Cellulose micro/nanocrystals reinforced polyurethane
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M.L. Auad University of Southern California, Gill Foundation Composites Center, Los Angeles, California 90089-0241
N.E. Bellesi Instituto de Investigaciones en Ciencia y Technologia de Materiales (INTEMA), Chemical Engineering Department, Universidad Nacional de Mar del Plata, 7600 Mar del Plata, Argentina
S.R. Nutt University of Southern California, Gill Foundation Composites Center, Los Angeles, California 90089-0241
M.I. Arangurena) Instituto de Investigaciones en Ciencia y Technologia de Materiales (INTEMA), Chemical Engineering Department, Universidad Nacional de Mar del Plata, 7600 Mar del Plata, Argentina (Received 14 September 2005; accepted 12 December 2005)
Nano- and micron-sized cellulose crystals were prepared and utilized as reinforcements for polyurethane composites. The cellulose crystals obtained from microcrystalline cellulose (MCC) were incorporated into a polar organic solvent, dimethylformamide (DMF), and ultrasonicated to obtain a stable suspension. The suspension was an effective means for incorporating the cellulose crystals into the polyol-isocyanate mixture, utilized to produce polyurethane composite films. The use of DMF presents an interesting alternative for the use of cellulose crystals as reinforcement of a broad new range of polymers. Moreover, the rheology of the uncured liquid suspensions was investigated, and analysis of the results indicated the formation of a filler structure pervading the liquid suspension. Besides, films were prepared by casting and thermal curing of the stable suspensions. Thermomechanical and mechanical testing of the films were carried out to analyze the performance of the composites. The results indicated that a strong filler-matrix interaction was developed during curing as a result of a chemical reaction occurring between the crystals and the isocyanate component.
I. INTRODUCTION
The combination of discrete materials has been used for decades to obtain composite materials with properties superior to either individual component. In particular, considerable effort has been devoted in recent years to the research and development of materials that utilize cellulose fibers as the load bearing constituents for different polymeric composites.1 Cellulose is one of the most abundant materials in nature, since it represents the main structural component of the plants and is also produced on a much smaller scale by some sea animals.2 In addition, attributes such as
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0105 870
J. Mater. Res., Vol. 21, No. 4, Apr 2006
low cost, low density, high stiffness, renewable nature, and biodegradability3–6 constitute major incentives for exploring new uses. Cellulose fibers exhibit a unique structural hierarchy derived from its biological origin. They are composed of assemblies of microfibrils,7–10 which form slender and nearly endless rods. Upon exposure to strong acids, these microfibrils break down into short crystalline rods or “cellulose microcrystals.” The diameter
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