Volume 57, Issue 1

Abstract: Polymer films with high refractive index are suitable for a wide range of applications, such as optical fibers, lens and other components for optoelectronic devices. In this work, polyvinyl alcohol films were prepared from aqueous solutions, which were homogenized by ultrasonication. In order to increase the refractive index, the polymer was reinforced with barium titanate nanoparticles, which are previously ultrasonicated for an adequate dispersion inside the host polymer. The dispersion of the refractive index in visible domain was analyzed as a function of filler percent introduced in polymer, showing that an increase in sample`s polarizability determined an increase in the refractive index values. The reinforcement caused a decrease of Abbe number indicating a higher light dispersion in the samples. Optical dispersion parameters were extracted from dispersion curves, revealing a reduction of band gap from 3.448 eV for pure polymer to 2.605 eV for the sample containing 2% barium titanate. Doping with the ceramic nanofiller determined a increase in optical conductivity and real part of dielectric constant as a result of appearance of new level states in the band gap. The increase of third order nonlinear optical susceptibility and nonlinear refractive index indicates the suitability of the analyzed nanocomposites for nonlinear optics applications.

Abstract: Composite resin materials for posterior restorations are becoming more and more popular. According to the market, Ormocer materials are more expensive than composite resin this paper is comparing the resistance to fracture between nanohybrid composites and Ormocers under vertical forces to evaluate their cost efficiency in the dental cabinets. 20 teeth were prepared and filled with Ormocer and 20 with nanohybrid composite respectively. All the samples were sent for measuring under vertical pressure with the use of a universal testing machine. The average value of fracture for Ormocer was slightly higher (1541 N) than the average value of fracture of the nanohybrid composite (1431 N). Considering the similarity in the average values of the two materials we should look into the other properties (biocompatibility, shrinkage, aesthetics, etc) to take a final decision. Both materials can be used with the same rate of success taking in account always the protocol provided by the manufacturer.

Abstract: The form of the outer and inner surfaces of hollow spherical parts determines the developments of some particular categories of efforts during the compression tests. The overall purpose of the research presented in this paper was to study the behaviour of the hollow spherical parts under axial compression. The PLA hollow spherical parts were obtained by 3D printing and using distinct values for certain process input factors. The finite element method was used to theoretically investigate the behaviour of the parts and it highlighted the total plastic deformation of the test pieces. To experimentally verify the theoretical considerations, an L9 Taguchi orthogonal design was performed. The empirical mathematical model thus determined highlighted the stronger influence exerted by the printing plate temperature, printing speed, and part wall thickness.

Abstract: The needs of environmental protection led to the introduction of composites based on the use of plastics reinforced with biodegradable materials or other easily accessible materials. The overall purpose of the research was to experimentally investigate the possibilities of using some accessible reinforcement materials. Textile based on plants fibers and glass fibers were used as reinforcement materials, while the matrix was a polymer type material. An empirical mathematical model was proposed to highlight the effect of the number of glass fiber reinforcements on the tensile strength. The determined mathematical empirical model and graphical representations highlight how the number of glass fiber reinforcements affects the modulus of elasticity of the composite materials.

Abstract: It is actual now to work out new radiation protecting sheeting on the basis of non-curing polymeric composition which possess self-adhesion properties, are easily mounted and dismantled and provide high tightness and low permeability. Mechanical properties of non-curing composites consisting of ethylene propylene diene monomer (EPDM), industrial oil (IO), alkyl phenol-formaldehyde resin (PF) with addition of barite (52 %) to the total material volume were investigated in this article. The aim of investigation is to find optimal content of the above mentioned components at which it would be possible to get the following properties: composite would be sticky enough (peel strength not less than 4 N/cm); character of a separation would be cohesive (on a material) and thus there would be no migration of softener and satisfactory resistance of fluidity. The results showed that PF addition till 20 % in the system EPDM/PF leads to the increasing of adhesive strength, in this case optimal oil concentration in the system EPDM/PF/IO is in the interval from 45 till 55 %. New self-adhesion lead-free material, exhibited higher X-ray-shielding properties, is also received in the result of investigation.

Abstract: The paper presents the mechanical behaviour and properties of a new hybrid vegetal based resin. For this, through static loading tests, the main mechanical characteristics were determined: static Young modulus, breaking strength, breaking elongation and transversal Poisson ratio. Samples of the proposed materials were subjected also to free vibration tests, by clamping them at one end and leaving them free at the other. The observation and results from these were used for deduction of the first vibration mode eigenfrequency, the dynamic Young modulus, the loss and damping factors. Some representative SEM images with an electronic microscope were collected and the samples surface roughness was determined. By using the Thermogravimetric analysis (TGA), the mass loss up to 800° C was investigated. Compared to the other resins that have dammar in composition, the proposed dammar based resin from this research has a 15.32 times higher static Young modulus than the oil palm trunk and 8.885 times higher than the oil palm trunk (OPT) with 20% dammar resin.

Abstract: The first part of the paper presents the specific issues from the injection molding associated with the water content of the hygroscopic plastics (water adsorption, equilibrium moisture level, chemical affinity, hydrolysis) and recommendations regarding the drying of plastics for injection, the drying methods and defects specific to products injected due to the moisture content. The experimental results on the injection of a polyamide (AKULON) and of a thermoplastic polyurethane (DESMOPAN) presented in the second part of the paper are focused on the surface appearance fault `splay` associated with the different values of moisture content for these two materials, verify the value for the admitted moisture content for two hygroscopic materials, polyamide and thermoplastic polyurethane, and ends with conclusions on the residual humidity allowed and opinions on choosing the drying technology and parameters.

Abstract: In this paper, experimental investigation, modeling and optimization of the drilling of PMMA are performed using the Taguchi Design of Experiments (DOE), analysis of variance (ANOVA) and artificial neural networks (ANN) methods. Drilling experiments were conducted on PMMA to assess the impact of process parameters (drill diameter, spindle speed, and feed rate) on the hole-quality characteristics (surface roughness, circularity error, and cylindricity error). ANOVA was performed to identify the drilling parameters that have a statistically significant influence on the hole-quality characteristics. A predictive model for the hole-quality characteristics was derived using a four-layer ANN with a backpropagation algorithm and a sigmoidal transfer function at the hidden layers. The ANN model was able to accurately predict the hole-quality parameters with the absolute mean relative errors of the testing data in the limits of 3 to 7%. Based on the experimental results and analytical modeling, it was found that drilling of PMMA requires lower spindle speed and high feed rate when the integrity of the drill hole is the main quality criterion.

Abstract: This article is devoted to the problem of working out of damping polymer materials which are effective in the wide temperature and frequency range. In the modern world, work is being carried out to create damping polymer composite materials (DPM) from which it is possible to manufacture protective elements and parts of engineering structures of reduced vibration excitability. Existing DPM have a narrow temperature range, within which effective vibration absorption is observed, moreover, most of them go through a vulcanization stage, which increases the cost of the final product, has a harmful effect on environment and allows limited recycling of waste. One of the ways to solve this problem is to replace traditional rubber vibration-absorbing materials with thermo-elastoplasts (TEP). The most promising polymer for TEP is ethylene vinyl acetate (EVA), which has high damping properties, oil resistance and relative incombustibility. In this regard, experimental studies were conducted to establish the patterns of influence of the type and concentration of structure-forming components (plasticizers, fillers, modifiers) on the dynamic mechanical properties of TEP based on EVA in order to develop a new DPM effective in a wide temperature range. The leading method to investigate this problem is a method of dynamic mechanical analysis which allows to get information about changes of mechanical characteristics under mechanical load and controlled temperature and frequency. With the help of detected patterns it was possible to determine type of plasticizer which significantly decreases glass temperature of EVA. The percentage ratio of EVA/plasticizer system is stated, and the type of plasticizer at which the maximum of mechanical losses takes over greater values is accordingly detected. It is revealed, that to work out DPM on EVA basis, which are effective in wide temperature range it is more preferable to add not less than 40 % on volume basis inert fillers, such as talc or mica with addition of 5-10 % of carbon as the hardening additive. The kind of resin improving damping properties and raising rigidity of composites on EVA basis is defined. On the basis of the research, a material was developed which has the following properties: the maximum value of tan δ is at least 0.45 at a temperature of plus 5°C (oscillation frequency 10 Hz); width of the temperature interval within which tan δ is not less than 0.3 from minus 40 to plus 50°С (oscillation frequency 10 Hz); conditional tensile strength of not less than 10 kg/cm2, cold resistance up to minus 50°C.

Abstract: Carbon fibre reinforced (CFR) laminates were manufactured by prepreg lay-up and deposition of interlaminar carbon nanotubes (CNTs). An easy and innovative manufacturing procedure was used. CNTs were separated in solvent by ultrasonication, and poured on the woven fabric prepreg. Solvent evacuation was performed at low temperature, and dry functionalized prepregs were used for composite lamination. Laminates were cured by compression moulding on a heating plate. Peeling tests, differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA) were carried out on multiply samples with and without 1 wt% of interlaminar CNTs. Results show that the glass transition temperature of the resin matrix reduces because of the interaction with CNTs. Nevertheless, peeling strength shows 10% increase at room temperature.

Abstract: Carbon fibre reinforced composites were manufactured by using recycled carbon fibres (CF) and carbon nanotubes (CNT). Dry fabrics were impregnated by hot melting with 1 wt% CNT filled epoxy resin to produce prepregs. Subsequently, composite laminates were manufactured by vacuum bagging and autoclave moulding. Only materials and industrial equipment were used for the laminate production. Laminates with unfilled resin and virgin CFs were also manufactured for comparison. Samples were extracted for physical and mechanical measurements. Dynamic mechanical analyses and bending tests were carried out to evaluate the interaction between CNTs, resin matrix and recycled CFs.

Abstract: In recent years, the rapid development of electronic equipment led to millions of tons of waste printed circuit boards (WPCB) generated in the entire world rising important concerns regarding its recycling. Besides the metals recovery, intensively studied, the reuse of the nonmetals is especially difficult. In this study, the non-metallic fraction from the waste of printed circuit boards is used as reinforcing filler of a styrene-butadiene block-copolymer. The composites were characterized by mechanical and dynamo-mechanical analysis and thermo-gravimetry. The study aimed the reintroduction into the economic circuit of WPCB as composites suitable for the production of shoe soles injected directly on the footwear faces and as bitumen modifiers for road coverings.

Abstract: Molecularly imprinted polymer (MIP) beads for proto-hypericin recognition were prepared by suspension polymerization. In order to study the impact of monomers on the MIPs properties, various monomers such as acrylic acid (AA), hydroxyethyl methacrylate (HEMA), methacrylic acid (MAA) and itaconic acid (IA) in their combinations were crosslinked with ethylene glycol dimethacrylate (EDMA) in the presence of a complex phyto-extract template derived from Hypericum perforatum L. The synthesized MIPs and corresponding non-imprinted polymers NIPs were characterized by infrared spectroscopy analysis, morphology and thermogravimetric analysis. High-performance liquid chromatography combined with UV–Visible spectroscopy, used to investigate the recognition properties of the MIPs for various naphthodianthrones, pointed out that the MIP IA-AA system seemed to be the most adequate for favoring quantitative rebinding of proto-hypericin and proto-pseudohypericin against competitors with similar structures, like hypericin and pseudo-hypericin, which are usually present in high quantities in the primary Hypericum perforatum L. phyto-extracts.

Abstract: This paper presents experimental research results obtained from testing the compression of polymer matrix composites. The four types are analyzed by thin layers of polymer composite material of various thicknesses were subjected to the test of mechanical compression. The analyzed samples were obtained by reinforcing the siloxane rubber with FeSi powder and stretching the mixture on the metallic mesh (PM), as well as stretching the simple siloxane rubber, without reinforcing agent on the metallic mesh. The mathematical modeling of the experimental results obtained on the LFM 30kN compression tester, Walter & Sai AG was performed using the Excel program. Establishment of material was based on regression analysis performed later. The modulus of elasticity of the samples was determined according to the deformation range 0.1 ÷ 0.3%, corresponding to the maximum correlation coefficient resulting from the regression of the experimental data. Following the compression analyzes it was found that in the case of simple siloxane rubber (S) without filling, the average modulus of elasticity decreases from 80 MPa to 39 MPa for the siloxane rubber laying on the metallic mesh. For the composite material (siloxane rubber with FeSi powder addition) noted SF, the value of the module is 81, and in the case of the laying composite (siloxane rubber reinforced with silicon iron powder filler on the metallic mesh, noted PMSF), the value of the module decreases to 31 MPa. We conclude that the addition of silicon iron powder leads to an increase in the elasticity of the siloxane rubber, and its reinforcement with the metallic mesh leads to a decrease in the elasticity modulus of the siloxane rubber, as well as of the siloxane rubber reinforced with the iron powder.

Abstract: Through gravimetric determinations, volume resistivity, dielectric spectroscopy, and comparative thermal analysis (TG, DTA and DTG), the interactions between the distilled water and three different types of alkyd-epoxy-melamine, epoxy and polyurethane lacquers were studied. From the experimental determinations it was found that after 700 h of immersion in water at 20 ± 2°C the alkyd-epoxy-melamine based lacquer has a maximum water uptake, respectively 1.76%, followed by the epoxy lacquer 1.4% and polyurethane 0.93%. The thermal analysis sugests that because the water retained by the investigated polymers does not change the TG diagrams in the temperature range up to 150 °C, which suggests that the weight increase of the samples during the immersion could be due to some chemical processes between the water and polymer by which the chemistry structure of the polymer changes. Through electrical measurementes one can observe that after the immersion in water (over 700 hours), dielectric loss increases and the volume resistivity (measured in DC) of the investigated lakes decreases, which is explained by the increasing of polar groups (–OH) in the polymer structure. A comparative analysis of the experimental data reveals that in electrical applications the lacquer LS (polyurethane) is superior to the lacquers L-528 (alkyd-epoxy-melamine) and LG (epoxy), because it has no mass losses (structural changes) up to 280°C it has a volume resistivity of about 21 % higher than L-G, and about 300 % higher than L-528, and has water uptake and dielectric loss substantially lower comparing to L-528 and L-G.

Abstract: This paper studies the influence of the volume proportion between components on the mechanical behaviour of a hybrid resin obtained by combining the natural resin Dammar and epoxy resin. We analyse three sets of hybrid resin samples, in which we used a Dammar volume proportion of 60%, 70%, and 80% respectively and epoxy resin (employed together with its associated reinforcement in order to generate a quick process of polymerization). Following the tensile test we found the characteristic curves, the tensile strength and the elongation at break for each of the three types of resins. We also looked into the vibration damping properties of bars made of this resin. We experimentally determined the frequency and the damping coefficient of the first particular vibration mode for one bar taken out of each set of resins, with one end fixed and the other free. On the basis of the results, we calculated the loss coefficient for each type of resin.

Abstract: UV curing is a photochemical process in which high-intensity ultraviolet light is used to instantly cure or ‘’dry’’ coatings, inks, adhesives and thin film technology. It has been around as a coating for wood, paper and as a clear coating via photolithography process on printed circuit boards PCBs or integrated circuit boards ICBs for years. It is fast becoming one of the most popular techniques in the paint and coatings industry. Most of the formulation use multifunctional acrylate monomers or oligomers or a mixture of them that crosslink under exposure to UV/EB radiations in a free radical process. We briefly present the advantages of EB vs. UV. A new type of formulation based on multifuctional monomer of dicyclopentadiene epoxy derivative with additional diluent as co-reactive solvent will be described and evaluated. This formulation differs from the acrylate one by the use of a cationic photoinitiator. The final product presents all the advantages of epoxy resins viz. better adherence, mechanical and thermal properties, compared to acrylate systems. Formulation has been optimized thanks to the differential scanning photocalorimetry DPC. This type of formulation is developed for additive digital manufacturing - 3D Printing (building layer by layer).

Abstract: This paper presents the influence of component concentration for a class of polymeric blends with different concentration of PP (polypropylene) and PA6 (polyamide 6) and a constant concentration of additives: CaCO3, LDPE (low density polyethylene) and a compatibilizer POLYBOND® 3200. Mechanical properties has been investigated for four different test speeds, from 10 mm/min to 1000 mm/min. Young’s modulus performs in a band between 1500...1900 MPa, except for the value for PA6 at the lowest testing speed (v=10 mm/min), that is 1444 MPa. At high concentration of PA6, there were noticed voids in the longitudinal direction of the samples, forming large parallel ‘empty channels’, as the two polymers are immiscible. Except for values at low testing speed, the average values for tensile stress at break perform in a band of less than 8 MPa. The elongation at break is less than 10% for all materials, except for PA6 at the lowest testing speed, when a higher value was obtained. The lowest values were obtained for the blend with 20% PA6. For blends with 60% and 80% PA6, the difference between values, at the same testing speed, is the smallest. Energy at break has a slightly increase with the concentration of PA6. From the mechanical point of view, among the formulated blends, material D (with 80% PA6) is the most promising as has the highest values for stress and energy at break (11.8 J at v=10 mm/min and 9.6 J at v=1000 mm/min), but values are still less than those for PA6.

Abstract: We analyze polymer dynamics in a fractal paradigm. Then, it is shown that polymer dynamics in the form of Schrödinger – type regimes imply synchronization processes of the polymers’ structural units, through joint invariant function of two simultaneous isomorphic groups of SL(2R) – type, as solutions of Stoka equations. In this context, period doubling, damped oscillations, self – modulation and chaotic regimes emerge as natural behaviors in the polymer dynamics. The present model can also be applied to a large class of materials, such as biomaterials, biocomposites and other advanced materials.

Abstract: The research carried out within this paper addresses the issue of impact analysis with a spherical ball of an automobile fender, following two directions: the finite element method modeling of named part and situation, and experimental validation of the study mentioned beforehand. The part itself – car fender – is represented by a thermoset composite panel armed with Kevlar-Carbon fibers, while the analyzed situation is depicted as a Charpy/Izod test with a spherical ball on the specified component. The evaluation of named inquiry is performed in a virtual environment by means of FEA and verified accordingly within laboratory testing.

Abstract: Dental sealants are important components of preventive dentistry. The aim of this clinical trial was to compare the effectiveness of an unfilled resin-based sealant and a carbomer-based dental sealant. 42 child patients with completely erupted inferior first molars and with diagnosed bruxism were included in the study. At 2 weeks, respectively 6, 12 and 18 months were evaluated the effectiveness of sealants after marginal deterioration, retention and the presence of caries. The results of the trial showed that unfilled resin-based sealant presented fewer modifications.

Abstract: The work focuses some experimental aspects concerning the weight gain, differential scanning calorimetric (DSC), dilatometer analysis (DIL) and thermo - gravimetric analysis (TG/DTA) for a composite material, based on cotton tissue and unsaturated polyester resin noted MCTDBN and immersed in salt water with 5% NaCl for 90 days. Following these analyzes are emphasized the thermal expansion, temperature glass transition and thermal decomposition. Before of thermal analysis, the treated specimens were dried in an oven at temperature of 30°C for several days. The paper presents also the effect of salt solution treatment and comparative analysis between untreated and treated composites.

Abstract: The aim of our study was to evaluate the deformation resistance of two palatal plate type connectors of removable partial dentures and to make a comparison between the reduced palatal plates and the large ones, in terms of bending resistance during function. We tested 10 maxillary class I Kennedy removable partial dentures made for real clinical cases and duplicated their connectors, 5 of each type. A Universal Loading Machine was used to apply a bilateral progressive force to the PM2-M1 area until the samples bended, recording the force value at which the first change occurred. The results were analyzed using the ANOVA method. For the reduced palatal plate group, the minimum bending force value was 1584 N, the maximum bending force value being 2920 N. For the large palatal plate group, the minimum bending force value was 3150 N, the maximum value being 3380 N. Statistical analysis of data using the ANOVA method shows that the results are statistically relevant, with a p value of 0,001031 (p[0,05). The results showed that decreasing the width of the palatal plate can have a significant effect on the deformation resistance of the major connector and can affect its rigidity; in clinical practice, these results can help dentists to use alternative appropriate design methods of increasing the rigidity of reduced palatal plates, in order to protect both the remaining structures and the acrylic components of the dentures during the years of its functioning.

Abstract: Aortic valvulopathies, and especially aortic stenosis (AS), are the most common valvular disorders. Untreated, 50% of patients with severe AS will die within 2-3 years from the onset of symptomatology. The standard treatment consists in the surgical replacement of the aortic valve with mechanical or biological prosthesis. 40 patients were included in the study after replacement of the aortic valve with double disc mechanical prosthesis for severe degenerative AS. The disks of the prosthesis are made of pyrolytic carbon characterized by extreme hardness, which provides wear protection over the years. The ring is composed of a graphite substrate coated with pyrolytic carbon and attached to a suture collar made of polyethylene (polytetrafluoroethylene - PTFE) or polyester (Dacron® or Teflon®). This study evaluates mass regression and left ventricular mass index at three months and one year postoperatively. The regression of the left ventricular mass at 3 months after the surgery is 25.86%, and at one year after the surgery this regression was reduced - 15.11%. The regression of the mass of the left ventricle and especially the premature regression, correlated with the degree of hypertrophy of the left ventricle preoperatively, highlight the beneficial effect of the double disc mechanical prosthesis.

Abstract: The current paper presents the advantages and disadvantages of the polypropylene mesh used for patients who underwent abdominoplasty associated with the treatment of abdominal wall defects. The study was based on data obtained from 64 patients who benefited from abdominoplasty associated with the surgical treatment of abdominal parietal defects, such as: hernias, eventrations and diastasis. The results of the research show that the use of the polypropylene mesh is associated with an increased resistance of the rectus abdominis sheath plication, the reduction of the postoperative complications rate and the improvement of the patients’ satisfaction regarding the aesthetic result of the surgical intervention.

Abstract: Objective of this study was to develop and validate HPLC-UV method for detection of LTG in lipid nanoformulations. HPLC-UV method was developed according to ICH Q2(R1) guidelines. Central composite design was used effectively to optimize and study the effect of buffer strength, flow rate, pH of buffer and mobile phase composition on responses such as tailing factor, peak area, retention time and number of theoretical plates. The 30 mM ammonium formate buffer and acetonitrile (in the ratio 65:35 %v/v) was used as mobile phase in the study. The mobile phase was delivered at the flow rate of 1.0 mL/min. The detection of buffer was performed at 256 nm using UV detector. The drug entrapment of prepared formulation was also determined using developed HPLC method. Retention time of lamotrigine was found to be 3.844 min. The coefficient of determination (r2) value from linearity was found to be 0.9982. Percent relative standard deviation value of precision was found to be within the acceptable range. The estimated LOD and LOQ were found to be 9.07 ng/mL and 27.48 ng/mL, respectively. Drug entrapment of prepared lipid nanoformulation was found to be 73.44 ± 6.65%. The results conclude that the developed analytical method is simple, precise, sensitive, fast and reproducible. Applications of developed method for determination of drug entrapment in prepared lipid nanoformulation confirmed that the developed analytical method is suitable for estimation of lamotrigine in lipid nanoformulations.

Abstract: The main purpose of this study is to evaluate three different adhesiveprotocols between two composites. We used 60 composite specimens (Kerr’s Herculite XRV Ultra), randomly divided into 3 equal experimental groups, in which adhesion was performed using different protocols: Group 1 (n= 20) surface preparation with a 1.4 mm cylindrical diamond bur (Kerr Dental, FG503C-5) + etch and rinse technique in 2 steps; Group 2 (n= 20) surface preparation with a 1.4 mm cylindrical diamond bur (Kerr Dental, FG503C-5) + Al2O3 (Zhermack Dental) sandblasting + etch and rinse technique in 2 steps; Group 3 (n= 20) surface preparation with a 1.4 mm cylindrical diamond bur (Kerr Dental, FG503C-5) + glycine (EMS) sandblasting + etch and rinse technique in 2 steps. Adhesion assessment was made by measuring tensile strength with a universal testing machine, the INSTRON 3343 (Instron®, USA). At the end, the results were statistically compared using the ANOVA test. Group 3 (glycine protocol) had the greatest values in terms of tensile strength.

Abstract: The wastes from polyethylene terephthalate (PET) packaging can be turned into armatures for concrete used in the transports infrastructure (roads with rigid concrete structure, pedestrian and concrete pavements and borders), as well as in the construction of safety elements (support walls, bulwark foundations). This experimental research was meant to create dispersed reinforced concrete with armatures from polyethylene waste, originated from the recycling programmes of PET–type packaging. The experimental programme was aimed at constructing some samples of dispersed reinforced concrete from recycled material coming from polyethylene terephthalate (PET) packaging wastes, their testing to the compressive strength and the comparison of results with the characteristics of the standardised samples of concrete (class C30/37). All the reinforcements used in this work to consolidate the dispersed reinforced concrete type were made from a mix of polyethylene terephthalate (PET) packages, of different types and characteristics, which are found daily in supermarkets and which then reach waste. The choice of a mix of polyethylene terephthalate (PET) packaging was chosen in order to render the general recycling of these types of materials as good as possible.

Abstract: This paper is the second part of a study regarding the biomechanical behaviour of mandibular bone in the context of different periodontal splinting systems, occlusal forces and load distributions. Electric resistive tensometry method was used to measure the strains developed in mandibular bone replica. The tests were carried out on six mandibular acrylic models, each with 8 natural teeth. The experimental groups were defined corresponding to the bone condition and splint type: normal height bone; bone resorption without splint; bone resorption and wire-composite splint; bone resorption and polyethylene fiber-reinforced composite splint. Each sample was subjected to three similar loading cycles, the force being applied successively on four incisors, two central incisors and canines, and the specific deformation values were read for four loading forces: 30 N, 50 N, 100 N and 150 N. In case of bone loss, the bone deformations are up to 110%. Periodontal splinting redistribute forces, reducing incisors bone strains associated with a slight increase in canine bone strains.

Abstract: Woven fiber reinforced concrete is a material, which contains various quantities of polymer materials in composition, in addition to the conventional components of an ordinary concrete (mineral binder – cement, aggregates, water and additives). The present work refers to the concrete in which the reinforcement is made of polymeric materials (polyethylene terephthalate), originated from the recycling programs of PET–type packaging. The experimental program was aimed at constructing some samples of woven fiber reinforced concrete from recycled material coming from PET packaging wastes, their testing to the compression demands and the comparison of results with the characteristics of the standardized samples of concrete (class C30/37). Based on a sufficient number of determinations, certain correlations can be established between the compressive strength of the concrete at 28 days depending on the dosage of components (aggregate, binder, and reinforcement), water / cement ratio, reinforcement volume, etc., essential parameters from a compositional point of view. These correlations, customized by cement type and strength class, are very important to determine – with approximation – to what dosage of components (aggregate, binder, reinforcement) the respective level of compressive strength of concrete is obtained.

Abstract: Simulating the biomechanical behavior of a reconstruction using the finite element analysis method is a modern method necessary before the practical stage of a research, thus enabling the precise shaping of certain trajectories in the approach of certain directions of practical applicability, as well as obtaining final results with relevant data (results coupled with experimental models that reiterate the clinical situation that will be later analyzed).

Abstract: The present paper is focused on evaluating the mechanical characterization of dicyclopentadiene (DCPD) and 5-ethylidene-2-norbornene (ENB) healing systems synthetized by in-situ polymerisation. Both healing systems were embedded in glass fibre reinforced polymer (GFRP) composite and subjected to three-point bending test regime. Microstructural and FT-IR analysis showed the formation of microcapsules and a successful integration in the composite material. To observe the influence of temperature variation, some specimens were exposed to thermal cycling (-20oC to +100oC) for 12 hours and tested in the same conditions. It was observed that the addition of microcapsules in the composite material decreased its mechanical properties by 8% and 10% for DCPD system and ENB system respectively. Thermal cycling suggested a drop of 24% on bending strength for DCPD system and 17% for ENB. Resting after 24 hours showed a healing recovery of 74% for DCPD healing system and of 97% for ENB system.

Abstract: The main objective of this study was to investigate thermoplastic materials design and fabrication processes for manufacturing composite impeller blades. Polyurethane (Necuron) and ABS (3D printed) thermoplastics were chosen due to their good mechanical properties, tooling applications, easy manufacturing and lifetime. For both thermoplastics, workability and hardness tests were performed, as well as microstructural and mechanical characterization evaluating their physical and mechanical properties. A 1:2.5 scale mould was designed and milled from Necuron N651 and N1001 and used for manufacturing of 1:2.5 scale composite impeller blades. Also, 1:1 scale ABS mould components were 3D printed and used to manufacture full scale composite impeller blades. All composite impeller presented good surface quality and tolerances with respect to CAD design, thus answering to requirements related to composite processing

Abstract: The aim of our study was to compare the fracture resistance of teeth presenting non-carious cervical lesions restored with different types of esthetic composite materials. 20 extracted unspoiled maxillary first molars were mechanically cleaned and immersed in saline solution containing 0.1% thymol at 4°C for a period of 48 hours. Cervical cavities with a cervical-occlusal diameter of 2 mm and a mesial-distal diameter of 3mm were filled with ormocer, flow nano-composite, nano-composite and compomer. Fracture resistance was tested with a universal loading machine (Lloyd Instruments), with a maximum force of 5 kN and a crosshead speed of 1.0 mm/min; the authors used NEXYGEN Data Analysis Software and ANOVA method. For the group A (commercial grade ormocer), the smallest load that determined the sample failure was 650 N and the highest load was 1050 N, the mean value being 858 N ± 150.89 N. For the group B (commercial grade flow nano-composite), the smallest load is 530 N, the highest load is 800 N, mean value being 654 N ± 112.6 N. For the group C (commercial grade nano-composite), the smallest load is 680 N, the highest load is 1200 N, mean value being 926 N ± 209.35 N. For the group D (commercial grade compomer), the smallest load is 1100 N, highest load is 1250N, mean value being 1180 N ± 62.04 N. A p value of 0.000311 (p[0.05) shows that there are significant differences between the four groups. Conclusions. The best fracture resistance of teeth presenting non-carious cervical lesions, restored with different types of esthetic composite materials is assured by the compomer, followed by the nano-composite, which proved to be superior to ormocer. The flow nano-composite gives the lowest fracture resistance.

Abstract: The global concern in wastewater recycling technologies has grown steadily since the early 1990s and is gaining more and more interest due to the increase in water supply needs. This growing need affects many global regions and leads to an increase in the strictness of environmental regulation, both in developing and developed countries. Many countries, cities and local governments are trying to recycle wastewater as a potential source of water for various uses, especially non-potable uses, such as land use, water for toilets and industrial processes. Analysts and statisticians around the world are trying to provide a perspective on an industry that is poised to see significant developments in the next decade. The researches summarize the experimental tests carried out using a new cellulosic adsorbent material to purify the wastewater resulted from the industrial processes for leather manufacturing. The study highlights the influence of the pH used for the wastewater depollution. The tracked and measured parameters include the pH, chemical oxygen demand, biochemical oxygen demand, total suspended solids, ammoniac nitrogen, organic compounds extractable in organic solvents and the solid residue adsorbed by the material. The obtained values were discussed in concordance with the national legislation for wastewater treatment and the levels accepted for releasing the used water in the surface waters.

Abstract: This study aims to find the most effective method in terms of clinical working time when applying fibreglass splints in the lower frontal group, depending on the type of composite material used. We have selected a group of 30 patients, aged between 50 and 70, with an average age of 57, in the interval March 2016 – June2017. These patients received immobilisations as part of their periodontal treatment, using a system consisting of fibreglass and three different types of composites. The shortest work time was obtained when using the Grandioso heavy flow composite, the next closest time being obtained with Gaenial flow universal. Our study indicated that the highly viscous flow composite resins offers the shortest clinical working time out of all tested materials.

Abstract: Painful periapical manifestations are inflammatory responses of periapical connective tissue to pulpal irritants, when the exudative forces become hyperactive. From the point of view of tooth preservation, apical resection is a valuable procedure in avoiding early edentation, as it is a factual surgical method that comes to aid the conservative endodontic therapy. Polymers are chemical compounds (in most cases organic) with large molecules (macromolecules) obtained from the union of a molecular chain (catena) of a large number of monomers usually with identical structural units. In our research we evaluated the resistance to traction 9 test specimens for which the structure was aimed at the improvement of the self-polymerizable acrylic structure by adding sodium maleate co-polymers, namely maleic anhydride, whose structure was linked to the anti-microbial substances, of the thymol type with controlled release, versions with greater resistance, they found clinical applicability on 244 cases. An increased resistance to fracture was registered for the test specimens II, which unites polymer powder together with the sodium maleate co-polymer, in a ratio of 3 to 1 (F = 1030 and max = 37.73), test specimen III, which unites polymer powder together with the co- anhydride maleic polymer, in a ratio of 3 to 1 (F = 950 and max = 37.88), followed by the same combinations to which it was added the care antibacterial substance, thymol. An important role in the long term in the success of the apical resection, in addition to the applied surgical technique, accrues to the retrograde obturation material, which insures an optimal healing at the peri-apical level insuring the bony apposition at this level.

Abstract: The exhaustive use of light advanced polymer composites into the development of the future high-efficiency long-range commercial aircrafts (primary) structures for increasing strength while decreasing weight for lower fuel consumption and less pollution has attracted great attention in the last decade. In this context, solutions for the integration and joining composites into the aircraft structures metallic sub-assemblies or components, while providing the necessary strength to sustain heavily loaded joints, are urgently required. The paper comes to meet an area of interest for many researchers and large integrators and manufacturers, by presenting several type of metallic join geometrical designs, along with metallic joint part integration solutions into a composite structure directly during production. Performances evaluation of the developed metallic join geometrical designs was performed in static regime by means of „pull-out” compressive tests. The paper focuses on the strength of the hybrid metallic/advanced polymer composites joints. It was concluded that an efficient design of the metallic joint and a proper transition from hybrid to the composite structure can lead to proper integration solutions while assuring safety requirements.