Polypropylene/filler nanocomposites by melt compounding and in situ polymerization

Soltan, Omar (2010-12)

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: The properties of polymer nanocomposites depend greatly on the chemistry of the polymer matrices, the nature of the nanofillers, and the way in which they are prepared. Understanding the synthesis–structure–property relationship of nanocomposites is vital for the development of advanced polymer nanocomposites with enhanced mechanical strength, stiffness and toughness for structural engineering applications. To this end, the primary aim of this study was to determine the impact that the preparation methods have on the properties of PP/filler nanocomposites, with specific focus on the in situ polymerization of propylene via the methylaluminoxane (MAO) activated metallocene catalyst technique. Two different fillers (Silica and Calcium carbonate) were used as support for the metallocene catalysts. Different supporting methodologies for the synthesis of the supported catalyst were examined. A C2 symmetric metallocene catalyst ansa dimethylsilylbis(2-methyl benzoindenyl) zirconium dichloride (MBI) was used in this study. The catalyst systems were then evaluated for propylene polymerization. The early observation shows that a direct adsorption of the metallocene onto the filler has a diminishing effect on the catalyst productivity and the fillers had to be treated with MAO in order to avoid catalyst deactivation by the filler surface. Due to the low productivity of the supported active species, the presence of soluble catalyst active species, besides the supported active species is required in the synthesis of PP nanocomposites via in situ polymerizations. The syntheses of PP nanocomposites were carried out via in situ polymerization in which different quantities of MAO treated fillers were reacted with pre-activated catalyst solution. The effect of the addition of MAO-filler on the polymerization kinetics and consequently on PP matrix microstructure was investigated. Changes in the in situ polymerization kinetics, compared to kinetics of homogeneous polymerization, were observed. Therefore, the microstructure of the polymer matrix was also influenced by the presence of nanofillers in the polymerization media. The influence of the different synthesis methods on the performance of the nanocomposites was investigated using melt-mixed PP/filler nanocomposites obtained using PP homopolymer. The dispersed phase morphologies of the different nanocomposites were investigated by transmission electron microscopy (TEM). Results show that PP nanocomposites with improved filler dispersion were achieved by in situ polymerization compared to melt-mixed nanocomposites. The influence of the synthesis method on the crystallization behaviour of PP nanocomposites was also investigated. It was found that, for the in situ prepared nanocomposites the tacticity of the PP matrix plays the major role in determining the degree of crystallinity. Results also show that when nanocomposites with comparable PP matrices are compared, the overall crystallization rate of the in situ polymerized nanocomposites is higher than that of the melt mixed nanocomposites. The mechanical properties of in situ polymerized PP and melt mixed PP nanocomposite were also investigated and compared. Due to improved nanoparticle dispersion in the PP matrix, in situ polymerized nanocomposites show enhanced mechanical properties, especially tensile and impact properties, compared to pure PP and melt mixed prepared nanocomposites when a PP matrix of equivalent microstructure was used. Finally, the melt compounding method was further investigated using different fillers and commercial PP as a matrix. The effect of filler type, size and applied surface coating on the flow and mechanical properties of PP nanocomposites was studied. The aim of this part of this study is to obtain a good trade-off between the processability and the mechanical properties and to gain insight into the cause of the emergence of different properties for nanocomposites prepared by melt compounding.

AFRIKAANSE OPSOMMING: Die eienskappe van polimeer nanokomposiete hang grotendeels af van die chemie van die polimeer matriks, die wese van die nano-vullers, en die manier waarop hierdie materiale berei word. Om die sintese-struktuureienskap verwantskap te verstaan is noodsaaklik vir die ontwikkeling van gevorderde nanokomposiete met beter meganiese eienskappe, styfheid en taaiheid vir strukturele ingenieurstoepassings Die primêre doelstelling van hierdie studie was dus om die impak van voorbereidingsmetodes op die eienskappe van PP/vuller nanokomposiete te bestudeer, met spesifieke fokus op die in-situ polimerisasie van propileen met metiel alumoksaan-geativeerde metalloseen kataliste. Twee verskillende vullers (silika en kalsium karbonaat) is gebruik as ondersteuning vir die metalloseen kataliste. Verskillende metodiek is gebruik om die ondersteunde kataliste te berei. ‘n C2 simmetriese metalloseen katalis ansa-dimetielsiliel(2-metiel bensoindeniel) sirkonium dichloride (MBI) is in die studie gebruik. Die katalissisteme is daarna evalueer vir propileen polimerisasie. Daar is oorspronklik vasgestel dat direkte adsorpsie van die metalloseen op die vuller ‘n negatiewe effek op die katalis aktiwiteit gehad het, en dat die vuller oppervlak eers met MAO behandel moes word om deaktivering van die katalis deur die vuller-oppervlak te vermy. As gevolg van die lae aktiwiteit van die ondersteunde aktiwe katalisspesies, is die teenwoordigheid van opgeloste aktiewe katalis nodig vir die voorbereiding van PP nanokomposiete via in situ polimerisasie-reaksies. Die sintese van PP nanokomposiete is uitgevoer deur in –situ polimersiasie waartydens verskillende hoeveelhede MAO-behandelde vullers gereageer is met vooraf-geaktiveerde katalis oplossings. Die effek van die byvoeging van MAO-vuller op die polimerisasie-kinetika en gevolglik op die PP matriks mikrostruktuur is ondersoek. Dit is gevind dat die mikrostruktuur van die polimeer-matriks beinvloed word deur die teenwoordigheid van nanovullers in die polimerisasie-medium. Die invloed van verskillende bereidingsmetodes op die eienskappe van die nanokomposiete is ondersoek deur smelt-vermengde PP/vuller nanokomposiete te maak. Die dispersie-fase morfologie van verskillende nanokomposiete is ondersoek deur transmissie elektron mikroskopie (TEM). Resultate wys dat PP nanokomposiete met verbeterde vuller-dispersie berkry is deur in situ polimerisasie in vergelyking met die smelt-vermengde materiale. Die effek van die sintese-metode op die kristallisasie van die PP nanokomposiete is ook ondersoek. Daar is gevind dat, vir die in situ bereide nanokomposiete, die taktisiteit van die PP matriks die grootste rol speel in die bepaling van die persentasie kristalliniteit. Resultate het ook gewys dat, wanneer nanokomposiete met soortgelyke PP matrikse vergelyk word met die in situ nanokomposiete, die laasgenoemde se tempo van kristallisasie hoer is as vir die smelt-vermengde nanokomposiete. Die meganiese eienskappe van die in situ bereide en smelt-vermengde PP nanokomposiete is ook ondersoek en vergelyk. As gevolg van verbeterde nano-partikel dispersie in die PP matriks, het die in situ bereide nanokomposiete beter meganiese eienskappe openbaar, in vergelyking met die smelt-vermenge nanokomposiete, veral trek- en slagsterkte. . Laastens is die smelt-vermengings metode verder ondersoek deur gebruik te maak van verskillende vullers en kommersiële PP as matriks. Die effek van die tipe vuller, die grootte en die oppervlakbedekking van die vullerpartikels op die vloei en meganiese eienskappe van die PP nanokomposiete is ondersoek. Die doel van hierdie studie was om ‘n balans te kry tussen prosesseerbaarheid en meganiese eienskappe en om insig te verkry oor die verskille in eienskappe wat openbaar word wanneer smeltvermengde nanokomposiete bereie word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/5310
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