Polypropylene/filler nanocomposites by melt compounding and in situ polymerization
[摘要] ENGLISH ABSTRACT: The properties of polymer nanocomposites depend greatly on thechemistry of the polymer matrices, the nature of the nanofillers, and the way inwhich they are prepared. Understanding the synthesis–structure–propertyrelationship of nanocomposites is vital for the development of advancedpolymer nanocomposites with enhanced mechanical strength, stiffness andtoughness for structural engineering applications. To this end, the primary aimof this study was to determine the impact that the preparation methods haveon the properties of PP/filler nanocomposites, with specific focus on the in situpolymerization of propylene via the methylaluminoxane (MAO) activatedmetallocene catalyst technique.Two different fillers (Silica and Calcium carbonate) were used assupport for the metallocene catalysts. Different supporting methodologies forthe synthesis of the supported catalyst were examined. A C2 symmetricmetallocene catalyst ansa dimethylsilylbis(2-methyl benzoindenyl) zirconiumdichloride (MBI) was used in this study. The catalyst systems were thenevaluated for propylene polymerization.The early observation shows that a direct adsorption of the metalloceneonto the filler has a diminishing effect on the catalyst productivity and thefillers had to be treated with MAO in order to avoid catalyst deactivation by thefiller surface. Due to the low productivity of the supported active species, thepresence of soluble catalyst active species, besides the supported activespecies is required in the synthesis of PP nanocomposites via in situpolymerizations.The syntheses of PP nanocomposites were carried out via in situpolymerization in which different quantities of MAO treated fillers were reactedwith pre-activated catalyst solution. The effect of the addition of MAO-filler onthe polymerization kinetics and consequently on PP matrix microstructure wasinvestigated. Changes in the in situ polymerization kinetics, compared tokinetics of homogeneous polymerization, were observed. Therefore, the microstructure of the polymer matrix was also influenced by the presence ofnanofillers in the polymerization media.The influence of the different synthesis methods on the performance ofthe nanocomposites was investigated using melt-mixed PP/fillernanocomposites obtained using PP homopolymer. The dispersed phasemorphologies of the different nanocomposites were investigated bytransmission electron microscopy (TEM). Results show that PPnanocomposites with improved filler dispersion were achieved by in situpolymerization compared to melt-mixed nanocomposites.The influence of the synthesis method on the crystallization behaviourof PP nanocomposites was also investigated. It was found that, for the in situprepared nanocomposites the tacticity of the PP matrix plays the major role indetermining the degree of crystallinity. Results also show that whennanocomposites with comparable PP matrices are compared, the overallcrystallization rate of the in situ polymerized nanocomposites is higher thanthat of the melt mixed nanocomposites.The mechanical properties of in situ polymerized PP and melt mixedPP nanocomposite were also investigated and compared. Due to improvednanoparticle dispersion in the PP matrix, in situ polymerized nanocompositesshow enhanced mechanical properties, especially tensile and impactproperties, compared to pure PP and melt mixed prepared nanocompositeswhen a PP matrix of equivalent microstructure was used.Finally, the melt compounding method was further investigated usingdifferent fillers and commercial PP as a matrix. The effect of filler type, sizeand applied surface coating on the flow and mechanical properties of PPnanocomposites was studied. The aim of this part of this study is to obtain agood trade-off between the processability and the mechanical properties andto gain insight into the cause of the emergence of different properties fornanocomposites prepared by melt compounding.
[发布日期] [发布机构] Stellenbosch University
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