Mechanical Properties of Polymer-Clay Nanocomposite Thin Films
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Clay-containing polymer nanocomposites applied as thin films have been found to have superior mechanical properties over isolated clay or polymer treatments. The majority of early studies of polymer-clay nanocomposites (PCNs), contain only 2 to 5% of clay relative to polymer and become very brittle when the concentration exceeds 10%. Studies in our lab have discovered self-assembling PCNs that contain as much as 50% clay yet retains flexibility. This thesis reports on the physical properties of these self-assembling PCNs. The composition and concentration of polymers and clays chosen for this work is inherently non-toxic, inexpensive, and ideal as a packaging additives. PCNs were prepared with water-soluble vinyl polymers and cationic phyllosilicate clays in low combinatory concentrations in the dispersed phase (>1% by weight) and applied to substrate as layered thin film coatings. PCN films with ductile polymers maintained flexibility, transparency, and mechanical performance. Tensile strength of the PCN coated substrate were shown to increase as a result of layer-by-layer (LBL) spray coating treatments, even at loadings as low as 0.3% and film thicknesses of 0.01 mm.
Neat PET substrate treated with clay solutions of 0.45% LAP or MMT increased tensile strength by 106% and 158% with 12 layers of applications and total coating thicknesses of 0.01 and 0.02 mm, respectively. The same trend was observed for PVOH and PVP polymer coatings solutions of 0.3%.
‘Premixed’ polymer/clay solutions outperformed neat substrate, solitary clays and polymer films but not films of alternating polymer/clay layers of the same concentration combinatory bilayered polymer/clay treatments of PET in either 12 or 24 layers showed an increase in tensile strength from that of layered treatments of only clays or polymers with coating thicknesses ranging from 0.03 to 0.05 mm.
PVP 0.3% and LAP 0.45% at 24 layers (12 bilayers) at a total film thickness of 0.05 mm increased tensile strength of substrate by 475% and increased yield and failure points considerably. Construction of bilayered LAP and PVP appeared to be more cohesive than adhesive to substrate, allowing deformation at the film before fracturing at substrate and increasing mechanical strength.
Durability and chemical resistance appeared to improve for PCNs as a function of treatment, assembly, and evaporation on the substrate, making the thin films practical as protective barriers. Optical transparency and flexibility and were maintained for PCNs with the exception of MMT, which may be modified with proper purification processing.
PCNs prepared with synthetic vinyl polymers prepared in combination with phyllosilicate clays display self-assembly behavior and intercalation interactions ideal for application as reinforcement and performance materials. When applied layer-by-layer via spray coating deposition, PCNs produced thin film coatings with increased tensile strength at relatively low loadings making them highly applicable as environmentally friendly packaging alternatives.