Studies On The New Technology And Process Of Antistatic PAN Fiber Modified By Inorganic Particles

Polyacrylonitrile (PAN) fiber has many excellent performances, such as bright color, soft handle and mothproofing. So it was widely used in industry and civil field. But because of its high hydrophobicity and insulating property, PAN fiber has serious static electricity effect. This disadvantage has limited its using in more fields. The purpose of this paper is to improve the antistatic property of PAN fibers by inorganic particles.The study of inorganic particles modified antistatic fibers is still in leading strings. There are two kinds of inorganic antistatic agents in use. One is nano-carbon black filler. The fiber modified by the agent is black in color. This color limited its using in more fields, the other is metal oxide particles, using for manufacturing white antistatic fibers.The development direction of antistatic fibers is producing white fibers. At the same time, somethings must be taken into account. For example, the production technology is simple and easy to carry out, the holes of spinneret are not jammed by antistatic agents when spinning, the developed fiber has to keep antistatic property for a long time, and has good spinnability and mechanical property. So Zinc oxide (ZnO) and antimony doped tin oxide (ATO) as antistatic agents were first used to prepare antistatic PAN fiber in unique adding process in this paper.Through research on the morphological structure of PAN fiber in spinning process, a unique inorganic particles addition method has been determined That is , making use of the characteristic of loose structure of PAN as-spun fiber, we put stabilized ATO or ZnO suspension into preheat bath. When the as-spun fiber run through the preheat bath, due to concentration difference of ATO or ZnO particles between inside of the fiber and in the bath, ATO or ZnO particles would diffuse into the fiber through these micropores and grooves in the fiber surface. During the process of stretching and drying, these ATO or ZnO particles were embedded in thefiber and were orientated along the axis of the fiber. Then an electric access is formed in the cortex of the fiber, and the antistatic property of PAN fiber was improvedDuring PAN dope trickle concreting into as-spun fiber, due to the effect of phase separation and congelation, the crosslink density inside of PAN as-spun fiber is lower, the net work structure is loose, and there are many micropores inside of the fiber and in the fiber surface. The patterns of Polarizing microscope and SEM have proved that in the surface of PAN as-spun fiber produced by NaSCN process there are many grooves and micropores, the width of grooves and diameter of micropores are about hundreds of nanometer . The existence of these grooves and micropores provides good conditions for nano-ATO or ZnO particles diffusing into the fiber.The diffusion and transplant of inorganic particles toward PAN as-spun fiber in spinning process accords with Ficks law of diffusion and Brownian movement theory, based on Brownian movement formula and Einstein-Brownian displacement equation of sphericity particle movement, It is shown by analysis that the effect of improvement diffusion coefficient (D) is very limited through heighten diffusion temperature and increase diffusion time. But to reduce particle radius (r) and medium viscosity ( η ) will result in increase diffusion coefficient (D) in order of magnitudes. Therefore, in order to ensure that inorganic particles can diffuse into PAN as-spun fiber, we must prepare nano-ATO or ZnO suspension with low viscosity and good stability and dispersibility.The stabilizing and dispersing behavior of ATO or ZnO particles in aqueous solution were studied in order to prepare nano-ATO or ZnO suspension with low viscosity and good stability and dispersability, The effect of sort of disperser, amounts of ATO or ZnO, pH values and amounts of disperser on stability, dispersibility and rheological property of suspension systems were discussed. The properties of nano ATO suspension were characterized using sedimentation volume experiment, Zeta Potential, LaserSize Analyzer and TEM. The experimental results indicated that choice anion polyelectrolyte PAM as ZnO s disperser and cation polyelectrolyte PEI as ATO s disperser can make ATO or ZnO particles stably disperse in aqueous solution, which is electrostetic stabilization mechanism. The factors of amount of disperser, disperser molecular weight and dispersing time have bigger effect on the stability of suspension. When using PAM as the disperser of ZnO suspension and disperser molecular weight is 10,000, the amount of disperser is 6 % (relative to the amount of ZnO), the prepared suspension has the characteristics of good stability and dispersibility. When using PEI as the disperser of ATO suspension, and the amount of disperser is 8% (relative to the amount of ATO), pH value of the solution is 6-7, the prepared ATO suspension has good stability and dispersibility. The suspensions prepared by above-mentioned conditions are colloidal state and non-colloidal state mixing suspensions, their size distrbution have polydispersibility and their everage size are less than lOOnm, so they could satisfy the need of PAN fiber modification.In order to modify the antistatic property of PAN fiber, the surface finished ATO or ZnO suspension were put into preheat bath that is in spinning process. Depend on surface shape of PAN fiber in spinning process, the diffusion process of inorganic particles entering into fiber was deeply researched using TEM and EDM to observe the ATO or ZnO diffusion and distribution. When PAN as-spun fiber with high swelling run through preheat bath that contains suspension, inorganic particles in suspension firstly diffused toward fiber and adsorbed on fiber surface in quantity, then these particles diffused into fiber through microvoids in fiber formed during coagulation formation process and caused by the change of free volume of fiber. In addition, the low-ratio drawing to fiber in preheat bath also is advantageous to inorganic particles diffusing into fiber. The experiment results by TEM and EDM have proved that ATO or ZnO particles is certainly diffusing into PAN fiber, and mainly distributing in surface layer ofPAN fiber. The content of ATO or ZnO in finished fiber were measured by incineration test. When the content of ATO in suspension was 4%(wt.) and the content of PEI relative to ATO was 8%(wt.), the the content of ATO in finished fiber was 0.179 %. When the content of ZnO in suspension was 3%(wt.) and the content of PAM relative to ATO was 6%(wt), the the content of ZnO in finished fiber was 0.303 %.The effects of the amount of inorganic particle in suspension and the location of preheat bath on the properties of PAN fiber were studied. The results indicated: when the amount of ATO and ZnO in suspension were separately no less than 5 % and 3 %, no matter where the preheat bath was located, the modified PAN fiber has good antistatic property, the bulk resistivities of modified PAN fiber could reach 107-108SX#cm level, and dye uptake was improved and came to 90 % ? At the same time, the modified fiber still kept basically intrinsic mechanical property of common PAN fiber.In this paper, the structures of modified PAN fiber also were characterized, using TEM, XRD and DSC. The TEM study demonstrates that the average diffusion displacement of ATO and ZnO particles in fiber is about 100-200nm, only diffuse into surface layer of PAN fiber and doesn't cuase large influence on the main structure of fiber. So the mechanical property of PAN fiber modified by inorganic particle kept basically invariable compared with pure PAN fiber,and influenced neither spinnability or service performance of fiber. The studies of XRD showed that the crystalline morphology and degree of crystallinity of modified PAN fiber ware hardly changed, despite of differ in the amounts of ATO or ZnO and the position of preheat bath. The studies of DSC explained that the glass transition temperature of modified PAN fiber was hardly changed compared with pure PAN fiber, maintaining basically 100 °C. It shows the enter of inorganic particles doesn't changed the glass transition temperature of PAN fiber, it is of benefit to hot drawing and post treatment of modified PAN fiber.Depend on the analysis on TEM pattern of distribution of inorganic particles in fiber interior and equivalent electrocircuit of polymer/carbon black conductive composite system, and the amounts of inorganic particles diffusing into fiber measured by incineration test, it was concluded that the antistatic mechanism of PAN fiber modified by inorganic particles mainly followed Electroconductive channels Theory. With the PAN as-spun fiber drawn and dried and the volume shrinkage of the fiber occurred, inorganic particles diffused into the fiber contacted each other and formed local aggregational structure. Consequently, electroconductive channels was formed and the static charge accumuiated on PAN fiber would be emitted through the electroconductive channels.At the same time, from the TEM pattern the calculating results of distribution of ATO and ZnO particles in fiber, we know ATO and ZnO particles mainly distribute fiber circumference near fiber surface 100-200nm and arrangement rather compact. When activated electron jumps the potential formed by PAN matrix in fiber, from an electroconductive particle jumping another neighbouring particle, the tunnel electric current was formed. Hence, the antistatic effect of modifying PAN fiber in this study should has contribution of Tunnel Effect conducting electric charges.Finally, this study fruit has been successfully applied to a 1000 t/a production facilities. 1.5ton good quantity antistatic PAN fibers modified by ATO and ZnO have been produced, on the basis of kept basically intrinsic mechanical property(the breaking tenacity of the fiber was bigger than 3.0 cN/dtex ), the bulk resistivities of modified PAN fibers dropped 108il-cm level and the dye uptake of the fibers came to 90%.The post processing property of the fibers was all right and the outside material weaven by the fiber was bright color and soft handle, and the produced apparel bacically haven't antistatic phenomenon during dress and friction. The technology of product antistatic PAN fiber by adding inorganic particles in spinning process is advanced, and independence intellectual asset has been formed. Two patentsfor invention has been applied (one of them has been patented, the patent no. is ZL 03 1 41474.5 ),...