Oxyalkylation of Lignoboost™ Kraft Lignin with Propylene Carbonate: Design of Experiments towards Synthesis Optimization

Abstract

Oxyalkylation with propylene carbonate (PC) is a safe process to convert lignin into a reactive liquid polyol to be used in polyurethane formulations. In this study, the effect of operating conditions of oxyalkylation (temperature, time and quantify of PC) on the quality of lignin-based polyol in terms hydroxyl number (IOH) and viscosity was studied. Full factorial modeling and response surface methodology (RSM) were applied to study the effect and interaction of process variables on the IOH and viscosity of lignin-based polyols. The results revealed that the IOH is highly affected by the reaction time, while the viscosity is affected by the amount of PC. Validation experiments confirmed the model is reliable. Furthermore, RSM optimization allowed to reduce the amount of PC by about 50% and to increase the lignin content in the polyol from 12.5% to 25% (w/w) depending on the temperature and time of the process and also on the purpose of the polyol produced (i.e., application in rigid foams or adhesives).

Polyurethane Adhesives Based on Oxyalkylated Kraft Lignin

“…The hydroxyl number (I OH ) of LBP was 225 mg KOH/g and its viscosity (0.56 Pa . s) allowed effective mixing with diisocyanate (pMDI) to prepare different adhesives formulations [ 23 ].…”

“…The production and characterization of crude lignin-based polyol (LBP) was carried out according to our previous work, under optimized conditions using kraft lignin (KL) as the substrate, 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) as the catalyst was supplied by Aldrich Chemical Company (St. Louis, MO, USA) and propylene carbonate (PC) as oxyalkylation reagent was purchased from Acros Organics Company (Geel, Belgium) [ 23 , 29 ]. The final LBP consisted of PC-modified lignin and PC-derived oligomer (homo-oligomer) herein referred to as PC oligomer.…”

“…This process has been evaluated and used to produce PU [ 20 , 21 , 22 ]. In fact, our group has optimized the oxyalkylation process to produce LBP with a suitable hydroxyl number (I OH ) and viscosity for rigid foams and adhesive formulations [ 23 ].…”

Lignin as a Renewable Building Block for Sustainable Polyurethanes

“…The number can be determined by the reaction of the terminal hydroxyl groups using organic anhydrides (acetic anhydride or phthalic anhydride) [ 3 ]. The range of I OH values of polyols required for the production of PUs is quite wide, e.g., polyether polyols used to produce rigid foams have I OH values between 300–800 mg KOH/g, while for PU adhesives production the range of I OH values is usually lower [ 3 , 90 ].…”

“…An alternative to ensure the incorporation of lignin as cross-linker is its chemical modification via acid liquefaction and oxyalkylation, among others, as discussed in Section 4 , which affords polyether polyol with up to 35 wt.% of lignin [ 9 , 10 , 57 ]. Recently, our group optimized the oxyalkylation of LignoBoost TM kraft lignin with propylene carbonate (PC) to produce a crude LBP with suitable I OH and viscosity to be used in the production of different PU products, such as rigid foams and adhesives [ 90 ]. In most studies, the lignin-based polyether polyol obtained from oxyalkylation using PO [ 144 , 145 ] or cyclic carbonates [ 15 , 146 ] has been used for the production of rigid PUF for thermal insulation.…”