Excellent Thermal Insulation Properties Research Articles

A novel “reinforcing-foaming-recovering” strategy for achieving thermally insulating green foams with ultrafast degradation

Lightweight porous materials have garnered increasing attention in application domains of intelligent construction and flexible thermal insulation, owing to their customizable 3D porous structures and outstanding performances. Nonetheless, the severe environmental pollution resulting from the accumulation of non-degradable plastic waste in the ecosystem has sparked significant interest in developing bio-degradable thermal insulation foams. The preparation of biodegradable foam, however, typically requires operating specialized equipment for long periods under extreme conditions, which diminishes its environmental friendliness as claimed. Herein, we present a pioneering "Reinforcing-Foaming-Recovering" strategy to achieve ultralight and recyclable green foams with excellent thermal insulation properties. This innovative strategy, involving materials reinforcing and low-pressure foaming complemented by nitrogen-assisted gas recovering enables the preparation of low-density (0.08 g/cm3) biodegradable foams with restricted shrinkage ratio (<5%). Thanks to the easy-to-control foaming method, combined with the improved 3D network cellular structures caused by nitrogen-assisted gas exchange, the achieved green foams exhibit favorable thermal insulation (39.8 mW/m·K) and superior biodegradation efficiency (11.5%/2 months). The approach of energy-efficient nitrogen-assisted low-pressure foaming of degradable polymers offers a promising and practical solution for producing eco-friendly and multifunctional porous materials with economic advantages.

Preparation and properties of phosphogypsum-based calcined coal gangue composite cementitious materials

Phosphogypsum (PG) and coal gangue (CG), as the largest solid waste today, the effective utilization of this part of the resource can help to alleviate environmental pollution and resource waste. The aim of this study was to utilize the excellent thermal insulation properties of original PG and the regulation of hydration products by calcined coal gangue (CCG) to produce phosphogypsum-based calcined coal gangue composite cementitious materials (PBCM). The optimal ratio of PBCM was studied through a combination of mechanical properties and thermal insulation properties. Finally, the effect of the foam factor is further investigated. The results show that: CCG can be used as a silicon-rich material with gelling properties to regulate the hydration products generated. The test block with a foam content of 8% has the best performance, with a compressive strength of 2.53MPa and a thermal conductivity of 0.1427W/(m·K). The optimal experimental scheme obtained from the orthogonal test was as follows: The optimal experimental design obtained from orthogonal experiments was as follows: PG, quicklime (QL), sulfoaluminate cement (SAC) and foam contents were 45%, 8%, 8% and 8%, respectively. The CCG: cement and water-solid ratios (W/S) were 3:7 and 0.275, respectively. The development of high-performance composites presented in this study is conducive to enhancing waste utilization and provides a novel approach as well as a theoretical foundation for insulating building materials in practical engineering applications.

Industrial Scale Sea-Island Melt-Spun Continuous Ultrafine Fibers for Highly Comfortable Insulated Aerogel Felt Clothing.

Aerogels are most attractive for thermal clothing. However, mechanical fragility and structural instability restrict their practical applications. These issues are overcome by developing industrial scale sea-island melt-spun ultrafine fibers with large and uniform length-to-diameter as building blocks, which are assembled into aerogel felts with corrugated lamellar structure through freeze-shaping technology. These aerogels possess excellent mechanical properties to meet fabric elasticity and comfort needs, including super-flexibility (25% tensile strain, 95% compression, 180° bending performance) and fatigue resistance of over 10,000 cycles. The aerogels are also self-cleaning, waterproof, breathable, and flame-retardant, making them suitable for application requirements in extreme environments. Moreover, the obtained aerogel felt clothing exhibits excellent thermal insulation properties close to that of dry air, and is only one-third as thick as down clothing with similar insulating properties. Expanding sea-island melt-spun fiber to construct aerogel in this strategy provides scalable potential for developing multifunctional insulating aerogel clothing.

A novel ultra-light bio-based fiberboard from mexican feather grass for thermal and acoustic insulation in green building construction applications

The use of natural fibers as raw materials for insulation fiberboard production is emerging as a strategy to replace wood fibers. This study developed an ultralightweight natural fiber insulation core fiberboard (CFB) with high mechanical strength, hygroscopic resistance, and excellent acoustic and thermal insulation properties. This study examined the production of CFB, which utilizes Mexican feather grass fibers with an epoxy resin binder across a range of densities of 0.18–0.36 g∙cm−3. Furthermore, the impact of incorporating a reinforcing skin layer of woven glass fibers on the core fiberboard's physical, mechanical, acoustic, and thermal properties was evaluated. All the fiberboard samples exhibited excellent thermal conductivity values (0.048–0.057 W/mK), which increased with increasing panel density (0.18–0.36 g∙cm−3). In addition, all of them displayed superior mechanical properties following the ASTM C208 standard. In terms of climatic resistance of the fiberboards, the results displayed excellent water resistance, exhibiting minimal humidity content (<5 %), thickness swelling (<6.5 %), and a hydrophobic surface, as indicated by the high-water contact angle (>121.96 at 30 s). Sound reduction exhibited a frequency-dependent tendency, with denser and sandwich fiberboards showing greater sound reduction of up to 27.9–36.56 dB at 3150 Hz for CFB-0.36 and SFB-0.52, respectively. Following ASTM C208, both core fiberboards and those coated with woven glass fiber skins (sandwich fiberboards, SFB) met the thermomechanical property requirements for regular and structural wall sheathing applications, respectively. These findings highlight the potential of Mexican feather grass as a bio-based alternative to wood, enabling the production of eco-friendly ultralightweight fiberboards with excellent thermomechanical properties suitable for building construction, such as regular and structural wall sheathing applications and ceiling decorations.

Lightweight, ultrahigh-strength and flame-retardant cellulose aerogel crosslinked with a reactive P/N-rich curdlan derivative

Cellulose aerogel, recognized for its eco-friendliness, bio-sustainability and excellent thermal insulation property, holds immense potential as an insulation material. However, the application of cellulose aerogel has been hindered by its inherent drawbacks, particularly its low strength and flammability. In this study, a reactive P/N-rich curdlan derivative (NT) was synthesized and characterized. Lightweight, ultrahigh-strength and flame-retardant composite aerogels were then prepared by slow freezing, freeze-drying and chemical crosslinking methods. Composite aerogel crosslinked with 30% NT exhibited exceptional thermal insulation property with a low thermal conductivity of 33.9 mW/(m·K), which rivaled the value of petroleum-based thermal insulation materials. It possessed an ultrahigh compressive modulus (0.786 MPa) at low density (21.6 mg/cm3), which supported >12,000 times its weight. It also displayed superior flame-retardant property, with a limiting oxygen index of up to 33.1% and a V-0 rating in the UL-94 test. This study provides a new insight into the high-value utilization of natural polysaccharide and an innovative solution to the problem of low strength and flammability of cellulose aerogel. Cellulose aerogels with ultrahigh strength, superior flame retardancy and thermal insulation property possess a promising application in the fields of construction, aerospace and thermal protective clothing as high-performance thermal insulation materials.

Sustainability-oriented construction materials for traditional residential buildings: From material characteristics to environmental suitability

The increasing replacement of traditional construction materials with modern alternatives often overlooks their superior environmental adaptability and sustainability, resulting in missed opportunities for energy efficiency and carbon emission reductions. This study aimed to address this issue by scientifically evaluating the material properties of volcanic rock from Hainan Island, China, to assess its potential for sustainable building practices in tropical climates. A series of material characterization techniques were employed to analyze the composition and structure of the volcanic rock, including optical profilometry (OP), polarized light microscopy (PLM), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), transient plane source technique (TPS), and mercury intrusion porosimetry (MIP). Our findings identified the rock as vesicular cryptocrystalline basalt, with its unique pore structure and mineral composition jointly contributing to a low thermal conductivity of 0.22 ± 0.04 W/(m·K). The pore structure was characterized by closed spherical cavities, needle-like lava fillings, nanoporous surfaces, complex pore-throat networks, and an extensive pore size distribution. These features significantly reduced gas convection and enhanced thermal resistance. Additionally, the rock composition, dominated by the amorphous volcanic glass and scattered hollow skeletal crystalline plagioclase, further diminished heat transfer. These characteristics indicated that Hainan volcanic rock possessed excellent thermal insulation properties, making it highly suitable for energy-efficient construction in hot climates. This study highlighted the potential for traditional materials like volcanic rock to contribute to sustainable building practices and the preservation of cultural heritage.

Double cross-linked biomass aerogels with enhanced mechanical strength and flame retardancy for construction thermal insulation

Biomass aerogels are expected to be a popular material in construction field due to their sustainability, eco-friendliness and excellent thermal insulation properties. In this paper, high modulus biomass aerogels based on the principle of double cross-linking of physics and chemistry were synthesized by freeze-drying technique using gelatin, sodium carboxymethyl cellulose, glutaraldehyde, phytic acid and diatomite as raw materials. The presence of a double cross-linked network structure endowed the prepared aerogels with a low thermal conductivity (0.021–0.029 W·m−1·k−1). The density of only 0.0865 g·cm−3 biomass aerogel exhibited an extrastrong compression modulus of 31.5 MPa, which was superior to common biomass aerogels. Biomass intumescent flame retardant system composed of sodium carboxymethyl cellulose (carbon source), gelatin (gas source) and phytic acid (acid source) was used in combination with diatomite to enhance flame retardancy (limit oxygen index value up to 36.5 %, UL-94 V-0 rating and total smoke production reduced from 0.31 m2 to 0.18 m2) and thermal stability (the residue up to 48.91 %). Remarkably, the modified aerogel showed incredible hydrophobicity (hydrophobic angle of 137°). In summary, the results indicated this study proposed a novel green idea for the preparation of construction thermal insulation materials with a combination of high modulus, flame retardancy and hydrophobicity.

Lightweight and highly heat-resistant copolymerized polyimide foams for superior thermal insulation and acoustic absorption

The development of lightweight and highly heat-resistant polyimide foams (PIFs) remains a great challenge in areas of aerospace, military ships, transportation, and industries. Herein, a series of lightweight and highly thermal-resistant copolymerized PIFs are successfully fabricated by the “stepwise heating-holding” thermal foaming of the copolymerized polyester ammonium salts (C-PEAS), using 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) and 2,3,3′,4′-biphenyl tetracarboxylic acid dianhydride (α-BPDA) as codianhydride, and p-phenylenediamine (PDA) as diamine. The introduction of α-BPDA increases the rigidity of PI molecule chains and foamability of C-PEAS, and significantly improves the heat resistance of PIFs. The resultant copolymerized PIFs exhibit ultra-low densities (<10 kg·m-3), excellent heat resistance (Tg ranging from 351.2°C to 405.6°C), and high thermal stability. Moreover, they possess high flame retardancies (LOI>44%) and low thermal conductivities (as low as 0.0463 W·m-1∙K-1 at 20°C and no more than 0.0825 W·m-1∙K-1 at 200°C), demonstrating their excellent thermal insulation properties in a wide temperature range. After the continuous heating at 200°C for 40 min, the upper surface of PIFs present low average temperatures less than 60°C. Additionally, the copolymerized PIFs exhibit remarkable acoustic properties with average acoustic absorption coefficients above 0.6 and noise reduction coefficients (NRC) above 0.3. Therefore, the lightweight and highly heat-resistant copolymerized PIFs show great application potentials in the extreme environments of aerospace, military ships, transportation, and industries.

PI-SiO2 aerogel as a versatile high transparent material for photothermal cooperative management

Effectively insulating against excessive heat generated by sunlight while also avoiding harmful ultraviolet (UV) and maintaining suitable levels of visible light transparency is vital for minimizing energy consumption and optimizing sunlight utilization. To address the challenge of photothermal collaborative management, the PI consisted of high fluorinated dianhydride and aliphatic diamine was used to effectively improve the performance of SiO2 aerogels. The resulting PI-SiO2 aerogels retain the characteristics of SiO2 aerogels, such as low density, high transparency between 82∼89 %, and excellent thermal insulation properties with an ultralow thermal conductivity range from 0.023 W/(m.K) to 0.028 W/(m.K). Meanwhile, the coarsened skeleton of aerogels can withstand the extreme temperature difference between −196 ℃ and 200 ℃ without brittle fracture and yellowing. In addition, PI-SiO2 aerogels exhibit the capability to absorb a significant proportion of UV light within the 200–400 nm, offering distinct advantages in transparent thermal insulation materials. The multifunctional PI-SiO2 aerogels can be used as candidate materials in the fields of architecture, automobile, electronics, solar energy and aerospace.

Innovative preparation of polyimide/polysulfone amide (PI/PSA) membrane-pore-like nanofibers with biomimetic penguin feather shaft structure and thermal insulation performances

The white-browed penguin can survive in extreme environments due to its unique feather structure. The feather shafts of penguins are porous, separated by the membrane-pore-like structure made of keratin fiber membranes. The feather branches are densely arranged around the feather shafts. This unique structure provides inspiration for researchers. In this work, we developed a simple method to construct polyimide/polysulfone amide (PI/PSA) membrane-pore-like structure nanofibers resembling penguin feather shafts and studied the effects of different low-boiling point solvents (tetrahydrofuran (THF), ethyl acetate (EA), and acetone (AC)) on the morphology, tensile properties, and thermal insulation properties of PI/PSA membrane-pore-like structure nanofibers. Comprehensive characterization was also performed using scanning electron microscope, total reflection infrared spectrometer, X-ray diffractometer, universal testing machine, thermal conductivity meter, pore size analyzer, thermal gravimetric analyzer, infrared thermal imaging instruments, and thermocouple testing instruments. The results showed that when the mass ratio of THF to N, N-dimethylacetamide (DMAC) was 20/80, the prepared PI/PSA membrane-pore-like structure nanofibers exhibited excellent thermal insulation properties, with a low thermal conductivity of 0.0436 W·m−1·K−1, a breaking strength of 7.72 ± 2.64 MPa, and a breaking elongation of 8.19 ± 4.07 %. The biomimetic membrane-pore-like structure with excellent thermal insulation properties is expected to be applied in various fields, such as heat-protective clothing and architectural coatings in harsh environments.

PAM material that instantly gives ordinary fabrics excellent flame retardant and thermal insulation properties for fire rescue

To effectively reduce the damage caused by flame burns or heat transfer to the human body during fire, we used PAM aqueous solution as the matrix, XG as the thickener, HPMC as the water-retaining agent to form the basic material system, and added different functional particles (APP, PTW, HCB) to prepare a fire-proof and heat-insulating PAM flame-retardant material for fire emergency rescue. Ordinary cotton fabrics were impregnated into PAM flame-retardant materials using a simple impregnation process. After the impregnation, the test was performed in a non-dropping state (simulating the thermal protection effect of PAM flame retardant materials directly acting on the outside of the human body at the fire scene). The results show that the PAM flame retardant material prepared by adding 4 wt% HCB has the best comprehensive performance. TPP test shows that spraying PAM flame retardant material on the outside of the fabric can instantly give the fabric a higher thermal protection performance. Under the total heat flux of 84 kW/m2, the thermal performance protection value of the fabric is 2641.8 kW·s/m2, and the second-degree burn time can reach 31.45 s. PAM flame retardant material does not damage the fabric. After soaping, the air permeability of the fabric decreases slightly, the moisture permeability and wettability are improved, and the breaking strength is almost unchanged. The CCT test showed that the thermal radiation flux was 50 KW/m2, the PHRR value of PAM flame retardant material was 10.64552 KW/m2, the THR was 6.9 MJ/m2, and the flame retardant performance was excellent. The PAM flame retardant material prepared in this project can be applied to the fire scene and directly sprayed on the outside of the clothing of rescuers and recipients, giving the fabric a better thermal protection effect. It can also be used to extinguish fires in the external environment. This material offers a novel solution for enhancing fire rescuers' and victims' safety protection levels.

HNTs Improve Flame Retardant and Thermal Insulation of the PVA/CA Composite Aerogel.

Porous materials are widely used in construction, batteries, electrical appliances, and other fields. In order to meet the demand for flame-retardant and thermal insulation properties of organic porous materials, in this work, poly(vinyl alcohol)/calcium alginate/halloysite nanotube (PVA/CA/HNTs) aerogels with a hierarchical pore structure at micrometer-nanometer scales were prepared through freeze-drying using PVA as the substrate. The cross-linking reactions of PVA with H3BO3 and sodium alginate (SA) with CaCl2 constructed a double cross-linking network structure within the aerogel. And the HNTs were incorporated as reinforcing agents. The experimental results showed that the PVA/CA/HNTs aerogels had excellent flame-retardant and thermal insulation properties, and the heat release rate (HRR) and total heat release (THR) were effectively reduced compared to the PVA/CA aerogel. In addition, PVA/CA/HNTs aerogels had a high limiting oxygen index (LOI 60%) and low thermal conductivity (0.040 W/m·K). While their surface was subjected to a flame (800-1000 °C) for 25 min, the temperatures of the back surface were still lower than 80 °C. The low thermal conductivity of HNTs with hollow nanotube-like structures and the excellent flame-retardant properties of CA contributed to this phenomenon. The presence of HNTs and CA facilitated the formation of a dense carbon layer during combustion, enhancing the flame retardancy for PVA. In addition, the interpenetrating cross-linking network and the unique nanopores of HNTs collectively established a hierarchical pore structure within the gel, effectively impeding substance and heat exchange between the substrate and external environment. As the flame-retardant and thermal insulating material, PVA/CA/HNTs aerogels have a promising development prospect and potential in the fields of construction, transportation, electronics, and electrical appliances.

Investigating the emissions and performance of ethanol and biodiesel blends on Al2O3 thermal barrier coated piston engine using response surface methodology design - multiparametric optimization

The Response Surface Methodology (RSM) optimization technique was used to examine the effect of load, Tomato Methyl Ester (TOME), and Ethanol injection enhanced diesel on engine performance and exhaust gas emissions with a normal piston and an Al2O3 coated piston. TOME biodiesel (10, 20, and 30%) and ethanol (10, 20, and 30%) were chosen to increase BTE while minimizing BSFC, NOx, CO, smoke, and HC. The RSM technique was used to operate the engine by load (0–100%). The results revealed that engine load, TOME, and ethanol concentration all exhibited a considerable effect on the response variables. The ANOVA results for the established quadratic models specified that for each model, an ideal was discovered by optimizing an experiment's user-defined historical design. The present research efforts to improve the performance of a diesel engine by using a thermal barrier-coated piston that runs on biodiesel blends. Al2O3 is the chosen material for TBC due to its excellent thermal insulation properties. B20E30 has a 4% higher brake thermal efficiency than diesel, but B10E20 and B30E20 mixes have a 3.6% and 12% reduction in BSFC. The B20 blends lowered CO and HC emissions by 6% and 8% respectively. In terms of performance and emissions, biodiesel blends performed similarly to pure diesel, and the combination was optimized through the design of an experiment tool.

Improving the ablation performance of largely deformed silicone rubber-based composites under coupled mechanical-thermal-oxidative conditions by implementing deformable carbon fiber fabrics

Silicone rubber-based composites are used as thermal protection materials due to their large deformability and excellent thermal insulation properties. In this study, two types of commercially available silicone rubbers were selected as the matrices for preparing flexible thermal protection materials. The influence of applied strain rates on the microstructure, ablation and ceramifiable behavior of silicone rubbers was studied. The research showed that the ablation performance of silicone rubbers deteriorated greatly at large strain rates. The reinforcement using deformable carbon fiber fabrics was proposed to effectively counter the deterioration of the ablative properties incurred by applying external strain. The back-face temperature reached as low as 186 °C when the samples were ablated at above 1000 °C for 50s at a strain rate of 20 %. The proposed strategy was proved helpful in developing high performance flexible thermal protection systems that exhibit promising application in the fields of aerospace and fire protection among others.

Enhanced flame retardancy and thermal insulation of epoxy resins composites incorporated with ammonium polyphosphate and ionic liquids loaded CuO-ZnO hollow spheres

Epoxy resin, as a thermosetting polymer material with good performance, has been limited in application due to its high flammability. In this investigation, porous CuO-ZnO hollow spheres (CZHS) were prepared by a hydrothermal method. By incorporation with ionic liquids loaded CuO-ZnO hollow spheres (CZHS@Ils) and ammonium polyphosphate (APP) into epoxy resin (EP) matrix, a new composite flame retardant material, named as EP/7.5APP/1.5CZHS@ILs, was developed for improvement of their thermal insulation and flame retardancy. The thermal conductivity of EP/7.5APP/1.5CZHS@ILs was measured to be 0.0197 W m −1 K −1, which is lesser than that of APP incorporated epoxy resin (EP/APP), demonstrating good thermal insulation capability. The flame retardancy were assessed using the limiting oxygen index (LOI) test, the Vertical flame testing (UL-94) test, and the cone calorimeter (CC) test. The results obtained from LOI test show that the EP/7.5APP/1.5CZHS@ILs has good flame retardancy with a LOI value of up to 28, better than that of pure EP which has a LOI value of 19.2. Moreover, a V-0 level of the EP/7.5APP/1.5CZHS@ILs was observed from the UL-94 test. The peak heat release rate (PHRR) was reduced to 257.9 kW m−2, which is 74.8 % lower than that of the pure EP. Such results are attributed to the synergy effect of CZHS@ILs and APP which offers the epoxy resin excellent flame retardancy. Taking advantages of the excellent thermal insulation, flame retardancy and better mechanical properties, the as-resulted EP/7.5APP/1.5CZHS@ILs may hold great potential for future thermal insulation and flame-retardant applications of energy saving building.

Robust and Density Tunable Kevlar/Hexagonal Boron Nitride Microribbon Aerogels with Excellent Thermal, Mechanical, and Oil-Absorption Properties.

With rapid advancements in aerospace and supersonic aircraft technology, there is a growing demand for multifunctional thermal protective materials. Aerogels, known for their low density and high porosity, have garnered significant attention in this regard. However, developing a lightweight multifunctional aerogel that combines exceptional thermal and mechanical properties through a straightforward and time-efficient method remains a significant challenge. Herein, a facile and universal approach is developed for the preparation of Kevlar/hexagonal boron nitride (h-BN) aerogels, in which a spin-assisted method is applied to create robust microribbons and further accelerate solvent displacement. The resulting microribbon scaffold, with its entangled nanofiber-nanosheet morphologies, exhibits sufficient strength to prevent volume shrinkage during drying, thereby allowing precise control over aerogel density. The porous hybrid aerogels, featuring controllable geometric characteristics and tailored densities ranging from 6.9 to 100 mg cm-3, can be successfully fabricated. These aerogels exhibit excellent thermal insulation properties, and the thermal conductivities of the as-prepared KBX aerogels have a wide distribution in the range of 0.0269-0.0450 W m-1 k-1. The thermal stability of the hybrid aerogels is enhanced to 566 °C. Moreover, the resulting hybrid aerogels exhibit an ultrahigh bearing ratio, supporting more than 2000 times their own weight while maintaining stable structural integrity. These aerogels also demonstrate high compressive strength, hydrophobicity, and excellent sorption performance for various oils and solvents. Additionally, the oil-saturated aerogels can be easily recovered through heat treatment or combustion in air. The features endow hybrid Kevlar/h-BN aerogels with significant potential for applications in thermal management, environmental protection, and neutron protection.

Mesoscopic structure modeling of silica aerogels using cluster‐cluster aggregation

AbstractSilica aerogels are nanostructured materials known for their low density, high porosity, and excellent thermal insulation properties. Among silica aerogels, organosilane‐derived aerogels have received considerable interest for their additional chemical functionalities such as hydrophobicity and flexibility. This work investigates the mesoscopic modeling of such aerogels, extending an aggregation based model developed for conventional silica aerogels. The pH of sol–gel polymerizations is one of the most critical reaction and processing parameters in determining the porosity, density, strength, and transparency of the resulting gels. Achieving optical transparency in aerogels depends on the presence of homogeneous mesoporous network structures. To account for the effect of pH, a relationship between pH and adhesion probability was incorporated into a three‐dimensional cluster‐cluster aggregation (CCA) model, providing insight into the gelation process. In addition, size‐dependent diffusivities are considered in this study. By incorporating different factors into the CCA model, the gelation kinetics are evaluated. The obtained mesoscopic structure is compared with experimental characterizations, together with preliminary mechanical simulations.

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Study on synergistic enhancement of modified nucleating‐blowing agent and its application in foaming polyethylene

AbstractPolyethylene (PE) foams are widely used for the advantages of light weight and reducing energy consumption. So, the preparation of environmental friendly and efficient blowing agent is essential. The use of supercritical carbon dioxide (CO2) as physical blowing agent requires harsh experimental conditions such as high‐pressure and temperature. In this study, CO2 was captured by 1, 2‐cyclohexanediamine (TRK) under atmospheric pressure, and reversibly released under heating as a blowing agent with nanosponges (NS) used as the carrier (NS:TRK‐CO2). Furthermore, three ethoxy silane coupling agents were selected to improve the compatibility between heterogeneous nucleating agent (cyclodextrin nanosponges, NS) and PE, so as to improve the nucleation effect of NS and the comprehensive properties of PE composites. Analyses showed that triethoxyvinyl silane (VTES) was a suitable candidate for improving the compatibility of NS and PE. The addition of NS:TRK‐CO2@VTES not only improved the crystallization performance, but also improved the complex viscosity and storage modulus, and enhanced the thermal properties of PE composites. The optimal cell morphology was obtained by introduction of NS:TRK‐CO2@VTES with 5 wt%, the minimum cell diameter was 50 μm, and the maximum cell density was 9.4 × 104 cells/cm3. Compared with the other PE composites, PE/NS:TRK‐CO2@VTES composites showed excellent mechanical, thermal, and sound insulation properties. The maximum impact strength was 7.62 KJ/m2, which was two times higher than pure PE. The thermal conductivity was 0.054 W/m k, the sound absorption coefficient was 0.836 at 1500 Hz.

Thermal, mechanical property and flame retardant analysis of bio-based rigid polyurethane foam modified with expandable graphite

As an energy-efficient building material, rigid polyurethane foam (RPUF) has attracted attention. However, there are still great challenges in how to easily prepare RPUF materials with good mechanical properties, flame retardant properties, thermal insulation and other properties. In the current work, expandable graphite (EG)-modified lignin-based polyol (RPUF) was prepared by a one-step method. Thermogravimetric analysis was used to study the pyrolysis of modified foams under nitrogen conditions. It was found that the RPUF-4 with an EG of 10 wt% had the highest the apparent activation energy (E), integral procedural decomposition temperature (IPDT), initial temperature and residue rate. And RPUF-4 also had excellent thermal insulation properties. In addition, RPUF-4 exhibited excellent flame retardancy and smoke suppression properties (peak heat release rate (RHRR), total heat release rate (THR) and Ds were 65.46 %, 23.92 % and 45.94 % lower than those of the unadded RPUF, respectively). At the same time, RPUF-4 also had good mechanical properties and energy absorption properties. These results will lay the foundation for the development and application of RPUF in the field of building insulation.