Cellulose Nanofibril (CNF) Reinforced Starch Insulating Foams
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Cellulose Nanofibril (CNF) Reinforced Starch Insulating Foams
N. Yildirim1,2, S.M. Shaler1,2, D.J. Gardner1,2, R. Rice2 , D.W. Bousfield3 1. The Advanced Structures and Composites Center, University of Maine, 35 Flagstaff Road, Orono, ME, 04469-5793 T: (207) 581-2123, F: (207) 581-2074 2. School of Forest Resources, University of Maine, 5755 Nutting Hall, Orono, ME 04469-5755 T: (207) 581-2841, F: (207) 581-2875 3. Department of Chemical and Biological Engineering, University of Maine, 5737 Jenness Hall, Orono, ME 04469-5737 T: (207) 581-2277, F: (207) 581-2323
ABSTRACT In this study, biodegradable foams were produced using cellulose nanofibrils (CNFs) and starch (S). The availability of high volumes of CNFs at lower costs is rapidly progressing with advances in pilot-scale and commercial facilities. The foams were produced using a freeze-drying process with CNF/S water suspensions ranging from 1 to 7.5 wt. % solids content. Microscopic evaluation showed that the foams have a microcellular structure and that the foam walls are covered with CNF`s. The CNF's had diameters ranging from 30 nm to 100 nm. Pore sizes within the foam walls ranged from 20 nm to 100 nm. The materials` densities ranging from 0.012 to 0.082 g/cm3 with corresponding porosities between 93.46% and 99.10%. Thermal conductivity ranged from 0.041 to 0.054 W/m-K. The mechanical performance of the foams produced from the starch control was extremely low and the material was very friable. The addition of CNF's to starch was required to produce foams, which exhibited structural integrity. The mechanical properties of materials were positively correlated with solids content and CNF/S ratios. The mechanical and thermal properties for the foams produced in this study appear promising for applications such as insulation and packaging. INTRODUCTION In this study cellulose nanofibril and starch foams were produced and characterized. The main reason for using cellulose is that it is an abundant material, which can be obtained from renewable sources including a broad range of plants and sea animals (tunicates) [1]. Starch is another abundant natural polymer, which is a promising raw material for the development of novel materials [2]. It is a widely available biopolymer with a price half that of polyethylene and polystyrene. The mechanical properties of starch are highly correlated with density and amylose content. Increasing the solids content of starch suspensions increases the starch paste viscosity, which decreases the rate of steam bubble expansion, resulting in higher densities and mechanical properties. Normal cornstarch has higher elastic modulus (E=220 MPa) than wheat, potato and tapioca starches [3]. Annually, millions of metric tons of starch are used as non-food
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products in the paper and textile industries [4]. Starch, which has two major components, amylose consisting of ɲ-(1-4)-linked D-glucose and amylopectin with a myriad ɲ-(1-6)-linked branch point, is not a good choice as a replacement for any plastic because it is mostly water soluble
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