| Aramid fiber is widely used in military protection,high-temperature gas filtration,automotive engineering and other fields due to its excellent physical,mechanical,and chemical properties.During the internship in the factory,the author found that aramid fiber has a higher moisture content in a high-humidity environment,and aramid fiber will be affected by the moisture content during actual trade,storage and use.At present,there is a lack of quantitative evaluation on the influence of different moisture content on the properties of aramid fibers and their fabrics.Therefore,this topic focuses on the structural properties of aramid fibers,the moisture absorption and tensile properties of aramid fibers under different moisture content conditions,and the aramid base The structural properties of aramid needle-punched nonwovens and the changes in their mechanical properties under different moisture content conditions have been studied in four aspects to provide reference for actual industrial trade,transportation and storage.The main research content and conclusions are as follows:(1)Structure and tensile properties of aramid fiberUsing three brands of aramid fibers from Shengou,Longbang,and Korea,the longitudinal surface morphology of the aramid fibers is relatively smooth using scanning electron microscopy.According to the spectrum of 4000-400cm-1 measured by the infrared spectrometer,it is found that the aramid fibers are There are obvious amide bond and benzene ring stretching vibration in this range;the crystallinity and orientation degree of aramid fiber measured by X-ray diffractometer are 44.5-54.5% and 54.2-56.0% respectively;measured by electronic fiber strength meter The breaking strength of aramid fiber under standard moisture content conditions is between8.3-9.3c N,the elongation at break is between 37.1-40.3%,and the initial modulus is between40.5-46.6c N/dtex.Aramid from different manufacturers There are certain differences in fiber tensile properties due to processing reasons.(2)The influence of different moisture content on the properties of aramid fiberThe moisture content of aramid fiber under standard atmospheric conditions measured by an eight-basket oven is basically between 7.05-7.30%,and the moisture content of aramid fiber from different manufacturers is slightly different.By recording the quality change of aramid fiber in the process of moisture absorption and desorption under a certain temperature and humidity,the moisture absorption and desorption curve is prepared,and the hysteresis of moisture absorption can be analyzed based on this: at constant temperature and humidity(20±2?,65 When placed under the condition of ±5%),when the moisture content of the aramid fiber is 10%,20%,and 30%,the time to reach the dynamic equilibrium of moisture release is 410-730 min,690-890 min,890-980 min,respectively,and reach the dynamic equilibrium of moisture absorption.The time is500-570min;when the environment of the aramid fiber is 16.7-18.5?,43.8-53.3%RH,and the moisture content of the aramid fiber is 10%,20%,and 30%,the time to reach the dynamic equilibrium of moisture release is 370 respectively.-550 min,550-640 min,620-820 min,the time to reach the dynamic equilibrium of moisture absorption is 530-580 min.Using pure water and 3.5%Na Cl two liquid media to prepare aramid fibers with moisture content of 10%,20%,and 30%,and testing their tensile properties under standard conditions,the results show that the aramid fiber has a moisture content of 10%.,20%,30%,the breaking strength compared with the standard moisture content of the breaking strength decreased by 5.2-12.7%,16.0-21.8%,21.2-28.5%,respectively;the elongation at break showed an upward trend with the increase of the moisture content.,But the overall change is small,and the maximum increase is 2.2-4.6%;the initial modulus shows a downward trend,decreasing by 5.1-25.0%,26.1-35.3%,and 29.8-50.0% respectively.The tensile properties after treatment with two media The difference is not big,but there are certain differences between the fibers of different manufacturers.(3)Structure and mechanical properties of aramid-based aramid needle-punched nonwovensThree kinds of aramid-based aramid needle-punched non-woven fabrics with a weight of550g/m2,a weight of 600g/m2 and a weight of 550g/m2 of finishing coating film were used.All the fabrics have hairiness on the reverse fiber,and the surface of the fiber becomes smoother after being coated and singed on the front,and the fiber after singeing has holes and damage,and there are obvious bonding points between the fabric fibers after the film.The longitudinal and transverse tensile strengths of three aramid-based aramid needle punched nonwoven fabrics under standard moisture content conditions measured by a multifunctional electronic fabric strength machine are719.2-1079.3N and 828.8-1493.7N respectively;the front and back sides The bursting strength is1667.8-2046.0N,1676.7-2124.5N;the longitudinal and transverse tearing strength are309.2-365.4N,318.7-375.5N,respectively.There are certain differences in the mechanical properties of aramid nonwovens of different specifications.(4)The influence of different moisture content on the mechanical properties of aramid-based aramid needle-punched nonwovensThree kinds of aramid-based aramid needle-punched non-woven fabrics with a weight of550g/m2 for finishing film,600g/m2 for finishing film,and 550g/m2 for finishing singeing,use pure water,3.5% Na Cl two liquid media were prepared into samples with water content of 10%,20%,and 30%,and the tensile,bursting,and tearing properties were tested under different water content conditions;the results showed that the film weight 550g/m2 fabric,when the moisture content is 10%,20%,30%,its longitudinal and transverse breaking strength are reduced by4.7-8.4%,3.8-14.2%,respectively;the fabric with a film weight of 600g/m2,its longitudinal strength The transverse breaking strength has decreased by 1.4-11.7% and 0.3-10.4% respectively;the longitudinal and transverse breaking strength of the aramid nonwoven fabric with a singeing weight of 550g/m2 has dropped by 12.2-18.5% and 11.5-18.9% respectively;For fabrics with a gram weight of 550g/m2,when the moisture content is 10%,20%,and 30%,the burst strength of the front and back sides decreases by 10.1-18.2% and 0.7-11.4% respectively;the gram weight of the film is 600g/m2 The bursting strength of the front and back side of the fabric has decreased by2.7-17.1% and 0.1-5.1% respectively;the singeing aramid nonwoven fabric with a weight of550g/m2,the bursting strength of the front and back side has decreased by 7.1-11.6,respectively %,15.3-21.3%;aramid nonwovens with a film weight of 550g/m2,when the moisture content is 10%,20%,and 30%,the longitudinal and transverse tearing strength are reduced by 18.7-29.3%,13.0-24.1%;the longitudinal and transverse tearing strength of the fabric with a weight of 600g/m2 of the film has decreased by 0.4-10.0% and 5.5-12.1% respectively;the fabric with a singeing weight of 550g/m2 has the longitudinal and transverse tearing strength Respectively decreased by8.7-17.4%,1.3-13.7%;the mechanical properties of the fabric treated with the two media have little difference.By testing the tensile properties of the fabric stored in the warehouse,comparing August and December,it is found that the tensile strength of the fabric will be reduced by about 10%under actual storage conditions. |
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