| Recently,most of the plastic products used in the world are mianly refined from petroleum and plastic products provide fast and convenient in people's daily life,at the same time,they also give rise to a series of new problems to us.Petroleum-based plastics are non-degradable and difficult to recycle,and a large use of them will cause environmental pollution problems such as difficult disposal of global waste.Moreover,the depletion of oil has brought great threat and challenge to the production of petroleum based plastic products.Therefore,it's urgent to develop the research and development of green,biodegradable and sustainable new products.In this paper,potato starch(PS)was used as the main raw material to prepare a new biodegradable biomass foaming material by microwave heating.On the basis of the successful preparation of chitosan(CTS)/starch-based foams,the composite foams with different macrostructure and function were prepared by strengthening and plasticizing modification,and properties of foams were characterized to improve practical application advantages of starch based composites.The main research conclusions are as follows:(1)Chitosan/starch-based biological composite foams were successfully prepared by microwave expansion method,and the influences of molecular weight,mass fraction of chitosan and mass ratio of chitosan solution to starch on the properties of starch-based foam materials were investigated to determined the optimal foaming ratio of starch-based foams and revealed the binding mechanism of foam materials.The results showed that the molecular weight of chitosan was 4.4×10~5,the mass fraction of chitosan was 4%,and the mass ratio of starch to chitosan was4.2:3,the comprehensive properties of foams were the best.The starch-based foams prepared at this ratio have low porosity,high density and relatively high compressive strength,which is 1.077MPa.The amino group on the chitosan chain forms hydrogen bond with the hydroxyl group on the starch molecule and this interaction can not only make the starch-based foams have a certain mechanical strength,but also improve the thermal stability and enthalpy of foams.In addition,solubility tests in water showed that this hydrogen bond interaction could keep the morphology and structure of foams intact in water for a period of time,until the foam was completely decomposed after 30 days.(2)Four different kinds of biomass nanocellulose were used to enhance the modification of CTS/PS foams,and the differences in type and content of nanocellulose on structure and mechanical properties of starch-based composite foams were compared.The results showed with the increase of nanoscale cellulose content,the number of pores in starch-based foams decreased,the obturator rate and compressive strength increased significantly.Compared with nanocellulose crystals(CNC)with acicular structure,CNF with complex network structure had a relatively good effect on the mechanical strength of foam materials,especially cotton CNF had the most prominent effect on the enhancement of starch-based foams,and the compression strength of foam could reach to 1.311 MPa when the content of CNF was 1.2%.In addition,a large number of hydroxyl groups in nanocellulose bonded with starch,chitosan and other macromolecules,which enhanced the thermal stability of starch-based foams,and improved its glass conversion temperature and enthalpy.Through the water solubility test,it was found that the starch-based foams reinforced by nanocellulose could still be degraded by the microorganism in the environment,which confirmed that it is a kind of green environmental protection material.(3)Based on(1)(2),glycerol was used to plasticized CTS/PS foam and cotton CNF enhanced CTS/PS foam.The effects of glycerol concentration and soaking time on the macro and micro structure of foams were investigated to reveal the glycerin plasticizing mechanism of starch composite bubble and impacts on the thermal stability of materials.The results showed that after the plasticization of glycerol,the pore wall of foams were thickened,and the overall foams were soft and ductile,and had a certain stress buffering effect.With the increase of glycerol concentration and the prolonging of soaking time,the residual rate and density of glycerol in the foams increased gradually,and the rebound rate increased to 99%nearly.The peak pyrolysis temperature and glass transition temperature of the plasticized starch-based foams were lower than those of unplasticized starch-based foams,the compression property also showed a significant decrease trend,indicating that the addition of glycerol enhanced the rebound rate of foams,but compression property and thermal stability were decreased. |
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