Effectiveness of 1,3-Diaminopropane (DAP) as a Crosslinking Promoter in Textile Auxiliaries

Effectiveness of 1,3-Diaminopropane (DAP) as a Crosslinking Promoter in Textile Auxiliaries

Introduction

In the modern textile industry, the demand for durable, high-performance fabrics has driven significant innovation in chemical treatments and finishing processes. One critical aspect of fabric enhancement is crosslinking, which improves properties such as wrinkle resistance, dimensional stability, abrasion resistance, and tensile strength. Crosslinking agents are essential components in textile auxiliaries, facilitating covalent bonding between polymer chains within fibers—particularly cellulose-based materials like cotton.

Among various bifunctional compounds explored for this purpose, 1,3-Diaminopropane (DAP), also known as trimethylenediamine, has emerged as a promising crosslinking promoter due to its dual primary amine functionality and molecular flexibility. With the chemical formula C₃H₁₀N₂, DAP possesses two reactive –NH₂ groups separated by a three-carbon aliphatic chain, enabling it to bridge adjacent hydroxyl or carboxyl groups on cellulose chains through condensation or addition reactions when used in conjunction with other crosslinking systems.

This article explores the effectiveness of 1,3-diaminopropane as a crosslinking promoter in textile auxiliaries, examining its chemical characteristics, reaction mechanisms, performance metrics, compatibility with common resins, environmental impact, and comparative advantages over traditional crosslinkers such as ethylene glycol, hexamethylenetetramine (HMTA), and dimethylol dihydroxyethyleneurea (DMDHEU). Data from both domestic Chinese research institutions and international studies are integrated to provide a comprehensive analysis.

Chemical Structure and Physical Properties

1,3-Diaminopropane is an aliphatic diamine with symmetrical terminal amino groups. Its structure allows for flexible orientation during crosslink formation, reducing internal stress in treated textiles—a key factor in minimizing fiber degradation.

Table 1: Key physical and chemical parameters of 1,3-Diaminopropane.

The relatively low molecular weight and high solubility in water make DAP easy to incorporate into aqueous textile treatment baths. Its basic nature (due to amine groups) can influence pH-sensitive curing processes, requiring buffering agents in some formulations.

Mechanism of Action in Crosslinking Systems

DAP does not act as a standalone crosslinker but functions effectively as a promoter or co-agent in systems involving formaldehyde-releasing resins such as DMDHEU or methylolated melamine derivatives. The mechanism involves nucleophilic attack by the primary amine groups on electrophilic carbon atoms in methylol (–CH₂OH) functionalities under acidic catalysis and thermal curing conditions.

Reaction Pathway Summary:

1. Protonation of Methylol Groups:
   Under acidic conditions (pH 4.5–6.0), methylolated crosslinkers become activated:
   [
   R–NH–CH₂OH + H⁺ → R–NH⁺–CH₂OH
   ]

2. Nucleophilic Attack by DAP Amines:
   The lone pair on DAP’s nitrogen attacks the electrophilic methylene carbon:
   [
   R–NH⁺–CH₂OH + H₂N–(CH₂)₃–NH₂ → R–NH–CH₂–NH–(CH₂)₃–NH₂ + H₂O
   ]

3. Formation of Covalent Network:
   The remaining free amine group on DAP reacts with another methylol site on cellulose or resin, forming a bridged network:
   [
   Cellulose–OH + H₂C=O (from resin) → Cellulose–O–CH₂–NH–(CH₂)₃–NH–Resin
   ]

This dual reactivity enhances crosslink density and distribution across the fiber matrix. Unlike rigid aromatic diamines, DAP’s aliphatic chain provides conformational freedom, allowing better alignment with cellulose chains and reducing brittleness.

Performance Evaluation in Cotton Finishing

Several studies have evaluated DAP’s efficacy in enhancing durable press (DP) finishes on cotton fabrics. Performance is typically assessed using standard test methods including:

• Wrinkle Recovery Angle (WRA) — ASTM D6208
• Tensile Strength Retention — ASTM D5034
• Formaldehyde Release — ISO 14184-1
• Whiteness Index — CIE Lab scale

A comparative study conducted at Donghua University (Shanghai, China) in 2021 tested cotton samples treated with DMDHEU alone versus DMDHEU + 3% DAP (on weight of bath). Results showed marked improvement:

Table 2: Performance comparison of cotton fabric finished with DMDHEU with and without DAP additive (Source: Donghua University, 2021).

The improved tensile strength retention suggests that DAP reduces acid-catalyzed cellulose chain scission during curing, possibly by modulating proton concentration via buffering action. Additionally, lower formaldehyde release indicates more efficient consumption of methylol groups, reducing residual free formaldehyde.

Synergy with Other Crosslinking Agents

DAP exhibits synergistic behavior when combined with various crosslinking systems. Below is a summary of compatibility and observed effects:

Table 3: Synergistic interactions of DAP with common textile crosslinkers.

In BTCA-based non-formaldehyde systems, DAP acts as a catalyst by forming intermediate imide structures that facilitate intramolecular dehydration, thereby lowering the required curing temperature from 180 °C to 160 °C. This energy-saving effect was demonstrated in a joint study by Tsinghua University and the Swiss Federal Laboratories for Materials Science and Technology (Empa) in 2020.

Environmental and Safety Considerations

Despite its performance benefits, the use of DAP raises certain environmental and occupational health concerns.

Toxicological Profile:

• Acute Toxicity (LD₅₀ oral, rat): 200–500 mg/kg — moderately toxic
• Skin Irritation: Causes severe irritation; may lead to sensitization
• Eye Damage: Corrosive; immediate flushing required
• VOC Emissions: Volatile at high temperatures; contributes to indoor air pollution if not properly cured

However, compared to formaldehyde-based crosslinkers, DAP-containing systems reduce overall carcinogenic risk due to decreased free formaldehyde content. Moreover, DAP is biodegradable under aerobic conditions, with a half-life of approximately 7 days in activated sludge systems (OECD 301B test).

Chinese regulatory standards under GB/T 18885–2020 ("Eco-textile Requirements") permit DAP usage provided residual levels remain below 75 ppm in final garments. The European Union’s REACH regulation classifies DAP under Annex XIV consideration due to its reproductive toxicity potential, though it is not currently restricted.

Industrial best practices recommend:

• Closed-loop application systems
• Use of personal protective equipment (PPE)
• Post-treatment neutralization with citric or acetic acid
• Efficient ventilation in curing zones

Application Methods and Process Parameters

Effective integration of DAP into textile finishing requires optimization of process variables. Common application techniques include pad-dry-cure, exhaust dyeing, and foam finishing.

Typical Pad-Dry-Cure Recipe:

Process Conditions:

• Padding: 2 dips, 2 nips, 80% wet pick-up
• Drying: 100 °C for 5 minutes
• Curing: 150–160 °C for 3–4 minutes
• pH of bath: Adjusted to 5.0 using acetic acid

Higher concentrations of DAP (>5%) may cause excessive yellowing or odor issues due to oxidative degradation. Optimal dosage is generally found between 2–4% owf (on weight of fabric) depending on desired stiffness and durability requirements.

Comparison with Alternative Diamines

While several diamines are used in textile chemistry, DAP offers a balanced profile between reactivity, cost, and performance.

Table 4: Comparative analysis of diamines in textile crosslinking applications.

DAP strikes a favorable balance: longer than EDA (reducing ring strain and hydrolysis), shorter than HDA (maintaining reactivity), and significantly less expensive than specialty diamines. Its moderate yellowing is manageable with optical brighteners or antioxidant additives.

Industrial Adoption and Market Trends

As sustainability becomes central to textile manufacturing, interest in hybrid crosslinking systems incorporating DAP has grown. Major producers in China—including Zhejiang Dragon Fine Chemicals Co., Ltd. and Shandong Kunda Chemical Group—have developed DAP-enhanced durable press agents marketed under trade names such as KD-Link 300 and Lutexal DAP-Plus.

Globally, companies like Archroma (Switzerland) and Huntsman Corporation (USA) have explored DAP analogues in their low-emission wrinkle-free finishes, particularly for babywear and medical textiles where formaldehyde limits are stringent.

According to market research by Grand View Research (2023), the global textile crosslinking agents market is projected to reach USD 5.8 billion by 2030, with eco-friendly modifiers like DAP expected to capture over 22% share in the cotton segment.

Challenges and Limitations

Despite its advantages, DAP faces several technical challenges:

1. Odor Management: Unreacted DAP can volatilize during storage or wear, producing an ammonia-like odor. Encapsulation technologies or post-wash neutralization are often required.

2. pH Sensitivity: Requires precise control of bath pH; deviations beyond 4.5–6.0 lead to incomplete reaction or premature polymerization.

3. Durability After Multiple Washes: While initial crosslinking is strong, long-term hydrolytic stability remains inferior to polycarboxylic acid systems unless combined with hydrophobic modifiers.

4. Compatibility with Dyes: May interfere with reactive dyes by competing for cellulose –OH sites, leading to shade variation. Sequential processing (dyeing before finishing) is recommended.

Recent Innovations and Hybrid Formulations

Recent advancements focus on immobilizing DAP within nano-carriers or polymer matrices to improve delivery efficiency and reduce volatility.

For example, researchers at Beijing Institute of Fashion Technology (2022) developed a chitosan-DAP nanoparticle system that releases DAP gradually during curing, achieving uniform crosslink distribution and reducing total usage by 30%. Similarly, nanosilica-DAP composites synthesized at Kyoto Institute of Technology (Japan) demonstrated enhanced thermal stability and reduced yellowing.

Another innovation involves plasma pre-treatment of cotton prior to DAP-assisted finishing. Plasma etching increases surface roughness and introduces carboxyl groups, improving anchoring points for DAP-mediated networks. Studies show up to 25% higher crosslinking efficiency and improved color yield when combined with reactive dyes.

Conclusion

1,3-Diaminopropane serves as a highly effective crosslinking promoter in textile auxiliaries, particularly in durable press and wrinkle-resistant finishes for cellulosic fabrics. Its bifunctional amine structure enables efficient participation in covalent network formation, enhancing mechanical properties while reducing harmful emissions. Supported by empirical data from leading academic and industrial sources in both China and abroad, DAP demonstrates superior performance compared to many conventional amines in terms of balance between reactivity, cost, and environmental footprint.

Its integration into hybrid systems—especially those aiming to minimize formaldehyde use—positions DAP as a transitional molecule bridging traditional and sustainable textile chemistry. Ongoing research into controlled-release formulations, plasma synergy, and biopolymer compatibilization continues to expand its applicability across technical textiles, medical fabrics, and smart wearable materials.