Preparation Of Polyacrylic Acid / Cellulose Hydrogel Fibers And Study On The Adsorption Of Heavy Metal Ions

With the acceleration of industrialization,the composition of water quality is complex.In polluted water bodies,there are a large number of refractory substances such as heavy metal ions,organic dyes and some algae microorganisms.Heavy metal ions,which are difficult to degrade and easy to accumulate,are easy to enter the human body through the food chain,posing a certain threat to human health.The adsorption method is the most commonly used water treatment method.The selection of suitable adsorbent plays a key role in the adsorption effect.Sodium carboxymethyl cellulose hydrogel as a green new adsorption functional material,is a good choice.However,carboxymethyl cellulose-based hydrogels on the market have some disadvantages such as low strength,poor plasticity and poor adsorption effect.The main research purpose of this project is to prepare carboxymethyl cellulose-based hydrogel fibers with high tensile strength and good adsorption effect on heavy metal ions,to address water pollution more efficiently and environmentally friendly.In this paper,PAAS/CMC composite hydrogel fiber was prepared using sodium polyacrylate(PAAS)and sodium carboxymethyl cellulose(CMC)as raw materials by physical crosslinking method,and its strength could reach 26.9 MPa.The mechanical properties of PAAS/CMC composite hydrogel fibers with different CMC contents were tested.The results showed that the strength and tensile properties of hydrogel fiber were the best when the CMC quality fraction was 1%.The PAAS/CMC composite hydrogel fiber surface was coated with a layer of 3-5(?)m of polymethyl acrylate(PMA)or polybutyl acrylate(PBA),to fabricate core-shell fibers with the PAAS/CMC fiber as core and PMA or PBA coating as shell,namely PAAS/CMC-PMA hydrogel fiber or PAAS/CMC-PBA hydrogel fiber respectively.The improvement of PAAS/CMC composite hydrogel fiber performance by PMA and PBA were analyzed and compared.The results showed that coating with PMA or PBA significantly improved the stretchability of raw hydrogel fiber.The elongation at break reached 210±10%,the strength increased by 1±1.4 MPa.The mechanical properties of PAAS/CMC-PMA hydrogel fiber are better than those of PAAS/CMC-PBA hydrogel fiber.The hydrogel fibers were characterized by scanning electron microscope(SEM),X-ray diffraction(XRD)and infrared spectroscopy(FTIR).The results indicated that the gelation of hydrogel fiber is a physical process.The PAAS and CMC were well blended.Both PMA and PBA coated PAAS/CMC hydrogel fiber well and repair the cracks and wrinkles on the surface of the PAAS/CMC hydrogel fiber.Compared to the PBA,PMA coating is better.TGA analysis showed that the thermal stability of hydrogel fibers coated with PMA or PBA was better than that of PAAS/CMC composite hydrogel fiber.According to the test results of conductivity,CMC reduces the conductivity of hydrogel fiber,while PMA and PBA have little influence on the conductivity of PAAS/CMC hydrogel fiber.Under the condition that four kinds of hydrogel fibers are repeatedly stretched,the light intensity of the LED bulb can change in the circuit periodically.The water resistance test results of hydrogel fibers showed that both PAAS/CMC-PMA and PAAS/CMC-PBA hydrogel fibers had good water resistance.In the experiments of heavy metal ions of adsorption by PAAS/CMC-PMA hydrogel fiber and PAAS/CMC-PBA hydrogel fiber,the adsorption effects of Cu²⁺,Pb²⁺,Cd²⁺and Ni²⁺with different adsorption time,p H,temperature and initial concentration were studied.The results showed that the adsorption effect of PAAS/CMC-PMA and PAAS/CMC-PBA hydrogel fibers on metal ions was Pb²⁺>Cd²⁺>Cu²⁺>Ni²⁺,and the adsorption effect of PAAS/CMC-PBA hydrogel fiber is better than that of PAAS/CMC-PMA hydrogel fiber.There were competitive adsorptions among Cu²⁺,Pb²⁺,Cd²⁺and Ni²⁺,suggesting that the higher the molecular weight of the same periodic element,the better the adsorption effect,and the higher the period,the better the adsorption effect.To study the adsorption mechanism of these two hydrogel fibers,the kinetic model,the intra-particle diffusion model,and the isothermal adsorption model were employed to explain the adsorption process of PAAS/CMC-PMA and PAAS/CMC-PBA hydrogel fibers.The results showed that the adsorption process follows a quasi-second order kinetic model.That is,the adsorption process is controlled by chemical adsorption.From the intra-particle diffusion model,the two kinds of hydrogel fibers have three rate-determining steps in the adsorption process of heavy metal ions,and it is more likely to occur internal diffusion phenomenon at the first stage,have larger boundary layer effect at the second stage,balance at the third stage.The whole adsorption process was controlled by multiple adsorption stages.Overall,the adsorption isotherm of the adsorption experiments can be represented by the Freundlich isothermal adsorption model,indicating the adsorption of Cu²⁺,Pb²⁺,Cd²⁺and Ni²⁺by hydrogel fibers is not monolayer adsorption.But for the adsorption process of Pb²⁺,PAAS/CMC-PBA hydrogel fiber followed the Langmuir isothermal adsorption model,and it is single layer adsorption.By comparing K_Fand 1/n,it is concluded that both PAAS/CMC-PMA and PAAS/CMC-PBA hydrogel fibers had strong adsorption capacity for Pb²⁺.