جستجوی مقالات مرتبط با کلیدواژه « mechanical properties » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Although the recycling of polymer products is beneficial for the environment and economy, the main goal is to achieve the efficiency of raw (intact) polymers in recycled polymers. The best type of recycling to have maximum energy efficiency and minimum environmental consequences is mechanical recycling. However, there are a number of differences between virgin and recycled polymers. Due to the structural changes and the presence of impurities in the polymer, it is difficult to achieve a quality recycling. Whether the recycled polymer is suitable for obtaining new applications or not is measured by mechanical tests (such as tensile test, impact test), physical tests (such as hydraulic stability, surface roughness) and operational tests (extrusion and molding) under standard conditions. When these tests are performed, most recycled polymers do not meet the requirements required for various applications, unless we use additives that improve their properties. These additives may include coupling agents, impact improvers, metal deactivators, melt flow regulators, antioxidants, masterbatches, etc., and each is used in some way to improve specific properties of the polymers. Although the recycling of polymer products is beneficial for the environment and economy, the main goal is to achieve the efficiency of raw (intact) polymers in recycled polymers.

The composite solid propellant based on the three main components AP/Al/HTPB containing 19 wt.% of Aluminum has special physical, mechanical and combustion properties due to the high solid load. Increasing the solid load is done in order to improve the performance properties of solid propellant, such as specific impulse and volume combustion heat, which are requirements of space missions. On the other hand, increasing the solid load (reducing the binder system) leads to limitations in the production process, such as increasing the viscosity, reducing the pot life, and reducing the processability of the propellant slurry, and also reducing the quality of other propellant properties such as mechanical properties. In this study, the effect of ammonium perchlorate (AP) as one of the key parameters on the physical, mechanical and combustion properties of composite solid propellant has been studied experimentally. The results showed that by reducing the average size of AP particles, the density does not change significantly, the tensile strength and modulus increase and the elongation decreases, and the burning rate of the propellants increases slightly. The average density of propellants is 1792 kg/m3, For the propellant sample with the NCO/OH ratio = 0.88 and the mass average AP particle size equal to 251 μm, the ultimate tensile strength is 0.523 MPa, the maximum elongation is 35.1%, the modulus is 1.5 Mpa, and the burning rate at 65 bar is equal to 6.9 mm/sec.

Advances in the synthesis and industrial production of carbon nanomaterials, particularly carbon nanotubes (CNTs) have been widely used in the polymer materials industry in the past few decades, leading to the creation of a group of carbon nanotube-reinforced polymer composites that exhibit the potential to be used in several applications, such as military, transportation, aerospace, automotive, and sports equipment. The advantageous thermal, electrical, and mechanical properties of CNTs, in conjunction with their low density, which encourages researchers to use them in making polymer composites. Polymeric composites have been welcomed by many researchers and industrialists due to their special properties including low weight, favorable mechanical properties and diverse production processes compared to other types of composites and other engineering materials. On the other hand, CNTs are unique as mechanical reinforcement components for structural applications due to their nanometer dimensions and extraordinary strength. Therefore, in this review study, an attempt has been made to examine the researches carried out in the field of mechanical properties of polymer composites reinforced with CNT. The implications of several factors affecting mechanical properties of CNT reinforced polymer composites such as amount, shape, and contact area of the reinforcing agents with the polymer matrix, have been highlighted.

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 The technology of preparing materials with desired dielectric constants is used in designing and manufacturing telecommunication equipment. Foaming of the polymers is an effective method to reduce their dielectric constant further, as the influence of the microstructural characteristics of the expanded polystyrene foams is important for their dielectric characteristics and mechanical properties. This article focuses on the effect of cell wall thickness of the expanded polystyrene foams on their dielectric constant, loss factor, hardness and resilience.

Many samples of the expanded polystyrene foam with different porosity and overall thickness values were prepared using a specific thermal procedure in a programmable oven. At first, the physical properties such as density and porosity of the expanded polystyrene foams were measured. Next, their microstructural characteristics such as the average cell wall thickness of the expanded polystyrene foams were investigated using a scanning electron microscope. The dielectric constant and loss factor of the samples were assessed with a vector network analyzer with a lens horn antenna. The mechanical properties of the expanded polystyrene foams were evaluated according to Shore D hardness, and the value of mechanical energy stored in them was measured by a resilience tester.

By increasing cell wall thickness in samples at equal overall thickness, the dielectric characteristics such as dielectric constant and dielectric loss factor increase by 12% and 53%, respectively. Moreover, the mechanical properties such as hardness and resilience reveal an increase of 40 and 42%, respectively, due to the increase of cell wall thickness in samples at the same overall thickness. While the dielectric constant and the dielectric loss factor decrease with the reduction of the overall thickness at the same cell wall thickness, the variation of the overall thickness depicts no effect on the hardness and resilience.

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Fused filament fabrication (FFF) method is widely used in additive manufacturing due to its benefits, such as ease of use, cost-effectiveness, and availability. The mechanical properties of polylactic acid (PLA) printed by the FFF method can be significantly improved by combining them with nanomaterials such as nanoclay and optimizing the printing process parameters such as printing temperature and raster angle.

In order to investigate and optimize the multi-objective 3D printing process of PLA nanocomposite samples reinforced by nanoclay, the response surface method (RSM) was used as one of the methods of design of experiments. Nozzle temperature (190, 210 and 230°C), raster angle (0, 45 and 90°) and nanoclay weight percentage (0, 2 and 4% by wt) were studied to optimize output responses. Melt mixing of PLA with nanoclay particles was done using a twin-screw extruder machine and a granulator machine. The composite granules of PLA were prepared with 2 and 4% (by wt) of nanoclay. The prepared composite granules were entered into a single-screw extruder and composite filaments were produced.

The analysis of parameter participation in the density data reveals that the weight percentage of nanoclay and the nozzle temperature exhibit the most substantial influence, while raster angle has the least impact. Conversely, when considering tensile strength results, the weight percentage of nanoclay is the dominant factor, while the interaction between the weight percentage of nanoclay and raster angle has the smallest influence among the parameters under investigation. The multi-objective optimization results revealed that the optimal process conditions to achieve maximum strength are a nanoclay weight percentage of 4% (by wt), a nozzle temperature of 230°C, and a raster angle of about 25.5°. The tensile strength of the parts produced is 33.78 MPa, and their density is at least 1.089 g/cm3.

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 The curing process for phenolic resin composites is always carried out under press or autoclave pressure, as water by-products are released during curing process. As a result, when phenolic composite parts are formed using the vacuum bag-only method, the costs of the mold and challenges of the pressure vessels would be eliminated, and a significant step is taken in easier manufacture of these parts.

For the purpose of comparing the two methods, phenolic laminates were prepared using 3 bar pressure autoclave and vacuum bag-only methods. In order to investigate the effects of thickness on different properties, the samples were subjected to bending tests, short beam strength tests, void percentage tests, and fractured surface morphology tests.

As the sample’s thickness increases, the flexural modulus increases while the flexural strength and short beam strength decrease. Furthermore, the modulus, bending strength, and strength of the short beam in the autoclave sample have increased by 27%, 17%, and 17%, respectively, compared to the vacuum bag-only sample. Morphological studies also showed that more void content was formed in the vacuum bag samples and the resin-fiber interaction was reduced compared to the autoclaved samples. A decrease in the bonding between resin and fibers and in the penetration of resin between fiber strands has also been observed with increasing thickness. Samples with a thickness of 1 mm had a void content of 3.5 ± 1% and in samples with a thickness of 9 mm, it was 15% ± 1%.

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In elastomeric composites, interfacial phenomena such as the effect of reinforcing filler on molecular dynamics of the rubber chain in the interphase and the way of rubber-filler interaction are the source of strain energy change or viscoelastic loss of the composite in highly filled rubber compound. To obtain a preliminary approximation of how the strain energy is influenced by interfacial phenomena, including stiffness, loss and the quality of this region, in this research, the finite element microstructural model was created in two-dimensional and three-dimensional mode and the effective characteristic changes in mechanical properties were studied. The effect of the change in stiffness of the interphase and the change in viscoelastic nature, the amount of contact between the rubber-filler in completely bonded and frictional sliding states were modeled.

The solution styrene butadiene rubber composites reinforced with silica were prepared by melt mixing. For this purpose, rubber was mixed with silica and silane coupling agent in an internal mixer. Then the masterbatch was mixed with the curing system on a two-roll mill and finally the sample was cured under pressure at 160°C.

In agreement with the modeling results, the composite tensile test showed that the most important controlling parameter is the type of rubber-filler connection in the interphase. The simulation results showed that considering the interphase region with frictional sliding greatly reduces the stress transfer from the matrix to the particle. But in the case of the completely bonded interphase region, due to the complete transfer of stress from the particle to the matrix, the mechanical properties showed a significant deviation compared to the experimental results. Also, the 3D models provided better predictions than the 2D ones.

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Chemical cross-linked shape memory polyurethanes (CSMPUs) can have various applications in different fields such as medicine, where mechanical behavior and shape memory are improved in these samples compared to linear shape memory polyurethanes. Shape memory polyurethanes consist of at least two different phases. The first phase, which is in the form of a net point, is responsible for maintaining the permanent shape of the shape memory polyurethane. In contrast, the second phase, also known as shape memory switches, temporarily fixes the temporary shape of the polyurethane by crystallinity. The aim of this research is the synthesis of linear and star polycaprolactones (PCLs) in the first step and the synthesis of CSMPUs using linear and star PCLs in the second step, as well as the investigation and comparison of hydrogen-bonding indices through -C=O groups and -NH CSMPU samples that were synthesized using glycerol as the initiator of the soft segment or the chain extender of the hard segment.

Linear and star polycaprolactones (PCLs) were synthesized using ring-opening polymerization (ROP) of caprolactone, and shape memory polyurethanes with chemical cross-linking (CSMPU) were synthesized using a two-step pre-polymerization method. By changing the molar ratios of the functional groups, the weight percentage of the hard segment in polyurethane samples was kept constant at 10%.

The hydrogen-bond index is decreased with the introduction of glycerol as a chain extender. Also, the degree of crystallinity in CSMPU samples is decreased compared to those of pure PCLs. With the increase of chemical cross-linking the crystallinity of CSMPU samples is decreased. In addition, in the studies of mechanical behavior no significant difference was observed in the presence of glycerol in the soft segment or the hard segment.

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Nowadays, polymer nanofibers have been extensively used in different industries especially for medical applications. Electrospinning is a simple, versatile and cost-effective technique to prepare nanofibers. For biomedical applications such as tissue engineering poly(lactic acid) (PLA), a biocompatible and biodegradable polymer, has gained great interest. To improve the physical and mechanical properties of electrospun PLA, nanofibers and nanoparticles can be included.

PLA nanofibers were prepared through electrospinning. Silver nitrate was added to increase the conductivity of electrospinning solution, resulting in finer nanofibers. To improve morphology and mechanical properties of the electrospun fibers, silicone rubber nanoparticles (NSR) were added into the electrospinning solution. Scanning and transmission electron microscopies (SEM and TEM) were employed to investigate the morphology of electrospun nanofibers and dispersion of nanoparticles, respectively. To investigate thermal and mechanical properties of the obtained nanofibers, differential scanning calorimetry (DSC) and tensile test were used.

To obtain poly(lactic acid) electrospun nanofibers with fine and defect-free morphology, PLA was dissolved in a mixture of dichloromethane and dimethylformamide (DCM/DMF) solvents with a volumetric ratio of 3/2 Electrospinning solution with 7% poly(lactic acid) containing 0.5% (by wt) silver nitrate led to defect-free nanofibers with a diameter of less than 200 nm. Inclusion of silicone rubber nanoparticles of 1% resulted in finer nanofibers with a diameter of about 123 nm. This was attributed to enhanced elasticity of the solution with addition of elastomeric nanoparticles. Adding silicone rubber nanoparticles increased the cold crystallization temperature and decreased the crystallinity of polylactic acid. Toughness of nanofibers considerably increased in the presence of silicone rubber nanoparticles without sacrificing modulus and strength, indicating high capability of NSR as an impact modifier

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Among the types of bioplastics, poly(lactic acid) (PLA) has the ability to compete with petroleum-based polymers due to its favorable properties such as high tensile strength and high modulus of elasticity. Brittleness is the main disadvantage of PLA which limits its practical applications in some industrial fields like packaging and textile. Blending of PLA with other flexible bioplastics like polycaprolactone (PCL) and adding nanoparticles like graphene into PLA are among the techniques that can be used to balance the stiffness and toughness of PLA.

Nanocomposites based on PLA/PCL/graphene (G) were prepared by melt mixing using an internal mixer with direct feeding method. In all samples the weight ratio of PCL dispersed phase to PLA matrix phase was 30:70, and three different weight percentages of nanographene (0.5, 1 and 2) were used. A rheometric mechanical spectrometer (RMS), X-ray diffractometer (XRD), and a scanning electron microscopy (SEM), as well as tensile and differential scanning calorimetry (DSC) measurements were used to study the microstructure, morphology, mechanical and thermal properties, respectively.

The results of XRD showed that graphene nanoparticles are well dispersed in the polymer matrix. The SEM results demonstrated that incorporation of graphene nanoparticles into the PLA/PCL sample led to a decrease in the PCL droplet size. The melt linear viscoelastic measurements showed that incorporation of 2% (by wt) of nanographene into PLA/PCL sample enhanced the storage modulus and complex viscosity by about 200 and 400% due to well-dispersion of nanoparticles in the matrix that led to the formation of a 3D network between nanographene and/or nanographene-polymer chains. The tensile test results showed that the elastic modulus tensile strength, and elongation-at-break increased by 126.63%, 80.48%, and 97.36% respectively, by adding 2% graphene nanoparticles to the PLA/PCL sample. The results of the thermal tests also showed that the addition of nanographene and PCL to the PLA polymer causes the nucleation effect and the creation of active nucleation centers, and the crystallinity percentage of the PLA phase increases, but the effect of PCL in this research was more evident than that of nanographene.

In the last few decades, various polymer industries have witnessed the increasing use of nanoparticles for various applications. Rubber industry is one of these industries and nanodiamond is one of these nanoparticles. Nanodiamond has received special attention in various industries due to its outstanding properties such as excellent mechanical properties and high thermal conductivity. For example, the use of nanodiamond in rubber compounds alone or in combination with other fillers has recently received a lot of attention. By combining these nanoparticles with rubber matrix, different types of rubbers with more capabilities have been produced. These capabilities include better physical, mechanical and thermal properties as well as easier curing procedures. The mentioned properties are mostly due to the active surface of the nanodiamond as well as its excellent thermal conductivity. In general, nanodiamonds are used in the rubber industry for different purposes. In this article, while introducing these reasons and purposes, the use cases of this nanoparticle in various types of rubber such as natural rubber, styrene-butadiene, nitrile, etc. have been discussed.  The latest research in this field has been reviewed and the final results have been presented in summary.

The application of edible coatings is one of the most effective ways to maintain the quality of fruits. In this study, the quality of sweet lemon fruit was evaluated in a completely randomized factorial design with edible coating of chitosan-clay nanocomposite in three levels, olive oil and carnauba wax in comparison with uncoated samples during refrigeration for 4 months. During the storage period of sweet lemon fruits, chemical characteristics (acidity, brix and ascorbic acid) as well as mechanical properties (maximum skin tensile force, fruit skin punch modulus) were measured. The results showed carnauba wax and chitosan-clay nanocomposite had better performance in maintaining lemon quality and mechanical properties than samples without coating. Moreover, among the coatings used, 5%chitosan-clay nanocomposite coating had higher preference than other coatings. In this research, Artificial Neural Networks (ANN) , linear and nonlinear regression method were used to predict the quality of lemon The results showed that the ANN has a better forecasting accuracy to predict the lemon properties compared to linear and nonlinear regression models and the LM learning algorithm with tansig transfer function had the best result. The best fit for the qualitative parameter was acidity with the coefficient of determination (R|) of 95%. The result of sensivity analysis indicated that the highest sensitivity coefficient was obtained for the punch modulus against the time feature with 47.96%.

Industrial equipment's lifetime and efficiency depend mainly on its structures and performances in the harsh conditions of aggressive environments. Therefore, the protection of the equipment's surface is significant. In recent decades, multi-component hard coatings have been highly regarded in scientific and industrial communities. Different types of transition metal-based multi-component coatings, such as coatings based on chromium, titanium, and refractory metals, have been widely used as protective coatings. However, other components of these coatings (such as carbon, nitrogen, and silicon), surface morphology, and grain size will play essential roles in their properties and applications. For example, two-component transition-metal nitride coatings can not be used in abrasion conditions, while transition-metal carbide coatings are a significant candidate. However, three-component transition-metal Carbonitride coatings can provide better mechanical properties and tribological performances than Two-component coatings. On the other hand, some properties of transition metal-based coatings, such as oxidation resistance, residual stress, and frictional performance, can be significantly improved by doping silicon (Si).