Structural Rheology Of Molten Polymer Nano-composites

Understanding the rheological properties of polymer-layered silicate nanocomposites is crucial to gain a fundermental understanding of the processability and structure-property relations for these materials. The scope and innovation of this dissertation were summarized as following.The series of hybrids of polypropylene (PP)/clay (PPCH) were prepared by a melt extrusion process with different quantity of maleic anhydride modified PP (PP-MA) and clays. The rheological behavior, together with WAXS and TEM, of molten PPCH is investigated showing the nano-scale and the meso-scale structure were affected by the d-space of clay, the amount of filled PP-MA, and the different processing route. The structure of intercalated clays correlated with the amount of filled PP-MA and processing route.Fully exfoliation was achieved by sufficient loading of PP-MA and annealing after extrusion mixing. Comprehensive linear viscoelasticity and non-linear rheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on the time, temperature and deformation dependency of the "solid-like" state in molten nanocomposites. The strong-association platelets networks is developing gradually at quiescent state or small strain oscillation along with hours annealing to maximum at fully exfoliated state depending on temperature histories. The strong-association platelets network causes characteristic linear and non-linear rheological behaviors. It will be broken down by melt frozen/crystallization and weakened at large shear or strong flow and will be recovered after annealing during in shorter times comparatively. These solid-like rheological characteristics can be disrupted by filler treatment using 1 wt.‰ ( ratio to clay) of silane coupling agent. Our results reveal that the strong solid-like structuring does not rely on the intercalated clay tactoids and polymer diffusion in plate galleries, but more on the association and networking of exfoliated platelets of silicate. These evidences supportour suggested conceptual model, which claims that the percolated band-like chain networking structure of associated layered silicate is responsible for the "solid-like" rheological characteristics.The amount of the stress overshoot in flow reversal experiments was observed to be a function of the rest time between the reversal for the nanocomposites with or without annealing. Both the amount of the double overshoot and time after the inception of flow were found to be a strong function of the shear rate and the stress in start-up of steady shear scaled with the applied strain for the annealed nanocomposites. The stress overshoot observed in the transient rheological experiments is attributed to the strong- association platelets networks (percolation network).Further study showed that the introduction of nano-rubber into PPCH will lead tothe exfoliation of organo-clay.In conclusion, we synthesized the kind's material functions and the results of structural measurement to clear the mass between the rheology and structure model, and to result the discussion about them. The strong- association exfoliated platelets network (percolation network) of clay in molten polymer was demonstrated directly for the first time.The establishment of the model in this work, which has the property of generalization, is helpful for to set up the quantified constitutive equation, is helpful for the development of the processability and structure-property relations of the nanocomposites.