bstract
Modification of polypropylene at the pre-spinning stage, using a melt-bending technique, is found to be a convenient route to improve fibres performance. A number of attempts have been reported to improve dyeability, as well as stiffness, strength, shrinkage, flammability, etc, by using additives and various other polymers at the melting stage.
In the present work, an attempt was made to incorporate aroma chemicals, such as 3,4- methylenedioxybenzaldehyde, during melt spinning of PP, and the spun fibres thus obtained were studied for improved properties such as the aroma or fragrance, and antibacterial activity, as well as improvement in dyeability. Needless to say, this explored the application potential of modified PP in various fields of textiles such as apparels, sportswear, automotive, medical textiles etc.
Blended modified fibres were found to be giving a powerful aroma, which was durable over a 2- year period. This aroma fibre also exhibited enhancement in disperse dyeability, to the extent of 200 to 700%. The optimum level of aroma additive in PP was predicted, keeping in view the tenacity and odour durability of melt-blend fibres.
Key words: Aroma fibres, Crystallinity, Fibre Additives, Melt blending, Polypropylene.
Introduction
The smell of aroma chemicals bears many therapeutic attributes. The sense of smell directly connects to the mind, exhibiting a strong influence on our personality. Fragrances are used in products to give it a scent, to mask the odour of other ingredients or to alter the mood or emotions (Ref: 1). Fragrant materials can be either synthetic or natural or both, and in the last decade innumerable synthetic organic chemicals have been used in consumer products to add value to their performance. However, if these finishes are applied after the fabric is dyed, the durability of such finishes has been found to be always limited. Hence, the present study explored the potential of application of aroma chemicals during melt spinning of PP to obtain durable fragrant fibres with improved dyeability.
In our laboratory also the melt blending of PP was carried out with Polybutylene Terephthalate (PBT) and Cationic Dyeable Polyester (CDPET), and thus not only was the disperse dyeability of PP improved, but also its cationic dyeability (Ref: 2). It has been reported that the thermal shrinkage of PP can be greatly reduced when a minor component of liquid-crystal polymer is blended in it (Ref: 3).
The recent trend in the market is to obtain fabric with speciality finishes such as waterrepellent, antibacterial or fragrance-emitting. Many a times the fabric is finished with encapsulated perfume finishes. However, their durability to washing during their service life is always limited (Ref: 4,5). The present study explored the potential for the application of the aroma chemical 3,4 methylenedioxybenzaldehyde during melt spinning of PP to obtain aromatic fibres. It was also aimed at studying the dyeability characteristics of such aromatic fibres.
Materials
Commercial grades of polymers, dyes, chemicals and auxiliaries were used in the present study. Polypropylene (PP) chips REPOL H200FG, having Melt Flow Index 20.0 and Flexxural Modulus 1650 MPa, supplied by Reliance Industries Ltd, Mumbai, were used. Aroma chemical, namely 3,4 methylenedioxybenzaldehyde, was used for experimentation. These are white crystals, having molecular weight 150.13 and boiling point 263.0°C- 265.0°C. Generally, the substance is extracted from the Heliotrope flower, which gives a sweet, powdery, coconut-vanilla aroma. It is insoluble in paraffin oil, water and glycerin.
Experimental
Blending of Polymer Chips: In order to have a proper distribution of aroma chemicals throughout the PP polymer, a twin-screw extruder was used, maintaining the temperature of its three different zones of heating as 190°C, 210°C and 220°C, respectively. The polymer chips were melt blended with 2.5 and 5% of aroma additive 3,4 methylenedioxybenzaldehyde.
Melt Spinning and Dyeing of Polymer Blend Filament Yarns: The melt spinning of the PP chips blended with aroma was carried out on a Laboratory Melt Spinning machine, obtained from Fair Deal Associates, New Delhi, India, at draw ratio of 1:3, which was optimised prior to the experimentation. Using the standard method of dyeing synthetic fibres in a hightemperature/ high-pressure (HTHP) beaker dyeing machine, the modified fibres were subjected to disperse dyeing with three disperse dyes, such as CBENE Yellow GNL, CBENE Red 3BLS and CBENE Navy Blue 3RT, for a 1% shade. The dyed samples were then subjected to reduction clearing. A treatment for 20 min. at 70°C with 2gpl of both caustic soda and sodium hydrosulphite (hydrose) was given. All fibre samples were thoroughly washed at room temperature, followed by neutralisation with 1gpl acetic-acid solution. The fibre samples were finally washed in water and dried(Ref: 6).
Evaluation of Wash Fastness and Colour Strength: The dyed samples were then tested for washing fastness [ISO 3] in a Launder-OMeter for 20 min. at 60°C, using 2g/l non-ionic soap and 2g/l soda ash at a liquor ratio of 50:17. Then the samples were evaluated for colour depth in terms of the Kubelka Munk function K/S, using a Spectra Flash SF 300 computer colourmatching system, supplied by Datacolor International, USA (Ref: 8).
Analysis of Fibre Structure: Measurement of tenacity and elongation at break, X-ray diffraction analysis, FTIR analysis and Differential Scanning Calorimetry (DSC) analysis were carried out using standard techniques.
Wide Angle X-Ray Diffraction (WAXD): The finely cut fibre samples were gently pressed into a rectangular felt, using an appropriate spacer. WAXS patterns were recorded from 2θ angle 0° to 40° with Lab X XRD – 6000 Shimadzu Diaffractometer, equipped with a Graphite Monochromator in the diaffracted beam (Ref: 9).
Fourier Transform Infrared Spectroscopy (FTIR): FTIR spectra were obtained with a Shimadzu IR Prestige 21 Spectrophotometer. A total of 46 scans for each sample were taken. Modified fibres were cut into fine powder, dried and 1mg of the same was dispersed in dry KBr. The pallets were then obtained using hydraulic press and were immediately subjected to FTIR analysis (Ref: 9).
Differential Scanning Calorimetry (DSC): Differential Scanning Calorimetry of the PP samples with various loadings of aroma chemical, ie. 6-Acetyl-1,1,2,4,4,7-hexamethyltetraline, was carried out to evaluate compatibility of PP additive and the effect of loadings of 6- Acetyl-1,1,2,4,4,7-hexamethyltetraline (aroma chemical) on the crystallanity of modified PP. This was carried out on DSC-60 supplied by Shimadzu, Japan (Ref: 10).
Scanning Electron Microscopy (SEM): SEM is widely used to study the morphological features and surface characteristics of the polymeric materials. The modified and pure PP samples were studied for their morphology using SEM (Ref: 11).
Tensile Strength and Elongation at Break: The tensile strength and elongation at break of PP filaments were measured on a ‘Tinius Olsen’ machine, supplied by Aimil Ltd. Testing was carried out as per the test method ISO 5079 for breaking strength of fibres (Ref: 12).
Thermo Gravimetric Analysis (TGA): The thermal stability was studied by TGA. The weight loss due to the formation of volatile products after degradation at high temperature was monitored as a function of temperature. TGA for pure PP and modified PP was characterised with DTG-60H thermogravimetric analyser (Shimadzu, Japan). The samples were heated under nitrogen atmosphere at a heating rate of 5°C/min from 40°C to 425°C.
Results and Discussion
Antibacterial Properties: The antibacterial activity of the modified composite filament was tested by the standard procedure, using the broth dilution method. The organisms employed in the in-vitro testing of the compounds were Staphylococcus aureus and E. coli. At the end of the incubation period the results were interpreted by visual comparison with control. The study indicated that 3,4- methylenedioxybenzaldehyde showed antibacterial activity for both the organisms.
FTIR Study: The FTIR spectrum of PP modified with 3,4- methylenedioxybenzaldehyde indicates the dominant presence of –CH bond at 2922.26cm-1, representing PP structure in the FTIR spectrum of modified PP. The absorption band of –OH stretching at 3412cm-1, and the aromatic rings seen at the absorption band near 1161.15 cm-1 correspond to the presence of aromatic rings of aroma additive in the modified PP sample.
Dyeability Study: In the case of fibre modified with 3,4- methylenedioxybenzaldehyde the improvement in the dyeability was found to be of the order of 225.05% to 306.72% when additive content was 2.5%. This improvement was further enhanced in the range of 439.38% to 607.64% for 5% aroma additive content.
This significant improvement in dyeability of the modified PP, which otherwise in its pure form is difficult to dye with disperse colours, may be due to the reduction in the crystallinity of the modified fibre and consequent increase in the amorphous region as a result of incorporation of the bulkier aroma-additive molecule in the polymer matrix.
The accessibility to disperse dye and its diffusion during dyeing of PP seem to have been significantly increased as a result of increase in amorphous region. The percentage improvement in dye uptake (K/S) was maximum in case of CBENE Navy Blue 2GLS with molecular weight of 625 and minimum for CBENE Yellow SGL with molecular weight of 428. This is also in conformity with the fact that higher-molecular-weight disperse dyes, having relatively low diffusion coefficient, are more sensitive to changes in internal structure, such as decrease in crystallinity or increase in amorphous content, and thus are expected to show a greater improvement. The reverse is the case for relatively lower-molecular-weight disperse dyes. The dyed samples exhibited a high level of washing fastness.
By looking at the structure of CBENE Yellow SGL, it is clear that in this dye molecule the groups that are responsible for hydrogen bonding are the hydroxyl group, sulphoxy group and azo group, which are electron donors, and the cyano group, which act as electron acceptors. In CBENE Red 3BLS the number of groups which are electron donors is very high as compared to CBENE Yellow SGL, as there are tertiary amino groups and an azo group. The electron acceptors present as an amido group and keto groups. Hence it is likely to have more interaction with the substrate, which results in more dye uptake for Red dye than Yellow dye.
In case of CBENE Navy Blue 2GLS, the number of electron-donor groups is very high compared to Yellow dye and Red dye, as there are tertiary amino groups, methoxy group and an azo group. The electron acceptors present as amido group and keto groups. The presence of a methoxy group, which increases the number of electron-donating groups in the Blue dye, increases the interaction with the substrate, and hence it is expected to have more dye uptake and increase the strength of the dyeing.
This drastic improvement in the dyeing of modified PP was an additional promising feature of this work. The subsequent analysis of the internal structure of the fibre was carried out to understand the reasons behind the improved dyeability of the modified PP.
Differential Scanning Calorimetry Study (DSC): The percent crystallinity of the sample was calculated using the following relationship:
% Xtal = ( Hm/ΔHm°) x 100%,
where, in this expression, % Xtal is the total percentage crystallinity, ΔHm is the measured heat of melting by DSC and ΔHm° is the reference value for the heat of melting. For Polypropylene, this reference value is 207 J/g. As per the DSC study, the melting peak for pure PP appears at 164.58 °C, showing ΔHm as 163.77 J/g. The melting peak for PP fibre modified with 5% 3,4- methylenedioxybenzaldehyde additive is seen at 162.55°C, with ΔHm as 72.59 J/g, showing a percentage crystallinity of 35.07%.
The decrease in crystallinity, which consequently implies an increase in the amorphous-region content due to incorporation of the aroma additive, must be responsible for the significant increase in dyeability as observed earlier. This clearly indicates that a drastic reduction in the crystallinity of PP as a result of melt blending with aroma additive, which has a bulkier aromatic ring structure, is possibly the cause of opening up of the PP fibre structure, enhancing the disperse-dye diffusion and dye uptake.
X-ray Diffraction Study: The X-ray crystallinity of pure PP and PP fibres modified with aroma chemical was analysed by the WAXD method. The pure PP sample showed a highly crystalline ordered structure, with crystallinity 83.92 %. The pure PP fibre showed sharp crystalline peaks at 2θ angle of 14.217°, 16.813°, 18.529° and 21.731°, indicating highly ordered and crystalline regions in its structure. In the case of fibre modified with 5% 3,4- methylenedioxybenzaldehyde aroma additive, X-ray diffractogram showed broad peaks at 2θ angle of 14.329°, 17.346°, 18.702° and 21.795°, with reduced intensity, indicating significantly reduced crystallinity to the level of 25.75 %.
This consequently implies a significant increase in the amorphous regions in the modified PP fibre. The comparison of crystallinity derived from DSC analysis and that obtained by the X-ray diffractograms shows that the former is slightly higher than the latter, as obviously the two techniques vary in their underlying principles of measurement. However, the general trend is supported by both the methods. In any case, they are very near, and the values of crystallinity obtained by X-ray diffractogram of modified PP are given more weightage. The X- ray diffraction study thus supports the reduction in crystallinity or a significant increase in the amorphous content and justifies the drastic improvement in the dyeability when PP is blended with a bulkier aroma additive.
SEM Study: The surfaces of the original PP and the PP fibres modified with 3,4- methylenedioxybenzaldehyde was examined under SEM and the results are shown in Figures 1 and 2, 1. Anon, Perf. Flav., Perfumary: respectively. The morphology of PP fibre modified with aroma additive is significantly different from that of the pure PP fibre substrate. The modified PP surface shows a markedly opened-up, cavited texture, while the pure PP surface appears clean and smooth. The fractured, rough, bumpy surface of the modified fibre sample further supports an increase in accessibility or amorphous region as a result of incorporation of aroma additive. Thus, SEM analysis also supports the reasons behind increased dyeability.
TGA Study: The temperature for 50% weight loss was calculated for both pure and modified PP samples. The study showed that in case of pure PP the temperature required for 50% weight loss was 394.07°C, while for PP modified with 3,4- methylenedioxybenzaldehyde it was 393.36°C. This difference is quite negligible.
Tensile Strength Properties: The tensile strength and elongation at break study of pure PP and PP fibres modified with 3,4- methylenedioxybenzaldehyde indicated that as the aromaadditive content in the melt-blend PP polymer fibre increased, the tensile strength of the resultant fibre commensurately decreased. This is quite logical, as we have seen a commensurate decrease in crystallinity of modified PP, when X-ray or DSC analysis was carried out. Fibre modified with 3,4- methylenedioxybenzaldehyde aroma additive showed the loss in tensile strength from 7.86% to 18.58% for 2.5% and 5% aroma loading.
Thus, the incorporation of bulkier aroma additives in the PP matrix reduces the crystallinity, and hence a reduction in tensile strength is quite logical. Consequently, elongation at break increased accordingly, as the amorphous content of the melt-blend PP fibre increased and so the flexibility of the chain molecules to extend before final breakage was increased. However, even at 5% concentration of aroma additives the loss in tensile strength was limited to 10%, which is quite acceptable.
Conclusion
Thus, the PP could be imparted durable fragrance by incorporating aroma additive 3,4- methylenedioxybenzaldehyde during the melt blending. Increase in the extent of loading of aroma additive increases the intensity of odour and the dyeability with disperse dyes.
Also, the significant increase in the dye uptake might be due to a drastic reduction in the crystallinity, which was consequent to melt blending of PP with the bulkier molecule of aroma additive.
WXRD, DSC, TGA and SEM analysis supported the reduction in crystallinity and increase in amorphous content of modified fibre and thus explain the enhanced dyeability. The loss in tensile strength and slight decrease in thermal stability were well within the tolerance limits. The results thus clearly provide the route for obtaining PP with durable fragrance and improved disperse dyeability.
References:
1. Anon, Perf. Flav., Perfumary: Techniques in Evaluation, Allured Publication, 1 (2000), 24 .
2. M.D. Teli, R.V. Adivarekar, V.Y. Ramani, A.G. Sabale, Fibres and Polymers, (2004) 5(4).
3. Y. Gin and D.L. Brydon, Journal of Applied Polymer Science, 1287 (1996) 61.
4. F. Jones, Rev. Prog. Coloration, 20 (1989) 19.
5. Matthias Wormuth, Martin Scheringer, and Konrad Hungerb¨uhler, Journal of Industrial Ecology, 237.
6. M. D. Teli and A.G. Sabale, International Dyer, 35(2009).
7. “Colour Fastness to Textiles and Leather”, 4th Edn., CO3, CO6/1, Test 3 (1978).
8. Wilfred Ingamells, Colour for Textiles, 154(1993).
9. M. Baiardo, G. Frisoni, M. Scandola and A. Licciardello, Journal of Applied Polymer Science, 83, 38(2002).
10. Y. S. Chung, C. A. Ming, T. Takako, “Shimadzu (Asia Pacific ) Pte. Ltd., Application News”, (2004).
11. A. Z. Dong, Z. Liu, B. Han, J. He, T. Jiang and G. Yang, J. Mater. Chem., 3565 (2002)12,.
12. “Breaking strength of fibres: ISO 5079”.