جستجوی مقالات مرتبط با کلیدواژه "polystyrene" در نشریات گروه "مهندسی شیمی، نفت و پلیمر"

Hypothesis: 

One of the existing challenges in the foam production industry is to achieve the desired mechanical and thermal insulation properties required, which are directly related to cellular density, size, and distribution of bubbles. Therefore, predicting the bubble size distribution in each foam production system significantly contributes to the final properties of the desired foam. Nucleation, growth, coalescence of bubbles, and their final stabilization are influential stages in the ultimate properties of the foam that should be considered in predicting the bubble size distribution and laboratory testing phase.

Initially, a modified classical nucleation model was used for predicting cell nucleation, and then a population balance model was employed to predict the size distribution of bubbles in a batch system for the production of polystyrene foam. The modeling of this process was one-dimensional, and changes in bubble diameter were included as the characteristic variable of the system's equations. The foam production stage was carried out at temperatures of 70°C, 90°C, and 110°C, under a pressure of 20 MPa, and the consolidation stage was performed within 0.1 s and 1 s and without consolidation. To calculate the average cell size and size distribution, SEM images and software tools such as Axiovision.v4.82.SP2 and SPSS 26 were used, and the results were compared with the modeling outcomes.

Using the bubble size distribution obtained from modeling, the average bubble size at a saturation temperature of 70°C and a consolidation time of 1 s was 4.3 µm. With an increase in temperature from 70°C to 90°C, the average bubble size increased to 36.7 µm due to the higher rate of gas diffusion into the bubbles. With an increase in the amount of gas in polystyrene, the free volume increased, and glass transition temperature decreased. At 110°C, the average size of bubble cells increased to 78.1 µm. Since this temperature was higher than the glass transition temperature of polystyrene, in addition to the high gas diffusion rate into the bubble cells, the growth process did not stop, and gas diffusion and coalescence between the bubbles continued. Finally, the model predictions were compared with experiments under various conditions and demonstrated acceptable agreement.

Every year, an enormous amount of 2.5 million tons of plastic enter the oceans. On land, plastic also accumulates in landfills, beaches and other sensitive ecosystems around the world which has been a huge concern through the years. Recent research has been conducted to show us that one type of worm may help us solve the huge problem of plastic waste. Scientists have discovered that the larvae of a type of worm, Mealworm called Tenebrio Molitor, can include styrofoam and other polystyrenes as well as polyethylene in their diet. Not only do worms go on a styrofoam diet, they say, but the microorganisms in their gut can break down plastics during their digestive process, turning it into carbon dioxide and eventually use it as the nutrients that their bodies need. Biodegradable materials disposed by worms also seem to be used as fertilizer to fertilize and impregnate agricultural soil. We are looking for solutions to implement this discovery in a way that eliminates plastic waste therefore can be a solution to clearer oceans, rivers and the entire environment from the inevitable consequences of plastic accumulation. In this review study, narrations from articles related to the biodegradation of polyethylene, polystyrene and polypropylene have been reviewed.

The increasing production of non-degradable polymer wastes such as polystyrene (PS) and expandable polystyrene (EPS) is known as one of the most important environmental issues. Pyrolysis is one of the strategic and suitable methods for recycling of non-degradable polymeric wastes to fuels and useful chemicals. Therefore, investigation of pyrolysis kinetic of polystyrene waste, especially for available materials in Iran, is an essential issue for their use in industries. Obtaining the polystyrene pyrolysis kinetic can be used in designing industrial reactors and where it has economic credibility, styrene monomers can be produced in an industrial scale from polystyrene wastes.

Polystyrene (PS) and expandable polystyrene (EPS) samples that are available in Iran were collected, and their TGA analysis was performed in a nitrogen atmosphere in the temperature range of 25 to 600oC, at heating rates of 5, 10, 15, and 20 C/min, and sample mass changes were measured. The activation energy of pyrolysis was estimated by the Coats Redfern (CR), Ozawa Flynn Wall (OFW), Kissinger Akahira Sunose (KAS), Augis Bennetis (AB) and Vyazovkin methods.

The Vyazovkin model can predict the experimental data better than the other models, and therefore this model was used to estimate the activation energy. The activation energies of PS and EPS were calculated in the range of 158-201 kJ/mole and 182-195 kJ/mole, respectively. Furthermore, the pre-exponential factors of PS and EPS were estimated by Vyazovkin approach as 3.08×1012 and 1.05×1015, respectively. The results of kinetic analysis of polystyrene (PS) and expandable polystyrene (EPS) pyrolysis of samples in Iran can help simulate waste recycling processes and consequently reduce the environmental problems.

The porosity and pore size of polystyrene (PS) porous films prepared by immersion precipitation can be adjusted by varying the composition of the ingredients. The effect of composition variations on the characteristics of porous films can be elucidated by thermodynamic parameters.

A PS/chloroform solution with additives (polystyrene-block-poly(acrylic acid), polyethylene glycol (PEG), and glycerol) and/or non-solvent (2-propanol) was prepared. Then, the solution was cast and immersed in a 2-propanol/chloroform coagulation bath. The resultant porous film was imaged by scanning electron microscopy (SEM) and investigated by image analysis. The phase diagram of system was plotted through experimental measurements (cloud point) and theoretical method. The thermodynamic properties of the solution and coagulation bath were evaluated using non-solvent osmotic pressure difference (ΔΠNS) and solvent osmotic pressure difference (ΔΠNS) between the solution and coagulation bath. Moreover, the approaching ratio of solution (ARSolution) and bath (ARBath) to the binodal curve was also obtained.

The porosity and pore size of the films increased with decreasing the polymer concentration and adding the additives to the casting solution. By decreasing polymer concentration from 17% wt to 12% wt, the film structure changed from dense to porous (35% porosity and average pore diameter 2.8 μm). Addition of small amounts of PEG400 and glycerol to the solution (20% by weight relative to PS) significantly increased the porosity of the films from 35% to 54% and 66%, respectively. The porosity and pore size decreased first and then increased with adding non-solvent to the solution. Adding solvent to the bath helps increase porosity. Addition of non-solvent to the solution and addition of solvent to the bath were accompanied by decreasing solvent quality (ARSolution increase) and decreasing precipitation power of coagulant (ARBath increase) for the polymer, respectively. The increase in porosity and pore size was mainly associated with increasing ΔΠNS and decreasing ΔΠS.

Chemical modification of commercial and industrial copolymers and polymers such as polypropylene (PP) is one of the challenges of polymer chemistry. In this research work, a polypropylene nanocomposite modified with polystyrene (PSt) and carbon nanotube was synthesized by new methods, including living free radical polymerization (LFRP).

Maleic anhydride was grafted onto polypropylene (PP) followed by opening of the anhydride ring with ethanolamine to produce hydroxylated polypropylene (PP-OH). Hydroxyl groups were esterified using α-phenyl chloroacetyl chloride to obtain PP-Cl. Then 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was immobilized onto the PP backbone using a nucleophilic substitution reaction to produce PP-TEMPO macroinitiator. Afterward, the monomer (St) was grafted onto the backbone (PP) through “grafting onto” technique to afford (PP-TEMPO)-g-PSt. The chloride-end-caped PP-g-PSt copolymer was then attached to the oxidized MWCNTs in the presence of DMF as solvent to produce the MWCNTs-g-(PP-g-PSt) nanocomposite by solution intercalation method. Also, the present study confirmed that PP-g-MA was efficient to promote the dispersion of MWCNTs in the PP matrix, which solved the problem of CNTs aggregation and limited compatibility between nanotubes and polymer matrices. In another study nanotubes-polypropylene nanocomposities were prepared through esterification process.

The chemical structures of all samples were identified using Fourier transform infrared spectroscopy. Chemical bonding (PP-TEMPO)-g-PSt to MWCNTs was confirmed by thermogravimetric analysis and differential scanning calorimetry results. In addition, morphology studies were investigated using TEM and SEM images. A synthesized MWCNTs-g-(PP-g-PSt) nanocomposite can be used as a reinforcement for polymer (nano-) composites due to the superior features of MWCNTs as well as their compatibility with polymer materials after functionalization processes.

 Graphene oxide (GO) modified with a double bond-containing chemical was used in the preparation of polystyrene composites by combination of “grafting through” and reversible addition-fragmentation chain-transfer (RAFT) polymerization methods. The main objectives were (1) application of two reaction sites for in situ grafting of polystyrene chains from the GO surface, (2) increasing of grafting density in the polymerization process by grafting through two different sites and (3) evaluation of styrene RAFT polymerization in two different grafting densities and various GO contents.

After modification of GO with ethylenediamine (EDA) using nucleophilic ring opening reaction that is resulted in amine-functionalized GO (GOA), coupling reaction was conducted between the GOA and (3-methacryloxypropyl) dimethylchlorosilane (MCS) to obtain GOOHD layers with different modifier contents. Then, grafting through RAFT polymerization method was utilized for preparation of polystyrene composites.

X-ray photoelectron spectroscopy shows successful modification of the GO layers with EDA and MCS. Molecular bonding characterization was performed by Fourier transform infrared spectroscopy for the neat and modified GO. Variations in electron conjugation were studied by Raman spectroscopy. Molecular weight and polydispersity index of the free and anchored polystyrene chains were calculated from the size exclusion chromatography. By using thermogravimetric analysis, thermal properties and grafting ratios of the modifiers and polystyrene chains were studied. Grafting ratio of the modifiers was 12.9% and 7.5% for the modified GO layers with high and low grafting densities, respectively. Morphology of the GO layers was investigated through transmission and scanning electron microscopy. Oxidation changed the flat and smooth graphite to wrinkled layers, and grafting polystyrene chains resulted in turbid layers.

To improve the basic indexes of the hydrate formation process, , a proposed hybrid structure was used in this study, and a surface behavior engineering has been implemented to synthesize and select the components of it. The main agent of this structure is SDBS, a surfactant which has been selected as the driving factor for the dissolution stage. In this structure, zinc metal nanoparticles were stabilized to increase the efficiency of the hydrate growth stage and the polystyrene has been layered to provide an ideal and flexible nanoparticle and control the foam formation. The polymer layer, while capable of significantly reducing the amount of foam formation and decreasing the instability of the system during gas decomposition, provides a bridge between the carboxyl functional groups for bonding the zinc nanoparticles to the surfactant. Thus, polymer layer for surfactants makes them susceptible to industrial applications in the storage and especially release of hydrate from the gas. Experimental evidences also suggest that using a fluid containing a low concentration of the proposed composite structure can reduce the hydrate formation time by up to a quarter, and also double the volume of gas storage. These results are very attractive to use this engineered structure in industrial scale and its quantities are suggested.

Edge-functionalized graphene nanolayers with polystyrene chains were prepared by a “grafting through” reversible addition-fragmentation chain transfer (RAFT) polymerization. For this purpose, double-bond containing modifier (MD) was prepared. After edge-functionalization of graphene oxide (GO) by two different amounts of MD and preparation of modified graphenes (LFG and HFG), RAFT polymerization of styrene was applied for preparation of functionalized GO with different densities of polystyrene chains. Fourier transform infrared spectroscopy showed that MD and polystyrene chains were grafted at the edge of GO. Gas chromatography showed that conversion decreased by the addition of modified GO content and also grafting density of MD. Number-average molecular weight and polydispersity index of polystyrene chains were derived from gel permeation chromatography. Increase of modified graphene content results in a decrease in molecular weight of attached polystyrene chains and also an increase in their PDI value. Increase of grafting density of MD results in decrease of molecular weight of polystyrene chains with no considerable variation in PDI value. Thermogravimetric analysis results showed that char residue is about 45.1 and 46.8% for LFG and HFG, respectively. The content of degradation ascribed to polystyrene increased with increase of grafting density of MD and decreased with increase of modified graphene content. X-ray diffraction results were used for evaluation of interlayer spacing of graphene layers after functionalization process and also study of nanocomposites structure. The results of scanning electron microscopy and transmission electron microscopy show that graphene layers with high clarity turned to opaque layers with lots of creases by oxidation and attachment of polystyrene chains.

This study addresses the effect of temperature and nanoparticle on PS foam structure in order to control its structure more accurately. For this purpose, a theoretical hypothesis was proposed by explaining the classical nucleation theory. The PS in the presence of nanosilica and CO2 was foamed. Foaming process was carried out in a vessel suitable under high pressure and temperature conditions, and with instantaneous pressure release and high-speed stabilization capabilities. The most important factors affecting foam properties including foaming temperature, size, content and surface properties of nanosilica were investigated. Increasing of foaming temperature was effective on the initial nuclei formation and cell growth. These two effects determined the final foam structure. When the temperature was changed from 90 to 180°C, cell density of PS foam increased thousand fold to 2.2×1012 number of cells per unit volume of foam (cell/cm3). The results showed that a small amount of nanosilica had a substantial effect on decreasing the cell size and increasing the cell density. An increase in nanoparticle concentration also increased its effectiveness. Moreover, the quality and structure of foam were improved by adding the nanoparticle. As the size of nanosilica increased from 20 to 40 nm, its cell density decreased from 3.3×109 to 1.78×109 numbers of cells per unit volume of foam (cells/cm3). Surface treatment of the nanosilica using triethoxysilane, in addition to improving nanoparticle dispersion, increased its cell density. The efficiency of nanosilica in improving cell density after surface treatment increased by more than double.

Polystyrene/MCM–41 nanocomposites were synthesized by atom transfer radical polymerization (ATRP) at 110°C. Activators generated by electron transfer (AGET) and activators regenerated by electron transfer (ARGET)، as two novel initiation techniques، for ATRP were used. Specific structure، surface area، particles size and their distribution and spongy and porous structure of the synthesized MCM–41 nanoparticles were evaluated using X–ray diffraction، nitrogen adsorption/desorption isotherm analysis، scanning and transmission electron microscopy images، respectively. The final monomer conversion was determined using gas chromatography. Number and weight average molecular weights (Mn and Mw) and polydispersity index (PDI) were also evaluated by gel permeationchromatography. According to the results، addition of 3 wt% MCM–41 nanoparticles into the polymerization media resulted in lowering conversion from 81 to 58% in the AGET ATRP system. Moreover، a reduction in the molecular weight of the products from 17116 to 12798 g/mol was also occurred، although، the polydispersity index increased from 1. 24 to 1. 58. The similar results were also obtained by ARGET ATRP system; lowering conversion from 69 to 43% and molecular weight from 14892 to 9297 g/mol، and an increase of PDI from 1. 14 to 1. 41. The improvement in thermal stability of the nanocomposites، as a result of higher MCM–41 nanoparticles loading، was confirmed by thermogravimetric analysis. In addition، according to the analytical results of differential scanning calorimetry، a decrease in glass transition temperature، due to the addition of 3 wt% of MCM–41 nanoparticles (from 100. 1 to 91. 5°C in AGET ATRP system and from 100. 3 to 85. 8°C in ARGET ATRP)، was achieved.

This study was an effort to control foam structure with controlled shear rate in a slit die with addition of nanosilica in the extrusion process. We used general purpose polystyrene as the matrix، nanosilica as a nucleating agent and nitrogen gas as the blowing agent. For better dispersion of nanoparticles in the matrix، a combination of solution and melt methods were employed. The foams were produced in a twin screw extruder by studying the effects of shear rate on the slit die، size and weight percentage of nanosilica on foam density، cell density and average cell size. Scanning electron microscopicy (SEM) pictures were used to obtain the main characterizing parameters of the foams i. e.، cell density and cell size. The results showed that when the shear rate of 8 min-1 on the slit die was increased to 12 min-1، due to the breakage of the large cells into several smaller cells، there were observed 61% enhancement in cell density and 18% reduction in average cell size. When the size of nanosilica was decreased from 40 to 12 nm، the cell density was increased from 1. 24×108 to 1. 73×108 cells/cm3 and average cell size was decreased from 11. 5 to 9 micrometer. By changing the nanosilica content from 0. 1 to 4% (by weight)، it was observed that at 2% (by weight) of nanosilica، the maximum cell density was obtained. In conclusion it was observed that the nanocomposite was produced by 2% (by weight) of 12 nm silica nanoparticles at 12 min-1 shear rate shows the maximum cell density and minimum cell size.

Polystyrene latexes with dispersion of nanoclay layers were synthesized by using in situ miniemulsion reverse atom transfer radical polymerization at 90 °C. Final monomer conversion was determined by employing gravimetric method and droplet and particle size distributions were obtained by using dynamic light scattering (DLS) analysis. Also, the number- and weight- average molecular weight and polydispersity index of the nanocomposites were evaluated by using GPC. It was found out that the PDI value of the neat polystyrene is lower than that of the polystyrene chains extracted from the nanocomposites; PDI rose by increasing nanoclay content in the polymer matrix. The XRD results indicated that clay layers were dispersed in the polystyrene matrix and therefore exfoliated nanocomposites were formed. The successful formation of polystyrene chains and their living nature were demonstrated by FTIR spectra. The living nature of the polymerization was also confirmed by the HNMR results. The SEM micrograph presents the monodisperse distribution of spherical particles with sizes in the range of around 200 nm in the nanocomposite containing 1 wt% of nanoclay.

Atheoretical hypothesis was put forward on the effect of nanoparticle size on cell nucleation in polystyrene (PS) matrix foam. At first the heterogeneous factor was calculated in different wetting angles from zero to 180º. Then، to verify this hypothesis a combination of the solution and melting methods was used to prepare PS-nanosilica nanocomposites at different concentrations and different sizes of nanosilica. In this regard a novel apparatus، including a high-pressure/ high-temperature vessel capable of instantaneous pressure release and stabilization control، was used to prepare a polystyrene-nanosilica nanocomposite foam in its melt state. To reach the foaming conditions، the vessel was pressurized with dry ice at the specified temperature. After reaching the foaming conditions، the sample was saturated with supercritical carbon dioxide (CO2) for 8 more hours. Then، the pressure was released with an on/off valve and the temperature was instantaneously dropped to below glass transition temperature. The scanning electron microscopy pictures were used to calculate the effect of nanosilica on the main foaming parameters including cell density and cell size. The results showed that a small amount of nanosilica has substantial effect on decreasing cell size and increasing the cell density. Moreover، the foam quality and structure was improved by addition of the nanoparticle.