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Browsing by Author "Goodell, Barry"

Now showing 1 - 5 of 5
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    Biopolymer Structure Analysis and Saccharification of Glycerol Thermal Processed Biomass
    Zhang, Wei (Virginia Tech, 2015-01-31)
    Glycerol thermal processing (GTP) is studied as a novel biomass pretreatment method in this research with the purposes to facilitate biopolymer fractionation and biomass saccharification. This approach is performed by treating sweet gum particles on polymer processing equipment at high temperatures and short times in the presence of anhydrous glycerol. Nine severity conditions are studied to assess the impact of time and temperature during the processing on biopolymer structure and conversion. The GTP pretreatment results in the disruption of cell wall networks by increasing the removal of side-chain sugars and lignin-carbohydrate linkages based on severity conditions. After pretreatment, 41% of the lignin and 68% of the xylan is recovered in a dry powdered form by subsequent extractions without additional catalysts, leaving a relatively pure cellulose fraction, 84% glucan, as found in chemical pulps. Lignin structural analysis indicated GTP processing resulted in extensive degradation of B-aryl ether bonds through the C-y elimination, followed by abundant phenolic hydroxyl liberation. At the same time, condensation occurred in the GTP lignin, providing relatively high molecular weight, near to that of the enzymatic mild acidolysis lignin. Better thermal stability was observed for this GTP lignin. In addition to lignin, xylan was successfully isolated as another polymer stream after GTP pretreatment. The recovered water insoluble xylan (WIX) was predominant alkali soluble fraction with a maximum purity of 84% and comparable molecular weight to xylan isolated from non-pretreated fibers. Additionally, the narrow molecular weight distribution of recovered WIX, was arisen from the pre-extraction of low molecular weight water-soluble xylan. Additionally, a 20-fold increase of the ultimate enzymatic saccharification for GTP pretreated biomass was observed even with significant amounts of lignin and xylan remaining on the non-extracted fiber. The shear and heat processing caused a disintegrated cell wall structure with formation of biomass debris and release of cellulose fibrils, enhancing surface area and most likely porosity. These structural changes were responsible for the improved biomass digestibility. Additionally, no significant inhibitory compounds for saccharification are produced during GTP processing, even at high temperatures. While lignin extraction did not promote improvement in hydrolysis rates, further xylan extraction greatly increases the initial enzymatic hydrolysis rate and final level of saccharification. The serial of studies fully demonstrate glycerol thermal processing as a novel pretreatment method to enhance biomass saccharification for biofuel production, as well as facilitate biopolymer fractionation. Moreover, the study shows the impact of thermally introduced structural changes to wood biopolymers when heated in anhydrous environments in the presence of hydrogen bonding solvent.
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    Experimental Characterization of Mode I Fracture Toughness of Reinforced Carbon Fiber Laminate with Nano-Cellulose and CNT Additives
    Berry, Seth David (Virginia Tech, 2016-08-10)
    Effective treatment of carbon fiber components to improve delamination resistance is vital to the application of such materials since delamination is one of the biggest concerns regarding the use of composites in the aerospace sector. Due to the significant application benefit gained from increased stiffness to density ratio with composite materials, innovative developments resulting in improved through-thickness strength have been on the rise. The inherent anisotropy of composite materials results in an added difficulty in designing structural elements that make use of such materials. Proposed techniques to improve the through-thickness strength of laminar composites are many and varied; however all share the common goal of improving inter-laminar bond strength. This research makes use of novel materials in the field of wet flocking and Z-pinning. Cellulose nanofibers (CNFs) have already demonstrated excellent mechanical properties in terms of stiffness and strength, originating at the nano-scale. These materials were introduced into the laminate while in a sol-gel suspension in an effort to improve load transfer between laminate layers. The effect of CNFs as lightweight renewable reinforcement for CFRPs will be investigated. Carbon nanotube (CNT) additives were also considered for their beneficial structural properties.
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    Lignocellulose deconstruction using glyceline and a chelator-mediated Fenton system
    Orejuela, Lourdes Magdalena (Virginia Tech, 2017-12-15)
    Non-edible plant biomass (lignocellulose) is a valuable precursor for liquid biofuels, through the processes of pretreatment and saccharification followed by fermentation into products such as ethanol or butanol. However, it is difficult to gain access to the fermentable sugars in lignocellulose, and this problem is principally associated with limited enzyme accessibility. Hence, biomass pretreatments that destroy native cell wall structure and allows enzyme access are required for effective biomass conversion techniques. This research studied two novel pretreatment methods on two wood species: 1) a deep eutectic solvent (DES) that, under heat, swells lignocellulose and partially solubilizes cell wall materials by causing breakage of lignin-carbohydrate linkages and depolymerization of the biomass components, and 2) a chelator-mediated Fenton reaction (CMF) that chemically modifies the nanostructure of the cell wall through a non-enzymatic cell wall deconstruction. After pretreatment, utilizing analytical techniques such as nuclear magnetic spectroscopy, wide angle x-ray scattering, and gel permeation chromatography, samples were analyzed for chemical and structural changes in the solubilized and residual materials. After single stage DES (choline-chloride-glycerol) and two stage, CMF followed by DES pretreatments, lignin/carbohydrate fractions were recovered, leaving a cellulose-rich fraction with reduced lignin and hemicellulose content as determined by compositional analysis. Lignin and heteropolysaccharide removal by DES was quantified and the aromatic-rich solubilized biopolymer fragments were analyzed as water insoluble high molecular weight fractions and water-ethanol soluble low molecular weight compounds. After pretreatment for the hardwood sample, enzyme digestibility reached a saccharification yield of 78% (a 13-fold increase) for the two stage (DES/CMF) pretreated biomass even with the presence of some lignin and xylan remained on the pretreated fiber; only a 9-fold increase was observed after the other sequence of CMF followed by DES treatment. Single stage CMF treatment or single stage DES pretreatment improved 5-fold glucose yield compared to the untreated sample for the hardwood sample. The enhancement of enzymatic saccharification for softwood was less than that of hardwoods with only 4-fold increase for the sequence CMF followed by DES treatment. The other sequence of treatments reached up to 2.5-fold improvement. A similar result was determined for the single stage CMF treatment while the single stage DES treatment reached only 1.4-fold increase compared to the untreated softwood. Hence, all these pretreatments presented different degrees of biopolymer removal from the cell wall and subsequent digestibility levels; synergistic effects were observed for hardwood particularly in the sequence DES followed by CMF treatment while softwoods remained relatively recalcitrant. Overall, these studies revealed insight into two novel methods to enhance lignocellulosic digestibility of biomass adding to the methodology to deconstruct cell walls for fermentable sugars.
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    Mechanisms of biogenic formaldehyde generation in wood
    Wan, Guigui (Virginia Tech, 2017-02-10)
    This work addresses biogenic formaldehyde (CH₂O) generated by wood during the manufacture of non-structural wood-based composites, from which CH₂O emissions are regulated. The target for regulation has been anthropogenic CH₂O released from hydrolytically unstable amino resins like urea-formaldehyde. However, current regulations (the Formaldehyde Standards for Composite Wood Products Act, signed into law in 2010 and implemented in 2016) restrict allowable emissions to such low levels that biogenic CH₂O may affect regulation compliance. The industry has met the latest regulations with new amino resin technologies. Nevertheless persistent anecdotal reports suggest that biogenic CH₂O complicates regulation compliance. This work represents an industry/university cooperation to seek a more thorough understanding of biogenic CH₂O, to begin documentation of biogenic CH₂O levels in wood, and to study the conditions and chemical mechanisms of its formation. Efforts began by establishing CH₂O analysis using the fluorimetric acetylacetone determination. A custom 12-liter chamber with controlled temperature and relative humidity, and "ultrapure" nitrogen (N₂) ventilation was created to measure CH₂O emissions from flakes sampled from four Virginia pine (Pinus virginiana) trees. Emissions from never-heated specimens varied significantly among the four trees, ranging from 0.02 – 0.19 µg CH₂O/m³g dry wood. Heating (200°C, 1 hour), followed by chamber equilibration, resulted in significantly increased emissions on the order of 50%. Sequential heating, followed by chamber equilibration (in other words, heat/equilibrate/measure emission/repeat), resulted in declining emissions suggesting that a finite chemical source of CH₂O was being depleted by the sequential heat treatment. Flake specimens were stored in the open laboratory, and over 2-3 months laboratory storage, initially high emitting specimens gradually emitted less CH₂O, and initially low emitters gradually emitted more CH₂O. Concerns over laboratory contamination were perhaps allayed when background levels of laboratory CH₂O were determined to be similar to the background levels in the ultrapure N₂ used to ventilate the chamber. Measurement of emissions was abandoned, and thereafter a simple water extraction technique (~ 94% CH₂O recovery) was used to measure the CH₂O content of never-heated and heated wood specimens, where the difference was identified as CH₂O generated due to heating. Increment cores from living Virginia pine (Pinus virginiana), yellow-poplar (Liriodendron tulipifera), and radiata pine (Pinus radiata) trees were used to measure CH₂O content and CH₂O generation due to heating (200°C, 10 min). Significant variations within and between trees of the same species were observed. Tissue types (juvenile/mature, heartwood/sapwood) sometimes correlated to higher CH₂O contents and greater heat-generation potential; but sometimes not depending upon species. Heating increased CH₂O levels 3-60 fold. Heating with high moisture levels caused greater CH₂O generation than for dry specimens. This moisture effect and a separate serendipitous observation suggested that CH₂O generation is acid catalyzed. Radiata pine generated extraordinarily high CH₂O levels when heated, far exceeding the other two species. It was suggested that pine extractives might catalyze CH₂O generation, perhaps in lignin. Pinus virginiana wood was heated (200°C, 10 or 60 min) while dry or after aqueous/acid or base pretreatment in order to reveal mechanisms of formaldehyde (CH₂O) generation. Among wood structural polymers, lignin was the overwhelming source of biogenic CH₂O, consistent with prior reports. The effects of wood extractives are mentioned below. The selection of acid catalyst strongly affected CH₂O generation as predicted in the acidolysis literature of lignin model compounds and isolated lignins. Lignin methoxyl cleavage was also observed, but was considered an unlikely source of thermochemical CH₂O. Alkaline pretreatments suppressed CH₂O generation. Regarding wood-based composite manufacture, the implications are that lignin reactions can be manipulated during hot-pressing. Potential benefits include reduced product emissions, and/or novel crosslinking strategies using biogenic CH₂O. Heat generation of CH₂O in Virginia pine and radiata pine was substantially reduced by extractives removal, but there was no such effect in yellow-poplar wood. Results suggested that pine extractives promote CH₂O generation by catalyzing or otherwise promoting C2 cleavage (acidolysis) in lignin. Thioacidolysis demonstrated that pine lignin reactions were strongly dependent upon the presence or absence of the extractives. When present, pine extractives seemed to promote C2 cleavage (CH₂O generation), but otherwise reduced the overall extent of lignin degradation. When pine extractives were removed, lignin suffered substantial degradation, but apparently less C2 cleavage since CH₂O generation was reduced. In contrast, thioacidolysis showed that yellow-poplar extractives appeared to promote lignin degradation, but extractives removal had no detectable impact on CH₂O generation. Implications exist for biorefinery research because it was shown that lignin reactions can be strongly affected by wood extractives. Two dimensional, proton-carbon, correlation NMR spectroscopy (2D NMR), and solvent submersion dynamic mechanical analysis (DMA) was used to investigate wood changes caused by heating in the presence or absence of external acid catalysis. 2D NMR was relatively insensitive to fine lignin changes that were detected using thioacidolysis. 2D NMR was effective for observing lignin changes under more extreme heating conditions, and evidence was found for lignin crosslinking reactions that probably occurred through substitution into lignin aromatic rings. DMA showed that most heating conditions caused an increase in the lignin glass transition temperature (Tg), consistent with heat-induced lignin crosslinking. Under one experimental condition of wood heating, DMA showed a reduction in the lignin glass transition temperature (Tg). This suggested that lignin cleavage without subsequent repolymerization might be promoted by carefully controlled conditions, and this has implications for biorefinery research where lignin repolymerization can be problematic. Finally, this work strongly supported the hypothesis that lignin generates CH₂O through well-known acidolysis pathways where CH₂O is borne from the lignin gamma-methylol group. Therefore, it was predicted that upon heating corn (Zea mays L.) stalk should generate less CH₂O than wood because corn stalk lignins exhibit a high degree of coumaric acid esterfication at the gamma-methylol group. This hypothesis was perhaps verified- it was found that in 4 out of 6 experimental heating conditions that corn stalk generated significantly less CH₂O than Virginia pine.
  • Variegatic acid from Serpula lacyrmans reduces FeIII and interacts with other fungal metabolites for location-specific generation and scavenging of reactive oxygen species
    Zhu, Yuan; Mahaney, James; Jellison, Jody; Cao, Jinzhen; Gressler, Julia; Hoffmeister, Dirk; Goodell, Barry (2016)
    This study aims to clarify the role of variegatic acid (VA) secreted from Serpula lacyrmans in a chelator-mediated Fenton (CMF) system, including FeIII reduction and the generation of reactive oxygen species (ROS) in the presence of H2O2 and oxalate. As the principle component of the fungal extracellular matrix (ECM), β-glucan isolated from Basidiomycota species was also assessed in scavenging ROS with regard to its potential as a protective barrier for fungal hyphae. Our results demonstrate that VA was effective in reducing FeIII and promoting ROS generation. It is known that oxalate is necessary for solubilization of iron, but both iron reduction and ROS generation were impeded in the presence of oxalate. However, we observed that a higher pH (4.4) favored FeIII transfer from oxalate to VA to drive Fenton-based ROS generation as opposed to a lower pH (2.2), which would be found within the ECM. We propose that a pH-dependent FeIII transfer to VA is employed by S. lacyrmans to permit ROS generation within the higher pH wood cell wall, while limiting ROS production near the fungal hyphae. Further, β-glucan was found to scavenge ROS in acid environments and we postulate that this allows ROS scavenging within the ECM to further limit damage to the fungal hyphae when CMF reactions are active. Data support a role for the ECM in protecting fungal hyphae from ROS generated during decay processes and also support a potential role for a VA-mediated Fenton system in deconstruction of lignocellulose materials by S. lacyrmans.