Preparation of polymer-clay nanocomposites using emulsion polymerization : influence of clay modifiers on the final nanocomposites morphology

Greesh, Nagi Giuma (2006-12)

Thesis (MSc) -- University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: Modification of clay surfaces is an essential requirement for the formation of polymerclay nanocomposites. The clay surface can usually be modified by the replacement of inorganic cations on the clay surface by cationic surfactants. Further, clay has the ability to adsorb some organic compounds that have specific functional groups, such as sulphate and amides, by the formation of hydrogen bonds between these functional groups and hydroxyl groups of the clay. Therefore a clay surface can be treated using non-cationic organic compounds. The marn objective of this study was to modify a clay surface usmg 2-acrylamido-2-methyl-l-propanesulphonic acid (AMPS), and investigate the interaction occurring between AMPS and clay. The adsorption behaviour of AMPS was compared to organic molecules having similar groups namely: Sodium l-allyloxy-2-hydroxypropyl (Cops), N-isopropylacrylamide (NIPA) and Methacryloyloxy (MET). An understanding of the type of interaction between clay and organic modifier is useful in terms of understanding the mechanism of clay exfoliation in emulsion polymerization. The properties and structure of nanocomposites were characterized using SAXS, TEM, DMA, and TGA. The strncture of the nanocomposite was affected by the type of clay modifiers. Nanocomposites prepared using AMPS show an exfoliated structure, while other nanocomposites, i.e. those prepared using Cops, NTPA, and MET showed structures between intercalated and partially exfoliated. The mechanical and thermal properties of nanocomposites were found to be strongly dependent on the degree of clay distribution through the polymer matrix. The nanocomposites with exfoliated structures were found to have higher Tg values, improved mechanical prope1ties, and also better thermal stability than nanocomposites with intercalated structures.

AFRIKAANSE OPSOMMING: Die wys1g111g van 'n kleioppervlak is 'n belangrike vereiste v1r die vormmg van polimeer-klei-nanosamestellings. Gewoonlik kan die kleioppervlak gewysig word deur die anorganiese katione op die kleioppervlak te vervang met kationiese sepe. Boonop het klei die vermoe om sekere organiese verbindings met spesifieke funksionele groepe, b.v. sulfate en amiede, te absorbeer. Dit vind plaas d.m.v. die vonning van waterstofbindings tussen hierdie funksionele groepe en die hidroksielgroepe van die klei. Die kleioppervlakke kan dus met nie-kationiese organise verbindings behanclel word. Die hoofdoel van hierdie studie was om die kleioppervlak met 2-akrielamido-2-metiel-lpropaansulfoonsuur (AMPS) te wysig, en die interaksie tussen AMPS en klei te bestudeer. Die adsorpsiegedrag van AMPS is met organiese verbindings met soortgelyke groepe vergelyk (naamlik: natrium-l-alieloksi-2-hidroksiepropiel (Cops), N-isopropielakrielamied (NlPA) en metakrielolieloksi (MET)). 'n Begrip van die tipe interaksie tussen die klei en die organise wysiger is nuttig om die meganisme van kleiski lfering (Eng. clay exfoliation) in emulsiepolimerisasie beter te verstaan. Die eienskappe en struktuur van die nanosamestellings is met behulp van SAXS, TEM, OMA en TGA bepaal. Daar is bevind dat die tipe kleimodifiseerder 'n invloed op die struktuur van die nanosamestellings gehad het. Nanosamestellings wat met AMPS berei is, bet 'n geskilferde struktuur (Eng. exfoliated structure) gehad, terwyl die ander nanosamestellings (cl.w.s. die wat met Cops, NIPA en MET berei is) het strukture tussen die van ge·interkaleerde (Eng. intercalated) en gedeeltelike verskilfering (Eng. partially exfoliated) gehad het. Die meganiese en termiese eienskappe van die nanosamestellings het grootliks afgehang van die graad van kleiverspreiding in die polimeermatriks. Die nanosamestellings met 'n geskilferde struktuur het hoer 'l~-waardes, beter meganiese eienskappe, asook beter tenniese stabiliteit gahad as nanosamestellings met gei'nterkaleerde strukture.

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