High Thermal Insulation Research Articles

Transparent and Flexible Composite Films with Excellent Electromagnetic Interference Shielding and Thermal Insulating Performance.

As the working environment becomes more complex, the visualization of windows in electronic devices increasingly requires transparent and flexible electromagnetic interference (EMI) shielding films. There is a need for materials with EMI shielding properties, while maintaining excellent high light transmission and good thermal insulation. However, the preparation of such multifunctional materials remains challenging due to the respective mechanisms of action of the different properties. Herein, a multilayer structure strategy is proposed to fabricate transparent and flexible indium tin oxide (ITO)/silver nanowire (AgNW) composite films, achieving a multifunctional integration of high light transmission, strong EMI shielding, and good thermal insulation properties of the composite films. Simultaneously, the layered structure was designed and the potential optimization mechanism of the EMI shielding performance of the composite film was analyzed, providing great flexibility for the preparation of transparent composite films. The combination of excellent EMI shielding performance, outstanding near-infrared shielding performance, and high light transmittance makes the ITO/AgNW (IA) composite films promising for abundant potential applications.

Electrically Insulative Film Adhesive with Enhanced Thermal Performance to Assemble High Power Density Electronic Devices

Assembly adhesives play a critical role in microelectronic packaging and contribute significant value for circuit assembly interconnection, protection, and thermal management. Of particular interest with today’s more powerful systems is thermal management of high-power density electronic systems, including power modules, power amplifiers, communication systems, and directed energy systems. As requirements for performance and functionality increase, heat generated from these devices increases exponentially. For example, local heat flux can easily exceed 50 W/cm2 for IGBT power modules while it may reach several hundred Watts/cm2 at active areas for Gallium Nitride (GaN) power amplifiers. Simultaneously, many of these systems demand a higher level of electrical insulation to eliminate or minimize current leakage to ensure high reliability over a long service life. Effectively and safely dissipating the high heat and ensuring excellent electrical insulation has become an increasingly critical and challenging task in the microelectronics packaging technology for aerospace and defense systems. This paper presents integration of thermally conductive adhesives with an electrically insulative polyimide film into a carefully engineered laminate, which enables high thermal transfer and robust electrical insulation. This new film adhesive provides outstanding compliance and augmented tolerance to large topographical features and warpage (5-7 mils). This film adhesive is one of the potential solutions to addresses the evolving needs of the electronics assembly industry in the areas of management of high-power systems

Versatile spider-web-like cross-linked polyimide aerogel with tunable dielectric permittivity for highly sensitive flexible sensors

With the development of intelligent electronic power systems, the performance of flexible electronic sensors with portability and miniaturization is increasingly in demand. It is extremely challenging to achieve high modulus and high elasticity of polymer matrix simultaneously due to the inherent strength-elasticity conflict of elastic polymer. Here, a series of “spider-web-like” cross-linked polyimide aerogels (CPAs) had been successfully prepared. Benefiting from the robust dynamic network structure, the CPAs exhibited excellent compressive resilience, tunable dielectric permittivity, high thermal insulation property (λ = 0.040 W/m∙K) and modulus (E = 1073 KPa). Additionally, due to the excellent resilience of the CPAs and tunable permittivity, a CNTs/CPA-3 composite aerogel-based strain sensor obtained by assembling the CPA-3 with carbon nanotubes (CTNs) possessed synergistically enhanced sensitivity, high selectivity and “multi-touch” stress detection, without deterioration even after 2000 cycles. Furthermore, the established mathematical model revealed the internal mechanism of the synergistic enhancement of sensing performance of sensor with strain-controllable permittivity. Thus, the fabricated CPAs might be an ideal substrate material for flexible electronic sensors in electronic power systems, and the mathematical model established could also provide a reliable reference for improving the sensitivity and detection limits of sensors.

Development and characteristics of multifunctional ultra-lightweight engineered cementitious composites incorporating cenospheres and PE fibre

Ultra-lightweight, high ductility, high strength, and multi-functionality are recent development trends in concrete. This study proposed a design concept of multifunctional ultra-lightweight engineered cementitious composites (ULW-ECCs) without functional fillers using fly ash cenosphere (FAC) and polyethylene (PE) fibre, which has heat insulation, self-sensing, and self-healing functions. The mechanical (tension, compression, flexure) and corresponding self-sensing properties under monotonic and cyclic loading, self-healing, thermal conductivity, and thermal effusivity properties were examined. The ULW-ECCs were developed based on the maximum packing density of the matrix, which showed high pseudo-strain-hardening indices and had an apparent density of 1055–1333 (Oven-dry density: 946–1261) kg/m3, compressive strength of 36–58 MPa, and a tensile strain capacity of 4%–8% under standard curing condition. With the use of FAC with a highly stiff shell, the ULW-ECCs show high strength and high thermal insulation properties. ULW-ECCs incorporating FAC show excellent self-sensing properties without any conductive fillers under compression, bending and tension. The electromechanical behaviour was consistent and repeatable during cyclic and monotonic loading processes, and a microstructure model was used to explain the self-sensing mechanism. The cement paste in the matrix can form a 3D-like honeycomb structure because a large number of FACs evenly divide the cement paste, which shows sensitive self-sensing ability. Additionally, the multiple micro-cracks of ULW-ECCs show excellent self-healing properties. Optical microscope and SEM analyses of ULW-ECC were used to explain the results. The developed multifunctional ULW-ECCs without functional fillers would be a promising material for sustainable development.

A flexible silica aerogel paper with temperature-switch opacifier for thermal insulation

Aerogels have an impressive thermal insulation performance at room temperature. However, with high infrared transmittance, pure aerogels have no advantages in thermal insulation at high temperature. Opacifiers can reduce infrared transmittance to make a low thermal conductivity with sacrifice of that at room temperature. Herein, VO2 powders undergoing reversible insulator to metal transition at 67.8 °C as opacifier with temperature-switch were introduced into silica aerogel composites to prepare aerogel reinforced by VO2@SiO2 fibers paper (AVSP). At 25 °C, insulator VO2 made little contribution to thermal conductivity (0.025 W/(m·K)) so that it was close to aerogel reinforced by pure SiO2 fibers papers without opacifier (0.023 W/(m·K)). When temperature rose to 500 °C, metal VO2 made thermal conductivity of AVSP (0.051 W/(m·K)) much lower than that of aerogel reinforced by pure SiO2 fibers papers without opacifier (0.076 W/(m·K)). Meanwhile, SiO2 fibers papers with three-dimensional network structure improved flexibility of aerogel. The tensile strength of AVSP was 2.1 MPa with density of 0.186 g/cm3. With 152° contact angle and flame resistance, AVSP showed a great potential in high temperature thermal insulation in a nonplanar condition. Thereby, this work provides a novel strategy to improve thermal insulation property at high temperature with little contribution to that at room temperature.

Development of thermal liner for extreme heat protective clothing using aerogel technology

In this research, an attempt was made to develop and explore the thermal protective performance of the thermal liner and the effect of various preparation parameters of aerogel technology on it. Efforts have also been made to explore the scope of nanotechnology in finding the solution to problems coming in the way of high thermal stability and insulation of the thermal liner. Silica aerogel is a colloidal suspension of silica-based oxides in the air. Hence, it is a highly insulating material and shows one of the lowest densities for a similar performance. Here we took an approach to deploy silica aerogel composite as a thermal liner layer in order to ensure the aforesaid functionalities. To realize the objective, we tried to find the suitable fibre as well as suitable fabric structure for developing an aerogel on it. Further, we studied the effect of processing parameters such as ageing time, the effect of base catalyst and silylation time during aerogel synthesis on the protective performance of the developed thermal liner. Electrospun Nomex® fibre-aerogel composite and nomex® fibre-aerogel composite was also made, and it was compared to the thermal liner made of Nomex® IIIA nonwoven to find out how it worked. Aerogel treated sample with ammonium fluoride as catalyst performed best compared to sample with ammonium hydroxide as a base catalyst. An increase in ageing and silylation time led to significant increase in the thermal protective performance of the developed aerogel-Nomex® composite due to a better aerogel formation inside the composite.

Paper-based building envelopes – Thermal and environmental properties of original envelope designs

Paper-based materials, due to their availability, environmental benefits and high thermal properties, have already been implemented in several building envelope designs. However, most of them either did not optimise the use of the material or did not provide sufficient thermal insulation for use in permanent buildings. The presented research analyses six original paper-based building envelope core proposals, suitable for use in permanent buildings in temperate climate of Europe, in terms of thermal and environmental efficiency. Proposals include cores with embedded paper tubes structural elements, timber-cardboard studs and sandwich designs. The heat transfer coefficient of the envelopes was obtained for repeatable modules via 2D computer simulations (ThermCAD software), and the environmental impact was assessed for a representative square metre of the envelope via LCA analysis, based in ecoinvent 3.8 database. All analysed designs showed high thermal insulation properties and met the requirements for Umax = 0.20 W/m2K, did not cause the risk of surface condensation, nor have excessive thermal bridges. The analysed building envelope designs based on embedded frame wall structure showed environmental superiority over conventional envelopes (timber frame and SIP panels). The research may serve as a proof of concept, for using paper-based building envelopes in sustainable architecture.

Light-weight and high thermal insulation building material; a comparative study between cenosphere & fly ash

The increasing demand for light-weight sustainable materials have led researchers to find the alternatives to the available natural resources used as construction materials. Cenospheres are hollow fly ash particles which are obtained from fly ash waste by burning coal in thermal plants. Cenospheres have been widely used as filler materials in various industries like aircraft, automation etc, due to its light-weight and high thermal resistivity, However, the use of cenospheres in construction industry has been limited, Therefore, in this research an attempt has been made to replace OPC with cenosphere particles. The cement was replaced from 0 to 30% to produce a light-weight and high thermal insulation concrete. This concrete was studied for the properties like fresh, heat of hydration mechanical, durability and thermal conductivity. It was observed that the heat of hydration significantly reduced by the use of cenosphere particles. The density of the concrete was also reduced with the increment in the content of cenosphere in concrete, however with the decrease in the density the mechanical strength of concrete also reduced but was within the design strength of concrete. It was also observed that the cenosphere contribute to the late gain in the strength of the concrete similar to the fly ash concrete. The thermal conductivity of the concrete reduced by more than 50% with the incorporation of the cenosphere in the concrete. From this research it can be concluded that cenosphere can be used as a replacement to cement in the concrete to produce a light-weight and high thermal insulated concrete.

Improvement of Moisture Susceptibility for Asphalt Mixture with Ceramic Fiber

Moisture damage is one of the most significant troubles that destroy asphaltic pavement and reduces road serviceability. Recently, academics have noticed a trend to utilize fibers to enhance the efficiency of asphalt pavement. This research explores the effect of low-cost ceramic fiber, which has high tensile strength and a very high thermal insulation coefficient, on the asphalt mixture's characteristics by adding three different proportions (0.75%, 1.5%, and 2.25%). The Marshall test and the Tensile Strength Ratio Test (TSR) were utilized to describe the impact of ceramic fiber on the characteristics of Marshall and the moisture susceptibility of the hot mix asphalt mixture. The Field Emission Scanning Electron Microscopy (FE-SEM) analysis was used to investigate ceramic fibers' microscopic structure and clarify the mechanics of their improved behavior and their distribution within the asphalt concrete mixture. The results showed that the incorporation of ceramic fibers improved the Marshall properties and the asphalt mixture's susceptibility to moisture damage with an optimum fiber content equal to 1.5%, where Marshall stability increased by 39.04%, and the TSR increased by 11.06% at this content compared with the control asphalt mixture.

Structural, mechanical and thermal properties of cubic bixbyite-structured high-entropy oxides

Cubic bixbyite-structured high-entropy oxides (HEOs) are regarded as potential candidates in high temperature thermal insulation field in recent years. However, their relevant properties are still needed to be explored for possible applications. In this work, twelve new high-entropy oxides (HEO1-12) of (5Re0.2)2O3 (Re represents five elements selected from Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb) are prepared by solution combustion synthesis method combined with conventional sintering. Except HEO10 with a single monoclinic phase, other samples have a single bixbyite phase. The average grain size of bixbyite-structured samples is within 0.76 ∼ 4.96 μm. Then, the samples of HEO4, 5, 7–9 are chosen to study their mechanical and thermal properties. Their nano-modulus, nano-hardness, fracture toughness KIC, brittleness M and surface fracture energy are in the range of 152.42 ∼ 237.33 GPa, 9.22 ∼ 12.65 GPa, 1.77 ∼ 2.51 MPa·m1/2, 2.35 ∼ 3.09 μm−1/2 and 9.00 ∼ 22.49 J m−2, respectively. HEO4, i.e., (Ce0.2Nd0.2Sm0.2Dy0.2Gd0.2)2O3, exhibits higher KIC (1.92 MPa·m1/2) and lower M (2.71 μm−1/2) than another reported cubic bixbyite-structured HEO of (Eu0.2Er0.2Lu0.2Y0.2Yb0.2)2O3. Among the five samples, HEO4 has the lowest thermal conductivity κ (1.88 ∼ 2.55 W·m−1·K−1 in 25 ∼ 500 °C), which is much lower than bixbyite-structured Y2O3. In addition, HEO4 possesses a lower oxygen diffusion compared with 8YSZ in 600 ∼ 700 °C, which endows it the better oxygen barrier property. To sum up, HEO4 could be a promising candidate for high temperature thermal insulation applications due to its excellent comprehensive properties.

Thermophysical Parameters and Hygrothermal Simulation of Aerogel-Based Fibre-Enhanced Thermal Insulating Renders Applied on Exterior Walls

Aerogel-based renders have been the subject of research in the last few years due to their high thermal insulation characteristics and the need for buildings to become more energy-efficient. This study compares the hygrothermal behaviour of an aerogel-based render (reference) with the same base formulation, replacing the powder with three different fibres (aramid 0.5%, sisal 0.1%, and biomass 0.1%, by total volume) that can be used in buildings’ envelopes. The experimental programme allowed us to characterise and compare the thermophysical properties of the different formulations and then simulate the hygrothermal performance of these solutions when applied to walls for different climatic conditions, considering additional parameters such as total water content, drying potential, water content levels, and thermal insulating performance. These thermophysical parameters were then included in hygrothermal numerical simulations. The results allowed us to verify that the incorporation of fibres improved the hygrothermal properties due to lower capillary absorption and higher water vapour permeability. These renderings showed a high potential for application to building envelopes in different climatic conditions, improving their energy efficiency by up to 20% when compared to other conventional solutions.

Ceramicization mechanism and thermal insulation/ablative properties of hollow microspheres/boron phenolic composites

Phenolic resins with excellent ablative properties and thermal insulation are required in aerospace technology. However, the composites suffer from pyrolytic carbonaceous residues, resulting in susceptible erosion and peeling. This work provides a novel phenolic resin composite with high thermal insulation capacity by introducing hollow silica microspheres (HSMs) as an insulation layer. The effect of HSMs content on the ablation behavior of the composites was investigated, and the ablation mechanism was elucidated. The results show that the composites with microspheres exhibit high uniformity and improved bending strength. By introducing microspheres, the fiber distribution is uniform, resulting in an increase of the bending strength after static ablation to be 7.4 MPa, which is 87% higher than the matrix. The thermal stability of the composite is improved simultaneously and the ablation residual rate after static ablation increases from 67% to 73%. When oxyacetylene ablation for 20 s at the oxygen and acetylene flow rates of 1145 L/h and 838 L/h, respectively, the microspheres construct an insulating network, and the back surface temperature decreases from 280 °C to 178 °C.

Cooling Energy and Climate Change Nexus in Arid Climate and the Role of Energy Transition

Buildings are significant contributors to climate change through their energy consumption, particularly in countries with hot and dry climates where cooling services require substantial amounts of energy. Climate change is expected to increase cooling demand, further exacerbating the problem. This study investigates the impact of climate change on cooling demands in different building types in Qatar and evaluates related environmental impacts. Using a high-resolution regional climate model, future climate data were obtained for 2071 and 2100 under the Representative Concentration Pathway (RCP) 4.5. The energy consumption of eight prototype buildings was simulated under baseline and future climates, and the environmental impacts were assessed using Life Cycle Assessment (LCA) for natural gas and solar power as energy sources. The study found that the cooling demand could increase by 13–53% and 19–67% in 2071 and 2100, respectively, with buildings having higher thermal insulation and lower window-to-wall ratio being less affected by climate change. The LCA results showed that replacing natural gas with solar power can reduce cooling energy-associated CO2 emissions by 92%. However, challenges such as human toxicity and metal depletion need to be addressed. The study highlights the importance of considering potential climate change scenarios to develop more resilient buildings and encourages implementing efficient recycling and waste management strategies before implementing PV panels.

Highly transparent silanized cellulose aerogels for boosting energy efficiency of glazing in buildings

To maintain comfortable indoor conditions, buildings consume ~40% of the energy generated globally. In terms of passively isolating building interiors from cold or hot outdoors, windows and skylights are the least-efficient parts of the building envelope because achieving simultaneously high transparency and thermal insulation of glazing remains a challenge. Here we describe highly transparent aerogels fabricated from cellulose, an Earth-abundant biopolymer, by utilizing approaches such as colloidal self assembly and procedures compatible with roll-to-roll processing. The aerogels have visible-range light transmission of 97–99% (better than glass), haze of ~1% and thermal conductivity lower than that of still air. These lightweight materials can be used as panes inside multi-pane insulating glass units and to retrofit existing windows. We demonstrate how aerogels boost energy efficiency and may enable advanced technical solutions for insulating glass units, skylights, daylighting and facade glazing, potentially increasing the role of glazing in building envelopes.

New class of high‐entropy rare‐earth niobates with high thermal expansion and oxygen insulation

AbstractTailoring the structure and properties of materials using the high‐entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare‐earth niobates was successfully prepared by a solid‐phase reaction method, including (Sm1/5Dy1/5Ho1/5Er1/5Yb1/5)NbO4 (5HERN), (Sm1/6Dy1/6Ho1/6Er1/6Yb1/6Lu1/6)NbO4 (6HERN), (Sm1/7Dy1/7Ho1/7Er1/7Yb1/7Lu1/7Gd1/7)NbO4 (7HERN), and (Sm1/8Dy1/8Ho1/8Er1/8Yb1/8Lu1/8Gd1/8Tm1/8)NbO4 (8HERN), along with eight single rare‐earth niobates (RENbO4, RE = Sm, Dy, Ho, Er, Yb, Lu, Gd, and Tm). X‐ray diffraction analysis showed that 5–8HERN are single‐phase solid solutions with a monoclinic structure (space group C12/c1). The thermal expansion coefficients of 7HERN and 8HERN exceed 11 × 10−6 K−1 at 1200°C and are much higher than those of the RENbO4 compositions (10.13–10.74 × 10−6 K−1) and other some HE rare‐earth oxides (10.27–10.87 × 10−6 K−1). Importantly, 5–8HERN have lower oxygen‐ion conductivity and higher activation energy than yttrium‐stabilized zirconia (YSZ) and the RENbO4 compositions. The oxygen‐ion conductivity of 5HERN (7.52 × 10−7 S cm−1, 900°C) was 105 times lower than that of YSZ (0.01 S cm−1, 750°C). The hardness of 5–8HERN is ∼7.81–8.46 GPa and these compositions have low intrinsic lattice thermal conductivity at high temperature (1.28–1.69 W m−1 K−1 at 900°C). The mechanism by which the HE effect improved the material properties was elucidated. Young's modulus, hardness, thermal expansion coefficient, and intrinsic lattice thermal conductivity are linearly related to the mass, size, and distortion degree of samples. In contrast, the oxygen‐ion conductivity depends on both the degrees of disorder and distortion and the oxygen‐ion vacancy concentration. Based on their overall performance, especially their high thermal expansion coefficients and excellent oxygen‐barrier performance, HE rare‐earth niobates show potential for further development as TBC materials.

Development and characterization of sandwich panels for thermal insulation in a cold storage chamber

Sandwich composites are materials that have superior properties including low weight, high impact energy absorption and high thermal insulation features, compared to conventional materials. In this study, four different sandwich samples were explored for use in cold storage chambers. The composites were created using an injection molding process with polyurethane foam as the core and different materials (glass fiber reinforced polyester, galvanized steel, aluminum sheets and crimped aluminum) as face materials. Morphological, physical and mechanical properties were evaluated. An inexpensive and nondestructive method was used to determine the thermal behavior of the sandwich panels, and the surface temperature evolution was thermally monitored during the tests. In general, results showed that polyurethane had a homogeneous distribution of size and shape with closed cells, which can improve the retention of the insulating gas. Additionally, the compressive strength of polyurethane within the composites exhibited typical values to be used in specific applications. Thus, the sandwich with galvanized steel exhibited lower flexural strength, which provides more freedom in panel design. The overall heat transfer coefficient of the panels in the form of cubes presented values below the maximum limit requested by ABNT NBR-15457. Finally, the composite galvanized steel/polyurethane/galvanized steel achieved the best performance for use as a thermal insulation material in a cold storage chamber.

Elevated temperature and performance behaviour of rice straw as waste bio-mass based foamed gypsum hollow blocks

The present study explores mechanical, thermal, acoustic, and fire performance evaluation of locally available rice straw as waste bio-mass in foamed gypsum hollow blocks. Two-core hollow gypsum blocks with various agro-waste compositions have been studied in detail and presented. Aluminum sulphate and potassium alum in 1:1 ratio are used as foaming agents in gypsum blocks. The density of two-core hollow blocks varies from 1070 to 730 kg/m3 for 0–15 wt% rice straw addition. The compressive strength of solid cubes and two-core hollow blocks lies in the range of 4.6-1.4 MPa and 2.2–1.1 MPa respectively. Whereas, the thermal conductivity lies between 0.15 and 0.07 W/m.K. exhibiting excellent thermal insulation. The sound transmission class (STC) of straw based foamed gypsum varies over the range of 23 to 20 dB for 20 mm thick with 0–15 wt% agro-waste added samples. The 5 wt% foamed rice straw gypsum sample has shown resistance to the surface spread of flame and the wallette unit of 600 mm × 600 mm has 70.5 kN of load carrying capacity at 800 °C. The foamed agro-waste-based hollow gypsum blocks may be used as a potential building material for non-load bearing wall application owing to its high thermal insulation, moderate acoustic and excellent fire retardant properties.

Recycling the Leftover Fabrics for Use in Lining Surfaces as Heat Insulators for Hot Areas

The study is based on the descriptive experimental method, where the research deals with the creation of a new type of surface insulator and its use as a heat insulator, where the remnants of fabrics and threads are used with paper pulp of different thicknesses to determine the extent of their ability to heat insulation. The two researchers prepared the study samples represented in non-woven with a thickness of 3 cm - 2 cm - 1.5 cm. The research objective lies in highlighting the role of recycling yarns and fabric remnants in reflecting ultraviolet rays, insulating heat, and determining the most appropriate thickness to getting the highest thermal insulation. The results were obtained with a thermal conductivity meter with hot square technology. There is a difference in the value of the thermal conductivity coefficient of the samples according to the thickness used. The higher the thickness of the sample, the lower the coefficient of thermal conductivity, and thus, the higher the thermal insulation value. The results of the thermal conductivity coefficient of the samples under study were, in general, significantly low, which indicates the success of the samples in isolating the surfaces well, as the value was between 0.032 and 0.0178. From here, it is possible to benefit from paper and fabric waste in the material savings resulting from the use of air conditioning devices and high-priced insulators. This is an attempt by the two researchers to save electricity consumption, which increases when air conditioners are used in places with high temperatures for a long time.

Thermal insulation, flame retardancy, smoke suppression, and reinforcement of rigid polyurethane foam enabled by incorporating a P/Cu-hybrid silica aerogel

The frequent occurrence of fires caused by rigid polyurethane foam highlights the importance of its fire safety, however, the existing flame-retardant methods often seriously deteriorate the mechanical properties and thermal insulation of the foam. Here, we demonstrate a new idea for thermal insulation, flame retardancy, smoke suppression, and reinforcement of polyurethane foams only by incorporating a P/Cu-hybrid silica aerogel. This unique aerogel combines with the carbon-promoting action of P, catalytic attenuation of Cu, and the barrier effect of aerogels, thus leading to high smoke-suppressing and flame-retardant efficiency for polyurethane foam. At a low addition amount of 5 wt% aerogel, the total heat release, peak heat release rate, total smoke release, and toxic CO production of the composite foam are all significantly reduced. Interestingly, the aerogel-containing composite foam exhibits a special hierarchical porous structure, which enables lower thermal conductivity and higher thermal insulation than pure RPUF. Benefitting from the good compatibility and nano-enhancing effect of the aerogel, the compressive strength of the composite foam remarkable increase of 52.2%. This research offers an effective method for designing high-performance foam materials with high fire safety and low thermal conductivity, which has broad application prospects in the field of thermal insulation.

Direct ink writing of polyimide/bacterial cellulose composite aerogel for thermal insulation

Polyimide (PI) aerogels are well known for their high porosity, low density, thermal insulation and outstanding mechanical strength, thus expected to be applied in aerospace vehicle, intelligent driving and batteries. However, currently most PI aerogels are fabricated through traditional molding process, seriously restricted their practical applications. Although some researches on 3D printing of PI aerogels have been reported, there are some critical restrictions in present work such as complex support structures, low porosity and high thermal conductivity resulting from high solid content in printed ink. Herein, we choose bacterial cellulose (BC) with high aspect ratio as rheological modifier to construct water-based polyamic acid (PAA)/BC ink with low solid content but high yield stress enough for direct ink writing (DIW). Due to the good printability and formability of PAA/BC ink, the PI/BC aerogel with various macrostructures can be easily printed. Owing to the orientation from printing, the obtained printed PI/BC aerogel shows lower shrinkage, lower thermal conductivity and enhanced mechanical properties compared with molded PI/BC aerogels. Such printed PI/BC aerogel is potentially to be applied as thermal insulators for designated products with specific complex structure in fields of buildings and petrochemical engineering.