Molecular Mechanics of Organic Composite Materials: A Case Study of Cellulose-Adhesive System
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Molecular Mechanics of Organic Composite Materials: A Case Study of Cellulose-Adhesive System Lik-ho Tam1 and Denvid Lau2 1 Ph.D. Student, Department of Civil and Architectural Engineering, City University of Hong Kong, Hong Kong, China 2 Assistant Professor, Department of Civil and Architectural Engineering, City University of Hong Kong, Hong Kong, China ABSTRACT Organic composite materials can be readily found in our daily life, such as plywood used in construction industry and bamboo composites as indoor and outdoor flooring materials. These organic composite material systems consist of cellulose fibers bonded with each other through adhesives, leading to a bonded system with a gradient structure that possesses a unique structural behavior which has a great potential to be used as load-bearing building materials. In view of the manufacturing process of such composite material systems and the structure in-between the cellulose fibers and the adhesives, the interfacial adhesion of such systems at multiscale would play a major role in determining their capability in load-bearing structural applications. In this research work, the interface between cellulose fiber and phenol-formaldehyde adhesive is chosen as a representative of the organic composite material system and molecular dynamics simulation is used for quantifying their mechanical properties and the corresponding interfacial adhesion. Here we demonstrate that cellulose fiber has a strong affinity to a phenol-formaldehyde adhesive with an adhesion energy of 151.3 mJ/m2. To the best of our knowledge, this is the first study that reports this material property for cellulose-adhesive system, which is three times larger than that between the gecko foot’s hair and the mineral surface. The mechanism of such strong adhesion is due to the possible hydrogen bonding between the cellulose and the adhesive. INTRODUCTION Organic composite materials are intrinsic to excellent sustainability, eco-efficiency, and industry ecology, which are critical to many applications1. In building construction industry, plywood is a notable structural organic composite, which is manufactured from the orthotropic oriented cellulose fibers bonded together by the wood adhesives, resulting in the improved mechanical properties than the normal wood products. Compared to most metals, plywood has greater strength-to-weight ratio and fracture toughness, emerging as a competitive alternative to the products of steel and fiber reinforced composites, which has been increasingly used in modern architectures of large scales as walls, floors and roofs. The durability of plywood structure becomes the main problem in these applications which require long-term service life. As a result, a structural analysis of cellulose-adhesive system in plywood structure is necessary and critical to the production of plywood products. In this study, the cellulose fiber and adhesive are the major concern. The Young’s modulus of cellulose fiber and cross-linked adhesive is measured by uniaxial tensile deformation using m
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