Development and characterization of a lignin–phenol–formaldehyde wood adhesive using coffee bean shell

Abstract

In the present study, the possibility of development of a wood adhesive using coffee bean shell lignin (Cbsl) has been explored. Cbsl-modified phenolic adhesive has been prepared by replacing phenol with lignin at different weight percents. The optimization of weight percent lignin incorporation was carried out with respect to mechanical properties. It was found that up to 50 wt% of phenol could be replaced by Cbsl to give lignin-phenol-formaldehyde adhesive (LPF) with improved bond strength in comparison to control phenol-formaldehyde (CPF). Optimized LPF and CPF adhesives were characterized by IR, DSC and TGA. The IR spectrum of LPF showed structural similarity to CPF. Thermal stability of LPF adhesive was found to be lower as compared to that of CPF. DSC studies revealed a higher rate of curing in the LPF adhesive.

Performance of bonded boards using lignin-based resins

“…The differences in the viscosity could be as a result of variation in the chemical composition of each lignin which subsequently affects the chemical composition of the prepared LPF and thus having an overall effect on the viscosity. The viscosity obtained for LPF in this work was compared well with that reported by Khan and Ashraf (2006), using different percentage of groundnut shell lignin. They reported a viscosity value of 3.5 when 25% lignin was substituted for phenol in preparation of LPF, 4.5 for 35% lignin, 5.5 for 50% lignin, and 6.0 for 60% lignin.…”

“…Synthesis of resins PF and lignin-phenol-formaldehyde (LPF) resins were synthesized in a four-neck round-bottom flask equipped with a stirrer, thermometer, and condenser, by modification of Gothwal et al (2010) and Khan and Ashraf (2006) methods. For the preparation of PF, 23.28 g of phenol, 37.8 g of formaldehyde solution, 20 g of water, and 19.84 g of methanol were added into the flask and mixed together for 5 min at 25°C.…”

Laccase, an Emerging Tool to Fabricate Green Composites: A Review

“…These free radicals are highly reactive and can participate in polymerization, depolymerization, copolymerization, and grafting (Saastamoinen et al 2012). Since the lignin structure is very similar to that of phenol-formaldehyde (PF) resins, similar polymerization can be achieved (Khan and Ashraf 2006;Laurichesse and Avérous 2014). To transform lignin into an insoluble adhesive, it must be additionally cross-linked; a lower number of free positions in the aromatic nuclei and a lower rate of reactivity limit the utility of lignin as an adhesive (Khan and Ashraf 2006).…”

“…Since the lignin structure is very similar to that of phenol-formaldehyde (PF) resins, similar polymerization can be achieved (Khan and Ashraf 2006;Laurichesse and Avérous 2014). To transform lignin into an insoluble adhesive, it must be additionally cross-linked; a lower number of free positions in the aromatic nuclei and a lower rate of reactivity limit the utility of lignin as an adhesive (Khan and Ashraf 2006). Furthermore, the methoxy or methoxyequivalent groups present on the aromatic ring of lignin are considerably less reactive toward hydroxybenzyl alcohol groups than the hydroxyl groups found in phenol (Pizzi 2003;Khan and Ashraf 2006;Schorr et al 2014).…”

“…To transform lignin into an insoluble adhesive, it must be additionally cross-linked; a lower number of free positions in the aromatic nuclei and a lower rate of reactivity limit the utility of lignin as an adhesive (Khan and Ashraf 2006). Furthermore, the methoxy or methoxyequivalent groups present on the aromatic ring of lignin are considerably less reactive toward hydroxybenzyl alcohol groups than the hydroxyl groups found in phenol (Pizzi 2003;Khan and Ashraf 2006;Schorr et al 2014). Because of these reasons, lignin cannot be utilized as effectively as a potential adhesive as synthetic PF resins.…”