Flexible Piezoresistive Strain Sensors Made Of Cellulose Carbon Gel Composite Material

With the rapid development of wearable electronic devices,flexible strain sensors have a wide range of applications in health monitoring,biomedical,sports management,and electronic skin,etc.Traditional strain sensors based on metals or semiconductors have problems such as poor flexibility and low strain range.In recent years,a series of flexible materials have been fabricated by combining conductive nanomaterials such as carbon nanotubes,graphene,gold and silver nanowires with a flexible polymer matrix.These piezoresistive composite materials made of conductive nanomaterials and flexible polymers greatly promote the development of flexible strain sensors.However,these nanomaterials have disadvantages,such as difficult preparation and high cost,and these limit their wide applications.Cellulose,as the most widely distributed and most abundant biomass material in nature,has the characteristics of cheap raw materials,easy accessibility,sustainability,and environmental friendliness;related research shows that biomass-based cellulose aerogels can be obtained after high temperature treatment.A carbon gel with a three-dimensional conductive network structure can be built to prepare flexible piezo-resistive composite materials.Therefore,the development of flexible strain sensors based on biomass materials has the characteristics of low cost and environmental protection,and has a good development prospect.In this paper,waste paper and bamboo were used as raw materials for making cellulose.After a simple hydrothermal reaction,freeze-drying and high-temperature carbonization process,a cellulose carbon gel with a three-dimensional network structure was prepared.The cellulose carbon gel and silicone rubber were used to fabricate flexible composite materials with piezoresistive characteristics and the as-obtained composite material was successfully prepare a flexible strain sensor.The application of the strain sensor was explored as a wearable device in human body movement,health signal monitoring,and thermal physiotherapy.The specific research content and results are summarized as follows:1.Waste paper as raw material was used to obtain a good conductive cellulose gel through the pulping,freeze-drying and pyrolysis treatment,and then piezoresistive flexible paper carbon gel/silicone rubber composite materials was successfully prepared.The paper carbon gel/silicone rubber composite material is highly sensitive to the resistance change and shows a fast and repeatable dynamic load response.The sensor prepared has a stable and reliable strain response within 0-20% in an effective working frequency of 0.01Hz-10 Hz.After the paper carbon gel/silicone rubber composite material was subjected to 1000 cycles of compression loading,no significant attenuation of the composite material was observed.The as-obtained composite can not only be used to make strain sensors for monitoring human health signals,but also can be used for thermal physiotherapy.The flexible strain sensor based on paper carbon gel/silicone rubber composite material can monitor human body movement(such as walking)and human health(such as breathing).In addition,the sensor can also be used as a heater at the working voltage of 15 V and shows the temperature difference up to 20 degrees from the environment.The paper carbon gel/silicone rubber composite material has the dual functions of stress sensing and heating,and is of significance for the development of multifunctional flexible electronic devices.2.Bamboo fiber carbon gel was prepared by oxidation-drying-carbonization process using bamboos in Chongqing as raw materials.After being compounded with silicone rubber,bamboo carbon gel/silicone rubber composite materials were prepared.A flexible strain sensor made of the composite material has high piezoresistive sensitivity,short response time(50 ms),repeatability,and high stability.By adjusting the initial bamboo fiber slurry concentration,bamboo fiber carbon gels with different densities can be prepared.As a result,the smaller the carbon gel density is,the higher the piezoresistive sensitivity of the composite material is.The flexible strain sensor based on bamboo carbon gel/silicone rubber composite material can recognize human signals such as finger bending,breathing and sound,and has great potential for human health monitoring and human-computer interaction.In short,carbon-gel/silicone rubber composites based on waste paper and bamboo are used for monitoring human physiological signals due to their low price and moderate conductivity,have good applications in electronic skin,biopharmaceuticals,and wearable electronic devices.