| Rigid polyurethane foam(RPUF)has the characteristics of light weight,high compression strength,and excellent thermal insulation performance,and is often used in construction,furniture and other industries.In recent years,with the continuous rise in global oil prices,the energy crisis has gradually intensified.Reducing the reliance on petroleum-based polyurethane materials and developing new bio-based polyurethane materials has become a research hotspot for scientific researchers and is also one of the future development directions of the polyurethane industry.In the production process of biodiesel,complex by-product glycerol is produced,which is called crude glycerol.If crude glycerol can be converted into some high-value chemicals,this can not only realize the utilization of waste,but also greatly reduce the production cost of biodiesel.At the same time,China is also a big agricultural country,producing nearly 1 billion tons of straw every year,but most of them are burned or buried,which is not only a waste of resources,but also causes serious pollution to the environment.Therefore,this topic explores the synthesis of wheat straw bio-based polyol using wheat straw as raw material and crude glycerol as liquefied solvent,and uses it in the preparation of RPUF.By adjusting the foaming formula,a foaming formula suitable for wheat straw bio-based polyurethane foam was obtained.At the same time,due to the flammability of RPUF,flame retardant modification of RPUF was studied and explored with added flame retardant The effects of flame retardants on their mechanical properties,thermal insulation properties,microstructure and flame retardant properties are discussed.The main results of the paper are as follows:1.With the liquefaction rate and hydroxyl value as the main indicators,the preparation conditions of wheat straw bio-based polyols were optimized using a two-step method.The reaction conditions in the first step were 240°C,6%Na OH,4 h,and10%solid-liquid ratio.In the second step,the compound polyol(CP)loading was 25%and the reaction time was 4.5 h.Under this condition,the bio-based polyol has a hydroxyl value of 658 mg KOH/g and an acid value of 2.3 mg KOH/g,which is suitable for the preparation of RPUF.2.RPUF was prepared by partially replacing commercial polyether polyol with bio-based polyol,and its foaming formula was optimized.The optimization results were 20 parts bio-based polyol,80 parts commercial polyether polyol,1.15 isocyanate index,40 parts monofluorodichloroethane(HCFC-141b),1 part triethylenediamine(A-33),3 parts of dibutyltin dilaurate(T-9),and 4 parts of silicone oil(AK8805).Under this foaming formula,the polyurethane foam has a compressive strength of 231 k Pa,a density of 0.033 g/cm~3,and a thermal conductivity of 0.027 W/(m K).3.In order to improve the flame retardant performance of bio-based polyurethane foam,different flame retardant combinations were compared,and the best flame retardant compounded with dimethyl methylphosphonate(DMMP)and expandable graphite(EG)was determined.When the DMMP and EG is 2:1 and the total loading is 25%,the oxygen index(LOL)of the flame retardant rigid polyurethane foam FRPUF-2:1 can reach 26.2%.Compared with RPUF,the carbon residue ratio of FRPUF-2:1 increased from 23.4%to 31.3%.The peak heat release rate decreased from229.7 k W/m~2 to 161.8 k W/m~2,and the total smoke emission decreased from 3.1 m~2 to2.4 m~2.In the UL-94 test,the FRPUF samples all reached the V-0 combustion level.In the smoke density test,the FRPUF also showed higher light transmittance and lower specific optical density,indicating that DMMP and EG can not only improve flame retardant performance but also suppresses the generation of smoke. |
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