| Currently,electromagnetic pollution from electronic devices has become a serious threat to human health and the safe use of sophisticated electronic devices,and has received widespread attention from researchers worldwide.Conductive textile materials with good electrical conductivity and stable structure have important application prospects in the field of aerospace,intelligent electronics and other electromagnetic shielding protection.Among them,biomass-based charcoal fabrics derived from the charring of cotton textiles have a greater potential for application due to their lightness and flexibility,heat and weather resistance and structural stability.In addition,the raw material has the advantages of natural availability,low cost and biodegradability,which is suitable for the current development of strong,light,wide,thin and green electromagnetic shielding materials.However,the traditional charred cotton fabric method requires strict oxygen limitation and generally has the disadvantages of being time-consuming,complex preparation process and harsh reaction conditions,which makes it difficult to meet its wide application and rapid development in flexible electromagnetic shielding materials.Therefore,how to explore a rapid,scalable and structurally controlled preparation conditions under air atmosphere has become the key issue of the day.In this paper,by constructing a modifiable carbon formation coating on the surface of cotton fibres with the aid of an intumescent flame retardant,which undergoes rapid pyrolysis under high temperature and air atmosphere,an oxygen barrier protective intumescent carbon layer is formed on the surface of cotton fibres;the micro-inert environment formed can effectively promote the conversion of cotton fibres into highly graphitized carbon materials and achieve conductive conversion while promoting the carbon formation of cotton fibres.Based on this,this thesis investigates the effects of charring temperature,time and loading on the structure,composition and electrical conductivity of the charred fabric,explores the formation and evolution of the conductive char structure,and investigates its effect on the electromagnetic shielding performance and its constitutive relationship;then,using the prepared conductive char fabric as the substrate,two types of conductive char fabric-based electromagnetic shielding composites are prepared by in situ physical adsorption and chemical modification.The structure and morphology of these composites and their effects on the electromagnetic shielding properties were investigated.This high-temperature,short-time,airborne carbonization method is more efficient than the conventional preparation method and is expected to show significant overall advantages in flexible electromagnetic shielding materials.The main research and conclusions of this paper are as follows:(1)Formation mechanism and influencing factors of biomass conductive ca rbon fabric under air atmosphereUsing spraying technology,the three components of ammonium polyphosphate,urea and silk glue protein were sprayed on the surface of cotton fabric in a certain ratio to construct an intumescent flame retardant coating.The effects of charring temperature,time and loading on the charring process and the structure and properties of the charred fabric were investigated.The results showed that the charring temperature was the most important factor affecting the electrical conductivity,and the electrical conductivity of the charred fabric gradually increased with the increase of charring temperature.The study showed that the electrical conductivity of the fabric increased slowly with increasing charring time at 900 °C,but the shielding effectiveness increased and then decreased due to the increase in the gap between the fibres caused by the increase in charring time,which resulted in certain wave leakage behaviour.Finally,based on the optimum charring temperature and time,we discussed the effect of the content of the intumescent flame retardant on the electrical conductivity of the charred fabric and its shielding effectiveness,which tended to increase and then decrease with increasing loadings.Based on this,we concluded that at a loading of 5 mg/cm2 and charring at900 °C for 15 min,the electromagnetic shielding efficiency of the fabric reached a maximum of 29.04 d B,which can shield more than 99% of the electromagnetic waves.(2)Preparation of biomass conductive carbon/Ag NWs composite carbon ma terial and its performance studyA flexible electromagnetic shielding composite with high electrical conductivity and self-cleaning effect was prepared by using the above conductive carbon fabric as the substrate and spontaneously assembling highly conductive silver nanowires on the surface of the cotton fabric through capillary action,followed by PDMS treatment of the biomass conductive carbon/Ag NWs composite.The results showed that the composite achieved a square resistance of 2.32 Ω/sq and an average electromagnetic shielding efficiency of 68.52 d B when the silver nanowires were loaded at 4 mg/cm2.The PDMS coating not only gave the composite a hydrophobic effect of 141.8°,but also gave the material good mechanical properties.(3)Preparation of biomass conductive carbon/PPy composites and its perfo rmance studyThe conductive charcoal fabric was chemically modified in situ and polypyrrole was grown on its surface by in situ polymerisation to compensate for the wave leakage through the seams of the charcoal fabric caused by the high temperature charring process.The results show that the growth of polypyrrole further increases the electrical conductivity of the material,and when the polypyrrole is grown for 2 h,the square resistance of the composite can reach 13.57 Ω/sq,and the electromagnetic shielding effectiveness reaches28.22 d B.More importantly,the loading of polypyrrole further improves the thermal stability of the composite,and the residual carbon at 800 ℃ is 53.24%,63.18%,and63.18%,respectively,63.18%.This study provides a novel way of preparing charred conductive textiles by shorttime charring under high temperature and air atmosphere,and investigates the evolution and structural characteristics of charring under different conditions of air atmosphere,while the prepared charred textiles can also be used as a good conductive substrate and provide a good carrier for the preparation of flexible electromagnetic shielding materials. |
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