Low Apparent Density Research Articles

Zinc oxide pieces obtained by pressing and slip casting: physical, structural and photocatalytic properties

ABSTRACT Photocatalysis is a promising alternative for the decontamination of effluents. In this paper, immobilized ZnO-based photocatalysts were obtained by pressing and by slip casting. The cylindrical pieces were heat-treated at 800°C. The samples were characterized by the method based on the principle of Archimedes, XRD, FTIR, Raman, diffuse reflectance and SEM. The samples obtained by slip casting presented lower apparent density (3.12 ± 0.04 g/cm3), higher apparent porosity (44.87 ± 0.47%) and smaller grain size (0.48 ± 0.05 µm) when compared to the pressed samples, with mean apparent density of 5.37 ± 0.08 g/cm3, apparent porosity of 1.56 ± 0.10% and grain size of 0.64 ± 0.02 µm. The performances of the samples were attested by the photocatalytic degradation of Rhodamine B (RhB) under UV-C irradiation (maximum intensity at 254 nm). The samples obtained by slip casting showed photocatalytic degradation between 80% and 90%, while the pressed samples showed degradation between 40% and 60%. The reuse of the photocatalysts was evaluated over five cycles of photocatalytic degradation, in which there was no loss of performance of the samples obtained by slip casting; however, the pressed samples showed a loss of photocatalytic efficiency starting from the third-cycle. Photocatalytic assays were carried out with different dye concentrations, in which the slip casting samples showed better photocatalytic efficiency (degradation of 80% for a RhB concentration of 10 mg/L) due to higher porosity and surface area compared to pressed samples, and there was a loss of performance in higher concentrations.

Synthesis of thermal insulating polyurethane foams from lignin and rapeseed based polyols: A comparative study

Nowadays, a large number of polyurethane (PU) system modifications relies on the use of different bio-polyols. In this context, two bio-based polyols, one synthesized from lignin and one from rapeseed oil were evaluated in the replacement of a petrochemical polyol at an amount of 10–30 wt.% in rigid polyurethane foam formulations (RPU). The lignin-based polyol was produced by oxypropylation from an organosolv lignin (ALCELL) and the rapeseed oil-based one prepared by a two-step method of epoxidation followed by oxirane ring opening with diethylene glycol. The replacement of the petrochemical polyol with the lignin bio-polyol increased the reactivity of the reactive mixtures, while the rapeseed oil bio-polyol gave the opposite effect. This was confirmed by the respective changes observed in the dielectric polarization of the reactive mixtures together with the maximum temperature achieved in the foam core during the foaming process. The foams modified with the tested bio-polyols had both lower apparent density (40–45 kg/m3) and closed cell content (86–89%), comparatively with a reference foam. The replacement of petrochemical polyol with the bio-polyols up to 30 wt% caused, in the modified foams, a slight decrease of the compressive strength. Moreover, the introduction of the bio-polyols into PU formulations generally did not influence the thermal conductivity coefficient that was around 23 mW/m·K for the obtained materials.

Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application.

This article raised the issue of studies on the use of new bio-polyol based on white mustard seed oil and 2,2’-thiodiethanol (3-thiapentane-1,5-diol) for the synthesis of rigid polyurethane/polyisocyanurate (RPU/PIR) foams. For this purpose, new formulations of polyurethane materials were prepared. Formulations contained bio-polyol content from 0 to 0.4 chemical equivalents of hydroxyl groups. An industrial flame retardant, tri(2-chloro-1-methylethyl) phosphate (Antiblaze TCMP), was added to half of the formulations. Basic foaming process parameters and functional properties, such as apparent density, compressive strength, brittleness, absorbability and water absorption, aging resistance, thermal conductivity coefficient λ, structure of materials, and flammability were examined. The susceptibility of the foams to biodegradation in soil was also examined. The increase in the bio-polyol content caused a slight increase in processing times. Also, it was noted that the use of bio-polyol had a positive effect on the functional properties of obtained RPU/PIR foams. Foams modified by bio-polyol based on mustard seed oil showed lower apparent density, brittleness, compressive strength, and absorbability and water absorption, as well as thermal conductivity, compared to the reference (unmodified) foams. Furthermore, the obtained materials were more resistant to aging and more susceptible to biodegradation.

Scalable fabrication of monolithic porous foam based on cross-linked aromatic polymers for efficient solar steam generation

Cost-effective and scalable solution to fabricate high-performance photothermal materials is the key to enable widespread application for solar steam generation. Herein, we report the facile and scalable fabrication of monolithic porous foam based on cross-linked aromatic polymer (PDVB-PS) using styrene as monomer and divinylbenzene as cross-linking agent through a facile one-step hydrothermal method. The resulting PDVB-PS foam possesses well-controlled porous structure, open channel structure, low apparent density and low thermal conductivity (0.038Wm−1k−1). After modification with sodium alginate and polypyrrole, the as-modified PDVB-PS (named as PPy-coated M-PDVB-PS) shows a superhydrophilic wettability (water contact angle ∼ 0°) and stronger light absorption (ca. 90%), which could dramatically enhance its water transportation ability and photothermal property. Taking advantages of these unique physicochemical properties mentioned above, a high solar-vapor conversion efficiency of 87.6% for the PPy-coated M-PDVB-PS was obtained under 1-sun irradiation, showing great potentials for real applications. More importantly, as a kind of representative synthetic polymers, the success in employment of the PPy-coated M-PDVB-PS as efficient photothermal materials shown in this study may also open a new opportunity for rational design and fabrication of polymer-based solar generators derived from commercial available low-cost raw chemicals with simple and scalable manufacture process for practical solar steam generation on large scale.

Modification on Recycled Aggregates and its Influence on Recycled Concrete

Recycled aggregates produced from waste concrete are widely accepted as green building material. However, demolition processes will bring recycled aggregates with a lower apparent density, bulk density whereas a higher porosity, silt content, water absorption, crushing index value when compared with natural aggregates. So the strengthening and modification of recycled aggregates have become a prominent technological issue in the producing process.This paper introduces current modification methods on the recycled aggregates, which mainly include: (1) physical technology, its basic idea is to remove the waste cement paste adhered to recycled aggregates, such processions as rubbing, heating, particle shaping, and micro-heating; (2) chemical technology, carried out by immersing recycled aggregates in different kinds of chemical grout, which can be mixed with additive Kim powder, silica fume, fly ash, and any other fine mineral powder or slag; (3) carbonation technology, when newly collected crushed aggregates are put into atmosphere with high CO2 concentration, the adhesive cement paste can react with CO2 and produce CaCO3 that will precipitate in the capillary pores or cracks, which will improve properties of recycled aggregates; (4) nano technology, the use of nanomaterials can promote the hydration reaction, react with cement based materials, fill pores and control the process of crystallization. Conclusions are put forward and several problems concerning modification need to be considered for further research and application are proposed and discussed. Compared with natural concrete, RAC is superior to environmental value in the reduction of CO2 emission in Life Cycle Assessment.

Sugarcane‐Based Photothermal Materials for Efficient Solar Steam Generation

AbstractSolar steam generation is a promising strategy for harvesting solar energy for diverse applications such as desalination and wastewater treatment. Here, we demonstrate the fabrication of polypyrrole modified sugarcane (PPy‐SC) as efficient photothermal material for solar steam generation. The PPy‐SC possesses various close‐packed open channels in horizontal plane and super hydrophilic wettability which is beneficial for rapid transportation of water molecules. In combination with its abundant porosity (47%), low apparent density (80 mg cm−3), low thermal conductivity (0.042 W m−1 K−1), and broad light absorption (90%). The prepared PPy‐SC exhibits a high evaporation rate of 1.59 kg m−2 h−1 and conversion efficiency of 90.6%, under 1 sun irradiation. In addition, the PPy‐SC also shows good performance in desalination. With the merits of low‐cost, eco‐friendly, simple fabrication process, high solar energy conversion efficiency, the PPy‐SC shows great potential as an efficient photothermal material for solar steam generation.

Bio-based thermosetting epoxy foams from epoxidized soybean oil and rosin with enhanced properties

Bio-based thermosetting epoxy foams were synthesized via an epoxide ring opening reaction of epoxidized soybean oil (ESO) with fumaropimaric acid (FPA) by using N, N-dimethylbenzylamine as the catalyst and sodium bicarbonate as the foaming agent. The reactivity of the ESO/FPA polymeric matrix became stronger as the proportion of FPA increased. Thermal gravimetric (TG) analysis showed that these thermosetting epoxy foams had high thermal stability. The introduction of the rigid hydrogenated phenanthrene ring structure of FPA improved the viscosity of the ESO/FPA polymeric matrix and the cell wall structure of the foams. Therefore, the apparent density of foams decreased from 361 to 231 kg/m3 with the increase in FPA content in the ESO/FPA polymeric matrix. The compressive modulus (E*) and compressive strength (σc) of the foams improved due to the rigid hydrogenated phenanthrene ring structure of FPA. Furthermore, the foam could be adjusted to become flexible foam or rigid foam by changing the molar ratio of the ESO/FPA polymeric matrix. Foams with low apparent density, high porosity, and closed cells had a lower thermal conductivity coefficient which decreased to 0.031 W/(m·K).

Additive manufacturing of fire‐retardant ethylene‐vinyl acetate

Thermocompression (with also extrusion and injection molding) is a classical polymer shaping manufacturing, but it does not easily allow designing sophisticated shapes without using a complex mold, on the contrary to 3D printing (or polymer additive manufacturing), which is a very flexible technique. Among all 3D printing techniques, fused deposition modeling is of high potential for product manufacturing, with the capability to compete with conventional polymer processing techniques. This is a quite low cost 3D printing technique, but the range of filaments commercially available is limited. However, in some specific 3D printing processes, no filaments are necessary. Polymers pellets feed directly the printing nozzle allowing to investigate many polymeric matrices with no commercial limitation. This is of high interest for the design of flame‐retarded materials, but literature is scarce in that field. In this paper, a comparison between thermocompression and 3D printing processes was performed on both neat ethylene‐vinyl acetate (EVA) copolymer and EVA flame retarded with aluminum triHydroxyde (ATH) containing different loadings (30 or 65 wt%) and with expandable graphite (EG), ie, EVA/ATH (30 wt%), EVA/ATH (65 wt%), and EVA/EG (10 wt%), respectively. Morphological comparisons, using microscopic and electronic microprobe analyses, revealed that 3D printed plates have lower apparent density and higher porosity than thermocompressed plate. The fire‐retardant properties of thermocompressed and 3D printed plates were then evaluated using mass loss calorimeter test at 50 kW/m2. Results highlight that 3D printing can be used to produce flame‐retardant systems. This work is a pioneer study exploring the feasibility of using polymer additive manufacturing technology for designing efficient flame‐retarded materials.

Self-healing and recyclable biomass aerogel formed by electrostatic interaction

Achieving self-healing capacity in porous materials is highly attractive, but still remains a huge challenge. Here we disclosed a new strategy for the fabrication of self-healable biomass aerogels, which is achieved by assembling the positively charged chitosan (CS) and negatively charged itaconic acid (IA) in aqueous solution, followed by a freeze-drying process. Due to relatively strong electrostatic interaction and unique morphology, the aerogel shows outstanding mechanical property even at very low apparent density. More importantly, it possesses ultrafast self-healing ability at room temperature. Once the aerogel is cut apart, it can repair both its structure integrity and mechanical performance within 30 s at room temperature via wetting one fractured surface. After self-healing, its compression strength is almost twice the value of the original one. In addition, the aerogel can be completely dissolved and reshaped, thus displaying excellent recyclability of the materials. Since both CS and IA are derived from natural resources, this work provides a promising solution to the fabrication of self-healable biomass aerogels with both high-performance and sustainability.

New Poly(lactide-urethane-isocyanurate) Foams Based on Bio-Polylactide Waste.

The article presents the results of research on the synthesis of a new eco-polyol based on polylactide (PLA) waste and its use for the production of rigid polyurethane-polyisocyanurate (RPU/PIR) foams. The obtained recycling-based polyol was subjected to analytical, physicochemical and spectroscopic tests (FTIR, 1H NMR, 13C NMR) to confirm its suitability for the synthesis of polyurethane materials. Then, it was used to partially replace petrochemical polyol in polyurethane formulation. The obtained RPU/PIR foams were characterized by lower apparent density, brittleness, and water absorption. In addition, foams modified by eco-polyol had higher flame retardancy, as compared to reference foam. The results of the research show that the use of PLA polyol based on plastic waste may be an alternative to petrochemical polyols. This research matches with the current trends of sustainable development and green chemistry.

A novel inorganic thermal insulation material utilizing perlite tailings

Installing thermal insulation materials on the external and/or interior wall is a primary means for the conservation of building energy. Expanded perlite is one of the most widely used inorganic building insulation materials nowadays. However, it not only consumes a large amount of energy in the fabricated process, but also produces a great deal of perlite tailings during the exploiting or smashing process. In this work, a new kind of light foamy thermal insulation materials were prepared utilizing perlite tailings by an energy-saving and environment-friendly method. The influences of each raw materials, including perlite/sodium silicate, H2O2, cetyltrimethyl ammonium bromide and rock wool, on the physical properties (such as pores characters, thermal conductivity and mechanical strength) were discussed in detail based on the formation processes of the foamy thermal insulation materials. The optimized foamy materials showed low thermal conductivities (0.040–0.060 W·m−1·K−1) with low apparent densities (0.1–0.2 g cm−3) and relatively high mechanical strength (0.09–0.6 MPa). As compared with other reported inorganic thermal insulation materials, this new type of thermal insulation material was very light and exhibited much better heat-insulated performance. Therefore, this work not only proposed a new energy-saving method for obtaining a kind of promising non-flammability insulating materials, but also solved the problem of solid tailings utilization.

Peculiarities of Granulation of the PAP-2 Aluminum Powder in the Technology of the Al–Al2O3 Powder Composite with a Layered Structure

An analysis of modern scientific-and-technical information evidences great prospects for using composite materials (CMs) based on the Al–Al2O3 system. It is shown in works of the Materials Science Department of the Moscow Aviation Institute that one promising method of fabricating aluminum-based CMs is the reaction sintering in air of blanks made of highly dispersed powders of the PAP-2 brand. However, to implement the proposed method in practice, it is necessary to solve a series of problems, in particular, associated with their low manufacturing properties, such as a lack of fluidity and extremely low apparent density. To granulate the PAP-2 aluminum powder, various process approaches are applied. They are based on process operations such as powder heating in air with subsequent isothermal holding at 350°C, introducing water-diluted sodium silicate glass into its composition, mechanical processing of the powder in a high-energy planetary mill, its heat treatment in vacuum at 650°C, and initiating the stearin saponification reaction on the surface of the PAP-2 flaked particles with the formation of the organic plasticizer component. It is found that the proposed granulation methods of the industrial PAP-2 powder make it possible to improve and vary the process characteristics of the initial powder, as well as modifying its composition and structure. The highest apparent density (up to 1.25 g/cm3) is attained when using the mechanical treatment of the initial powder in a high-energy planetary mill with the formation of rounded granules 50–150 μm in size. The most producible and cost-effective method is based on the initiation of the chemical reaction of stearin saponification on the surface of powder particles (the apparent density is ~0.4 g/cm3).

Fabrication of bilayered attapulgite for solar steam generation with high conversion efficiency

Solar steam generation has been attracting wide attention for boosting the evolution of solar-energy-harvesting technology. Here, we demonstrate the fabrication of a novel bilayer photothermal material based on attapulgite/poly acrylamide composite (APAC), which was prepared by the solution polymerization of acrylamide (AM) in the presence of attapulgite using N, N′-Methylene bisacrylamide (MBA) as a crosslinker, for efficient solar steam generation. The APAC shows better thermal stability with a decomposition temperature of 250 °C, good mechanical property with a compress strength of up to 125 KPa at 75% strain and a low apparent density (0.0191 g·cm−3) with abundant porosity accompanying with a low thermal conductivity (0.07 W m−1 K−1). To enhance the light absorption of APAC, a thin carbon layer was created on the surface of APAC via a facile flame treatment. Under our conditions, the bilayered APAC shows a high vapor rate of 1.2 kg m−2 h−1 under 1 sun illumination, equal to 85% solar-to-vapor efficiency. With the merits of cost-efficient, scalable manufacture, high solar energy conversion efficiency, the APAC may hold the great potential as high-performance photothermal materials for solar energy generation.

New foaming formulations for production of bio-phenol formaldehyde foams using raw kraft lignin

The submitted work presented new foaming formulations demonstrated for production of bio- phenol formaldehyde (BPF) resins and thermal insulation foams using raw kraft lignin (KL) as a green feedstock, reducing both petroleum-based phenol and formaldehyde by up to 50%. The obtained lignin-based BPF foams exhibited low apparent density (20–80 kg/m3), strong compressive strength (up to 1.01 MPa), excellent thermal conductivity (0.03–0.048 W/m·K) and combustion properties (LOI: 32–33%), and satisfactory closed cell structure, all comparable to commercial phenol formaldehyde (PF) foams. These BPF foams, using KL, can act as flame retardant and insulation materials for construction or retrofitting of buildings, thereby future commercialization of these lignin-derived phenolic foams would lead to cleaner production of flame retardant and insulation materials using forestry and agricultural residues/waste.

Effect of Evening Primrose Oil-Based Polyol on the Properties of Rigid Polyurethane⁻Polyisocyanurate Foams for Thermal Insulation.

The article presents the results of research on the synthesis of a new biopolyol based on evening primrose oil, and its use in the production of rigid polyurethane–polyisocyanurate foams intended for thermal insulation. The obtained biopolyol was subjected to analytical, physicochemical, and spectroscopic tests (Fourier transform infrared (FTIR), 1H NMR, 13C NMR) to confirm its suitability for the synthesis of polyurethane materials. Then, it was used for the partial replacement of the petrochemical polyol in the polyurethane formulation. Obtained rigid polyurethane–polyisocyanurate foams are characterized by a lower apparent density, brittleness, water absorption, and thermal conductivity coefficient λ. In addition, foams modified by biopolyols had a higher content of closed cells and higher aging resistance. The results of the conducted research showed that the use of the biopolyol based on evening primrose oil may be an alternative to petrochemical polyols. The research presented herein is perfectly consistent with the trends of sustainable development and the philosophy of green chemistry.

Preparation of glass-ceramic foams using extracted titanium tailing and glass waste as raw materials

Extracted titanium tailing, a large amount of solid waste produced from Panzhihua in China, not onlyoccupiesa lot oflands, but alsoseriously pollutes the environment. Glass-ceramic foams could be synthesized using extractedtitaniumtailing as a raw material, mixed with glass waste, foaming agent Na2CO3 and fluxing agent B2O3 by a simple powder foaming method. The effects of preparing conditions such as sintering temperature (760–790 °C), sintering time (10–40 min), Na2CO3 content (0–3 wt%) and B2O3 content (0–3 wt%) on the micromorphology have been systematically investigated by scanning electron microscopy. The crystallinity, compressive strength, thermal conductivity, and thermal expansion coefficient are investigated by X-ray diffraction, electronic universal testing machine, heat flow method and thermal dilatometer. The pore size, percent, and distribution of the glass-ceramic foams can be controllably prepared by adjusting the preparing conditions. And the pore structure plays an important role in determining the apparent density, compressive strength, thermal conductivity, and thermal expansion coefficient. The glass-ceramic foam has a low apparent density of 0.30 ± 0.01 g cm−3, an available compressive strength of 1.0 ± 0.1 MPa, a thermal conductivity of 0.060 ± 0.002 W m−1 °C −1, a high porosity of 88.0% and an average thermal expansion coefficient of 5.27 × 10−6 m m−1 °C−1 under the optimal preparation parameters, indicating that the glass-ceramic foam could be widely used in construction and building industry.

Microcellular polyetherimide/graphene‐polysiloxane composite foam: intercalation structure, mechanical and thermal properties

AbstractBased on the industrialized reduced graphene oxide (RGO) product, polyetherimide (PEI)/RGO composite foam was prepared by a water‐vapor‐induced phase separation process by incorporation of polysiloxane (SI) as a compatibilizer. It was found that PEI/SI molecules were intercalated into the RGO layers through strong interfacial interaction and RGO with increased layer thickness was uniformly distributed in the PEI matrix. The composite foam possessed a homogeneous spherical‐like cell structure with narrow cell size distribution and low apparent density. In the range of 0–1 wt% RGO‐SI content, the area under the stress–strain curves increased dramatically, indicating the significantly increased toughness of the composite foam, while the tensile strength reached a maximum of 14.5 MPa at 1 wt% RGO‐SI as a result of the reinforcing effect of RGO‐SI on the foam. The addition of RGO‐SI led to a remarkable increase in Tg. Compared with neat PEI foam, the thermal degradation temperature and char yield of the composite foam clearly increased, while in the range of 0.5–3 wt% RGO‐SI a high storage modulus was maintained at high temperature, reaching about 300 MPa at 200 °C, indicating a remarkable improvement of the thermal mechanical stability of the foam. © 2018 Society of Chemical Industry

Wet-end addition of nanofibrillated cellulose pretreated with cationic starch to achieve paper strength with less refining and higher bulk

Nanofibrillated cellulose (NFC) treated with cationic starch was evaluated as a bonding system to permit lower degrees of refining and lower apparent density of high-mass handsheets made from bleached kraft pulp. Mixed pulp (70% hardwood, 30% softwood) was formed into sheets with the optional addition of 5% by dry mass of NFC. The default addition of NFC was compared with a system in which the NFC had been pretreated either with cationic starch (at various levels) or optionally followed by colloidal silica. Comparative tests also were carried out with separate addition of cationic starch to the main furnish. Unrefined fibers (514 mL CSF) were compared with low-refined (473 mL CSF) and high-refined (283 mL CSF) pulp mixtures. The NFC that had been pretreated with cationic starch at a high level was especially effective at boosting the tensile strength and stiffness of sheets prepared from pulp that had been refined at a low level, thus achieving improved strength at relatively low apparent density (high bulk) of the handsheets. The results support a strategy, for applicable grades of paper, of using cationic starchpretreated NFC in place of refining energy applied to the main fiber furnish. It was further established that colloidal silica can be employed as a further pretreatment of the cationic starch–treated NFC as a means of promoting dewatering in the combined system.

Nitrogen Oxides Mitigation Efficiency of Cementitious Materials Incorporated with TiO₂.

We explored the photocatalytic capacities of cementitious materials (cement paste and mortar) incorporating titanium dioxide (TiO2). P-25 is a commercial TiO2 preparation which, if incorporated into large civil buildings, is extremely expensive. It is essential to produce low-cost TiO2. A cheap anatase form of TiO2 powder, NP-400, manufactured under relatively low burning temperature, was considered in this paper. Addition of NP-400 to 0, 5, 10, and 20 wt % did not significantly affect the compressive strengths of mortar or cement paste. However, the compressive strengths of P-25-containing specimens were more consistent than those of NP-400-containing materials. The nitrogen oxide (NO) removal efficiencies by mortar with 5 and 10 wt % TiO2 were similar at ca. 14–16%; the removal efficiency by mortar with 20 wt % NP-400 was ca. 70%. Although the NP-400 cluster size was almost halved by ultrasonication, NO removal efficiency was not enhanced. Removal was enhanced by the presence of accessible surface area: NP-400 dispersed in these surfaces readily adsorbed NO, aided by the large surface areas of the top and bottom faces. Scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDX) confirmed that NP-400 tended to sink when added to cement, fine aggregates, and water because the true densities of P-25, NP-400, and cement powder differed (3.41, 3.70, and 3.15 g/mL). The true density of NP-400 was thus the highest of all ingredients. The relatively low apparent density of P-25 compared to that of NP-400 was associated with a more bulky distribution of P-25 within cementitious materials. Nevertheless, NP-400 could be a viable alternative to the definitive product, P-25.

Effect of MgO on the Crystallization Behavior and Properties of Glass-Ceramics

ABSTRACTAs an important advanced decoration material, glass-ceramics has attracted much attention. By means of XRD, SEM and mechanical properties tests, this research studied the sintering and crystallization behavior during the preparation of CaO-MgO-Al2O3-SiO2 glass-ceramics. Results showed that with increase in MgO content, crystallization temperature increased, linear sintering shrinkage (%) decreased and porosity number increased, leading to a lower apparent density. However, with increase in temperature and time, linear shrinkage (%) increased. In addition, the increase of MgO made the vibration frequency of infrared spectrum move to the low-frequency, showing transformation from wollastonite to pyroxene phase. With increase in MgO content, particle size decreased, crystallization rate increased, microhardness of glass-ceramic material increased and flexural strength increased initially, then decreased. The flexural strength of glass-ceramics with 10% MgO can be 103 MPa.