Synthesis And Properties Of Reed-based Polyurethane

Polyurethane is regard as the fifth plastic in the world and widely used in coatings,adhesives,foam,elastomer,and so on with excellent weather resistance,thermal stability,and mechanical properties.But PU is root in petroleum and petroleum will be exhausted in the21st century.In contrast,biomass is sustainable and substitute for fossil sources.The development of bio-based materials has attracted the attention of researchers,and the bio-based industry is imperative.China is a largely agricultural country,products from agricultural waste straws replacing petroleum-based products can achieve multi-win results in alleviating the oil crisis and turning to a low-carbon economy,and solving environmental problems.With the establishment of the Xiongan New Area,the ecological management of the reeds in Baiyangdian has been put on the agenda.The high value-added reuse of reeds harvested in large quantities every year faces challenges.Therefore,a series of PU coating film and PU foam was prepared using reed containing amounts of-OH and natural nano Silicon dioxide（Si O₂）and Castor oil（CO）and Polyethylene glycol-400（PEG-400）as solvent by normal pressure solvent method in this paper.The mechanism of preparation and properties for PU are explored through the structural and performance characterization.The development of environmental protection and green reed-based PU is expected to replace petroleum-based PU and promote China to achieve the"carbon peak"by 2030 and"carbon neutrality"by 2060.The main contents of this paper are as follows:First of all,the reed was liquefied.Using the liquefaction rate of the reed as the evaluation index,the best experimental scheme of reed liquefaction under different catalysts（H₂SO₄,Ts OH,H₃PO₄）and ratios of different solvents was studied.The results show that the optimum liquefaction conditions are as follows:the catalyst is H₂SO₄,the ratio of solvent is PEG-400（wt%）:CO（wt%）=4:1,the reaction temperature is 150°C,and the reaction time is 1.5 h,that the liquefaction rate is the largest,which is 97.16%and higher than that reported in the literature.Further,the products of the reed were characterized by Fourier Translation Infrared spectroscopy（FTIR）,Scanning Electron Microscope（SEM）,X-ray diffraction（XRD）,Gel Permeation Chromatography（GPC）,etc.The result reflects that the liquefied product is a polyol,the hydroxyl value 171 mg KOH/g,the viscosity 1.221 Pa·S,the number average molecular weight（M_n）1.202 Kg/mol.Then,the preparation and properties of reed-based polyurethane coating are studied.The reed-based two-component PU was prepared by the method of direct polymerization with different isocyanates（isophorone diisocyanate（IPDI）,toluene diisocyanate（TDI）,4,4’-diphenylmethane diisocyanate（HDI））and reed polyols（R-P）,which containing a large amount of hydroxyl（-OH）and natural nano Si O₂.The reed-based waterborne one-component PU was synthesized through the steps of pre-polymerization,chain extension,cross-linking,and water-based by the prepolymer method with TDI and R-P.The mechanical properties and thermal properties of the samples were investigated by FTIR,SEM,Transmission Electron Microscope（TEM）,Thermogravimetric Analysis（TGA）,Water Contact Angle（WCA）,Differential Scanning Calorimetry（DSC）,pencil hardness,and other characterization methods.The results show that the series of reed-based polyurethane has excellent mechanical properties,the maximum hardness of 6 H,good hydrophobic effect,maximum contact angle of 109°,high thermal stability,and maximum initial decomposition temperature can reach299.1°C.Finally,the synthesis and flame retardant modification of reed-based polyurethane foam was investigated.The reed-based PU foam（R-PUF）was prepared by the one-pot method and free rise method using the reed-based polyol and 4,4’-diphenylmethane diisocyanate（MDI）,water as a foaming agent,silicone oil as a surfactant,and dibutyltin dilaurate as the catalyst.Its properties were measured,the density of 33.03 kg/m³,the thermal conductivity of 0.0350W/（m·K）,and the limiting oxygen index（LOI）of 20.5%,which was higher than that reported in other works of literature.Due to the special structure of the internal cells of the foam,which is relatively flammable.The foam was modified using9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）as the flame retardant.The properties and mechanism of DOPO flame retardant reed-based PU foam was explored by the limiting oxygen index（LOI）test,cone calorimetry test（CCT）,SEM,TEM,etc.The results show that when the addition amount of DOPO is 6%,the flame retardant effect is the best.The heat release rate is reduced by 46.8%,and the formed carbon residue is denser.The mechanism of DOPO flame retardant reed-based PU foam is the result of the synergy effect of gas-phase and coacervation,that the condensed phase blocks the transfer of oxygen and heat to the interior of the foam and the gas-phase suppresses the combustion chain reaction.