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Two types of cellulose fibers were obtained from microcrystalline cellulose (MCC) by acid hydrolysis and ultrasound treatment using different concentrations of sulphuric acid. The effect of acid concentration on cellulose fibers characteristics was studied by scanning electronic microscopy (SEM), dynamic light scattering (DLS), and X-ray diffraction analysis (XRD), pointing out interesting features from the standpoint of different end-use properties. An important increase of MCC crystallinity, from 51.4% to 74.3%, was observed by XRD analysis after the treatment with 60% sulphuric acid. The cellulose fibers were used as reinforcements in a polyvinyl alcohol (PVA) matrix and the crystallinity, transparency and mechanical properties of the resulted composites being investigated. The incorporation of the two types of cellulose fibers into PVA led to transparent composites films with improved mechanical properties. A steady improvement of the tensile modulus of PVA composites was observed with the increasing amount of fibers, an increase of 83.3 % being obtained with cellulose fibers resulted from MCC treatment with higher acid concentration (60%). Key words: PVA composites, cellulose nanofibers, acid hydrolysis of cellulose, mechanical properties

This paper studies the influence of positioning angles of neoprene vibration isolation elements from the first elastic stage, upon the natural frequencies of the vibrator-roller type CVA-10. A simplified computing dynamic model with four degrees of freedom has been used in order to determine the influence of positioning angle on the natural frequency by means of experimental results. Keywords: neoprene elements, positioning angle, vibrator-roller, natural frequencies

Dimethacrylate-based resins cured using a photoinitiator system are widely used as matrices in dental restorative composites. In this work, the thermal degradation of copolymers based on urethane dimethacrylate (UDMA) and bis-phenol A glycidyl dimethacrylate (BisGMA) were investigated by thermogravimetric analysis. Different weight ratios (100/0, 70/30, 50/50, 30/70 and 0/100) between the UDMA and BisGMA comonomers were employed. The camphorquinone – ethyl-4-dimethylaminobenzoate photoinitiator system was used. The degradation of copolymers occurs in three steps, contrarily to two steps for UDMA homopolymer and a single step for BisGMA homopolymer. Activation energies of the degradation processes were calculated using differential and integral isoconversional methods. The influence of copolymers composition on the activation energy as a function of the degradation conversion degree was studied. Keywords: thermal degradation, dimethacrylate copolymers, UDMA/BisGMA

Aiming to develop a self-contained presentation regarding the thermorheodynamical behaviour of solid-like polymer materials, the Zener - Arrhenius model is used, the frequency or/and temperature dependences being considered in the case of stress-controlled conditions. Accordingly, the full set of the explicit general analytical relations for the primary characteristic thermorheodynamical quantities - the storage, loss and absolute compliances, as well as the loss factor - and the corresponding secondary ones - the storage, loss and absolute moduli - is obtained by using the appropriate rheological parameters including the low and high frequency limit values of the storage compliance, as well as the retardation time. These underlying analytical relations are provided in forms directly suitable for numerical simulation of frequency dependence in isothermal frequency - dependence, and as well for the temperature - dependence in isochronal circumstances. Keywords: analytical relations, characteristic thermorheodynamical quantities, stress-controlled conditions, Zener - Arrhenius model, isothermal and isochronal circumstances

Bacterial cellulose offers an interesting potential as natural biodegradable alternative to glass and carbon fibers that are currently used in structural composite. In the present paper, bacterial cellulose produced by Gluconacetobacter Xylinus ATCC 23768 was used as reinforcement fiber to develop four new type composites. The composites were prepared using bacterial cellulose sheets and epoxy resin infused at 10, 15, 250 MPa. These materials were composed of 8 layers of BC pressed at 10 MPa, 8 layers of BC pressed at 15 MPa, 8 layers of BC pressed at 250 MPa and 28 layers of BC pressed at 10 MPa. The first three obtained materials were subject to uniaxial tensile tests, while the fourth material was subject to three-point flexural tests. By using this unique natural material and the resin infusion method it was possible to obtain a composite with the highest reported strength for bacterial cellulose based composites until now. The tensile strength revealed is of about 465 MPa and Young’s modulus of about 60 GPa. Keywords: bacterial cellulose, Acetobacter xylinum,Gluconacetobacter Xylinus Epoxy composite

The paper presents the main aspects of dynamic modelling of steel/plastic geared systems with high gear ratios in relation to the nonlinear parameters, such as time-varying mesh stiffness and load sharing alternation. Firstly, the specific aspects of geometrical design criteria for helical gear with small number of pinion teeth are presented in order to prevent the negative phenomena of the involute tooth generation and gear engagement. Then, the dynamic analysis is conducted to investigate the shared dynamic loads and dynamic transmission error of steel/plastic gear pairs along the line of action. The effects of the time-varying mesh stiffness are incorporated in the nonlinear dynamic model for numerical analysis. An improved model of the mesh stiffness is developed by including specific meshing characteristics of helical gear pairs. The variation of the dynamic transmission error is simulated and examined in relation to the teeth number, addendum modification coefficients and input torques. A computational algorithm is developed for instantaneous dynamic contact analysis. Keywords: plastic gears, high gear ratio, mesh stiffness, dynamic transmission error

The use of fine fiber has become an important design tool for filter media. Nanofibers-based filter media have some advantages such as lower energy consumption, longer filter life, high filtration capacity, easier maintenance, lower weight compared to other filter media. The nanofibers based filter media made up of fibers with diameters ranging from 100 to 1000 nm were conveniently produced by electrospinning technique. Typically filter media are produced with a layer of fine fibers that can be used lonely or as a component in a media structure. The fine fiber increases the efficiency of filtration by trapping small particles which increases the overall particulate filtration efficiency of the structure. Improved fine fiber structures have been developed in this study in which a controlled amount of fine fiber is placed on both sides of the media to result in an improvement in filter efficiency and a substantial improvement in lifetime. In this research, regenerated silk fibroin obtained from industrial silk wastes and polyacrylonitrile (PAN) fibers was used to produce filter. Characteristics such as fibers diameter and its distribution, porosity and thickness of nanofiber filters obtained in lab were examined by Scanning Electron Microscopy (SEM) and analysed using image processing algorithms. Keywords: electrospinning, nanofilter, image processing, Fourier Transform, porosity

When great damages occur on gas-pipes, a quick intervention is often needed, as close to the place of damage as it can be. That is the reason why recently it has more and more been used a procedure of squeezing the pipe using a squeeze-off tool and thus stopping the flow. After the damage has been removed, the deformed pipe returns to the original shape by using re-rounding clam and the flow is established yet again. After the above-described process, the pipe is permanently deformed, as far as shape and thickness are concerned. The size of the deformation is important for the assessment of further use of the existing pipes or for determining the parameters for the newly-projected pipes. So far, the researches have been dealing with the hydrostatic and stress states after the squeezing of the pipe. The subject of this research is the decrease of the pipe thickness after the squeezing, and the goal is to help the designers of distributive plastic gas-pipes to determine the pipe wall thickness, as well as to help the managers of distributive networks so that they would know what happens to the existing gas-pipes after the intervention on the pipe. Keywords: sqeeze – off tool, polyethilene gas pipe

In the present study EP142-C510-50 woven carbon fiber composite was investigated from structural/mechanical point of view aiming manufacturing parts for aeronautical industry. The composites were obtained by hand lay-up process. Prior to mechanical tests, the cure reaction results of composite resins specimens were analyzed by using DSC technique. The EP142 epoxy matrix was cured/polymerized at 160°C. After molding, the laminates were cut into specimens for 3 points flexure, tensile and fatigue tests. The mechanical tested samples observed by scanning electron microscopy revealed their fractured and microstructure aspects. A nondestructive US method allowing elastic constant determination on a composite plate was proposed during this study. Keywords: carbon/epoxy composite material, mechanical properties, structural characterization, aeronautical industry

The options to deposit chemically a functional composite copper-diamond coatings from trilonic electrolyte have been studied with respect to the influence of the air flow stiring conditions of deposition. They have been elucidated in regard to the structure of the copper metal-matrix and the number of the co-deposited diamond particles. Optimal composition has been established as well as the best hydrodynamic regime for chemical deposition of the functional composite copper-diamond coatings (with respect to the number of the co-deposited diamond particles observed by SEM and the thickness of the composite layer) upon the addition of an appropriate surfactant compound Na-laurylsulfonate (NaLS) to the electrolyte, which is preventing the agglomeration and precipitation of the diamond particles in the electrolyte. Keywords: functional composites; coating; metal-matrix composites (MMCs); non-metallic substrate