Initial Thermal Decomposition Temperature Research Articles

Novel resveratrol-based hyperbranched epoxy resin suitable for comprehensive modification of epoxy resins

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A2-type monomer) and resveratrol (B'B2-type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (KIC), critical crack propagation energy release rate (GIC), flexural strength, tensile strength, storage modulus, glass transition temperature (Tg), and initial thermal decomposition temperature (Td5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER.

Influence of Complex Plasticizer on Plasticizing Effects and Rheological Properties of Plasticized Poly(Vinyl Alcohol)

AbstractPoly(vinyl alcohol) (PVA) was modified using D‐mannitol (DM) and 1‐butyl‐3‐methylimidazole bromide (BMIMBr) as the complex plasticizer (DB), and PVA/DB composite was prepared. The plasticizing effect of DB on PVA was studied by Fourier transform infrared spectroscopy (FT‐IR), differntial scanning calorimetry (DSC), thermos gravimetric analysis (TGA) and melt flow indexer (MI). FT‐IR analysis indicated that Br− of BMIMBr and OH of DM could form H‐bonds with OH of PVA. With the increase of DB, the melt temperature (Tm2) and crystallization temperature (Tc1) of PVA/DB composite decreased, the initial thermal decomposition temperatures (Td), thermal processing window (ΔT) and MI values increased respectively. Based on above studies, the influence of DB content on rheological properties of PVA/DB composite was investigated by the capillary rheometer. The result displayed that apparent viscosity of PVA/DB composite decreased with increasing DB content, shear rate and measured temperature. The non‐Newtonian index (n) increased and structural viscosity index (Δη) decreased with the increase of measured temperature and DB. The viscous flow activation energy (Eη) decreased as the shear rate and DB content increased. When the measured temperature, DB content and shear rate were in the range of Tm2+30 −Tm2+35 °C, 40–50 wt% and 764.8–1504.9 s−1, respectively, the spinnability of PVA/DB composite was optimal, which will lay a theoretical foundation for the exploration of melt spinning process in the future.

Synthesis of a silicon‐containing cyclotriphosphazene derivative for flame‐retardant modification of epoxy resin

AbstractAlthough epoxy resin (EP) has been widely used in many fields, it is still urgent to effectively improve its flame retardancy by halogen‐free strategies. Herein, a silicon‐containing cyclotriphosphazene derivative (HEP‐Si) was synthesized by nucleophilic substitution and silicon‐hydrogen addition reaction using eugenol, hexachlorophosphazene, and triethylsilane as raw materials. Then it served as a halogen‐free flame retardant for EP/4,4′‐diaminodiphenylmethane system, and its performance was compared with that of commercial flame retardant hexaphenoxycyclotriphosphazene (HPP). The results showed that although the initial thermal decomposition temperature (T5%) of the cured products of EP/HEP‐Si was slightly lower than that of pure EP, the T5% did not decrease further as the amount of HEP‐Si increased, indicating that the good thermal stability was maintained. In addition, the char yield of the cured products of EP/HEP‐Si was significantly increased (more than 20 wt%) compared to that of pure EP. The cured EP with the addition of HPP and HEP‐Si both achieved a V‐0 rating in UL‐94 vertical burning test at 0.5 wt% phosphorus content, while the limiting oxygen index of the EP/HEP‐Si system was higher, reaching 33.2%. From the cone calorimetric test results, the peak heat release rate, total heat release, and total smoke production of the cured products of EP/HEP‐Si decreased by 61.5%, 37.1%, and 26.2%, respectively, compared with that of pure EP. The cured EP/HEP‐Si materials also exhibited good thermal mechanical and mechanical properties. Therefore, HEP‐Si is suggested to be a promising P/N/Si‐containing halogen‐free flame retardant for EP.This article is protected by copyright. All rights reserved.

The Influence of Solar Ageing on the Compositions of Epoxy Resin with Natural Polyphenol Quercetin.

Epoxy resin compositions are used in modern railways, replacing other materials. However, epoxy composites in public transport are subject to many requirements, including that they should be flame retardant and resistant to weather conditions. The aim of the research was to analyse the resistance to solar ageing of epoxy resin composites containing flame retardants and the addition of the natural stabilising substance-quercetin. The homogeneity of the samples (optical microscopy and FTIR spectroscopy) and their thermal stability (TGA thermogravimetry) were analysed. The T5 temperature, which is the initial temperature of thermal decomposition of the samples, was 7 °C higher for the epoxy resin containing quercetin, so the material with polyphenol was characterised by better thermal resistance. Changes in material properties (hardness, surface energy, carbonyl index, colour) after 800 h solar ageing were investigated. The tensile tests on materials were executed for three different directions before and after ageing effect. The samples showed good resistance to degradation factors, i.e., they retained the functional properties (hardness and mechanical properties). However, analysis of carbonyl indices and surface energies showed that changes appeared in the composites after solar ageing, suggesting the beginning of material degradation. An approximately 3-fold increase in the polar component in epoxy resin compositions (from approximately 3 mN/m to approximately 11 mN/m) is associated with an increase in their hydrophilicity and the progress of ageing of the materials' surface. The obtained results are an introduction to further research on the long-term degradation processes of epoxy resins with plant stabilisers.

Effect of Fluoroalcohol Chain Extension Modified HTPB Binder on the Combustion Performance of Aluminized Propellants

To enhance both the mechanical properties of hydroxyl-terminated polybutadiene (HTPB) binder and the combustion efficiency of aluminized propellants, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol (OFHD) was employed as a chain extender to impart mechanical regulation to the HTPB binder. Mechanical testing showed that the mechanical properties of fluoride-modified HTPB polyurethane (FPU) were significantly improved: the peak tensile strength of the optimized samples reached 1.99 MPa, and the elongation at break attained 486%. The structural characterization of the FPUs was conducted using Fourier transform infrared (FTIR) spectroscopy. Thermogravimetry-mass spectrometer (TG-MS) analysis revealed that the initial thermal decomposition temperature of the FPU shifted from 170 °C to 162 °C, accompanied by the release of fluorine-containing fragments during decomposition. Analysis of the combustion residue indicated that the addition of OFHD can reduce the agglomeration of aluminum (Al) powder in aluminized propellants. Dynamic pressure characteristics results showed an augmented pressurization rate under argon and oxygen atmospheres, increased by 18.67% and 37.29%, respectively. Heat release tests indicated that the aluminized propellants with the addition of OFHD had a higher combustion heat, being increased by 6.57%. The binder system is expected to be applied in aluminized propellants to improve the mechanical properties and combustion efficiency of Al powder.

Novel four-in-one intumescent flame retardants for polypropylene: Synthesis, characterization and properties

To address the shortcomings of traditional intumescent flame retardants (IFRs), a novel four-in-one IFR (M [APP/NiCo2O4]) was constructed for the first time. It integrates acid source, gas source, carbon source (crosslinking β-CD), and synergistic agent (NiCo2O4 nanoparticles) into a single entity by a co-encapsulation technology. Under the loading of 20 wt%, its flame retardant performance was significantly better than that of simple mixed flame retardants, and it could increase the limiting oxygen index of polypropylene (PP) from 18 to 30.2 and pass the UL-94 V-0 rating. At the same time, it could reduce the peak of heat release rate, total heat release, and peak of CO production of PP by 77%, 22%, and 80%, respectively, showing excellent flame retardant performance. The excellent flame retardant performance is mainly because the synergist NiCo2O4 nanoparticles in the four-in-one flame retardant can easily combine and efficiently interact with the acid source, carbon source, and gas source in the intumescent flame retardant to form a more stable protective char residue. In addition, the crosslinking β-CD shell enhances both the water resistance and initial thermal decomposition temperature of PP containing the four-in-one IFR compared to PP with simple mixed control samples. After 72 h of water resistance test, it can still maintain the UL-94 V-0 rating. The presence of the crosslinking β-CD shell also improves the compatibility of the four-in-one flame retardant in PP, and its adverse effects on the mechanical properties of PP are also significantly smaller than those of the mixed control sample.

Effect of Starch Plasticization on Morphological, Mechanical, Crystalline, Thermal, and Optical Behavior of Poly(butylene adipate-co-terephthalate)/Thermoplastic Starch Composite Films.

Starches plasticized with glycerol/citric acid/stearic acid and tributyl 2-acetylcitrate (ATBC), respectively, were processed with poly (butylene adipate-Co-terephthalate (PBAT) via extrusion and a film-blown process. All the composite films were determined for morphology, mechanical, thermal stability, crystalline, and optical properties. Results show that the most improved morphology was in the 30% glycerol plasticized PBAT/thermoplastic starch (TPS) composite films, characterized by the smallest and narrowest distribution of TPS particle sizes and a more uniform dispersion of TPS particles. However, the water absorption of PBAT/TPS composite films plasticized with glycerol surpassed that observed with ATBC as a plasticizer. Mechanical properties indicated insufficient plasticization of the starch crystal structure when using 10% ATBC, 20% ATBC, and 20% glycerol as plasticizers, leading to poor compatibility between PBAT and TPS. This resulted in stress concentration points under external forces, adversely affecting the mechanical properties of the composites. All PBAT/TPS composite films exhibited a negative impact on the initial thermal decomposition temperature compared to PBAT. Additionally, the haze value of PBAT/TPS composite films exceeded 96%, while pure PBAT had a haze value of 47.42%. Films plasticized with 10% ATBC, 20% ATBC, and 20% glycerol displayed lower transmittance values in the visible light region. The increased transmittance of films plasticized with 30% glycerol further demonstrated their superior plasticizing effect compared to other PBAT/TPS composite films. This study provides a simple and feasible method for preparing low-cost PBAT composites, and their extensions are expected to further replace general-purpose plastics in daily applications.

A facile method to prepare biobased flexible polydimethylsiloxane − Benzoxazine resin: Dielectric properties and high heat resistance

For the benefit of meet the industrial demand of integrated circuits for low dielectric constant (k) and the environmental requirements of sustainable development, it is important to prepare biobased benzoxazine resin with low k and high heat resistance by solvent-free method. In this paper, the biobased monomer V-fa containing aldehyde group was synthesized by biobased raw materials furfurylamine and vanillin, and then reacted with amino-terminated polydimethylsiloxane (PDMS) to prepare benzoxazine monomer V-fa-pdms containing schiff base structure by a solvent-free method. Then, the monomer was cured to obtain biobased benzoxazine resin poly(V-fa-pdms), and the heat resistance, mechanical and dielectric properties of poly(V-fa-pdms) were studied. The results indicate that the resin exhibits excellent thermal stability and toughness by combining benzoxazine and PDMS reasonably. The initial thermal decomposition temperature (Tdi, 5% thermogravimetric loss) is 387 °C, and the material also exhibits excellent dielectric properties. When the frequency increases from 1 Hz to 1 MHz, the k of the material decreases from 2.71 to 2.60, and the fluctuation range of dielectric loss is 0.0051–0.0049. With the increase of frequency, both k and dielectric loss show a downward trend. At the same time, the material shows good corrosion resistance in commonly used solvents. These excellent properties of poly(V-fa-pdms) are due to the existence of a high cross-linked network structure formed by multiple cross-linking sites in the polymer network and the combined effect of low k and high heat-resistant PDMS components.

Thermal decomposition and combustion performance of the organic-inorganic hybrid crystal structure oxidant DAN-2

In this paper, we investigated the potential use of a new organic-inorganic hybrid crystal structure based on KNO3 in ignition compositions. H2dabco[K(NO3)3] (DAN-2) with organic-inorganic hybrid crystal structure is synthesized through intermolecular assembly technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to detect the crystal morphology, structure and molecular structure of DAN-2, which has a regular cubic structure. Experimental data were obtained using thermogravimetric/differential scanning calorimetry (TG-DSC), closed bomb test and high-speed photography, which were then used to study and analyze the thermal decomposition properties and combustion properties of DAN-2. The initial thermal decomposition temperature of DAN-2 was low (194 °C) and the activation energy of the thermal decomposition was 154 kJ/mol. Possible thermal decomposition mechanisms are further discussed and proposed. This research pushed forward the application of organic-inorganic hybrid crystal structure oxidant DAN-2 in ignition system.

Cycloaliphatic epoxy-functionalized polydimethylsiloxanes for comprehensive modifications of epoxy thermosets

Polydimethylsiloxane (PDMS) are known as a class of efficient modifiers for epoxy thermosets, but the simultaneous improvement in thermal stability, thermomechanical and mechanical properties remain a challenge. Herein, we report a cycloaliphatic epoxy-functionalized polydimethylsiloxane (PDMS-CE) with a designed epoxy value for comprehensive modifications of diglycidyl ether of bisphenol A (DGEBA)/methylhexahydrophthalic anhydride (MeHHPA) thermosets. Compared to neat epoxy thermoset, the 4 wt% PDMS-CE modified epoxy thermoset showed a 79 %, 120 % and 503 % increase in flexural strength, impact strength and fracture toughness, respectively, as well as a slight increase in the initial thermal decomposition temperature (Td5%) and glass transition temperature (Tg), and a desirable decrease in the dielectric constant and water absorption rate. This comprehensive modification performance was caused by the combined effects of crosslinking density improvement, rigid cycloaliphatic structure, as well as the flexible PDMS chains.

Synthesis and properties of low viscosity robust biobased benzoxazine resin

The preparation of biobased benzoxazine resin with low melting point and low curing temperature has important significance for environmental sustainable development and practical application in industrial field. In this paper, biobased benzoxazine monomer HA-fa was synthesized from p-hydroxybenzyl alcohol, paraformaldehyde and furfurylamine, and H-fa were prepared by Mannich reaction of hordenine with paraformaldehyde and furfurylamine. The two benzoxazine organic molecules showed different thermodynamic behaviors. HA-fa and H-fa were liquid at room temperature. The viscosity of HA-fa and H-fa at room temperature (25 °C) were 1.683 Pa/s and 0.602 Pa/s, and the curing peak temperature was 220 °C and 208 °C, respectively, both organic molecules showed excellent processability. Then poly(HA-fa) and poly(H-fa) were prepared by two organic molecules through thermal curing procedure. The comprehensive properties of two benzoxazine resins were investigated. The glass transition temperature (Tg) of poly(H-fa) is 223 °C, while the Tg of poly(HA-fa) has two peak temperatures, 225 °C and 281 °C, respectively. This may be due to the existence of two different crosslinking networks in the resin, which leads to the phase separation of the resin, thus reflecting two Tg. Meanwhile, the initial thermal decomposition temperatures Tdi of poly(HA-fa) and poly(H-fa) were 330 °C and 331 °C, respectively, showing excellent thermal stability of the newly prepared resin. In addition, poly(HA-fa) and poly(H-fa) have both high storage modulus (3174 MPa and 2608 MPa, respectively, measured at 25 °C) and good flexural strength (121 ± 2.7 MPa and 96 ± 3.6 MPa). Among the two resins, poly(HA-fa) showed more excellent comprehensive properties, which may be based on the joint action of resin multi-crosslinking sites and hydrogen bond crosslinking network.

Preparation and Properties of Phenolic Epoxy Modified Silicone Resin

Phenolic epoxy resin (F51) was first reacted with silane coupling agent (3-aminopropyl)triethoxysilane (KH550) to form a silanized phenolic epoxy resin (SPER); then the SPER was copolymerized with methylphenyl silicone resin (MPS) to synthesize phenolic epoxy modified silicone copolymer (PEMSC). The chemical structure of the PEMSC was characterized by FT-IR. The results of tensile strength and shear strength measurements indicated that the successful introduction of F51 significantly improved the mechanical and adhesive properties of the PEMSC; compared with the PEMSC with 10 phr of F51 added, the tensile strength and shear strength of the PEMSC with 40 phr increased by 8.5 and 3.5 times respectively. The TGA and DTGA analysis showed that the initial thermal decomposition temperature and the residual weight of PEMSC at 800 °C decreased compared to MPS, but the temperature corresponding to the maximum thermal decomposition rate in the second stage increased. Qualitative analysis was conducted on the decomposition products of PEMSC using gas chromatography coupled with mass spectrometry (GC-MS). The results showed that the relative content of aromatic hydrocarbons and their derivatives in the decomposition products of PEMSC was 64.11%, and the relative content of cyclic trimers and higher cyclomers was 20.41%.

Polyurethane Acrylate Oligomer (PUA) Microspheres Prepared Using the Pickering Method for Reinforcing the Mechanical and Thermal Properties of 3D Printing Resin

Some photosensitive resins have poor mechanical properties after 3D printing. To overcome these limitations, a polyurethane acrylate oligomer (PUA) microsphere was prepared using the Pickering emulsion template method and ultraviolet (UV) curing technology in this paper. The prepared PUA microspheres were added to PUA-1,6-hexanediol diacrylate (HDDA) photosensitive resin system for digital light processing (DLP) 3D printing technology. The preparation process of PUA microspheres was discussed based on micromorphology, and it was found that the oil-water ratio of the Pickering emulsion and the emulsification speed had a certain effect on the microsphere size. As the oil-water ratio and the emulsification speed increased, the microsphere particle size decreased to a certain extent. Adding a suitable proportion of PUA microspheres to the photosensitive resin can improve the mechanical properties and thermal stability. When the modified photosensitive resin microsphere content was 0.5%, the tensile strength, elongation at break, bending strength, and initial thermal decomposition temperature were increased by 79.14%, 47.26%, 26.69%, and 10.65%, respectively, compared with the unmodified photosensitive resin. This study provides a new way to improve the mechanical properties of photosensitive resin 3D printing. The resin materials studied in this work have potential application value in the fields of ceramic 3D printing and dental temporary replacement materials.

Development of a Low-Molecular-Weight Filtrate Reducer with High-Temperature Resistance for Drilling Fluid Gel System.

Currently, conventional polymeric filtrate reducers with high-temperature resistance for use in drilling fluids have high molecular weights, which greatly affects the rheological properties. Therefore, to address the challenges in regulating the rheology and filtration performance of high-density drilling fluids at high temperatures, it is essential to develop low-molecular-weight filtrate reducers with high-temperature resistance. In this study, a low-molecular-weight filtrate reducer with high-temperature resistance (LMF) was prepared via free radical polymerization from acrylamide and 2-acrylamido-2-methyl-1-propanesulfonic acid as monomers, tertiary dodecyl mercaptan as a chain transfer agent, and ammonium persulfate as the initiator. LMF was then characterized by infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The obtained filtrate reducer exhibits a weight-average molecular weight (Mw) of 3819 and an initial thermal decomposition temperature of 300.7 °C, indicating good thermal stability. The effects of LMF dosage, temperature, and NaCl dosage on the rheology and filtration performance of mud samples were also investigated, and the mechanism of action was revealed by zeta potential, particle size distribution, scanning electron microscopy, and adsorption measurements. The results reveal that LMF increases the mud sample viscosity and reduces its filtration. For example, the filtration of the mud sample with 2 wt% LMF was 7.2 mL, a reduction of 70% compared to that of a blank mud sample. Further, after aging at 210 °C for 16 h, the filtration of the same sample was 11.6 mL, and that of a mud sample with 2 wt% LMF and 35 wt% NaCl after aging at 180 °C for 16 h was 22 mL. Overall, we have reported a scheme to prepare a low-molecular-weight filtrate reducer with high-temperature resistance and superior filtrate-reducing effects, laying the foundation for the investigation and development of low-molecular-weight filtrate reducers.

A strategy for synthesis of silane terminated polyether triggered by click reaction and its application in preparation of modified silane sealants

A new hydroxy-silane coupling agent was synthesized from 3-butene-1-alcohol and mercaptopropyl-3-methoxysilane based on a click reaction between double bonds and sulfhydryl groups and was successfully used in the synthesis of silane-modified polyether (STPE). The effect of molecular weight of polypropylene glycol (PPG) on the properties of silane-modified polyether was studied. It was found that with the increase in PPG molecular weight, the initial thermal decomposition temperature and hardness of STPE elastomers decreased, but the molecular structure hardly changed. In addition, with the increase in molecular weight, the elongation at break of the elastomer will gradually increase, but the tensile strength of the elastomer does not change much. When the molecular weight reaches 20 000 g/mol, the resin with a viscosity of 1.6 × 105 mPa s can be obtained, and the elongation at break of the cured elastomer reaches 383.4% and the tensile strength is 0.25 MPa. After the STPE resin was prepared into a silane modified sealant, the tensile strength reached 1.31 MPa and the elongation at break reached 406.2%, which had the best mechanical properties among the prepared sealants. This shows that the sealant prepared from high molecular weight resin has stronger mechanical properties, which provides a new idea for the preparation of sealants.

Bismaleimide resin co‐modified by allyl ether of resveratrol and allyl ether of eugenol‐grafted polysiloxane with enhanced toughness, heat resistance, and flame retardancy

AbstractModifying bismaleimide (BMI) resin to improve its toughness and flame retardancy without sacrificing the glass transition temperature (Tg) and thermal decomposition stability is still a challenge. In this study, we employed the allyl ether of resveratrol (AER) and eugenol allyl ether grafted polysiloxane (PMES‐Allyl) to co‐modify BMI resin. For the BMI/AER/PMES‐Allyl (BAPA) resin, the content of PMES‐Allyl was 15 wt%, and the molar ratio of maleimide and allyl groups was controlled as 1:0.8. Compared to commercial 2,2′‐diallyl bisphenol A modified BMI (BD) resin, the BAPA resin exhibited superior thermal properties after curing, due to the role of AER in improving the crosslinking density and chain rigidity of the network. The cured BAPA resin had a Tg more than 380°C, and its initial thermal decomposition temperature (Td5%) and char yield (Y800°C) reached 424.8°C and 46.4%, respectively. Meanwhile, PMES‐Allyl as a rubber phase could effectively improve the toughness of the cured resin. The impact strength of the cured BAPA resin was 15.2 kJ/m2. Moreover, the two modifiers both helped to improve the flame retardancy of the material. Compared with the cured BD resin, the cured BAPA resin showed a decrease of peak heat release rate (PHRR), total heat release (THR), and maximum average rate of heat emission (MARHE) by 25.5%, 35.5%, and 31.5%, respectively. Its total smoke production (TSP) was only 35.6% of that of the cured BD resin. In addition, the cured BAPA resin also displayed a lowered water absorption and improved thermal aging resistance. Therefore, it is suggested to be a promising and high‐performance thermosetting resin for cutting‐edge applications.

Unidirectional infiltrated PI/SiO2 composite aerogels with a confined reinforcing strategy for integrated thermal and acoustic insulation

It is of great significance to develop integrated thermal insulation and noise reduction materials for energy saving and pollution control. As a nanoporous material, aerogels have excellent thermal and acoustic properties, however, the thermal stability of organic aerogels is insufficient, and the mechanical properties of inorganic aerogels limit their practical application. Herein, we designed a confined reinforcing strategy for organic-inorganic composite aerogels with high strength and excellent acoustic insulation properties. A directional freezing technology was utilized to control the pore structure of a polyimide (PI) aerogel, and then a continuous SiO2 aerogel was filled in the unidirectional pore channels, forming a double-network structure consisting of both PI and SiO2 aerogels. The results showed that the compressive strength of the composites was 1.83 MPa at 10% strain, the initial thermal decomposition temperature was about 530 °C, and the lowest thermal conductivity was 22.37 mW m−1·k−1 at radial direction. Moreover, the average sound transmission loss (STL) of the composites with an 18 mm thickness was 30–33 dB in the range of 500–6300 Hz. This confined reinforcing strategy can safeguard fragile aerogels while maximize their inherent characteristics, which offers a novel approach to the creation of multi-functional aerogel composites.

Preliminary characterization and thermal evaluation of a direct contact cascaded immiscible inorganic salt/high-density polyethylene as moderate temperature heat storage material

The present work assesses the direct contact cascaded immiscible phase change material (PCM) for solar heat storage systems (SHSS) in water heating applications. The direct contact cascaded immiscible PCM uses ternary salt mixture (TSM) and high-density polyethylene (HDPE). Improvement on phase behavior and thermal properties are obtained for the direct contact cascaded immiscible TSM/HDPE. The plasticity effect of HDPE leads to a stable phase transition of the mixture with the lowest supercooling degree by 0.9 °C. The initial thermal decomposition temperature for TSM and HDPE is above 400 °C, which is suitable for moderate temperature operation of SHSS. The immiscibility between TSM and HDPE leads to a multistep phase transition between 110.2 and 139.6 °C. The phase behavior during the liquid-solid transition demonstrates the lowest temperature gradient of 13.9 °C, implying a steady phase transition. It allows the stored heat can be released effectively without causing significant volume expansion of the TSM. Moreover, the enthalpy of fusion for TSM/HDPE is increased, making it favorable as solar thermal energy for water heating applications in SHSS.

High-strength, self-reinforcing and recyclable multifunctional lignin-based polyurethanes based on multi-level dynamic cross-linking

The preparation of lignin-based polyurethanes with excellent mechanical properties and recyclability remains extremely challenging because of the poor compatibility of lignin and matrix. Inspired by the multiple structures of spider silk and pearl layers, high-strength, heat-resistant and recyclable lignin-based polyurethanes (LPUs) were prepared by introducing weak hydrogen bonds, strong hydrogen bonds and dynamic silyl ether covalent bonds. Multiple hydrogen bonds provided a large energy dissipation mechanism. The covalent linkage between lignin and matrix promoted their compatibility and formed a robust cross-linking network. Depending on the multi-level dynamic interactions, the prepared elastomer exhibited a mechanical strength of 73 MPa, which was 1.9 times higher than that of the blank sample, with an initial thermal decomposition temperature of 310.5 °C and a good recyclability. Especially, the mechanical strength of LPUs was up to 99 MPa after mechanical training. In addition, the abundant conjugated structure of lignin endowed LPUs with an excellent photothermal conversion ability. Under the irradiation of NIR light with 4000 w m−2, the surface temperature increased to 95 °C within two minutes, exhibiting a stable photothermal performance even after 6 cycles. This work showed the application prospects of LPUs in the fields of high strength engineering materials and photo-induced actuators.

Synthesis and characterization of cyano-terminated bisphenol AF-type polyarylene ether nitrile

Four novel phthalonitrile-capped polyarylene ether nitrile oligomers containing trifluoromethyl groups (FPEN-Ph) with different molecular weight were designed and synthesized by adjusting the ratio of bisphenol AF (BPAF) and 2,6-dicholorobenzonitrile (DCBN). The molecular structure of FPEN-Ph oligomers were characterized and analyzed by FTIR, 1HNMR and Gel permeation chromatography. Their curing behaviors were studied by Differential scanning calorimetry and rheological tests, and curing kinetics were also discussed by gel method in detail. The glass fiber cloth reinforced FPEN-Ph composites (FPEN-Ph/GF) had flexural strengths of 415.9–497.5 MPa, shear strengths of 34.5–50.5 MPa, and glass transition temperatures ( Tgs) in the range of 211.3°C–416.6°C. The initial thermal decomposition temperatures ( T5%) of various FPEN-Ph cured products were higher than 500°C under nitrogen. Meanwhile, Fracture morphologies showed that the GF/FPEN-Ph composites had excellent interfacial adhesion between FPEN-Ph matrix and GF reinforcement. Herein, the FPEN-Ph resin could be a good candidate for high-performance polymeric composites and the advanced FPEN-Ph/GF composites can be used under high temperature environment.