Pressure-Affected Flow Properties of Powder Injection Moulding Compounds

Vliv tlaku a teploty na tokové vlastnosti materiálů určených pro zpracování Powder Injection Moulding (PIM) technologií byl studován na modifikovaném kapilárním reometru. Vliv těchto parametrů byl kvantifikován pomocí koeficientů Carreau-Yasuda modelu. Teplotní senzitivita 50 vol. % kompoundu (slinuté karbidy) je nižší než u čistého polymerního plniva a s tlakem se výrazně nemění. Tlaková senzitivita, naproti tomu, s plněním roste a je značně teplotně závislá.The effect of pressure and temperature on the flow properties of the materials intended for Powder Injection Moulding (PIM) technology was studied using a single-piston capillary rheometer modified by additional backpressure chamber. The influence of pressure and temperature on shear viscosity has been quantified through pressure and temperature sensitivity coefficients derived from Carreau-Yasuda model. The temperature sensitivity of the 50 vol. % compound based on cemented carbide powder is lower than that of pure polymeric binder, and it varies only slightly with pressure. In contrast, the pressure sensitivity of compounds was found to be higher than that of pure polyolefin binder, and it is decreasing function of temperature. In addition, it is shown that temperature sensitivity of binder, which is considerably enhanced by pressure (in contrast to the PIM demands), cannot be determined as being equal to the properties of particular binder components

Antibacterial effect of phosphates and polyphosphates with different chain length

The aim of this study was to monitor the antibacterial effect of seven phosphate salts on selected strains of Gram-negative and Gram-positive bacteria, which could be considered responsible for food-borne diseases (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Micrococcus luteus, Staphylococcus aureus, Citrobacter freundii, Escherichia coli, Proteus mirabilis, Salmonella enterica ser. Enteritidis and Pseudomonas aeruginosa). For these purposes, phosphates differing in chain length were used. The tested concentrations were in the range of 0.1-2.0% (wt v ; 1) applied at the model conditions. In the majority of cases the visible inhibitory effect on the growth of observed microorganisms could be seen. Due to the chemical structure of salts and their dissociation both the pH values of cultivation broth and similarly the growth characteristics of bacterial strains were affected. The inhibition of above mentioned bacteria was apparently supported by this dissociation. Phosphates obviously made the development of most Gram-positive bacteria impossible. Especially Micrococcus luteus was extremely sensitive to the presence of these substances. On the other hand, Gram-negative bacteria seemed to be resistant to the phosphate incidence. The exemption clause from the tested salts was represented by a high alkaline trisodium phosphate. It should be pointed out that generally the most significant antibacterial effects were shown by polyphosphates HEXA68 and HEXA70, trisodium phosphate undecahydrate, tetrasodium pyrophosphate and finally trisodium phosphate. By comparing the inhibitory effects of various phosphate salts can be concluded that the antibacterial activity was not determined only by the condensation degree but there was also proved the dependence on pH values

On the preparation and characterization of nanoemulsions produced by phase inversion emulsification

Formation, appearance, particle size and viscosity of n-undecane in water (nano)emulsions prepared by the phase inversion method using non-ionic surfactants (Igepal, Brij) were investigated. The effects of the HLB value, oil-in-water ratio (5/95 to 30/70), surfactant type and its concentration (3 and 5%) on the physico-chemical characteristics of emulsions were studied. Emulsions were characterized by visual and microscopic observations and the particle size and distribution as well as emulsion viscosity were determined. The results showed that all the variables mentioned above considerably influenced both the particle size and the viscosity. The smallest particle sizes (lower than 250. nm) and the best emulsion stability were determined at optimum HLB of 10.5 for all the studied oil-in-water ratios, both types and concentrations of surfactants. Typically, the emulsion droplets prepared with Igepals were bigger than those prepared with Brij systems

Superposed Flow of CIM Compounds

Superposition of steady shear and oscillatory flows represents the possibility to investigate viscoelastic behaviour of the materials which are processed under complex deformations far from simple steady or oscillatory shear flows. Ceramic-based compounds intended for Ceramic Injection Moulding (CIM) undergo deformation through channels under various conditions. Their parallel superposed steady and oscillatory shear flows were measured on a cone-plate rheometer. Flow properties at high shear rates were evaluated on a capillary rheometer. The compounds showed highly non-Newtonian behaviour and apparent yield stress; their viscoelastic properties were influenced remarkably under the superposed shear flow at low shear rate and angular frequency; and they exhibited significantly different behaviour than fibre-filled systems

Dynamic light scattering in analysis of colloidal systems

Dynamic light scattering (DLS) is a non-invasive technique, capable of measuring the size of submicron particles in the submicron range. The study was focused on the applicability of DLS in measurement of colloidal particles of different types. The micelle sizes of surfactants (Tween 60, Tween 20, Igepal CA 720 and Na lauryl sarcosinate) and particle sizes of micro-and nanoemulsions were measured. The diameters of surfactant micelles were 13.0±0.1 nm, 8.4±0.1 nm, 7.1±0.2 nm and 2.7±0.1 nm for Tween 60, Tween 20, Igepal CA 720 and Na lauryl sarcosinate, respectively. Stability of nanoemulsions as a consequence of the changes of particle size distributions in storage was monitored. The results revealed the presence of uni-, bi-and trimodal distributions reflecting the occurrence of various particle populations as well as a shift of distribution curves due to the particle growth. It was confirmed that DLS can provide reliable and rapid determinations of particle sizes of micro-, nano-and classical emulsions

Antimicrobial Effects of Monocaproylglycerol

The efficiency of an antimicrobial treatment for lining and insole textile materials based on the use of monocaproylglycerol in contrast to textile materials with commercial antimicrobial treatment was investigated. The antimicrobial testing was carried out by agar-diffusion test, 2-layer method to various species of saprophytic and pathogenic moulds, pathogenic yeast, gram-negative and gram-positive bacteria. The results show that the lining and insole materials treated by monocaproylglycerol causes highly effective elimination of all tested strains of bacteria and pathogenic microorganisms with an only exception of saprophytic mould, which is partially resistant

The influence of colloids on the particle size and stability of O/W emulsions in the presence of nonionic surfactants

The effect of the presence of colloids on formation, stability and particle size of n-undecane in water nanoemulsions prepared by the Emulsion Inversion Point (EIP) method using nonionic surfactants (Igepals) was studied. The influence of oil-to-water ratio, the HLB value and concentration of the surfactant on their physico-chemical characteristics was also investigated. The stability of emulsions was assessed from changes in the particle size and the particle size distribution as well as through visual assessment of their appearance. The results obtained show that the anticipated positive effect of the colloids on emulsion stability was not confirmed. Phase separation of these systems usually occurred soon after preparation or during a few days of their storage. The particle size of emulsions prepared in the presence of colloids was mostly bigger in comparison with emulsions where colloids were absent. Nevertheless, nanoemulsions with the particle size smaller than 200 nm were also obtained. The best long-term stability was observed in emulsions prepared at the HLB value of 11.5, oil content of 20 and 30 wt. % stored at 4 degrees C

Moisturizing effect of topical cosmetic products applied to dry skin

One of the complications of "diabetes mellitus" is termed diabetic foot syndrome, the first symptoms of which include changes in the skin's condition and properties. The skin becomes dehydrated, dry, and prone to excessive formation of the horny layer, its barrier function becoming weakened. This function can be restored by applying suitable cosmetic excipients containing active substances. The aim of this study was to evaluate and compare the effects of commercially available cosmetic products (CPs) designed for the care of diabetic foot, through a group of selected volunteers using noninvasive bioengineering methods. Statistical surveys (p < 0.05) evaluated these CPs as regards to their hydration effect and barrier properties. Special attention was devoted to CPs with the declared content of 10% urea, and that the influence of this preparation's ability to hydrate and maintain epidermal water in the epidermis was confirmed