Development of disperse dye polypropylene fiber and process parameter optimization Part I: development of dyeable polypropylene fiber and parameter optimization

Abstract

This study develops polyester modified polypropylene (PP) with disperse dye dyeability. The thermal properties, rheological properties, and spectral properties are used for validation and differential analysis.

The optimum PP dyeable particle process uses polyester as the mixed copolymer. The melt temperature of polyester material is significantly different from PP, which may lead to a failure of the mixing process. Therefore, this study aims to develop low-melting co-polyester. Different proportions of adipic acid are used in the co-polyester molecular chain to reduce the melting point. The melting point has been controlled successfully, the thermal properties of the modified ester pellet are discussed, and the functional group is then verified by Fourier infrared spectroscopy. Afterwards, the low-melting co-polyester and PP are made into a composite through a dual-screw mixing process with PP grafting maleic anhydride compatilizer. The PP is endued with the dyeability of disperse dye through the molecular behavior of the co-polyester chain segment. The optimum process parameters of the made material are designed by using the Taguchi method, gray relational analysis, and fuzzy C means clustering algorithm, aiming at two quality characteristics: dyeing power and melt index (MI). The results show that the MI of the pure PP polymer is 35.78 g/10 min and the color strength is 100 K/S, while the MI of the PP/co-polyester is 37.63 g/10 min and the color strength is 211.20 K/S. The results suggest that the developed polymer exhibits good processing in circulation and color strength.

Keywords

polypropylenes Taguchi method disperse dyes gray relational analysis fuzzy C means clustering algorithm

Polypropylene (PP) has been extensively used in the artificial textile industry. It is a polymer with high resistance to wear, low gravity, high strength, and chemical resistance.¹ Traditional PP is dyed by mixing with color concentrate, but the dyed fiber after granulation spinning has the problem of color mending. The PP polymer chain lacks ionic bonds or polar groups, and so it is difficult for the dye molecule to bond the PP molecule by a hydrogen bond or Van der Waals Force.² In addition, PP crystallinity is very high, thereby reducing the ability of the dye molecules to enter the amorphous region of PP molecules and resulting in the dyeing effect.^3,4 Therefore, PP dyeing has become an important research subject of PP fiber application. Conzatti et al.⁵ combined PP with 20 wt% wool fiber, and used polypropylene grafted with maleic anhydride (PP-g-MA) as a compatibility agent to prepare the composite. They also discussed the fiber/matrix modified dye adsorption on the fiber surface. The silane coupling agents trimethoxy silane and octadecyl silane were used to oxidize or functionalize the wool fiber, so that the fiber could react with the polyolefine matrix. The results showed improvement in the composite fiber exhaustion, thermal stability property, and mechanical property. Ujhelyiova et al.⁶ combined PP with polyester to produce dyeable blended fiber, and used the group of polyester to enhance the bonding of the molecular chain and disperse dye. Polyethylene terephthalate (PET), poly butylene terephthalate (PBT), and PP were used for melt mixing to prepare dyeable fiber. The results showed that the PP/PBT had a higher dyeing rate than PP/PET. Reddy et al.⁷ used PP and polylactic acid for melt mixing to enhance the dyeability of PP. The results showed that the composite fiber had excellent resistance to hydrolysis and dyeing ability. Rabiei et al.⁸ used PP and nano organic montmorillonite as composited, and added 0.5 wt% PP-g-MA as the compatibility agent. The results showed that the diffusion coefficient, activation energy, and fiber dye uptake could be increased effectively by temperature control.

Past studies have bonded PP and polyester by melt mixing, thus allowing PP to have the disperse dye dyeing effect. The T_m of PP is very different from that of PET, as it is likely to cause different flowabilities in the mixing process, thus resulting in agglomeration or cladding. This study prepares a copolymer by the condensation reaction of isophthalate and glycol, so that the T_m remains at 185–200℃ in order to replace PET at a high T_m. The compatibility agent is then added in the melt mixing, so that the copolymer and PP are mixed more uniformly for a good dyeing effect.

Dyeing theory

According to kinetic molecular theory,⁹ the molecular chain in the amorphous region generates heat motion due to a temperature rise. When the temperature exceeds the glass transition temperature, the heat motion of the molecular chain turns from a frozen state into violent motion. The fiber expands, thus dilating the fiber gap, and allowing the disperse dye molecule to enter the compact fiber molecules. When the temperature decreases, the pores of material are restored, so that the dye molecules are fixed in the fiber. The disperse dye dyeing is generally based on polyester fiber. The group of polyester fiber and the amine or carbonyl of dyes form a Van der Waals Force between the hydrogen bond and benzene ring (Figure 1), which contributes to the bonding of the dye molecule and the fiber molecule.¹⁰
Figure 1.
The bonding mechanisms of polymer and disperse dye.

For a compact structure, high crystallinity and non-polarity, the dye molecule does not enter the PP fiber, thus resulting in poor dyeability. Since the fiber has very low hydrophilicity, its affinity to dyes and chemical additives is poor. Traditional dyeing and printing methods cannot achieve the coloring effect. Therefore, this study proposes blending low-melting co-polyester with PP material. From the microscopic view, the ester group of co-polyester and the amine or carbonyl of the dye form a hydrogen bond (Figure 1), and so the dye bonds the molecules. From the macroscopic view, the blended co-polyester can reduce the crystallinity of PP material, so that the PP fiber provides more gaps in heat motion, fixing the dye to the fiber. The dyeing method and conditions used in this study are described below.

Dyeing method

The staining tester and disperse dyes are used for dyeing. Figure 2 illustrates the schematic diagram of the heating curve of the dyeing of disperse dyes.
Figure 2.
Dyeing heating curve of this study.

Formulae and conditions

Table 1 lists the dyeing and reductive cleaning formulae and conditions.
Table 1.
Dyeing and reductive cleaning formulae and conditions

Dyeing stage Formulae and conditions

Dyeing Dyeing temperature: 130℃

Dye strength: 0.15 % o.w.f. (Navy Blue e-SE)

Dye leveler: 1% (Welleven PL-34)

Acid releasing agent: 0.8 g/L (Welsol PHC-98)

Bath ratio: 1:30

Reductive NaOH: 3 g/L

Hydros: 3 g/L

Soaping agent: 1 g/L

Materials and dye

Polypropylene

PP is a thermoplastic polymer derived from addition polymerization of propylene molecules, made by tactic polymerization. PP fiber is made by melt spinning and is the lightest fiber among all synthetic fibers (specific gravity 0.9). PP is a hydrophobic fiber and has poor dyeability.¹¹ This study used spinning class PP polymer (T_m: 165℃, melt index (MI): 36 g/10 min) as the key substrate.

Polypropylene grafted with maleic anhydride

This study utilized PP-g-MA as the compatibility agent, which is the polar monomer in PP modification. The principle of the compatibility agent is that after melt mixing, PP and maleic anhydride are bonded by grafting. In other words, the acid anhydride group has polarity, thus generating a carboxylic acid functional group, so that PP has polar and reactive groups.

Low-melting co-polyester

This study has successfully developed a co-polyester material at a melting point of 185–200℃ by changing the proportions of adipic acid and terephthalic acid. The difference in the PP melt temperature of 160–175℃ is within the permissible range, ensuring that the working process is not affected by the modification result. Different polymers are added in the co-polyester development process. The adipic acid increases the carbochain, thus damaging the crystallinity and enlarging the amorphous area of the co-polyester. As a result, the T_m falls, and the workability and dye adsorption rate are enhanced.

Figure 3 presents the modified co-polyester reaction mechanism.
Figure 3.
The modified co-polyester reaction mechanism.

Disperse dyes

The model of disperse dyes used in this study is Navy Blue e-SE. The molecular formula is C₁₄H₉ClN₂O₄. For the dye test, the schematic diagram of the chemical structure is as shown in Figure 4.
Figure 4.
Schematic diagram of the chemical structure.

Dyeing assistants

This study used a dye leveler and acid releasing agent as the additives for the disperse dye dyeing process. The dye leveler could enhance the homodisperse of disperse dyes and prevent the dyes from agglomerating at a high temperature. The acid-releasing agent effectively controls the coloring rate and increases the dye level. The fabric dyeing with disperse dyes depends on Van der Waals Force and a hydrogen bond. The dye diffused in the fiber forms an ionic bond with the −NH− group.

Quality engineering theory

Taguchi method

This study used the orthogonal array of the Taguchi method as its experimental design. The orthogonal factor levels in the orthogonal array can reduce the number of required testing experiments. The influence of various factor levels on the end product quality is calculated by an orthogonal array. The signal-to-noise (S/N) ratio is used as the quality measurement unit. The signal represents the required element, indicating the mean value of quality characteristics. The closer the characteristic is to the target, the better. The noise is the variability measurement unit of quality characteristics, and a smaller value is better. The two objective function equations of the S/N ratio used herein are expressed as follows.¹²
Nominal the Best (NTB)
$S / N = - 10 \log (\bar{y} - m) 2 + S 2$
(1)

Smaller the Better (STB)
$S / N = - 10 \log [\frac{1}{n} \sum_{i = 1}^{n} y_{i}^{2}]$
(2)

Larger the Better (LTB)
$S / N = - 10 \log [\frac{1}{n} \sum_{i = 1}^{n} \frac{1}{y_{i}^{2}}]$
(3)

where the S/N is signal/noise rate; n is the number of experiments; $\bar{y}$ is the average of experiments results; m is the nominal of quality; and S is the standard deviation.

According to the results of the Taguchi experiment design, the main effector analysis¹² design is used to plot a corresponding response diagram and response table for various quality characteristics. It shows the influence of various factor levels on the quality characteristics and the optimum factor level for the quality characteristics.

Analysis of variance

The Taguchi method uses an analysis of variance (ANOVA) to calculate the variance and contribution of the factor level to quality characteristics. The variance represents the dispersion degree between the observation data and mean value. A smaller variance indicates that the data distribution is more concentrated and the experimental stability is better. The contribution represents the influence of the factor level on quality characteristics. A larger value indicates a significant factor of quality characteristics.

Gray relational analysis and fuzzy C-means algorithm

This study combined gray relational analysis (GRA) with the fuzzy C-means algorithm (FCM) for calculating the optimum proportion and processing parameters for PP dyeing modification. The coefficient of GRA is used as an initialization matrix of the FCM, and the cluster center calculated by the FCM is taken as a target value. The objective function value is calculated by the cluster center to obtain the optimal solution. This study adopted two quality theories to prevent local optimal solutions. The computing process is described below.¹³
Generate the gray correlation grade sequence

The gray relational grade sequence is generated by Equations (4) and (5) from the experimental data of the Taguchi method. The quality characteristic MI is generated by NTB equation (4), and the color strength is generated by LTB equation (5)
$x_{i} (k) = \frac{min x_{i} (k) - x_{i} (k)}{max {max x_{i} (k) - x_{i} (k), x_{i} (k) - min x_{i} (k)}}$
(4)

$x_{i} (k) = \frac{x_{i} (k) - min x_{i} (k)}{max x_{i} (k) - min x_{i} (k)}$
(5)
where $x_{i} (k)$ is the value after gray relational generating; $max x_{i} (k)$ is the maximum value in the original sequence; and $min x_{i} (k)$ is the minimum value in the original sequence.
Gray coefficient correlation

According to Equation (6) and the universal recognition coefficient of gray correlation grade (ξ = 0.5), the form created by difference sequence is used to calculate the coefficient
$ξ_{i} (k) = \frac{{{min}_{i} {min}_{k} | x_{0} (k) - x_{i} (k) | + ζ {max}_{i} {max}_{k} | x_{0} (k) - x_{i} (k) |}}{| x_{0} (k) - x_{i} (k) | + ζ {max}_{i} {max}_{k} | x_{0} (k) - x_{i} (k) |}$
(6)

Initialize the fuzzy matrix

An initialization fuzzy matrix is created based on the gray coefficient result, and the value range is redefined as the weight sum of 1.
Calculate the Euclidean distance cluster center

The data obtained from actual experiment are used for Euclidean distance clustering by cluster center equation (7) where μ _ij is the fuzzy matrix, x_j is the input discrete data, and m is the weight coefficient of the arbitrary real number, generally set as 2.
Establish the objective function

The objective function is established by Equation (8)
$J_{m} = \sum_{i = 1}^{c} \sum_{j = 1}^{n} μ_{ij}^{m} ‖ c_{i} - x_{j} ‖ 2$
(8)

Multi-quality optimization analysis result

The objective function result is made into a response table and a response diagram by the main effect analysis. The optimum parameter combination is calculated.

Experimental details

Development of low-melting co-polyester

This study used esterification and polymerization to develop low-melting co-polyester. For esterification, different mix proportions of isophthalate and adipic acid were added in the terephthalic acid polymerization process. The PET, PBT, and polyethylene glycol oxalate copolymers were formed simultaneously in the condensation reaction process, so as to reduce the crystallinity of the co-polyester and to lower the T_m. Diethanol was added as the esterification stabilizer to reinforce the acid modification result, thus forming an alcohol end group in the polymer and achieving the inhibitory effect. The planning of the reaction formula appears in Tables 2 and 3.
Table 2.
The material content of the esterification reaction

T_m Terephthalic acid (g) Glycol (g) Isophthalate (g) Adipic acid (g) Diethanol (g)

200℃ 668.9 401.45 87.5 92.2 0.3

195℃ 652.3 401.45 87.5 108.0 0.3

185℃ 634.1 401.45 87.5 123.5 0.3

Table 3.
The material content of polymerization

T_m H₃PO₄ 5% (g) Sb₂O₃ 1.5% (g)

200℃ 1 20

195℃ 1 20

185℃ 1 20

For polymerization, phosphoric acid was added as a stabilizer to prevent the condensation polymerization from generating pyrolysis. The polyatomic acid properties of phosphoric acid resulted in a high pH. There was buffering in the reaction. Finally, the antimony trioxide was added as a catalyst. Table 4 shows the test material formula.
Table 4.
Polymerization test material mix proportion

Formula\T_m 200℃ 195℃ 185℃

Terephthalic acid 53.30 wt% 51.36 wt% 49.43 wt%

Glycol 31.99 wt% 31.61 wt% 31.29 wt%

Isophthalate 7.35 wt% 8.50 wt% 9.63 wt%

Adipic acid 7.35 wt% 8.50 wt% 9.63 wt%

Diethanol 0.02 wt% 0.02 wt% 0.02 wt%

Process The temperature is increased from room temperature to 250℃ gradually, and the pressure is increased by 1–3 kg/cm². The reaction lasts about 6 h until the water is distilled completely. After esterification, the polycondensation catalysts, comprising 20 g of antimony trioxide and 1 g of stabilizer are added. The prepolymerization in low vacuum is carried out for about 50 min. After condensation polymerization in high vacuum for less than 1 torr, the reaction temperature is 250–280℃, and the reaction time is 210 min.

Development of dyeable polypropylene material

This study blended PP and low-melting co-polyester by a twin-screw extruder and added PP-g-MA as the catalyst. Experiments were planned by the Taguchi orthogonal array L₁₈, setting the modified co-polyester T_m, modified co-polyester content, compatilizer content, dye temperature, and screw speed as the factors, with MI and color strength as the quality characteristics. The experiment plan is shown in Tables 5 and 6.
Table 5.
Factors and levels plan

Factors Levels

1 2 3

A Modified co-polyester T_m (℃) 185 195 200

B Modified co-polyester content (wt%) 5 7 9

C Compatilizer content (wt%) 3 6 9

D Dye temperature (℃) 210 220 230

E Screw speed (rpm) 200 400 600

Table 6.
L₁₈ Taguchi experimental design

A (℃) B (wt%) C (wt%) D (℃) E (rpm) Result

1 185 5 3 210 200 R₁

2 195 5 6 220 400 R₂

3 200 5 9 230 600 R₃

4 200 7 3 210 400 R₄

5 185 7 6 220 600 R₅

6 195 7 9 230 200 R₆

7 195 9 3 220 200 R₇

8 200 9 6 230 400 R₈

9 185 9 9 210 600 R₉

10 195 5 3 230 600 R₁₀

11 200 5 6 210 200 R₁₁

12 185 5 9 220 400 R₁₂

13 200 7 3 220 600 R₁₃

14 185 7 6 230 200 R₁₄

15 195 7 9 210 400 R₁₅

16 185 9 3 230 400 R₁₆

17 195 9 6 210 600 R₁₇

18 200 9 9 220 200 R₁₈

Results and discussion

Discussion about co-polyester material characteristics

As the melting point of PP material is quite different from that of polyester material, aliphatic adipic acid is added in order to change the symmetry and stiffness of the polyester molecular chain, bringing down the melting point. The proportions of terephthalic acid and adipic acid are controlled to keep the melting point of the modified polyester material at 185℃, 195℃, and 200℃. The effect of the mixing process of the modified polyester material and PP material at different melting points on the MI and dyeability of PP is discussed.

According to Table 2, the co-polyester material decreases linearly to some extent as the adipic acid addition increases. Because the adipic acid molecular structure is linear aliphatics, the molecular chain is relatively soft. In the polymerization process of co-polyester, adipic acid is used in the main chain of co-polyester, so that the carbochain length and quantity of co-polyester molecular chain are increased. The molecular chain is lengthened and becomes soft, while the ordered structure of polyester material is damaged, crystallinity is reduced, and the melting point can be controlled at 185–200℃, which is lower than for general polyester material.

MI optimization analysis

Based on the L₁₈ Taguchi experimental design, this study analyzed the MI experimental data by the main effect and integrated the response table and response graph, as shown in Table 7 and Figure 5.
Table 7.
Response table of the melt index

A B C D E

Level 1 0.34 −4.66 −4.81 −5.47 −4.58

Level 2 −4.42 −5.00 −4.77 −3.99 −4.30

Level 3 −9.98 −4.40 −4.48 −4.60 −5.18

Max 0.34 −4.40 −4.48 −3.99 −4.30

Min −9.98 −5.00 −4.81 −5.47 −5.18

Effect 10.32 0.60 0.33 1.47 0.88

Figure 5.
Response figure of the melt index.

Table 7 and Figure 5 show that the optimum factor levels are A₁, B₃, C₃, D₂, and E₂, which are modified co-polyester T_m 185℃, modified co-polyester content 9 wt%, compatilizer content 9 wt%, dye temperature 220℃, and screw speed 400 rpm, respectively.

Table 8 shows the ANOVA for the MI, where the definitions of the degree of freedom (DOF), sum of square (SS), mean square (MS), F-ratio, and contribution can be found from the ANOVA.¹²
Table 8.
Analysis of variance of the melt index

Item DOF SS MS F-ratio SS’ Contribution (%)

A 2 14.3918 7.1959 44.6749 14.0697 54.1964

B 2 1.0631 0.5315 3.3000 0.7409 2.8541

C 2 0.3926 0.1963 1.2186 0.0704 0.2713

D 2 6.5936 3.2968 20.4678 6.2715 24.1577

E 2 2.3919 1.1960 7.4250 2.0698 7.9729

Error 2 1.1275 0.0067 – – 10.5477

Sum 17 25.9605 – 2.1509 100

DOF: degree of freedom; SS: sum of square; MS: mean square.

As can be seen, the modified co-polyester T_m has the greatest effect on the MI, meaning that it has the greatest influence on the MI quality characteristic, followed by dye temperature, screw speed, modified co-polyester content, and compatilizer content.

Color strength optimization analysis

Based on the L₁₈ Taguchi experimental design, this study analyzed the color strength experimental data by the main effect and integrated the response table and response graph, as shown in Table 9 and Figure 6.
Table 9.
Response table of color strength

A B C D E

Level 1 46.25 45.81 45.82 45.82 45.81

Level 2 45.72 45.85 45.79 45.79 45.88

Level 3 45.51 45.81 45.87 45.87 45.79

Max 46.25 45.85 45.87 45.87 45.88

Min 45.51 45.81 45.79 45.79 45.79

Effect 0.74 0.04 0.08 0.09 0.10

Figure 6.
Response figure of color strength.

Table 9 and Figure 6 show that the optimum factor levels are A₁, B₂, C₃, D₃, and E₂, which are modified co-polyester T_m: 185℃, modified co-polyester content: 7 wt%, compatilizer content: 9 wt%, dye temperature: 230℃, and screw speed: 400 rpm, respectively.

Table 10 shows the ANOVA for color strength. As can be seen, the modified co-polyester T_m has the greatest effect on color strength, meaning that it has the greatest influence on the color strength quality characteristic, followed by screw speed, dye temperature, modified compatilizer content, and co-polyester content.
Table 10.
Analysis of variance of color strength

Item DOF SS MS F-ratio SS’ Contribution (%)

A 2 0.0291 0.0145 18.6166 0.0275 29.4709

B 2 0.0056 0.0028 3.6039 0.0041 4.3561

C 2 0.0124 0.0062 7.9328 0.0108 11.5980

D 2 0.0196 0.0098 12.5390 0.0180 19.3037

E 2 0.0212 0.0106 13.5839 0.0197 21.0517

Error 2 0.0055 0.0067 – – 14.2197

Sum 17 0.0934 – – 0.0934 100

DOF: degree of freedom; SS: sum of square; MS: mean square.

Materials optimization analysis

This study used GRA combined with the FCM to find the optimized processing parameters of both the MI and color strength quality characteristics. The result appears in Table 11 and Figure 7.
Table 11.
Response table of multiple characteristics optimization

A B C D E

Level 1 0.214 0.003 0.072 0.007 0.008

Level 2 0.001 0.136 0.136 0.131 0.074

Level 3 0.001 0.078 0.009 0.078 0.135

Max 0.214 0.136 0.136 0.131 0.135

Min 0.001 0.003 0.009 0.007 0.008

Effect 0.214 0.133 0.127 0.124 0.127

Figure 7.
Response figure of multiple characteristics optimization.

Form Table 11 and Figure 7, the study found that the optimized processing parameters are modified co-polyester T_m: 185℃, modified co-polyester content: 7 wt%, compatilizer content: 6 wt%, dye temperature: 220℃, and screw speed: 600 rpm. Table 12 lists the optimum parameters of modified PP compared with pure PP.
Table 12.
Modified polypropylene (PP) compared with pure PP

Quality Melt index (g/10 min) Color strength (K/S)

Goal 37–40 200≧

Pure PP 35.78 100

Modified PP 37.63 211.20

Table 12 shows that the MI of pure PP is 35.78 g/10 min and the color strength is 100 K/S, while the MI of modified PP is 37.63 g/10 min and the color strength is 211.20 K/S. The result clearly shows that modified PP is closer to our target.

Thermogravimetry analyzer

The low-melting co-polyester developed in this study was analyzed by a thermogravimetry analyzer. Table 13 lists the pyrolysis temperatures of modified PP and pure PP.
Table 13.
Thermogravimetry analysis of polymer in this study

Sample Pure PP co-PET T_m = 200℃ co-PET T_m = 195℃ co-PET T_m = 185℃ Optimum PP/co-PET

T_d 275.26℃ 376.74℃ 375.14℃ 350.917℃ 275.14℃

PP: polypropylene; PET: polyethylene terephthalate.

According to Table 13, the modified PP and pure PP have similar pyrolysis points, which can be processed below 270℃. The pyrolysis temperature of the low-melting co-polyester is higher than 350℃, and it can be processed at the tested processing temperature.

Differential scanning calorimetry analysis

A differential scanning calorimeter was used to analyze the low-melting co-polyester. The T_m and crystallinity of the modified PP and pure PP are listed in Table 14.
Table 14.
Differential scanning calorimetry analysis of polymer in this study

Sample Pure PP co-PET T_m = 200℃ co-PET T_m = 195℃ co-PET T_m = 185℃ Optimum PP/co-PET

T_c 109.36℃ 109.05℃ 141.09℃ 122.78℃ 111.7℃

T_m 163.47℃ 197.8℃ 193.66℃ 186.77℃ 161.53℃

Crystallinity (%) 42 39 38 29 40

PP: polypropylene; PET: polyethylene terephthalate.

Table 14 shows that the T_m of the modified PP is similar to that of the pure PP, but the crystallinity of the modified PP is slightly lower than that of the pure PP. This suggests that the modified PP has a better dyeing effect in the amorphous region than the pure PP. The T_m of the low-melting co-polyester can be accurately controlled within the preset T_m ± 2.5%.

Fourier transform infrared spectroscopy analysis

The functional groups contained in the pure PP and modified PP were analyzed by Fourier transform infrared spectroscopy (FTIR). The results appear in Figures 8 and 9.
Figure 8.
Fourier transform infrared spectroscopy of pure polypropylene (PP).

Figure 9.
Fourier transform infrared spectroscopy of modified polypropylene.

According to Figures 8 and 9, the pure PP only contains −CH−, –CH₂−, and –CH₃− non-polar groups. There is no functional group for bonding dyes during dyeing, and thus the dyeing effect fails. There is a characteristic absorption peak of the benzene ring functional group at wavelength 1246–1257 cm⁻¹ of the modified PP. There is a characteristic absorption peak of the ester functional group at 1708–1716 cm⁻¹. There is a characteristic absorption peak of the acid anhydride functional group at wave number of 2360–2364 cm⁻¹. This suggests that the modified PP has successfully mixed the PP and low-melting co-polyester, so that the PP contains the polar group, forming a hydrogen bond with disperse dyes in order to achieve the dyeing effect.

Conclusions

The optimum PP dyeable particle process in this study used polyester as a mixed copolymer. The PP, the low-melting co-polyester, and the PP-g-MA compatilizer were utilized to produce a composite through twin screw blending. The disperse dye dyeability was achieved by the molecular behavior of the co-polyester chain segment. The conclusions are described below.
The color strength test results showed that the low-melting co-polyester developed in this study has good dye uptake. After copolymerization mixing with PP, the color strength increased greatly. When the co-polyester T_m is 185℃, the color strength is relatively high, and the color strength increases with the co-polyester addition level.

For the development of the multi-quality optimized PP fiber, GRA was combined with the FCM to obtain the multi-quality optimization parameters: modified co-polyester T_m: 185℃, modified co-polyester content: 7 wt%, compatilizer content: 6 wt%, dye temperature: 220℃, and screw speed: 600 rpm. The results proved that the MI of the pure PP polymer is 35.78 g/10 min and the color strength is 100 K/S, while the MI of the PP/co-polyester dyeable particle of the optimum process is 37.63 g/10 min and the color strength is 211.20 K/S, suggesting that the developed polymer has good circular processing characteristics and color strength.

Dyeing stage	Formulae and conditions
Dyeing	Dyeing temperature: 130℃
Dye strength: 0.15 % o.w.f. (Navy Blue e-SE)
Dye leveler: 1% (Welleven PL-34)
Acid releasing agent: 0.8 g/L (Welsol PHC-98)
Bath ratio: 1:30
Reductive	NaOH: 3 g/L
Hydros: 3 g/L
Soaping agent: 1 g/L

T_m	Terephthalic acid (g)	Glycol (g)	Isophthalate (g)	Adipic acid (g)	Diethanol (g)
200℃	668.9	401.45	87.5	92.2	0.3
195℃	652.3	401.45	87.5	108.0	0.3
185℃	634.1	401.45	87.5	123.5	0.3

T_m	H₃PO₄ 5% (g)	Sb₂O₃ 1.5% (g)
200℃	1	20
195℃	1	20
185℃	1	20

Formula\T_m	200℃	195℃	185℃
Terephthalic acid	53.30 wt%	51.36 wt%	49.43 wt%
Glycol	31.99 wt%	31.61 wt%	31.29 wt%
Isophthalate	7.35 wt%	8.50 wt%	9.63 wt%
Adipic acid	7.35 wt%	8.50 wt%	9.63 wt%
Diethanol	0.02 wt%	0.02 wt%	0.02 wt%
Process	The temperature is increased from room temperature to 250℃ gradually, and the pressure is increased by 1–3 kg/cm². The reaction lasts about 6 h until the water is distilled completely. After esterification, the polycondensation catalysts, comprising 20 g of antimony trioxide and 1 g of stabilizer are added. The prepolymerization in low vacuum is carried out for about 50 min. After condensation polymerization in high vacuum for less than 1 torr, the reaction temperature is 250–280℃, and the reaction time is 210 min.

Factors	Levels
A	Modified co-polyester T_m (℃)	185	195	200
B	Modified co-polyester content (wt%)	5	7	9
C	Compatilizer content (wt%)	3	6	9
D	Dye temperature (℃)	210	220	230
E	Screw speed (rpm)	200	400	600

	A (℃)	B (wt%)	C (wt%)	D (℃)	E (rpm)	Result
1	185	5	3	210	200	R₁
2	195	5	6	220	400	R₂
3	200	5	9	230	600	R₃
4	200	7	3	210	400	R₄
5	185	7	6	220	600	R₅
6	195	7	9	230	200	R₆
7	195	9	3	220	200	R₇
8	200	9	6	230	400	R₈
9	185	9	9	210	600	R₉
10	195	5	3	230	600	R₁₀
11	200	5	6	210	200	R₁₁
12	185	5	9	220	400	R₁₂
13	200	7	3	220	600	R₁₃
14	185	7	6	230	200	R₁₄
15	195	7	9	210	400	R₁₅
16	185	9	3	230	400	R₁₆
17	195	9	6	210	600	R₁₇
18	200	9	9	220	200	R₁₈

	A	B	C	D	E
Level 1	0.34	−4.66	−4.81	−5.47	−4.58
Level 2	−4.42	−5.00	−4.77	−3.99	−4.30
Level 3	−9.98	−4.40	−4.48	−4.60	−5.18
Max	0.34	−4.40	−4.48	−3.99	−4.30
Min	−9.98	−5.00	−4.81	−5.47	−5.18
Effect	10.32	0.60	0.33	1.47	0.88

Item	DOF	SS	MS	F-ratio	SS’	Contribution (%)
A	2	14.3918	7.1959	44.6749	14.0697	54.1964
B	2	1.0631	0.5315	3.3000	0.7409	2.8541
C	2	0.3926	0.1963	1.2186	0.0704	0.2713
D	2	6.5936	3.2968	20.4678	6.2715	24.1577
E	2	2.3919	1.1960	7.4250	2.0698	7.9729
Error	2	1.1275	0.0067	–	–	10.5477
Sum	17	25.9605	–		2.1509	100

	A	B	C	D	E
Level 1	46.25	45.81	45.82	45.82	45.81
Level 2	45.72	45.85	45.79	45.79	45.88
Level 3	45.51	45.81	45.87	45.87	45.79
Max	46.25	45.85	45.87	45.87	45.88
Min	45.51	45.81	45.79	45.79	45.79
Effect	0.74	0.04	0.08	0.09	0.10

Item	DOF	SS	MS	F-ratio	SS’	Contribution (%)
A	2	0.0291	0.0145	18.6166	0.0275	29.4709
B	2	0.0056	0.0028	3.6039	0.0041	4.3561
C	2	0.0124	0.0062	7.9328	0.0108	11.5980
D	2	0.0196	0.0098	12.5390	0.0180	19.3037
E	2	0.0212	0.0106	13.5839	0.0197	21.0517
Error	2	0.0055	0.0067	–	–	14.2197
Sum	17	0.0934	–	–	0.0934	100

	A	B	C	D	E
Level 1	0.214	0.003	0.072	0.007	0.008
Level 2	0.001	0.136	0.136	0.131	0.074
Level 3	0.001	0.078	0.009	0.078	0.135
Max	0.214	0.136	0.136	0.131	0.135
Min	0.001	0.003	0.009	0.007	0.008
Effect	0.214	0.133	0.127	0.124	0.127

Quality	Melt index (g/10 min)	Color strength (K/S)
Goal	37–40	200≧
Pure PP	35.78	100
Modified PP	37.63	211.20

Sample	Pure PP	co-PET T_m = 200℃	co-PET T_m = 195℃	co-PET T_m = 185℃	Optimum PP/co-PET
T_d	275.26℃	376.74℃	375.14℃	350.917℃	275.14℃

Sample	Pure PP	co-PET T_m = 200℃	co-PET T_m = 195℃	co-PET T_m = 185℃	Optimum PP/co-PET
T_c	109.36℃	109.05℃	141.09℃	122.78℃	111.7℃
T_m	163.47℃	197.8℃	193.66℃	186.77℃	161.53℃
Crystallinity (%)	42	39	38	29	40

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministry of Science and Technology of the Republic of China (grant no. MOST 104-2221-E-011-156).

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