NANOCOMPOSITES OF POLYMERS WITH LAYERED INORGANIC NANOFILLERS: ANTIMICROBIAL ACTIVITY, THERMO-MECHANICAL PROPERTIES, MORPHOLOGY, AND DISPERSION

Open Access
Author:
Songtipya, Ponusa
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 08, 2010
Committee Members:
  • Evangelos Manias, Dissertation Advisor
  • Evangelos Manias, Committee Chair
  • Maria Del Mar Jimenez Gasco, Committee Chair
  • James Patrick Runt, Committee Member
  • Sridhar Komarneni, Committee Member
  • Gary Lynn Messing, Committee Member
Keywords:
  • ION-EXCHANGE REACTIONS
  • CLAY NANOCOMPOSITES
  • MECHANICAL-PROPERTIES
  • MONTMORILLONITE NANOCOMPOSITES
  • MODIFIED LAYERED SILICATES
  • POLYMER/LAYERED SILICATE NANOCOMPOSITES
  • ANTIFUNGAL ACTIVITY
  • HIGH DENSITY POLYETHYLENE
  • ANTIMICROBIAL ACTIVITY
Abstract:
In the first part of the thesis, polyethylene/layered silicate nanocomposites that exhibit an antimicrobial activity were synthesized and studied. Their antimicrobial activity was designed to originate from non-leaching, novel cationic modifiers –amine-based surfactants– used as the organic-modification of the fillers. Specifically, PE/organically-modified montmorillonite (mmt) nanocomposites were prepared via melt-processing, and simultaneous dispersion and antimicrobial activity was designed by proper choice of the fillers’ organic modification. The antimicrobial activity was measured against three micotoxinogen fungal strains (Penicillium roqueforti and claviforme, and Fusarium graminearum). Various mmt-based organofillers, which only differ in the type or amount of their organic modification, were used to exemplify how these surfactants can be designed to render antifungal activity to the fillers themselves and the respective nanocomposites. A comparative discussion of the growth of fungi on unfilled PE and nanocomposite PE films is used to demonstrate how the antimicrobial efficacy is dictated by the surfactant chemistry and, further, how the nanocomposites' inhibitory activity compares to that of the organo-fillers and the surfactants. An attempt to improve the thermomechanical reinforcement of PE/mmt nanocomposites while maintaining their antimicrobial activity, was also carried out by combining two different organically modified montmorillonites. However, a uniform microscopic dispersion could not be achieved through this approach. In the second part of this thesis, a number of fundamental studies relating to structure-property relations in nanocomposites were carried out, towards unveiling strategies that can concurrently optimize selected properties of polymers by the addition of nanofillers. Specifically, the dispersion-crystallinity-reinforcement relations in HDPE/mmt nanocomposites was investigated. The influence of a functional HDPE compatibilizer’s characteristics to the thermo-mechanical properties of their nanocomposites was systematically explored. The appropriate compatibilizer, based on HDPE-g-MA, was identified from achieving the best mechanical performance, i.e., maximizing the tensile modulus improvement without sacrificing the polymer ductility, which was found to be achieved where the smallest crystallinity change occured. It was revealed that lower-than-the matrix molecular weight HDPE-g-MA better enhanced the tensile properties across three HDPEs, compared to that of high viscosity HDPE-g-MA, while the flexural properties were not markedly affected by this parameter, but rather were mostly determined by the amount of clay nanofiller. Finally, polymer/layered double hydroxide (LDH, positively-charged layered clays, also termed as ‘anionic’ clays referring to their anion exchange capacity) were characterized as potential fillers for a variety of polymer matrices. The main focus in this part of the research was on the morphology and dispersion of the LDH as it related to their composition and their organic modification in relation to the nature of various polymers. Exemplary polymer matrices that span the range from non-polar to polar interactions –including Polypropylene (PP), polyethylenes (PE, and PE-copolymers), polymethyl-methacrylate (PMMA), polystyrene (PS)– were explored. It was observed that the LDH composition, organic modification, and polymer types were the parameters which controlled the LDH structure and dispersion, albeit in a rather involved fashion.