Excellent Thermal Mechanical Properties Research Articles

Lignocellulose Nanofibers Enhanced Mechanical and UV-Blocking Properties of Polyvinyl Alcohol Films

Lignin-containing cellulose nanofibers (LCNFs) from bamboo were prepared by choline chloride–lactic acid solvent treatment at 110–130∘C in combination with ultrasonication. Effects of LCNFs dosages on UV-blocking property, mechanical property, thermal stability and water vapor barrier property of LCNFs/PVA composite film were determined by UV spectrophotometer, universal mechanical testing machine, thermogravimetric analysis and weightlessness method, respectively. The results indicated that PVA film composited 10% LCNFs obtained from 120∘C showed best properties. As compared to pure PVA film, the UV-blocking property of composite film increased from 30% to 53%. LCNFs addition enhanced mechanical properties, resulting increment of tensile strength from 42[Formula: see text]MPa to 81[Formula: see text]MPa and elongation at break from 3% to 9%, respectively. LCNFs also introduced 2.4 times increment of water vapor barrier property of PVA film. The LCNFs/PVA composite films not only have excellent thermal stability and mechanical properties but also have UV-resistance and water vapor barrier properties. It provides a new idea for replacing some petroleum-based packaging materials and also shows the great potential of LCNFs materials.

Silane cross-linked network and concentrated flexible sulfoalkyl groups for forming a novel C-SPAEK membrane with enhanced methanol resistance and proton conductivity for DMFC applications

In the present work, a novel poly(arylene ether ketone) with a unique molecular design that included concentrated flexible sulfoalkyl groups and a silane cross-linked network (C-SPAEK) was prepared and used as a PEM for DMFCs. The chemical structures, sulfonation degree and phase-separated morphology were characterized and identified by 1H NMR, FT-IR and SAXS. The resulting copolymers exhibited excellent thermal stability (T5%>263.8 °C) and mechanical properties (tensile strength>52.88 MPa). Additionally, the high IEC values and obvious hydrophilic/hydrophobic phase-separated structure (d > 2.71 nm) ensured that the C-SPAEK membranes possessed high proton conductivities. The C-SPAEK PEMs also displayed enhanced methanol resistance and dimensional stability, which were much better than those of a recast Nafion membrane under the same conditions. The C-SPAEK-0.4 membrane maintained a low methanol absorption of less than 48.7%, even in 4 M methanol solution. In particular, the C-SPAEK-0.6 membrane exhibited the best comprehensive performance, with a high proton conductivity (0.164 S cm−1), low methanol uptake (52.1%) and permeability (3.63 × 10−7 cm2 s−1), and maximum power density (83.2 mW cm−2), when immersed in 2 M methanol at 80 °C in a DMFC single-cell. These results suggested that the C-SPAEK membranes were sufficiently tough and had the potential to overcome the problems caused by the high methanol permeability of PEMs. The unique molecular design of C-SPAEK guaranteed a rare combination of high proton conductivity and enhanced methanol resistance, which are the key determining factors for DMFC applications.

Microcell morphology evolution and mechanical performance of UHMWPE/PEG porous materials with bimodal cell structure

The bimodal cell structure with both large and small cells has been reported to have more excellent thermal insulation, vibration damping and mechanical properties. In this work, UHMWPE/PEG porous materials with bimodal cell structure were prepared by a simple one-step decompression micro-foaming technology using only supercritical carbon dioxide (sc-CO2). The effects of PEG content, molecular weight of PEG, saturation temperature, pressure and time on the evolution of cell morphology were investigated. The results show that when the content of PEG is 7%, the UHMWPE/PEG composite porous material exhibits stable bimodal cell morphologies in most process range, and a mechanism for the formation of bimodal cell is proposed. Moreover, UHMWPE/PEG porous materials with bimodal cell structure show higher mechanical properties. When the relative densities are similar, the anti-compression properties of bimodal porous materials are significantly better than those of unimodal porous materials.

Thermal Decomposition and Solidification Characteristics of BFFO

A novel energetic material, Bifurazano [3,4-b: 3′,4′-f] furoxano [3″,4″-d] oxacyclo-heptatriene (BFFO), has been investigated regarding two aspects, namely its thermal decomposition and solidification characteristics. The DSC curves indicate that the peak temperature of BFFO decomposition process is 271.1 °C under the static pressure of 2 MPa and the volatility of BFFO at 120 °C is significantly lower than that of TNT, DNAN and DNTF. The solidification curve indicates that the solidification of BFFO is a basic linear uniform solidification process, which is obviously different from that of TNT, DNAN and DNTF. In addition, the facet of BFFO appears much smoother and fewer defects are observed in the solidified body after solidification via CT and SEM. The reduction in solidification defects also further improves the mechanical properties of BFFO, with significant improvements in compressive and tensile strength compared to DNTF, DNAN and TNT. In summary, BFFO is a potential melt-cast carrier explosive with excellent thermal stability, solidification characteristics and mechanical properties.

Effects of temperatures on microstructure evolution and deformation behavior of Fe–32Ni by in-situ EBSD

Fe–32Ni alloy has attracted the attention of researchers owing to its excellent thermal expansion properties and mechanical properties. In this study, the macroscopic mechanical properties, surface morphology, crystal orientation, evolution of grain boundary and kernel average misorientation (KAM) and deformation mechanism of Fe–32Ni alloy were systematically investigated by in-situ loading equipment from 25 °C to 800 °C combined with electron backscatter diffraction (EBSD). The results showed that the grains with (111) and (101) orientations formed a special ring texture in {100} and {110} poles of the polar diagram after grain deformation and rotation. The rotational ability of the grains with (111) and (101) orientations were significantly promoted as the temperature increased. The number and proportion of low-angle grain boundaries (LAGBs) increased with increasing strain and temperature. By analyzing the microstructure evolution during in-situ EBSD testing, it was found that the rotation of the crystals significantly improved the deformability of the material. The effect of selective passage for dislocations by LAGBs both enhanced the plasticity and caused hardening of the material. Dislocations tended to accumulate at grain boundaries causing strain concentration. Cracks sprouted at grain boundaries and expand along the grain boundaries. This study can provide profound insights on the deformation mechanism of Fe–32Ni alloy for the possible design and process optimization.

Preparation and Application of Flexible Ethylene Vinyl Acetate Adhesive Composites by Ultrasonic‐Assisted Forced Infiltration

Herein, carbon nanotubes (CNTs)–cellulose nanocrystals (CNCs)/ethylene‐vinyl acetate (EVA) composite are prepared with excellent bonding properties, electrical conductivity, and thermal conductivity using an ultrasonic‐assisted forced infiltration (UAFI) method. The CNTs–CNCs (10:1)/EVA composite had the highest shear (82.9 N) and strip (12.2 N) forces at the interface when bonding leather to fabric as an interface bonding material (IBM). Different mass ratios of CNTs to CNCs in the composites lead to different electrical and thermal conductivity properties. When the mass ratio of CNTs to CNCs is 10:1, the CNTs–CNCs(10:1)/EVA composites reach an electrical and thermal conductivity of 158.37 S m−1and 6.351 W (m·K)−1, respectively. In addition, the CNTs–CNCs(10:1)/EVA composite shows excellent thermal stability, mechanical properties, thermal performance, and electromagnetic shielding. The prepared EVA composite has a broad application prospect in IBM.

Ultrafine-grained Al–La–Mg–Mn alloy with superior thermal stability and strength-ductility synergy

Ultrafine-grained (UFG) structures are highly desirable in microstructural design for their substantial improvements in strength and ductility; however, they often face challenges such as thermal instability and high manufacturing costs. In this work, powder hot-extrusion was employed as a cost-effective method to fabricate an Al–La–Mg–Mn alloy with a UFG structure (∼0.8 μm). The as-fabricated alloy exhibited a high-volume fraction of bimodal sub-micron intermetallics, with coarse intermetallics (∼270 nm) distributed primarily along the grain boundaries and fine ones (＜80 nm) in the grain interior. This unique structure cooperatively retarded the grain growth, resulting in a UFG structure with excellent thermal stability. The grain size grew slightly to 1.08 μm after thermal exposure at 400 °C for 100 h. Moreover, the UFG structure exhibited an excellent combination of strength and ductility, with yield strength, ultimate tensile strength, and elongation of 365 MPa, 543 MPa, and 13%, respectively. The UFG structure, decorated with bimodally distributed intermetallics, presents a promising microstructural design for UFG-structured alloys with excellent thermal stability and mechanical properties.

Programmable shape memory bismaleimide composite claw with two-way grabbing function

• A series of shape memory polymers (SMPs) based on bismaleimide (BMI) were synthesized. The BMI-based polymers are made of a 4,4'-bismaleimidodiphenylmethane (BDM) matrix and chain extender polyether diamine poly(propyleneglycol) bis(2-aminopropylether) (D400). Then crosslinking agent 2,4-tolylene diisocyanate (TDI) was added to form a crosslinking network. Last, it was toughened by adding liquid nitrile rubber (ETBN). • These BMI-based SMPs achieved wide T g ranges of 170-200 °C. This property allows these SMPs to remember two pre-deformed shapes. By designing the second pre-deformed shape similar to the original shape, the 2W-SME can be achieved. • Carbon fabric reinforced BMI-based shape memory composites (SMPCs) were prepared. By exploring the preparation process, the claw structure was formed with this BMI-based SMPC. The composite claw realizes the motion of reach out and grab 250g items. Functional polymer materials with a two-way shape memory effect (2W-SME) have attracted great interest recently. Herein, by introducing 2,4-tolylene diisocyanate (TDI) into the bismaleimide (BMI) network, the shape memory polymers we synthesized are a series thermosetting polymers with adjustable T g and triple-shape memory effect(triple-SME), and realized two-way behavior by programming. Those shape memory polymers (SMPs) were toughened by acrylonitrile-butadienerubber (ETBN) and reinforced with carbon fabric to make composites. The cured network with varying transition temperatures and flexibility was synthesized by varying the cyanate ester and rubber concentration in the system. Polymers with a broad glass transition temperature ( T g ) range can achieve triple-SME. Due to the complex cross-linked structure, the two-way behavior demonstrated above for BMI-based SMPs stem from its broad T g ranges. Select two temperatures higher and lower than T g as the switching temperature, and fix the pre-deformed shape in the opposite direction at these two temperatures to achieve the two-way behavior. These BMI-based SMPs could grab objects through the design of the structure. Results indicated that the above BMI-based SMPs with two-way function have excellent thermal stability and mechanical properties, which provides the basic attempts for the further development of thermosetting SMPs and their composite materials.

D−π−A Strategy to boost dielectric breakdown strength of polyimide insulation

Polyimide (PI) possesses multiple advantages including excellent thermal stability, mechanical property and chemical resistance, which has been considered as one of the promising candidates for high-performance electrical insulation materials. Optimizing the polymer structure such as extending the band gap can yield high intrinsic breakdown strength, attributed to the inhibition of impact ionization. However, in most cases, large band gap is achieved at the cost of reducing the backbone coplanarity and rigidity or the intermolecular interaction, resulting in undesirable thermal and mechanical performance. Herein, we introduce an effective strategy to produce thermally stable and mechanically strong polyimide insulation with high breakdown strength through introducing aromatic donor groups into the main chains to construct a D−π−A structure. On the one hand, the formation of D−A effect increases the materials polarization and enhances dipole-induced scattering. On the other hand, enhanced intermolecular interaction via π−π stacking decreases free volume in PIs. Then, increased conjugation degree of the backbone and high packing density between the polymer chains benefit to thermal stability and mechanical properties. Based on this strategy, N-arkyl carbazole groups are preferred, in which the soft alkyl side groups can occupy the pores between the polymer chains to further decrease free volume. As a result, we afford polyimide insulation with significantly improved breakdown strength from 291 kV mm−1 to 570−632 kV mm−1, as compared to the reference PI ODA-PMDA. Simultaneously, the resultant PIs, such as PI-Bu, preserve high Td5% above 524 ℃, high Tg above 364 ℃ and tensile strength above 80 MPa.

Closed-loop recycling of lignin-based sustainable polymers with an all-hydrocarbon backbone

Recyclable lignin-based polymers with an all-hydrocarbon backbone showing excellent thermal stability and mechanical properties are reported. These polyolefins can be depolymerized back to pristine monomers quantitatively under mild conditions.

Preparation and Study of Borosilicate Foam Glass with High Thermal Insulation and Mechanical Strength

Foam glass is a kind of green building material that is widely used because of its excellent thermal insulation and mechanical properties. In this study, the borosilicate foam glass was fabricated by powder sintering method using recycled soda lime waste glass, quartz, and borax as the primary raw materials. CaCO3 was used as a foaming agent and Na2CO3 as a flux agent. Results showed that as the quartz content decreases from 30 to 17.5 wt.% and borax content increases from 5 to 17.5 wt.%, the pore size, porosity, and thermal insulation of borosilicate foam glass increase significantly, while the compressive strength decreases slightly. When the content of quartz and borax are both 17.5 wt.%, borosilicate foam glass with outstanding performance can be prepared, whose pore distribution is uniform, mean pore size is 1.93 mm, total porosity is 83.44%, thermal conductivity is 0.0711 W/(m⋅K), and compressive strength is 2.37 MPa. Finally, the influences of foaming agent content, flux agent content, foaming temperature, and holding time on the pore structure and various properties of borosilicate foam glass were investigated by orthogonal test. According to the results, the foaming temperature has a significant effect, and appropriate foaming agent content, flux agent content, and holding time help to form a uniform pore structure, thereby improving the thermal insulation and mechanical strength of the borosilicate foam glass.

Molecular engineering of a polyimide copolymer enables excellent dielectric and energy storage performance

A novel polyimide copolymer (ZnTPP-PI) was synthesized through molecular engineering and a copolymerization method, which achieves high energy storage density, and excellent thermal stability and mechanical properties.

Boosting fire safety and mechanical performance of thermoplastic polyurethane by the face-to-face two-dimensional phosphorene/MXene architecture

• A black phosphorus-MXene@polydopamine nanohybrid was synthesized. • The TPU/BP-MXene@PDA nanocomposite simultaneously showed reinforcing and toughening effects towards TPU. • The TPU/BP-MXene@PDA nanocomposite could be achieved excellent thermal stability, mechanical properties and flame retardancy. • A synergistic flame-retardant mechanism between black phosphorus and MXene in the TPU were discussed and clarified. Black phosphorus (BP), as one of the most promising fillers for flame retarding polymer, has been seriously limited in practical application, due to the agglomeration and poor structural stability challenges. Here, the BP was modified by MXene and polydopamine (PDA) via ultrasonication and dopamine modification strategy to improve the structural stability and dispersibility in the matrix. Then, the obtained (BP-MXene@PDA) nanohybrid was employed to promote the mechanical performance, thermal stability, and flame retardancy of thermoplastic polyurethane elastomer (TPU). The resultant TPU composite containing 2 wt.% of BP1-MXene2@PDA showed a 19.2% improvement in the tensile strength and a 13.8% increase in the elongation at break compared to those of the pure TPU. The thermogravimetric analysis suggested that BP-MXene@PDA clearly enhances the thermal stability of TPU composites. Furthermore, the introduction of the BP-MXene@PDA nanohybrids could considerably improve the flame retardancy of TPU composite, i.e., 64.2% and 27.3% decrease in peak heat release rate and total heat release, respectively. The flame-retardant mechanisms of TPU/BP-MXene@PDA in the gas phase and condensed phase were investigated systematically. This work provides a novel strategy to simultaneously enhance the fire safety and mechanical properties of TPU, thus expanding its industrial applications.

Significantly Enhanced Electromagnetic Interference Shielding Performances of Epoxy Nanocomposites with Long-Range Aligned Lamellar Structures

HighlightsTi3C2Tx@Fe3O4/CNF aerogels (BTFCA)/epoxy electromagnetic interference (EMI) shielding nanocomposites with long-range aligned lamellar structures were prepared by bidirectional freezing, freeze-drying and vacuum-assisted impregnation of epoxy resins.Successful construction of 3D long-range aligned lamellar structures and electromagnetic synergistic effect could significantly increase the EMI shielding effectiveness and reduce the secondary contamination.BTFCA/epoxy EMI shielding nanocomposites possessed outstanding EMI shielding effectiveness of 79 dB, and also presented excellent thermal stabilities and mechanical properties.

3D needle-punched carbon/quartz fabric reinforced nanoporous phenolic composites with co-optimized mechanics, insulation and ablation

Phenolic composites are the most reliable ablatives for thermal protection system, but integrating low density, good insulation and excellent mechanical/anti-ablation performance remains challenging. Here, a density-porosity trade-off method for synthesizing mid-density and high-strength phenolic composites is proposed. This method uses 3D needle-punched preforms to reinforce nanoparticle phenolic matrix. Proper compromise between porosity and density enables phenolic matrix to combine excellent thermal insulation and acceptable mechanical properties. And in-situ micro-CT results indicate that 3D needle-punched preforms can greatly improve the mechanical performance by restricting crack propagation from felt piles to woven piles. Furthermore, the mechanical, insulative and ablative properties can be optimized using hybrid carbon/quartz preforms. The resultant composites exhibit mid-densities of ∼0.9 g/m3 with integrated performance of high tensile strength (70–120 MPa), low thermal conductivity (0.08–0.12 W/(m·K)) and good ablation resistance. These schemes will encourage the development of phenolic composites that can withstand different heat fluxes.

Lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties via an ultralow shrinkage process

Lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties is an attractive material for thermal engineering applications. However, to synthesize such material, generally, a significant volume shrinkage would occur during the aerogel formation and the processing time is long. To conquer such issues, the lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties was synthesized by an elaborately designed process, where linear thermoplastic phenolic resin (LPR) and boron-modified thermosetting phenolic resin (BPR) were used as the raw materials. It was found that the shrinkage rate and the processing time of the phenolic resin aerogel were significantly reduced. By optimizing the synthesis process, the aerogel with a density of 0.105 g/cm3 and a thermal conductivity of 0.0352 W/(m·K) was achieved.

Smart Self-Nourishing and Self-Healing Artificial Skin Composite Using Bionic Microvascular Containing Liquid Agent.

Artificial skin composites have attracted great interest in functional composite materials. The aim of this study was to prepare and characterize a smart artificial skin composite comprising a bionic microvascular with both self-nourishing and self-healing functions. A poly(vinyl alcohol)–glycerol–gelatin double network organic hydrogel was used as the artificial skin matrix. The hydrogel had high mechanical strength because of the strong hydrogen bond formed between the PVA and glycerol (GL). The gelatin (GEL) increased the toughness and elasticity of the hydrogel to ensure the strength of the artificial skin and fit of the interface with the body. The bionic polyvinylidene fluoride (PVDF) microvascular had excellent thermal stability and mechanical property in artificial skin. Results indicated that self-nourishing was successfully realized by liquid release through the pore structures of the bionic microvascular. The bionic microvascular healed microcracks in the artificial skin when damage occurred, based on a self-healing test.

Design and synthesis of novel phenolphthalein-based poly (aryl ether) resin containing isopropyl groups

With the rapid development of 5G technology, low dielectric constant materials present a widespread application prospect in microelectronic devices. Poly (aryl ether) resins have been widely used in this field due to their excellent thermal stability, mechanical properties and electrical insulation properties, however, reducing its dielectric constant remains a challenge. In this study, novel phenolphthalein poly (aryl ether ketone) containing isopropyl groups and fluorene groups was successfully synthesized with high molecular weight via SN2 aromatic nucleophilic polycondensation reaction. At lower frequencies ranging from 10 Hz to 1 MHz and higher frequencies from 10 GHz to 42 GHz, the films exhibit the intrinsic dielectric constant in the range of 2.4–2.7. The resin has good thermal stability, mechanical properties and insulation properties. Thus, the functional poly (aryl ether ketone) possesses attractive potential applications in the field of high-performance flexible electronic packaging materials.

Flexible and Robust Ti3C2Tx/(ANF@FeNi) Composite Films with Outstanding Electromagnetic Interference Shielding and Electrothermal Conversion Performances

Flexible and robust multifunctional electromagnetic interference (EMI) shielding materials are playing an increasingly important role in areas of aerospace, electronic communication, artificial intelligence, and wearable electronic devices. Herein, the magnetic and conductive Ti3C2T x /(ANF@FeNi) EMI shielding composite films are fabricated via in situ growth and vacuum‐assisted filtration methods. The introduction of magnetic FeNi nanoparticles can effectively enhance the electromagnetic recombination losses, leading to improved EMI shielding effectiveness (EMI SE) of the composite films. The obtained Ti3C2T x /(ANF@FeNi) composite films show excellent EMI shielding and electrothermal conversion performances. When the mass fraction of Ti3C2T x and FeNi fillers is 60 wt% and their mass ratio is 4:1, the EMI SE of the composite films (50 μm) reaches 60.7 dB in the X‐band (8.2–12.4 GHz). When a low voltage of 3 V is applied, the surface heating temperature of the composite films quickly reaches 111.2 °C. Moreover, the composite films possess satisfied long‐term heating stability under the constant applied voltage. In addition, the composite films exhibit excellent thermal conductivity and mechanical properties. The thermal conductivity (λ) and thermal diffusivity (α) reach 4.72 W m−1 K−1 and 4.36 mm2 s−1, respectively, and the tensile strength and tensile modulus reach 113.4 MPa and 3.1 GPa, respectively.

Pore structure design and optimization of electrospun PMIA nanofiber membrane

BackgroundPoly (m-phenylene isophthalamide) (PMIA) has been widely used in many applications due to its excellent thermal stability, flame resistance and mechanical properties. MethodsIn this study, PMIA nanofiber membranes were fabricated by electrospinning method, and then, the solvent welding was used to optimize the pore structure and mechanical strength. Effects of solvent concentration (volume fraction of solvent) and welding temperature on the PMIA nanofiber membranes’ morphology, pore structure and mechanical properties were investigated, respectively. Significant findingsThe mechanical strength and pore size was simply controlled by solvent welding and heat pressing. And the process of solvent welding and heat pressing was classifiable regulation. In addition, the separation accuracy of nanofiber membrane was controllable in the range of ultrafiltration. The mechanical strength of PMIA nanofiber membrane raised from 5.5 MPa to 99.0 MPa, while the mean pore size decreased from 459.1 nm to 33.6 nm after post-treatment. The Congo red rejection rate of PMIA nanofiber membrane after heat pressing increased from 4.9% to 94.7%, which showed excellent ultrafiltration performance.