ARTICLE pubs.acs.org/IECR
Dyeing Natural Cellulose Fibers from Cornhusks: A Comparative Study with Cotton Fibers Narendra Reddy,† Vigneshwar Arul Thillainayagam,† and Yiqi Yang*,†,‡,§ †
Department of Textiles Clothing and Design, ‡Department of Biological Systems Engineering and §Nebraska Center for Materials and Nanoscience, 234 HECO Building, East Campus, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0802, United States ABSTRACT: This research shows that natural cellulose fibers extracted from cornhusks have better dyeing properties for direct and sulfur dyes and similar dyeing properties for reactive and vat dyes compared to cotton fibers dyed under similar dyeing conditions. Cornhusk fibers have unique structure and properties compared to cotton and common lignocellulosic fibers. However, the short single cells, higher amounts of lignin and hemicellulose, lower percent crystallinity and relatively coarse fibers make the common cellulose fiber dyeing conditions unsuitable to dye cornhusk fibers. In this research, cornhusk fibers were dyed with one dye each from four dye classes, direct, reactive, vat, and sulfur dyes. The dyeing behavior of the fibers was fit in to the common isotherms and the kinetic parameters such as dyeing rate constant, diffusion coefficient, and half-time for dyeing were calculated. It was found that the physical properties of the fibers and structure of the dye had considerable influence on the dye sorption and rate of dyeing. Lower percent crystallinity, smaller crystal size, and presence of hemicellulose, lignin, and higher amounts of surface impurities are mostly responsible for the higher dye sorption on corn fibers compared to cotton.
1. INTRODUCTION Dyeing lignocellulosic fibers using traditional cotton dyeing conditions is challenging due to the presence of noncellulosic impurities.1,2 Lignocellulosic fibers contain about 6070% cellulose, 3040% hemicellulose, and 1015% lignin whereas cotton is mostly cellulose (>90%). Impurities in the lignocellulosic fibers inhibit penetration of dyes into the fibers, can sorb dyes and reduce the amount of dyes available and the impurities may degrade during dyeing and affect the uniformity of dyeing. Similarly, the physical properties of lignocellulosic fibers such as their low crystallinity and larger fiber diameters will affect the thermodynamics and kinetics of dyeing.3 Lignocellulosic fibers such as linen and jute have been dyed with common cellulose dyes such as direct, reactive, vat and sulfur dyes. Attempts are being made to develop alternative sources for lignocellulosic fibers in an effort to reduce our dependence on fiber crops and petroleum resources for fibers. Similarly, attempts are also being made to find alternative sources for protein fibers.4 Lignocellulosic agricultural byproducts such as cornstover, wheat, and rice straw are abundant, inexpensive, and renewable sources that can be used to obtain lignocellulosic fibers. It has been reported that natural cellulose fibers obtained from cornhusks, cornstalks, wheat, rice, and soybean straw have properties better or similar to that of the common lignocellulosic fibers.4 However, fibers obtained from the lignocellulosic byproducts have considerably different chemical, physical, and morphological structures. Lignocellulosic fibers obtained from agricultural byproducts generally have lower cellulose content (5060%) and higher lignin (515%) and hemicellulose (3040%) content than cotton and some lignocellulosic fibers such as hemp and linen.57 The nonconventional lignocellulosic fibers also have lower percent crystallinity (5060%) and crystal size compared to cotton. This means that the lignocellulosic fibers are more amorphous and can therefore absorb dyes and chemicals r 2011 American Chemical Society
more easily than fibers with higher percent crystallinity.57 Morphologically, lignocellulosic fibers such as cornhusk and corn stalk fibers have small unit cell lengths whereas linen and hemp have long unit cell lengths.57 The short unit cell lengths make the fibers to be easily degraded (form small fragments) at high temperatures and alkaline conditions. Therefore, the traditional cellulose fiber dyeing conditions may not be suitable to dye the cellulose fibers extracted from agricultural byproducts. The presence of high amounts of lignin also makes it difficult to bleach lignocellulosic fibers. It is necessary to delignify the fibers to achieve good bleaching efficiency.810 Methods have been developed to sulfonate lignin and achieve good dyeing and bleaching of jute and cornhusk fibers without affecting the properties of the fibers.810 It has been reported that progressive removal of lignin and hemicellulose affects the functional groups and therefore the dyeability of jute fibers.11 Removal of lignin was reported to reduce the dye uptake for both acid and direct dyes on jute fibers. Cellulose fibers extracted from pineapple leaves were found to have higher dye absorption when dyed with reactive dyes.2 The fastness properties of the dyed pineapple leaf fibers were similar to that of cotton. In another report, pineapple leaf fibers were dyed with various direct dyes and it was found that cotton dyeing conditions were suitable to dye pineapple leaf fibers.12 The dyeing behavior of wheat straw was studied using direct, acid and basic dyes.1 It was reported that wheat straw had high substantivity for basic dyes due to the presence of lignin and hemicellulose but had poor exhaustion for acid and direct dyes. Received: January 30, 2011 Accepted: March 15, 2011 Revised: March 15, 2011 Published: March 22, 2011 5642
dx.doi.org/10.1021/ie200217w | Ind. Eng. Chem. Res. 2011, 50, 5642–5650
Industrial & Engineering Chemistry Research
ARTICLE
Table 1. Properties of Cornhusk Fibers from Reference 5 composition
morphology
physical structure
tensile properties
cellulose: 8087%
single cell length: 0.51.5 mm
crystallinity: 4850%
strength: 23 g/den
lignin: 68%
single cell width:1020 μm
crystal size: 3.2 nm
elongation: 1218%
fiber length: 220 cm
modulus: 70 g/den
color: yellowish white
Scheme 1. Structure of C.I. Direct Red 80
Scheme 2. Structure of C.I. Reactive Blue 19
Scheme 3. Structure of C.I. Vat Green 1
As seen from the above discussions, lignocellulosic fibers require different dyeing conditions than those used for cotton to achieve good dyeing efficiency and color fastness. Natural cellulose fibers extracted from cornhusks are quite unique compared to the lignocellulosic fibers such as jute and linen. Cornhusk fibers have short unit cell lengths, are considerably coarser, and have low percent crystallinity but with much higher elongation than the common lignocellulosic fibers.5 Cornhusk fibers were blended with cotton and polyester and processed to develop yarns. It was found that cornhusk fiber blended polyester yarns had better properties than cotton blended polyester yarns.13 However, the presence of lignin imparts a natural yellow color to cornhusk fibers and it was difficult to obtain bleached cornhusk fibers with good whiteness.14 Controlled delignification was used to remove lignin and obtain cornhusk fibers with whiteness similar to that of bleached cotton.14 In this research, we have studied the dyeing behavior of cornhusk fibers in comparison to cotton fibers using four of the five common dye classes used for cellulose fibers. The thermodynamic and kinetic parameters were calculated and compared with cotton.
Table 2. Dyes Used in This Research and Their Properties
2. MATERIALS AND METHODS 2.1. Fibers. The cornhusk fibers used in this study was chemically extracted as reported earlier.5 Briefly, cornhusks were treated with 0.5% NaOH solution with a liquid to cornhusk ratio of 10:1 at 90 C for 30 min. After treatment, the fibers were thoroughly washed by hand and neutralized using 10% acetic acid solution. Properties of the cornhusk fibers used in this research are given in Table 1. Fibers obtained were allowed to dry under ambient conditions before using for the dyeing studies. Scoured cotton fibers were obtained from a research facility in India. 2.2. Dyestuffs. One dye each from the most prominent dye classes (direct, reactive, vat and sulfur dyes) used for cellulose
dye
C.I. number
chemical class
Direct Red 80
35780
polyazo
Reactive Blue 19 Vat Green 1
61200 59825
anthraquinone nitrobenzene
Sulfur Red 14
53440
p-(4-amino-m-toluidino)phenol
dyeing were selected for this study. Dyestuffs were selected based on the popularity of the dye, frequent use in research studies, dyeing characteristics, molecular structure of the dye and fastness properties. 2.2.1. Structure of the Dyes. The structure of the direct, reactive, and vat dyes used in this research are shown in Schemes 1,3 and properties of the dyes are given in Table 2. The structure of the sulfur dye used is not known. 2.3. Developing the Adsorption Isotherms. A batch dyeing using loose fibers was adopted to develop the isotherms. The exact concentration of dye in the dye bath was determined using a calibration equation with a regression value close to 0.999. The dyeing temperature and amount of auxiliary chemicals were chosen based on the recommendations from the manufacturer. The total dyeing time and material to liquor ratio were fixed at 3 h and 1:20, respectively, for all the trials. Six dye concentrations (115 g/L) were selected for each dye. Dyeing was carried out in 20 mL glass bottles in a hot air oven for a preset time for each dye. The temperature was held constant throughout the dyeing process with a particular dye but was varied for different dyes. Six different dye concentrations between 1 to 15 g/L were selected. The developed sorption isotherm curves were fitted into the Nernst, Langmuir, and Freundlich isotherm models.15 The best fitting model for each isotherm curve was identified by a series of calculation for each model. A regression analysis was performed for each curve after fitting them into the model. The 5643
dx.doi.org/10.1021/ie200217w |Ind. Eng. Chem. Res. 2011, 50, 5642–5650
Industrial & Engineering Chemistry Research
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Table 3. Temperature, Time Intervals, and Auxiliary Chemicals Used for the Dyeing Rate Study dyeing conditions
Direct Red 80
Reactive Blue19
Vat Green 1
Sulfur Red 14
temperature, C
100
40
50
66
time, mins
2180
2200
160
2180
auxiliary chemicals, g/L
sodium chloride: 20
sodium carbonate: 10
sodium dithionite: 4
Sodyefide B Liquid: 8
Glauber’s Salt: 50
sodium hydroxide: 3.5
sodium sulfate: 20
common salt: 20
model with higher r2 value was considered to be the best-fit isotherm model for that curve using eqs 1 to 3. The r2 value for all the three isotherms and the best fit isotherm are reported in this paper Nernst : ½Df ¼ K½Ds
ð1Þ
Freundlich : ½Df ¼ K½Ds x ð1 > x > 0Þ
ð2Þ
Langmuir :
½Df ¼ K½Ds ½S ½Df
ð3Þ
where [Df] is the dye on the fiber; [Ds] is the dye in solution, and [S] and [K] are proportionality constants. 2.4. Dyeing Rate Study. The rate of dyeing study was performed on a hot plate using glass beakers fitted with condensers. A constant dyeing temperature was maintained throughout the dyeing and the dye bath was stirred continuously. For each dyeing, 5 g of fiber was used and the dye liquor to fiber ratio was maintained at 40:1. Dyeing conditions and auxiliary chemicals used for each dyeing are shown in Table 3. Dyeing time was calculated from the instant the fibers were added into the bath and until equilibrium exhaustion was reached. Dye solution was pipetted at regular intervals and stored in sealed glass bottles at room temperature. The absorbance of the dye solution collected was measured on a spectrophotometer. The amount of dye in the solution was determined from the calibration equation developed earlier. Changes in the liquor ratio after removing the dye solution after each time point was appropriately accounted in the calibration equation. A graph was plotted with dyeing time (T) on the X-axis and the dye concentration on the fiber (DF) on the Y-axis. The following dyeing rate parameters were calculated from the dyeing rate curves. Dyeing rate constant also called the velocity constant describes the rate at which the dyeing proceeds was calculated according to eq 43 Kt ¼
1 1 ðC¥ Ct Þ C¥
ð4Þ
where K is the rate constant, C¥ is the dye sorption at equilibrium, and Ct is the dye sorption at time t. Diffusion coefficient which describes the ability of the dye molecules to penetrate into the fibers was calculated using eq 5 below 1=2 Ct Dt ¼4 ð5Þ πr 2 C¥ where D is the diffusion coefficient, and r is the radius of the fiber. Half dyeing time, which is described as the time required to reach 50% of the equilibrium sorption, was calculated using eq 6 below16 C¥ t1=2 ¼ t ð6Þ 2 where t1/2 is the half-dyeing time.
3. STATISTICS The influence of dye structure and the fiber type on overall dyeing performance was determined by ANOVA for each dyefiber combination. The main effects, simple effects, and interaction among the variables were identified using least-squares means. All the dependent variables for adsorption isotherm experiments and dyeing rates experiments were statistically analyzed with a nonlinear regression procedure. A p value of
