Nanomechanical properties of cellulose nanofibrils (CNF)
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Nanomechanical properties of cellulose nanofibrils (CNF) N. Yildirim1 and S.M. Shaler2,3 PhD. Candidate // School of Forest Resources, University of Maine, 5755 Nutting Hall, Orono, ME 04469-5755 2 Professor & Director // School of Forest Resources, University of Maine, 5755 Nutting Hall, Orono, ME 04469-5755 3 Associate Director // Advanced Structures & Composites Center, University of Maine, 35 Flagstaff Road, Orono, ME, 04469-5793 1
ABSTRACT Cellulose is an abundant green polymer, which can be obtained in a variety of nanoscale structures broadly grouped as nano/microfibrils (CNF/MFC), bacterial celluloses (BC) or nano/microcrystals (CNC/CMC). There is increasing interest of nanocelluloses by the research and industrial communities due to increasing available materials (facilities than can produce ton per day), impressive strength properties, low density, renewability and biodegradability. However, one problem is the lack of knowledge on the nanomechanical properties of cellulose nanofibrils, which creates barriers for the scientists and producers to optimize and predict behavior of the final product. In this research, the behavior of thin filmed (t≤100 μm) cellulose nanofibrils’, located on aluminum pin stubs, under nano compression loads were investigated using an Asylum Research MFP-3D Atomic Force Microscope equipped with a nanoindenter. Unloading curves were analyzed using Oliver-Pharr. As a result of 58 successful nanoindents, the average modulus value was estimated as 16.6 GPa with the reduced modulus value of 18.2 GPa. The CNF Modulus values varied between 12.4 GPa – 22.8 GPa with 16.9% coefficient of variation (COV) while the reduced modulus ranged from 13.7 GPa to 24.9 GPa with a 16.2 % COV. This research provides practical knowledge for producers of nanocellulose, researchers and applications developers who focus on nanocellulose reinforced composite materials. INTRODUCTION Cellulose is a biopolymer, which can be isolated from nature (woods, plants, bacteria and even animals) [1,2]. CNFs have received much attention because of their low density, nonabrasive, combustible, nontoxic and biodegradable properties [3], which makes them suitable for the reinforcement material in composite structures [4]. Previous studies have evaluated the nanomechanical properties of nanocellulose to understand its role in the composite structures. The elastic modulus of regenerated cellulose fibers (Lyocell) was determined as between 12 GPa and 17 GPa while that of viscose cellulose fibers to vary between 7 GPa and 13 GPa [5]. These impressive mechanical properties and the increased availability of large volumes of material (multiple facilities are in place in North America and Europe with production capacities up to 2000 lb per day) have made these organic polymers more attractive for the industry and the researchers. However, the limited knowledge on the nanomechanical properties [6] of cellulose nanofibrils creates an opportunity for research to provide information, which will be of value to the research community and i
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