O R I G I N A L P A P E R
Cellulose and microcrystalline cellulose from rice straw and banana plant waste: preparation and characterization
Maha M. Ibrahim •Waleed K. El-Zawawy• Yvonne Ju¨ttke•Andreas Koschella • Thomas Heinze
Received: 6 February 2013 / Accepted: 5 July 2013 ÓSpringer Science+Business Media Dordrecht 2013
Abstract As part of continuing efforts to prepare cellulose and microcrystalline cellulose (MCC) from renewable biomass resources, rice straw and banana plant waste were used as the available agricultural biomass wastes in Egypt. The cellulose materials were obtained in the first step from rice straw and banana plant waste after chemical treatment, mainly applying alkaline-acid or acid-alkaline pulping which was followed by hypochlorite bleaching method. The results indicate a highera-cellulose content, 66.2 %, in case of acid-alkaline treatment for rice straw compared to 64.7 % in case of alkaline-acid treatment.
A low degree of polymerization, 17, was obtained for the cellulose resulting from acid–alkaline treatment for banana plant waste indicating an oligomer and not a polymer, while it reached 178 in case of the cellulose resulting from alkaline–acid treatment for the rice straw. MCC was then obtained by enzymatic treatment of the resulting cellulose. The resulting MCC show an average diameter ranging from 7.6 to 3.6lm
compared to 25.8lm for the Avicel PH101. On the other hand, the morphological structure was investi- gated by scanning electron microscopy indicating a smooth surface for the resulting cellulose, while it indicates that the length and the diameter appeared to be affected by the duration of enzyme treatment for the preparation of MCC. Moreover, the morphological shape of the enzyme treated fibers starts to be the same as the Avicel PH101 which means different shapes of MCC can be reached by the enzyme treatment.
Furthermore, Fourier transform infrared spectroscopy was used to indicate characteristic absorption bands of the constituents and the crystallinity was evaluated by X-ray diffraction measurements and by iodine absorp- tion technique. The reported crystallinity values were between 34.8 and 82.4 %, for the resulting cellulose and MCC, and the degree of crystallinity ranged between 88.8 and 96.3 % dependent on the X-ray methods and experimental iodine absorption method.
Keywords CelluloseMicrocrystalline celluloseEnzyme treatment
Degree of polymerizationCrystallinity Abbreviations
MCC Microcrystalline cellulose DP Degree of polymerization NCC Nanocrystalline cellulose FT-IR Fourier transform infrared SEM Scanning electron microscopy XRD X-ray diffraction
M. M. Ibrahim (&)W. K. El-Zawawy National Research Center, Cellulose and Paper Department, El-Tahrir St., Dokki, Giza, Egypt e-mail: [email protected]
Y. Ju¨ttkeA. KoschellaT. Heinze
Center of Excellence for Polysaccharide Research, Institute for Organic Chemistry and Macromolecular Chemistry, Friedrich Schiller University of Jena, Humboldtstrasse 10, 07743 Jena, Germany DOI 10.1007/s10570-013-9992-5
DC Degree of crystallinity
DSC Differential scanning calorimetry
Introduction
Egypt is the largest rice producer in the Near East region. Most of the planted rice varieties arejaponica.
On the other hand, bananas are the world’s No. 4 dietary staple after rice, wheat and corn. They are known scientifically asMusa sapientum. The most cultivated banana in Egypt isMusa paradisiaca. Those cultiva- tions results in a huge amount of agricultural residues, namely rice straw and banana plant waste. The annually renewable agricultural residues represent an abundant, inexpensive, and readily available source of renewable lignocellulosic biomass, and their utilizations are attracting increased interests around the world, partic- ularly for the production of novel materials for environmentally friendly industrial utilizations after chemical modification (Azubuike et al.2011). Ligno- cellulosic resources have played a major role through- out human history. Even the earliest humans used lignocellulosic resources, such as wood, to make shelters, cook their food, construct tools, and make weapons. Lignocellulosic materials are generally sold as high volume, low performance products. A single lignocellulosic fiber is a three dimensional, hygroscopic composite composed mainly of cellulose, hemicellu- loses, and lignin with minor amounts of protein, extractives and inorganics. A variety of chemistries and processes can be applied to convert lignocellulosic materials to valuable fuels and chemicals (Huber et al.
2006; Lange2007).
In all biomass processing methods, the main technological problem is to liberate the cellulose material from the plant in a reasonable yield without large losses. This process is generally referred to as
‘‘treatment or pretreatment’’ of the biomass. The effect of the pretreatment has been described as a disruption of the cell-wall matrix including the connection between carbohydrates and lignin, as well as depoly- merizing and solubilizing hemicellulose polymers (Ramos2003).
There are several different ways of pretreating biomass, depending on the type, composition and subsequent processing technology that will be applied.
The most widely investigated pretreatment
technologies are thermochemical treatments such as dilute acid treatment (with or without rapid steam explosion) (Ballesteros et al. 2006; Chen and Liu 2007; Um et al.2003) and ammonia explosion (Kim and Lee 2006; Teymouri et al.2005). Hydrothermal pretreatment without the use of chemicals has also proven to be effective (Laser et al.2002; Negro et al.
2003).
Based on the application and type of pretreatment, the techniques have generally been divided into three distinct categories, including physical, chemical, and biological pretreatment. Chemical pretreatment is the most studied technique among these categories.
Chemical pretreatments that have been studied to date have had the primary goal of improving the biode- gradability of cellulose by removing lignin and/or hemicellulose, and also decreasing both the degree of polymerization (DP) and crystallinity of the cellulose component. Combination of two or more techniques from the same or different categories is also common (McMillan1994; Hsu1996).
As derived from cellulose, MCC and nanocrystal- line cellulose (NCC) offer many advantages such as high reactivity, renewability, biodegradability, etc.
MCC represents a novel form of cellulose and exists as a fine, white, crystalline powder. The most important characteristics of MCC are the dimensions and distribution of dimensions of the fibrillar material.
Due to its unique physical and chemical properties, MCC has been used for many years in different industries like medicine, food, coating, cosmetic, etc.
(Xiong et al.2012).
Jahan et al. (2011) have mentioned that different methods have been reported on the isolation of MCC/
NCC from lignocellulosics, where Moran et al. (2008) isolated MCC from sisal fibers by: (1) treatment with sodium chlorite, followed by NaOH; (2) acid hydro- lysis, while Alemdar and Sain (2008) isolated NCC from wheat straw and soy hull by: (1) soaking them in NaOH; (2) HCl treatment and peroxide bleaching; (3) cryocrushing. On the other hand, Wang et al. (2009) isolated MCC from jute fiber by: (1) mercerization with 12 % NaOH at room temperature for 2 h; (2) acid hydrolysis; (3) finally treated with NaOH, while Lee et al. (2009) prepared NCC from microcrystalline cellulose by: (1) acid hydrolysis in 2.5 N H2SO4; (2) followed by sonication.
Cellulose crystallinity, i.e. the relative portions of crystalline cellulose and amorphous cellulose, is an
important factor when the reactivity of cellulose chains in modification processes—or in cellulose dissolution—is considered (Virtanen et al. 2012).
The crystalline structure of cellulose has been studied for a long time (Terinte et al.2011). It is well known that crystallinity of cellulose can be measured using quite a number of methods, X-ray diffraction, solid state13C CP-MAS NMR, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy. The solid state 13C CP-MAS NMR and FT-IR spectros- copy considers contributions from both crystalline and non-crystalline cellulose regions resulting in relative values, while the alternative X-ray diffraction (XRD) approach gives more detailed data on features of crystalline and less on the non-crystalline fraction of cellulose (Terinte et al.2011).
The subject of this paper emphasizes the biomass treatment in preparation for high valued products. It primarily covers the impact of the structure of the biomass and the compositional features on the treat- ment, the action mode of different treatment methods, the treatment study status, challenges, and future research targets. Scanning electron microscopy (SEM) investigations of the effects of chemical treatment on rice straw and banana plant waste cell wall disruption, composition and surface properties were carried out in order to better understand treatment effects. The sugar- and lignin content of the samples was evalu- ated. Also, FT-IR spectroscopy was used as an analytical tool to qualitatively determine the chemical changes in the lignocellulosic material upon treat- ment. Also, the crystallinity of the cellulose and MCC samples was determined by XRD and FT-IR. The degree of crystallinity (DC) was determined by applying the iodine absorption method.
Experimental
Treatment
Alkaline-acid pulping
For pulping of rice straw and banana plant (100 g), a liquor to fiber ratio of 10:1 was chosen after a preliminary experiments and 10 % NaOH (wt/wt) related to the biomass was applied. The fibers were cooked at 170°C for 2 h. The pressure was released and the pulped fiber was washed with water till
neutrality then moisture content was determined. The pulp was remarked as RAand BAfor both rice straw and banana plant waste, respectively. The resulting pulps, RA and BA, were further applied for acid pulping, where sulfuric acid (H2SO4) was used in a percent of 5 % (wt/wt) to the pulped raw material, and liquor to fiber ratio was 10:1. The fibers were cooked at 170°C for 2 h. At the end, the pressure was released to atmosphere and the pulped fiber was washed with water till neutrality then air dried. The pulps from both treatments were marked as RACand BACwith a yield of 41.3 and 52.5 %, respectively.
Acid-alkaline pulping
On the other hand, a reverse process was carried out where acid pulping was carried out first followed by alkaline pulping. The pulping conditions were 5 % H2SO4, 10 % NaOH and liquor ratio 10:1 and the procedure was carried out as described above, where first acidic pulping of rice straw and banana plant waste (100 g), a liquor to fiber ratio of 10:1 was chosen and 5 % H2SO4 (wt/wt) related to the biomass was applied. The fibers were cooked at 170°C for 2 h. The pressure was released and the pulped fiber was washed with water till neutrality then moisture content was determined. The pulp was remarked as RCand BCfor both rice straw and banana plant waste, respectively.
The resulting pulps, RCand BC, were further applied for alkaline pulping, where sodium hydroxide (NaOH) was used in a percent of 10 % (wt/wt) to the pulped raw material, and liquor to fiber ratio was 10:1. The fibers were cooked at 170°C for 2 h. At the end, the pressure was released to atmosphere and the pulped fiber was washed with water till neutrality then air dried. The pulps from both treatments were marked as RCA and BCA with a yield of 43.6 and 48.5 %, respectively.
Bleaching
Bleaching was carried out for the treated lignocellu- losic fibers, RAC, BAC, RCA and BCA, by the hypochlorite bleaching method. The treated lignocel- lulosic fibers were bleached with sodium hypochlorite solution equivalent to 60 % of the chlorine require- ment for 2 h at 40 °C (Ibrahim and El-Zawawy2004).
The liquor to fiber ratio was 10:1 and the pH was maintained at 9 during the hypochlorite process. The
bleached cellulosic fibers, i.e. bleached RAC, BAC, RCA and BCA, were washed till neutrality, and left to dry in air. The resulting yields were 95.6, 90.8, 62.7 and 77.6 % for bleached RAC, BAC, RCA and BCA, respectively.
Preparation of MCC
The bleached fibers isolated from rice straw and banana plant waste, were subjected to enzyme treat- ment in order to produce MCC. Cellulase from Trichoderma reesei ATCC 26921 was used. The fibers were slurried in 100 mL of sodium acetate buffer at pH 4.7–5.0 with 2.0 mL of cellulase in a 100 mL conical flask at an initial sample concentra- tion of 10 % (w/v). The enzymatic treatment was carried out in a water bath shaker at 75 rpm for, 1, 1and 2 h at 50°C. At the desired time, filtration was carried out and the produced MCC was washed with hot water and then dried.
Fiber characterization
Compositional analysis of isolated cellulose and microcrystalline cellulose
The chemical composition of the isolated fibers was determined by methods shown in the following sequence: holocellulose and a-cellulose (TAPPI T257 om-85), Klason lignin (TAPPI T222 om-88) and ash content (TAPPI om-85).
Determination of the degree of polymerization (DP) The determinations of the DP, the molar mass and molar mass distribution were carried out by means of size exclusion chromatography. The cellulose samples were converted to the corresponding carbanilates in order to render them soluble in THF (Terbojevich et al.
1995).
Degree of crystallinity (DC)
The DC was measured by using the iodine absorption method (Kortschagin et al.1991). For this method, the pretreated fibers were added to iodine (5 g I2, 40 g KI, 50 mL distilled water) and Na2SO4solution and stored and stirred for several hours in darkness. The amounts of Na2S2O3solution titrated with and without fibers
were used to calculate the ‘‘DC’’ from the following equation:
DC¼10037:925
m 1Vsample
Vcontrol
ð1Þ where,m(g) as mass of the sample,Vsample(ml) and Vcontrol(ml) are the volumes Na2S2O3titrated with and without fibers. Three samples were investigated in each case.
FT-IR spectroscopy
Fourier transform infrared spectroscopy was used to evaluate the influence of different pulping methods on the product composition. The IR spectra of bleached treated rice straw and banana plant waste, i.e. bleached RAC, BAC, RCA and BCA, were recorded using a Thermo-Nicolet Model 670 Instrument (Thermo Elec- tron, Inc, Madison, WI), where the bleached samples were ground, mixed with KBr in a ratio of 1:200 mg (cellulose/KBr), and pressed under a vacuum to form pellets. The absorption was then measured over a range of 4,000–400 cm-1.
Powder X-ray diffractometry
Powder X-ray diffractometry patterns of all the cellu- losic and MCC samples were pressed to form pellets and recorded on X’Pert PRO MPD diffractometer (PANa- lytical, The Netherlands) using Ni-filtered CuKaradi- ation (30 kV and 30 mA). The diffraction intensities were measured between Bragg angles (2h) of 5–69°.
The crystallinity index (CrI) was calculated by Segal’s formula (Segal et al. 1959) using intensity measurement at 22.5° and 18.5° (amorphous back- ground) 2h:
CrI¼I0 0 2Iam
I0 0 2 ð2Þ
CrIð%Þ ¼CrI100 ð3Þ
whereI0 0 2denotes the maximum intensity of the 0 0 2 peak at about 2h =22.5° and Iam is the lowest intensity corresponding to 2hvalue near 18.5°.
Scanning electron microscopy
Scanning electron microscope (SEM) characterization of the cellulosic fiber and MCC was performed using a
JEOL JXA-840A electron microprobe analyzer (JOEL USA Inc, Peabody, MA).
The diameter of the resulting samples were measured by the morphometric analysis as descriped a previous work (Ibrahim et al. 2010a, b), where Electrophoretic mobilities of the particles in pure water were measured. Briefly, the sample suspension was prepared, and analyzed with a Zeiss EM-10 (W.
Germany) at 60 kV with a magnification of 40,000.
The morphometric analysis was performed using the Leica Qwin 500 Image Analyzer (LEICA Imaging Systems Ltd, Cambridge, England) which consists of Leica DM-LB microscope with JVC color video camera attached to a computer system Leica Q 500IW, where we start measuring the length of the nucleus (x-axis) by drawing a line starting from one edge to the other. Then we measure the width of the nucleus (y-axis) by drawing a line from one edge till the opposite by using the interactive measurement software of the system on a total magnification of (2009). We can also measure the nuclear area or diameter by choosing the suitable software. The results appear automatically on the monitor in the form of the distant measured in (lm) or area in (lm2) with the mean, SD, the minimum length and the maximum length measured.
Thermal analysis
Differential scanning calorimetry (DSC) of both bleached rice straw and banana plant waste as well as MCC resulting from both bleached rice straw and banana plant waste were carried out on SDT Q600 with samples from 15 to 20 mg in the temperature range from 30 to 700°C at a heating rate of 1°C/min in nitrogen atmosphere.
Results and discussion
Fiber composition
A pre-requisite for the conversion of lignocellulosic biomass to cellulosic products is the release of the cellulose portion from the tightly woven lignocellu- losic structure. For this, the biomass needs to be treated to make it more amenable to subsequent cellulose production. However, there is no general rule. From Table1, one can noticed that there are differences in the composition of both the rice straw and the banana plant waste. Higher holocellulose, i.e.
68.1 %, was noticed for the rice straw compared to 57.5 % for the banana plant waste, while higher lignin content, i.e. 20.3 %, was notice for the banana plant waste compared to 14.4 % for that in rice straw. Thus, the most important features of an effective treatment strategy include breaking the lignocellulosic complex and affecting the cellulose crystallinity. It can be described as a disruption of the cell-wall matrix including the connection between carbohydrates and lignin, as well as depolymerizing and solubilizing hemicelluloses.
The alkaline-acid and acid-alkaline pulping, PAC and PCA, respectively, were selected as a chemical pulping method. They were applied on both rice straw and banana plant waste. The resulting pulps were coarse and had dark-brown color. These color changes during the pulping could have resulted from the degradation of the cell wall components and extrac- tives as well as incomplete lignin removal (Ibrahim et al.2010a,b).
The chemical characterization revealed the propor- tion of each component of the fibers from agricultural residues. As seen in Table1, the main effect of the treatment on the composition of the biomass is the Table 1 Chemical analysis for unbleached treated biomasses
Treated methods Rice straw Banana plant waste
Holocellulose Lignin Ash Holocellulose Lignin Ash
(%) SEx (%) SEx (%) SEx (%) SEx (%) SEx (%) SEx
Raw material 68.1 0.629 14.6 0.645 16.3 0.854 57.5 0.645 20.3 0.238 13.6 0.725
PAC 90.8 0.478 6.1 0.314 13.3 0.788 76.8 0.712 11.9 0.420 8.7 0.506
PCA 86.8 0.478 10.32 0.522 16.9 0.420 81.2 0.271 13.8 0.898 8.4 0.627
SEx: Standard error of mean; PAC: alkaline-acid pulping with 10 % NaOH followed by 5 % H2SO4; PCA: acid-alkaline pulping with 5 % H2SO4followed by 10 % NaOH
increase in the overall holocellulose, from 68.1 and 57.5 % for rice straw and banana plant waste raw material, respectively, to 90.8 and 76.8 % after PAC treatment for both rice straw and banana plant waste, respectively, and 86.8 and 81.2 % after PCAtreatment for rice straw and banana plant waste, respectively.
Consequently, after delignification of the treated material, a decrease in the Klason lignin from 14.5 to 10.3–6.1 % for rice straw, and from 20.3 to 13.8–11.9 % for banana plant waste can be detected (Table1). The content of the Klason lignin after PAC treatment is less than that after PCAtreatment, Table1.
This can be due to the fact that alkaline treatment is basically a delignification process, in which a signif- icant amount of the lignin is dissolved and separated in the resulting black liquor, while the action mode of dilute acid is to solubilize hemicellulose and remain lignin and cellulose intact.
Further decrease of the Klason lignin was noticed after bleaching, where the lignin content reached to 2.2 % for bleached RAC and to 1.6 % for RCA, Table2. For bleached banana plant waste, the lignin content decreased to 6.15 % for BACand to 5.9 % for BCA. Thea-cellulose can be up to 66.2 % for bleached rice straw and up to 62.6 % for bleached banana plant waste, Table2. Moreover, for bleached RAC, a higher DC was reached, i.e. 96.3 %, compared to bleached RCA, while for bleached BCA, the DC was higher and reached to 92.6 % compared to the bleached BAC. This indicates that the results depend on the lignocellulosic biomass used.
On the other hand, the results in Table2showed that the DP of samples of bleached banana plant and rice straw are low and comparable to microcrystalline
cellulose (Avicel PH 101, DP 427.4). Bleached BAC was noticed to be with low DP which means that one can reach a low DP by applying a suitable treatment method.
Morphology and surface structure
Figure1shows SEM micrographs of raw banana plant waste and rice straw fibers and of bleached treated fibers. The SEM results indicate that treatment and bleaching process affects the morphological structure of the resulting samples, where from this morpholog- ical analysis, it is possible to observe the rough surface of the fibers before treatment. On the other hand, the morphology of bleached treated fibers is completely different. For bleached treated fibers from banana plant waste and rice straw a smooth surface, which corresponds to cellulose hornification, was noticed.
The bleaching treatments lead to fiber fibrillation that indicates the presence of microfibrillated cellulose.
Furthermore, the EDX graphs, Fig. 2a and b, indicate the presence of silica in both bleached rice straw and banana plant waste fibers. This correlates with the high ash content of both bleached rice straw and banana plant waste fibers (Table2).
On the other hand, Fig. 3a shows the SEM micro- graph for Avicel PH101, which indicates a fibrous structures rather than rounded powder cores. The average diameter for the Avicel PH101 particles was 25.8lm. The resulting cellulosic fibers from the agricultural residues were noticed to have smaller diameters compared to the Avicel PH101. Table2 showed that the diameter for the bleached treated rice straw ranged from 5.9 to 5.5lm for both bleached RAc
and RCA, respectively, while it showed a range of 10.8 Table 2 Chemical analysis, DC, average diameter and DPnfor bleached treated rice straw and banana plant waste
Raw material
Treatment methods
a-cellulose Lignin Ash DC Average
diameter
DPn Unbleached Bleached
(%) SEx (%) SEx (%) SEx (%) SEx (%) SEx (%) SEx (%) SEx Rice straw RAC 64.7 0.506 6.1 0.314 2.2 0.200 11.3 0.122 96.3 0.248 5.5 0.204 178 0.678
RCA 66.2 0.454 10.3 0.522 1.65 0.194 13.4 0.471 88.8 0.313 5.9 0.267 175 0.653 Banana
plant waste
BAC 60.1 0.100 11.9 0.420 6.15 0.227 6.38 0.238 88.8 0.348 10.2 0.071 17 0.408 BCA 62.6 0.356 13/8 0.898 9 0.158 3 0.122 92.6 0.216 10.8 0.141 108 0.707 SEx: Standard error of mean; RAC: rice straw treated with alkaline-acid pulping with 10 % NaOH followed by 5 % H2SO4; RCA: rice straw treated with acid-alkaline pulping with 5 % H2SO4followed by 10 % NaOH; BAC: banana plant treated with alkaline-acid pulping with 10 % NaOH followed by 5 % H2SO4; BCA: banana plant treated with acid-alkaline pulping with 5 % H2SO4followed by 10 % NaOH
to 10.2lm for the bleached treated banana plant waste.
The cellulase treatment was applied to the bleached samples in order to produce MCC. The morphology of the enzyme treated samples prepared from rice straw and banana plant waste was strongly influenced by the duration of the partial hydrolysis (Fig.3). The SEM micrographs for the cellulase treated bleached rice straw, Fig.3b–i, showed a smaller length of the produced cellulosic fibers with a smaller diameter compared to the untreated cellulosic fibers resulted from the bleached rice straw, Fig.1. After a treatment time of 2 h, the SEM micrograph indicated a shorter length of the cellulosic fibers with a smaller diameter compared to the sample isolated afterh. The length and the diameter appeared to be affected by the duration of enzyme treatment. Moreover, the mor- phological shape of the enzyme treated fibers starts to be the same as the Avicel PH101 which means that time of enzyme treatment has its effect on the shape of the resulting MCC.
Moreover, the SEM micrographs for the cellulase enzyme treated bleached banana plant waste, Fig.3j–q,
showed a shorter length of the produced cellulosic fibers with a smaller diameter compared to the untreated cellulosic fibers resulted from bleached banana plant waste, Fig. 1. Again, samples hydrolyzed for 2 h possessed a smaller length of the produced cellulosic fibers with a smaller average diameter compared to samples isolated after h. The length and the diameter of the prepared MCC appeared to be affected by the duration of enzyme treatment, Table3.
FT-IR and X-ray diffraction
Figure4a and b showed the infrared spectrum of bleached rice straw and banana plant waste. It can be seen that the peak at 1,735 cm-1, which is assigned mainly to C=O stretching vibration of the carbonyl and acetyl groups in the xylan component of hemicellulose and also typical for structural features of lignin (Ibrahim et al.2010a,b), disappeared after bleaching with sodium hypochlorite. Further absorption bands of lignin at approximately 1,595 (Agblevor et al. 2007) and, in particular, 1,510 cm-1(aromatic ring stretch) disappeared in the bleached fibers as well (Fig.4a, b).
Banana plant waste raw material Rice straw raw material
BAC RAC
BCA RCA
Fig. 1 SEM micrographs of both banana plant waste and rice straw raw materials and bleached fibers after different chemical pulping
Moreover, the band near 1,240 cm-1corresponding to axial asymmetric strain of =C–O–C, appears in a very low intensity in the bleached fibers. It is assigned to
=C–O- resulting from ether-, ester-, and phenolic groups. This band of very low intensity was detected in the spectra of the bleached fibers, Fig.4a and b, which results from a very low lignin content in the bleached fibers. Thus, the almost complete removal of lignin and hemicellulose by chemical treatment was proofed.
The other bands are well-known and specific to cellulose. We can quote as an example the large band at 3,300–3,500 cm-1related to O–H groups or the C–
H band at 2,900 cm-1(Ciolacu et al.2011). Moreover, bands at 1,431, 1,372, 1,322, 1,162, 1,059 and 896 cm-1 are typical of pure cellulose (Ibrahim et al. 2010a, b) and can be assigned in the FT-IR spectra. Generally, bands at 897 and 1,165 cm-1are assigned as C–O–C stretching vibrations of the
characteristic b-(1?4)-glycosidic linkage (Ciolacu et al.2011). On the other hand, the band at 1,337 cm-1 is assigned as the C–O–H bending at C-2 or C-3, while the band at 1,431 cm-1is assigned to the absorbance of C–O–H bending in plane at C-6 which arises by changing the environment at C-6.
Crystalline regions are formed due to hydrogen bonds between the cellulose chains and van der Waals forces between the glucose molecules (Bansal et al.
2010). Ciolacu et al. (2011) mentioned that X-ray diffraction (XRD) is used to reveal the modification in the supramolecular structure of celluloses, while FT- IR is performed to investigate the differences of crystallinity and hydrogen bond of the fiber cellulose.
Also, DSC is used to establish the dehydration heat and to estimate crystallinity. According to this XRD, FT-IR and DSC were used in our study to estimate the crystallinity of the resulting samples.
Fig. 2 EDX spectra for ableached banana plant waste fibers andbbleached rice straw fibers
The degree of crystallinity, an average property, is the fraction of the crystalline content in the sample under consideration. The XRD is the most widely used technique for determining the CrI of cellulose.
A ‘‘CrI’’ was defined in which the intensity of the 002 diffraction maximum was compared to the so- called amorphous intensity at a Bragg angle of approximately 18°. This amorphous intensity was
determined by studying the patterns of cellulose samples resulting from bleached rice straw and bleached banana plant waste, Fig.5a and b. It can be seen that the two cellulose samples exhibited different crystallinity patterns. It can be observed that the half width of the intensities at 2h =22.2°and 15.6°differs in both samples. The CrI for the cellulose resulting from bleached banana plant waste was noticed to be Fig. 3 SEM micrographs of a commercial microcrystalline
cellulose (Avicel PH 101) (9300), b–e bleached RAC after enzyme treatment for 0.5, 1.0, 1.5 and 2.0 h, respectively,f–
ibleached RCA after enzyme treatment for 0.5, 1.0, 1.5 and
2.0 h, respectively,j–mbleached BACafter enzyme treatment for 0.5, 1.0, 1.5 and 2.0 h, respectively, andn–qbleached BCA after enzyme treatment for 0.5, 1.0, 1.5 and 2.0 h, respectively
lower than that of the cellulose resulting from bleached rice straw, i.e. 34.8 and 65.0 %, respectively (Table4).
It must be emphasized that the values obtained from this index do not imply an absolute percentage of crystalline material in the specimens examined, but can merely serve to show relative differences between them.
It suffers from all the limitations discussed earlier concerning attempts to classify portions of the cellulose structure as either ‘‘crystalline’’ or ‘‘amorphous.’’ In addition, Nichols (1954) has pointed out that all the XRD techniques rest upon the assumption that equal masses of the two regions will exhibit equivalence in scattering power. However, when only relative differ- ences between or relative ranking of samples are desired, as in this work, the X-ray techniques are quite attractive, considering the ease and convenience of their
40 50 60 70 80 90 100
400 900 1400 1900 2400 2900 3400 3900
Wavelength (cm-1)
% T
80 82 84 86 88 90 92 94 96 98 100
400 900 1400 1900 2400 2900 3400 3900
Wavelength (cm-1)
% T
Bleached BAC
Bleached BCA
Bleached RCA
Bleached RAC
(a)
(b)
Fig. 4 FT-IR spectra of a bleached RAC and RCA and bbleached BACand BCA
Table 3 Average diameter for the enzyme treatment of bleached treated rice straw and banana plant waste
Treated bleached samples
Time for enzyme treatment (h)
Average diameter (lm) SEx
RAC 0.5 3.6 0.135
1.0 5.6 0.082
1.5 3.7 0.041
2.0 4.1 0.041
RCA 0.5 5.5 0.082
1.0 3.9 0.041
1.5 5.0 0.108
2.0 3.9 0.082
BAC 0.5 5.6 0.042
1.0 4.5 0.082
1.5 4.5 0.108
2.0 4.4 0.091
BCA 0.5 7.6 0.071
1.0 6.7 0.082
1.5 5.0 0.071
2.0 6.6 0.058
Table 4 CrI for bleached rice straw and banana pulp as well as MCC resulting from both bleached treated rice straw and banana plant waste
Samples CrI (%)
Bleached rice straw pulp 65.0
Bleached banana pulp waste 34.8
MCC from bleached RAC 66.7
MCC from bleached RCA 82.4
MCC from bleached BAC 60.0
MCC from bleached BCA 66.7
0 100 200 300 400 500 600 700 800 900
0 10 20 30 40 50 60 70 80
0 10 20 30 40 50 60 70 80
I (CPS)
0 100 200 300 400 500 600 700 800
I (CPS)
(a)
(b)
Fig. 5 X-ray diffractograms for a bleached rice straw and bbleached banana plant waste
operation. The method of Segal, et al. (1959) is especially attractive in view of the limited calculations involved; no measurements of areas are required.
Moreover, changes of the crystallinity of MCC resulting from the enzymatic hydrolysis were also evidenced by FT-IR spectroscopy, Fig. 6. An alter- ation of the crystalline organization leads to a significant simplification of the spectral contour through reduction in intensity or even disappearance of the bands characteristic of the crystalline domains.
The broad band in the 3,500–3,400 cm-1region, which is due to the OH-stretching vibration, gives considerable information concerning the hydrogen bonds (Ciolacu et al.2011). It was noticed for MCC prepared from bleached banana plant waste, Fig.6c and d, that the peaks characteristic of the hydrogen bonds are sharper than those for the MCC prepared from rice straw. This can give an indication of more amorphous celluloses in case of the MCC prepared from bleached banana plant waste and this can be correlated with the scission of the intra- and intermo- lecular hydrogen bonds. Also, in the case of MCC samples, the peak shifted to higher wavenumber values (Table5).
The presence of amorphous cellulose in the samples can be further confirmed by the shift of the band from 2,900 cm-1, corresponding to the C–H stretching vibration, to higher wavenumber values and by the strong decrease in the intensity of this band, as can be seen in Fig. 6.
In addition, the X-ray diffractograms proved that the MCC samples prepared from bleached banana plant waste are less crystalline compared to those prepared from bleached rice straw, Fig.7and Table4, where the CrI for the MCC prepared from bleached RAC was 66.7 % lower than those resulting from bleached RCA, 82.4 %. While for those prepared from Fig. 6 FT-IR spectra of MCC fromableached RAC,bbleached
RCA,cbleached BACanddbleached BCA
Table 5 Main FTIR absorption band assignments for cellulose (bleached samples) and MCC samples Wavenumber,
cm-1
Sample Bleached RAC
Bleached RCA
Bleached BAC
Bleached BCA
MCC RAC
MCC RCA
MCC BAC
MCC BCA
mOH 3,437 3,454 3,463 3,480 3,455 3,455 3,466 3,465
mCH 2,930 2,931 2,938 2,938 2,935 2,929 2,929 2,944
H2O absorbed 1,676 1,659 1,668 1,664 1,660 1,660 1,636 1,644
dCH2 1,444 1,451 1,458 1,448 1,457 1,452 1,468 1,468
dCH,mCOO 1,386 1,394 1,376 1,376 1,385 1,381 1,386 1,383
mC-O,dOH 1,169 1,193 1,161 1,161 1,171 1,172 1,149 1,172
mC-O 1,070 1,069 1,075 1,075 1,071 1,070 1,013 1,068
dCH2 855 866 879 879 810 808 868 905
bleached banana plant waste, the CrI was 60.0 % for MCC resulting from bleached BAC and 66.7 % for those resulting from bleached BCA.
Differential scanning calorimetry (DSC) measurements
Bertran and Dale (1986) mentioned earlier that the cellulose crystallinity can be determined by the DSC method as a ratio between the heat of dehydration of a preconditioned sample at constant relative humidity and the dehydration heat of the completely amorphous cellulose preconditioned under the same conditions.
Starting from the idea that thermal degradation is influenced by the supramolecular structure of cellulosic materials, the effect of the structural organization form of celluloses on their thermal behavior was analyzed.
The endothermic peaks characteristic of both bleached rice straw and banana plant waste, occurring in the 50–200°C region of the DSC curves, are presented in Fig.8a and b. A shift of the maximum temperature of the dehydration process to higher values may be observed with the decrease of the crystallinity degree.
Thus, in the case of bleached rice straw, the maximum temperature of the peak appears at 148°C, followed by bleached banana plant waste at 164°C.
The same effect is also noticed for the 250–400 °C region (Fig.8), which corresponds to the scission of Fig. 7 X-ray diffractograms for MCC fromableached RAC,
bbleached RCA,cbleached BACanddbleached BCA
(a)
(b)
(c)
(d)
Fig. 8 DSC curves registered in the 0–400°C temperature range forableached rice straw,bbleached banana plant waste,cMCC resulting from bleached rice straw anddMCC resulting from bleached banana plant waste
the glycosidic bonds, with laevoglucose formation (Ciolacu et al.2011). Ciolacu et al. (2011) mentioned that this behavior is explained by the fact that the thermal degradation reaction starts in the amorphous domain of the cellulosic materials by statistical degradation of cellulose. In the present case, the amorphous content increases for cellulose resulting from bleached banana plant waste to that resulting from bleached rice straw.
On the other hand, the endothermic peaks charac- teristic of both MCC resulting from bleached rice straw and bleached banana plant waste, occurring in the 50–200°C region of the DSC curves, are presented in Fig.8. The maximum temperature of the dehydra- tion process occurred at*153°C for MCC prepared from bleached rice straw compared to 148 °C for that prepared from bleached banana plant waste. For the region of 250–400°C (Fig.8c and d) the thermal degradation reaction starts at *301 °C in case of MCC prepared from bleached rice straw compared to 268 °C for that prepared from bleached banana plant waste. This case can give an indication that the amorphous content increases for MCC resulting from bleached banana plant waste to that resulting from bleached rice straw.
Conclusions
Rice straw and banana plant wastes were used for the preparation of cellulosic fibers after pretreatment with alkaline-acid pulping (PAC) and PCA followed by bleaching. Moreover, enzyme treatment was applied for the resulting cellulosic fibers in order to prepare microcrystalline cellulose. The less content of the Klason lignin after PACtreatment can be due to the fact that alkaline treatment dissolves the lignin which can be separated and results in the black liquor. Also, a low DP was noticed for the resulting cellulosic fiber from the treated banana plant waste. On the other hand, it was noticed by the SEM that both the treatment and the bleaching processes affect the morphological structure of the resulting microfibrillated cellulose.
Moreover, the enzyme treatment has also an effect of the morphological structure of the resulting MCC. In addition, the X-ray diffractograms prove that the MCC samples prepared from bleached banana plant waste are less crystalline compared to those prepared from bleached rice straw. Furthermore, from the DSC, it
was noticed that the amorphous content increases for the resulting cellulosic fibers from bleached banana plant waste compared to that resulting from bleached rice straw which can give an indication of the increase of the amorphous content for the MCC resulting from bleached banana plant waste compared to that result- ing from bleached rice straw.
Acknowledgments The authors acknowledge the Science and Technology Development Fund (STDF) (Egypt) and the International Bureau of the Federal Ministry of Education and Research (Germany) for funding the project entitled: Conversion of agriculture waste products into cellulosic products of industrial significance (ID: 624).
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