International Journal of Biological Macromolecules 67 (2014) 91–98
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Effect of Fe3 O4 on the sedimentation and structure–property relationship of starch under different pHs S. Palanikumar, P. Siva, B. Meenarathi, L. Kannammal, R. Anbarasan ∗ Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar 626 001, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 24 August 2013 Received in revised form 5 February 2014 Accepted 4 March 2014 Available online 19 March 2014 Keywords: Starch Ferrite VSM Sedimentation velocity Characterizations
a b s t r a c t The nanosized ferrite (Fe3 O4 ) was synthesized and characterized by analytical techniques such as Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). The structure–property relationship of starch was studied under three different pHs namely 3.8, 7.1 and 12.5. The starch treated under acidic condition was degraded. In a similar manner, the structure–property relationship of starch in the presence of ferrite nanoparticles at three different pHs, as mentioned above was studied. The starch/ferrite nanocomposite prepared under acidic condition showed a degraded structure. Further, the polymer/nanocomposite systems were characterized by analytical techniques such as FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vibrating sample measurement (VSM), TEM and scanning electron microscopy (SEM). Finally, the settling velocity of starch under three different pHs both in the presence and absence of Fe3 O4 was carried out to ensure the role of pH and effect of Fe3 O4 on the settling velocity of starch. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Starch is a renewable, very abundant polysaccharide, biocompatible, colorless, biodegradable and water insoluble amorphous fibrous substance and is characteristic of the source of the starch. Starch is ubiquitous, polysaccharide, naturally occurring cheapest food, biodegradable polymer worldwide and the extraction of which includes different processes such as washing, peeling, rasping, sieving, settling, pulverization and drying [1,2]. During the separation process, 5% of starch remains in the medium as slime. Quick isolation and separation of starch in the medium must be carried out otherwise degradation occurs due to the various fungal activities. The biodegradation of starch during the isolation process leads to the loss of economy as well. In order to isolate starch from aqueous medium quickly various techniques are adopted. Among which flocculation and pH adjustment are two important methodologies. The settling velocities of starch under different experimental conditions were done by Sajeev et al. [3]. In 2010, Yang and co-workers [4] reported about the neutral starch microspheres by using epichlorohydrin as a cross linker. Flocculating behavior of cationic starch derivatives was elaborately studied by Wei and research team [5]. Ultracentrifugation is also one of the
∗ Corresponding author. Tel.: +91 4549 278171. E-mail address: anbu [email protected] (R. Anbarasan). http://dx.doi.org/10.1016/j.ijbiomac.2014.03.012 0141-8130/© 2014 Elsevier B.V. All rights reserved.
methods used for the isolation of starch [6]. Starch was isolated from the source through phase separation method by using gallachtomannan [7]. Electro flocculation of cassava starch was studied by Sajeev et al. [8]. Rate of sedimentation of starch by using pectin was reported in the literature [9]. The other research team had also reported about the sedimentation of starch at different experimental conditions [10]. The above literature review indicates that starch can be settled with the aid of additives and contaminants and sometimes may be harmful to the human beings health. To avoid such an unwanted situation and at the same time to boost up the settling velocity of the starch without any harmful effect, the present investigation is made. Moreover, we know that iron is a bio-metal with high magnetic power under the influence of magnet which leads to the fast settling velocity of starch or any material which can be adhered on the surface of Fe3 O4 . Above all, we would like to introduce a new methodology for the fast settling of starch under different pHs without adding any additives and by saving time and money. By thorough literature survey we could not find any report based on the study of effect of pH on the structure–property relationship of starch. In the present investigation, for the first time, we studied the effect of pH and Fe3 O4 on the structure–property relationship of starch particularly in the sedimentation velocity. The starch and its nanocomposites have applications in various fields. Starch is a bio-food material and it should be carefully utilized for our present and future generations. The present investigation signals an advent of a new era in the naturally occurring food
92
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
material and its importance in human life, i.e. the complete isolation of starch without wastage during its extraction process from the source material. 2. Materials and methods 2.1. Materials Starch, NaOH pellet, Ferric chloride (FeCl3 ), Ferrous sulphate (FeSO4 ) and hydrochloric acid (HCl) were purchased from Reachem, India and used without any further purification. Double distilled (DD) water was used for the experimental purpose. In the present investigation only one type of starch was used for experimentation. The potato starch was purchased from Reachem, India as a readymade sample. 2.2. Synthesis of ferrite nanoparticles 30 g ferric chloride and 15 g ferrous sulphate were mixed with 200 mL of DD water and stirred for about half an hour at 45 ◦ C. The stirring was continued for another 2 h at room temperature for nucleation. Then 10 g NaOH in 20 mL of DD water was added to the mixture in drop wise manner. This resulted in the formation of a black colored precipitate and it was dried in the oven for about 6 h at 110 ◦ C. The size of the thus obtained Fe3 O4 nanoparticle was determined by using TEM technique as 10–25 nm. In the present investigation, the ferrite synthesis procedure was referred from the reported literature [11,12]. 2.3. Reaction of starch at different pHs 2 g starch was mixed with 25 mL of water and stirred for about 6 h at 45 ◦ C and then it was allowed to dry in the oven at 110 ◦ C, ground to get fine powder. In a similar way 2 g starch was mixed with 25 mL of 1 M HCl and stirred for about 6 h at 45 ◦ C, dried and the resulting sample was ground to fine powder. In the same way 2 g starch was mixed with 25 mL of 0.5 M NaOH and stirred for 6 h, dried in hot air oven at 110 ◦ C and ground to get fine powder. 2.4. Reaction of starch/ferrite nanocomposite at different pHs 2 g starch and 0.50 g ferrite nanoparticle was mixed with 25 mL of DD water and stirred for about 2 h at room temperature and then it was allowed to dry in the oven at 110 ◦ C and ground to get fine powder. In a similar way starch/ferrite nanocomposites were prepared as mentioned above at different pHs.
the secondary forces of attraction like hydrogen bonding, Vander walls forces etc. Starch exhibited a wide range of particle size while treated under acidic and alkaline pH in the absence of ferrite. In this case, the particle size analysis was carried out and their average particle size was determined by using arithmetic mean method. The other systems are not having that much wide range of particle size. According to this formula, the average particle size of starch was determined as 2642.8 nm and 2385.7 nm, respectively, for acidic and alkaline pH. The schematic diagram of sedimentation of starch under the influence of magnet is given in Fig. S1. Supplementary Figure 1 related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ijbiomac. 2014.03.012. 2.6. Characterization Fourier transform infrared (FTIR) spectrum was taken by using Shimadzu 8400 S, Japan model instrument from 4000 to 400 cm−1 by KBr pelletization method [13]. Jasco V-570 instrument was used for UV–visible spectrum measurements. 2 mg of sample was dissolved in 10 mL of water under ultrasonic irradiation for 10 min and subjected to UV–visible spectral measurements. Photoluminescence spectrum was measured with the help of PL, Jasco Model FP-6000, Japan, instrument from 300 to 700 nm. DSC and TGA were measured by using Universal V4.4A TA Instruments (simultaneous DSC and TGA analyzer) under nitrogen atmosphere at the heating rate of 10 K/min from room temperature to 373 K. X-ray diffraction (XRD, XS08, BRUKER, USA) was recorded with an advanced instrument and scanning from the 2 value of 2–60◦ at a scanning rate of 2◦ /min [14]. The surface morphology of the samples was scanned by scanning electron microscopy (SEM, JSM 6300, JEOL model) instrument [15]. The samples were lyophilized on glass slides and then coated with gold. The samples were observed under a SEM instrument. Transmission electron microscopy (TEM) was carried out by using a JEOL 2010 instrument and was operated at 200 kV. The samples were prepared after drying on carbon coated Cu grid and observed under a TEM instrument. Magnetic measurements were carried out with a superconducting quantum interference device magnetometer (Lakesore-7410-VSM, USA) with magnetic fields up to 7 T at 32 ◦ C [16]. 3. Results and discussion For the sake of convenience, the present investigation is subdivided into two parts namely: (i) characterizations of nanosized Fe3 O4 and (ii) characterizations of starch/Fe3 O4 nanocomposites at different pHs.
2.5. Determination of sedimentation velocity
3.1. Characterization of ferrite
The settling velocity of starch in the presence and absence of ferrite nanoparticle under three different pHs was determined by using the following formula [10].
The FTIR spectrum of ferrite synthesized in the present investigation is shown in Fig. 1a. The important peaks are characterized below: The spectrum showed one broad peak around 3363 cm−1 due to the OH stretching of intercalated water molecules. The OH bending vibration appeared at 1574 cm−1 . The metal-oxide stretching can be seen at 566 cm−1 with higher % transmittance and sharpness. This explains the crystalline nature of the ferrite nanoparticles [17]. The remaining peaks are associated with the carbonate stretching. Appearance of a sharp M O stretching peak confirmed the structure of ferrite. The UV–visible spectrum of ferrite is represented in Fig. 1b. It showed one broad hump around 372.5 nm due to the scattering of light by nanoparticles. Appearance of this peak confirmed the structure of ferrite [17]. The photoluminescence spectrum of ferrite is shown in Fig. 1c. One peak appeared at 381.8 nm with less intensity [18]. This confirmed the biomedical applications of ferrite particularly in the bio-imaging field.
v0 =
gds2 (s − w ) 18w
(1)
where, V0 – free falling velocity in ms−1 , g – acceleration due to gravity in ms−2 , ds – diameter of average particle size of starch was determined from SEM images and also from the particle size analysis report, s – density of starch particle in kg m−3 , w – density of water in kg m−3 , w – viscosity of water in kg m−1 s−1 . The key idea behind the present investigation is, under the influence of magnet the ferrite nanoparticles can move fast toward the force of attraction and also toward the gravitational force of attraction. During this travel process, the physisorbed polymer molecules also move toward the magnetic and gravitational forces through
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
93
Fig. 1. (a) FTIR spectrum of Fe3 O4 , (b) UV–visible spectrum of Fe3 O4 , and (c) fluorescence spectrum of Fe3 O4 .
The crystalline nature of ferrite was confirmed by XRD. It shows two peaks at 31.9◦ and 45.6◦ (Fig. 2a) corresponding to the d311 and d400 crystal planes respectively. Appearance of these two peaks confirmed the crystalline nature of ferrite (JCPDS# 19-629). Iida et al. [19] reported that appearance of more crystalline peak is an indication of the formation of both Fe3 O4 and Fe2 O3 mixture. But in the present investigation it showed peaks corresponding to the Fe3 O4 only. This proved the purity of the product obtained. Fig. 2b indicates the VSM hysteresis of ferrite. The present system exhibits the VSM value 55.3 emu/g and this value is enough to interact with starch and bring it down under the influence of both magnetic field and gravitational forces. The VSM value is associated with the size
of the ferrite nanoparticles synthesized under a given pH and the presence of a capping agent. The magnetic moment value is continuously increasing slowly up to an applied field of 15,000 even in the absence of capping agent. In 2010, Gang et al. [16] reported about the ethylenediamine functionalized ferrite nanoparticles for the removal of Cr6+ present in the waste water. In the present investigation the ferrite nanoparticles are used for the isolation of starch from the reaction medium. In such a way the applications of ferrite nanoparticle are extended in different sciences, engineering and medicine fields. The surface morphology and the size of ferrite are confirmed by recording SEM. Fig. 2c reveals the SEM image of ferrite. It shows some sphere like structure with some
Fig. 2. (a) XRD of Fe3 O4 , (b) VSM of Fe3 O4 , (c) SEM of Fe3 O4 , and (d) TEM of Fe3 O4 .
94
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
Fig. 3. FTIR spectrum of starch treated with (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
agglomeration. The size is determined as 30–45 nm. This confirms that the ferrite synthesized in the present investigation is in a typical nanosize which can be further confirmed by TEM image (Fig. 2d). The image shows a distorted sphere like shape with agglomerated structure [18]. The particle size is found to be 12–25 nm. Again the TEM confirmed the nanosize of the ferrite. It implies that the nanomaterials with smaller size have surface catalytic effect due to the increase in surface area to volume ratio. The difference in the SEM and TEM value is due to the measurement error. The manual and computer calculations are always differing from each other. The surface catalytic effect of various nanomaterials was proved in our earlier publications [20–22]. A material with higher surface area will be more active and can effectively participate in the chemical reactions particularly in redox reactions. One can expect the same surface catalytic effect in the present ferrite system also. It means that the nanosized ferrite can absorb the starch molecules on its surface through the OH group of starch. Hence the starch molecules can fast settle under the influence of magnetic force. This concept is practically tried in the present investigation and confirmed through the calculation of settling velocity. 3.2. Characterization of starch/Fe3 O4 nanocomposite 3.2.1. FTIR study Fig. 3 shows the FTIR spectrum of starch at different pHs. Fig. 3a indicates the FTIR spectrum of starch treated under acidic pH (pH 3.8). A broad peak around 3400 cm−1 is due to the O H stretching of starch. The C H symmetric and anti-symmetric stretching appears at 2918 and 2960 cm−1 respectively. A peak at 1714 cm−1 is associated with carbonyl stretching (C O). Under acidic condition there is no chance for the oxidation of secondary alcoholic group into a keto group. Under acidic pH, there is a chance for the hydrolysis of intermolecular as well as intra molecular ether linkages. The ring opening of intramolecular ether linkage leads to the formation of secondary alcoholic group with a linear chain arrangement. At the same time the ether linkage connecting the cyclic pyranose units are hydrolyzed and converted into a lower molecular weight starch. As a result of these reactions, the bending vibration of O H group was shifted to 1614 cm−1 . The intramolecular ether linkage can be seen at 1019 cm−1 with the absence of intermolecular ether linkage peak. The C H out of plane bending vibration can be seen at 809 cm−1 with reduced peak intensity. Appearance of these peaks concluded that during the acid treatment of starch there will be a formation of keto group (due to the
Fig. 4. FTIR spectrum of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
conversion of secondary alcoholic group into keto group) and also due to the hydrolysis of intramolecular ether linkage. Recently, Rodriguez et al. [23] explained the effect of acid treatment on the physico-chemical and structural characterizations of starch. Our results are co-inside with their report. Fig. 3b confirms the FTIR spectrum of starch treated at the pH of 12.5. As mentioned above, the O H, C H, O H bending, C O C ether linkage and C H out of plane bending vibrations are observed at 3431, 2954, 1676, 1009 and 799 cm−1 respectively. Apart from the above, one sharp peak is observed at 1448 cm−1 due to the C H bending vibration. This informs that under strongly alkaline pH all the OH groups of starch are converted into CO2 − Na+ like structure. This can be further confirmed by the appearance of a broad peak at 581 cm−1 , due to the metal oxide stretching. The broad peaks infer that under strong alkaline pH the alcoholic groups of starch are converted into metal alkoxides. Fig. 3c represents the FTIR spectrum of starch treated at neutral pH (pH 7.1). The above mentioned O H, C H stretching also appeared here. The bending vibration of O H can be seen at 1649 cm−1 . The C O C ether linkage appeared at 1010 cm−1 . The C H out of plane bending vibration is noted at 809 cm−1 . Fig. 4a represents the FTIR spectrum of starch/ferrite nanocomposite prepared at the pH of 3.8. Here one can observe O H, C H stretching, bending vibration of C H, C O C ester linkage, C H out of plane bending vibration, as mentioned for the simple starch system. A broad twin peak around 560 cm−1 accounts for the presence of ferrite in the starch ferrite nanocomposite system. Under strong acidic medium, the carbonyl stretching appeared clearly, it means that the added acid influenced the conversion of secondary alcoholic group into a keto group in the presence of ferrite. One can say that the added ferrite can act as a mild oxidizing agent (i.e.) in the presence of ferrite and only the conversion of alcoholic group into a keto group was favored. Fig. 4b represents the FTIR spectrum of starch ferrite nanocomposite synthesized at the pH of 12.5. Peak can be seen again. Under strong alkaline medium the oxidation of secondary alcoholic group is not favored instead it increases the nucleating behavior of ferrite formation and also it stabilizes the structure of ferrite. On thorough analysis, it is found that the carbonyl formation is strongly enhanced under acidic medium whereas the same was absent under strongly alkaline medium. Fig. 4c indicates the FTIR spectrum of starch ferrite nanocomposite synthesized at a pH of 7.2. As usual the spectrum shows O H stretching, C H stretching, bending vibration of O H group, C H bending vibration and C O C ether linkage. Apart from these peaks
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
95
Fig. 5. DSC thermogram of starch treated at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
550 cm−1
a twin peak appeared around confirms the presence of ferrite in the starch ferrite nanocomposite system. A small hump at 1726 cm−1 declares the presence of carbonyl group in starch. The pristine starch does not have any carbonyl stretching. Appearance of such a carbonyl might be associated with the oxidizing nature of the nano-ferrite, i.e. the secondary alcoholic group of starch is converted into a keto group by the influence of nano-ferrite in an aqueous medium. Conversion occurs in an aqueous medium too but in the acidic medium due to the degradation of ferrite structure, FeCl3 may be reappeared. FeCl3 is a well known oxidizing agent and hence the alcoholic group could be converted into a keto group. In the case of alkaline pH, due to the strong nucleation process such an effect was prohibited by the added NaOH. 3.2.2. DSC analysis Fig. 5a denotes the DSC thermogram of starch treated under acidic pH. The thermogram shows one broad peak at 68.8 ◦ C corresponding to the melting temperature of starch. Fig. 5b illustrates the DSC thermogram of starch treated under alkaline pH. The thermogram shows one broad endothermic peak at 102.3 ◦ C due to the melting of starch. Fig. 5c indicates the DSC thermogram of starch treated in an aqueous medium with the melting temperature of 89.2 ◦ C. The broadening of the melting behavior is ascribed to the widening of the molecular weight of starch. On comparison, the starch treated under alkaline condition exhibited higher melting temperature. This can be explained on the basis of conversion of alcoholic group into O− Na+ group. Fig. 6a represents the DSC thermogram of starch/ferrite nanocomposite system treated under strongly acidic pH. The thermogram shows one endothermic melting peak at 67.44 ◦ C. Fig. 6b exhibits the Tm of starch at 68.8 ◦ C for the starch/ferrite under alkaline medium. Fig. 6c shows the Tm of starch/ferrite nanocomposite system at 92.4 ◦ C treated under neutral pH (pH 7). In overall comparison, the starch/ferrite nanocomposite synthesized under neutral pH exhibits higher melting temperature. This can be explained by two factors: (i) under neutral pH the added ferrite can form hydrogen bonding to the free OH group of starch and (ii) due to the influence of added ferrite, the secondary alcoholic group of starch was converted into a keto group. Due to these two coupled effects starch exhibits higher melting temperature at neutral pH. Under acidic condition even though the hydrogen bonding is favored, the intramolecular ether linkage was hydrolyzed and led to the reduction in molecular weight of starch. Investigation on change in molecular weight of starch is going on in our lab. Moreover, under strongly acidic pH the structure of ferrite has degraded. As a result of degradation in the structure of ferrite, starch-ferrite nanocomposite system exhibited lower Tm . In the
Fig. 6. DSC thermogram of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
case of alkaline pH, all the OH groups were converted into O− Na+ form and hence reduction in intermolecular hydrogen bonding. The Tm of raw horn starch is 150 ◦ C (due to gelatinization effect). Moreover, the added NaOH nucleated the ferrite structure and hence the Tm showed a lower value when compared to the Tm of starch treated under neutral pH. In 2009, Liu et al. [24] studied the DSC of starch film at different heating rates. In the present investigation, the nanocomposite prepared under acidic condition exhibits higher thermal property. Our results coincide with their investigations. 3.2.3. TGA history Fig. 7a shows the TGA thermogram of acid treated starch. The thermogram exhibits a two step degradation process. The first minor weight loss step up to 180 ◦ C is due to the removal of moisture, physisorbed and chemisorbed water molecules. The second major weight loss step is associated with the backbone degradation. At 600 ◦ C it shows 32% weight residue remained. Fig. 7b exhibits the alkaline treated starch with three step degradation process. As usual, up to 200 ◦ C the weight loss is ascribed to the removal of water molecules. The second weight loss is due to the cleavage of ether linkages in starch backbone. The third weight loss is corresponding to the degradation of starch backbone slowly. At 600 ◦ C it shows 44% weight residue remained. The thermogram of starch treated under neutral pH is represented in Fig. 7c. The three step degradation process is explained below: The weight loss
Fig. 7. TGA of starch treated at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
96
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
steps at 100, 228 and 367 ◦ C are corresponding to the removal of water molecules, as a condensed product of OH groups and the degradation of ether linkages respectively. At 600 ◦ C it Exhibits 12% weight residue remained. On comparison, the alkaline treated starch exhibited lower structural degradation temperature but with higher % weight residue remained at 600 ◦ C. Currently, Piyada and co-workers [25] explained the TGA of starch nanocrystals with two step degradation processes with approximately 10% weight residue remained. The thermal degradation of starch treated under neutral pH is co-inside with the report of Piyada et al. [25]. Fig. 8 represents the TGA thermogram of starch/Fe3 O4 nanocomposite synthesized under acidic pH (Fig. 8a), alkaline pH (Fig. 8b) and neutral pH (Fig. 8c) media. Starch treated under alkaline pH showed three step degradation processes, due to the removal of water molecules, breaking of structure with simultaneous degradation of ether linkages of starch. At 500 ◦ C they showed 47, 47 and 38% weight residue remained for acid, alkaline and neutral pH treated starch respectively. On comparison, the starch/Fe3 O4 nanocomposite system synthesized under alkaline pH exhibits lower thermal stability. In over all comparison, one can say that starch in the presence of ferrite exhibits lower initial degradation temperature but with high % weight residue remained at higher temperature. Again the structure of ferrite depends on the pH of the reaction medium, because under highly acidic medium, the structure of ferrite is degraded and hence it loses the magnetic attraction behavior of ferrite. As a result of degraded structure of ferrite, the thermal, optical and mechanical properties of starch will be varied. In the present investigation, the main concentration was on the
Fig. 8. TGA of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
thermal property and morphological behavior of starch under different pHs both in the presence and absence of ferrite nanoparticles. In 1998, Hulleman and research team [26] explained the role of water during the plasticization of native starches. This proves that the structure of starch is not only affected by the processing temperature, nanomaterial and pH but also altered by the water molecules. Now, our research team is analyzing the effect of water molecules on the
Fig. 9. SEM morphology of starch (a–c) and starch/Fe3 O4 nanocomposite (d–f) treated at (a and d) pH 3.8, (b and e) pH 12.5, and (c and f) pH 7.1.
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
97
Fig. 10. Settling behavior of starch under (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
structure–property relationship of starch in the presence of ferrite nanoparticles. This will provide us the information about the role of nanoparticle in the presence of various amounts of water molecules. 3.2.4. SEM report Fig. 9 indicates the surface morphology of starch treated under different pHs. Fig. 9a denotes the surface morphology of starch treated under acidic condition. The size of the starch granules varies from 500 to 2000 nm. Fig. 9b exhibits the SEM morphology of starch treated under alkaline pH. Starch granules with different sizes and different shapes were observed. The size was varied from 200 to 1000 nm. When compared to starch granules under acidic pH, the present system exhibits smaller size starch granules due to the formation of O− Na+ like structure. Fig. 9c confirms the SEM morphology of starch treated at neutral pH. The size of the starch granules is determined as 8–25 m with different shapes. This is too big when compared to either two systems. Fig. 9d denotes the surface morphology of starch/ferrite nanocomposite system synthesized under acidic condition. Here the term nanocomposite is introduced due to the presence of 10–20 nm sized Fe3 O4 (Fig. 2d). The combination of macro sized starch with the nanosized ferrite explained the definition of the term nanocomposite. The morphology exhibits a coarser like structure with the size of 1–10 m and with agglomerated structure. This is due to the structural degradation of ferrite under highly acidic pH. Fig. 9e represents the surface morphology of starch/ferrite nanocomposite system synthesized under alkaline pH. Here one can see the broken stone like morphology with the size of 1–20 m. Fig. 9f declares the surface morphology of starch/ferrite nanocomposite system synthesized under neutral pH. The particle size varies between 1 and 20 m. Here also one can see both the agglomerated and non-agglomerated structure. The non-agglomerated sphere like particles may be associated with ferrite, whereas the agglomerated white color is associated with the starch granules. In overall comparison, starch/ferrite nanocomposite synthesized under neutral pH exhibited the non-agglomerated structure with the smallest size of starch. In general, it is noted that under acidic pH, the structure of ferrite was degraded whereas under alkaline pH the increase in pH was very much useful for the nucleation of ferrite nanoparticles. Due to these two distinct effects the size of the starch was altered. Under neutral pH there will be a simple mixing of starch and nanosized ferrite. 3.2.5. Settling velocity study of starch/Fe3 O4 nanocomposite Fig. 10 indicates the plots of time against the settling height of starch under different pHs. Fig. 10a represents the settling behavior
Fig. 11. Settling behavior of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
of starch under acidic medium. The plot declares that within 15 min the settling of starch is completed with the height of 0.5 cm. Fig. 10b shows the settling of starch under alkaline medium. For the complete settling of starch the system availed approximately 60 min with the settling height of 0.49 cm. Fig. 10c reveals the settling behavior of starch under neutral pH. Again one can see that starch consumed approximately 60 min for its settling with the height of 0.58 cm. The acidic pH treated starch settled with the settling velocity of 2.01 × 10−9 m/s whereas the starch studied under alkaline and neutral pH exhibited the settling velocity of 1.447 × 10−9 m/s and 1.347 × 10−5 m/s respectively. Under neutral condition, the starch settled very fast but somewhat lower settling height. The settling velocity of starch treated under different pHs was varied. This is due to the alteration in the structure of starch. The structure of starch was largely altered under the influence of both acidic and alkaline pH. Hence, the SEM image exhibited the starch with different sizes and shapes. In this situation the particle size of starch was determined from the particle size analysis report (figure is not included) by arithmetic mean method. The particle size of starch at different places in the SEM image was calculated and their average particle size was determined by using the arithmetic mean method. In comparison, starch treated under neutral pH exhibited the highest settling velocity. Fig. 11 represents the settling behavior of starch at different pHs in the presence of ferrite nanoparticle. Fig. 11a–c indicates the settling behavior of starch under acidic, alkaline and neutral pH respectively. On comparison, the acid treated starch settles with the maximum height of 0.41 cm whereas the alkaline pH treated starch settles with the height of 0.20 cm. The starch under neutral pH settles with the height of 0.30 cm. The acid treated starch exhibits the maximum settling height whereas the starch treated under alkaline pH exhibits the lowest settling height. This can be explained as follows: (i) under acidic condition, due to hydrolysis reaction, the starch settles in the presence of acid degraded ferrite nanoparticles. The settled starch/ferrite particle system is closely watched and it is observed that the precipitate is loosely bound. Due to the lack of compression, the settled height increases. Under alkaline condition, the OH groups of starch were converted into metal oxide linkage with the breaking of inter as well as intra molecular hydrogen bonding. Under alkaline condition, the ferrite nanoparticles are highly nucleated with the increase of magnetic attraction power. As a result the starch material settled down. On closely watching the precipitated material, the column height was tightly bound together. Hence the close packing materials increases abnormally under alkaline pH. Due to this reason the settling height
98
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
is reduced with the increase of close packing of starch materials. The sedimentation behavior of starch under neutral condition is normal. In overall comparison, the settling behavior of starch under acidic pH abnormally increases. The settling behavior of starch under alkaline pH in the presence of ferrite exhibits the fast settling process. In the presence of ferrite, the settling behavior of starch raises by ten times [3]. The settling behavior of starch under alkaline pH in the presence of ferrite leads to more close packing of starch materials. This can be further supported by determining the sedimentation velocity. The sedimentation velocity of starch under acidic, alkaline and neutral pH in the presence of ferrite is 1.144 × 10−5 m/s, 8.27 × 10−5 m/s and 1.149 × 10−5 m/s respectively. In over all comparison, the starch settled very fast under alkaline pH in the presence of ferrite. Pure ferrite has high magnetic attraction power under the influence of a magnet. This key idea is used in the present investigation. When the ferrite nanoparticles come down under the influence of a magnetic force, due to the secondary forces of attraction like hydrogen bonding, the added ferrite interacts with the OH group of starch and brings it down very fast, due to the gravitational attraction force. As a result, the starch granules settle fast in the presence of ferrite at any given pH. During the sedimentation process of starch, surface catalytic effect of ferrite nanoparticle plays a vital role and leads to the alteration in the structure of starch. This is similar to that of our earlier publication [20–22]. 4. Conclusions The structure–property relationship of starch treated under different pHs was studied and the important points are presented here as conclusion. Ferrite synthesized in the present investigation has the size of 10–25 nm. The XRD of ferrite confirmed the presence of d311 and d400 crystal planes. Starch treated under acidic condition exhibits the functionality of carbonyl stretching. The magnetic moment value confirmed the settling behavior of starch under the influence of magnetic force. The starch ferrite nanocomposite synthesized under alkaline pH did not show any carbonyl stretching. The starch treated under alkaline pH exhibited the higher melting temperature. The melting temperature of starch ferrite nanocomposite synthesized at neutral pH exhibited a highest Tm . Starch treated under acidic condition exhibited coarser like structure. Starch settled very fast in the neutral pH condition with the settling velocity of 1.348 × 10−5 m/s. The starch/ferrite system exhibited the highest settling velocity of 8.27 × 10−5 m/s under alkaline condition due to the nucleation of ferrite and simultaneous conversion of OH group into O− Na+ like structure of starch. Due to the gravitational forces of attraction, ferrite nanoparticles were going down
very fast under the influence of a magnet and as a result of secondary forces of attraction between the added ferrite and starch, the starch granules settled very fast. Due to the very smaller in size (10–25 nm) of ferrite the surface catalytic effect will also be very high toward the settling of starch. By using the present technology one can completely isolate the starch from the reaction medium. This leads to the effective utilization of natural resources without wastage. The present investigation also infers that during the isolation of starch from the medium, the structural degradation at different pHs is restricted by the nanosized ferrite. Acknowledgement Mrs. G. Vijayalakshmi, Assistant Professor, Department of English is gratefully acknowledged for her valuable help during this manuscript preparation. References [1] P. Manivasagam, P. Sivasankar, T. Venkatesan, K. Senthilkumar, K. Sivakumar, S.K. Kim, Int. J. Biol. Macromol. 52 (2013) 29–38. [2] K.G. Battacharya, S.S. Gupta, Sep. Purif. Technol. 50 (2006) 388–397. [3] M.S. Sajeev, R. Kaliappan, K. Thangavel, Biosyst. Eng. 83 (2002) 327–337. [4] Y. Yang, X. Wei, J. Wang, Molecules 15 (2010) 2872–2885. [5] Y. Wei, F. Cheng, H. Zheng, Carbohydr. Poly. 74 (2008) 673–679. [6] M. Majzoobi, A.J. Rove, S.E. Hill, Carbohydr. Poly. 52 (2003) 269–274. [7] C.B. Closs, B.C. Pefit, I.D. Roberts, F. Eschor, Carbohydr. Poly. 39 (1999) 67– 77. [8] M.S. Sajeev, R. Kaliappan, J. Roof, J. Roof Crops 34 (2008) 148–156. [9] N.P. Dzogbefia, G.A. Ofosu, J.H. Oldham, Sci. Res. Essays 3 (2008) 365–369. [10] M.S. Sajeev, S.N. Moorthy, R. Kaliappan, V.S. Rani, Starch 55 (2003) 213–221. [11] J. Wang, J. You, Z. Li, P. Yang, Nanoscale Res. Lett. 3 (2008) 338–342. [12] S.X. Wang, Y. Zhou, W. Guan, B. Ding, Nanoscale Res. Lett. 3 (2008) 289–294. [13] H.H. Chen, R. Anbarasan, L.S. Kuo, P.H. Chen, J. Mater. Sci. 46 (2011) 1796–1805. [14] R. Anbarasan, P. Arvind, V. Dhanalakshmi, J. Appl. Polym. Sci. 121 (2011) 563–573. [15] R. Anbarasan, C.A. Peng, J. Appl. Polym. Sci. 124 (2012) 3996–4006. [16] Z.Y. Gang, S.H. Yu, P.S. Dong, H.M. Qin, J. Hazard. Mater. 182 (2010) 295–302. [17] S. Ahmad, U. Riaz, A. Kaushik, J. Alam, J. Inorg. Organomet. Polym. 19 (2009) 355–360. [18] S. Thomas, D. Sakthikumar, Y. Yoshida, R. Anantharaman, J. Nanopart. Res. 10 (2008) 203–206. [19] H. Iida, K. Takayanagi, T. Nakanishi, T. Osaka, J. Colloid Interface Sci. 314 (2007) 274–280. [20] S. Gandhi, R. Harihara Subramani, A. Sivabalan, R. Anbarasan, J. Mater. Sci. 45 (2010) 1688–1694. [21] S. Gandhi, N. Nagalakshmi, V. Dhanalakshmi, R. Anbarasan, J. Appl. Polym. Sci. 1118 (2010) 1666–1674. [22] M.F. Parveen, V. Dhanalakshmi, R. Anbarasan, Nano 4 (2009) 147–156. [23] H.M.P. Rodriguez, E.A. Acevedo, G.M. Montealvo, L. Perez, Starch 64 (2012) 115–125. [24] P. Liu, L. Yu, L. Chen, L. Li, Carbohydr. Poly. 77 (2009) 250–253. [25] K. Piyada, S. Waranyou, W. Thawien, Int. Food Res. J. 20 (2013) 439–449. [26] H.D. Hulleman, H.P. Janssen, H. Feil, Polymer 39 (1998) 2043–2048.
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Effect of Fe3 O4 on the sedimentation and structure–property relationship of starch under different pHs S. Palanikumar, P. Siva, B. Meenarathi, L. Kannammal, R. Anbarasan ∗ Department of Polymer Technology, Kamaraj College of Engineering and Technology, Virudhunagar 626 001, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 24 August 2013 Received in revised form 5 February 2014 Accepted 4 March 2014 Available online 19 March 2014 Keywords: Starch Ferrite VSM Sedimentation velocity Characterizations
a b s t r a c t The nanosized ferrite (Fe3 O4 ) was synthesized and characterized by analytical techniques such as Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). The structure–property relationship of starch was studied under three different pHs namely 3.8, 7.1 and 12.5. The starch treated under acidic condition was degraded. In a similar manner, the structure–property relationship of starch in the presence of ferrite nanoparticles at three different pHs, as mentioned above was studied. The starch/ferrite nanocomposite prepared under acidic condition showed a degraded structure. Further, the polymer/nanocomposite systems were characterized by analytical techniques such as FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vibrating sample measurement (VSM), TEM and scanning electron microscopy (SEM). Finally, the settling velocity of starch under three different pHs both in the presence and absence of Fe3 O4 was carried out to ensure the role of pH and effect of Fe3 O4 on the settling velocity of starch. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Starch is a renewable, very abundant polysaccharide, biocompatible, colorless, biodegradable and water insoluble amorphous fibrous substance and is characteristic of the source of the starch. Starch is ubiquitous, polysaccharide, naturally occurring cheapest food, biodegradable polymer worldwide and the extraction of which includes different processes such as washing, peeling, rasping, sieving, settling, pulverization and drying [1,2]. During the separation process, 5% of starch remains in the medium as slime. Quick isolation and separation of starch in the medium must be carried out otherwise degradation occurs due to the various fungal activities. The biodegradation of starch during the isolation process leads to the loss of economy as well. In order to isolate starch from aqueous medium quickly various techniques are adopted. Among which flocculation and pH adjustment are two important methodologies. The settling velocities of starch under different experimental conditions were done by Sajeev et al. [3]. In 2010, Yang and co-workers [4] reported about the neutral starch microspheres by using epichlorohydrin as a cross linker. Flocculating behavior of cationic starch derivatives was elaborately studied by Wei and research team [5]. Ultracentrifugation is also one of the
∗ Corresponding author. Tel.: +91 4549 278171. E-mail address: anbu [email protected] (R. Anbarasan). http://dx.doi.org/10.1016/j.ijbiomac.2014.03.012 0141-8130/© 2014 Elsevier B.V. All rights reserved.
methods used for the isolation of starch [6]. Starch was isolated from the source through phase separation method by using gallachtomannan [7]. Electro flocculation of cassava starch was studied by Sajeev et al. [8]. Rate of sedimentation of starch by using pectin was reported in the literature [9]. The other research team had also reported about the sedimentation of starch at different experimental conditions [10]. The above literature review indicates that starch can be settled with the aid of additives and contaminants and sometimes may be harmful to the human beings health. To avoid such an unwanted situation and at the same time to boost up the settling velocity of the starch without any harmful effect, the present investigation is made. Moreover, we know that iron is a bio-metal with high magnetic power under the influence of magnet which leads to the fast settling velocity of starch or any material which can be adhered on the surface of Fe3 O4 . Above all, we would like to introduce a new methodology for the fast settling of starch under different pHs without adding any additives and by saving time and money. By thorough literature survey we could not find any report based on the study of effect of pH on the structure–property relationship of starch. In the present investigation, for the first time, we studied the effect of pH and Fe3 O4 on the structure–property relationship of starch particularly in the sedimentation velocity. The starch and its nanocomposites have applications in various fields. Starch is a bio-food material and it should be carefully utilized for our present and future generations. The present investigation signals an advent of a new era in the naturally occurring food
92
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
material and its importance in human life, i.e. the complete isolation of starch without wastage during its extraction process from the source material. 2. Materials and methods 2.1. Materials Starch, NaOH pellet, Ferric chloride (FeCl3 ), Ferrous sulphate (FeSO4 ) and hydrochloric acid (HCl) were purchased from Reachem, India and used without any further purification. Double distilled (DD) water was used for the experimental purpose. In the present investigation only one type of starch was used for experimentation. The potato starch was purchased from Reachem, India as a readymade sample. 2.2. Synthesis of ferrite nanoparticles 30 g ferric chloride and 15 g ferrous sulphate were mixed with 200 mL of DD water and stirred for about half an hour at 45 ◦ C. The stirring was continued for another 2 h at room temperature for nucleation. Then 10 g NaOH in 20 mL of DD water was added to the mixture in drop wise manner. This resulted in the formation of a black colored precipitate and it was dried in the oven for about 6 h at 110 ◦ C. The size of the thus obtained Fe3 O4 nanoparticle was determined by using TEM technique as 10–25 nm. In the present investigation, the ferrite synthesis procedure was referred from the reported literature [11,12]. 2.3. Reaction of starch at different pHs 2 g starch was mixed with 25 mL of water and stirred for about 6 h at 45 ◦ C and then it was allowed to dry in the oven at 110 ◦ C, ground to get fine powder. In a similar way 2 g starch was mixed with 25 mL of 1 M HCl and stirred for about 6 h at 45 ◦ C, dried and the resulting sample was ground to fine powder. In the same way 2 g starch was mixed with 25 mL of 0.5 M NaOH and stirred for 6 h, dried in hot air oven at 110 ◦ C and ground to get fine powder. 2.4. Reaction of starch/ferrite nanocomposite at different pHs 2 g starch and 0.50 g ferrite nanoparticle was mixed with 25 mL of DD water and stirred for about 2 h at room temperature and then it was allowed to dry in the oven at 110 ◦ C and ground to get fine powder. In a similar way starch/ferrite nanocomposites were prepared as mentioned above at different pHs.
the secondary forces of attraction like hydrogen bonding, Vander walls forces etc. Starch exhibited a wide range of particle size while treated under acidic and alkaline pH in the absence of ferrite. In this case, the particle size analysis was carried out and their average particle size was determined by using arithmetic mean method. The other systems are not having that much wide range of particle size. According to this formula, the average particle size of starch was determined as 2642.8 nm and 2385.7 nm, respectively, for acidic and alkaline pH. The schematic diagram of sedimentation of starch under the influence of magnet is given in Fig. S1. Supplementary Figure 1 related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ijbiomac. 2014.03.012. 2.6. Characterization Fourier transform infrared (FTIR) spectrum was taken by using Shimadzu 8400 S, Japan model instrument from 4000 to 400 cm−1 by KBr pelletization method [13]. Jasco V-570 instrument was used for UV–visible spectrum measurements. 2 mg of sample was dissolved in 10 mL of water under ultrasonic irradiation for 10 min and subjected to UV–visible spectral measurements. Photoluminescence spectrum was measured with the help of PL, Jasco Model FP-6000, Japan, instrument from 300 to 700 nm. DSC and TGA were measured by using Universal V4.4A TA Instruments (simultaneous DSC and TGA analyzer) under nitrogen atmosphere at the heating rate of 10 K/min from room temperature to 373 K. X-ray diffraction (XRD, XS08, BRUKER, USA) was recorded with an advanced instrument and scanning from the 2 value of 2–60◦ at a scanning rate of 2◦ /min [14]. The surface morphology of the samples was scanned by scanning electron microscopy (SEM, JSM 6300, JEOL model) instrument [15]. The samples were lyophilized on glass slides and then coated with gold. The samples were observed under a SEM instrument. Transmission electron microscopy (TEM) was carried out by using a JEOL 2010 instrument and was operated at 200 kV. The samples were prepared after drying on carbon coated Cu grid and observed under a TEM instrument. Magnetic measurements were carried out with a superconducting quantum interference device magnetometer (Lakesore-7410-VSM, USA) with magnetic fields up to 7 T at 32 ◦ C [16]. 3. Results and discussion For the sake of convenience, the present investigation is subdivided into two parts namely: (i) characterizations of nanosized Fe3 O4 and (ii) characterizations of starch/Fe3 O4 nanocomposites at different pHs.
2.5. Determination of sedimentation velocity
3.1. Characterization of ferrite
The settling velocity of starch in the presence and absence of ferrite nanoparticle under three different pHs was determined by using the following formula [10].
The FTIR spectrum of ferrite synthesized in the present investigation is shown in Fig. 1a. The important peaks are characterized below: The spectrum showed one broad peak around 3363 cm−1 due to the OH stretching of intercalated water molecules. The OH bending vibration appeared at 1574 cm−1 . The metal-oxide stretching can be seen at 566 cm−1 with higher % transmittance and sharpness. This explains the crystalline nature of the ferrite nanoparticles [17]. The remaining peaks are associated with the carbonate stretching. Appearance of a sharp M O stretching peak confirmed the structure of ferrite. The UV–visible spectrum of ferrite is represented in Fig. 1b. It showed one broad hump around 372.5 nm due to the scattering of light by nanoparticles. Appearance of this peak confirmed the structure of ferrite [17]. The photoluminescence spectrum of ferrite is shown in Fig. 1c. One peak appeared at 381.8 nm with less intensity [18]. This confirmed the biomedical applications of ferrite particularly in the bio-imaging field.
v0 =
gds2 (s − w ) 18w
(1)
where, V0 – free falling velocity in ms−1 , g – acceleration due to gravity in ms−2 , ds – diameter of average particle size of starch was determined from SEM images and also from the particle size analysis report, s – density of starch particle in kg m−3 , w – density of water in kg m−3 , w – viscosity of water in kg m−1 s−1 . The key idea behind the present investigation is, under the influence of magnet the ferrite nanoparticles can move fast toward the force of attraction and also toward the gravitational force of attraction. During this travel process, the physisorbed polymer molecules also move toward the magnetic and gravitational forces through
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
93
Fig. 1. (a) FTIR spectrum of Fe3 O4 , (b) UV–visible spectrum of Fe3 O4 , and (c) fluorescence spectrum of Fe3 O4 .
The crystalline nature of ferrite was confirmed by XRD. It shows two peaks at 31.9◦ and 45.6◦ (Fig. 2a) corresponding to the d311 and d400 crystal planes respectively. Appearance of these two peaks confirmed the crystalline nature of ferrite (JCPDS# 19-629). Iida et al. [19] reported that appearance of more crystalline peak is an indication of the formation of both Fe3 O4 and Fe2 O3 mixture. But in the present investigation it showed peaks corresponding to the Fe3 O4 only. This proved the purity of the product obtained. Fig. 2b indicates the VSM hysteresis of ferrite. The present system exhibits the VSM value 55.3 emu/g and this value is enough to interact with starch and bring it down under the influence of both magnetic field and gravitational forces. The VSM value is associated with the size
of the ferrite nanoparticles synthesized under a given pH and the presence of a capping agent. The magnetic moment value is continuously increasing slowly up to an applied field of 15,000 even in the absence of capping agent. In 2010, Gang et al. [16] reported about the ethylenediamine functionalized ferrite nanoparticles for the removal of Cr6+ present in the waste water. In the present investigation the ferrite nanoparticles are used for the isolation of starch from the reaction medium. In such a way the applications of ferrite nanoparticle are extended in different sciences, engineering and medicine fields. The surface morphology and the size of ferrite are confirmed by recording SEM. Fig. 2c reveals the SEM image of ferrite. It shows some sphere like structure with some
Fig. 2. (a) XRD of Fe3 O4 , (b) VSM of Fe3 O4 , (c) SEM of Fe3 O4 , and (d) TEM of Fe3 O4 .
94
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
Fig. 3. FTIR spectrum of starch treated with (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
agglomeration. The size is determined as 30–45 nm. This confirms that the ferrite synthesized in the present investigation is in a typical nanosize which can be further confirmed by TEM image (Fig. 2d). The image shows a distorted sphere like shape with agglomerated structure [18]. The particle size is found to be 12–25 nm. Again the TEM confirmed the nanosize of the ferrite. It implies that the nanomaterials with smaller size have surface catalytic effect due to the increase in surface area to volume ratio. The difference in the SEM and TEM value is due to the measurement error. The manual and computer calculations are always differing from each other. The surface catalytic effect of various nanomaterials was proved in our earlier publications [20–22]. A material with higher surface area will be more active and can effectively participate in the chemical reactions particularly in redox reactions. One can expect the same surface catalytic effect in the present ferrite system also. It means that the nanosized ferrite can absorb the starch molecules on its surface through the OH group of starch. Hence the starch molecules can fast settle under the influence of magnetic force. This concept is practically tried in the present investigation and confirmed through the calculation of settling velocity. 3.2. Characterization of starch/Fe3 O4 nanocomposite 3.2.1. FTIR study Fig. 3 shows the FTIR spectrum of starch at different pHs. Fig. 3a indicates the FTIR spectrum of starch treated under acidic pH (pH 3.8). A broad peak around 3400 cm−1 is due to the O H stretching of starch. The C H symmetric and anti-symmetric stretching appears at 2918 and 2960 cm−1 respectively. A peak at 1714 cm−1 is associated with carbonyl stretching (C O). Under acidic condition there is no chance for the oxidation of secondary alcoholic group into a keto group. Under acidic pH, there is a chance for the hydrolysis of intermolecular as well as intra molecular ether linkages. The ring opening of intramolecular ether linkage leads to the formation of secondary alcoholic group with a linear chain arrangement. At the same time the ether linkage connecting the cyclic pyranose units are hydrolyzed and converted into a lower molecular weight starch. As a result of these reactions, the bending vibration of O H group was shifted to 1614 cm−1 . The intramolecular ether linkage can be seen at 1019 cm−1 with the absence of intermolecular ether linkage peak. The C H out of plane bending vibration can be seen at 809 cm−1 with reduced peak intensity. Appearance of these peaks concluded that during the acid treatment of starch there will be a formation of keto group (due to the
Fig. 4. FTIR spectrum of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
conversion of secondary alcoholic group into keto group) and also due to the hydrolysis of intramolecular ether linkage. Recently, Rodriguez et al. [23] explained the effect of acid treatment on the physico-chemical and structural characterizations of starch. Our results are co-inside with their report. Fig. 3b confirms the FTIR spectrum of starch treated at the pH of 12.5. As mentioned above, the O H, C H, O H bending, C O C ether linkage and C H out of plane bending vibrations are observed at 3431, 2954, 1676, 1009 and 799 cm−1 respectively. Apart from the above, one sharp peak is observed at 1448 cm−1 due to the C H bending vibration. This informs that under strongly alkaline pH all the OH groups of starch are converted into CO2 − Na+ like structure. This can be further confirmed by the appearance of a broad peak at 581 cm−1 , due to the metal oxide stretching. The broad peaks infer that under strong alkaline pH the alcoholic groups of starch are converted into metal alkoxides. Fig. 3c represents the FTIR spectrum of starch treated at neutral pH (pH 7.1). The above mentioned O H, C H stretching also appeared here. The bending vibration of O H can be seen at 1649 cm−1 . The C O C ether linkage appeared at 1010 cm−1 . The C H out of plane bending vibration is noted at 809 cm−1 . Fig. 4a represents the FTIR spectrum of starch/ferrite nanocomposite prepared at the pH of 3.8. Here one can observe O H, C H stretching, bending vibration of C H, C O C ester linkage, C H out of plane bending vibration, as mentioned for the simple starch system. A broad twin peak around 560 cm−1 accounts for the presence of ferrite in the starch ferrite nanocomposite system. Under strong acidic medium, the carbonyl stretching appeared clearly, it means that the added acid influenced the conversion of secondary alcoholic group into a keto group in the presence of ferrite. One can say that the added ferrite can act as a mild oxidizing agent (i.e.) in the presence of ferrite and only the conversion of alcoholic group into a keto group was favored. Fig. 4b represents the FTIR spectrum of starch ferrite nanocomposite synthesized at the pH of 12.5. Peak can be seen again. Under strong alkaline medium the oxidation of secondary alcoholic group is not favored instead it increases the nucleating behavior of ferrite formation and also it stabilizes the structure of ferrite. On thorough analysis, it is found that the carbonyl formation is strongly enhanced under acidic medium whereas the same was absent under strongly alkaline medium. Fig. 4c indicates the FTIR spectrum of starch ferrite nanocomposite synthesized at a pH of 7.2. As usual the spectrum shows O H stretching, C H stretching, bending vibration of O H group, C H bending vibration and C O C ether linkage. Apart from these peaks
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
95
Fig. 5. DSC thermogram of starch treated at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
550 cm−1
a twin peak appeared around confirms the presence of ferrite in the starch ferrite nanocomposite system. A small hump at 1726 cm−1 declares the presence of carbonyl group in starch. The pristine starch does not have any carbonyl stretching. Appearance of such a carbonyl might be associated with the oxidizing nature of the nano-ferrite, i.e. the secondary alcoholic group of starch is converted into a keto group by the influence of nano-ferrite in an aqueous medium. Conversion occurs in an aqueous medium too but in the acidic medium due to the degradation of ferrite structure, FeCl3 may be reappeared. FeCl3 is a well known oxidizing agent and hence the alcoholic group could be converted into a keto group. In the case of alkaline pH, due to the strong nucleation process such an effect was prohibited by the added NaOH. 3.2.2. DSC analysis Fig. 5a denotes the DSC thermogram of starch treated under acidic pH. The thermogram shows one broad peak at 68.8 ◦ C corresponding to the melting temperature of starch. Fig. 5b illustrates the DSC thermogram of starch treated under alkaline pH. The thermogram shows one broad endothermic peak at 102.3 ◦ C due to the melting of starch. Fig. 5c indicates the DSC thermogram of starch treated in an aqueous medium with the melting temperature of 89.2 ◦ C. The broadening of the melting behavior is ascribed to the widening of the molecular weight of starch. On comparison, the starch treated under alkaline condition exhibited higher melting temperature. This can be explained on the basis of conversion of alcoholic group into O− Na+ group. Fig. 6a represents the DSC thermogram of starch/ferrite nanocomposite system treated under strongly acidic pH. The thermogram shows one endothermic melting peak at 67.44 ◦ C. Fig. 6b exhibits the Tm of starch at 68.8 ◦ C for the starch/ferrite under alkaline medium. Fig. 6c shows the Tm of starch/ferrite nanocomposite system at 92.4 ◦ C treated under neutral pH (pH 7). In overall comparison, the starch/ferrite nanocomposite synthesized under neutral pH exhibits higher melting temperature. This can be explained by two factors: (i) under neutral pH the added ferrite can form hydrogen bonding to the free OH group of starch and (ii) due to the influence of added ferrite, the secondary alcoholic group of starch was converted into a keto group. Due to these two coupled effects starch exhibits higher melting temperature at neutral pH. Under acidic condition even though the hydrogen bonding is favored, the intramolecular ether linkage was hydrolyzed and led to the reduction in molecular weight of starch. Investigation on change in molecular weight of starch is going on in our lab. Moreover, under strongly acidic pH the structure of ferrite has degraded. As a result of degradation in the structure of ferrite, starch-ferrite nanocomposite system exhibited lower Tm . In the
Fig. 6. DSC thermogram of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
case of alkaline pH, all the OH groups were converted into O− Na+ form and hence reduction in intermolecular hydrogen bonding. The Tm of raw horn starch is 150 ◦ C (due to gelatinization effect). Moreover, the added NaOH nucleated the ferrite structure and hence the Tm showed a lower value when compared to the Tm of starch treated under neutral pH. In 2009, Liu et al. [24] studied the DSC of starch film at different heating rates. In the present investigation, the nanocomposite prepared under acidic condition exhibits higher thermal property. Our results coincide with their investigations. 3.2.3. TGA history Fig. 7a shows the TGA thermogram of acid treated starch. The thermogram exhibits a two step degradation process. The first minor weight loss step up to 180 ◦ C is due to the removal of moisture, physisorbed and chemisorbed water molecules. The second major weight loss step is associated with the backbone degradation. At 600 ◦ C it shows 32% weight residue remained. Fig. 7b exhibits the alkaline treated starch with three step degradation process. As usual, up to 200 ◦ C the weight loss is ascribed to the removal of water molecules. The second weight loss is due to the cleavage of ether linkages in starch backbone. The third weight loss is corresponding to the degradation of starch backbone slowly. At 600 ◦ C it shows 44% weight residue remained. The thermogram of starch treated under neutral pH is represented in Fig. 7c. The three step degradation process is explained below: The weight loss
Fig. 7. TGA of starch treated at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
96
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
steps at 100, 228 and 367 ◦ C are corresponding to the removal of water molecules, as a condensed product of OH groups and the degradation of ether linkages respectively. At 600 ◦ C it Exhibits 12% weight residue remained. On comparison, the alkaline treated starch exhibited lower structural degradation temperature but with higher % weight residue remained at 600 ◦ C. Currently, Piyada and co-workers [25] explained the TGA of starch nanocrystals with two step degradation processes with approximately 10% weight residue remained. The thermal degradation of starch treated under neutral pH is co-inside with the report of Piyada et al. [25]. Fig. 8 represents the TGA thermogram of starch/Fe3 O4 nanocomposite synthesized under acidic pH (Fig. 8a), alkaline pH (Fig. 8b) and neutral pH (Fig. 8c) media. Starch treated under alkaline pH showed three step degradation processes, due to the removal of water molecules, breaking of structure with simultaneous degradation of ether linkages of starch. At 500 ◦ C they showed 47, 47 and 38% weight residue remained for acid, alkaline and neutral pH treated starch respectively. On comparison, the starch/Fe3 O4 nanocomposite system synthesized under alkaline pH exhibits lower thermal stability. In over all comparison, one can say that starch in the presence of ferrite exhibits lower initial degradation temperature but with high % weight residue remained at higher temperature. Again the structure of ferrite depends on the pH of the reaction medium, because under highly acidic medium, the structure of ferrite is degraded and hence it loses the magnetic attraction behavior of ferrite. As a result of degraded structure of ferrite, the thermal, optical and mechanical properties of starch will be varied. In the present investigation, the main concentration was on the
Fig. 8. TGA of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
thermal property and morphological behavior of starch under different pHs both in the presence and absence of ferrite nanoparticles. In 1998, Hulleman and research team [26] explained the role of water during the plasticization of native starches. This proves that the structure of starch is not only affected by the processing temperature, nanomaterial and pH but also altered by the water molecules. Now, our research team is analyzing the effect of water molecules on the
Fig. 9. SEM morphology of starch (a–c) and starch/Fe3 O4 nanocomposite (d–f) treated at (a and d) pH 3.8, (b and e) pH 12.5, and (c and f) pH 7.1.
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
97
Fig. 10. Settling behavior of starch under (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
structure–property relationship of starch in the presence of ferrite nanoparticles. This will provide us the information about the role of nanoparticle in the presence of various amounts of water molecules. 3.2.4. SEM report Fig. 9 indicates the surface morphology of starch treated under different pHs. Fig. 9a denotes the surface morphology of starch treated under acidic condition. The size of the starch granules varies from 500 to 2000 nm. Fig. 9b exhibits the SEM morphology of starch treated under alkaline pH. Starch granules with different sizes and different shapes were observed. The size was varied from 200 to 1000 nm. When compared to starch granules under acidic pH, the present system exhibits smaller size starch granules due to the formation of O− Na+ like structure. Fig. 9c confirms the SEM morphology of starch treated at neutral pH. The size of the starch granules is determined as 8–25 m with different shapes. This is too big when compared to either two systems. Fig. 9d denotes the surface morphology of starch/ferrite nanocomposite system synthesized under acidic condition. Here the term nanocomposite is introduced due to the presence of 10–20 nm sized Fe3 O4 (Fig. 2d). The combination of macro sized starch with the nanosized ferrite explained the definition of the term nanocomposite. The morphology exhibits a coarser like structure with the size of 1–10 m and with agglomerated structure. This is due to the structural degradation of ferrite under highly acidic pH. Fig. 9e represents the surface morphology of starch/ferrite nanocomposite system synthesized under alkaline pH. Here one can see the broken stone like morphology with the size of 1–20 m. Fig. 9f declares the surface morphology of starch/ferrite nanocomposite system synthesized under neutral pH. The particle size varies between 1 and 20 m. Here also one can see both the agglomerated and non-agglomerated structure. The non-agglomerated sphere like particles may be associated with ferrite, whereas the agglomerated white color is associated with the starch granules. In overall comparison, starch/ferrite nanocomposite synthesized under neutral pH exhibited the non-agglomerated structure with the smallest size of starch. In general, it is noted that under acidic pH, the structure of ferrite was degraded whereas under alkaline pH the increase in pH was very much useful for the nucleation of ferrite nanoparticles. Due to these two distinct effects the size of the starch was altered. Under neutral pH there will be a simple mixing of starch and nanosized ferrite. 3.2.5. Settling velocity study of starch/Fe3 O4 nanocomposite Fig. 10 indicates the plots of time against the settling height of starch under different pHs. Fig. 10a represents the settling behavior
Fig. 11. Settling behavior of starch/Fe3 O4 nanocomposite synthesized at (a) pH 3.8, (b) pH 12.5, and (c) pH 7.1.
of starch under acidic medium. The plot declares that within 15 min the settling of starch is completed with the height of 0.5 cm. Fig. 10b shows the settling of starch under alkaline medium. For the complete settling of starch the system availed approximately 60 min with the settling height of 0.49 cm. Fig. 10c reveals the settling behavior of starch under neutral pH. Again one can see that starch consumed approximately 60 min for its settling with the height of 0.58 cm. The acidic pH treated starch settled with the settling velocity of 2.01 × 10−9 m/s whereas the starch studied under alkaline and neutral pH exhibited the settling velocity of 1.447 × 10−9 m/s and 1.347 × 10−5 m/s respectively. Under neutral condition, the starch settled very fast but somewhat lower settling height. The settling velocity of starch treated under different pHs was varied. This is due to the alteration in the structure of starch. The structure of starch was largely altered under the influence of both acidic and alkaline pH. Hence, the SEM image exhibited the starch with different sizes and shapes. In this situation the particle size of starch was determined from the particle size analysis report (figure is not included) by arithmetic mean method. The particle size of starch at different places in the SEM image was calculated and their average particle size was determined by using the arithmetic mean method. In comparison, starch treated under neutral pH exhibited the highest settling velocity. Fig. 11 represents the settling behavior of starch at different pHs in the presence of ferrite nanoparticle. Fig. 11a–c indicates the settling behavior of starch under acidic, alkaline and neutral pH respectively. On comparison, the acid treated starch settles with the maximum height of 0.41 cm whereas the alkaline pH treated starch settles with the height of 0.20 cm. The starch under neutral pH settles with the height of 0.30 cm. The acid treated starch exhibits the maximum settling height whereas the starch treated under alkaline pH exhibits the lowest settling height. This can be explained as follows: (i) under acidic condition, due to hydrolysis reaction, the starch settles in the presence of acid degraded ferrite nanoparticles. The settled starch/ferrite particle system is closely watched and it is observed that the precipitate is loosely bound. Due to the lack of compression, the settled height increases. Under alkaline condition, the OH groups of starch were converted into metal oxide linkage with the breaking of inter as well as intra molecular hydrogen bonding. Under alkaline condition, the ferrite nanoparticles are highly nucleated with the increase of magnetic attraction power. As a result the starch material settled down. On closely watching the precipitated material, the column height was tightly bound together. Hence the close packing materials increases abnormally under alkaline pH. Due to this reason the settling height
98
S. Palanikumar et al. / International Journal of Biological Macromolecules 67 (2014) 91–98
is reduced with the increase of close packing of starch materials. The sedimentation behavior of starch under neutral condition is normal. In overall comparison, the settling behavior of starch under acidic pH abnormally increases. The settling behavior of starch under alkaline pH in the presence of ferrite exhibits the fast settling process. In the presence of ferrite, the settling behavior of starch raises by ten times [3]. The settling behavior of starch under alkaline pH in the presence of ferrite leads to more close packing of starch materials. This can be further supported by determining the sedimentation velocity. The sedimentation velocity of starch under acidic, alkaline and neutral pH in the presence of ferrite is 1.144 × 10−5 m/s, 8.27 × 10−5 m/s and 1.149 × 10−5 m/s respectively. In over all comparison, the starch settled very fast under alkaline pH in the presence of ferrite. Pure ferrite has high magnetic attraction power under the influence of a magnet. This key idea is used in the present investigation. When the ferrite nanoparticles come down under the influence of a magnetic force, due to the secondary forces of attraction like hydrogen bonding, the added ferrite interacts with the OH group of starch and brings it down very fast, due to the gravitational attraction force. As a result, the starch granules settle fast in the presence of ferrite at any given pH. During the sedimentation process of starch, surface catalytic effect of ferrite nanoparticle plays a vital role and leads to the alteration in the structure of starch. This is similar to that of our earlier publication [20–22]. 4. Conclusions The structure–property relationship of starch treated under different pHs was studied and the important points are presented here as conclusion. Ferrite synthesized in the present investigation has the size of 10–25 nm. The XRD of ferrite confirmed the presence of d311 and d400 crystal planes. Starch treated under acidic condition exhibits the functionality of carbonyl stretching. The magnetic moment value confirmed the settling behavior of starch under the influence of magnetic force. The starch ferrite nanocomposite synthesized under alkaline pH did not show any carbonyl stretching. The starch treated under alkaline pH exhibited the higher melting temperature. The melting temperature of starch ferrite nanocomposite synthesized at neutral pH exhibited a highest Tm . Starch treated under acidic condition exhibited coarser like structure. Starch settled very fast in the neutral pH condition with the settling velocity of 1.348 × 10−5 m/s. The starch/ferrite system exhibited the highest settling velocity of 8.27 × 10−5 m/s under alkaline condition due to the nucleation of ferrite and simultaneous conversion of OH group into O− Na+ like structure of starch. Due to the gravitational forces of attraction, ferrite nanoparticles were going down
very fast under the influence of a magnet and as a result of secondary forces of attraction between the added ferrite and starch, the starch granules settled very fast. Due to the very smaller in size (10–25 nm) of ferrite the surface catalytic effect will also be very high toward the settling of starch. By using the present technology one can completely isolate the starch from the reaction medium. This leads to the effective utilization of natural resources without wastage. The present investigation also infers that during the isolation of starch from the medium, the structural degradation at different pHs is restricted by the nanosized ferrite. Acknowledgement Mrs. G. Vijayalakshmi, Assistant Professor, Department of English is gratefully acknowledged for her valuable help during this manuscript preparation. References [1] P. Manivasagam, P. Sivasankar, T. Venkatesan, K. Senthilkumar, K. Sivakumar, S.K. Kim, Int. J. Biol. Macromol. 52 (2013) 29–38. [2] K.G. Battacharya, S.S. Gupta, Sep. Purif. Technol. 50 (2006) 388–397. [3] M.S. Sajeev, R. Kaliappan, K. Thangavel, Biosyst. Eng. 83 (2002) 327–337. [4] Y. Yang, X. Wei, J. Wang, Molecules 15 (2010) 2872–2885. [5] Y. Wei, F. Cheng, H. Zheng, Carbohydr. Poly. 74 (2008) 673–679. [6] M. Majzoobi, A.J. Rove, S.E. Hill, Carbohydr. Poly. 52 (2003) 269–274. [7] C.B. Closs, B.C. Pefit, I.D. Roberts, F. Eschor, Carbohydr. Poly. 39 (1999) 67– 77. [8] M.S. Sajeev, R. Kaliappan, J. Roof, J. Roof Crops 34 (2008) 148–156. [9] N.P. Dzogbefia, G.A. Ofosu, J.H. Oldham, Sci. Res. Essays 3 (2008) 365–369. [10] M.S. Sajeev, S.N. Moorthy, R. Kaliappan, V.S. Rani, Starch 55 (2003) 213–221. [11] J. Wang, J. You, Z. Li, P. Yang, Nanoscale Res. Lett. 3 (2008) 338–342. [12] S.X. Wang, Y. Zhou, W. Guan, B. Ding, Nanoscale Res. Lett. 3 (2008) 289–294. [13] H.H. Chen, R. Anbarasan, L.S. Kuo, P.H. Chen, J. Mater. Sci. 46 (2011) 1796–1805. [14] R. Anbarasan, P. Arvind, V. Dhanalakshmi, J. Appl. Polym. Sci. 121 (2011) 563–573. [15] R. Anbarasan, C.A. Peng, J. Appl. Polym. Sci. 124 (2012) 3996–4006. [16] Z.Y. Gang, S.H. Yu, P.S. Dong, H.M. Qin, J. Hazard. Mater. 182 (2010) 295–302. [17] S. Ahmad, U. Riaz, A. Kaushik, J. Alam, J. Inorg. Organomet. Polym. 19 (2009) 355–360. [18] S. Thomas, D. Sakthikumar, Y. Yoshida, R. Anantharaman, J. Nanopart. Res. 10 (2008) 203–206. [19] H. Iida, K. Takayanagi, T. Nakanishi, T. Osaka, J. Colloid Interface Sci. 314 (2007) 274–280. [20] S. Gandhi, R. Harihara Subramani, A. Sivabalan, R. Anbarasan, J. Mater. Sci. 45 (2010) 1688–1694. [21] S. Gandhi, N. Nagalakshmi, V. Dhanalakshmi, R. Anbarasan, J. Appl. Polym. Sci. 1118 (2010) 1666–1674. [22] M.F. Parveen, V. Dhanalakshmi, R. Anbarasan, Nano 4 (2009) 147–156. [23] H.M.P. Rodriguez, E.A. Acevedo, G.M. Montealvo, L. Perez, Starch 64 (2012) 115–125. [24] P. Liu, L. Yu, L. Chen, L. Li, Carbohydr. Poly. 77 (2009) 250–253. [25] K. Piyada, S. Waranyou, W. Thawien, Int. Food Res. J. 20 (2013) 439–449. [26] H.D. Hulleman, H.P. Janssen, H. Feil, Polymer 39 (1998) 2043–2048.
![[The effect of phospholipids on starch metabolism].](/assets/img/hold.png)
