Biocomposites of polyamide 4.10 and surface modified microfibrillated cellulose (MFC): influence of processing parameters on structure and thermomechanical properties

Biocomposites of polyamide 4.10 and surface modified microfibrillated cellulose (MFC): influence of processing parameters on structure and thermomechanical properties Agnieszka Leszczyn´ ska . Paweł Kicilin´ ski . Krzysztof Pielichowski 0 0 A. Leszczyn ́ska (&) P. Kicilin ́ski K. Pielichowski Department of Chemistry and Technology of Polymers, Cracow University of Technology , ul. Warszawska 24, 31-155 Krako ́w , Poland Novel bio-polyamides obtained from renewable resources, e.g. PA4.10, are considered nowadays as promising 'green' engineering materials consisting of building blocks derived from castor oil. In this work the composites of heterogeneously acetylated microfibrillated cellulose (MFC) and biopolyamide 4.10 have been prepared by melt blending. Thermoplastic processing of PA4.10/MFC composites was possible in a narrow temperature window due to significant improvement of thermal stability of acetylated MFC as compared to raw MFC. The increase of thermooxidative stability of filler was due to removal of non-cellulosic components from the raw material and introduction of acetic moieties that had additional slight stabilizing effect on MFC. Moreover, the modified MFC showed significant changes in morphology that favoured its dispersibility in viscous polymer melt. Combined treatment of MFC by chemical agents, which caused partial hydrolysis of amorphous regions, and physical disintegration by ultrasonic waves resulted in formation of fibrous material with low degree of entanglement and submicron or nanometric diameters. In the tested range of screw speeds it was found that at screw speed of 100 rpm the shearing forces were sufficient for dispersing MFC agglomerates and the melt pressure secured evacuation of gases introduced to plasticizing system of extruder with MFC-Ac aerogel. The dynamic mechanical properties of obtained (nano)composites were influenced by both mechanical strengthening of rigid cellulose micro and nanofibers as well as susceptibility of biopolymers towards oxidation and thermomechanical degradation during processing. Microfibrillated cellulose; Nanocomposites; Surface modification; Processing; Thermomechanical properties - Due to demands of sustainable development the need for progressive replacement of petroleum based polymers with plastics obtained from renewable raw materials has been widely emphasised. The issue of large volumes of non-biodegradable waste materials is a special concern of e.g. packaging industry. In applications where good barrier properties are demanded multilayer films composed of polyolefin and polyamide films are frequently applied. Though this technology offers a good combination of limited permeability of non-polar polyolefins towards water with low permeability of organic vapours through polar polyamide layer, it involves difficulties in recycling of mixed polymer films and has high environmental impact. In a wide variety of commercially available biopolymers a new group of biopolyamides has recently been introduced on the market. They are obtained in the condensation reaction of diamines and dicarboxylic acids from castor oil (Niaounakis 2015). Importantly, the amount of carbon dioxide emitted during production of PA4.10 is compensated by the amount of CO2 absorbed during plant growth. In the group of natural fillers with submicronic and nanometric dimensions the microfibrillated and nanofibrillated cellulose (MFC and NFC, respectively) combine high strengthening potential and good barrier properties (Rodionova et al. 2011). However, due to highly hydrophilic character of the filler interfacial adhesion in polymer/MFC composites is usually not sufficient for proper dispersion of filler and efficient stress transfer during deformation. Numerous methods of surface modification have been recently developed and showed high efficiency in improving dispersibility of MFC and NFC in polymer and strengthening interfacial adhesion leading to better functional properties (Missoum et al. 2011; Miao and Hamad 2013). Despite the promising characteristics of NFC and MFC the application of this group of fillers was basically limited to polymers with low temperature of melting/softening due to insufficient thermal stability of polysaccharide modifiers. As reported in the literature, chemical modification of MFC and NFC influenced the thermal stability of material. However, only few works reported an increase of thermal stability of nanocellulose by e.g. surface acetylation (Nogi et al. 2006) or silanization (Qua et al. 2011). In this work MFC was submitted to heterogeneous acetylation by acetic anhydride, then characterised and used for preparation of a new type of micro/nanocomposites based on a biopolyamidePA4.10. The effects of processing conditions on the dispersion degree of modified MFC as well as on the thermal and dynamic mechanical properties of PA4.10/MFC composites were investigated. Microfibrillated cellulose under the commercial name Arbocel MF (...truncated)