فهرست مطالب rezgar hasanzadeh

Polymeric foams are of great importance due to their special features such as lightweight, heat, and sound insulation properties. Also, production of polymeric foams saves the consumption of materials due to the use of less raw materials. As a result, it reduces the pollution in the environment. Researchers have shown that by increasing the cell density and decreasing the cell size, better properties of polymeric foams can be achieved. It is accessible by increasing the pressure drop rate of the system with changes in the geometry of the extrusion mold. In this research, the effect of mold geometry, including mold diameter, was assessed on the structural properties of polyethylene foams produced by the physical foam extrusion method with carbon dioxide foaming agent at a process temperature of 130 °C and 2 wt% of nucleating agent. The diameter of the mold was set at 1, 2, and 3 mm to create different pressure drop rates. The results showed that the decrease in the diameter of the nozzle caused an increase in the system pressure. This increase of 1 mm resulted in the system pressure prevailing over the gas injection pressure and caused insufficient gas to enter the system. In the sample with a 2 mm, the pressure of the gas entering the system was higher and the expansion was about 2.25 times, which is more than the 1 and 3 mm molds.

Hypothesis: 

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.

Hypothesis:

Polymeric foams have fascinating specific properties due to their cellular and porous structure and these properties have attracted much attention in industrial and scientific societies nowadays. The variations in cellular structure of polymeric foams including expansion ratio, cell density, and cell size may affect their final properties. For this reason, it seems necessary to study the effect of process parameters on the cellular structure of polymeric foams. On the other hand, the rotational molding method is developing rapidly compared to other processing methods due to its ability to fabricate large complex hollow parts Different process parameters can affect the structural properties of polymeric foams Utilizing nucleation agents as a material parameter improves the structural properties of polymeric foams significantly in different processing methods.

The effect of adding two types of nucleating agents including talc microparticles and clay nanoparticles in different sizes on the structural properties of polyethylene foams made by rotational molding process was investigated Azodicarbonamide was used as the chemical blowing agent. Talc microparticles (1% by weight) and clay nanoparticles were added to polyethylene and foamed using rotational molding process. Cell density, cell size, and expansion ratio were investigated as structural properties.

The findings revealed that the effect of talc microparticles on increasing cell density and decreasing cell size was more significant than the effect of clay nanoparticles. Cell density of polyethylene foam was improved by 96% and 89% by adding 1% (by weight) of talc microparticles and clay nanoparticles, respectively. A 20% and 17.5% decrease in the cell size of polyethylene foam was also observed with the addition of 1% (by weight) of talc microparticles and clay nanoparticles respectively.

Rotational molding is a process used to produce seamless, one-piece, and hollow polymeric parts. Foam rotational molding has recently become an increasingly important process in the foam industry. However, foam rotational molding is still a challenging process to fabricate polymeric foams. The focus of this manuscript was to assess the effect of material parameters on the foam properties of samples produced by rotational molding. Rotational molding experiments were performed on a laboratory-scale two-axis rotational machine, designed and manufactured by the authors. The effects of microtalc as nucleating agent, nanoclay as reinforcing agent, and their synergetic effect were investigated on the cell density, cell size, and expansion ratio of hybrid microtalc/nanoclay polyethylene nanocomposites. The cell density was improved by 96% and 89% by addition of 1 wt% of microtalc and nanoclay, respectively, compared to pure polyethylene foams. The cell size was reduced by 20% and 17.5% in 1 wt% of microtalc and nanoclay, respectively. However, the synergetic effect of using both microtalc and nanoclay at 1 wt% was more significant compared to their individual effects. The cell density was enhanced by 313% and the cell size was decreased by 35% compared to pure samples.

The importance of environmental issues has increased the use of biodegradable polymers which nowadays have become among main components in medical and biological applications. In the present study, a new combined method of fused filament fabrication (FFF) and batch foaming was introduced to improve the properties of poly lactic acid. For this purpose, FFF samples were produced with infill percentages of 100, 80 and 60 and then, foamed in batch process. Due to the importance and effect of the void fraction on structural and mechanical performance as well as the biodegradability of materials with porous structure, especially for medical purposes, void fraction and impact strength were evaluated. The results showed that the void fractions of FFF samples were 3%, 13% and 25% in infill percentages of 100, 80 and 60, respectively while after the foaming they reached to 14%, 19% and 30%. The findings revealed that the impact strength of FFF foamed samples was improved compared to FFF solid samples. For samples with 100 infill percentage, the impact strength improved from 207 to 506 J/m2 due to the foaming procedure with nano-sized cells created by the batch foaming.

In this study, the mechanical properties of poly lactic acid samples produced by FDM 3D printing technique were investigated. The 3D printing process parameters were optimized using design of experiment (DOE) Taguchi approach for achieving the optimum mechanical performance. In this regard, infill percentage (at three levels of 30, 50, and 70%), raster angle (at three states of 0/90, -30/30, and -45/45 degree), and layer thickness (at three levels of 200, 250, and 300 µm) were considered as process parameters for optimization procedure. Their effects on density (as porosity degree), impact strength (as mechanical property), and specific impact strength (the impact strength to density ratio) were investigated. Analysis of variance (ANOVA) was utilized to find the most effective processing parameters. The findings revealed that the infill percentage was the most effective parameter on the density and the impact strength. The density and the impact strength were reduced with the decrease of the infill percentage. These decrements were in a way that their ratio, specific impact strength, was almost constant. The layer thickness had the most influence on the specific impact strength. The specific impact strength was improved by reducing the layer thickness due to the raster entanglement. The optimum conditions to achieve the highest mechanical performance were the raster angle of 30/-30 degree and the layer thickness of 200 µ. The optimum infill percentage depended on the application.

The loss of energy especially in industrial and residential buildings is one of the main reasons of increased energy consumption. Improving the thermal insulation properties of materials is a fundamental method for reducing the energy losses. Polymeric foams are introduced as materials with excellent thermal insulation properties for this purpose. In the present study, a deep theoretical investigation is performed on the overall thermal conductivity of low-density polyethylene (LDPE) foams. The thermal conductivity by radiation is predicted using two different methods. The most appropriate model is selected in comparison with experimental results. The results show that the theoretical model has an appropriate agreement with the experimental results. The effects of foam characteristics including foam density, cell size, and cell wall thickness on the overall thermal conductivity are investigated. The results indicate that by decreasing the cell size and increasing the cell wall thickness, the overall thermal conductivity is decreased significantly. Also, there is an optimum foam density in order to achieve the smallest thermal conductivity. The lowest overall thermal conductivity achieved in the studied ranges is 30 mW/mK at foam density of 37.5 kg.m-3, cell size of 100 μm, and cell wall thickness of 6 μm.

Nowadays polymeric nanocomposite foams have attracted the attentions in both academic and industrial communities due to their advantages. Foams with open-cell structures have high ability to absorb sound, water, impact and moisture. The cell wall thickness can be used as a parameter to evaluate the approaches for achieving open-cell structures. In this study the structural and mechanical properties of polypropylene/nano Fe2O3 nanocomposite foams were investigated in batch foaming process using CO2 gas as blowing agent. Nano Fe2O3 content, foaming temperature and foaming time were considered as variable parameters. Design of experiments using L9 orthogonal array of Taguchi approach was used for studying cell wall thickness and specific impact strength. The signal to noise ratio and analysis of variance were carried out. The scanning electron microscope results showed that appropriate microcellular structures with cell density of 109 and 1010 cell/cm3 were achieved. The results indicated that foaming temperature was the most effective parameter on the properties of nanocomposite foams. Decreasing foaming temperature leads to decreasing cell wall thickness and increasing specific impact strength. Also, the results illuminated that specific impact strength was enhanced almost 20% by increasing 4 wt% of nano Fe2O3.

In the present study, the properties of polymeric nanocomposite foams investigated in variant multi-walled carbon nanotubes (MWCNTs) content and under various processing parameters. For this purpose, polyamide 6 (PA6) selected as matrix and melt compounded with MWCNT in variant weight percentages (i.e. 0, 0.5, 1 and 1.5%) using a twin-screw extruder. Then, the prepared nanocomposites were foamed using Azodicarbonamide as blowing agent by injection molding machine based on Design of Experiments (DOE) using Taguchi method according to L16 orthogonal array. Influence of weight percentage of MWCNTs and injection molding processing parameters including holding pressure and holding pressure time (all in four levels) investigated on mechanical and structural properties of nanocomposite foam samples. Specific tensile strength investigated as mechanical property and for investigation of structural properties of nanocomposite foam samples, SEM test has been done that the results of this test showed that a well microcellular structure achieved. According to the results of signal to noise ratio (S/N) weight percentage of MWCNTs is the most effective parameter on specific tensile strength and structural properties of nanocomposite foam samples. The results demonstrated that by adding 1 wt% of MWCNTs, specific tensile strength of samples increased about 147%. Also, the results indicated that by addition of MWCNTs, cell density increased and mean cell size decreased that means providing optimal conditions for foaming.

In present study, the tensile strength and hardness of polymeric nanocomposites containing multi-walled carbon nanotubes (MWCNT) are investigated. For this purpose, polyamide-6 and MWCNTs in various weight percentages are melt compounded using a twin-screw extruder. To investigate the influence of MWCNTs and injection molding processing parameters on tensile strength and hardness, the samples in various MWCNT contents including 0, 0.5, 1 and 1.5 weight percentages and under different processing parameters including holding pressure and injection temperature, are injection molded according to Taguchi design of experiments. According to the results of signal to noise (S/N) ratio, the weight percentage of MWCNT is the most effective parameter on the tensile strength and hardness of samples. Also, the results indicate that by adding 1 wt% of MWCNT, the tensile strength of samples increased almost 31% and by addition of 1.5 wt% MWCNT, the hardness increased about 15%. Furthermore The results of analysis of variance (ANOVA) indicates that wt% of MWCNT with 68% and 76% contribution percentage on tensile strength and hardness of samples, are the most effective processing parameters, respectively.