Emission and Mechanical Properties of Glass and Cellulose Fiber Reinforced Bio-Polyamide Composites.

Climate change, access, and monopolies to raw material sources as well as politically motivated trade barriers are among the factors responsible for a shortage of raw materials. In the plastics industry, resource conservation can be achieved by substituting commercially available petrochemical-based plastics with components made from renewable raw materials. Innovation potentials are often not used due to a lack of information on the use of bio-based materials, efficient processing methods, and product technologies or because the costs for new developments are too high. In this context, the use of renewable resources such as fiber-reinforced polymeric composites based on plants has become an important criterion for the development and production of components and products in all industrial sectors. Bio-based engineering thermoplastics with cellulose fibers can be used as substitutes because of their higher strength and heat resistance, but the processing of this composite is still challenging. In this study, composites were prepared and investigated using bio-based polyamide (PA) as a polymer matrix in combination with a cellulosic fiber and, for comparison purposes, a glass fiber. A co-rotating twin-screw extruder was used to produce the composites with different fiber contents. For the mechanical properties, tensile tests and charpy impact tests were performed. Compared to glass fiber, reinforced PA 6.10 and PA 10.10, a significantly higher elongation at break with regenerated cellulose fibers, can be achieved. PA 6.10 and PA 10.10 achieve significantly higher impact strengths with the regenerated cellulose fibers than the composites with glass fibers. In the future, bio-based products will also be used in indoor applications. For characterization, the VOC emission GC-MS analysis and odor evaluation methods were used. The VOC emissions (quantitative) were at a low level but the results of the odor tests of selected samples showed values mostly above the required limit values.

Influence of Processing Glass-Fiber Filled Plastics on Different Twin-Screw Extruders and Varying Screw Designs on Fiber Length and Particle Distribution.

Due to their valuable properties (low weight, and good thermal and mechanical properties), glass fiber reinforced thermoplastics are becoming increasingly important. Fiber-reinforced thermoplastics are mainly manufactured by injection molding and extrusion, whereby the extrusion compounding process is primarily used to produce fiber-filled granulates. Reproducible production of high-quality components requires a granulate in which the fiber length is even and high. However, the extrusion process leads to the fact that fiber breakages can occur during processing. To enable a significant quality enhancement, experimentally validated modeling is required. In this study, short glass fiber reinforced thermoplastics (polypropylene) were produced on two different twin-screw extruders. Therefore, the machine-specific process behavior is of major interest regarding its influence. First, the fiber length change after processing was determined by experimental investigations and then simulated with the SIGMA simulation software. By comparing the simulation and experimental tests, important insights could be gained and the effects on fiber lengths could be determined in advance. The resulting fiber lengths and distributions were different, not only for different screw configurations (SC), but also for the same screw configurations on different twin-screw extruders. This may have been due to manufacturer-specific tolerances.

Modulation doping and charge density wave transition in layered PbSe-VSe2 ferecrystal heterostructures.

Controlling charge carrier concentrations remains a major challenge in the application of quasi-two-dimensional materials. A promising approach is the modulation doping of transport channels via charge transfer from neighboring layers in stacked heterostructures. Ferecrystals, which are metastable layered structures created from artificial elemental precursors, are a perfect model system to investigate modulation doping, as they offer unparalleled freedom in the combination of different constituents and variable layering sequences. In this work, differently stacked combinations of rock-salt structured PbSe and VSe2 were investigated using X-ray photoelectron spectroscopy. The PbSe layers act as electron donors in all heterostructures, with about 0.1 to 0.3 donated electrons per VSe2 unit cell. While they initially retain their inherent semiconducting behavior, they themselves become metallic when combined with a larger number of VSe2 layers, as evidenced by a change of the XPS core level lineshape. Additional analysis of the valence band structure was performed for selected stacking orders at different sample temperatures to investigate a predicted charge density wave (CDW) transition. While there appear to be hints of a gap opening, the data so far is inconclusive and the application of spatially resolved techniques such as scanning tunneling microscopy is encouraged for further studies.

Surface Transport Properties of Pb-Intercalated Graphene.

Intercalation experiments on epitaxial graphene are attracting a lot of attention at present as a tool to further boost the electronic properties of 2D graphene. In this work, we studied the intercalation of Pb using buffer layers on 6H-SiC(0001) by means of electron diffraction, scanning tunneling microscopy, photoelectron spectroscopy and in situ surface transport. Large-area intercalation of a few Pb monolayers succeeded via surface defects. The intercalated Pb forms a characteristic striped phase and leads to formation of almost charge neutral graphene in proximity to a Pb layer. The Pb intercalated layer consists of 2 ML and shows a strong structural corrugation. The epitaxial heterostructure provides an extremely high conductivity of σ=100 mS/□. However, at low temperatures (70 K), we found a metal-insulator transition that we assign to the formation of minigaps in epitaxial graphene, possibly induced by a static distortion of graphene following the corrugation of the interface layer.

From complementarity to comprehensiveness--targeting the membrane proteome of growing Bacillus subtilis by divergent approaches.

The analysis of integral membrane proteins (IMPs) with mass spectrometry-centered technologies has undergone great progress during the past few years, allowing for the analysis of several hundreds of IMPs. In this study, we investigated three promising shotgun approaches for the identification of IMPs of the model organism Bacillus subtilis. One comprises a classical membrane preparation procedure with carbonate and high-ionic-strength buffers, followed by SDS-PAGE and LC-MS/MS analysis. The two others are based on enzymatic trimming of the crude membrane fraction either with trypsin or proteinase K and subsequent gel-free analysis. As a result, we observed the highest degree of complementarity between the gel-based and the proteinase K approach, since the first exclusively addresses soluble loops and domains of IMPs and gave rise to 8709 unique peptides, whereas the latter contributed 1180 unique peptide identifications from otherwise inaccessible transmembrane helices (TMHs). All three methods contribute significant numbers (381, 284, and 276, respectively) to the total of 527 IMP identifications from the membrane fraction of exponentially growing B. subtilis cells, thus representing approximately 69% of all transcribed IMPs.

Complementary analysis of the vegetative membrane proteome of the human pathogen Staphylococcus aureus.

The Gram-positive bacterium Staphylococcus aureus is a serious human pathogen causing a wide variety of diseases, and its increasing resistance toward all available antibiotics makes its further investigation absolutely essential. We examined the membrane proteome of exponentially growing cells of S. aureus COL because this subproteome plays a major role in the virulence of the bacterium in its host. In general, an analysis of membrane proteins is impeded by their hydrophobic nature as well as by a high abundance of many cytosolic proteins. The implementation of three different technologies, one-dimensional gel-LC, two-dimensional LC, and a membrane shaving approach combined with MS/MS analyses, enabled an identification of 271 integral and 86 peripheral membrane proteins from exponentially growing cells. In particular, the latter approach that combined membrane shaving with a subsequent chymotrypsin digest of integral membrane domains of proteins greatly facilitated the detection of hydrophobic peptides derived from membrane-spanning segments (713 peptides, 60% of all peptides) and therefore yielded almost exclusively highly hydrophobic integral membrane proteins (96.7%). A comparison of the various methods disclosed the one-dimensional gel-LC and the shaving approach to be highly complementary techniques. A combination of them will reveal a most comprehensive view on membrane proteomes.

In vitro comparison of peracetic acid and bleach cleaning of polysulfone hemodialysis membranes.

Dialyzer reuse has been employed throughout the history of hemodialysis, but the practice remains controversial. Many studies have found changes in the beta(2)-microglobulin clearance for reused dialyzers, but it is difficult to draw quantitative conclusions from the clinical data. The objective of this study was to quantitatively compare the effects of bleach and peracetic acid cleaning on the clearance and surface charge characteristics of Fresenius F80B polysulfone dialyzers (Fresenius Medical Care, Lexington, MA, USA). Clearance experiments were performed using urea, vitamin B(12), and polydisperse dextrans, with data obtained before and after exposure to human plasma in an in vitro dialysis circuit. Dialyzers cleaned with peracetic acid had significantly lower clearance of the larger dextrans due to the presence of residual protein on or within the membrane. Bleach was able to remove this protein deposit, restoring the clearance characteristics, but there was a significant increase in the net negative charge of the membrane due to chemical reaction with the bleach. In addition, longer time exposure to bleach altered the membrane transport characteristics, increasing the solute clearance. These results provide important insights into the effects of bleach and peracetic acid on the properties of the F80B dialyzers.

Towards the entire proteome of the model bacterium Bacillus subtilis by gel-based and gel-free approaches.

With the emergence of mass spectrometry in protein science and the availability of complete genome sequences, proteomics has gone through a rapid development. The soil bacterium Bacillus subtilis, as one of the first DNA sequenced species, represents a model for Gram-positive bacteria and its proteome was extensively studied throughout the years. Having the final goal to elucidate how life really functions, one basic requirement is to know the entirety of cellular proteins. This review presents how far we have got in unraveling the proteome of B. subtilis. The application of gel-based and gel-free technologies, the analyses of different subcellular proteome fractions, and the pursuance of various physiological strategies resulted in a coverage of more than one-third of B. subtilis theoretical proteome.

Gel-free and gel-based proteomics in Bacillus subtilis: a comparative study.

The proteome of exponentially growing Bacillus subtilis cells was dissected by the implementation of shotgun proteomics and a semigel-based approach for a particular exploration of membrane proteins. The current number of 745 protein identifications that was gained by the use of two-dimensional gel electrophoresis could be increased by 473 additional proteins. Therefore, almost 50% of the 2500 genes expressed in growing B. subtilis cells have been demonstrated at the protein level. In terms of exploring cellular physiology and adaptation to environmental changes or stress, proteins showing an alteration in expression level are of primary interest. The large number of vegetative proteins identified by gel-based and gel-free approaches is a good starting point for comparative physiological investigations. For this reason a gel-free quantitation with the recently introduced iTRAQ (isobaric tagging for relative and absolute quantitation) reagent technique was performed to investigate the heat shock response in B. subtilis. A comparison with gel-based data showed that both techniques revealed a similar level of up-regulation for proteins belonging to well studied heat hock regulons (SigB, HrcA, and CtsR). However, additional datasets have been obtained by the gel-free approach indicating a strong heat sensitivity of specific enzymes involved in amino acid synthesis.

Proteome analyses of Staphylococcus aureus in growing and non-growing cells: a physiological approach.

Staphylococcus aureus is a versatile human pathogen causing a wide variety of diseases ranging from wound infection to endocarditis, osteomyelitis, and sepsis. In order to investigate this pathogen, we sought to analyze the cytoplasmic proteome of S. aureus COL by using two different approaches: two-dimensional (2D) gel analyses combined with matrix-assisted laser ionization-time of flight mass spectrometry and a gel-free system using multidimensional liquid chromatography followed by mass spectrometry. By combining both analyses we identified 1123 cytoplasmic proteins that represent two-thirds of the cytoplasmic proteome of the organism. With our standard 2D gel setup (pI 4-7) we identified 473 proteins that cover about 40% of the cytoplasmic proteome predicted for this proteomic window. The identified proteins belong to a variety of cellular functions ranging from the transcriptional and translational machinery, tricarboxylic acid cycle (TCC), glycolysis, and fermentation pathways to biosynthetic pathways of nucleotides, fatty acids, and cell wall components. While most of the metabolic pathways predicted for S. aureus were covered by this gel-based proteomics 650 additional proteins were identified by the gel-free approach, among them alkaline or hydrophobic proteins. In our work, we established a master 2D gel that enabled us to study the regulation of core carbon metabolism in S. aureus cells grown in a complex medium. Our comparison of the protein pattern of exponentially growing cells with that of stationary-phase cells revealed a higher amount of enzymes involved in protein synthesis, transcription, and glycolysis in exponentially growing cells. In contrast, enzymes of the TCC and gluconeogenesis are increased at the stationary phase. With this comprehensive proteome map we have an essential tool for a better understanding of cell physiology of the human pathogen, S. aureus.

Effect of peracetic acid reprocessing on the transport characteristics of polysulfone hemodialyzers.

Peracetic acid is used extensively for reprocessing hemodialyzers, despite several indications that reprocessing alters the dialyzer transport characteristics. The objective of this study was to obtain quantitative data for the effects of peracetic acid reprocessing on the clearance and sieving coefficients of urea, vitamin B12, and polydisperse dextrans using Fresenius F80A polysulfone dialyzers. Reprocessing restored the urea and vitamin B12 clearance to close to their original values. However, the reprocessed dialyzers had substantially lower clearance of the larger molecular weight dextrans, which was attributed to reductions in the effective pore size caused by residual plasma proteins within the membrane. Storage in peracetic acid provided some additional removal of residual proteins, although the clearance and sieving coefficients of the larger dextrans remained well below their original values. Peracetic acid caused no degradation of the membrane polymer, in sharp contrast to results obtained with bleach reprocessing.