Preparation And Properties Of Starch Based Flexible Conductive Materials And Flexible Electronic Devices

With the development of science and technology,flexible electronic equipment is gradually entering people’s daily life.However,the traditional flexible substrates are expensive,complex structure,non-degradable and difficult to recycle.Starch based material could effectively solve the above problems.However,the properties of ordinary starch gel were not good.Aiming at these defects,starch based flexible hydrogel was prepared from high amylose starch by using calcium chloride solution to deconstruct its starch granules.On this basis,the materials are further optimized to improve its sensing sensitivity,and a series of starch based flexible electronic devices such as flexible battery and self-powered sensing materials are designed and developed.The specific research work is as follows:Firstly,the preparation process of starch based ionic conductive materials was discussed.It was determined that the concentration of calcium chloride solution was 33%,and the ratio of starch to calcium chloride was 2.5:2.0～2.5:3.1.Secondly,the properties of the material were investigated:the elongation at break was determined to be 16～32%,the young’s modulus was4～9 MPa and the resistivity was 3.7～9.2Ω·m.Besides,it had the stimulation response of strain and could be used for the sensing of human fingers,footsteps,sound and expression met the needs of conventional wearable devices.Then the structure of the material was investigated:the main structure of the material was composed of starch chain network and water.Some calcium ions could coordinate and combine with starch chain to increase the winding between starch chains.Most of the ions are conductive media provided electrical conductivity in the gel system.Subsequently,the performance of the material was optimized.Glycerol was added to the system to weaken the hydrogen bonding between starch chains,formed a starch/Ca/glycerol composite conductive hydrogel and enhanced the tensile properties and electrical conductivity of the material.It was found that the elongation at break of the material was increased to 208%,the young’s modulus was reduced to 770 kpa,and the conductivity increased to 1.35 S/m after glycerol addition.The sol-gel transition of the material was at about 65℃and the material had reprocessing and self-healing properties according to this characteristic.The conductivity and mechanical properties of the material did not change significantly after secondary processing.After 5 hours of self-healing,the material could basically return to the original mechanical properties.At the same time,the glass transition temperature（T_g）of the material was-55℃,indicated that the material had certain low temperature resistance.Finally,according to the mechanism of galvanic cell,metal powder was added to starch/Ca/glycerol composite hydrogel to form positive and negative pole of battery.The starch based flexible battery was constructed by driving electrons from negative electrode to positive electrode by redox potential difference.The voltage of Zn/Cu battery was 0.81 V,the voltage of Fe/Cu battery and Sn/Cu battery were 0.65 V and 0.3 V respectively,and the voltage of Zn/H₂battery was 0.59 V.At the same time,starch based flexible battery had stimulated responsing performance and its output current would increase with the increase of pressure or deformation.After it was cycled compressed for 1000 times under 20%deformation,its current change could still correspond to the compression action.In addition,the T_g of starch based flexible battery was-55℃,which had certain frost resistance property.Then,the materials were formed into a flexible self-powered sensing material,and its sensitivity under different stress ranges was measured to be 1.54 kpa^-1（0～10 k Pa）,0.68 kpa^-1（10～80 k Pa）and 0.10 kpa^-1（80～400 k Pa）,which was much higher than before.Through calculation,it could discharge 2.1×10⁵ times under cycle compression of current variation of 1500%with certain use stability.When it was used for sensing,it could generate current response to pulse beating,clapping,finger bending,throat vibration,foot activity,etc.without external power supply.When testing pulse signal,the generated signal was more obvious than before,and the sensitivity was further improved.