The effect of surface modification of microfibrillated cellulose (MFC) by acid chlorides on the structural and thermomechanical properties of biopolyamide 4.10 nanocomposites

Microfibrillated cellulose (MFC) has recently been identified as an innovative product of wood and agriculture industry with potential applications as reinforcement and carrier for functional properties of polymer composite materials, such as improved barrier and optical properties. The widespread commercial application of MFC in polymer technology still requires the development of new methods of MFC surface modifications in order to provide stong interfacial adhesion and good dispersibility of additive in polymer matrix. In this work micro fibrillated cellulose was modified by acid chlorides arranged in a homologous series that showed high efficiency in changing the surface properties of the material. The modified MFC displayed hydrophobic character combined with preserved fibrillar morphology and high crystallinity. Chemical modification of MFC was assessed by Fourier transformed infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses. Despite the fact that the reactivity of acid chloride slightly decreased with increasing chain length the total effect on MFC wetting with water was most pronounced for the modifier with the longest alkyl chain. Completely bio-based engineering nanocomposites of biopolyamide 4.10 (PA4.10) and surface modified MFC were prepared by melt blending. Structural, morphological and thermomechanical analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) methods evidenced clear dependence of composite performance on the length of alkyl chain attached to the MFC surface. The modification of MFC by hexanoyl chloride produced nanofiller with good dispersibility in PA4.10 matrix and was favorable in terms of dynamic mechanical properties of composites. While PA4.10 composites containing MFC functionalized by longer alkyl chains (more than 10 carbon atoms) showed a decrease of storage modulus due to insufficient interfacial interactions or plasticization effect.