Comparative Enactment of Formaldehyde-free and Formaldehyde-based Cross-linkers on Cotton Woven

The performances of formaldehyde-based and non-formaldehyde cross-linkers on pretreated cotton woven fabric were assessed and compared in this research. Fixapret CL was considered as the formaldehyde-based resin and Fixapret NF as the formaldehyde-free resin. Dry cross-linking method was adopted for the application of cross-linkers. Diff erent properties of resin treated fabrics investigated and compared were as follows: DP (durable press) rating, wrinkle recovery, stiff ness, tensile strength, tear strength, shrinkage, skewness, hydrophobicity, whiteness and yellowness index. Marginally low performances in smoothness appearance and dimensional stability on fabric were exhibited with formaldehyde-free cross-linkers although indicating lower amount of the strength loss percentage. The formaldehyde-based compounds imparted more yellowing tendency to the treated fabric. The formaldehyde-free resins may be a good choice of replacements considering the overall eff ectiveness on fabric.


Introduction
Cotton is wonderfully versatile bre either single or blended, it can be washed or dry-cleaned easily [1].It absorbs moisture readily, hence it is used extensively to produce comfortable end products but it has easy wrinkling properties that o en create troubles for the end users [2].Since a wrinkle occurs from the break or reshaping of hydrogen bonds, preventing the distortions of those bonds could be a solution [3].Durable press nish or wrinkle free nish is just like that which forms covalent bonds with cellulosic hydroxyl groups of cotton bres and creates crosslinks among cellulose molecules [4].ese cross-linkers are also known as easy care or wash-n-wear nishing agents.ey can be de ned as the chemicals used for improving the properties and performance of washable fabrics.According to Tommasino [5], there are two types of durable press nishing agents conventionally used: rstly, those which predominately crosslink cellulose, known as cellulose reactants, and secondly, those which self-polymerize as well as crosslink cellulose, known as aminoplasts.Both of them contain formaldehyde which can be responsible for human cancer [3].Even the textiles containing high levels of formaldehyde can cause eczema and allergic reactions [6].
e rst group of nishing agents is N-methylol compounds, namely urea formaldehyde or melamine-formaldehyde.Fixapret CL, a formaldehyde based resin (Fig. 1) is the concentrated aqueous solution of a reaction product of DMDHEU (dimethylol-4,5-dihydroxyethylene urea) with methanol.
e N-methylol groups in DMDHEU react with cellulose forming a crosslinking net which is shown in Figure 2. On the other hand, Fixapret NF is an example of non-formaldehyde resin (Fig. 3) and an aqueous solution of 1,3-dimethyl-4,5-dihydroxyethylene urea (DMeDHEU).
e environmental impact of formaldehyde based resin and the potential danger of formaldehyde led to the introduction of non-formaldehyde nishes later on [2] and according to Can et al. [8], the use of non-formaldehyde resin is inexpensive and hygienic too.But before replacing formaldehyde-based resin by formaldehyde free resins, comparative studies are de nitely needed to evaluate their performances from di erent angles which is the focus of this paper.

Literature review
Mukthy and Azim [9] observed the e ects of DMD-HEU on cotton blended woven fabrics.ey tested wrinkle recovery, tensile strength, bending length and DP ratings of cotton and cotton blended fabrics on this aspect.Durable press rating was found close to 4 for cotton and cotton-blend fabrics.e in uence of resin was far greater on cotton fabrics than cotton-blends in aspect of tensile strength and wrinkle recovery.Wrinkle recovery angle increased approximately by 42% and breaking strength reduced by about 64% a er the crease resistant nishing.Figure 1: Chemical formula of Fixapret CL [7] Figure 3: Chemical formula of Fixapret NF [7] Tekstilec, 2017, 60(2), 107-115 Comparative Enactment of Formaldehyde-free and Formaldehyde-based Cross-linkers on Cotton Woven Fabrics aseen [4] also investigated the e ect of formaldehyde based resin (DMDHEU) on cotton, bamboo, lyocell and viscose fabrics with three levels of concentration and four levels of curing temperature.
ough the tensile strength was unchanged in the cases of other bres, the strength of cotton decreased at higher curing temperature and lower concentration of resin.Saleemuddin et al. [10] did their research from a broader aspect to obtain eco-friendly nishes as well as to optimize application parameters for wrinkle free nishing on cotton polyester blend.ey applied di erent pH values and resin concentrations using three types of formaldehyde based resins: dihydroxy ethylene urea, modi ed dimethylol dihydroxy ethylene urea (DMDHEU) and modi ed Nmethylol dihydroxy ethylene urea.ey compared the wrinkle recovery and tensile strength of treated fabrics.Formaldehyde extraction was lowest for the rst one at 30 g/L concentration at a pH 5.0.e treatment with the rst mentioned resin was more eco-friendly but provided low tensile strength.On the other hand, the mechanical properties of the blend fabrics treated with other resins were good with slightly elevated free formaldehyde.Another group of researchers Lau et al. [11] tested the e ect of wrinkle-free treatment on the fabric tear strength and dynamic water absorbency.ey considered nitrogen content as a better indicator of the level of wrinkle-free treatment than the swelling index.ey found that the swelling index (water retention) had a strong linear relationship with the total nitrogen content in the fabric.e higher the nitrogen content, the lower the swelling index (water retention).High nitrogen content or low swelling index resulted from the wrinkle-free treatment, caused low tear strength and reduced the water absorption rate of the fabric but increased the contact angle when the water drop was in initial contact of the fabric.Safdar et al. [12] compared the e ectiveness of three di erent types of resin nishes for improving the dimensional stability of cotton knitted fabrics.ey used two formaldehyde based resins: dimethylol dihydroxy ethylene urea (DMDHEU) and a methylolation product of glyoxal monourein; the third one, modi ed dihydroxy ethylene urea (DHEU), was formaldehyde free.From their results, it was found that the DHEU, the non-formaldehyde resin, had better bursting strength as well as higher shrinkage problem.
Can et al. [8] used glyoxal reactive, a non-formaldehyde resin as the nishing agent to examine the effect of wrinkle free nish on cotton fabric properties.
e result shows that a er applying glyoxal reactive, the fabric achieved better crease recovery angle and also improved in pilling performance (decreased pilling).But the strength properties such as breaking strength and tearing strength were decreased by the resin application.Tusief et al. [3] also took formaldehyde free nish (dihydroxy ethylene urea and dimethyl dihydroxy urea) for investigating the impact on wrinkle recovery of cotton fabric under di erent variables like concentrations and methods.A high concentration like 120 mg/L using pad-ash-cure method gave the best wrinkle recovery.Talebpour and Holme [13] worked on easy care nished cotton fabric to see the e ect on physical properties of bleached cotton.ey used the DMeDHEU based resin and observed that static and kinetic friction was also increased along with crease recovery.
ey also applied a silicone based so ener on an easy care nished fabric which reduced the friction as well as bending length but further increase in the crease recovery angle was observed.
ere was also an initiative to design the factors affecting the printing with reactive dye combined with crease resistance nishing on cotton fabrics by Asim and Mahmud [14].ey took DMDHEU as a cross-linker and found that the crease recovery angle depended on the interaction e ect of factors as well as individual factors.
ough there are a lot of works on resin nishing of cotton, there is no speci c comparison done between the performances of formaldehyde based and non-formaldehyde resin, excluding Safdar et al. [12].Even in that research, evaluations were done on a knitted fabric (shrinkage and bursting strength only), whereas a woven fabric tends to be more wrinkled due to its intensive structural nature and needs more treatment from cross-linkers than a knitted fabric.
erefore, this paper aims to investigate di erent properties of 100% cotton woven fabric including DP rating, wrinkle recovery, sti ness, skewness, hydrophobicity, abrasion resistance, shrinkage and strength (both tensile and tear) using formaldehyde containing and formaldehyde free resins.Moreover, it focuses on the comparative study of the treated samples with the non-treated one as Tekstilec, 2017, 60(2), 107-115 Comparative Enactment of Formaldehyde-free and Formaldehyde-based Cross-linkers on Cotton Woven Fabrics reference which can guide the scientists to make a better decision about the substitution of the formaldehyde based resin with the non-formaldehyde one.

Fabrics and chemicals
100% cotton woven fabrics (enzyme-desized, scoured with non-ionic detergents and bleached with hydrogen peroxide) were used for this experiment to apply di erent types of crosslinking agents by padding method.e speci cations of fabrics are given in Tab. 1. Trade names and types of all the commercial grades of chemicals for nishing supplied by BASF are listed in Tab. 2. Non-ionic surfactant

Resin application by padding in fi nishing (dry-crosslinking method)
Fabrics were treated with di erent resins (at concentrations: 50g/L, 60g/L, 70g/L, 80g/L, 90g/L and 100g/L) from a separate bath with the same nishing bath conditions.e process was adopted as recommended by the supplier (BASF).e bath setup is given in Tab. 3.

Evaluation of smoothness
Smoothness appearance of fabrics was tested according to the standard method AATCC 124.DP (durable press) rating was evaluated using 3-D standard replicas on a rating of 1 to 5 where 1 and 5 indicated severely wrinkled appearance and very smooth appearance respectively

Measurement of wrinkle recovery properties
Wrinkle recovery angle (in degrees) was measured using Shirley crease recovery tester taking the average values of warp and we results.

Stiff ness measurement
Sti ness was measured by bending length (in cm) using Shirley sti ness tester.Both warp and we way strength were determined and loss of strength percentages were calculated using Equation 1.

Dimensional properties measurement: shrinkage and skewness
Shrinkage and skewness percentage were calculated adopting the standard methods BS EN 26330-2A (60°C, tumble dry) and AATCC 179 respectively.

Assessment of hydrophobicity (water resistance)
Hydrophobicity of the samples was determined by the absorbency test.A drop test was performed according to AATCC 79 method where time required (in s) of a drop of water to be absorbed was recorded.Water absorbency of the treated samples was evaluated according to the wicking test method (column test).Each sample of 2.5cm width was hung vertically immersing 1cm length into 0.1% direct dye solution for 1min.e height of the liquid (in cm) absorbed by the sample was taken as a measure of absorbency.

Measurement of abrasion resistance
Abrasion resistance was evaluated by the method ISO 12947-3, with 9kPa loading for 10.000cycles.e weight loss percentage was calculated (a er 10.000cycles) comparing to the initial weight of each sample according to the Equation 2.

Refl ectance evaluation: whiteness and yellowness
e e ect of cross-linkers on whiteness and yellowness were evaluated a er applying resins and also in combination with Optical Brightening Agent (only whiteness with nonionic Fluorescent brightener by BASF -5g/L) for each sample from a separate bath following Tab.3. e degree of whiteness (Berger) and yellowness (CIE) of the samples was measured using a spectrophotometer with 10° observer and standard illuminant D65.All the values were measured in four di erent places making four folds of the samples and their average was taken for the analysis of the results.

Crease recovery properties: DP rating (smoothness) and wrinkle recovery angle
Durable press performance and wrinkle recovery angle of the samples treated with formaldehyde containing resins were pronouncedly improved more than those of the samples treated with formaldehyde free resins with increasing concentrations.As the bath concentration approached 70-80g/L, smoothness appearance and wrinkle recovery power began to level-o .Beyond this level the rate of increment was less rapid for both types of resin.Massive amounts of cross-linkers produced only modest gains of crease recovery properties in every case.e results of DP rating and wrinkle recovery angle in degrees (both warp and we way) are listed in Tab. 4.

Stiff ness: bending length
Sti ness was evaluated measuring bending length in cm which increased from a level of 3.25cm bending length for both types of the treated samples with the resin add-on but the formaldehyde-based resin treated sample was comparatively sti er with a maximum of 3.65cm as compared to 3.51cm at 100g/L with the non-formaldehyde reactants.Sti fabrics were torn more easily than so er ones.e values of bending length are listed in Tab. 4.

Strength: tensile and tear
e strength (tensile and tear) of the treated sample was greatly reduced but the formaldehyde cross-linker resulted in higher strength loss.Comparative Enactment of Formaldehyde-free and Formaldehyde-based Cross-linkers on Cotton Woven Fabrics strength loss percentage was ranged within 20 to 42% and 14 to 32% of original fabric values for the formaldehyde containing and formaldehydefree resin treated samples respectively.e rate of improvement is more rapid with increasing resin level.e tear strength also indicated in sharp decrease with increasing amounts of resin.e percentage loss of tear strength amounted to the range from about 26 to 44% and 19 to 37% of the non-treated samples for formaldehyde containing   and non-formaldehyde product.e tear loss percentage was obtained somewhat more as compared to the tensile loss percentage due to bre rigidi cation or sti ness.A comparative pro le of tensile and tear strength loss percentage with both types of resins are shown in Fig. 4 and Fig. 5 respectively.

Dimensional stability: shrinkage and skewness percentage
Dimensional stability was measured in terms of the shrinkage and skewness percentage of the treated samples.e results indicated that the degree of stabilization of the treated samples was increased with the increased number of crosslinkings.Crosslinking reduced the shrinkage and skewness more in case of formaldehyde-containing resins compared to the other.e percentage of both physical parameters dropped with the increased concentrations of resins.e comparison of the shrinkage and skewness percentage for di erent resins was shown in Fig. 6 and Fig. 7 respectively.

Eff ect on hydrophobicity: absorbency test
Absorbency by drop test and column test of the treated samples indicated that the resins imparted hydrophobicity to the treated samples in both cases.is might be explained that because of the participation of hydroxyl groups of cellulose in crosslinking with resins, there was less availability of such groups to attract water molecules which eventually compensated to reduce water absorbency.As the fabrics became less absorbent the time of absorption of a drop of water was delayed and correspondingly found lower wicking distance on the treated fabric with formaldehyde-free crosslinking agent.Tab. 5 is showing the results of drop test in seconds and column test in centimeters.

Abrasion resistance: weight loss measurement
Abrasion damage had a rapid increase with the resin add-on as the loss was obvious due to the number of crosslinks but the trends appeared to level o at 70-80g/L which was obtained as same as in case of strength loss and improved DP performance.e damage occurred on a slower rate a er the speci c concentration level for both types of cross-linkers applied.Abrasion resistance was evaluated in terms of the weight loss percentage and the formaldehydecontaining resin su ered weight loss most as is shown in Fig. 8.

Refl ectance: whiteness and yellowness index
e formaldehyde based cross-linker treated fabric surfaces appeared duller and hence, whiteness (with and without OBA) was a ected most and for the same reason the yellowness values were increased gradually with concentrations.e brightness was least a ected by the formaldehyde free compound.Tab.6 shows the re ectance data of all types of samples.Yellowing and deterioration of whiteness as well might be the consequences of using the formaldehyde reactants in combination with the catalysts and elevated curing temperature.

Conclusion
e objective of applying resins to textile fabrics is to impart speci cally wrinkle free smooth surface to cellulosic fabrics as well as apparels so as to eliminate the daily pressing or ironing of garments a er wash on usage.In this study, an investigation was performed comparing the e ectiveness on a woven fabric between basically two types of resins which are commercially very common.
e crease recovery properties in terms of durable press rating and smoothness appearance were increased with concentrations for both formaldehyde and non-formaldehyde reactants.It was found that the formaldehyde based resin imparted best smoothness appearance to  the fabric as compared with the other resin.Sti er fabrics were produced with the resin add-on but the formaldehyde-free containing samples produced comparatively so er handle with an increased bending length of only 8% as compared to the other types with 12% increment.Higher loss in fabric tensile strength was accompanied by the formaldehyde reactants which reached to as much as 42% with higher concentrations applied.e fabric tear strength was also impaired with gradual increase of concentrations and maximum loss in percentage of 44% was obtained for formaldehyde-based products.Both types of cross-linkers produced dimensionally stable fabric structures in terms of shrinkage and skewness a er wash.Shrinkage and skewness were more or less similar in case of both.Cross-linked sites participated in lowering fabric absorbency in both cases.e fabric treated with formaldehyde containing crosslinking agents contributed in higher weight loss percentage but showed a tendency to get a slower rate of increment beyond a certain concentration in case of both.A considerable rise in yellowness and the reduction in whiteness values resulted due to gradual increment of resin levels for both.Although the target of performance was achieved in most cases of formaldehyde based compounds, the use of formaldehyde free cross-linkers as a replacement is of much concern due to ecological aspects and safety issues.

Figure 4 :
Figure 4: Loss of tensile strength of fabrics treated with cross-linkers

Figure 5 :
Figure 5: Loss of tear strength of fabrics treated with cross-linkers

Figure 8 :
Figure 8: Weight loss for abrasion of treated fabrics by cross-linkers

Table 2 :
Trade names and types of chemicals and auxiliaries used

Table 3 :
Resin application bath * Catalysts were taken as 25% of the amount of resin at each concentration.

Table 4 :
DP rating, wrinkle recovery angle and bending length

Table 6 :
Whiteness and yellowness index of treated fabrics