Novel Natural Sorbent for Oil Spill Cleanup - Industrial & Engineering

Jul 10, 2014 - A novel sorbent was developed using the aligning of raw unprocessed cotton fibers leading to low-density, hydrophobic, oleophilic, and ...
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Novel Natural Sorbent for Oil Spill Cleanup Vinitkumar Singh,† Sudheer Jinka,† Kater Hake,‡ Siva Parameswaran,§ Ronald J. Kendall,† and Seshadri Ramkumar*,† †

Nonwovens and Advanced Materials Laboratory and §Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409, United States ‡ Cotton Incorporated, Cary, North Carolina 27513, United States ABSTRACT: A novel sorbent was developed using the aligning of raw unprocessed cotton fibers leading to low-density, hydrophobic, oleophilic, and sustainable cotton batt. Cotton batting developed using immature cotton exhibited oil sorption capacity of 50.27 g/g, which is significantly higher than the oil sorption capacity of many commercial sorbents reported in the literature. Fundamental mechanisms such as adsorption, absorption, and capillary action govern the oil sorption phenomenon, which were verified using environmental scanning electron micrographs. In addition, optical microscopy was used to understand the difference in the longitudinal cross section of the mature (base range) and immature (low micronaire) cotton, which was determined quantitatively using Brunauer−Emmett−Teller surface area analysis. Effect of cotton characteristics such as fineness and maturity on the oil sorption capacity was also investigated. Nonwoven cotton batts consisting of immature and finer cotton fibers showed oil sorption capacity that was 7% higher than that of cotton batts developed using mature and coarser fibers.

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For practical applications, loose fibrous sorbents need to be compacted in the form of mats, booms, or pads17−19 and should be easily recoverable without leading to secondary contamination so that these sorbents do not disintegrate when applied to oil spill cleanup. Radetic et al.19 studied recycled wool fibers as well as its nonwoven form to compare the difference in oil sorption capacity. Needlepunching technology was used in this study to develop nonwoven pads. The authors reported that needlepunched recycled wool nonwoven webs were easy to use in a practical scenario, but a 100% decrease in the oil sorption capacity was observed with use of these nonwoven webs as compared to its loose fiber form. Similarly, Choi et al.17 investigated cotton nonwoven pads for cleaning up oil spills and studied the effect of needlepunching process parameters on oil sorption capacity of cotton nonwoven pads. Although nonwoven webs developed in this study were easy to handle, sorption capacity of these needdlepunch mats was significantly lower than that of its loose fiber form. Their analysis concluded that reduction in the capillary pore diameter is the leading factor in the decrease in oil sorption capacity of needlepunched nonwoven webs, as needlepunching makes the structure compact. In the needlepunching process, consolidated webs are formed wherein capillary movement is restricted between the pores formed among mechanically interlocked fiber assemblies. This observation was also substantiated by a mathematical relationship between interfiber capillary uptake and pore diameter of the nonwoven webs presented by Choi.18 As is evident from the aforementioned studies, these authors have attempted to develop sorbents that are practically useable; however, it was observed that sorption capacity of the mechanically bonded nonwoven composite decreased, resulting

INTRODUCTION Oil spill incidents have detrimental effects on our ecosystem from environmental and economic points of view.1−3 Although there have been many technological developments in processes to extract oil from nature,4,5 available cleanup technologies to combat any accidental or deliberate oil spill are decades old and incompetent.6,7 More importantly, these oil spill remediation techniques such as in situ burning, bioremediation, chemical dispersants, and synthetic sorbents are used extensively despite inadequate information on their environmental consequences.8 For example, most commonly used oil sorbent materials are made from polypropylene fibers,9,10 which are not biodegradable and hence may lead to secondary contamination.7 Among the aforementioned oil remediation techniques, many research and industrial case studies have emphasized sorbents as the most economic and sustainable solution for effective containment of oil spills.11 Recently, numerous research groups have attempted to investigate sustainable oil sorbents such as carbon nanotube sponges,12,13 nanocellulose aerogels,14 and thermodegradable polyolefin superabsorbent,7 to name a few. Although these materials show higher oil sorption capacity (g/g), because of high raw material cost and complex processes involved in developing these sorbents, using them in real-time scenarios is still an issue. Wahi et al.15 and Majed et al.16 have extensively reviewed the use of natural materials for oil spill cleanup. Particularly, Wahi et al. have reported that natural fibers such as cotton and kapok are the best materials for cleaning-up oil spills in oil−water systems based on their sorption performance and environmentally friendly characteristics. Overall, these authors in their elaborate reviews have concluded that natural fibers, because of their higher oil sorption capability, biodegradability, and recyclability, are the preeminent materials for developing environmentally sustainable sorbents for oil spill cleanup. It should be noted that most of the work cited in the aforementioned overview papers are for sorbents consisting of loose fibers, which presumably have limited their application. © 2014 American Chemical Society

Received: Revised: Accepted: Published: 11954

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Table 1. HVI Properties of Cottona sample

micronaireb

length (in.)

uniformity index (%)

strength (g/tex)

elongation (%)

cotton-1 cotton-2

3.16 (0.04) 4.36 (0.03)

1.13 (0.01) 1.07 (0.02)

80.82 (0.64) 80.77 (0.61)

28.03 (1.08) 29.12 (0.99)

7 (0.74) 4.8 (0.21)

a

Values within parentheses indicate the standard deviation. For the micronaire measurement, the following procedure was used: one repeat per sample and three samples per cotton type. For the length, uniformity, strength and elongation, the following procedure was used: two repeats per sample and three samples per cotton type. bMicronaire is related to the fineness and maturity of the cotton fiber.

Table 2. AFIS Properties of Cottona

in poor sorption capacity and commercial acceptability. In addition, these authors have also concluded that further studies focusing on understanding nonwoven material processing parameters are needed to develop practically useable and highly efficient oil sorbents. In this study, we report a novel oil sorbent which not only gives significantly higher oil sorption capacity along with environmental sustainability, but also is easy to use in practical settings. Nonwoven cotton batting for oil sorption was developed using minicard to obtain unique alignment of raw unprocessed cotton fibers, which heretofore has not been reported. Cotton batting developed in this work resembles a spongy low density membrane, wherein raw cotton fibers are loosely interlocked via fiber entanglement without disturbing the capillary network between the fibers. No bonding process was employed so that pore structure and capillary network are not affected. Environmental scanning electron microscopy (ESEM), optical microscopy, and Brunauer−Emmett−Teller (BET) surface area analyses were performed to understand the oil uptake mechanism, fiber morphology of different grades of cotton, and the effect of fiber specific surface area on oil sorption capability, respectively. In addition, the effect of cotton characteristics on oil sorption capacity was also studied.

sample

fineness (millitex)b

immature fiber content (%)c

maturity ratiod

cotton-1 cotton-2

149 (1.2) 162 (1.5)

9.93 (0.5) 7.27 (0.3)

0.79 (0.01) 0.85 (0.01)

a

Values within parentheses indicate the standard deviation. For the fineness, immature fiber content, and maturity ratio, the following testing procedure was used: one repeat per sample and three samples per cotton type. bFineness is related to the linear density of the fiber (measured in millitex); the smaller the millitex value, the finer the fiber. cImmature fiber content is relatedto the percentage of fibers with less than 0.25 circularity. dMaturity ratio defines the degree of cellulose deposition in the process of cell-wall development. Ideally, maturity ratio of one correlates to fully matured fiber.

Table 3. Carding Machine Details

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EXPERIMENTAL SECTION Cotton Samples. Two cottons having micronaire values 3.16 and 4.31 were obtained from Plains Cotton Cooperative Association, Lubbock, Texas. In this study, 3.16 micronaire and 4.31 micronaire correspond to discounted immature and mature varieties of cotton, respectively, and the terms cotton1 and cotton-2 are used to identify these two cotton fibers in the following sections. Characterization of Cotton Fibers. Cotton quality characterization using the standard and most commonly used cotton quality testing instruments such as the high volume instrument (HVI) and the advanced fiber information system (AFIS) was carried out at Texas Tech University’s Fiber and Biopolymer Research Institute. Fiber characteristics such as micronaire, fineness, and maturity obtained using HVI and AFIS are given in Tables 1 and 2. Fabrication of Cotton Batt. A carding process which individualizes fibers and aligns them in one direction20 was used to develop cotton batt as a low-density and lofty fibrous network of cotton fibers. Fibers were loosened by hand before carding. Carding of cotton fibers was done in the Platt’s minicard, wherein the fiber tufts were converted into batts of 10 in. width. Process parameters used to develop cotton batt are given in Table 3. In this experiment, the same quantity of cotton fibers were fed to the carding machine for both types of cotton during the batt formation as the amount of fibers fed to the carding machine determines the thickness and basis weight of the batt. Characterization of Cotton Batt. Basis weight and thickness of cotton batt were calculated using 4 × 4 in.2

particulars

size

speed (RPM)

number of flats machine width feed roller licker-in cylinder doffer doffer comb web collector drum

8 10 in. 2.3 in. 4 in. 10 in. 6 in. − 10

stationary − 0.3 859 369 9.5 1264 7

swatches cut carefully using a similar size of plastic stencil. Thickness was measured using ASTM Standard D 5729-9721 method under a constant load of 2 kilopascals (kPa). Bulk density of cotton batt was calculated using weight and volume of the batt. Basis weight, thickness, and bulk density values are given in Table 4. In addition, surface and structural morphology Table 4. Physical Characteristics of Cotton Batta sample

gsm (g m−2)

thickness (mm)

bulk density (g cm−3)

cotton-1 cotton-2

337.48 (20.07) 328.16 (12.05)

4.04 (0.46) 4.13 (0.26)

0.085 (0.005) 0.078 (0.004)

a

Values within parentheses indicate the standard deviation. For basis weight (gsm) measured in grams per square meter and bulk density measured in grams per cubic centimeter, the following procedure was followed: one repeat per sample and five samples per cotton type. For thickness of the batt, the following procedure was followed: two repeats per sample and five samples per cotton type.

of cotton fibers were studied using a Hitachi S-4800 field emission environmental scanning electron microscope and an optical microscope Olympus BX50, respectively. Detailed procedures of ESEM and BET analyses techniques used in this study have been described in our previous work.8 Sorption Testing Method. Oil sorption and retention capacity of the cotton batt using regular motor oil was determined using ASTM Standard F 726-06 test procedure previously described.8,22 The schematic of the experimental 11955

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Figure 1. ASTM Standard F 726-06 test method for oil sorption study. (A) Top view of cotton batt. (B) Side view of cotton batt. (C) Lofty structure of the cotton batt. (D) Experimental setup for dynamic oil sorption study. (E) Oil bath and sample cell assembly. (F) Oil-soaked cotton sample after soaking for 15 min. (G) Oil-draining setup. (H) Oil-soaked cotton after draining for 30 min.

Figure 2. Dynamic oil retention capacity (g/g) for cotton-1 and cotton-2 in the batt form versus time.

setup is shown in Figure 1A−H. Then, to further evaluate the practical performance of the sorbent, additional tests such as sorbent water uptake capacity, long-term oil sorption capacity,

and dynamic degradation analysis of the cotton batts were performed by following ASTM Standard F 726-12.23 The characteristics of regular motor oil at 22 ± 1 °C were as 11956

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Figure 3. Average oil sorption capacity (g/g) for cotton-1 and cotton-2 in the batt form was found to be 50.27 and 47.01, respectively. Statistical analysis was performed using two-sample t-test. Statistical significance in oil sorption was observed between low-micronaire cotton (cotton-1, micronaire 3.1) and regular cotton (cotton-2, micronaire 4.3). Cross bars represent standard error of means, n = 30; the region denoted by an asterisk (*) represents P < 0.05.).

follows: density, 0.866 g cm−3; dynamic viscosity, 0.12 Pa s; and surface tension, 30.89 mN m−1. A Kruss K-100 SF tensiometer was used to determine surface tension and density, and a Brookfield LV, DV++, Pro viscometer was employed to calculate the dynamic viscosity of the oil. Wax Extraction Analysis. Wax content of raw unprocessed cotton was calculated using a slightly modified method based on the AATCC Test Method 97-2009.24 Approximately 3 g of the sample was taken and dried to a constant weight, and an accelerated solvent extractor (Dionex ASE 100) was used with hexane as a primary solvent to extract waxes from cotton. The amount of waxes in cotton was determined gravimetrically using eq 1. ⎡ A − B⎤ E=⎢ 100 ⎣ A ⎥⎦

reported heretofore. The main focus of our work was to develop a novel sorbent using unprocessed raw cotton with high oil sorption capacity, which can be used in real-life oil spill scenarios. Important characteristics for developing an efficient oil sorbent using cotton are (1) type of cotton used, (2) fiber size, (3) specific surface area, (4) bulk density, (5) pore volume, (6) fiber lumen, (7) chemical composition such as wax content, and (8) hydrophobic and oleophilic properties.11,25 Our research primarily focuses on using environmentally sustainable materials such as raw unprocessed cotton for oil spill cleanup. Additionally, we focused on reducing the bulk density of the fibrous assembly of cotton fibers using the carding process. A lofty fibrous network of cotton fibers was obtained (Figure 1C), which not only exhibited higher oil sorption capacity but also was easy to handle. The dynamic oil retention and maximum oil sorption capacities of low-grade discounted cotton with low micronaire (cotton-1) and base range (cotton-2) cotton batts tested using regular motor oil are shown in Figures 2 and 3, respectively. As is evident from Figure 2, for the first 5 min of the draining cycle, a drastic decrease in the oil retention capacity was observed because of the removal of excessive oil that was adhered superficially to the surface of the sorbent.8 In other words, oil that was not adsorbed or absorbed within the cotton batt was released from the sorbent because of reduced capillary retention pressure developed between the fibrous assembly8,22 owing to excessive oil present within the lumen of the fiber as well as interfiber capillary network.17,18,22,28 Finally, after 30 min of drain time, sorbent−oil equilibrium was observed (Figure 2) and oil sorption capacity was calculated. It was determined that cotton1 showed oil sorption capacity higher than that of cotton-2. For cotton-1 (3.16 micronaire), 1 g absorbed 50.27 g of oil; for cotton-2 (4.31 micronaire), 47.01 g of oil sorption capacity was. The difference in the average oil sorption capacity observed

(1)

where E is percent waxes extracted, A the mass of the specimen before the extraction (g), and B the mass of the specimen after the extraction (g).

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RESULTS AND DISCUSSION Numerous researchers have studied a wide range of materials for oil spill cleanup.4−11 Recently, Hubbe et al., in their elaborative review on cellulosic materials for oil spill cleanup, concluded that the most important criteria to evaluate the sorbent performance is its per unit oil sorption capacity (g/g)11 and oil retention capacity. In addition, properties that govern the oil sorption capacity of the sorbent are mainly viscosity and surface tension of the oil in conjunction with geometry and pore structure of the sorbent.25 Although there have been many reports in the literature showcasing the effect of oil viscosity and/or surface tension on the sorption capacity of the sorbent,26,27 limited studies investigating the effect of sorbent structure, particularly of unprocessed raw cotton, have been 11957

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Figure 4. Relation between oil sorption capacity of raw cotton batt and its fiber characteristics such as fineness, immature fiber content, and maturity ratio. Cotton batt consisting of finer (smaller fineness value) and immature fibers (cotton-1) has an oil sorption capacity higher than that of cotton batt made of coarser and mature fibers (cotton-2). Cross bars represent standard error of means, n = 30.

Figure 5. ASTM Standard F 726-12 dynamic degradation test: Average water pick-up (g/g) for cotton-1 and cotton-2 in the batt form was found to be of 5.4 and 7.1, respectively. Statistical analysis was performed using two-sample t-test. Statistical significance in water pick-up was observed between low-micronaire cotton (cotton-1, micronaire 3.1) and regular cotton (cotton-2, micronaire 4.3). (Cross bars represent standard error of means, n = 3; the region denoted by an asterisk (*) represents P < 0.05, and the region marked as “n.s.” denotes data that are not significant.).

earlier work and focuses on practically applicable aligned batt structure. In addition, water uptake and maximum oil sorption capacity are important parameters for evaluating effectiveness of the sorbent for it to be used in real-time oil spill cleanup scenarios. Therefore, static and dynamic water uptake tests for cotton sorbent were performed, and it was observed that in the

among these two cotton batts (cotton-1 and cotton-2) was statistically significant as explained in Figure 4. Micronaire is a characteristic that collectively quantifies the fiber linear density and maturity of cotton fiber.29 In our previous report,8 we studied extensively the influence of micronaire on oil sorption by unprocessed raw loose cotton, and an inverse nonlinear relationship was observed. The present study differs from our 11958

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Figure 6. ASTM Standard F 726-12 oil sorption-long test: Average oil sorption capacity (g/g) for cotton-1 and cotton-2 in the batt form was found to be 52.5 and 45.8, respectively. Statistical analysis was performed using two-sample t-test. Statistical significance in oil sorption was observed between low-micronaire cotton (cotton-1, micronaire 3.1) and regular cotton (cotton-2, micronaire 4.3). Cross bars represent standard error of means, n = 3; the region denoted by an asterisk (*) represents P < 0.05.).

an environmentally sustainable oil sorbent with high sorption capacity. The fact that sorption capacity is a function of sorbent density has been validated by several researchers.11,25 However, bulky fibrous substrates developed using fibers such as milkweed, polypropylene, hemp, and carbon have been studied. Very limited work has been reported using raw cotton; in particular, research using raw unprocessed cotton in the batt form has not been reported heretofore. In this work, significantly high oil sorption capacity exhibited by raw unprocessed cotton batts could be attributed to low bulk density of the batt via unique arrangement of cotton fibers that creates air pockets between fibrous networks, which act as an oil reservoir. Also, oil is absorbed inside the cotton fiber into its lumen, which is the hollow tubular portion in a cotton fiber. As is evident from the ESEM micrograph (Figure 7), oil uptake between the fibrous network via capillary uptake and within the fiber via adsorption and absorption are dominant mechanisms causing high oil uptake and retention.8,27,30 As briefly described in the Introduction, Choi et al.17 have reported oil sorption capacity of needlepunched nonwoven matts produced using raw cotton. We differ from the aforementioned work based on the process used to develop raw cotton sorbents. In our work, a carding process was used to obtain aligned cotton fiber batts with low density and hydrophobic characteristics. More importantly, we found a significant increase in oil sorption capacity while using cotton batts as compared to the decrease in oil sorption capacity reported by Choi18 and Gupta et al.,31 wherein a needlepunching process was used to develop bulky sorbents. The needlepunching process used by Choi et al. and Gupta et al. makes cotton fibers compact, thereby reducing the

dynamic water system, the water uptake capacity for cotton-1 and cotton-2 were 5.4 g/g and 7.1 g/g, respectively. Although raw cotton fibers, because of the presence of waxes, are hydrophobic in nature,8,17−19 the dynamic water uptake capacity evidenced for these cotton batts could be attributed to the physical trapping of water molecules within the interfiber pores. In the static system, wherein stagnant water could not penetrate within the bulk structure of the sorbent, very minimal (less than 0.5 g/g) water uptake capacities were determined for cotton-1 and cotton-2, as shown in Figure 5. More importantly, in both dynamic and static systems, these batts passed the dynamic degradation test (water uptake test), as sorbents were afloat for more than 24 h, according to ASTM Standard F 72612. In the oil−water system, there was no visible oil sheen on the surface of the water as the entire oil slick was completely absorbed by the cotton sorbent. Furthermore, to evaluate the ideal maximum oil sorption capacity of these batts, a long-term oil sorption test was performed.23 In this test, cotton batts were free-floated in the oil bath for 24 h for complete saturation, and it was determined that immature cotton bats (cotton-1) showed ideal maximum oil sorption capacity 14% higher than that of mature cotton batts (cotton-2). As is evident from Figures 3, 4, and 6, low-micronaire cotton shows higher oil sorption compared to higher-micronaire cotton. More detailed discussion on the difference in oil sorption capacity will follow later in the discussion. Moreover, it is worth noting that unprocessed raw cotton in the batt form shows oil sorption capacity (50.27 g/g) significantly higher than that of various forms of cotton sorbents used by other researchers for oil spill cleanup.11,15,16 Therefore, we believe using unprocessed raw cotton in the batt form would be a viable option for developing 11959

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Figure 7. (a) ESEM micrograph of sorption of regular motor oil by raw cotton batt showing complex mechanisms such as absorption and oil uptake via interfiber capillary action. (b) Oil sorption within the fiber causing swelling of cotton fiber is shown in the ESEM.

Figure 8. Light micrograph of a longitudinal sectional of raw cotton fiber. (a) In cotton-1, because of immaturity, there is less cellulose deposition, causing collapsed structure leading to finer fibers. (b) In cotton-2, being mature cotton, thick cellulose deposition forming an intact secondary wall is evident.

void space available in the sorbent, which leads to decrease in oil sorption capacity. Cotton Fiber Characteristics and Oil Sorption. In this study, immature discounted cotton showed oil sorption capacity higher than that of mature cotton, as shown in Figures 3, 4, and 6. Higher oil sorption capacity was observed for raw unprocessed cotton fiber batts compared to sorption capacity for cotton sorbents reported in the literature,15−18 and there was at least a 7% difference in the sorption capacity of immature and mature cotton batts. In addition, we have endeavored to investigate if the difference in the oil sorption capacity observed in these cotton batts was due to the batt structure or the batt composition. The study also investigated the effect of cotton fiber characteristics on the oil sorption capacity of cotton batts. Furthermore, to eliminate the effect of batt structure on oil sorption capacity, the process used for developing cotton batts from cotton-1 and cotton-2 was maintained identical; hence, no visual difference in the bulk structure of batt of the two cottons was observed. Moreover, quantitatively, bulk density for cotton-1 and cotton-2 were 0.085 and 0.078 g cm−3, respectively, and statistically no significant difference was observed (*p < 0.01). Therefore, it could be safely assumed that the batt structure played a significant role in increasing the oil sorption capacity of cotton batts; however, it was not the sole contributing factor for the statistical difference observed in the average oil sorption capacity of the two cottons in the batt form. Thus, the difference in sorption capacity of immature and mature cotton batts may be related to the differences in their fiber characteristics, such as fineness, immature fiber content, maturity ratio, and micronaire index. It is of interest to note that cotton 1 was finer with high immature fiber content and lower maturity ratio compared to cotton-2. This difference may be attributed to the fact that the immature cotton, because of less cellulose deposition, has a collapsed structure with larger lumen, whereas in mature cotton, there is thick cellulose deposition leading to coarse fibers with smaller or no lumen,32 as evident in the light micrograph shown in Figure 8. Because of the collapsed structure and higher fineness, the available surface area for cotton-1 (BET surface area, 0.661 m2 g−1) in the micronaire measuring cell was higher than that of cotton-2 (BET surface area, 0.462 m2 g−1). Therefore, cotton-1 showed a micronaire value smaller than that of cotton-2. Furthermore, previous researchers have proven that immature cotton has a wax content higher than that of mature cotton.33,34 In this study, percentage wax content values for cotton-1 and cotton-2,

determined according to AATCC 97-2009, were 0.633 and 0.252, respectively. Cotton-2, being mature, showed 60% less wax than immature cotton fibers (cotton-1), and this difference observed in the percentage wax content values were statistically significant (p < 0.05). Thus, presence of wax on the surface of cotton fiber aids the oleophilic nature of the fiber, leading to higher intermolecular interaction of C−H bonds between surface waxes and absorbed oil.30,35−37 The presence of higher wax and enhanced fineness in low micronaire cotton leads to increased oil sorption compared to base and high micronaire cotton. These observations corroborate well with our earlier work reported on crude oil sorption by raw cotton fibers, wherein higher oil sorption capacity for immature cotton was found.8

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CONCLUSIONS In summary, environmentally friendly, low-density, hydrophobic cotton batts have been developed using the fiberaligning carding process without the use of any synthetic or natural binders. Cotton batts obtained using low-grade and regular-grade cottons were examined as potential oil sorbents. Low-grade cotton batt showed oil sorption capacity 7% higher than regular-grade cotton. ESEM analysis performed on oilsoaked cotton confirmed the occurrence of sorption mechanisms such as absorption and capillary action for absorption and retention of oil in the cotton fiber assembly. Light micrographic images showed the presence of a collapsed structure in low-grade cotton, resulting in lower micronaire and increased fineness, exhibiting oil sorption capacity higher than that of regular-grade cotton. Overall, the significantly higher oil sorption capacity (50.27 g/g) observed for low micronaire cotton batt clearly demonstrates the potential for these batts to be used as an environmentally sustainable material for oil spill cleanup. The structure of the cotton assembly, in this case the batt form, and the characteristics of raw cotton influence the overall oil sorption capacity.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: 806 742 4567. E-mail: [email protected]. Author Contributions

All the authors contributed to the work. V.S. and S.R. designed and executed the study.All the authors approve the manuscript. Notes

The authors declare no competing financial interest. 11960

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(19) Radetic, M. M.; Jocic, D. M.; Jovancic, P. M.; Petrovic, Z. L.; Thomas, H. F. Recycled wool-based nonwoven material as an oil sorbent. Environ. Sci. Technol. 2003, 37, 1008. (20) Lawrence, C. A. The opening, blending, cleaning, and carding of cotton. In Cotton: Science and Technology; Gordon, S., Hsieh, Y.-L., Eds.; Woodhead: Cambridge, U.K., 2007; pp 217. (21) American Society for Testing and Materials (ASTM). ASTM Standard D 5729-97(2004): Standard Test Method for Thickness of Nonwoven Fabrics. In 2004 Annual Book of ASTM Standards; American Society for Testing and Materials (ASTM): West Conshohocken, PA, 2004. (22) Cojocaru, C.; Macoveanu, M.; Cretescu, I. Peat-based sorbents for the removal of oil spills from water surface: Application of artificial neural network modeling. Colloids Surf., A 2011, 384, 675. (23) American Society for Testing and Materials (ASTM). ASTM Standard F 726-12: Standard Test Method for Sorbent Performance of Adsorbents. In 2012 Annual Book of ASTM Standards; American Society for Testing and Materials (ASTM): West Conshohocken, PA, 2012. (24) American Association of Textile Chemists and Colorists (AATCC). AATCC Standard: Wax Extraction−AATCC TM 972009. In Technical Manual of the American Association of Textile Chemists and Colorists, Vol. 87, NC, 2012. (25) Browers, S. Understanding sorbents for cleaning up spills. Plant Eng. 1982, 3, 219. (26) Zhu, H.; Qiu, S.; Jiang, W.; Wu, D.; Zhang, C. Evaluation of electrospun polyvinyl chloride/polystyrene fibers as sorbent materials for oil spill cleanup. Environ. Sci. Technol. 2011, 45, 4527. (27) Choi, H. M.; Moreau, J. P. Oil sorption behavior of various sorbents studied by sorption capacity measurement and environmental scanning electron-microscopy. Microsc. Res. Tech. 1993, 25, 447. (28) Lim, T.-T.; Huang, X. Evaluation of kapok (Ceiba pentandra (L.) Gaertn.) as a natural hollow hydrophobic−oleophilic fibrous sorbent for oil spill cleanup. Chemosphere 2007, 66, 955. (29) Montalvo, J. G., Jr. Relationships between micronaire, fineness and maturity. Part I. Fundamentals. J. Cotton Sci. 2005, 9, 81. (30) Carmody, O.; Frost, R.; Xi, Y.; Kokot, S. Surface characterisation of selected sorbent materials for common hydrocarbon fuels. Surf. Sci. 2007, 601, 2066. (31) Gupta, B.; Hong, C. Absorbent characteristics of nonwovens containing cellulosic fibers. Int. Nonwovens J. 1995, 7, 34. (32) Long, R. L.; Bange, M. P.; Gordon, S. G.; Constable, G. A. Measuring the Maturity of Developing Cotton Fibers using an Automated Polarized Light Microscopy Technique. Text. Res. J. 2010, 80, 463. (33) Cui, X. L.; Price, J. B.; Calamari, T. A.; Hemstreet, J. M.; Meredith, W. Cotton wax and its relationship with fiber and yarn properties - Part I: Wax content and fiber properties. Text. Res. J. 2002, 72, 399. (34) Gamble, G. R. Variation in surface chemical constituents of cotton (Gossypium hirsutum) fiber as a function of maturity. J. Agric. Food Chem. 2003, 51, 7995. (35) Choi, H. M.; Cloud, R. M. Natural Sorbents in Oil-spill Cleanup. Environ. Sci. Technol. 1992, 26, 772. (36) Deschamps, G.; Caruel, H.; Borredon, M. E.; Bonnin, C.; Vignoles, C. Oil removal from water by selective sorption on hydrophobic cotton fibers. 1. Study of sorption properties and comparison with other cotton fiber-based sorbents. Environ. Sci. Technol. 2003, 37, 1013. (37) Singh, V.; Ramkumar, S. Comments on Hollow Carbon Fibers Derived from Natural Cotton as Effective Sorbents for Oil Spill Cleanup. Ind. Eng. Chem. Res. 2014, 53, 3412.

ACKNOWLEDGMENTS The work was supported by the Texas State Support Program of Cotton Incorporated (Grants TX08-307 and TX 12-119) and The CH Foundation, Lubbock, TX. We acknowledge Plains Cotton Growers, Inc., TX for supporting the research, Dr. Eric Hequet, Texas Tech University for helping with fiber evaluation, and Mr. Riaz Ahmad, Quantachrome Instruments, for the BET testing. The authors also acknowledge Dr. Todd Anderson, Texas Tech University, for allowing the usage of the wax extraction instrument.

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REFERENCES

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dx.doi.org/10.1021/ie5019436 | Ind. Eng. Chem. Res. 2014, 53, 11954−11961