1. Introduction:
Recent health risk assessment of the possible effects of continued exposure to formaldehyde vapour to humans has increased the desirability of finding durable press reagents, which do not release formaldehyde. Such cellulose cross-linking agents must meet a number of stringent requirements to be considered for practical use in crease proof or Durable Press (DP) finishing. Many classes of chemical compounds have been investigated as replacement for formaldehyde emitting cross-linking agents based on dimethylol dihidroxy ethylene urea (DMDHEU), which are still the most widely used finishing agents [1]. Majority of the Poly- carboxylic acids (PCA) give satisfactory results of DP performance and wrinkle recovery angle.
The creasing behavior of cotton fabric is directly related to the free hydroxyl groups present in the amorphous regions, which are bound to each other. To impart crease resistance finish to the cotton material, the hydrogen bond formation of the hydroxyl groups should be either masked or totally removed. A popular and widely used method of imparting the crease resistant finish is the one in which the hydroxyl groups of adjacent macro molecules are reacted with bi-functional chemicals forming a cross-link with elimination of water or methanol molecules [2].
Formaldehyde has many advantages as a cross-linking agent, including low chemical cost and high finish durability, whereas this process is notorious for lack of control, high strength loss of treated cotton and release of excessive fumes in the atmosphere. It was found that formaldehyde and hydrochloric acid in the presence of water can form Bichloromethyl ether (BCME), which is human carcinogen, irritant and causes allergy to human beings. Citric acid has been identified as a successful non-formaldehyde based cross-linking agent.
PCA which react readily with cotton at an elevated temperature, Citric acid has showed higher reactivity when applied to cotton in the same way. [2]
One of the aims of this paper is to combine ecological with economical demands, which we have tried to accomplish with the application of cheaper PCA – Citric acid. Citric acid mixed with Trisodiumcitrate in different ratios to obtain similarly good crease-proof effects as with the DMDHEU. Citric acid formed a cross-link with elimination of water [3] in following mechanism:
2. Materials & Methods:
2.1. Materials:
A bleached 100% cotton knit fabric (Single Jersey) having 140 GSM has been used.
Chemicals:Cross-linking agent Citric Acid, catalyst Trisodiumcitrate, wetting agent Lissopal-N and softening agent silicone emulsion have been used to impart crease resistant finish to the fabric.
2.2. Methods:
In this experimental plan, three levels and their three variables were selected (Table 1).
Bleached and dried fabric was padded in a solution containing Citric acid, Trisodiumcitrate, wetting agent (0.1%) and softener (1%).
The padded fabric was dried at 80°C and then the curing process was carried out at 160°C, 180°C and 200°C for 2 min. The cured fabric was treated with soap solution (sodium lauryl sulphate 2 gm per litre (g/l) for 5 min, rinsed for 10 min at room temperature and then dried. Thirteen trials were conducted (Table 2).
Table 1- Details of process parameters and different levels for crease recovery finish.
Used testing instruments:
1. The Shirley crease recovery tester to measure recovery angle.
2. Bursting strength tester (JAMES H.HEAL & CO. LTD.)
3. Spectrophotometer (Data Color) to measure the whiteness index of fabric.
3. Results and Discussion:
Table -2 trials show the various physical appearance of cotton fabric treated with Citric acid as cross-linking agent in the presence of Trisodiumcitrate as catalyst at different curing temperatures.
Figure 2 shows 13 trials treated samples
Effect of concentration of Citric acid,
Trisodiumcitrate and curing temperature over whiteness index:
Higher curing temperature gives yellowish effect. In trials 2, 3, 5, 6, 10 where curing temperature were higher, showed negative value of whiteness index.
In trials 1, 2 curing temperature (180°C) and concentration of Trisodiumcitrate remained constant, where concentration of Citric acid were variable. Due to higher conc. of citric acid in trial 2 gives negative value of whiteness index.
In trials 11, 12 curing temperature and concentration of Trisodiumcitrate was same, variable was concentration of citric acid, higher concentration of citric acid gives lower whiteness index than lower concentration of citric acid.
In trials 4, 7, 8, 9 lower curing temperature (160°C) and with variable concentration of citric acid (even with higher concentration) and Trisodiumcitrate gives better whiteness index though these values (whiteness index) are lower than whiteness index of untreated fabric.
Hence, the whiteness index of fabric is not affected by the catalyst. Hence, Trisodiumcitrate is one of the best catalysts to reduce the yellowness is given by citric acid.
As whiteness index is the most important requirement of finished fabric, hence we gone through testing for 4 trials treated fabric (trial no.4, 7, 8, 9) whose whiteness index much better than other’s.
Table 4- Physical properties of untreated and treated samples using different process parameter.
Effect of concentration of citric acid and trisodiumcitrate over crease recovery angle:
Table-4 shows satisfactory result on crease recovery angle compared with untreated sample. According to trial 4, 7, 8 increase of concentration of citric acid increases crease recovery angle. As in trial 4, 9 concentration of citric is constant but concentration of catalyst trisodiumcitrate varies. Here increase of concentration of catalyst in trial no. 9 by keeping constant concentration of citric acid and curing temperature in response to trial no. 4, increases crease recovery angle.
Effect of concentration of citric acid, trisodiumcitrate and curing temperature over bursting strength:
In 160°c curing temperature and at variable concentration of citric acid and trisodiumcitrate in trial 4, 7, 8, 9 shows satisfactory result as compared with untreated sample. High concentration of citric acid reduces the bursting strength.
Effect on absorbency power:
Approximately 80% absorbency power increased due to this treatment. Higher concentration of citric acid increases wicking percentage. So, crease resistant finished garments with citric acid will be much comfortable due to high moisture absorbency percentage.
Comparative study with glyoxal treated fabric:
The fabric was treated with Glyoxal resin at 60g/l while curing temperature was 160°C.
Table 5: Physical properties of glyoxal resin treated fabric
Citric acid finished fabric was cured at 160°C same as glyoxal treatment curing temperature and that shows nearly close result in case of whiteness index but better strength retention and moisture absorbency.
The whiteness index of cotton fabric treated with 15% citric acid and 6% trisodiumcitrate at 180°C curing temperature show more than 90% retention and it is greater than that of other conventional cross-linking agents. [4]
Conclusion:
Among the environmentally acceptable and inexpensive PCA presently available, citric acid seems the most likely to find a place in formaldehyde free DP finishing. Citric acid is found to be one of the most effective cross-linking agents for crease resistant finish. High concentration of citric acid and Trisodiumcitrate shows excellent crease resistance, where whiteness index became reduced at higher concentration of citric acid. The optimum curing temperature of 160°C gives best crease recovery angle. At 160°C curing temperature and 10% citric acid with different levels of Trisodiumcitrate, better whiteness index and bursting strength is obtained. Crease resistant finished garments with citric acid will be more comfortable due to high moisture absorbency percentage. It is concluded that this research was aimed at using cheaper ecofriendly citric acid to replace formaldehyde based cross-linking agent in maximum possible quantities, while maintaining high degree of cross-linking without yellowing.
6. References:
[1]. SB VUKUSIC-bib.irb.hr.(crease proof finishing using phosphono based .catalyst)
[2].nopr.niscair.res.in/bitstream/1/IJFTR%2034(4)%20359-367.pdf(Indian Journal of Fibre & Textile Research Vol .34,December 2009,pp.359-367) [3].www.usc.es/congresos/ecsos/13/hall_f_psc/f3.pdf(13rd International Electronic Conference on Synthetic Organic Chemistry (ECSOC-13),1-30 November 2009).
[4]. Yamamoto Kazuhide, Text Res J,52(6)(1982)357
This project is one of the Textile Talent Hunts (TTH 2012) research projects.To know more About TTH please visit www.tth.textiletoday.com.bd
