Doctoral Dissertations

Date of Award

8-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Polymer Engineering

Major Professor

Gajanan Bhat,

Committee Members

Roberto Benson, Joseph Spruiell, David Joy

Abstract

In this research, influence of different levels of Closite Na+ additives on the microstructure, morphology and mechanical properties of polymer products was studied. Importance was given to understand the additive level, extent of dispersion in matrix, change in microstructure and respective property observed in the end product. Polypropylene spunbond and meltblown web samples with various levels of Closite Na+ additives were produced and characterized. Injection molded polypropylene nanocomposite with 1 to 15 wt% nanoclay additives were also prepared and characterized for microstructure and mechanical properties.

Crystallization kinetics studies showed significant increase in crystallization rates on nylon 6 even at 0.25 wt % additives. Near surface and bulk stiffness of the film significantly increased in the presence of nanoclay additives. Intercalated and flocculated morphology was observed for all the polypropylene concentrate and the same morphology was retained in spunbond fibers also. About 25 to 30 % increase in cross direction tear strengths were observed for 1 to 2 wt % clay loading. Fibers with even as low as 1 % clay retains their morphology and integrity in bond point after thermal bonding. At higher weight percentage, stiffness of webs significantly increased and tear strength of webs decreased due to exclusion of excess clay platelets in the interspherulite regions.

Property benefits were not observed in the case of melt blown samples with nanoclay additives, but the additives were well dispersed in the fiber web. Compared to control meltblown webs, stiff and open web structure with high irregularity was obtained for samples with clay additive. In case of injection-molded polypropylene composite, significant increase in breaking energy was observed for sample with just with 1 wt % clay additive. At higher weight percentage, segregation was observed in the inter-spherulitic region and failure mode shifted from ductile to brittle.

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