Processing affects the polymer nanocomposites properties

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The thermomechanical properties of the materials were established by dynamic mechanical thermal analysis (DMTA). In the dry state, all nanocomposites show much higher tensile storage moduli, E′, than the neat SBR or the SBR latex. E′ increases with the CNC content and depends strongly on the processing method, which appears to influence the morphology of the SBR nanocomposites produced. The highest E′ values were observed for the solution cast samples involving an SBR latex, where E′ increased from 3 MPa for the neat SBR to ca. 740 MPa for the nanocomposite containing 20% v/v CNCs. Upon submersion in deionized water, a dramatic reduction of E′ was observed, for example from 740 to 5 MPa for the solution-cast nanocomposite containing 20% v/v CNCs. This change is interpreted as a disengagement of the percolating CNC network, on account of modest aqueous swelling and competitive hydrogen bonding of water molecules with the CNCs. It is shown that the method of preparation also influenced the swelling behavior and kinetics of modulus switching, consistent with different arrangements of the CNCs, which serve as channels for water absorption and transport within the hydrophobic SBR matrix.

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