| Enzymatic hydrolysis lignin (EHL) a novel lignin which is isolated from the enzymatichydrolysis residues of corn stalk for production of butanol.Compared to lignosulfonate or kraftlignin, EHL has various reaction groups and greater chemical reactivity. The polyhydricalcohol liquefaction of EHL and the modified polyurethane (PU) foaming materials derivedfrom the liquefaction product were studied in this dissertation.The preparation of EHL-basedPU foaming materials by chemaical modified method will be favorable to not only improvingthe application of agricultural wastes and the economic benefit of biological enzymolysistechnology, but also gaining better social benefit.Corn stalk EHL was liquefied using the mixed solvents of polyethylene glycol400(PEG400) and glycerol in the presence of sulfuric acid as a catalyst under atmospheric pressure.The liquefaction residue ratio and hydroxyl number as evalution indexes were used to evaluatethe effects of the liquefaction temperature, the liquefaction time, the catalyst dosage and theliquid-solid ratio on the liquefaction. The optimal reaction conditions was proposed.When theliquefaction temperature was at120°C, the liquefaction time for50min, the liquefactionsolvent/corn stalk EHL ratio at5:2and sulfuric acid dosage at0.6%, the liquefied productshowed hydroxyl number of397mgKOH/g, residue ratio of0.59%and viscosity of5405mPa·s.When the liquefaction solvent/corn stalk EHL ratio increased from5:3to5:1, theaverage molecular weights, polydispersities, residue ratio of the liquefied EHL polyolsdecreased while the hydroxyl number increased.The methods such Fourier transform infrared spectroscopy (FT-IR), Nuclear maggneticresonance spectrum (NMR), Gas chromatography-mass spectrometry (GC-MS) and Gelpermeation chromatography (GPC) were used to analyze the functional groups, molecularstructure, molecular weight and distribution of liquefaction product from different liquefactiontime to study the EHL modification mechanism in polyhydroxyl acohol.The results showed that at the first stage of liquefaction process, the average molecular weights and polydipersitiesdecreased,while at the latter stage of liquefaction process, they presented the upward trend.Itindicated that the degradation reaction and condensation reaction occurred in the liquefaction.At the presence of sulfuric acid, the EHL was firstly degraded into structural units ofp-coumaric alcohol, erucic alcohol and so on, and then the demethylation reaction occurred,finally, there were oxidation and esterification reaction.There were three kinds of chemicalcompounds in the liquefaction products.The compounds of the first group had phenol andbenzene ring structure;the compounds of the second group had phenylmethoxy structure;thecompounds of the third group stemmed from condensation reaction between the EHLdeviatives and liquefaction solvents.Polyurethane foams were made from the liquefied product and diphenylmethanediisocynane diisocyanates (MDI). Furthermore,the impacts of liquefaction product additioncontent on properties of PU foaming materials were investigated. The result showed that theoptimal conditions for preparing EHL-based PU foaming materials were the ratio of4110/40340:60, the liquefaction product30%, catalyst dosage2.5%, foaming dosage20%, isocyanateindex1.2, flame retardant dosage25%～30%, water content1%and silicone surfactant2%.The preparation formulations were choosed according to the end use purpose of PU foamingmaterials.The foams with bio-polyol presented better compressive strength than conventionalpolyurethane foams. When the bio-polyol content was30%, the compressive strength reachedits maximum value of291kPa, which was36%higher than that of conventional PU foamingmaterials. It indicated that a high dosage of bio-polyol in the foaming mixture would lead tobrittle foams. The addition of liquefied EHL polyol into the foaming mixture resulted inimproved the thermal stability and flame resistance.The initial degradation temperature and themost rapid degradation temperature during the first degradation stage of the PU foamingmaterials with bio-polyol were higher than those of conventional PU foaming materials.Whenthe contents of bio-polyol were10%and50%, the peak of heat release rate were200.60kW·m-2and191.33kW·m-2, respectively, which were23.85%and27.37%lower thanthat of conventional PU foaming materials (263.43kW·m-2). In addition, mass loss rate of PU foaming materials based on bio-polyol significantly decreased.The thermal conductivity wasimproved when the liquefaction products replaced a part of trational polyether polyol. Thethermal conductivity of polyurethane foams with30%bio-polyol was0.02517W/mK,whichwas significantly36%lower than that of conventional polyurethane foams (0.03027W/mK).The scanning electron microscopy images indicated that polyurethane foams containing lessthan70%bio-polyol had smooth surface.Corn stalk EHL-based polyurethane foams were prepared by two methods: blending andliquefaction modification. The effects of the two types of preparation methods on the structureof PU foaming materials, process parameters, gel content, density, compressive strength,surface morphology and dynamic mechanical property of EHL-based polyurethane foams werediscussed.The results showed that EHL-based polyol involving in liquid in the foamingreactionand acted as nucleation sites and diluent.The reaction molecular interval became larger.Therefore, the gel time of PU foaming materials derived from liquefaction modification waslonger than that of PU foaming materials from the blending modification.The density ofpolyurethane foams from liquefaction modification method was lower than that from blendingmethod. The gel content and compressive strength of polyurethane foams based on liquefactionproduct were higher than those from blending method. When the substitution for polyol waslower than30%, the glass transition temperature of the polyurethane foams from liquefactionmethod was higher than those from blending method. The liquefaction modification wassuperior to the synthesis of EHL-bassed PU materials.
|
PDF Full Text Request