38 research outputs found
Structure-property relations of highly ordered bio-nanocomposites
Bio-nanocomposites with superior mechanical, transport and flame-retardant properties can be produced from the combination of biopolymers and silicate nanoclay platelets, such as montmorillonite (MMT) [1,2,4]. The highly ordered nanostructure observed in such systems is often compared to natural ones, such as in the brick-and-mortar arrangement of aragonite plates in nacreous materials [3]. Previous work on nacre-mimetic alginate/MMT nanocomposites has shown good compatibility between the biopolymer and inorganic filler and a dependence on MMT concentration to the level of alignment [4]. In this study, we investigate the effect of gelation on the orientation of nanoparticles and its impact on clay stacking and effective aspect ratio. Thermo-reversible gelling biopolymers, i.e. gelatin and carrageenan, were used as matrices to induce early gelation; and compared to sodium alginate (late gelling reaction). Self-supporting bio-nanocomposite films based on gelatin or carrageenan, with a wide range of Na-montmorillonite concentration – up to 80 wt.% MMT – were successfully prepared by solvent casting. The obtained films display a highly aligned nacre-like structure (Fig. 1). To investigate the effect of MMT ordering on the mechanical properties, we have analyzed the obtained films with dynamic mechanical thermal analysis. The bio-nanocomposite films display exceptional mechanical properties, with storage modulus as high as 33 GPa (carrageenan/MMT); and high reinforcement depending on MMT concentration (Fig. 2). At remarkably high inorganic fraction, 80 wt.% MMT, early gelling biopolymers showed a continued increase in material reinforcement, whereas late gelation shows a slight decrease. This suggests that early gelling might reduce restacking of MMT platelets, thus, improving the effective aspect ratio of the filler. The highly ordered structure observed in the gelatin 80 wt.% MMT composite was also reflected in its high heat distortion temperature, implying lower oxygen diffusivity. To better understand the influence of gelation and MMT addition on the mechanical properties, we further applied a conventional composite theory (Halpin-Tsai model), which considers the individual contributions of filler, such as the level of alignment, aspect ratio, volume fraction, and the modulus of the MMT platelets.
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A comparison between chemical cleaning efficiency in lab-scale and full-scale reverse osmosis membranes : role of extracellular polymeric substances (EPS)
Chemical cleaning is vital for the optimal operation of membrane systems. Membrane chemical cleaning protocols are often developed in the laboratory flow cells (e.g., Membrane Fouling Simulator (MFS)) using synthetic feed water (nutrient excess) and short experimental time of typically days. However, full-scale Reverse Osmosis (RO) membranes are usually fed with nutrient limited feed water (due to extensive pre-treatment) and operated for a long-time of typically years. These operational differences lead to significant differences in the efficiency of chemical Cleaning-In-Place (CIP) carried out on laboratory-scale and on full-scale RO systems. Therefore, we investigated the suitability of lab-scale CIP results for full-scale applications. A lab-scale flow cell (i.e., MFSs) and two full-scale RO modules were analysed to compare CIP efficiency in terms of water flux recovery and biofouling properties (biomass content, Extracellular Polymeric Substances (EPS) composition and EPS adherence) under typical lab-scale and full-scale conditions. We observed a significant difference between the CIP efficiency in lab-scale (~50%) and full-scale (9–20%) RO membranes. Typical biomass analysis such as Total Organic Carbon (TOC) and Adenosine triphosphate (ATP) measurements did not indicate any correlation to the observed trend in the CIP efficiency in the lab-scale and full-scale RO membranes. However, the biofilms formed in the lab-scale contains different EPS than the biofilms in the full-scale RO modules. The biofilms in the lab-scale MFS have polysaccharide-rich EPS (Protein/Polysaccharide ratio = 0.5) as opposed to biofilm developed in full-scale modules which contain protein-rich EPS (Protein/Polysaccharide ratio = 2.2). Moreover, EPS analysis indicates the EPS extracted from full-scale biofilms have a higher affinity and rigidity to the membrane surface compared to EPS from lab-scale biofilm. Thus, we propose that CIP protocols should be optimized in long-term experiments using the realistic feed water
LEM-3 is a midbody-tethered DNA nuclease that resolves chromatin bridges during late mitosis
Chromosome segregation and genome maintenance require the removal of DNA bridges that link chromosomes just before cells divide. Here the authors show that the LEM-3/Ankle1 nuclease processes DNA bridges before cells divide and define a previously undescribed genome integrity mechanism
Clinical approach for the classification of congenital uterine malformations
A more objective, accurate and non-invasive estimation of uterine morphology is nowadays feasible based on the use of modern imaging techniques. The validity of the current classification systems in effective categorization of the female genital malformations has been already challenged. A new clinical approach for the classification of uterine anomalies is proposed. Deviation from normal uterine anatomy is the basic characteristic used in analogy to the American Fertility Society classification. The embryological origin of the anomalies is used as a secondary parameter. Uterine anomalies are classified into the following classes: 0, normal uterus; I, dysmorphic uterus; II, septate uterus (absorption defect); III, dysfused uterus (fusion defect); IV, unilateral formed uterus (formation defect); V, aplastic or dysplastic uterus (formation defect); VI, for still unclassified cases. A subdivision of these main classes to further anatomical varieties with clinical significance is also presented. The new proposal has been designed taking into account the experience gained from the use of the currently available classification systems and intending to be as simple as possible, clear enough and accurate as well as open for further development. This proposal could be used as a starting point for a working group of experts in the field
Influence of compaction on chloride ingress
Experiences from practice show the need for more of an understanding and optimization of the compaction process in order to design a more durable concrete structure. Local variations in compaction are very often the reason for initiation of local damage and initiation of chloride induced corrosion. Poor compaction is often manifested locally in concrete structures in the form of large voids, profuse honeycombing and heterogeneity. Controlling compaction in practice today depends largely on the operator and his experience. The reliability of such a practice goes with many uncertainties. Depending on the exposure conditions, cement based materials maybe attacked by aggressive substances which can influence the performance of a concrete structure. Therefore the change in chloride ingress was investigated as a function of compaction time and sample depth. In this paper the Rapid Chloride Migration method, (RCM), was used and test results show a change of the diffusion coefficient with time of compaction. Along with the RCM results, the compressive strength was measured and the results are presented as well.Structural EngineeringCivil Engineering and Geoscience
Exploring the Structure, Properties, and Applications of Highly Ordered Bionanocomposites
Nature displays a multitude of fascinating materials, from beautiful colors of butterfly wings to the toughness of mullosc shells, which are formed in mild enviornmental conditions with commonly occuring materials, such as chitosan or calcium carbonate. These composite materials display an intricate interplay of biopolymers and minerals forming highly ordered structure. The function of these materials is primarily determined by the selective pressure of the enviornment that certain organisms are placed in. It varies from the “delicate” signaling colors to a robust impact resistence.BT/Environmental Biotechnolog
Using bio-based polymers for curing cement-based materials
Curing is the process of controlling the rate and extent of moisture loss from the surface of cement based materials. It is the final stage in the production of cement-based materials and it is the essential part for achieving continuous hydration of cement, while avoiding cracking due to drying shrinkage. Continuous cement hydration also guarantees a strong bond between aggregate, fewer voids, and depercoliation of capillary pores. Thus, a properly cured cement-based material is prepared for a long service life. Using environmentally friendly, water based bio-polymers could help to achieve more durable cement-based materials, and, therefore preventing a premature end of service life of building materials. Rapid Chloride Migration tests and Environmental Scanning Microscope are employed to investigate the functional properties, e.g. transport property, and microstructure properties, respectively. Mortar samples were cured in air and applied by water-based curing compound, made of sodium alginate. We observed strong beneficial effects of applying sodium alginate as a curing compound in terms of microstructure and hydration development. Based on these results, a less porous microstructure and an improved durable cement-based material was achieved that was prepared for longer service life
Supplementary data for PhD thesis "Biopolymer nanocomposites: lessons from structure-property relationships"
Supplementary information accompanying Ph.D. thesis "Biopolymer nanocomposites: lessons from structure-property relationships"</p
Using bio-based polymers for curing cement-based materials
Curing is the process of controlling the rate and extent of moisture loss from the surface of cement based materials. It is the final stage in the production of cement-based materials and it is the essential part for achieving continuous hydration of cement, while avoiding cracking due to drying shrinkage. Continuous cement hydration also guarantees a strong bond between aggregate, fewer voids, and depercoliation of capillary pores. Thus, a properly cured cement-based material is prepared for a long service life. Using environmentally friendly, water based bio-polymers could help to achieve more durable cement-based materials, and, therefore preventing a premature end of service life of building materials. Rapid Chloride Migration tests and Environmental Scanning Microscope are employed to investigate the functional properties, e.g. transport property, and microstructure properties, respectively. Mortar samples were cured in air and applied by water-based curing compound, made of sodium alginate. We observed strong beneficial effects of applying sodium alginate as a curing compound in terms of microstructure and hydration development. Based on these results, a less porous microstructure and an improved durable cement-based material was achieved that was prepared for longer service life
Supplementary data for PhD thesis "Biopolymer nanocomposites: lessons from structure-property relationships"
Supplementary information accompanying Ph.D. thesis "Biopolymer nanocomposites: lessons from structure-property relationships"</p