Volume 57, Issue 4

Abstract: The paper aims to evaluate the gel time and exotherm temperature properties of the curing of unsaturated polyester resin at various amounts of Methyl ethyl ketone peroxide, cobalt octoate and porcelain powder. The gel time of samples are determined using the simple method, while the exotherm temperature are evaluated using the thermocouple. The variation of these properties is discussed theoretically and experimentally.

Abstract: The most significant disadvantage of cold cured poly (methyl methacrylate) – PMMA is its poor mechanical properties, mainly in flexure. The aim of this work is to explore the modulus and flexural strength of modified cold cured PMMA modified with low TiO2 addition, which can also have antibacterial properties. Commercial cold cured PMMA resin, consisting of powder and liquid components, were modified by adding 0.05 %, 0.2 %, and 1.5 wt. % 20 nm hydrophobic TiO2. The specimen`s flexural modulus and strength were tested, while heat properties were determined with DSC analysis. SEM and EDX were used to study fracture surfaces of tested specimens. In all modified specimens, an increased flexural modulus and flexural strength were recorded. In all specimens, the appearance of agglomerates was noted. Glass transition temperatures also increased, as the result of the appearance of polymer chains with reduced mobility around nanoparticles. 0.2 % of 20 nm TiO2 nanoparticle content proved to be the most efficient in increasing flexural modulus and strength.

Abstract: With the development of unmanned aerial vehicle (UAV) systems for a multitude of real-time applications, 3D printing technologies have been developed to make thermoplastic structures by fusing filament Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF). However, we consider that the realization of new technologies of experimental models / technological demonstrators / prototypes becomes profitable by using 3D printing technologies. The main aim of the paper is to highlight how the use of three types of materials, which are processed differently, influences the Von Mises stresses of the payload used for a UAV, with the mission of photographing and filming from high altitude.

Abstract: The aim of this paper is to obtain two types of bio-based membranes by electrospinning process: one based on polylactic acid (PLA), and PLA/polyhydroxybutyrate (PHB), and the second by coating the PLA/PHB membrane with chitosan (CS) and CS/activated coal (AC), respectively for removal of micropollutants from aqueous water. The designed bio-based electrospun membranes were analyzed through scanning electron microscopy (SEM), attenuated total reflectance (ATR) – Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), the removal of solid suspension and Pb (II) from aqueous water. The quality of filtrates was evaluated by physical-chemical methods, while the retaining of Pb (II) from wastewaters was reported.

Abstract: In the present work, the effect of the addition of different types of carbon nano structures on the mechanical, thermomechanical and thermal properties of a radial structure of styrene-butadiene-styrene (SBSR) copolymer matrix is reported. Different carbon nanostructures were used as nano-rein-forcements: expanded graphite (XG), graphene oxide (GO), reduced graphene oxide (RGO) and exfo-liated graphene (EG). These carbon structures present various functional groups, such as carbonyl, epoxy, and others, which are the responsible for the interaction between the polymer matrix and the nano particles. The compatibility induced between the nanomaterials and the elastomeric matrix fa-vors the stable dispersion of the nanocomposites during their obtention process. For instance, the ad-dition of GO increased in 10 and 16% the tensile strength and storage modulus of the nanocomposites. The fracture surface patterns in the nanocomposites after the tensile test was observed by scanning electron microscopy. Also, the dynamic mechanical analysis (DMA) and thermal characterization showed differences in the viscoelastic behavior of the reinforced nanocomposites with different carbon nanomaterials.

Abstract: Membrane research has managed to reach ever greater heights. The optimization of membrane processes is of common interest to industry, research and the domestic environment. Nanomaterials have been progressively researched in the membrane sector within the last decade, contributing in particular to their beneficial properties for the prevention of membrane fouling. This research investigates the effect of two shapes of ZnO nanomaterials, respectively nanoparticles and nanowires, on the properties of ultrafiltration membranes composed of 25 wt.% polysulfone. The method of membrane manufacturing is phase inversion, the immersion precipitation technique, and the procedure of nanomaterial incorporation into the polymeric matrix is known as blending. The results demonstrated the positive influence of nanomaterials on the performance of membranes, regardless of their shape, compared to the control membrane. In terms of permeability, the membrane with addition of ZnO nanoparticles showed an increase of 207.19 %, while the membrane with addition of zinc oxide nanowires recorded an increase of 89.16%.

Abstract: The aim of this paper was to present the synthesis, characterization and application of the Fe3O4 - chitosan composite as potential adsorbent for removing lead ions from industrial wastewater. The nanocomposite nanomaterial was characterized by XRD and SEM analyzes. The influence of some parameters (pH of wastewater, lead ions concentration and dose of Fe3O4 - chitosan absorbent) upon the efficiency of wastewater treatment were investigated. The Pb (II) ions concentrations in wastewater were 0.5, 1, 1.5 and 2 mg/L. The amounts of Fe3O4 - chitosan nanocomposite adsorbent tested were 0.05, 0.1 and 0.2 g. In some experimental conditions, Fe3O4 - chitosan nanocomposite adsorbent leaded to obtaining of 100% wastewater treatment efficiency.

Abstract: The article presents results regarding the use of the melt flow index method (MFIM) in estimating the rheological properties of polylactic acid (PLA) and PLA-based materials, as tool in the selection of the operating conditions at their shaping into filaments and for 3D printing with thus obtained filaments. Based on the MFIM, the molecular weight of various PLA grade commonly used in melt processing techniques, including printing, were qualitatively compared. It was found that PLA for printing has the lowest molecular weight as compared with the PLA melt processed through injection, extrusion, thermoforming. It has been also shown that the MFIM can be used to verify the efficiency of drying, pre-treatment always needed to be done, before filaments obtaining and/or printing, especially in case of renewable polyesters. By simulating the printing at the indexer, via depositing successive layers, one over the other, it was possible to estimate the optimal flow conditions that ensure a good adhesion between the deposited layers. The estimation of the condition which ensure the needed adhesion between the deposited layers with the help of the MFIM was verified with good results on a grade of high loaded PLA achieved according to an original formulation.

Abstract: Composites of Silver nanoparticles/chitosan were obtained in aqueous solution, in-one step and eco-friendly synthesis, under ambiental conditions, using gamma irradiation. The radiochemical synthesis enabled obtaining of controlled size, monodisperse and high stability Silver nanoparticles. The obtained composites presented UV-Vis surface plasmon resonance comprised between 406-414 nm, depending on composition of the reactant system, spherical shape and narrow particle size distributions, with mean dimensions between 3-55 nm, and good antibacterial properties proven against Staphylococcus aureus and Escherichia coli. The influence of the Silver ions/chitosan ratio and of the pH of the initial solution on the final Ag Np properties is also discussed.

Abstract: The main purpose of our study was to demonstrate the antioxidant properties of novel propolis nano-formulation, incorporated in spherical chitosan nanoparticles. The electrochemical methods (cyclic voltammetry and differential pulse voltammetry) were successfully applied to propolis extract and nanopropolis formulation, confirming that the content in phenolic acids and flavonoids is responsible for the antioxidant activity of propolis. The quantitative and qualitative results are also supported by high performance liquid chromatography (HPLC) and ultraviolet-visible (UV-Vis) spectroscopy.

Abstract: Pyrotechnic compositions using polyurethane as binder were designed to maximize the temperature of combustion and the burn rate. The flares consisted in mixtures of potassium perchlorate/Mg-Al alloy/polyurethane/additives. In order to determine the optimum input ratio that conducts to the most appropriate solution in terms of theoretical amount of heat released, specific volume of gaseous products and chemical composition, Explo5® thermochemical software runs were executed. Further, the temperature of combustion and the burn rate were determined by infrared thermography, while the heat of combustion and the specific volume of gases were obtained using an adiabatic calorimeter coupled with a Julius-Peters volumeter. The fuel ratio was varied in the compositions in order to optimize the combustion, and the addition of chlorinated rubber confirmed a significant enhancement in both parameters.

Abstract: This paper presents some of the authors’ theoretical and experimental research related to the use of low-power lasers (diode laser) for the engraving, photoengraving and cutting of the parts made of plastics. There shall be presented the research carried out using a small machine, covering a net area of 150x150mm2. Small-sized companies or the persons having such pursuits can afford this type of machines. The authors also put forward several solutions to improve the performance of such machines by introducing at least one new axis of the “Z” or “A” type.

Abstract: Using a drop casting method, stronger absorbent and photosensitive composite thin films based on a copper-phthalocyanine (CuPc) oligomer and a poly (N-epoxypropylcarbazole) (PEPC) copolymer were developed. Morphology, structural behavior and optical properties of CuPc:PEPC composite thin films have been studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-VIS spectroscopy. The SEM images of pure CuPc organic thin films show the formation of some elongated shapes, while the morphology of CuPc:PEPC composite thin films is mainly controlled by the content of CuPc. XRD analysis of the CuPc:PEPC composite thin films reveal good crystallinity and the beta-copper phthalocyanine phase. Study of optical properties of CuPc:PEPC composite thin films after annealing in hydrogen atmosphere show decrease of the average optical transmittance. In addition, the broadening of the absorption bands increases the light harvesting capacity of the composite material for photovoltaic applications.

Abstract: The study presents the synthesis and characterization of two series of hydrophilic chitosan derivatives, based on imine or amine linkage through PEGylation. The impact of PEGylation on the morphology and supramolecular architecture along with the wettability were studied. The obtained results proved that PEGylation is an appropriate method for tuning chitosan’s hydrophilicity. Adding to that, the properties of the derivatives can be designed according to the targeted application.

Abstract: Controlled drug release is a promising pathway of biomedicine, meant to suppress side effects with the aim of increasing patient`s comfort. A route to achieve this goal represents the encapsulation of drugs into matrixes, capable to develop physical forces, which further can control the drugs release. To this purpose, mathematical modeling is an important tool, which offers the possibility to understand the drug release mechanisms and to further design new performant systems. In this paper, a theoretical model for drug release from an amphiphilic matrix is presented. This is achieved using a conservation multifractal law of probability density followed by validation of the model. Moreover, because non-steroidal anti-inflammatory drugs (NSAIDs), such as diclofenac, are widely used in endometriosis as painkillers for dysmenorrhea management or Asherman syndrome for reducing the endometrial inflammation, some implications of our model for drug delivery systems applied in the field of gynecology have been discussed.

Abstract: Type II collagen has been perceived as the indispensable element and plays a crucial role in cartilage tissue engineering. Thus, materials based on type II collagen have drawn farther attention in both academic and research for developing new systems for the cartilage regeneration. The disadvantage of using type II collagen as a biomaterial for tissue repairing is its reduced biomechanical properties. This can be solved by physical, enzymatic or chemical cross-linking processes, which provide biomaterials with the required mechanical properties for medical applications. To enhance type II collagen properties, crosslinked collagen scaffolds with different cross-linking agents were prepared by freeze-drying technique. The present research work studied the synthesis of type II collagen biomaterials with and without crosslinking agents. Scaffolds morphology was observed by MicroCT, showing in all cases an appropriate microstructure for biological applications, and the mechanical studies were performed using compressive tests. DSC showed an increase in denaturation temperature with an increase in cross-linking agent concentration. FTIR suggested that the secondary structure of collagen is not affected after the cross-linking; supplementary, to confirm the characteristic triple-helix conformation of collagen, the CD investigation was performed. The results showed that the physical-chemical properties of type II collagen were improved by cross-linking treatments.

Abstract: Cationic dextran hydrogels having pendent 51-59 mol% N-alkyl-N,N-dimethylammonium chloride groups were synthesized and tested as adsorbents for sodium cholate. The bile acid salt sorption by these gels was evaluated by equilibrium analysis in water and 10 mM NaCl solution. The best adsorption results were obtained with amphiphilic dextran-based gels having two types of pendant ammonium chloride groups with different polarities. Experimental adsorption data for all polymers fitted good with Langmuir, Dubinin-Raduskevich and Temkin models over the entire range of ligand concentrations. The maximum experimental adsorption capacity of dextran sorbents for sodium cholate was in the range 850–1075 mg/g.

Abstract: Paper explores the influence of the infill density (%), as a process parameter in additive manufacturing (3D printing), upon the mechanical (tensile, impact) and thermo-physical properties of PLA samples. The results indicated degradation of both tensile strengths and moduli with decrease of samples’ relative density from 100% to 25% with 49.9% and 42.0%, respectively. Similar behaviour holds on impact strength values that degrades with 56.0% for the samples printed using a 25% infill density. The Young’s modulus variation with relative density values was approximated using a 3rd order polynomial function, in accordance with the expression for closed-cell thick edge rhombus cellular structures. All PLA samples revealed small difference on their coefficients of linear thermal expansion, irrespective of their infill densities, with a decrease of 6.34% in the lowest relative density value specimens, indicating enhanced stability within selected temperature range. Glass transition temperatures were approximately located at 65°C whereas cold-crystallization around 80°C, thus unaffected by selected process parameter.

Abstract: Due to the good properties related to wear resistance and vibration absorption capacity, the polymeric materials successfully replace the metallic materials. These are used in the production of sliding motion couples. Rubbing couples whose materials are polymer / steel based are of particular interest for technical use. In order to operate any mechanical system with sliding motion at optimum parameters, the indication of tribological characteristics for the materials of the frictional coupling is a convenient means of characterizing faster the tribological behavior, when the working conditions are modified. In this paper it is analyzed by the help of an experimental study, the factors affecting the wear of a coupling of polymer material/steel. Materials subjected to tribological analysis are polymeric materials, such as polyamide (PA) and polytetrafluoroethylene (PTFE) in contact with a metallic material (steel). The connection between the friction coefficient and the operating parameters (load, speed) and the rate of wear of these materials under experimental conditions will be established. Testing of the two materials was made on a pine stand on disc. The tribological tests were performed varying load and speed for a given length of friction, traveled pine. The wear of the two materials tested for the experimental conditions was measured. The experimental researches were carried out in dry friction conditions.

Abstract: The experimental study conducted for this article was made using the butt fusion welding procedure for high density polyethylene (HDPE) pipes. PE100 (SDR 17, PN 10) water pipes were used, as for the experimental study parts of around 200 to 300 mm were welded, using different welding parameters. The influence of the welding parameters on the pipes resistance was analyzed, through visual examination and experimental tests such as tensile, bending and pressure tests.

Abstract: Fibre–reinforced concrete cannot replace the ordinary reinforced concrete. However, there are areas of use in which fibre–reinforced concrete can be used alternatively or in addition to the ordinary reinforced concrete, offering several advantages, some of that being presented in this study. The basic idea is that reinforcements create a multi–directional “mesh” within the cementitious matrix that will make concrete stronger. In fact, adding the fibrous material to concrete will increase the strength. In this sense, the micro–fibres primarily work to prevent micro– or shrinkage cracking, which mostly occurs during the initial curing process of the concrete, or those critical first 28 days. By contrast, the macro–fibres provide load–bearing strength after the concrete cracks. But, in fact, the subject is more complex. The types and size of fibres, their distribution and orientation are a hugely complex topic. Fibres, of whatever nature, have been found to improve the properties of concrete. Fibre–reinforced concrete provides an alternative to conventional reinforcement, with the advantage of time and reduced costs of performing maintenance work. The complexity of various fibre use presents challenges for the construction sectors that may be beyond current levels of expertise. In this study, particularities of concrete reinforced with polymer fibres are presented. Also, a comparative study is presented, based on our previous works in area of the concrete reinforcing with recycled polyethylene terephthalate (PET).

Abstract: In this study, carboxymethyl cellulose (CMC) was synthesized from the cellulose of cassava peel using alkalization and etherification reaction, and it was subsequently characterized with various techniques. Microcellulose was obtained by hydrolyzing á-cellulose from cassava peel using H2SO4 with concentrations of 45%, 47%, and 49%. The experimental results indicate that the varying concentrations of acid affect the particle size of the cellulose, with 49% H2SO4 solution producing a cellulose with particle size of around 0.45-2.42 µm and relative percentage of 11.3% according to PSA analysis. Other analyses conducted included determination of substitution degrees, DTG/DTA/TGA, FTIR, SEM, and XRD. The value of the substitution degree was determined at 0.27. TGA decomposition thermograms at a temperature of 150oC-320oC of 19.60 % indicate CMC compounds. DTA thermograms show that these CMC compounds have endothermic properties at 140oC and exothermic properties at 260oC. FTIR spectra show the presence of absorption band at wave number 1605 cm-1, which is a characteristic absorption of carbonyl group bound to cellulose. The results of SEM analysis indicate that the CMC has a tenuous surface morphology, and the XRD diffractograms are marked by the presence of weak peak at 2è = 20o, implying the existence of CMC as mostly amorphous.

Abstract: In the context of the COVID-19 pandemic and the lack of protective equipment worldwide, we aimed to study the literature for finding guidelines in the 3D manufacture of respiratory masks. We have searched for papers in CI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC, using `3D printing materials sterilization` and `3D printing materials disinfection` keywords. From 80 results in databases, after refining, we selected six papers. We have also searched for manufacturers` information regarding 3D printing materials sterilization or disinfection. We have found seven materials that are suitable for 3D printing and sterilization, with regards to multiple utilizations. Analyzing the properties and recommendations for sterilization of elements obtained by 3D printing, a thorough filaments structures/behavior research for most of the 3D models for printing is needed regarding synthetic polymers suitable for 3D printing; also, to establish the physical and chemical properties resulted after the reactions with sterilizing substances. In the context of the COVID-19 pandemic, the authors want to help and find guidelines in the 3D manufacture for producing respiratory masks.

Abstract: The paper presents the application of 3D printing in the forensic field in order to perform facial reconstruction on a 3D printed replica of the victim’s skull. Firstly, imagine data from a computed tomography of a skull was converted into a 3D model. Then, the 3D skull model was sliced and printed in different positions in order to optimize the 3D printing configuration. Since the quality of the 3D printing process depends on the thermal and rheological properties of the 3D printing filaments, the rheological behavior of the ABS was investigated using melt flow rate and capillary rheometry. Lastly, an accurate skull replica was achieved using the optimal printing parameters. The 3D printed skull was used to perform the facial reconstruction of the victim by the forensic team. Based on the results of the present research, the 3D printing technology is a feasible solution to obtain anatomically accurate skull replicas.

Abstract: In the endeavor to explore more and more materials, this work is focused on the study of the potential applicability of a chelating sorbent based on an acrylic copolymer functionalized with amidoethylenamine groups in Cu(II) removal from wastewaters in batch and dynamic conditions. The proposed sorbent was synthesized by the chemical transformation reaction of ethylacrylate (EA): acrylonitrile (AN):2% divinylbenzene (DVB) copolymer with ethylenediamine (EDA). Batch sorption results pointed out that the Cu(II) retention by the acrylic copolymer functionalized with amidoethylen-amine groups was dependent on the initial solution pH, initial metal concentration and contact time. The sorption of Cu (II) on the tested chelating copolymer obeyed both Langmuir and Freundlich isotherms. The Langmuir maximum sorption capacity was 65.21mg Cu (II)/g of polymer. The kinetic experimental data fitted well with the pseudo - second order model. The dynamic behavior of a fixed bed column filled with the acrylic copolymer functionalized with amidoethylenamine groups has been studied in terms of breakthrough curve. The experimental breakthrough data have been well described by Thomas model. The tested chelating copolymer is suitable for multiple processes of Cu(II) sorption-desorption. The column studies with real wastewater sample presented a removal efficiency of 100% for Cu (II) and a significant improvement of the wastewater quality. The acrylic copolymer functionalized with amidoethyleneamine groups can be successfuly applied for the Cu (II) removal - recovery - recycling.

Abstract: The preparation of polyether polyols from waste rigid polyurethane foam has been achieved by chemical degradation of ethylene glycol and diethylene glycol as the degradation agent. Then, the modified rigid polyurethane foam was prepared by polyether polyols and glass fiber. To detect the characteristic of rigid polyurethane foam, the density, water absorption, compressive strength, thermal conductivity, infrared spectrum, morphology structure had been tested. Finally, the best degradation formula was explored, and the modified rigid polyurethane foam had been prepared from the recycled polyol.

Abstract: Posterior endodontically treated teeth are exposed to risk fracture due to the great masticatory forces developed in the area. Fiberglass posts are considered a practical solution for such situations, but their main disadvantage yet remains the poor adhesion to the remaining tooth structures. The purpose of the present study was to evaluate a material that could replace the use of fiberglass posts on posterior teeth. 32 premolars were selected and divided into 4 groups (n=8): the first group was considered the control group; the second group was composed of endodontically treated teeth that were filled with gutta-percha, but without any coronal restoration; the third group was composed of teeth that received the same endodontic treatment as in the second group but were restored with a fibreglass post and a light cured microfilled hybrid composite material; the fourth group was similar to the third one, except teeth were restored with a short-fibre-reinforced composite (EverX Posterior, GC Europe N.V., Leuven, Belgium) and a microfilled hybrid composite over it. The fracture resistance of all the teeth was tested using a universal testing device. One-way ANOVA and the Tukey post-hoc variation tests for multiple comparisons were used to analyze the results. The short-fibre-reinforced composite material increased the fracture resistance of endodontically treated teeth (1159.42 N), twice as much as that obtained by using fiberglass posts (522.35 N)). Within the limitations of the present study, EverX Posterior represents a better alternative compared to fiberglass posts in the crown and root reconstruction of posterior endodontically treated teeth.

Abstract: Despite the advantages of the non-flammable, good performance and low price, poly (vinyl chloride) (PVC) still suffer from poor thermal stability, restricting its melting process and applications. Although addition of some heat stabilizers can be used to improve the low thermal stability, so far, they normally compromise the environmental issues and smoke density of PVC during combustion. In this work, a series of La doping Mg-Al layered double hydroxides (LaLDHs) with different molar ratio of La3+ / Al3+ were successfully synthesized by coprecipitation-hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), Scanning Electron Microscopy (SEM) and Transmission electron microscopy (TEM). The results showed that the as-prepared LaLDHs exhibit plate-like morphology with a lateral size around 100-180 nm. The different as-prepared LaLDHs were introduced into PVC as heat stabilizer to prepare PVC nanocomposites. The thermal stability and smoke suppression of PVC nanocomposites were investigated by TGA, thermal aging, Congo red and smoke density rating test (SDR), respectively. All the results demonstrated that PVC-LaLDHs2 nanocomposites containing 2% LaLDHs2 (the molar ratio of La3+ / Al3+ is 1 / 3) were optimized, which achieved the maximal T50% value of 337.2 oC, minimal SDR value of 45.6%, and prolonged the thermal aging time from less than 10mins to 90mins, respectively thermal stability time from 1242s to 2751s. In addition, the tensile strength and elastic modulus of PVC-LaLDHs2 respectively increased by 84.4% (56.6 MPa) and 75.5% (1019.4 MPa) with little affecting elongation at break of PVC. LDHs (layered double hydroxides); rare earth ions; thermal stability; smoke suppression; poly (vinyl chloride)

Abstract: Hybrid composites of in-situ microfibrillar recycled polyethylene terephthalate (rPET)/glass fiber (GF)/polypropylene (PP) were developed as an economical and environmentally friendly alternative to glass fiber reinforced thermoplastic PP composites. The effect of replacing glass fibers with in-situ formed polymer microfibrils on mechanical and viscoelastic properties of the composites was investigated with tensile, flexural, and dynamic mechanical tests. Characterization results showed that mechanical and viscoelastic performance of 34% glass fiber reinforced PP can be obtained with 24% glass fiber, 10% microfibrillar rPET composites. Compatibilization effect of the maleic anhydride grafted PP (MA-g-PP) was studied using Fourier transform infrared (FTIR) spectroscopy. The scanning electron microscopy (SEM) images confirmed the formation of the rPET microfibrils in the hybrid matrix. Besides, composites with MA-g-PP compatibilizers showed significantly improved fiber-matrix interfacial adhesion on the SEM images.

Abstract: The study performed the biomechanical testing of polymethylmethacrylate (PMMA) specimens with unreinforced progressive antibiotic loading, compared to samples reinforced with Kirschner wires, by subjecting these specimens to mechanical compression forces. A difference was observed in the yield of the reinforced specimens with Kirschner wires, in which an antibiotic concentration that exceeded the usual amount was used. In this antibiotic combination of vancomycin powder and liquid gentamicin, the spacer seemed to have a superior structure compared to using only the antibiotic in liquid form. These results are superior to the usually loaded specimens (not exceeding the threshold of 4 g of antibiotic per 40 g of cement), the maximum force recorded being of 20.98 kN and the minimum of 11.54 kN. The reinforced specimens indicated higher values of force, registering differences that varied between 10 kN and approximately 19 kN, thus considering that through the reinforcement with Kirschner wires, the biomechanical qualities of the cement spacers considerably improved.

Abstract: The study is highlighting the possibility of modeling the properties of composite materials based on recycled polypropylene (PPR), flour feathers(FF), and compatibilizers (C). The composite materials with 10% and 20% feather flour content were mixed and processed with a two-stage extruder having four heating zones between 200-230°C, in order to obtain granules. The granules were injected in various forms to evaluate the properties. The composite materials have been evaluated for determination of melt flow index (1900C; 2.16kg), density, Charpy impact, breaking strength, elongation at break, and the dielectric behavior. The results showed that the introduction of feather flour in the polymer matrix based on PPR leads to decreased flow properties as well as physical and mechanical properties. The solution in solving these deficiencies was to use compatibility agents, that would improve these properties. The physico mechanical properties were analyzed in order to identify a composite with optimal properties for industrial application.

Abstract: The goal of the research is to develop an experimental mathematical model of pan coating process effect on the biodegradable polymer and to determine optimal process parameters. The polymer solution was conducted with phosphated di-starch phosphate, polyvinyl alcohol, and polyacrylic acid and performed as material coating for the controlled-release urea fertilizer. The image analysis method has been used to determine the particle size distribution, Sauter mean diameter of the particle and layer thickness that is novel. The central composite rotatable design has been selected to determine the regression models of the process, which described the relationship between two objective variables as layer thickness, release time with angle of pan, spray flow, and coating time. The statistical analysis results indicate the fitness of model.

Abstract: The Additive Manufacturing (AM) industry has expanded steadily, occupying the market very quickly. New types of 3D printers have appeared and new types of polymeric and composite materials have been developed for these printers. Thus it passed very quickly from the stage in which the parts that were made by rapid prototyping (RP) only to be exposed (demonstration parts) to stage AM the parts are fully functional. Of course, the future of AM is still on the horizon, it is barely visible. The other technologies for forming the geometry of the part, ie subtractive manufacturing technology and formative manufacturing technology are still the basis of industrial production. Each technology has its own advantages and disadvantages and is chosen on a case-by-case basis, depending on the objectives pursued. In this paper, a study is made on the rapid prototyping of a single pump rotor part. The material of the piece is of polymer type, ABS. The piece was made in two variants: by additive manufacturing technology (PolyJet) and by subtractive manufacturing technology (milling). After processing, several parameters were followed, such as the functionality of the part, the surface quality, the mechanical tensile strength, the dimensional accuracy, and last but not least the manufacturing cost and the duration of the manufacturing cycle. The data thus obtained were processed with an artificial intelligence program for decision making.

Abstract: The materials used in additive techniques are initially in a plastic state so that they can be inserted into various cavities or easily molded after which they pass into a rigid phase. This process is performed by various methods, depending on the nature of the material. The study aims at analyzing the chemical and biological behavior of flexible acrylates compared to classical acrylates, whose structure was optimized through the introduction, at a structural level, of certain polymeric and antiseptic structures in view of obtaining a high degree of biocompatibility, the elements of variability consisting in the difference between the two polymerization regimes, the polymerization under pressure and the classical polymerization.The polymerization of acrylic resins by the technique of thermobaro-polymerization with injection compensation leads to the formation of materials with superior impact resistance. The pressure regime is very important, being a factor that influences the polymerization without being initiated. Breaking strength is an essential element in assessing the quality and duration of the prosthesis use.

Abstract: The acrylic resins are the materials most frequently used for dentures realization, which allow to obtain resistant prosthetic constructions with a suitable aesthetic appearance. Depending on the polymerization mechanism, these resins are classified in self-curing, heat-curing or light-curing materials. In order to obtain a properly cured resin with a good mechanical strength, it is necessary to know the properties of the material, the correct dosage of the components and the strict observance of the curing regime. This article aims to evaluate the mechanical parameters of two main categories of resins frequently used in dental practice for removable dentures realization - heat-curing and self-curing resins. For this purpose, the tensile strength and the fracture strength, the Young`s modulus values, the surface roughness were analyzed comparatively. The results demonstrate that, after processing and finishing, both types of resins have similar structures and no significant differences regarding the mechanical behavior are registered.

Abstract: In this paper, the problem of the behaviour of soft jaws that can be used to replace the steel jaws of grippers is studied. One of the advantages of additive manufacturing is the printing of fully functional parts. Choice of material is often related to the part strength. The mechanical properties of 3D printed parts should meet the service loading and, also, must be comparable with parts produced by traditional manufacturing techniques - machined parts or injection moulding. From the specialized literature information regarding the test results for effect of various printing parameters on part strength are available made in laboratory conditions and for standard test sample. For ABS materials various values for Young module are presented varying from 1.5 GPa to 2.15 GPa, for 100% infill rate and various modified parameters such as raster orientation. In order to study the behaviour of soft gripper jaws several part were printing and the resistance to bending was tested, by simulating the way a gripper works. An experimental stand was built using a force transducer and a displacement transducer to measure the deformation of the jaw, obtained by 3D printing, under load. The mechanical elastic hysteresis loop during an experimental loading/unloading was plotted and the amount of mechanical energy lost during a cycle, dissipated because the internal friction, was determined. Finite element analysis method was applied to make a comparison with the experimental results. In the finite element analysis, several simulations were considered, varying Young`s modulus for the tested material.