Study On The Construction And Composite Mechanism Of Hydroxyethyl Cellulose Based Multifunctional Films

The rapid development of the Internet and the Internet of Things has turned people’s lives upside down and brought new demands and challenges.Flexible electronic devices and sensors play an important role in the development system of the Internet of Things as the hubs linking people,machines,and things.Different from traditional sensors,flexible sensors focus on the wearability of the human body and versatility.Hydroxyethyl cellulose(HEC),as a typical cellulose derivative,has the characteristics of abundant yield,low price,environmental protection,and strong processing capacity,and can be used as the matrix material of wearable devices.The development of flexible electronic devices based on cellulose can be improved significantly by using different nanomaterials and HECs to prepare multi-functional nanocomposites.To solve the above problems,firstly,cellulose nanocrystalline(CNC),arylon nanocrystalline(ANFs),hydroxyapatite nanowire(HNs)and HEC were used to construct single-layer composite films,to research the relationship between onedimensional nanomaterials and single function.Then boron nitride nanosheets(BNNS)were prepared by ball grinding assisted by high viscosity HEC solution,to study the relationship between two-dimensional nanomaterials and thermal conductivity.On the basis of improving the thermal conductivity and insulation properties of composite films,bifunctional Janus films were prepared by coating transfer process,and the effects of different AgNWs content on the electrical conductivity were studied.HEC/BNNS and graphene/AgNWs were used as upper and lower layers and core layers respectively to prepare sandwich structure composite films.The effects of AgNWs on the sensing properties and electromagnetic shielding properties of materials were studied.The influence mechanism of sandwich structure on self-supporting and stability was revealed.The main conclusions are as follows:(1)The mechanical properties and water resistance of HEC films were effectively improved by polyisocyanate(BPIC)and CNC.When the CNC content is 4%and BPIC content is 10%,the tensile strength and contact Angle of the composite film are 30.2 MPa and 100.1°,respectively,which are increased by 24.5MPa and 51.6° compared with the HEC film.The introduction of CNC reduced the aggregation phenomenon of HEC microspheres after crosslinking,and formed an isolated island between HEC and CNC complex.The strength of HEC matrix is improved and the problem of hydrophobicity of HEC as electronic packaging material is solved.(2)ANFs and HEC were mixed to produce three-dimensional interpenetrating stable network composite films,which enhanced the mechanical properties of the materials through hydrogen bonding and physical entangling.The electron conjugated structure of ANFs is used to give the film ultraviolet shielding properties,which solves the problems of poor mechanical properties and weak ultraviolet resistance of HEC in the field of outdoor equipment packaging materials.When ANFs content is 1.0 wt.%,the tensile strength and elongation at break of HEC/ANFs composite film are 55.6 MPa and 38.4%,respectively.ANFs improves the comprehensive mechanical properties of HEC/ANFs composites through the unique traction effect of one-dimensional nanofibers.When the ANFs content is 1.5 wt.%,the UPF value of HEC/ANFs composite film is 43.41.This significantly improves the UV shielding effect of HEC based composite films,which is conducive to the application potential of HEC as a packaging material in outdoor wearable devices.(3)The mussel-like structure was formed by the combination of polyhydroxyl inorganic HNs and organic HEC,which enhanced the electrical insulation performance of the composite film.When the HNs content is 20 wt.%,the characteristic breakdown strength and volume resistivity of the composite film is 12.7 kV/mm and 2.13 × 1011 Ω/cm,respectively,which are 32%and 120%higher than that of the HEC film.HNs formed a layered inorganic structure inside the HEC matrix,which could effectively reduce the damage of high voltage electric field on the film.This strengthens the resistance of the material to solves the disadvantage of poor insulation,which is conducive to the application of HEC in the flexible wearables field.(4)HEC/BNNS solution was obtained by liquid ball milling of boron nitride powder with high viscosity HEC solution.The preparation of nanomaterials and the production of polymers/nanomaterials are formed in one pot,which greatly reduces the production cost and preparation time.HEC solution can effectively reduce the damage and agglomeration of BNNS in the milling process,and improve the composite effect of BNNS and HEC matrix by organic modification of nanomaterials.When the BNNS content is 20 wt.%,the tensile strength,elongation at break and thermal conductivity of HEC/BNNS20 composite films are 34.0 MPa,51.0%and 0.234W·m-1·K-1,respectively.The results show that BNNS can effectively improve the mechanical properties and thermal conductivity of HEC materials,and HEC/BNNS composite films can be used as thermal management materials for flexible electronic devices.(5)The prepared HEC/BNNS(HB)film was used as thermal management matrix,and the surface of the film was coated with AgNWs to give the film conductive property.The Janus composite film with one side conducting electricity and the other side insulating and conducting heat was prepared and applied in flexible wearable devices as bending sensor and electric heater.When the concentration of AgNWs is 1.0 wt.%,the tensile strength,conductivity and thermal conductivity of HB/AgNWs composite film are 36.4 MPa,79.1 S/m and 0.244 W·m-1·K-1,and the film still has good bending sensing performance after 500 bending cycles.(6)One-dimensional AgNWs and two-dimensional electrostripped graphene(EG)were used to form a conductive core layer like a blade structure by vacuum assisted filtration method,and HB material was used as the upper and lower surface layer of thermal insulation.Multilayer composite film with sandwich structure is prepared,which can be used as motion sensor,flexible heater,and electromagnetic shielding layer in the field of flexible wearable devices.When AgNWs content is 20 wt.%,the HB/GA20/HB films have tensile strength up to 22.0 MPa.The double conductive network formed by AgNWs and EG has a good complementary effect,and the bending sensor still has good sensing performance after 1500 times.In this paper,one-dimensional nanomaterials are used to solve the problems of weak mechanical properties and poor insulation properties of HEC as flexible electronic devices.Moreover,BNNS is used to strengthen the thermal conductivity of materials.EG and AgNWs conductive core layer are introduced to construct the sandwich structure film,which has multifunctional characteristics of sensing,electrothermal conversion and electromagnetic shielding,effectively promoting the development of cellulose based flexible electronic devices.