- Email: [email protected]
Glass foams produced from glass bottles and eggshell wastes
Accepted Manuscript Title: Glass foams produced from glass bottles and eggshell wastes Authors: Marcelo T. Souza, Bianca G.O. Maia, Luyza B. Teixeira, Karine G. de Oliveira, Alexandre H.B. Teixeira, Antonio P. Novaes de Oliveira PII: DOI: Reference:
S0957-5820(17)30192-1 http://dx.doi.org/doi:10.1016/j.psep.2017.06.011 PSEP 1092
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
24-6-2016 3-5-2017 15-6-2017
Please cite this article as: Souza, Marcelo T., Maia, Bianca G.O., Teixeira, Luyza B., de Oliveira, Karine G., Teixeira, Alexandre H.B., Novaes de Oliveira, Antonio P., Glass foams produced from glass bottles and eggshell wastes.Process Safety and Environment Protection http://dx.doi.org/10.1016/j.psep.2017.06.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Glass foams produced from glass bottles and eggshell wastes
Marcelo T. Souzaa; Bianca G.O. Maiaa*; Luyza B. Teixeiraa; Karine G. de Oliveirab; Alexandre H.B. Teixeiraa; Antonio P. Novaes de Oliveiraa
a
Graduate Program in Materials Science and Engineering (PGMAT), Laboratory of Glass-Ceramic Materials
(VITROCER), Federal University of Santa Catarina (UFSC), 88040-900, Florianópolis (SC), Brazil. *e-mail: [email protected] b
Graduate Program in Environmental Engineering (PPGEA), Federal University of Santa Catarina (UFSC),
88040-900, Florianópolis (SC), Brazil.
Highlights
Glass foams were produced from discarded glasses and eggshells.
Eggshells are a calcium carbonate rich residue.
The obtained glass foams have potential as thermal insulating materials.
Thermal insulation and non-flammability are the main technical requirements.
Reusing glass bottles and eggshells contributes to minimize the environmental impacts.
Abstract: Glass foams were produced from discarded glass bottles (GB) and eggshells (ES) as foaming agent in contents between 1 and 30 wt%. The raw materials (GB, ES) were homogenized and uniaxially pressed (20 MPa). The obtained powder compacts were fired at 900 °C/30 min and characterized according to their chemical, physical and structural properties. The results (porosities between 60 and 95% with thermal conductivities between 0.177 and 0.055 W/m.K and compressive mechanical strength between 0.15 and 1.50 MPa) indicate that the obtained glass foams have potential for applications where thermal and acoustic insulation and non-flammability are the main technical requirements.
Keywords: glass; eggshell; foams; porous, wastes.
1. Introduction Glass foams are porous materials formed by a gas phase (present inside the pores) and a solid phase (glass matrix) (Sasmal et al., 2015). These materials have porosity usually higher than 60% vol., which can be open, close, or both. The pores features (size, distribution and morphology) determine specific properties, such as low density, low thermal conductivity, high surface area, permeability, chemical and thermal stability (Scheffler and Colombo, 2005). Some glass foams also presents bioactivity and bacteria-resistant (Chen et al., 2006; Midha et al., 2013). In addition to these properties, these foams are easy handling (Attila et al., 2013; Scheffler and Colombo, 2005). Hence, they are widely used as building blocks (e.g., for insulating roofs, walls, floors and ceilings in high or low temperatures), as filler for the restoration of failed slopes, as subgrade improvement material, as light-weight aggregate material in concrete and water folding material for greening (Lu and Onitsuka, 2004) and also as scaffolds for bone tissue engineering (Chen et al., 2006; Jonde et al., 2006; Bellucci et al., 2011). By the other hand, the glass foams applications are limited by their working temperature, which should not exceed their glass transition temperature between 500-600 oC. For higher temperatures, the foam exhibits deformation and loss of the porous structure (Scheffler and Colombo, 2005). The costs of glass foams have also constituted a key disadvantage for their diffusion in the building industry. In order to reduce the production costs, several alternative processing techniques and the starting materials have been explored (Bernardo et al., 2007). Recent studies have shown numerous advantages and possibilities to obtain glass foams from discarded glasses (Arcaro et al., 2016; Bernardo et al., 2010; Taurino et al., 2014; Wu et al., 2006; Mugoni et al., 2015). According to Institute of Applied Economic Research
(IPEA), in Brazil, around 260 thousand tons of glass are discarded in landfills every year. IPEA also estimates an expense of R$ 8 bi ($ 2.3 bi) to discard/bury wastes that could generally be reused. Among the various techniques for obtaining ceramic foams, replication, gelcasting, foaming and incorporation of foaming agents (pore formers) are mostly used (Studart et al., 2006). The technique of foaming agents’ incorporation, due to its simplicity, is the most used in the production of glass foams and consists of incorporating a foaming or pore-forming agent in the ceramic matrix. The foaming depends on decomposition (usually due to carbonates and sulphates releasing) or oxidation reactions (interaction of carbon-containing species mainly with the atmosphere of the sintering furnace). The pores sizes generated by foaming decomposition are associated with the particle size of the foaming agent used (Bernardo et al., 2007; Romano and Pandolfelli, 2006; Souza et al., 2006). Wastes in general provide many value-added opportunities and can be a low cost alternative for use as foaming agents (Bernardo et al., 2007). As example, aviculture produces a significant amount of eggshells (ES) (Fernandes et al., 2013). According to the United States Department of Agriculture (USDA), in 2014 it was produced about 8 billion dozen chicken eggs. In Brazil, according to Brazilian Institute of Geography and Statistics (IBGE), the production was about 2.8 billion dozen in the same year. Eggshell, which corresponds to about 10 wt% egg (Stadelman, 2000), contains about 94 wt% calcium carbonate (CaCO3) in its composition. Although the ES is not being considered a hazardous waste, its inappropriately landfill disposal can result in considerable environmental liabilities due to the large amount of eggs produced. Since ES is a calcium carbonate rich residue, the possibilities of its reuse may include the incorporation in soil for agricultural purposes (Gaonkar and Chakraborty, 2016), as adsorbent for removal of coloring matter in aqueous solutions (Tsai et
al., 2008), as a replacement for limestone in the production of Portland cement (Pliya and Cree, 2015), among other applications. Therefore, despite glass bottles and eggshell wastes have well established solutions, a huge amount of both wastes are still discarded. Thus, from an environmental point of view, glass foams production is an interesting alternative destination for these wastes (Bernardo et al., 2007). In this context, the aim of this work is to produce glass foams with low cost starting materials, i.e., from the use of recycled soda-lime glasses (matrix) and ES (foaming agent).
2. Experimental Procedure 2.1. Obtainment and characterization of the raw materials Glasses from discarded glass bottles (GB) of different colors, mixed in equal proportions, (white, green and brown) were used as raw materials. Eggshells (ES) were used as pore-forming agent (foaming agent). It was also used commercial calcium carbonate (LABSYNTH), CaCO3, with purity greater than 99%, as reference material (RM). Chemical compositions of GB and ES were obtained by X-Ray Fluorescence (Philips, model PW 2400). To investigate the crystalline phases of the ES and commercial calcium carbonate used as reference material (RM), powdered samples were analyzed using X-ray diffractometry, XRD (Philips X’Pert) with CuKα radiation. GB were dry crushed in a hammer mill (Servitech, CT-058) and milled for 120 min in a fast mill (Servitech, CT -242) using a porcelain jar containing alumina balls. ES were provided by a commercial establishment and, because of their physical characteristics (brittleness), were directly milled in a fast mill (Servitech, CT-242) for 5 min. The particle size distribution of the wastes after grinding was obtained by laser scattering particle size analyser (Malvern, Mastersizer 2000).
2.2. Obtainment and characterization of glass foam Samples containing different proportions of GB (between 70 and 99 wt%) and ES (between 1 and 30 wt%) were prepared by wet mixing (40% solids) using a mechanical stirrer (IKA RW 20) at 200 rpm for 10 min. After drying (110 °C/24 h) of the aqueous suspension in a laboratory dryer (SP LABOR®), the resulting powders were uniaxially pressed (20 MPa) in a steel die using a hydraulic press (Bovenau P10 ST) with addition of 5% moisture. The obtained compacts (30 mm in diameter and 10 mm thick) were fired (oxidizing atmosphere) in a laboratory furnace (Jung J200) at 900 °C during 30 min, using a heating rate of 10 °C/min. The thermal behavior of raw materials (GB, ES) was investigated using an optical dilatometer (Misura ODHT) and a contact dilatometer (Netzsch, DIL 402) and also by thermogravimetric analyses, TG (SDT, TA Instruments Q-600) at 10 °C/min (oxidizing atmosphere). Digital photographs of fired samples were also performed. From the results of the dilatometric analysis it was possible to determine the viscosity curve from Vogel-FulcherTammann equations (Vogel, 1921). The true densities (ρt) of the powdered samples were determined by using a helium pycnometer
(Ultrapycnometer
1200
P/N,
Quantachrome
Instruments).
The
linear
shrinkage/expansion (%) and geometric densities (ρg) of the fired samples were determined relating their geometrical measurements, obtained using a caliper (Mitotoyo, accuracy ± 0.01 mm), and their masses (Shimadzu AX200 at 0.001 g). The porosities () of the fired glass foams were calculated from geometrical (g) and true (t) densities measurements ratios, i.e., 𝜀 = (1 − 𝜌𝑔/𝜌𝑡 ) × 100. The porous size distribution were determined by photographs of the samples and the image analyzer ImageJ.
To determine the mechanical strength of the samples, compression tests (EMIC DL 2000 model) were performed on five disc samples (30 x 10 mm) with loading speed of 1 mm/min. Thermal conductivity of the glass foams
was determined by a TCi Thermal
Conductivity C-THERM TECHNOLOGIES on samples with 30 mm diameter and 10 mm thick.
3. Results and Discussion 3.1. Characterization of the raw materials and compositions Table 1 shows the results of the chemical analysis of the recycled GB and ES obtained by X-Ray Fluorescence. TABLE 1 The chemical composition of the glass in this study is typical of soda-lime glasses used to manufacture bottles and flat glass windows. The ES used as pore-forming agent are composed mainly of calcium carbonate (CaCO3). In fact, chemical analysis (Table 1) indicates that ES contain approximately 94 wt% of CaCO3, calculated from the CaO content (52.4 wt%). Figure 1 shows XRD patterns of the (a) ES and (b) high purity commercial calcium carbonate used as reference material (RM). INSERT FIGURE 1 Besides the very significant chemical similarity between ES and commercial calcium carbonates, X-ray patterns of these materials confirm this compositional and structural similarity since it was detected only calcium carbonate, CaCO3 (JCPDS Nº. 33-1161).
Figure 2 shows the particle size distributions for GB and ES after milling processes obtained by laser scattering particle size analyzer. INSERT FIGURE 2 The analysis indicated that the GB, after milling process, had an average particle size (D50) of about 2.9 m. The foaming agent (ES), on the other hand, exhibits average particle size (D50) of 56.6 m. Glasses for such applications must be milled and sieved to obtain a particle size lower than 4000 m, otherwise the foam formation process is inefficient. Although the literature cites that to facilitate homogenization of the formulation, the sizes of the powders of the pore agent forming and the glass must be similar, no problems occurred during the preparation of the formulations. The particles size of the foaming agent also influences the structural characteristics (pore size) of the glass foam (Scheffler and Colombo, 2005). Figure 3 shows a curve relating the logarithm of viscosity versus temperature for recycled GB from the Vogel-Fulcher-Tammann equations (Vogel, 1921), obtained by optical dilatometry and contact dilatometry. Figure 3 also shows some ranges of viscosities related to practical operations. INSERT FIGURE 3 Adequate selection of the firing temperature for the production of glass foams is critical since it is directly related to the glass viscosity and its expansion caused by the gas release from the foaming agent decomposition. Indeed, in the glass working range temperature, the viscosity (106.6 to 103 Pa·s) is low enough to allows the expansion of the produced gases. The most convenient viscosity range for the glass foams production with maximum porosity is between 10³ and 105 Pa·s. This range corresponds to temperatures between 800 and 1000 °C for soda-lime glasses, as indicated in Figure 3 (Petersen et al., 2017).
Figure 4 shows linear shrinkage curves of GB and mass loss for ES and a calcium carbonate (the same reference calcium carbonate used for XRD) in function of temperature, obtained by optical dilatometry and thermogravimetric analysis. INSERT FIGURE 4 Glass densification starts at approximately 600 °C and its softening begins from 700 °C (Littleton softening point). From approximately 900 °C (when the glass reaches its highest shrinkage and densification) the glass expansion occurs up to 1000 °C due to viscous liquid phase formation. From 1000 °C the viscosity of the glass continues gradually decreasing. Thermogravimetric analysis (Figure 4) show ES gas release (CO2) related to calcium carbonate decomposition in the temperature range between approximately 600 and 790 °C, similar to commercial calcium carbonate. These results indicate that the gases released in this temperature range, in which the glass is relatively dense, will be partially retained on glass matrix and will cause its expansion. At 900 oC the glass viscosity is sufficiently low to cause expansion and, consequently, porosity formation. In this same temperature, glass reaches a greater shrinkage and higher densification.
3.2 Characterization of the glass foams Figure 5 shows the influence of the ES additions in the GB on the volumetric expansion and geometric density of samples fired at 900 °C for 30 min. INSERT FIGURE 5 Maximum expansion (109%vol) and minimum density (0.25 g/cm³) were achieved for samples with 3 wt% ES. For ES additions between 3 and 30 wt% it can be observed an expansion decrease and a density increase. Probably, the excess gases generated promote an increase in internal pressure, which results in the rupture of the pore walls and its releasement (Bernardo and Albertini, 2006; König et al., 2015).
Figure 6 relates thermal conductivity (k) with porosity () of glass foams produced without and with different contents of ES (fired at 900 °C for 30 min). INSERT FIGURE 6 It can be clearly seen that the thermal conductivity depends on porosity. The higher porosity is reached for glass foams containing 3 wt% ES and slightly decreases with larger ES contents. The composition containing 30 wt% ES, in comparison to others, presents a less porous structure caused by the excessive amount of foaming agent. Commercial glass foams show thermal conductivity values in the 0.04 - 0.08 W/m.K range and porosity between 85 and 95% (Scheffler and Colombo, 2005). As also shown in Figure 7, samples with 1 up to 15 wt% ES show mean values of thermal conductivity ranging between 0.055 and 0.083 W/m.K and porosities between 83 and 92%. The composition with 30 wt% ES presents a k value of 0.177 W/m.K. Fundamental mechanisms of heat transfer in a stationary system are conduction, convection and radiation. Since the glass foams working temperature range is limited to about 500 ºC due to its glass transition temperature (usually between 520 and 600 ºC), the radiation mechanism can be neglected. According to literature (Collishaw and Evans, 1994), glass foams with pore sizes less than 4 mm (4000 µm), as the foams produced in this work, heat transfer by convection mechanism can also be omitted. Hence, heat transfer in these materials is governed by thermal conduction (Fourier's law) and thermal conductivity (k) is the main parameter related to the material structure strongly influenced by the porosity. Figure 7 relates compressive strength (σc) with the porosity () of the glass foams produced with different contents of ES. Mechanical strength is greatly influenced by the porosity: the sample with higher porosity and thinner pore walls (3 wt% ES) presented the lowest mechanical resistance value (~0.15 MPa) and the sample with one of the lowest porosity values (15 wt% ES) showed the highest mechanical resistance (~1.5 MPa).
INSERT FIGURE 7 According to Scheffler and Colombo (2005) commercial glass foams typically show compressive strength values between 0.4 and 6 MPa for porosity values higher than 70%. As shown in the Figure 8, ES contents between 6 and 15 wt% achieved the compressive strength range established by the same authors. Figure 8 shows the dimensional changes and porosity of samples fired at 900 °C/30 min, obtained by photographs in natural scale. Regarding the compositions with porosity higher than 80% (1 to 15 wt% ES), smaller pore sizes are noticeable for compositions containing 1 wt% ES (Figure 8a), from 0.5 to 1.8 mm. However, in composition containing 3 wt% ES, the size distribution is from 1.7 to 8.0 mm (Figure 8b). INSERT FIGURE 8 Pore size can define the application of the glass foam. It is a parameter easily controlled during processing of the pore-forming agent since particle size of the foaming agent and the pore sizes in the obtained glass foams are strictly related (Scheffler and Colombo, 2005). Therefore, one way to vary the pore size distribution is varying the particle size of the pore forming agent used, which can result in an open structure with interconnected pores (large particles) or closed with isolated pores (smaller particles) or a mixed structure (with interconnected and isolated pores) depending on the use of the glass foam.
4. Conclusions Discarded glass bottles (99-70 wt%) were successfully converted into glass foams using ES (1-30 wt%) as foaming agents, thus contributing to the sustainable life cycle of these materials, usually deposited in landfills, by the recycling of glass and valorization of eggshells.
After firing the glass foams with increasing additions of ES at 900 oC for 30 min, porosity, thermal conductivity and compressive strength obtained ranged from 83 to 92%, 0.055 to 0.177 W/m.K and 0.15 to 1.5 MPa, respectively. Due to the similarities between the eggshell and pure calcium carbonate features, the possibility of replacing the commercial raw material for the residue was proved. The photographs of the produced foams showed glass structures with partially open porosity (interconnected pores) in the compositions up to 15 wt% ES. It is suggested that foams with closed porosity (isolated pores) can be obtained by reducing the particle size of the foaming agent. Acknowledgements The authors are grateful for the support provided by FAPESC/CNPq (PRONEX TO nº17431/2011-9).
References Arcaro, S., Maia, B.G.O., Souza, M.T., Cesconeto, F.R., Granados, L., Oliveira, A.P.N., 2016. Thermal insulating foams produced from glass waste and banana leaves. Mat. Res. 19 (5), 1064-1069. Attila, Y., Güden, M., Taşdemirci, A., 2013. Foam glass processing using a polishing glass powder residue. Ceram. Int. 39 (5), 5869-5877. Bellucci, D., Cannillo, V., Sola, A., Chiellini, F., Gazzarri, M., Migone, C., 2011. Macroporous Bioglass®-derived scaffolds for bone tissue regeneration. Ceram. Int. 37 (5), 1575-1585. Bernardo, E., Albertini, F., 2006. Glass foams from dismantled cathode ray tubes. Ceram. Int. 32 (6), 603-608. Bernardo, E., Cedro, R., Florean, M., Hreglich, S., 2007. Reutilization and stabilization of wastes by the production of glass foams. Ceram. Int. 33 (6) 963-968. Bernardo, E., Scarinci, G., Bertuzzi, P., Ercole, P., Ramon, L., 2010. Recycling of waste glasses into partially crystallized glass foams. J. Porous Mater. 17 (3), 359-365. Chen, Q.Z., Thompson, I.D., Boccaccin, A.R., 2006. 45S5 Bioglasss®-derived glass–ceramic scaffolds for bone tissue engineering. Biomaterials. 27 (11), 2414-2425. Collishaw, P.G., Evans, J.R.G., 1994. An assessment of expressions for the apparent thermal conductivity of cellular materials. J. Mater. Sci. 29, 486-498. Fernandes, H.R., Andreola, F., Barbieri, L., Lancellotti, I., Pascual, M. J., Ferreira, J.M.F., 2013. The use of egg shells to produce Cathode Ray Tube (CRT) glass foams. Ceram. Int. 39 (8), 9071-9078. Gaonkar, M., Chakraborty, A.P., 2016. Application of eggshell as fertilizer and calcium supplement tablet. Int. J. Inno. Res. Sci. 5 (3), 3520-3525.
Jones, J.R., Ehrenfried, L.M., Hench, L.L., 2006. Optimising bioactive glass scaffolds for bone tissue engineering. Biomaterials. 27 (7), 964-973. König, J., Petersen, R.R., Yue, Y., 2015. Fabrication of highly insulating foam glass made from CRT panel glass. Ceram. Int. 41 (8), 9793-9800. Lu, J., Onitsuka, K., 2004. Construction utilization of foamed waste glass. J. Environ. Sci. 16 (2), 302-307. Midha, S., Kim, T.B., Van den Bergh, W., Lee, P.D., Jones, J.R., Mitchell, C.A., 2013. Preconditioned 70S30C bioactive glass foams promote osteogenesis in vivo. Acta Biomater. 9 (11), 9169-82. Mugoni, C., Montorsi, M., Siligardi, C., Andreola, F., Lancellotti. I., Bernardo, E., Barbieri, L., 2015. Design of glass foams with low environmental impact. Ceram. Int. 41 (6), 34003408. Petersen, R.R., König, J., Yue, Y., 2017. The viscosity window of the silicate glass foam production. J. Non. Cryst. Sol. 456 (15), 49-54. Pliya, P., Cree, D., 2015. Limestone derived eggshell powder as a replacement in Portland cement. Constr. Build. Mater. 95 (1), 1-9. Romano, R.C.O., Pandolfelli, V.C., 2006. Production and properties of porous ceramics obtained by foam addition technique. Cerâmica. 52, 213-219. Sasmal, N., Garai, M., Karmakar, B., 2015. Preparation and characterization of novel foamed porous glass-ceramics. Mater. Charac. 103, 90-100. Scheffler, M., Colombo, P., 2005. Cellular Ceramics: Structure, manufacturing, properties and applications. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Stadelman, W.J., 2000. Eggs and egg products - Encyclopedia of Food Science and Technology. John Wiley & Sons, New York, USA. Studart, A.R., Gonzenbach, U.T., Tervoort, E., Gauckler, L.J., 2006. Processing routes to macroporous ceramics: A review. J. Am. Ceram. Soc. 89 (6), 1771-1789. Taurino, R., Lancellotti, I., Barbieri, L., Leonelli, C., 2014. Glass–Ceramic foams from borosilicate glass waste. Int. J. Appl. Glass Sci. 5 (2), 136-145. Tsai, W.T., Hsien, K.J., Hsu, H.C., Lin, C.M., Lin, K.Y., Chiu, C.H., 2008. Utilization of ground eggshell waste as an adsorbent for the removal of dyes from aqueous solution. Bioresource Technol. 99 (6), 1623-1629. Vogel, H., 1921. Viscosity of liquids. Physikalische Zeitschrif. 22, 645-646. Wu, J., Boccaccini, A.R., Lee, P.D., Kershaw, M.J., Rawlings, R.D., 2006. Glass ceramic foams from coal ash and waste glass: production and characterization. Adv. Appl. Ceram. 105 (1), 32-39.
FIGURE CAPTIONS
Figure 1. X-ray diffraction patterns of: (a) Eggshell (ES) and (b) high purity calcium carbonate (RM). C = calcium carbonate (CaCO3).
Figure 2. Particle size distribution of glass bottle (GB) and eggshell (ES) powders.
Figure 3. Viscosity logarithmic (η) in function of temperature for the recycled glass bottle (GB).
Figure 4. Linear shrinkage curve of the recycled glass bottle (GB) and mass losses of the eggshell (ES) and a commercial calcium carbonate (CaCO3) as function of the temperature.
Figure 5. Volumetric expansion (VE) and geometric density () of glass foams with different contents of eggshell (ES).
Figure 6. Thermal conductivity (k) and porosity () of glass foams with different contents of eggshell (ES).
Figure 7. Compressive strength (σc) and porosity () of glass foams made with different contents of eggshell (ES).
Figure 8. Photographs of glass foams (GB) with several contents of eggshell (ES): (a) 1 wt%, (b) 3 wt%, (c) 6 wt%, (d) 9 wt%, (d) 12 wt%, (e) 15 wt% and (f) 30 wt% ES.
Table 1. Chemical compositions of the recycled glass bottles (GB) and eggshells (ES). Constituents oxides (wt%) Raw materials
SiO2
CaO
Na2O
MgO
Fe2O3
Al2O3
P2O5
L.O.I.
Glass bottle (GB)
70.2
9.50
16.6
-
0.10
2.10
-
1.50
Eggshell (ES) 52.4 (93.6)* 0.20 0.60 0.30 L.O.I. = Loss on ignition. * The value in parenthesis represents the CaCO3 content in the eggshell
.
46.5
S0957-5820(17)30192-1 http://dx.doi.org/doi:10.1016/j.psep.2017.06.011 PSEP 1092
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
24-6-2016 3-5-2017 15-6-2017
Please cite this article as: Souza, Marcelo T., Maia, Bianca G.O., Teixeira, Luyza B., de Oliveira, Karine G., Teixeira, Alexandre H.B., Novaes de Oliveira, Antonio P., Glass foams produced from glass bottles and eggshell wastes.Process Safety and Environment Protection http://dx.doi.org/10.1016/j.psep.2017.06.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Glass foams produced from glass bottles and eggshell wastes
Marcelo T. Souzaa; Bianca G.O. Maiaa*; Luyza B. Teixeiraa; Karine G. de Oliveirab; Alexandre H.B. Teixeiraa; Antonio P. Novaes de Oliveiraa
a
Graduate Program in Materials Science and Engineering (PGMAT), Laboratory of Glass-Ceramic Materials
(VITROCER), Federal University of Santa Catarina (UFSC), 88040-900, Florianópolis (SC), Brazil. *e-mail: [email protected] b
Graduate Program in Environmental Engineering (PPGEA), Federal University of Santa Catarina (UFSC),
88040-900, Florianópolis (SC), Brazil.
Highlights
Glass foams were produced from discarded glasses and eggshells.
Eggshells are a calcium carbonate rich residue.
The obtained glass foams have potential as thermal insulating materials.
Thermal insulation and non-flammability are the main technical requirements.
Reusing glass bottles and eggshells contributes to minimize the environmental impacts.
Abstract: Glass foams were produced from discarded glass bottles (GB) and eggshells (ES) as foaming agent in contents between 1 and 30 wt%. The raw materials (GB, ES) were homogenized and uniaxially pressed (20 MPa). The obtained powder compacts were fired at 900 °C/30 min and characterized according to their chemical, physical and structural properties. The results (porosities between 60 and 95% with thermal conductivities between 0.177 and 0.055 W/m.K and compressive mechanical strength between 0.15 and 1.50 MPa) indicate that the obtained glass foams have potential for applications where thermal and acoustic insulation and non-flammability are the main technical requirements.
Keywords: glass; eggshell; foams; porous, wastes.
1. Introduction Glass foams are porous materials formed by a gas phase (present inside the pores) and a solid phase (glass matrix) (Sasmal et al., 2015). These materials have porosity usually higher than 60% vol., which can be open, close, or both. The pores features (size, distribution and morphology) determine specific properties, such as low density, low thermal conductivity, high surface area, permeability, chemical and thermal stability (Scheffler and Colombo, 2005). Some glass foams also presents bioactivity and bacteria-resistant (Chen et al., 2006; Midha et al., 2013). In addition to these properties, these foams are easy handling (Attila et al., 2013; Scheffler and Colombo, 2005). Hence, they are widely used as building blocks (e.g., for insulating roofs, walls, floors and ceilings in high or low temperatures), as filler for the restoration of failed slopes, as subgrade improvement material, as light-weight aggregate material in concrete and water folding material for greening (Lu and Onitsuka, 2004) and also as scaffolds for bone tissue engineering (Chen et al., 2006; Jonde et al., 2006; Bellucci et al., 2011). By the other hand, the glass foams applications are limited by their working temperature, which should not exceed their glass transition temperature between 500-600 oC. For higher temperatures, the foam exhibits deformation and loss of the porous structure (Scheffler and Colombo, 2005). The costs of glass foams have also constituted a key disadvantage for their diffusion in the building industry. In order to reduce the production costs, several alternative processing techniques and the starting materials have been explored (Bernardo et al., 2007). Recent studies have shown numerous advantages and possibilities to obtain glass foams from discarded glasses (Arcaro et al., 2016; Bernardo et al., 2010; Taurino et al., 2014; Wu et al., 2006; Mugoni et al., 2015). According to Institute of Applied Economic Research
(IPEA), in Brazil, around 260 thousand tons of glass are discarded in landfills every year. IPEA also estimates an expense of R$ 8 bi ($ 2.3 bi) to discard/bury wastes that could generally be reused. Among the various techniques for obtaining ceramic foams, replication, gelcasting, foaming and incorporation of foaming agents (pore formers) are mostly used (Studart et al., 2006). The technique of foaming agents’ incorporation, due to its simplicity, is the most used in the production of glass foams and consists of incorporating a foaming or pore-forming agent in the ceramic matrix. The foaming depends on decomposition (usually due to carbonates and sulphates releasing) or oxidation reactions (interaction of carbon-containing species mainly with the atmosphere of the sintering furnace). The pores sizes generated by foaming decomposition are associated with the particle size of the foaming agent used (Bernardo et al., 2007; Romano and Pandolfelli, 2006; Souza et al., 2006). Wastes in general provide many value-added opportunities and can be a low cost alternative for use as foaming agents (Bernardo et al., 2007). As example, aviculture produces a significant amount of eggshells (ES) (Fernandes et al., 2013). According to the United States Department of Agriculture (USDA), in 2014 it was produced about 8 billion dozen chicken eggs. In Brazil, according to Brazilian Institute of Geography and Statistics (IBGE), the production was about 2.8 billion dozen in the same year. Eggshell, which corresponds to about 10 wt% egg (Stadelman, 2000), contains about 94 wt% calcium carbonate (CaCO3) in its composition. Although the ES is not being considered a hazardous waste, its inappropriately landfill disposal can result in considerable environmental liabilities due to the large amount of eggs produced. Since ES is a calcium carbonate rich residue, the possibilities of its reuse may include the incorporation in soil for agricultural purposes (Gaonkar and Chakraborty, 2016), as adsorbent for removal of coloring matter in aqueous solutions (Tsai et
al., 2008), as a replacement for limestone in the production of Portland cement (Pliya and Cree, 2015), among other applications. Therefore, despite glass bottles and eggshell wastes have well established solutions, a huge amount of both wastes are still discarded. Thus, from an environmental point of view, glass foams production is an interesting alternative destination for these wastes (Bernardo et al., 2007). In this context, the aim of this work is to produce glass foams with low cost starting materials, i.e., from the use of recycled soda-lime glasses (matrix) and ES (foaming agent).
2. Experimental Procedure 2.1. Obtainment and characterization of the raw materials Glasses from discarded glass bottles (GB) of different colors, mixed in equal proportions, (white, green and brown) were used as raw materials. Eggshells (ES) were used as pore-forming agent (foaming agent). It was also used commercial calcium carbonate (LABSYNTH), CaCO3, with purity greater than 99%, as reference material (RM). Chemical compositions of GB and ES were obtained by X-Ray Fluorescence (Philips, model PW 2400). To investigate the crystalline phases of the ES and commercial calcium carbonate used as reference material (RM), powdered samples were analyzed using X-ray diffractometry, XRD (Philips X’Pert) with CuKα radiation. GB were dry crushed in a hammer mill (Servitech, CT-058) and milled for 120 min in a fast mill (Servitech, CT -242) using a porcelain jar containing alumina balls. ES were provided by a commercial establishment and, because of their physical characteristics (brittleness), were directly milled in a fast mill (Servitech, CT-242) for 5 min. The particle size distribution of the wastes after grinding was obtained by laser scattering particle size analyser (Malvern, Mastersizer 2000).
2.2. Obtainment and characterization of glass foam Samples containing different proportions of GB (between 70 and 99 wt%) and ES (between 1 and 30 wt%) were prepared by wet mixing (40% solids) using a mechanical stirrer (IKA RW 20) at 200 rpm for 10 min. After drying (110 °C/24 h) of the aqueous suspension in a laboratory dryer (SP LABOR®), the resulting powders were uniaxially pressed (20 MPa) in a steel die using a hydraulic press (Bovenau P10 ST) with addition of 5% moisture. The obtained compacts (30 mm in diameter and 10 mm thick) were fired (oxidizing atmosphere) in a laboratory furnace (Jung J200) at 900 °C during 30 min, using a heating rate of 10 °C/min. The thermal behavior of raw materials (GB, ES) was investigated using an optical dilatometer (Misura ODHT) and a contact dilatometer (Netzsch, DIL 402) and also by thermogravimetric analyses, TG (SDT, TA Instruments Q-600) at 10 °C/min (oxidizing atmosphere). Digital photographs of fired samples were also performed. From the results of the dilatometric analysis it was possible to determine the viscosity curve from Vogel-FulcherTammann equations (Vogel, 1921). The true densities (ρt) of the powdered samples were determined by using a helium pycnometer
(Ultrapycnometer
1200
P/N,
Quantachrome
Instruments).
The
linear
shrinkage/expansion (%) and geometric densities (ρg) of the fired samples were determined relating their geometrical measurements, obtained using a caliper (Mitotoyo, accuracy ± 0.01 mm), and their masses (Shimadzu AX200 at 0.001 g). The porosities () of the fired glass foams were calculated from geometrical (g) and true (t) densities measurements ratios, i.e., 𝜀 = (1 − 𝜌𝑔/𝜌𝑡 ) × 100. The porous size distribution were determined by photographs of the samples and the image analyzer ImageJ.
To determine the mechanical strength of the samples, compression tests (EMIC DL 2000 model) were performed on five disc samples (30 x 10 mm) with loading speed of 1 mm/min. Thermal conductivity of the glass foams
was determined by a TCi Thermal
Conductivity C-THERM TECHNOLOGIES on samples with 30 mm diameter and 10 mm thick.
3. Results and Discussion 3.1. Characterization of the raw materials and compositions Table 1 shows the results of the chemical analysis of the recycled GB and ES obtained by X-Ray Fluorescence. TABLE 1 The chemical composition of the glass in this study is typical of soda-lime glasses used to manufacture bottles and flat glass windows. The ES used as pore-forming agent are composed mainly of calcium carbonate (CaCO3). In fact, chemical analysis (Table 1) indicates that ES contain approximately 94 wt% of CaCO3, calculated from the CaO content (52.4 wt%). Figure 1 shows XRD patterns of the (a) ES and (b) high purity commercial calcium carbonate used as reference material (RM). INSERT FIGURE 1 Besides the very significant chemical similarity between ES and commercial calcium carbonates, X-ray patterns of these materials confirm this compositional and structural similarity since it was detected only calcium carbonate, CaCO3 (JCPDS Nº. 33-1161).
Figure 2 shows the particle size distributions for GB and ES after milling processes obtained by laser scattering particle size analyzer. INSERT FIGURE 2 The analysis indicated that the GB, after milling process, had an average particle size (D50) of about 2.9 m. The foaming agent (ES), on the other hand, exhibits average particle size (D50) of 56.6 m. Glasses for such applications must be milled and sieved to obtain a particle size lower than 4000 m, otherwise the foam formation process is inefficient. Although the literature cites that to facilitate homogenization of the formulation, the sizes of the powders of the pore agent forming and the glass must be similar, no problems occurred during the preparation of the formulations. The particles size of the foaming agent also influences the structural characteristics (pore size) of the glass foam (Scheffler and Colombo, 2005). Figure 3 shows a curve relating the logarithm of viscosity versus temperature for recycled GB from the Vogel-Fulcher-Tammann equations (Vogel, 1921), obtained by optical dilatometry and contact dilatometry. Figure 3 also shows some ranges of viscosities related to practical operations. INSERT FIGURE 3 Adequate selection of the firing temperature for the production of glass foams is critical since it is directly related to the glass viscosity and its expansion caused by the gas release from the foaming agent decomposition. Indeed, in the glass working range temperature, the viscosity (106.6 to 103 Pa·s) is low enough to allows the expansion of the produced gases. The most convenient viscosity range for the glass foams production with maximum porosity is between 10³ and 105 Pa·s. This range corresponds to temperatures between 800 and 1000 °C for soda-lime glasses, as indicated in Figure 3 (Petersen et al., 2017).
Figure 4 shows linear shrinkage curves of GB and mass loss for ES and a calcium carbonate (the same reference calcium carbonate used for XRD) in function of temperature, obtained by optical dilatometry and thermogravimetric analysis. INSERT FIGURE 4 Glass densification starts at approximately 600 °C and its softening begins from 700 °C (Littleton softening point). From approximately 900 °C (when the glass reaches its highest shrinkage and densification) the glass expansion occurs up to 1000 °C due to viscous liquid phase formation. From 1000 °C the viscosity of the glass continues gradually decreasing. Thermogravimetric analysis (Figure 4) show ES gas release (CO2) related to calcium carbonate decomposition in the temperature range between approximately 600 and 790 °C, similar to commercial calcium carbonate. These results indicate that the gases released in this temperature range, in which the glass is relatively dense, will be partially retained on glass matrix and will cause its expansion. At 900 oC the glass viscosity is sufficiently low to cause expansion and, consequently, porosity formation. In this same temperature, glass reaches a greater shrinkage and higher densification.
3.2 Characterization of the glass foams Figure 5 shows the influence of the ES additions in the GB on the volumetric expansion and geometric density of samples fired at 900 °C for 30 min. INSERT FIGURE 5 Maximum expansion (109%vol) and minimum density (0.25 g/cm³) were achieved for samples with 3 wt% ES. For ES additions between 3 and 30 wt% it can be observed an expansion decrease and a density increase. Probably, the excess gases generated promote an increase in internal pressure, which results in the rupture of the pore walls and its releasement (Bernardo and Albertini, 2006; König et al., 2015).
Figure 6 relates thermal conductivity (k) with porosity () of glass foams produced without and with different contents of ES (fired at 900 °C for 30 min). INSERT FIGURE 6 It can be clearly seen that the thermal conductivity depends on porosity. The higher porosity is reached for glass foams containing 3 wt% ES and slightly decreases with larger ES contents. The composition containing 30 wt% ES, in comparison to others, presents a less porous structure caused by the excessive amount of foaming agent. Commercial glass foams show thermal conductivity values in the 0.04 - 0.08 W/m.K range and porosity between 85 and 95% (Scheffler and Colombo, 2005). As also shown in Figure 7, samples with 1 up to 15 wt% ES show mean values of thermal conductivity ranging between 0.055 and 0.083 W/m.K and porosities between 83 and 92%. The composition with 30 wt% ES presents a k value of 0.177 W/m.K. Fundamental mechanisms of heat transfer in a stationary system are conduction, convection and radiation. Since the glass foams working temperature range is limited to about 500 ºC due to its glass transition temperature (usually between 520 and 600 ºC), the radiation mechanism can be neglected. According to literature (Collishaw and Evans, 1994), glass foams with pore sizes less than 4 mm (4000 µm), as the foams produced in this work, heat transfer by convection mechanism can also be omitted. Hence, heat transfer in these materials is governed by thermal conduction (Fourier's law) and thermal conductivity (k) is the main parameter related to the material structure strongly influenced by the porosity. Figure 7 relates compressive strength (σc) with the porosity () of the glass foams produced with different contents of ES. Mechanical strength is greatly influenced by the porosity: the sample with higher porosity and thinner pore walls (3 wt% ES) presented the lowest mechanical resistance value (~0.15 MPa) and the sample with one of the lowest porosity values (15 wt% ES) showed the highest mechanical resistance (~1.5 MPa).
INSERT FIGURE 7 According to Scheffler and Colombo (2005) commercial glass foams typically show compressive strength values between 0.4 and 6 MPa for porosity values higher than 70%. As shown in the Figure 8, ES contents between 6 and 15 wt% achieved the compressive strength range established by the same authors. Figure 8 shows the dimensional changes and porosity of samples fired at 900 °C/30 min, obtained by photographs in natural scale. Regarding the compositions with porosity higher than 80% (1 to 15 wt% ES), smaller pore sizes are noticeable for compositions containing 1 wt% ES (Figure 8a), from 0.5 to 1.8 mm. However, in composition containing 3 wt% ES, the size distribution is from 1.7 to 8.0 mm (Figure 8b). INSERT FIGURE 8 Pore size can define the application of the glass foam. It is a parameter easily controlled during processing of the pore-forming agent since particle size of the foaming agent and the pore sizes in the obtained glass foams are strictly related (Scheffler and Colombo, 2005). Therefore, one way to vary the pore size distribution is varying the particle size of the pore forming agent used, which can result in an open structure with interconnected pores (large particles) or closed with isolated pores (smaller particles) or a mixed structure (with interconnected and isolated pores) depending on the use of the glass foam.
4. Conclusions Discarded glass bottles (99-70 wt%) were successfully converted into glass foams using ES (1-30 wt%) as foaming agents, thus contributing to the sustainable life cycle of these materials, usually deposited in landfills, by the recycling of glass and valorization of eggshells.
After firing the glass foams with increasing additions of ES at 900 oC for 30 min, porosity, thermal conductivity and compressive strength obtained ranged from 83 to 92%, 0.055 to 0.177 W/m.K and 0.15 to 1.5 MPa, respectively. Due to the similarities between the eggshell and pure calcium carbonate features, the possibility of replacing the commercial raw material for the residue was proved. The photographs of the produced foams showed glass structures with partially open porosity (interconnected pores) in the compositions up to 15 wt% ES. It is suggested that foams with closed porosity (isolated pores) can be obtained by reducing the particle size of the foaming agent. Acknowledgements The authors are grateful for the support provided by FAPESC/CNPq (PRONEX TO nº17431/2011-9).
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Jones, J.R., Ehrenfried, L.M., Hench, L.L., 2006. Optimising bioactive glass scaffolds for bone tissue engineering. Biomaterials. 27 (7), 964-973. König, J., Petersen, R.R., Yue, Y., 2015. Fabrication of highly insulating foam glass made from CRT panel glass. Ceram. Int. 41 (8), 9793-9800. Lu, J., Onitsuka, K., 2004. Construction utilization of foamed waste glass. J. Environ. Sci. 16 (2), 302-307. Midha, S., Kim, T.B., Van den Bergh, W., Lee, P.D., Jones, J.R., Mitchell, C.A., 2013. Preconditioned 70S30C bioactive glass foams promote osteogenesis in vivo. Acta Biomater. 9 (11), 9169-82. Mugoni, C., Montorsi, M., Siligardi, C., Andreola, F., Lancellotti. I., Bernardo, E., Barbieri, L., 2015. Design of glass foams with low environmental impact. Ceram. Int. 41 (6), 34003408. Petersen, R.R., König, J., Yue, Y., 2017. The viscosity window of the silicate glass foam production. J. Non. Cryst. Sol. 456 (15), 49-54. Pliya, P., Cree, D., 2015. Limestone derived eggshell powder as a replacement in Portland cement. Constr. Build. Mater. 95 (1), 1-9. Romano, R.C.O., Pandolfelli, V.C., 2006. Production and properties of porous ceramics obtained by foam addition technique. Cerâmica. 52, 213-219. Sasmal, N., Garai, M., Karmakar, B., 2015. Preparation and characterization of novel foamed porous glass-ceramics. Mater. Charac. 103, 90-100. Scheffler, M., Colombo, P., 2005. Cellular Ceramics: Structure, manufacturing, properties and applications. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Stadelman, W.J., 2000. Eggs and egg products - Encyclopedia of Food Science and Technology. John Wiley & Sons, New York, USA. Studart, A.R., Gonzenbach, U.T., Tervoort, E., Gauckler, L.J., 2006. Processing routes to macroporous ceramics: A review. J. Am. Ceram. Soc. 89 (6), 1771-1789. Taurino, R., Lancellotti, I., Barbieri, L., Leonelli, C., 2014. Glass–Ceramic foams from borosilicate glass waste. Int. J. Appl. Glass Sci. 5 (2), 136-145. Tsai, W.T., Hsien, K.J., Hsu, H.C., Lin, C.M., Lin, K.Y., Chiu, C.H., 2008. Utilization of ground eggshell waste as an adsorbent for the removal of dyes from aqueous solution. Bioresource Technol. 99 (6), 1623-1629. Vogel, H., 1921. Viscosity of liquids. Physikalische Zeitschrif. 22, 645-646. Wu, J., Boccaccini, A.R., Lee, P.D., Kershaw, M.J., Rawlings, R.D., 2006. Glass ceramic foams from coal ash and waste glass: production and characterization. Adv. Appl. Ceram. 105 (1), 32-39.
FIGURE CAPTIONS
Figure 1. X-ray diffraction patterns of: (a) Eggshell (ES) and (b) high purity calcium carbonate (RM). C = calcium carbonate (CaCO3).
Figure 2. Particle size distribution of glass bottle (GB) and eggshell (ES) powders.
Figure 3. Viscosity logarithmic (η) in function of temperature for the recycled glass bottle (GB).
Figure 4. Linear shrinkage curve of the recycled glass bottle (GB) and mass losses of the eggshell (ES) and a commercial calcium carbonate (CaCO3) as function of the temperature.
Figure 5. Volumetric expansion (VE) and geometric density () of glass foams with different contents of eggshell (ES).
Figure 6. Thermal conductivity (k) and porosity () of glass foams with different contents of eggshell (ES).
Figure 7. Compressive strength (σc) and porosity () of glass foams made with different contents of eggshell (ES).
Figure 8. Photographs of glass foams (GB) with several contents of eggshell (ES): (a) 1 wt%, (b) 3 wt%, (c) 6 wt%, (d) 9 wt%, (d) 12 wt%, (e) 15 wt% and (f) 30 wt% ES.
Table 1. Chemical compositions of the recycled glass bottles (GB) and eggshells (ES). Constituents oxides (wt%) Raw materials
SiO2
CaO
Na2O
MgO
Fe2O3
Al2O3
P2O5
L.O.I.
Glass bottle (GB)
70.2
9.50
16.6
-
0.10
2.10
-
1.50
Eggshell (ES) 52.4 (93.6)* 0.20 0.60 0.30 L.O.I. = Loss on ignition. * The value in parenthesis represents the CaCO3 content in the eggshell
.
46.5