IRANIAN POLYMER JOURNAL
Year:2022 | Volume:31 | Issue:8|Papers Count:10

Ethylene–, vinyl acetate (EVA) copolymers with different vinyl acetate (VAc) contents can be used in a wide range of daily application areas. However, the relationship between VAc contents and the thermal behavior and optical properties of EVA are rarely reported. This work aims to investigate the effect of varied VA contents on thermal behavior and optical properties of EVA copolymers, and further analyze the suitable application areas of different EVA copolymers. Crystallization behaviors present that three-dimensional spherulitic crystallites or two-dimensional crystallites of lamella type were formed presumably during the crystal growth from the primary crystallization process. Meanwhile, the lamellar thickness of EVA copolymers decreased from 3. 05 nm to 1. 34 nm with VAc content increases from 0 to 33% (by wt). Thermal behavior indicated that the thermal stability of EVA copolymers was weakened with the increase in VAc content. EVA copolymers involved two decomposition steps as deacetylation process of the VAc group and polyethylene chain scission. Nevertheless, the transmittance of EVA copolymers increased to 92% with rising the VAc content to 33% (by wt). The dynamic mechanical thermal analysis (DMTA) technique was adopted to study the glass transition temperature and viscoelastic behaviors of EVA copolymers. The thermal behavior, optical, and mechanical properties would ultimately influence the application areas. Thus, combining the thermal behavior, optical, and mechanical properties can provide a better perspective on the application areas of EVA copolymers with different VAc contents.

Piezoelectric materials can generate electrical activity under deformation. Various types of these materials have been used for tissue regeneration, especially in bone repair, in which the charges caused by mechanical stress can increase bone formation. Designing polymeric scaffolds with mechanical and biological properties similar to the extracellular matrix is an important approach in tissue engineering. Therefore, developing nanofiber scaffolds that mimic the extracellular matrix is a positive step toward the formation of new functional tissue. In the present study, we aimed to fabricate a nanofiber scaffold with piezoelectric properties, containing hydroxyapatite particles. Initially, the optimum conditions for electrospinning of the composite fibers were determined from the combination of poly-capro-lactone (PCL), poly-vinylidene fluoride (PVDF) and hydroxyapatite (HA). Then, the effect of mechanical strain on voltage generation was investigated and the piezoelectric property of the scaffolds was calculated. Finally, the behavior of cells (MG63) on the scaffolds was evaluated. The PVDF/PCL/HA scaffold showed an approximate 20% increase in piezoelectric properties compared to a PCL scaffold. Similarly, the three-component scaffold (PVDF/PCL/HA) revealed significant improvement in cell adhesion and function compared to the PCL counterpart and presented almost 12% growth in alkaline phosphatase activity and mineralization. Overall, the results showed that the PVDF/PCL/HA scaffold has the features to induce the proper function of bone cells and satisfy the necessities of bone tissue engineering. To the best of the authors’,knowledge, the simultaneous effect of PVDF and PCL with HA nanoparticles in the form of nanofibers has not yet been investigated and it is considered a novelty in this aspect, in which the presence of poly-capro-lactone as a companion polymer seems to improve the degradation of scaffolds.

Natural polysaccharides were used as adsorbents for the removal of toxic dyes from effluents. First, nanocomposites of chitosan (CH), graphene oxide (GO), sodium alginate (ALG), and β,-cyclodextrin (β,-CD) were synthesized. The synthesized nanocomposites were characterized by XRD, FTIR, FE-SEM, and EDS to know their interactions and morphology. The adsorption performance of GO/ALG/CH and GO/ALG/CH/β,-CD nanocomposites was studied by adsorbing rose Bengal (anionic dye) under different reaction conditions (e. g., concentration of dye solution, temperature, adsorbent dosage, adsorption time, and pH). Among the two studied adsorbents, a higher adsorption capacity was reached using GO/ALG/CH/β,-CD nanocomposite. It was seen that adsorption of dye increased with the agitation period and attained equilibrium at 540 min for GO/ALG/CH/β,-CD and at 660 min for GO/ALG/CH nanocomposite. Various kinetic models were analyzed and from all models, pseudo-second-order was the best fit model for adsorption. The adsorption equilibrium data followed the Langmuir isotherm model that indicated that the adsorption process is a monolayer. The adsorption process was exothermic and spontaneous, and the lower temperature was favorable for rose Bengal dye adsorption. The mechanism of adsorption of rose Bengal involves both physical and hydrogen bonding due to polymer and inclusion formation due to β,-CD through host–, guest interactions.

It is of great interest and remains a challenge to simultaneously improve the compatibility and flame-retardant performance of lignin/epoxy resin (EP) composites. In this work, a polysiloxane-enwrapped phosphorus-containing lignin-based flame retardant (PHMS-lig-P) was prepared through reactions of lignin, PHMS and TCP to address this issue, with results showing significantly improved flame-retardant performance and comprehensive performance. The influence of PHMS-lig-P on the flame retardancy of EP was investigated by vertical burning test (UL-94V), limiting oxygen index (LOI), smoke density test and cone calorimeter (CC) test. The PHMS-lig-P/EP achieved a V-1 rating, and its LOI value increased to 25. 3%. The maximum smoke density (Ds, max) decreased by 83. 2%. Furthermore, pHRR, avHRR, and MLR of PHMS-lig-P/EP decreased by 37. 5%, 22. 6%, and 25. 1%, respectively. In addition, the evolved gases and char residues were studied using thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TG-FTIR) and scanning electron microscopy (SEM). The results certified the flame-retardant mechanism of PHMS-lig-P was attributed to the synergistic effect of lignin, phosphonate, and polysiloxane, producing a compact and cohesive char layer that acted as a physical barrier, limiting the transfer of heat and oxygen and preventing the spread of pyrolysis volatiles and flammable gases. Moreover, the flame-retarded epoxy resin possessed good dispersion uniformity in mechanical properties and insulation performance, showing good applicability.

Due to serious environmental pollution which is derived from petroleum-based plastic wastes, poly(lactic acid) (PLA) has been seen as a potential bioplastic to overcome the problem. It has been predicted that the usage and disposal of PLA will continuously increase in the coming years. Recycling is one of the realistic ways to minimize resources and waste management. This work intended to investigate the degradation or mechanical properties of virgin PLA (VPLA) and recycled PLA (RPLA) aged in outdoor weathering and immersed in seawater and river water. The results demonstrated that the reduction in mechanical properties was most dominant in river water, which was aged for 150 days. The findings demonstrated that the reduction in mechanical properties was higher in RPLA than VPLA. Scanning electron microscopy images showed the formation of gullies on the fracture surface of samples aged in seawater and river water. No significant differences in thermal properties were observed in RPLA and VPLA after aging in outdoor weathering. Nevertheless, a marginal decrease in the glass transition temperature (Tg), melting temperature (Tm), and degradation temperature was observed after aging in seawater and river water. The findings could help in elucidating the degradation on mechanical and thermal properties of VPLA and RPLA. The results also revealed great significance for expanding the application of VPLA and RPLA in various environments.

In this work, melamine cyanurate (MCA) and boehmite (BM) were used to improve the flame retardancy of polyamide 6 (PA6), and a series of BM/MCA/PA6 composites were prepared. The effects of MCA and BM on flame retardancy, combustion and thermal degradation behavior of 15-MCA/PA6 and BM/MCA/PA6 composites were investigated by methods of limited oxygen index (LOI) measurement, vertical burning test, cone calorimeter test and thermogravimetric analysis (TGA). The results showed that MCA can effectively flame retardant PA6. When 15 wt% MCA was added to PA6, composite sample (15-MCA/PA6) possessed LOI value of 30. 4% and V0 rating (3. 2 mm) in UL-94 test. By replacing part of MCA with BM, with an increase of BM amount, the flame retardancy of BM/MCA/PA6 composite was better at first, but then got worse, and mechanical properties were increased. The flame retardancy, thermal stability and combustion behavior data of 4-BM/11-MCA/PA6 composite were better than 15-MCA/PA6 composite, indicated that appropriate amounts of MCA and BM in PA6 had synergistic flame-retardant effects. The time to ignition (TTI), the peak of heat release rate (PHRR), total heat rate (THR), total smoke release /total mass loss (TSR/TML) and fire performance index (FPI) of 4-BM/11-MCA/PA6 composite were 53 s, 322. 5 KW. m−, 2, 79. 8 MJ. m−, 2, 98. 3 g−, 1 and 0. 16 s. m2. kw−, 1, respectively. The LOI value of 4-BM/11-MCA/PA6 composite was 33. 8% with V0 rating (2. 0 mm) in UL-94 test.

A series of well-defined acrylamide/methyl methacrylate random copolymers (PAM-ran-PMMA) were synthesized in this work. The polymerization reactions were carried out in N, N-dimethylformamide (DMF) at 25 °, C using Cu(0)/hexamethylenetetramine (HMTA) and CCl4/hydrazine as the catalyst system and the initiator system, respectively. The number average molecular weights (Mn) and the distribution of molecular weight (Mw/Mn) of copolymers were analyzed by gel permeation chromatography (GPC). Experimental results revealed that the copolymerization reaction follows a pseudo first-order kinetic model. Mn of PAM-ran-PMMA increased linearly with the conversion of monomers while a narrow molecular weight distribution was obtained. By means of Fineman–, Ross equation, the reactivity ratios of r1 (AM) and r2 (MMA) were calculated to be 0. 81 and 3. 21, respectively. The results implied that the amount of AM unites in PAM-ran-PMMA copolymers increased with the increase of the molar ratios of AM/MMA. The structure and the thermal stability of the resultant PAM-ran-PMMA copolymer were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometry (1H NMR) and thermogravimetric analysis (TGA). TGA revealed that copolymers with a greater content of AM unit exhibited a higher thermal stability. The obtained PAM-ran-PMMA copolymer was used as a macroinitiator to perform Cu(0)-catalyzed chain extension experiment, which led to the increase of Mn and demonstrated the living character of the polymerization. This current approach provided a controlled route for the synthesis of well-defined PAM-ran-PMMA.

Graphene oxide (GO) or reduced graphene oxide (rGO) was used as nanofillers in the fabrication of poly(ethylene terephthalate)/poly(butylene terephthalate)/graphene (PET/PBT/G) nanocomposites. The nanocomposites were produced via melt blending and injection molding processes. The morphological, mechanical, thermomechanical, thermal, and electrical properties of the prepared nanocomposites were investigated. The SEM micrographs proved that GO-containing samples were brittle, while rGO-containing samples were more ductile. Also, there were agglomerations with the increase in the loading levels of nanofiller. The Young and storage moduli of PET/PBT/G nanocomposites were increased with increasing nanofiller loading levels and their increases in case of rGO was greater than those of GO. The glass transition temperatures of the PET/PBT blends were shifted to lower temperatures with the incorporation of nanofillers. While the tensile strength increased at lower amounts of nanofillers and decreased at higher amounts, elongation values showed a sharp decrease at all nanofiller loading levels. GO and rGO slowed the thermal degradation rate of the polymeric matrix. The char residue of the neat PET/PBT blend was 14. 3% and increased with increasing GO and rGO loading levels. Electrical resistivity decreased significantly, and semiconductor type materials were obtained. Consequently, rGO was found to be a more suitable nanofiller to improve the properties of the prepared PET/PBT/G nanocomposites, compared to GO.

Discharge of oil water from industrial activities can have significant effects on environment with potentially considerable economic consequences. Some current approaches to oil and polycyclic aromatic hydrocarbon (PAH) remediation do not lead to any desired effect and may have detrimental environmental results. However, oil pollution remediation was developed through nanotechnology via oil-absorbing method. In this work, a simple hydrothermal approach for preparing poly(lauryl acrylate)-grafted magnetite Fe3O4 nanoparticles (GMNPs) to separate PAH, i. e., naphthalene from water is presented with a high removal efficiency under relevant conditions. At first, the Fe3O4 NPs were synthesized and then chemical modification was performed through the reaction with (3-aminopropyl) triethoxysilane (APTES) and acryloyl chloride (AC) as sequentially polymerizable groups. Finally, poly(lauryl acrylate) was grafted to the modified Fe3O4 via free radical polymerization technique to form hydrophobic surfaces for absorbing naphthalene selectively. The results disclosed that as-prepared adsorbent exhibited high specific surface area (105. 36 m2/g). The removal efficiency was optimized for the most important variables, e. g., pH and contact time and the highest removal efficiency (%) was obtained 97. 4%. Furthermore, kinetic and equilibrium function of the absorbent in the absorption process was investigated in detail and correlated with pseudo-second-order and Freundlich model, respectively, and maximum adsorption capacity was about 32. 87 mg/g. Moreover, this adsorbent can be eliminated from solution through applying an external magnet and then recycled and re-used in five consecutive cycles, successfully.

It is necessary to recover dimethyl sulfoxide (DMSO) from pharmaceutical organic wastewater. In recent years, organic solvent nanofiltration (OSN), as an important means of recovering organic solvents, is being studied and paid attention constantly. Here, we prepared a solvent-resistant composite nanofiltration membrane with stable performance for the recovery of DMSO solvent using orcinol (OL), a natural alkyl resorcinol compound to synthetize a thin-film composite polyarylester membrane with trimesoyl chloride (TMC) by interfacial polymerization (IP) on the polyetherimide (PEI) substrate crosslinked by ethylenediamine (EDA). The results of chemical characterization such as X-ray photoelectron spectroscopy (XPS) and attenuated total reflection fluorescence transform infrared spectroscopy (ATR-FTIR) show that interfacial polymerization occurs between TMC and orcinol on the surface of PEI and forms polyarylester top-layer. The rejection of crystal violet (CV, 407. 99 g/mol) in DMSO takes place by 91%, and the maximum permeance is about 3. 1 L. m−, 2. h−, 1. bar−, 1. To further improve selectivity of membrane, microwave heating was adopted as a strengthening method of interfacial polymerization. The results illustrate that the microwave heating can significantly increase the rejection of OL-TMC membrane. The optimized membrane shows stable solvent resistance in DMSO with a rejection of 98% for CV and the permeance of 1. 8 L. m−, 2. h−, 1. bar−, 1 and a rejection of 81% for clindamycin phosphate (CLP) with the permeance of 1. 9 L. m−, 2. h−, 1. bar−, 1. This study not only opens up an interesting research field for more natural polyphenols as solvent-resistant nanofiltration membrane materials, but also indicates that microwave-assisted heating can be used as an important means during IP process to strengthen the properties of OSN membranes.