In-situ Load Modification On The Surface Of Aramid Ⅲ Fiber And Microwave Absorbing Properties Of The Products

Microwave absorbing materials can convert electromagnetic energy into heat energy or dissipate it through interference,and have important applications in the fields of military stealth and electromagnetic radiation protection.Conductive polymers have gradually become a class of light-weight microwave absorbing materials that have attracted much attention due to their superior electrical loss and outstanding light characteristics.Polypyrrole（PPy）and polyaniline（PANI）have become the two conductive polymers that have attracted much attention in the research of lightweight microwave absorbing materials due to their simple synthesis method,good stability and excellent electrical loss performance.However,with the further development of aerospace technology and military weapons,mechanical properties are further demanded for microwave absorbing materials,especially when the material needs to be stretched or folded.Many research groups have carried out research work on the combination of PPy and PANI with fiber materials,but the poor mechanical properties of traditional fiber materials cannot content the application requirements of high-strength microwave absorbing materials in military defense and aerospace.Aramid Ⅲ fiber（F3 fiber）has excellent fatigue resistance,wear resistance and mechanical properties.The composite of F3 fiber and conductive polymer is expected to obtain a class of high-strength lightweight absorbing materials,which will be used as a basis for further accelerating the accumulation of such composite products in the field of aerospace devices.In this paper,the in-situ modification of PPy and PANI on the surface of F3 fiber was studied,and the microwave absorbing properties of the composite product were discussed.The main works and contribution are as follows:（1）PANI/F3 were prepared by in situ different doping PANI on the surface of F3 fiber,with ammonium persulfate as oxidant,hydrochloric acid（HCl）,sulfuric acid（H₂SO₄）,phosphoric acid（PHA）,p-toluenesulfonic acid（PTSA）,oxalic acid（OA）as dopants,and the effects of dopant types on the absorbing properties of the composites were investigated.Selected HCl as the dopant,investigate the effect of oxidant concentration on the absorbing properties of the composite product,and obtain the optimal absorbing agent concentration（0.05 mol/L）.on the basis.The effect of dopant concentration on the microwave absorbing properties of the composite product was investigated,and the dopant concentration（0.7 mol/L）of the best microwave absorbing properties was obtained.The results show that under the optimal synthesis process,the minimum reflection loss of the prepared HCl-PANI/F3composite product reaches-18.6 dB at 14.8 GHz,and the effective microwave absorption bandwidth is 11.2-18.0 GHz,and the corresponding simulated thickness is 2.5 mm.（2）Three kinds of PPy/F3 were prepared by in situ different doping（oxalic acid（OA）,phosphoric acid（PHA）and sodium dodecylbenzenesulfonate（SDBS））PPy on the surface of F3 fiber,with FeCl₃ as oxidant,classify the products as PPy/F3-1,PPy/F3-2 and PPy/F3-3.Then,in situ PANI on the surface of three PPy/F3 composite products to obtain PANI/PPy/F3with PPy and PANI loaded at the same time,which were recorded as PANI/PPy/F3-1,PANI/PPy/F3-2 and PANI/PPy/F3-3.On this basis,the microwave absorbing properties of the six composite products were analyzed and compared.The results show that the three PANI/PPy/F3 products have better microwave absorbing properties than the corresponding PPy/F3 products.Among them,PPy/F3-3,PANI/PPy/F3-1 and PANI/PPy/F3-3 have relatively good absorbing properties,and the minimum reflection loss of PPy/F3-3 samples reaches-41.2 dB at 17.2 GHz.The effective absorption bandwidth is 12.5-18.0 GHz,and the corresponding thickness is 2.4 mm;the minimum reflection loss of the PANI/PPy/F3-1 sample reaches-39.7 dB at 12.2 GHz,and the corresponding effective absorption bandwidth is 8.2-18.0 GHz,correspondingly the thickness is 3.4 mm.At a thickness of 1.7 mm,the minimum reflection loss of the PANI/PPy/F3-3 sample is-24.5 dB at 18.0 GHz,the corresponding effective absorption bandwidth is 11.8-18.0 GHz,and the thickness is 2.2 mm,PANI/PPy/F3-3 The sample exhibits an effective absorption bandwidth of 8.2-18.0 GHz with a corresponding minimum reflection loss of-17.4 dB.（3）Fe₃O₄/F3 was prepared by in situ Fe₃O₄ on the surface of oxalic acid-modified F3fiber by co-precipitation method,Then,in situ doping（oxalic acid,sulfamic acid,hydrochloric acid）PPy on the surface of t Fe₃O₄/F3 composite products to obtain three kinds of Fe₃O₄/PPy/F3,which were recorded as Fe₃O₄/PPy/F3-1,Fe₃O₄/PPy/F3-2 and Fe₃O₄/PPy/F3-3.On the basis of this,the microwave absorbing properties of the seven composite products were analyzed and compared.The results show that the Fe₃O₄/PPy/F3 series composite fiber products have better microwave absorbing properties than the Fe₃O₄/F3 and PPy/F3 series composite fiber products prepared under the same conditions.The minimum reflection loss of the Fe₃O₄/PPy/F3-2 sample reached-27.1 dB at 18.0 GHz,the effective absorption bandwidth was 12.2-18.0 GHz,and the corresponding thickness was 2.4 mm.