Polymer cements by copolymerization of waste sulfur, oleic acid, and pozzolan cements

Sustainable Chemistry and Pharmacy 16 (2020) 100249

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Polymer cements by copolymerization of waste sulfur, oleic acid, and pozzolan cements Ashlyn D. Smith a, *, Rhett C. Smith b, Andrew G. Tennyson b, c, ** a

Department of Biology and Chemistry, Anderson University, Anderson, SC, 29621, USA Department of Chemistry and Center for Optical Materials Science and Engineering Technology, Clemson University, Clemson, SC, 29634, USA c Department of Materials Science and Engineering, Clemson University, Clemson, SC, 29634, USA b

A B S T R A C T

A host of emerging cementitious products derived from waste materials or sustainable precursors have drawn increasing interest in response to economic, social and regulatory pressures. Among the more well-studied and abundant of such cement products are sulfur cements and pozzolans like fly ash, silica fume, ground granulated blast furnace slag, and metakaolin. For the current study, oleic acid was combined with these compounds to make a series of pastes. Oleic acid is an attractive additive because it is a primary constituent of low value, high-volume by-products of biodiesel production and animal product rendering. The current work is thus a comparative study of pastes prepared by heating sulfur and oleic acid with either ordinary Portland cement or one of the pozzolan-extended cements. The mechanical properties of the cured sulfur-oleic acid pastes were assessed by dynamic mechanical analysis to provide stress-strain curves both before and after acid challenge. All of the blocks prepared from the pastes retain significantly more mechanical strength (up to 100%) after exposure to strong oxidizing acid solutions than does ordinary Portland cement. Surface damage to these sulfur cement blocks can be healed to varying extents by thermal annealing, as assessed by optical microscopy.

1. Introduction Sulfur-extended cements and asphalt formulations have attracted increasing attention for their potential to provide increased strength, chemical /corrosion resistance, and as more sustainable asphalt prod­ ucts wherein sulfur composites replace some of the fossil fuel-derived bitumen (Dehestani et al., 2017; Weil, 1991; Transportation, 1978; Deme, 1978, 2005; Gillott et al., 1978; Kennepohl and Miller, 1978; Al-Ansary et al., 2010; Taylor et al., 2010; Lee, 1975; Gwon et al., 2018, 2019; Gwon and Shin, 2019; Szajerski et al., 2020; Lewandowski and Kotynia, 2018; Mohammed and Poornima, 2018). As the cost of tradi­ tional asphalt and masonry components has increased, affordable al­ ternatives have been sought to “extend” their formulations without compromising performance. Elemental sulfur is a waste product of fossil fuel production and as such is an inexpensive and plentiful material with a well-established history of being used not only to extend products, but also to enhance the strength and weathering robustness of traditional construction materials (Transportation, 1978; Mohamed and Gamal, 2010). A notable commercial example is Thiopave® from Shell Oil (Al-Ansary et al., 2010; Taylor et al., 2010; Zuo et al., 2011; Hu et al.,

2013). We (Thiounn et al., 2018, 2019; Smith et al., 2019, 2020; Lauer et al., 2019; Karunarathna et al., 2019, 2020a, 2020b) and others (Wor­ thington et al., 2017; Herrera et al., 2019; Westerman and Jenkins, 2018) have developed a number of durable, sustainable copolymers and sulfur cements whose mechanical strengths derive from crosslinking of sulfur chains with organic agricultural products. One such sulfur cement, ZOS90, is comprised of 90 wt% elemental sulfur crosslinked with oleic acid and zinc oxide (Smith et al., 2019). Especially desirable properties of ZOS90 cement are that surface scratch damage can be thermally healed and that bulk samples can be pulverized, melted and recast into blocks over many cycles without loss of mechanical strength for facile recycling. Despite the attractive features of ZOS90, the need for zinc oxide in its preparation is problematic in many ways. First, zinc oxide is not sustainably sourced like the sulfur and oleic acid compo­ nents. Second, zinc oxide is expensive. Finally, cements containing zinc oxide have the potential to leach zinc ions into the environment. For these reasons, alternatives to zinc oxide were sought. The origin of zinc oxide addition to ZOS90 formulations derives from the fact that oleic acid and sulfur have limited miscibility. During the synthesis of ZOS90,

* Corresponding author. ** Corresponding author. Department of Chemistry and Center for Optical Materials Science and Engineering Technology, Clemson University, Clemson, SC, 29634, USA. E-mail addresses: [email protected] (A.D. Smith), [email protected] (A.G. Tennyson). https://doi.org/10.1016/j.scp.2020.100249 Received 1 January 2020; Received in revised form 7 March 2020; Accepted 7 March 2020 Available online 25 March 2020 2352-5541/© 2020 Elsevier B.V. All rights reserved.

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Sustainable Chemistry and Pharmacy 16 (2020) 100249

Table 1 Fineness moduli (F) determinations for compatibilizer materials.

Table 1 (continued ) SILICA FUME

SILICA FUME Seive No. 18 No. 30 No. 50 No. 100 No. 200 Pan Total

Retained Weight (g) 0.283

Individual Retained (%) 0.28%

Cumulative Passing (%) 99.72%

Cumulative Retained (%) 0.28%

2.728

2.71%

97.01%

2.99%

81.236

80.60%

16.42%

83.58%

9.104

9.03%

7.39%

92.61%

6.046

6.00%

1.39%

98.61%

1.398 100.795

1.39% 100.00%

0.00% 0.00%

100.00% F ¼ 3.78

Individual Retained (%)

Cumulative Passing (%)

Cumulative Retained (%)

0.064

0.06%

99.94%

0.06%

0.086

0.09%

99.85%

0.15%

0.316

0.32%

99.53%

0.47%

62.524

62.49%

37.04%

62.96%

25.975

25.96%

11.08%

88.92%

11.09 100.055

11.08% 100.00%

0.00% 0.00%

100.00% F ¼ 2.53

Retained Weight (g)

Individual Retained (%)

Cumulative Passing (%)

Cumulative Retained (%)

4.014

4.02%

95.98%

4.02%

4.372

4.38%

91.60%

8.40%

34.104

34.17%

57.43%

42.57%

40.938

41.01%

16.42%

83.58%

13.128

13.15%

3.26%

96.74%

3.258 99.814

3.26% 100.00%

0.00% 0.00%

100.00% F ¼ 3.35

Retained Weight (g)

Individual Retained (%)

Cumulative Passing (%)

Cumulative Retained (%)

2.891

5.71%

94.29%

5.71%

5.52

10.90%

83.39%

16.61%

11.835

23.37%

60.02%

39.98%

19.601

38.71%

21.31%

78.69%

9.616

18.99%

2.32%

97.68%

1.176 50.639

2.32% 100.00%

0.00% 0.00%

100.00% F ¼ 3.39

Individual Retained (%)

Cumulative Passing (%)

Cumulative Retained (%)

0.732

3.20%

96.80%

3.20%

13.836

60.54%

36.26%

63.74%

7.48

32.73%

3.53%

96.47%

0.759

3.32%

0.21%

99.79%

FLY ASH Seive Retained Weight (g) No. 18 No. 30 No. 50 No. 100 No. 200 Pan Total GGBFS Seive No. 18 No. 30 No. 50 No. 100 No. 200 Pan Total OPC Seive No. 18 No. 30 No. 50 No. 100 No. 200 Pan Total

METAKAOLIN Seive Retained Weight (g) No. 18 No. 30 No. 50 No. 100

No. 200 Pan Total

0.045

0.20%

0.01%

99.99%

0.003 22.855

0.01% 100.00%

0.00% 0.00%

100.00% F ¼ 4.63

Table 2 Characteristics of sulfur-oleic acid cements. Material

density (kg/ m3)

H2O uptakea (wt. %)

acid-induced mass lossb (wt. %)

ZOS90 PCOS FAOS GGBFSOS MKOS SFOS

1700 1600 1700 1700 170 1600

0.0 0.1 0.0 0.0 0.0 0.0

0.1 0.0 0.1 0.0 0.1 1.9

a b

after submerged for 30 min. after submerged in 0.5 M H2SO4 for 30 min.

Fig. 1. Compressive strength of sulfur cements compared to that of ordinary portland cement (OPC). Each value is the average of three trials. Table 3 Mechanical properties of sulfur cements before and after soaking the block in 0.5 M sulfuric acid for 30 min. Material ZOS90 PCOS FAOS GGBFSOS MKOS SFOS a

Flexural modulus As-prepared (MPa)

After acida (% retained)

90 70 70 50 40 40

55 57 57 100 100 75

After sample was submerged in 0.5 M H2SO4 for 30 min.

zinc oxide serves as a base to deprotonate the oleic acid, yielding a zinc carboxylate complex. The zinc ion in the zinc carboxylate complex also binds to the elemental sulfur, thus forming a molecular-level bridge between the sulfur and organic components and compatibilizing the formulation for facile reaction to form the target cementitious com­ pound. In the current work, it was hypothesized that ordinary Portland cement (OPC) or one of several pozzolanic cements comprising metal oxides might be able to compatibilize oleic acid and elemental sulfur in a manner analogous to that of zinc oxide. We test this hypothesis by preparing sulfur /oleic acid cements wherein OPC or one of several pozzolanic cement products was used as a compatibilizing agent in place 2

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Sustainable Chemistry and Pharmacy 16 (2020) 100249

Fig. 2. Stress-strain curves for sulfur cements demonstrating the mechanical strength following acid challenge. Untreated sample (solid purple line) and sample after 30 min in 0.5 M H2SO4 (solid orange line) and the extrapolation of the linear region shown in the dashed line of the corresponding color shown for each of the materials.

of the zinc oxide that was used to prepare ZOS90. The pozzolanic cement products selected for this study were silica fume, ground granulated blast furnace slag (GGBFS), fly ash (class F), or metakaolin (Massazza, 1993; Sabir et al., 2001; Gartner, 2004; Juenger et al., 2011; Thomas, 2011; Van Deventer et al., 2012). The thermal/chemical stability, phase transition behavior, and mechanical properties of the sulfur cements were determined and the extent to which surface damage can be ther­ mally healed was assessed.

Diversified Minerals, Inc., while metakaolin was manufactured by Opptipozz. Elemental analyses were performed by Atlantic Microlab, Inc. and Intertek Group, plc. 2.2. Instrumentation Dynamic mechanical analysis (DMA) was performed using a Mettler Toledo DMA 1 STARe System with a clamping force of 1 cN∙m for stressstrain experiments. For stress-strain studies, the force was varied from 0 to 10 N with a ramp rate of 0.1 N⋅min 1 measured isothermally at 25 � C. Acid challenge of samples was performed by submerging samples into 0.50 M H2SO4 for 30 min, after which they were removed, rinsed gently with DI water, and blotted dry.

2. Materials and methods 2.1. General considerations Fly ash (FA), silica fume (SF) and ground granulated blast furnace slag (GGBFS) pozzolanic cement components were purchased from 3

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Synthesis of GGBFSOS: The general synthesis above was followed using 5.557 g of sulfur, 0.478 g of oleic acid, and 0.138 g of GGBFS mixture. Synthesis of MKOS: The general synthesis above was followed using 5.557 g of sulfur, 0.476 g of oleic acid, and 0.138 g of MK mixture. Synthesis of SFOS: The general synthesis above was followed using 5.564 g of sulfur, 0.478 g of oleic acid, and 0.141 g of SF mixture. 3. Results and discussion 3.1. Material preparation OPC and several common pozzolanic cement materials – type F fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBFS), and metakaolin (MK) – were thus selected for screening as potential compatibilizers of oleic acid-sulfur cements. The characterization of fineness moduli for the compatibilizer samples are delineated in Table 1. The fineness moduli span a reasonable range from 2.53–4.63. Each cement was prepared by heating sulfur and oleic acid with the compatibilizer at 180 � C for 24 h, yielding five sulfur cements wherein the compatibilizer was OPC (PCOS), or one of the pozzolanic mixtures comprising silica fume (SFOS), fly ash (FAOS), GBBS (GGBFSOS), or metakaolin (MKOS). Each of the cements is comprised of 90 wt% sulfur and 10 wt% of the reinforcing oleic acid-compatibilizer mixture. Each material is a black, remeltable solid compound that was poured into moulds to prepare the blocks for mechanical testing. The density of each block was determined, and the water uptake was assessed by measuring the mass of a cured block before and after its being submerged in water for 24 h (Table 2). The densities spanned a narrow range from 1640–1740 kg/m3. These sulfur cements take up essentially no water by merit of the exceedingly hydrophobic nature of sulfur, as reflected in the low critical surface energy (27 mN/m) (Kelebek, 1988) of sulfur in its pure elemental form. For context, this critical surface energy is the same as that of butyl rubber (Kelebek, 1988). 3.2. Mechanical strength and resistance to oxidizing acid challenge Despite their superior resistance to water uptake and chemical degradation, sulfur cements often fall short of the mechanical strength of traditional cement products. Recent advances in sulfur-organic co­ polymers and composites, however, have yielded materials with supe­ rior strength (Hasell et al., 2019). As an initial assessment of mechanical strength, blocks of the sulfur cement were subjected to stress-strain analysis to determine their compressive strength compared to that of portland cement (Fig. 1). The compressive strengths of ZOS90, FAOS and PCOS are similar to that of OPC, with PCOS exceeding the strength of OPC. The other materials all had lower than 70% the compressive strength of OPC. The low compressive strength seems to reflect poor homogenization of materials observed by microscopic imaging (dis­ cussed below). The flexural strengths and moduli were also determined (Table 3 and Fig. 2), though these are notably lower than the flexural strength of portland cement, which has a flexural modulus of 580 MPa. Sulfur is exceedingly resistant to degradation by even oxidizing acids such as sulfuric acid (H2SO4). For this reason, sulfur-treated concrete has proven a significant upgrade to OPC in industrial applications where exposure to low-pH environments is unavoidable (Weber, 1993; Weber and McBee, 2000). Several recent studies in this journal highlight the importance of this problem (Gay et al., 2016; Huber et al., 2016, 2017; Khan et al., 2019; Yuan et al., 2013). When a block of OPC is submerged in a 0.5 M aqueous solution of H2SO4, it rapidly deteriorates, losing its shape after just 30 min, rapidly shedding mass through reaction and dissolution of reaction products, and the block loses its mechanical integrity (Lauer et al., 2019). In sharp contrast, blocks of the sulfur ce­ ments prepared in this work retain 98–100% of their mass and hold their shape even after being submerged in 0.5 M H2SO4 for 30 min. After the 30-min acid exposure, the stress-strain analysis of sulfur cements blocks

Fig. 3. Thermal healing of scratches demonstrated by optical micrographs of sulfur cement samples before (left) and after (right) thermally annealing.

2.3. Sulfur cement formulations General Synthesis: Sulfur was heated at 180 � C until a viscous redorange liquid formed. The amounts of oleic acid and Portland cement or the Pozzolanic cement (25% Pozzolan plus 75% OPC product) ac­ cording to the mix specified below were added, and the mixture was heated at 180 � C for 24 h. Synthesis of PCOS: The general synthesis above was followed using 5.553 g of sulfur, 0.481 g of oleic acid and 0.139 g of OPC mixture. Synthesis of FAOS: The general synthesis above was followed using 5.566 g of sulfur, 0.477 g of oleic acid, and 0.141 g of FA mixture. 4

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was undertaken for comparison to the as-prepared materials. While many of the samples exhibited a weakened mechanical strength after acid treatment when compared to their untreated counterparts, two of the samples (GGBFSOS and MKOS) suffered no decrease in strength, likely a result of the relative resistance of these mineral products to acid on their own.

Gartner, E., 2004. Industrially interesting approaches to "low-CO2" cements. Cement Concr. Res. 34 (9), 1489–1498. Gay, H., Meynet, T., Colombani, J., 2016. Local study of the corrosion kinetics of hardened Portland cement under acid attack. Cement Concr. Res. 90, 36–42. Gillott, J.E., Jordaan, I.J., Loov, R.E., Shrive, N.G., Ward, M.A., 1978. Characteristics of some sulfur-bonded civil engineering materials. Adv. Chem. Ser. 165 (New Uses Sulfur-2), 98–112. Griebel, J.J., Nguyen, N.A., Namnabat, S., Anderson, L.E., Glass, R.S., Norwood, R.A., MacKay, M.E., Char, K., Pyun, J., 2015. Dynamic covalent polymers via inverse vulcanization of elemental sulfur for healable infrared optical materials. ACS Macro Lett. 4 (9), 862–866. Gwon, S., Shin, M., 2019. Rheological properties of modified sulfur polymer composites containing cement-fly ash blend at different temperatures. Construct. Build. Mater. 228, 116784. Gwon, S., Oh, S.-Y., Shin, M., 2018. Strength and microstructural characteristics of sulfur polymer composites containing binary cement and waste rubber. Construct. Build. Mater. 181, 276–286. Gwon, S., Ahn, E., Shin, M., 2019. Self-healing of modified sulfur composites with calcium sulfoaluminate cement and superabsorbent polymer. Compos. B Eng. 162, 469–483. Hasell, T., Smith Jessica, A., Green Sarah, J., Petcher, S., Parker Douglas, J., Zhang, B., Wu, X., Kelly Catherine, A., Baker, T., Jenkins Mike, J., Willcock, H., Worthington Max, J.H., Gibson Christopher, T., Campbell Jonathan, A., Lewis David, A., Chalker Justin, M., 2019. Crosslinker Co-polymerisation for Property Control in Inverse Vulcanisation, Chemistry. Weinheim an der Bergstrasse, Germany). Herrera, C., Ysinga Kristen, J., Jenkins Courtney, L., 2019. Polysulfides synthesized from renewable garlic components and repurposed sulfur form environmentally friendly adhesives. ACS Appl. Mater. Interfaces 11 (38), 35312–35318. 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3.3. Thermal healing In addition to their superior oxidizing acid resistance, sulfur cements can be thermally healable (Thiounn et al., 2018; Michal et al., 2013; Griebel et al., 2015; Amaral and Pasparakis, 2017; Arslan et al., 2017; Takahashi et al., 2017), providing a facile avenue for repairing scratch damage to their surfaces. A sample of each of the sulfur cements was thus subjected to surface damage that was imaged under a microscope. The surface was then annealed at surface temperature of about 130 � C (measured using an infrared thermometer) for 5 min using a simple hand-held heat gun. Photomicrographs recording this process are pro­ vided in Fig. 3. Most of these samples healed quite well under these conditions, although the PCOS and MKOS show clear signs of phase separation as manifest by the dark regions in Fig. 3 and the emergence of phase-separated sulfur in its yellow crystalline form in the image of post-annealed MKOS. 4. Conclusions A series of six sulfur cement pastes have been prepared by combining elemental sulfur, oleic acid and either OPC or a pozzolanic cement. Not only are these pastes prepared primarily from waste or sustainable materials, they also show significant improvements in acid resistance compare to traditional OPC mixtures. Blocks prepared from these pastes have several characteristics typical of commercial sulfur cements with additional desirable characteristics of exceedingly low water uptake, thermal healing, and retention of significantly more mechanical strength after exposure to strong oxidizing acid solutions than ordinary Portland cement. Given the high compressive strength and low flexural strength of the materials reported herein, the most likely applications would be in static placements such as underground culverts where their stability to low-pH sewer fluids would be an added benefit of the ma­ terials. Follow-up studies on the applicability of these pastes as com­ ponents of mortar and concrete products are ongoing. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements We thank the Animal Coproducts Research and Education Center and the National Science Foundation (CHE-1708844) for financial support. References Al-Ansary, M., Masad, E., Strickland, D., 2010. Sulphur sustainable applications: initial field monitoring and performance of shell thiopave trial road in Qatar. In: Advances in Gas Processing 2(Proceedings of the 2nd Annual Gas Processing Symposium, 2010), pp. 121–130. Amaral, A.J.R., Pasparakis, G., 2017. Stimuli responsive self-healing polymers: gels, elastomers and membranes. Polym. Chem. 8 (42), 6464–6484. Arslan, M., Kiskan, B., Yagci, Y., 2017. Recycling and self-healing of polybenzoxazines with dynamic sulfide linkages. Sci. Rep. 7 (1), 1–11. Dehestani, M., Teimortashlu, E., Molaei, M., Ghomian, M., Firoozi, S., Aghili, S., 2017. Experimental data on compressive strength and durability of sulfur concrete modified by styrene and bitumen. Data in brief 13, 137–144. Deme, I., 1978. Sulfur as an asphalt diluent and a mix filler. Adv. Chem. Ser. 165 (New Uses Sulfur-2), 172–189. Deme, I., 2005. Sulphur Pellet Comprising H2S-Suppressant for Asphalt Paving Mixture.

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