Poly(butylene adipate-co-terephthalate) (PBAT) was first chemically modified via free radical grafting with maleic anhydride (MA) and the MA-g-PBAT graft copolymer was then used as a matrix material to obtain cellulose nanocrystal (CNC)-reinforced MA-g-PBAT bionanocomposites via reactive extrusion process to accelerate efforts to develop functional bioabsorbable polymer nanocomposites with improved properties. The molecular structure of the PBAT after chemical modification with maleic anhydride was confirmed by H NMR and FTIR spectroscopy. The morphological observation of the nanocomposites revealed that the CNCs were finely dispersed in the matrix. Thermal analysis of the hybrids showed an improvement of the thermal stability of the nanocomposites upon increasing the CNC content. In addition, it was found that the CNC nucleated crystallization of the PBAT in the nanocomposites. Extensive melt rheological characterization of the nanocomposite samples revealed a significant improvement of the viscoelastic properties of the matrix due to the strong interfacial adhesion of the CNC particles to the PBAT. Further, development of the nonterminal characteristics of the viscoelastic material functions and exhibition of yield stress were correlated with the evolution of a 3D-netowork nanostructure of CNCs in the matrix. This CNC nanostructure was interpreted in the framework of scaling theory of fractal elastic gels, and found to be consistent with the structure of open-porous flocs. Tensile testing of the samples showed considerable improvement in the modulus and ultimate strength of the samples with increasing the CNC content. In addition, a positive shift of the glass transition temperature was found in dynamic mechanical analysis. Finally, in vitro biocompatibility using Thiazolyl blue tetrazolium bromide (MTT) assay and cell adhesion studies with L929 fibroblast cells revealed no cytotoxic effect of CNCs, confirming the biocompatibility of the nanocomposites and the associated significant improvement of cell adhesion, suggesting the potential applicability of this nanocomposite in biomedical and tissue engineering applications.

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The creep behavior and solid and melt linear viscoelasticity of novel polyamide 6 (PA6) nanocomposites reinforced with cellulose nanocrystals (CNCs) prepared via in situ anionic ring-opening polymerization (ROP) were investigated to accelerate research efforts to develop new polymeric materials with improved properties for lightweight, load-bearing applications. The obtained results showed that incorporation of relatively small amounts of 2wt% CNCs into the PA6 thermoplastic matrix gave nanocomposite samples with significantly enhanced creep and viscoelastic materials functions of the PA6 as indicated by lower creep strain, lower creep compliance, improved elastic recovery after removal of load, and reduced Arrhenius activation energies for time-dependent viscoplastic flow. The obtained results were analyzed and interpreted by theoretical equations for predicting the viscoelasticity and creep behavior of polymeric systems. The melt rheological properties showed enhanced melt strength and elasticity. The formation of a percolated network structure of CNC was revealed by morphological observations that were consistent with the dynamic structure break-up and reformation rheological experiments. The stiffness, rigidity of the CNCs along with their special ROP-facilitated intrinsic strong chemical interactions with the PA6 matrix is believed to be responsible for the observed superior creep and viscoelastic materials functions even with very little CNC concentration. POLYM. ENG. SCI., 00:000-000, 2016.

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