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Molecular Origin of Strength and Stiffness in Bamboo Fibrils.

ABSTRACT: Bamboo, a fast-growing grass, has a higher strength-to-weight ratio than steel and concrete. The unique properties of bamboo come from the natural composite structure of fibers that consists mainly of cellulose microfibrils in a matrix of intertwined hemicellulose and lignin called lignin-carbohydrate complex (LCC). Here, we have used atomistic simulations to study the mechanical properties of and adhesive interactions between the materials in bamboo fibers. With this aim, we have developed molecular models of lignin, hemicellulose and LCC structures to study the elastic moduli and the adhesion energies between these materials and cellulose microfibril faces. Good agreement was observed between the simulation results and experimental data. It was also shown that the hemicellulose model has stronger mechanical properties than lignin while lignin exhibits greater tendency to adhere to cellulose microfibrils. The study suggests that the abundance of hydrogen bonds in hemicellulose chains is responsible for improving the mechanical behavior of LCC. The strong van der Waals forces between lignin molecules and cellulose microfibril is responsible for higher adhesion energy between LCC and cellulose microfibrils. We also found out that the amorphous regions of cellulose microfibrils are the weakest interfaces in bamboo fibrils. Hence, they determine the fibril strength.

SUBMITTER: Youssefian S

PROVIDER: S-EPMC4459167 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Project description:Microscopic tissue damage (microdamage) is an aspect of bone quality associated with impaired bone mechanical performance. While it is clear that bone tissue submitted to more severe loading has greater amounts of microdamage (as measured through staining), how microdamage influences future mechanical performance of the bone has not been well studied, yet is necessary for understanding the mechanical consequences of the presence of microdamage. Here we determine how stained microdamage generated by a single compressive overload affects subsequent biomechanical performance of cancellous bone. Human vertebral cancellous bone specimens (n=47) from 23 donors (14 males, 9 females, 64-92years of age) were submitted to a compressive overload, stained for microdamage, then reloaded in compression to determine the relationship between the amount of microdamage caused by the initial load and reductions in mechanical performance during the reload. Damage volume fraction (DV/BV) caused by the initial overload was related to reductions in Young's modulus, yield strength, ultimate strength, and yield strain upon reloading (p<0.05, R(2)=0.18-0.34). The regression models suggest that, on average, relatively small amounts of microdamage are associated with large reductions in reload mechanical properties: a 1.50% DV/BV caused by a compressive overload was associated with an average reduction in Young's modulus of 41.0±3.2% (mean±SE), an average reduction in yield strength of 63.1±4.5% and an average reduction in ultimate strength of 52.7±4.0%. Specimens loaded beyond 1.2% (1.2-4.0% apparent strain) demonstrated a single relationship between reload mechanical properties (Young's modulus, yield strength, and ultimate strength) and bone volume fraction despite a large range in amounts of microdamage. Hence, estimates of future mechanical performance of cancellous bone can be achieved using the bone volume fraction and whether or not a specimen was previously loaded beyond ultimate strain. The empirical relationships provided in this study make it possible to estimate the degree of impaired mechanical performance resulting from an observed amount of stained microdamage.

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Molecular Origin of Strength and Stiffness in Bamboo Fibrils.

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