Surface modification of cellulose isolated from Sesamun indicum underutilized seed: A means of enhancing cellulose hydrophobicity

SA may not be able to interact with Cu (II) ions because of the conversion of the hydroxyl group at its surface to the ester functional groups as a result of the modi ﬁcation.. Moreover,[r]

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Original Article

Surface modiﬁcation of cellulose isolated from Sesamun indicum

underutilized seed: A means of enhancing cellulose hydrophobicity Adewale Adewuyia,b,*, Fabiano Vargas Pereirab

aDepartment of Chemical Sciences, Faculty of Natural Sciences, Redeemer's University, Ede, Osun State, Nigeria

bDepartment of Chemistry, Federal University of Minas Gerais, Av Ant^onio Carlos, 6627, Pampulha, CEP 31270-901 Belo Horizonte, MG, Brazil

a r t i c l e i n f o

Article history: Received 25 May 2017 Received in revised form 10 July 2017

Accepted 20 July 2017 Available online xxx

Keywords: Cellulose Hydrophobicity Modiﬁcation Sesamum indicum Underutilized seed

a b s t r a c t

Cellulose (SC) isolated from sesame seed (SS) was surface modified with the introduction of an ester functional group via a simple reaction to produce the modified product (SA) SS, SC and SA were char-acterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), particle size distribution (PSD), zeta potential and scanning electron microscopy (SEM) SC and SA were evaluated for their water holding capacity (WC), oil holding capacity (OC), swelling capacity (SW) and their ability to adsorb heavy metals The FTIR revealed peaks corresponding to the formation of the ester functional group at the surface of SA The crystallinity of SC was 28.02% but after the modification it increased to 77.03% in SA The PSD of SC and SA was both monomodal with sizes of 10.1305mm in SC and 10.2511mm in SA The adsorption capacity of SC towards Pb (II) and Cu (II) ions was higher than that of SA However, SA was unable to adsorb Cu (II) ions SA exhibited the lower WC and SW values as compared to SC which suggested an improved hydrophobicity after the modification This study has shown that hydrophobicity can be improved in cellulose via surface modification

1 Introduction

With the recent increase in demand for products made from renewable and sustainable non-petroleum based resources, cellu-lose is gaining significant recognition for diverse applications due to its renewability, biodegradability, non-toxicity and molecular structure It represents the most abundant renewable polymer which is mostly used in the form offibers or derivatives Cellulose has been reported from a number of conventional sources, which are of both plant and microorganism origins[1] However, there is still a need to search for better alternatives as most of the previ-ously identified conventional sources are expensive On the other hand, these sources have found other applications

Sesame seed (Sesamum indicum) is an underutilized plant ma-terial in Nigeria which can serve as a source of cellulose This plant belongs to the Pedaliaceae family[2] It is about 60e120 cm tall and the fruit is a dehiscent capsule held close to the stem When ripe, the capsule shatters to release a number of small seeds The seeds

are ovate, slightlyflattened and thin The seed oil has been reported as an important source of phytonutrient for applications in food and pharmaceutical industries[3] The seed is an important source of oil and after oil is extracted from the seed, the seed cake left is usually discarded as waste Presently, the seed cake is considered as waste with no specific use The essence of this work is to find application for this discarded seek cake in Nigeria

Due to the wide range of potential applications and important inherent properties of cellulose, there is a continuous effort on how to improve and optimize the properties of cellulose-based natural ﬁbers Among these important inherent properties of cellulose, the hydrophobicity plays an important role in water repellency, self-cleaning, corrosion prevention, friction reduction and antifouling

[4] The poor hydrophobicity of cellulose has limited its application in a few areas of research such as in waste water treatment or purification Previous studies have shown that the properties of cellulose can be improved by surface modification[5] So, replacing the hydroxyl functional groups at the surface of cellulose via sur-face modification might be an effective means of improving on its hydrophobicity

In this regard, the present study is aimed at ﬁnding a cheap source of cellulose, which can be surface modiﬁed in order to improve its hydrophobicity This was achieved by isolating,

* Corresponding author Department of Chemical Sciences, Faculty of Natural Sciences, Redeemer's University, Ede, Osun State, Nigeria

E-mail address:walexy62@yahoo.com(A Adewuyi)

Peer review under responsibility of Vietnam National University, Hanoi

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

http://dx.doi.org/10.1016/j.jsamd.2017.07.007

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characterizing and surface modifying cellulose from a sesame seed To the best of our knowledge, there is no report on the isolation and surface modiﬁcation of cellulose from the sesame seed source from Nigeria

2 Experimental 2.1 Materials

SS was obtained from a local market in Ibadan, Oyo state, Nigeria This was later identiﬁed at the Department of Botany and Microbiology, University of Ibadan, Ibadan, Oyo state, Nigeria The seeds were air dried, ground in an industrial mill and stored in an airtight container Sodium chlorite, sodium hydroxide, acetic acid, chloroacetic acid, suberic acid, thionylchloride, ethylenediamine and all other chemicals used in this study were purchased from SigmaeAdrich (Brazil)

2.2 Isolation of cellulose from SS

The isolation of cellulose from SS was achieved following the method described by Flauzino Neto et al.[6] Brieﬂy, 200 g of SS was transferred into a L beaker containing alkali solution (2 wt% NaOH) This was heated at 80C for h with continuous stirring using a Fisatom mechanical stirrer The beaker with its content was cooled,ﬁltered, washed continuously with deionized water several times until alkali free and oven dried at 50C The residue obtained was bleached with a mixture of solution, which was made up of equal volumes (1:1) of acetate buffer (27 g NaOH and 75 mL glacial

acetic acid, diluted to L of distilled water) and aqueous sodium chlorite (1.7 wt% NaClO2in deionized water) The mixture was then

stirred at 80C for h The resultingfibers were washed repeatedly in deionized water until the pH of thefiber became neutral The bleaching step was repeated twice until the fiber became completely white and dried in an air-circulating oven at 50C for 24 h giving rise to SC of an estimated yield of about 25%

2.3 Modiﬁcation of SC

Chloroacetylchloride was synthesized by stirring a mixture of chloroacetic acid (0.03 mol), thionylchloride (0.04 mol) and chlo-roform at 75C for 30 SC (7.50 g) was added to the chlor-oacetylchloride (after the removal of excess thionylchloride under reduced pressure); this was allowed to react for h under constant stirring at 80C andfinally cooled in ice Suberic acid (50 mL) was added and stirred for h at 80C under reflux Cold distilled water was added to the mixture and centrifuged thrice for 10 at 8500 rpm to remove excess suberic acid Thefinal product was dried at 50C for 24 h giving rise to an SA yield of about 80% 2.4 Characterization

The functional groups in SS, SC and SA were determined using FTIR (Perkin Elmer, spectrum RXI 83303) SS, SC and SA were blended with KBr, pressed into pellets and analyzed in the range of 400e4500 cm1 The X-ray diffraction pattern was obtained using

X-ray diffractometer (XRD-7000X-Ray diffractometer, Shimadzu) withﬁltered Cu Karadiation at 40 kV and 40 mA XRD pattern was

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recorded from 10 to 80C of 2q/s with a scanning speed of 2.00/ Thermal stability and fraction of volatile components of SS, SC and SA were monitored by DTA-TG apparatus (SHIMADZU, C30574600245) under nitrogen atmosphere, while the surface morphology was studied using FEI quanta 200 (model EDAX EDS) that operates on Genesis software (version 5.21) The PSD was carried out using a zeta potential analyzer (DT1200, Dispersion technology) at 25 C, while observing a general calculation model for irregular particles Several measurements were taken using Dispersion technology-AcoustoPhor Zetasize 1201 software (version 5.6.16)

2.5 Water holding capacity

A known weight (0.5 g) of SC and SA was separately dispersed in 10 mL of distilled water in a pre-weighed, clean centrifuge tube (W) placed in a water bath at 37C for 30 These were centrifuged for 15 at 4000 rpm; the supernatant was removed and the centrifuge tube with the distilled water soaked SC and SA was weighed (W2) WC was estimated as[7]:

WCg g1¼ðW2 ðW þ W1ÞÞ

W1 (1)

2.6 Oil holding capacity

This was determined by weighing 0.2 g (W) of SC and SA separately into a calibrated centrifuge tube containing mL (V1) of

Picralima nitida seed oil The mixture was properly stirred for 10 after which it was centrifuged for 30 at 5000 rpm The supernatant oil (V2) was gently removed, while the absorbed oil

was estimated as the difference between V1 and V2 OC was

calculated as described by Lu et al.[8]: OCmL g1¼V1 V2

W (2)

2.7 Swelling capacity

SW was determined by placing 0.5 g (W) of SC and SA in a calibrated tube, the initial bed volume (V1) was measured, mixed

with 10 mL of distilled water and shaken vigorously The tube with its content was placed in a water bath at 25C for 24 h and theﬁnal volume (V2) measured SW was calculated as[9]:

SWmL g1¼V2 V1

W (3)

2.8 Heavy metal adsorption capacity

Lead nitrate (Pb(NO3)2) and copper sulfate (Cu(SO4).5H2O) salts

were used in the preparation of the salt solutions in de-ionized water Metal adsorption study was carried out by separately shaking 0.1 g of SC and SA with a 50 mL solution (100 mg/L) of metal in different beakers at 25C and 200 rpm for h This was later centrifuged for 10 at 5000 rpm, and the metal concentration before and after adsorption were determined using Atomic

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Absorption Spectrometer (Varian AA240FS) The metal ions adsorption capacity of SC and SA was calculated as

qeẳCo CMeịV (4)

where qeis the adsorption capacity in mg/g, Coand Ceare initial and

ﬁnal concentrations (mg/L) of adsorbate (Pb and Cu) in solution respectively; while V and M are volumes (L) of metal ion solution and weight (g) of SC and SA used

3 Results and discussion 3.1 Characterization

The FTIR result is presented inFig The spectra revealed peaks corresponding to the OH functional group at 3320 cm1 The band at 1745 cm1only found in SS was assigned to the C]O stretching of the acetyl group and the uranic ester groups of the hemicellulose, which may also be due to the ester linkage of the carboxylic group in the lignin and hemicelluloses The band at 1745 cm1 dis-appeared in SC which may be due to the removal of hemicellulose and lignin from SS but reappeared in SA which suggests the for-mation of the ester functional group in SA Bands corresponding to the amorphous characteristics of the cellulosic materials were seen at 354 cm1in SS, SC and SA while the band at 2911 cm1 was assigned to the CeH stretching of CH2in SS, SC and SA The peaks at

1094 and 1155 cm1was attributed to the deformation of the CeH

rocking vibration and the CeOeC pyranose ring skeleton, while the peak at 894 cm1was assigned to the symmetric CeOeC stretching of theb-1,4-glycosidic linkages of the glucopyranose units of the cellulose in SS, SC and SA

Cellulose and its derivatives tend to carbonize under heating through dehydration and cross-linking reactions, which can be described as the rearrangement of a cellulose structure that pro-motes theﬁnal production of char residue SS, SC and SA were pyrolyzed in order to investigate their effects of temperature and thermal stability as shown inFig Loss in mass wasﬁrst noticed in the temperature range of 85e115C, which was attributed to the

loss of internal water molecules in SS, SC and SA There was another loss in mass within the temperature range of 115e162C that may

be assigned to the loss of volatile organic compounds The loss in mass in the range of 189e320C may be attributed to the loss of

hemicellulose Loss in mass at temperatures above 450C in SS and SC were assigned to losses of lignin and char[10] There was steady loss in mass in SA at temperatures above 320C, which can be described as the loss in mass at 320e450C, 450e600 C and

600e715C This steady loss in mass was considered as being due

to the chain length of the suberic acid involved in the modiﬁcation This increase in the decomposition temperature of SA may be an indication of the thermal stability of the cellulose that was increased with the modiﬁcation

The diffraction pattern presented in Fig with 2q peaks is typical of cellulose I structure The crystallinity index (Ic) was

determined using the height of 200 peak (I002, 2q¼ 21.65) and the

minimum intensity between the 200 and 110 peaks (IAM,

2q¼ 17.75) which can be expressed as:

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Icð%Þ ¼I002 IAM I002 100

(5) where I002 represents both crystalline and amorphous materials

while IAMrepresents the amorphous material The crystallinity of

SC was 28.02% but after the modiﬁcation it increased to 77.03% in SA The increase in crystallinity may be due to the introduction of the ester group to the cellulose which may likely have reinforced the crystalline nature of the cellulose The particle size distribution

of SC and SA was found to be monomodal The size distribution was found to be 10.1305mm for SC and 10.2511mm for SA The zeta potential is presented inFig The values of the zeta potential increased in SC and SA just as the pH value increased The value of the zeta potential is suggestive that SC and SA are stable materials The SEM micrograph is presented inFig The surface of SS ap-pears to have irregular shape and size which seemed to be composed of several microfibrils with each fiber having a compact structure Surface of SC is different from that of SS, it appeared smooth and flaky which may be due to the removal of

Fig Zeta potentials of the sesame cellulose (a) and the modiﬁed sesame cellulose (b)

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hemicellulose, lignin and some other non-cellulosic materials while SA appears to be stacked particles of aggregated macromol-ecules; it exhibited a lumpish structure which may be due to the intramolecular interaction in the molecule The surface of SA is completely different from those of SS and SC

3.2 Water holding, oil holding and swelling capacities of SC and SA The values obtained for WC, OC and SW with respect to SC and SA are presented inFig WC was found to be 17.0372 g/g for SC and 2.6116 g/g for SA WC estimates the ability of SC and SA to hold water over a period of time, especially when subjected to an external centrifugal gravity or compression forces The values ob-tained for WC were lower in SA compared to SC, which may be due to the modification that might have improved the hydrophobicity of SA The value of WC for SA is also lower than those reported for the red beanflour[11]and the white lupin[12], but higher than that reported for the standardflour[13] OC can be related to the adsorption of organic compounds to the surface of SC and SA, which can be linked to the porosity of the structure of SC and SA[14] The value obtained for SA (4.0302 mL/g) was higher than that of SC (2.6165 mL/g) These values are lower than those reported for Polythia longifolia[15]but higher than those for the cowpea[16]

and the white lupin[12] SW estimates the amount of water that SC and SA can absorb at a given time The value was found to be higher in SC (3.6860 mL/g) than in SA (1.9488 mL/g) This once again shows an improved hydrophobicity in SA over SC These values are lower than those reported for the coconut kernel[14]

and the cowpea[16]

3.3 Heavy metal adsorption capacity

Heavy metals have been known to enter the human body through food chain and most time cause serious harm to human health as a result of the disease they bring Exposure to polluted water is one of the key sources of this problem in developing countries[17,18] This may be caused by contamination from ma-terials with strong afﬁnity for heavy metal adsorption Use of ma-terials with low afﬁnity for heavy metal adsorption is of interest during certain industrial applications like in the case of food and cosmetic industries SC and SA were evaluated for their ability to adsorb Cu (II) and Pb (II) ions from an aqueous solution The

adsorption capacities varied with SC showing the higher adsorption capacity towards the studied metals The results obtained for the adsorption capacities of SC and SA are presented inTable 1, these are also compared with those reported previously in the literature The adsorption capacity of SC towards Cu (II) was 5.695 mg/g, while SA was unable to adsorb Cu (II) ions from the solution, probably due to the inability of the modified surface to interact with the Cu (II) ions in the solution SA may not be able to interact with Cu (II) ions because of the conversion of the hydroxyl group at its surface to the ester functional groups as a result of the modification Moreover, the ester group lacks hydrogen atoms which could have been exchanged for the Cu (II) ion like in the case of the hydrogen atom in the hydroxyl group This reduction in the metal adsorption ca-pacity of SA suggests that the modification has taken place This suggests that SA mayfind applications, where interference from Cu (II) is not required or of limited importance SC was also found to have the higher adsorption capacity for Pb (II) ion which was 20.681 mg/g while the value obtained for SA was 0.888 mg/g This also showed that SA has little attraction for Pb (II) ions The value obtained for SA was far lower than those reported in the literature Conclusion

Cellulose was isolated from SS with an estimated yield of 25%, thanks to the surface modified using the suberic acid In this case, the hydroxyl group at the surface of SC was found to be converted to the ester functional group The improved hydrophobicity was indicated by the reduced WC and SW after the modification The SA exhibited the low adsorption capacity towards Pb (II) ions, but it was unable to adsorb Cu (II) ions from an aqueous solution This suggests that SA mayfind potential applications where interference from Cu (II) is not required or of limited importance

Acknowledgments

This research was supported by TWAS-CNPq The authors are also grateful to TWAS-CNPq for awarding a postdoctoral fellowship at Universidade Federal de Minas Gerais, Minas Gerais, Brazil References

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Fig WC, OC and SW of the sesame cellulose (a) and the modiﬁed sesame cellulose (b)

Table

Comparison of the adsorption of Pb (II) and Cu (II) ions on SC and SA with other adsorbents reported in the literature

Adsorbent Pb (II) Cu (II) Reference Adansonia digitata 54.417 9.349 [19]

Goethite 109.20 37.25 [20]

Rice husks 6.69 3.25 [21]

Banana peel 89.286 5.720 [22] Bionanocomposite 224.97 169.817 [23]

Cottonﬁber 21.62 6.12 [24]

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ZnO/MMT 88.50 54.06 [28]

Chitosan-coated bentonite 13.49 12.14 [29] Modiﬁed silica 65.54 104.12 [30]

SC 20.681 5.695 Present study

SA 0.888 Nil Present study

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