A practical approach to modeling time‐dependent nonlinear creep behavior of polyethylene for structural applications

The purpose of this work is to develop a practical method for constitutive modeling of polyethylene, based on a phenomenological approach, which can be applied for structural analysis. Polyethylene is increasingly used as a structural material, for example, in pipes installed by trenchless methods, where the relatively low stiffness of polyethylene reduces the required installation forces, chemical inertness makes it applicable for corrosive environments, and adequate strength allows its use in sewer, gas, and water lines. Polyethylene exhibits time‐dependent constitutive behavior which is also dependent on the applied stress level resulting in nonlinear stress–strain relationships. Nonlinear viscoelastic theory has been well established and a variety of modeling approaches have been derived from it. To realistically utilize the nonlinear modeling approaches in design, a simple method is needed for finding a constitutive formulation for a specific polyethylene type. This paper presents such a practical approach to nonlinear viscoelastic modeling utilizing both the multi‐Kelvin element theory and the power law functions to model creep compliance. Creep tests are used to determine material parameters and models are generated for four different polyethylene materials. The corroboration of the models is completed by comparisons with results from different tensile creep, step‐loading creep, and load‐rate tests. POLYM. ENG. SCI., 48:159–167, 2008. © 2007 Society of Plastics Engineers     

Theoretical model for calculating pulling loads for pipes in horizontal directional drilling

The paper presents a model for calculating installation loads imposed on pipes during the pulling operation in horizontal directional drilling. The model is implemented into a numerical program PipeForce 2005. The analysis includes pulling load contributions from directional changes, fluidic drag, solid friction and pipe’s weight. The emphasis in this paper is on details related to directional changes during the HDD installation. The formulation approximates the borepath as series of linear segments between the measured points (field-measured locations of the drilling head) and predicts the shape of the pipe in the borepath. Based on this shape, the layout of the borepath and the pipe stiffness, the contact forces between the pipe and the borepath are evaluated using the theory of deflections of flexible bars. The pulling force for the pipe is calculated to equilibrate the weight of the pipe and friction between the pipe and the soil and between the pipe and the drilling fluid. A comparison of theoretical predictions and field data is presented.     

Testing of PTA automatic braze-welding technology for producing absorber joints of solar collectors

The article presents research aimed at developing a PTA braze-welding technology for producing absorber connections between tubes and copper foil with EcoBraz 38102 self-fusible brazing solder in the form of wire 1 mm in diameter. Braze-welding process was carried out by means of two techniques of braze welding of flat copper foil to a tube, while the foil had a 0–1.5 mm wide gap: a connection with a butt joint made by braze welding with simultaneous stamping of a semi-circular channel in the copper foil (the channel diameter equal to the tube diameter); and a connection with two braze-welded fillet joints. Metallographic tests, hardness measurement, static tensile test and thermal conduction efficiency test were performed to determine the properties of prepared connections. It was demonstrated that there exists a field of PTA braze-welding parameters which assures high quality of absorber connections between tubes and copper foil.     

Synthesis and characterization of acryloyloxy guar gum

Guar gum is a galactomannan commonly used as a viscosity modifier in the food, pharmaceutical, and cosmetics industry. The aim of this study was to synthesize acryloyloxy guar gum via a Schotten‐Bauman reaction in aqueous media. The reaction products were characterized using FTIR, C¹³‐NMR, wide angle X‐ray diffraction techniques to ascertain the effect of acrylation on the structure of guar gum. The acrylation of guar gum was found to be limited to the primary hydroxyl groups on the guar gum molecule. The maximum degree of substitution (DS) was found to be 0.56, which was observed after 3 h of reaction. Since the reaction was carried out in an aqueous medium after 3 h of reaction the DS of the derivatised guar gum was found to decrease, because of hydrolysis of the formed ester linkages. The ester content and intrinsic viscosity of the derivatised guar gums were also evaluated. Thermal analysis showed that a higher DS resulted in products with lower thermal stability and there was no evidence of reaction via the acrylate groups on heating. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Silica nanoparticles as a tool for fluorescence collection efficiency enhancement

In this work we demonstrate enhancement of the fluorescence collection efficiency for chlorophyll-containing photosynthetic complexes deposited on SiO₂ spherical nanoparticles. Microscopic images of fluorescence emission reveal ring-like emission patterns associated with chlorophyll-containing complexes coupled to electromagnetic modes within the silica nanoparticles. The interaction leaves no effect upon the emission spectra of the complexes, and the transient behavior of the fluorescence also remains unchanged, which indicates no influence of the silica nanoparticles on the radiative properties of the fluorophores. We interpret this enhancement as a result of efficient scattering of electromagnetic field by the dielectric nanoparticles that increases collection efficiency of fluorescence emission.     

The Effect of Platelet-Rich Plasma on the Intra-Articular Microenvironment in Knee Osteoarthritis

Knee osteoarthritis (KOA) represents a clinical challenge due to poor potential for spontaneous healing of cartilage lesions. Several treatment options are available for KOA, including oral nonsteroidal anti-inflammatory drugs, physical therapy, braces, activity modification, and finally operative treatment. Intra-articular (IA) injections are usually used when the non-operative treatment is not effective, and when the surgery is not yet indicated. More and more studies suggesting that IA injections are as or even more efficient and safe than NSAIDs. Recently, research to improve intra-articular homeostasis has focused on biologic adjuncts, such as platelet-rich plasma (PRP). The catabolic and inflammatory intra-articular processes that exists in knee osteoarthritis (KOA) may be influenced by the administration of PRP and its derivatives. PRP can induce a regenerative response and lead to the improvement of metabolic functions of damaged structures. However, the positive effect on chondrogenesis and proliferation of mesenchymal stem cells (MSC) is still highly controversial. Recommendations from in vitro and animal research often lead to different clinical outcomes because it is difficult to translate non-clinical study outcomes and methodology recommendations to human clinical treatment protocols. In recent years, significant progress has been made in understanding the mechanism of PRP action. In this review, we will discuss mechanisms related to inflammation and chondrogenesis in cartilage repair and regenerative processes after PRP administration in in vitro and animal studies. Furthermore, we review clinical trials of PRP efficiency in changing the OA biomarkers in knee joint.     

Synthesis and properties of hybrid urethane polymers containing polyhedral oligomeric silsesquioxane crosslinker

The synthesis and properties of novel hybrid silsesquioxane‐containing urethane polymers using octakis(hydroxypropyldimethylsiloxy)octasilsesquioxane (OHPOSS) as a crosslinker and a hydroxyl‐terminated polybutadiene were studied. Mixing of the OHPOSS with polyurethane prepolymer and chain extenders in solution was found to be successful when tetrahydrofuran was used as the solvent. Thin films of hybrid polyurethanes were obtained. The hybrid materials were elastomers with improved water and solvent resistivity and good thermal stability. The studied OHPOSS appeared to be an effective crosslinker of polyurethanes suitable for, for example, surface coatings applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2023–2030, 2013     

Characterisation of fermentation of high-gravity maize mashes with the application of pullulanase,proteolytic enzymes and enzymes degrading non-starch polysaccharides

The aim of the research was to assess the possibility of the fermentation productivity rising through the increase in corn mashes extract from 16–17 to 20–21°Balling, yet keeping a 3-day fermentation period. The second goal was to obtain the highest possible utilization of starch in the raw material through deep enzymatic degradation and utilization of available sugars and simultaneous maintenance of high quality spirit. It was found that fulfilling the above during the 3-day fermentation period was possible with the application of pullulanase as an additional amylolytic enzyme. Adding pullulanase resulted in the acceleration of the starch hydrolysis degree, which led to lower amounts of unhydrolyzed dextrins and higher ethanol yield. When the supportive enzymes complex (pullulanase, protease and cellulase) was used, the final ethanol concentration reached 10.86 ± 0.04% v/v, with ethanol yield at 68.41 ± 0.23 dm³ of absolute ethanol (A₁₀₀) per 100 kg of starch, which was 95.25 ± 0.32% at the theoretical value. The acceleration of starch enzymatic degradation and the application of a proteolytic preparation visibly shortened both initial and main fermentation phases. This in turn increased the time of the final fermentation phase and resulted in more extensive utilization of substrates by yeasts with simultaneous reduction of the final concentration of acetaldehyde (26.0 ± 0.5 mg/dm³A₁₀₀) and diethyl acetal of acetaldehyde (2.5 ± 0.5 mg/dm³A₁₀₀). The quality of spirit obtained was positively verified also in terms of relatively low concentration of higher alcohol (3912.2 ± 9.8 mg/dm³A₁₀₀). Preliminary analysis of costs (without raw-material) of 1 l distillate production indicated the possibility to reduce the costs by 18–20%.     

Identification of local heat flux to membrane water-walls in steam boilers

A heat flux entering steam generating tubes in power station boilers may be a critical factor in considering the safety of the tubes. The knowledge of the distribution and magnitude of this flux during the operation of the power boiler is very important. The design of a modern boiler furnace requires the computation of furnace wall metal temperatures for the proper selection of the tube thickness and material. These temperatures are functions of the heat fluxes and the internal heat transfer coefficients. In this study, a measuring device (flux-tube) and a numerical method for determining the heat flux in boiler furnaces, based on experimentally acquired interior tube temperatures, are presented. An inverse method was developed, which can estimate the following parameters: the absorbed heat flux, the heat transfer coefficient on the inner tube surface and the temperature of water-steam mixture from temperature measurements at several interior locations of the flux-tube. The least squares method was used to minimize the differences between the calculated and measured temperatures. The unknown parameters are found using the Levenberg-Marquardt method. The number of temperature sensors (thermocouples) is greater than three because the additional information can help in more accurate estimations of the unknown parameters. The temperature dependent thermal conductivity of the flux-tube material was assumed. The developed flux-tube can work for a long time in the destructive high temperature atmosphere of a coal-fired boiler.