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Your search keyword '"McDonald, Armando G."' showing total 299 results
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299 results on '"McDonald, Armando G."'

20. Lodging Variability in Sorghum Stalks Is Dependent on the Biomechanical and Chemical Composition of the Stalk Rinds.

Author

Mengistie, Endalkachew, Bokros, Norbert, DeBolt, Seth, and McDonald, Armando G.

Subjects
SORGHUM, CROP yields, BIOMECHANICS, MICROFIBRILS, VISCOELASTICITY
Abstract

Stalk lodging contributes to significant crop yield losses. Therefore, understanding the biomechanical strength and structural rigidity of grain stalks can contribute to improving stalk lodging resistance in crops. From the structural constituents of the stalk, the rind provides the principal structure, supporting cells against tension and bending loads. In this work, the biomechanical and viscoelastic behavior of the rind from the internodes of two sweet sorghum varieties (Della and REDforGREEN (RG)), grown in two different growing seasons, were evaluated by three-point micro-bending tests using a dynamic mechanical analyzer (DMA). In addition, the chemical composition of rinds and the microfibril angle (MFA) of the cell wall were determined using XRD. The results revealed that the biomechanical behavior of Della varieties was stiffer and more resistant to loads than that of RG varieties. Two features of the rind biomechanical properties, flexural modulus (FM) and flexural strength (FS), showed a significant reduction for RG. Particularly, a reduction in FS of 16–37% and in FM of 22–41% were detected for RG1. Changes in the stalks' rind biomechanical properties were attributed to cell wall components. Total lignin and glucan/cellulose contents were positively correlated with the FM and FS of the rind. Subsequently, an increase in the two cell wall components drove an increase in stiffness. Furthermore, the MFA of the rind was also found to influence the rind strength. [ABSTRACT FROM AUTHOR]

Published
2024
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25. Video-rate spontaneous Raman imaging

Author

Shaked, Natan T., Hayden, Oliver, Dunn, Lochlannn, Luo, Haokun, Subedi, Nava R., Kasu, Ramachandran, McDonald, Armando G., Christodoulides, Demetrios N., and Vasdekis, Andreas E.

Published
2024
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37. Flow, curing and mechanical properties of thermoset resins – wood-fiber blends for potential additive-manufacturing applications.

Author

Orji, Berlinda O. and McDonald, Armando G.

Subjects
PSEUDOPLASTIC fluids, ENGINEERED wood, CURING, WOOD, FLEXURAL modulus, DIFFERENTIAL scanning calorimetry
Abstract

This study examined the use of softwood mill residues (50–90%) with two thermosetting resins (i) urea-formaldehyde (UF) and (ii) phenol-resorcinol-formaldehyde (PRF) resin, for potential use in additive manufacturing (AM) of wood composite materials. The curing behavior of these blends was evaluated using differential scanning calorimetry and dynamic rheology. Curing kinetics was determined using the Kissinger and Cranes method. The presence of wood fibers reduced the curing peak temperatures for both resin blends at the same heating rates but curing peak temperatures increased with heating rates. The activation energy (Ea) increased with the addition of wood for the wood-PRF blends but reduced for the wood-UF blends in comparison to the neat resins. Ea values were 51 and 271 kJ/mol for PRF and wood-PRF samples and 100 and 367 kJ/mol for UF and wood-UF samples. Frequency sweep flow curves of the green wood-resin blends showed shear thinning behaviors with viscosity values between 103–108 Pa.s at 30°C. Mechanical properties of the wood-resin composites generally showed a reduction in flexural modulus with an increase in wood content. Wet wood (50%)-PRF blend was successfully extruded and showed promise for use in AM; however, the wood-UF blend was not successful. [ABSTRACT FROM AUTHOR]

Published
2023
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