Synthesis and application of polyamine type aldehyde-free fixing agent

**Synthesis and Application of Polyamine-Based Aldehyde-Free Fixing Agents** Zhang Qingping, Fan Zenglu, Zhao Feifei, Cai Jianfang, Tang Wenfeng (School of Textiles and Materials, Xi'an Polytechnic University, Xi'an 710048, China) **Abstract**: A formaldehyde-free polyamine-based fixing agent was successfully synthesized using dimethylamine, epichlorohydrin, and tetraethylenepentamine as primary raw materials. Through a series of experiments, the optimal synthesis conditions and fixation process were determined. The best synthesis procedure involved reacting dimethylamine with epichlorohydrin in a molar ratio of 1:1.5 for about 2 hours at 28°C, followed by the addition of 4% tetraethylenepentamine based on the total monomer mass, and continuing the reaction at 70°C for an additional 5 hours. The most effective fixation process included two dips and two rolls of the fabric in a solution containing 40 g/L of the fixing agent with an 80% roll rate, followed by drying at 100°C. This treatment improved the wet fastness of direct dyes by 1–2 levels without significantly affecting the color shade. **Keywords**: Fixing agent; Synthesis; Fixation; Direct dye; Cotton fabric **CLC number**: TS 193.225 | **Document code**: A | **Article ID**: 1674-649X(2010)06-0734-05 Direct dyes are widely used in cotton dyeing due to their full color spectrum. However, they often exhibit poor wet fastness because of water-soluble functional groups like sulfonic acid and carboxyl groups. To address this, fixing agents are essential in post-dyeing treatments. Traditional agents such as fixing agent Y or coloring agent G improve fastness but may contain free formaldehyde, which is harmful to human health. With growing environmental awareness and stricter regulations like ISO 14000, there is a strong demand for eco-friendly alternatives. This study presents a novel polyamine-based fixing agent that is free from formaldehyde, cost-effective, and highly efficient, offering promising potential for commercial application. **1. Experiments** **1.1 Materials and Reagents** Direct Lake Blue 5B dyed cotton fabric, dimethylamine (33%), epichlorohydrin, tetraethylenepentamine, and a formaldehyde-free fixing agent (2011) were used. **1.2 Equipment** Electric Mixer , electric thermostatic water bath, rubbing fastness tester, wash fastness tester, and SF-300 computer colorimeter. **1.3 Methods** **(1) Fixing Agent Synthesis** A three-neck flask was charged with dimethylamine and placed in a cold water bath at ~23°C. Epichlorohydrin was slowly added dropwise while maintaining a controlled drip rate of 3–4 seconds per drop. After the reaction, the temperature was raised to ~28°C and maintained for 2 hours. Tetraethylenepentamine was then added dropwise, and the mixture was reacted for another 2 hours before being heated to 55–75°C for 3–6 hours to complete the polymerization. **(2) Fixing Process** Cotton fabric dyed with Direct Lake Blue 5B was treated by padding with the fixing agent (two dips and two rolls), followed by drying at 100°C. **1.4 Fastness Testing** **(1.4.1) Rubbing Fastness** Determined according to CB/T 3920-1997. **(1.4.2) Washing Fastness** Measured using SW-12 testing equipment following GB/T 3921-2008. **(1.4.3) Color Fastness Rating** Assessed using GB/T 251-1995 gray scale cards. **(1.4.4) Color Difference Analysis** ΔL, ΔC, ΔE, and ΔH values were measured using the SF-300 computer colorimeter. **2. Results and Discussion** **2.1 Synthesis Process of the Fixing Agent** The synthesized agent was applied to directly dyed cotton fabric, and its performance was evaluated through fastness tests. The results showed that the optimal molar ratio of dimethylamine to epichlorohydrin was 1:1.5, leading to higher cationization and better fixing efficiency. **2.1.1 Effect of Molar Ratio** As the molar ratio of epichlorohydrin increased, the color fastness improved, reaching a peak at 1:1.5. **2.1.2 Effect of Reaction Temperature** At 70°C, the fixing effect was optimal. Too low a temperature led to incomplete reaction, while too high a temperature caused excessive viscosity and reduced effectiveness. **2.1.3 Effect of Reaction Time** After 5 hours of reaction at 70°C, the fixing agent reached its maximum performance. Beyond that, energy waste and side reactions occurred, reducing the quality of the final product. **2.2 Fixing Process Optimization** The best process involved treating the fabric with 40 g/L of the fixing agent at 80% roll rate, followed by drying at 100°C. **2.2.1 Fixing Agent Dosage** Increasing the concentration up to 40 g/L improved fastness, beyond which no significant improvement was observed. **2.2.2 Drying Temperature** 100°C was found to be the ideal drying temperature. Lower temperatures resulted in poor bonding, while higher temperatures damaged the fabric and reduced the fixing effect. **2.2.3 Rolling Rate** An 80% rolling rate provided the best balance between liquid retention and uniform application. Higher rates led to excess residue and lower effectiveness. **2.3 Comparison with Commercial Products** The self-made polyamine fixing agent outperformed the commercial aldehyde-free agent 2011 in terms of washing fastness, while showing similar performance in other aspects. It improved the fastness of direct dyes by 1–2 levels. **2.4 Color Changes After Finishing** Minor color changes were observed, likely due to dye loss during the finishing process and chemical interactions during drying. **3. Conclusions** (1) The optimal synthesis process involved reacting dimethylamine and epichlorohydrin in a 1:1.5 molar ratio for 2 hours, followed by the addition of 4% tetraethylenepentamine and a 5-hour reaction at 70°C. (2) The best fixing process was two dips and two rolls with 40 g/L of the fixing agent at 80% roll rate, followed by drying at 100°C. This improved the fastness of direct dyes by 1–2 levels with minimal impact on color. **References** [1] Deng Yaoming. *Synthesis and properties of aldehyde-free fixing agents*. Journal of Dongguan University of Technology, 2009, 16: 88–92. [2] Huang Maofu, Yang Yuqin. *Development and current status of aldehyde-free fixing agents*. Printing and Dyeing Auxiliaries, 2002 (4): 1–4. [3] Yang Hua. *Development and application of aldehyde-free fixing agents*. Fine Chemical Raw Materials and Intermediates, 2007 (6): 15–18. [4] Liu Weiwei, Zhang Wei. *Low-aldehyde and non-aldehyde printing and dyeing auxiliaries*. Hebei Textile, 2009 (2): 69–73. [5] Huang Xinzhao, Zhang Zhongyi, Zhang Xiaodong. *Application of dimethylamine polymers in fixing and flocculation*. Journal of Qingdao University, 2008 (1): 56–62. [6] Li Zhanxiong, Wang Changyu, et al. *Preparation and application of cationic aldehyde-free fixing agents*. Printing and Dyeing Auxiliaries, 2007 (24): 10–12. [7] Yang Jingxin, Chen Xinhua. *Development and application of polycationic aldehyde fixing agents*. Printing and Dyeing Auxiliaries, 2009, 26: 23–26.

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