Browse Articles

A method for obtaining, with low experimental effort, desired properties for road bitumen, was conceived. This method is applicable in those situations when the quality of the road bitumen is understandard, there are no physical interaction between the used components for modification and their concentration varies in very narrow limits. Keywords: physical modification, road bitumen, polymer, experiments design

The thermal properties of nanofilled and microfilled restorative composites (Filtek Supreme XT and Filtek Z250) are studied in comparison with the ones of teeth. Our results show slightly decreased values of the thermal constants of Filtek Supreme XT with respect of Filtek Z250, due to the smaller filler particle size. Both analyzed composite materials have the values of the thermal conductivity and diffusivity very close to the one of enamel, with the better fitting in the case of Filtek Supreme XT. Comparing with the values for dentin, the thermal conductivity is about two times higher, while the thermal diffusivity is three times higher. Keywords: thermal properties, thermal conductivity, restorative composites

The effect of clay-hybrids treatment on physical and structural properties of polypropylene (PP J600) nanocomposite has been studied. The experiments carried out were focused on obtaining the polypropylene nanocomposite samples. In all the experiments the polypropylene with flow rate in melt of 9.21g/10min and nanoblend MB1201 were used. The structure analysis of polypropylene nanocomposites was made by means of XRD and FT-IR methods. XRD analysis shows that for nanocomposite based on polypropylene, the exfoliation of organo-bentonites takes place. The results shows a high improvement in the mechanic properties of the NPP4 with 5% and NPP4 with15% glass fiber nanocomposite compared to the NPP4 nanocomposite. Keywords: nanocomposite, structure; diffraction, absorption, mechanical properties

Poly(N-vinylcaprolactam)-poly(ethylene glycol) – poly(N-vinylcaprolactam) triblock copolymers were synthesized for the first time by the ATRP of N-vinylcaprolactam (NVCL) initiated from poly(ethylene glycol) (PEG) macroinitiators with 2-chloropropionate groups at both ends and catalyzed by the CuCl/5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6Cyclam) system. Their polydispersity was larger than 1.8, indicative for a lower control degree of the process, which was ascribed to the slow deactivating behaviour of the catalytic system. The triblock copolymers synthesized displayed thermosensitive behaviour in aqueous solution, undergoing sol – gel transition on the interval 30 - 60°C. It was found that the aggregation (cloud point) and gelation temperatures, as well as the rheological properties of the polymer aqueous solutions depended on the chain length of both PEG and PNVCL blocks. Keywords: N-vinylcaprolactam, poly(ethylene glycol), triblock copolymers, ATRP, thermal gelation

In this article we obtained the characteristic curves for polyester and epoxy resins used in the process of making composites, and determined their elastic and resistance properties as well as the characteristic curves on two directions for the epoxy and polyester resin composites, reinforced with woven polypropylene. We established the flow strain and two coefficients from the calculus relation for the plastic potential. We determined the equation of nonlinear dependency between strain and deformation in the plastic field using a fourth degree polynomial relation which indicates the specific elongation and resistance to fracture. Keywords: composite materials, polypropylene fabric, plastic field

The polymers with special properties represent the starting point in order to obtain a wide range of new materials used in various fields of activity. Poly (methyl methacrylate) (PMMA), a transparent thermoplastic material, is an attractive polymer because of it’s unique properties, in comparison with other polymers, such as: high mechanical strength, special optic properties, and durability. The incorporation of silicate layers (for example, clay, minerals) in the polymer microstructure in order to improve the mechanical, thermal and interface properties has become one of the interesting of the researchers nowadays. Thus, depending on the working conditions and the interactions between the clay layers and the polymer system, a series of composites with different morphology, for instance, agglomerated, intercalated and exfoliated, has become accessible. In order to promote solutions for improving PMMA properties and to have a better general view on the action of oxide nanoparticles, we chose to analyze the structure and mechanical properties of some methacrylic composites with TiO2, Al2O3, and PMMA fillers. Keywords: nanocomposites, mechanical properties, poly(methyl methacrylate), SEM

The paper presents a modern method to optimize welding procedures for PE 100 polyethylene pipelines using computer-assisted design of experiments. The design of experiments method RSD (Response Surface Design) was applied for optimizing the heated tool butt-welding of PE 100 type polyethylene pipes meant for pressure pipelines. Experimental researches made on 110mm diameter pipes had in view the mathematical modelling of the welding process, so that, on the basis of a number of 32 welding technological versions made, the optimum welding procedure was established, a procedure that met all the imposed conditions. Keywords: Optimizing, heated tool welding, polyethylene PE 100

Flow through tubular runners presented is a very important flow type encountered in polymer processing, especially during injection mold filling. The filling pattern developed during the mold filling plays a decisive role on the final part quality, thus, in this paper we have investigated the filling pattern and the volumetric flow rate during the filling of a tubular runner for three different materials. The melt is treated as an incompressible, non-Newtonian the Ostwald-de Waele model with a power-law relationship between the shear stress and the shear rate. Keywords: runner, injection molding, flow front, polymer melt

The paper aims to present a theoretical-experimental approach of a particular class of composite materials known as multiphase composites in order to retrieve its effective dynamic moduli and identify the major influencing factors on these variations. Supplementary, will be presented a two step homogenization concept based on the well known theoretical predictions from the micromechanics of composite materials approaches, the Mori-Tanaka that applies to the particle reinforced composites and Halpin-Tsai that applies to the random fibre composites. The theoretical values were compared with the experimental data, the later being retrieved during a two heating cycles with temperature ranging from -300C to 1600/2000C, in air, at a frequency of 1 Hz, using a DMA 242 C device, from Netzsch, Germany. The samples were manufactured using a self-developed technology. The samples were ceramics (Al2O3) and metal (Fe) reinforced particles embedded in small volume fraction along with random E-glass fibres (65%) into a polymeric matrix material. Keywords: composites, multiphase, polymer, dynamic modulus, testing

The replacement of glass fibers polymer composites with those containing polymers and cellulose fibers, friendly for environment and human health has gained a special importance in recent years. The paper presents some mechanical and thermal characteristics of composites of neat polypropylene and jute fibers from technological wastes, treated and untreated. The use of waste fibers in polypropylene led to a significant increase of the elastic modulus and tensile strength which highlights the reinforcing effect of the waste fibers, the effect being more important in case of jute fibers treated with aminosilane. Keywords: polypropylene, composites, jute, mechanical properties