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Molecular Origin of Strength and Stiffness in Bamboo Fibrils.

Youssefian S, Rahbar N - Sci Rep (2015)

Bottom Line: Good agreement was observed between the simulation results and experimental data.We also found out that the amorphous regions of cellulose microfibrils are the weakest interfaces in bamboo fibrils.Hence, they determine the fibril strength.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA.

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.

No MeSH data available.


Related in: MedlinePlus

a) The adhesion energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average energy between lignin molecules and a cellulose microfibril is higher than the energy between hemicellulose and cellulose microfibrils. b) The van der Waals energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. Lignin exhibits higher adhesive energy to cellulose microfibrils than hemicellulose. c) The electrostatic energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average electrostatic energy between lignin molecules and cellulose microfibrils exhibit no significant difference from the electrostatic energy between hemicellulose and cellulose microfibrils d) the hydrogen bond energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average hydrogen bond energies between cellulose microfibrils and the three materials are similar.
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f4: a) The adhesion energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average energy between lignin molecules and a cellulose microfibril is higher than the energy between hemicellulose and cellulose microfibrils. b) The van der Waals energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. Lignin exhibits higher adhesive energy to cellulose microfibrils than hemicellulose. c) The electrostatic energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average electrostatic energy between lignin molecules and cellulose microfibrils exhibit no significant difference from the electrostatic energy between hemicellulose and cellulose microfibrils d) the hydrogen bond energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average hydrogen bond energies between cellulose microfibrils and the three materials are similar.

Mentions: In the composite structure of a bamboo fiber, knowledge of adhesive interactions between the different layers determines its strength. Applied stresses on a microfibril are carried either by cellulose microfibrils, the LCC matrix or the interfaces of these two regions. To investigate the adhesion energies at these interfaces, twenty-four different assemblies of lignin, hemicellulose and LCC on top of cellulose substrates were created, each of which simulates the interaction between one of the materials and one face of the eight possible faces of cellulose microfibrils. The adhesion energies were computed from final trajectories of the simulations and presented in Fig. 4a. Although these results indicate that the overall adhesion energies for these materials are different, their tendencies to adhere to microfibril faces exhibit almost the same pattern. For each material, the interaction energies of (100) and () faces are the lowest whereas the energies of other faces vary around an average value. The average adhesion energy between lignin and microfibril faces was about 152 mJ/m2. This is higher than adhesion energy between LCC and microfibril faces which is about 133 mJ/m2. Hemicellulose with average adhesion energy of around 83 mJ/m2 shows the lowest adherence to microfibril among the three materials. This adhesion trend, also, has been shown by Hosoya et al. in the pyrolysis of hemicellulose and lignin with cellulose where lignin-cellulose interactions were significant compare to low hemicellulose-cellulose interactions43. Therefore, lignin with greater overall adhesion energy to cellulose is responsible for providing strong interaction between LCC matrix and cellulose microfibrils to create strong bamboo fibrils. To understand the mechanism of interactions between these materials and cellulose, we computed the electrostatic and van der Waals energies, accountable for the adhesion, as shown in Fig. 4b,c. These results suggest that the van der Waals energies do not change significantly over the microfibril faces whereas the electrostatic energies of (100) and () faces are less than that of other faces. Hence, the electrostatic energy is responsible for reduction of adhesion energy between cellulose (100) or () faces and hemicellulose, LCC and lignin. The average electrostatic energies between cellulose microfibril faces and hemicellulose, LCC and lignin are 38 mJ/m2, 57 mJ/m2 and 58 mJ/m2, respectively, and the average van der Waals energies between cellulose microfibril faces hemicellulose, LCC and lignin are 44 mJ/m2, 76 mJ/m2 and 95 mJ/m2, respectively. It is evident that lignin van der Waals energy is higher around 116% than that of hemicellulose whereas the electrostatic energy are higher just by about 50%. This indicates that the superiority of lignin adhesion energies to cellulose comes from the relatively higher van der Waals energies between cellulose microfibril and lignin. One of the major components of electrostatic energies at the interface of cellulose microfibril and hemicellulose, LCC and lignin, is hydrogen bonding which are illustrated in Fig. 4d. Regardless of the slightly higher average hydrogen bond energy between lignin and cellulose, all three materials have almost the same hydrogen bond interaction energies with cellulose microfibrils. The hydrogen bond energies show a similar pattern to the electrostatic energies presented in Fig. 4c. In other words, (100) and () faces have the lowest hydrogen bond energies which are similar to that of the electrostatic interactions. This suggests that different level of hydrogen bond energies at the interface of microfibril and hemicellulose, LCC and lignin are the main reason for different electrostatic energies from one face to another, causing the adhesion energies between the matrix and (100) and () faces of microfibril to drop.


Molecular Origin of Strength and Stiffness in Bamboo Fibrils.

Youssefian S, Rahbar N - Sci Rep (2015)

a) The adhesion energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average energy between lignin molecules and a cellulose microfibril is higher than the energy between hemicellulose and cellulose microfibrils. b) The van der Waals energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. Lignin exhibits higher adhesive energy to cellulose microfibrils than hemicellulose. c) The electrostatic energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average electrostatic energy between lignin molecules and cellulose microfibrils exhibit no significant difference from the electrostatic energy between hemicellulose and cellulose microfibrils d) the hydrogen bond energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average hydrogen bond energies between cellulose microfibrils and the three materials are similar.
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f4: a) The adhesion energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average energy between lignin molecules and a cellulose microfibril is higher than the energy between hemicellulose and cellulose microfibrils. b) The van der Waals energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. Lignin exhibits higher adhesive energy to cellulose microfibrils than hemicellulose. c) The electrostatic energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average electrostatic energy between lignin molecules and cellulose microfibrils exhibit no significant difference from the electrostatic energy between hemicellulose and cellulose microfibrils d) the hydrogen bond energy per unit area between different cellulose microfibril faces and hemicellulose, LCC and lignin. The average hydrogen bond energies between cellulose microfibrils and the three materials are similar.
Mentions: In the composite structure of a bamboo fiber, knowledge of adhesive interactions between the different layers determines its strength. Applied stresses on a microfibril are carried either by cellulose microfibrils, the LCC matrix or the interfaces of these two regions. To investigate the adhesion energies at these interfaces, twenty-four different assemblies of lignin, hemicellulose and LCC on top of cellulose substrates were created, each of which simulates the interaction between one of the materials and one face of the eight possible faces of cellulose microfibrils. The adhesion energies were computed from final trajectories of the simulations and presented in Fig. 4a. Although these results indicate that the overall adhesion energies for these materials are different, their tendencies to adhere to microfibril faces exhibit almost the same pattern. For each material, the interaction energies of (100) and () faces are the lowest whereas the energies of other faces vary around an average value. The average adhesion energy between lignin and microfibril faces was about 152 mJ/m2. This is higher than adhesion energy between LCC and microfibril faces which is about 133 mJ/m2. Hemicellulose with average adhesion energy of around 83 mJ/m2 shows the lowest adherence to microfibril among the three materials. This adhesion trend, also, has been shown by Hosoya et al. in the pyrolysis of hemicellulose and lignin with cellulose where lignin-cellulose interactions were significant compare to low hemicellulose-cellulose interactions43. Therefore, lignin with greater overall adhesion energy to cellulose is responsible for providing strong interaction between LCC matrix and cellulose microfibrils to create strong bamboo fibrils. To understand the mechanism of interactions between these materials and cellulose, we computed the electrostatic and van der Waals energies, accountable for the adhesion, as shown in Fig. 4b,c. These results suggest that the van der Waals energies do not change significantly over the microfibril faces whereas the electrostatic energies of (100) and () faces are less than that of other faces. Hence, the electrostatic energy is responsible for reduction of adhesion energy between cellulose (100) or () faces and hemicellulose, LCC and lignin. The average electrostatic energies between cellulose microfibril faces and hemicellulose, LCC and lignin are 38 mJ/m2, 57 mJ/m2 and 58 mJ/m2, respectively, and the average van der Waals energies between cellulose microfibril faces hemicellulose, LCC and lignin are 44 mJ/m2, 76 mJ/m2 and 95 mJ/m2, respectively. It is evident that lignin van der Waals energy is higher around 116% than that of hemicellulose whereas the electrostatic energy are higher just by about 50%. This indicates that the superiority of lignin adhesion energies to cellulose comes from the relatively higher van der Waals energies between cellulose microfibril and lignin. One of the major components of electrostatic energies at the interface of cellulose microfibril and hemicellulose, LCC and lignin, is hydrogen bonding which are illustrated in Fig. 4d. Regardless of the slightly higher average hydrogen bond energy between lignin and cellulose, all three materials have almost the same hydrogen bond interaction energies with cellulose microfibrils. The hydrogen bond energies show a similar pattern to the electrostatic energies presented in Fig. 4c. In other words, (100) and () faces have the lowest hydrogen bond energies which are similar to that of the electrostatic interactions. This suggests that different level of hydrogen bond energies at the interface of microfibril and hemicellulose, LCC and lignin are the main reason for different electrostatic energies from one face to another, causing the adhesion energies between the matrix and (100) and () faces of microfibril to drop.

Bottom Line: Good agreement was observed between the simulation results and experimental data.We also found out that the amorphous regions of cellulose microfibrils are the weakest interfaces in bamboo fibrils.Hence, they determine the fibril strength.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA.

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.

No MeSH data available.


Related in: MedlinePlus