Michael P. Wolcott

Study of the Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Cellulose Nanowhisker Composites Prepared by Solution Casting and Melt Processing

In this study cellulose nanowhiskers (CNW) were prepared by sulfuric acid hyrolysis from microcrystalline cellulose (MCC). The biopolymer composites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNW, was fabricated by solution casting using N,N-dimethylformamide (DMF) as the solvent. Homogeneous dispersion of the whiskers was achieved and the composites exhibited improved tensile strength and modulus and increased glass transition temperature. The melt processing (extrusion and injection molding) of PHBV/CNW composites was also attempted. Despite using polyethylene glycol (PEG) as a compatibilizer, CNW agglomerates formed during freeze-drying could not be broken and well dispersed by the extrusion process due to the large surface area and the polar nature of CNW. As a result, the melt processed PHBV/CNW composites exhibited decreased strength and constant glass transition temperature, a typical trend of microparticle filled polymer systems. MCC was also treated by high-speed mechanical homogenizer to reduce its particle size down to nanoscale range. The homogenized MCC (HMCC) was blended with PHBV by melt processing with the same conditions. The obtained composites were found to have similar properties as the melt-processed PHBV/CNW composites due to poor HMCC dispersion. To the best of our knowledge, PHBV/ CNW system has not been studied so far. The treatment of MCC with high-speed homogenizer has also not been reported. This study augments the research on CNW nanocomposites.

Interfacial contributions in lignocellulosic fiber-reinforced polyurethane composites

Whereas lignocellulosic fibers have received considerable attention as a reinforcing agent in thermoplastic composites, their applicability to reactive polymer systems remains of considerable interest. The hydroxyl-rich nature of natural lignocellulosic fibers suggests that they are particularly useful in thermosetting systems such as polyurethanes. To further this concept, urethane composites were prepared using both unused thermomechanical pulp and recycled newsprint fibers. In formulating the materials, the fibers were considered as a pseudo-reactant, contributing to the network formation. A di-functional and tri-functional poly(propylene oxide)-based polyol were investigated as the synthetic components with a polyol-miscible isocyanate resin serving as a crosslinking agent. The mechanical properties of the composites were found to depend most strongly on the type of fiber, and specifically the accessibility of hydroxy functionality on the fiber. Dynamic mechanical analysis, swelling behavior, and scanning electron micrographs of failure surfaces all provided evidence of a substantial interphase in the composites that directly impacted performance properties. The functionality of the synthetic polyol further distinguished the behavior of the composite materials. Tri-functional polyols generally increased strength and stiffness, regardless of fiber type. The data suggest that synthetic polyol functionality and relative accessibility of the internal polymer structure of the fiber wall are dominant factors in determining the extent of interphase development. Considerable opportunity exists to engineer the properties of this material system given the wide range of natural fibers and synthetic polyols available for formulation.

Unique low-molecular-weight lignin with high purity extracted from wood by deep eutectic solvents (DES): a source of lignin for valorization

This paper reports a new method of applying Deep Eutectic Solvents (DES) for extracting lignin from woody biomass with high yield and high purity. DES mixtures prepared from choline chloride (ChCl) and four hydrogen-bond donors – acetic acid, lactic acid, levulinic acid and glycerol – were evaluated for treatment of hardwood (poplar) and softwood (D. fir). It was found that these DES treatments can selectively extract a significant amount of lignin from wood with high yields: 78% from poplar and 58% from D. fir. The extracted lignin has high purity (95%) with unique structural properties. We discover that DES can selectively cleave ether linkages in wood lignin and facilitate lignin removal from wood. The mechanism of DES cleavage of ether bonds between phenylpropane units was investigated. The results from this study demonstrate that DES is a promising solvent for wood delignification and the production of a new source of lignin with promising potential applications.

Crystallization kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites

In this study, biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films with 1.2-4.6 wt% of cellulose nanowhiskers (CNWs) were manufactured by solution casting using N,N-dimethylformide (DMF) as the solvent. Crystallization behaviors of PHBV/CNW composites were studied under isothermal conditions using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The changes in PHBV crystalline structure were studied using wide angle X-ray diffraction (WAXD). Avrami analysis was performed to study the effects of CNW concentration and temperature on the crystallization rate and crystallinity of PHBV. POM study confirmed the results from the Avrami analysis. In particular, the results revealed the dual effects (i.e., nucleation and confinement) of CNWs on PHBV nucleation. Depending on the concentration of CNWs, the crystallization rate of PHBV could be either increased or decreased due to the combined effects. High crystallization temperatures increased the diffusion rate of PHBV chains and the growth rate of PHBV spherulites. However, the nucleation effect of CNWs decreased at high crystallization temperatures.

Preparation and properties of aligned poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanowhiskers composites

In this study a unidirectionally aligned cellulose nanowhisker (CNW) composite was developed. CNW in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrix was aligned using an external electric field and the morphology and mechanical properties of the resultant anisotropic composites were studied. PHBV films with 1.5-7 wt% of CNWs were manufactured using solution casting. A DC electric field of 56.25 kV/m was applied during solvent evaporation. Both microstructural and mechanical analyses were performed to study the orientation of CNWs in the films. Mechanical properties of the samples were tested at 0°, 15°, 30°, 45° and 90° with respect to electric field direction by a dynamic mechanical analyzer (DMA). DMA results showed that CNW concentration has a strong influence on the degree of CNW alignment. The electric field was effective in aligning CNWs up to 4 wt% CNW concentration. The samples with higher concentrations showed virtually isotropic behavior, due to significantly enhanced restraints on CNW mobility. The restrains were attributed to CNW/CNW and CNW/polymer interactions. Rheological results confirmed the enhance restraints.

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.

Functional stability of a mixed microbial consortium producing PHA from waste carbon sources

Polyhydroxyalkanoates (PHAs) represent an environmentally effective alternative to synthetic thermoplastics; however, current production practices are not sustainable. In this study, PHA production was accomplished in sequencing batch bioreactors utilizing real wastewaters and mixed microbial consortia from municipal activated sludge as inoculum. Polymer production reached 85, 53, and 10% of the cell dry weight from methanol-enriched pulp and paper mill foul condensate, fermented municipal primary solids, and biodiesel wastewater, respectively. Using denaturing gradient gel electrophoresis of 16S-rDNA from polymerase chain reaction-amplified DNA extracts, distinctly different communities were observed between and within wastewaters following enrichment. Most importantly, functional stability was maintained despite differing and contrasting microbial populations.

Evaluation of the cure kinetics of the wood/pMDI bondline

Abstract Micro-dielectric analysis (μDEA) and differential scanning calorimetry (DSC) were used to monitor cure of polymeric diphenylmethane diisocyanate (pMDI) resin with wood strands in a saturated steam environment. A first-order autocatalyzed kinetic model was employed to determine kinetic parameters. The kinetics were found to follow an Arrhenius relation. A single ramp DSC technique and μDEA produced models that predicted similar results at higher cure temperatures, but the μDEA-based model predicts a longer cure time at low temperatures. The isothermal μDEA method yields higher activation energies and Arrhenius frequency factors than models based on single DSC ramps. A modification to ASTM E698 was made to conform to the assumption of autocatalyzed kinetics. The modified ASTM E698 method predicted an earlier end of cure than the μDEA-based models and was in agreement with DSC results obtained by partial cure experiments. The activation energies and frequency factors for the different cure monitoring methods are sensitive to different stages of cure.

Partial depolymerization of enzymolysis lignin via mild hydrogenolysis over Raney Nickel

In this work, partial depolymerization of enzymolysis lignin collected from a woody biomass-to-ethanol process was studied via mild hydrogenolysis under the catalysis of Raney Ni. The depolymerized lignin products were low molecular weight oligomers with increased hydroxyl values. The solvent selected, use of base and various reaction parameters were all found to influence yield of depolymerization, the molecular weight and hydroxyl value of the hydrogenated product. The depolymerized lignins displayed greatly enhanced solubility in organic solvents, and therefore would have great potential to be used as feedstock for many valuable thermosetting polymer applications.

Compliance rate change of tapered double cantilever beam specimen with hybrid interface bonds

Abstract This paper presents a combined numerical and experimental study of compliance rate change of Tapered Double Cantilever Beam (TDCB) specimens for Mode-I fracture of hybrid interface bonds. The easily machinable TDCB specimen, which is designed to achieve a constant rate of compliance change with respect to crack length, is developed for Mode-I fracture tests of hybrid material bonded interfaces, such as wood bonded to fiber-reinforced plastic (FRP) composite. The linearity of compliance crack-length relationship of the specimen is verified by both Rayleigh–Ritz method and finite element analysis. An experimental compliance calibration program for specimens with wood–wood and FRP–FRP bonded interfaces is carried out, and a constant rate change of compliance with respect to crack length is obtained for a specific range of crack length. Fracture tests are further performed using TDCB specimens for wood–wood and wood–FRP bonded interfaces to determine the critical loads for crack initiation and crack arrest, and using the constant compliance rate change of the specimens determined by experiment or analysis, the respective critical strain energy release rates, or fracture energies, are obtained. This study indicates that the constant compliance rate change obtained from experiment or finite element analysis for linear-slope TDCB specimens can be used with confidence for fracture studies of hybrid material interface bonds.