Toward UV-Triggered Curing of Solvent-Free Polyurethane Adhesives Based on Castor Oil

Abstract

An o-nitrobenzyl-protected precursor was used as a phototrigger for the release of the diamine cadaverine in polyurethane adhesives based on castor oil as a renewable source of polyol and organic diisocyanates. This resulted in formulations with suitably controlled curing by photoactivation. This material shows faster curing when UV light is applied as compared to curing in the absence of irradiation, which was in situ monitored by rheological measurements. In addition, the adhesion performance is superior, reaching lap shear strength values of up to 4600 kPa, which is unprecedented for bio-based adhesives. On one hand, the in-depth chemical characterization with FTIR spectroscopy revealed that the slow release of cadaverine yields a well-balanced urethane/urea composition with direct impact on adhesion properties. The photocured bioadhesive was shown to bond a variety of surfaces, such as polyethylene or even wood. On the other hand, the direct one-time addition of cadaverine yields a material with approximately the same viscoelastic properties, which were achieved almost immediately as a consequence of the favored fast formation of urea bonds in detriment of urethanes, however, lacking adhesion properties.

A Bio‐Based Supramolecular Adhesive: Ultra‐High Adhesion Strengths at both Ambient and Cryogenic Temperatures and Excellent Multi‐Reusability

“…As shown in Figure 5b , the BSA outperforms reported bio‐based adhesives and supramolecular adhesives in bonding stainless steel, aluminum alloy, woods, and ceramics to the best of our knowledge. [ 14 , 17 , 19 , 28 , 31 , 32 , 37 , 39 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ] In addition, we made another two comprehensive comparisons between the BSA and reported supramolecular adhesives to further demonstrate its robust bonding strength, excellent multi‐reusability, and outstanding performances at low temperature. Figure 5c shows that the BSA exhibits the highest adhesion strength and the largest reuse number at the same time.…”

“…Significance levels were indicated as *p < 0.05, **p < 0.01, and ***p < 0.001.) b)The comparison of BSA with reported bio-based adhesives as well as supramolecular adhesives in bonding Fe, Al, woods, and ceramics [14,17,19,28,31,32,37,39,[52][53][54][55][56][57][58][63][64][65][66][67][68][69][70][71]. c) The comparison of BSA with reported supramolecular adhesives in adhesion strengths and reuse numbers [17,28,31,32,37,39,52,[55][56][57].…”

Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust

“…Polyurethane wood adhesives based on polyester polyol from soybean oil Improved performance by addition of additives [39] 2021 Solvent-free polyurethane adhesives based on castor oil and organic diisocyanates Fast curing; low adhesion [13] Liquefaction of biomass in the presence of polyhydric alcohols and acid catalysts is an effective thermochemical conversion method to turn solid biomass into liquids for various applications [40]. A large variety of virgin and waste biomass, such as wood, bark, cork, bagasse, and agriculture crop residues, have been used in liquefaction [40,41].…”

“…Table 1 presents the chronological evolution of research on the development of bio-based polyurethane adhesives including the development of synthesis technology and uses of natural resources. Good adhesion for rubber to rubber bonding [10] 2001-2021 Non-isocyanate polyurethane adhesives Need of high curing temperature; renewability; non-toxicity [11][12][13][14][15][16]…”

A review on room-temperature self-healing polyurethane: synthesis, self-healing mechanism and application

“…Therefore, choosing different raw materials and relative ratios of hard and soft segments can easily tune the phase-separated structure, thereby changing the properties of polyurethanes. Thanks to easy tailoring properties of PUs, they have been widely used in many fields such as coatings [4,5], adhesives [6], textiles [7], printing inks [8], biomaterials [9,10], flexible electronics [11,12], etc. However, polyurethane materials inevitably produce mechanical damages in the process of use, hence endowing them with self-healing function is of great significance to prolong the service life of materials and reduce the maintenance costs.…”