Investigation Of Different Bio-Mordants On Cotton Dyeing With Harmal Seed Extracted Natural Dyes

Technical Summary: Investigation of Different Bio-Mordants on Cotton Dyeing with Harmal Seed Extracted Natural Dyes

Problem Statement
The textile industry faces significant environmental challenges due to the reliance on synthetic dyes and chemical auxiliaries, which generate toxic wastewater with high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). These effluents contain carcinogenic and mutagenic compounds that threaten aquatic ecosystems and human health. While natural dyes offer a biodegradable, non-toxic alternative, their widespread adoption is hindered by poor color fastness and low color strength. Furthermore, traditional natural dyeing often requires metal salts as mordants, which pose their own environmental risks. This research addresses the need for a sustainable dyeing process that utilizes natural dye sources and eco-friendly bio-mordants to improve the performance of natural dyes on cellulosic substrates without relying on synthetic electrolytes or heavy metals.

Methodology
The study employed a comparative analysis to dye 100% cotton fabric using a natural dye extracted from Peganum harmala (Harmal) seeds. The research utilized a salt-free dyeing process where cotton fabrics were pre-mordanted with the bio-mordants to facilitate dye exhaustion, eliminating the need for traditional electrolytes.

Three distinct bio-mordants were investigated:

1. Citric Acid: Used as a reference synthetic bio-mordant.
2. Banana Peel Extract: An agro-waste source rich in phenolic compounds and potassium.
3. Grapefruit Peel Extract: An agro-waste source containing citric acid, flavonoids, and pectin.

The experimental procedure involved:

• Extraction: Harmal seeds were ground and extracted via a water bath method (70°C to 85°C). Banana and grapefruit peels were similarly processed to obtain active mordant solutions.
• Pre-Mordanting: Cotton samples were treated with the three mordants at varying concentrations (10% to 100% on weight of fabric, owf) at 70°C for 30 minutes.
• Dyeing: Pre-mordanted fabrics were dyed in an alkaline bath (pH 9–11.5) at 85°C for 45 minutes using the Harmal extract.
• Characterization: The dyed fabrics were evaluated for Color Strength (K/S values) using a spectrophotometer at 580 nm. Fastness properties were assessed according to AATCC standards for washing (AATCC 61), rubbing/crocking (AATCC 08), light (AATCC 16), and perspiration (AATCC 15).

Key Results

• Color Strength (K/S Values):
  • Citric Acid: Achieved optimal color strength at a 70% concentration. The K/S values increased with concentration until saturation, after which a slight decline occurred due to competitive zeta potential effects.
  • Banana Peel Extract: Showed the best K/S value at 70% concentration. The study noted that higher concentrations and temperatures (85°C) may lead to the partial degradation of thermolabile phenolic compounds, limiting further gains.
  • Grapefruit Peel Extract: Achieved the highest individual K/S value of 15.78 at a 60% concentration. This superior uptake was attributed to the synergistic effect of naturally occurring citric acid, flavonoids, and pectin acting as mordants.
• Fastness Properties:
  • Light Fastness: All mordanted samples exhibited "very good" light fastness ratings. The authors attribute this to the presence of UV-absorbing alkaloids (harmine, harmaline, harmol, and harmalol) inherent in the Harmal dye, rather than the specific mordant type.
  • Rubbing Fastness: All samples demonstrated good to excellent dry and wet rubbing fastness (ratings of 4–4.5), indicating strong interactions between the dye, mordant, and fiber via chelating and crosslinking mechanisms.
  • Washing and Perspiration Fastness: Washing fastness ranged from 3 to 3.5, which is typical for natural dye systems on cellulosic substrates. Perspiration fastness was rated between 3.5 and 4.5.
• Fluorescence: All dyed samples exhibited fluorescence under UV light, confirming the presence of Harmal alkaloids on the fabric surface.

Significance and Claims
The paper claims to be the first study to comparatively evaluate citric acid, grapefruit peel extract, and banana peel extract as bio-mordants for dyeing cotton with Harmal seed extract. The primary significance of the work lies in demonstrating that agricultural bio-wastes (banana and grapefruit peels) can serve as effective, sustainable, and low-cost alternatives to synthetic mordants like citric acid.

The study concludes that while citric acid is effective, the use of grapefruit peel extract yields superior color strength (K/S = 15.78) due to its complex chemical composition. Furthermore, the research highlights the potential for functional textile applications, specifically suggesting that the UV-absorbing and fluorescent properties of the dyed fabric could be utilized for UV-protective textiles, though the authors note that quantitative SPF measurements are required for future validation. The process is presented as an environmentally friendly, salt-free method that minimizes effluent while maintaining acceptable fastness properties.