Reduction Clearing of Simulated Disperse Dyed PLA Fabrics and Their Tensile Properties

Indian Journal of Fibre & Textile Research Vol. 38, March 2013, pp. 22-28

Reduction clearing of simulated disperse dyed PLA fabrics and their tensile properties

Gulzar A Baiga University College of Textile Engineering, B.Z.U 60800 Multan, Punjab, Pakistan Received 18 October 2011; revised received and accepted 19 March 2012

Polylactic acid (PLA) knitted fabric has been subjected to various textile wet processes, viz. scouring, bleaching and simulated disperse dyeing. Reduction clearing (RC) has been performed at various process conditions such as concentrations of sodium dithionite and sodium carbonate, bath temperature and process time and a full factorial experiment is designed. The results show that the pretreatment processes and RC parameters have pronounced effects on tensile properties of PLA yarns. Statistical analysis of variance is performed which show significant differences at a confidence interval of 99%. Attenuated total reflectance infrared spectroscopy of the PLA fabric is carried out to investigate chemical changes on fibre surface. Scanning electron microscopy reveals that the bleaching causes the formation of slits in the fibres. Since bleached fibres are already porous, the strength of PLA yarns is further decreased during simulated disperse dyeing and reduction clearing processes.

Keywords: Disperse dye, Fibres, Polylactic acid fabric, Reduction clearing wash, Tensile strength

1 Introduction surface cohesion PLA produces sound when fibres are Polylactic acid (PLA) is a renewable and rubbed against one another – scroopiness9. biodegradable polyester material1. The biodegradable PLA has been dyed with disperse dyes10,11. DyStar materials are broken down into smaller molecules in recommends dyeing PLA at 110oC and pH 4.5-5.0 for the presence of aerobic or anaerobic microorganisms2, 30 min12. At these process conditions, PLA does not 3. PLA is one of the first melt spun aliphatic polyester degrade appreciably. At the end of dyeing some of the fibres whose raw material is obtained from annually dye particles remain deposited on the surface of grown crops 4. PLA is prepared from lactic acid fibres. It is necessary to remove these loosely held monomer obtained from the enzymatic action on starch dye particles, particularly in medium and heavy 5, 6. Since PLA is a sustainable material, it does not shades, so that during laundering these dyes do not depend on fossil resources. Cargill Dow (now bleed and tint the light-dyed and white clothes13. NatureWorks) LCC, USA are producing PLA fibres Reduction clearing (RC) is the process that is carried under the brand name of IngeoTM and have a out to remove surface adsorbed dye14,15. RC is carried manufacturing capacity of 140,000 tons per year7. out with suitable reducing agents e.g. sodium Although PLA is being used in the medical industry as dithionite in the acidic or alkaline pH region although suture, it is only recently that it has been knitted and the later is preferably employed16. In the alkaline woven into textile fabrics. PLA possesses a number of region sodium dithionite has powerful reducing good properties that makes this material a possible action17. Reduction clearing may damage the fibres if substitute for other polyesters, e.g. PET8. PLA is excessive amounts of reducing agent, alkali, high lightweight, transparent to UV and IR, low specific process temperature or extended times are employed. gravity, higher refractive index and good moisture Avinc et al.18 studied the alkaline reduction clearing management properties. The disadvantages of PLA as of PLA and concluded that RC washing for 15 min at compared to PET include its high sensitivity to pH in 60oC in the presence of 2 g/L each of sodium carbonate aqueous medium. Particularly in the alkaline region, and ‘hydros’ are adequate to achieve optimised wash PLA loose mechanical properties rapidly at higher fastness. Burkinshaw et al.19 studied the effects of temperatures when processed for longer times. PLA water, ECE detergent and RC on the colorimetric cannot withstand very high ironing temperature. Due to properties of disperse dyed PLA in the presence of ______ultrasonic waves and concluded that ultrasonic waves aE-mail: [email protected] do not affect the effectiveness of either ECE detergent BAIG: REDUCTION CLEARING OF DYED PLA FABRICS & THEIR TENSILE PROPERTIES 23

or reduction clearing processes. Phillips et al.20 RC finally rinsed in cold water. All other chemicals were washed PLA fabric in the alkaline and acidic pH. The of laboratory grade. Scoured and bleached PLA knitted alkaline RC washing was carried out in the presence of fabrics were subjected to simulated dyeing conditions 3 g/L sodium dithionite and 5 ml/L sodium hydroxide of 110oC, 5 pH and LMR of 10:1 for 30 min followed (50% w/w) while acidic one was carried out in the by reduction clearing (Fig. 1). Factors included in presence of 2ml/L Cyclanone ECO at 70°C for 20 min, reduction clearing were sodium dithionite the pH being 3.5 in the later case. They reported almost concentration, sodium carbonate concentration, no deleterious effects on molecular weight or tensile temperature and time. A full factorial experiment 2k properties. There was hardly any literature available was designed, where k is the number of factors (k = 4). about the detailed investigation of the effects of RC The experiment was full factorial of resolution V. Total parameters on the mechanical properties of PLA yarns. number of runs were 24, number of replicates was 01 The present work deals with the degradation of PLA and number of blocks were 2 with 4 centre points per yarns during pretreatments and dyeing processes in block. The blocks denoted the scoured and bleached general and with reduction clearing in particular. fabrics subjected to simulated high temperature dyeing.

Greige knitted PLA fabric was subjected to scouring 2.3 Tensile Measurements and bleaching processes followed by simulated Yarns were taken out from control and each of the disperse dyeing conditions. The pretreatment and treated knitted fabrics and then conditioned at standard dyeing were carried out at commercial process conditions of 25oC and 65% R.H before testing. Tests conditions. The scoured-dyed (SD) and bleached-dyed were performed according to BS EN ISO 2062:1995, (BD) fabrics were then subjected to reduction clearing using Instron (Model 1122) tensile tester with a gauge at selected process conditions. The parameters of length of 100 mm and at a strain rate of 1 min-1. Ten reduction clearing were reducing agent and alkali tests were performed on each of the yarn samples and concentrations, temperature and time. At the end of the the results acquired through desktop computer reduction clearing process, pH of the bath was also interfaced to the testing machine. The data were measured. PLA yarns were taken from knitted fabrics received and analyzed through computer software QT. and tensile strength measured. A detailed statistical analysis of tensile strength was carried out. Infrared 2.4 FTIR Spectroscopy spectroscopy and scanning electron microscopy (SEM) The attenuated total reflectance fourier transform were used to investigate morphology of PLA fibres. infrared spectroscopy (ATR-FTIR) spectra of PLA fabric was recorded to determine the effect of various 2 Materials and Methods textile processes and reduction clearing on functional 2.1 Materials groups of PLA polymer. The ATR-FTIR was performed PLA fabric of pique´ structure was knitted on a lab using a Perkins Elmer (Model spectrum 2000). The scale knitting machine from spun yarn of count Ne 30s. spectrometer was used in the absorption mode with a -1 -1 High temperature (HT) infrared (IR) dyeing machine resolution of 4 cm in the range of 4000-500 cm .

Labomat BFA-12 was used to process PLA samples. 2.5 SEM Analysis Tensile measurements of yarns were carried out on Surface morphology of the PLA fabric was Instron 1122 interfaced to a dedicated PC. S 3000N investigated using scanning electron microscope. scanning electron microscope (Hitachi, Japan) was used Samples were sputter-coated with Au in Polaron in observing the surface morphology of PLA fibres.

2.2 Treatments The PLA knitted fabric was given a mild scour with o 2 g/L Na2CO3 at 60 C for 20 min at a liquor-to-material ratio (LMR) of 10:1 followed by overnight drying at ambient conditions. Half of the fabric was bleached with 5 mL/L hydrogen peroxide (35% w/w), 3 g/L sodium hydroxide, 1 g/L Baystabil DB (hydrogen peroxide stabilizer, BASF) at 90oC for 30 min at LMR o of 10:1. Fabric was then washed in hot water (60 C) followed by neutralization with acetic acid (1 g/L) and Fig. 1  Schematic profile of RC washing of PLA fabric 24 INDIAN J. FIBRE TEXT. RES., MARCH 2013

coating unit (Model E5100), followed by loading viscose or TencelTM fibres, pretreatments would not sample holder in the Hitachi SEM (Model S-3000N). damage PLA due to mild process conditions being Gun-to-sample distance was 8-9 mm and voltage of employed in the processing of polyester-regenerated 5kV was applied to accelerate electron toward the cellulosic fibre blends. Normally PLA fibres do not samples under high vacuum. Electron beam focusing, require bleaching; however, if blended with cotton the image magnification and brightness/contrast were H2O2 bleaching severely damages the PLA fibres. If adjusted to take the photographs. SmatSEM software the effects of scouring and bleaching on tensile strength was used to acquire the photographs. are to be minimized then either bleaching with hydrogen peroxide should have been carried out at low 3 Results and Discussion temperature or alternative bleaching agents e.g. sodium 3.1 Mechanical Properties of Yarns hypochlorite and chlorites must be employed. Table 1 shows the effects of various textile wet Ahmad21carried out a study on the bleaching of PLA processes, viz. scouring (S), bleaching (B) and fabric with various bleaching systems and concludes simulated high temperature disperse dyeing (D) on the that sodium hypochlorite or sodium chlorite are the tensile properties of PLA yarns. Tensile strength of most appropriate ones in terms of whiteness and tensile greige (G) PLA yarns is 14.6 cN/tex. The data strength retention. No doubt a material with initial presented in Table 1 show that strength of PLA yarns higher strength can better withstand the severity of any reduces during commercial scouring, bleaching and post processing. dyeing processes. H2O2 bleaching causes more damage than alkaline scouring. Although scouring and Polyester fabrics are dyed with disperse dyes at o bleaching processes were carried out in the alkaline elevated temperature in the range of 110 - 130 C. medium, the later was carried out at relatively higher DyStar recommended dyeing PLA fibres in the pH o temperature and in the presence of a strong alkali range 4.5-5 at 110 C for 30 min. The ANOVA of the (NaOH). Moreover, bleaching was carried out in the tenacity of G-S-Dyed PLA fabric shows that there are oxidative-alkaline conditions while scouring was significant differences in tensile strength at 1% level carried out in alkaline medium only. It is inferred from of significance. The strength of scoured fabric Table 1 that oxidative-alkaline conditions at high decreases appreciably during dyeing. The ANOVA of temperature were deleterious to the integrity of PLA G-S-B-Dyed PLA fabric was also carried out. Like yarns. The bleaching process decreases the G-S-Dyed PLA, G-S-B-Dyed PLA fabric also shows modulus/stiffness and elongation of PLA yarns. Since loss in strength and significant differences are found scouring and bleaching decreases both tenacity as well in tensile strength at 1% level of significance. Unlike as strain, the energy to break yarns is decreased as well. scoured fabric, high temperature (HT) dyeing of Unlike natural materials, PLA is a man-made fibre bleached PLA causes a massive decrease in modulus and therefore does not require severe process of PLA yarns. These results show that during HT conditions during scouring and bleaching. A mild dyeing strength of PLA yarns reduces appreciably. scouring treatment would remove the surface deposited Scoured and bleached PLA yarns show 12.6% and dirt, dust, waxy and oily impurities. Table 1 shows 35.8% loss in their original strength during high only 0.8% decrease in tensile strength of PLA yarns temperature dyeing respectively. The inevitable loss during scouring. From commercial viewpoint fibre in mechanical properties of PLA demands careful blends are very important. When synthetic-natural fibre design and control of dyeing. blends are processed the synthetic fibres has to bear the Since disperse dyes exist as dispersions, during scouring and bleaching conditions of the natural dyeing some of the dye molecules are deposited on counterparts as well. If PLA fibres are blended with the fibre surfaces. These loosely-held dye molecules Table 1 — Tensile properties of PLA yarns during various textile lead to lower fastness properties and stain the adjacent wet processes light and white garments during laundering. The

Level Tenacity Modulus Strain objective of reduction clearing is to remove dye cN/tex cN/tex % molecules that are loosely held on fibre surfaces.

Greige (G) 14.6 83.6 61.5 Table 2 presents the results of tenacity of S-Dyed and Scoured (S) 13.4 66.4 62.0 S-B-Dyed PLA yarns subjected to various RC process Bleached (B) 10.8 56.5 59.3 conditions and Table 3 shows the results of ANOVA S-Dyed 10.2 62.8 60.3 S-B-Dyed 8.6 48.8 39.0 carried out on the data. The analysis shows that blocks BAIG: REDUCTION CLEARING OF DYED PLA FABRICS & THEIR TENSILE PROPERTIES 25

Table 2 — Tensile properties of PLA yarns at various RC washing conditions

Blocks Na2S2O4 Na2CO3 Temperature Time Tenacity Modulus Strain o g/L g/L C min cN/tex cN/tex % 05 01 50 10 10.0 65.2 54.0 01 05 50 10 10.5 66.2 55.3 01 01 80 10 9.3 60.5 52.0 05 05 80 10 9.2 58.2 52.8 S→D→RC 01 01 50 30 10.0 66.8 54.4 washed 05 05 50 30 10.2 68.2 51.1 05 01 80 30 9.1 60.7 51.6 01 05 80 30 9.1 57.9 53.8 03 03 65 20 10.1 64.5 53.0

01 01 50 10 8.7 53.6 50.9 05 05 50 10 8.7 52.7 51.1 05 01 80 10 9.0 53.4 57.0 01 05 80 10 8.5 55.7 52.5 S→B→D→RC 05 01 50 30 8.3 53.3 57.4 washed 01 05 50 30 7.9 48.3 55.8 01 01 80 30 7.3 48.1 51.4 05 05 80 30 8.0 51.5 50.6 03 03 65 20 8.7 54.1 49.9 and main interactions are significant at 1% level. The Table 3 — ANOVA for tensile strength of PLA yarns processed effects of blocks are prominent which means that at various RC washing conditions scouring and bleaching history of the yarns affect the mechanical properties. The results of blocks presented Source DF Seq SS Adj SS Adj MS F P in Table 2 are found to be in accordance with the afore- Blocks 1 12.4820 12.4820 12.4820 3053.28 0.000 mentioned results. The results also show that main Main effects 4 2.1632 2.1632 0.5408 132.29 0.000 effects are significant. Among the various factors of 2-Way 6 0.3771 0.3771 0.0628 15.37 0.001 RC washing, sodium carbonate and sodium dithionite interactions 3-Way 4 1.4028 1.4028 0.3507 85.79 0.000 concentrations and process temperature are important interactions at 1% level of significance. Two-way interactions and Curvature 1 0.9307 0.9307 0.9307 227.68 0.000 three-way interactions are also found to be significant Residual 7 0.0286 0.0286 0.0041 in determining the tensile strength of PLA yarns. The error modulus/stiffness and maximum strain of yarns Lack of fit 1 0.0286 0.0286 0.0286 o Pure error 6 0.0000 0.0000 0.0000 decrease at 80 C. Total 23 17.3845 Since HT dyeing severely damages bleached fabric, only scoured-dyed PLA fabric is subjected to Table 4  Effect of temperature and sodium carbonate on the reduction clearing. The stress-strain (S-S) curves of tensile properties of PLA yarns scoured-dyed PLA yarns reduction-cleared at various [Na2S2O4 2 g/L, time 15 min, LMR 20:1] sodium carbonate concentrations and bath temperatures are measured and tensile parameters are RC Na2CO3 pH Tenacity Modulus Strain temperature g/L cN/tex cN/tex % calculated from the raw data (Table 4). The results oC show that at fixed alkali concentration, the strength of PLA yarns decreases with increasing bath 40 0 3.3 12.2 78.4 66.6 temperature. At 40oC, well below the plastic region, 1 9.4 12.2 78.2 63.3 the mechanical properties of PLA are little affected. 5 10.5 12.0 78.0 62.1 o At 60 C Tg of PLA, the tenacity decreases with the 60 0 2.9 11.9 77.7 65.4 increase in concentration of Na2CO3. There is little 1 9.1 11.9 77.2 64.3 drop in strength upto 1 g/L Na2CO3 but at 5g/L 5 10.5 11.5 77.0 62.5 (pH 10.5) the tenacity decreases. There is a little change in strain and hence in work to break the yarns. 80 0 2.5 11.2 77.2 64.1 o 1 7.8 10.8 76.2 62.6 The bath temperature up to 60 C and sodium 5 10.2 10.5 75.5 61.1 26 INDIAN J. FIBRE TEXT. RES., MARCH 2013

Scheme I  Hydrolysis of PLA polymer carbonate concentration of 1 g/L offer acceptable Table 5  Effect of sodium dithionite and sodium carbonate on the tensile properties of PLA yarns results. Above Tg, the amorphous regions vanish and [Temperature 60oC, LMR 20:1, Time 15 min] the polymers have crystalline regions only as the later Na S O Na CO Tenacity Modulus Strain vanish at the melting point (Tm). Since glass transition 2 2 4 2 3 temperature (T ) of PLA lies in the range 55 – 65°C, g/L g/L cN/tex cN/tex % g 1 any increase in bath temperature would lead to 0 12.2 78.5 65.6 1 12.2 78.3 64.8 ingression of chemical liquor into the fibrous matrix. 5 11.6 77.7 64.1

Since the fibres are in plastic state the hydrolysis of 2 0 12.0 77.7 65.4 PLA would be multiplied around Tg and would result 1 11.9 77.2 64.3 in accelerated degradation of the polymer (Scheme 1). 5 11.6 76.5 62.5

We optimized the RC washing conditions in this work 5 0 10.7 76.2 64.5 from the tensile properties viewpoint. Avinc et al.18 1 11.1 75.4 63.8 have suggested the same temperature (60oC) for RC 5 10.9 73.2 61.5 washing at which optimized wash fastness properties carbonate there is little change in tensile properties, of disperse dyed PLA fabric are obtained. At 80oC the while at 5 g/L sodium carbonate there is only 5% loss in tensile strength, % strain and modulus decrease tenacity. At 5 g/L sodium dithionite the bath pH is acidic appreciably owing to high temperature and increased that causes loss in mechanical properties. There is amount of sodium carbonate in the chemical bath. On increase in tenacity at 1 g/L Na2S2O4 which decreases on commercial scale dyes are stripped to correct for increasing concentration again. The results are explained faulty dyeings. In principle, the chemical liquor as follows. In the absence of sodium carbonate, the bath should penetrate into the bulk of the fibres so that pH is too low (2.3), while in the presence of 5 g/L dyes residing in fibrous matrix are completely Na2CO3 bath pH is too high (10.5). At both pH values, destroyed. Stripping of disperse dyes from PLA; PLA hydrolyzes which results in loss of strength. At 1 therefore, will require temperature higher than Tg. The g/L sodium carbonate bath pH is 6.0 – a value not too previous discussion suggests that RC washing in the far away from 5 which is recommended for the wet presence of 3 g/L sodium dithionite and sodium processing of PLA materials. It is concluded from above carbonate each at 65oC does not affect much the discussion that these are not absolute quantities of mechanical properties. Therefore, it can be inferred sodium dithionite and sodium carbonate that determine that best mechanical and colour fastness properties tensile strength. However, from the commercial would be achieved at around Tg of PLA. viewpoint acidic conditions are not generally The tensile properties of PLA yarns RC washed at recommended, because it is the alkaline conditions that 60oC in the presence of various amounts of sodium are preferred during RC washing for most of the carbonate and sodium dithionite were measured (Table 5). disperse dyes. The results show that PLA yarns retain At 60oC PLA fibres are in the plastic region and good tensile properties upto 2 g/L sodium dithionite. At therefore prone to hydrolysis unless processed in the 2 g/L sodium dithionite and 60oC, the concentration of suitably buffered pH conditions. Since sodium dithionite sodium carbonate as high as 5 g/L can be used during generates acidic products on decomposition, increase in RC washing. It is inferred from the above results that if concentration of dithionite leads to drop in bath pH. To reduction clearing was carried out at 60 oC in the achieve the desired alkaline pH, the required amount of presence of 2 g/L sodium dithionite and sodium alkali is more than theoretical calculations so that the carbonate each, PLA yarns with good strength retention acidic by-products of sodium dithionite are also would be obtained. If disperse dyes are to be stripped, neutralized. At 1 g/L sodium dithionite and sodium sodium carbonate upto 5 g/L would not be detrimental to BAIG: REDUCTION CLEARING OF DYED PLA FABRICS & THEIR TENSILE PROPERTIES 27

the integrity of PLA. On commercial scale, reduction PLA occurs which results in the cleavage of ester bonds clearing or stripping of disperse dyes could be carried and the formation of carboxylic acid and hydroxyl out at the suggested process conditions to save strength groups. The spectra do not show any new peaks which of PLA materials. indicate no new functional groups. Bleached fabric exhibits a slight increase in absorbance which might be 3.2 FTIR Spectroscopy of PLA Fibres due to the higher degradation of PLA polymer under ATR-FTIR spectroscopic results of greige, scoured, -1 bleached, simulated-dyed and reduction cleared PLA alkaline-oxidative conditions. Peaks at 1746 cm are fabrics are shown in Fig. 2. Since in attenuated total assigned to the asymmetric stretching of carbonyl bonds reflectance mode infrared waves penetrate only a few in ester groups (-COOC-). A pair of peaks observed at 2983 cm-1 and 2930 cm-1 is assigned to stretching nanometers underneath the surface of fibres, the -1 chemistry of material surfaces can be studied. The vibration of –CH2 bonds. The peak at 1179 cm is assigned to -C-O-C- stretching of ester groups22-26. objective of IR study is to investigate the changes in surface chemistry of PLA fibres that might have taken 3.3 SEM Analysis of PLA Fibres place during various wet processes. On comparing the Figure 3 shows the SEM micrographs of PLA fibres IR spectra of greige and pretreated fabrics, no newer subjected to various textile wet processes. Figure 3(a) peaks are observed, suggesting little changes in shows the greige PLA fibres. In the greige state, fibres chemistry of the fibres. During scouring, hydrolysis of does not show any marked surface features. In this state,

Fig. 2  FTIR spectra of greige, scoured, bleached, simulated-dyed and reduction-cleared PLA yarns

Fig. 3—SEM micrographs of PLA fibres subjected to various textiles wet processes (5 kV) 28 INDIAN J. FIBRE TEXT. RES., MARCH 2013

fibres are characterized by smooth surfaces and well around 60 °C to avoid ingression of alkaline-reducing defined cross-sections. There are some oily and waxy liquor into the fibrous matrix. However, for stripping of substances on the surface which help during preparatory faulty dyeing, temperature upto 65°C would be processes of yarn and fabric manufacturing. Figures 3(b) acceptable. The amount of sodium carbonate and sodium and (c) show the scoured and bleached PLA fibres dithionite that minimize strength losses are upto 5 g/L and o respectively. Scouring was carried at 60 C in the 2 g/L respectively for 15 min. Reduction clearing presence of a mild alkali (Na2CO3). The scouring removes the surface debris and oligomers efficiently. temperature was kept around T of PLA. Therefore, g References minor changes in surface morphology are observed; 1 Sawyer D J, Nonwovens World, 10(2001) 49. however bleaching causes the formation of slits along 2 Stevens E S, BioCycle, March (2003) 24. the axis of fibres. The bleaching was carried out with 3 Ho K L G, Pometto A L, Gadea-Rivas A, Briceno J A & hydrogen peroxide in the presence of strong alkali. The Rojas A, J Environ Polym Degrad, 7 (1999) 173. high bleaching temperature and bath alkalinity 4 Kameoka T, Kawamura I, Ghoda I, Ajioka M, Takuma K, Yamaguchi A & Suizu H, US Pat 5630849 (to Mitsui Toatsu contribute to the degradation of fibres. The marked Chemicals), 1997. decrease in tensile strength of PLA yarns during 5 Blackburn R S, Biodegradable and Sustainable Fibres bleaching as compared to scouring is attributed to pin (Woodhead Publishing Limited), 2005. holes and slit formation in the fibres. Figures 3(d) and 6 Drumright R E, Gruber P R & Henton D E, Adv Mater, 12 (2000) 1841. 3(e) show the micrographs of scoured and bleached 7 Wilson A, Text Month, March (2003) 7. fibres after dyeing respectively. The micrographs show 8 Lunt J & Bone J, Properties and dyeability of fibers and that the fibres, already damaged during the previous fabrics produced from polylactide (PLA) polymers, paper processes, become more vulnerable to damage in the presented at the AATCC International Conference and forthcoming processes. Since bleached fibres are already Exhibition, Winston-Salem, USA, 17-20 September 2000. 9 Dugan J S, Novel Properties of PLA Fibres (Research Fibre rendered weak, dyeing at high temperature (110°C) Innovation Technology, Inc. INTC 2000, Dallas, Texas, increases the accessibility of chemical liquor to fibre USA), 2000. matrix. Figure 3(f) shows the scoured-dyed PLA fibres 10 Scheyer L E & Chiweshe A, Application and performance of after reduction clearing. The fibres show few tiny holes disperse dyes on polylactic acid (PLA) fabric, paper presented at the AATCC International Conference and here and there. Figures 3(b), (d) and (e) show some Exhibition, Charlotte, USA, June 1999. contamination/debris on the surface of fibres. It is 11 Yang Y & Huda S, The balance between dyeing and physical impossible to stop the degradation of materials; properties of PLA, paper presented at the AATCC International however, their degradation can be decelerated through Conference and Exhibition, Charlotte, USA, 1-4 October 2002. 12 Ingeo Fibre Coloration Pack (DyStar Plc), intelligent process design and control. During chemical www.ingeofibres.com (accessed 26th April 2006). wet processing PLA polymer is hydrolyzed. The 13 Nunn D M, Dyeing of Synthetic-polymer and Acetate Fibres hydrolysis leads to the formation of polymer chains, of (SDC, Bradford, 1979), 158. random lengths, called oligomers; the later can be linear 14 Moncrieff R W, Man-Made Fibre (Butterworth & Co. Ltd, or cyclic. After RC washing the fibre surface becomes London, 1975), 37. 15 Aspland J R, Text Chem Color, 24 (1992) 18. clean so that reduction clearing removes the hydrolyzed 16 Karl U & Freyberg P, Text Chem Color, 3 (2000) 23. products and oligomers efficiently. 17 Anders S & Schindler W, Melliand English, E21-E22 (1997) 1. 18 Avinc O, Bone J, Owens H, Phillips D & Wilding M, Colour 4 Conclusion Technol, 122 (2006) 157. o Scouring of PLA with 2 g/L Na2CO3 at 60 C does not 19 Burkinshaw S M & Jeong D S, Dyes Pigm, 77 (2008) 171. appreciably affect the tensile properties of PLA yarns; 20 Phillips D, Suesat J, Wilding M, Farrington D, Sawyer D, Sandukas S, Bone J & Dervan S, Colour Technol, 120 (2004) 41. however, the bath temperature above Tg would lead to 21 G Ahmad, A Study on the Hydrolytic Stability of PLA unacceptable fibre degradation. The bleaching with H2O2 Fabrics during Pretreatment and Dyeing (University of at commercial process conditions severely damages the Manchester, UK), 2012. PLA fibres. The alkaline-oxidative conditions are more 22 Kister G, Cassanas G & Vert M, Polymer, 39 (1998) 267. deleterious to the integrity of the PLA fibres than alkaline 23 Kister G, Cassanas G & Vert M, J Raman Spectroscopy, 26 conditions alone. High temperature dyeing causes more (1995) 307. 24 Kister G, Cassanas G & Vert M, Polymer, 39 (1998) 3335. damage to bleached PLA fibres than the scoured ones 25 Lee S H & Song W S, J Korean Soc Clothing Text, 35(2011) 670. owing to the former’s offering more accessibility to the 26 Vey E, Rodger C, Booth J, Claybourn M, Miller A F & chemical liquor. Reduction clearing should be carried out Saiani A, Polym Degradation Stability, 96 (2011) 1882.