Preparation And Properties Of The Cyanoethyl Cellulose Materials

With the development of electronic information industry,the demand has increased for high dielectric constant polymer substrates and capacitors such as miniaturized embedded devices.Thus,it is urgent to study polymer with high dielectric constant.In this thesis,Cellulose of different polymerization degrees was used as raw material,and cyanoethyl cellulose(CEC)was synthesized by different methods to prepare CEC membrane materials and composite membrane materials,whose structure and properties were studied.The main results are summarized as follows:(1)The CEC was synthesized by homogeneous and heterogeneous methods.The effects of synthesis method and polymerization degree of CEC on degree of substitution(DS)of CEC were studied.The research results showed that the polymerization degree of CEC had no obvious effect on the DS of CEC,but the synthesis method had a larger influence.The DS of CEC synthesized by homogeneous method increased with the increase of acrylonitrile content,and the maximum is 2;while the DS of CEC synthesized by heterogeneous method increased with the increase of reaction time,the maximum is 2.41.However,the DS of CEC was unchanged or decreased slightly for heterogeneous method when the reaction time increased and exceeding 2 h.The DS of CEC synthesized by heterogeneous method was higher than that of homogeneous method,meanwhile the relative DS of C-2 in CEC was higher than that of homogeneous method under the same total DS.(2)Dense CEC films were prepared by solution casting and thermocompression method.The effects of DS of CEC,synthesis method and molecular weight of CEC on the dielectric properties of CEC films were studied.The results indicated that the DS of CEC and synthesis method have a significant influence on the dielectric properties of CEC film,but the molecular weight of CEC has little effect.The dielectric constant increased with the increasing DS of CEC(low molecular weight)synthesized by homogeneous or heterogeneous method.The dielectric constant of CEC with medium and high molecular weight increased firstly and then decreased with the increase of the DS of CEC.The dielectric properties of CEC films synthesized by heterogeneous method were better than that of homogeneous method.(3)The porous CEC membrane was prepared by non-solvent induced phase separation(NIPS)technology.The effects of coagulating bath composition,concentration and molecular weight of polymer on CEC membrane aggregation structure and its dielectric properties were studied.The results indicated that using water,ethanol,DMF/H2O(65:35,w/w)as coagulation bath,and the dense membrane can obtained from DMF/H2O bath with a high dielectric constant.Increasing the concentration of polymer,the porosity of CEC membrane decreased but the dielectric constant increased.When the molecular weight increased gradually,the CEC membranes formed by the water bath changed from asymmetric structure with figher-like to stick-like intertwined symmetric structure.However,the symmetric CEC membranes formed by ethanol and DM F/H2O baths,their morphologies changed from cellular pores or flat pores to stick-like intertwined structure.The porosity decreases as the dielectric constant increases.(4)BaTiO3(BT)/CEC nanocomposite membrane was prepared by NIPS technology.The effect of the filling amount of BT nanoparticles on the dielectric properties of nanocomposite films was studied.The results showed that the dielectric constant increased gradually with the increase of the filling amount of BT nanoparticles,which dielectric loss remained constant.The dielectric constant reached the maximum when the filling amount of BT nanoparticles reached 80%and it was 40.51 at 100Hz.