Browse Articles

Two series of new self-coloured segmented polyurethane elastomers were successfully synthesized via the reaction of poly (tetramethylene ether) glycol (Terathane 1400) and hexamethylene diisocyanate / 4,5-dibromofluorescein with glycerine or castor oil as hard segments in a N,N-dimethylformamide solution. Polyurethane structure formation has been proven by infrared (IR) spectroscopy. Photosensitive-dibromofluorescein polyurethane elastomers exhibited high thermal stability and the addition of 4,5-dibromo-fluorescein in the preparation of the fluorescent polyurethane elastomers enhanced the tensile strength. This may be attributed to an increased cross-linking due to strong intermolecular interaction between the fluorescein polyurethane molecules. The fluorescence performance for the fluorescent polyurethane elastomers films appears at 560-580 nm, and increased concentration of 4,5-dibromofluorescein enhances the fluorescence performance of these polyurethane elastomers. Keywords: polyurethanes, fluorescence, chain extender, mechanical properties, thermal behavior

The paper presents the experimental results regarding the investigation of some physico-chemical and structural characteristics of starch modified by electron beam and microwave combined treatment. The combined electron beam (EB) and microwave (MW) treatment of granular starch was performed in four different regimes, successive and simultaneous. The experimental data showed that the acidity of starch aqueous solutions increased while the apparent viscosity reduced as a function of the treatment parameters and regime. No significant changes appeared in the morphological characteristics of the samples treated with combined EB-MW, but the spectral characteristics suffered minor changes suggesting that the stability of hydrogen inter- and intramolecular bonds is affected. At the same time, the degree of order increased after successive combined treatments indicating some molecular associations or rearrangements in amorphous component of starch due to the microwave field. The evolution of the molecular weights and molecular weight distribution indicated that the macromolecular degradation cannot be correlated with the specific absorbed energy as a consequence of the microwave field contribution. Keywords: starch, electron beam, microwave, viscosity, SEM, GPC

The thermal properties of a novel family of xerogels prepared from diepoxy-terminated poly(ethylene glycol)s of approximate molecular weights 600, 1000, 2000 and 4000 Da and various aliphatic polyamines (ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, 1,8-octanediamine, 1,10-decanediamine, 1,12-dodecanediamine, diethylenetriamine, triethylenetetramine, tris(2-aminoethyl)amine) were studied by DSC and TGA measurements in order to establish the influence of several structural parameters that may affect the physical state of the network-forming polymer at a certain temperature. All xerogels synthesized displayed crystallinity which was affected by the MW of the PEG precursors, number of carbon atoms within the diamine chain, amine functionality and structure and amine/epoxy groups mole ratio. Both melting temperature and amount of crystalline phase were lower for networks with either shorter PEG chains, longer diamine chain, higher amine functionality and stoichiometric amine/epoxy groups ratio, while the thermal stability was higher for either longer PEGs, diamines with higher carbon atom numbers, higher amine functionality and stoichiometric amine/epoxy groups ratio. Keywords: networks; poly(ethylene glycol); aliphatic polyamines; melting temperature; glass transition temperature; thermal stability

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