Study On Water Swellable Nitrile Rubber Modified By Polyacrylonitrile Fibers

Since the invention of water swellable rubber in the 1970 s,with its excellent elasticity and water swelling properties,it has been widely used in a variety of sealed waterproof areas.With the rapid development of industry,water swellable rubber products are required to be higher and higher performance.They are required to possess excellent mechanical properties,fast high-rate water absorption and low mass-loss rate after water absorption.For this purpose,this paper aims to find a suitable filler which can maintain high water swelling of water swellable rubber,but also improve its mechanical properties.In this paper,polyacrylonitrile fiber was selected as the main filler,and it hydrophilic modified by alkaline hydrolysis.The conditions of hydrophilic modification were optimized.The influence of hydrophilic modification on polyacrylonitrile fiber was analyzed by infrared spectroscopy and scanning electron microscope.In order to improve the compatibility between rubber and water-absorbent resin and improve the interfacial adhesion between rubber and fiber,nitrile rubber was hydrolyzed.The conditions of modification were optimized.The influence of hydrolytic modification on nitrile rubber was analyzed by infrared spectroscopy.Polyacrylonitrile fiber with and without hydrophilic modification,nitrile rubber and hydrolyzed nitrile rubber were used to prepare water swellable rubber.The effects of polyacrylonitrile fiber with and without hydrophilic modification on the mechanical properties and water absorption of water swellable rubber were studied.The formulation of water swellable rubber was optimized.Scanning electron microscope was used to visually examine the fracture surface of water swellable rubber systems.The interfacial adhesion parameters of these systems were calculated by the results of dynamic thermodynamic analysis in order to qualitatively evaluate the adhesion of water swellable rubber interface.The results shows that water swellable hydrolyzed nitrile rubber modified by hydrophilic polyacrylonitrile fiber possesses excellentmechanical properties,fast high-rate water absorption,low mass-loss rate after water absorption and good interface adhesion.The main results are as follows:(1)The conditions for the hydrolysis of nitrile rubber were optimized.The optimum reaction conditions are as follows: reaction temperature of 50?,reaction time of 24 h,NaOH concentration of 3mol/L and glycerol volume of 10 mL.The hydrolysis rate of nitrile rubber reached 6.07%.The successful hydrophilic modification of nitrile rubber was verified by infrared spectrum analysis.(2)The conditions of hydrophilic modified polyacrylonitrile fiber were optimized.The optimum reaction conditions are as follows: reaction temperature of 90?,reaction time of3 h,NaOH concentration of 3.75mol/L and glycerol volume of 20 mL.The base deweighting rate is 25.7%.The successful hydrophilic modification of nitrile rubber was verified by infrared spectrum analysis and scanning electron microscope analysis,the results showed that there were many grooves and protrusions on the surface of the polyacrylonitrile fiber,which created favorable conditions for the interfacial adhesion with rubber.(3)The optimal integrated performance of water swellable rubber modified by polyacrylonitrile fiber was obtained by addition of 10 phr polyacrylonitrile fiber and 60 phr water absorbent resin.Under the optimal conditions,the tensile strength and elongation at break in the direction of orientation were up to 6.37 MPa and 943.08%,respectively,while they were 5.86 MPa and 715.29% in the vertical direction.The Shore hardness climbed to74.The equilibrium time of absorbing water was shortened from 21 days for WSR without polyacrylonitrile fiber to 9 days for modified WSR.Besides the equilibrium mass of water absorption reached up to 570.34% with a mass-loss rate of 4.85%.When NBR is hydrolyzed,the performance of WSR is improved,but only to a point.The tensile strength and elongation at break in the direction of orientation were up to 7.43 MPa and 1096.42%,respectively,while they were 6.37 MPa and 731.82% in the vertical direction.The Shorehardness climbed to 69.It took 12 d for WSR to reach water absorption balance.Besides,the equilibrium mass of water absorption reached up to 617.95% with a mass-loss rate of4.13%.(4)The optimal integrated performance of water swellable rubber modified by hydrophilic polyacrylonitrile fiber was obtained by addition of 10 phr hydrophilic polyacrylonitrile fiber and 60 phr water absorbent resin.Under the optimal conditions,the tensile strength and elongation at break in the direction of orientation were up to 6.02 MPa and 843.75%,respectively,while they were 5.38 MPa and 652.93% in the vertical direction.The Shore hardness climbed to 73.The equilibrium time of absorbing water was shortened from 21 days for WSR without polyacrylonitrile fiber to 7 days for modified WSR.Besides the equilibrium mass of water absorption reached up to 592.17% with a mass-loss rate of3.92%.When NBR is hydrolyzed,the performance of WSR is improved,but only to a point.The tensile strength and elongation at break in the direction of orientation were up to7.08 MPa and 967.18%,respectively,while they were 5.67 MPa and 689.45% in the vertical direction.The Shore hardness climbed to 70.It took 9d for WSR to reach water absorption balance.Besides,the equilibrium mass of water absorption reached up to 664.89% with a mass-loss rate of 3.32%.(5)The mechanical properties and water absorption of water swellable rubber modified by polyacrylonitrile fiber and hydrophilic polyacrylonitrile fiber with the same components are compared and the conclusions are as follows: some of the fibers are easy to fall off and dissolved in the hydrolyzate in the hydrophilic modification process,which make the strength of polyacrylonitrile fiber decreased.The reinforced effect of WSR modified by hydrophilic polyacrylonitrile fiber is worse than that of WSR modified by polyacrylonitrile fiber;while at the same time,part of the cyano groups can be changed into hydrophilic groups by the hydrolysis of polyacrylonitrile fiber.It results that hydrophilic polyacrylonitrile fiber can play a good role in compatibilization and makewater absorbent resin adhesion better.Hydrophilic polyacrylonitrile fiber can also play the role of water channels to improve water absorption of water swellable rubber significantly.(6)After hydrolyzed,a small amount of cyano groups in the molecular chain of nitrile rubber can be hydrolyzed into hydrophilic groups,which can improve the compatibility with the water absorbent resin and disperse the water-absorbent resin evenly.It also can form strong interfacial adhesion with fiber,so that mechanical properties and water absorption of water swellable rubber are improved.(7)The scanning electron microscope analysis of water swellable rubber modified polyacrylonitrile fiber and hydrophilic polyacrylonitrile fiber with the same components was carried out to visually observe the fracture surface of water swellable rubber systems.Modified water swellable rubber with the same components of polyacrylonitrile fiber and hydrophilic polyacrylonitrile fiber were tested by dynamic thermodynamic analysis and the interfacial adhesion parameters of these systems were calculated.The results showed that water swellable hydrolyzed nitrile rubber system modified by hydrophilic polyacrylonitrile fiber possessed good interface adhesion.(8)The mechanism analysis showed that hydrophilic polyacrylonitrile fiber was composited with the rubber matrix by the synergistic effect of mechanical adhesion and molecular entanglement,which made the adhesion of the composites better.Water swellable hydrolyzed nitrile rubber modified by hydrophilic polyacrylonitrile fiber with excellent mechanical properties,fast high-rate water absorption,low mass-loss rate after water absorption and good interfacial adhesion were obtained.