Synthesis and mechanical properties of lightweight hybrid geopolymer foams reinforced with carbon nanotubes

A lightweight hybrid geopolymer foams reinforced with carbon nanotubes (CNTs) was exploited by adding the CNTs into geopolymeric matrix through hydrogen peroxide method. The synergistic effects of nanotubes and foaming agent on the phase evolution, microstructure, and mechanical properties were investigated. After introduction of nanotubes, the geopolymer foams reinforced with CNTs (CNTs/KGP) still showed amorphous structure. Porosity of the foams increased with the H₂O₂ content and decreased with the increase in CNTs content. The addition of CNTs (1-9 wt%) in foams refined the distribution of pore size from 523 to 352 μm. Compression strength of the CNTs/KGP samples elevated with the increasing content of CNTs, which was contributed to the crack propagation and bridging of CNTs in foams. The CNTs/KGP foams with considerable porosity show potential applications in adsorption, filtration, membrane supports, other industries, etc     

Effect of high temperature on the mechanical properties of hierarchical porous cenosphere/geopolymer composite foams

A hierarchical porous cenosphere/geopolymer composite foam (FHCs/KGP) was fabricated by the simultaneous incorporation of O₂ pore from hydrogen peroxide and cenosphere filler addition. Effects of both H₂O₂ content and high-temperature treatment on the microstructure, porosity and strength of porous FHCs/KGP foams were investigated systematically. The obtained FHCs/KGP foams showed typical amorphous structure and desirable porosity from 65 to 82%. The composites could crystallize in situ to FHCs/leucite foams above 1000℃. Compression strength of the FHCs/leucite foams showed a maximum value of 5 ± 0.3 MPa when treated at 1000°C. The improvement of mechanical properties for the composite foams was attributed to crack deflection, fractured microspheres and the good bond between the FHCs and matrix. This study could open opportunities to employ cellular foams as alternatives in structure and filtration applications.     

Improving the thermal insulation of high-temperature furnaces by the use of diatomite

Diatomite components are used in the design of the thermal insulation for a high-temperature furnace. It is shown that the proposed construction for the heat insulation has an advantage over existing ones. Translated from Novye Ogneupory, No. 4, pp. 85 – 87, April, 2009.     

Investigation on pore properties,thermal conductivity,and compressive behavior of fly ash/slag-based geopolymer foam

Geopolymer foam has emerged as a promising inorganic porous material in the last decade. Despite of the numerous advantages, there are some pending issues to be addressed, on top of that is the low compressive strength. To overcome this, this study synthesizes a high-strength geopolymer foam by the partial substitution of fly ash (FA) with ground granulated blast furnace slag and carries out an intensive investigation into its microstructure, pore properties, thermal conductivity as well as compressive behavior. The microstructure is firstly analyzed by X-ray diffraction and Fourier transform infrared spectroscopy techniques. The pore characteristics are also scrutinized, including pore size distribution, total porosity and water absorption. Then, the thermal conductivity is investigated and the applicability of basic effective thermal conductivity models to characterize the relationship with total porosity is evaluated. Afterward, the compressive strength together with the softening coefficient is examined, and the relationship with total porosity is also studied. Finally, comparisons between the proposed geopolymer foam and other FA-based geopolymer foams in the literature are performed. The results show that the proposed geopolymer foam possesses not only a comparable thermal conductivity but also a far superior compressive strength, which sheds light on the widespread applications in thermal insulation.     

硅酸钠模数对无机聚合物力学性能与微观结构的影响

用模数m=1.0、1.2、1.4和1.6的4种硅酸钠溶液作激发剂制备偏高岭土基无机聚合物,通过强度测试、红外分析(IR)、X线衍射(XRD)和扫描电镜(SEM)等方法考察激发剂模数对无机聚合物力学性能和微观结构的影响。结果表明:模数在1.0~1.6变化时,激发剂中硅氧四面体呈低聚合态;随养护时间延长,无机聚合物抗压强度和抗折强度提高,m=1.2的无机聚合物28 d抗压强度最高(74.6 MPa),抗折强度为11.2 MPa;4种无机聚合物主体相均呈非晶态,结构上由凝胶体和残留原料颗粒组成,其中,m=1.2时无机聚合物的显微结构最平整。     

Experimental research on the dynamic compressive properties of lightweight slag based geopolymer

The present study aims at preparing lightweight slag based geopolymer (LW-SG) and studying its mechanical properties under dynamic and quasi-static loads. Firstly, three LW-SG with different densities were prepared by replacing the slag with expanded perlite (EP). Secondly, the density, wave velocity and pore structure of LW-SG with different EP contents were tested. Thirdly, the mechanical properties under quasi-static and dynamic loads were compared. Finally, the effects of the strain rate and EP content on the mechanical properties and failure modes of LW-SG were discussed. The results showed that with the EP contents increase, the dry density and longitudinal wave velocity gradually decreased, while the porosity increased. In addition, the quasi-static compressive strength and elastic modulus of LW-SG increased with curing ages, but decreased with EP contents increased. The dynamic compressive strength, dynamic increase factor, strain energy density and damaged degree of LW-SG all showed an increasing tendency with the strain rates increase, which exhibits an obvious strain rate dependence. Under the same strain rate, the dynamic compressive strength and strain energy density decreased with the EP contents increase, while the damaged degree increased with the EP contents increase.     

Production and thermomechanical characterization of wool–geopolymer composites

Load‐bearing and thermal insulating wool waste/geopolymer composites with fire‐resistant properties were produced and characterized. Two formulations, with different amounts of wool fibers, corresponding in the final composites to about 23 vol% and 31 vol%, were tested. The composites exhibited an average density of 1.0 g/cm³, with a thermal conductivity of 0.2 W/mK, and compressive and flexural strength around 9 and 5 MPa, respectively. The flexural strength and fracture behavior were improved by the presence of the fibers, which promoted the onset of a toughening mechanism in the material. Results showed that a geopolymer matrix loaded with 23 vol% of wool fibers is suitable as flame‐resistant barrier, as reaction to fire is in class A2 (UNI‐EN 13501‐1), and as insulating structural partition in buildings because it ensures a consistent load‐bearing ability coupled with thermal insulating properties, similarly to other man‐made fiber products, with a considerable gain in terms of cost and environmental impact.     

Effect of antistatic additives on mechanical and electrical properties of polyethylene foams

Polyethylene foams with different antistatic additives (Atmer 7325, Atmer 7105, and Atmer 190) were prepared by extrusion and stored during 6 months of time span in a real life environment. The antistatic performance was evaluated by measuring the surface resistivity and throughout decay‐time experiments. Mechanical properties and migration tests were also performed. It was found that the migration of antistatic agents is in general low enough, which allows to maintain the antistatic performance for periods of time larger than 6 months. The tests revealed that the desired low surface resistance and required low static decay time could be achieved with all the antistatic agents under test. Moreover, the additives with amina (Atmer 7105 and 7325) as an active agent showed slightly better antistatic performance than the one with the ionic agent (Atmer 190). The addition of an antistatic agent does not significantly affect the mechanical behavior of the foam indicating a desired feature concerning industrial applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The preparation and thermomechanical properties of high-temperature foams based on thermoplastic poly(phthalazinone ether ketone)

Poly(phthalazinone ether ketone) (PPEK) is an amorphous thermoplastic polymer with a high glass transition temperature (T_g) exceeding 250°C. We describe the preparation of foams from PPEK and characterize their properties. PPEK foams were prepared using dichloromethane as a foaming agent. The foaming agent was swollen into discs of the PPEK, which were then foamed by heating. Foams could be prepared at temperatures far below the T_g of the PPEK due to plasticization of the polymer by the foaming agent. Foams with densities ranging from 0.1 to 0.65 g/cm³ were prepared. Their thermal conductivity and modulus (measured approximately by indentation tests) were found to decrease with density, and the trends were similar to those expected from existing models. The foams could be annealed at 200°C without collapse suggesting that they may be useful in structural or insulation applications where stability at high temperature is essential.     

Mechanical,thermal, morphological,and curing properties of geopolymer filled natural rubber composites

The main objective of this work was to investigate influence of natural rubber (NR) types on mechanical, thermal, morphological, and curing properties together with relaxation behavior of geopolymer filled NR composites with and without bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. Three alternative types of NR: unmodified NR, and epoxidized NR with 25 (ENR-25) or 50 mol % epoxide (ENR-50) were exploited. Rubber compounds filled with GP particles were prepared in an internal mixer at 60 °C and 130–150 °C for the ones with and without TESPT, respectively. It was found that incorporation of GP significantly affected cure characteristics and mechanical properties of the rubber composites. That is, decreasing cure time was observed from 11.6, 3.2, and 7.0 min in gum NR, ENR-25, and ENR-50 to 6.9, 2.1, and 5.0 min in NR/GP, ENR-25/GP, and ENR-50/GP compounds, respectively. Furthermore, the ENR-25/GP and ENR-50/GP composites showed finely dispersed GP particles which indicate high filler–rubber interactions. The in situ silanization with TESPT in rubber composites enhanced the mechanical properties of NR/GP and ENR-25/GP composites but no such enhancement was found in the ENR-50/GP composite. This matched the observations of Payne effect, maximum tan δ, and stress relaxation properties of the composites. We found that the ENR-25/GP composites exhibited the best overall properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47346.     

Relationship between the cell structure and mechanical properties of chemically crosslinked polyethylene foams

The main objective of this work was to study the effect of the controlling parameters on the morphology and mechanical properties of the peroxide crosslinked low‐density polyethylene foams. The relationship between the morphology and mechanical properties was also considered. Using different Dicumyl peroxide (DCP) and azodicrbonamide (ADCA) concentrations, various foams with different cell structures were prepared. Gel content and density of the foams were measured according to the standard methods. The morphology was examined using SEM technique. The mechanical properties of the foams were evaluated by means of compression and creep recovery tests. The results showed that the gel content and the density are mainly controlled by DCP and ADCA concentration, respectively. The results also showed that the cell size distribution is mainly controlled by DCP concentration. Increasing of DCP increased the gel content and decreased the cell size and cell size distribution. Foam density was mainly controlled by ADCA concentration, whereas the morphology was less affected with ADCA concentration. The foams with small cell size and narrow cell size distribution showed higher mechanical strength and lower plastic strain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization of epoxy foams

Epoxy foams were prepared from the commercial system (LY 5054 epoxy resin, HY 5054 amine as curing agent, and DY 5054 siloxane as foaming agent) supplied by Ciba‐Geigy. From the differential scanning calorimeter results the optimal epoxy–amine ratio was determined. A maximum T_g∞ value of 85°C was found for an epoxy–amine ratio of 100:35 by weight. In this system, the siloxane reacts with the amine releasing hydrogen that acts as the real foaming agent. The density decreased from 490 to 215 kg/m³ as the epoxy:blowing agent ratio increased from 100:1 to 100:3 by weight of the reactive mixture. Under the synthesizing conditions, the glass transition temperature (T_g∞) of the foam did not vary significantly as the blowing agent increased. The modulus and compressive strength of the foam exhibited a power‐law dependence with respect to density of the form: E∝(ρ)ⁿ, where n=1.8. Scanning electron microscopy analysis verified that the foam have a closed cell structure. The relation between composition, final morphology, density, and properties of the foam was analyzed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2992–2996, 2003     

Thin fly ash/ ladle furnace slag geopolymer: Effect of elevated temperature exposure on flexural properties and morphological characteristics

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na₂SiO₃) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na₂SiO₃/NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development.     

Mechanical properties and thermal stability of rice husk ash filled epoxy foams

Mechanical properties and thermal stability of epoxy foams filled with white and black rice husk ash were studied. Epoxy foams were prepared from a commercial system and filled with different amounts of both the ashes (0, 6.8, 12.8, 18.0, and 22.7 wt %). The incorporation of both the ashes modified the final morphology of the foam, decreasing the average cell size and increasing the number of cells per volume unit. For all filler percentages used, the specific modulus and strength results showed that the white ash is more effective as reinforcing agent than the black ash. The initial degradation temperature was not affected by the content and type of ash used as the filler. The integral procedure decomposition temperature, weight loss, and char residue results were related to the ash type and atmosphere used in the thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effects of high-temperature heat treatment on the mechanical properties of unidirectional carbon fiber reinforced geopolymer composites

Unidirectional carbon fiber reinforced geopolymer composite (C_uf/geopolymer) is prepared by a simple ultrasonic-assisted slurry infiltration method, and then heat treated at elevated temperatures. Effects of high-temperature heat treatment on the microstructure and mechanical properties of the composites are studied. Mechanical properties and fracture behavior are correlated with their microstructure evolution including fiber/matrix interface change. When the composites are heat treated in a temperature range from 1100 to 1300 °C, it is found that mechanical properties can be greatly improved. For the composite heat treated at 1100 °C, flexural strength, work of fracture and Young's modulus reach their highest values increasing by 76%, 15% and 75%, respectively, relative to their original state before heat treatment. The property improvement can be attributed to the densified and crystallized matrix, and the enhanced fiber/matrix interface bonding based on the fine-integrity of carbon fibers. In contrast, for composite heat treated at 1400 °C, the mechanical properties lower substantially and it tends to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve.     

Mechanical and acoustic absorption properties of lightweight fly ash/slag-based geopolymer concrete with various aggregates

Acoustic absorption and thermal insulation play a key role in modern buildings to make living comfortable and energy-saving. This paper aims to study the workability, physical and mechanical properties, thermal conductivity, and acoustic absorption of modified geopolymer concrete (GPC) with various types of lightweight aggregates (LWA) such as extruded polystyrene foam beads waste (EPS), vermiculite, or lightweight expanded clay aggregate (LECA). The mixtures of geopolymer concrete have been modified by substituting for the ordinary aggregates (dolomite) by volume with various ratios of 0, 25, 50, 75, and 100% for each type of LWA. Besides, the mechanisms of specimens were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and mapping. The results illustrated that the compressive strength values range between 8.5 and 47.50 MPa. The hardened density of concrete was between 1500 and 2450 kg/m³, and thermal conductivity was between 0.45 and 1.16 W/m.K. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. EPS, vermiculite, and LECA will be beneficial for applications in lightweight geopolymer concrete due to their capability to reduce weight and excellent thermal conductivity, and the property of improving acoustic absorption. The mechanical results indicated that 25% LECA was the best compared with the ratios of other LWA and gained 35.0, 2.7, and 4.3 MPa of compressive, splitting tensile and flexural strength, respectively. It had positive workability; the thermal conductivity was 1.1 W/m.K, and hardened density was decreased to 10% compared to the control. In addition, LECA is considered the superior and suitable material for acoustic absorption compared with other aggregates.     

Physical and mechanical properties of fly ash-based geopolymer with disposable medical mask reinforcement

A tremendous amount of the nonbiodegradable microplastic waste has been generated after the outbreak of COVID-19 by the widespread use of single-use personal protective equipment, especially disposable medical masks (DMMs). This has caused harm to the health and safety of human beings and various organisms. Finding a way to properly deal with these single-use medical wastes has become an urgent problem. In this paper, an innovative way was explored to use DMMs in geopolymer (GP). The physical properties, mechanical strength, and resistance to high temperatures (200–800°C) of the composites were investigated. The findings of the study revealed that DMMs had negligible influence on resistance to high temperatures, but showed a positive influence on enhancing the compressive and flexural strengths of GPs at ambient temperature. The optimum DMMs content was 0.4 wt%, at which the compressive and flexural strengths of the GP composites were enhanced by 5.8% and 22.68% compared with the pure GP, respectively. The same polypropylene (PP) fiber amount increased compressive and flexural strengths by 7.49% and 9.76%, respectively. This thus confirmed that DMMs can be sustainably utilized in green building materials, playing a role as PP fibers toughening and contributing to the effective management of waste plastics.     

Effects of inorganic fillers on the flame‐retardant and mechanical properties of rigid polyurethane foams

Rigid polyurethane foam (RPUF) composites filled with expandable graphite (EG), hollow glass microspheres (HGM), and glass fibers (GF) have been synthesized and characterized by limiting oxygen index, radiation ignition, compressing and torsion testing, and scanning electron microscopy. The results indicate HGM and GF benefit to the mechanical properties, while EG is good for flame retardancy. Proper ingredient of additive can lead to good flame retardancy and mechanical properties of the RPUF. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40253.     

Mechanical properties of polybenzoxazine syntactic foams

Syntactic foams of polybenzoxazine, containing moderately high volume percentage of glass microballoons, were prepared. The specific gravity decreased with increase in microballoon content. The disproportionate decrease in specific gravity was ascribed to entrapment of air voids during compaction. The high content of microballoon increased the possibility for air voids that tended to get accumulated. The effect of microballoon concentration on tensile, compressive, and flexural strengths of the foams was studied. Tensile and compressive properties were optimized at about 68% by volume of microballoon while flexural strength decreased marginally on increasing the microballoon content. Althought the specific tensile and compressive strength showed a maximum followed by a decrease, the specific flexural strength systematically increased with microballoon content. The increased packing density of syntactic foam of a given constituent composition increased the compressive strength. The property variation was corroborated by morphological features, as evidenced in scanning electron micrographs. The syntactic foams showed “multiple resin‐neck formation” and “disc‐shaped microballoon regions.” The crushing of microballoons during molding was inevitable when compaction was effected to achieve a density beyond the theoretical one. Low‐density syntactic foams tend to fail at lower loads because of fracturing of microballoons. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical properties and morphology of modified celluloid foams

Celluloid is a highly flammable plastic made of nitrocellulose and camphor, as a plasticizer, and it has recently received interest as a material for making combustible containers. For this particular application, the inherent combustion properties of celluloid are enhanced by foaming the material. This work evaluates novel celluloid-like formulations in which camphor is replaced by alternative plasticizers and alternative nucleating agents are also evaluated to further improve the properties of the foams. The effects of these new components on the tensile properties and on the morphology of the combustible plastic are investigated for three plasticizers and for two nucleating agents. Results show that some plasticizers bring mechanical properties exceeding those of regular celluloid, an improvement of Young modulus and tensile stresses by more than 100% was observed. The effect of the nucleating agent on the foamed material's microstructure is also clearly observed, size and number of cells are correlated to the nature and the concentration of the nucleating agent.