Highly Branched Polyurea-Based Resins: Clean Synthesis and Wood Bonding Performance

Abstract

Development of green and safe adhesives with high performance is important for sustainability of the wood industry. In this work, highly branched polyureas (HBPUs) were synthesized via polycondensations of urea (U) with triethylenetetramine by a one-pot and one-step strategy. Structural characterization studies by employing Fourier-transform infrared spectrometry, electrospray ionization−mass spectrometry, gel permeation chromatography determination, and thermogravimetric analysis were also performed. HBPU solutions were used as formaldehyde-free wood adhesives and exhibited good bonding performance. The effects of the synthetic conditions and hot-press on bonding performance were investigated and discussed. Best bonding performance was achieved with a U/TETA molar ratio of 3.0, a reaction time of 13 h and a hot-press temperature of 220 °C.HBPUs were further reacted with formaldehyde (F) in different low F/U molar ratios to produce HBPU−formaldehyde (HBPUF) resins. Differential scanning calorimetry analysis demonstrated that the HBPUF resins exhibited similar curing behavior to conventional urea-formaldehyde (UF) resin, but relatively lower cure temperature. When HBPUF resins were used as wood adhesives, they showed better bonding performance and a much lower formaldehyde emission level than UF resin. Facile synthesis and satisfactory performance of HBPU and HBPUF resins make their applications in the wood industry promising.

Easy Preparation, High Water Resistance Glucose-Based Environment-Friendly Wood Adhesives

“…This may be due to the symmetric and asymmetric stretching vibrations of the NH 2 group and is characteristic of primary amines. 34 As in secondary amines, this band is not split; this confirms that the synthesized HU contains enough amino groups. The peaks at 2931 and 2857 cm −1 are both assigned to C−H deformation.…”

A Review on CO2‐Based Polyureas and Polyurea Hybrids

“…HBPUF resins displayed solid contents >60% and a lower curing temperature than the conventional urea‐formaldehyde resin (UF), but the curing behaviors were similar. Moreover, for HBPUF, a better bonding performance (cold‐water bonding strengths >0.7 MPa) and a much lower formaldehyde emission level (≤ 0.93 mg/L) was found by comparison to UF [78] …”

“…[77] If triethylenetetramine (TETA) was used to replace TAEA, a new series of HBPUas can also be synthesized (M n > 5 × 10 4 Da, M w > 1.2 × 10 5 Da, a PDI of about 2). [78] HBPUas were further reacted with formaldehyde in different and low formaldehyde/urea molar ratios to produce HBPUas-formaldehyde resins (HBPUF). The best bonding performance of HBPUas (lap shearing strength: 2.19 ~2.97 MPa) was achieved with a urea/TETA molar ratio of 3.0.…”

“…Moreover, for HBPUF, a better bonding performance (cold-water bonding strengths > 0.7 MPa) and a much lower formaldehyde emission level (� 0.93 mg/L) was found by comparison to UF. [78] A kind of wood adhesives derived from highly-branched PUas was prepared from polyamines and urea by Du et al [79] First, five multifunctional polyamines were prepared by reacting of ethylenediamine, diethylenetriamine, tris(2aminoethyl)amine, triethylenetetramine, or tetraethylenepentamine with methyl acrylate, and then with ethylenediamine. Second, a series of hyperbranched PUas with excellent bonding properties were synthesized via the one-pot and one-step polycondensation of multifunctional polyamines with urea.…”

“…Besides, the bonding performance of the resins did not vary significantly in a wide range of urea/TAEA molar ratio of 1.5∼2.5 [77] . If triethylenetetramine (TETA) was used to replace TAEA, a new series of HBPUas can also be synthesized ( M n >5×10 4 Da, M w >1.2×10 5 Da, a PDI of about 2) [78] . HBPUas were further reacted with formaldehyde in different and low formaldehyde/urea molar ratios to produce HBPUas‐formaldehyde resins (HBPUF).…”