مطالعه و تحلیل تأثیر فناوری آلتراسونیک بر کیفیت رنگرزی نخ پرز پشمی با رنگزاهای حنا و پوست انار در فرش دستباف

Introduction: Natural dyeing is one of the central technical and aesthetic foundations of the Iranian handwoven carpet. In this context, color is not merely a surface quality applied to wool yarn; it contributes to the visual identity of the carpet and to the material quality of the finished object. Wool yarn, as a major material in handwoven carpets, has a decisive role in receiving, retaining, and displaying color. Therefore, any attempt to improve the dyeing behavior of wool yarn must be evaluated as both a textile process and a factor affecting the chromatic quality of the Iranian carpet. In recent decades, environmental concerns, the high ecological cost of synthetic colorants, and renewed attention to natural colorants have encouraged researchers to reconsider plant-based dyes. Nevertheless, the practical use of natural dyes still faces limitations such as process variability, insufficient reproducibility of shade, dependence on dye source and mordanting conditions, and differences in color strength and fastness. Ultrasonic treatment has been introduced in textile coloration as an auxiliary technology that may intensify mass transfer, facilitate the penetration of dye molecules into fibers, reduce processing time, and improve dyeing efficiency. However, its effectiveness is not fixed or universal; it depends on the chemical nature of the dye, the structure of the fiber, bath pH, temperature, concentration, mordanting, and the overall dyeing method. The present study investigates this problem through the dyeing of handwoven carpet wool yarn with two plant-based dyes, henna and pomegranate peel, under conventional and ultrasonic conditions. Accordingly, the research questions are as follows: how does ultrasonic treatment affect the dyeing behavior of handwoven carpet wool yarn dyed with henna and pomegranate peel; how is this effect reflected in color strength, CIELAB coordinates, and fastness properties; and should ultrasonic dyeing be considered superior to conventional dyeing or interpreted as a condition-dependent auxiliary process?
Literature review: Previous studies on natural dyeing emphasize that plant dyes can contribute to environmentally responsible textile coloration, but their successful use requires careful control of processing variables. Research on wool dyeing with madder, lac, pomegranate peel, and other natural sources has shown that color strength and fastness are strongly influenced by the chemical structure of the dye, the mordant, the acidity or alkalinity of the bath, and the duration and temperature of dyeing. Studies on ultrasonic-assisted dyeing have also indicated that acoustic cavitation can enhance diffusion and accelerate dye-fiber interactions in some cases. At the same time, these studies warn against assuming the automatic superiority of ultrasonic treatment, because different dyes respond differently to sonication. Within the context of carpet studies, the assessment of dyeing is not limited to K/S values or laboratory measurements, but also concerns visual harmony, shade reproducibility, material behavior, and color fastness in wool yarn. Henna and pomegranate peel are particularly relevant in this regard, because both produce warm and earthy color ranges that suit the aesthetic character of the Iranian handwoven carpet.
Methodology: This research is applied-developmental in purpose and experimental in method. Wool yarn samples used for handwoven carpets were dyed with henna and pomegranate peel dyes under controlled laboratory conditions. The experimental design compared conventional dyeing and ultrasonic-assisted dyeing while considering dye type, dyeing method, bath pH, temperature, dye concentration, and aluminum sulfate mordanting. After dyeing, the samples were evaluated through instrumental and standard tests. Color strength was measured using the K/S index, and colorimetric characteristics were analyzed within the CIELAB system in order to determine changes in lightness, redness-greenness, yellowness-blueness, and overall shade behavior. Light fastness and washing fastness were examined to assess the practical durability of the dyed yarns. In addition, scanning electron microscopy (SEM) was used to observe surface changes in wool fibers after dyeing, and Fourier-transform infrared spectroscopy (FTIR) was applied to identify possible interactions among wool fiber, mordant, and natural dye compounds. This combination of colorimetric, fastness, microscopic, and spectroscopic analyses made it possible to interpret the results both technically and in relation to the artistic application of naturally dyed wool yarn in handwoven carpets.
Findings: The findings show that ultrasonic treatment did not necessarily increase color strength in all dyeing conditions. In pomegranate peel dyeing, the dyeing method had a significant effect on K/S values, and in some samples the conventional method produced higher color strength, especially under acidic conditions and higher temperatures. This result suggests that the tannin-rich structure of pomegranate peel may interact effectively with wool and mordant under conventional thermal conditions, and that sonication does not automatically improve this interaction. In henna dyeing, the difference between conventional and ultrasonic methods was not statistically strong enough to prove the clear superiority of the ultrasonic method. Across both dyes, bath pH played a decisive role, and acidic conditions generally produced more favorable color strength and more stable dyeing behavior. The CIELAB results confirmed that the final shades were affected by dye type, process conditions, and the interaction between dye molecules and wool fiber. The SEM observations indicated visible surface modifications in dyed wool fibers, while FTIR spectra supported the presence of interactions between natural dye compounds, aluminum sulfate mordant, and the functional groups of wool. The fastness results were generally acceptable for handwoven carpet yarns, although they varied according to dye type and dyeing conditions.
Conclusion: The study concludes that ultrasonic technology should be regarded as a conditional auxiliary method rather than a universally superior substitute for conventional natural dyeing. Its effectiveness depends on the dye source, bath pH, temperature, concentration, mordanting, and fiber structure. Henna and pomegranate peel can be used as natural dyes for handwoven carpet wool yarn, but their dyeing behavior must be controlled carefully to achieve desirable color strength, chromatic quality, and fastness. Thus, the value of ultrasonic treatment lies in its potential to improve or regulate some processing conditions, not in replacing the conventional dyeing method in all cases. The findings also show that the interpretation of ultrasonic dyeing must be based on the simultaneous reading of K/S, CIELAB coordinates, fastness results, SEM observations, and FTIR spectra.