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Cationic Modified Cotton Knitted Fabric Reactive Material Anti-dyeing Process

Views: 3 Author: Site Editor Publish Time: 2026-07-15 Origin: Site

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1. What is Cationic Modified Cotton?

Cationic modified cotton = modified cotton fiber with cationic groups (mainly quaternary ammonium salts) introduced onto or inside the cotton fiber surface. Its purposes include:

• Cotton fibers carry a negative charge under neutral/alkaline conditions (-OH dissociation)

• Ordinary cotton has limited affinity for anionic dyes (reactive dyes)

• Modified fibers carry a positive charge, significantly increasing their affinity for anionic reactive dyes

• Cationization introduces positive charges onto cotton fibers, significantly improving the affinity between cotton and anionic reactive dyes. This can increase dye exhaustion, reduce salt consumption and improve dyeing efficiency.

Advantages	Effects
High Dye Uptake	Conventional Cotton: 60–70% → Modified Cotton: 90%+
Water & Energy Saving	Reduce water consumption by 30% and electricity consumption by 30%
Lower Pollution & Emissions	Lighter-colored dyeing effluent and lower COD level

One major challenge of cationic modified cotton – Easy to dye. Dyeing rate: Ordinary cotton <2%, modified cotton 5-15%. This leads to:

• First-grade yield dropping from 95% to 80-85%

• Rework cost of 0.5-1 RMB/meter for color correction

• Customer complaints, returns, and claims

Therefore: Solving dyeing issues = 50% success rate in modified cotton dyeing

Mechanism of Dyeing in Cationic Modified Cotton

The root cause of uneven dyeing is excessively rapid dyeing rate (main reason):

• Cationic fiber (+) + anionic reactive dye (-) = strong electrostatic attraction

• Dyeing rate is 3-10 times that of ordinary cotton

• Dye is fully applied in a short time → uneven dyeing

Excessively high affinity:

• Strong binding force between fiber and dye (ionic bond)

• Once adsorbed, it is difficult to migrate

• Difficult to achieve even dyeing (unlike ordinary cotton)

Temperature has little effect on dyeing rate

• Ordinary cotton: Increased temperature → faster dyeing (can be controlled by temperature)

• Modified cotton: Charge attraction is the main driving force, temperature has little effect

PH Sensitivity

• High pH → more fiber ionization → weakened cation exchange

• Low pH → more dye hydrolysis

• Narrow critical pH range

Electrolyte Sensitivity

• Sodium sulfate (electrolyte) changes charge distribution

• Adding sodium sulfate = weakened electrostatic attraction = slower dyeing

• However, excessive amounts can cause "salting out"

Four major factors that lead to flower dyeing

No.	Causes	Impact Level
1	Excessively Fast Dye Uptake Rate	⭐⭐⭐⭐⭐
2	High Affinity and Poor Dye Migration	⭐⭐⭐⭐⭐
3	Low Influence of Temperature on Dye Uptake	⭐⭐⭐⭐
4	Sensitivity to pH and Electrolytes	⭐⭐⭐

Three main characteristics of flower dyeing

Performance	Severity
End-to-End Color Difference	Common
Inner-Outer Color Difference	Common
Severe Shade Variation / Uneven Dyeing	In Severe Cases

Anti-dyeing flower large-scale solution

Solution: The low-temperature isothermal dyeing method achieves uniform dyeing by lowering the initial dyeing temperature and slowly increasing the temperature to control the dyeing rate.

Process Parameters

Process Step	Temperature	Time	Function
Initial Dyeing	30–40℃	–	Critical! Low-temperature slow dye uptake
Temperature Raising	1–2℃/min	20–30 min	Slow heating rate! Avoid rapid temperature increase
Dyeing	50–60℃	30–60 min	Maintain constant temperature
Fixation	60–80℃	30–60 min	Alkali addition promotes further dye uptake and fixation

Key Operating Points

• Dyeing should begin at 30℃. Never dye at high temperatures (high-temperature dyeing = inevitable color changes).

• Heating rate: 1-2℃/min (use programmed temperature control).

• Hold at 50-60℃ for 30-60 min (to achieve dye balance).

• Cool to 50℃ before adding alkali (to avoid localized color fixation).

Retarding Agent Method

Adding a cationic retarder agent competes with the dye for cationic sites (occupying sites initially but not fixing the color), allowing the dye to apply later → retarded dyeing + leveling dyeing.

Hangzhou Tiankun Sylic® Cationic Retarder

Item	Parameter
Dosage	0.5–2 g/L
Addition Timing	Add 5 minutes before dye addition
Function	Compete for cationic sites
Effect	Slow dye uptake & improve levelness

Key Operating Points

• Add the retarder before the dye (to reserve space)

• Adjust the amount of retarder according to the amount of dye used

• Ratio of retarder to dye: 1:3 ~ 1:5

PH Control Process (Two-Stage Method):

First, apply dye with neutral pH (without fixing) → then add alkali to fix the color, avoiding color fixing immediately after dyeing, which can lead to uneven dyeing.

Stage	pH	Temperature	Function
Dye Uptake Stage	Neutral (pH 6–7)	30–60℃	Dye adsorption without reaction
Fixation Stage	10.5–11.0	60–80℃	Alkali addition promotes dye reaction and fixation

Key Operating Points

• Do not add alkali during the dyeing stage (to avoid color fixation)

• Add alkali only after the dyeing has reached equilibrium

• Add alkali in stages and slowly

One-bath dyeing and color-fixing method:

Start dyeing at 30℃ + slowly heat to 80℃ (dyeing and color fixing at the same time), reducing intermediate steps.

Process Step	Temperature	Time
Initial Dyeing	30℃	–
Slow Temperature Raising	2℃/min	25 min
Dyeing & Fixation	80℃	30–60 min

Operating Points

• Strictly control the heating rate to 2℃/min

• Hold at 80℃ for 30-60 min

• Suitable for light and medium colors

Quick Answers to Common Questions

Problem	Cause	Solution
End-to-End Color Difference	Concentration difference caused by different fabric feeding times	Add dye in stages / Increase liquor ratio / Improve circulation
Inner-Outer Color Difference	Insufficient dye liquor penetration into inner layers	Use low-speed circulation / Add penetrating agent / Extend circulation time
Severe Uneven Dyeing	Excessively fast dye uptake / Uneven temperature distribution	Low initial dyeing temperature at 30℃ + Slow temperature raising + Add dye migration agent (leveling agent)

Evaluation indicators for dyeing flowers

Grade	Evaluation	First-Time Success Rate
Excellent	No color variation	> 98%
Good	Slight color variation (can be corrected by shade adjustment)	95–98%
Average	Noticeable color variation (requires rework)	90–95%
Poor	Severe color variation (scrap)	< 90%