Indian Journal of Textile Research

Vol. 10, June 1985, Pp. 68-70

Acetylation of Jute and Infrared Spectra of Acetylated Jute

MADHUBAN GOPAL' , S K BHADURI, S K BANERJEE and K P SAO

Jute Technological Research Laboratories, 12, Regent Park, Calcutta 700040

Received 21 November 1984; accepted 31 December 1984

~ simple and quick method for partial acetylation of jute is reported. Infrared spectrum of acetylated fibre indicated a shiftof the carbonyl absorption band to higher a wave number. Differential IR spectra of jute and acetylated jute showedabsorption for acetate of phenolic hydroxyl groups, indicating acetylation of the lignin component with unprotected hydroxylgroups in the fibre. The acetylated fibre, though it lost its strength to some extent, showed reduced hygroscopicity and dye

uptdke and increased resistance to microbial damage.~Keywords: Acetylated jute, Infrared spectra, Jute

Absorbance. cm ~1

Table I-Infrared Spectra of Jute and Acetylated Jute

Acetylation-Jute fibre (2 g) was soaked in glacialacetic acid for 1 h at 25-35°C, decanted and then

soaked in acetic anhydride (50 m!) containing twodrops (0.05-0.1 ml) of conc. sulphuric acid for 5-10min. The fibre was filtered over a Buchner funnel,washed with water till it was free from acid, and driedIII air.

The acetyl content of the fibre was estimated by thestandard procedure9.

Infrared studies-Infrared spectra of the raw andacetylated jute samples in the form of KBr Pellets wererecorded by a Shimadzu IR-440 spectrophotometer.Infrared spectral data of acetylated jute are comparedwith those of raw jute in Table I.

I595-very weak, aromaticC=C stretch

1430-very weak

Acetylated jute

3450-strong, OH stretch

2925-medium, aliphaticCH stretch

I740-1760-very strong,carbonyl stretch

I375-medium, CH3 bendingI225-strong, C - 0 stretchImO'-strong, C - 0 stretch895-very weak,' Ii-linkage

of anhydroglucose60Q'-medium

Jute

3400-broad, very strong,OH stretch

2925-medium, aliphaticCH stretch

I735-weak, carbonyl stretchof carboxyl and ester

1675-shoulder

1599-very weak, aromaticC=C stretch

1460-weak, CH3 bending1420-weak, CH3 and CH2

bending1375-weak, CH3 bending1240-weak, C-O stretch1020-very broad, medium895-very weak, Ii-linkage

'Present address: Division of Agricultural Chemicals, IndianAgricultural Research Institute, New Delhi 110012.

Althougl?- hydroxyl groups can be acetylated almostquantitaiively in common organic molecules byvarious methods I -3, such methods are not suitable

for the acetylation of natural fibres like jute. This isbecause jute is insoluble and the reactions cannot becarried qut under heterogeneous conditions.

The preparation of ceHulose triacetate fromactivated cotton linters by a heterogeneous fibrousprocess4 was reported a few decades ago. Recently,Ananthakrishnan and Debsarkars have reported amethod for making cellulose acetate from rayon-gradepulp of jute sticks an-d directly from caddies6.Acetylation of the jute fabric and X-ray studies on theacetylated jute fabric were reported by Roy 7; in thisstudy, the jute fabric was dewaxed with ethanol­

benzene (1:2 v/v) before subjecting the fabric to

acetylat~on with acetic acid-perchloric acid and aceticanhydride. Infrared studies8 on jute have beenrestricteo to the region 2500-3500 cm -1 (OH and CHstretch) and hence the need for an elaborate IR study ofjute.

This paper proposes a quick and simple method forpartial acetylation of jute and discusses the results ofIR studies of raw and acetylated jute.

Materials and Methods

AtteIl}pts to acetylate jute with acetic anhydride invapour phase under ambient conditions wereunsuccessful. Acetylation with acetic anhydride inpyridine was found to be only slightly better than that'in acetic acid medium, as evident by weight gain afteracetylation.

68

MADHUBAN GOPAL el al.: ACETYLATION OF JUTE

Fig. l--IR spectra of raw jute (1) and acetylated jute (A1)

Table 2-Breaking Tenacity and Extension at Break of Rawand Acetylated Jute Fibres

1.81.6

600

Extension

at breaka

%

1000

c-o

Breaking

tenacitya

g/tex

29.820.9

Linear

density

mg/m

3.5

4.6 .

AJ

o

5000 4000 3000 2000 1800 1400WAVENUMBER, em-'

"'.60wuz;;•...~<fl

Z

g 30

Sample

Raw juteAcetylated

jute

aGauge length, 2 em; cross-head speed, 0.5 cm/min; magnification,20

100

90r J

----'-\

lost during washing. Moreover, accessibility ofchemicals in a woven fabric is less unless it is swelled

for a longer period.The fibrous structure of jute was retained after the

treatment but there was a loss in strength (Table 2), asmeasured by an Instron tensile tester. The strength lossmay be due to the loss of some acid-soluble lignin andhemicellulose of the fibre during acetylation. Onacetylation of the fibre, filtration and addition of water

to the filtrate, a white amorphous precipitate wasobtained, which might be the acetate of hemicellulose.

The lignin and hemicellulose components in alignocellulosic fibre like jute have a profound effect onthe tensile properties of the fibre13.

The acetyl content of the treated ju te was estimatedto be 30% on dry weight basis. The moisture content ofsuch modified jute was 6.2% as compared with 16% inraw jute. Furthermore, dye uptake (Congo Red) wasreduced after acetylation because of the protection offree hydroxyl groups in jute. Naturally, suchacetylated jute showed reduced hygroscopicity andincreased microbial resistance14 in comparison withjute.

AcknowledgementThe authors thank Dr C.R. Debnath, Director,

JTRL, for permission to publish the paper.

Quantitative IR spectra (Fig. 1) of raw andacetylatedjute were recorded by taking 2.9 mg of fibreand 200 mg of potassium bromide. In comparison toraw jute, acetylated jute showed a reduction in peaksize around 3450 cm -1, indicating protection of somefree hydroxyl groups. The vC =0 in raw jute appearedat 1735 cm -1 (for normal esters), which underwentshift to higher wa venumbers (vC = 0 around 1740­

1760 cm -1) in the acetylated jute, thereby providingevidence for successful acetylation.

Differential IR spectra of jute and acetylated jute, inwhich jute-KBr film was used as reference, showedonly four peaks at 1760 cm -1 (vC =0 of acetate ester),1375 cm -1 (vCH3) and 1210, 1035 cm -1 (vC-O).Absorption at 1760 cm -1 is characteristic of an ester of

acetic acid with aromatic hydroxyl groups. Thepresence of such aromatic hydroxyls in jute seemspossible because jute resembles hardwood10, in which

lignin possesses both syringaldehyde and vanillin typeunprotected hydroxyls along with aliphatic hy­droxylsll. Recently, Roy and Sen12 have isolatedlignin from jute sticks and estimated its phenoliccontent. The present study indicates the presence ofsuch free hydroxyls in jute fibre also.

Results and Discussion

Raising the temperature of the reaction above 35°C

was injurious to the fibre, which, turned into agelatinous mass. Increasing the duration of soaking inacetic acid to 3 h followed by soaking in acidified aceticaNhydride for 5-10 min at 35-40°C led to a rise in

temperature, the fibre disintegrating. Increasing theamount of catalyst (conc. sulphuric acid) from 0.05 to

0.2 ml decreased the strength of the fibre. Keeping thereaction period for longer than 10 min also led to a fall

in the strength of the fibre and the first washing of thetreated fibre gave a greater amount of white colloidal

suspension. The optimum conditions for partialacetylation of jute in which the fibre retained its

strength and gained weight by 11% were: (i) soaking inacetic acid for I h, (ii) keeping the reaction period inacetic anhydride for 5 min at 35°C (temperature beingmaintained by cooling in water-bath), and (iii) using0.05 ml of conc. sulphuric acid as catalyst.

While the fibre had a weight gain of 30% after thereaction was carried out under the conditions (reactionperiod, 10 min; temp., 25°C) given in the procedureabove, bleached jute fabric, when subjected to similartreatment, did not show any significant weight gain.This may be explained as due to the loss of lignin andsome hemicellulose, the cementing materials in thecell-wall structure of the fibre. These molecules,compared to cellulose, are more reactive to suchacetylation. In the bleached fabric, hemicellulose is

exposed to a greater extent to acetylation and is easily

69

INDIAN J. TEXT. RES., VOL. 10, JUNE 1985

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