Surface Hydrophobization of Micro- and Nanofibrillated Cellulose and Blending Property in PLA Nanocomposites H. Taheri * , P. Samyn * * University of Freiburg, Freiburg Institute for Advanced Studies (FRIAS), Chair for Bio-based Materials Engineering, 79085 Freiburg, Germany, pieter.samyn@fobawi.uni-freiburg.de ABSTRACT In this research, we have investigated the influence of differet fiber morphologies including microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) on the uniformity of mixing and extrusion properties with a bio- based poly (lactic acid) or PLA polymer matrix. The polar nature of PLA was also expected to result in enhanced interfacial bonding with the MFC, but the highest polarity of microfibrillated cellulose compare to polarity of PLA leads to agglomeration of MFC in polymer matrix phase. At present, its aggregation and flocculation problem has restricted the use of these reinforcements in polymer matrix. The mixing of MFC/NFC fibers with PLA has been improved by an in-situ surface modification of the cellulose fibers, resulting in the deposition of poly(styrene-co- maleimide) or SMI nanoparticles on the fiber surface. By controlling the MFC consistency and its surface properties during the production phase in a microfluidizer, the degree of dispersion could be varied in order to reach dispersive and distributive mixing. Depending on the number of homogenization steps and in-situ surface modification of the MFC, the degree of defibrillation and surface charges on the cellulose fibers could be varied. The further optimization of the MFC/PLA compositions has been based on rheometrical testing to evaluate the concentration ranges for mixing MFC as a filler into PLA composites. Keywords: nanocomposites, biopolymers, microfibrillated cellulose, interface, hydrophobicity 1 INTRODUCTION Cellulose fibers are advantageous reinforcing materials for the formulation of bio-based composites because of their availability and good mechanical properties. The hierarchical structure of macro-scale cellulose fibers organized in the plant cell walls contains multiple bundels of cellulose microfibrils that have alternative amorphous and crystalline domains (Figure 1). Several chemical processes have been developed to turn the native fibers into micro- (MFC) or nanofibrillated (NFC) cellulose fibers [1]. These nanofibers are believed to even have stronger reinforcing capacity than native cellulose fibers because of surface interaction effects at the nanoscale and formation of Figure 1. Hierarchical structure of cellulose with organized microfibrils and nanofibrils. a fine web structure. During processing of fibrillated cellulose in combination with a hydrophobic biopolymer matrix, however, there is evidence of agglomeration due to the highly hydrophilic nature of the fibers leading to incompatibility with the polymer matrix. Several methods have been developed for the surface hydrophobization of cellulose fibers [2] and nanofibers [3]. In view of replacing petroleum-based products with bioplastics, especially poly(lactic acid) (PLA) is of interest. However, the PLA polymer does not have properties that allow it to compete directly with the main-stream plastics such as PE, PP, PS, and PVC. Plasticizers already exist to tailor the flexibility of PLA to meet a variety of application requirements, but this comes at the cost of strength and stiffness. Otherwise, NFC and MFC may be used to strengthen and toughen PLA. In recent work, the hydrophobic-modified NFC was obtained by grafting hydrophobic monomers on NFC to improve the compatibility between NFC and PLA during blending [4]. In contrast with traditional chemical surface modifi- cation, the hydrophobization of micro- and nanofibrillated cellulose in this study is done by deposition of hydrophobic nano-particles, allowing to tune the required hydrophobicity of the cellulose additives and to make them compatible with PLA for, e.g., extrusion applications. In order to get more fundamental insight in the blending characteristics of the surface-modified MFC/NFC and the PLA, rheological measurements have been performed. 376 TechConnect Briefs 2015, TechConnect.org, ISBN 978-1-4987-4727-1