Abstract
Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed to the selective adsorption of the polymer high molar mass fraction onto nanoparticles surface when the polymer radius of gyration is comparable to the nanoparticles characteristic dimensions. Carbon nanotubes seem to be the ideal candidate to induce viscosity reduction of polymer due to both their high surface-to-volume ratio and their nanometric sizes, comparable to the gyration radius of polymer chains. However, the amount of nanotube in a polymer system is limited by the percolation threshold as, above this limit, the formation of a nanotubes network hinders the viscosity reduction effect. Based on these findings, we have used multiwalled carbon nanotubes MWCNT “aggregates” as viscosity reducers. Our results reveal both that the use of nanotube clusters reduce significantly the viscosity of the final system and strongly increase the nanotube limiting concentration for viscosity hindering. By using hydroxyl and carboxyl functionalized nanotubes, this effect has been rather maximized likely due to the hydrogen bridged stabilization of nanotube aggregates.
Highlights
Polymer compounding is one of the most used way to obtain plastics which ensure processing and performances demands from markets and industries
They concluded that the polymer melt must be entangled and that the average separation distance among nanoparticles has to be comparable to the polymer radius of gyration (Rg), under such conditions, nanoparticles can perturb polymer chain configurations [19]
Raw Materials: the thermoplastic epoxy system was provided by ELANTAS Italia S.r.l. (Parma, Italy). This system is based on diglycidyl ether of bisphenol A (DGEBA) with a low average epoxide equivalent weight (EEW) and abi-functional co-monomers with hydroxyl reactive groups in terminal positions
Summary
Polymer compounding is one of the most used way to obtain plastics which ensure processing and performances demands from markets and industries. Tuteja et al [19,20] have expanded these experimental evidences, by disclosing more specific conditions to achieve a reduction in bulk viscosity They concluded that the polymer melt must be entangled and that the average separation distance among nanoparticles has to be comparable to the polymer radius of gyration (Rg), under such conditions, nanoparticles can perturb polymer chain configurations [19]. Lippits and Rastogi [21] tested dispersions of SWCNTs in ultrahigh molecular weight polyethylene by revealing a similar behavior They have attributed the decrease in viscosity to the selective interaction among nanotubes and to the higher molar mass fraction of polymeric bulk, which, leads to a decrease of dynamic viscosity for very low percentage (less than 0.1 wt%) of nanoparticles. The interesting phenomena of viscosity reduction is for the first time investigated for an epoxy-thermoplastic system with the aim to discuss and rationalize it irrespective of network formation
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