A Method for Evaluating Lignin Mobility Distributions Obtained by Capillary Zone Electrophoresis

Abstract

The profile of the mobility distribution of lignin-containing samples depends on type of sample. To facilitate comparison, a procedure for determining the average mobility (μ_av), i.e. the average charge density, of lignin is presented. The procedure is applied to black liquor (Sb), isolated dissolved lignin (Sd) and isolated residual (Sr) lignin samples, obtained from flow-through kraft cooks of softwood. The μ_av of the isolated lignin samples is compared with the concentration of phenol and carboxyl groups and relative molecular size. As the cook proceeds the μ_av for a particular type of lignin sample increases, reflecting an increase in average charge density. The μ_av, measured at pH 12, decreases in the order Sd>Sb>Sr, except at the end of the cook, when the average charge densities of the Sb and Sr samples are similar. Associations between lignin and carbohydrate fragments are proposed to cause the lower mobility of black liquor compared to isolated dissolved lignin. Characterisations performed at pH 10 indicate that the isolated dissolved lignin samples may have a higher pK_a in the middle of the cook than the other samples.     

Detection of Pinosylvins in Solid Wood of Scots Pine Using Fourier Transform Raman and Infrared Spectroscopy

Abstract

Diffuse reflectance Fourier transform infrared (DRIFT) and near infrared (NIR) FT-Raman spectroscopy were used to detect pinosylvins in the wood of Pinus sylvestris L. trees. NIR FT-Raman spectroscopy offered the possibility of revealing pinosylvins simply by visual inspection of Raman spectra whereas DRIFT spectra needed a more complicated evaluation. Pinosylvin and resin acids from Scots pine were examined as to the possibility of their being the cause of observed spectral differences between sapwood and heartwood. Since pinosylvins are important compounds for the decay resistance of Scots pine wood, the detection of pinosylvins with Raman spectroscopy might be used to assess durability of wood products.     

Phase separation and gelation of epoxy resin/hyperbranched polymer blends

The structural buildup during reticulation of thermoset systems containing reactive modifiers can strongly influence the final properties of such blends. This was studied by considering the rheological behavior during cure of an epoxy/amine thermoset system blended with reactive dendritic hyperbranched polymers (HBPs). Depending on the chemical structure of the HBP used in the blend, a phase separation could be observed. The onset and offset of the phase separation process could be detected by observing the evolution of the viscoelastic properties. The phase separation onsets obtained by rheological measurements were compared with the values obtained by traditional cloud point observations. Good agreement between the two techniques was observed. Hyperbranched polymers that did not phase separate during the curing process were used to study gelation phenomena and its dependence on the reactivity and functionality of the HBP. The gelation of the homogeneous blend system using the Flory‐Stockmayer theory was also modeled. This highlighted the influence of both functionality and reactivity of the components, and the appearance of co‐operative polymerization mechanisms in homogeneous blends.     

Flow through a convergence. Part 1: Critical conditions for unstable flow

The critical conditions leading to fracture in elongation and different types of flow instabilities were examined in uniaxial elongation and in a capillary rheometer equipped with dies having different entry profiles. Either ductile or brittle fracture may be observed, ductile being related to necking of material. The critical stress approach was used to predict fracture in elongation. All linear polymers studied in this work exhibited ductile fracture in uniaxial elongation, but the transition to brittle fracture is discussed in relation to existing experiments with other materials. In a ductile fracture regime, critical stress and work both increase with an increasing rate of deformation, whereas in a brittle regime the critical values remain constant. The converging flow studies indicated that two types of flow instability that have been previously related to each other, namely, pressure oscillations and voltions distortions, are of different origins. The critical flow rate for pressure oscillations is independent of entry profile, and the origin for this type of instability lies along the wall of the capillary. On the other hand, the critical flow rate for volume distortions increased with a decreasing entry angle, indicating that volume distortions are not a consequence of pressure oscillation, nor are their origin at the capillary wall. Numerical simulations were used to determine the stress profiles within the flow, and it was shown that the onset of volume distortions is directly related to the magnitude of elongational stress and work, and may therefore be considered to be caused by fracture in elongation. In dies with 90° entry profile, volume distortions were observed simultaneously with pressure oscillations, making it difficult to distinguish between the two phenomena.     

Viscoelasticity in Polymer Films on Rigid Substrates

The viscoelasticity of two thermally crosslinked polymer coatings was examined in terms of relaxation of the applied stress after a sudden strain. Two different transient methods were utilized: flat‐ended cylindrical indentation testing of a polymer film on a rigid substrate and tensile testing of a corresponding free‐standing polymer film. The correlation between tensile and indentation tests was studied. The mechanical response of a viscoelastic layer deposited on a rigid substrate was investigated as a function of indentation depth. There was good agreement between the results of the tensile and indentation tests for thick film layers at moderate indentation depths. The findings indicate that the substrate influences the coating performance by reducing the viscous contribution to the stress response and amplifying the magnitude of the equilibrium modulus for large indentation depths. The indentation method utilized here was shown to be a potentially suitable tool for the determination of Poisson's ratio of polymer films.

     

Rheological properties of hyperbranched polymer/poly(ethylene terephthalate) reactive blends

The rheological properties in solution, in shear and in uniaxial elongation of poly(ethylene terephthalate) (PET) reacted together with hyperbranched polymers (HBPs) were investigated. Two different PET grades, of low and high molecular weights, were compounded with sub‐ to over‐stoichiometric concentrations of HBPs of second and fourth pseudo‐generation, and subsequently subjected to a solid‐state polycondensation (SSP). The formation of microgels, which occurs at high HBP concentration, gave rise to a large increase in melt elasticity and a related decrease in melt strength. At low HBP concentrations, the complex viscosity of the unreacted HBP/PET was considerably reduced, thus demonstrating a lubrication effect of the HBP molecules. During SSP, the intrinsic and shear viscosities exhibited a gradual increase, which was similar for both PET and HBP/PET blends, and was correlated to an increase in molecular weight, through linear‐chain extension and branching reactions. The elongational viscosity of the reactive blends was also increased as a function of reaction time, and this increase was much larger in the case of the HBP/PET blends. A 400% increase in melt strength of the PET was obtained by combining SSP and trace amounts of an HBP of second generation, without any decrease in drawability.     

Danger Control Programs Cause Tissue Injury and Remodeling

Are there common pathways underlying the broad spectrum of tissue pathologies that develop upon injuries and from subsequent tissue remodeling? Here, we explain the pathophysiological impact of a set of evolutionary conserved danger control programs for tissue pathology. These programs date back to the survival benefits of the first multicellular organisms upon traumatic injuries by launching a series of danger control responses, i.e., 1. Haemostasis, or clotting to control bleeding; 2. Host defense, to control pathogen entry and spreading; 3. Re-epithelialisation, to recover barrier functions; and 4. Mesenchymal, to repair to regain tissue stability. Taking kidney pathology as an example, we discuss how clotting, inflammation, epithelial healing, and fibrosis/sclerosis determine the spectrum of kidney pathology, especially when they are insufficiently activated or present in an overshooting and deregulated manner. Understanding the evolutionary benefits of these response programs may refine the search for novel therapeutic targets to limit organ dysfunction in acute injuries and in progressive chronic tissue remodeling.     

Toll-Like Receptor and Accessory Molecule mRNA Expression in Humans and Mice as Well as in Murine Autoimmunity,Transient Inflammation,and Progressive Fibrosis

The cell type-, organ-, and species-specific expression of the Toll-like receptors (TLRs) are well described, but little is known about the respective expression profiles of their accessory molecules. We therefore determined the mRNA expression levels of LBP, MD2, CD36, CD14, granulin, HMGB1, LL37, GRP94, UNC93b1, TRIL, PRAT4A, AP3B1, AEP and the respective TLRs in human and mouse solid organs. Humans and mice displayed significant differences between their respective mRNA expression patterns of these factors. In addition, the expression profiles in transient tissue inflammation upon renal ischemia-reperfusion injury, in spleens and kidneys from mice with lupus-like systemic autoimmunity, and in progressive tissue fibrosis upon unilateral ureteral obstruction were studied. Several TLR co-factors were specifically regulated during the different phases of these disease entities, suggesting a functional involvement in the disease process. Thus, the organ- and species-specific expression patterns need to be considered in the design and interpretation of studies related to TLR-mediated innate immunity, which seems to be involved in the tissue injury phase, in the phase of tissue regeneration, and in progressive tissue remodelling.     

A new device for coating single particles under controlled conditions

A new device for coating a single levitated particle in a controllable environment is designed and tested. This enables fluidized bed processing to be simulated experimentally on a single-particle level. The device consists of a coating chamber, which contains a capillary tube for levitating the particle, a micro-dispenser for producing discrete drops of controlled size and velocity and a device for supplying gas with specified temperature and humidity. The coating chamber consists of two parts, a confined space where the particle is levitated and a droplet insertion cone where the coating solution is injected into the particle suspending gas flow. A capillary with a well-defined diameter connects the droplet insertion cone and the area where the particle is levitated. The device is equipped with a piezo-actuated flow-through micro-dispenser that has the ability to produce discrete droplets with high reproducibility in terms of droplet size and velocity. The gas required for the coating process is taken from a gas container where the water content is analysed and kept at a minimum. A liquid flow is then introduced into the gas flow at a well-defined flow rate, mixed and evaporated in a three-way mixing vault. The humidified gas flow is then split into two separate flows; a suspending gas flow and a protecting gas flow for the inside of the coating chamber. The device is equipped with a high-speed video camera for monitoring both droplet production and droplet impact. Temperatures and flow rates throughout the device are measured and logged. Preliminary results show the influence of solvent, gas quality and coating procedure on the quality of the coating.