Iranian Polymer Journal / Volume 10 Number 6 (2001), 377-383

1026-126512001

Dynamic Properties and Swelling Behaviour of Bamboo Filled

Natural Rubber Composites : The Effect of Bonding Agent

Hanafi lsmail l( ' ) , Mohammad Rabu Edyham l and Basuki Wirjosentono 2

(1) School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia(2) Department of Chemistry, Universitas Sumatera Utara, Medan 20155, Indonesia.

Received 7 April 2001 ; accepted 27 September 2001

ABSTRACT

The effect of filler loading and bonding agent on the dynamic properties and

swelling behaviour of bamboo fibre filled natural rubber composites were

carried out. Bamboo fibre was used as a filler and the loading range was from

0 to 50 phr . Dynamic properties were determined using a Monsanto moving

die rheometer (MOR 2000) at 150 'C . Results show that the maximum elastic

torque (S-raw) and minimum elastic torque (S 'ML) increase with increasing filler

loading and the addition of bonding agent . However, the viscous torque

(S -MN) and tan Sae decrease with the addition of bonding agent. For swelling

behaviour, the water absorption of the composites increases with increasing

filler loading but decreases with the addition of bonding agent. The presenceof bonding agent is found to improve the adhesion between bamboo fibre and

natural rubber matrix as indicated by the tensile fracture surfaces of the

composites using scanning electron microscope (SEM).

Key Words : dynamic properties, swelling behaviour, bamboo fibre, natural rubber, bonding agent

INTRODUCTION

Over the last decade, short-fibre reinforcement of

polymer composites has gained considerable attention

as a viable alternative to particulate filler reinforcement[1-5] . Short fibres are used in rubber compounding due

to the considerable processing advantages, improve-ment in certain mechanical properties, and to economic

consideration [6] . Both natural and synthetic fibres canbe incorporated into the rubber matrix along with other

additives using extrusion, calendering, and various

types of moulding operations such as compression,

injection and transfer [7].In this study, a new type of composite material

i .e ., bamboo fibre reinforced natural rubber compositewas developed . Bamboo fibre was used as the rein-

forcement because bamboo is an . abundant naturalresource in Asia including Malaysia, and its overall

mechanical properties are comparable to those ofwood . In our previous work [8], we have reported theeffects of filler loading and bonding agent on curing

characteristics and mechanical properties of bamboo

{t) To whom correspondence should be addressed . E-mail: ihanafi@usm.my

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Dynamic Properties and Swelling Behaviour of Bamboo Filled NR Composites.

Tablet Formulations for bamboo fibre reinforced natural rubber composites.

Compound composition (phr) A S C D E F G H 1SMR L 100 100 100 100 100 100 100 100 100Zinc oxide 5 5 5 5 5 5 5 5 5

Stearic add 2 2 2 2 2 2 2 2 2

CBS 0 .5 0.5 0.5 0.5 0 .5 0 .5 0 .5 0.5 0 .5

Sulphur 2 .5 2 .5 2 .5 2.5 2 .5 2 .5 2 .5 2.5 2 .5

Flectol H 1 1 1 1 1 1 1 1 1Phenol formaldehyde (PF) - - - - 10 10 10 10Silica (Sil) - - - - - 2 2 2 2

Hexamethylene tetramine (Hexa) - - - - - 5 5 5 5

Bamboo fibre 10 20 30 50 10 20 30 50

filled natural rubber composites . The adhesionbetween the bamboo fibre and the natural rubber wereenhanced by the addition of bonding agent asexhibited by the tensile fracture surfaces of thecomposites using a scanning electron microscopy(SEM). The presence of bonding agent also givesshorter curing time and enhanced mechanicalproperties such as tensile strength, tensile modulus,tear strength, and hardness. In this study, the effect ofsimilar bamboo species (viz bambusa paravariabilis)on dynamic properties and swelling behaviour isreported.

EXPERIMENTAL

Compounding Ingredients and FormulationThe formulation used in this study is shown in Table

1 . Natural rubber (SMR L) was obtained from theRubber Research Institute of Malaysia (RRIM) . Thebamboo used in this work belongs to the species ofbambuca paravariabilis and supplied by ForestResearch Institute of Malaysia (FRIM) . It consists ofabout 73% of holocellulose and 21% of lignin.

Bamboo chips were produced by means of awood planer which were then ground into sizes of180-270 sm and used in rubber compounding withoutfurther treatment. Figure 1 shows the SEM micro-graph of bamboo fibres used in this study . It can beseen that the bamboo fibres consist of various shapes,sizes and lengths . Other chemicals such as sulphur,

zinc oxide, stearic acid, N-cyclohexylbenzothiazolesulphenamide (CBS) and silica were all purchasedfrom Bayer (M) Ltd . Flectol H (poly-1,2-dihydro-2,24-trimethylquinoline) was supplied by Monsanto(M) Co.

Bonding agents used in this study were phenolformaldehyde (Borden Chemical (M) Ltd) and hexa-methylenetetramine (Fluka Chemical (M) Ltd) . Theconcentration used is based on optimum propertiesobtained as reported in our previous paper [31.

CompoundingBamboo fibres were dried in an oven at 80 'C for 24 hto expel moisture . Mixing was carried out on aconventional laboratory two roll mill size (160x

Figure 1 . Scanning electron microscopy of bamboo fibres(Mag : 20X),

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Ismail H. a al.

320 nun) according to ASTM designation D3184-80.Nip gap, mill roll speed ratio, time of mixing, and thesequence of addition of the ingredients were kept thesame for all the composites . The sheeted rubbercompound was conditioned at a temperature of 23±2 ` C for 24 h in a closed container.

Measurement of Dynamic PropertiesThe MDR 2000 moving die rheometer (MDR), arotorless cure-o-meter, has gained much acceptanceby the rubber industry since its introduction in 1988.In many cases, this instrument is replacing theoscillating disk rheometer (ODR) as described inASTM Standard Test Method D2084 . The dynamicproperties before, during and after cure were studiedat 150 'C . A unique signal processing system andFourier transform software separates the complextorque into elastic torque (S') and viscous torque (5").

The tan S is derived by dividing S" by S' . Inaddition to the dynamic properties, the MDR givesdigital outputs of scorch time and cure time.

Water Absorption TestSamples were immersed in distilled water at 30 'C.Weights of the samples were recorded at differenttimes. Samples were wiped with tissue paper toremove surface water before weighing . Finally, theweight gain and the weight loss were calculated [9].

Figure 2 . Variation of S'MH and filler loading of bamboo fibrefilled natural rubber composites with and without bondingagent.

Iranian Polymer Journal/ Volume 10 Number 6 (2007)

(a) Weight GainWater absorption (i.e ., weight gain) was determinedby the following equation:

Wg = WW° x100

Where : Wg°weight gain (%), We =equilibrium weightafter water treatment, and Wooven dry weight beforewater treatment.

(b) Weight LossSamples, which were immersed in water, were thendried at 70 ' C for 24 hour, after which they werecooled at the ambient temperature under normalcondition . Their final weights were taken to determinethe weight loss according to the following equation:

W,= WW

W`xl00

Where : WE = oven dry weight after immersion inwater.W,, = oven dry weight before water treatment.W, = weight loss (%).

RESULTS AND DISCUSSION

The effects of filler loading and bonding agent on themaximum elastic torque (S', u) and minimum elastictorque (S' I n, ) are shown in Figures 2 and 3 . It can beseen in Figures 2 and 3 that the S' and S 'Hn,increased with increasing filler loading and thepresence of bonding agent . S'm[I generally correlateswith durometer hardness or cure modulus . S' l a, is ameasure of compound viscosity [10,11] . These resultsindicate that the incorporation of bamboo fibre andthe presence of bonding agent has increased thestiffness of the composites . However, at a similarfiller loading composites with bonding agent exhibithigher S'; and S'MI, than the similar composites butwithout the presence of bonding agent . This isattributed to the fact that the adhesion between thefibre and rubber matrix is improved because of thegreater . interaction between the bamboo fibres andrubber matrix through the bonding agent .

379

Dynamic Properties and Swc3ling Behaviour of Bamboo Filled NR Composites,

Figure 3. Variation of S'ML and filler loading of bamboo fibrefilled natural rubber composites with and without bondinggent.

Figures 4-7 show the SEM comparison of thetensile fracture surface of bamboo fibre filled naturalrubber composites with and without bonding agent at10 and 30 phr of filler . Figures 3 and 4 exhibit thefailure surface of composites with bonding agent . Itcan be seen that the pull-out of fibre from the surfaceis minimum and the failure occurred at the fibre dueto strong adhesion between the fibre and the matrix.In Figures 5 and 6 (composites without bondingagent) the fracture surface clearly show weak

Figure S. Scanning electron microscopy tensile fracturesurface of bamboo fibre filled natural rubber composites at30 phr of filler and with bonding agent (Mag: 150X).

interfacial adhesion between fibre and the rubbermatrix which resulted many holes being left after thefibres were pulled-out from the matrix . In ourprevious work [8), scanning electron microscopystudies of tensile fracture surface of bamboo fibrereinforced natural rubber composites show evidencethat the adhesion between the bamboo fibre andnatural rubber matrix were improved with the use ofbonding agent.

Figures 8 and 9 show the effect of filler loading

Figure 4. Scanning electron microscopy tensile fracturesurface of bamboo fibre filled natural rubber composites at10 phr of filler and with bonding agent (Mag: 150X) .

Figure 6 . Scanning electron microscopy tensile fracturesurface of bamboo fibre filled natural rubber composites at10 phr of filler and without bonding agent (Mag : 150X)_

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Lsinatl I I . et al.

Figure 7 . Scanning electron microscopy tensile fracturesurface of bamboo fibre filled natural rubber composites at30 phr of filler and without bonding agent (Mag : 150X).

and bonding agent on the viscous torque (S"MH) andtanSMH . Viscous torque relates to the damping charac-teristics of a rubber compound whereas, the lower thetant3 for a cured compound, the greater its resiliency[ 1 l ] . It can be seen that both properties increased withincreasing filler loading . Ibarra [12] also reportedsimilar observation . As the bamboo fibres in thenatural rubber matrix increase . the incorporation timealso increases and consequently generates more heatdue to the additional friction . Senapati et al . [13] whowork on characterization of short nylon ' fibre rein-forced natural rubber composites also found that

lrauia,s Polymer Journal / Volume 1(1 Wumber i (200l„i

00

10

20

30

40

50

60Filler loading (phr)

Figure 9 . Tan 8MH versus filler loading of bamboo fibre fillednatural rubber composites with and without bonding agent.

the rebound resilience of the composites decrease andthe composites exhibit a steady and rapid increase inheat build-up as the fibre loading increases.According to them this is due to high loss modulus athigher concentration of fibres.

However . at a similar filler loading, compositeswith bonding agent exhibit lower S"MII and tan SMH

values than the similar composites but withoutbonding agent . The lower properties for both with theincorporation of bonding agent indicate that bamboofibre reinforced natural rubber composites possess alower dissipation energy which is due to the better

Figure 10 . The effect of filler loading on water absorption ofbamboo fibre filled natural rubber composites withoutbonding agent.

.70t'''*•bonslingg agent

10

20

30 40

50 60Filler loading (phr)

Figure 8 . S°MH versus filler loading of bamboo fibre filled

natural rubber composites with and without bonding agent .

381

50

40

30

20

•30 pr

.3apr

15

25

35

45Time (min)

Figure 13 . Variation of weight loss and time for 30 phr of

bamboo fibre filled natural rubber composites with andwithout bonding agent.

10

0

Dynamic Properties and Swelling Behaviour of Bamboo Filled NR Composites.

bamboo fibre-rubber matrix interaction as shown inprevious SEM tensile fracture surfaces.

Figure 10 shows the effect of filler loading onwater absorption, Wg of bamboo fibre reinforced

natural rubber composites . It can be seen that thewater absorption becomes constant after 45 days.However at a similar absorption time, compositeswith higher loading of bamboo fibres exhibit higherwater absorption . One of the physical properties ofthese natural fibres is the hydrophilic characteristic.In polymer composites with lignocellulosic fibre such

- 20•10 own 20phr

1D' ♦sopr

x50 phr

0

5

10

15

20

25

30

35Time (min)

Figure 12 . The effect of filler loading on weight loss of

bamboo fibre filled natural rubber composites without

bonding agent.

as bamboo, water is absorbed mainly by the fibresbecause the rubber material is hydrophobic and itswater absorbability can be neglected.

The comparison of water absorption, Wg of30 phr of bamboo fibre reinforced natural rubbercomposites with and without bonding agent is shownin Figure 11 . It can be seen that at a similar swelling

time, the Wg value for composite with bonding agentis lower than the similar composite (control) with nobonding agent . As discussed before, this is due to thebetter adhesion between the bamboo fibres and rubbermatrix when the bonding agent is present. As a result,the composites become stiffer and stronger (Figures 2and 3) and less penetrable by the water molecule.

Khan et al . [14, 15] studied the sorption isotherm ofwood and wood-plastic composites and found that theabsorption of water is higher in untreated wood.

Figure 12 shows the weight loss, W 1 , of the

composites with different filler loading, whereasFigure 13 shows the weight loss comparison of thesimilar composites but with and without bonding:

agent. Both figures exhibit that composites withhigher loading of filler and without bonding agenthave higher weight loss, W I , compared to similarcomposites but with lower loading of filler andbonding agent . As explained before, this is due to thepresence of more hydroxyl group on the filler surfaceand the weaker adhesion between bamboo fibres and

p/ I 1 I 1 10

20

40

60Time (days)

Figure 11 . Variation of water absorption and time of 30 phr

of bamboo fibre filled natural rubber composites with andwithout bonding agent .

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Ismail H. et al.

natural rubber matrix. As the composites with higherfiller loading exhibit weak adhesion between fillerand matrix, more water will be absorbed (Figures 9and 10) and consequently higher water loss will beobserved during drying.

CONCLUSION

The incorporation of bamboo fibres in natural rubbercomposites has resulted an increase of maximumelastic torque (S'rm), minimum elastic torque (S'ML),viscous torque (S"nut), tan 8l„m and water absorption,Virg of the composites . However, with the presence ofbonding agent, some beneficial effects were obtained,such as higher maximum elastic torque (Sia l) andlower viscous torque (S-rot), tan 8mi.i and water

absorption . The addition of bonding agent is found to

improve the adhesion between bamboo fibres andnatural rubber composites.

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