Tk

Ta

b

a

ARRA

KKDOK

1

ao2atcdtw

aesgzap

5T

h0

Industrial Crops and Products 61 (2014) 325–330

Contents lists available at ScienceDirect

Industrial Crops and Products

jo ur nal home p age: www.elsev ier .com/ locate / indcrop

heoretical and experimental study on the oil sorption behavior ofapok assemblies

ing Donga, Fumei Wanga,b, Guangbiao Xua,b,∗

College of Textiles, Donghua University, Shanghai 201620, ChinaKey Laboratory of Textile Science and Technology Ministry of Education, Donghua University, Shanghai 201620, China

r t i c l e i n f o

rticle history:eceived 4 May 2014eceived in revised form 2 July 2014ccepted 14 July 2014

eywords:

a b s t r a c t

Kapok fiber is a natural hollow fiber whose assemblies show high oil sorption capacity for various oils.In this article, a dual-scale model based on Washburn Capillary Theory was developed to study the oilsorption behavior of kapok assemblies with relation of their pore structure. The validity of this modelwas evaluated by oil sorption coefficient obtained from the curve of oil mass increase versus sorptiontime, which was measured by a wicking method. Diesel and motor oil were chosen as experimental oils.

apok assembliesual-scale modelil sorption coefficientapok lumen

It turned out that theoretical values of sorption coefficients of the two oils were highly consistent withtheir experimental results. On the basis of theoretical analysis, we found that the big lumen of kapok fibercontributed considerably to the oil sorption capacity of kapok assembly, which was further enhanced withincreasing kapok packing density. At the tightly packed condition of 0.10 g/cm3, oil absorbed by kapoklumens accounted for up to one fifth of the total oil absorption of kapok assembly for both test oils.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

With the expansion of oil exploration and production activitiesround the world, water pollution caused by oil spillage has becomene of the major environmental problems. It was estimated that2,000 tonnes of oil spilled into marine between 2010 and 2013lone, forming oil film on the water by 12 square kilometers peron (ITOPF, 2013). To remove and recover the spilled oil, mechani-al extraction by sorption materials is regarded as one of the mostesirable choices, as they can concentrate and transform liquid oilo semi solid or solid phase, which can then be removed from theater and handed in a convenient manner (Karan et al., 2011).

A large volume of published studies have reported oil removalnd collection by sorption materials. These materials are gen-rally divided into three types: inorganic mineral materials,ynthetic organic materials and natural organic materials. Inor-anic mineral sorbents like graphite, perlite, vermiculite, silica,

eolites and organic clay, are less performed due to their low oilbsorption and inadequate buoyancy. Synthetic organic materials,rimarily polypropylene, show high oil sorption capacity but are

∗ Corresponding author. Present address: College of Textiles, Donghua University,047 room, 2999 North Renmin Road, Songjiang district, Shanghai 201620, China.el.: +86 021 67792803.

E-mail address: guangbiao xu@dhu.edu.cn (G. Xu).

ttp://dx.doi.org/10.1016/j.indcrop.2014.07.020926-6690/© 2014 Elsevier B.V. All rights reserved.

non-biodegradability (Wahi et al., 2013). Natural organic sorbentsincluding straw, sawdust, rice husks, bagasse, cotton, wool, kenaf,cattail, milkwood, kapok fiber, silk-floss fiber and populus seedfiber receive increasing attention for their highly biodegradabilityand low cost. It has been observed that straw, sawdust, rice husksand coconut husk suffer drawbacks in terms of high water uptakeand relatively low oil absorbency (Ali et al., 2012; Annunciado et al.,2005; Husseien et al., 2008). While cotton, milkwood, silk-flossfiber, cattail, kapok fiber and populus seed fiber can absorb sig-nificantly more oil than synthetic organic materials (Annunciadoet al., 2005; Choi, 1996; Choi and Moreau, 1993; Rengasamy et al.,2011; Singh et al., 2013). Among these natural oil sorbents, kapokfibber is a natural hollow fiber extracted from the seedpod ofkapok tree. It has a big cylindrical lumen and very thin cell wallwhich mainly consists of cellulose, lignin, polysaccharide and smallamount of waxy coating (Rijavec, 2008).Traditionally, kapok fiberswere used as stuffing in mattresses, pillows, and upholstered furni-ture. Machine spinning of kapok was difficult and limited to coarseyarns only or to the yarns blended with cotton due to its brit-tleness and poor cohesiveness. In recent years, however, kapokfibers gained great academic interests as an oil sorption material(Abdullah et al., 2010; Hori et al., 2000; Lim and Huang, 2007a,b;

Rahmah and Abdullah, 2011; Rengasamy et al., 2011; Wang et al.,2012b, 2013). In their studies, kapok fibers exhibited good waterrepellency with high capability of absorbing various oils, demon-strating great potential for oil pollution control.

3 s and

ofiaHladbtcCa

2

cas(cf

(

(

(

d

wd

pTb

Q

Q

wra

ε

ε

ε

26 T. Dong et al. / Industrial Crop

It has been found that the high capability of oil absorptionf kapok assemblies is attributed to the big lumen of kapokber, regardless of the existence of the plant wax coating whichccounts for the hydrophobicity (Rijavec, 2009; Wang et al., 2012a).owever, the oil sorption mechanism, the contribution of hollow

umens and inter-fiber pores to the oil sorption capacity of kapokssemblies still cannot be well recognized. In the present work, aual-scale model was developed to characterize the oil sorptionehavior of kapok assemblies with relation of their pore struc-ure, and a wicking method was carried out to verify the model byomparing experimental and theoretical oil sorption coefficients.onclusions from this research will be helpful in designing thepplicable structure of kapok assemblies for oil sorption purpose.

. Theoretical section

The dual-scale model was developed based on classical capillaryhannel theory, in which fibrous structures were modeled as anssembly of many cylindrical capillary tubes of equivalent dimen-ions and liquid transport was driven by the capillary pressureWashburn, 1921). For kapok assemblies which include cylindri-al lumens and irregular-shaped inter-fiber pores, we made theollowing assumptions:

1) All kapok fibers in the testing container were of the same diam-eter and length and arranged vertically.

2) The pores made of kapok lumens were regarded as a series ofparallel capillary tubes with diameters equating to the innerdiameter of kapok fiber.

3) The pores in inter-fiber distances with noncircular cross-sectional shapes were considered as a series of parallel capillarytubes with equivalent diameter defined by hydraulic diameter,which met the following conditions (Mao and Russell, 2008):a) The wetted area of capillary tube assembly was identical to

the wetted area of inter-fiber pores.b) The porosity of the capillary tube assembly was the same as

that of inter-fiber pores.

Based on the assumption (2), we got the following equation:

hi = di (1)

here dhi is the equivalent capillary diameter of kapok lumens andi is the inner diameter of kapok fiber.

To calculate the equivalent capillary diameter of inter-fiberores, we employed � as the packing density of kapok assemblies.hen the volume of kapok fibers Qf and kapok cell walls Qw coulde expressed as follows:

f = �

�f(2)

w = �

�w(3)

here �f and �w are the density of kapok fiber and kapok cell wall,espectively. Therefore, the total porosity ε, inter-fiber porosity εe

nd inner-fiber porosity εi were obtained as follows:

= 1 − Qw = 1 − �

�w(4)

e = 1 − Qf = 1 − �(5)

�f

i = ε − εe = �

(1�f

− 1�w

)(6)

Products 61 (2014) 325–330

We used n representing the number of capillary tubes for inter-fiber pores and dhe the corresponding hydraulic diameter. Based onthe assumption (3), the following equations were established:

Sv(1 − εe) = �dhen (7)

εe = �d2he

n

4(8)

where Sv is the specific surface area of kapok fibers, which couldalso be expressed as:

Sv = �de

(�/4)d2e

= 4de

(9)

where de is the external diameter of kapok fiber. Combining Eqs.(7)–(9), the hydraulic diameter for inter-fiber pores was obtained:

dhe = εe

(1 − εe)de (10)

According to Washburn equation, the liquid wicking length Land wicking time t of a capillary tube with diameter of dc have thefollowing relationship (Washburn, 1921):

L2 = � cos �

4�dct (11)

where � is the liquid surface tension, � is the contact angle betweenthe liquid and the solid surface, � is the viscosity of the liquid. Asthe liquid wicking length could also be expressed in the form ofabsorbed liquid mass by:

W = Aε0�1L (12)

where A is the cross-sectional area of filled medium, ε0 is the poros-ity of filled medium, �l is the liquid density. Therefore, the massincrease of oil absorbed by kapok lumens Wi and their inter-fiberpores We were obtained by substituting Eqs. (1), (10) into (11) and(12), respectively, as follows:

W2i = A2�2

1ε2i

�l cos �

4�dit (13)

W2e = A2�2

1ε2

e

(1 − εe)�l cos �

4�det (14)

For the same system (the packing density of kapok assem-blies and the type of oil), the ratio between the mass square ofabsorbed oil and sorption time is a constant and defined as oilsorption coefficient (Nishi et al., 2002). In the following section,comparisons between experimental and theoretical oil sorptioncoefficients were carried out to verify the validity of the abovemodel.

3. Materials and Experiment

3.1. Kapok and oils

The kapok fibers used in this study was java kapok got fromPate County, Java Tengah, Indonesia. The characteristics of the fiberwere examined using SEM (TM3000, Hitachi, Japan). Before SEMobservation, kapok fibers were immersed in liquid nitrogen andthen fractured to reserve the intact hollow structure of the fibers.As shown in Fig. 1, the fiber had a hollow structure with big lumen.The external diameter, inner diameter and linear density of kapokwere measured according to the methods adopted by Chang (2012).The densities of kapok fiber and kapok cell wall were calculatedaccording to the following equations:

Af = �

4d2

e (15)

Ao = �

4d2

i (16)

T. Dong et al. / Industrial Crops and Products 61 (2014) 325–330 327

N

�

wkcct

tsvteotdtons

3

mk14qal0bwwal

TB

Fig. 1. SEM image of the cross-section of a kapok fiber.

dt = 10, 000G

L= 10, 000(Af − Ao)�w (17)

f =(

Af − Ao

)�w

Af(18)

here de and di are the average external and inner diameter ofapok, �f is the density of kapok fiber, �w is the density of kapokell wall, Ndt is the linear density of kapok fiber, Af and Ao are theross-sectional area of kapok and kapok lumen, respectively. Allhese basic parameters of kapok fiber are presented in Table 1.

Two types of oils, namely diesel and motor oil, were used inhe study. The densities and surface tensions of the oils were mea-ured by the Tensionmeter (DCAT11, Dataphysics, Germany). Theiriscosities were determined by SNB2 Digital Rotary Viscosime-er. For measurement of contact angle between kapok and thexperimental oils, a captive bubble method was adopted by usingptical contact angle meter (OCA15EC, Dataphysics, Germany). Inhe testing process, kapok fibers were attached to a glass slide byouble-side tape and paved in the form of plane. As shown in Fig. 2,he captive bubble method was conducted by forming an air bubblento the immersed kapok surface in the oil by using a ‘U’-shapedeedle. The final contact angle was an average of three trials. Table 2ummarized the testing results.

.2. Method of oil sorption experiments

The oil sorption experiments were carried out by wickingethod, performing on DCAT11. The sample tube which held the

apok fibers was 40 mm in length with an internal diameter of2 mm. The calculated tube volume and cross-sectional area were.524 cm3 and 1.131 cm2, respectively. In the test process, differentuantities of kapok fibers were packed evenly into the sample tubend then compressed by screwing the piston of the tube to a filledength of 20 mm, producing packing densities ranging from 0.03 to.10 g/cm3. The filled tube was then suspended under the electro-alance through a special sample holder. A transparent glass beaker

ith test oil was placed on constant-temperature chamber whichas fixed on a lifting platform. The oil temperature was maintained

round 22–24 ◦C. When the test started, the test oil held by theifting platform automatically moved up until a force change was

able 1asic structure parameters of kapok fiber.

External diameter de (�m) Inner diameter di (�m) Linear density N

16.29 14.29 0.65

Fig. 2. Contact angles between kapok surface and (a) motor oil, (b) diesel measuredby captive bubble method.

registered as a result of initial contact with the sample, and then itsposition was fixed for the rest of the experiment. The absorbed oilmass due to capillary action was detected by the electro-balanceand memorizing on a computer with analog-digital converter.

4. Results and discussions

4.1. Oil sorption behavior of different packed kapok assemblies

The sorption curves of motor oil and diesel at different pack-ing densities of kapok assemblies are presented in Fig. 3(a and b).Each curve is characterized in triplicate and plotted as average ofthree trials with error bars indicating one standard deviation. Fortwo types of experimental oils, the mass square of oils absorbedby kapok assemblies, m2, versus sorption time, t, exhibit notablylinear relationship, which are further enhanced with the increaseof kapok packing density. The least linear relationship appeared at0.03 g/cm3 might be because the large pores within inter-fiber dis-tance did not have sufficient capillary pressure to fill themselveswith oil, as evidenced by Jurin’s equation (Zhu et al., 2008). Whenthe liquid rises inside a circular pore of radius r, the capillary forcewill be balance by the gravitational force and the liquid will ceasesto rise beyond the equilibrium wicking height h*,

h∗ = 2� cos �

�lgr(19)

where g is the acceleration due to gravity.

4.2. Theoretical and experimental oil sorption coefficients

4.2.1. Theoretical oil sorption coefficientsOil sorption coefficient is defined as the ratio between m2 and

t. According to Eqs. (13) and (14), the total oil sorption coefficient

dt (dtex) Fiber density �f (g/cm3) Cell wall density �w (g/cm3)

0.305 1.35

328 T. Dong et al. / Industrial Crops and Products 61 (2014) 325–330

Table 2Properties of experimental oil and its contact angle with kapok fiber.

Oil type Density (g/cm3) Viscosity (mPa s) Surface tension (N/m) Contact angle(◦)

Motor oil 0.87 257.60 30.27 × 10−3 69.05

cc

c

c

c

w�rsdapa

Ffi

Diesel 0.83 6.50

, oil sorption coefficient of inter-fiber pores ce and kapok lumensi would be expressed as:

i = A2�21ε2

i

�l cos �

4�di (20)

e = A2�21

ε3e

(1 − εe)�l cos �

4�de (21)

= ci + ce (22)

here A is the cross-sectional area of the sample tube, 1.131 cm2;l, � and � are the density, surface tension and viscosity of test oil,espectively; � is the contact angle between the oil and the kapokurface; de is the average external diameter of kapok, 16.29 �m;

i is the average inner diameter of kapok, 14.29 �m; εi and εe

re porosity contributed by kapok lumens and their inner-fiberores, respectively. They were calculated according to Eqs. (5)nd (6). When substituting all these parameters to the above

0 50 0 100 0 150 0 200 0 250 0 300 0

0

1

2

3

4

5

Mas

s sq

uar

e (g

2)

Time (s)

Differe nt pac king densities ( g/cm3)

0.03 0.04 0.05

0.06 0.07 0.08

0.09 0.10

(a)

0 5 10 15 20 25 30 35 40

0

1

2

3

4

5

Mas

s sq

uar

e (g

2)

Time (s)

Diffete nt pac king densities ( g/cm3

)

0.03 0.04 0.05

0.06 0.07 0.08

0.09 0.10

(b)

ig. 3. (a and b) Plots of m2 versus t for (a) motor oil, (b) diesel absorbed by kapokbers at different packing densities.

27.76 × 10−3 45.73

equations, we obtained the theoretical sorption coefficients ofdiesel and motor oil under different packing densities, as shown inTable 3.

4.2.2. Experimental oil sorption coefficientsPhysically, oil sorption coefficient presents the curve slope of

m2 versus t. Fig. 4(a and b)shows the linear fitting results of oilsorption curves of motor oil and diesel for kapok packing densitiesranging from 0.04 g/cm3 to 0.10 g/cm3. All correlation coefficientsR2 > 0.99 and the slopes of these fitting lines, namely experi-mental oil sorption coefficients expressed as c0, are presented inTable 3.

4.2.3. Comparisons between theoretical and experimental oilsorption coefficients

As we can see from Table 3, theoretical sorption coefficient c ofboth motor oil and diesel exhibit excellent agreement with theirexperimental results c0 for all kapok packing conditions between0.04 g/cm3 and 0.10 g/cm3. This suggests that the dual-scale modelwe have developed could predict the actual oil sorption behav-ior of kapok assemblies effectively and provide some guidance inpractical applications. However kapok assemblies packed less than0.04 g/cm3 are not fitted in the study, because the unfilled big poreswithin inter-fiber distances could lead to deviations between theo-retical predictions and experimental results, as explained in Section4.1.

4.3. Analysis of kapok lumens on oil sorption capacity

To illustrate how kapok lumens affect the oil sorption capac-ity of kapok assemblies, the theoretical ratios of diesel and motoroil absorbed by inter-fiber pores and kapok lumens under differ-ent packing densities were calculated according to Eqs. (13) and(14). The results expressed by We/Wi are presented in Table 4.Also the ratios of oil sorption coefficient between their inter-fiberpores and kapok lumens ce/ci and the total porosity ε, porosityof lumens εi and inter-fiber pores εe are calculated and listed inthe table. It can be seen that with the increase of packing den-sity, the porosity of kapok lumens is increased, and the influenceof kapok lumens on the oil sorption capacity of kapok assembliesis also enhanced significantly. When the packing density reachesat 0.10 g/cm3, oil absorbed by kapok lumens account for up to onefifth of its total oil absorption for both two oils. While comparedwith the ratios of We/Wi, the large ratios of ce/ci of motor oil anddiesel at all kapok packing densities suggest that the oil sorptionrate of kapok assemblies is dominantly determined by inter-fiberpores.

4.4. Impact of packing densities on oil sorption capacity

The oil sorption capacities, the amounts of absorbed oilsper unit mass of kapok fibers were obtained from the satu-rated mass increase of wicking tests. Fig. 5(a and b) showssorption capacities of kapok assemblies to motor oil and diesel

as a function of packing densities and furthermore each ofabsorbencies is divided into theoretical ratios of contributionsfrom kapok lumens and inter-fiber pores according to figureslisted in Table 4. Similar to the previous observations (Abdullah

T. Dong et al. / Industrial Crops and Products 61 (2014) 325–330 329

Table 3Comparisons between theoretical and experimental oil sorption coefficients.

Packing density(g/cm3)

Motor oil Diesel

Experimental Theoretical Experimental Theoretical

c0 R2 ce ci c c0 R2 ce ci c

0.04 8.300 0.996 8.286 0.015 8.301 536.490 0.996 535.041 0.967 536.0080.05 5.970 0.998 5.906 0.023 5.946 383.010 0.992 381.381 1.511 382.8930.06 4.44 0.991 4.365 0.034 4.399 285.110 0.999 281.875 2.176 284.0510.07 3.347 0.998 3.302 0.046 3.346 216.460 0.997 213.213 2.962 216.1750.08 2.600 0.999 2.536 0.060 2.596 168.780 0.997 163.744 3.869 167.6130.09 1.970 0.999 1.967 0.076 2.043 131.900 0.997 126.994 4.896 131.8901.61 1.590 0.999 1.534 0.094 1.628 107.090 0.998 99.076 6.045 105.121

T

ekikdtt

omt

Fa

kapok assemblies, especially for oil with high density (as depictedin Fig. 3).

he unit of oil sorption coefficient in the above table is g2 10−3/s.

t al., 2010; Lim and Huang, 2007b), the sorption capacities ofapok assemblies decrease exponentially with the increase of pack-ng density. At the loose packing condition of 0.04 g/cm3, theapok fibers could absorb 25.10 g/g and 23.72 g/g of motor oil andiesel, separately. As the packing density increases to 0.10 g/cm3,heir absorbencies decrease to only 8.86 g/g and 8.16 g/g, respec-ively.

The reasons for drastic decrease of oil sorption capacities arebvious. As showed in Table 4, the void fraction inside the kapokicrostructure is decreased linearly with increasing packing densi-

ies, therefore leading to reduced space for oil absorbing. However,

0 500 1000 1500 2000 2500 3000

0

1

2

3

4

5

Mas

s sq

uar

e (g

2)

Time (s)

Different packing densities (g/cm3)

0.04 0.05 0.06

0.07 0.08 0.09

0.10

(a)

0 5 10 15 20 25 30 35 40

0

1

2

3

4

5

Mas

s sq

uar

e (g

2)

Time (s)

Diffetent packing densities (g/cm3

)

0.04 0.0 5 0.0 6

0.07 0.0 8 0.0 9

0.10

(b)

ig. 4. (a and b) Linear fittings of plots of m2 versus t for (a) motor oil, (b) dieselbsorbed by kapok fibers at different packing densities.

this does not mean that a lower packing density would be moredesirable for oil sorption, because the large pores within inter-fiberdistances will be not filled up with oil when the packing den-sity is less than 0.04 g/cm3, resulting in insufficient utilization of

0.04 0.05 0.06 0.07 0.08 0.09 0.10

0

5

10

15

20

25

30O

il s

orp

tion c

apac

ity (

g/g

)

Packing density (g/cm3)

(a)

theoretical contribute d by kapok l umens

0.04 0.05 0.06 0.07 0.08 0.09 0.10

0

5

10

15

20

25

Oil

sorp

tion c

apac

ity (

g/g

)

Packing density (g/cm3)

(b)

theoretical contribute d by kapok l umens

Fig. 5. (a and b) Sorption capacity of kapok assemblies to (a) motor oil, (b) diesel asa function of packing densities.

330 T. Dong et al. / Industrial Crops and Products 61 (2014) 325–330

Table 4Theoretical ratios of oil absorbed by kapok lumens and their inter-fiber pores.

Packing density (g/cm3) ε Motor oil Diesel

εe εi ce/ci We/Wi =√

ce/ci ce/ci We/Wi =√

ce/ci

0.04 86.89 10.15 552.40 23.50 553.20 23.520.05 83.61 12.69 256.78 16.02 252.37 15.890.06 83.61 12.69 128.38 11.33 129.53 11.380.07 77.05 17.77 71.78 8.47 71.98 8.480.08 73.77 20.30 42.27 6.50 42.33 6.51

88

32

5

wtcbWm

A

Rea2Xp

R

A

A

A

C

C

C

0.09 70.49 22.84 25.0.10 67.21 25.38 16.

. Conclusions

The dual-scale model we have developed fitted excellently wellith the actual oil sorption behavior of kapok assemblies. Based on

he theoretical analysis, we found that the big lumen of kapok fiberontributed considerably to the oil sorption capacity of its assem-lies, which was further enhanced with increasing packing density.hile the oil sorption rate of kapok assemblies is dominantly deter-ined by inter-fiber pores.

cknowledgments

The research is financially supported by “The Fundamentalesearch Funds for the Central Universities” and “Zhejiang Sci-nce and Technology Planning Project for the manufacture andpplication of high oil-taking kapok nonwomens” (numbered by013C31139). The authors are also thankful to Chang M.M. and Sun.L. for help with the measurement in determining kapok structurearameters.

eferences

bdullah, M., Rahmah, A.U., Man, Z., 2010. Physicochemical and sorption character-istics of Malaysian <i> Ceiba pentandra </i> (L.) Gaertn. as a natural oil sorbent.J. Hazard. Mater. 177, 683–691.

li, N., El-Harbawi, M., Jabal, A.A., Yin, C.-Y., 2012. Characteristics and oil sorp-tion effectiveness of kapok fibre, sugarcane bagasse and rice husks: oil removalsuitability matrix. Environ. Technol. 33, 481–486.

nnunciado, T., Sydenstricker, T., Amico, S., 2005. Excellent oil absorbent kapok[Ceiba pentandra (L.) Gaertn.] fiber: fiber structure, chemical characteristics, andapplication. Mar. Pollut. Bull. 50, 1340–1346.

hang, M.M., 2012. Study on morphological characteristics and tensile propertyof kapok fibers from Indonesia and Hainan Island. In: Master Thesis. DonghuaUniversity.

hoi, H.M., 1996. Needlepunched cotton nonwovens and other natural fibers as oil

cleanup sorbents. J. Environ. Sci. Health, A: Toxic/Hazard. Subst. Environ. Eng.31, 1441–1457.

hoi, H.M., Moreau, J.P., 1993. Oil sorption behavior of various sorbents stud-ied by sorption capacity measurement and environmental scanning electronmicroscopy. Microsc. Res. Tech. 25, 447–455.

5.09 25.94 5.094.04 16.39 4.05

Hori, K., Flavier, M.E., Kuga, S., Lam, T.B.T., Iiyama, K., 2000. Excellent oil absorbentkapok [Ceiba pentandra (L.) Gaertn.] fiber: fiber structure, chemical characteris-tics, and application. J. Wood Sci. 46, 401–404.

Husseien, M., Amer, A., El-Maghraby, A., Taha, N.A., 2008. Experimental investigationof thermal modification influence on sorption qualities of Barley Straw. J. Appl.Sci. Res. 4, 652–657.

Karan, C.P., Rengasamy, R., Das, D., 2011. Oil spill cleanup by structured fibre assem-bly. Indian J. Fibre Text. Res. 36, 190–200.

Lim, T.-T., Huang, X., 2007a. Evaluation of hydrophobicity/oleophilicity of kapok andits performance in oily water filtration: comparison of raw and solvent-treatedfibers. Ind. Crops Prod. 26, 125–134.

Lim, T.-T., Huang, X., 2007b. Evaluation of kapok (<i>Ceiba pentandra</i> (L.) Gaertn.)as a natural hollow hydrophobic–oleophilic fibrous sorbent for oil spill cleanup.Chemosphere 66, 955–963.

Mao, N., Russell, S., 2008. Capillary pressure and liquid wicking in three-dimensionalnonwoven materials. J. Appl. Phys. 104, 034911.

Nishi, Y., Iwashita, N., Sawada, Y., Inagaki, M., 2002. Sorption kinetics of heavy oilinto porous carbons. Water Res. 36, 5029–5036.

Rahmah, A.U., Abdullah, M., 2011. Evaluation of Malaysian <i>Ceiba pentandra</i>(L.) Gaertn. for oily water filtration using factorial design. Desalination 266,51–55.

Rengasamy, R., Das, D., Praba Karan, C., 2011. Study of oil sorption behavior of filledand structured fiber assemblies made from polypropylene, kapok and milkweedfibers. J. Hazard. Mater. 186, 526–532.

Rijavec, T., 2008. Kapok in technical textiles. Tekstilec 51, 319–331.Rijavec, T., 2009. Influence of kapok hollowness on its liquid retention capacity.

Tekstilec, 52.Singh, V., Kendall, R.J., Hake, K., Ramkumar, S., 2013. Crude oil sorption by raw cotton.

Ind. Eng. Chem. Res. 52, 6277–6281.Wahi, R., Chuah, L.A., Choong, T.S.Y., Ngaini, Z., Nourouzi, M.M., 2013. Oil removal

from aqueous state by natural fibrous sorbent: an overview. Sep. Purif. Technol.113, 51–63.

Wang, J., Zheng, Y., Wang, A., 2012a. Effect of kapok fiber treated with varioussolvents on oil absorbency. Ind. Crops Prod. 40, 178–184.

Wang, J., Zheng, Y., Wang, A., 2012b. Superhydrophobic kapok fiber oil-absorbent:preparation and high oil absorbency. Chem. Eng. J. 213, 1–7.

Wang, J., Zheng, Y., Wang, A., 2013. Coated kapok fiber for removal of spilled oil. Mar.Pollut. Bull. 69, 91–96.

Washburn, E.W., 1921. The dynamics of capillary flow. Phys. Rev. 17, 273.Zhu, L., Perwuelz, A., Lewandowski, M., Campagne, C., 2008. Static and dynamic

aspects of liquid capillary flow in thermally bonded polyester nonwoven fabrics.

J. Adhes. Sci. Technol. 22, 745–760.

ITOPF, 2013. Oil Tanker Spill Statistics. International Tanker Owners Pollution Fed-eration’s (ITOPF) publications, Download from 〈http://www.itopf.com/information-services/publications/documents/OilSpillstats 2013.pdf〉.