Optimization of durable press finishing process of cotton fabric with a combination of BTCA and CA by response surface methodology

CHU Xudong, WANG Huaifang, ZHU Ping, SUI Shuying

(College of Textile & Clothing/Institute of Functional Textiles and Advanced Materials/State Key Laboratory of Bio-fibers and Eco-textiles/Collaborative Innovation Center of Marine Biomass Fibers, Materials and Textiles of Shandong Province, Qingdao University, Qingdao 266071,Shandong, China)

Abstract:A two-dimensional numerical model was developed to investigate and optimize the durable press (DP) finishing process of cotton fabric with a combination of 1, 2, 3, 4-butanetetracarboxylic acid (BTCA) and citric acid (CA).The numerical model was validated by experimental data. Response surface methodology (RSM) was used to establish mathematical models of the wrinkle recovery angle (WRA) and the breaking strength as the function of the operating parameters involving BTCA concentration, CA concentration, sodium hypophosphite (SHP) concentration, curing temperature, and curing time. Analysis of variance (ANOVA) for the models revealed that the curing time was the most significant factors affecting WRA, followed by the concentration of BTCA and CA, the curing temperature and the concentration of SHP. As to the breaking strength, the curing time was the most significant variable, followed by the curing temperature, the concentration of SHP, the concentration of CA and the concentration of BTCA. The optimal process is as follows:BTCA 50 g/L, CA 45 g/L, SHP 33 g/L, curing at 162℃ for 63 s, and WRA of the finished cotton fabric in this condition is 260° and breaking strength retention is 72%.

Key words:DP finish; response surface methodology (RSM); BTCA; citric acid; cotton fabric

0 Introduction

In the early 1990s, Clark M. Welch et al. found that alkali metal salts containing phosphoric acid can be used as catalysts for esterification of polycarboxylic acid with cellulose[1-2], and that treated fabrics have excellent durable press (DP) property. This discovery laid the foundation for the application of polycarboxylic acids as formaldehyde-free DP finishing agents for cotton fabrics, avoiding the possible harm of formaldehyde to the environment and human body.

Polycarboxylic acids have been considered to be the most promising formaldehyde-free DP finishing agents to replace Di-Methylol Di-Hydroxy Ethylene Urea (DMDHEU), and 1, 2, 3, 4-butane tetracarboxylic acid (BTCA) is the best one among them. The DP grade of cotton fabrics treated with this compound can reach 4-5 grades. In addition to the fine DP property of cotton fabrics, the finished cotton fabrics also possess the desired whiteness and washability. However, the price of BTCA is too high that few industrial applications were carried out till now. Citric acid (CA) is also a kind of polycarboxylic acid for DP finishing agent with much lower cost[3-4]. Although the wrinkle resistance of fabrics finished with CA is not as good as that of BTCA, it still has great application value.

Response surface methodology (RSM) introduced by BOX and Wilson[5], is a collection of mathematical and statistical techniques with wide applications in food engineering, analytical chemistry, biological engineering and so on by designing experiments, building models and analyzing the effects of independent factors[6-7]. This method would establish a mathematical quadratic model between response value and design factors by statistical techniques based on experimental results. The optimal values of experimental conditions would be obtained by this model.

Conventionally, DP finishing process with polycarboxylic acid is mainly carried out by single factor experimental method[8-9]. Based on this method, only the parameter to be examined is varied while the others are fixed at a certain value. Compared with single factor experimental method, the empirical model of RSM cannot only clarify the interactive effects among experimental parameters, but also can predict the experimental parameters to obtain the needed experimental results[10-11]. In this study, the effect of finishing parameters like BTCA concentration, CA concentration, SHP concentration, curing temperature, and curing time was investigated on the wrinkle recovery angle (WRA) and the breaking strength. Furthermore, the optimization of the finishing process of cotton fabrics was successfully conducted by RSM.

1 Experimental

1.1 Materials

The materials used in this study are desized, scoured, bleached and mercerized plain cotton woven fabrics (weight:140 g/m2, warp density:52.4 ends/cm, weft density:28.3 picks/cm, yarn count:14.75 tex×14.76 tex), which are supplied by Weifang Qirong Textile Co., Ltd. BTCA, sodium hypophosphite (SHP) and CA were obtained from China National Pharmaceutical Group Co. Ltd., Shanghai, China. DA-26 silicon oil (solid content:40%) was used as a fabric softener and purchased from Shanghai Xingzhou chemical industry limited Co. Ltd., Shanghai, China. All chemicals were of chemically pure and used as received unless otherwise stated.

1.2 Fabric treatment

The fabrics were finished by pad-dry-curing method. The finishing solution contained BTCA and SHP as well as 20 g/L silicon oil (DA-26). The sample was impregnated in the solution and padded with a laboratory padder with two dips and two nips. The wet pickup of the padded sample is approximately 80%. Padded samples were dried at 100 ℃ for 2 minutes, and then cured at a desired temperature for a time period. Finally, the cured fabrics were rinsed in water to remove all unreacted agents and dried at 80 ℃ for 5 minutes.

1.3 Measurements

1.3.1 Wrinkle recovery angle (WRA) Wrinkle recovery property was tested both in wrap and weft direction according to GB/T 3819—1997 “Textile fabrics——Determination of the recovery from creasing of a folded specimen by measuring the angle of recovery”. After maintaining in the standard atmospheric balance box for 24 h, each sample was tested 6 times and the mean value was recorded as the index of fabric wrinkle recovery.

1.3.2 Breaking strength Breaking strength property of cotton fabric was tested according to GB/T 3923.1—2013 “Textiles—Tensile properties of fabrics——Part 1:Determination of maximum force and elongation at maximum force using the strip method”. All samples were 30×6cm2sized. After maintaining in the standard atmospheric balance box 24 h, each sample was tested 5 times and the mean value recorded. During the testing process, the gauge length is 20 cm, the drawing speed is 100 mm/min, and the recovery speed is 300 mm/min.Breaking strength retention (%)=(Rb/Ra)×100%.

WhereRbis the breaking strength (N) of the finished fabric andRais the breaking strength (N) of the fabric before finishing treatment.

The loss of weft strength of finished fabric is normally greater than that of warp strength[12]. All measurements were measured in weft direction only.

1.4 Experimental design

This article aims at developing a two-dimensional numerical model for investigating and optimizing the DP finishing process of cotton fabric with a combination of BTCA and CA. In the optimization procedure, WRA and the breaking strength are selected as the responses, and five operating parameters include: BTCA concentration, CA concentration, SHP concentration, curing temperature, and curing time are chosen as the variable factors. According to actual finishing process, the effective domains of five factors are determined. Five-factor and three-level experimental matrix shown in Tab.1 is designed and generated by the Box-Behnken Design (BBD).

Table 1 Range and levels of independent variables in BBD

According to the design matrix arranged by BBD, the model based on Design Expert 8.0.6 (Stat-Ease Inc., USA) mentioned above is performed to obtain the corresponding responses. The experimental design and results of BBD response surface are shown in Tab. 2. The first column of the Table shows the run number of experiments. The next five columns represent the actual conditions of runs and the last three columns represent the results of experiments.

Table 2 Design of experimental matrix and its responses

2 Results and discussion

2.1 Effect of CA concentration on DP property

Effect of CA concentration on WRA and breaking strength of finished fabrics was investigated and the results are shown in Fig.1.In Fig.1,BTCA conc. is 40 g/L,SHP conc., 40 g/L,curing temperature, 170 ℃,Curing time,90 s.

Fig.1 Effect of CA concentration on the property of the finished fabrics

Fig.1 shows that WRA increases with the increase of CA concentration, while the breaking strength increases slightly and then decreases dramatically. When the concentration of CA is 50 g/L, WRA reaches 269° and the breaking strength is 212 N. The DP property would satisfy the practical production. An excess of CA will lead to the decreases of breaking strength. Therefore, the concentration of CA was fixed at 50 g/L in subsequent experiments.

2.2 Effect of BTCA concentration on DP property

Effects of BTCA concentration on WRA and breaking strength of finished fabrics were investigated. The results are shown in Fig.2.

Fig.2 Effect of BTCA concentration on the property of the finished fabrics

Fig.2 shows that WRA could be significantly improved with the increase of BTCA concentration. However, the breaking strength has a slight decrease when the BTCA concentration was less than 30 g/L and more breaking strength loss can be observed along with the continue increase of BTCA concentration. Therefore, the concentration of CA was fixed to 30 g/L in subsequent experiments.In Fig.2, CA conc.is 50 g/L; SHP conc., 40 g/L; Curing temperature, 170℃; Curing time, 90 s.

2.3 Effect of SHP concentration on DP property

Effect of SHP concentration on WRA and breaking strength of finished fabrics was investigated. The results are shown in Fig.3.In Fig.3,BTCA conc. is 30 g/L,CA conc.,50 g/L,Curing temperature, 170 ℃,Curing time, 90 s.

Fig.3 Effect of SHP concentration on the property of the finished fabrics

Fig.3 shows that WRA and breaking strength follow a similar trend as the concentration of SHP increases. After reaching the highest point when the concentration of SHP is 40 g/L, there is a decrease of different extent in the figure of WRA and breaking strength. This may be due to the fact that SHP is both a cross-linking catalyst and a buffer, which promotes the cross-linking of BTCA with cellulose to a certain extent, and also reduces the acid degradation of the fabric by solution and improves its strength. Continuous increase of SHP concentration has little effect on WRA, but the breaking strength of fabric decreases with the increase of crosslinking degree.

2.4 Effect of curing temperature on DP property

Effect of curing temperature on WRA and breaking strength of finished fabrics was investigated. The results are shown in Fig.4.In Fig.4, BTCA conc.is 30 g/L; CA conc., 50 g/L; SHP conc., 40 g/L; Curing time, 90 s.

Fig.4 Effect of curing temperature on the property of the finished fabrics

Fig.4 shows that WRA of the fabric grow obviously at the first period in question, then the growth slows down when the curing temperature is over than 170 ℃. However, figures of the breaking strength witnessed a different trend to WRA, which decrease sharply from 246 N to 216 N as the temperature rises from 150 ℃ to 170 ℃; from then onwards, it sees a slight decrease. This is possibly because the esterification degree of carboxyl group and fabric increases with the increase of baking temperature, so WRA increases, but high temperature will accelerate the acid degradation of cellulose, resulting in more serious strength loss.

2.5 Effect of curing time on DP property

Effect of curing time on WRA and breaking strength of finished fabrics was investigated. The results are shown in Fig.5.In Fig.5,BTCA conc.is 30 g/L,CA conc.is 50 g/L,SHP conc.is 40 g/L,curing temperature, 170 ℃.

Fig.5 Effect of curing time on the property of the finished fabrics

Fig.5 shows that WRA of the fabric increases with the increase of curing time. Longer curing time has little effect on improvement of WRA of the fabric whereas it would cause a serious strength.

2.6 Optimization by response surface methodology

2.6.1 Analysis of variance (ANOVA) The ANOVA for the regression model of WRA and breaking strength were shown in Table 3.

Table 3 shows thatPvalues of quadratic polynomial models for WRA and breaking strength are all less than 0.000 1, which indicates that the models are of high significance. The adjusted judgment coefficient (Radj2) of WRA model is 0.998 7, which shows that the model can accurately predict 99.87% of the response values. The coefficient of variation (CV) is 0.28%, which indicates that the correlation of the model is good and the reliability is high. ThePvalue of the lack of fit item is greater than 0.05, which is not significant. Therefore, the fitting degree of WRA model is high, and the model can be used to predict and analyze WRA. It can be seen fromFvalue that the importance of factor effects on WRA isX5>X1=X2>X4>X3. The first term of SHP concentration cannot fit WRA model, but the second term fits significantly, which shows that there is not a simple linear relationship between each factor and the response value.

TheRadj2of the breaking strength model is 0.979 7, which shows that the model can accurately predict 97.97% of the response changes. TheCVof the model is 1.57%, and thePvalue of the lack of fit term of the breaking strength model is greater than 0.05, which is not significant. Therefore, the model can also be used to predict and analyze the breaking strength. It can be seen from theFvalue of a term that the order of the influence degree of each factor on breaking strength isX5>X4>X3>X2>X1.

In conclusion, it can be concluded that the two regression models can predict WRA and breaking strength of cotton fabric treated with BTCA-CA mixed polycarboxylic acid. According to the results of variance analysis, the accurate relationship model between the parameters and the response value is obtained. Finally, after converting the actual value of the model into the coding value, the quadratic regression model is obtained as follows:

Table 3 Variance analysis of regression model and significance test of regression coefficients

*=significant (P<0.05). **=highly significant (P<0.001)

2.6.2 Interactive effect of BTCA and CA concentrations on response values The interactive influence between BTCA and CA concentration on WRA and the breaking strength of finished fabrics are separately shown in Fig.6 and Fig.7.

(a) 3-D surface plot

(b) 2-D contour plotFig.6 Effects of concentration of BTCA and CA on WRA. Other variables take place at zero level (X3=40 g/L, X4=170 ℃, X5=90 s)

Fig.6 shows the effect of BTCA on WRA is similar to CA, as WRA figures for cotton fabric treated with CA and BTCA experienced a similar trend when the concentration increases. Fig. 7 shows the breaking strength increases slightly with the increase of the amount of CA when the amount of BTCA is unchanged. This may be due to the esterification of some CA with BTCA, which improves the cross-linking length and forms a larger three-dimensional network structure on the fabric. Therefore, it improves the ductility of cross-linked fabrics, reduces the restriction of fiber activity and reduces the strength loss of fabrics to a certain extent. Continuous increase of CA concentration will increase the degree of crosslinking and decrease the breaking strength.

(a) 3-D surface plot

(b) 2-D contour plotFig.7 Effects of concentration of BTCA and CA on the breaking strength. Other variables take place at zero level (X3=40 g/L, X4=170 ℃, X5=90 s)

2.6.3 Verification of the optimized parameters In order to achieve higher WRA and retain a higher breaking strength, optimum finishing parameters with a signal-to-noise ratio of 1.000 were obtained by taking WRA of 260° and the breaking strength of 230 N as objective response values: BTCA 50 g/L, CA 45 g/L, SHP 33 g/L and curing at 162 ℃ for 63 s. Confirmation experiments were carried out and the tested results of WRA and breaking strength under this finishing process are 260° and 227 N, respectively. The strength retention rate is 72%. The actual value is close to the predicted value, which shows that the regression model can truly reflect the influence of various factors on WRA and breaking strength of BTCA-CA mixed polycarboxylic acid finished process.

3 Conclusion

(1) Effects of the operating parameters and their interactive effects on WRA and the breaking strength had been explained in detail by ANOVA. It was found that five operating parameters have different influence on the response value. The order of them on WRA model is: Curing time>BTCA concentration>curing temperature>SHP concentration. In terms of concentration effect, effect of CA on WRA is similar to that of BTCA. The order of them in breaking strength model is:Curing time>curing temperature>SHP concentration>CA concentration>BTCA concentration.

(2) Optimized process was carried out to determine the optimized parameters and the accuracy of the regression model were verified. Results showed a good agreement between numerical and predicted results. This study could provide an efficient and accuracy method to guide and optimize the BTCA-CA mixed polycarboxylic acid finished process. The optimum parameters DP finishing process with the mixed compounds of BTCA and CA is: BTCA 50 g/L, CA 45 g/L, SHP 33 g/L, curing at 162 ℃ for 63 s. WRA is 260° and the retention rate of breaking strength is 72%.