CREASEPROOF FINISHING USING PHOSPHONO-BASED CATALYST WITH POLYCARBOXYLIC ACIDS SANDRA BISCHOF VUKUSIC, M.Sc. and Prof. DRAGO KATOVIC, Ph.D.
Faculty of Textile Technology
University of Zagreb, Croatia
1. INTRODUCTION Interes in easy-care cotton and viscose apparel, which should have creaseproof properties and dimensional stability during the washing, has intensified in recent years. During the creaseproof finishing cellulose material is stabilised by agents which have caused lowered swelling of materials in the water. Hydrogen bonds between the adjacent cellulose molecules are broken by water molecules and than re-established during the drying process.
Parallel with greater chemicals development and their industrial application, problems with human environment endangering have occurred. Life standard in developed countries is growing constantly, but greatly at the cost of the natural resources and environment pollution. Strict regulations over the applied chemicals and energy consumption reduction have been established recently. These regulations have been important for the textile industry, especially for the textile-finishing field.
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 crosslinking agents must meet a number of stringent requirements to be considered for practical use in creaseproof or Durable Press (DP) finishing .
Many classes of chemical compounds have been investigated as replacement for formaldehyde emitting crosslinking agents based on dimethyloldihidroxy-ethyleneurea (DMDHEU), which are still the most widely used finishing agents.
Majority of the PCA give satisfying results of DP performance and wrinkle recovery angles, but the differences in resistance to alkaline laundering are significant. A variety of PCA have been compared as DP or creaseproof finishing agents with different catalysts – alkali metal salts of phosphoric, phosphorous, hypophosphorous and polyphosphoric acid. The best results are obtained with sodium hypophosphite catalyst [2,3]. Unfortunately, it has some serious disadvantages as high cost, influence on shade changes in most sulphur and some reactive dyes because of its reducing character, and major concern is its environment impact.
The number of covalent bonds or linkages, which can be formed with cellulose, is limited to one less than the number of carboxyls in the PCA. Fabric performance after the treatment depends on the amount of reagent actually retained in the fabric after the laundering process, as well as on the effectiveness of crosslinking with the cotton cellulose.
Esterification reaction of cotton cellulose with BTCA is believed to proceed by intermediate formation of cyclic anhydrides of BTCA, as actual esterifying agents. Acceleration of weak bases for the esterification of alcohols by anhydrides is well known. Weak bases may also serve to accelerate the formation of the cyclic BTCA anhydrides at high cure temperatures. Intermediate cyclic anhydride reacts with the cellulose hydroxyl, forming a covalent bond, to complete the ester linkage. In further reaction, formation of a second anhydride follows, which subsequently reacts with another cellulose hydroxyl.
Investigation of possibility of polycarboxylic acid application have been conducted already for a long time period, but they are not in the wider usage yet. Despite their ecologically accepted properties, economical request has not been fulfilled – they are still too expensive.
One of the aims of this paper was to combine ecological with economical demands, which we have tried to accomplish with the application of cheaper PCA - citric acid. CA was mixed with BTCA in different ratios to obtain similarly good creaseproof effects as with the high required BTCA quantity. Further in addition to economical demands, phosphono-based catalyst were added to reduce high concentration of SHP catalyst in the system.
EXPERIMENTAL Desized, scoured, bleached and mercerised 100% cotton and viscose materials were used in the investigation and their properties are showed in Tab.I.
Table I. Properties of textile fabrics used for the experiment:
97 g / m2
120 g / m2
Density W / F
27 / 27
41 / 27
W / F
60 / 60 tex
110 dtex f 24 S 100 /
17 tex Z 900
Fabric treatments were carried out on a laboratory scale. The fabrics were impregnated in a solution containing CA, BTCA or their mixture in different ratios, together with esterification catalyst – SHP alone or mixed with one of the catalyst based on phosohonic acid (DETMPA or HEDPA). Pre-weighted cotton fabric was impregnated in an aqueous treating bath containing CA, BTCA or their mixture in different ratios. Wet-pickup was 100% on the weight of the fabric.
Table II. List of applied finishing baths and concentration of catalyst in g/l
g/l of catalyst
1 – 5
65 g/l SHP
6 – 10
41 g/l SHP
41 g/l SHP + 52 g/l HEDPA
16 – 20
41 g/l SHP + 40 g/l DETMPA
Esterification catalyst was SHP alone, or mixed with one of the catalyst based on phosphonic acid (DETMPA or HEDPA).
Phosphonic acid was added to PCA and hypophosphite (SHP) catalyst system in two different forms of its Na-salt (Fig. 1a and 1b) for the reduction of high concentration of sodium hypophosphite required.
Fig. 1A Octasodium salt of the diethylene- Fig.1B Tetrasodium salt of the triaminepentamethylenphosphonic acid hydroxyethylidene 1,1-
(DETMPA) diphosphonic acid (HEDPA)
Fabrics were dried at T=100C for 2 minutes and cured at T=180C for 90 seconds at Benz dryer.
Whiteness of the fabric was evaluated by CIE whiteness index measured before and after the treatment on a Datacolor 3890 spectrophotometer.
Infrared spectra of the treated fabrics were obtained on Perkin Elmer FT spectrometer using IR-DM (Data Manager) program. The potassium bromide technique was used to prepare samples of the treated fabric ground in a Wiley mill. For semi-quantitative determination of the finishes on the fabrics, normalisation of the carbonyl intensities in the infrared spectra was done against the 1317 cm-1 band, which represents C-H structures in cellulose molecules.
3. RESULTS AND DISCUSSION Many performance parameters for wrinkle-resistant fabrics have been investigated included whiteness and yellowing degree (CIE Wh.), conditioned and wet wrinkle recovery angles (DIN 53 891), strength retention (DIN 53 837), finish durability to washing and shade retention.
Fig. 2. Whiteness degree of cotton and viscose material treated with finishes 1-10
F ig. 3. Whiteness degree of cotton and viscose material treated with finishes 11-20
After the curing process at high temperatures, decrease of whiteness degree is more significant on cotton material than on viscose, especially in a case where only CA was applied. It is well known that optimal concentration of SHP is 65 g/l [4,5] and that with the reduction of SHP whiteness degree decreases as well 6.
Yellowness of the fabric did not occure on viscose fabric when CA was applied, what can be explained with the influence of viscose fibres on double conugated bonds which are the main cause of this problem.
With the addition of phosphono based catalysts we have obtained equally good results of whiteness degree or even better is some instances, than in a system where only SHP was applied in non-reduced quantity.
Table III. Wrinkle recovery angles (cond. and wet) of cotton and viscose fabrics treated with finishes 1-10
WRA cond. (W + F)
WRA cond. (W + F)
WRA wet (W + F)
WRA wet (W + F)
Table IV. Wrinkle recovery angles (cond. and wet) of cotton and viscose fabrics treated with finishes 11-20
WRA cond. (W + F)
WRA cond. (W + F)
WRA wet (W + F)
WRA wet (W + F)
With different ratios of CA/BTCA similar results of cond. and wet WRA have been obtained on cotton material compared with the treatment where BTCA alone was applied. This data’s are confirming the statement of possible substitution of greater BTCA part with an extender, CA in this case.
With HEDPA addition improvement of WRA was obtained with maximum BTCA concentration only, while in all other instances the results of WRA were even lower. Viscose fabric has shown very low results of cond. WRA, except in a case of BTCA treatment. Results of wet WRA on viscose materials are not as high as the cotton ones, but results of CA treatment are quite similar to BTCA ones.
With DETMPA addition to a maximum BTCA concentration, WRA showed equal results as in a system without the second catalyst. In other instances, the values of WRA were even lower than in the system where only SHP was applied (Table IV).
Although we have expected better results of DETMPA catalyst because of its numerous phosphono groups, results or WRA did not show any improvement. One of the probable reasons of DETMPA molecules impossibility to catalyses the esterification reaction is their size (molecular weight is 749).
Major loss of mechanical properties, even more than 50 %, is quite common in resin treatment of cellulose fabrics aimed at imparting wrinkle resistant properties.
In the case of SHP reduction (finishes 6-10), breaking strength retention was lower as well, which was to be expected because of the nature of sodium hypophosphite (Fig. 5). The viscose fabric showed lower reduction of breaking strength retention than cotton. This manifestation of higher breaking strength retention is valid in the case of SHP reduction as well.
The strength of cotton fabric is higher in wet state and lower in dry, while the situation is opposite with viscose. Strength loss is less pronounced with viscose than with cotton, which is generally true for this type of finishes. Moreover, strength of a viscose fabric can be increased after crease-resistant treatments. It is generally explained by reduction of moisture regain after crease-resistant finishes.
F ig. 4 Breaking strength retention of cotton and viscose materials treated with finishes 1-10
F ig. 5 Breaking strength retention of cotton and viscose materials treated with finishes 11-20
According to Shin 7, there are two major factors contributing the loss of mechanical properties: degradation of fibres caused by the acid catalysts and restriction of stress distribution within the fibres.
It has been previously shown by Young 8, that pH value has an influence over the breaking strength of the treated materials. Our results 9 have confirmed the fact that the higher pH values, in a range 2,2-2,8 where efficiency of BTCA is equally good, had caused better results of breaking strength retention (Fig. 6).
Table V. Physical properties of cotton material treated with CA or BTCA at different concentrations of SHP and DETMPA (A) or HEDPA (B) catalyst
A or B (g/l)
CIE wh. (A)
CIE wh. (B)
F % (A)
F % (B)
In a BTCA treatment system, it was possible to reduce expensive SHP catalyst to 30% by its partially replacement with DETMPA and HEDPA, while maintaining satisfactory results of WRA. Further reduction of SHP concentration caused unacceptably pronounced reduction of WRA. In a CA treatment system, maximum of SHP reduction was 50%, while the results of WRA were equally good (Table V).
In a case of extender/hypophosphite system whiteness decreases with higher extender ratio.
The method enabling determination of ester crosslinked cotton material, employing infrared spectroscopy FT-IR, was developed by Yang . Carbonyl groups on a cellulosic material treated with PCA are retained in three forms: ester, carboxyl acid and carboxylate anion. All three forms could be present in a single molecule, if PCA contains 3 or more carboxyl groups.
Unfortunatelly, carbonyl and carboxyl carbonyl bands overlap in the spectra of the finished cellulose and both peaks occurs in the range between 1735 and 1715 cm-1. Usual procedure is to treat the fabric with 0.1 M NaOH solution, to convert all the free carboxyl groups in the fabric to carboxylate. The band at 1725 cm-1 represents the carbonyl of ester, while the band at 1582 cm-1 represents the carbonyl of carboxylate, the basic form of the free carboxylic acid. Two anhydride carbonyl bands disappear completely after the sodium hydroxide treatment, and two carbonyl bands at 1725 and 1552 cm-1 appear in the spectrum [11-14].
Fig. 6 FTIR spectra of (base-rinsed) cotton fabrics treated with:
a – BTCA
b – BTCA/CA 1/1
c – CA
The bath contains 60 g/l PCA and 40 g/l SHP.
Fig. 7 FTIR spectra of cotton fabric treated with BTCA/HEDPA and 40 g/l SHP
acid rinsed with 0,1 M HCl and (b) base rinsed with 0,1 M NaOH
The amount of ester in the finished fabric can be determined quantitatively by measuring the ester carbonyl band intensity at 1725 cm-1. Ratios of peak heights at 1725 cm-1 between base-rinsed and acid-rinsed samples indicate the degree of esterification.
The carbonyl band intensity ratio (ester/carboxylate) is a function of the average number of ester groups formed for each PCA molecule and represents the effectiveness of the PCA molecules bonded.
The best effectiveness is obtained with CA, but the best results of WRA and the highest amount of ester are obtained with BTCA and mixed catalyst system (SHP and HEDPA).
4. CONCLUSIONS Among the environmentally acceptable and inexpensive PCA presently available, citric acid seems the most likely to find a place in formaldehyde free DP finishing, alone or in a system with some other PCA 15. Although BTCA shows the best results among different PCA investigated, there are still problems that should be solved before it can be commercially used on a wider basis. One of them is the price, which is three to four times higher than for conventional formaldehyde-based reactants. The other problem is finding an optimum catalyst systems for curing PCA . Sodium hypophosphite, which shows the best results for the esterification reaction, while maintaining good strength and whiteness properties, is quite expensive as well.
Therefore, our research was aimed at using cheaper citric acid to replace BTCA, in maximum possible quantities, while maintaining high degree of crosslinking without yellowing. In our research we have used 3 different mixtures CA/BTCA with the addition of second - phosphono based catalyst which served as extenders as well. Their salts act as buffers to control pH during drying and curing steps and minimize the acid degradation of the cellulose.
Resiliency effects of wrinkle free treatment on cotton fabric were improved only in a case of maximum BTCA concentration, but on viscose fabric improvement have not been obtained with addition of phosphono based catalyst.
Major improvement achieved in this research with phosphono based catalysts was a possible reduction of high required quantities of SHP catalyst by its partially replacement with DETMPA or HEDPA, which was 30 % in a case of BTCA and 50 % in a case of CA treatment.
The highest results of WRA obtained with BTCA and mixed catalyst system (SHP and HEDPA) were confirmed with FTIR spectroscopy analysis by ester carbonyl band intensity. The carbonyl band intensity ratio (ester / carboxylate) show that CA is capable of very good results concerning effectiveness.
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Finding competitively priced non-formaldehyde DP finishes has become the highest priority for the textile finishing industry. Polycarboxylic acids are gaining recognition as a new class of formaldehyde-free DP agents.
Exceedingly high costs of BTCA have prevented its commercial application in the industry. Citric acid has some advantages, such as low costs, widespread availability and ecological acceptability, but its great disadvantage is noticeable fabric yellowing under conventional curing conditions.
Modification was made in the present study with phosphonic acid as catalyst added to CA, BTCA or their mixture together with hypophosphite (SHP) catalyst system. Textile properties of the fabric treated with the new system are better than or equal to those treated with a PCA – SHP system.
More significant is a possible reduction of 50% SHP in CA treatment, and 30% in the case of BTCA treatment, while keeping good resiliency results.
From the ecological point of view, polycarboxylic acids (PCA) are highly justified, while economical problem of high price is still tried to be solved in various ways. When there will be a balance between ecology and economy, polycarboxylic acids will certainly find its place at the market, not just in the creaseproof finishing processes.