effect of water absorption on pultruded jute/glass fiber-reinforced unsaturated polyester hybrid...

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JOURNAL OFC O M P O S I T EM AT E R I A L SArticle

Effect of water absorption on pultrudedjute/glass fiber-reinforced unsaturatedpolyester hybrid composites

Mohd Hafiz Zamri, Hazizan Md Akil, Azhar Abu Bakar,Zainal Arifin Mohd Ishak and Leong Wei Cheng

Abstract

The use of natural fibers in polymer composites has given renewed interest to the development of green composites

today. However, the moisture absorption of natural fibers gives serious concern, especially for their potential outdoor

applications. This article reports the study results on the water absorption of pultruded jute/glass fiber-reinforced

unsaturated polyester hybrid composites, which was subjected to various water conditions and their effects on its

mechanical properties. Water absorption tests were performed by immersing composite specimens into three different

water conditions, namely: distilled water, sea water, and acidic water, which were at room temperature, for a period of 3

weeks. The characteristic parameter of diffusion coefficient (D) and maximum moisture content (Mm) were determined

from the obtained water absorption curves. The water absorption behavior of the glass/jute fiber-reinforced unsaturated

polyester hybrid composite was found to follow a non-Fickian behavior. The effects of the various aqueous environments

on the flexural and compression characteristics were investigated in this study. The flexural and compression properties

were found to decrease with an increasing percentage of water uptakes.

Keywords

fibers, hybrid composites, environmental degradation, mechanical property, pultrusion

Introduction

With an increasing environmental awareness by thegeneral public, there are active research interests onthe studies of natural fiber-reinforced polymer matrixcomposites. This is largely due to their eco-friendlinessand cost effectiveness.1 The advantages of natural fibercomposites are, reasonable strength, lightweight, freefrom health hazards, biodegradable, and therefore,their potential to be used as building materials.2–4 Thenatural fibers also promise sustainability, cheaper, andlighter in weight, which provides better stiffness perweight than glass.5

Despite the advantages listed above, their limitationsinclude, a lower modulus, low strength and poor mois-ture resistance, and especially their absorption whencompared with synthetic fibers, such as glass.6

Natural fibers also have poor wettability by non-polarplastics, and insufficient adhesion between untreatedfibers and the polymer matrix, which can lead to de-bonding with age.7,8 The moisture absorption, by

composites containing natural fibers, has severaladverse effects on their properties and thus, affectstheir long-term performance. For example, increasedmoisture causes the fibers to swell, decreases theirmechanical properties, provides the necessary condi-tions for biodegradation, and changes theirdimensions.9

Several research works have been reported on effectof water absorption in natural fiber-reinforced compos-ites, such as bamboo–glass fiber, sisal, flax pineappleleaf fiber, jute, short roselle and sisal fiber, andbamboo fiber, which shows the relevancy of the subject.Presence of moisture in the natural composites would

School of Materials and Mineral Resources Engineering, Engineering

Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia.

Corresponding author:

Hazizan Md Akil, School of Materials and Mineral Resources Engineering,

Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal,

Penang, Malaysia

Email: [email protected]

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DOI: 10.1177/0021998311410488

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lower the flexural strength, tensile strength, and othermechanical properties of the composites system.9–12

All polymers and composites absorb moisture inhumid atmospheres when immersed in water. In gen-eral, moisture diffusion in composites, depends on fac-tors, such as the volume fraction of fiber, void volume,additives, humidity, and temperature.13,14 Moisture dif-fusion in polymer composites has been shown to begoverned by three different mechanisms. The firstinvolves the diffusion of water molecules inside themicro gaps between the polymer chains. The secondinvolves capillary transportation into the gaps andflaws at the interfaces between the fiber and thematrix. The third involves transportation of microcracks in the matrix, arising from the swelling offibers, particularly in the case of natural fibercomposites.9,12

One possibility, to obtain a composite with bettermechanical performance, is reinforcement by two ormore fiber-types in a single matrix, leading to hybridcomposites with a greater diversity of material proper-ties. The advantage of using a hybrid composite; is thatone type of fiber could complement what is lacking inthe other. Besides that, hybridization significantlyenhances the mechanical properties of composites.12,15

In this research, glass fibers, which have higher mechan-ical properties, were combined with the jute fibers togive biodegradable properties to the composite sam-ples.16 Hybridization of natural fiber, with strongerand more corrosion-resistance synthetic fiber (e.g.,glass fiber), can improve the stiffness, strength, as wellas the moisture resistance of the composites, and there-fore, a balance between environmental impact and per-formance may be achieved. Besides the increase in themechanical properties of the composites, hybridizationalso reduces the weight of composites and their produc-tion costs.

Importantly, hybridization between natural fibersand glass fibers is expected to improve the propertiesof the materials and decrease their water uptake, andsubsequently reducing the water absorption problem.By improving the water absorption resistance, the com-posite will maintain its properties, even though it isbeing used in humid environment. It is really importantto consider the water absorption into composites, sincethe presence of moisture in the composite sample,reduces its mechanical properties.

The influence of the moisture absorption effect, onthe mechanical properties of a hybrid sandwich com-posite, formed by polyester resin-reinforced woven fab-rics of glass and jute fiber, has been discussed inprevious studies.10 The objective of this study was toinvestigate the effect of moisture absorption on thehybrid jute/glass fiber-reinforced unsaturated polyester,after exposure to different types of solution.

Samples of pultruded jute/glass fiber-reinforcedunsaturated polyester hybrid composites, have beensuccessfully produced, using the pultrusion method.The pultrusion process was selected, because of itsunique processing technique of composite manufacture.Pultruded composite is always associated with highstrength and stiffness, which is particularly due to itshigh fiber content i.e., 70%. So, pultrusion is one ofseveral composite processing techniques that could pro-cess composites with up to 70% fiber content, in a uni-directional fiber configuration.5,17

In this study, the hybrid-pultruded composite wasmanufactured with a higher ratio of matrix to fiberloading i.e., 30:70, with a ratio of glass to jute of50:50, by volume. A maximum fiber loading wasselected to observe maximum moisture absorptionand will be used as a reference or standard, for thenext study (the results from another study will be pub-lished soon). Water immersion tests in various waterconditions have been successfully performed. Hybridjute/glass fiber-reinforced polyester-pultruded compos-ites, were immersed in three different solutions of dis-tilled water, seawater, and an acidic solution at roomtemperature. The data collected were used to comparethe maximum water absorption (Mm) with the diffusioncoefficient (D), of composites made using 100% naturaland synthetic fibers. Finally, the effect of water absorp-tion on the properties of jute/glass fiber-reinforcedhybrid composites were evaluated, based on flexuraland compression testing. Compression properties,before and after immersion, were analyzed anddiscussed.

Materials

Jute fibers were supplied by Alam Fiber Impex Ltd,Bangladesh, in a twisted roving form. Glass fiberswere in a direct roving form and were supplied byMMFG Composites Sdn. Bhd. Unsaturated polyesterresin (Crystic P9901) was purchased from the RevertexCompany, Malaysia. Table 1 gives an overview of thejute fibers’ properties. The properties of the glass fiberand unsaturated polyester resin can be found inTables 2 and 3.

Preparation of pultruded composites

The hybrid composite used in this study was a unidi-rectional jute fiber/glass fiber-reinforced composite rod,measuring 12.7mm in diameter, and produced using athermoset pultrusion machine. The parameters used forpultrusion processing, are shown in Table 4.

This machine is equipped with a creel, guidancedevices, resin bath, preforming guide, heated die,

2 Journal of Composite Materials 0(0)


pulling device, and cut-off saw, as shown in Figure 1.The continuous jute and glass fibers were first impreg-nated with an unsaturated polyester resin in a resinimpregnation tank. A pulling device was used to pullthe impregnated jute and glass fiber through a steel die,to achieve the desired shape, and also establish the cor-rect resin/fiber ratio. A curing process was carried outusing a curing die, which is precision machined toimpart the final shape. A pulling device draws thestock though a die and also determines the productionspeed. Finally, a cut-off mechanism was used to cut thecontinuous pultruded composites into the desired

lengths.17,18 The average diameter, of all compositerods, is 12.7mm.

Material characterization

Water absorption investigation. Specimens wereimmersed into three different aqueous environments,which were distilled water, sea water, and an acidicsolution. For the water absorption measurements, thespecimens were withdrawn from the solution, wiped dryto remove surface moisture, and then weighted using anelectronic balance (accurate to 10�4 g) to monitor the

Figure 1. The schematic of pultrusion machine.

Table 2. Properties of the glass fiber

Properties Unit Value

Tex g/km 4400

Density14 g/cm3 2.5

Diameter15 mm 5–25

Tensile strength14 MPa 2500–3500

Specific strength UTS/density 1000–1400

E-modulus14 GPa 70.0

Specific modulus E/density 28

Elongation14 % 2.5

Table 3. Properties of unsaturated polyester resin1

Properties Unit Value Standard

Viscosity at 23�C

Brookfield RVT 2/10 rpm MPa�s 1200 ISO 2555

Density kg/dm3 1.2 ISO 2811

Reticulation at 23�C

Operational time min 20

Young’s modulus MPa 4000 ISO 527

Tensile stress at break MPa 61 ISO 527

Tensile strain at break % 2.5 ISO 527

Table 1. Properties of the jute fiber

Properties Unit Value

Tex g/km 828

Density g/cm3 1.3

Diameter mm 25.2

Tensile strength MPa 393–773

Specific strength UTS/density 302–595

E-modulus GPa 26.5

Specific modulus E/density 20.4

Elongation % 1.5–1.8

Table 4. Details of pultrusion parameter

Pulling

speed

(mm/min)

Temperature

(�C)

Jute fiber-pultruded composites 195 135

Glass fiber-pultruded composites 350 135

Zamri et al. 3


mass during the aging process. The moisture contentM (%), absorbed by each specimen was calculatedfrom its weight before, wo and after, wt absorption, asfollows:

Mð%Þ ¼ 100M1 �M0

M0

� �ð1Þ

whereM (%), is the moisture content in percentage;M1

(g) the weight of the wet sample at a given time, andM0

(g) the initial weight of the sample. Further analysis ofwater absorption characteristics of pultruded samplesin various solutions, was performed by measuring thediffusion coefficient (D). The diffusion coefficient (D),

Figure 2. Weight gain as a function of time for (a) flexural specimen and (b) compression specimen of jute–glass reinforced

unsaturated polyester hybrid composite materials exposed to distilled water, sea water, and acidic solution at room temperature.

Table 5. Effect of immersion environments on the diffusion

coefficient, D and the maximum moisture content, Mm of jute–

glass fiber reinforced unsaturated polyester hybrid composite

Flexural specimen Compression specimen

Distilled water

D (m2/s) 7.14� 10�12 2.68� 10�11

Mm (%) 4.46 5.16

Sea water

D (m2/s) 5.98� 10�12 2.23� 10�11

Mm (%) 3.55 4.72

Acidic solution

D (m2/s) 6.17� 10�12 2.30� 10�11

Mm (%) 4.30 4.92



for the composite specimen was calculated usingEquation (2):

D ¼ �kh

4Mm

� �2

ð2Þ

where Mm (%) is the maximum weight gain (%); h(mm) the thickness of the composites; and k the initialslope from a plot of M (%) vs. ˇT (ˇh), as shown inEquation (3).9

k ¼M2 �M1ffiffiffiffiffiffiT2

p�

ffiffiffiffiffiffiT1

p

� �2

ð3Þ

The times were chosen at a very early stage ofthe moisture process, so that the weight change couldstill be taken to vary linearly with the square rootof time.

Flexural testing. A flexural test was carried out usingInstron 8802 according to the standard ASTM D4476–03. Specimens (pultruded rods with diameters of12.7mm) were cut into two parts, where the cross-sec-tion of each part is smaller than a half-round section.The total specimen length was 125mm with an over-hang length of 12.5mm, at both supports. The cross-head speed for the flexural test was set at 5mm/min.Three specimens for each condition were used to obtaina satisfactory result.

Compression testing. A compression test was carriedout using Instron 3367 according to the standardASTM D 695-02 a. The diameter and length of thespecimen were 12.7 and 25.4mm, respectively. Thecrosshead speed for compression test was set at 5mm/min. Three specimens for each condition were used tominimize errors.

Results and discussions

Water absorption behavior of pultruded jute/glasshybrid composites

In this study, hybrid composite samples were immersedinto three types of aqueous environments, which weredistilled water (pH¼ 7), sea water (pH¼ 8), and anacidic solution (pH¼ 3). These three types of solutionwere selected because they represent real-life condi-tions, where these samples can be applied. These solu-tions have also been used in previous studies.5,7 Waterabsorption curves, for flexural and compression speci-mens of jute/glass fiber-reinforced unsaturated polyes-ter hybrid composites, are shown in Figure 1(a) and (b), T

ab

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66:3

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(4700)a

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(hours

).

Zamri et al. 5


respectively. Each curve represents the average data ofall three specimens. From the water absorption curves,it is clear that the absorbed water content increasedwith an increasing immersion time. This finding hasbeen reported previously concerning the natural fiber-reinforced composites.5–7,19

In general, the water absorption behavior of hybrid-pultruded composites in all three solutions can be con-sidered as a non-Fickian process, where it shows anincreasing trend and the moisture uptake never reachesequilibrium after the initial take-off. Similar observa-tions have been reported previously.5,7 In principle, thediffusion process of water in polymers and polymericcomposites may depart from the idealizations inherentin the classical formulation of Fick’s law.9,20,21 Sincethe moisture uptake does not reach equilibrium, anon-Fickian moisture absorption process may have sig-nificant effects for long-term applications in humidenvironments.

Further analysis of the water absorption character-istics of hybrid-pultruded composites in various solu-tions was done by measuring the diffusion coefficient(D). The diffusion coefficient (D), for the compositespecimens, was calculated using Equation (2).

Diffusion coefficient, D and the maximum of mois-ture content, Mm for flexural specimens and

compression specimens of jute/glass fiber-reinforcedunsaturated polyester hybrid composite are representedin Table 5. From the values shown in Table 5, the high-est diffusion coefficient was recorded for jute/glasshybrid-pultruded composites, immersed in distilledwater, followed by an acidic solution, and seawater.Based on the diffusion coefficient D’s value inTable 5, diffusion of water into jute/glass hybrid-pul-truded composite was more favorable in distilled water,compared to the acidic solution and seawater. This wasdue to the presence of large salt molecules in the seawater (notably sodium chloride), which slows the diffu-sion process into the matrix of the composite materials,resulting in lower absorption kinetic parameters.22 Thistrend can be related to the hydrolysis mechanism of thecellulose within natural fiber. The hydrolysis of cellu-lose is expected to be more pronounced in seawater(alkaline) and acidic solution, compared to distilledwater. In seawater (alkaline), it is expected that theelectro negativity of the solution has a strong influenceon the diffusion process, which can make the jute fibersswell with a highly positive charge. In terms of electronegativity, seawater has the highest, compared to theacidic water, and then the distilled water. This finding isin agreement with previously reported work(Figure 2).23

Figure 3. (a) Flexural strength, (b) maximum flexural strain, and (c) flexural modulus for jute–glass fiber-reinforced unsaturated

polyester hybrid composite after exposed to environmental conditions.


jayabal.s

1

Hafiz Zamri

Sticky Note

Accepted set by Hafiz Zamri


The most common glass, used in fiber reinforcement,consists of 54% SiO2, 17.2% CaO, 15.2% Al2O3, 8.0%B2O3, 4.7% MgO, and 0.6% Na2O, by weight. Weakacidic solutions, such as acetic acid solutions, bufferedat pH values of 3–5, do not cause significantly moreextensive corrosion than distilled water. However,during immersion, there was an ion exchange of pro-tons for metal ions on the glass surfaces and thus, acidwould catalyze depolymerization of the polymer matrixand hydrolysis of the siloxy bonds, in the interphaseregion, causing a degradation of the glass fibers.24

The maximum water absorption (Mm) and diffusioncoefficient (D) for various composites systems are sum-marized in Table 6. In comparison, the maximum mois-ture absorption (Mm) for jute/polyester and kenaf/polyester composites system, show higher values com-pared to the other composites. The maximum moisture

absorption for jute/polyester composites, immersed indistilled water is reported at 10.71%.7 For kenaf/poly-ester composites system immersed in distilled water, themaximum moisture absorption is higher i.e., 25.30%.5

The addition of natural fibers to the composites systemcauses a higher moisture uptake compared to syntheticfibers. This is due, in particular, to the hydrophilicnature of natural fibers, that are more sensitivetoward water absorption than synthetic fibers, whichcause instability in the properties of the composites.5,7

The synthetic fiber composites system shows mini-mum moisture absorption, compared to others. Forcomposites reinforced by glass fibers immersed in dis-tilled water, it shows that moisture absorption is lessthan 1.00%. For graphite/epoxy composites systemimmersed in distilled water, the moisture absorption isonly 1.20%.25–27 The incorporation of glass fiber with

0

100

200

300

400

500

600

700

800

900(a) (b)

(c)

Strain, x10–3

Str

ess,

MP

a

0

100

200

300

400

500

600

700

800

900

Strain, x10–3

Str

ess,

MP

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0 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90

0 10 20 30 40 50 60 70 80

Strain, x10–3

Str

ess,

MP

a

Standard1st Day

1st Week2nd Week

3rd Week

Standard

1st Day

1st Week

2nd Week

3rd Week

Standard

1st Day

1st Week

2nd Week

3rd Week

Figure 4. Stress–strain curves for flexural specimen of jute–glass fiber-reinforced unsaturated polyester hybrid composite after

exposed to (a) distilled water, (b) sea water, and (c) acidic solution.

Zamri et al. 7


jute fiber in polyester decreases the water absorption ofthe composites. As shown in Table 6, due to the hybrid-ization of jute and glass fibers, the maximum absorp-tion decrease to 4.46%, which lies between the 100%natural fiber composites systems and the 100% of syn-thetic fibers. It is expected that the hybridization notonly reduces the moisture uptake, but also increases thephysical and mechanical properties of the polymercomposites.

Effect of water absorption on flexural properties

Flexural strength, maximum flexural strain, and flex-ural modulus, for jute/glass fiber-reinforced unsatu-rated polyester hybrid composite, after exposure tovarious environmental conditions, are shown inFigure 3(a)–(c), respectively. Each value represents theaverage data of three specimens. Consequently, theflexural stress–strain curves, corresponding to the sam-ples immersed in distilled water, sea water, and theacidic solution, are depicted in Figure 4(a)–(c), respec-tively. Figure 3 shows that for all environmental con-ditions, as the immersion time increases, both flexuralstrength and flexural modulus decrease. Jute fiber is anatural fiber, which tends to absorb high amounts ofmoisture after exposure to aqueous environments andthis may lead to a higher degradation rate. This can

also be related to the weak fiber–matrix interface, dueto water absorption after exposure to the aqueous envi-ronments.9 From the figure, it was found that there aresome extraordinary increases in strength and modulus,during the immersion. This is due to the presence ofglass fiber in the hybrid composite. During immersionin the aqueous environments, all the voids and crackswithin the composite would be filled with water, andthe absorbed water molecules act as a plasticizer, toimprove its bending strength and stiffness.28 However,excessive water absorbed may weaken the fiber–matrixinterface. On the other hand, the maximum flexuralstrain changes unpredictably. Jute fiber tends to be duc-tile once the loss of cellulose in its structure after wateris absorbed into its structure and integrity has takenplace.9 Glass fiber showed one of its natural properties,which is a high resistance to water absorption.

For comparison purposes, the flexural properties forglass fiber-reinforced unsaturated polyester-reinforcedpultruded composite and jute fiber-reinforced unsatu-rated polyester-pultruded composite, are shown inFigure 3(a)–(c). The flexural strength for polyesterresin is shown in Figure 3(a).29 Both of the unsaturatedpolyester (UP)/glass and UP/jute samples are made ofthe same fiber:matrix ratio i.e., 70:30, respectively. ForUP/glass-pultruded composite flexural properties, thedata is obtained from standard samples i.e., without

Figure 5. (a) Compression strength, (b) maximum compression strain, and (c) compression modulus for jute–glass fiber-reinforced

unsaturated polyester hybrid composite after exposed to environmental conditions.



any immersion process. This is because unsaturatedpolyester and glass fiber are hydrophobic to moisture,and thus, do not absorb water. The 21-day period ofimmersion is too short for any significant changes tothe composites and its properties. On other hand, theUP/jute-pultruded composite flexural properties areobtained after 21 days of immersion for each solution.By referring to Figure 3(a) the polyester resin showlower flexural, compared to the UP/jute-pultrudedcomposite and the hybrid-pultruded composites. TheUP/glass-pultruded composite shows a higher flexuralstrength. This statement is clearly proved and demon-strates that hybridization of jute fiber with glass fiberinsignificantly enhanced the flexural properties of thepultruded composites.

Effect of water absorption on compression properties

Figures 5(a)–(c) show the variations of compressionstrength, maximum compression strain, and compres-sion modulus for jute fiber-reinforced unsaturated poly-ester composite, after exposure to distilled water, seawater, and acidic solutions, respectively. Each valuerepresents the average data of three specimens. On

the other hand, Figure 6(a)–(c), show the correspond-ing stress–strain curves for each environmental condi-tion investigated (i.e., distilled water, sea water, and theacidic solution). Figure 5 indicates a trend of decreasein compression strength and compression modulus withan increasing immersion time. However, it was foundthat there are some extraordinary increases in strengthand modulus, during the immersion. These compres-sion results show a similar trend with the flexural test-ing discussed in the above section. There arefluctuations, as indicated by the error bars, causing var-iations in the results, which could be attributed to theuneven surfaces of the compression specimen. As aresult, a slightly eccentric applied load will cause pre-mature buckling in the composite materials, rather thanthe intrinsic compressive failure. This produced similarresults to those discussed in flexural testing.

The compression properties for glass fiber-reinforcedunsaturated polyester-reinforced pultruded compositeand jute fiber-reinforced unsaturated polyester-pul-truded composite are shown in Figure 5(a)–(c), forcomparison purposes. On the other hand, the compres-sion strength for polyester resin is shown in Figure 5(a).Both of the UP/glass and UP/jute samples are made of

Figure 6. Stress–strain curves for compression specimen of jute–glass fiber-reinforced unsaturated polyester hybrid composite after

exposed to (a) distilled water, (b) sea water, and (c) acidic solution.

Zamri et al. 9


the same fiber:matrix ratio i.e., 70:30, respectively. ForUP/Glass-pultruded composite compression properties,the data is obtained from the standard samples i.e.,without any immersion process. The reason why thissample has been taken into account was discussed ear-lier. By referring to Figure 5(a), the polyester resinshows lower compression strength compared to theUP/jute-pultruded composite and hybrid-pultrudedcomposites. Once again, the UP/glass-pultruded com-posite shows a higher compression strength comparedto the other pultruded composites. This also clearlyproves that hybridization of jute fiber with glass fiberinsignificantly enhanced the mechanical properties ofthe pultruded composites.

Conclusion

The study of water absorption effects, on the mechan-ical properties of jute/glass fiber-reinforced unsaturatedpolyester hybrid composite, has been performed underdifferent water conditions, which were distilled water,sea water, and acidic solutions at room temperature.From the results obtained, the following conclusionscan be drawn:

. The water absorption pattern is found to follow non-Fickian behavior. The highest values of diffusioncoefficient (D) and maximum moisture contentvalue (Mm) were recorded for specimens immersedin distilled water, then followed by the acidic solu-tion, and finally seawater.

. Hybridization of natural fibers with synthetic fibersdecreases the maximum moisture absorption andincreases the mechanical properties of thecomposites.

Acknowledgment

The authors are grateful to Universiti Sains Malaysia (USM-814023) for their assistance and contribution that has resultedin this article.

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