József Gábor Kovács

Two cardenolides from Calotropis procera

Two cardiotonic glycosides were isolated from Calotropois procera; one of them (1) is a new natural product. Their structures were elucidated by extensive application of one‐ and two‐dimensional 1H and 13C NMR spectroscopy. Copyright

Comparison of thermal, mechanical and thermomechanical properties of poly(lactic acid) injection-molded into epoxy-based Rapid Prototyped (PolyJet) and conventional steel mold

The number of renewable-resource-based and inherently biodegradable poly(lactic acid) (PLA) products is growing in the market, resulting in an increasing demand to produce even small series of injection-molded PLA prototypes for testing purposes by using rapid molds. In our research, it was first demonstrated that it is possible to use epoxy-based molds made by PolyJet Rapid Prototyping technology for conventional injection molding to produce small series of PLA parts. The effect of mold material, namely conventional steel mold and epoxy-based PolyJet mold, was analyzed on the thermal and mechanical properties of the injection-molded products. PLA was used with no, moderate and high nucleating agent contents [talc and poly(ethylene glycol)] to obtain a model material with slow, moderate and high crystallization rates, respectively. It was demonstrated that the mold used and thus the thermal conductivity of the mold had significant effect on the crystallinity of the PLA parts and thus on its mechanical and thermomechanical properties. Finally, it was found that it is possible to mimic the thermomechanical properties of nucleated PLA injected into hot mold used for mass production by injecting it into the epoxy-based PolyJet mold used for small series production.

Thermally conductive polymer compounds for injection moulding: The synergetic effect of hexagonal boron-nitride and talc

The aim of the research project was to investigate and maximize the thermal conductivity of polymer compounds with low filler content (<30 vol%). The study focused on the effect of the matrix material, the filler type, the processing method and the interaction of the fillers. It was concluded that compression-moulded samples have higher thermal conductivity than injection-moulded samples due to the segregation effect and the orientation of the anisotropic fillers. Conductivity can be improved by adding fillers with higher thermal conductivity, and also by combining, or hybridizing the fillers. A synergetic behaviour between hexagonal boron-nitride and talc which improved thermal conductivity was found.

Micromechanical Property Investigations of Poly(lactic acid)–Kenaf Fiber Biocomposites

In this research, investigation on the interfacial shear strength of poly(lactic acid)–kenaf fiber biocomposite was investigated using microbond tests. Tensile properties and fracture behaviors of single kenaf fiber are tested via in situ monitoring with acoustic emission (AE). During tensile loading, acoustic signal recorded higher amplitude of above 20 dB up to the maximum force, which corresponds to breakage of single kenaf fiber. Based on microbond tests and AE evaluation, a correlation has been established on failure of kenaf fiber, which is due to debonding of filament and internal structure, cracking of fiber and breakage of fiber.

Deformation analysis of short glass fiber-reinforced polypropylene injection-molded plastic parts

The warpage of injection-molded plastic parts is a complex problem being affected by different technological parameters, material properties, and mold design. Hence, the description of the deformation is difficult as well. This article presents the effect of fiber content and mold temperature difference on the deformation of polypropylene parts. Based on the measurement results, a linear approximation and a calculation method are shown, which can be used to jointly determine the ideal fiber content and mold temperature difference to produce undeformed plastic parts.

Development of Thermally Conductive Polymer Materials and their Investigation

In the recent years a remarkable development can be observed in the electronics. New products of electronic industry generate more and more heat. To dissipate this heat, thermally conductive polymers offer new possibilities. The goal of this work was to develop a novel polymer based material, which has a good thermal conduction. The main purpose during the development was that this material can be processed easily with injection molding. To eliminate the weaknesses of the traditional conductive composites low-melting-point alloy was applied as filler. Furthermore in this work the effect of the filler content on thermal conductivity, on structure and on mechanical properties was investigated.

Developments in the Field of Rapid Prototype Production

Characteristics of 3D printed specimens are porous structure and low mechanical strength. Due to porous structure post treatment is possible, and in most cases infiltration with an epoxy resin, wax or cyanoacrylate material takes place. As a result of post treatment, the mechanical strength can be increased by 100%, although this is strongly influenced by the infiltration depth that depends on the porous structure and the resin viscosity. In the framework of the common research of the Department of Polymer Engineering, BME and Varinex Zrt. the applicability of a 3D printer is examined in the field of direct tool making. As the first step, the resin uptake ability of specimens prepared with a Z810 3D printer is examined.

Creep behaviour of injection-moulded basalt fibre reinforced poly(lactic acid) composites

In this paper, the creep of short (chopped) basalt fibre reinforced poly(lactic acid) composites was investigated; 5, 10, 20 and 30 wt.% short basalt fibre reinforced composites were prepared by using twin-screw extrusion followed by injection moulding. Differential scanning calorimetry measurements revealed that the basalt fibres had nucleating effect on the poly(lactic acid)grade used in this study, while scanning electron microscopy demonstrated that there was strong adhesion between the fibre and the matrix. Fibre distribution analysis showed that there was no significant statistical difference between the average fibre lengths of all of the produced composites. Finally, creep mastercurves were constructed using the single creep curves obtained by applying 10, 20, 30,…, 90% of the tensile strength of the composites as a static creep loading force. It was demonstrated that the basalt fibres as reinforcements can effectively reduce the strain and increase time to failure of the composites during creep load and thus could open the possibilities for poly(lactic acid)-based composites to be used in long-term constantly loaded structural or engineering applications.

Injection Molding of Degradable Interference Screws into Polymeric Mold

Nowadays the need for faster development cycle can be found all over in the industry. Rapid prototyping has become a common tool in product development, but available materials in these technologies can not always substitute the materials needed for product. Rapid tooling makes it possible to produce a small series of a product with the same technology and materials as that of the final product. In our work we have used the Polyjet technology (Objet Geometries Ltd.) to produce mold for the injection molding of biodegradable interference screws. Our goal was to produce enough quantity of interference screws for biomechanical measurements, with a technology that is more cost efficient than selective laser sintering (SLS). Two types of mold materials were tested. The first mold was prepared from Fullcure720, an acrylic based, UV curing resin on an Object ALARIS machine. The second mold was prepared with resin casting from AH-12/T-58 (100:40) epoxy resin filled with 25 m% Al2O3 powder. For injection molding Natureworks 3051D polylactide (PLA) was used. After injection molding the weight and the geometry of the screws were measured. The results showed that the molds can withstand 5-10 injection cycles, and the screws manufactured meet the requirements for biomechanical tests on porcine knees.

Interfacial shear strength of Polylactic Acid-Kenaf fibre biocomposites

This paper reported the interfacial shear strength (IFSS) between kenaf fibre (KF) and polylactic acid (PLA) matrix which was measured using microbond tests device. The value of IFSS obtained in PLA-KF is comparable to other polymer with natural fibre reinforcements. The properties of single kenaf fibre was determined from tensile tests and also described in this paper. From single kenaf fibre properties, various mechanical properties can be estimated for various applications.