Abstract
Nowadays the fabrics produced from Tencel fibres have the largest share in the regenerated textiles market. The durable press (DP) finishes used for improving the crease-resistance of Tencel fabrics are mostly achieved by Di-Methylol Dihydroxy Ethylene Urea (DMDHEU) or its derivatives. However, this process results in the release of formaldehyde during the fixation procedure; and formaldehyde has been identified as a potential human carcinogen. The present work dealt with the application of Polymaleic acid and its impact on various properties of Tencel, such as crease resistance angle (CRA), tensile strength, tearing strength and abrasion resistance. Finally Polymaleic acid treated fabric was compared with DMDHEU treated fabrics.
Key words: Cellulose, Crease Resistance Angle (CRA), Cross Linking, Durable Press, DMDHEU, Polymaleic acid, Poly carboxylic acid, Sodium Hypophosphite, Whiteness Index.
Introduction
Non-formaldehyde crease-resistant and DP finishing has been the need of the hour, as there is a ban for formaldehyde-based finishes in many countries1,2, and for Indian domestic purpose too. Poly carboxylic acids (PCA) are achieving notability as a new class of formaldehyde-free, eco-friendly cross-linking agents2,3. Therefore PCAs are considered to be safe alternatives to the formaldehyde-based cross linking resins.
Polycarboxylic acids react with hydroxyl groups of cellulose to form ‘ester cross links’, connecting adjacent cellulose chains in a three-dimensional network inside the cellulosic fibres4,5,6. It has been reported in the literature that there is a high degree of Crease Resistance, as well as smooth drying properties, in Tencel fabrics treated with Polycarboxylic acids having three or more carboxyl groups7, in the presence of alkali metal salts, particularly sodium hypophosphite8,9. Polycarboxylic acids react with cellulose via an anhydride mechanism.
In the presence of heat and catalyst, two carboxylic groups form a five-membered anhydride ring and release one molecule of water. The cyclic anhydride reacts with cellulose to form an ester and regenerate one carboxylic acid group2,9.
Experimental
2.1 Materials and Methods
Poly Maleic Acid (PMA) is applied to woven fabric (ring spun warp and weft) to produce a Crease Resistant finishes. For this present work, PMA and Sodium Hypophosphate were used in laboratory grade. Tables 1 and 2 give the fabric properties and padding recipe respectively. The fabric used in this study was a desized, scoured and bleached Tencel. 
After bleaching process, the procedure adopted was as follows: The fabric was padded in different concentrations of PMA (2, 4, 6, 8, 10 & 12% (w/w)), NaH2PO2 5 %, followed by squeezing to a wet pick-up of ca. 100%. The fabric sample was then dried at 80°C for 5 min and cured at 150°C for 6 min. It was then washed several times with cold water and dried in ambient conditions.
2.2 Test Methods
Samples were conditioned for 8 hours at 20±2°C and 65±4% relative humidity, according to TS EN ISO 139, before testing. Crease-recovery angle, tensile strength, tearing strength and abrasion resistance of the PMA treated fabrics were measured according to respective standards, as given in Table 3. The abrasion resistance was determined by end point founds per number of cycles.
The above test results will help to compare the samples effectively and to arrive at a conclusion. In all tests, five fabric specimens were evaluated and the average value for each test is given in the results and discussion10-14.
Results and Discussion
3.1 Properties of DMDHEU Treated Fabric
For estimating the efficiency of Poly Maleic Acid as a cross-linking agent, a comparative study should be made with samples made from standard cross-linking agents. For that purpose a resin-based cross-linking agent was selected. Control samples were prepared using DMDHEU resin. Tencel fabric samples were treated with 17% DMDHEU resin along with other auxiliaries required. 
3.2 Crease Recovery Angle
The results indicate that the PMA treated fabric shows a greater Crease Resistance Angle than DMDHEU treated fabric. Because PMA molecules have their carboxyl groups linked to adjacent carbons of their molecular backbone they are capable of forming a five member cyclic anhydride, being more effective for esterifying cellulose than those polycarboxylic acids having their carboxyl groups linked to their alternate carbons.
3.3 Tensile Strength
The effect of PMA concentration on tensile strength was investigated. Conventional resin treatment has a negative impact on tensile strength. Resin-treated fabric loses around 30- 40% of its original strength before treatment, whereas strength loss in the case of PMA-treated samples is significantly lower than in resin-treated sample. The use of PMA reduces the acidity of the polymerisation mixture and, hence, reduces the loss of fabric strength caused by acid degradation as the polymerisation time increases.
The average tensile strength of PMA-treated samples is exhibited in the table and figure. For 2% concentration of acid, the strength loss is negligible. As the concentration increases the strength loss increases, but not to a great extent; even for 12% concentration, the strength loss only 18%.
3.4 Tearing Strength
Based on the result, resin-treatment has a negative impact on tearing strength. Resin-treated fabric loses around 30-35% of its original strength before treatment, whereas strength loss in the case of PMA-treated samples is significantly lower than for resin-treated samples. The average tensile strength of PMA-treated samples is exhibited in the table and figure. For 2% concentration of acid, the strength loss is negligible. As the concentration increases the strength loss increases, but not to a great extent. Even for 12% concentration, the strength loss only 15%.
3.5 Abrasion Resistance
The results indicate the abrasion resistance of the both treatments. Generally the end point found per rubs is of a higher value for PMA treatments because PMA reduces the acidity of the polymerisation mixture and, hence, reduces the loss of fabric-strength properties. The mean results are given in the respective tables.
3.6 Whiteness
Table 9 shows the variation of whiteness index with factors affecting the PMA treatment and DMDHEU treatment. As per the result shown, up to 6% PMA will not affect the whiteness of the fabric, in comparison to DMDHEU, which, on the contrary, will reduce the Whiteness index when the concentration is increased.
Conclusions
This paper reports the crease-resistant finishing of Tencel fabrics with PMA. The results showed that PMA is a very effective reagent for the crease-resistant finishing of Tencel fabrics.
The PMA treatments of the Tencel fabric significantly improve its crease-recovery angle, tensile strength, tearing strength and abrasion resistance compared with DMDHEU-treated Tencel fabric. Optimised finishing variables were given and up to 286° of CRA was obtained, with 82%, 85% tensile strength and tearing strength retention reserved respectively.
As the concentration PMA increased above 10%, the crease-recovery angle degree decreased.
By using this PMA treatment, the following advantages were observed:
- No formaldehyde releases
- Flame retardancy effect
- Environmentally friendly
References
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