Browse Articles

An assay on the thermal stability of isotactic polypropylene stabilized with Sanduvor PR 31, a hindered amine (O1-(1,2,2,4,6,6-hexamethyl-4-piperidyl) O3 - (1,2,2,6,6-pentamethyl-4-piperidyl) (2Z) – 2 - [(4-methoxyphenyl) methylene] propanedioate, was performed. The oxidability of modified polymer previously subjected to weathering treatment or UV irradiation was investigated in air by isothermal (1550C) and isobaric (normal pressure) oxygen uptake. The exposure time was sufficient enough to attend a slow degradation rate (281 days for weathering test and 550 h for accelerated UV ageing). The main kinetic parameters, oxidation induction time and oxidation rate, were determined from the dependencies of chemically consumed oxygen on testing time. Comparative results on reference samples (control or stabilized polypropylene) and degraded materials are analyzed for depicting the influence of ageing factors on the polypropylene durability. Keywords: polypropylene, UV degradation, weathering, oxygen uptake, Sanduvor PR 31

Graphite-based Teflon composites find various applications in many engineering fields. For certain applications, the use of composites rather than metals has in fact resulted in savings of both cost and weight. The usage in many fields demands several machining operations to be performed on engineering polymers. The paper deals with two different materials: polytetrafluoroethylene with regenerated graphite (PTFE GR) and polytetrafluoroethylene with 32% carbon and 3% graphite (PTFE CG 32-3). At the beginning of the study it was performed an advanced characterization for both materials that have been used: PTFE GR and PTFE CG 32-3. The chemical composition was determined using X-ray photoelectron spectroscopy (XPS). Complementary information about the chemical structure is obtained with Fourier transform infrared spectroscopy (FTIR). This combination of spectroscopic methods was used to establish individual differences between the chemical structures for the used materials. Second part of the present paper investigates the effect cutting parameters on the cutting force in the turning of PTFE GR and PTFE CG 32-3 materials. The effects of different parameters on cutting force are analyzed and presented in this study. This paper presents that the success of the machining operation is affected by the chemical structure of the work material. Keywords: engineering polymers, spectroscopy analysis, cutting force, turning

The UHMWPE has a plastic behaviour but it is specified only the surface wear, unless the evaluation of the great importance of this behaviour of plasticity for the calculation of the depth of penetration. This work tries to demonstrate the fact that there are components of the wear by plastic deformation. Also, by this type of wear an explanation of smooth surface of the UHMWPE in the contact zone, after millions of gaits cycles may be explained Keywords: hip endoprosthesis, wear, penetration depth, roughness, plastic behavior

This paper presents the synthesis of complex nanostructures of the Fe3O4-n[SiO1.5g-(CH2)3(NH2)](NH2)nd-(GL)ne type [Fe3O4 = magnetic core; n[SiO1.5g-(CH2)3(NH2)] = coated layer; (NH2)nd,-NH2= surface and deep amino groups which play an important role in biochemical interfacing; (GL)ne= exterior superficial glutaraldehyde layer]. These nanostructures have several interesting physical and chemical characteristics, such as: biochemical fixing without destructing the microorganisms on the Fe3O4-n[SiO1.5g-(CH2)3(NH2)](NH2)nd-(GL)ne surface and the ability to differentiate the microorganisms in magnetic field, according to the mass and volume. In order to obtain superior biochemical fixing performances we have analysed and determined the chemical and physical distributional mechanisms of (NH2)nd, -NH2 groups on the surface and in the depth of the above-mentioned nanostructure. For this purpose we have deduced the control equations according to the synthesis parameters, which triggers the growth of the silicone polymer layer and the distribution of the amino groups in its structure. Keywords: Magnetite, coated nanoparticle, biochemical fixing, crosslinking molecules

This paper presents the influence of processing temperature on the mechanical-physical properties of thermoplastic polyurethanes (TPU) used at injection moulding of performance sport products. The test-pieces were moulded at the following real injection temperatures : 200°C, 210°C, 220°C, 230°C and 240°C. It was determined that the in-mould pressure decreased with increasing of the processing temperature. Also the following thermal analysis were performed : Thermogravimetry (TG), Differential Scanning Calorimetry (DSC) and Dynamic-Mechanical Analysis (DMA). It was established that the processing temperature has a significant influence on the thermal stability and on the glass transition temperature of polymer while the flow temperature is slightly influenced by the processing temperature. Keywords: thermoplastic polyurethane (TPU), injection moulding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC) , Dynamic-Mechanical Analysis (DMA)

This paper presents a study of the reactivity new carbosiloxane cyclic structures in anionic ring opening polymerization reactions in the presence of catalyst potassium siloxanolate. For this purpose, 2,2,5,5-tetramethyl-3,4-diphenyl-1-oxa-2,5-disilacyclo-pentane, 2,2,5,5-tetramethyl-3,3-diphenyl-1,4-dioxa-2,5-disilacyclopentane, 2,2,7,7-tetra-methyl-3,3,6,6-tetraphenyl-1-oxa-2,7-disilacycloheptane and bis-[1,4-bis-(dimethylsiloxanyl)-dihydronaphthalene] were used. The evolution of the polymerization reaction was observed through measurements of the reaction mixture inherent viscosity at various temperatures. The obtained results were processed in order to obtain the influence of the chemical structures on the processes conditions of development and kinetic parameters related to the transformation of the cycles to linear compounds. Keywords: cyclocarbosiloxanes, siloxanes, anionic polymerization, ring opening polymerization, organo-silicon compounds

The more reliable values of the crystallization temperature were obtained from the non – isothermal DSC thermograms recorded at low cooling rate. The crystallization time was evaluated from the isothermal DSC thermogrames recorded at those temperatures at which the crystallization occurs. PP nucleated with Irgastab NA 21, has crystalline phase that contains the smallest spherulites, as compared to those nucleated with Irgastab NA 04 and Irgaclear DM. The incorporation of the nucleating / clarifying agents into the polymer matrix is homogeneous only if the melt processing conditions were well defined for each of them. A dependence on the molecular weight of the nucleated PP morphology was observed. The spherulite size decreases with the increase of the molecular weight. Keywords: crystalization, nucleation, polypropylene, nucleating agent, spherulite

This article presents the experimental results regarding the glucose influence on poly (vinyl alcohol) (PVA) films. The results of infrared spectroscopy (FTIR), atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements revealed the surface and structural changes induced by increasing the glucose concentration. Keywords: PVA, AFM, XRD, FTIR

In this paper the 3D simulation model of typical porous polymer is presented. Porosity growth was caused by numerical handling of a spatial pores network. Although the algorithm has a good accuracy it is noticed that the final average pore sizes for simulated polymer networks are larger than the desired pore size. Keywords: polymer network, porosity, tissue engineering

Mixing and processing characteristics, mechanical properties and thermal characteristics of dimethyl vinyl silicone/poly(tetrafluoroethylene)(MVQ/PTFE) blends were investigated. With the rise Poly(tetrafluoroethylene) (PTFE) portion in blends, the values of both torque and total torque of blend materials decrease. In MVQ/PTFE blends, PTFE act as inactive filler and some mechanical properties decreases in blends compared to component polymers with the increases portion of plastic in blend compositions. The heterogenity of MVQ/PTFE blends was determined by thermomechanical analysis-dilatometry. Silicone (MVQ) and PTFE show separate Tgs, which indicate that they are not compatible. Thermogravimetric analysis of these blends, show that with increased portion of PTFE in blends, the TGA characteristics Tbeg and T5% is moved at higher temperature, which mean increased of thermal blend stability. Keywords: blends, dilatometry, TGA