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Abstract

In this study, an attempt was made to enhance the oil sorption capacity of nettle fibers by grafting of butyl acrylate. Box–Behnken experimental design was used to study the effect of parameters such as reaction time, reaction temperature and monomer concentration-to-fiber ratio on graft add-on (%) and oil sorption capacity. At 4-h reaction time, 70℃ temperature and 2% monomer concentration-to-fiber ratio, highest graft add-on (%) and oil sorption were attained. Maximum oil sorption capacity of grafted nettle was 36.60 g/g and 25.56 g/g against crude oil and vegetable oil, respectively. Grafted nettle fibers were also subjected to characterization by Fourier-transform infrared spectroscopy, scanning electron microscopy and contact angle tests. Reusability test results showed that grafted nettle exhibited better oil sorption capacity than unmodified nettle even after seven sorption–desorption cycles. It is also observed that the oil sorption capacity of grafted nettle was higher than that of commercial polypropylene material. Based on these results, it is concluded that functionalized nettle prepared by grafting technique can be a potential material for oil spill treatment.

Keywords

Industrial textiles coated fabrics fibrous materials chemical modification chemistry sorption

Introduction

One of the naturally available substances is oil. It has been a component of the natural surroundings for million years. Once oil is spilled on sea, it extends for kilometers around and causes major environmental harms. So, it is necessary to clean the oil spill immediately. Oil spill cleanup products normally used to remove the oil from water include dispersants, skimmers, gelling agents and sorbents. Among different products, sorbent materials are generally considered as the most efficient for cleanup of spilled oil due to its uniqueness [1].

Sorbents may be classified into three different materials such as synthetic organic polymers, inorganic mineral materials and organic natural materials. Polypropylene, polyacrylate and polyethylene are popular synthetic organic sorbent materials used for oil spill removal. Examples of inorganic mineral materials include graphite, silica, fly ash organic clay, zeolites, vermiculite and perlite. Organic natural sorbents include different fibrous materials such as cotton, kapok, milkweed, cattail, jute, coir, cotton, kapok, banana, nettle, luffa, etc. [2]. Sorbents prepared from fibrous webs contain small pores to assist the passage of liquids into the sorbent materials and hold the liquids subsequent to sorption [3].

The ideal oil sorbents are likely to possess the features such as (i) high sorption capacity, (ii) hydrophobicity, (iii) high sorption rate, (iv) high retention capacity, (v) mechanical properties, (vi) reusability and (vii) sustainability and biodegradability. However, it is still a challenge to get ideal oil sorbents that could meet all the above criteria [4].

Nettle is a cellulosic plant fiber that exists in tropical wasteland areas around the globe. It grows on rich soils and up to 1.20 m high [5]. Several researchers studied the characteristic features of nettle fibers for textile and technical textile product development. One-hundred percent of natural sustainable fabrics for apparel applications were developed from nettle, nettle–cotton, nettle–ramie, nettle–wool and nettle–flax combinations. Summer apparels and winter apparels with closed and open weave structures were also developed by some researchers [6]. Nettle fibers were also used to develop fashionable and luxurious products, namely wall hangings, hand bags, door chain, flower vase, decorative items for rooms, etc. There is enormous potential to develop different technical textile products using nettle fibers [7 –9].

In recent years, considering the advantages of natural fibers, including low cost, biodegradability and reusability, the fibers such as kapok [4,10], cattail [11], cotton [12], banana [13], nettle [7 –9], milk weed [14], jute [15], coir [16], poplar seed fiber [17], chitosan [18] and other various vegetable fibers have been investigated for the oil spill cleanup applications. It was also recommended that natural fibers of low cellulosic content cannot be simply degraded by cellulose degrading microbes [4]. Even though natural fibrous sorbents are cost-effective than most synthetic sorbents, one of the main drawbacks associated with these materials is their low oil sorption capacity. Several approaches such as acetylation [19], grafting with oleic acid [20], thermal carbonization [21], coating with poly-n-butylmethacrylate (PBMA)/SiO₂ [22], thermal bonding [23] and polymerization [24] are normally employed to improve the oil sorption capacity of natural fibers. Amongst the abovementioned methods, polymerization is a simple and effective method to graft monomers onto fiber surface [24]. This method has been used by researchers for different materials such as polypropylene [24], banana [13] and coir [16]. Previous studies showed that the maximum oil sorption capacity of grafted coir is only 13.45 g/g [16] and grafted banana is only 14.45 g/g [13].

It is also noted that no extensive work has been carried out with respect to the grafting of nettle fiber and its influence on graft add-on (%) and oil sorption behavior. In this study, nettle fibers are grafted with butyl acrylate monomer and Box–Behnken experimental design has been used to study the effect of various preparation parameters such as time, temperature and monomer concentration (%) on graft add-on (%) and oil sorption. The aim of this study was to enhance the oil sorption capacity of nettle fiber through the surface grafting and evaluate the effects of preparation variables on the oil sorption and characterization.

Materials and methods

The Himalayan nettle (Girardinia diversifolia) filament was used for the study. The nettle fibers were cleaned manually and subsequently washed with distilled water to remove mud, dirt and other water-soluble impurities. These fibers were dried in hot air oven at 60℃ for 24 h. The characteristic of nettle fibers used in this study is shown in Table 1. Butyl acrylate monomer, potassium persulfate and N,N-methylene-bis-acrylamide chemicals were supplied by Precision Scientific Company, Tamil Nadu, India. Crude oil and vegetable oil were purchased from local market. The strength and elongation of the fibers were measured in accordance with ASTM D3822-07 standard by using Instron tensile tester. Nettle fiber density was measured in accordance with ASTM D 1505-03 standard by density-gradient technique. Fiber fineness was measured in accordance with ASTM D1577-07 standard. The surface tension and density of the liquids were measured using DCAT Tensiometer. The viscosity of the oil was measured using Brookfield viscometer. The properties of crude oil and vegetable oil used in this study are given in Table 2.

Table 1.

Characteristics of nettle fiber.

Parameter	Nettle
Fiber length (mm)	60
Fiber fineness (denier)	3.75
Single fiber strength (cN/tex)	60.18
Fiber density (g/cc)	1.21
Elongation (%)	1.52

Table 2.

Properties of oils.

Type of oil	Density (g/cm³)	Viscosity (cP)	Surface tension (cN.cm⁻¹)
Crude oil	0.92	340.5	3.1 × 10⁻²
Vegetable oil	0.82	210.4	2.5 × 10⁻²

Graft copolymerization of butyl acrylate on to nettle fiber

As reported earlier, the grafting reaction was performed in a three-neck round bottom flask [16].

In order to control the reaction temperature, the flask was positioned in a thermo stated heating mantle. The required weight of nettle fibers and butyl acrylate monomer was placed in the flask and agitated for 10 min. Subsequently, cross-linking agent N,N-methylene-bis-acrylamide and initiator potassium persulfate were added to the flask. The reaction was performed under nitrogen atmosphere and the mixture was agitated continuously as per the experiment conditions. Homopolymer generated through the graft-copolymerization reaction was separated out from the grafted copolymer by stirring for 12 h in ethyl alcohol for entire elimination of homopolymer [16]. The nettle fiber samples were dried in oven at 50℃ and weighed.

Graft add-on (%) is calculated as follows

Graftadd-on (%) = [(W_{2} - W_{1}) / W_{1}] \times 100

(1)

where W₁ and W₂ are the weight of raw and grafted nettle fibers, respectively.

Measurement of oil sorption capacity

Measurement of oil sorption capacity of raw and grafted nettle fibers was carried out in a batch system as per the existing literature. One gram of nettle fiber was immersed into crude oil and vegetable oil for 15 min and then wet samples were taken out and hung in free air for 1 min to drip out the surplus oil absorbed by the samples. Subsequently, the weight (W_w) of wet nettle samples was measured [7]. The oil sorption capacity was calculated using the relationship given below

Oilsorptioncapacity (g / g) = [W_{w} - W_{d} / W_{d}]

(2)

where W_w and W_d are the weight of wet nettle samples and dry nettle samples, respectively.

Experimental design

To study the individual and interactive effects of time, temperature and monomer on graft add-on (%) on crude oil sorption and vegetable oil sorption, samples were produced according to Box and Behnken factorial design for three variables. Based on the preliminary works carried out, it was decided to choose the values of independent variables, namely time, temperature and monomer-to-fiber ratio as shown in Table 3.

Table 3.

Particulars of process parameters.

S. No.	Parameters	Units	(−1)	(0)	(1)
1	Time	h	2	3	4
2	Temperature	℃	60	70	80
3	Monomer-to-fiber ratio	ratio	1:1	1.5:1	2:1

Reusability test

As per the method described earlier, reusability of the nettle fibers was carried out [25]. Initially, the oil sorption capacities of nettle fibers were measured and then samples were squeezed between two rollers at a pressure of 10 kgf/cm and loss in weight of the sample was measured. The squeezed fibers were again dipped in the oil for 15 min and oil sorption capacity was measured [25]. The efficiency of nettle fiber reusability was determined by oil sorption capacity of fibers after repeated sorption and desorption cycles.

Fourier-transform infrared spectroscopy

The infrared (IR) spectra of unmodified and grafted nettle fiber samples were recorded using Fourier-transform infrared spectroscopy (FTIR) spectrophotometer (Shimadzu 8400s, Japan) using Attenuated Total Reflection (ATR) sampling technique by recording 45 scans in % T mode in the range of 4000–600 cm⁻¹.

Scanning electron microscopy

Analysis of the morphology of untreated and modified sample was carried out using field emission scanning electron microscope (SWIZZ, Turkey), from PSGTECHS COE INDUTECH, Coimbatore. The nettle fibers were sputter coated with gold layers and figures were recorded using scanning electron microscopy (SEM).

Results and discussion

Table 4 shows the experimental runs of Box–Behnken design on graft add-on (%) and oil sorption of grafted nettle fiber. The surface response curves (Figure 1) were drawn to understand the individual and interaction effect of reaction time, temperature and monomer-to-fiber ratio on graft add-on (%) and oil sorption of nettle fiber using standard statistical software.

Figure 1.

(a) Effect of time and temperature on graft add-on (%) on monomer-to-fiber ratio 1:1. (b) Effect of time and temperature on graft add-on (%) on monomer-to-fiber ratio 1.5:1. (c) Effect of time and temperature on graft add-on (%) on monomer-to-fiber ratio 2:1.

Table 4.

Experimental runs of Box–Behnken design on graft add-on (%) and oil sorption of grafted nettle fiber.

S. No.	Time (h) (A)	Temp. (℃) (B)	Monomer concentration- to-fiber ratio (C)	Graft add-on (%)	Crude oil sorption (g/g)	Vegetable oil sorption (g/g)
1	2	60	1.5	10.13	22.12 ± 0.70	15.09 ± 0.30
2	2	80	1.5	11.21	24.98 ± 0.75	16.33 ± 0.28
3	4	60	1.5	11.36	25.14 ± 0.64	16.67 ± 0.33
4	4	80	1.5	13.85	34.90 ± 1.38	23.59 ± 0.42
5	2	70	1	10.74	22.56 ± 0.56	15.55 ± 0.55
6	2	70	2	12.85	32.75 ± 1.18	21.29 ± 0.55
7	4	70	1	12.37	25.26 ± 0.65	18.98 ± 0.61
8	4	70	2	14.01	36.60 ± 0.72	25.56 ± 0.68
9	3	60	1	10.49	26.00 ± 0.65	18.64 ± 0.70
10	3	60	2	11.78	26.16 ± 0.68	19.29 ± 0.78
11	3	80	1	12.34	27.75 ± 0.68	19.43 ± 0.72
12	3	80	2	13.65	34.48 ± 0.76	23.13 ± 0.28
13	3	70	1.5	12.27	29.75 ± 0.94	20.75 ± 0.66
14	3	70	1.5	12.21	29.65 ± 0.85	20.15 ± 0.82
15	3	70	1.5	12.29	29.86 ± 0.90	20.85 ± 0.66

Effect of preparation parameters on graft add-on (%)

The effects of reaction time and temperature on graft add-on at different monomer concentration-to-fiber ratio 1:1, 1.5:1 and 2:1 are shown in Figure 1(a) to (c), respectively. It is observed from Figure 1(a) that the graft add-on increases with increase in reaction time and temperature. At monomer concentration-to-fiber ratio 1:1, with the increase in reaction time from 2 h to 4 h, the graft add-on increases from 10.74% to 12.37%, respectively. The positive dependence of grafting on time may be attributed to the increase in the number of grafting sites, owing to the higher amount of initiator involving in the arrangement of reactive sites on the backbone of cellulose structure [13]. The rate of reaction also depends on the accessibility of the cellulose which takes part in the reaction. Therefore, on grafting, the modified nettle is expected to provide high graft add-on (%). Our results are in line with the findings of Teli and Valia [13]; they performed grafting of banana fibers for oil spill cleanup applications. Similar trend is observed at monomer concentration-to-fiber ratio 1.5:1 (Figure 1(b)) and 2:1 (Figure 1(c)).

It is also observed from Figure 1(a) that, at 1:1 level of monomer concentration-to-fiber ratio, with the increase in reaction temperature from 60℃ to 80℃, the graft add-on (%) increases from 10.49% to 12.34%, respectively. The increase in graft add-on with temperature is mainly due to the higher rate of initiator dissociation, in addition to the higher diffusion and mobility of the monomer from aqueous bulk phase to cellulosic fiber phase [16]. Our results are correlated with previous published data [13,16]. Similar trend is also observed at 1.5:1 (Figure 1(b)) and 2:1 (Figure 1(c)) ratio levels of monomer-to-fiber ratio.

The effect of monomer concentration and reaction temperature on graft add-on at reaction times 2, 3 and 4 h was also studied. It is observed that the graft add-on (%) increases with increase in monomer concentration and reaction temperature. At 2-h reaction time, with the increase in monomer concentration-to-fiber ratio from 1:1 to 2:1, the graft add-on increases from 10.13% to 12.85%, respectively. The reason for increase in graft add-on may be attributed to the higher availability of the monomer with respect to fixed quantity of fiber in the reaction bath for grafting [13]. Similar findings are observed at 3-h reaction time and 4-h reaction time. Further, it is noted that with the increase in reaction temperature from 60℃ to 80℃, the graft add-on (%) increases. The reason for the same has been explained earlier.

The effect of reaction time and monomer concentration on graft add-on (%) at reaction temperatures 60, 70 and 80℃ is also studied. It is observed that the graft add-on increases with increase in reaction time and monomer concentration at all levels of reaction time and monomer concentration. The reason for the same has been explained in the earlier section.

Characterization

FTIR spectra

The FTIR spectrum of unmodified and grafted nettle is presented in Figure 2. FTIR spectra grafted nettle fibers show a peak at 1735 cm⁻¹; this can be attributed to the presence of carbonyl group (C=O) or ester groups, whereas the peak at 1162 cm⁻¹ can be due to the saturated esters, which were absent in raw fibers, confirming the grafting of butyl acrylate onto the nettle fibers through covalent bonds [26]. These findings clearly indicate that the nettle fiber undergoes modification by means of grafted reaction. The esterification enhances the hydrophobicity and oleophilicity of the grafted nettle fibers.

Figure 2.

FTIR spectra of raw and grafted nettle fiber.

SEM analysis

From SEM images (Figure 3(a) and (b)), it can be seen that there is a significant variation in the exterior surface structure of the unmodified and modified nettle fibers. This indicates that the grafting process altered the physical arrangement of the nettle fiber. An undulant and corrugated structure can be seen on the grafted nettle fiber. The undulant and corrugated structure surface increases the surface area of the material, which can prevent absorbed oil escaping from the surface [24]. Heterogeneous grafting of butyl acrylate onto the fiber has made the fiber hydrophobic and oleophilic, and thus in turn makes it a good material for absorbing oil. It may be possible that the high amount of oil can be trapped into the interior porous structure of the fiber (Figure 4) exhibiting the improved oil sorption capacity. The porous interior of the fiber improves the penetration of oil through the fiber and enhances the sorption properties of fiber. Hence, two key factors that synergize in improving the sorption behavior are hydrophobic/oleophilic rough surface arrangement along with the porous nature of interior fiber. Oil is initially adsorbed on undulant and corrugated surface structure and then fills up the porous interior of the sorbent. Accordingly, the sorption mechanism depends on both adsorption and absorption.

Figure 3.

SEM images: (a) raw nettle fibers and (b) grafted nettle fibers.

Figure 4.

Hollow structure of a nettle fiber.

Contact angle measurements

For characterization of hydrophobic and oleophilic property of nettle fibers, the static contact angles of water and the oil were measured by an optical contact angle meter. The water and oil contact angles of unmodified nettle and modified nettle are shown in Table 5. As we can see in Table 5, there were difference in water contact angle and oil contact angle for umodified nettle and modified nettle fibers. The higher water contact angles and low oil contact angles of modified nettle fibers recommended their hydrophobic–oleophilic characteristics. As we can see, grafted fibers and ungrafted fibers showed a water contact angle of 131.5° and 70.54°, respectively. The excellent water repellency of grafted fibers can be a result of heterogeneous grafting of butyl acrylate onto the fiber. Further it is observed that the oil contact angle varied considerably between crude oil and vegetable oil. This difference could be due to the lower surface tension of vegetable oil than crude oil (Table 2).

Table 5.

Contact angles of raw and grafted nettle fibers.

S. No.	Sample description	Mean contact angle
1	Grafted nettle with crude oil	0
2	Grafted nettle with vegetable oil	0
3	Grafted nettle with normal water	131.5°
4	Raw nettle fiber with crude oil	43.43°
5	Raw nettle fiber with vegetable oil	36.45°
6	Raw nettle fiber with normal water	70.54°

Oil sorption behavior of grafted nettle

The effect of graft add-on (%) on oil sorption of nettle fiber is shown in Figure 5. From Figure 5, it is observed that the oil sorption capacity of nettle fiber increases with graft add-on (%) against both crude oil and vegetable oil. This could be due to the hydrophobicity and oleophilicity imparted to the nettle fiber as a result of surface modification with butyl acrylate monomer and ester formation. From Figure 5, it is also observed that the oil sorption capacity of grafted nettle fibers are higher for crude oil than vegetable oil, which might be due to the inherent density difference along with the possible polarity of asphaltenic compounds such as resins, asphaltenes, etc. [27]. Further, the crude oil was more viscous and the rate at which it was coming out from the fibrous structure was low. Microscope images of crude oil and vegetable oil absorbed nettle fiber bundle are shown in Figure 6.

Figure 5.

Effect of graft add-on (%) on oil sorption.

Figure 6.

Oil absorbed nettle fiber bundle: (a) crude oil and (b) vegetable oil.

The analysis of variance results of individual and interaction effects of various independent variables such as time, temperature and graft add-on (%) are shown in Table 6.

Table 6.

The f-values and p-values for different response variables.

Source	Graft add-on (%)		Crude oil sorption (g/g)		Vegetable oil sorption (g/g)
Source	f-Value	p-Value	f-Value	p-Value	f-Value	p-Value
Model	12.69	0.0010	6.08	0.0115	4.92	0.0214
A – Time	23.75	0.0012	7.34	0.0267	10.09^a	0.0131
B – Temperature	28.46	0.0007	9.95	0.0135	6.03^a	0.0395
C – Monomer- to-fiber ratio	21.59	0.0017	15.61	0.0042	10.25	0.0126
AB	2.13	0.1827^a	1.84	0.2120^a	2.38	0.1615^a
AC	0.2366	0.6397^a	0.0511	0.8268^a	0.0520	0.8253^a
BC	0.0004	0.9840^a	1.67	0.2325^a	0.6862	0.4315^a

^aValues which are not significant.

The “p” values and “f” values for different response variables are shown in Table 6. From Table 6, it is observed that individual effects of parameters such as time, temperature and monomer concentration on graft add-on (%), crude oil sorption and vegetable oil sorption were found to be significant, whereas the interaction effects such as time vs. temperature, temperature vs. monomer concentration and monomer concentration vs. time were not significant.

The coefficient determination (R²) of the graft add-on (%), crude oil and vegetable oil sorption (g/g) are given in equations (3) to (5) is 0.9049, 0.8201 and 0.7866, respectively. From the value of R², it can be understood that more than 80%, 82% and 78% of variability can be explained by the chosen variables for the variation in graft add-on (%), vegetable oil and crude oil sorption (g/g), respectively. Adequate precision is the measurement of signal-to-noise ratio, and the values greater than 4 are desirable to select the model. In this study, for all the three factors, the adequate precision is 11.634, 7.904 and 7.178 for reaction time, temperature and monomer concentration, respectively. The regression equation in terms of actual factors is shown in Table 7.

Table 7.

Regression equation for graft add-on (%), crude oil and vegetable oil sorption.

Variables	Equation	R²
Graft add-on (%)	Y = 12.10 + 0.8325 × A + 0.9112 × B + 0.7923 × C + 0.3525 × A × B − 0.1175 × A × C + 0.0050 × B × C (3)	0.9049
Crude oil sorption (g/g)	Y = 28.53 + 2.44 × A + 2.84 × B + 3.55 × C + 1.73 × A × B + 0.2875 × A × C + 1.64 × B × C (4)	0.8201
Vegetable oil sorption (g/g)	Y = 19.68 + 2.07 × A + 1.60 × B + 2.08 × C + 1.42 × A × B + 0.21 × A × C + 0.7620 × B × C (5)	0.7866

Reusability

Reusability is a key indicator for assessing the capacity of oil sorbent material to recover the oil absorbed. Superior recycling performance of oil sorbent material can reduce the price of oil pollution treatment. The oil sorption capacity of grafted nettle fiber for both vegetable oil and crude oil after seven sorption–desorption cycles is illustrated in Figure 7. It can be seen that the oil sorption capacity continuously decreases during seven cycles. The reduction in oil absorbency after each sorption/desorption cycle could be due to the factors such as irreversible deformation of partial fiber structure, the reduction of fiber interspace and the presence of residual oil in fiber bundles [28]. After seven cycles, the losses in oil sorption capacity for vegetable and crude oil are 12.29 and 9.12, respectively. In addition, after seven cycles, the resulting grafted nettle still exhibits better oil sorption capacity than unmodified nettle for both oils. The results indicate that grafted nettle fiber shows excellent reusability capability.

Figure 7.

Reusability of grafted nettle fiber.

Comparison between nettle and commercial sorbents

Oil sorption capacity of unmodified nettle, grafted nettle and commercial polypropylene is shown in Table 8. For grafted fiber, the best oil sorption capacity and graft add-on (%) are achieved at 4-h reaction time, 70℃ temperature and 2% monomer concentration-to-fiber ratio (Table 8). The oil sorption capactiy of raw nettle fibers is 10.59 g/g and 8.32 g/g for crude oil and vegetable oil, respectively. These values are much lower than the sorption capacity of grafted nettle, which are 36.60 g/g and 25.56 g/g sorption for crude oil and vegetable oil, respectively. Further, it is noted that sorption capacity of grafted nettle fibers are higher than that of synthetic polypropylene sorbents (33.35 g/g and 22.19 g/g against crude oil and vegetable oil, respectively). Based on these findings, it is apparent that the grafted nettle is appropriate for cleanup of oil spill in marine environments.

Table 8.

Oil sorption capacity of raw nettle, grafted nettle and commercial polypropylene.

S. No.	Material	Crude oil (g/g)	Vegetable oil (g/g)
1	Raw nettle	10.59	8.32
2	Grafted nettle (produced at optimum conditions)	36.60	25.56
3	Commercial polypropylene	33.35	22.19

Conclusions

The grafting process played a significant role in deciding the oil sorption capacity of nettle fibers. Highest graft add-on (%) and oil sorption were achieved at 4-h reaction time, 70℃ temperature and 2% monomer concentration-to-fiber ratio. Maximum oil sorption capacity of grafted nettle was 36.60 g/g and 25.56 g/g against crude oil and vegetable oil, respectively. Reusability test results showed that grafted nettle exhibited better oil sorption capacity than unmodified nettle even after seven sorption–desorption cycles. It is also noted that the oil sorption capacity of grafted nettle was higher than that of commercial polypropylene material. Based on these results, it is concluded that functionalized nettle prepared by grafting technique could be a potential material for oil spill treatment.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Funding received from University Grant Commission (UGC), Government of India under Project Number (F.No-43-158/2014) for carrying out this research work is gratefully acknowledged.

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Surface modification of nettle fibers by grafting to improve oil sorption capacity

Abstract

Keywords

Introduction

Materials and methods

Graft copolymerization of butyl acrylate on to nettle fiber

Measurement of oil sorption capacity

Experimental design

Reusability test

Fourier-transform infrared spectroscopy

Scanning electron microscopy

Results and discussion

Effect of preparation parameters on graft add-on (%)

Characterization

FTIR spectra

SEM analysis

Contact angle measurements

Oil sorption behavior of grafted nettle

Reusability

Comparison between nettle and commercial sorbents

Conclusions

Footnotes

Declaration of conflicting interests

Funding

References