Preparations and properties of polyurethane adhesives modified by corn straw lignin

Abstract

The conversion of lignin into valuable products has attracted the interest of researchers. A series of modified polyurethane adhesives were prepared by blending corn straw enzymatic hydrolyzed lignin with polyester polyol and tolylene-2,4-diisocyanate. Mechanical properties, chemical structures, and thermal stability of the adhesives were characterized by mechanical properties tests, Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). The results of shear strength test under room temperature and high temperature showed that the shear strength for modified polyurethane adhesives was improved by introduction of lignin. The introduction of lignin also improved the heat resistance of polyurethane adhesive. The TGA analysis results showed there were two stages in the thermal decomposition of the lignin blend modified polyurethane adhesive, and the maximum decomposition temperature of the first stage increased with the increase of lignin content, while the maximum decomposition temperature of the second stage decreased with the increase of lignin content. The TGA-FTIR combination analysis studied the main gas generated in the two decomposition stage’s peak times, of which CO2 was produced in the first stage, and CH4 was created in the second stage, indicating that the molecular chain fracture process of the two kinds of adhesives was similar in the whole decomposition process.

Polyurethane adhesives from castor oil and modified lignin via reaction with propylene carbonate

“…Regarding the elongation at break, a slight increase was verified up to 20 wt%. This improvement of mechanical performance of PU with the addition of lignin is reported by other studies 17,41,55 …”

“…The practical adhesion improvement is supported by uniaxial tensile test results, which revealed the mechanical property enhancement of adhesives with the incorporation of HKL_PC. Several other studies have also verified this improvement with the addition of lignin in PU adhesives 19,55,56,59 . Furthermore, the resulting lignin‐based PU adhesives presented similar adhesive performance as the ones obtained from lignin that was hydroxypropylated with PO.…”

“…Several other studies have also verified this improvement with the addition of lignin in PU adhesives. 19,55,56,59 Furthermore, the resulting ligninbased PU adhesives presented similar adhesive performance as the ones obtained from lignin that was hydroxypropylated with PO. In the previous work, 16 our group modified a Kraft lignin via hydroxypropylation with PO under mild conditions and then blended the modified lignin with CO (30 wt%) for bio-based PU adhesive synthesis.…”

“…This improvement of mechanical performance of PU with the addition of lignin is reported by other studies. 17,41,55 Despite having the highest modulus, the sample containing 30 wt% of HKL_PC presented lower values of UTS and elongation at break in comparison to the one containing 20 wt%. This behavior corroborates the results of other works in the literature that reported worsening of mechanical properties in PU systems containing more than 20 wt% of lignin.…”

Toughness improvement of epoxy composites using a kind of environment-friendly bio-based polyester polyol

“…Then, segmented polymerization occurred from 150 ℃ to 250 ℃ for 5 hours. In the post-polycondensation stage, the temperature of the system was reduced to 100 ℃, and the reaction continued for 2 hours in the presence of the Sb 2 O 3 catalyst to increase the reaction rate [14,15].…”