Using, urea, one of the cheapest chemicals and convenient deamination polycondensation (solvent-free, catalyst-free, one-pot, one-step) provides an industrially relevant and environmentally benign synthesis of branched polyurea. Inspired by the structural analysis of traditional resin adhesives, we hypothesized that the higher the cross-linking degree of the adhesive after curing, the better the bonding performance. Improving the branching cross-linking degree of resin adhesives is the key to improve their bonding performance. In this work, in order to verify the relationship between the branching degree of the polymer adhesives and their bonding properties, branched polyureas with different branching degrees were designed and synthesized. Five polyamines of PA4N, PA5N, PA6N‑1, PA6N‑2, and PA7N were synthesized from ethylenediamine, diethylenetriamine, tris(2-aminoethyl)amine, triethylenetetramine, and tetraethylenepentamine, respectively. Polycondensation of urea with polyamine (PA4N, PA5N, PA6N‑1, PA6N‑2, and PA7N) by deamination achieved branched polyureas including PA4N–urea, PA5N–urea, PA6N‑1–urea, PA6N‑2–urea, and PA7N–urea via a solvent-free, catalyst-free, one-pot, and one-step approach. The polyureas were detailedly investigated as robust adhesives for wood bonding. The bonding performance of the branched polyureas, including PA4N–urea, PA5N–urea, PA6N‑1–urea, PA6N‑2–urea, and PA7N–urea, was represented by lap shear strengths of 1.52, 2.08, 2.23, 2.36, and 2.64 MPa for poplar wood after soaking the specimens in boiling water for 3.0 h, respectively, which indicated the superior lap shear strength and enhanced water resistance for use as a wood adhesive. As we expected, the results showed that the bonding strength of branched polyurea increased with an increase of the number of terminal functional groups. Besides, the adhesive performance on other substrates, including glass, aluminum, stainless steel, and polyvinyl chloride, was also studied, and the adhesion strengths to glass, aluminum, stainless steel, and polyvinyl chloride are 3.52, 3.29, 1.45, and 1.25 MPa, respectively.
The increasingly serious environmental problems make it urgent to develop a new type of sustainable green material which can degrade pollutants and monitor human health. However, the traditional preparation methods are frequently limited by tedious operations, high-energy consumption, and massive pollution. Herein, we present a facile and green method for preparation of MnO2 nanoflakes mediated by macrocyclic molecule calix[8]arene. The MnO2 nanoflakes in situ grew on the preformed gold nanoparticles, forming an impressive core–shell Au@MnO2 flake-like nanocomposite. The catalytic properties of Au@MnO2 composite for reduction of 4-NP and degradation of MB were 2.4 and 187 times better than commercial Pd/C, respectively. Meanwhile, the as-synthesized Au@MnO2 nanocomposite exhibited specially excellent sensitivity and selectivity for detection of GSH with a limit of detection (LOD) of 0.11 μM. The core–shell nanostructured Au@MnO2 shows great potential value for the sustainable development of the environment and human health.
Green, environment friendly, and sustainable biomass-based adhesive has been considered as an optimum alternative of petroleum-derived adhesive, yet poor water resistance restricts their advancement and popularization to a large extent. Herein, a hyperbranched cross-linking cellulose-based adhesive with a synergistic effect of covalent bonds and secondary bonds (mainly include hydrogen bond and hydrophobic effect) is synthesized based on the Maillard reaction between dialdehyde cellulose (DAC) and polyamines. The active aldehyde sites on the DAC skeleton anchor the amino group to form covalent bonds consuming a large number of hydrophilic groups, the remaining aliphatic segments of polyamines criss-cross to knit a hydrophobic network and endow the adhesive the ability to resist water erosion; integrant-exposed hydrophilic groups form intermolecular hydrogen bonds preferentially after curing and clustering due to the agglomeration effect of cellulose, which reduces the opportunity of forming hydrogen bonds with water molecules. The outstanding water resistance is manifested in two aspects: (1) the dry lap shear strength of modified adhesive increased from 1.47 to 3.29 MPa, making increments of 123.8% compared with the original DAC adhesive, the re-dry strength after 3 h of immersion in water of 63 °C or boiling achieved a breakthrough from 0 to 2.27 and 2.36 MPa; (2) the modified adhesive has a higher residual rate (above 77%) and a lower moisture absorption value (less than 22.2%) compared with the neat DAC adhesive (49 and 26.6%). The work provides an underlying approach to prepare wood adhesive with excellent bonding performance and eminent water resistance based on green and cheap raw materials and simple cooking chemistry.
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