Solid Mechanics and Crystal Physics as Tools for Cellulose Structure Investigation

Abstract

The physical “law of mixtures” and its many refinements have been extensively employed in analyses of engineering problems involving anisotropic composite materials. The plant cell wall, which is structurally a laminated composite of generally anisotropic laminae, can be analyzed in this way. The cellulosic microfibrils are considered as reinforcing filaments and the other constituents as an embedding matrix. Experimental results of mechanical tests on such cellulosic materials as wood, textile fibers, and tissue microsections can be used for comparison with elastic constants of crystalline cellulose, calculated from bending and stretching force constants of primary and secondary bonds for specific supermolecular configurations. By such means, certain configurations proposed for cellulose can be eliminated as possibilities, since, by the law of mixtures, the experimental elastic modulus of a fiber must not be greater than that calculated for the aligned, perfect cellulose crystal. Such a failure to satisfy the law of mixtures is found, for example, upon examination of a folded-chain proposal for the structure of cellulose.