Preparation And Properties Of Plant Fiber Reinforced Starch-based Foam

At this stage,foamed plastic products have become an indispensable part of human daily life.They have been widely used in many industries and fields such as agriculture,industry,and service industries.At present,a wide range of foam materials are obtained by various types molding method using petroleum and petroleum derivatives as substrates.However,petroleum based foams are difficult to degrade,have low recycling rates,and bring a great burden on the natural environment.The starch based foam has the advantages of renewable raw materials and complete biodegradation.Therefore,there is great prospect in replacing petroleum based foams.In addition,the starch based foam prepared from natural corn starch has poor flexibility,cushioning and mechanical properties,and ultimately affects the application properties of the product.In this study,the method of destroying the hydrogen bond of starch plasticization modification was used to disorder the molecular structure of starch and improve the plasticization of natural starch.By utilizing the characteristics that the plant fiber has a large aspect ratio and similar molecular structure to the starch,a network structure is constructed in the foam material to serve as a mechanical support skeleton to improve the compression mechanical properties of the foam material.The main findings are as follows:(1)A small internal mixer was used as a corn starch plasticizing tool.The glycerin,ethylene glycol,formamide and composite plasticizer were used to plasticize the corn starch,and the effect of the dosage on the plasticizing effect of corn starch was discussed.The results showed that the four plasticizers can destroy the crystal structure of starch and form intermolecular hydrogen bonds with starch.And the best plasticizing effect was formamide,followed by composite plasticizer and glycerin,and glycol had the worst plasticizing effect.When the composite plasticizer plasticizes the modified starch,its plasticizing effect on the starch did not produce synergy and resistance,but a simple blending effect was produced.When the ratio of starch to formamide is 10:4.5,the plasticization modification effect on corn starch was the best.(2)The optimum process conditions for starch based foam were studied by orthogonal experiments and single factor experimental design methods.The physical,mechanical properties and optimum conditions of starch based foam that was based on plasticized modified starch were studied by the amount of PVA,foaming temperature and the amount of montmorillonite.The results showed that the optimum conditions for the preparation of starch based foam were:foaming temperature of 145°C,foaming time of 4 min,PVA solution concentration of25%,PVA content of 40%and AC content of 3%relative to starch mass ratio,and montmorillonite content accounts for 4%of the starch mass ratio.Under these conditions,starch based foam had a density of 0.460 g/cm~3,a porosity of40.1%,a rebound rate of 51.5%,a compressive strength of 2.020 MPa,a elastic modulus of 1.9 MPa,and had good compression mechanical strength.In addition,montmorillonite as a nucleating agent could effectively improve the cell structure of starch based foam,increase the porosity of starch based foam,and reduce the density.(3)In order to further improve the compression mechanical of starch based foam,the effects of the amount of hardwood fibers and softwood fibers on the properties of starch based foam were investigated by single factor experiments.The result showed that the compressive strength of plant fiber reinforced starch based foam mainly depends on the network structure formed between plant fibers and starch,and the strength of the fibers themselves to resist the damage of the internal structure of the foam by external forces.The plant fiber could effectively reduce the density of the starch based foam and increase its compressive strength.Among them,when the addition amount of hardwood fiber was 5%,the compressive strength of starch based foam was the best,reaching 6.062 MPa;when the addition amount of the softwood fiber was 6%,starch based foam had the best compressive strength of 7.431 MPa.Due to its high fiber strength,The softwood fiber had a relatively uniform network structure with plasticized modified starch,which made the starch based foam have better compressive strength.In summary,the starch based foam prepared by using plasticized modified starch as a substrate had good cushioning and compression mechanical properties.The addition of montmorillonite could effectively adjust the cell structure of the starch based foam and improve the performance of foam.In addition,because of the good compatibility between the starch and plant fibers,the addition of plant fibers could be combined with the starch substrate to form a network structure,thereby effectively improved the compression mechanical properties of the starch based foam,which was a good promotion for the practical application of starch based foam.