Indian Journal of Textile Research

Vol. 7, September 1982, pp. 87-92

Evaluation of Jute as a Reinforcement in Composites

M K SRIDHAR, G BASAVARAJAPPA, S G KASTURI & N BALASUBRAMANIAN

Materials Science Division, National Aeronautical Laboratory, Bangalore 560017

Received 20 January 1982; accepted 4 July 1982

A detailed evaluation of jute fibres for use in polymer composites has been made. The mechanical properties, thermalstability, moisture absorption and resin consumption of jute fibres have been studied. Methods for reducing moistureabsorption and resin consumption are reported.

Table I-Mechanical Properties of Some Natural Fibres

The major thrust in the area of composite materials hasbeen directed towards the development and study ofhigh performance materials like glass, carbon, kevlarand boron fibres in appropriate polymer or metalmatrices. Natural fibres like jute and sisal have theadvantage of low cost and are likely to be useful in anumber of less demanding applications, such. as inconstruction of grain storage silos and small fishingboats.

The mechanical properties of some natural fibres arelisted in Table I. Of these, jute is the most importantone, since it is systematically cultivated in India and isavailable in large quantities. Jute is made up of 60%cellulose, 24% hemicellulose, 13% lignin and 3% otherminor constituents. The chains of cellulose andhemicellulose run almost parallel to the fibre axis. Thehydrogen bonds and other linkages between theconstituents provide high stiffness to jute fibres. Someattempts have been made to fabricate jute reinforcedlaminates and structures2.3 and the mechanicalproperties of jute reinforced laminates have beenreported in a number of publications4 • However, it hasbeen observed that the jute fibres require largequantities of resin to wet the fibres and a good portionof this resin is squeezed out by the application ofpressure during curing3 . Also, it has not been possible

Fibre

CottonWoolSilkFlexJuteSisalRamie

Tensile ElongationYoung'sstrength

at break,%modulus

x 103, Ibjsq inx 106, Ibjsq in

44-109

3.0-7.00.83-1.82

20-29

25-350.39-0.57

42-88

20-251.22-1.87

50-150

2.7-3.24.0

57-112

1.7-1.87.3

74-922.0-2.5

58-136

3.6-3.88.9

to prepare jute composites with more than 40% (byvol.) fibres4 • Consequently, the mechanical propertiesof jute composites are generally poor and jute fibresare considered for use as low-cost fillers in glassreinforced plastics4• Absorption and desorption ofmoisture by jute is also one of the factors which affectthe properties of jute fibres5 •

No attempt seems to have been made so far forreducing the resin consumption and controllingmoisture adsorption and desorption by jute fibres.This paper reports the results of microscopicobservations, measurement of thermal stability andmechanical properties of jute fibres. Methods forreducing moisture absorption and resin consumptionare described. The tensile properties of treated anduntreated jute/polyester composites are also reported.

Experimental ProcedureMicroscopic observations-The jute fibres were cast

in a polyester resin in rubber cups with the help of cardsupports. The polyester resin, mixed with catalyst andhardener, was allowed to stand for 30-45 min to enableit to attain sufficiently high viscosity. The jute fibresalong with card supports were then introduced into theresin. The high viscosity of the resin is necessary toprevent extensive impregnation of resin into the fibres,which may lead to changes in structure of fibres. Thespecimens were then polished and observed under thescanning electron microscope after gold sputtering.Some specimens were observed under an opticalmicroscope and the image was projected on the screen.The images were then traced on tracing paper forcross-sectional area measurements.

Mechanical properties-The tensile strength andtensile modulus of the fibres were measured on anInstron universal testing machine with a type A loadce1l6. The cross-head speed was 0.05 mm/min and thechart speed was 10 cm/min. The gauge length of thefibres was 50 mm.

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INDIAN J TEXT RES, VOL. 7, SEPTEMBER 1982

The fibres were mounted on card supports with 50mm long windows and their diameters were measuredby viewing the fibres longitudinally under an opticalmicroscope with a graduated eyepiece having aresolution of 0.25 pm. The specimens were thenmounted on the Instron testing machine using the fibregrips and the card support was cut off and the cross­head actuated. The tensile strength was calculatedfrom the breaking load and the tensile modulus fromload elongation plots obtained from the strip chartrecorder.

Thermal stability-Samples of jute fibres wereheated in air at 100°C for 24 hr and in vacuum of 10-1

mm Hg at 150,200,250 and 300°C for 2 hr. The heatedfibres were examined for weight loss, change inmechanical properties and chemical degradation.Chemical degradation was evaluated by taking IRspectra of heated fibres. The heated' fibres werepulverized in a pulverizer and 20 mg of the fibres werethoroughly mixed with 200 mg of KBr and were thenpelletized in a pelletizer under pressure. The pelletsthus made were used to take the spectra. The effect of

prolonged exposure to high temperature was studiedby heating the fibres in a vacuum of 10 -1 mm Hg at200°C up to 8 hr. Samples were withdrawn at intervalsof I hr and their mechanical properties were evaluated.

Reduction in resinconsumption-A solution ofligninin acetone, containing 10% (by wt) lignin, wasprepared. Jute fibre yarns, dried at 80°C for 24 hr, wereimmersed in the lignin solution for 30 min and thenthey were removed and dried in air for 24 hr at ambienttemperature and further dried at 80°C for I hr. Thetensile strength and tensile modulus of the fibres weremeasurea.

The resin consumption of treated and untreated jutesamples was measured by fabricating fibre reinforcedpolyester rings by hand winding. A previously weighedquantity of yarn was passed through a resin bath andresin impregnated yarn was wound on a cylindricalsand mandrel to form a ring. The ring was allowed tocure for 24 hr and then removed by collapsing the sandmandrel and was weighed. The difference in the weightof the ring and the fibre used gives the quantity of resinconsumed.

Moisture absorption- The jute fibres were soaked inaqueous solutions of ethylenediamine (EDA) for 10min. The fibres were then washed with water and dried

under vacuum of 10-1 mm Hg at 150°C to constantweight. The dried fibres were placed on the pan of asingle pan balance and the increase in weight with timewas recorded until the weight remained constant,indicating saturation of moisture. The tensile strengthand tensile modulus of the treated fibres were thenmeasured.

88

Composite preparation and testing-Unidirectionalcomposites were prepared by winding lignin-coatedand uncoated fibres on a flat plate, impregnating withgeneral purpose polyester resin and then curing undera pressure of 40 lb/sq in between flat plates. Both thelignin-coated and uncoated fibres were given EDAtreatment before making composites. The tensilestrength and tensile modulus of the composites weremeasured on I x 8 in specimens with aluminium tabs atthe gripping portion using an Instron universal testingmachine.

Results and Discussion

A schematic diagram of a cross-section of a jutefibre, based on microscopic observations, is shown inFig. 1. The middle lamella contains lignin andhemicellulose and runs between the cells. The cell wallcontains cellulose fibrils and at the centre of the cell isthe lumen.

The scanning electron micrographs of a cross­section of a jute fibre are shown in Fig. 2. Themulticellular nature of jute and the lumen can be seenclearly.

The tensile strength and tensile modulus of jutefibres show that there is considerable scatter instrength and modulus values (Table 2). Part of thisscatter is due to the variation in cross-sectional areas.The cross-sections of jute fibres are irregular and themajor axis of the cross-section varies from 20 to 60 pm(Table 2). Thus, the strength and modulus are onlyapproximate values and the average strength andYoung's modulus are found to be 50 x 103 Ib/sq in and4 x 106 lb/sq in respectively. These appear to beunderestimates, considering the strength of jute fibrecomposites.

Jute fibre can withstand up to 100°C in air withoutany serious degradation. It suffers a weight loss of 6%,but the lost weight is regained on exposure to theatmosphere, indicating that the weight loss is due todesorption of moisture.

Fig. I-Schematic diagram of a cross-section of a jute fibre

SRIDHAR et al.: EVALUATION OF JUTE AS A REINFORCEMENT IN COMPOSITES

Data on the weight loss injute on heating at varioustemperatures for 2 hr under vacuum show that the lossin all the cases is 11-12% (Table 3). On exposure toambient conditions for 24 hr, the heated jute regainedall the lost weight in each case, once again indicatingthat the loss in weight is due to the desorption of waterand that no volatile degradation products are formeddue to heating.

The average tensile strength and modulus of fibresheated to various temperatures for 2 hr are given inTable 4. Each value represents the average of at least25 tests. It is observed that there is no significantdecrease in strength of jute fibres due to heating up to250°C. In fact, a slight increase is observed in thestrength of fibres heated at 200°C. Jute fibres heated at300°C, however, became slightly dark in colour and

w ~Fig. 2-Scanning electron micrographs of a cross-section of a jute fibre (A) x 1200, and (B) x 900

Table 2- Tensile Strength and Tensile Modulus of Jute Fibres

SINo.

Fibre diampm

Breakingstrain

Tensile strength

I 28. \32 35.163 35.174 56.275 36.96 19.67 22.68 38.29 59.5

10 44.511 53.212 25.1213 47.214 50.4915 26.616 27.3817 42.518 28.\319 25.9

Average

0.01550.01530.01650.01680.01780.0210.0190.01580.01550.02450.02480.02150.01130.0150.01250.0180.02

0.0210.020

GPa0.590.48

0.330.240.251.211.090.120.200.400.330.400.180.440.210.380.270.220.690.34

x 103, Ibjsq in

8670483436

176160

1729564830266432544032

10050

GPa45.035.031.017.525.376.754.29.4

15.2319.916.818.230.139.118.332.621.415.046.826.5

Tensile modulus

X 106, Ibjsq in

6.55.24.52.53.6

11.07.91.4

2.32.92.4

2.64.4

5.72.74.73.12.26.73.8

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INDIAN J TEXT RES, VOL. 7, SEPTEMBER 1982

their strength was reduced by about 60%. The tensilemodulus did not show much variation even in fibresheated at 300°C.

Data presented in Table 5 show that the tensilestrength of the fibres heated at 200GC for differentdurations is not affected significantly. Up to about 6 hrof exposure there is no significant change, except aslight increase in strength when heated up to 4 hr.When heated for 8 hr, the strength of the fibres wasreduced by about 20%. The tensile modulus was'almost insensitive to the duration of exposure to hightem pera ture., 'IR spectra of jute fibres heated at 200, 250 and300°C were analyzed for ascertaining whether anydegradation occurs due to heating. The possibledegradation of cellulose injute was found out from thedecrease in the intensity of the peaks at 2900, 1430,1162 and 895 wave numbers (as suggested by Higgins 7

for pure cellulose). The vibrations corresponding tothe above peaks are given below.

Table 3-Weight Loss in Jute Fibres Heated at VariousTemperatures for 2 hr under Vacuum

Temperature.X'

100150200250300

Weight loss, %10.2811.8312.3411.1413.34

Table 4-Average Tensile Strength and Tensile Modulus ofJute Fibres Heated at Various Temperatures for 2 hr under

Vacuum

Temperature°C

Unheated150200250300100 (in air)

Tensile strengt hx 103, lb/sq in

50.0045.0054.0045.0015.0048.00

Tensile modulusx 106, lb/sq in

3.85.44.32.64.14.2

2900 em -I-Symmetric and antisymmetric CH2stretching

1430 em -1-CH2 bending1162 em -I-Antisymmetrical bridge C-O-C

stretching895 cm-I- Antisymmetrical out of plane ring

stretching CH deformation.

The dip in the peaks at 2900 and 1430 em -I.indicates decrease in the number ofCH2 groups due tooxidation or formation of volatile degradationproducts, such as low molecular weight hydrocarbons.The dip in the peak at 1162 em -I indicatesde polymerization due to breaking of ether bridges andthat in the peak at 895 em -I indicates oxidationand inthe absence of oxidation loss in crystalline order.However, more precise crystallinity index values areobtained by taking the ratio of intensities of peaks at1430 em -1 to that of the peak at 895 em -I. Theintensities of the peaks at various frequencies for jutefibres heated at 200, 250 and 300°C and also forunheated jute fibres are given in Table 6. It is observedthat up to 250°C, the intensities of peaks at 2900 and895 em -1 do not decrease. This shows the absence ofoxidation and fragmentation to form low molecularweight hydrocarbons. Similarly, the peak at 1162em -1 does not show a significant fall, indicating only a

Table 6~IR Absorption at Various Frequencies in SamplesHeated at Various Temperatures for 2 hr under Vacuum

Sample Frequency, cm-1

2900 1430 1162 895

Unheated jute 10 4 41 7

Heated at 200°C 10 2 4 6

Heated at 250cC 10 2 4 6

Heated at 300'C 4 2 3 21L..1

Table 7-Resin Consumption and Resin Wastage in MakingJute-Polyester Composites with Coated and Uncoated Jute

Table 5-Average Tensile Strength and Tensile Modulus of Fibre Fibre Qtyof Qty of QtyofJute Fibres Heated at 200°C under Vacuum for Various (l00 g) vol. resin resin resin

Durationsfract. required retained wasted

to wet the in the gfibres laminate

Duration of Tensile strength Tensile modulus g gheating, hr x 103, lb/sq in x 106, lb/sq in Uncoated 0.3 350 200 150

1 44.0 3.9 jutef2 54.0 4.3 Lignin- 0.4 350 175 175

4 57.0 4.3 coated 0.4 200 175 306 37.0 4.7 jute8 33.0 3.7

-----

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SRIDHAR et at.: EVALUATION OF JUTE AS A REINFORCEMENT IN COMPOSITES

Table 8-Tensile Properties of Lignin-Coated Jute Fibres

SI Diameter Breaking Tensile strength Tensile modulusNo. 11m strain

GPa x 103, lb/sq in GPa x 106, lb/sq inI 64.81 0.0159 0.3 43.517 15.731 2.2812 39.438 0.007 0.177 25.598 23.327 3.3823 34.917 0.006 0.515 74.665 41.736 6.054 74.606 0.007 0.193 27.962 20.039 2.9065 44.965 0.0069 0.482 69.818 79.015 11.4576 45.467 0.0141 0.202 29.327 14.554 2.117 27.883 0.0099 0 ..546 79.142 54.727 7.9358 49.989 0.0063 0.239 34.762 36.96 5.3599 55.013 0.0083 0.202 29.301 23.919 3.468

10 36.926 0.01 0.449 65.034 43.587 6.32II 28.386 0.0065 0.387 56.151 88.514 12.83412 88.171 0.0099 0.153 22.231 16.884 2.41913 42.202 0.0071 0.168 24.388 28.032 4.06514 64.056 0.005 0.243 35.285 18.927 2.74415 35.168 0.0056 0.172 24.875 34.133 4.949

Table 9-Tensile Strength of Jute Fibres Treated withAqueous Ethylenediamine Solutions

Treatment Tensile strengthx 103, lb/sq in

5040432415

Percentagereduction

Untreated20% EDA4.0% EDA60% EDAAcetylated jute

20143270

Table 10-Tensile Properties of Jute Composites

Jute composite Tensile strengthx 103, lb/sq in

22.240

Tensile modulusx 106, lb/sq in

1.214Untreated jute/polyester

Lignin-coatedjute/polyester

20.8 1.00

slight depolymerization. The peak corresponding toCH2 bending at 1430 em -1 decreases significantly, buta part of this decrease is due to increase in crystallinity.This enhanced crystallinity might also be the reasonfor the slight increase in strength of fibres heated at200°C,

Thus, jute fibres are stable up to 250°C in theabsence of air. This fact is important, because itenables the use of high temperature curing resins likephenolic resins which cure at 180°C for impregnatingjute fibres. Under the curing condition, jute fibresmight have been protected from exposure to air andhence the stability in the absence of air is all that isrequired.

Data presented in Table 7 show the effect of lignincoating on resin consumption. It is observed that lignincoating brings down the wastage of resin by asignificant margin. The tensile properties of the lignin-

REATED wiTH 60'1, EDA

JUTE T

JUTE TREATED WITH 40'1, EDA

JUTE TREATED WITH 20'1, EDA

SO 80 100Duration, rrun

120

Fig. 3-Moisture absorption by untreated and EDA-treated jutefibres

coated fibres are given in Table 8. The strength of thefibres is not affected significantly, but the elongation tofracture is lowered slightly as compared to that ofuncoated fibres (Table 2).

It is reported that EDA and hydrazine formcomplexes with hydroxyl groups of cellulose 8,9 . Thiswould reduce the absorption of moisture by the fibres.The moisture absorption curves for untreated andEDA treated jute fibres are shown in Fig. 3. Themoisture absorption is reduced significantly in jutefibres treated with 20 and 40% EDA solutions. In thefibres treated with 60% EDA solution, extensiveswelling occurs and the moisture absorption is higherthan in fibres treated with EDA solutions of lowerconcentrations. The mechanical properties of EDA-treated fibres are given in Table 9. It is seen that thestrength (If jute fibres is reduced by 20-25% in the caseof fibres treated with 20 and 40~~ EDA solutions.However, the reduction in strength is considerably lessas compared to that in the case of esterified fibres.

Jute fibres treated with 64% hydrazine solutionswelled extensively and disintegrated into a powderymass.

The tensile properties of treated and untreatedjute/polyester composites are given in Table 10. It is

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INDIAN J TEXT RES, VOL. 7, SEPTEMBER 1982

seen that the average tensile strength and modulus areslightly lower in the case of lignin-coated fibres.

Conclusions(I) Jute fibres have good tensile strength and

modulus and can be used for making low costcomposite materials. The strength, modulus anddiameters of jute fibres show considerable scatter.

(2) :Jute fibres are stable in air up to 100°C and thereis no significant change in their strength on heating invacuum up to 250°C.

(3) Jute fibres do not show any significant chemicaldegradation on heating in vacuum up to 250°C.

(4) The high resin consumption in making jutecomposites can be brought down by a factor of 2 bycoating the fibres with organic polymers. Lignincoating has been shown to bring down the resinconsumption without exerting any deleterious effectson the properties of the fibres.

(5) Moisture absorption can be reduced by EDAtreatment. But there is always a reduction in thestrength of the fibres.

92

AcknowledgementThe authors are thankful to Dr R.V. Krishnan and

his group for help in scanning electron microscopy.They also acknowledge the help rendered by Shri Y.Ramachandra and Shri G Subramani.

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1960.2 Winfield A G & Winfield B Z, in Fillers and reinforcements for

plastics, Advances in Chemistry Series No 134 (AmericanChemical Society, Ohio) 1974.

3 Satya C R, Progress report from VSSC ofthe Project Newer Fibresand Composites, III International Symposium on NewerFibres and Composites, SASMIRA, Bombay, 1978.

4 Shaw A N & Lakkad S L, Fibre Sci Technol, 15 (1981) 41-46.5 Balasubramanian N, Progress Report from NAL of the Project

Newer Fibres and Composites, " International Symposiumon Newer Fibres and Composites, CLRI, Madras, January1977.

6 Grafil test methods. Test ReI 101.11 (Courtlauds Limited,Coventry) May 1969.

7 Higgins H G, J Polym Sci, 28 (1958) 118.8 Creely J J, Segal L & Loeb L, J Polym Sci, 36 (1959) 205.9 Segal L & Creely J J, J Polym Sci, 50 (1961) 451.