Published online: 05 Nov 2012.

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1 This article was downloaded by: [Pamukkale Universitesi] On: 07 April 2014, At: 06:28 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK The Journal of The Textile Institute Publication details, including instructions for authors and subscription information: Effects of enzymatic treatments on the mechanical properties of corn husk fibers Nazire Deniz Yılmaz a a Department of Textile Engineering, Pamukkale University, Denizli, Turkey Published online: 05 Nov To cite this article: Nazire Deniz Yılmaz (2013) Effects of enzymatic treatments on the mechanical properties of corn husk fibers, The Journal of The Textile Institute, 104:4, , DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 The Journal of The Textile Institute, 2013 Vol. 104, No. 4, , Effects of enzymatic treatments on the mechanical properties of corn husk fibers Nazire Deniz Yılmaz* Department of Textile Engineering, Pamukkale University, Denizli, Turkey (Received 4 August 2012; final version received 1 October 2012) Corn husk fibers were extracted by water retting, alkalization, and enzymatic processes at different concentration and duration levels. The effects of extraction process parameters on the mechanical and thermal properties and chemical characteristics of corn husk fibers were investigated. Chemical structures of the fibers were studied by IR measurements. The finest and the stiffest fibers were produced by water retting followed by an enzymatic treatment. The highest breaking strength and breaking tenacity were obtained by water-retted fibers. While resulting in loss of breaking tenacity and elongation in water-retted fibers, enzymatic treatment resulted in increase in initial moduli and breaking tenacity of alkalized fibers. No significant effect of enzymatic treatment duration was obtained on the mechanical properties of corn husk fibers. Alkalized fibers gave higher elongation and lower stiffness compared to water-retted ones. The IR spectra showed higher amount of lignin and hemicellulose in water-retted fibers compared to alkalized and enzyme-treated ones. Enzymatic treatment and alkalization enhanced the thermal durability of the fibers. The ranges for properties of the produced corn husk fibers can be summarized as a linear density tex, initial modulus cn/tex, breaking tenacity cn/tex, and elongation %. Keywords: corn husk; fibers; enzymes; mechanical properties; water retting Introduction For the last two decades, lignocellulosic fibers have started to be considered as alternatives to conventional man-made fibers in the academic as well as commercial arena, for a number of areas including transportation, construction, and packaging applications. Some species of plants such as hemp, flax, kenaf, jute, and sisal, which have been utilized as fiber sources since historical times, once again has become the focus of research attention (Kannan, 2012; Nam & Netravali, 2006; Panthapulakkal, Law, & Sain, 2006; Thilagavathi, Pradeep, Kannaian, & Sasikala, 2010; Vigneswaran & Jayapriya, 2010; Wang, Xu, Cai, & Yu, 2010; Yılmaz, Powell, Banks-Lee, & Michielsen, 2012). Nevertheless, agricultural plants have solely been utilized as food source. Most recently, the possibility of making use of agricultural by-products have gained interest. Some of these agricultural by-products are rice and wheat straws; corn and rice husks; corn, okra, cotton, and reed stalk fibers; banana bunch; and pineapple leaf fibers (Arifuzzaman Khan et al., 2009; Ashori & Nourbakhsh, 2009; Huda & Yang, 2008; Panthapulakkal et al., 2007; Thilagavathi et al., 2010; Tutuş, Ezici, & Ateş, 2010). Utilization of these byproducts would benefit rural development providing additional value to the agricultural activities, the environment by saving the field leftovers from burning, which is unfortunately a common practice, and the growing world population by preserving the land for the production of edible plant species (Arifuzzaman Khan et al., 2009; Huda, 2008). Lignocellulosic agro-based materials mostly show a composite structure. This composite structure is constituted by an organic matrix which is reinforced by bundles of cellulose microfibers. The organic matrix is mainly composed of lignin, hemicelluloses, pectin, waxes, and proteins (El Oudiani, Chaabouni, Msahli, & Sakli, 2012; Reddy & Yang, 2005; Yılmaz et al., 2012). Several procedures have been reported to extract fibers from agro-based by-products. Water extraction, alkalization, and enzymatic treatments may be given as examples to these processes. During these processes, noncellulosic parts are removed from the plant and cellulosic fibers are exposed (El Oudiani et al., 2012; Reddy & Yang, 2005). Among agricultural by-products, very limited amount of research efforts have been devoted to investigate extraction of fibers from corn husks (Huda, 2008; Reddy, Salam, & Yang, 2007; Reddy & Yang, * ndyilmaz@pau.edu.tr Copyright Ó 2013 The Textile Institute

3 The Journal of The Textile Institute ; Yılmaz, 2013). This situation is interesting considering the abundance of corn husks as a fiber supply. Global grain production more than tripled in the past five decades, whereas corn production quadrupled in the same period to give an all-time high 868 million tons for the year Moreover, the increase observed in corn production, especially in the last decade, is greater than that of wheat and rice. Corn is the most commonly produced grain in the world surpassing wheat and rice (Larsen, 2012), and it is grown in wide regions of the world (Reddy & Yang, 2005). These facts evidence that corn shows promise as a fiber supply to provide in large amounts of corn husk fiber with availability and sustainability in most of the world. Corn husk fiber is a lignocellulosic fiber which contains about 80 87% cellulose. The remainder of the fiber is constituted by hemicelluloses, lignin, pectin, waxes, and proteins. Corn husk fiber is, in fact, a fiber bundle where individual fibers are bound by hemicelluloses, lignin, and pectin (Reddy & Yang, 2005). Academic literature related to corn husk fibers is limited to a few studies. Among few studies devoted to fiber extraction from corn husks, Reddy and Yang (2005) extracted fibers from corn husks via alkalization treatment at 20 g/l NaOH for 60 min at 95 C. The alkalization treatment was followed by an enzymatic treatment with 5% pulpzyme and cellulase at 50 C for 60 min. The textile characteristics and morphological and physical structure of the fibers were investigated. The researchers reported good pliability, moderate strength, high elongation, and high moisture regain properties for the fibers. Reddy et al. (2007) investigated the effects of lignin content of corn husk fibers on the fibers breaking tenacity, breaking elongation, and yellowness of samples due to heat and light exposure. They reported delignification of corn husk fibers to provide higher resistance to heat and light. Yılmaz (2013) extracted fibers from corn husk by alkalization at concentrations varying from 2.5 to 10 g/l and durations from 30 to 120 min at boiling temperature. She reported the highest tensile performance to be obtained from alkalization concentration range of 5 10 g/l and duration range of min. Fibers which were produced by alkalization treatments with higher temperature and concentration levels had lower moisture content than that of fibers produced by milder alkalization treatments. The author attributed this situation to the decrease in the number of OH groups in the fibers during alkalization treatment. The author was not able to find any information about the water retting of corn husk fibers in the academic literature, although trials with some other crop-based materials have already been reported by a number of researchers (Arifuzzaman Khan et al., 2009; El Oudiani et al., 2012). Furthermore, no information on the effects of different enzymatic treatments on the characteristics of corn husk fibers could be obtained from the research literature. This study has been carried out in order to fill these gaps in the literature. In this study, corn husk fibers were extracted by water retting and alkalization processes at different levels of alkali concentration and duration which were followed by enzymatic treatments. The effects of extraction process parameters on the mechanical and thermal properties of corn husk fibers were investigated. The chemical structures of the fibers were studied by IR measurements. The color measurements of corn husk fibers were taken by using a spectrophotometer. Materials and methods Materials Corn husks were collected from a local farmer s market in Denizli Province of Turkey. Fresh and young husk leaves with lighter green color were subjected to fiber extraction treatment. To decrease variation in fiber characteristics, darker green color mature leaves were not included in the analysis. Corn husks were used in undried form. Cellulase and xylanase enzymes, with commercial names of Celluclast 1.5 L and Pentopan Mono BG, respectively, were supplied by Novozymes A/S, Denmark. Pentopan Mono BG is a purified endo-β (1 4)- xylanase from Thermomyces lanuginosus produced by submerged fermentation of a genetically modified Aspergillus oryzae micro-organism (Sigma-Aldrich, 2012a). It acts as a catalyst in the endohydrolysis of 1,4-β-D-xylosidic linkages (Sigma-Aldrich, 2012b). Xylanases break the covalent bond between lignin and cellulose and cause depolymerization of hemicelluloses in the corn husks (Reddy & Yang, 2005). Pentopan was selected as the xylanase, as no studies were reported to investigate the use of that particular enzyme in corn husk fiber extraction. Celluclast 1.5 L is a cellulase which is produced by submerged fermentation of a selected strain of the Trichoderma reesei fungus. It acts as a catalyst in the breakdown of cellulose into glucose, cellobiose, and higher glucose polymers (Sigma-Aldrich, 2012c). Cellulase was used to remove the short fibers from the bunch. Sample preparation Corn husks were subjected to water retting or alkalization treatment succeeded by enzymatic treatments following different routes given in Table 1. Water retting was carried out at room temperature (avg. 20 C)

4 398 N.D. Yılmaz Table 1. Routes of fiber extraction treatments from corn husks. Route Water retting NaOH concentration (g/l) Alkalization duration (min) for around 60 days in a 2 l beaker with tap water. The beaker was not covered with a lid. The amount of water was determined to ensure that all husks were submerged in water. The water was changed occasionally to avoid fungi or mildew growth. When most of the fibers split off from of the husks, the water retting was ended and the fibers were rinsed several times with tap water to be cleaned from extra fibrous materials. The alkalization treatment was carried out at boiling temperature at 1:20 liquor ratio in distilled water under various concentrations of NaOH (2.5, 5, 7.5, and 10 g/ l) and durations (30, 60, 90, and 120 min). The alkalization was followed by rinsing five times in tap water and neutralizing with 10% acetic acid solution and rinsed again until ph 7 is reached. The fibers obtained after water retting or alkalization reactions were dried under ambient conditions before undergoing enzymatic treatments. The enzymatic treatments were carried out in beakers at 50 C with a liquor ratio of 1:50 in distilled water. Enzyme concentrations, shown in Table 1, were calculated based on the percentage ratio of enzyme mass to the fiber mass. As the fibers had already been exposed in alkalization or water retting processes, no other mechanical work was needed to separate the fibers. All enzymatic treatments were carried out concurrently to avoid any effects of uncontrollable variables. For each route, a batch containing a minimum of 100 fibers was treated. The fibers were left to dry under ambient conditions after being rinsed following the enzymatic treatments. As this is one of the very few studies on corn husk fiber extracting, the characteristics of fibers obtained by various methods are compared. With the particular Cellulase concentration (%) Xylanase concentration (%) Enzymatic treatment duration (min) set of routes, it would be possible to detect and compare the effects of different methods with varying concentrations of alkali and enzymes at various durations. In the light of the findings, further research can be carried out with more depth into the subject by systemically changing the parameters while selecting only one treatment method combination. Characterization Linear density, mechanical and thermal properties, and IR spectra of the extracted fibers were obtained. The samples were subjected to conditioning at 21 C and 65% relative humidity for at least 24 h prior to fiber characterization processes. The linear density of corn husk fibers were determined according to ASTM D Standard Test Methods for Linear Density of Textile Fibers (American Society for Testing and Materials [ASTM], 2007a). The fiber lengths were measured using a ruler to the mm scale and the weight was measured to the 0.1 mg accuracy. The averages of at least 13 fibers for each batch were measured. Fiber initial modulus, breaking strength, breaking tenacity, and elongation at break were measured according to ASTM D 3822 Standard Test Method for Single Textile Fibers (ASTM, 2007b). At least, 20 specimens of each fiber set were measured at a crosshead speed of 155 mm/min. The gage length was set at 2.54 cm. A 10 N load cell was used. The measurement device was Tinius Olsen H10KT (R) Tester with QMat for Textiles (R) software. Obtained results of linear density and mechanical properties were subjected to analysis of variance testing at α: 0.05 significance level.

5 The Journal of The Textile Institute 399 The IR spectra of the extracted fibers were recorded with a Shimadzu IR-470 (Shimadzu Corporation, Kyoto, Japan) spectrophotometer using KBr pellet technique. A mixture of 5.0 mg ground fibers and 20.0 mg of KBr were pressed into a disk for IR measurement. The IR spectra were obtained for three different samples with different treatment routes. Thermogravimetric analyses were carried out simultaneously in a Shimadzu DTG-60H (Shimadzu Corporation, Kyoto, Japan) Thermal Analyzer in flowing nitrogen atmosphere (100 ml/min). Highly sintered Al 2 O 3 was used as the reference material. The ground samples were scanned from 25 to 600 C at a heating rate of 10 C per minute. The thermogravimetric analyses were carried out for three different samples with different treatment routes. A Datacolor spectrophotometer with a D 65/10 o observer was used to measure Stensby whiteness indices of corn husk fibers. At least, seven replications were taken from each sample and the average was reported. The Stensby whiteness index is determined according to Equation (1). WI (Stensby) ¼ L þ 3a 3b; (1) where L represents lightness of the observed color, a the position of the color between red/magenta and green, and b its position between yellow and blue (TAPPI, 2007). Results and discussion Linear density Linear density values of treated corn husk fibers are given in Figure 1, in tex (grams per kilometer) units. The coefficient of variation in the percentages of the produced fibers ranges between 19 and 52%. Treatments had significant effect on linear density of corn husk fibers (p value ) when all samples are tested through analysis of variance. The finest fibers were obtained by enzymatically treated Figure 1. The effect of treatments on linear density (tex) of corn husk fibers. Table 2. Linear density of corn husk fibers before and after enzymatic treatments. Linear density a (tex) Linear density b (tex) Treatment # Mean σ Mean σ CV c (%) p value 1 N/A N/A N/A Notes: a Linear density before enzymatic treatment; b linear density after enzymatic treatment; c coefficient of variance values after enzymatic treatment; σ, standard deviation; and n = 13.

6 400 N.D. Yılmaz water-retted fiber #15 with 17.0 tex and the coarsest fibers were #3 with 25.6 tex. Table 2 shows the linear densities of corn husk fibers before and after enzymatic treatments. The effect of enzymatic treatment on the fibers was tested by analysis of variance and the obtained statistical significance is presented with p values in the table. As can be seen from the table, enzymatic treatment resulted in a decrease of fiber linear density for alkalized fibers. This effect is more pronounced for fibers extracted with milder conditions of alkalization. This finding might hint that alkali and the enzymes affect similar sites that are present on the lignocellulosic fiber. Increasing xylanase concentration from 0.5% in sample #4 to 1% in sample #5 led to a decrease in linear density from 23.6 to 18.4 tex (p value 0.03). Sample #4 and sample #5 were pretreated with 2.5 g/l NaOH which was the lowest among other alkalization concentrations that had been applied. The difference in enzyme concentrations between samples #6 and #7 and that between samples #13 and #16 did not cause a variation in linear density value of related fiber sets. Samples #6, #7, #13 and #16 were alkalized at higher concentrations or durations compared to samples #4 and #5. This situation supports the former statement that the effect of enzymes became less with the increase in the concentration or duration levels alkalization pretreatment. No effect of enzymatic treatment duration has been detected on fiber linear density. Mechanical properties A typical stress strain graph of a corn husk fiber is shown in Figure 2. The stress strain curve follows the same trend with the one obtained from the corn husk fibers extracted by Reddy and Yang (2005). An elastic elongation zone with a high tensile modulus value is followed by a plastic elongation zone with lower modulus. Enzymatic treatments were found to significantly affect the initial modulus, breaking tenacity, and elongation of corn husk fibers (p values , , and , respectively), when the whole samples set of fibers were tested through analysis of variance. When fibers #1, 14, and 15 are compared, it will be seen that enzymatic treatments increased the initial modulus of water-retted fibers as seen in Figure 3 (p value ) and in Table 3, while they caused significant decrease in breaking tenacity and breaking force as shown in Figures 4 and 5 and Table 4 (p values and , respectively). It will also be seen that the enzymatic treatment resulted in lower elongation ( p value ) and higher stiffness of water-retted fibers, when Figures 3 and 6 and Table 5 are investigated. This situation was explained by Karaduman, Gokcan, and Onal (2012) with the reduction of hemicelluloses into smaller polysaccharides. In the absence of hemicelluloses, the cellulose chains position in the loading direction. This increase in the molecular orientation and packing density imparts stiffness to the fiber. Increase in xylanase concentration (samples #4 and #5) led to a decrease in breaking force was observed ( p value 0.04). This situation supports the former statement. Increasing cellulase concentration from 2 to 3% results in an increase in initial modulus ( p value ) when fibers #2 and #3 are compared. Accordingly, as seen from Table 3, enzymatic treatments caused increase in breaking tenacity and especially in the initial moduli of alkalized fibers. This situation can be explained by the removal of nonload bearing mass from fibers and an increase in crystallinity which was also reported by Roncero, Torres, Colom, and Vidal (2005) on cellulosic fibers with the use of xylanase enzymes. The tensile properties of water-retted (#1, 14, and 15) fibers had higher stiffness and lower elongation Figure 2. A typical stress strain curve of corn husk fibers. Figure 3. The effect of treatments on initial moduli (cn/tex) of corn husk fibers.

7 The Journal of The Textile Institute 401 Table 3. Initial moduli of corn husk fibers before and after enzymatic treatments. Initial modulus a (cn/tex) Initial modulus b (cn/tex) Treatment # Mean σ Mean σ CV c (%) p value 1 N/A N/A N/A Notes: a Initial modulus value before enzymatic treatment; b initial modulus value after enzymatic treatment; c coefficient of variance values after enzymatic treatment; σ, standard deviation; and n = 20. Figure 4. The effect of treatments on breaking tenacity (cn/tex) of corn husk fibers. Figure 5. The effect of treatments on breaking force (N) of corn husk fibers. than that of the alkalized fibers. This can be explained by the loss of cellulosic crystalline orientation due to the alkalization treatment carried out under no tension, which is not the case in water retting treatment. Alkalization might have caused the transition from native cellulose (cellulose I) to cellulose II, which generally presents a lower chain modulus. Furthermore, alkalization at higher concentrations may cause degradation in cellulosic chains. Zhou, Yeung, Yuen, and Zhou (2002) and El Oudiani et al. (2012) also reported decrease in stiffness that comes with alkalization treatment of lignocellulosic fibers. Increasing xylanase percentage from 0.5 to 1% resulted in a decrease in breaking force (p value for samples #4 and #5; p value for #6 and #7). Such significant effect of xylanase percentage on breaking tenacity was not detected. That means xylanase resulted in material loss which in turn decreased fiber diameter. Thus, tenacity was not strongly affected.

8 402 N.D. Yılmaz Table 4. Breaking tenacity values of corn husk fibers before and after enzymatic treatments. Breaking tenacity a (cn/tex) Breaking tenacity b (cn/tex) Treatment # Mean σ Mean σ CV c (%) p value 1 N/A N/A N/A Notes: a Breaking tenacity before enzymatic treatment; b breaking tenacity after enzymatic treatment; c coefficient of variance values after enzymatic treatment; σ, standard deviation; and n = 20. Figure 6. The effect of treatments on elongation (%) of corn husk fibers. Enzymatic treatments resulted in decrease in breaking tenacity of fibers which had been pretreated under higher concentrations as shown in Table 4. Thus, we can conclude that the applied enzymatic treatment caused damage to fibers that had been heavily treated by alkalization. In contrary, fibers alkalized by average conditions underwent an increase in breaking tenacity, supporting the fact that nonload bearing materials were eliminated. The same situation is also valid for initial modulus results. As presented in Table 5, the enzymatic treatment resulted in a decrease in elongation at break percentages of fibers alkalized under milder conditions, which was not the case for fiber treated under concentrations of alkali. This supports the fact that the enzymes treated the same extra cellulosic materials in corn husk fibers which have already been consumed up at stronger levels of alkalization treatment. Elongation at break values of extracted corn husk fibers are generally greater compared to that of other plant fibers in textile use. This finding is in agreement with that reported by Reddy and Yang (2005). This can be explained by the lower crystallinity of corn husk fibers (48 50%) compared to that of cotton, flax, and jute which is in the range of 65 75% (Reddy & Yang, 2005). The variation in the mechanical properties can be interpreted by their coefficient variation degrees. The coefficients of variation ranges of initial modulus, breaking force, breaking tenacity, and elongation at break values of produced corn husk fibers can be given as 24 45, 39 62, 39 61, and 30 49%, respectively. Cellulase did not appear as a significant factor as xylanase on mechanical properties of corn husk fiber when samples #2, 3 and #13 16 are studied. Similarly, statistical analyses showed no evidence of a significant effect of enzymatic treatment duration on the mechanical properties of corn husk fibers, when samples #8, #9 and #14, #15 are investigated. For further studies,

9 The Journal of The Textile Institute 403 Table 5. Elongation at break values of corn husk fibers before and after enzymatic treatments. Elongation at break a (%) Elongation at break b (%) Treatment # Mean Σ Mean σ CV c (%) p value 1 N/A N/A N/A Notes: a Elongation at break before enzymatic treatment; b elongation at break after enzymatic treatment; c coefficient of variance values after enzymatic treatment; σ, standard deviation; and n = 20. the duration range of treatments may be broadened; durations shorter than 60 min and longer than 240 min may be investigated. FTIR spectroscopy The FTIR spectroscopy of the corn husk fibers can be seen in Figure 7. The broadband absorbance peak of corn husk fibers around 3400 cm 1 was assigned to the O H stretching. The peak at 2923 cm 1 corresponded to the C H stretching, 2361 cm 1 peak was C = O, the 1380 cm 1 absorbance peak was characterized by C H bending vibration of the aromatic ring in polysaccharides, the 1419 cm 1 peak was attributed to CH 2 symmetric bending, and the 1250 cm 1 peak was assigned to C O stretching in the aryl group of lignin. The 1159 cm 1 peak corresponded to anti-symmetrical deformation of C O C band in cellulose and hemicelluloses, the peak around 1044 cm 1 to C O and O H stretching, and the peak at 897 cm 1 was interpreted as C O C stretching at the beta-(1 4)-glycosidic linkage in cellulose (Jonoobi, Harun, Shakeri, Misraand, & Oksman, 2009; Yılmaz, 2013). Water-retted corn husk fiber gave a stronger 1250 cm 1 peak, compared to the alkalized ones, which hints higher lignin amount in water-retted fibers compared to alkalized ones. The 1509 cm 1 and 801 cm 1 peaks observed in water-retted fibers were not present alkalized fibers. These peaks, assigned to the phenyl groups in lignin and out-of-plane ä(c H) vibration, respectively, also suggest the presence of lignin in water-retted fibers. Gonzales, Reguera, Mendoza, Figueroa, and Sanchez-Sinencio (2004) similarly detected the loss of these three peaks after Figure 7. The IR spectra of corn husk fibers. ( ) #5, ( ) #15, and ( ) control (alkalized at 5 g/l NaOH for 90 min).

10 404 N.D. Yılmaz alkalization of corn hulls and Islam, Pickering, and Foreman (2011) reported decrease of 1509 cm 1 peak after alkalization of hemp. The band at 1737 cm 1 of water-retted fibers was attributed to the hemicellulose uronic acids, disappeared in alkalized fibers. This hints lower amount of hemicellulose in alkalized fibers compared to water-retted fibers. Similarly, Islam et al. (2011) reported a decrease in 1737 cm 1 peak in hemp due to alkalization. Water-retted corn husk fiber gave a weaker 897 cm 1 peak, compared to the alkalized ones, which suggests lower cellulose content resulted by higher amount of lignin and hemicellulose. Gonzales et al. (2004) and Islam et al. (2011) also reported a stronger 897 cm 1 peak for alkalized hulls and alkalized hemp, respectively, compared to unalkalized ones. Thermal properties The thermo-gravimetric analysis (TGA) curves, presented in Figure 8, show the first two degradation steps in the ranges of around C and C for all three sets of fibers. The third degradation step was C for fibers #5 and #15, and C for the control sample which was alkalized at 5 g/l NaOH concentration for 90 min but not enzyme-treated. In the first degradation region, nearly 10% weight loss was observed due to water vaporization. Second range, which corresponds to 66 69% material loss for all three sets of fibers, is attributed to degradation of hemicelluloses and cellulose. In the third degradation step, 10, 18, and 20% weight loss occurred for fibers #5, #15, and the control sample, respectively. In the third region, which can be associated cellulose with lignin, the most amount of material loss was observed for fibers extracted with the harshest alkalization treatment. Yılmaz (2013) also obtained increased material loss in the third degradation step for corn husk fibers extracted with harsher conditions. Jonoobi et al. (2009) attributed the lower amount of residual with alkalization treatment to lower amount of ash and lignin degradation of which is slower compared to cellulose. Thermal durability of corn husk fiber has been enhanced with alkalization treatment as the onset of second thermal degradation shifted from 185 C for water-retted fibers (#15) to C for alkalized fibers (#5 and control). This result is in accordance with the findings of Yılmaz (2013). Fibers #5 gave the highest temperature for the second thermal degradation step. The alkalization and enzymatic treatment combination might have led to lower amount of hemicellulose, which is less durable to heat compared to cellulose; and this, consequently, yielded higher thermal durability. When the differential thermal analysis (DTA) diagrams (Figure 9) are observed, it would be clear that the fibers treated with the harshest alkalization treatment, i.e. the control sample, followed a different trend than that of the other fibers. The exothermic peak at C which can be explained by cellulose degradation is only found for control fibers. This can be explained by the fact that cellulose in the control sample was higher in amount and was less protected by slow-degrading lignin compared to the other two sets of fibers. The findings related to higher amount of cellulose in alkalized fibers vs. higher amount of lignin and hemicellulose in water-retted fibers complies with IR spectra results which were explained in the former section. Yılmaz (2013) also reported an exothermic peak in corn husk fibers alkalized at higher concentrations, which was not the case for fibers treated at lower alkali concentrations. Figure 8. The TGA analysis of corn husk fibers. ( ) #5, ( ) #15, and ( ) control (alkalized at 5 g/l NaOH for 90 min). Figure 9. The DTA analysis of corn husk fibers. ( ) #5, ( ) #15, and ( ) control (alkalized at 5 g/l NaOH for 90 min).

11 The Journal of The Textile Institute 405 Figure 10. Stensby whiteness indices of corn husk fibers. Color measurement In Figure 10, Stensby whiteness indices of corn husk fibers are given. Here, water-retted fibers gave the lowest whiteness index values. Accordingly, alkalized fibers gave lower yellowness results. This result is in accordance with the IR spectra findings which evidences higher amount of extra cellulosic materials in water-retted fibers compared to alkalized ones. Reddy et al. (2007) also found higher yellowness with higher lignin content in corn husk fibers. Conclusion Corn husk fibers were extracted by water retting, alkalization, and enzymatic processes at different concentration and duration levels. The effects of extraction process parameters on the physical and thermal properties and chemical characteristics of corn husk fibers were investigated. The chemical structures of the fibers were studied by IR measurements. The linear density of the obtained fibers decreased with enzymatic treatments. The highest initial moduli results were obtained from water-retted and enzyme-treated fibers. Alkalized fibers gave higher elongation and lower stiffness compared to water-retted ones. While resulting in loss of breaking tenacity and elongation in water-retted fibers, enzymatic treatment resulted in increase in initial moduli and breaking tenacity of alkalized fibers. No significant effect of enzymatic treatment duration was obtained on the mechanical properties of corn husk fibers. The IR results showed higher amount of lignin and hemicellulose in water-retted fibers compared to alkalized ones. The enzymatic treatment and alkalization enhanced the thermal durability of the fibers. Acknowledgement This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. References American Society for Testing and Materials. (2007a). ASTM D standard test methods for linear density of textile fibers. West Conshohocken, PA: ASTM. American Society for Testing and Materials. (2007b). ASTM D standard test method for tensile properties of single textile fibers. West Conshohocken, PA: ASTM. Arifuzzaman Khan, G.M., Shaheruzzaman, M., Rahman, M.H., Abdur Razzaque, S.M., Sakinul Islam, M., & Shamsul Alam, M. (2009). Surface modification of okra bast fiber and its physico-chemical characteristics. Fibers & Polymers, 10(1), Ashori, A., & Nourbakhsh, A. (2009). Mechanical behavior of agro-residue-reinforced polypropylene composites. Journal of Applied Polymer Science, 111(5), El Oudiani, A., Chaabouni, Y., Msahli, S., & Sakli, F. (2012). Mercerization of Agave americana L. fibers. Journal of The Textile Institute, 103(5), Gonzales, R., Reguera, E., Mendoza, L., Figueroa, J.M., & Sanchez-Sinencio, F. (2004). Physicochemical changes in the hull of corn grains during their alkaline cooking. Journal of Agricultural and Food Chemistry, 52, Huda, S. (2008). Composites from chicken feather and cornhusk preparation and characterization. (Unpublished Ph.D. dissertation). University of Nebraska-Lincoln, Lincoln, NE. Huda, S., & Yang, Y. (2008). Chemically extracted cornhusk fibers as reinforcement in light-weight poly (propylene) composites. Macromolecular Materials and Engineering, 293, Islam, M.S., Pickering, K.L., & Foreman, N.J. (2011). Influence of alkali fiber treatment and fiber processing on the mechanical properties of hemp/epoxy composites. Journal of Applied Polymer Science, 119(6), Jonoobi, M., Harun, J., Shakeri, A., Misraand, M., & Oksman, K. (2009). Chemical composition, crystallinity, and thermal degradation of bleached and unbleached kenaf bast (Hibiscus cannabinus) pulp and nanofibers. Bioresources, 4(2), Kannan, T.G., Wu, C.M., Cheng, K.B. & Wang, C.Y. (2012). Effect of reinforcement on the mechanical and thermal properties of flax/polypropylene interwoven fabric composites. Journal of Industrial Textiles. Advance online publication. doi: / Karaduman, Y., Gokcan, D., & Onal, L. (2012). Effect of enzymatic pretreatment on the mechanical properties of jute fiber-reinforced polyester composites. Journal of Composite Materials. Advance online publication. doi: / Larsen, J. (2012). Bumper 2011 grain harvest fails to rebuild global stocks. Eco economy indicators [Internet]. Retrieved from C54/grain_2012 Nam, S., & Netravali, A.N. (2006). Green composites. I. Physical properties of ramie fibers for environmentfriendly green composites. Fibers & Polymers, 7(4), Panthapulakkal, S., Law, S., & Sain, M. (2006). Effect of water absorption, freezing and thawing, and photo-aging on flexural properties of extruded HDPE/rice husk composites. Journal of Applied Polymer Science, 100(5), Reddy, N., Salam, A., & Yang, Y. (2007). Effect of lignin on the heat and light resistance of lignocellulosic fibers. Macromolecular Materials and Engineering, 292,

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