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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
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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)