Stephen S. Kelley

Relaxation behaviour of the amorphous components of wood

The viscoelastic properties of mod were investigated using dynamic mechanical thermal analysis and differential scanning calorimetry. Under a limited set of conditions, two separate glass transitions (Tg) could be identified with both techniques. These two transitions were identified as arising from the amorphous lignin and hernicellulose matrix in the wood cell wall. Moisture dramatically affected the temperature at which the two dispersions occurred and, consequently, the ability to resolve their independent responses. The relationship betweenTg and moisture for both components could be modelled with the Kwei equation, which accounts for the presence of secondary interactions. Annealing and specific interactions of a series of organic diluents were wed in an attempt to enhance the resolution of the two components values ofTg. Time-temperature superposition was shown to be applicable to wood plasticized with ethyl formamide, following Williams-Landel-Ferry behaviour over the temperature rangeTg toTg + 85° C. These observations allow certain conclusions to be drawn concerning the applicability of existing models of the wood cell walls supermolecular morphology. Most notably, models of thein situ morphology of the three wood components can be limited to those which consider the amorphous matrix of lignin and hemicellulose to be immiscible.

The effect of degree of acetylation on gas sorption and transport behavior in cellulose acetate

Abstract Cellulose acetate films with degrees of substitution of 1.75, 2.45, and 2.84 were characterized in terms of chemical composition, acetyl group distribution, glass transition, crystallinity, and dynamic mechanical properties. Permeability coefficients for a series of gases, at 1 atm and 35°C, were found to increase with degree of acetylation. Sorption isotherms for CO 2 and CH 4 at 35°C were analyzed in terms of the dual-mode sorption model, and it was shown that conditioning of the films by CO 2 caused an increase in the Langmuir sorption capacity. The permeability of CO 2 was found to increase with pressure above 10 atm due to plasticization. Highly sorbing CO 2 swells the polymer such that interchain interactions are disrupted and segmental mobility increases. Infrared analyses support this conclusion and show that after complete removal of CO 2 and a sufficient relaxation period, the cellulose acetate returned to its original condition. Therefore, the response of the films to plasticization by CO 2 is not only time and pressure dependent but also reversible.

FT-IR imaging and pyrolysis-molecular beam mass spectrometry: new tools to investigate wood tissues

Fourier transform infrared (FT-IR) microimaging spectroscopy and pyrolysis molecular beam mass spectrometry (py-MBMS) were used as rapid analysis tools to evaluate differences in the chemical composition of 1-year-old transgenic aspens. Multivariate analysis of the spectroscopic data sets was used to compare the cell wall composition of nontransformed control to transgenic aspen plants with GRP-iaaM gene and with GRP-iaaM/35S-ACCase gene. Principal component analysis (PCA) was applied to both the FT-IR and py-MBMS spectra, which revealed sample groupings due to differences in chemical composition. Evaluating the PCA loadings allows determination of the chemical features responsible for the groupings. The FT-IR microimaging data was also used to monitor changes in the chemical composition as a function of the distance from the pith to the bark using partial least squares (PLS) analysis. The analysis shows that the changes in the composition of the xylem that occur over one annual growth ring can be monitored with FT-IR microimaging.

Crystallization of poly(hydroxybutrate‐co‐hydroxyvalerate) in wood fiber‐reinforced composites

Wood fiber-reinforced composites were prepared from poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB/HV) copolymers containing 9 and 24% valerate. The effects of fibers on crystallization were investigated. Thermomechanical pulp, bleached Kraft fibers, and microcrystalline cellulose filler were used as the reinforcing phase. The crystallization of PHB/HV in composite materials was examined using Modulated Differential Scanning Calorimetry (MDSC) and hot-stage microscopy. Hot-stage microscopy showed that polymer crystallites are nucleated on the fiber surface and that the density of nuclei was greater in fiber-reinforced composites than in unfilled material. Dynamic crystallization experiments showed that bleached Kraft, thermomechanical pulp, and microcrystalline cellulose increased the crystallization rate of PHB and PHB/HV both from the glass and melt. However, ultimate crystallinity determined from the heat of crystallization was the same in unreinforced and reinforced materials. The kinetics of PHB/HV crystallization were examined using nonisothermal Avrami-type analysis. Unreinforced and Kraft-reinforced PHB were characterized and compared with unreinforced PHB/9%HV. The Avrami exponent of crystallization, related to nucleation mechanism and growth morphology, is 2.0 for unreinforced PHB, 2.8 for kraft-reinforced PHB, and 3.0 for unreinforced PHB/9%HV.

Effect of yeast fermentation by-products on poly[1-(trimethylsilyl)-1-propyne] pervaporative performance

The pervaporation recovery of ethanol from yeast fermentation broth was investigated using poly[1-(trimethylsilyl)-1-propyne]. The deterioration of membrane performance in the presence of fermentation broth was observed. The fouled membrane was characterized by gas permeation and density measurements, and sorption of pure components of the fermentation broth in PTMSP was studied to clarify the fouling mechanism. It was concluded that properties of the membrane deteriorate due to internal contamination of the PTMSP free volume with non-volatile by-products of the fermentation. The PTMSP film did not show appreciable deterioration of membrane properties in the pervaporation of aqueous solution of organic compounds with high volatility.

A new technique for the simultaneous, real-time measurement of membrane compaction and performance during exposure to high-pressure gas

Abstract Membrane compaction accounts for a major source of the flux decline that occurs during gas separation using polymeric membranes. Previous membrane compaction studies have been limited by the inability to simultaneously measure membrane performance. In this study, we report the development of a technique based on ultrasonic time-domain reflectometry (TDR) that enables the simultaneous, real-time, noninvasive measurement of membrane compaction and performance during gas separation. In order to demonstrate the utility of the technique, representative data are presented for membrane compaction and pressure-normalized flux of a commercial asymmetric cellulose acetate (CA) gas separation membrane. Data obtained during the recovery cycle, i.e., after the pressure difference across the membrane is removed, are also described. These preliminary results indicate that the ultrasonic TDR technique can be successfully applied to quantify the effect of high-pressure gases on polymeric films and asymmetric membranes.

Engineering Plastics from Lignin. IX. Phenolic Resin Synthesis and Characterization

Abstract The performance of phenol-formaldehyde (PF) resins, formulated with lignin derivatives previously synthesized as phenolic resin prepolymers, was evaluated by thermal analysis of the curing process, and by a hard maple shear block test. At 54 and 60% phenol replacement levels, respectively, kraft (KL) and steam explosion lignin (SEL)-based resoles exhibited cure behavior very similar to a standard PF resin. Acid hydrolysis lignin gelled prematurely, and was found to be incompatible with the normal synthesis procedure. Differential scanning calorimetry (DSC) was used to compare kinetic parameters for the curing process of neat and lignin derived phenolic resins. Activation energies and cure rates determined by DSC showed no difference between adhesives. High lignin contents had no inhibitory effect on resin cure. Shear strength properties were evaluated in a compression test, and results illustrate that both lignin-based resins have acceptable strength properties, both in a dry and accelerated agin...

Development of Langmuir―Schaeffer Cellulose Nanocrystal Monolayers and Their Interfacial Behaviors

Model cellulose surfaces based on cellulose nanocrystals (CNs) were prepared by the Langmuir-Schaeffer technique. Cellulose nanocrystals were obtained by acid hydrolysis of different natural fibers, producing rodlike nanoparticles with differences in charge density, aspect ratio, and crystallinity. Dioctadecyldimethylammonium bromide (DODA-Br) cationic surfactant was used to create CN-DODA complexes that allowed transfer of the CNs from the air/liquid interface in an aqueous suspension to hydrophobic solid substrates. Langmuir-Schaeffer horizontal deposition at various surface pressures was employed to carry out such particle transfer that resulted in CN monolayers coating the substrate. The morphology and chemical composition of the CN films were characterized by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Also, their swelling behavior and stability after treatment with aqueous and alkaline solutions were studied using quartz crystal microgravimetry (QCM). Overall, it is concluded that the Langmuir-Schaeffer method can be used to produce single coating layers of CNs that were shown to be smooth, stable, and strongly attached to the solid support. The packing density of the films was controlled by selecting the right combination of surface pressure during transfer to the solid substrate and the amount of CNs available relative to the cationic charges at the interface.

Evaluation of PTMSP Membranes in Achieving Enhanced Ethanol Removal from Fermentations by Pervaporation

The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years. Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne] (PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance in operation with cell-containing fermentation broths.

Bicomponent Lignocellulose Thin Films to Study the Role of Surface Lignin in Cellulolytic Reactions

Ultrathin bicomponent films of cellulose and lignin derivatives were deposited on silica supports by spin coating, and after conversion into the respective polymer precursor, they were used as a model system to investigate interfacial phenomena relevant to lignocellulose biocatalysis. Film morphology, surface chemical composition, and wettability were determined by atomic force microscopy, X-ray photoelectron spectroscopy, and water contact angle, respectively. Phase separation of cellulose and lignin produced structures that resembled the cell wall of fibers and were used to monitor enzyme binding and cellulolytic reactions via quartz crystal microgravimetry. The rate and extent of hydrolysis was quantified by using kinetic models that indicated the role of the surface lignin domains in enzyme inhibition. Hydrophobic interactions between cellulases and the substrates and their critical role on irreversible adsorption were elucidated by using acetylated lignin films with different degrees of substitution. Overall, it is concluded that sensors based on the proposed ultrathin films of lignocellulose can facilitate a better understanding of the complex events that occur during bioconversion of cellulosic biomass.