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.

Bioethanol: Feedstock Alternatives, Pretreatments, Lignin Chemistry, and the Potential for Green Value-Added Lignin Co-Products

“…By comparing the abundance of hydrogen bonds against the abundance of O-H bonds, it is argued that most hydroxyl group hydrogens are engaged in hydrogen bonding in lignin. However, in hemicellulose the contribution of hydroxyl groups to hydrogen bonding is only ~60% [179]. Lignin also exhibits greater hydroxyl group-mediated hydrogen bonding than those in LCC or hemicellulose.…”

“…It has been reported that holocellulose and lignin make up 90-98% of the composition of the cell wall with the remaining 2-10% consisting of a variety of extractives, resins, tannins, waxes and inorganic salts [174,177,178]. These components ultimately make up the physical structure of bamboo -the epidermis, parenchyma cells, vascular bundles, and supporting fibers that tie these together in a hierarchical structure [179]. Cellulose microfibrils traverse and intertwine densely through the lignin-holocellulose matrix ( Figure 3).…”

“…For example, radial distribution functions (RDF) may be generated to assess the relative contribution of cellulose, hemicellulose, lignin, and bonds between these macromolecules (e.g., hemicellulose-to-lignin) to the overall mechanical strength of bamboo [179]. Using molecular modeling and dynamics methods (i.e., atomistic simulations), Youssefian and Rahbar demonstrated that C-H bonds are most abundant in bamboo lignin and C-C bonds are more abundant than O-H bonds (Figure 4).…”

Strengthening diversity and cooperation through international collaborations: A focus on Africa, South America, and the Caribbean

“…Ting Tan (a USAMI PhD student) developed a bamboo wind turbine at the University of Vermont, while Nima Rahbar (USAMI PhD student) carried out pioneering molecular dynamic simulations to develop a fundamental understanding of the molecular origins of strength and stiffness in bamboo. 50 Similarly, collaborations between Emelio da Silva (University of São Paulo, Brazil) and Glaucio Paulino (Georgia Institute of Technology) (see Figure 9) were facilitated by the Americas Ghana, Kenya, Cameroon, Burkina Faso, and Senegal, significant efforts are under way in materials research and education, compared to those that existed about 20 years ago.…”

Bamboo reinforced concrete: a critical review

“…Correal [8] reports that bamboo properties degrade above 50°C. Youssefian and Rahbar [64] report the glass transition temperatures of lignin and hemicellulose (the primary components of the bamboo matrix) to range from 97 to 171°C and 140 to 180°C, respectively. It is likely that the behaviour of bamboo reinforcement under fire conditions is inferior to that of steel.…”