Predicting Bursting Strength Behavior of Weft Knitted Fabrics Using Various Percentages of Cotton, Polyester, and Spandex Fibers ()
1. Introduction
1.1. Background of the Research
The study focused on seeing the effect of the bursting behavior of blended weft knitted fabric by using cotton, polyester, and spandex with varying percentages of blend ratio of cotton, polyester, and spandex. There are several reasons behind the selection of the topics. The requirement of bursting strength of sportswear or functional wear is high. The sportswear garment is manufactured from CVC (Chief Value Cotton) fabric. A certain percentage of spandex is incorporated with cotton. The price of both cotton and spandex is high. The cost of spandex is much higher than cotton. In the blends, the third fiber polyester appeared in this study. Polyester is a man-made fiber with high tenacity and elongation that tends to provide higher bursting strength value. Moreover, the regression equation comes into the picture to predict the required bursting strength of knit fabrics before manufacturing CVC fabrics.
1.2. Research Done in This Field
The literature survey found that many researchers studied bursting behavior on weft-knitted fabrics to better enrich related research topics. A study investigated the effect of increasing spandex ratio, loop length, stitch density, fabric structure (lock knit, interlock), and fabric weight on bursting strength using cotton/spandex and nylon/spandex. It was found from their Research that the spandex fiber blend ratio influences the bursting strength [1] . Another study was done on banana/cotton blends to see the effect of blend ratio on bursting strength, abrasion resistance, and pilling resistance. That study revealed that the bursting strength increased with the percentage of bananas, and increasing the banana fiber blend ratio increased bursting strength [2] . Another study investigated the effect of knit structure and mechanical properties by using 80% lambswool and 20% polyamide with the washed sample. The knit structure influenced bursting strength and other related properties [3] . Research on bursting strength using virgin polyester with recycled polyester revealed no significant differences in bursting strength compared to 100% polyester [4] . The loop length and raw material raw material affect bursting strength [5] .
1.3. Missing in Previously Done Research
Previous researchers used blended materials with two fibers: cotton/spandex and nylon/spandex, wool/polyamide. The literature survey did not find the Research concerning more than two fibers in the blend.
1.4. Author’s Explanation of Those Not Addressed in Previously Done Research
This study was conducted with natural and manufactured fibers with varying percentages of cotton, polyester, and spandex fibers. Earlier Research concentrated on comparative study rather than predicting dependent variables (bursting strength). The study involved predicting a suitable regression equation or model for the bursting strength test value.
1.5. Originality of the Research
This study is a new and original research work. The study findings are helpful to the fabric manufacturers and buyers who decide the percentage of fiber blend proportion in terms of the bursting behavior of knit fabrics.
1.6. What Is Bursting Strength?
The bursting strength of a knit fabric is the pressure force required to rupture the fabric. The measurement unit of the bursting strength test is kPa (kilopascal). Kilopascal is a unit of pressure. The other units, like Psi (pound per square inch), kN/m2, and N/cm2, are also used. The conversion factor can transform the kPa into Psi. The Psi = kPa × 0.145038. Once the bursting machine operates, the diaphragm moves upward through hydraulic or pneumatic pressure. This pressure is required to inflate the specimen, known as tare pressure recorded in kPa. After inflation, the specimen starts to burst. The difference between the total pressure needed to break the sample and the pressure to inflate the expandable diaphragm is known as bursting strength. This tare pressure is to be deducted from the final reading (kPa) to get the actual bursting strength test value. The development and application of blended fabrics are the present focus of R&D efforts globally. The title of this publication corresponds to the current worldwide demand.
Cotton is the best natural fiber. The polyester links several monomers (esters) within the fiber. Polyester is a fiber with high tenacity (g/tex) and elongation%, which can help to increase fabric strength. Spandex is a non-biodegradable fiber typically used in sportswear and comfort wear. The spandex can stretch up to 500% or even more than 500%. DuPont’s laboratory first invented spandex in 1959 in Virginia. Spandex takes 20 - 200 years to break down but not degrade. After a few years, spandex may break into microplastics.
1.7. Factors Responsible for Bursting Strength
1.7.1. Fiber Stage
Fiber parameters influence the bursting strength; the higher the staple length, the higher the bursting strength test value (kPa). The higher the staple length, the higher the bursting strength test value (kPa). The higher the micronaire (fineness) and length, the higher the bursting strength test value (kPa). The higher the fiber strength (g/tex), the higher the bursting strength test value (kPa). The higher the uniformity ratio, the higher the bursting strength test value (kPa). The higher the fiber elongation, the higher the bursting strength test value (kPa). The higher the fiber maturity index, the higher the bursting strength test value (kPa). The type of fibers influences bursting strength. The bursting strength of polyester fiber is higher than that of cotton.
1.7.2. Yarn Stage
The type of fibers used in yarn influences bursting strength. The yarn made from polyester fiber is higher than cotton. The higher the yarn C.S.P. (count strength product), the higher the bursting strength. The higher the single yarn strength (cN/tex), the higher the bursting strength. The higher the imperfections in the yarn, the lower the bursting strength. The higher the T.P.I. (Twist per inch), the higher the bursting strength. The lower the u%, the higher the bursting strength. The yarn made with double-ply or triple-ply gives a higher bursting strength [6] . The fiber types and blend proportions percentage in blends influence bursting strength. The linear density of yarn or yarn count also influences bursting strength. The higher the yarn count, the higher the bursting strength.
1.7.3. Fabric Stage
The fabric parameters influence bursting strength such as fabric count, stitch density, fabric GSM, fabric structure, fabric composition, fabric cover factor, fabric tightness factor, fabric shape factor, fabric porosity, fabric thickness, stitch length, shrinkage% [7] . The air permeability of fabric influences bursting strength. A fabric with higher air permeability tends to lower bursting strength value.
1.7.4. Dyeing Stage
The fabric dyeing parameters influence bursting strength, such as the variation of pH value in the dye bath, dosing of dispersing agent, amount of sodium chloride and soda (NaOH), types of soda and salt, dyeing process, dyeing shade% [8] .
1.7.5. Finishing Stage
The fabric finishing parameters influence bursting strength such as heat-setting, fabric compacting process, application of softener in finishing process, the application of different finishes like wrinkle-free finish, paper touch finish, silky soft finishes, water repellent finish, polyethylene finish, silicon finish, international finish [9] .
1.7.6. Testing Stage
The fabric test parameters influence bursting strength, and this is categorized into three groups:
Man: Skillness, knowledge of test procedure, ability to analyze results.
Machine: Time to burst/rupture, bursting speed of Bursting strength tester. Calibration status of bursting strength tester.
Material: Regular use of control fabric, maintaining repeatability test, retest, duplicate test, or related in-house quality control activities [10] .
2. Materials & Methods
2.1. Materials
2.1.1. Blended Fabrics
The study used single jersey weft blended knitted fabrics with three different fibers: cotton, polyester, and spandex, with varying percentages of blend ratios. The yarn count and fabric weight were 34/1 ring-spun and 190 GSM (Gram per square meter). Table 1 shows the names of fifteen blended fabrics used and those categorized into groups: Group 1, Group 2, and Group 3.
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Table 1. Fifteen types of blended knit fabrics.
2.1.2. Preparatory Process Involved in the Study
The yarn had been produced from BCI (Better Cotton Initiative) U.S. Upland cotton, staple polyester, and spandex. USTER HVI 100 ensures raw cotton parameters like maturity index, uniformity ratio index, spinning consistency index S.C.I. (138), strength, elongation%, Rd (71.0), +b (9.8), upland grading (42-1), short fiber content S.F.C. (243), trash grade (4). The state-of-the-art spinning machine used for manufacturing quality yarn. The count of the yarn was 34/1Ne ring-spun. The latest model knitting machine (Terrot, Germany) knitted the grey fabrics. The fundamental knitting parameters were 32-inch diameter, 24 machine gauge, stitch length of 29.0 mm, yarn linear density (34/1Ne), grey GSM (190), and finished GSM (180). The excellent brand dyes from BEZEMA, Germany, and disperse dyes from Taiwan, and suitable brand auxiliaries treated the fabrics as usual. Two dye-stuff types (reactive and dispersed dyes) dyed the blended fabrics. The Stenter (Monfortis, Germany) and Compactor (Lafer, Italy) machines finished the study samples.
2.2. Method
2.2.1. Test Standard
The international test standard ISO 13938-2:2019-Textiles, Bursting properties of fabrics Part 2: Pneumatic method for determination of bursting strength and distension [11] .
2.2.2. Test Equipment & Apparatus
The bursting strength test used the Digital Bursting Strength Tester TRUBURST (James Heal, UK). Figure 1 shows a Digital Bursting Strength Tester used for this study.
2.2.3. Test Procedure
The materials (fabric samples) are cut from the fabric roll 150 mm from the fabric’s selvage, as shown in Figure 2.
The bursting strength test followed the test standard (ISO 13938-2:2019). The sample was initially maintained in an atmosphere that met international standards for atmospheric conditioning environment (RH: 65% ± 4%, temperature: 20◦C ± 2◦C) (ISO 139:2005) [12] . After conditioning, the test was conducted with a dome size (specimen test area) of 7.3 cm2. The unit of measurement for the bursting strength test result is kPa. Figure 3 shows the main testing stages of bursting strength.
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Figure 1. The digital bursting strength tester.
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Figure 2. The position of the sample collection from fabric.
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Figure 3. (a) the testing zone, (b) the test in action, and (c) the test done.
2.2.4. Calculation of the Test Result
The following formula calculated the bursting strength:
Bursting Strength = P1 − P2
where,
P1 is the pressure required to rupture the specimen.
P2 is the pressure required to inflate the diaphragm.
The unit of bursting strength is kPa (Kilopascal).
The equipment used for this experiment was digital and automatic. The manual calculation was not required.
3. Result and Discussion
3.1. Group 1 Fabrics Data Analysis
Table 2 and Figure 4 represent the bursting strength average data for fabrics in
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Table 2. Bursting strength test results (kPa) of Group 1 Fabrics.
Note: C stands for cotton, P stands for polyester, and E stands for spandex fiber.
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Figure 4. A graphical display of the bursting strength of Group 1 Fabrics.
Group 1, and these are C90%P5%E5%, C90%P6%E4%, C90%P7%E3%, C90% P8%E2%, and C90%P9%E1%. The x-axis indicates the types of blended fabrics, and the y-axis shows the bursting strength in kPa. The upward trend of the graphical data indicated that the bursting strength (kPa) increased as the percentage of polyester fiber blend gradually increased. The fabric with C90%P5%E5% shows the lowest bursting value, and the fabric with C90%P9%E1% shows the highest.
3.2. Group 2 Fabric Data Analysis
Table 3 and Figure 5 represent the bursting strength average data for fabrics in Group 2, and these are C85%P10%E5%, C85%P11%E4%, C85%P12%E3%, C85%P13%E2%, and C85%P14%E1%. The fabric with C85%P10%E5% shows the lowest bursting value, and the fabric with C85%P14%E1% shows the highest.
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Table 3. Bursting strength test results (kPa) of Group 2 Fabrics.
Note: C stands for cotton, P stands for polyester, and E stands for spandex fiber.
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Figure 5. A graphical display of the bursting strength of Group 2 Fabrics.
3.3. Group 3 Fabric Data Analysis
Table 4 and Figure 6 show the average bursting strength data for fabric with group 3, which is C80%P15%E5%, C80%P16%E4%, C80%P17%E3%, C80%P18%E2%, and C80%P19%E1%. The fabric with C80%P15%E5% shows the lowest bursting value, and the fabric with C80%P19%E1% shows the highest.
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Table 4. Bursting strength test results (kPa) of Group 3 Fabrics.
Note: C stands for cotton, P stands for polyester, and E stands for spandex fiber.
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Figure 6. A graphical display of the bursting strength of Group 3 Fabrics.
3.4. Effect of Cotton Blend Ratio on Bursting Strength
The strength (gm/tex), fiber length, and elongation properties of cotton fiber play a vital role in achieving the required bursting strength value. American upland BCI cotton with 31.8 g/tex (tenacity), 28.8 mm length, and 7.0% elongation was employed in this study. Count, stitch length, and tightness factor affect knit fabric bursting strength inversely [13] . Cotton needs to go through opening, cleaning, carding, and combing; consequently, the degree of crystallinity decreases, reducing its bursting strength. The cross-linking agent can reduce bursting strength as this agent resists the mobility of fibers in the fabric structure [14] . When the cotton is associated with blending, the strength and elongation of other fibers interfere and provide combined output.
The chemical structure of the cotton cellulose is also responsible for the variation in test results [15] . Each glucose unit of cellulose is attached to the next by a covalent bond, the C-O-C linkage, flanked by two hydrogen bonds. These bonds are comparatively weaker and tend to break while stretching for a bursting test operation. Figure 7 shows the chemical structure of cellulose [16] .
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Figure 7. The chemical structure of cellulose.
3.5. Effect of Polyester Blend Ratio on Bursting Strength
The strength (gm/tex), fiber length, and elongation value are responsible for getting a higher bursting value (kPa). The higher the tenacity, length, and elongation, the higher the bursting value. The percentage of polyester in the blend increased by 1% incrementally, from 5% - 19%. The study fabrics with a higher rate of polyester blend ratio showed a better or higher bursting value (kPa) and vice versa [17] . Polyester fiber has excellent mechanical properties and improved bursting strength. The chemical structure of polyester fibers is another factor for the variation of the bursting test value (kPa). Polyester consists of a long-chain polymer. It is chemically at least 85% of the weight of an ester group, an ethylene group (dihydric alcohol), and a terephthalate group [14] . Polyester’s filaments and staple forms are strong due to its highly effective vander wall’s forces and hydrogen bonds. Consequently, polyester gives higher tensile strength for woven fabrics and higher bursting strength for knit fabrics. Figure 8 shows the chemical structure of polyester [18] .
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Figure 8. The chemical structure of polyester.
3.6. Effect of Spandex Blend Ratio on Bursting Strength
Spandex comprised 1%, 2%, 3%, 4%, and 5% of the blend. The spandex fiber has a significantly lower tenacity. Because of its reduced tenacity and extremely high stretchability, spandex with blend ratios starting at 1%, 2%, 3%, 4%, and 5% does not contribute to obtaining a specific bursting strength value (kPa). Spandex is a long-chain synthetic polymeric fiber. The soft and rubbery segments allow the fiber to stretch and recover to its original shape, and hard segments provide rigidity and strength [15] . The primary role of spandex is to give comfort and an aesthetic feel instead of directly participating in increasing or decreasing fabric strength (bursting or tensile). Figure 9 shows the chemical structure of spandex [19] .
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Figure 9. The chemical structure of spandex.
3.7. Statistical Analysis through Pearson Correlation
The Pearson correlation was conducted for group 1, group 2, and group 3 fabrics [20] .
The correlation graph (Figures 10-12) generated from Tables 2-4. In Figure 10, it shows the positive correlation, with a coefficient of 0.8914 for group 1 fabrics. In Figure 11, it shows the positive correlation, with a coefficient of 0.9732 for group 2 fabrics. In Figure 12, it shows the positive correlation with a coefficient of 0.9384 for group 3 fabrics. This means a strong relationship exists between polyester blend proportions and bursting strength test value (kPa).
3.8. Regression Analysis through ANOVA—Group 1 Fabrics
The regression analysis through ANOVA was conducted for group 1, group 2, and group 3 fabrics [21] . A hypothesis statement was prepared before conducting the regression analysis through ANOVA (Analysis of Variance).
H0: There is no relationship between the dependent variable (Bursting Strength)
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Figure 10. The correlation for Group 1 Fabrics.
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Figure 11. The correlation for Group 2 Fabrics.
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Figure 12. The correlation for Group 3 Fabrics.
and the set of independent variables (Polyester Blend Proportion%).
Ha: There is a relationship between the dependent variable (Bursting Strength) and the set of independent variables (Polyester Blend Proportion%).
Table 5 represented ANOVA for regression and Figure 13 represented regression graph for group 1 fabrics.
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Table 5. ANOVA Table for Regression of Group 1 Fabrics.
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Figure 13. The Regression Graph for Group 1 Fabrics.
The suggested equation for the bursting strength test value for group 1 fabrics is Y = 1.190 * X + 247.3.
The correlation coefficient (R) and the coefficient of determination (R2) were found to be 0.8914 and 0.7947, respectively. It indicates a strong relationship between polyester blend proportion and bursting strength test value (kPa). From Table 5, it was observed that the p-value (0.04223) < α (0.05). Then, the null hypothesis was rejected. A 95% confidence interval or 5% significance level is chosen for the study. The analysis shows that the regression ANOVA is significant, meaning that the regression equation for group 1 fabric is Y = 1.190 * X + 247.3 is statistically significant.
3.9. Regression Analysis through ANOVA—Group 2 Fabrics
A hypothesis statement was prepared before conducting the regression analysis through ANOVA (Analysis of Variance).
H0: There is no relationship between the dependent variable (Bursting Strength) and the set of independent variables (Polyester Blend Proportion%).
Ha: There is a relationship between the dependent variable (Bursting Strength) and the set of independent variables (Polyester Blend Proportion%).
Table 6 represents ANOVA for regression, and Figure 14 represented regression graph for group 2 fabrics.
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Table 6. ANOVA Table for Regression of Group 2 Fabrics.
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Figure 14. The Regression Graph for Group 2 Fabrics.
The suggested equation for the bursting strength test value for group 1 fabrics is Y = 3.060 * X + 229.8.
The correlation coefficient (R) and the coefficient of determination (R2) were found as 0.9732 and 0.9471, respectively. It indicates a strong relationship between polyester blend proportion and bursting strength test value (kPa). From Table 6, it was observed that p-value (0.005251) < α (0.05). Then, the null hypothesis was rejected. A 95% confidence interval or 5% significance level is chosen for the study. The analysis shows that the regression ANOVA is significant, meaning that the regression equation for group 2 fabric is Y = 3.060 * X + 229.8 is statistically significant.
4. Regression Analysis through ANOVA—Group 3 Fabrics
A hypothesis statement was prepared before conducting the regression analysis through ANOVA (Analysis of Variance).
H0: There is no relationship between the dependent variable (Bursting Strength) and the set of independent variables (Polyester Blend Proportion%).
Ha: There is a relationship between the dependent variable (Bursting Strength) and the set of independent variables (Polyester Blend Proportion%).
Table 7 represents ANOVA for regression, and Figure 15 represents regression graph for group 3 fabrics.
The suggested equation for the bursting strength test value for group 1 fabrics is Y = 3.45 * X + 223.19.
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Table 7. ANOVA Table for Regression of Group 2 Fabrics.
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Figure 15. The Regression Graph for Group 3 Fabrics.
The correlation coefficient (R) and the coefficient of determination (R2) were found to be 0.9381 and 0.8801, respectively. It indicates a strong relationship between polyester blend proportion and bursting strength test value (kPa). From Table 7, it was observed that the p-value (0.01819) < α (0.05). Then, the null hypothesis was rejected. A 95% confidence interval or 5% significance level is chosen for the study. The analysis shows that the regression ANOVA is significant, meaning that the regression equation for group 2 fabric is Y = 3.45 * X + 223.19 is statistically significant.
4.1. Regression ANOVA Summary for Group 1, Group 2, and Group 3 Fabrics
A regression ANOVA summary was prepared for group 1, group 2, and group 3 fabrics.
Table 8 represents the Regression ANOVA Summary for group 1, group 2, and group 3 fabrics.
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Table 8. Regression ANOVA Summary Table.
4.2. Interpretation of Regression Model for Group 1, Group 2, and Group 3 Fabrics
For group 1 fabric, the regression equation is Y = 1.190 * X + 247.3 is statistically significant. In other words, a positive relationship exists between the polyester fiber blend proportions% and the bursting strength test value (kPa). The regression equation can be written as Bursting Strength (kPa) = 1.190 * Polyester blend proportion% + 247.3. The regression equation shows that a 1% increase in polyester fiber blend proportion will increase bursting strength by 1.190 times. The y-intercept is 247.3, meaning that when x (polyester fiber blend proportion) equals 0, the y (bursting strength value is 247.3 kPa.
For group 2 fabric, the regression equation is Y = 3.060 * X + 229.8 is statistically significant. In other words, a positive relationship exists between the polyester fiber blend proportions% and the bursting strength test value (kPa). The regression equation can be written as Bursting Strength (kPa) = 3.060 * Polyester blend proportion% + 229.8. The regression equation shows that a 1% increase in polyester fiber blend proportion will increase bursting strength by 3.060 times. The y-intercept is 229.8, meaning that when x (polyester fiber blend proportion) equals 0, the y (bursting strength value is 229.8 kPa.
For group 3 fabric, the regression equation is Y = 3.45 * X + 223.19 is statistically significant. In other words, a positive relationship exists between the polyester fiber blend proportions% and the bursting strength test value (kPa). The regression equation was expressed as Bursting Strength (kPa) = 3.45 * Polyester blend proportion% + 223.19. The regression equation shows that a 1% increase in polyester fiber blend proportion will increase bursting strength by 3.45 times. The y-intercept is 223.19, meaning that when x (polyester fiber blend proportion) equals 0, the y (bursting strength value is 223.19 kPa.
5. Conclusions
The high-tenacity polyester fiber dominated the fiber blend, reflected in correlation, regression equation, and regression ANOVA. Considering the actual experimental facts and scenario, the concluding remarks for the study are as follows:
1) The blended fabric’s bursting strength value increases as the percentage of polyester increases, and vice versa.
2) The cotton and spandex in blends did not reflect remarkably on the bursting strength.
3) There is no other alternative to choosing the appropriate blend proportion with polyester fibers regarding quality, cost, and sustainability development.
4) The suitable regression equation facilitated the textile manufacturing industry personnel to predict the bursting strength value.
Due to technical limitations, the study used fabrics of three different fibers, cotton, polyester, and spandex, with various percentages of the blend ratio. The future scope is to deal with recycled and virgin fibers with various blend proportions to achieve sustainable development in textile fields.
Acknowledgements
The authors thanked Textile Testing Services Ltd., Matin Spinning Mills Ltd., Jinnat Knitting Ltd., Color City Ltd., and the Department of Physics at Jahangirnagar University for their cooperation and support.