Synthesis And Properties Elucidation Of Bio-based Polyurethane Foams Based On Bio-polyols From Bioconversion

Bio-based flexible polyurethane foams were successfully prepared using bio-oil derived from fast pyrolysis of wheat straw.Crude bio-oil from fast pyrolysis of wheat straw was extracted with ethyl acetate,and the extracted bio-oil was used as bio-polyol(hydroxyl number: 77.8 mg KOH/g)for the preparation of bio-based flexible polyurethane foams.GC-MS and FTIR analysis of the extracted bio-oil or bio-polyol evidenced that it has the presence of a larger amount of compounds containing multiple hydroxyl groups than the crude bio-oil.Single factor experimental design was used to investigate the effects of amount of bio-polyol(30-70 wt%),PM200 of the total isocyanets(PM200 and PMDI)(0-40 wt%,the total percentage of PM200 and PMDI was 40 wt%),catalyst A-1/A-33 weight ratio(0.1wt%/0.3-0.7 wt%),surfactant(0.8-1.2 wt%),crosslinking agent(0.0-2.0 wt%),catalyst T-9(0.1-0.3 wt%)and blowing agent(2.0-4.0 wt%)on the appearance of prepared bio-based PU foams.The percentages were all based on 100 pieces of the total polyols.After selection according to the results of the single experiment,response surface methodology(RSM)was employed to optimize several independent variables(30-50 wt% of bio-polyol,10-30 wt% of polymethylene polyphenylene isocyanate(PM200),10-30 wt% of polymeric diphenylmethane diisocyanate(PMDI),and 0.5-1.5 wt% of cross linking agent,total amounts of isocyanates for their effects on the foam resilience.Under the optimized conditions,i.e.,30wt% bio-polyol,17.9 wt% PM200,0.5 wt% cross linking agent,the resulted foam has resilience of 37.0 % and is thermally stable up to 200 °C,implying the potential application for car cushion materials.Bio-polyol obtained from the liquefaction of wheat straw under mild conditions was successfully used for the preparation of bio-based PU foams.Based on the conditions for the synthesis of bio-based PU foams using fast pyrolysis oil,the feasibility of using bio-polyol derived from liquefaction of wheat straw was further analyzed.Highly efficient liquefaction of wheat straw(WS)was achieved using alcohol/water mixed solvent at low temperaturesunder medium pressure in the presence of an alkaline catalyst.Effects of liquefaction conditions,e.g.,temperature,residence time,catalyst,and type of solvents on the yields of bio-polyols(BP)and solid residue were investigated.Liquefaction of WS in ethanol/water(50/50,v/v)using NaOH(15 wt% w.r.t.WS weight)at 270 °C for 120 min produced 72.1 %yield and the BP has a weight-average molecular weight of 1000 g/mol and hydroxyl number of 449 mg KOH/g.Influence of various substitution of petroleum polyol with bio-polyol(30-50 wt%)on the properties(including appearance,density,mechanical and thermal properties)of bio-based PU foams were investigated.The obtained BP was successfully utilized to substitute up to 50 wt% of PPG400 for the preparation of bio-based PU(BPU)foams using a low amount of foaming catalyst(0.5 wt%).The BPU foams exhibit good thermal conductivity(0.040-0.050 W/(m·K))and thermal stability comparable to those of a reference foam prepared with 100 % PPG400.Process optimization of the preparation of BPU foams were conducted by using single factor experimental design and RSM.Single factor experimental design was applied to determine the effects of amount of glycerol(0-20 wt%),catalyst(0.5-2.0 wt%),blowing agent(0.5-2.0 wt%)and NCO/OH(1.1-1.5)on the appearance of bio-based polyurethane(BPU)foams.were successfully prepared using hydrothermally liquefied wheat straw(WS)to substitute up to 50 %(w/w)polyols.Response surface methodology(RSM)based on central composite design(CCD)was employed to optimize four process parameters: NCO/OH molar ratio,addition amount of crosslinking agent(glycerol),loading amount of catalyst(a mixture of triethylene diamine,stannous octoate,and triethanolamine),and addition amount of blowing agent(water)for the maximum compression strength of the BPU foams.With the quadratic orthogonal regression model,verified by experimentation,the maximum compression strength of approx.180 kPa was obtained at the optimal conditions: NCO/OH1.24,12.11 wt% glycerol,0.76 wt% catalyst,and 1.31 wt% blowing agent.The optimal BPU foam prepared exhibits good thermal conductivity(0.045 W/m·K)and thermal stability,implying the potential in insulation application.Bio-based hydrophilic polyurethane(BHPU)foams with open-cell structure and high water absorption capacity were prepared using hydrothermally liquefied wheat straw(WS)to substitute up to 40-50 wt% petroleum polyols.Effects of synthesis conditions,e.g.,surfactants,catalysts,blowing agents,and type of petroleum polyols(PPG 400 and VORANOL 280)on the appearance and properties(density,water absorption capacity,open cell content,et al.)of BHPU foams were investigated.Under the optimal conditions: 4 wt% surfactant,10 wt%blowing agent,NCO/OH 0.4.The prepared bio-based PU foams with 40-50 wt% bio-polyols have very high water absorption capacity of 594-1085 %,and 6 s to 140 s water absorptiontime.The mechanical,SEM,DSC,TGA,germination experiment and ultraviolet(UV)radiation and water spraying results also show that the prepared BHPU foams can be applied as a plant growth medium for horticultural use.Bio-polyol obtained from organosovl-fractionation of biomass was was used for the preparation of BHPU foams.Based on the conditions for the synthesis of BHPU foams using liquefied wheat straw,the feasibility of using bio-polyol derived from organosovl-fractionation of biomass was further analyzed.This study aimed to optimize the parameters(i.e.,amount of catalyst,temperature and residence time)for fractionation of Miscanthus(MCT)/wheat straw(WS)into crude cellulose and hydrolysis product(hydrolyzed hemicellulose and lignin).The crude cellulose yield,and residual lignin content in the crude cellulose products were investigated.The experiments were carried out at a fixed solid/solvent ratio of 1:9(g/mL)in a mixed solvent of acetic acid-water at the ratio of 9:1(v/v).The obtained optimal conditions for the fractionation of MCT/WS are: 10 wt% of catalyst(based on dried biomass),temperature of 100 °C and residence time of 120 min.Under the optimal conditions,the yields of the crude cellulose and residual lignin content were were 54 % and4.2 % for MCT,49.6 % and 11 % for WS.The bio-polyol yields were 44 %(MCT)and49.5 %(WS),with the hydroxyl number of 157 mgKOH/g(MCTBP)and 608 mgKOH/g(WSBP)respectively.Effects of solvent content within bio-polyol,amount of crosslinking agent,NCO/OH,dosage of surfactant and bio-polyol content on the appearance and physical properties of BHPU foams were investigated.The optimal conditions for the preparation of BHPU foams were found as follows: MCTBP/WSBP content 100 wt%,solvent content within BP 30-50 wt%,crosslinking agent 0-20 wt% and NCO/OH 0.4-0.8.Under this conditions,the compression strength(10 % deformation)and modulus of elasticity were 6-33 kPa and 4.5-24 kPa respectively with the water absorption capacity and water absorption time of 317-494.8 %and 41.5-90.5 s.These properties of the prepared BHPU foams based on WSBP/MCTBP were really comparable with those of the foams prepared using bio-polyol derived from the liquefaction of wheat straw as discussed above.TGA/DTG results show that the BHPU foams were thermally stable,implying that the foams also has the potential for horticultural application as a plant growth medium.