
Umesh AgarwalUS Forest Service | FS · Forest Products Laboratory
Umesh Agarwal
Ph.D.
About
146
Publications
134,142
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Introduction
Research interests:
•Cellulose nanomaterials
•Understanding roles of lignin and cellulose-crystallinity in the enzyme hydrolysis of wood
•Wood cell wall nanostructure
•Advancing Raman spectroscopy for characterzation of nanocelluloses, nanocellulose-composites, wood, and lignocelluloses
•Methods for estimating crystallinity of cellulose-containing materials
•Surface Enhanced Raman in lignin analysis
•Cellulose interactions with water
•Raman database of lignin models and interpretation of spectra
Additional affiliations
July 1989 - present
August 1984 - June 1989
Institute of Paper Chemistry
Position
- Scientist and Assistant Professor
October 1982 - July 1984
Institute of Paper Chemistry
Position
- PostDoc Position
Publications
Publications (146)
Hydrolysis experiments with commercial cellu-lases have been performed to understand the effects of cell wall crystallinity and lignin on the process. In the focus of the paper are loblolly pine wood samples, which were systematically delignified and partly ball-milled, and, for comparison, Whatman CC31 cellulose samples with differ-ent crystallini...
The structure of wood cell wall cellulose in its native state remains poorly understood, limiting the progress of research and development in numerous areas, including plant science, biofuels, and nanocellulose based materials. It is generally believed that cellulose in cell wall microfibrils has both crystalline and amorphous regions. However, the...
Properties of cellulose nanocrystals (CNCs) depend upon their supramolecular structures, which are important to understand in order to optimize their applications. In this investigation, the structures of CNCs produced upon 48–64% H2SO4 hydrolysis of hydrothermally-treated poplar, bleached kraft pulp, cotton microcrystalline cellulose, bacterial ce...
Aggregated states of celluloses remain poorly understood, and therefore, the topic requires careful investigation. In this study, Raman, IR, and X-ray diffraction (XRDs) were used to study cotton microcrystalline cellulose (MCC) and MCC that has been ball-milled to various degrees. Raman and IR spectroscopy methods indicated that when these ball-mi...
Wood and plants are made of fibers that contain, in addition to cellulose, lignin and hemicelluloses. Xylan and galactoglucomannan are the dominant secondary cell wall hemicelluloses. In modern times, fibers are important materials for the biorefinery industry and for developing biocomposites. For these and other applications, the structural analys...
The native state of wood-cellulose has proven to be difficult to explore. Contrary to the traditional acceptance of wood-cellulose being crystalline, in 2016, the authors' research reported that the cellulose was not crystalline.[1] New evidence, presented here, further supports the non-crystalline model. This evidence consisted of 64% H2SO4 hydrol...
Of the many observations reported in cellulose literature, the phenomena of “cocrystallization” and “moisture-induced shift in XRD” (XRD-shift) need re-examination. Does cocrystallization really occur or, entirely, something else is going on? Recent research carried out by the authors suggests that upon hydrothermal treatment of wood-cellulose, whe...
Morphological characterization of microfibrillated cellulose (MFC) is critically important to process control in production and product specification for trade and product development yet is extremely difficult. This study evaluated several indirect methods for relative comparison of the morphology of lignin-free and lignin-containing ((L)MFCs). Th...
Cellulose nanofibrils (CNFs) were produced from bleached eucalyptus kraft pulp using microfluidization varying the number of passes through the microfluidizer. CNFs were processed into dry films to elucidate the effect of CNFs morphology on the physical, optical and barrier properties of the films. As the number of passes through the microfluidizer...
Although highly desirable, the nature of wood-cellulose in its native state has remained difficult to comprehend. Contrary to the traditional acceptance of wood-cellulose being crystalline, in 2016, the authors’ research found that the cellulose was not crystalline. Here, additional evidence is presented that further supports the non-crystalline mo...
This chapter first briefly discusses the current understanding of plant cell wallCell wall biosynthesis and celluloseCellulose ultra-structure prerequisites for understanding nanocelluloseNanocellulose. From this fundamental understanding, the chapter is devoted to discussing conventional methods for producing two predominant types of cellulose nan...
This study compared oxidative delignification of birch kraft pulp fibers to pulp fibers from acid hydrotropic fractionation (AHF) using p-toluenesulfonic acid (p-TsOH). Under oxygen delignification at 20% consistency, AHF pulps with lower hemicellulose content showed higher delignification than kraft pulps with similar lignin content despite its re...
In the bio-based economy, conversion of biomass to biofuels and other products is essential for developing a sustainable alternative to fossil fuels. For this to become a reality, understanding of the biomass ultrastructure is critically important. For instance, to enhance the yield of fermentable sugars from enzymatic hydrolysis of cellulose, the...
In cellulose materials, the cellulose II allomorph is often present either exclusively or in conjunction with cellulose I, the natural cellulose. Moreover, in regenerated and mercerized fibers (e,g., lyocell and viscose), natural cellulose adopts to the crystal structure cellulose II. Therefore, its detection and quantitation are important for a co...
In cellulose materials, the cellulose II polymorph is often present either exclusively or in
conjunction with cellulose I, the natural cellulose. Moreover, in regenerated and
mercerized fibers (e,g., viscose and lyocell), natural cellulose adopts to the crystal
structure cellulose II Therefore, its detection and quantitation are important for a
com...
Plant-biomass-based nanomaterials have attracted great interest recently for their potential to replace petroleum-sourced polymeric materials for sustained economic development. However, challenges associated with sustainable production of lignocellulosic nanoscale polymeric materials (NPMs) need to be addressed. Producing materials from lignocellu...
In order for sustainable nanomaterials such as cellulose nanocrystals (CNCs) to be utilized in industrial applications, a large-scale production capacity for CNCs must exist. Currently the only CNCs available commercially in kilogram scale are obtained from wood pulp (W-CNCs). Scaling the production capacity of W-CNCs isolation has led to their use...
This study describes a class of cellulosic nanomaterials, cellulosic nanowhiskers (CNWs), and demonstrates scaled-up production with acid recovery using less expensive equipment made of common stainless steel rather than glass-lined steel. CNWs produced using concentrated maleic acid (MA) hydrolysis followed by mechanical fibrillation have morpholo...
Enzymatic conversion of cellulosic biomass into fermentable sugars such as glucose is a slow and catalytically inefficient process, largely due to limited accessibility of cellulose. Cellulose crystallinity can be reduced to increase substrate accessibility toward cellulolytic enzymes by either swelling or dissolving biomass in chemicals such as co...
This review is a summary of the Raman spectroscopy applications made over the last 10 years in the field of cellulose and lignocellulose materials. This paper functions as a status report on the kinds of information that can be generated by applying Raman spectroscopy. The information in the review is taken from the published papers and author’s ow...
Syringyl (S) lignin content and syringyl-to-guaiacyl (S/G) lignin ratio are important characteristics of wood and lignocellulosic biomass. Although numerous methods are available for estimating S lignin units and S/G ratio, in this work, a new method based on Raman spectroscopy that uses the 370 cm⁻¹ Raman band-area intensity (370-area) was develop...
A new method is described for producing high-lignin-containing and lignin-free cellulose nanocrystals from poplar wood (HLCNCs and LFCNCs, respectively). This was accomplished by first hydrothermally treating the poplar wood fibers at 170 °C for 45 min in a Parr reactor. For obtaining HLCNCs, the treated fibers were directly hydrolyzed by 64% sulfu...
A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and
functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were
once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique comb...
High lignin-containing cellulose nanocrystals (HLCNCs) were successfully isolated from hydrothermally treated aspen fibers and freeze-dried and compounded with poly (lactic acid) (PLA) by extrusion and injection molding. As a comparison, PLA composites containing commercial lignin-coated CNCs (BLCNCs) were also produced. HLCNCs showed higher crysta...
Native celluloses in plant cell walls occur in a variety of highly periodic fibrillar forms that have curvature and varying degrees of twist about their longitudinal axes. Though X-ray measurements reveal diffraction patterns, the celluloses are not crystalline in the traditional sense. The diffraction patterns rather are a consequence of the high...
Cellulose nanomaterials (CNs) are new types of materials derived from celluloses and offer unique challenges and opportunities for Raman spectroscopic investigations. CNs can be classified into the categories of cellulose nanocrystals (CNCs, also known as cellulose whisker) and cellulose nanofibrils (CNFs, also known as nanofibrillated cellulose or...
Cellulose nanocrystals (CNCs) are renewable and sustainable filler for polymeric nanocomposites. However, their high hydrophilicity limits their use with hydrophobic polymer for composite materials. In this study, freeze-dried CNCs were modified by transesterification with canola oil fatty acid methyl ester to reduce the hydrophilicity. The transes...
We fabricated cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) from different cellulose materials (bleached eucalyptus pulp (BEP), spruce dissolving pulp (SDP) and cotton based qualitative filter paper (QFP) using concentrated oxalic acid hydrolysis and subsequent mechanical fibrillation (for CNFs). The process was green as acid can b...
In this chapter, applications of Raman spectroscopy to nanocelluloses and nanocel-lulose composites are reviewed, and it is shown how use of various techniques in Raman can provide unique information. Some of the most important uses consisted of identification of cellulose nanomaterials, estimation of cellulose crystallinity, study of dispersion of...
Although X-ray diffraction (XRD) has been the most widely used technique to investigate crystallinity index (CrI) and crystallite size (L200) of cellulose materials, there are not many studies that have taken into account the role of sample moisture on these measurements. The present investigation focuses on a variety of celluloses and cellulose co...
Cellulose nanocrystals (CNCs), produced from dissolving wood pulp, were chemically functionalized by transesterification with canola oil fatty acid methyl ester (CME). CME performs as both the reaction reagent and solvent. Transesterified CNC (CNCFE) was characterized for their chemical structure, morphology, crystalline structure, thermal stabilit...
This chapter presents the most common techniques used to characterize lignin without depolymerization. These are used to identify the lignin being investigated as well as to evaluate the impact of modifications to lignin and lignin-containing products. A brief discussion of lignin chemistry is included. Understanding the chemical structure can be a...
Traditionally it has been accepted that the cell walls are made up of microfibrils which are partly crystalline. However, based on the recently obtained Raman evidence that showed that the interior of the microfibril was significantly disordered and water accessible, a new model is proposed. In this model, the molecular chains of cellulose are stil...
In this study, morphologies and supramolecular structures of CNCs from wood-pulp, cotton, bacteria, tunicate, and cladophora were investigated. TEM was used to study the morphological aspects of the nanocrystals whereas Raman spectroscopy provided information on the cellulose molecular structure and its organization within a CNC. Dimensional differ...
Understanding of formation of irreversible H bonds in cellulose is important in a number of fields. For example, fields as diverse as pulp and paper and enzymatic saccharification of cellulose are affected. In the present investigation, the phenomenon of formation of irreversible H-bonds is studied in a variety of celluloses and under two differen...
Two simple methods based on the 370 cm-1 Raman band intensity were developed for estimation of syringyl-to-guaiacyl (S/G) ratio in woods. The methods, in principle, are representative of the whole cell wall lignin and not just the portion of lignin that gets cleaved to release monomers, for example, during certain S/G chemical analyses. As such, it...
Cellulose 22:1753-1762, 2015
Cellulose nanocrystals (CNC) have recently received much attention in the global scientific community for their unique mechanical and optical properties. Here, we conducted the first detailed exploration of the basic properties of CNC, such as morphology, crystallinity, degree of sulfation and yield, as a function of p...
Cellulose nanocrystals (CNC) have recently
received much attention in the global scientific
community for their unique mechanical and optical
properties. Here, we conducted the first detailed
exploration of the basic properties of CNC, such as
morphology, crystallinity, degree of sulfation and
yield, as a function of production condition variables....
Cellulose nanocrystals (CNC) have recently
received much attention in the global scientific
community for their unique mechanical and optical
properties. Here, we conducted the first detailed
exploration of the basic properties of CNC, such as
morphology, crystallinity, degree of sulfation and
yield, as a function of production condition variables....
Influences of fiber orientation and milling on wood cellulose crystallinity were studied using jack pine wood. The fiber orientation effects were measured by sampling rectangular wood blocks in radial, tangential, and cross-sectional orientations. The influence of milling was studied by analyzing the unsieved and sieved milled wood fractions (all <...
Raman spectroscopy with its various special techniques and methods has been applied to study plant biomass for about 30 years. Such investigations have been performed at both macro- and micro-levels. However, with the availability of the Near Infrared (NIR) (1064 nm) Fourier Transform (FT)-Raman instruments where, in most materials, successful fluo...
The research carried out in this report provided an explanation
why the crystallinity of the delignified loblolly pine wood has no
negative influence on the enzyme hydrolysis. More specifically,
based on Raman analysis, the explanation has to do with the noncrystalline
nature of wood-cellulose. This has important implications
for future work in the...
Of the recently developed univariate and multivariate near-IR FT-Raman methods for estimating cellulose crystallinity, the former method was applied to a variety of lignocelluloses: softwoods, hardwoods, wood pulps, and agricultural residues/fibers. The effect of auto-fluorescence on the crystallinity estimation was minimized by solvent-extraction...
Southern yellow pine (Pinus taeda) wood char powder was thermally treated at 1,0008C in the presence of a 25-nm-size Fe nanoparticle catalyst. The thermally treated carbon materials were analyzed by Raman spectroscopy and high-resolution transmission electron microscopy. Well-aligned graphitic carbon structures with 15 to 17 layers on average were...
Raman spectroscopy was used to analyze cellulose nanocrystal (CNC)-polypropylene (PP) composites and to investigate the spatial distribution of CNCs in extruded composite filaments. Three composites were made from two forms of nanocellulose (CNCs from wood pulp and the nanoscale fraction of microcrystalline cellulose), and two of the three composit...
Considering that crystallinity is one of the important properties that influence the end use of cellulose nanomaterials, it is important that the former be measured accurately. Recently, a new method based on near-IR FT-Raman spectroscopy was proposed to determine cellulose I crystallinity. It was reported that in the Raman spectrum of cellulose ma...
Raman spectroscopy was used to analyze cellulose nanocrystal (CNC) -polypropylene (PP) composites and to investigate the spatial distribution of CNCs in extruded composite filaments. Three composites were made from two forms of nanocellulose (CNCs from wood pulp and the nano-scale fraction of microcrystalline cellulose) and two of the three composi...
Raman spectroscopy is being increasingly applied to study wood and other lignin-containing biomass/biomaterials. Lignin's contribution to the Raman spectra of such materials needs to be understood in the context of various lignin structures, sub structures, and functional groups so that lignin-specific features could be identified and the spectral...
Conversion of lignocellulose to biofuels is partly inefficient due to the deleterious impact of cellulose crystallinity on enzymatic saccharification. We demonstrate how the synergistic activity of cellulases was enhanced by altering the hydrogen bond network within crystalline cellulose fibrils. We provide a molecular-scale explanation of these ph...
Deconstruction of lignocellulosic plant cell walls to fermentable sugars by thermochemical and/or biological means is impeded by several poorly understood ultrastructural and chemical barriers. A promising thermochemical pretreatment called ammonia fiber expansion (AFEX) overcomes the native recalcitrance of cell walls through subtle morphological...
Because of the structural complexity of biomass, quantitation of lignin in a variety of wood and plant cell walls is difficult. Consequently, to measure lignin in different plant species, a number of different methods exist. The methods can give different values for the same material samples and such differences result from the nature of the biomas...
Enzymatic hydrolysis of cellulose in plant and wood cell walls is expected to be affected by its chemical composition as well as structural and morphological features. In the present study, different crystallinity cellulose samples and varying size fractionated loblolly pine wood cell wall particles were hydrolyzed using a mixture of Celluclast and...
Two new methods based on FT–Raman spectroscopy, one simple, based on band intensity ratio, and the other using a partial least
squares (PLS) regression model, are proposed to determine cellulose I crystallinity. In the simple method, crystallinity in
cellulose I samples was determined based on univariate regression that was first developed using th...
AFEX (ammonia fiber expansion) pretreatment of lignocellulosic biomass substantially increases the rate and extent of enzymatic digestion of glucan and xylan. Using crystalline cellulose (Avicel) as a model substrate to study the effect of AFEX on cellulose has several advantages since it is free of lignin and hemicellulose. Ongoing experiments hav...