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The radiation stability of low density polyethylene in the presence of several additives as antioxidants (two derivatives from rosin, two commercial stabilizers, Irganox 1076 and Irganox 1081 and elementary selenium) was carried out by oxygen uptake method. The values of oxidation induction times of stabilised PEjd were discussed. A stabilisation mechanism concerning derivatives of rosin was reported. The antioxidant efficiency of studied compounds was compared to propose a reliable alternative to commercial antioxidants for the radiation sterilisation of PEjd. Keywords: LDPE, oxygen uptake, gamma irradiation.

This study focuses on possible applications of polystyrene in the medical field. Nonwoven fiber mats were produced through electrospinning, using limonene or, as control, the conventionally used ethyl acetate. Subsequently, different types of dilutions were tested. Electrospinning (ES) was performed with different parameters to study the effect upon the fibrous materials resulted, in view of obtaining structures with high porosity and a specific desired morphology. Thin fibers were obtained using both solvents, with fibers average diameter of 1.98-2.58 mm for limonene and 8.87-13.81 mm for ethyl acetate. The obtained various materials are a result of the different solvent densities, surface tensions and polymer concentrations. Best quality fibers, when using limonene, were obtained for 35 % polystyrene, while when using ethyl acetate the high quality fibers were obtained for 60 % polystyrene in solution. The mats morphology and structure were compared and analyzed through optical microscopy, scanning electron microscopy and Fourier Transform Infrared Spectroscopy. This study proposes the fabrication of nonwoven fibrous mats from polystyrene using a natural, economical, biocompatible and environmentally friendly solvent that can successfully replace the common and toxic solvents in medical applications involving wound dressing or tissue reconstruction. Keywords: electrospinning, limonene, polystyrene, ethyl acetate, wound dressings

Radiation-induced polymerization can produce a wide variety of water-soluble polyelectrolytes which are used to increase the performance of the waste water treatment. The main goal of this study was to investigate the influence of the radiation dose (D), initiator concentration [I], sodium chloride concentration, total monomer concentration [TMC] and monomer ratio (R) on the physical and chemical properties of the acrylamide – acrylic acid based polyelectrolites, obtained by copolymerization in accelerated electron beam fields. In accordance with the established purposes, the polyelectrolyte must have high conversion coefficient (CC > 95%), low residual monomer content (Mr < 0.01), high intrinsic viscosity (hintr > 7 dL/g), low linearity coefficient (kH < 0.4) and a very good solubility in water. The experiments were performed using a linear accelerator facility (ALIN-10, built in NILPRP Accelerators Laboratory, Bucharest) of 6.23 MeV at irradiation doses between 0.9 kGy and 1.8 kGy at room temperature and ambient pressure. The best results were obtained at 1.5 kGy. Keywords: acrylamide, acrylic acid, ionizing radiation, polyelectrolytes

Generally the fillers are used in order to diminish the amount of matrix for a certain composite structure but in the last period fillers are used to change also the basic properties of the material used as matrix, especially in the case of PMC (polymer matrix composites). The actual study is carried out in order to determine the influence of starch over the properties of epoxy resin and is based on the well known fact that starch is creating its own network inside of a matrix. In this case it is possible to talk about a nano-reinforcement of the matrix which might be used to form fiber reinforced materials with better mechanical or thermal properties. Due to its properties starch might be used also to ensure the dispersion of other fillers which generally tend to aggregate as CNT or ferrite and in this case it is necessary to know the upper limit of starch concentration for which the polymer properties are not changed or suffer negligible modifications. Not at least the presence of starch into the epoxy matrix might determine a higher alterability of the polymer making it easier to neutralize. Being easy to functionalize starch might be used as vector to transport positive and/or negative ions inside the polymer matrix via complex combinations which might lead to controllable electro-magnetic properties of the formed material or to multi-functional materials. The thermal, mechanical, tribological and electrical properties of starch/epoxy composites were studied using appropriate methods for materials with various starch concentrations. Key words: starch, epoxy, physical properties, mechanical properties

In this paper, we determined a state of stress, which verifies the Cauchy equations of equilibrium, the conditions of continuity on the surfaces between layers and boundary conditions for a sandwich beam subjected to tensile test. We customized the relations, previously obtained, for a composite beam consisting of two layers. Using a mediation formula for strain and stress, we obtained a new formula for the calculus of the longitudinal modulus of elasticity, when the constituent materials have different Poisson ratios. Considering the maximum stress reached in the layers, we determined a formula, which helps us to determine the order in which the two layers will break. We did experimental measurements for test samples made from polyesteric resin, reinforced with fiber glass fabric, carbon and carbon-kevlar. Keywords: composite materials, characteristic curve, elasticity modulus

This paper presents the influence of the position of an applied static load on a honeycomb sandwich with core made of resin impregnated honeycomb and caps made of epoxy resin. The nonlinear analyses were concentrated underneath the area of applied force and on the side of one wall of the honeycomb. The results obtained can be used to determine the effect of a small area impact on a honeycomb sandwich or to establish the stress distribution pattern during compression tests on the walls of a cellular structure. Keywords: honeycomb, sandwich, nonlinear, resin impregnated paper, epoxy resin

In this study interpenetrating polymer networks (IPNs) based on bisphenol A diglycidyl dimethacrylate (BisGMA) and diglycidyl ether of bisphenol A (DGEBA) with or without native fumed silica nanoparticles were prepared by in situ polymerization. The properties of the IPNs and hybrid IPNs were evaluated using different thermal techniques as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetrical analysis (TGA). The mechanical properties were also determined. Keywords: dimethacrylate, epoxy resin, interpenetrating polymer network, fumed silica

Manufactured in various geometric forms, containing secondary materials (colorants, reinforcements, fireproof etc.), all these make the composites based on resin-textile fibre, basic materials for obtaining lateral walls, ceilings, floors, compartments for luggage and sanitary installations. The materials were made as stratified plates using polyesteric resin POLIKON P210 FA and natural fibres: cotton, flax and hemp. This paper presents the determination of mass and volume content of the resin in these composites.

A laurylsulfate-selective electrode is presented. The sensing material of the electrode consists of an ion pair 1:1 water insoluble salt that has been prepared using sodium laurylsulfate and hexadecyl trimethylammonium bromide and was immobilized in a PVC membrane plasticized with orto-nitrophenyl octyl ether. This electrode gives a linear response for sodium laurylsulfate between 8x10-7 - 5x10-3 M with a slope of 57,7 mV per decade of sodium laurylsulfate concentration. The electrode has been applied to potentiometric titration of anionic surfactant using cationic surfactant as titration agents.

This paper presents a study of the electrical conductivity of wood-polymer composites, determined by measurements done in DC and AC current. It is also noticed that the values of sdc, s’ and s” are strongly influenced by the nature of matrix and filler content of the composite. Finally, it is shown that samples of PE and PP matrices can be used for applications in power frequency electric fields (0 ... 100 Hz) and at temperatures between 30 and 90 °C. Keywords: compozite lemn-polimer, conductivitate electrica