Institute for Sustainable Innovative Technologies

Ljubljana, Slovenia

Institute for Sustainable Innovative Technologies

Ljubljana, Slovenia
SEARCH FILTERS
Time filter
Source Type

Stringari G.B.,University of Ljubljana | Stringari G.B.,Institute for Sustainable Innovative Technologies | Zupancic B.,University of Ljubljana | Zupancic B.,Institute for Sustainable Innovative Technologies | And 5 more authors.
Powder Technology | Year: 2011

Powder Injection Molding is applied for manufacturing complex and precise components from metal, ceramics or cemented carbide powder. It basically consists of mixing the powder and a polymeric binder, injecting this mixture in a mold with the desired form, debinding and then sintering. Among the debinding techniques applied, catalytic debinding of polyoxymethylene (POM) stands out due to the high debinding rates and low risk of cracking. In this work, the potential use of a bimodal POM-based material as the main binder component was evaluated by comparing its thermal and time-dependent properties to a standard monomodal POM. In addition, the potential optimization of this bimodal material was investigated by preparing five new formulations of bimodal POM with higher concentration of short polymeric chains (wax). This work has shown that macroscopic properties of POM are sensitive to the addition of these short chains. For instance, the magnitude of the complex viscosity for the commercial bimodal material was found to be more than 67% lower than for the monomodal POM in the whole range of frequencies studied. Finally, a new formulation of bimodal POM was suggested with 8% of added wax concentration (in weight), resulting in a material with very fine structure that has shown even better flowability than the commercial bimodal POM, without compromising its thermal and mechanical properties. © 2010 Elsevier B.V.


Gergesova M.,University of Ljubljana | Saprunov I.,United Research and Development Center | Emri I.,University of Ljubljana | Emri I.,Institute for Sustainable Innovative Technologies
Rheologica Acta | Year: 2016

The closed-form shifting (CFS) algorithm is a simple mathematical methodology which determines the unique solution in the process of constructing master curves at selected reference temperature and pressure conditions. In a previous paper, the CFS algorithm has been fully described for monotonically increasing or monotonically decreasing functions only. This paper presents detailed steps of the generalized CFS methodology for non-monotonic functions, like the loss tangent. Performing shifting on the loss tangent, which does not require vertical shifting, is particularly important for materials which require vertical adjustment of dynamic viscoelastic functions, i.e., loss and storage moduli. Thus, based on horizontal shifting of the loss tangent, the CFS-based procedure of consecutive horizontal-vertical superposition for the storage modulus is proposed and analyzed. The analysis is done on the example of two synthetically generated non-monotonic tan delta segments and corresponding storage modulus segments in respect to different experimental parameters. It has been shown that the error brought by the shifting method into non-monotonic loss tangent and storage modulus master curves is twice smaller than the corresponding experimental noise level. © 2016 Springer-Verlag Berlin Heidelberg


Oseli A.,Institute for Sustainable Innovative Technologies | Emri I.,University of Ljubljana
Key Engineering Materials | Year: 2014

This paper describes a novel apparatus for measuring dynamic bulk compliance B* (ω) of time-dependant materials. System can measure dynamic bulk compliance at room temperature, at pressures up to 100 ± 1,5 bar and frequencies from 100 Hz to 1000 Hz. Functionality of the apparatus is demonstrated by performing measurements of dynamic bulk compliance for two different materials, i.e., polyvinyl acetate (PVAc) and thermoplastic polyurethane (TPU). Measurements were conducted at room temperature, atmospheric pressure and frequencies from 100 Hz to 1000 Hz. Copyright © 2014 Trans Tech Publications Ltd, Switzerland.


Gonzalez-Gutierrez J.,University of Ljubljana | Oblak P.,University of Ljubljana | Von Bernstorff B.S.,BASF | Emri I.,University of Ljubljana | Emri I.,Institute for Sustainable Innovative Technologies
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2014

Polyoxymethylene (POM) is considered a high performance engineering polymer with many applications primarily in the automotive industry. Currently, POM has also found uses in powder injection molding (PIM) technology, where it acts as a carrier medium for metal or ceramic powders during the injection molding process, it is later removed and a metallic or ceramic piece is obtained after sintering. The main advantage of using POM in PIM technology is the faster debinding process compare to polyolefin-based feedstock, since POM sublimates into its monomer directly when exposed to an acid vapor. During the process of PIM, the binder has two contradictory requirements: viscosity should be as low as possible when in the molten state, but mechanical properties in the solid state, like toughness, should be as high as possible. One way to lower the viscosity is to use POM with lower molecular weights. In this work it has been observed that the viscosity follows a power law function as with other linear polymers, while the fracture toughness follows an exponential function of the average molecular weight. Therefore, a molecular weight can be chosen in a way that a compromise between low enough viscosity and sufficient fracture toughness can be reached. © The Society for Experimental Mechanics, Inc. 2014.


Oblak P.,University of Ljubljana | Gonzalez-Gutierrez J.,University of Ljubljana | Zupancic B.,University of Ljubljana | Aulova A.,University of Ljubljana | And 2 more authors.
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2016

In the plastics industry it has been common practice to mechanically recycle waste material arising from a production. However, mechanical recycling affect material mechanical properties and consequently quality of the end products; therefore it needs to be quantified. Mechanical recycling of high density polyethylene (HDPE) was simulated by one-hundred consecutive extrusions. After every cycle, portion of material was removed for the purpose of characterization. Solid mechanical properties of the material were characterized in terms of hardness and modulus measured with nanoindentation. Furthermore, shear creep compliance was measured to characterize the materials’ time-dependent mechanical properties in solid state. In addition, differential scanning calorimetry (DSC) measurements were performed in order to study structural changes through the degree of crystallinity. The results on hardness and modulus show deterioration of the material mechanical properties through the process of repeating recycling. This becomes increasingly evident after 10th extrusion. Similarly, shear creep compliance measurements show an unfavourable effect of mechanical recycling on the time-dependent mechanical properties. In this case, evident changes are visible in particularly after the 30th extrusion. After 100th recycling material mechanical properties reduces for about 20%. All those changes are well supported by changes of the degree of crystallinity. © The Society for Experimental Mechanics, Inc. 2016.


Gonzalez-Gutierrez J.,University of Ljubljana | Oblak P.,University of Ljubljana | Megen Z.M.,University of Ljubljana | Emri I.,University of Ljubljana | Emri I.,Institute for Sustainable Innovative Technologies
Polimery/Polymers | Year: 2015

The effect of average molecularweight (Mw) of polyoxymethylene (POM) on melt viscosity and solid state creep compliance were investigated. Viscosity follows the power function of Mw. Creep compliance results indicate that time-Temperature superposition applies to POM copolymers. Creep compliance in a short time (0.25 s) is independent of Mw, but in a longer time (10 years) it follows an inverse power law relation withMw, up to a critical value ofMw = 81 100, where creep compliance becomes independent of Mw. At intermediate time (17 min), similar to short one, no effect on susceptibility to creep compliance was observed. It was also stated that the activation energy is independent of Mw.


Oblak P.,University of Ljubljana | Gonzalez-Gutierrez J.,University of Ljubljana | Zupancic B.,University of Ljubljana | Aulova A.,University of Ljubljana | And 2 more authors.
Materials Today: Proceedings | Year: 2016

In the plastics industry it has been common practice to mechanically recycle waste material arising from a production. However, mechanical recycling affects material mechanical properties and consequently quality of the end products; therefore, it needs to be quantified. Mechanical recycling of high density polyethylene (HDPE) was simulated by one-hundred consecutive extrusions. After every cycle, portion of material was removed for the purpose of characterization. Solid mechanical properties of the material were characterized in terms of hardness and modulus measured with nanoindentation. Furthermore, shear creep compliance was measured to characterize the materials' time-dependent mechanical properties in solid state. In addition, differential scanning calorimetry (DSC) measurements were performed in order to study structural changes through the degree of crystallinity. The results on hardness and modulus show deterioration of the material mechanical properties through the process of repeating recycling. This becomes increasingly evident after 10th extrusion. Similarly, shear creep compliance measurements show an unfavourable effect of mechanical recycling on the time-dependent mechanical properties. In this case, evident changes are visible in particularly after the 30th extrusion. After 100th recycling material mechanical properties reduces for about 20%. All those changes are well supported by changes of the degree of crystallinity. © 2016 Elsevier Ltd.


Gergesova M.,University of Ljubljana | Gergesova M.,Institute for Sustainable Innovative Technologies | Zupancic B.,University of Ljubljana | Zupancic B.,Institute for Sustainable Innovative Technologies | And 4 more authors.
Journal of Rheology | Year: 2011

Time-dependent material functions of engineering plastics within the exploitation range of temperatures extend over several decades of time. For this reason material characterization is carried out at different temperatures and/or pressures within a certain experimental window. Using the time-temperature and/or time-pressure superposition principle, these response function segments can be shifted along the logarithmic time-scale to obtain a master curve at selected reference conditions. This shifting is commonly performed manually ("by hand") and requires some experience. Unfortunately, manual shifting is not based on a commonly agreed mathematical procedure which would, for a given set of experimental data, yield always exactly the same master curve, independent of person who executes the shifting process. Thus, starting from the same set of experimental data two different researchers could, and very likely will, construct two different master curves. In this paper, we propose a closed form mathematical methodology (CFS) which completely removes ambiguity related to the manual shifting procedures. This paper presents the derivation of the shifting algorithm and its validation using several simulated-and real-experimental data. It has been shown that error caused by shifting performed with CFS is at least 10-50 times smaller then the underlying experimental error. © 2011 The Society of Rheology.


Gonzalez-Gutierrez J.,University of Ljubljana | Stringari G.B.,University of Ljubljana | Megen Z.M.,University of Ljubljana | Oblak P.,University of Ljubljana | And 3 more authors.
Journal of Physics: Conference Series | Year: 2015

Polyoxymethylene (POM) has found applications as a binder material in Powder Injection Moulding (PIM) due to its ability to depolymerize rapidly under acidic conditions. Such ability represents an advantage during the binder removal step of PIM. However, currently available POM has high viscosity that can complicate the injection moulding process of parts with complex geometry. For this reason it is necessary to investigate methods of lowering the viscosity of POM-based binders, but without affecting their solid mechanical properties (i.e. creep compliance). In this investigation, the addition of a low molecular weight polymer, and the reduction of the average molecular weight of POM were investigated as possible ways of decreasing the viscosity of PIM binders. The addition of the low molecular weight additive (WAX) caused a small decrease in the viscosity of the POM-based binder and a small increase in its solid creep compliance. On the other hand, lowering the average molecular weight of POM caused a large decrease in viscosity, but also an acceptable increase in creep compliance. Therefore, by selecting an appropriate molecular weight of POM, it is possible to improve the performance of POM-based binders for PIM. © Published under licence by IOP Publishing Ltd.


Nikonov A.,University of Ljubljana | Nikonov A.,Institute for Sustainable Innovative Technologies | Saprunov I.,University of Ljubljana | Saprunov I.,Institute for Sustainable Innovative Technologies | And 4 more authors.
International Journal of Impact Engineering | Year: 2011

Recently developed experimental-numerical-analytical (ENA) methodology presented in Ref. [13] by Emri et al. based on a simple non-standard falling weight experiment, was used for mechanical characterization of "dry" and "wet" climbing ropes. Analysis of the maximum impact force; the visco-plastic component of rope deformation; the amount of stored, retrieved and dissipated energy; the stiffness of the rope; and the maximum value of the first derivative of the de-acceleration (jolt) showed that moisture significantly affects the functionality and durability of ropes. "Wet" ropes create larger maximum force, dissipate less energy, and generate larger retrieved energy that propels climbers in the opposite vertical direction. Properties of "wet" ropes are also more sensitive to number of repeated drops. Major changes of all physical quantities are, as a rule, observed during the first three to four drops. It has been shown that for the safety of climbers the most indicative properties are dissipated energy and jolt (first derivative of climber de-acceleration). The ratio of dissipated and retrieved energy, ψ=Wdys/Wret, could be used as a criterion for evaluation of the quality of climbing ropes. © 2011 Elsevier Ltd. All rights reserved.

Loading Institute for Sustainable Innovative Technologies collaborators
Loading Institute for Sustainable Innovative Technologies collaborators