Band 42, Heft 8

The advent of high frequency communication era presents new challenges for further development of dielectric polymer materials. In the field of communication, efficient signal transmission is critical. The lower the dielectric constant of the dielectric material used, the lower the signal delay and the higher the signal fidelity. The preparation of polymer materials with low dielectric constant or reduce the dielectric constant of polymer materials becomes a key research topic. Summarizing past progress and providing perspective, this paper primarily discusses the intrinsic low dielectric polymers, fluorine doped low dielectric polymers, and microporous low dielectric polymers, while predicting the research trend of low dielectric materials.

Polyurethane chain was successfully grafted onto carbon nanotubes, affording polyurethane-functionalized multiwalled carbon nanotubes (P-MWCNTs) with super-hydrophobic property, which shows improved abrasive resistance obviously and enhanced thermal conductivity for natural rubber (NR) vulcanizate. Under the optimized conditions, the akron abrasion loss of NR vulcanizate combined with 5 parts per hundred rubber (5 phr) P-MWCNTs is 0.9 cm 3 /1.61 km compared to 2.96 cm 3 /1.61 km of pristine NR vulcanizate. The thermal conductivity of NR vulcanizate combined with 5 phr P-MWCNTs has been improved by 40.3% compared to that of pristine NR vulcanizate. The decreased height of the maximum tan δ peak shows that P-MWCNTs can reduce the heat buildup and damping capability of NR/P-MWCNTs composites. The good dispersion of P-MWCNTs with a continuous network, particularly at high loading (5 phr) in the NR composites, was evidenced from transmission electron microscopy (TEM).

The necessity of new electromagnetic interference shielding materials has expanded scientific research, especially with regard to microwave frequency range (X-band). In this context, polymer-based composites with nanoparticles – such as graphene – are promising electromagnetic interference shielding materials. In this work, epoxy resin/graphene nanoplatelets (NPG) composites with 0.10, 0.25 and 0.5% w/w were developed and applied to galvanized steel substrates. Dynamic-mechanical tests showed that the addition of NGPs increased the resin rigidity due to molecular restrictions of the organic chains imposed by the NPG. With the increase of the NPG concentration to 0.50%, the impact strength and the adhesion of the composites significantly decreased due to the formation and propagation of large cracks, followed by delamination. The epoxy resin sample containing 0.25% NPG presented the best microwave absorber performance with an increase of 48% in the attenuated energy and 80% in the reflection loss, respectively. Moreover, this sample extended the microwave absorption range to 10 GHz.

In this article we discuss in detail the effective approaches to enhance the thermal conductivity in polymer composites. Numerical simulations show that maximizing interfacial area between filler and polymer enhances very significantly the effective thermal conductivity in composites. We show that among the different geometries thermal conductivity is high for those geometries for which the ratio of surface-area to volume is high. For fillers of a particular geometry, by maximizing its surface area without changing the volume fraction of the metallic filler, the effective thermal conductivity increases. Thus, the interfacial area between filler and polymer plays an important role in the enhancement of thermal conductivity. It is also observed that as this interfacial area increases, increase in effective thermal conductivity follows from linear to the logarithmic growth. It should be noted that to inherit the polymer properties there is a restriction on the upper bound of volume fraction of the fillers. The current study brings out an important step in this direction. Our results are technologically very important in designing composite polymers for better heat conduction and are very cost-effective. This study also provides a connection between the bulk and the surface area in effective determination of the thermal conductivity.

The use of magnetorheological elastomers in the mechanical and acoustic fields, by the automotive, aeronautical, and building industries, is currently developing strongly and rapidly. The perfect understanding of the capacity of smart insulation based on the absorption of the vibratory waves by magnetorheological elastomers materials passes by the knowledge of their dynamic mechanical behavior. In this present work, we have characterized the dynamic mechanical properties of the magnetorheological elastomer off axes anisotropy by the inclination, of different angles (15°, 30°, and 45°), of the pseudo-fibers of the iron particles formed by the application of a magnetic field at different intensities using an optimal loading rate of 30%. The rubber specimens were prepared by mixing micron-sized iron particles dispersed in room temperature vulcanized (RTV) silicone rubber by solution mixing. The experimental results obtained show a clear dependence of the effect of inclusion of ferromagnetic chains on the magnetomechanical properties. It is observed that the mechanical properties are better when applying a magnetic field of 0.6 T with an angle of inclination of 45°. The improvements added in this work could be useful in several industrial applications, such as automotive, aeronautic through adaptive control of damping and vibration level.

This research investigates the optical and biocompatible properties of alkali-treated cpTi immersed in aspirin and different molecular weights of polyethylene (PEG). Instrumental characterizations were performed using scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet–visible spectroscopy. Additionally, drug release, antithrombotic, and cell adhesion studies were conducted in in-vitro conditions. The SEM micrographs showed that heat treatment of NaOH modified cpTi substrates increased the average surface pore size by 217%. Raman spectra’s active modes confirmed the presence of titanate groups which intensified the semiconductive nature of alkali-treated cpTi substrates. Further, the semiconductive nature was confirmed through the shift of the energy bandgap from 2.69 to 2.9 eV. The continuous redshift of the absorbance edge with an increase in the molecular weight of PEG indicates improved optical property. Following the Rigter–Peppas dynamic model, the drug release kinetics showed a non-Fickian dispersion ( n  < 1) and super case II transport ( n  = 2.21) for PEG-coated cpTi substrates. The alkali-treated cpTi-aspirin-PEG surface exhibits suitable antithrombotic property and interstitial cell adhesion with PEG coating. The modified surface on cpTi demonstrated a promising technique to improve the optical, antithrombotic, and biocompatibility performances, which are the prime requirement for the blood-interacted cardiovascular devices such as stents.

The present study was developed to reinforce a thermoplastic matrix with carbonaceous material to improve its thermal and mechanical properties. Composite materials formed from the homogenization of polylactic acid (PLA) and reduced graphitic oxide (RGO) were synthesized and characterized, reinforcement of the polymer’s thermomechanical properties and the adequate homogeneity ratio in the dispersion of the composite material were studied. Graphitic oxide (GO) was synthesized by the modified Hummers method, followed by thermal exfoliation. The chemical composition and the structure of RGO were studied by infrared (FT-IR) and Raman spectroscopies, respectively. PLA composites with different RGO contents (2 and 3% by weight) were prepared and compared in terms of distribution of RGO in the matrix and morphology, using scanning electron microscopy. The thermal stability of the composites was determined through thermogravimetric analysis. Torque of the different composites was measured, which increased at 21%; the tensile test showed an improvement in the mechanical parameters of the composites because the RGO favors the rigidity of the composite. In addition, the oxygenated functional groups present in the RGO allowed a more significant interaction with the PLA matrix, which results in an effective reinforcement of the mechanical properties of the composite material.

To impart durable flame retardant property to cotton fabric, a kind of multilayered hybrid film based on environmentally friendly phytic acid, sepiolite, polyaspartic acid, and Fe 3+ were deposited on the surface of cotton fabric by layer-by-layer and spraying method to form a dense protective layer. Compared with cotton fabric, hybrid film coated cotton showed excellent flame retardant property and low fire hazard, which can be demonstrated by vertical flame test, limiting oxygen index (LOI) and cone calorimeter test. After-flame time and after-glow time of hybrid film coated cotton is 1 s and 1 s, respectively. LOI value of hybrid film coated cotton increased by 44.4% compared with control sample. Cone calorimeter test revealed a total heat release rate reduction of 52.6% and peak heat release rate reduction of 73.6% for hybrid film coated cotton fabric. This work demonstrates that the hybrid film composed of phytic acid, sepiolite, polyaspartic acid, and Fe 3+ could improve the durable flame retardant property of cotton fabric.

Poly(aryl ether nitrile) (PEN) was used to fabricate ultrafiltration membrane via immersion precipitation phase inversion method. The effects of polyvinyl pyrrolidone (PVP) of different molecular weights and concentrations on the structure and performance of PEN membranes were investigated. The membranes were observed by scanning electron microscope, atomic force microscope, equilibrium water content (EWC), porosity ( ε ), and so on. The membranes were subjected to ultrafiltration characterizations such as pure water flux (PWF), compaction factor (CF), hydraulic permeability ( P m ), and bovine serum albumin (BSA) rejection rate. The hydrophilicity was characterized by infrared spectroscopy and contact angle tests. Results showed that molecular weight of PVP had significant effect on PEN membrane formation, which the membrane prepared by PVP-k30 exhibited excellent comprehensive performance. Meanwhile, the concentration of PVP-k30 could effectively control the select-permeability of PEN membrane. With PVP-k30 concentration increased from 7 to 13 wt%, the prepared PEN membranes got higher EWC, ε , CF, and P m . The PWF increased from 146.5 to 249.1 L m −2  h −1  bar −1 , while the overall rejection of BSA remained above 90%. Further increasing the addition amount to 16 wt%, the membrane performance began to decline. Finally, the addition of PVP-k30 could effectively improve the hydrophilicity of prepared PEN membrane surface.

The subsequent activated carbons of resorcinol-formaldehyde xerogels are synthesized and exposed to wide range of gamma irradiation dose. Xerogels and their subsequent activated carbons are characterized by diverse techniques; FTIR, Raman, porosity analysis, SEM, EDX and AFM. The composite membranes are fabricated from polyacrylonitrile and activated carbon xerogels as composite membranes to be utilized in ultrafiltration process of salted oily wastewater. The soybean oil is exploited as organic feeding solution. The results declared that values of flux and rejection reach 157 (L m −2  h −1 ) and 99.8 (%), respectively. Overall, the best performing composite membrane is conducted by maximizing pure water flux. The optimally synthesized membrane performs well for purification of salted oily wastewater, and a significant increment in permeate flux is obtained with soybean oil rejection is at ∼99.8% and with maximum flux is at 32 (L m −2  h −1 ). Further, the composite membranes showed good promise for ultrafiltration of salted oily wastewater.

Electrospinning is a trendy method because of the ease of use and the high surface-to-volume ratio. The mechanical and biological properties of polylactic acid (PLA) make it one of the most enticing polymers. Gelatin and PLA together are thought to enhance cellular behavior and hydrophilicity of scaffolds. Furthermore, chitosan nanoparticles (CNPs) can be incorporated into PLA fibers to achieve controlled growth factor release. This study utilized PLA–gelatin nanofibrous scaffolds in which CNPs were encapsulated within PLA fibers to achieve a controlled release of basic fibroblast growth factor (bFGF). To produce CNPs, a simple ionic gelation reaction was used. The optimal diameter of CNPs was determined by investigating chitosan to tricalciumphosphatesodium (TPP) ratio and TPP concentration. Using a spectrophotometer, we measured the release rate of bFGF from CNPS and scaffolds. Images from a scanning electron microscope (SEM) were used to assess the effect of various concentrations of PLA and gelatin on fiber diameter. The results showed that PLA–gelatin scaffolds could stimulate the release of growth factors and promote cell proliferation. Using a two-jet electrospinning device to produce PLA–gelatin fibers in combination with CNPs incorporated within PLA fibers to release the bFGF growth factor is the novelty of this study.

Polyacrylonitrile (PAN) was often used as a composite fiber matrix due to its good spinning characteristics. Herein, photoluminescent quantum dot-doped nanofibers with tunable diameters were successfully prepared using electrospinning by adding CdSe/CdS quantum dots (QDs) in PAN spinning solution. The morphology and structure of CdSe/CdS-PAN nanofibers were characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), and the mechanical and photoluminescent properties of CdSe/CdS-PAN nanofibers were investigated. Stable photoluminescent nanofibers were obtained owning to the improved stability of photoluminescent property of CdSe/CdS QDs in the PAN nanofiber. The stable photoluminescent CdSe/CdS-PAN nanofibers might be used for anti-fake labels, ultraviolet sensors, smart textiles and optoelectronic devices.