|Natural dye; Wool dyeing; Mordant; Pistachio hull;
|Today, natural colorants are emerging globally due to the fact
that are safer and environment-friendly and thus the application of
natural dyes should be considered as a better alternative to synthetic
dyes. Using natural dyes contributes to the added value of textiles and
also responses to the increasing demand of compatibility with the
environment [1-7]. From the point of color chemist view, the actual
coloring matters used and the methods by which they were so skillfully
applied are of considerable interest. So, it is necessary to study and
modify the ways of using natural materials in textiles [5,7]. Many
studies have been done on natural dyes covering such areas as: variation
in the quantity of dyes concerning natural sources, combination of
dyes, properties of natural dyes, effects of mordant and auxiliaries on
different properties of dyed samples, light fastness behavior of natural
dyes, improvement in natural dyes production and discovering other
natural dye sources [8-16]. The colorimetric properties of natural
yellow dyes including henna (lawsonia inermis), dolu (rheum emodi),
kamala (mallotus phillipinensis), onion (allium cepa) and turmeric
(curcuma tinctoria) with different mordants have been studied by
Gulrajani et al. [11-13]. Tsatsaroni and Eleftheriadis also discussed
the color and fastness of natural saffron . Many research papers
have been published on natural dyes and mordanting but a few papers
have been published on the alteration of all different factors in one
approach. Pistacia vera L., from family Anacardiaceae, genus Pistacia
is a small tree up to 10 meters tall, with deciduous pinnate leaves and
edible delicious nuts. It is native to southwestern Asia and Asia Minor,
from Syria to the Caucasus, Iran, Turkey and Afghanistan. There are
archaeological evidences of pistachio nuts were used for food as early
as 7,000 B.C. The plant was then introduced to Italy from Syria early in
the first century A.D. Subsequently, its cultivation spread over other
Mediterranean countries, USA, Australia and China. Botanically a
drupe consists of Pericarp (ovary wall) (hull), Endocarp (shell) and
ripened ovule (seed) that is the edible portion. Pericarp, in turn,
consists of Exocarp and Mesocarp. Pistachio hulls are the byproduct
of nut production, which is usually useless. Iran is the world’s leading
pistachio producer and produces over 350 thousands metric tons every
year. There are thousands tons of pistachio hull wastes which can be used as a valuable source of natural dye for carpet piles. To optimize
the design of an existing process, it is necessary to identify which
factors have the greatest influences and which appropriate values
produce the most consistent performance. Experimenting with the
design variables, one at a time or by trial and error, until a first feasible
design found would be a common approach to process optimization.
However, this approach could lead one to a very long and expensive
time span in completing the design process. A technique for laying out
the experiments when multiple factors involved is popularly known as
the “factorial design of experiments”. This method helps researchers
to determine possible combinations of factors and to identify the
best combination. Since it is extremely costly to run a number of
experiments to test all combinations, application of a full factorial
design of experiments is restricted when many factors and levels are
studied. The statistical experimental analysis is proposed to investigate
the significances of systematic effects. The application of this kind of
experiments requires careful planning, prudent layout of experiment,
and expert analysis of results. A commonly applied statistical method,
Taguchi experimental design and analysis of variance (ANOVA), could
be used to analyze results of the experiments on the response and to
determine how much variation quality influencing factors contribute
[18-25]. Orthogonal arrays can be used to assign factors to a series of
experimental combinations, in which results could then be analyzed by
using a common mathematical procedure. The variables can generally
be grouped into two major classifications: (a) independent variables
or factors, and (b) dependent variables or responses. In this factorial
design, the main effects of independent variables and the interactions
between dependent variables can be studied. The latter would be the major advantage of this technique while a major disadvantage for oneat-
a-time variable testing method.
|In this research, the usage of the dried pistachio hulls for dyeing
wool yarns was studied. To achieve the maximum color strength of
wool samples dyed with the pistachio hulls with a minimum number
of experiments, a Taguchi experimental design L18 orthogonal array
(seven factors in three levels and one factor in 2 levels) was employed to
evaluate the effect of different factors in the dyeing process. The Iranian
wool yarn was first scoured with a nonionic detergent and mordanted
with some metal salts including: KAl(SO4)2, CuSO4, and K2Cr2O7. The
yarn was then dyed with different amounts of dried pistachio hull
powder. The colorimetric properties of the dyed yarns were evaluated
in CIELAB system.
|The following materials were used:
|• Iranian wool yarns of 432/2 Tex with 144 twists per meter.
|• Nonionic detergent (Shirley Development Limited) for scouring
of wool yarns.
|• Aluminum potassium sulfate (KAl(SO4)2), copper sulfate
(CuSO4) and potassium dichromate (K2Cr2O7) from Merck for
|• Hydrochloric acid and sodium hydroxide for controlling the pH.
|• Dried powdered pistachio hulls from genus Pistacia vera L.
collected from Kerman province, Iran.
|The wool yarns were treated in four steps as follows:
|Scouring: Wool yarns were scoured with 0.5% nonionic detergents
for 30 minutes at 50ºC. The L:G (Liquor to Good ratio) of the scouring
bath was kept at 40:1. The scoured material was thoroughly washed
with tap water and dried at room temperature. The scoured material
was soaked in clean water for 30 minutes prior to dyeing or mordanting.
|Mordanting: The scoured wool yarns were mordanted with
KAl(SO4)2, CuSO4, and K2Cr2O7. The L:G of the mordanting bath was
kept at 40:1. Hydrochloric acid was used in the mordanting bath for
adjusting the pH at 5. The mordanting temperature was started at 40°C
and then gradually raised to the required temperature during 20 min
and kept at this temperature for 1 hr. The mordanted material was then
rinsed with water thoroughly, squeezed and dried.
|Dyeing: First the dye solution was prepared by pouring the
appropriate amount of dye powder in water for 24 hours before dyeing.
Then, the dyeing process was carried out. Dyeing started at 40°C and
temperature was raised to required temperature in 20 minutes and
resumed at this temperature 1 hr. The pH of the dyebath was kept at pH=5 using dilute acid or base. The dyed material was then rinsed with
water thoroughly, squeezed and dried.
|Measuring of color strength: To investigate the effects of different
parameters on the reflectance spectra of dyed samples, a GretagMacbeth
spectrophotometer model 7000A computer integrated, was used.
CIELAB color co-ordinates (L*, a*, b*, C) and color strength values
(K/S) were calculated from the reflectance data (R) of dyed samples
for 10º observer and D65 illuminant based on the Kubelka–Munk
|In which, K, is the sorption coefficient, R is the reflectance of the
dyed sample and S is the scattering coefficient.
|Results and Discussion
|In this research work, the optimization of the dyeing factors in
applying the pistachio hulls as a new source of natural dye for wool
yarns was carried out employing Taguchi method for statistical design
of experiments. According to Taguchi parameter design methodology,
one experimental design should be selected for the controllable factors.
A L18 orthogonal array (that accommodates seven factors in three
levels and one factor in two levels each in 18 runs) was employed to
identify the optimum conditions for dyeing wool yarns with pistachio
hulls . Seven influencing factors were taken into account and one
column was set for the determination of errors as following:
|• Amount of colorant (A)
|• Amount of mordant (B)
|• Type of mordant (C)
|• Temperature of mordanting bath (D)
|• Temperature of dyeing bath (E)
|• Duration of mordanting (F)
|• Duration of dyeing (G)
|The three levels of factors were selected in accordance with the
preliminary test and the previous author’s experience [26,27]. The
factors and levels considered for this experiment are shown in Table 1.
The K/S ratios for all samples from different conditions was calculated
and shown in Table 2. In these experiments, the system was optimized
according to the maximum response value of (K/S). The analysis of the
variance (ANOVA) was employed to determine the factors influencing
the average response (K/S) ratios. Table 3 presents the degree of
freedom (df), the sum of squares (SS), the mean square (variance, V),
and the F ratio of variances (F). The insignificant factors are pooled
to reduce the chance of making alpha mistakes. As a role, the factor,
which influence is 10% or lower than the most influential factor is
pooled . The F-Value implies that the model is significant. One
column was set for the determination of errors to consider the effects of factors excluded from the experiment and/or Uncontrollable factors
|The variation of K/S against the different levels of factors is shown
in Figure 1.
|The response of software calculation shows that the optimum levels
of each factor are as follows:
|• Amount of colorant at level 1 (0.4 g).
|• Amount of mordant at level 1 (2.0 g).
|• Type of mordant at level 3 (CuSO4).
|• Temperature of mordanting bath at level 1 (50oC).
|• Temperature of dyeing bath at level 1 (60oC).
|• Duration of mordanting at level 3 (120 min).
|• Duration of dyeing at level 3 (120 min).
|The ANOVA predicts the maximum value of K/S=0.7 for the above
optimum conditions. It also suggests that the factors influencing the
dye absorption of the wool yarn are of different importance and that
the most important factor is the amount of mordant (F=3.835796) followed by the type of mordant (F=3.582426), and temperature of
mordanting bath (F=3.418584). The amount of colorant is the forth
most important factor presenting the F ratio of 3.340098. The higher
the percent influence of a factor, the tighter the tolerance, and vice
|Effect of mordant
|Most of the natural dyes have poor affinity for natural fibers.
Moreover, their fastness is often enhanced by metal mordants, which
form an insoluble complex with the dye molecules. It is known that
flavonols have greater tendency towards chelate formation due to the
presence of hydroxyl–keto functionality [28,29]. The probable way of
chelation depends on the nature of the mordant–dye complex which
has been discussed earlier . Mordant makes strong coordination
bonds with the wool yarn on one side and the colorant molecule on
the other side. The dye molecules are capable of forming five- and sixmembered
chelate rings with different metal ions. These chelates utilize
the ortho-dihydroxy structure and/or carbonyl ortho to the hydroxyl
group in the flavonol dye molecules, which in turn greatly enhance
the affinity of natural dye and fiber. Therefore the type and amount of
mordant is of the great importance to make such chelation .
|The use of the experimental design is described for optimizing
analytical methods. Many factors can be studied, so the interactions
can be determined. In addition to the factors identified as being
significant, they have more credibility since they are studied several
times. The Taguchi’s method simplifies both the assignments of factors
and the calculations.
|The designs described in this work include three level factors. The
results and analysis of the variance show that the above-mentioned
conditions were considered as optimum. Experiments were carried
out at the stated levels, and the optimum conditions were achieved.
Confirming experiments were also carried out. Limitations to the
experimental design may be seemed obvious, but they are worth being
stated, neglecting them often leads to the failing of this approach. The
variance observed for a factor is only valid over the range studied for
that factor. Pistachio hulls found to have good agronomic potential as
a natural dye in Iran. Metal mordants when used in conjunction with
pistachio hulls were found to enhance the dyeability and its fastness
properties. The color shades on wool yarns ranges from light orange
to dark orange. The stepwise process of dyeing with pre-mordanting
showed to be energy and time saving and found to achieve high dye retention. Therefore this natural dye has good scope in the commercial
dyeing of wool yarns used as Persian carpet piles.
|The authors express their sincere thanks to Institute for Color Science and
Technology of Iran (ICST) for financial support.
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