Hollow Glass Microspheres Content Research Articles

Waterborne novolac epoxy‐based thermal resistant and fire‐retardant thermal insulation coatings

AbstractWaterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance.

Comprehensive performance evaluation of HGM hybrid modified resins: Excellent high resistivity terahertz shielding and impact energy absorption properties

AbstractThe development of electronic fuze has placed higher demands on encapsulation resins, which are required to provide not only insulation and protection, but also higher impact resistance and good electromagnetic shielding performance. A new composite material consisting of hollow glass microspheres (HGM) and modified epoxy resin was developed. This material exhibits significant electromagnetic shielding capabilities for terahertz (THz) waves, as well as superior impact energy absorption properties. Bisphenol A‐type epoxy resin (E‐44) was modified using Al(OH)3, red phosphorus, carbon black, and SiO2, and the material properties were optimized by adjusting the HGM content. The electromagnetic shielding effectiveness and impact energy absorption of the composite material in the THz band were comprehensively tested using THz time‐domain spectroscopy and split Hopkinson pressure bar testing systems. Additionally, a comprehensive evaluation of the mechanical and dielectric properties, thermal conductivity, and thermal stability of the material was conducted. The results showed that the electromagnetic shielding effect of 60 vol.% HGM hybrid‐modified resins was the best, reaching 43.78 dB. The 20 vol.% HGM hybrid‐modified resins not only has a specific absorption energy of 18.51 J/cm3, but also has the best overall performance. This work has advanced the design and development of multifunctional and impact‐resistant potting epoxy resins.

Development of epoxy-based sandwich composite panel with hollow glass microspheres/clay hybrid core and banana fiber facesheet for structural applications

This study focuses on improving the mechanical properties of sandwich composites by developing epoxy-based sandwich composite panels with hollow glass microspheres/nanoclay hybrid core and banana fiber facesheets for structural applications. The mechanical performance of sandwich composite panels made with hollow glass microspheres (HGM)/nanoclay hybrid core with banana fibers face-sheet composites panel is investigated in this work. The HGM content of the core was varied from 1 wt% to 3 wt% in the sandwich composites panel, while the nanoclay content of the core was varied from 1 wt% to 5 wt% in each of the HGM-filled series of the sandwich composite panel, these sandwich composite panels were fabricated using a conventional resin casting method. In this investigation, the mechanical, water absorption, and buoyancy behavior are thoroughly studied and the findings revealed better improvement at the sandwich composites with hybrid core formulation with banana fiber facesheets than the sandwich composites without hybrid core formulation. This demonstrates that banana fiber with epoxy resin has a limited amount of strength when used without a hybrid core but delivers better performance when HGM and clay particles are mixed as the hybrid core because of excellent interfacial adhesion between the hybrid core and the matrix. The improved mechanical properties could suggest that this material may be suitable for application in industries where sandwich structures that are lightweight with good mechanical properties are required. This study showed a new area of sandwich structure development by enhancing mechanical properties using hybrid core and banana fibers.

Lightweight, hydrostatic pressure‐resistance, thermal insulating epoxy syntactic foam with a multiscale ternary structure for marine engineering application

AbstractThe study of lightweight epoxy syntactic foams is of great significance for the exploitation of marine resources. In this work, glass fibers reinforced epoxy hollow spheres (GFs‐EHS) were first prepared using a template method, and a lightweight three‐phase epoxy syntactic foam (LWTP‐ESF) with a multiscale ternary structure was prepared using a molding pressing method with epoxy resin as matrix, hollow glass microspheres (HGMs), and GF‐EHS as the lightweight fillers. The effect of HGMs content on the density, uniaxial compression properties, water absorption, and thermal conductivity of obtained LWTP‐ESF was evaluated. The results indicated that the density, uniaxial compression strength, and thermal conductivity of LWTP‐ESF were consistently decreased, while the water absorption was increased with the increase in HGMs content. The highest specific compression strength and lowest thermal conductivity of LWTP‐ESF could reach 52.77 ± 0.82 MPa·cm3/g and 0.113 ± 0.005 W/(m·K), respectively. Moreover, the effect of hydrostatic pressure on the water absorption and thermal conductivity of LWTP‐ESF were also systematically analyzed. This study provides a novel system and method to prepare lightweight epoxy syntactic foams, and the prepared composites have potential applications in the field of lightweight thermal insulation materials for marine.Highlights The composites with a multiscale ternary structure were designed. The composites possessed significantly lower density and thermal conductivity. The water absorption of composites under hydrostatic pressure was evaluated. The thermal conductivity of composites under hydrostatic pressure was evaluated. The water absorption mechanism and thermal insulation mechanism were proposed.

Constructing ‘bayberry shape’ structure on HGMs surface using CNTs to enhance the mechanical properties of HGMs/epoxy composites

The lightweight composites, composed of epoxy resin (EP) and hollow glass microspheres (HGMs), have been widely applied in marine buoyancy materials, insulation for marine pipelines, and aerospace. However, achieving lower density often requires a significant addition of HGMs, leading to a compromise in mechanical properties. To address this problem, this paper proposes a method to enhance the mechanical properties of HGMs/EP composites without altering the HGMs content. Here, the ‘bayberry shape’ structure of HGMs was achieved by chemically grafting carbon nanotubes (CNTs) onto their surface through an esterification reaction. Subsequently, a lightweight CNTs-HGMs/EP composite with improved strength was fabricated using these ‘bayberry’ HGMs as fillers and EP as the matrix. The effect of different grafted-CNTs content on HGMs' surface on the mechanical properties of CNTs-HGMs/EP composites, along with the enhancement mechanism, were systematically analyzed. The tensile strength, flexural strength and compressive strength of CNTs-HGMs/EP composites demonstrated remarkable increases of 39.14%, 21.78% and 17.87%, respectively, compared to pure HGMs/EP composites. Our results demonstrate that surface modification of HGMs could significantly improved the mechanical properties of HGMs/EP composites without affecting their density. Moreover, this method was characterized by its simplicity in operation and batch preparation, which holds great significance for the efficient production of lightweight composites.

Thermal and Wettability Properties of Nanoclay-Filled Epoxy-Based Foam Composite as Lightweight Material

Abstract Epoxy-based foam composite (EBFC) materials have received considerable attention recently because of their wide range of applications in the aerospace and marine industries. EBFC materials made from hybrid fillers are materials generated to have improved thermal properties. This work focuses on improving the thermal properties and wettability of EBFC materials with hybridized fillers by infusing hollow glass microspheres (HGM) and clay. The HGM content varied between 1 weight percent (wt.%) and 5 wt.% in foam composite materials while clay content varied between 1 wt.% and 5 wt.% in each of the HGM-filled series of foam composite materials. These foam composite materials were fabricated using a conventional resin casting method. The thermal properties, such as thermal conductivity, thermal expansion, coefficient of thermal expansion, as well as specific heat capacity, water contact angles, and percentage of water absorption of hybrid-filled foam composite materials were investigated and compared with neat epoxy and epoxy foam materials. It was found that hybrid-filled foam composite materials exhibited improved thermal properties over neat epoxy material because of good chemical reactions and excellent interfacial adhesion between the fillers and matrix. These improved thermal properties may suggest that this material may be suitable for application in industries where lightweight materials with good thermal properties are required. This reveals a new area in foam composite manufacturing research by enhancing thermal properties with hybrid fillers.

Study on properties of Ultra-Lightweight Insulated Cementitious Composites for concurrent seismic and energy improving of existing RC frames

In the present paper, the properties of Ultra-Lightweight Insulated Cementitious Composites (ULICC) were investigated experimentally. Hollow Glass Microspheres (HGM) were used to improve thermal insulation capacity. The influence of water to blind ratio (W/B) and HGM volume content on the mechanical and thermal properties of ULICC mixtures was considered. The ULICC mixtures exhibited dry density of 1071–1358 kg/m3, tensile strength of 2.25–3.09 MPa, tensile strain capacity of 1.84–2.95%. Compressive strengths of ULICC were 35.2–57.1 MPa at 28 days by 100 mm cubic specimens. Noobvioussizeeffect on compressive strength was observed. The thermal conductivity coefficients ranged from 0.193 W/m.K to 0.227 W/m.K. Linear trend of compressive strength and thermal conductivity coefficient with HGM content were acquired. Three ULICC tensile curves considering compressive strength and tensile strain capacity were chosen for infills retrofitting analysis based on FEM. Skeleton curves, stiffness degradation, characteristic values, stress of ULICC plates were investigated by FEM results. FEM results indicated that infilled RC frame retrofitted by ULICC with higher compressive strength exhibited higher lateral carrying capacity. Strut effect of retrofitted infills acting at surrounding frame was enhanced due to ULICC mixture with highest strain capacity. Energy efficiency improvement was analyzed by heat transfer coefficients calculated. Energy saving requirements in Chinese codes can be met in hot summer and cold winter zone, as well as, cold zone after retrofit. Thermal insulation capacity of existing RC frames can be improved concurrently after retrofitted by ULICC.

Influence of hybridizing fillers on mechanical properties of foam composite panel

AbstractFoam composite panels made from hybrid fillers are materials developed to have low density with high mechanical properties. This work focuses on improving the mechanical properties of epoxy‐based foam composite panels with hybridized fillers by combining hollow glass microspheres (HGM) and nanoclay. The HGM content was varied from 1 wt.% to 3 wt.% in foam composites panel, while nanoclay content was varied from 1 wt.% to 5 wt.% in each of the HGM‐filled series of foam composites panel, these foam composite panels were fabricated using a conventional resin casting method. The mechanical properties such as tensile strength, impact strength, hardness, flexural strength of the prepared hybrid‐filled foam composite panels were determined and compared with the neat epoxy. It was found that the hybrid‐filled foam composite panels exhibited improved mechanical properties than the neat epoxy. These improved properties were because of excellent interfacial adhesion between the hybrid fillers and the matrix. The improved mechanical properties could suggest that this material may be suitable for application in industries where lightweight materials with good mechanical properties are required. This study showed a new area of synthetic foam development research by enhancing mechanical properties using hybrid‐filled.

Experimental investigation of the shear bond strength between HGM cement and shallow formation in deepwater environments

Due to its low density and high strength, hollow glass micro-sphere (HGM) has become a popular additive to cement slurry in deepwater cementing. The shear bond strength (SBS) between the well cement and formation ensures the safety and integrity of oil and gas wells. We designed a simulation experiment to measure the SBS between HGM cement and shallow formations in deepwater environments. We studied the evolution of the tensile force when pulling a simulated pipe string and cement ring out of the soil layer with a constant force. The results suggest that the HGM content and size of the cement ring have no effect on the change in the tensile force over time. At the peak of the tension curve, the cement ring and soil begin to slip, causing the tensile force to decrease with time. We divided this curve into two sections, with the peak value as the dividing point. The first section is the accumulating section where the tension increases without displacement of the cement ring and the soil. The second section is the dynamic slip section. Additionally, we proposed the concepts of static SBS and dynamic shear bond coefficient. The static SBS is the strength at the pull-off position, and the dynamic shear bond coefficient is the cementation coefficient of the cement ring in the dynamic slip stage. We divided the cement ring into segments along its length, calculated the shear bond coefficient of the cement ring at different depths, and studied the variation in the dynamic shear bond coefficient with depth. The static SBS increases with decreasing HGM content and casing size, and the static SBS of the small casing is significantly greater than those of the middle casing and the large casing. The dynamic shear bond coefficient decreases after the occurrence of dynamic slip. This study provides important insights into the evolution of the cement-formation SBS, and the results can provide guidance for future cementing design.

Effects of the absorber, thickness and surface roughness on the electromagnetic wave absorption characteristics of magnesium phosphate cement

Magnesium phosphate cement (MPC) functionalized with excellent electromagnetic wave absorption performance, bonding capacity, fast hardening and early strength can meet the requirements for rapid electromagnetic radiation protection of military and civil building structures. Hollow glass microsphere (HGM) is added uniformly to improve the impedance matching of MPC to free space, so that the electromagnetic wave is able to be maximally introduced into MPC and effectively absorbed by carbon nanotubes (CNT) through high dielectric loss effect. Influences of HGM contents, thickness and surface roughness of specimens on the electromagnetic wave absorption performance of MPC are systematically investigated. Test results demonstrate that the electromagnetic absorption performance of MPC is significantly enhanced by the additions of HGM and CNT. The peak reflection loss and the bandwidth below −10 dB first increase and then decrease with increasing HGM content. Increasing the thickness of the MPC improves the electromagnetic reflection loss. The electromagnetic absorption properties of MPC are improved further by cutting notches. MPC blended with 50 vol% HGM and 1 wt% CNT (by MgO) with 5 mm deep notches spaced 18 mm apart has excellent electromagnetic absorption capacity as featured by a peak reflection loss of –33.5 dB and a bandwidth of 7.03 GHz below −10 dB. In the perspective of structural strengths, the modified MPC is able to repair damaged concrete of pre-fractured concrete. It achieves the dual features of absorbing electromagnetic waves and repairing existing concrete structures.

Thermal, Mechanical, and Acoustic Properties of Polydimethylsiloxane Filled with Hollow Glass Microspheres.

Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.

Study on the optimal addition of hollow glass microsphere into an anticorrosive cool coating for oil storage tanks

The addition amount of hollow glass microsphere (HGM) in a newly developed waterborne, fluorocarbon resin-based, anticorrosive cool coating is investigated through a series of indoor tests, combined with real and simulated storage tank tests on site. The heat insulation, corrosion and chemical resistance properties of the coatings with different HGM content are studied. The results show that the temperature reduction of coatings tested indoors rises from 22 to 31.1 °C due to the decrease of thermal conductivity as the HGM content raises from 0% (wt.%) to 16% (wt.%), though the overall reflectivity decreases simultaneously. In addition, both indoor and outdoor spray tests manifest that adding 8 and 12% content of HGM increase the corrosion resistance of the coating. When the content increases to 16%, however, the corrosion resistance becomes worse, which can be attributed to the voids in the coating, along which the corrosive medium enters. Furthermore, all the water, acid and alkaline resistance are improved when the HGM content is 8%. Finally, by optimizing with 8% HGM addition, the temperature reductions of the two simulated tanks in dry-heat desert and tropical marine zones can reach 15 and 18 °C, respectively. And the aging resistance in both two climatic conditions is good.

Effect of hollow glass microspheres addition on density reduction and mechanical properties of PA6/glass fibers composites

The strategy of combining the traditional reinforcement of glass fibers (GF) with lighter hollow glass microspheres (HGM) can afford to fulfill the need for potential light-weight and high-strength modern materials required in various sectors, such as automotive and aerospace industry applications. This work fabricated composites of PA6/GF/HGM by melting blending in a co-rotating twin-screw extruder, and subsequently, injection molded. The effects of HGM content on the density, morphological and mechanical properties were investigated and the PA6/GF/HGM composites properties were compared to the properties of the traditional PA6/GF (70/30) wt% composite, widely used today in automotive industries. With the increase of HGM amount in the formulations, a reduction of between 3 and 12% in density was achieved with a slight reduction in its mechanical properties, showing that this new strategy can be applied to replace the PA6/GF (70/30) wt% composite, providing a considerable weight reduction for these materials.

Feasibility of Using the Hollow Glass Microsphere to Develop Lightweight CAC-GGBFS-Blended Strain-Hardening Cementitious Composites

Strain hardening cementitious composites (SHCCs) with superior tensile strength and ductility have been utilized as an effective repair material. A corrosion-resistant binder, calcium aluminate cement (CAC)–ground granulated blast-furnace slag (GGBFS) blends, has been introduced into SHCC to expand its application in the concrete sewage network rehabilitation. As a repair material, the lightweight property is particularly favorable as it can broaden its functionality. This article presents a study on developing a novel lightweight CAC-GGBFS-blended SHCC using hollow glass microsphere (HGM), namely, HGMLW-SHCCs. The fine silica sand content was substituted with HGM at 25, 50, 75, and 100 vol% in HGMLW-SHCC. We examined flowability, density, uniaxial compressive behavior, direct tensile behavior, and pseudo strain-hardening indices. Microstructure analysis was also conducted to understand the meso-scale behavior of this new lightweight composite. The newly developed HGMLW-SHCC had a 28-day density of only 1756 kg/m3. Compressive and tensile strengths were determined in the range of 62.80–49.39 MPa and 5.81–4.19 MPa, respectively. All mixtures exhibited significant strain-hardening behavior. Even though the increased HGM content negatively affected the tensile strength of HGMLW-SHCC, it had a positive effect on its ductility. In addition, HGM can reduce crack width and tensile stress fluctuations significantly. The results showed that HGM was a promising material for producing strong and lightweight corrosion-resistant SHCCs to be used as a retrofitting material in the wastewater industry.

Preparation and Performance of HGM/PPENK-based High Temperature-resistant Thermal Insulating Coatings

Novel high temperature-resistant coatings with high mechanical strength and thermal-insulating performance were prepared with poly(ether nitrile ketone) (PPENK) resin as matrix and hollow glass microspheres (HGMs) as thermal-insulating filler. The corresponding mechanical and thermal-insulating study indicated that the mechanical properties of the coatings decreased with the increase of HGM content, and were improved after surface modification of HGM by KH570 resulting in enhancement of interaction between HGM and PPENK resin. The thermal conductivity of HGM/PPENK thermal-insulating coating decreased with the increase of HGM content and coating thickness, along with the decrease of the true density. It also showed slight increase trend due to HGMs surface modification. The HGM/PPENK coating filled with modified HGMs showed better thermal resistance than that of unmodified HGM/PPENK coating. The thermal decomposition temperature at 5% weight loss of the coating containing modified HGMs was 10 °C lower than that of pure PPENK, and 40 °C higher than that of neat HGM/PPENK coating. The coating exhibited commendable appearance after 400 °C for 30 min. The merits of HGM/PPENK-based thermal coatings obviously demonstrated promising prospect in thermal protection fields.

Polyimide hollow glass microspheres composite films with low dielectric constant and excellent thermal performance

AbstractNowadays, polyimide (PI) with low dielectric constant is expected to be widely applied in microelectronics. For this reason, hollow glass microspheres (HGM) modified by silane coupling agent KH‐550 (K‐HGM), a series of HGM/PI and K‐HGM/PI composite films with excellent thermal performance, hydrophobic and low dielectric constant were fabricated by in situ polymerization. The effect of HGM/K‐HGM content on the properties of composite films was studied. The superior heat resistance of HGM can improve the thermal performance of composite films. Due to silane coupling agent KH‐550, K‐HGM exhibits a good interfacial compatibility with PI matrix and forms an interfacial adhesion region. With the HGM loading of 6%, comparing with pure PI films, the glass transition temperatures (Tg) of composite films were dramatically increased by 32.3°C. Especially, the low dielectric constant of 2.21 and dielectric loss of 0.0059 at 1 MHz were obtained for the PI/K‐HGM composite film with addition of 8 wt%. Thus, PI/K‐HGM composite films show more excellent performance. The current work provides a promising solution for fabrication of PI with low dielectric constant and superior thermal performance that may be applied in microelectronics industry.

Development of thermally conductive and high‐specific strength polypropylene composites for thermal management applications in automotive

AbstractThis study reports the preparation of multifunctional hybrid composites based on polypropylene (PP) for potential thermal management applications in automotive. Short carbon fiber (CF) at 5 and 8 wt%, and silane‐treated hollow glass microsphere (HGM) at 5, 10, 20, 30, and 40 wt% were incorporated separately in PP along with maleic anhydride‐grafted‐polypropylene (MA‐g‐PP). The interplay of filler content and its dispersion and distribution had a significant effect on the thermal conductivity (Kc) of the composites. Highest Kc of 1.20 W/m K was obtained for a CF and HGM wt% of 5 and 20, respectively. The rheological analysis revealed improved flowability as the complex viscosity of composites up to 20 wt% of HGM content was found to be less than PP. The thermal stability improved upon HGM incorporation and the highest thermal stability of ~26°C higher than that for PP was exhibited by hybrid composite with 8 wt% CF and 40 wt% HGM. Furthermore, Nielsen model demonstrated to be the closest fit for the experimental thermal conductivity value of hybrid composites among various micromechanical models used.

Processing and properties of hollow glass microsphere particulate-filled PA2200 composites produced by selective laser sintering

Selective laser sintering (SLS) to prepare composites by adding filler into polymer is an effective method to save costs and reinforce the sintered parts. This article investigated the fabrication of PA2200 composites filled with different volume fractions of hollow glass microsphere (HGM) by SLS. HGM was prepared by silane coupling agent surface treatment. The particle size distribution, microstructure, thermal and mechanical properties of PA2200/HGM composites were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and tensile experiment. The results indicated that the density of the composite was significantly reduced compared to the neat PA2200 and the density decreased with the HGMs content increasing. HGM improved the warping deformation in the process of sintering. The tensile modulus increased while tensile strength and elongation at break decreased as a function of HGM volume fraction in a certain range. This work indicated that thermal properties and tensile properties of polyamide-matrix composites can be reinforced by adjusting HGM content, and PA2200/HGM composite powder is a good material for SLS with less density and lower cost.

Processing of Hollow Glass Microspheres (HGM) filled Epoxy Syntactic Foam Composites with improved Structural Characteristics

Abstract The objective of this work is to improve the structural characteristics of hollow glass microsphere (HGM) filled epoxy syntactic foam composites with little voids content and improved HGM dispersion in the composite. A modified degassing technique has been introduced during resin casting process of the HGM filled syntactic foam composites. The effect of HGM content volume fractions (5–25%) on the degassing techniques was examined. The syntactic foam composites were characterized by analysing structural morphology using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy(TEM), and density measurements (theoretical and experimental). Less than 5% void content has been achieved in this study. This resulted in improved tensile and dynamic mechanical properties (DMA).

High‐damping polyurethane/hollow glass microspheres sound insulation materials: Preparation and characterization

AbstractThe high‐damping property of polyurethane elastomers and the low density of the hollow glass microspheres (HGM) were used to prepare the sound insulation materials in the present work. The transmission loss (TL) was measured to evaluate the HGM content on the sound insulation properties. The experimental results showed that the addition of HGM improved the hardness and compression modulus of the HGM‐filled polyurethane composites, and the loss factor (tan δ) of polyurethane composites were greater than 0.9. The average transmission loss (ATL, from 63 to 6300 Hz) reached 37.32 dB when the content of HGM was 10 wt%. The ATL of the HGM‐filled polyurethane composites with 15 wt% HGM in the damping control region and the mass control region were 31.94 and 46.78 dB, respectively. The synergistic effect of the microphase separation, the interfacial effect and the rigidity of polyurethane composites resulted in the improvement on sound insulation property. The polyurethane composite has a great potential application for the field of sound insulation materials.