Band 42, Heft 5

Due to environmental challenges, the demand for natural fibers (NFs) in biocomposites is expanding. Therefore, the study of the mechanical behavior of these natural fibers is increasingly requested. There is more than two thousands species of plant fibers that have been investigated. In this work, a statistical study involving, namely chemical content, mechanical and physical properties is conducted on a set of natural fibers. The relationship between these factors is studied. The Pearson correlation method is applied to investigate the sensitivity between these parameters. For this aim, a selected data set, collected from the literature, has been used. Results show that Young’s modulus exhibits greater correlation with physical and chemical parameters compared to the other mechanical properties. Additionally, the crystallinity index (CI) is a reliable parameter on predicting the mechanical behavior of natural fibers. Moreover, although the MFA° and diameter are important parameters for NFs modeling purpose, the experimental measurement of these two quantities is a source of unbiased interpretation that partially explains the large variation of the mechanical properties, reported in the literature.

The purpose of this research is to investigate the effect of gamma irradiation, concentration of microcrystalline newsprint fibers (MNF) and maleic anhydride as coupling agent for treating microcrystalline newsprint fibers (MA–MNF) on the mechanical and thermal properties of ethylene propylene diene monomer rubber matrix (EPDM). Maleic anhydride (MA) was used at a different ratios (5, 10, and 15 wt% according to the MNF). The EPDM/MA–MNF composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The results confirm the adhesion between MA–MNF and EPDM rubber matrix in presence of radiation. EPDM/MA–MNF composites have achieved higher mechanical properties than EPDM rubber matrix and EPDM/MNF composites. EPDM composites containing MNF that treated with 15% MA and gamma irradiated at 80 kGy have the highest tensile strength, tensile modulus at 100% strain, crosslink density and thermal stability over all other composites.

Soft polymers such as polyether ether ketone (PEEK), polyurethane (PU) and polytetrafluoroethylene (PTFE) have gained significant research interest in the last few decades owing to their excellent material properties which can be harnessed to meet the demands of various applications such as biomedical implants and accessories, insulation panels to cooking utensils, inner coating material for non-stick cookware etc. In the present study, we provide a comprehensive review on the mechanical and tribological behaviour of PEEK, PU and PTFE polymers. Samples of these materials were also fabricated and the experimentally obtained tensile strength, flexural strength, wear rate and coefficient of frictions were ascertained with values reported in literature. It is highlighted that coefficient of friction of polymers were highly dependent on the surface texture of the polymer’s surface; where an uneven surface exhibited higher coefficient of friction. Perspectives for future progress are also highlighted in this paper.

Multiwalled carbon nanotubes (MWCNTs) were functionalized with acid then coated with poly( p -phenylenediamine) (PpPD). Various concentrations of modified multiwalled carbon nanotubes (MWCNTs@PpPD) were introduced to a polysulfone (PSU) and poly( p -phenylenediamine) (PpPD) blend providing nanocomposites in form of sheets. Chemical oxidative polymerization was used to polymerize p -phenylenediamine. PpPD is then applied as a compatibilizer in such heterogeneous system to facilitate a successful percolation for MWCNTs in the polymeric matrix as an enhanced conductive filler. The morphological investigations showed homogeneous distribution for MWCNTs in the polymeric matrix. The prepared composites were investigated demonstrating favorable thermal and electrical properties. Thermogravimetric analysis (TGA) emphasized that MWCNTs@PpPD contributed in enhancing the thermal stability of the prepared sheets. The electrical conductivity of PSU/PpPD/MWCNTs@PpPD nanocomposites boosted upon raising the magnitude of loaded MWCNTs. The existence of MWCNTs@PpPD in the polymeric matrix extended the interfacial polarization effects with elevating the conductance. The loaded composite with (7.5 wt%) MWCNTs@PpPD showed the optimum electrical conductivity values. It was then treated with HCl to protonate the amine groups in PpPD showing higher conductivity value than its corresponding untreated one. PpPD and MWCNTs contributed synergistically in modifying the insulation feature of PSU to a favorable electrical conductivity one.

Graphene oxide (GO) was prepared by improved Hummer’s method, and the boehmite nanorods (AlOOH) were obtained by hydrothermal synthesis. Hybrid fillers were acquired of the surface-modified boehmite ( m AlOOH) nanorods attached on GO nanoplatelets ( m AlOOH-GO), then the hybrids were added into epoxy matrix. Both mechanical and thermal properties of the epoxy resin composites were increased through the addition of m AlOOH-GO hybrid fillers. The dispersion was promoted of GO because of introduction of m AlOOH, and the roughness of GO surfaces were increased by appropriate m AlOOH nano-rods, which this allows for a better interfacial formation between EP and hybrid fillers. Thus, remarkable enhancement on impact and flexural strength were achieved by introduction of A3G03 (3 wt% m AlOOH and 0.3 wt% GO), and the yielded enhancements are 302.6 and 46.4%, respectively. In addition, the thermal conductivity increases to 0.264 W m −1  K −1 and the thermal stability is significantly improved.

Calcium alginate hydrogels are used in a wide range of applications in the food, medical, pharmaceutical, and cosmetic industries. I have studied a calcium alginate hydrogel as an ultrasound phantom material. This hydrogel is formed using sodium alginate, calcium sulfate dihydrate, trisodium phosphate 12-hydrate, glycerol, and water, and mimics the ultrasound properties of human soft tissue. In this study, the structure of the calcium alginate hydrogel was observed with a fluorescence microscope after staining with the calcium indicator calcein. Two types of hydrogel structures, tape-like and thread-like, were observed by this method. The thread-like structures were rare in the hydrogel, which made them more difficult to find than the tape-like structures. These structures were several micrometers in diameter and longer than the tape-like structures, which were several micrometers to several tens of micrometers wide. The thread-like structures spread out in three dimensions, and existed singly or in aggregates. The outer shape of the aggregated thread-like structures resembled the shape of the tape-like structures, which suggested that the tape-like structures were made up of thread-like structures. The tape-like and thread-like structures are thought to contribute to retention of water, which is the main component of a hydrogel, by surrounding it.

Mixed matrix membranes were prepared by blending technique between nanoceramic powder and polyethersulfone. Nanoceramic powder (NC) as a fine powder was produced from ceramic industries. The effect of NC as an additive on the membrane matrix was studied. Increasing in NC% on polymeric blend enhances the membrane mechanical properties, where the tensile strength was 13.92 MPa with elongation of 23.67 mm for prepared blend membrane with NC 1 wt%. The highest salt rejection was about 89.3% with permeate flux of 34.6 L/m 2  h for R1 membrane using NS of percentage 4 wt% and nonwoven polyester support. The increase in NS% to 6 wt % leads to an increase in the salt rejection to 94.2% after 1 h operating time. The coating was achieved using the layer by layer technique which was carried out on the membrane surface to improve the salt rejection percentage. The salt rejection was found to reach about 99.8% after such coating process; but for permeate flux, it shows a certain decrease. The flux of membrane before the coating was 23.4 L/m 2  h for R2 membrane (1 wt% NC & 6 wt% NS), while after coating the flux was reduced to reach 21.6 L/m 2  h.

The relevance of this study is conditioned by the high degree of importance of creating the latest modifications of the polymer–bitumen binder for the manufacture of high-quality asphalt concrete, for its subsequent use in the construction of motorways and concrete pavements of airfields. In this context, the purpose of the study is to obtain new, scientifically substantiated technological solutions for the development and practical application of effective nanomodified polymer-bitumen binders (PBBs) that can improve the operational characteristics and duration of practical use of asphalt. The study results clearly demonstrate the fact that carbon nanotubes (CNTs) are a stabiliser and an ageing inhibitor of polymer–bitumen binders (PBBs), while contributing to a decrease in the intensity of its operational destruction over time by more than 10 times relative to the compositions of PBB with structuring additives, which is essential in the preparation and practical use of asphalt concrete for the construction of motorways and airfields. The results obtained are of significant importance for developers of modern technologies for manufacturing asphalt concrete for road construction, and road maintenance workers who professionally solve the problems of road maintenance, applying the latest practical developments in the field of road construction and repair in their activities.

This paper investigates the isothermal calendering process for Sutterby fluid model. Lubrication approximation theory (LAT) is used for the simplification of the governing equations. The perturbation technique is utilized to find the system solution. The zeroth-order and first-order solutions of velocity profile, sheet thickness, pressure gradient and pressure are obtained while numerical solution of other mechanical quantities is evaluated. The values of the parameters influencing the different flow and engineering parameters are obtained through graphs and in a tabular manner. It is observed that the material parameter mainly controls the sheet thickness, roll separating force, flow rate, power input, exiting sheet thickness, and pressure distribution. It is to be noted from the results that with the increase in the material parameter, the sheet thickness and power input increase while roll separating force decreases.