Lamellar Thickening Research Articles

A single polymer folding and thickening from different dilute solution

The primary nucleation and crystal growth of a single chain from different dilute solution are studied by Monte Carlo simulations. The interplay of crystallization and demixing/collapse is conveniently investigated in chain folding. We find the solvent qualities affect the nucleation mechanism, crystal morphology and the thickening process. In good solution the swollen coil allows the stems more extended and facilitates to form thicker crystalline stems. The poor solvent condition is helpful to perform fast nucleation and produce a dense crystal. But to get more reorganization the critical athermal solution is the best choice, where the longitudinal thickening and width contraction of the folded stem is well coupled. Our results may complement the kinetic mechanism of crystal growth beyond the point of lamellar thickening.

The effects of acute boric acid treatment on gill, kidney and muscle tissues in juvenile rainbow trout

Boric acid (BA) is an essential nutrient for plants and many organisms, but it has become an environmental contaminant because of widespread use. Pesticide and its compounds are a serious threat to aquatic organisms. This study was carried out to determine the histopathological effects of acute exposure to BA concentrations in rainbow trout. The fish were exposed to 102 and 103 mg/L concentrations of BA. Tissues were sampled at 6, 12, 24, 48 and 96 h. Histopathological alterations occurring in tissues were common in both doses of BA. Gill tissues showed lamellar oedema, cellulary infiltration, lamellar disorganization, degenerative changes and lamellar thickening. Kidneys had glomerular oedema and glomerulonephritis, degeneration of the tubulary epithelium, interstitial fibrosis and a hyaline cast within the tubular lumens. Muscle tissues displayed interstitial oedema and degenerative and atrophic changes to varying degrees in the myofibrils. Our study shows that BA can be toxic for rainbow trout and cause histopathological damage in fish tissue.

Oxidative stress, genotoxicity and histopathology biomarker responses in Mugil cephalus and Dicentrarchus labrax gill exposed to persistent pollutants. A field study in the Bizerte Lagoon: Tunisia

The use of biomarkers has become an important tool for modern environmental assessment as they can help to predict pollutants involved in the monitoring program. Despite the importance of fish gill in several functions (gaseous exchange, osmotic and ionic regulation, acid-base balance and nitrogenous waste) its use in coastal water biomonitoring focusing on protection and damage is scarce.This field study investigates biochemical (catalase, superoxide dismutase, lipid peroxidation), molecular (DNA integrity) and morphological (histology) parameters in gill of mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) and originating from Bizerte lagoon (a coastal lagoon impacted by different anthropogenic activities) and from the Mediterranean Sea (a reference site). Remarkable alterations in the activities of oxidative stress enzymes and DNA integrity in the tissue of the two studied fish species were detected in Bizerte Lagoon. The study of histopathological alterations of gills in both two fish species from Bizerte Lagoon suggest thickening of primary lamellae, cellular hyperplasia, aneurism, curving, shortening and fusion of secondary lamellae.The adopted approach, considering simultaneously protection responses and damaging effects, revealed its usefulness on the pollution assessment.

Generalized kinetic analysis of heterogeneous PET glycolysis: Nucleation-controlled depolymerization

The kinetics of poly(ethylene terephthalate) depolymerization by glycolysis has been commonly modeled as a second-order reaction. However, the occurrence of an activation stage and anomalous kinetic behavior does not fit into this reaction model. Utilizing the concept of reference theoretical master plots, we show in terms of generalized kinetics that the chain depolymerization can be controlled by a nucleation-based kinetic behavior. We associate the reported anomalous “activation” stage and chain scission-induced recrystallization in PET glycolysis with the induction period and chain reordering processes during polymer nucleation and growth. The kinetic profile and microscopic images of the polymer surface during degradation support the mechanism of sporadic nucleation and lamellar thickening. Using the matching nucleation-based conversion function we obtained an activation energy of 29 kJ/mol, the closest value reported so far to the experimental and simulated activation energy of thermal and glycolytic breakage of a PET ester bond.

Tuning the crystalline and mesophase structure of olefin block copolymer through self-nucleation and annealing treatments.

As a type of novel semi-crystalline block copolymers, the final properties of olefin block copolymers (OBCs) greatly depend on the crystalline and phase-separated structures. In the present work, we systematically investigated the influence of self-nucleation and annealing on the lamellar and mesophase-separated structure of OBCs. According to the crystalline and melting behavior after self-nucleation and annealing treatments, four different regimes can be recognized with the self-seeding temperature Ts varying from 125 to 109 °C. In regime A, only self-nucleation occurs, while it coexists with lamellar thickening in regime B. In regime C, there is only lamellar thickening behavior. The lamellar thickening induced inconsecutive lamellar crystals observed revealed that the rearrangement of the hard blocks, which are next to the soft blocks and trapped in the intermediate regime between crystalline and amorphous phases, into neighboring lamellar crystals should be the mechanism for the lamellar thickening of the OBCs. Surprisingly, no lamellar thickening occurs and a new small melting peak appears at lower temperatures in regime D. Considering the block dispersity of OBCs, the emergence of a small melting peak at lower temperatures can be attributed to the crystallization of the ethylene sequence with relatively weaker crystallization abilities, which are not able to crystallize in a standard crystalline state. Based on these findings, we gained some new understandings on lamellar thickening behavior of OBCs and established the self-nucleation and annealing process as a powerful tool for tuning the crystalline and phase-separated structures of OBCs.

Histopathological and bacterial study of Persian sturgeon fry, Acipenser persicus (Borodin, 1897) exposed to copper sulfate and potassium permanganate.

Persian sturgeon frys were exposed to different concentrations of copper sulfate and potassium permanganate in order to the evaluation of their impacts on bacterial load of skin, gill and surrounding water and also the histopathological alternations of gill tissue. For this purpose, the sublethal doses were determined after a pre-test and then the experiment was done in 4 (for copper sulfate: 0.07, 0.14, 026 and 0.5mg/l) and 5 (for potassium permanganate: 0.07, 0.14, 026, 0.5 and 1mg/l) treatments with three replicates inside the glass aquaria. Also, one group without disinfecting drug was considered as control for each experiment. The microbial and histopathological investigations were done after 96h exposure. According to our results, a range of histopathological alternations were observed in gills tissue including mucus coagulation and secretion, hyperplasia, lamellar necrosis, hyperplasia, lamellar adhesion, haemorrhage, thickening of secondary lamellae, hypertrophy of supporter cartilage, clubbing of gill lamellae and sliming of primary lamellae. The severity of these alternations increased with increasing of the doses of the copper sulfate and potassium permanganate. The bacterial load (CFU/g) of gill, skin and surrounding water was lower in 0.07mg/l copper sulfate treatment and 1mg/l potassium permanganate treatment (P<0.05) than in other treatments. In conclusion, our results showed that the certain doses of the copper sulfate and potassium permanganate have disinfecting effects on bacterial load of gill, skin and surrounding water, although this is along with some histopathological alternations. Also, it seems that the copper sulfate has higher disinfecting power than potassium permanganate.

Kinetic mechanism of chain folding in polymer crystallization.

I develop a kinetic mechanism to explain chain folding in polymer crystallization which is based on the competition between the formation of stems, which is due to frequent occupations of trans states along the chains in the supercooled polymer melt, and the random coil structure of the polymer chains. Setting equal the average formation time of stems of length d(l) with the Rouse time of a piece of polymer of the same arc length d(l) yields a lower bound for the thickness of stems and bundles. The estimated lamellar thickness is inversely proportional to the supercooling. The present approach emphasizes the importance of repulsive interactions in polymer crystallization, which are expected to be responsible for the logarithmic lamellar thickening and the increase of lamellar thickness with pressure. An expression for the growth rate for formation and deposition of stems is derived by considering the growth as a dynamic multistage process.

Mechanism and kinetics of ultra‐high molecular weight polytetrafluoroethylene sintering

ABSTRACTThe effect of sintering time on the melt evolution of Ultra‐High Molecular Weight Polytetrafluoroethylene was studied in situ by high temperature Wide Angle X‐ray Scattering, and by cyclic thermal loading profiles within a Differential Scanning Calorimeter (DSC) and Thermo‐Mechanical Analyzer (TMA). Results obtained from these techniques support the concept of molecular ordering in the melt state as a function of sintering time well above the melting temperature. TMA, which is not a conventional technique for monitoring thermal transitions, is shown to be sensitive enough for such purposes. Both DSC and TMA exhibit nonequilibrium melt behavior even 30°C above its equilibrium melting temperature for long time periods. A correlation between the DSC and TMA results is established. The cyclic thermal profile leads to a dramatic growth in enthalpy of crystallization/melting. The mechanism for this growth is associated with two independent processes; isothermal annealing at the sintering temperature and lamellar thickening in the solid state. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40967.

Corilagin attenuates aerosol bleomycin-induced experimental lung injury.

Idiopathic pulmonary fibrosis (IPF) is a progressing lethal disease with few clinically effective therapies. Corilagin is a tannin derivative which shows anti-inflammatory and antifibrotics properties and is potentiated in treating IPF. Here, we investigated the effect of corilagin on lung injury following bleomycin exposure in an animal model of pulmonary fibrosis. Corilagin abrogated bleomycin-induced lung fibrosis as assessed by H&E; Masson’s trichrome staining and lung hydroxyproline content in lung tissue. Corilagin reduced the number of apoptotic lung cells and prevented lung epithelial cells from membrane breakdown, effluence of lamellar bodies and thickening of the respiratory membrane. Bleomycin exposure induced expression of MDA, IKKα, phosphorylated IKKα (p-IKKα), NF-κB P65, TNF-α and IL-1β, and reduced I-κB expression in mice lung tissue or in BALF. These changes were reversed by high-dose corilagin (100 mg/kg i.p) more dramatically than by low dose (10 mg/kg i.p). Last, corilagin inhibits TGF-β1 production and α-SMA expression in lung tissue samples. Taken together, these findings confirmed that corilagin attenuates bleomycin-induced epithelial injury and fibrosis via inactivation of oxidative stress, proinflammatory cytokine release and NF-κB and TGF-β1 signaling. Corilagin may serve as a promising therapeutic agent for pulmonary fibrosis.

Small-angle X-ray scattering studies on melting and recrystallization behaviors of poly(oxyethylene) crystallites in poly(d,l-lactide)/poly(oxyethylene) blends

Direct determination of the discrete distribution for crystalline lamellar thickness has been performed for poly(d,l-lactic acid)/poly(oxyethylene) (PDLLA/PEG) blends by conducting small-angle X-ray scattering (SAXS) measurements using synchrotron radiation. The PDLLA used was an random (racemic) copolymer of bio-based poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) with the lactide monomer ratio of l:d = 50:50. It is known that PLA is miscible with PEG in the amorphous state. In the current paper, we report comprehensive results on structural analyses of PDLLA/PEG blends in the course of heating and cooling process using SAXS to elucidate the change in the thickness distribution of the lamellae. As a consequence, it was found that the distribution of the lamellar thickness moves toward the larger value (in other words, lamellar thickening) as temperature approaches the melting point. Typically, the thickness distribution was dispersed in the range of 10–20 nm at room temperature and it changed toward 40 nm in the vicinity of the melting temperature. To the best of our knowledge, this is the first report of direct determination of the discrete distribution for the crystalline lamellar thickness and their in-situ changes in the course of the lamellar thickening process. As a result, the lamellar thickening was found to occur at much lower temperature for the blend samples with 10% and 20% of PDLLA contents as compared to the PEG 100% sample. This phenomenon can be ascribed to the melting point depression owing to the miscibility between PEG and PDLLA. Thereby, thinner lamellae were melted and thicker ones appeared at much lower temperature for the blends than for the PEG 100% sample. As for the average repeating distance (long period) of the lamellar stacks, an abrupt increase similar to the critical divergence was observed (from 25 nm to 50 nm) in the heating process. Not only for the melting behavior but also in the course of recrystallization, change in the lamellar-thickness distribution was uncovered, which shows strong hysteresis depending on what temperature the sample was cooled down from.

How the Calorimetric Properties of a Crystalline Copolymer Correlate to Its Surface Nanostructures

Thin film surface nanostructures of semicrystalline diblock copolymer are promising for the fabrication of photonic crystals and bioanalytical devices because they might be tailorable by controlled crystallization. One approach to systematically control polymer crystallization is a self-nucleation experiment. The self-nucleation experiment for block copolymers has only been reported for the bulk and so far not for thin films. Considering the versatility of a tailorable surface nanostructure, it is promising to apply the controlled crystallization of a bulk self-nucleation experiment to thin films of a diblock copolymer. In the current study we tested the hypothesis that within two self-nucleation experiments, i.e., in the bulk and thin film, the calorimetric bulk properties of a polybutadiene-block-poly(ethylene oxide) can be correlated to the resulting thin film surface nanostructures and to understand as well as predict their formation. The calorimetric bulk properties measured by differential scanning calorimetry in the bulk self-nucleation experiment were correlated to surface nanostructures measured by atomic force microscopy of the thin film self-nucleation experiment samples. In analogy to the bulk self-nucleation experiment, we introduced a crystalline standard for the thin film self-nucleation experiment where the crystalline lamellae consisted of once-folded chains. Annealing the thin film crystalline standard promoted the thickening of crystalline lamellae on the film surface which is explained by the formation of less folded chain crystals that obtain higher melting temperatures. The crystalline lamellae thickness was steplessly variable within the range of 8–16 nm. In analogy to the Hoffman–Weeks and Gibbs–Thomson plots, we derived a function which can be used to predict the lamellae thickness as a function of the annealing temperature. Bulk and thin film self-nucleation experiments were successfully related, since thin film surface nanostructures were consistently correlated to calorimetric results. We established the dual self-nucleation experiment as a powerful tool to predictably tailor thin film nanostructures in the range of several nanometers.

Industrial Experiment Research on a Vibration Lamella Thickener’s Application to Concentration of Tailings

In order to test the performance of a vibration lamella thickener, a ZXN32 was applied to a industry experiment.We carried out a series of experiment and measured the test parameter of the equipment which was based on particle size analysis and settlement experiment.The test results show that the calculation of the capacity meets with the practical capacity.The test equipment runs stably and compares with the thickener used in the plant,the test equipment is 2.7~2.8 times as much as thickener in capacity per unit area at the same conditions.

Stress induced lamellar thickening in poly(ethylene succinate)

The crystalline structure evolution of poly(ethylene succinate) during tensile deformation was investigated by in-situ synchrotron X-ray scattering. Crystal phase transition from α to β form was confirmed to be fully reversible upon stress loading and unloading. An increase of long period was observed during the α–β crystal transition, which was attributed to the increase of both amorphous layer thickness and crystalline layer thickness (lamellar thickness). The crystalline layer thickness was scaled with the fraction of β crystal, and the change of which was in well agreement with the difference in the repeating length along the crystallographic c axis. Both the crystalline layer thickness and the amorphous layer thickness were fully recoverable. A possible molecular model was proposed to visualize the mechanism for the crystal transition and lamellar thickening.

Study on the Classification Performance of Vibration Lamella Thickener

This paper mainly describes the relation between the overflow quantity, separation size, classification efficiency and Reynolds number under the stable stage of vibration lamella thickener. Using a device with one tilting-narrow flow classification element, experiments on classification of pure quartz slurry have been carried out.we can conclude that the overflow quantity is proportional to the separation and classification is best under the condition of turbulent flow.

High-pressure crystallization of poly(lactic acid) with and without N2 atmosphere protection

High-pressure crystallization experiments of poly(lactic acid) (PLA) were conducted under air and N2 atmosphere. Compared with the sharp decrease of the molecular weight of air sample from 1.63 × 105 to 3.11 × 104, the weight loss of N2 protection sample was successfully restricted to the value below 10 %. Stable α-crystals were generated in both air and N2 protection samples which both exhibited very high crystallinity up to 66.3 and 64.5 %, respectively. It is high pressure that leads to the perfect crystalline structure by inducing crystalline reorganization and lamellar thickening. A diffraction streak appeared in the 2D-SAXS pattern of air sample in contrast to the broad scattering signal in N2 protection sample, implying the formation of oriented crystals during PLA degradation. As observed from scanning electron microscopy, the spherulite size of air sample was larger than that of N2 protection sample, for the radius growth rate of PLA crystals increased as molecular weight decreased. Accordingly, N2 atmosphere protection can not only effectively prevent PLA from degradation, but also acquire highly crystallized PLA.

Crystalline Structure Changes in Preoriented Metallocene-Based Isotactic Polypropylene upon Annealing

Partially melted metallocene-based isotactic polypropylene (m-iPP), which was preoriented with a high degree of molecular orientation and a shish-kebab structure, was annealed at various temperatures and isothermally crystallized at 130 °C. The melting and crystallization process was examined using synchrotron wide-angle X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. For the m-iPP samples annealed at relatively low temperatures, lamellar thickening, lateral growth, and a decrease in the γ-crystal fraction occurred. Because of parallel evolution of α- and γ-crystal growth in the limited crystallizable melt volume, the fraction of γ-crystals was very low. Furthermore, topological constraints in the melt dominate the chain flux in crystal evolution; the chains are consumed by the thickening lamellae and lateral growth, forming α-crystals with parallel chains in the unit cell. For the m-iPP samples isothermally annealed at medium annealing temperatures, the increase in the amount of crystallizable melt caused the γ-crystal fraction to increase. A shish-kebab (α-crystals) structure with high thermal stability and a newly formed macro-unoriented structure coexisted in the final sample. After annealing at high temperatures, at which no crystals survived, γ-crystal formation was greatly favored; this was attributed to the nature of m-iPP molecules and their dynamic behavior at 130 °C. Because of the lack of oriented nuclei, randomly oriented lamellae were formed. On the basis of the structural cooperative changes at different scales, the morphological features at different annealing temperatures were proposed.

Paste Thickening of Iron Tailings with Vibrating Lamella Thickener

Vibrating lamella thickener (VLT) developed by Kunming University of Science and Technology is a new generation of inclined plate settling device, and in this device such long-standing problems in traditional lamella thickener (LT) as material bonding and blockage between channels in inclined plates, material deposits and blockage in cone bucket, as well as unsteady discharging of high solids underflow, etc. are effectively resolved, through periodic vibration of inclined plate modules, the use of built-in device for removal of deposited material on cone wall and of forced discharging device for high solids underflow. Paste discharging is now a new way for the effective treatment of tailings in recent years, due to its superiority for mining safety and environmental protection. The industrial tests for paste thickening of iron tailings were carried out in a mineral processing plant of Mining Co., Ltd. of Panzhihua Iron and Steel Group, using a ZXNQP-32 VLT. In the test the size distribution and settling characteristics of the tailings were analyzed, and the main operating parameters in the VLT were tested under the natural settling and flocculated settling conditions, respectively. The results of test indicate that the solids concentration of underflow from the VLT is capable of reaching higher than 70%; meanwhile, the solids content in overflow from the VLT is as low as less than 300 mg/l while flocculant is added in the ore pulp for pretreatment and such an overflow can be directly discharged into environment or be recycled in the plant. It is thus concluded that VLT is effective for paste thickening of iron tailings.

Structure development during isothermal crystallisation of high-density polyethylene: Synchrotron small-angle X-ray scattering study

Isothermal melt crystallisation in high-density polyethylene (HDPE) was studied using the time-resolved SAXS method with synchrotron radiation over a wide range of crystallisation temperatures. The SAXS profile was analysed by an interface distribution function, g1(r), which is a superposition of three contributions associated with the size distributions of crystalline (LC) and amorphous (LA) layers and a distribution of long period (LP). The morphological parameters extracted from the g1(r) functions show that the lamellar thickness increases with time, obeying a logarithmic time dependence. The time evolution of LC observed for the sample crystallised at 122°C leads to the conclusion that crystallisation proceeds according to the mechanism of thickening growth. For samples crystallised at lower temperatures (116°C and 118°C), the lamellar thickening mechanism has been observed. The rate of lamellar thickening in these cases is much lower than that at 122°C. At 40°C, thickening of the crystalline layer does not occur. The interface distribution functions were deconvoluted, and the relative standard deviation σC/LC obtained in this way is an additional parameter that is varied during crystallisation and can be used for analysis of this process. Time-dependent changes in the σC/LC at large supercooling (TC=40°C) indicates that LC presents a broad distribution in which the relative standard deviation increases with time. At lower supercooling (TC=122°C), LC shows a much sharper distribution. In this case, the relative standard deviation decreases with time.

Mechanism of accelerated spheroidization of steel during cyclic heat treatment around the upper critical temperature

An investigation has been carried out on the mechanism of accelerated spheroidization in 0.6 wt.% carbon steel under cyclic heat treatment involving repeated short duration holdings above its upper critical temperature (A 3) followed by forced air cooling. Thermal grooving, modified capillarity induced perturbation and lamellar thickening, were found to be the main processes responsible for rapid spheroidization. This is in contrast to the conventional subcritical spheroidization process where the termination migration process dominates the mechanism. The new effect is attributed to the higher atomic mobility above A 3 and the generation of potential diffusion sites of lamellar faults causing rapid breakdown of lamellar pearlite into spheroids of cementite even with short duration holding in each cycle.

The kinetics of crystallization of poly(ethylene terephthalate) measured by FTIR spectroscopy

The kinetics of crystallization of poly(ethylene terephthalate), PET, have been measured by FTIR spectroscopy using the absorbances of the crystalline and amorphous phase carbonyl bands at 1717 and 1727cm−1 to determine the fractional crystallinity as a function of time and isothermally over the temperature range 230–240°C. Both primary and secondary crystallization could be measured with similar accuracy limited only by the length of time over which the measurements were made.The primary and secondary crystallization time dependences were fitted to Avrami equations with n values of 2.0 and 1.0, respectively. The initial primary process was interpreted as due to two-dimensional spherulites restricted early in the crystallization by the thickness of the film sample, 1.5–3.0μm. Secondary crystallization was considered to be due to one dimensional thickening of lamellae produced in the initial production of the spherulites.FTIR spectroscopy was considered to have some advantages in measuring the development of crystallinity over other techniques, such as DSC and DTA, which measure the rate of crystallization and are limited by the sensitivity of the calorimeter to measure the rate of heat evolution.