A Study on the Impact of Non-aqueous Solvent Mixtures on the Crystallanity of Polyester/Cotton Composite Fibre

S. Laya1, 2+ and B. Muralidharan1

1BITS Pilani, Dubai Campus, International Academic City, Dubai, United Arab Emirates 2School of Chemistry, Department of Industrial Chemistry, Alagappa University, Karaikudi, 630002, India.

Abstract. Polymer composites from natural and synthetic sources have attracted the scientific world, predominantly due to their better performance. A composite fibre can be modified either thermally or by treating with single solvent or mixture of solvents. The present work aims to study the effect of solvent pretreatment on the molecular orientation surface modification and the dyeability of 67:33 Polyester/cotton blended yarns. The treated samples were also subjected to tensile testing, scanning electron microscopy, differential scanning calorimetry and X-ray diffraction analysis to investigate their mechanical, physical and crystalline properties. From the investigation, it was observed that the polymer crystals got re-oriented through solvent induced crystallization with surface modification resulting in enhanced dyeability of the fibre due to solvent pretreatment. The tensile strength of the treated fibre also found to get improved and was dependant on the nature of the solvent system and duration of treatments.

Keywords: Solvent Induced Crystallization, Polymer-Solvent Interaction, Crystalline Distribution, Dye Penetration, Plastization Effect and Crystalline Orientation.

1. Introduction A fibre composite is versatile in its properties as it is combinations of fibres which can be designed

depending on the end use providing a number of advantages as compared to individual fibres. Combining natural cotton fibres with synthetic polyester fibres offer its consumers the benefit of both. Fibre blends can also aid in the development of new low-cost products with better performance. These blends are extending the utilization of polymers into new value-added products. When these blends are used in the field of textile industry, colouring them is inevitable. The dyeability features of individual fibres would be unique and the chemicals and dyes may not be compatible. Due to this contradiction in dyeing characteristics, the composite fibres need modification.

The modification of fibres using solvents depends upon the extent of interaction of solvents and their solubility parameters. The presence of solvent can cause disturbance in the structural order of the fibre and the polymer matrix get restructured after the removal of solvents. Many reports are available on modification of the polymer fibres through solvent pretreatments and induced crystallization [1-5]. In these treatments solvents are reported to disrupt the secondary bonds in the fibre and enhance the segmental mobility of the polymer chains and result into the formation of stable crystallites after the removal of the solvent molecules. During the solvent pretreatment process, the solvent attacks the more susceptible amorphous region and reduces the strength of polymer –polymer interaction compensating with polymer solvent interaction. The polymer-polymer interaction re-establishes when the solvent molecule is withdrawn from the fibre matrix. This generates stable crystallites with different molecular orientation depending on the nature of the solvent.

+ Corresponding author: Tel. +971 4 4200700, Fax. +971 4 4200844, Email address: layarajendran@hotmail.com

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2012 3rd International Conference on Chemistry and Chemical Engineering IPCBEE vol.38 (2012) © (2012) IACSIT Press, Singapore

Reports are available in improving the dyeability of polyester/cotton blends using solvent mixtures and other pretreatments [2-7]. The modifications depend on the duration of interaction and type of solvents. In the present work a study has been carried out using four different solvent mixtures with different polarity index in modifying the fibre composite consisting of 67:33 polyester and cotton. The solvent treated fibres were investigated for changes in their morphology through Scanning Electron Microscopic (SEM) studies, crystallanity by X-ray Diffraction studies (XRD) and Differential Scanning Calorimetric (DSC) method. The physical properties like weight loss and tensile strength of the both control and treated samples were also studied. Also the changes in dyeing behaviour were studied and analyzed.

2. Materials and Methods

2.1. Materials 67:33 Polyester/cotton blended yarn (67:33 PCY) of fine filament yarn of count 50’s supplied by

Karpaka Vinayaka Mills, Karaikudi, Tamilnadu, India was used in this study For treating the yarns, organic liquids of Fischer-LR grade which were prepared as per the composition

stated in Table 1. The composition was fixed by referring to azeotropic data published by Ryland [8] and Lecat[9].

The following Foron Disperse dye and Drimarene Reactive dye were respectively used for dyeing of polyester and cotton component of the fibre composite

Foron Brilliant Orange S-FL (C.I. Disperse Orange 96) Drimarene Brilliant Orange (C.I. Reactive Orange 64)

2.2. Methods The yarns were made into 0.5 g hanks and were treated with azeotropic ternary mixture of solvents

prepared based on the composition stated in Table 1 at room temperature for various time intervals, viz. 2, 4, 6, 8, 10, 20 and 30 minutes. Pretreatments were carried out in a closed trough preventing the vaporization of the solvent system. The solvents were reused and consequently the air pollution was minimized. The pre-treated samples were then dried at room temperature ensuring no residual solvent to be present in the solvent treated fibre.

The treated samples were subjected to weight loss measurements using an electronic balance of accuracy ±0.0001 g (Sartorius-GD 503-Germany). The tensile strength of the untreated and solvent pretreated yarns was measured using ASTM D638 standard test procedures.

Scanning Electron Microscopy (SEM) observations were carried out for solvent pre-treated and untreated samples using S-3000H–Hitachi, Japan to evaluate the surface modification of the fibre due to solvent pretreatments. Both treated and untreated samples were subjected Differential Scanning Calorimetric (DSC) analysis using PERKIN ELMER Pyris 6 model-USA. Approximately 10 mg of each sample was fed into the instrument at a heating rate of 50°C/min. Pure Nitrogen gas was used to provide inert atmosphere at a rate of 20 mL/min. X-ray diffraction (XRD) studies were carried out using PANalytical - Model X’pert PRO, The Netherlands for yarns before and after solvent treatment to analyze changes in crystallanity and molecular orientation if any.

Dyeing of pre-treated and untreated yarns was performed using the rota dyer bath (Rota dyer 18x100-N machine, R.B. Electronic and Engineering Pvt. Ltd., Mumbai-53, India). The dye bath was prepared with the following recipe and dyeing conditions

Disperse and Reactive Dye - 2 % each Glauber’s salt - 5 g/l

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Soda ash - 3 g/l Borax - 5 g/l Temperature - 80, 95 and 110 ºC. Dyeing Duration - 30, 45 and 60 minutes pH of the dye bath - 10 to 11 Material to liquor ratio (MLR) - 1:50

The dyed and washed yarns were reduction cleared to remove unfixed dye from the surface of the fibre by using commercially available reduction clearing agent, Ladipur MCL (Clariant Chemicals, India) then it was washed with water and dried in a hot air oven. The amount of dye uptake of the samples during dyeing were measured spectrophotometrically using UV-VIS Spectrophotometer (Labomed- model spectro 23 RS, USA).

3. Discussion

3.1. Weight Loss Measurements Weight loss measurements were carried out to assess the effect of solvent on the polymer by weighing

the samples before and after solvent pretreatments. The results of the weight loss measurements are presented in Table 2. The loss in weight percentage for a pre-treatment duration of 30 min. was found to be 1.50% for fibres treated with Ac-MA-MAc and 0.995 % for fibres treated with Ac-MAc-nH, whereas the weight loss found to be 0.09 % and 0.04% respectively for samples treated for 2 min. with Ac-MA-MAc and Ac-MAc-nH. This indicates that loss in weight percentage is dependant on the nature of solvent and duration of treatment. Among the four solvents, it was found that the one with higher polarity index caused more loss in weight. These observations are in conformity with the observations reported earlier [2-3]. Since the weight loss due to solvent pretreatment is up to a maximum of 1.5 % even during longer pretreatment duration of 30 min., indicating that the solvent treatment have not affected the fibre to a larger extent.

3.2. Tensile Strength Measurements The tensile strength measurements of untreated and solvent pretreated 67:33 yarns (Table 2) showed that

the strength have been found to get improved for samples treated for duration time up to 8 min. and then found to decrease in the case of all the four solvent systems with increase in duration of solvent treatment. Treatment duration of 6 min. showed the maximum 13.25% improvement in the strength using Ac-MA-MAc solvent system with higher polarity index and the solvent system with least polarity index (Ac-MAc-nH) showed 10.75 % improvement. These observations can be attributed to the fact that solvents penetrate into the polymer matrix and improve the structural order creating stable crystallites [1, 2 and 5]. The XRD and DSC observations further support this point. The deterioration in strength for higher treatment durations can be due the surface cavitations and void creation in the polymer matrix due to the attack of the solvents [10]. SEM observations further support this hypothesis. The extent of cavitations was found to be dependent on duration of treatment and the polarity index of the solvent.

3.3. Differential Scanning Calorimetry The thermograms obtained for control and solvent pre-treated samples are presented in Fig 1. It is

evident from the thermogram patterns that the melting heat has considerably got increased for solvent treated samples as compared to the untreated samples and the extent of increase is in accordance with the polarity index of the solvent. This is due to the increase in crystallanity of the fibre due to solvent treatment, solvents would have interacted with polymer chains disturbing the morphology and fine structures leading to solvent induced crystallization [1] The solvent molecules penetrate into the polymer structure weakening the polymer-polymer interaction, compensating with polymer-solvent interaction [2-3, 12]. There are two types of solvent-fibre interaction namely inter-crystalline interaction and intra-crystalline interaction. The solvents penetrate into the amorphous region in the case of former type and in the latter case the solvents penetrate in to the crystalline region. In the case of inter-crystalline interaction, the susceptible amorphous regions get attacked and this causes rearrangement within the polymer matrix increasing the crystalline area [13]. As the solvent treated samples have shown a considerable increase in the melting heat due to increase in the crystallanity, the interaction of solvent with the fiber material is found to be inter-crystalline interaction [4,5].

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3.4. XRD Studies The XRD observations (Fig 2) showed that the curves corresponding to solvent treated samples got

sharpened with increased peak height. The sharp peaks correspond to crystalline regions of the polymer and the broad ones stands for amorphous regions [11]. As the interaction of solvent with the fibre results in increased crystallization, the peaks got sharpened for solvent treated samples. The extent of sharpness increased with increase in the polarity index of the solvent as they could induce crystallization to a large extent. The results confirms that the solvents acted as plasticizer in the amorphous region breaking intermolecular bonds and enhancing segmental mobility of the polymer which induced crystallization leading to the formation of stable crystallites [1,2] The creation of micro-voids in the polymer structure due to solvent treatment which was clearly seen in SEM photographs. The results reported earlier in the literature supports these observations [2, 3 and 12]

3.5. SEM Morphology The surface morphology of the untreated and solvent pre-treated fibres was examined using scanning

electron microscopy and the results obtained are presented in Figs. 3. The untreated control sample exhibits smooth surface texture and the solvent pretreated samples exhibited a rough texture. The solvents caused the formation of micro voids and pits in the amorphous part of the polymer. Also the solvents with high polarity index could attack the fibre more effectively opening the structure as visible from the SEM photos. The deposition of tiny particles (oligomers) found to be more for the treated samples indicating that they have diffused in to the surface as a result of treatment. During solvent pretreatment, the solvents penetrate into the non-crystalline region of the polymer releasing the stresses due to solvent induced swelling. These observations are further supported by weight loss studies. A similar observation was already indicated in the literature [2, 3, 12-13].

3.6. Dyeability Characteristics To confirm the modification in the internal structure of the composite fibre after solvent pre-treatment,

the samples were subjected to dyeing. The effects of solvent pre-treatment on the dyeing behaviour of the samples were studied by dyeing the pre-treated and untreated samples under different conditions using a different pairs of disperse and reactive dye. The percentages of dye uptake of pretreated and untreated samples are presented in Table 3. A maximum up to 71 % improvement in dye uptake was observed for samples treated with solvent of highest polarity index (Ac-MA-MAc). An improvement in the dyeability was observed for all the four different solvent mixture treated samples for a pretreatment duration up to 6-8 min. and above which the dyeability was found to get lowered. The improvement in dyeability was not only dependent on solvent pre-treatment duration, but also dependent on dye bath temperature and dyeing duration. The improvement in the dyeability as a result of solvent pretreatment is due to the change in the internal structure of the amorphous region by the formation of voids and cracks facilitating the dye molecule in to the polymer structure. SEM photographs revealed the formation of voids and cracks in the fibre structure. The amount of dye uptake was found to be dependent on the degree of interaction between the polymer and nature of the solvent. The solvents with high polarity index could cause a better molecular rearrangement with proper orientation making the dye reception effective. The decrease in improvement with increase in pretreatment duration is attributed to the fact that prolonged solvent pre-treatment led to increase in crystallanity of the fibre and made dye penetration difficult. The increase in crystallanity as a result of solvent pretreatment is substantiated by the XRD and DSC results. Similar observations have been reported earlier in the literature [10-17].

4. Conclusions The following conclusions are drawn from the present study; • Treatment of 67:33 polyester/cotton composite fibre with four different solvent mixtures have

resulted in solvent induced crystallization leading to re-orientation in the internal structure of the composite fibre matrix.

• This observation is supported by the experimental data derived using DSC, XRD and SEM. • This is then further supported by the weight loss measurements and tensile strength measurements

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• Change in dyeing behaviour of the polymer composite also provides additional support to the above observations.

• The extent of modification is found to be dependent on the duration of treatment time and polarity index of the solvents used.

• Since the dye uptake of the fibre is improved by the solvent by pre-treatments, the amount of dye thrown to the environment is minimized.

5. References [1] H. Jameel, J. Waldman and L. Rebenfeld. The effects of orientation and crystallinity on the solvent-induced

crystallization of poly (ethylene terephthalate). 1. Sorption- and diffusion-related phenomena, J. Appl. Polym. Sc., 1981, 26:1795-1811.

[2] B. Muralidharan, T. Mathanmohan and J. Ethiraj Effect of acetonitrile pretreatment on the physicochemical behavior of 100% polyester fabric, J. Appl. Polym. Sci. , 2004, 91: 3871-3878.

[3] B. Muralidharan and S. Laya. A new approach to dyeing of 80:20 polyester/cotton blended fabric using disperse and reactive dyes. ISRN Mater. Sci., 2011. doi:10.5402/2011/907493.

[4] B. Muralidharan, S. Laya, R. Venkatachalam and S. Vigneswari. Energy efficient dyeing method of polyester/cotton blended fabric by one bath one step dyeing using Azeotropic mixtures. Proceedings of the International Conference on Emerging Green Technologies ICEGT-2011, July 27-30, 2011, Periyar Maniammai University, Thanjavur, Tamil Nadu, India.

[5] B. Muralidharan, S. Laya, R. Venkatachalam, K. Balakrishnan and S. Vigneswari. Energy saving in dyeing of polyester fabric involving solvent pretreatments. Proceedings of the International Conference on Emerging Green Technologies ICEGT-2011, July 27-30, 2011, Periyar Maniammai University, Thanjavur, Tamil Nadu, India.

[6] B. Kazimierz, P. Joanna and C. Wojciech. Reactive Dyes for Single-Bath and Single Stage Dyeing of Polyester-Cellulose Blends. Fibres & Textiles in Eastern Europe, 2005, 13:75-78.

[7] H. Najafi, M. Hajilari, and M. Parvinzadeh. Effect of chitin biopolymer on dyeing polyester/cotton fabrics with disperse/reactive dyes, J. Appl. Sci., 2008, 8:3945-3950

[8] G. Ryland. Liquid Mixtures of constant Boiling Point. American Chemical Journal, 1899, 22:384.

[9] M.L. Lecat. Vapour Pressure of the azeotropic liquids, Lamartin: Bruxelles, Belgium, 1918

[10] H. Jameel, H.D. Noether and L. Rebenfeld. The effects of orientation and crystallinity on the solvent-induced crystallization of poly (ethylene terephthalate). II. Physical structure and morphology, J. Appl. Polym. Sci., 1982, 27(3): 773-793.

[11] V.R. Gowarikar, N.V. Viswanathan and S. Jayadev. Polymer Science, New Delhi, New Age International (P) Ltd., 1996.

[12] B. Muralidharan, S. Laya and S. Vigneswari. An Investigation on the Effect of Azeotropic Solvent Mixture Pretreatment of 67:33 PET/CO Blended Fabric and Yarn- Part-I, Asian Textile Journal, 2011 1(3):114-129.

[13] B.Muralidharan, S.Laya and G.Gopu, ‘ An Investigation on the impact of azeotropic solvent mixture pretreatment on the fibre composite of a natural and synthetic origin’, Paper presented in the International Conference on Sustainability in Polymer Materials S-PolyMat2012, May 20-23, 2012, Rolduc Polymer Meetings organized by European Polymer Federation, Kerkrade, Netherlands.

[14] B. Muralidharan, S. Laya and S. Vigneswari. An Investigation on the Effect of Azeotropic Solvent Mixture Pretreatment of 67:33 PET/CO Blended Fabric and Yarn- Part-II, Asian Textile Journal, 2011 1(4):145-160.

[15] J.J. Lee, N.K. Han, W.J. Lee, et al. Dispersant-free dyeing of polyester with temporarily solubilised azo disperse dyes from 1-substituted-2-hydroxypyrid-6-one derivatives, Colouration Technology, 2002 118:154-158.

[16] G.F. Ruppenicker and R.M.H. Kullman. Properties of yarns and fabrics produced from high cotton content blends with polyester fibres, Text. Res. J., 1981, 51: 590-596.

[17] M. Shingo, K. Katsushi, H. Toshio and M. Kenji. One Bath Dyeing of Polyester/Cotton Blends with Reactive Disperse Dyes in Supercritical Carbon Dioxide, Text. Res. J.,2004, 74: 989-994

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Table 1: Details of azeotropic ternary solvent mixture used for pretreatment

S.No. Solvent System weight % volume % Solubility parameter

Solubility parameter of the mixture

Polarity Index

B.P. (oC)

1

Acetone Methyl alcohol Methyl acetate (Ac-MA-MAc)

5.8 17.4 76.8

7.3 22.0 82.4

10.0 14.5 9.6

11.14

16.4

53.7

2

Acetone Ethyl alcohol Chloroform (Ac-EA-Cf)

24.3 10.4 65.3

30.6 13.2 44.0

10.0 12.7 9.3

11.73

14.5

63.2

3

Acetone Methyl alcohol n-Hexane (Ac-MA-nH)

30.8 14.6 59.6

38.9 18.4 91.0

10.0 14.5 7.3

10.10

12.0

47

4

Acetone Methyl acetate n-Hexane (Ac-MAc-nH)

51.1 5.6 43.3

64.3 6.0 66.1

10.0 9.8 7.3

13.22

9.5

49.7

Table 2: Weight loss percentage and Change in tensile strength of untreated and solvent pretreated fibre samples

Solvent System

000000000 Pretreatment Time (min.) Percentage of weight

loss Tensile Strength

(Kgf) % Change in Strength

Ac- MA- MAc

2 0.090 11.475 +4.090 4 0.280 11.850 +7.727 6 0.769 12.460 +13.250 8 0.895 12.265 +11.500 10 0.920 10.735 -2.272 20 1.100 10.400 -5.500 30 1.500 10.000 -9.090

Ac- EA- Cf

2 0.085 11.410 +3.750 4 0.210 11.700 +6.325 6 0.685 12.400 +12.750 8 0.790 12.200 +10.909 10 0.890 10.860 -1.272 20 1.050 10.490 -4.650 30 1.175 10.050 -8.636

Ac-MA- nH

2 0.055 11.300 +2.727 4 0.150 11.630 +5.750 6 0.600 12.320 +12.000 8 0.695 12.100 +10.000 10 0.820 10.910 -0.750 20 1.000 10.550 -4.100 30 1.110 10.150 -7.127

Ac-MAc-nH

2 0.04 11.200 +2.000 4 0.110 11.560 +5.100 6 0.450 12.180 +10.750 8 0.600 12.080 +9.800 10 0.730 11.000 0 20 0.940 10.600 -3.600 30 0.995 10.280 -6.525

Untreated - - 11.000 -

Fig. 1: DSC of samples treated for 30 min. Fig 2 XRD of samples treated for 30 min.

UT=Untreated, S1=Ac-MA-MAc, S2= Ac-EA-Cf, S3=Ac-MA-nH and S4= AC-MAc-nH

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Table 3: Dye uptake percentages for control and pretreated fibre samples

Solvent System

Dyeing Temperature 80°C 95°C 110°C

Dyeing time (min.) Dyeing time Dyeing time Pretreatment

time min. 30 45 60 30 45 60 30 45 60

Ac-

MA

-MA

c

2 45 47 57 53 58 61 56 61 65

4 48 50 55 60 67 71 64 72 75

6 51 54 59 75 81 84 78 83.5 87.5

8 47 51 55 71 75.5 78.5 73 78 81

10 42.5 47 50.5 68 72 75 70 74 79

20 40 45.5 48.5 57 63 68 60 64 69.5

30 37.5 42.5 45 51 55 60 54 57.5 63

Ac-

EA

-Cf

2 43 46 49.5 51 54.5 57.5 53.5 58 63

4 46.5 49 53.5 56.5 59 63 59.5 62 65.5

6 49 51.5 57 67 70 74.5 70 73 78

8 53 56 59.5 72 75 80 75 78.5 83

10 40 45 49.5 55 61 68 57.5 64 72

20 39 43.5 46 51 55 59.5 54.5 57.5 62

30 36 40 43 46 50 53 48 52 55.5

Ac-

MA

-nH

2 42.5 45 48 50 53 56 52 55 61.5

4 45 48 51.5 55.5 58 61 57 60 63.5

6 48.5 50 55 60 63 66 68 70.5 74

8 50.5 53.5 57.5 70 73 76 74.5 76 80

10 41 44 48 65 68 71.5 56 61 70

20 38 42 45 48 52 57.5 52 56 60

30 35 38 42 43 46.5 49.5 47 50 53

Ac-

MA

c-nH

2 42 44 47 48.5 51 55 50 53 58.5

4 43.5 47 50 51.5 54 58 53.5 57.5 61

6 47 49.5 53 54.5 57.5 62.5 60 64 70

8 49 51.5 56.5 67 71 74 71 73.5 77.5

10 40 43 47 61 65.5 69.5 64 69 74

20 38 41.5 44 45 49.5 55 48 52 59

30 36 37.5 41 40 43 45.5 43 47 51.5

Untreated 41 42.5 46 42 44.5 49 43 45.5 50

Fig. 3: SEM photographs of untreated and solvent treated 67:33 PCY

Untreate Ac-MA-MAc treated Ac-EA-Cf treated Ac-MA-nH treated Ac-MAc-nH treated

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