Course Of Extrusion Research Articles

Formation of microfibrillar structure of polypropylene/copolyamide blends in the presence of nanoparticles of metal oxides

The influence of nanoparticles made of ifferent metals oxides (ZnO, Al2O3, TiO2, and ZnO/Al2O3) on the in situ formation of microfibrils by the components of a dispersed phase was studied in a thermodynamically incompatible blend of polypropylene/copolyamide (PP/CPA). The viscosity of the melts was determined by capillary viscometry method. Elastic properties were evaluated by the degree of extrudate swelling. The morphology of the compositions was studied by optical polarization microscopy. The method of image analysis was used to quantify the structural characteristics of the blends. It was established that the introduction of 1.0 wt.% of nanoparticles of the studied oxides made from different metals allows tuning the microstructure of the melt of the PP/CPA blend, which is realized in the course of extrusion. More perfect morphology is formed in nanofilled systems: the average diameter of PP microfibrils decreases and their mass fraction increases. The modifying effect of oxide nanoparticles is manifested due to their influence on interfacial phenomena and rheological properties of nanofilled PP melt. The viscosity of the PP melts increases and their elasticity decreases in the presence of nanoparticles of the studied metal oxides. The values of the ratio of the viscoelastic characteristics of the dispersed phase and the matrix in nanofilled systems depend on the nature of oxide and indirectly correlate with the microstructure of the extrudate. As these ratios approach unity, the diameter of PP microfibrils decreases and their share increases. The efficiency of the studied oxides to improve the microfibrillar structure increases in the following series: ZnO, Al2O3, TiO2, ZnO/Al2O3. The obtained results demonstrate the possibility to create the microfiber textile and filter materials with improved consumer characteristics by adjusting the phase morphology of the blends.

EXPERTISE OF POTATO SNACKS BY OPTICAL MICROSCOPY, FTIR - SPECTROSCOPY, SPECTROFLUORIMETRY AND THIN LAYER CHROMATOGRAPHY

Expertise of four samples of potato snacks with the flavours Barbecue, Ketchup, Cheese, Sour Cream and Onion has been carried out with the use of analytical physicochemical methods. It has been found that the mass fraction of moisture in the samples under study ranges 4.4 to 4.7%, and the mass fraction of chlorides does not exceed 2.5%. The mass fraction of starch, which was determined polarimetrically, varies from 66.1% (Sample 2) to 66.7% (Sample 3). The mass fraction of sugars in the potato snack samples does not exceed 1.9%. None of the samples contains foreign material and mineral impurities. The product’s physicochemical quality parameters established by the tests conform to the manufacturer’s indication that the product contains such ingredients as starch and potatoes (starch and proteins are part of potatoes), oil, maltodextrin, sugars, salt, proteins. Based on characteristic absorption bands in the composition of snacks, FTIR has allowed detecting the presence of the two main components: triglycerides of fatty acids (oils) and polysaccharides (the latter include starches and maltodextrins). Optical microscopy has revealed that the samples have a porous (cellular) structure, with pores distributed throughout the whole mass, which is typical of snacks. Heat treatment of the snacks in the course of extrusion and frying changes the structure of starch to the glassy state: only single whole starch grains are found in the samples. The dietary supplement monosodium glutamate E621 has been identified by thin-layer chromatography on chromatographic plates Sorbfil AF-A-UV. The mobile phases were mixtures of ethanol and distilled water in the ratio 7:3, and n- butanol, acetic acid, and water mixed in the ratio 3:1:1. It has been shown that the turmeric extract E100(i), a natural yellow food colourant, being adsorbed on potato snacks, can be identified in them by its own spectra of diffuse reflection and luminescence spectra, without destroying the samples.

Observational study of movements in lateral extrusion

This is a report of an observational study of tooth movement during the course of extrusion of upper laterals with aligners. Pure extrusion along the long axis is a most difficult movement for the aligner. Digital image data were collected from volunteer patients in a private practice setting, throughout the treatment period. Compliance of the enrolled subjects has been excellent. Their serial CBCT data were analyzed for the trajectory of tooth crowns and roots. The small sample data exposed a non-linear movement pattern both for the root and the crown. We termed this motion wobbling. The pattern of wobbling was not consistent across the subjects. Understanding the causes, directions, and magnitude wobbling may be expected to instigate novel algorithms for programmed aligner appliances.

Influence of ultrasound on the basic parameters of the extrusion of polymer melts

The process of imposing ultrasound and its influence on the rheological properties of polymers, the high-elasticity properties of extrudates, the changes in the power of ultrasonic vibrations absorbed by a polymer in the course of extrusion, and also on the strength properties of extrudates are considered.

Effect of screw axial vibration on polymer melting process in single‐screw extruders

AbstractA model for investigating the melting process of polymer in a vibration‐induced single‐screw (VISS) extruder is presented. The key feature of this model is as follows: vibration force field is introduced into the overall course of extrusion by the axial vibration of the screw, and the velocity distribution in the polymer melt behaves strongly nonlinear and time‐dependent. To analyze this model, half‐open barrel visible experimental method and low‐density polyethylene material are adopted to investigate the effect of the vibration parameters on the melting process, which goes into further details of study and research on the melting mechanism, and thus, a novel physical melting model is derived. Combining the conservation equations of mass, movement, energy, and constitutive, analytical expressions of the melting rate, the energy consumption, the length of melting section, and the distribution of solid bed are obtained. This model enables the prediction of the processing and design parameters in the VISS extruders from which the optimum conditions for designing VISS extruder and polymer processing are obtained. The theory is supplemented by a calculation sample and experiment, which shows that the introduction of vibration force field can improve the melting capacity and decrease the power consumption of extruder greatly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3860–3876, 2006

Effect of composition on phase morphology and mechanical properties of PP/PA66 in situ composites via extrusion-drawing-injection method

The reinforced and toughened PP/PA66 in situ composites were prepared via extrusion-drawing-injection method. The relationship among composition, phase morphology and mechanical properties, together with their functional mechanism, was investigated. The results show that in the range of PA66 weight fraction (fw) from 0 to 20% and under the experimental processing conditions, the main changes in phase morphology of the composites with fw are that the number of in situ formed PA66 microfibers and remained PA66 particles increases with fw whereas the fiber transverse size and its dispersity decrease till fw = 15% and then increase. This can be attributed to the combined effect of break-up, coalescence and deformation of the PA66 phase in the PP phase in the course of extrusion and drawing. The tensile strength of composites has a maximum value at fw of 15% and Young's modulus increases with fw up to a plateau level, while impact strength continuously rises with fw, an effect which can be ascribed to the distinct dependence of these properties on the phase-morphological factors mentioned above.

The association of vesicular contents and its effects on release.

The oxidation of catecholamines with a carbon-fiber electrode can be used to monitor exocytosis at the single cell level at a variety of different types of cells. These measurements allow release to be followed from individual vesicles and have revealed several unique aspects concerning the coupling between release and storage. The strong association of the vesicular components in chromaffin cells dictates the time course of extrusion of the vesicle contents. Furthermore, liberation of the Ca(2+) normally stored within the vesicles can promote exocytosis without an external Ca(2+) source.

Temporal Separation of Vesicle Release from Vesicle Fusion during Exocytosis

During exocytosis, vesicles in secretory cells fuse with the cellular membrane and release their contents in a Ca2+-dependent process. Release occurs initially through a fusion pore, and its rate is limited by the dissociation of the matrix-associated contents. To determine whether this dissociation is promoted by osmotic forces, we have examined the effects of elevated osmotic pressure on release and extrusion from vesicles at mast and chromaffin cells. The identity of the molecules released and the time course of extrusion were measured with fast scan cyclic voltammetry at carbon fiber microelectrodes. In external solutions of high osmolarity, release events following entry of divalent ions (Ba2+ or Ca2+) were less frequent. However, the vesicles appeared to be fused to the membrane without extruding their contents, since the maximal observed concentrations of events were less than 7% of those evoked in isotonic media. Such an isolated, intermediate fusion state, which we term "kiss-and-hold," was confirmed by immunohistochemistry at chromaffin cells. Transient exposure of cells in the kiss and hold state to isotonic solutions evoked massive release. These results demonstrate that an osmotic gradient across the fusion pore is an important driving force for exocytotic extrusion of granule contents from secretory cells following fusion pore formation.

Extrusion of an imperfect palindrome to a cruciform in superhelical DNA: complete determination of energetics using a statistical mechanical model

We present a detailed study of the extrusion of an imperfect palindrome, derived from the terminal regions of vaccinia virus DNA and contained in a superhelical plasmid, into a cruciform containing bulged bases. We monitor the course of extrusion by two-dimensional gel electrophoresis experiments as a function of temperature and linking number. We find that extrusion pauses at partially extruded states as negative superhelicity increases. To understand the course of extrusion with changes in linking number, Δ Lk, we present a rigorous semiempirical statistical mechanical analysis that includes complete coupling between Δ Lk, cruciform extrusion, formation of extrahelical bases, and temperature-dependent denaturation. The imperfections in the palindrome are sequentially incorporated into the cruciform arms as hairpin loops, single unpaired bases, and complex local regions containing several unpaired bases. We analyze the results to determine the free energies, enthalpies and entropies of formation of all local structures involved in extrusion. We find that, for each unpaired structure, the Δ G, Δ H and Δ S of formation are all approximately proportional to the number of unpaired bases contained therein. This surprising result holds regardless of the arrangement or composition of unpaired bases within a particular structure. Imperfections have major effects on the overall energetics of cruciform extrusion and on the course of this transition. In particular, the extent of the Δ Lk change necessary to extrude an imperfect palindrome is considerably greater than that required for extrusion of the underlying perfect palindrome. Our analysis also suggests that, at higher temperatures, significant denaturation at the base of an imperfect cruciform can successfully compete with extension of the cruciform arms.

Viscoelasticity of liquid-crystalline copolymer/poly(methyl methacrylate) blends. Effect of reinforcement by aluminum borate whiskers

The elastic moduli and mechanical losses for blends of liquid-crystalline copolyester (LCP) and PMMA have been determined at various temperatures. The specimens were produced by the extrusion of preliminary mixed components. In the course of extrusion, a system is formed where the LCP forms thin fibers imbedded into a PMMA matrix. The greatest effect of the reinforcement of the thermoplastic matrix with LCP was found for a 7/3 ratio of components. The effect of fillers (whiskers) was also investigated. It is shown that the reinforcing action of the filler is much higher for the 7/3 blends as compared with the reinforced pure components. The effects observed are explained by features of the interphase formation in the reinforced systems and the surface segregation of an LCP-component.

A singularity in the melt flow of polyethylene with wider implications for polymer melt flow rheology

This is a summarising report on a recently discovered melt flow singularity during capillary extrusion of polyethylene including the description of the effect, the principal parameters affecting it, the functional relations which arise and the explanation which emerges together with some significant still open-ended issues. The singularity itself is a sharply delineated minimum in flow resistance within a narrow temperature window observed in the course of extrusion of high molecular weight polyethylene. This ‘window’ effect, leading to smooth extrudates under conditions where otherwise distortions would arise, can be tracked down to the formation of a ‘low viscosity’ phase conclusively identified with the ‘mobile’ hexagonal phase, itself arising through flow-induced alignment of presumably adsorbed molecules, this alignment being critical in strain rate and molecular weight in a quantitatively definable fashion. This ‘window’ effect thus links up with current theoretical trends in melt flow focusing on events along the boundaries of flow channels, while on the other hand it opens up new practical possibilities. From the applied science point of view it offers a new handle to the more general understanding and minimisation of extrudate distortions beyond the confines of the window effect. Amongst the open-ended issues are two power laws, specifically precise − 4.0 and − 1.5 power laws in molecular weight defining the onset strain rates of the ‘window’ effect and for gross shape distortions respectively, both of direct practical consequence yet with pointers to some still unexplained basic features of polymer melt flow.

A singularity in the melt flow of polyethylene with wider implications for polymer melt flow rheology

This is a summarising report on a recently discovered melt flow singularity during capillary extrusion of polyethylene including the description of the effect, the principal parameters affecting it, the functional relations which arise and the explanation which emerges together with some significant still open-ended issues. The singularity itself is a sharply delineated minimum in flow resistance within a narrow temperature window observed in the course of extrusion of high molecular weight polyethylene. This ‘window’ effect, leading to smooth extrudates under conditions where otherwise distortions would arise, can be tracked down to the formation of a ‘low viscosity’ phase conclusively identified with the ‘mobile’ hexagonal phase, itself arising through flow-induced alignment of presumably adsorbed molecules, this alignment being critical in strain rate and molecular weight in a quantitatively definable fashion. This ‘window’ effect thus links up with current theoretical trends in melt flow focusing on events along the boundaries of flow channels, while on the other hand it opens up new practical possibilities. From the applied science point of view it offers a new handle to the more general understanding and minimisation of extrudate distortions beyond the confines of the window effect. Amongst the open-ended issues are two power laws, specifically precise −4.0 and −1.5 power laws in molecular weight defining the onset strain rates for the ‘window’ effect and for gross shape distortions respectively, both of direct practical consequence yet with pointers to some still unexplained basic features of polymer melt flow.

Time course of release of catecholamines from individual vesicles during exocytosis at adrenal medullary cells

The time course of extrusion of the vesicular contents during exocytosis has been examined at adrenal medullary cells with carbon-fiber microelectrodes. Two electrochemical techniques were used: cyclic voltammetry and amperometry. Spikes obtained by amperometry had a faster time course than those measured by cyclic voltammetry, consistent with the different concentration profiles established by each technique. However, the experimental data obtained with both techniques were temporally broadened with respect to dispersion of an instantaneous point source by diffusion. Measurements with the electrode firmly pressed against the cell surface established that the temporal broadening is a result of a rate-limiting kinetic step associated with extrusion of the vesicular contents at the cell surface. The data do not support a rate-limiting process due to restricted efflux from a small pore. When combined with previous results, the data suggest that the rate-limiting step for chemical secretion from adrenal medullary cells during exocytosis is the dissociation of catecholamines from the vesicular matrix at the surface of the cell.

Modification of the structure of casein preparations in the course of extrusion

AbstractStudies were carried out on the modification of the supermolecular structure of casein obtained from milk in the form of calcium paracaseinate, low‐calcium (20 mg Ca/g dry weight) paracaseinate, acid casein and alkali‐neutralized casein in the course of extrusion performed using a twin screw extruder “Clextral” BC 92. Due to the transformation of casein micelles, the extruded products showed anisotropic supermolecular structure. In the casein preparations neutralized to form caseinates, there was no change to anisotropic structure. It was shown that calcium bound to casein played an important role in stabilizing the structural modification of casein in the course of its extrusion.

Manufacture of bi-layered plain-bearings by bimetallic cold backward extrusion. II - mechanical modelling

This paper reports work into an analysis of the manufacture of bi-layer bearings — with a soft anti-friction inner layer — by backward extrusion. From the results of experimental simulation of bimetallic backward extrusion reported in a companion paper (J. Mech. Work. Tech. 8 (1983) 327–336), a velocity field has been deduced. An upper-bound solution based upon this field has been developed which gives the extrusion force and the trajectories of material points. Two hypotheses — the height of the plastic zone either decreasing or else constant — lead to two different models, which may follow each other in the course of extrusion. Two different sequences of these models have been chosen, and compared with experimental results: they are shown to be quite good at predicting both the punch force and the distribution of the two materials in the bearing wall.

UV exposure, systems and control : Ted C. Bettes. Semiconductor Int., 83 (April 1982)

This is a report of an “observational study” of tooth movement during the course of extrusion of upper laterals with aligners. Pure extrusion along the long axis is a most difficult movement for the aligner. Digital image data were collected from volunteer patients in a private practice setting, throughout the treatment period. Compliance of the enrolled subjects has been excellent. Their serial CBCT data were analyzed for the trajectory of tooth crowns and roots. The small sample data exposed a non-linear movement pattern both for the root and the crown. We termed this motion “wobbling.” The pattern of wobbling was not consistent across the subjects. Understanding the causes, directions, and magnitude wobbling may be expected to instigate novel algorithms for programmed aligner appliances.

Morphology of extruded polypropylene-polystyrene blends

The authors have studied the dependence of the phase structure of PP-PS belnds obtained by extrusion at 200°C on the ratio of the values of the viscosity and normal stresses of the phases, the ratio of the components, the initial degree of dispersity of the blends and also the length of the capillary and the shear stress in the course of extrusion. In accord with the Vanoen theory in the given system where the elasticity of the dispersion medium (PS) is higher than that of the disperse phase (PP) a mixed fibrous-lamellar type of structure forms. The lamellar morphology is represented by a wide diversity of structures—ribbon, lamellar, stellate, reticular, occluded. The influence of the variables studied on the possible formation of each type of phase structure of the PP-PS blends is discussed. The possible spontaneous rupture of the fibres of the disperse phase on annealing of the extrudates is shown.