Volume 42, Issue 9

Nanodiamonds (NDs), the allotropic carbon nanomaterials with nanosize, durable inert core, adjustable surface morphology, high thermal constancy, and super mechanical performances, possess the characteristics of promising reinforcement materials for various technological applications. However, ND particles hold a vigorous propensity to aggregate in liquid media, obstructing their implementation in mechanical and thermal sciences. This aggregation is caused by high surface to volume ratio. By reducing the surface energy and lowering cluster formation, the mechanical and thermal properties of NDs can be polished. Herein, we report on the covalent functionalization of NDs with amine moiety through ball milling method. Their dispersion was checked in ethanol and polymethyl methacrylate (PMMA polymer) against nonfunctionalized NDs. The dispersive behavior showed that ball mill functionalized NDs produced preferably stable aqueous dispersions in ethanol media. Furthermore, 0.1, 0.2, and 0.4 wt% ND/PMMA composites were synthesized, and their mechanical and thermal behaviors were studied in terms of hardness, compression, Young`s modulus, flexural strength, tensile strength, and thermogravimetric analysis (TGA). Results revealed that the composites containing 0.2 wt% functionalized ND loaded with PMMA matrix showed outstanding mechanical and thermal performances indicating that 0.2 wt% is the optimum amount for achieving excellent outcomes.

Plastic gear applications are rapidly increasing in transmission systems in automotive, domestic and kitchen machineries. Biopolymer gears are now being preferred over polymer gears due to its biodegradable properties. Hence, a comparative investigation of wear characteristics between polymer and biopolymer gears is studied. Injection molded biopolymer, PLA (polylactic acid) gear and polymer, ABS (acrylonitrile butadiene styrene) gear have been fabricated with appropriate properties. Gears are experimentally tested for the period of 3 h at three different rotational speeds (500, 1000 & 1500 rpm) with and without load (1 kg). Wear debris, material loss, thermal damage and microstructure surface condition monitoring have been investigated. PLA presents better adhesive wear resistance and shows thermal deformation and tooth breakage. Biopolymer gives better thermal and wear resistance than polymer gear. At low rotational speed of 500 rpm under no-loading condition, both PLA and ABS show higher weight loss and wear rate due to thermal damage occurred due to gear pump effect. Whereas when load is applied, PLA shows wear loss at all rotational speeds due to inferior thermal conductivity and ABS shows wear loss at high rotational speeds of 1000 rpm or 1500 rpm due to loading effect.

A new reactive flame retardant (DTA), containing phosphaphenanthrene and triazine-trione groups was synthesized and applied to improve the flame retardancy of unsaturated polyester resin. The thermal stability, flame retardancy and combustion behaviors of UP/DTA thermosets were detected by thermogravimeric analysis (TG), limited oxygen index (LOI), vertical burning (UL94) test and cone calorimeter test. According to the research results, the addition of DTA contributed to improving the flame retardancy of UP. After adding 20 wt% DTA, the LOI of UP composite increased from 19.0% of the neat UP to 26.6%, and UL94 rating reached V-0. In addition, compared with pure UP, the peak heat release rate (pk-HRR), average heat release rate (av-HRR) and total heat release rate (THR) of UP/DTA-20 thermosetting material decreased by 44.0, 26.2 and 29.5%, respectively. In the gaseous phase, DTA decomposed to generate nitrogen-containing fragments with diluting effect and phosphorus-containing free radicals with quenching effect to inhibit the combustion. In the condensed phase, phosphaphenanthrene group of DTA decomposed to generate phosphorus-based compounds, which promoted the carbonization of the UP matrix and cooperated with triazine-trione group to increase the char yield. Therefore, DTA plays an important role in flame retardancy in the gas and condensed phases.

The current society is experiencing serious problems in terms of energy and environmental pollution. Environmentally friendly and renewable sources such as phase change materials have been employed as a reliable and effective source of energy storage. Phase change materials (PCMs) are known to absorb or release sizeable amount of energy during melting and solidification process. PCMs have been employed in both thermal protection and energy storage systems, more in active as well as passive cooling applications. However, PCMs are associated with low thermal conductivity, which hinders the process of heat rate exchange during the melting/solidification cycles. To improve the thermal conductivity of PCMs, various conductive fillers have been incorporated to such systems. Thermal cycle test is done to verify the stability of PCMs in thermal energy storage systems. This review emphasizes on the morphology, preparation methods and thermal cycle of various types of PCMs in the presence of conductive filler. Furthermore, the bibliometric analysis based on key research areas, top ten leading countries, and citations by country on phase change materials for energy storage research are reported in this review paper. The bibliometric analysis shows the dominance of the People’s Republic of China on PCMs for energy storage research.

In this paper, tiny amount of methacryloxyethyl trimethylammonium chloride (DMC) was added in poly(vinyl alcohol) (PVA) in order to widen its thermoplastic processing window. The effects of DMC content on thermal, mechanical, optical, and water resistance were investigated. The results showed that the thermal stability of PVA/DMC was improved obviously. Compared with pure PVA, with tiny amount (∼0.6 wt%) of DMC, the initial decomposition temperature and the fastest decomposition temperature of DMC/PVA increased from 246 °C and 287.6 °C–320.8 °C and 364.8 °C respectively. Moreover, this tiny amount of DMC did not affect the crystallization performance of PVA. PVA/DMC (0.6 wt%) blend have similar mechanical, optical properties and low temperature water resistance as those pure PVA have. The melting temperature of the PVA/DMC remained at 221 °C as that of pure PVA. This work might provide a new method for widening the thermoplastic processing window of PVA without sacrificing its other inherent properties. The reasons why DMC could improve the thermal stability for PVA was explored as well.

Composites have become attractive to many industries today and are a good alternative to many traditional materials. Epoxy granite (EG) is used as a competitive alternative to ground ceramics, especially as a foundation for machine tools. This is because of their high damping ratio compared to other traditional materials such as cast iron. In the present study, a lightweight and cost-effective EG composite material was developed as a new foundation for machine elements. The composite material EG was prepared by mixing epoxy resin (12 wt %) and granite particles by casting method. The crushed granite particles were sieved and separated into coarse particles ≤2.36 ≥ 1.18 mm, medium particles ≤1.18 ≥ 0.6 and fine particles ≤0.6 mm. Vibration modal analysis is performed using an impact hammer to measure the natural frequencies occurring at each material size and the damping ratios. Microbial and fungal resistance is tested to understand applicability in humid environments, and water absorption and soak resistance were also measured. Scratch tests are performed using a top scratch tester to measure scratch width for fine and coarse samples. The electrostatic discharges generated by friction on the rubber and granite-epoxy composite sole are measured. It was found that as the particle size decreases, the damping ratio increases and the damping capability is improved, both microbial and fungal resistance increases, the scratch width is small for fine particles, while it is difficult to achieve for other granite sizes. Electrostatic discharges show a better feel for the composite material, but it is better with fine particles.

Three kinds of lyocell fibers with different cross-sectional profiles including circular, Y-shape, and H-shape (abbreviated as O-, Y-, and H-lyocell) and similar mechanical properties were used to reinforce polylactic acid (PLA) by melt compounding and injection molding. The influence of lyocell cross-section shape on the interfacial shearing force, interface morphology, and mechanical properties of lyocell/PLA composites was investigated. Single fiber pull-out tests showed that the interfacial shearing force between lyocell fibers and PLA matrix was in the order of H-lyocell > Y-lyocell > O-lyocell, which was correlated with the fiber non-roundness factor. The higher the non-roundness factor of lyocell fibers, the better were the mechanical properties of lyocell/PLA composites. The tensile strength, impact strength, and initial dynamic storage modulus of different lyocell/PLA composites were in the order of H-lyocell/PLA > Y-lyocell/PLA > O-lyocell/PLA, which was attributed to higher interfacial contact area and stronger interfacial adhesion of profiled lyocell/PLA composites. Therefore, profiled lyocell fibers may be more promising for use in bio-composite reinforcement than conventional circular lyocell fibers.

ECG recorders are precision medical devices, but their thin-walled shells are susceptible to warpage and shrinkage during injection molding production due to the injection molding process, which greatly shortens their service life. To address this problem, a multiobjective optimization method for injection molding process parameters based on a combination of a BP neural network model optimized by an ant colony algorithm (ACO-BP) and an improved non-dominated sorting genetic algorithm (NSGA-II) is proposed. The study takes the warpage deformation amount and volume shrinkage rate of the plastic part as the optimization objectives, and the melt temperature, mold temperature, injection pressure, holding pressure, holding time, and cooling time as the design variables. However, for BP neural networks, it is crucial to choose an appropriate number of hidden layer neurons, so the particle swarm algorithm combined with the grey wolf algorithm (GWO-PSO) is used to solve for the optimal number of hidden layer neurons. Firstly, the number of hidden layer neurons of the BP network model was solved based on the samples obtained from the Box–Behnken experimental design and the GWO-PSO algorithm, and the ACO-BP algorithm was used to build the prediction models for warpage and volume shrinkage, respectively, and then combined with NSGA-II for global optimisation. The pareto optimal solution set was subjected to CRITIC analysis and the optimal process parameters were finally obtained, with a minimum warpage of 0.3293 mm and minimum volume shrinkage of 4.993%, a reduction of 8.93 and 6.95% respectively compared to the pre-optimisation period. At the same time, injection molding tests were carried out on the optimum process parameters, and it was found that the molding quality of the plastic parts was better and met the actual production requirements through measurement. The research in this paper provides a theoretical basis for further improving the quality defects of the thin-walled injection molded parts.

Multiwall carbon nanotubes (MWCNTs) are often used to modify polymer membranes as additives, however, MWCNTs are easy to agglomerate and entangle in polymer matrix due to their own strong van der Waals force. MWCNTs were doubly modified by bonding octadecylamine (ODA) and SiO 2 through the respective amidation and esterification reactions to prepare SiO 2 -MWCNT-ODA nanocomposites. The amino groups on ODA were amidated with the carboxyl groups on MWCNT-COOH. Then the hydroxyl groups on SiO 2 were bonded to MWCNT-COOH through esterification to obtain SiO 2 -MWCNT-ODA nanocomposites. PES/SiO 2 -MWCNT-ODA composite ultrafiltration (UF) membrane was prepared by non-solvent induced phase separation (NIPS) method. SiO 2 -MWCNT-ODA nanocomposites and PES/SiO 2 -MWCNT-ODA membrane were characterized by FTIR, XRD, TGA, and SEM, etc. The results showed that PES/SiO 2 -MWCNT-ODA membrane had significantly improved permeability, rejection, and antifouling properties for comparison with PES membrane. The pure water flux of PES/Nano.2-0.5 reached 212.5 L m −2  h −1 , which was approximately 2.6 times than that of PES membrane, and the rejection of BSA protein for composite membrane was as high as 94.2%. PES/SiO 2 -MWCNT-ODA composite membrane had excellent antifouling performance and the flux recovery rate ( FRR ) of PES/Nano.2-0.5 membrane could still maintain at higher value of 84.82% after two cycles in the antifouling test.

The review considers the possibilities of new methods of solid-state extrusion of polymers based on the use of deformation schemes that include simple shear - equal-channel angular extrusion, equal-channel multi-angle extrusion and combined extrusion. Information on the evolution of the physico-mechanical properties of glassy, semi-crystalline polymers, polymer blends and composites is given.

As the most outstanding type of organic fiber in terms of the comprehensive performance, polyimide fiber is more conducive to reduce the composites weight than inorganic fibers, such as carbon fiber or glass fiber. A polyimide-fabric-reinforced polyether ether ketone (PEEK) composite was prepared by a hot-press molding process. The melt flow rate of the PEEK resin was measured to reveal its rheological behavior and guide the selection of the molding process parameters of the composite. The tensile properties of the composites were determined. The results revealed that the rheological properties of the resin manifested through the melt viscosity, which was more sensitive to pressure changes than to temperature changes. The tensile properties of the composites were affected by two competitive mechanisms. First, increases of molding temperature and duration time could facilitate the infiltration of the resin into the fiber fabric and improve the internal quality and tensile properties of the composite. Second, an excessively high molding temperature and long duration time could decrease the strength of the polyimide fiber, thereby reducing the tensile properties of the composites.