Bleaching of linen (Linum usitatissimum)

Transcription

1 . Indian Journal of Fibre & Textile Research Vol. 18, June 1993, pp Bleaching of linen (Linum usitatissimum) K K Goswami R & D Department, Jayashree Textiles, Rishra , India and A K Mukherjee Applied Chemistry Division, Indian Jute Industries' Research Association, 17 Taratola Road, Calcutta , India Revised received 29 June 1992; accepteq 7 December 1992 The effect of scouring by deviating from the optimized scouring conditions (9S0C; Na2C03, 10 gji; 30 min) has been compared with respect to existing bleaching conditions in combination sequences. Various combinations of bleaching sequence are also assessed against all the required parameters such as weight loss, reflectance, fluidity and light fastness. Linen fabrics of widely varied reflectance in terms of yellowness index, whiteness index and redness index have been assessed through comparative index to adjudge whether the existing bleaching recipes can produce levelled reflectance or not. It is observed that the linen fabric scoured under the optimized conditions incur lesser weight loss and perform better towards the bleaching sequence NaOCl- H2O2 -NaCI02. Modified bleach combination sequence NaCIO2 -NaOCI- no rinse -H2O2 results better and uniform whiteness in addition to saving in costs. Keywords: Bleaching, Fluidity, Linen, Reflectance, Scouring 1 Introduction applied is thus adjusted to the purpose for which the. At present, linen (Linum usitatissimum) is mainly cloth is intended. In the present work, the effect of used for furnishings, tableware, handkerchiefs, dry- scouring conditions by deviating frum optimized coing clothes and relatively in small amount for apparel, ndition8 has been compared with respect to existing canvas, tentings and industrial fabrics. To increase its bleaching conditions in combination sequences. Varend uses, research efforts are needed into product de- ious combinations of bleaching sequence are also assvelopment as well as purely' technical aspects of proc- essed against all the required parameters such as weessing1. In this way, the market share oflinen incert- ight Joss, reflectance, fluidity and light fastness. Linen ain existing areas might be expanded and new areas fabrics of widely varied reflectance in terms of yellowdeveloped. ness index, whiteness index and redness index have The art of bleaching has been practiced since the been assessed through comparative index to adjudge beginning of civilization2 as well described and men- whether the existing bleaching recipes can produce tioned in old texts3. Unlike cotton, retted flax (linen) levelled reflectance or not. contains only about 70% (X-cellulose and the high proportion of non-cellulosic matter which complica- 2 Materials and Methods tes the bleaching process4. The major difference between cotton and flax is the presence of small amount 2.1 Materials of dark coloured lignin in retted flaxs.about 75% of Grey linen fabric (plain weave, 220 g/m2, 150 ends the impurities in linen are hemi-cellulose with low and 158 picks per dm) was used. degree of polymerization and these are soluble in Sodium carbonate, sodium hydroxide, surfactant, strong alkali. Hence, the action of conventional blea- sodium hypochlorite (30 g/l available chlorine), hydching agents such as hydrogen peroxide, sodium rogen peroxide (50% w/w), sodium chlorite (80% chlorite, peracetic acid and sodium hypochlorite are w/w), all of AR grade, were used. somewhat different on these fibres as compared to 2.2 Methods cotton6 and can cause weight lqss of up to 25%. Milder condition with longer treatment duration are the Scouring and Bleaching, refore advantage used 7. and The the degree presence of of scouring residual and cellulose bleaching is an carried Scouring out in and laboratory bleaching under of grey the linen conditions fabric given were

2 GOSWAMI & MUKHERJEE: BlEACHING OF UNEN 83 in Tables I and 2 respectively. However, laboratory and representative rating against grey scale (1-8) is jigger was used for studying the comparative indices reported. - ofyi, WI and RI of basic linen of widely varied reflectance Calculation of Comparative Index. The comparative indices of weight loss, YI, WI, RI Determination of Weight Loss and fluidity were calculated using the following equa- The change in fabric weight (oven dry basis) was tion: measured using the following equation: Original weight -Final weight Comparative Perfonnance value for SI condition Weight loss (%)= x 100.d =..x 100 Original weight m ex Perfonnance value for S3 condition The performance comparison between water Measurement of Reflectance retted (WR) and dew-retted (DR) materials was also The reflectance of samples was measured by colo~r made by substituting WR and DR for S) and S3 respecomputer (JA Y P AK 4800 II computer.colo~r predi- ctively in above equation. ction system of MIL TON ROY) under IdentIcal conditions. Representative values of yellowness index 3 Results and Discussion (YI), whiteness index (WI) and redness index (RI) are Table 3 shows the comparison of grey-state bleareported. ched[naocl(b)fh2o2(b2)fnaclo2(b3)] linens with grey and desized cotton, scoured linen, and scoured Dctermination of Fluidity and bleached linen. It is observed that the reflectance Cuprammonium fluidity v-:as dete~ned as per B:S values in terms ofyi and WI of grey linen are higher The representative value IS expressed In and lower respectively from those of grey and desized poise -1 at 20 C. cotton, and the whiteness index of scoured linen is still less than that of cotton. Grey-state bleaching when Determination of Light Fastness compared with scour-state bleaching reveals that the Samples were exposed to Xenotester as per IS 2454 performance of latter is better in all respects for all the bleaching agents used. This shows that grey-state T bl I Sc. d 't ' bleachin g is not effective and scouring is a prerequia e -ounng con I Ions. site. Parameter Scouring condittons Table 4 shows the weight loss, reflectance, fluidity S S S and light fastness of linen samples scoured only under I 2 3 different scouring conditions (S)-S3) as well as of Temperature, C 95 9j 95 the scoured samples subjected to NaOCl(B)- Sodiumcarbonate,gjl H2O2(B2)-NaClO2(B3)bleachoneafteranother.ltis Sodium hydroxide, gjl Nil Nil 2 observed that differential scouring treatments resul- Surfactant, gjl ted in different amounts of weight loss, change in col- Duration, min our and fluidity. The performance parameters were Material-to-liquor ratio 1:30 1 :30 1 :30 also compared between extreme conditions of scour-...ing (S) and S3) at each scour-bleach stage (I to IV) and Table 2-Bleachmg conditions the values of their comparative index are given in Ta- Parameter Bleaching conditions ble 5. It is observed from this table that the weight loss for S) is lower by 42.1 % at stage I and it gradually. BI B2 B3 decreases at stages II-IV. Finally, at stage IV, the Sodiumhypochlorite(av.CI2,%owf) weigthloss fors)-b)-b2-b3 is lower by 29.4% as com- Sodium carbonate, % (owf) -;::-;;, 5.0.,- pared to that for S3-B)-B2-B3. The reason for this is Sodium silicate, % (owf, 84 TW) more activity of each bleaching agent on S 1 scoured 50% Hydrogen peroxide, % (owf) f substrate due to higher amount of inter-cellular mat- 80% Sodium chlorite, % (owf) ter retained therein. Level performance ofyi for S) at Temperature, C stage I is attributable to optimized weight loss and it Du~ation, min remained fairly stable at stage II, showing comparaph ble bleaching performance. However at stage III, the Material-to-liquor ratio 1:30 1:30 1:30 situation reversed, presumably due to more yellowing tendency ofh2o2-treated linen towards S) gro-

3 84 INDIAN J. FIBRE TEXT. RES., JUNE 1993 Table 3--Comparative evaluation of grey-state bleached linen with grey and desired cotton, scoured linen, and scoured and bleached linen Fabric Weight Yellowness index (ASTM) Whiteness index Redness Fluidity loss index (poises-') % 2 deg 10 deg CIE Hunter (2 deg) at 20.C 2 deg 10 deg 2 deg 10 deg Grey linen (G) Scoured (SI) Grey cotton Desized cotton G-B G-B G-B S(-B, : S)-B S(-B Table 4---Effects of scouring conditions on weight loss, reflectance, fluidity and light fastness of linen Sample code Weight Yellowness index (ASTM) Whiteness index Redness Fluidity Light loss index (poises-') fastness % 2 deg 10 deg CIE Hunter (2 deg) at 20.C ratin~ 2 deg 10 deg 2 deg 10 deg S( : """', S ~ S ~ S(-B S2-B( ,. S3-B S,-B(-B S2-B1-B S3-B(-B S,-B(-B2-B S2-B(-B2-B S3-B(-B2-B3 21: "Assessed on the rating scale 1-8. Table 5-Percentage expression between extreme scouring conditions Stage Parameter Comparative index for -! Weight Yellowness index Whiteness index Redness Fluidity Light loss (ASTM) index (poises-') fastness % CIE Hunter (2 deg) at 20.C 2 deg 10deg 2 deg 10 deg 2 deg 10 deg I (S(/S3) II (S(B1/S3BJ c,~ III (S,B(B2/S3B(B2) IV (S(B1B2B3/S3B(B2B3)

4 . GOSWAMI & MUKHERJEE: BLEACHING OF LINEN 85 undo At final stage (IV) of bleaching, comparative weight loss is attributed to this. Comparative index of index of 98.0 suggests better activation of NaCIO2 100 for light fastness rating further confirms that the towards 81-B1-B2 ground. With regard to WI, the stability of colour (reflectance) for 81 ~comparableto lesser value for 81 condition over 83 at stage I improves that for 83 at final stage (IV). Thus, the suitability of81 slightly and the results get almost levelled at subsequ- condition towards combined bleach is established. ent stages (II, III & IV). However, for redness index at However, existing recipes (B1/B2/B3) did not result stage III, deteriorating result for 81 condition isobse- levelled colour as evident from the results shown in rved which gets levelled at stage IV. These happenings Table 6. The above analysis indicates that the existing are due to the differential reciprocation of8( condi!-.bleaching recipes need further modification to suit ion to various stages of bleaching. The comparative wide variation in basic linen. Various combinations index values for fluidity show that 81 is superior to 83 of existing bleaching recipes including rinse and no by 9.1 %,7.8% and 7.1 % at stages I, II and III respect-! rinse in between B( and B2 were, therefore, tried. The ively. However, at final ~tage (IV), the superiority of results (Table 7) indicate that the weight loss varies 8( over 83 stands at 18.7%. The benefit of retained considerably between the combinations and especiaintercellular matter observed in terms of29.4% lesser lly for no rinse, the weight loss is higher but the quality Table 6-Reflectance and comparative index of yellowness, whiteness and redness for water- and dew-retted linen Sample code Yellowness index (ASTM) Compara- Whiteness index (Hunter) Compara- Redness index Comparative index tive index tive index WR DR for YI WR DR for WI WR DR for RI Grey-state S] S,-B S.-B]-B S,-B.-B2-B Scouring (S.) and bleaching (B./B2/B3) were carried out in laboratory jigger at material-to-liquor ratio I: 10. Temperature was raised from room temperature at the rate of approx. 3.C/min. Comparative index = (Performance value of WR material/performance value of DR material) x 100 WR-Water-retted linen; and DR-Dew-retted linen. Sample code Table 7-Results of various bleach combinations Weight Whiteness index (Hunter) Yellowness index (ASTM) Redness index Fluidity Light loss (poises-i) fastness % Av.:l:Q95%a CV% Av.:l:Q95%a CV% Av.:l:Q95%a CV% at 20.C ratingb S B.-B2-B :1: :1: :1: B.-no rinse- B2-B :1: :1: :1: B]-B3-B :1: :1: :1: B2-B.-B :1: :1: :1: B2-no rinse- B.-B :1: :1: :1: B2-B3-B :1: :1: :1: B2-B.-B :1: :1:0: :1: B3-B2-B :1: : :1: B3-B2-no rinse- B :1: :1: :1: B3-B]-B :1: :1: :1: B3-B.-no rinse-." B :1: :1: :1: ' aconfidence interval; and bassessed on rating scale 1-8.

5 86 INDIAN J. FmRE TEXT. RES., JUNE 1993 improves. The poorest performance in bleachcombi- ing levelness in colour while processing linen of wide-. nation ofb2-b3-b\ is due to unsuitability ofb2 over S\ ly varied colour. ground and B\ as finish bleach. The best performance in bleach combination of B3-B\-no rinse-b2 conf- Acknowledgement irms the efficacy ofb3 over S\ ground and ofb2 over The authors gratefully acknowledge the support B3-B\ due to no rinse and built-in antichlor process. received from Mr G L Moondra, Mr A N Choudhary and Mr H C Daga ofm/s Jayashree Textiles. They are 4 Conclusions also thankful to Mr A Chakravorty, Mr B Ghosh and 4.1 Scouring condition S\ (95 C, 10 g/l Na2CO3, 30 Mr S Kar for valuable assistance. min), optimized earlier8 by us, is valid even after combination bleach. 4.2 Optimized scouring condition (S\) with B\-B2-B3 References bleach combination reduces the weight loss by 29.4% 1 Hamilton 1 T, Textiles, 15(2) (1986) 30. and results in saving of time by 90 min. 2 Eastan B K, Ciba.Geigy ~ev, 3 (1971) M h d d t 3 Peters R H, Textile chemistry, Vol 2 (Elsevier Publication), 4.3 uc eeperco ourmgrey men as compare cotton suggests further modifications in bleaching re- 4 Sloa~ F R, Rev Prog Color, 5 (1974) 12. cipe for achieving whiteness matching to cotton. 5 Trotman E R, Textilescouring & bleaching (Griffin Co, Lond- 4.4 Modified bleach combination sequence, sodium chlorite-sodium hypochlorite-no rinse-hydrogen on), 196.8, Mukherjee R R & Radhaknshnan T, Text Prog, 4 (1972) 54.. d h b so d b h b. 1.7 Angstrnan D, Pretreatment of hardfibres (BASi'), July 1987, peroxl e as een loun to e t e est marnpu ation 3. ty. of combination However, it needs bleach further both in optimization terms of cost for and obtain- quali- 8 Goswami (1992) 136. K K & Mukherjee A K ' Indian J Fibre Text Res, 17,.