Orientation Behavior Of Polyacrylate/SiO₂ Grafted Composite Microspheres In Shear Flow Field

With the rapid development of the chemical fiber industry,the market demand for diversified and functionalized chemical fiber is increasing.Filling one-dimensional materials in chemical fibers by in-situ orientation is a novel chemical fiber modification method,which not only enhances the mechanical properties,but also imparts special functions such as electrical conductivity and anti-UV ability.Furthermore,this method can promote the future development of chemical fiber production.Carbon nanotubes and carbon fibers are the most commonly used one-dimensional materials for orientationally filling modification of chemical fibers.However,these materials is difficult to be uniformly dispersed in the melt even after chemical modification.The poor dispersibility leads to the sharp increase of the viscosity of blend system,making the further molding very difficult.Inorganic nanoparticles possess a series of unique physical and chemical properties.Using them as modification materials can improve the basic properties of textiles,including strength,toughness,flexibility,elasticity,light stability and thermal stability,and endow textile with special functions,such as catalysis,energy storage,and magnetism.Therefore,the inorganic nanoparticles have been widely used in the field of chemical fiber textile.However,inorganic particles also have disadvantages such as poor compatibility,easy agglomeration,and non-durable functionality.To overcome these drawbacks,this study intends to use crosslinked polymer microspheres containing inorganic particle clusters to fill and modify fiber materials.Molecularly crosslinked polyacrylate microspheres(mcPA)and polyacrylate/SiO2 grafted composite microspheres(mcPA/SiO2)with different crosslinking degree and structure were prepared by in-situ micro-suspension polymerization,inwhich we use methyl methacrylate(MMA)and butyl acrylate(BA)and styrene(St)as the typical monomers,polyethylene glycol dimethyl acrylate(PEGDMA-550)and divinylbenzene(DVB)as the crosslinking agents,nano-SiO2 as the inorganic particles,and 3-(Trimethoxysilyl)propyl methacrylate(MPS)as the silane coupling agent.The influence of the amount and type of crosslinking agent and the content of Si02 on the crosslinking degree and structure of the microspheres was investigated by solvent extraction and 3D video microscopy.By adjusting the amount and type of crosslinking agent and the amount of SiO2,microspheres with controllable crosslinking degree and structure in a wide range could be prepared.In particular,when both crosslinking agent and SiO2 are present,the composite microspheres have a double crosslinking structure.Subsequently,mcPA microspheres with a gel content of-53.2%were used as the dispersed phase and were shear blended with PMMA by two-stage blending method.By adjusting premixed time of PMMA,flow field temperature,screw speed and mixing time,a very good orientationally filling result was obtained.We also obtained the phase diagram of the distribution of the dispersed phase morphology.The average length to diameter ratio of the dispersed phase can reach 14.68 under the optimum technological conditions,which are listed below:flow field temperature is 165 ?,premixed time of PMMA is 120 s,screw speed is 45 rpm,and mixing time is 120 s.When the temperature is too high or the PMMA premixed time is too long,the viscosity of PMMA will be too low,which is not favorable for the transfer of shear force.When the temperature is too low or the PMMA premixed time is too short,the PMMA viscosity will be too high,resulting in rapid dissociation and poor orientation of the microspheres.If the screw speed is too high,the crosslinking network will be destroyed,i.e.the microspheres will be excessively disassociated.On the contrary,if the screw speed is too low,the shear force cannot overcome the crosslinking and interfacial tension,making the microspheres difficult to be dispersed and deformed.The mixing time is also vital for the oriented filling.Too long mixing time will lead to excessive dissociation of the microspheres,and too short mixing time will keep the microspheres undeformed.Finally,the influence of crosslinking degree and crosslinking structure of mcPA microspheres and mcPA/SiO2 microspheres on the orientation morphology was investigated.In addition,the difference between molecularly crosslinking network and dual crosslinking network was analyzed,by which the phase diagram of morphological distribution of dispersed phase was obtained.The results show that both kinds of cross-linked microspheres can form oriented structure,and the flow field conditions of the two kinds of cross-linked microspheres are similar.The microspheres with a gel content of?53%have the best oriented state.Uniform flexible cross-linked network is also favorable for the formation of the oriented structure.When keeping other conditions unchanged,the mixing time required for the orientation of mcPA/SiO2 microspheres is shorter than that of molecularly crosslinking microspheres.Under appropriate technological conditions,with the extension of blending time,the microsphere first undergo a one-dimensional orientation process from spherical to ellipsoidal,then to rod-shaped or microfibrillar,and eventually to random fragments.At the same time,the SiO2 particle clusters inside the composite microspheres will undergo orientational rearrangement with the microspheres.Composite microspheres are easier to be dissociated and broken due to the heterogeneity of molecular/particle dual crosslinking structure.This should be the reason for the phenomenon abserved above.This study focuses on the deformation and orientation behavoir of mcPA/SiO2 grafted composite microspheres under strong shear interaction of external flow field.The purpose of this study is to construct the phase diagram of morphology distribution on the basis of oriented structure.The study can provide reference for oriented filling modification of chemical fiber materials.