Superstrong Adhesive of Isocyanate-Free Polyurea with a Branched Structure

Abstract

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.

Developing High-Performance Cellulose-Based Wood Adhesive with a Cross-Linked Network

“…The arresting exothermic peaks were measured in the DSC curves of 2DAC–PA 4N , 2DAC–PA 5N , and 2DAC–PA 6N , and peaks indicating curing temperatures are 2DAC–PA 4N at 152.3 °C, 2DAC–PA 5N at 150.6 °C, and 2DAC–PA 6N at 152.7 °C (Figure a). There is a drastic reduction in curing temperature compared with about 250–300 °C of single PA 4N , PA 5N , and PA 6N , which contribute to cut down the energy consumption of the production process . The hot pressing temperature of the follow-up experiment was set as 160 °C to mediate discrepancy of divers adhesives.…”

“…The enhancement of adhesive viscosity via introducing hyperbranched polymers has been the concern of numerous research studies by virtue of its highly branched 3D structure, low chain entanglement, versatile terminal functional groups, and brief synthetic route for the past decades. − Beyond functioning in ensuring low viscosity, fine solubility, elevated reactivity, increased cross-linking sites, reduced formaldehyde emission level, − additionally, free volume and internal cavities formed when the hyperbranched polymer is cross-linked with the target molecular structure will induce the cavitation effect, which can absorb energy under stress, so making the material more tough . Plenty of studies, including our previous work, , have demonstrated that the application of hyperbranched polymers in wood adhesives is feasible; herein, it is expected to be used to modify cellulose-based adhesives.…”

“…Based on the work of former people, , we aim to develop an environmentally friendly biomass adhesive with excellent adhesion property, mechanical and thermal performance, and intensive water tolerance. In order to fulfill this expectation, microcrystalline cellulose (MCC) was oxidized selectively by sodium periodate and formed DAC with the multifunctional active aldehyde group.…”

Ultrafast Universal Fabrication of Metal‐Organic Complex Nanosheets by Joule Heating Engineering

“…Based on above, the composition of the MOC was proposed as shown in the scheme. Urea was catalytically partially decomposed and condensed to form longer chains [HOOC‐NH‐CO‐NH‐CO‐NH…] ( Figure e), [ 38 ] four of which were bridged via linking to the same metal ions under the coordination function of N atoms, forming the metal‐organic complexes.…”

High‐performance thermoplastic polyureas via a non‐isocyanate route from urea and aliphatic diamines

“…These plastics do not show competitive mechanical properties to the commercially available plastics. This route was also used to form branched PUrs as adhesives or crosslinking site in the chemical modification of urea‐formaldehyde resin 30,31 . However, high‐performance thermoplastic PUrs via this urea‐based method have not been studied systematically.…”