| With the rapid development of global industry,the consumption of petroleum resources is increasing day by day.How to develop and utilize biomass raw materials to replace non-renewable resources has become an issue of worldwide concern.In this thesis,dextrin and castor oil-based polyol were used as raw materials to obtain bio-based polyols through a green and low-consumption process.The petroleum-based polyols were completely replaced by this polyol,and the fully water foamed method produced polyurethane rigid foam with good mechanical properties and bio-based content.The main research was divided into the following aspects:(1)By simple physical mixing,dextrin was dissolved in glycerin to prepare dextrin-based polyols.The effects of different components and proportions on the rheological properties of polyols were explored.Afterwards,polyurethane foams were prepared with different dextrin-based polyols and compared with the properties of petroleum-based polyurethane foams.The results showed that the dextrin-based polyurethane foam had more excellent flame retardancy and biodegradability,and the foam prepared with the dextrin-based polyol with a higher proportion of glycerol also had higher compressive strength.Afterwards,the influence of different foaming agent water content and isocyanate index on the performance of polyurethane foam was explored.The results showed that with the increase of water content,the density and compressive strength of the foam decreased,and the expansion ratio increased.The increase in the isocyanate index increased the compressive strength.When the isocyanate index was 0.9,the compressive strength of the foam can reach 0.327 MPa.(2)Castor oil-based composite polyols were prepared by mixing castor oil polyols in different proportions with glycerin,and the polyols were used as raw materials for the preparation of polyurethane foams.When exploring the effect of different composite polyols on foam performance,it was found that with the increase of the glycerin content in the composite polyol,the cell size decreased slightly.The pore size was the smallest when the glycerin content was 80 wt%,which was 110.7 μm.When the glycerol content of the compound polyol was higher,the foam had very high compressive strength,up to 2.03 MPa.However,the increase of glycerol content will increase the foam density,resulting in lower foaming rate.When the glycerol content was 80 wt%,the foaming rate was only 7.1.Moreover,because of the low content of fat long chain,the foam will be more vulnerable to defects.When studying the effect of isocyanate index on foam,it was found that when the isocyanate index was 0.9,the hydroxyl group was closer to the reaction,so the density of foam was the lowest.As the isocyanate index increased,the compressive strength of the foam changed little.When the isocyanate index was 0.6,the polyurethane foam with a compressive strength of 1.01 MPa and a biologically basic content of 42.1% could be obtained.(3)Dextrin-based polyols and castor oil-based polyols in different proportions were mixed to obtain dextrin/castor oil-based polyols.This polyol was used to prepare polyurethane foam and to explore the influence of different isocyanate indexes and dextrin/castor oil-based polyols in this system.The results showed that when the mass ratio of dextrin-based polyol and castor oil-based polyol was 1/1 as the reaction raw material,the compressive strength of the foam increased with the increase of the isocyanate index.When the isocyanate index was 0.8,the compressive strength of the foam was 43.8% higher than when the index was 0.6.The foam compressive strength when the isocyanate index was 1.0was only 7.9% higher than when the index was 0.8.This showes that under these conditions,the active hydroxyl group in the system was close to react completely when the isocyanate index was 0.8.Under the same dextrin-based polyol,increasing the content of castor oil-based polyol can make the cells more uniform and the structure more complete.In terms of mechanical properties,as the content of castor oil polyol increased,the foam density tended to decrease first and then increase.The resilience of the foam was improved,but the compressive strength was reduced.Under the same castor oil polyol content,as the proportion of glycerin in dextrin polyol increased,the crosslinking density of the system increased.Therefore,the density and compressive strength of the foam were improved,and the compressive strength can reach up to 1.07 MPa.The results showed that by changing the ratio of the two biological polyols,the properties of the polyurethane foam can be adjusted.The polyurethane foam with high compressive strength and excellent bio-based content can be successfully prepared. |
