دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و پنجم شماره 6 (پیاپی 182، بهمن و اسفند 1401)

Hypothesis: 

Due to the special properties of nanomaterials, the production of nanoparticles has received much attention in recent years and various methods have been used to produce these materials. One of the methods is to use polymer structures to control nanostructures. Therefore, it is possible to produce cobalt chromate nanoparticles with certain dimensions using a polymer network with controllable pore size.

Polyacrylamide gel was used as a template to trap metal ions to form nanoparticles in this polymer template, and the polymer network was removed with the aid of heat treatment to produce the final nanoparticles. Therefore, cobalt chromate nanoparticles were fabricated by polyacrylamide gel method. The synthetic parameters like the temperature of polymer network formation and calcination temperature on the products were investigated. The manufactured product was characterized by different methods of analysis.

The results showed that the gel formation rate becomes faster with increasing temperature. X-Ray diffraction results showed that although the initial product is amorphous, a cobalt chromate crystalline spinel was produced after heat treatment at 800°C. Scanning electron microscope images showed the formation of particles with dimensions in the range of 50 to 150 nm. The thermal analysis results revealed that the polymer gel formation is destroyed after heat treatment up to 650°C. Electron microscope images showed that most of the particles have dimensions between 50 and 150 nm. The produced samples were used as photocatalysts for the degradation of methylene blue dye. The degradation results showed that the nanoparticles produced by this method effectively degrade the dye as a water pollutant. Also, the effect of the amount of photocatalyst on photodegradation yield was investigated and the results showed that by increasing the powder to maximum 3 mg, the degradation efficiency increases.

Hypothesis: 

Sand production from oil reservoirs is marked by many problems, such as well productivity reduction, operating equipment corrosion, and an increase in production costs; therefore, sand control in unconsolidated reservoirs is crucial for operating companies. Chemical injection into the production vessel, in order to strengthen and reduce sand formation, would be one of the most important methods of sand control.

In this study the effectiveness of a Co[AM-AMPS-AAC]/PEI-MBA(CO) hydrogel nanocomposite in sand control was investigated. The acrylamide-based nanocomposite is strengthened structurally and thermally by the addition of double crosslinkers and nanoparticles. Structural, morphological, thermal, rheological, compressive strength and flooding tests were carried out to define and assess its efficacy.

According to X-ray diffraction test findings, nanoparticles are evenly distributed throughout the structure. Morphological tests demonstrated the production of a dense, homogenous, and porous structure and validated the presence of nanoparticles in the structure. According to the thermal gravimetric test, adding nanoparticles increased the starting temperature of degradation from 80 to 195°C. The strain and frequency sweep rheological tests investigated the behavior of the material under different strains and stresses; they confirmed the preservation of the strong structure and linear viscoelastic behavior at a temperature of 90°C, strains between 0.1 and 20%, and frequencies between 0.1 and 10 Hz. The injection of 0.5 PV (pore volume) of 1% (by wt) nanocomposite to the sand pack resulted in a 730% increase in the axial strength of the sand pack according to the compressive strength test and 90% reduction in sand production measured by the chemical flooding test. Considering the stability and proper efficiency in the reservoir's harsh conditions, having linear viscoelastic properties, increasing compressive strength, and reducing sand production, the hydrogel nanocomposite designed in this research is proposed as a new and optimal product to control sand production and migration.

Hypothesis: 

Hydrophobic silicone rubber is used as coatings that create hydrophobic properties for different surfaces. Silicone rubbers have high chemical and physical stability. Hydrophobic properties and resistance to creeping flow are unique features of silicone rubber coatings. The purpose of this research is to synthesize and assess silicone rubber and alter its surface wettability by roughening and modifying the surface using materials with low surface energies.

Silicone rubber was first synthesized by hydrosilylation method in presence of a platinum catalyst, and subsequently coated onto polytetrafluoroethylene (PTFE) sheet as an example of a low surface energy substrate. In order to create roughness on the surface, industrial sandpapers were used of having grit sizes of 120, 220, and 400. In the next step, low surface energy silicon nanofilaments (SNF) were used to modify the desired surface, which were decorated on the surface of the sample through vapor deposition method. 

The SEM images show that the roughness density on the surface of the samples created by a 400-grit sandpaper is higher than that of a 220-grit sandpaper, and this sandpaper is also higher than that of a 120-grit sandpaper. Increasing the roughness density increases the static water contact angle (WCA) because in this case the Wenzel model is no longer dominant, and the hydrophobic mechanism follows Cassie Baxter theory. Due to the highest degree of roughness density created on the surface, the PTFE substrate treated with a 400 grit sandpaper was used for the next stage of silicone rubber coating and finally for the growth of SNF on top of the silicone layer. Applying SNF coating on the sample surface leads to a significant increase in the WCA (~159°). This hydrophobicity enhancement after SNF coating can be attributed to the low surface energy of the coating and the increase in roughness caused by the random growth of nanofilaments.

Hypothesis:

 Determination of the parameters of the material models for rubber compounds is usually carried out under simple modes such as uniaxial tension. These models are typically consisted of hyper-viscoelastic and stress-softening equations. However, due to the complicated behaviors of rubbery materials, the effectiveness and accuracy of such models under combined loads of tension, compression, and shear should be verified.

Three rubber compounds were prepared based on SBR reinforced by three different amounts of carbon blacks and underwent uniaxial cyclic under two loading/unloading rates and volumetric tests. The experimental data were used for the determination of parameters of three complex material models using a nonlinear curve fitting method. These models were selected based on the results of our previous findings. We have verified the uniaxial condition of the chosen test method and sample size using finite element method. The computed parameters were employed to simulate cylindrical rubber samples prepared from the same compounds through the finite element method using Abaqus code under compressive-contact loads. The predicted results were next compared with their experimentally measured data.

The results showed that the effectiveness of a material model in the prediction of stress-strain or stress-time behavior of a rubber compound under a simple load case does not necessarily guarantee that the same level of accuracy is obtained for the other loading modes, especially for highly filled compounds.  It is shown here that to obtain accurate results in such cases, in addition to hyper-viscoelastic and stress softening equations, the material model should include proper terms to consider the effect of the filler-filler interactions into account, especially for highly carbon black-loaded compounds. It is found that the best model is the one in which the viscoelastic behavior of the filler-filler structure is independently included.

Hypothesis: 

Incorporating different types of nanoparticles, especially metal oxide nanoparticles, into the polymeric nanofiber substrate improves different properties of the web. In this research, citric acid is used as an environmentally friendly cross-linking agent to reduce the hydrophilic property of chitosan-polyvinyl alcohol web. Cerium oxide nanoparticles (nanoceria) as an antioxidant and antibacterial agent are used to increase the biological capabilities of the web for healing applications.

Chitosan (CS)/poly(vinyl alcohol) (PVA)/citric acid (CA) nanofibers with the mass ratios of 1:1:0.5 and 2:3:1 (CS:PVA:CA) were prepared and electrospun. Nanoceria was loaded into the optimal blend prepared for electrospinning. In continuation, the physical-morphological properties, cell compatibility, non-cytotoxicity, and antibacterial activity of the resulting webs were investigated.

Physical-morphological investigations show that the CS:PVA:CA (2:3:1) nanofiber which was electrospun under 15 kV and 18 cm is the optimal nanofiber with an average diameter of 175±29 nm. The contact angle is about 42 degrees, indicating a suitable decrease in hydrophilicity and maintaining the physical integrity of the web. The SEM images show a bead-less morphology with an average diameter of 274±38 nm for nanofibrous web containing 1.5% (by wt) CeO2. The presence of nanoceria and interactions of the functional groups in the components were evident in their EDS and FTIR spectra, respectively. The results of the cell-culturing demonstrate the proper growth and proliferation of fibroblast cells on both with and without-nanoceria webs. The result of the MTT test confirms the non-toxicity of both scaffolds. The antibacterial investigations show improvements in antibacterial activities of the nanofibers containing cerium-oxide against both gram-positive and gram-negative bacteria. In general, the results determined that the presence of nanoceria in chitosan-polyvinyl-alcohol-citric acid electrospun nanofibers has clearly improved the biological properties, especially the antibacterial behavior of the obtained web, so it can be used as a suitable dressing for wound healing application.

Hypothesis:

 A nanocomposite layer including graphene nanosheets could be used to enhance the barrier properties of high density polyethylene through a layer-by-layer assembly method. Planar graphene nanoparticles help to decrease the gas permeability of polyethylene substrates by making a tortuous pathway for gas molecules transmittance.

Two different methods were used to increase the barrier properties of high density polyethylene and the results were compared with each other. In the first method, a thin film of polymer nanocomposite including graphene oxide nanoparticles and polyvinyl alcohol was coated on the surface of high density polyethylene film using a film applicator. The effective variables in this method were the weight fraction of graphene oxide particles in polyvinyl alcohol and thickness of the nanocomposite layer. In the second method, a layer-by-layer assembly was used. Chitosan solution acted as a positive charge and graphene oxide suspension in water was utilized as a negative charge.

In high density polyethylene samples coated by polyvinyl alcohol nanocomposite (10 micrometers), the oxygen transmittance rate decreased drastically to 3 cm3m2 bar. This decrease was expected due to the structure of polyvinyl alcohol and its inherent barrier properties. By adding graphene oxide into polyvinyl alcohol, the permeability values showed a slight decrease and reached 0.8 cm3 m2 bar.Statistical analysis based on the surface response method for the layer-by-layer method showed that permeability depends on pH, number of bilayers and graphene concentration. At high pH, the graphene oxide sheets take on a smoother and more stretched shape and are more likely to aggregate, which increases permeability.