Wrong expectation of superinsulation behavior from largely-expanded nanocellular foams

Buahom, Piyapong; Wang, Chongda; Alshrah, Mohammed; Wang, Guilong; Gong, Pengjian; Tran, Minh-Phuong; Park, Chul

doi:10.1039/d0nr01927e

Cited by 39 publications

(23 citation statements)

References 136 publications

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“…This result corresponds also to the lowest bulk density materials of Table 3. However, the same authors have recently theoretically proved that such low thermal conductivity cannot be reached with the reported characteristics of the material [51]. Martin-de León et al produced nanocellular materials by means of homogeneous PMMA with cell sizes of 225 nm and 25 nm and a range of densities.…”

Section: Thermal Conductivity In Nanocellular Polymersmentioning

confidence: 99%

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

et al. 2022

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Nowadays, our society is facing problems related to energy availability. Owing to the energy savings that insulators provide, the search for effective insulating materials is a focus of interest. Since the current insulators do not meet the increasingly strict requirements, developing materials with a greater insulating capacity is needed. Until now, several nanoporous materials have been considered as superinsulators achieving thermal conductivities below that of the air 26 mW/(m K), like nanocellular PMMS/TPU, silica aerogels, and polyurethane aerogels reaching 24.8, 10, and 12 mW/(m K), respectively. In the search for the minimum thermal conductivity, still undiscovered, the first step is understanding heat transfer in nanoporous materials. The main features leading to superinsulation are low density, nanopores, and solid interruptions hindering the phonon transfer. The second crucial condition is obtaining reliable thermal conductivity measurement techniques. This review summarizes these techniques, and data in the literature regarding the structure and thermal conductivity of two nanoporous materials, nanocellular polymers and aerogels. The key conclusion of this analysis specifies that only steady-state methods provide a reliable value for thermal conductivity of superinsulators. Finally, a theoretical discussion is performed providing a detailed background to further explore the lower limit of superinsulation to develop more efficient materials.

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Section: Thermal Conductivity In Nanocellular Polymersmentioning

confidence: 99%

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

et al. 2022

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“…[ 26,27 ] In addition, increasing the cell density can improve the number of multiple reflection and absorption of infrared electromagnetic waves in the foams. [ 19 ] It has been mentioned earlier that the cell density increased as the Cu content increased (Figure 3c). Therefore, the improvement of thermal insulation performance for c‐PVC foam may be attributed to the weakening of the thermal radiation term from two aspects: 1) the presence of Cu flake sheets in the cell wall increases effectively the reflection capacity of the cell wall to infrared electromagnetic waves; 2) smaller cell size and larger cell density increases the number of multiple reflection and absorption in the foam.…”

Section: Resultsmentioning

confidence: 70%

“…[ 22 ] Generally, the cellular structure of the foam has a significant impact on the various properties of the foam, such as mechanical properties and thermal insulation properties. [ 19 ] Within an appropriate range, smaller cell diameters have better mechanical properties and thermal insulation performance. The SEM micrographs of pure c‐PVC foam and c‐PVC composite foams are shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…However, it is still difficult to prepare nanoporous foams with higher expansion ratio. Recently Park et al showed that the radiant thermal conductivity of nanoporous foams with low‐density will be greatly increased, [ 19 ] so the superinsulation still cannot be obtained. In fact, the current method for improving the thermal insulation performance of polymer foams is mainly to add fillers that absorb or reflect infrared electromagnetic waves to weaken the heat transfer contribution of the thermal radiation term in the low‐density foam.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Simultaneously Improving Thermal Insulation, Flame Retardancy, and Smoke Suppression for Rigid Cross‐Linked Polyvinyl Chloride Foam through Combined Copper/Molybdenum Trioxide

et al. 2021

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The rigid cross-linked polyvinyl chloride (c-PVC) foam, which is often used as low-density core materials in the sandwich structure composites, is widely used in wind turbines, ships, vehicles, and aircraft applications, owing to its high strength-to-weight ratio, low water absorption, good chemical resistance, and excellent insulation properties. [1][2][3][4] In fact, it is well known that these excellent properties of c-PVC foam benefit from the combination of PVC and polyurea, forming a semiinterpenetrating network structure. [5] With the increasing importance of fire safety in society, the flame retardant properties and smoke release of polymer foam have received widespread attention. Because PVC contains ≈56.7% of Cl atoms in the main chain, PVC itself has remarkable flame retardancy than other polymers such as polyurethane, polypropylene, and polystyrene resins. [6,7] However, almost half of the component in the c-PVC foam is polyurea, which causes flame retardancy to be destroyed. In addition, the c-PVC foam will produce toxic and corrosive gases and a large amount of smoke upon burning, [8] forming a threat to living and property. [6,9] Therefore, it is urgently needed to improve the flame retardancy and smoke suppression of c-PVC foam. At present, a lot of work has been devoted to enhance the smoke suppression and flame retardancy of soft or hard polyvinyl chloride solid materials, by adding various organic and inorganic flame retardants. Metal-based flame retardants (such as tin, [10] zinc, [11] copper, [12,13] iron, [14] aluminum, magnesium, [15] and molybdenum [16,17] ) have been widely concerned, because metal can catalyze the char formation and improve the quality of char residues. It has been observed that the combination between copper and molybdenum exhibits a significant synergistic effect, unfortunately, the detailed synergistic mechanism is still unclear. [16] Comparatively, there are currently few reports on the effects of metal-based flame retardants on the flame retardancy and smoke suppression of c-PVC foam.In addition, facing the increasingly serious global energy crisis, polymer foams can greatly reduce heat transfer and are widely used as thermal insulation materials. [18] The efficiency of reducing energy loss mainly depends on the thermal conductivity of the foam. In recent years, numerous studies have been carried out to develop polymer foams with higher thermal insulation properties. The nanocellular foam with high expansion ratio is expected to have very good thermal insulation. However, it is still difficult to prepare nanoporous foams with higher expansion ratio. Recently Park et al. showed that the radiant thermal conductivity of nanoporous foams with low-density will be greatly increased, [19] so the superinsulation still cannot be

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Fabrication of flat and sizeable nanocellular polymethyl methacrylate (PMMA) foam with tunable thermal conductivity

Gebremedhin,

Tolcha,

Yeh

2024

Polymer Engineering & Sci

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Polymeric nanocell foam is a promising material that faces manufacturing challenges. Producing sizable and thick foams for properties testing has been challenging. This study aims to scale up and understand the foaming mechanism of nanocellular foams by controlling the saturation temperature, pressure, and molecular weight distribution of the matrix to fine‐tune the glass transition temperature of the polymer/gas mixture. The hot‐press foamed samples possess a 100 × 70 × 6 ~ 8 mm3 dimension and a cell size of less than 200 nm. Bimodal structures can also be created by controlling the critical processing parameters. Introducing 37% microcells into unimodal nanocellular foam reduced the relative density from 0.29 to 0.19. The thermal conductivity of the foams was tuned by controlling the cell size distribution. Unimodal nanofoams have the lowest thermal conductivity for foams of the same density due to the Knudsen effect and tortuosity. The measured thermal conductivity is in agreement with theoretical models.Highlights PMMA nanofoam with a dimension of 100 × 70 × 6–8 mm3 and cell size below 200 nm. The morphology of nanofoams was tuned to be unimodal and bimodal. The foam density of the bimodal nanofoams was lowered below 0.238 g/cm3. The thermal conductivity of foams was tuned by controlling the cell structure.

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Wrong expectation of superinsulation behavior from largely-expanded nanocellular foams

Abstract: This work aims to predict the thermal conductivity of microcellular and nanocellular thermal insulation foams to explore the correlation between the cellular structure and the thermal insulating properties.

Cited by 39 publications

References 136 publications

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

Simultaneously Improving Thermal Insulation, Flame Retardancy, and Smoke Suppression for Rigid Cross‐Linked Polyvinyl Chloride Foam through Combined Copper/Molybdenum Trioxide

Fabrication of flat and sizeable nanocellular polymethyl methacrylate (PMMA) foam with tunable thermal conductivity

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