g after 10 cycles. In addition, the prepared cellulose-based foam exhibits an outstanding performance in terms of acid and alkali corrosion resistance. Importantly, owing to bamboo cellulose being a biodegradable, low-cost, natural polymer material that can be easily modified, superhydrophobic/superoleophilic bamboo cellulose foam has great application potential in the field of oily wastewater treatment.

Zn/Al/Pb Mixed Oxides as Efficient Heterogeneous Catalysts for the Synthesis of Methyl N-Phenyl Carbamate.

Dimethyl carbonate aminolysis is an effective and green pathway for the synthesis of methyl N-phenyl carbamate (MPC), which is an important intermediate for the synthesis of polyurethanes and many other chemicals. In this work, we demonstrate the fabrication of Zn/Al/Pb mixed oxides as efficient and stable heterogeneous catalysts for MPC synthesis. The catalysts are prepared via facile coprecipitation and subsequent thermal annealing. Their micromorphology and physical-chemical properties are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM (STEM), X-ray photoelectron spectroscopy (XPS), and NH3-TPD. The results show that rather than being doped into ZnO and/or Al2O3, PbO is highly dispersed in the ZnO/Al2O3 base forming ultrafine nanoparticles. Despite the weak interactions within the mixed oxides, the high density of active sites generates outstanding catalytic activity and cycling stability for MPC synthesis, with an aniline conversion of almost 100% and MPC yield of up to 90% during six repeated tests, providing great potential for their further application.