Study On The Preparation And Dispersion Of PMMA/SiO₂ Grafted Composite Pre-dispersed Masterbatch

Inorganic nanoparticles were widely used in the functional modification of textile fibers,attributing to their excellent functional properties. However, agglomeration of nanoparticles inlarge scale is easy to occur due to their inherent hydrophilic and nanoscale features, whichgreatlly limits their applications.This theoretical study focuses on this agglomeration problem, taking silica ?SiO₂? as typicalfunctional nanoparticles and poly?methyl methacrylate??PMMA? as typical organic substrate.The dispersion of silica in monomer media, PMMA/SiO₂pre-dispersed masterbatches,PMMA/SiO₂melting blends and PMMA/SiO₂fiber were studied, respectively. The grafting andcrosslinking status of PMMA/SiO₂were further studied. Then the relation between thedispersion and the grafting and crosslinking status were explored, in order to clarify the diluteddispersibility and dispersion mechanism of accumulated SiO₂nanoparticles into PMMA matrix,and simultaneously to product PMMA/SiO₂fiber with high silica dispersion.Firstly, the grafting and crosslinking status of PMMA/SiO₂composites were studied. Silicawere modified by3-?trimethoxysilyl?propyl methacrylate ?MPS? and then re-dispersed intoMMA. After that, a series of PMMA/SiO₂composites with different silica content and differentgrafting percentage were prepared via in-situ bulk polymerization. The dispersion of silica inMMA and PMMA were observed by DLS, TEM and section-TEM. The grafting and crosslinkingstatus of the composites were analyzed by soxhlet extraction, HF etching, GPC and gravimetricmethod. It was found that the dispersion of silica in MMA and PMMA can be effectivelyimproved by MPS modification, and two types grafting and crosslinking status, simple graftedand complex grafted, can be obtained. In simple grafted type, only a simple PMMA grafted layerwas formed on silica surface. While in complex grafted type, a three-dimensional crosslinkedstructure with silica as crosslinked point was formed in the whole of PMMA/SiO₂composite,due to higher silica content and higher MPS coupling amount and then higher PMMA graftingpercentage.Secondly, the dispersibility of the accumulated silica on melting shear field was studied.PMMA/SiO₂grafting composites with higher silica content were took as pre-dispersed masterbatches and melt-mixed with PMMA resin to prepare a series of PMMA/SiO₂blends withlower silica content. The effectes of silica content and grafting status on the dispersion of slicawere investigated, and the dispersion evolution of accumulated silica particles duringmelt-mixing process was monitored by section-TEM. It was found that the effect of graftingstates of pre-dispersed masterbatches on the dispersibility of accumulated silica particles wasvery obvious. Non-grafted silica particles were easily agglomerated into sub-micron levelaggregation in PMMA melt due to their poor compatibility. The accumulated silica particles incomplex grafted pre-dispersed masterbatche can't be released and then diffused into the matrixphase. Only the simple grafted pre-dispersed masterbatche can be swelled by matrix polymer andthen be torn by strong shear field force. Thus the accumulated silica particles in them canconstantly migrated from pre-dispersed masterbatche phase into matrix phase, and finally can beuniformly dispersed in the entire matrix phase at a primary-particles-size-level.Finally, the application of PMMA/SiO₂grafted composites in electrospinning was studied.Simple grafting pre-dispersed masterbatches were solution blended with PMMA and then themixed solution were electrospined to prepard a series of sub-micron level PMMA/SiO₂fiber. Thedistribution and dispersion of silica were measurd by elution experiments and section-TEM. Theeffectes of spinning recipe and parameters on silica dispersion in fiber were investigated, and aformation mechanism of PMMA/SiO₂composite fiber during solution blend and electrospinningprocesses was proposed. Above that, a primary-particles-size-level-dispersion status of silica inthe inner of PMMA/SiO₂composite fiber can be achieved.The above results are favourable for achieving the primary-particles-size-level-dispersion offunctional inorganic particles in monomer medium, in polymer matrix and in fiber interior, andthus they also can be used to guide the produce of functional composite fiber via melt spinningand electrospinning.