The Application Of Lignin In Polyurethane Foam

Lignin, a phoenolic polymer with a complicated molecular structure, has beenfound widely in plant cell tissue and it is the second most abundant fiber polymer onearth. Due to the complicated structure, lignin, this amorphous polymer, has limitedthe use in industries and always been regarded as the production waste. In recentyears, only about1%of it has been fully utilized in manufacture process. Therefore, itis a great challenge to find the new applications of lignin. In the past decades,researchers have done a great deal of work in the development of lignin polymermaterials. In this thesis, the author will mainly focus on the properties of a newmaterial–lignin-polyurethane foam.In this thesis, based on the properties and structural features, three different wayshas been employed to handle the selected lignin: hydroxymethylation, epoxidationand phenolation. Through these three methods, the number of reactive functionalgroups of the selected lignin has increased, especially the number of phenolichydroxyl group at the same time, it also lays the foundation for follow-up productionof polyurethane material. Moreover, among the dramatic increase of phenolichydroxyl groups, the content of lignin by the method of phenolation is the highest,reaching9.41%, nearly three times higher than that in the unmodified one. And undersuch circumstance, the optimum temperature for lignin phenolate is95oC and theoptimum reaction hour is3hours. Hydroxymethylation lignin is the second highestamong phenolic hydroxyl groups, followed by epoxidation lignin.By adding modified lignin into polyurethane foam material, it can not onlyincrease the decomposition temperature of the foam material, but also remarkablyimprove its mechanical properties. Besides, phenolic lignin, which contains thehighest content of phenolic hydroxyl group, represents a fine dispersion whengenerating blends with polyether glycol and it is almost completely dissolved in thepolyether glycol. This process also reveals the optimum reaction conditions for blends:the reaction time and temperature are4hours and80oC respectively. Moreover, byadding modified lignin into the polyether glycol and according to the mechanicalproperties of the obtained foam material and the decomposition temperature, the optimum amount of modified lignin can be achieved, that is,1%phenolic lignin and3%exposidised lignin. This thesis doesn’t carry on a detailed research abouthydroxymethylased lignin because its dispersion in polyether glycol is not good andthus, there is little improvement in the properties of the obtained polyurethanematerial.In order to obtain a polyurethane material with better thermal properties, a kind ofinorganic flame retardants, zinc borate, is added into the polyurethane material. Testsindicate that the decomposition temperature of the polyurethane material isremarkably increased after adding zinc borate and the cell structure of polyurethanefoam itself will not be affected. Therefore, with the above two addition agents, ligninand zinc borate are added into the polyurethane foam at the same time to obtain a newpolyurethane material with better thermal properties and better press-resistance.