Preparation And Mechanical Properties Of Modified Wheat Straw Foaming Material

Traditional foaming materials such as polyethylene,polypropylene and rubber-based foaming materials are made from non-renewable petroleum resources.They have poor biodegradability and high preparation costs,which will cause global“white pollution”problems.After incineration,gas and solid waste containing a variety of toxic substances will be produced,which seriously pollutes the natural environment on which human beings depend.In recent years,a large number of biomass lignocellulose in nature can be used as raw materials to prepare biomass foaming materials,which can selectively replace petroleum-based foaming materials.However,although the biomass foaming materials prepared by lignocellulose have high biodegradability,their density is generally higher than that of petroleum-based foaming materials,and the mechanical strength needs to be further improved.Therefore,the preparation and application of high-performance biomass lignocellulose foaming materials have always been the focus of attention.In this paper,wheat straw with rich lignocellulose was used as raw material to prepare wheat straw foamed materials by pretreatment,modification and foaming process,and its mechanical properties were mainly studied.The research contents are as follows:1.Firstly,wheat straw was pretreated with 2 wt%sodium hydroxide solution at 100℃for 2 h（straw:solution=1 g:20 m L）,and straw lignocellulose with a ratio of cellulose and hemicellulose to lignin content R of 2.56 was obtained.The straw lignocellulose before and after modification was analyzed by infrared,thermogravimetric and electron microscopy.The results showed that the characteristic peaks of ester bond and carbon-carbon double bond appeared at1738cm^-1and 1660cm^-1in infrared,respectively.The new diffraction peaks appeared at 34.93°and 32.06°in XRD.The electron microscope showed that there were attached copolymers on the surface.The thermal stability of modified straw was significantly improved in thermogravimetric.2.Modified wheat straw foaming materials were prepared by compression foaming method through orthogonal experiment.Esterification and esterification-acylation double modified straw were used as raw materials（mass ratio of 1:2）,acrylamide（AM）was used as crosslinking agent,water was used as plasticizer,azodiisobutyronitrile（AIBN）and azodicarbonamide（ADC）were used as foaming agents,and zinc oxide was used as foaming agent.The effects of AM and AIBN dosage,foaming temperature and time on the properties of wheat straw foaming material were discussed respectively.On this basis,the optimum process of AM and foaming temperature on the foaming material was further studied.The results showed that when the amount of raw materials was 3 g,the amount of AM was 5 g,the amount of water was 5 g,the amount of foaming agent was 10 wt%of ADC,the amount of AIBN was 0.5 g,the amount of ADC was 0.5 g,the foaming temperature was 160℃,the foaming pressure was 3.5 MPa,and the foaming time was 20 min,the straw lignocellulose-based foam material had better performance.The foam material had a smaller pore size and a more uniform cell distribution.It could be almost degraded after three months.The density was 0.34 g/cm³,and the load was 4500.15 N in the compressive strength test.The stress is 1.19 MPa and the elastic modulus is 26.50 MPa.In the bending strength test,the load is 69.38 N,the stress value is 2.96 MPa,and the elastic modulus is 60.81 MPa,which has good mechanical properties.3.Using freeze-drying foaming method,esterification modified wheat straw as raw material,polyvinyl alcohol（PVA）as crosslinking agent,calcium carbonate（Ca CO₃）as reinforcing agent,water as foaming agent,the effects of them on the properties of wheat straw foaming material were studied,and the optimum process conditions of the foaming material were studied.The results show that when the amount of PVA is 3.5 g,the amount of water is 22 g,the amount of Ca CO₃is 0.24 g,and the amount of raw material is 2 g,the density is 0.17 g/cm³,the specific surface area is 200 m²/g,the average pore size is 13.03 um,the porosity is 86.5%,the total pore size area is 1.384 m²/g,and the water absorption rate is 642.3%.It can be almost degraded after three months.In the compression strength,the load is1932.68 N,the stress is 4451.75 KPa,and the elastic modulus is 45.42 MPa,showing high mechanical strength.After 10 compression cycles,the stress is 38.41KPa,and the elastic recovery rate is 55.70%.In addition,the foam material modified by vacuum impregnation with 5 wt%phytic acid solution has the highest elastic recovery rate of 67.72%and high flame retardancy.