Effects of UV irradiation time on the molecular structure of typical engineering plastics and tribological properties under heavy load

Exposing engineering plastics to UV irradiation can easily destroy the original molecular structure of the materials and consequently affect their tribological properties. This study investigated the effects of UV irradiation on the molecular structure of typical engineering plastics, such as polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK), and on their tribological properties under heavy loads (20 MPa). The surface morphology results showed that the appearance of PEEK changed significantly under UV irradiation. However, the change in PTFE was negligible. Under micromorphology, the processing lines of the two materials gradually became lighter with increasing UV irradiation time. The resulting infrared spectra showed that the molecular chains of both materials were broken, and new functional groups were formed under UV irradiation. Tribology testing demonstrated that with prolonged UV irradiation, the average PTFE coefficient of friction remained relatively stable, whereas that of PEEK was approximately 0.55. As the UV irradiation time increased, the wear rate of PTFE increased significantly, whereas that of PEEK showed no significant change.

Effect of process parameters of fused deposition modeling on mechanical properties of poly-ether-ether-ketone and carbon fiber/poly-ether-ether-ketone

As a rapidly developing additive manufacturing technology, fused deposition modeling (FDM) has become widespread in many industry fields. It can fabricate complicated geometries using filament of thermoplastic materials such as PP, polylactic acid, acrylonitrile butadiene styrene, etc. However, poor mechanical properties of raw materials limit their application. Poly-ether-ether-ketone is a type of special engineering plastic with high performance, which could be further reinforced by adding carbon fibers (CFs). During FDM process, the mechanical properties of printed parts are largely subject to careful selection of process parameters. To improve the mechanical properties of PEEK and CF/PEEK 3D-printed parts, the effects of various process parameters including building orientation, raster angle, nozzle temperature, platform temperature, ambient temperature, printing speed, layer thickness, infill density, and number of printed parts on mechanical properties were investigated. The tensile fracture interfaces of printed parts were observed by scanning electron microscope (SEM) to explain the influence mechanism of process parameters. In the single factor experiments, flat and on-edge specimens show the best tensile and flexural strength, respectively; the specimens with raster angle ±45° and 0° show the best tensile and flexural strength, respectively. When the nozzle temperature at 500°C, platform temperature at 200°C, ambient temperature at 150°C, printing speed is 20 mm/s, layer thickness is 0.2 mm, and infill density is 100%, the printed parts exhibit the best mechanical properties.

Electromagnetic interference shielding effectiveness of polypyrrole-silver nanocomposite films on silane-modified flexible sheet

The conventional electromagnetic interference (EMI) shielding materials are being gradually replaced by a new generation of supported conducting polymer composites (CPC) films due to their many advantages. This work presents a contribution on the effects of silane surface–modified flexible polypyrrole-silver nanocomposite films on the electromagnetic interference shielding effectiveness (EMI-SE). Thus, the UV-polymerization was used to in-situ deposit the PPy-Ag on the biaxial oriented polyethylene terephthalate (BOPET) flexible substrates whose surfaces were treated by 3-aminopropyltrimethoxysilane (APTMS). X-ray Photoelectron Spectroscopy (XPS) analyzes confirmed the APTMS grafting procedure. Structural, morphological, thermal, and electrical characteristics of the prepared films were correlated to the effect of substrate surface treatment. Thereafter, EMI-SE measurements of the elaborated films were carried out as per ASTM D4935 standard for a wide frequency band extending from 50 MHz to 18 GHz. The obtained results confirmed that the APTMS-treated BOPET film exhibit higher EMI shielding performance and better electrical characteristics compared to the untreated film. In fact, a 32% enhancement of EMI-SE was noted for the treated films compared to the untreated ones. Overall, these results put forward the role played by the surface treatment in strengthening the position of flexible PPy-Ag supported films as high-performance materials in electronic devices and electromagnetic interference shielding applications.

Improved interfacial performance of carbon fiber/polyetherimide composites by polyetherimide and modified graphene oxide complex emulsion type sizing agent

In the field of interfacial enhancement of composite, sizing method has attracted extensive attention. In this research, a new complex emulsion type sizing agent containing polyetherimide (PEI) and covalently chemical functionalized graphene oxide (GO) was first proposed to further improve the interfacial adhesion of carbon fiber (CF)/PEI composites, adapt to the high processing temperature, and overcome the shortcomings of the solution type sizing agent. The emulsion was prepared by the emulsion/solvent evaporation method. In order to avoid the agglomeration of nanomaterials on CF surface, the monomer and polymer structure of PEI was used to functionalize GO, so as to achieve better compatibility and dispersion of GO in PEI. The physicochemical state of CF surface was characterized and the successful introduction of GO was verified. The microbond test revealed that the introduction of GO further improved the IFSS compared with only PEI sizing. When GO grafted with PEI was used as the main component of the sizing agent, the IFSS reached the largest with an increasement of 55.96%. The mechanism of interfacial reinforcement was proposed. Increased ability of mechanical interlocking, the mutual solubility between PEI molecular chains, and the improvement in wettability may be beneficial to the interfacial strength. This mild and effective modification method provided theoretical guidance for the interfacial enhancement of composites and was expected to be applied in industrial production.

Effect of forming process on mechanical and interfacial properties for thermoplastic composite I-stiffened structures

The forming process is the core factor to control the quality of thermoplastic composite components. In this paper, the common I-stiffened structures in the aerospace field were taken as the research object, and the forming process scheme was designed. Based on the prefabrication of C-shaped parts, the I-stiffened structures were prepared by the compression molding process. The influence law of molding temperature on the quality of the prefabricated C-shaped parts was explored. The time dependence of the PEEK melt viscosity was tested to provide the basis for the optimization of forming process parameters of I-stiffened structures. The influencing mechanism of thermoplastic composites repeatedly forming to the bonding strength of remelting interface was studied. The results show that repeated forming would lead to polymer aging and result in low bonding strength at the remelting interface of the I-stiffened structures. Optimizing the forming process could effectively reduce the aging of materials and improve the bonding strength of the remelting interface and overall mechanical properties of components. The research provides technical guidance for the manufacturing of complex thermoplastic composite components, especially the influence mechanism of the forming process on the bonding strength of remelting interface.

Effect of highly thermally conductive Ag@BN on the thermal and mechanical properties of phthalonitrile resins

Ag@BN/phthalonitrile resin composites were prepared using highly thermally conductive BN modified by Ag plating. The effects of different contents of Ag@BN particles on the dynamic mechanical properties, thermal stability, and thermal conductivity of composites were examined. The results of Fourier-transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analyses showed that Ag was successfully deposited on the surface of BN. The prepared Ag@BN was subjected to KH550 grafting treatment. With the increase in the content of Ag@BN/KH550, the storage modulus, thermal stability, and thermal conductivity of the composite increased. The storage modulus, decomposition temperature, and thermal conductivity of the Ag@BN/phthalonitrile composite with 20 wt.% Ag@BN/KH550 were 5.0 GPa, 539°C, and 0.80 W/(mK), respectively, which are 1.35, 1.18, and 3.33 times higher than those of pure resin, respectively. The compatibility and dispersibility of BN modified by Ag plating in phthalonitrile resin were effectively enhanced, thereby providing a potential candidate to be used at high-temperature devices with high thermal conductivity.

Effect of glass fibers length on the properties of polytetrafluoroethylene composites reinforced by glass fibers and graphite: Experimental and simulation study

Polytetrafluoroethylene (PTFE)-based matrix composites filled with glass fibers (GF) and graphite (GR) were prepared by an internal mixer and molded using a compression mold to produce test samples. The objective was to study the mechanical and tribological properties of PTFE composites filled with different lengths of GF. The fillers of GR and GF were 5 and 15 wt.%, respectively, with the lengths of the GF of 15, 20, 25, 30, and 35-μm in the work. The mechanical performance tests and tribological tests were carried out under the same conditions. The experimental results revealed that the mechanical properties and tribological properties of the PTFE composites filled with GF and GR were associated with the lengths of GF. When the length of GF increased from 15 to 20 μm, GF could be homogeneously dispersed in the PTFE-based matrix composites and the tensile strength reached the maximum value of 21.7 ± 3.3% MPa. Also, with 20-μm long GF, the composites exhibited the lowest coefficient of friction values and wear rates compared to PTFE with GF of the other lengths. The changes in frictional heat generation and frictional force of the composites during sliding friction were simulated using the finite element method. The theoretical simulation results matched with the experimental values, which proved the accuracy of the theoretical simulations.

Synthesis, characterization, theoretical investigations and fluorescent sensing behavior of oligomeric azine-based Fe3+Chemosensors

Three azine oligomeric esters were synthesized, characterized by IR, UV, 1H, 13C{1H} and GPC technique, and applied to chemosensor application. The sensitivity response of the oligomers towards the metal ion was evaluated for a metal ion series. The results have shown selective and sensitive “turn off” fluorescence response towards Fe3+ ion in DMF/H2O (1:1, pH: 7.4, fluorophore: 5 μM) solution. The binding stoichiometry and binding constant of the fluorophores were calculated using the Stern–Volmer equation and Benesi–Hildebrand plots, respectively. The quenching of fluorophores on the addition of Fe3+ ion indicates the capability of fluorophore towards quantitative analysis of Fe3+. The dimer of oligomers was theoretically studied using DFT, B3LYP/6-311G level basic set to support and explain the quenching mechanism of LMCT, PET process and to explain the DC, AC electrical studies results. The electrical conductivity measurements of solid-state, I2 doped and undoped oligomers were carried out and the conductivity gradually increases with increase in iodine vapor contact time of oligomers. The electrical conductivity was related with band gap and charge density values of imine nitrogen obtained by Huckel calculations. The dielectric measurements at different temperatures and frequencies were made by two probe method. Among the oligomers, EBHAP has recorded a high dielectric constant at the low applied frequency of 50 Hz at 373 K due to loosely attached π bonds resulting good polarization.

Synthesis of novel poly(arylene ether amide) containing aliphatic ring for optical property

In this work, the monomer N, N′-bis(4-fluorobenzamide)dicyclohexyl methane (BFDCM) was synthesized successfully by 4-fluorobenzoylchloride and 4,4′-diaminodicyclohexylmethane through interfacial reaction, and then the monomer BFDCM and 1,4-benzenediol (HQ) or 4.4′-biphenol (BH) were used to prepare the novel poly(arylene ether amide) (HQ-BFDCM and BH-BFDCM) containing an aliphatic ring in the main chain by nucleophilic substitution in NMP solution. These two polymers exhibited the inherent viscosities ranging from 0.828 to 1.044 dL g−1, high glass-transition temperatures (Tg) of 214.1–235.0 °C, and weight-loss temperature (T5%) of 425.2–441.3 °C. The polymers HQ-BFDCM and BH-BFDCM could completely or partly dissolve in some polar solutions, such as NMP, DMF, and so on, and they showed moderate corrosion resistance. Additionally, the obtained polymers HQ-BFDCM and BH-BFDCM exhibited good optical property, and the optical transmittances of HQ-BFDCM and BH-BFDCM were 74% and 80% at 450 nm, respectively, which showed that they could be applied to the heat-resistant optical films.

Highly selective sulfonated Poly (arylene ether nitrile) composite membranes containing copper phthalocyanine grafted graphene oxide for direct methanol fuel cell

To improve the performances of sulfonated poly (arylene ether nitrile) (SPEN)–based proton exchange membranes (PEMs) in direct methanol fuel cells (DMFCs), the copper phthalocyanine grafted graphene oxide (CP-GO) was successfully prepared via in situ polymerization and subsequently incorporated into SPEN as filler to fabricate a series of SPEN/CP-GO-X (X represents for the mass ratio of CP-GO) composite membranes. The water absorption, swelling ratio, mechanical properties, proton conductivity, and methanol permeability of the membranes were systematically studied. CP-GO possesses good dispersion and compatibility with SPEN matrix, which is propitious to the formation of strong interfacial interactions with the SPEN, so as to provide more efficient transport channels for proton transfer in the composite membranes and significantly improve the proton conductivity of the membranes. Besides, the strong π–π conjugation interactions between CP-GO and SPEN matrix can make the composite membranes more compact, blocking the methanol transfer in the membranes, and significantly reducing the methanol permeability. Consequently, the SPEN/CP-GO-1 composite membrane displayed outstanding tensile strength (58 MPa at 100% RH and 25°C), excellent proton conductivity (0.178 S cm−1 at 60°C), and superior selectivity (5.552 × 105 S·cm−3·s). This study proposed a new method and strategy for the preparation of high performance PEMs.