Initial Thermal Decomposition Research Articles

Investigation on improvement of thermal, mechanical, and barrier properties of lignin/poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) using inorganic nanoparticles as fillers

AbstractIn this study, four typical biocomposites from lignin blended with poly‐3‐hydroxybutyrate‐3‐hydroxyhexanoate (PHBH) using inorganic nanoparticles (INPs) (SiO2, MMT, CaCO3, and BN) as fillers were evaluated, which enhanced the thermal, mechanical, and barrier properties of composites. The results revealed that the selection of suitable INPs doped into the lignin/PHBH (L/P) composites was an important approach to achieve available function. MMT/L/P nanocomposites were significantly higher than those of untreated L/P composites in thermal stability (Tmax exceed 10%) and barrier properties (water vapor and oxygen resistance increased by 48% and 46%), and BN particles increased the initial thermal decomposition temperature by 8%. The elongation at break of CaCO3/L/P and BN/L/P composites were increased by 344% and 319%, while SiO2/L/P composites had the best tensile strength (18.8 MPa). Besides, the INPs/L/P nanocomposites in this paper exhibited excellent ultraviolet (UV) resistance and might become potential anti‐UV packaging materials for grease foods.

Effect of reduction time of functionalized graphene oxide on the morphology and properties of epoxy composite foams

In this study, N-aminoethylpiperazine (AEP)-functionalized and reduced graphene oxide (RGO) with different structures and properties was prepared by simply tuning the reduction time and then its effect on the rheological, curing and foaming behavior of epoxy resin was carefully investigated using the environment-friendly carbamate as a chemical foaming agent. As the reduction time of RGO increased, the reduction degree of RGO first increased and then levelled off but the grafted AEP was little affected by the reduction time. The addition of RGO undergoing long reduction time improved the viscoelasticity of epoxy/reduced graphene oxide (EP/RGO) composites but weakened the interfacial compatibility of RGO and EP. With increasing the reduction time of RGO, the cell size of EP/RGO composite foams decreased and the cell density increased. However, as compared with pure EP foam, the composite foams containing RGO with lower reduction degree had a larger cell size and a lower density. These results were attributed to the complicated effect of RGO, which not only acted as the heterogeneous nucleating and foaming agent but also affected the viscoelasticity of composites. In addition, as the reduction time of RGO increased, the initial thermal decomposition temperature, storage modulus at room temperature, electrical conductivity, thermal conductivity, and compressive properties of EP/RGO composite foams increased while the glass transition temperature remained unchanged. These results were related not only to the intrinsic properties and dispersion of RGO, but also to the density and cell morphology of the composite foams.

A Performance of a Nanofiber Polymer in Geotechnical Engineering Support

Geotechnical engineering is a new technical system established by European and American countries in the practice of civil engineering in the 1960s. There are many methods to manufacture nanofibers, such as stretching, template synthesis, self-assembly, microphase separation, and electrospinning. Among them, electrospinning is widely used because of its simple operation, wide application range, and relatively high production efficiency. This paper aims to study how to analyze and study the properties of engineering scaffolds along the way based on nanofiber polymers. In this paper, the performance of geotechnical scaffolds is proposed, which is based on nanofibers. This paper focuses on the concept of nanofibers and geotechnical physical mechanics. In this paper, the performance of geotechnical support is designed and analyzed. The experimental results show that the initial thermal decomposition temperature of the pure SF collagen nanofiber membrane is about 250°C and that of the pure PLLA nanofiber membrane is about 330°C. When SF collagen/PLLA = 70 : 30, the initial thermal decomposition temperature of the material is about 260°C. When the mass ratio is 50 : 50, the initial thermal decomposition temperature increases to about 270°C. When the mass ratio is 30 : 70, the initial thermal decomposition temperature increases to about 280°C. This is because PLLA is a semi-crystalline polymer with certain thermal stability. Its heat resistance is better than that of pure SF collagen. With the increase in the amount of PLLA, it can effectively improve the thermal stability of blended composite nanofiber scaffolds.

Constructing nano SiO2‐anchored hyperbranched polymer hybrid architectures for thermosetting epoxy systems with outstanding mechanical property

AbstractA hybrid architecture system was developed via in situ formation of SiO2 nanoparticles in the cavities of COOH‐terminated hyperbranched aromatic polyester (CHBPE). Results show that SiO2 nanoparticles can be successfully anchored in the cavities of CHBPE owing to the hyperbranched structure of CHBPE. The resulting CHBPE‐SiO2 system is applied to epoxy (EP) resins using 4,4′‐diaminodiphenyl sulfone (DDS) as curing agent. Because –COOH groups in CHBPE‐SiO2 system can react with epoxy groups, the conversion of epoxy groups in EP/CHBPE‐SiO2 systems can be improved, and the strong interface interaction between EP matrix and CHBPE‐SiO2 can be realized. The resulting EP/CHBPE‐SiO2 composites have excellent mechanical property. When the contents of CHBPE‐SiO2 are 8%–20%, the impact strengths, the flexural strengths and the tensile strengths of EP/CHBPE‐SiO2 composites can reach 24–46 kJ/m2, 121–165 MPa and 57–71 MPa, respectively, which are 16.1–31.9‐fold, 4.0–5.9‐fold and 8.9–11.3‐fold higher than those of pure EP, respectively. EP/16%CHBPE‐SiO2 composites have the optimal comprehensive mechanical property. The initial thermal decomposition temperature at 5 wt% weight loss (Tdi) and glass‐transition temperature (Tg) of EP composites can increase by 70–84°C and 30–43°C, respectively, after introducing 8%–20% CHBPE‐SiO2. Moreover, the dielectric constants of EP composites with 8%–20% CHBPE‐SiO2 decrease by 3%–11% as compared to pure EP. The high dispersion of SiO2 in EP/CHBPE‐SiO2 composite and the strong interface interaction between EP matrix and CHBPE‐SiO2 can contribute to the outstanding comprehensive property of EP/CHBPE‐SiO2 composite.

Preparation of HNTs‐d‐GO hybrid nanoparticles for gallic acid epoxy composites with improved thermal and mechanical properties

AbstractKH550 modified halloysite nanotubes (m‐HNTs) were hybridized with sulfoxide chloride acylated graphene oxide (m‐GO) to prepare hybrid nanoparticles (HNTs‐d‐GO). The microstructure and morphology analysis of HNTs‐d‐GO hybrid nanoparticles showed that the ordered lamellar structure of GO after acyl chlorination was stripped, and the organic groups on the surface of the lamellar increased. HNTs‐d‐GO hybrid nanoparticles were formed through the amidation of m‐HNTs and m‐GO. Then HNTs‐d‐GO hybrid nanoparticles were incorporated in galic acid epoxy resin to improve the thermal and mechanical properties. HNTs‐d‐GO/galic acid epoxy resin (HNTs‐d‐GO/GAER) bio‐based nanocomposites were prepared with methyl tetrahydrophthalic anhydride as curing agent. The galic acid epoxy composites with the addition of HNTs‐d‐GO exhibited significant enhancements of impact strength, tensile strength, storage modulus, and glass transition temperature. The initial thermal decomposition temperature (T5%) decreased, and the mass retention at 800°C increased, thermal stability of HNTs‐d‐GO/GAER composites were enhanced. At an optimum concentration of 0.75 wt% HNTs‐d‐GO, a simultaneous increase in strength and toughness was observed in comparison to the unfilled cured resin, the impact strength is 2.87 kJ/m2, which is 30.4% higher than pure GAER, and the tensile strength is 42.62 MPa, which is 29.2% higher than pure GAER. Compared with pure gallic acid epoxy resin, the content of HNTs‐d‐GO is 0.25 wt%, Tg increased by 28.9°C.

Effect of surface modification of SiO2 particles on the interfacial and mechanical properties of PBS composites

AbstractIn this study, WPU@SiO2 nanoparticles were obtained by grafting waterborne polyurethane (WPU) on the surface of silicon dioxide (SiO2). Then, WPU@SiO2 nanoparticles were introduced into the matrix of polybutylene succinate (PBS) to prepare a series of PBS/WPU@SiO2 composites. The dispersibility and interfacial compatibility of filler and matrix can be improved obviously by grafting a layer of WPU onto the surface of SiO2 nanoparticles. The FTIR and TGA results showed that WPU was successfully grafted onto the surface of SiO2. According to polarizing microscope images, it is clear that the size of the pure PBS crystals is much larger than that of the PBS/WPU@SiO2, and a large number of crystals are evenly distributed in the PBS/WPU@SiO2 composite. In addition, DSC and TGA results indicated that PBS/WPU@SiO2 composite films show excellent thermal properties. Meanwhile, the initial thermal decomposition temperature of PBS/WPU@SiO2 composite films is about 366–374°C. For the 10 wt% WPU@SiO2 reinforced PBS‐based composite films, the tensile strength reached the ultimate value (38.49 MPa), which is 32.04% higher than that of pure PBS. Based on its excellent mechanical and thermal properties, the PBS/WPU@SiO2 composites have a broad application prospect in the field of biodegradable materials.

Synthesis and Characterization of Bio-Based Poly(amide imide)s Derived from 11-Aminoundecanoic Acid and 1,10-Diaminodecane

Three diimide diacid (DIDA) monomers possessing different rigid groups (phenyl, biphenyl and diphenyl ether group) between two imide rings were prepared through the dehydration cyclization reaction of 11-aminoundecanoic acid and aromatic dianhydride. These DIDA monomers were polymerized with 1,10-diaminodecane to produce bio-based poly(amide imide)s (PAIs) by the ecofriendly and low-cost two-step polymerization method. All the PAIs have high thermal stabilities, and their initial thermal decomposition temperatures are above 400 °C at 5% weight loss. When the rigid group between two imide rings is changed from phenyl to diphenyl ether group, the glass transition temperature of PAI shows a decreasing trend from 54.7 °C to 42.4 °C, the tensile strength also reduces from 62.4 MPa to 49.5 MPa, but elongation at break increases from 3.7% to 6.8%. Moreover, the PAI with phenyl group between two imide rings is a semicrystalline polymer, while the PAI with biphenyl or diphenyl ether group is an amorphous polymer. It is a viable way to regulate the properties of PAIs by changing the structure of rigid group between two imide rings. Such bio-based PAIs with high thermal stabilities, low glass transition temperatures and good mechanical strength will provide great promise for their wider applications.

Improvement of Emulsion Stability and Plugging Performance of Nanopores Using Modified Polystyrene Nanoparticles in Invert Emulsion Drilling Fluids.

Drilling fluid invasion and pressure transmission caused by the development of micropores and fractures in shale oil and gas formations are the major factors contributing to wellbore instability during drilling using oil-based drilling fluids (OBFs). In this study, a modified polystyrene latex (MPL) material was synthesized through emulsion polymerization and was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), particle size analysis, scanning electron microscopy (SEM) observations, and contact angle testing. The influence of the MPL on the stability of a water-in-oil emulsion was analyzed via sedimentation observations and electrical stability tests. The effects of the MPL on the plugging mechanism of white oil and water-in-oil emulsions were evaluated using 0.1–1.0 μm micro-porous filtration films. The experimental results revealed that the MPL has a favorable thermal stability, with an initial thermal decomposition temperature of 363°C, a median particle size (D50) of 233 nm, and a three-phase contact angle of 103.5°. The MPL can enhance the sedimentation stability of an emulsion to a considerable extent and can improve the electrical stability (ES) of the emulsion, which is conducive to the stability of OBFs. Due to the deformability of the MPL, it has a wide range of adaptations for micro-scale pores and fractures. In both the white oil and water-in-oil emulsions, the MPL can reduce the filtration loss through microporous membranes with pore sizes of 0.1–1.0 μm to within 10 ml. This paper details the methodology of the synthesis of nanomaterials that can effectively plug a formation’s nanopores and fractures; thereby, stabilizing OBFs.

Developing thermally resistant and strong biobased resin from benzoxazine synthesized using green solvents

Developing thermally resistant and strong biobased resin from benzoxazine synthesized using green solvents is still an important and challenging issue. Herein, starting from biomasses, a new bifunctional benzoxazine monomer (ST-fa) was synthesized using green solvents (ethanol, ethyl acetate) during the whole synthesis and purification processes. The curing behavior and kinetics of ST-fa were studied with differential scanning calorimetry. Results show that ST-fa has outstanding process-ability reflected by lower melting point (102 °C), lower curing temperature (224 °C) and lower curing reaction activation energy. The investigation on the comprehensive performances of cured resin of ST-fa, coded as Poly(ST-fa), shows that Poly(ST-fa) not only has excellent thermal resistance (glass transition temperature: 325 °C; initial thermal decomposition temperature: 394 °C), but also has high tensile properties. These attractively high comprehensive properties of Poly(ST-fa) are derived from the structure with high crosslinking density and high rigidity formed by ring-opening reaction of bifunctional benzoxazine and the crosslinking of the furan group.

A long-life green fluorescent waterborne polyurethane-based Tb(III) ternary complex with UV shielding

A green fluorescent complex [Tb(PABA)3Phen] with fluorescence lifetime up to 0.837 ms was synthesized in ethanol by using p-aminobenzoic acid as the first ligand, o-phenanthroline as the second ligand and Tb3+ as the central ion. A long-life green fluorescent waterborne polyurethane-base Tb(III) ternary complex (Tb-WPU) with UV shielding was prepared by a modified acetone method using Tb(PABA)3Phen as chain extender. The structure and properties were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analyzer (TGA), fluorescence spectroscopy (FL), etc. The absolute value of Zeta potential increases with the increase of Tb(PABA)3Phen content, and all of them are greater than 40. Tb-WPU can effectively shield UV in the range of 200 nm–315 nm. With the increase of Tb(PABA)3Phen content, the fluorescence intensity of Tb-WPU increased gradually and the luminous life is up to an astonishing 1.375 ms. The initial thermal decomposition temperature of Tb-WPU is above 220 °C. In addition，Tb-WPU uses water as the dispersed phase and is suitable for environmental protection.

Poly (ethylene-butylacrylate-glycidyl methacrylate) reaction compatibilized poly (lactic acid)/poly (3-hydroxybutyrate-4-hydroxybutyrate) blends with enhanced mechanical property, biodegradability and thermal stability

Compatibilized poly (lactic acid)/poly (3-hydroxybutyrate-4-hydroxybutyrate) (PLA/P (3HB-co-4HB)) blends with poly (ethylene-butylacrylate-glycidyl methacrylate) (PTW) as compatibilizer were prepared by one-step melt blending in a twin-screw extruder. The mechanical properties, miscibility, phase morphology, thermal behavior, rheological behavior and degradation behavior of the blends were investigated. The reactive blending of epoxy groups in PTW and the carboxyl group or hydroxyl group in PLA/P (3HB-co-4HB) promotes the compatibility. The introduction of PTW enhances the initial thermal decomposition temperature of the P (3HB-co-4HB) phase in the PLA/P (3HB-co-4HB) blends and broadens the processable temperature range. Moreover, with the flexibility of PLA/P (3HB-co-4HB) blends greatly improved, their biodegradability has not been compromised. From the above perspectives, high-performance biodegradable PLA/P (3HB-co-4HB)/PTW displays promising prospects in fast-moving consumer goods and biomedical fields.

Study on the Design, Preparation, and Performance Evaluation of Heat-Resistant Interlayer-Polyimide-Resin-Based Neutron-Shielding Materials.

Polymers have an excellent effect in terms of moderating fast neutrons with rich hydrogen and carbon, which plays an indispensable role in shielding devices. As the shielding of neutrons is typically accompanied by the generation of γ-rays, shielding materials are developed from monomers to multi-component composites, multi-layer structures, and even complex structures. In this paper, based on the typical multilayer structure, the integrated design of the shield component structure and the preparation and performance evaluation of the materials is carried out based on the design sample of the heat-resistant lightweight polymer-based interlayer. Through calculation, the component structure of the polymer-based materials and the three-layer thickness of the shield are obtained. The mass fraction of boron carbide accounts for 11% of the polymer-based material. Since the polymer-based material is the weak link of heat resistance of the multilayer shield, in terms of material selection and modification, the B4C/TiO2/polyimide molded plate was prepared by the hot-pressing method, and characterization analysis was conducted for its structure and properties. The results show that the ball milling method can mix the materials well and realize the uniform dispersion of B4C and TiO2 in the polyimide matrices. Boron carbide particles are evenly distributed in the material. Except for Ti, the other elemental content of the selected areas for mapping is in good agreement with the theoretical values of the elemental content of the system. The prepared B4C/TiO2/polyimide molded plate presents excellent thermal properties, and its glass transition temperature and initial thermal decomposition temperature are as high as 363.6 °C and 572.8 °C, respectively. In addition, the molded plate has good toughness performs well in compression resistance, shock resistance, and thermal aging resistance, which allows it to be used for a long time under 300 °C. Finally, the prepared materials are tested experimentally on an americium beryllium neutron source. The experimental results match the simulation results well.

Explosion Test and Numerical Simulation of Coated Reinforced Concrete Slab Based on BLAST Mitigation Polyurea Coating Performance

The mechanical strength, thermal stability, thermal performance, and microstructure of Qtech T26 blast mitigation polyurea (T26 polyurea) were studied using quasi-static and dynamic mechanical experiments, thermogravimetric experiments, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) experiments, and contact explosion and non-contact explosion experiments with polyurea-coated reinforced concrete slabs. Additionally, the energy dissipation mechanism of the coating was analyzed. The blast mitigation ability and blast mitigation mechanism of T26 polyurea-coated reinforced concrete slabs were investigated by analyzing the macroscopic morphology of reinforced concrete slabs with or without coatings and the contact explosion simulation of polyurea-coated reinforced concrete slabs. The results showed that T26 polyurea exhibited a certain strain rate effect. Its initial thermal decomposition temperature reached 286 °C, and its thermal stability was good. After carbonization, carbon slag can form and adhere to the structural surface. The glass transition temperature Tgs of the soft segment was −44.9 °C, and the glass transition temperature Tgh of the hard segment was 36.5 °C, showing a certain amount of microphase separation morphology. After the explosion test, there was a small pit on the front surface of the coated reinforced concrete plate, and there was no damage on the back surface. The integrity of the plate was good. The uncoated reinforced concrete slab had a large crater on the front of the explosion surface, and the back of the explosion surface experienced explosion collapse, concrete crushing, and an overall loss of stability. The numerical simulation results showed that the failure mode of the coated plate was consistent with the test. The kinetic energy conversion rate of the uncoated reinforced concrete plate was 87.27%, and the kinetic energy conversion rate of the coated reinforced concrete plate was 95.36%. The T26 coating improved the kinetic energy conversion rate of the structure and improved the blast mitigation ability of the reinforced concrete plate structure.

3D Printing of Auxetic Metamaterials with High‐Temperature and Programmable Mechanical Properties

AbstractNegative Poisson's ratio mechanical metamaterials with typical auxetic behavior have great potential applications in aerospace and flexible electronics. However, the structure and properties of conventional mechanical metamaterials are fixed after fabrication, which greatly limit their applications. In recent years, some progress has been made in combining shape‐memory polymers (SMP) with 4D printing to develop auxetic metamaterials with programmable mechanical properties. Unfortunately the low‐temperature phase change of conventional SMP greatly hinders the further development of 4D printed mechanical metamaterials in the field of high‐temperature and high‐strength service. Here, the high‐performance polymer polyetheretherketone (PEEK) as the printing material is selected and a new mechanical metamaterial is prepared using fused deposition molding technology to program the material structure and properties by designing the structural parameters of the metamaterial mesh structure. In addition, thermal analysis shows that the printed samples have good thermal stability, including a phase change temperature of 170 °C, an initial thermal decomposition temperature greater than 500 °C, and qualified shape memory properties. Combining structural design with the shape memory properties of PEEK, reconfigurable metamaterial structure and properties are realized. Finally, 2D digital mesh structure is designed and fabricated with selective stretching strain positions and a stretchable circuit with constant resistance.

Mechanistic Investigation on the Initial Thermal Decomposition of Energetic Materials FOX-7 and RDX in the Crystal and Gas Phase: An MM/DFT-Based ONIOM Calculation.

Interpreting the initial decomposition mechanism is important for evaluating the thermal stability of explosives. In this study, we theoretically investigated the initial thermal decomposition reactions for two typical energetic materials, FOX-7 and RDX, in both the gas phase and crystal phase. Single molecular decomposition pathways in the gas phase are calculated using the density functional theory (DFT) method, and the crystal phase reactions are simulated through the MM/DFT-based ONIOM method. The calculation results indicate that the crystal environment has a significant influence on the initial thermal decomposition mechanism of FOX-7 and RDX. The cage effect induced by the crystal environment greatly confines molecular mobility and diffusion, rendering the generated small molecules to react with the remaining fragment and yield new decomposition channels compared with the gas phase condition. The crystal packing structures and intermolecular interactions (hydrogen bonds/π-π stacking) significantly increase the reaction barriers of FOX-7 and RDX, leading to the crystal phase reactions being more difficult to occur than in the gas phase. Since the practical application of explosives is mostly in the crystal state, it is important to consider the environmental effects on the initial decomposition reactions. The same insight can also be relevant for other energetic materials.

Development of a high temperature resistant nano-plugging agent and the plugging performance of multi-scale micropores

Nano-plugging agents (NPAs) are very important to stabilize the wellbore by reducing pressure transmission and drilling fluid invasion during drilling engineering. A functionalized polystyrene latex (FPL) was synthesized by micellar polymerization as a NPA for drilling fluids. The particle size and thermal stability of FPL were characterized by particle size analysis and thermogravimetric analysis (TGA). The experimental results showed that the initial thermal decomposition temperature of FPL was 310.6 ℃. The medium value of particle size distribution (D50) of FPL decreased from to 371–235 nm after aging at 220 ℃, indicating that FPL had good temperature resistance property. The plugging method and plugging performance of FPL for four filter media with pore sizes from 0.01 µm to 10 µm were introduced. FPL itself was difficult to plug the filter papers and ceramic filter disks, but FPL could reduce fluid loss of bentonite suspensions. SEM observation indicates that FPL could improve the quality of mud cakes and plug the small pores of ceramic filter disks. For microporous membranes and artificial mud cakes with low permeability, FPL aqueous suspensions had a good plugging performance. The plugging experimental results conformed well to the 2/3 bridging rule. This paper provides a good reference for the development of high temperature NPAs and the establishment of evaluation methods of NPAs.

Structure and properties of bast fiber of Alchornea Davidii Franch based on chemical alkali degumming and biological enzyme degumming

In this work, the effects of degumming treatment on the structure and properties of OS-BADF were discussed. Alkali degumming and biological enzyme degumming were used to obtain AD-BADF and BED-BADF respectively. Spinnability index, thermal property, macromolecular structure, bending property and antibacterial property of OS-BADF (Original Sample of Bast Fiber of Alchornea Davidii Franch), AD-BADF (Alkali Degummed Bast Fiber of Alchornea Davidii Franch), and BED-BADF (Biological Enzyme degummed Bast Fiber of Alchornea Davidii Franch) were tested. The surface morphology of the above three kinds of fiber was analyzed by SEM. The results showed that the main component of degummed OS-BADF was cellulose, and the fiber had stripes in longitudinal direction, and kidney ellipsoid, irregular polygon in the cross section. After degumming treatment, the fineness of fiber decreased obviously and reached the spinnability index. Non-cellulose substances in OS-BADF can be removed by degumming. SEM observation showed that AD-BADF and BED-BADF became smoother after degumming. Compared with AD-BADF, BED-BADF had finer linear density, better thermal stability and higher antibacterial property. The equivalent flexural modulus and flexural rigidity of AD-BADF and BED-BADF were decreased compared with OS-BADF. In particular, the equivalent flexural modulus and the flexural rigidity of BED-BADF were mostly reduced, which indicated that BED-BADF became thinner and softer. The initial thermal decomposition temperature and the highest thermal decomposition temperature of AD-BADF and BED-BADF had been significantly increased. And -OH (free group) decreased significantly after degumming treatment. The testing results of the antibacterial properties of the three blended fabrics showed that the antibacterial properties of AD-BADF and BED-BADF were improved. Compared with AD-BADF, the antibacterial properties of BED-BADF were improved significantly. On the one hand, this research can provide a basis for technological research for the development of ADF (Alchornea Davidii Franch) bast fiber blended yarn and its textile product development. On the other hand, because of the high mechanical properties of ADF bast fiber, it also provides new development idea for the development of natural high-performance fiber reinforcement composites.

Closed-Cell Rigid Polyimide Foams for High-Temperature Applications: The Effect of Structure on Combined Properties.

Closed-cell rigid polyimide foams with excellent thermal stability and combined properties were prepared by thermal foaming of a reactive end-capped polyimide precursor powder in a closed mold. The precursor powder was obtained by thermal treatment of a polyester-amine salt (PEAS) solution derived from the reaction of the diethyl ester of 2,3,3′,4′-biphenyl tetracarboxylic dianhydride (α-BPDE) with an aromatic diamine mixture of p-phenylenediamine (PDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) in the presence of an end-capping agent (mono-ethyl ester of nadic acid anhydride, NE) in an aliphatic alcohol. The effect of polymer mainchain structures on the foaming processability and combined properties of the closed-cell rigid polyimide foams were systematically investigated. The polyimide foams (100–300 kg/m3) with closed-cell rates of 91–95% show an outstanding thermal stability with an initial thermal decomposition temperature of ≥490 °C and a glass transition temperature of 395 °C. Polyimide foams with density of 250 kg/m3 exhibited compression creep deformation as low as 1.6% after thermal aging at 320 °C/0.4 MPa for 2 h.

Liquid oxygen compatibility of epoxy matrix and carbon fiber reinforced epoxy composite

Liquid oxygen compatibility is the key to evaluating whether carbon fiber reinforced epoxy composites (CF-composite) can be used in liquid oxygen environment. In this work, DOPO-PGE was prepared to improve the liquid oxygen compatibility of epoxy resin and CF-composite. The FTIR, 1H and 31P NMR spectrum was used to confirm the chemical structure of DOPO-PGE. According to the UL94 test results, TG-FTIR, char residue analysis, and XPS analysis, the mechanism of DOPO-PGE affecting the liquid oxygen compatibility of epoxy resin is mainly attributed to the fact that the radical PO released in the initial thermal decomposition stage of DOPO-PGE/epoxy can capture the highly active radical H, O, HO and terminated the radicals’ chain exothermic reactions. The CF-composites show better liquid oxygen compatibility than epoxy resin matrix. However, the long-term liquid oxygen immersion can deteriorate the liquid oxygen compatibility of CF-composites.

Molecular Dynamics Simulations of the Thermal Decomposition of 3,4-Bis(3-nitrofurazan-4-yl)furoxan.

When stimulated, for example, by a high temperature, the physical and chemical properties of energetic materials (EMs) may change, and, in turn, their overall performance is affected. Therefore, thermal stability is crucial for EMs, especially the thermal dynamic behavior. In the past decade, significant efforts have been made to study the thermal dynamic behavior of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF), one of the new high-energy-density materials (HEDMs). However, the thermal decomposition mechanism of DNTF is still not specific or comprehensive. In this study, the self-consistent-charge density-functional tight-binding method was combined with molecular dynamics (MD) simulations to reveal the differences in the thermal decomposition of DNTF under four heating conditions. The O–N (O) bond would fracture first during DNTF initial thermal decomposition at medium and low temperatures, thus triggering the cracking of the whole structure. At 2000 and 2500 K, NO2 loss on outer ring I is the fastest initial thermal decomposition pathway, and it determines that the decomposition mechanism is different from that of a medium-low temperature. NO2 is found to be the most active intermediate product; large molecular fragments, such as C2N2O, are found for the first time. Hopefully, these results could provide some insights into the decomposition mechanism of new HEDMs.