Synthesis and characterization of short Grewia optiva fiber-based polymer composites

Synthesis and Characterization of Short Grewiaoptiva Fiber-Based Polymer Composites

Amar S. Singha, Vijay Kumar ThakurMaterial Science Laboratory, National Institute of Technology, Hamirpur, Himachal Pradesh 177005, India

Natural fibers, such as Flax, Sisal, Hibiscus Sabdariffa,and Grewia optiva (GO) possess good reinforcingcapability when properly compounded with polymers.These fibers are relatively inexpensive, easily availablefrom renewable resources, and possess favorable val-ues of specific strength and specific modulus. The me-chanical performance of natural fiber-reinforced poly-mers (FRPs) is often limited owing to a weak fiber-matrix interface. In contrast, urea–formaldehyde (UF)resins are well known to have a strong adhesion tomost cellulose-containing materials. This article dealswith the synthesis of short G. optiva fiber-reinforcedUF polymer matrix-based composites. G. optiva fiber-reinforced UF composites processed by compressionmolding have been studied by evaluating their mechan-ical, physical, and chemical properties. This workreveals that mechanical properties such as: tensilestrength, compressive strength, flexural strength, andwear resistance of the UF matrix increase up to 30%fiber loading and then decreases for higher loadingwhen fibers are incorporated into the polymer matrix.Morphological and thermal studies of the matrix, fiber,and short FRP composites have also been carried out.The swelling, moisture absorbance, chemical resist-ance, and water uptake behavior of these compositeshave also been carried out at different intervals. Theresults obtained lay emphasis on the utilization ofthese fibers, as potential reinforcing materials in bio-based polymer composites. POLYM. COMPOS., 31:459–470, 2010. ª 2009 Society of Plastics Engineers

INTRODUCTION

Fiber-reinforced polymer (FRP) composites constitute

an important proportion of the engineered materials mar-

ket ranging from everyday products to sophisticated niche

applications [1]. These materials are able to meet diverse

design requirements with their good mechanical proper-

ties, simplicity in fabrication, economy, and significant

weight savings as well as high strength-to-weight ratio

compared with the conventional materials. Synthetic fibers

such as glass, aramid, carbon fibers, etc. have been exten-

sively used over the last decades as reinforcements of

polymeric matrices [2–4]. They are incorporated into mat-

rices with the main objective of improving the mechanical

properties of the polymer reducing the cost of the final

products. These synthetic fibers differ in price and me-

chanical properties, generally in an inverse manner: the

more expensive the fiber, the better the mechanical prop-

erties. Recently, the increasing environmental conscious-

ness throughout the universe has enforced the researchers

from various fields to produce new polymeric materials

and processes that improve the ecological quality of a

number of products [5–8]. In particular, in the past few

years, the synthesis of polymers starting from renewable

resources is an object of significant research efforts

because of the increasing environmental concerns. The

chemistry of the renewable resources applied to the pro-

duction of new feasible ecofriendly polymer products is

an issue of this research. This issue has captured the

global attention of researchers. The growth of natural

FRPs has been recently a subject of interest for both sci-

entists and technologists [9–11]. Recent developments in

the fields of natural fibers have shown that it is possible

to obtain an ecofriendly polymeric material that possesses

sufficient properties [12–15]. These natural fibers have a

number of advantages over synthetic fibers. When com-

pared with traditional synthetic fibers, these natural fibers,

which have low density, impart the polymer composite

various benefits such as lowering of toxicity, low machine

wear, less fuel consumption, and a high degree of flexibility

[12, 16–18]. These unique properties make the FRP com-

posite best material for fabrication of different components

in aerospace, automobile, sports, defense, marine industries,

etc. [13–15, 19, 20]. In fact, natural fibers have been found

to improve the mechanical properties of the reinforced poly-

mer matrix and, furthermore, reduce the total weight

because of their low density [21, 22].

Polymer composites are the materials which are

obtained by embedding fibers in a polymeric matrix to

improve its mechanical, thermomechanical, electrical,

sound-damping properties, etc. Several methods, such as

filament winding process, pultrusion method, vacuum bag-

Correspondence to: Amar Singha; e-mail: [email protected]

Contract grant sponsor: Ministry of Human Resource Development

(MHRD), New Delhi.

DOI 10.1002/pc.20825

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2009 Society of Plastics Engineers

POLYMER COMPOSITES—-2010

ging technique, autoclave technique, compression mold-

ing, resin transfer molding, etc. have been developed to

manufacture FRP products [21–25]. Among these, com-

pression molding is a very good technique [10, 11, 16].

Among various types of natural biomaterial, GrewiaOptiva fibers have high potential as a reinforcing material

in polymer composites. Traditionally, this fibrous material

belonging to Himalayan region has been used by the local

people for making low cost articles like socks, boots,

mats, ropes, bags, etc. since ancient time. While going

through the annals of literature, not much information is

available on the application of this fiber as reinforcing

material in the polymer composites [5–12, 16–18]. Keep-

ing in view the easy availability of this biomass, sincere

efforts have been made by our research group to substi-

tute the synthetic fibers by natural fibers as reinforcing

material for the synthesis of urea–formaldehyde (UF) ma-

trix-based polymer composites. The basic objectives of

this study were:

c Effective utilization of G. optiva fibers in the fabrication

of fiber-reinforced green polymer composites.

c Development of a novel and simple methodology for

fabrication of these FRP composites.

c To study the effect of fiber loading on the various

mechanical properties of the polymer matrix and the

polymer composites.

c To analyze the influence of fiber content and surface

chemistry on the mechanical properties of UF polymer

and its respective composites.

c To study the interaction between the UF resin and the G.optiva fibers using scanning electron microscopy (SEM).

c To analyze the thermal behavior of fiber, polymer ma-

trix, and FRP composites.

c To study the physical and chemical properties of poly-

mer matrix and FRP composites.

EXPERIMENTAL METHODOLOGY

Material and Methods

Urea, formaldehyde solution, and sodium hydroxide

supplied by Qualigens Chemicals were used as received.

UF was used as matrix polymer. The lignocellulosic G.optiva fibers of dimensions 3 mm were used as reinforce-

ment for the synthesis of FRP composites.

Synthesis of Urea–Formaldehyde Resin

Urea and formaldehyde were synthesized by the stand-

ard method used in the laboratory [23]. Urea and formal-

dehyde were taken in different molar ratio (1.0:1.0,

1.0:1.5, 1.0:2.0, 1.0:2.5, and 1.0:3.0) by weight, in the

reaction kettle and mixed with the help of mechanical

stirrer. The reaction was carried out in an alkaline me-

dium. Because the reaction is exothermic, proper care

was taken to maintain the temperature between 50 and

608C, for initial 2 h. Then temperature was increased to

80–858C at pH 5.5–6 and the mixture was heated at this

temperature, till the resinification started. UF resin formed

as a result of resinification is a colorless to milky viscous

liquid, with faint formaldehyde odor. After the completion

of resinification, the resin was cooled and ammonium

chloride was added in pinch to increase the bonding

between the molecules. The resin synthesized was then

transferred to a specially made mould. Resin sheets of

size 150 mm 3 150 mm 3 5.0 mm were prepared by a

closed mold method as described elsewhere [6]. The mold

was then closed and kept under pressure (4.0 MPa) until

the resin was set into a hard mass. All the specimens

were postcured at 1208C for 7 h.

Synthesis of Polymer Composites

G. optiva fibers collected from local resources were

initially thoroughly washed with detergent powder. These

fibers after washing with detergent powder were soaked

in hot distilled water for 7 h, air dried for 60 h, followed

by oven drying at 105–1108C for 12 h. The above fibers

were then chopped into dimensions of 3 mm. In compari-

son to raw fibers, the dried fibers have been found to

increase the mechanical properties of polymer composites.

This behavior can be attributed to the reduction of humid-

ity. The presence of moisture contents (MCs) in the natu-

ral fibers affects the chemical reaction between the ligno-

cellulosic fiber and polymer matrix resulting in poor

fiber-matrix adhesion. Water absorbed has OH2 anions

which act as dipoles and prevents close contact between

the fiber and the matrix [10, 16]. The reduction of these

anions at the fiber surface increases interface compatibil-

ity, and increase the efficiency of the stress transfer from

the matrix to the fibers and hence increase in mechanical

properties. Therefore, to prevent voids and a poor fiber-

matrix bonding, it is necessary to dry the fibers [10–12,

16–18].

The dried G. optiva fibers of dimension 3 mm were

mixed thoroughly with UF (1:2.5) resin, using a mechani-

cal stirrer with different loadings (10, 20, 30, and 40%) in

terms of weight. Then, the above mixture was poured into

specially made moulds. The surfaces of molds were

coated on inside with oleic acid to avoid adhesion of the

mixture and to allow easy removal of the composites. The

mixture was then spread equally on the surface of the

mold. Composite sheets of size 150 mm 3 150 mm 35.0 mm were prepared by compression molding technique

[12, 16–18]. Compression molding was performed in a

hot press using a mold preheated to 1108C. The material

first placed in a hot open mold was left for about 5 min,

and then the mold was closed. Composite sheets were

prepared by hot pressing the mold at 1308C for 30 min.

The pressure applied ranges from 3 to 4 MPa depending

on the loading of reinforcing material. All the specimens

were then postcured at 1208C for 12 h. During the fiber-

composite fabrication process, the resin undergoes poly-

460 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

merization reaction with itself and chemical reaction with

cellulosic under various environmental conditions, which

comprise temperature, MC, relative humidity (RH), water

vapor pressure, etc. These variables could significantly

affect the resin curing along with bonding behavior and

consequently affect the final performance of polymer

composites. The longer curing time is required for com-

plete conversion of resin into an insoluble three-dimen-

sional network along with the formation of mechanical

bonds between the fiber and resin matrix.

Mechanical Testing

Tensile, compressive, flexural, and wear tests were per-

formed on specimens cut from the above synthesized

polymer composite material. Testing of samples for ten-

sile, compressive, and flexural strengths was done on

Computerized Universal Testing Machine (HOUNSFIELD

H25KS). Wear testing was done on a Wear & Friction

Monitor (DUCOM- TR-20L). Seven specimens of each

sample were used for the measurement of the above men-

tioned mechanical properties at ambient laboratory envi-

ronment and average results have been reported.

Tensile Test

The tensile strength test was conducted on Computer-

ized Universal Testing Machine (HOUNSFIELD H25KS).

The specimens of dimension 100 mm 3 10 mm 3 5 mm

were used for analysis. The span length was fixed at 60

mm, and the test was conducted at the constant strain rate

of 10 mm/min in accordance with ASTM D 3039

method.

Compressive Test

The compression test was also conducted on Compu-

terized Universal Testing Machine (HOUNSFIELD H25

KS) in accordance with ASTM D 3410 method. The

specimens of dimension 100 mm 3 10 mm 3 5 mm

were used for analysis. The test was conducted at the con-

stant strain rate of 10 mm/min, whereas the total com-

pression range was 7.5 mm.

Flexural Test

The three-point bend flexural test was conducted in ac-

cordance with ASTM D 790 method. For flexural analy-

sis, the specimens of dimension 100 mm 3 10 mm 3 5

mm were used. Span length was fixed at 50 mm, and

the test was conducted at the constant strain rate of 2.54

mm/min.

Wear Test

The wear test of the sample was conducted on Wear &

Friction Monitor (DUCOM- TR-20L). Wear resistance of

composites was carried-out as per ASTM D 3702 method.

The wear of the sample was determined in terms of

weight loss.

Morphological and Thermal Analysis of Samples

To evaluate the changes in the composite surface mor-

phology, fibers and matrix were analyzed by SEM. The

excitation energy used was 5 keV. To achieve good elec-

tric conductivity, all samples were first carbon sputtered

followed by sputtering a gold palladium mixture before

examination. SEM micrographs of the samples show the

morphology of the biocomposites prepared. These micro-

graphs clearly show the difference between unloaded and

loaded UF matrix. Thermal analysis of natural and syn-

thetic polymers gives us good account of thermal stability

of materials. Thermogravimetric analysis (TGA), differen-

tial thermal analysis (DTA), and derivative thermogravi-

metric analysis (DTG) studies of samples were carried out

in nitrogen atmosphere on a thermal analyzer (Perkin

Elmer) at a heating rate of 108C/min. TGA is used to

characterize the decomposition and thermal stability of

materials under a variety of conditions and to examine

the kinetics of the physicochemical processes occurring in

the sample. Basically, in this method, a change in thermal

stability is examined in terms of percentage weight loss

as a function of temperature. The mass change character-

istics of a material are strongly dependent on the experi-

mental conditions, such as sample mass, volume and

physical form, the shape and nature of the sample holder,

the nature and pressure of the atmosphere in the sample

chamber, and the scanning rate all have important influen-

ces on the characteristics of the recorded TG curve. At

the same time, DTA involves comparing the precise tem-

perature difference between a sample and an inert refer-

ence material, while heating both. In thermal analysis

from time to time, overlapping reactions are difficult to

resolve, and in some cases, resolution can be improved by

hindering escape of evolved gas from the sample by plac-

ing a loosely fitting lid on the crucible, changing the

packing or form of the sample, choosing a different cruci-

ble, or by varying the heating rate. Altering the experi-

mental conditions may change the relative rates of the

overlapping reactions and led to the better resolution. Of-

ten, it is undesirable to alter optimized experimental con-

ditions and in this case overlapping reactions may be

more clearly resolved by plotting the derivative TG curve.

In DTG the mass change with respect to temperature (dm/dT) is plotted against temperature. A point of inflection in

the mass change step becomes a minimum in the deriva-

tive curve and for an interval of constant mass dm/dT is

zero, a peak in the DTG curve occurs when the rate of

mass change is a maximum. DTG peaks are characterized

by the peak maximum (Tmax) and the peak on set temper-

ature (Te). The area under a DTG curve is proportional to

the mass change, and the height of the peak at any tem-

perature gives the rate of the mass change at that temper-

DOI 10.1002/pc POLYMER COMPOSITES—-2010 461

ature. Although a DTG curve contains no more informa-

tion than the original TG curve, DTG curves are fre-

quently preferred when comparing results with DTA

curves because of the visual similarity.

Swelling, Moisture Absorbance, and Chemical Resistance

The effect of environmental conditions on the compo-

sites has been a subject of much debate and many studies

have been reported in the literature. The commercial via-

bility of the newly fabricated fiber-reinforced resin ma-

trix-based composites lies in their physical and chemical

properties. Therefore, a comprehensive study on swelling

behavior in different solvents, moisture absorbance (Mabs)

at different humidity levels, and chemical resistance

behavior against 1 N HCl and 1 N NaOH of UF compo-

sites has been carried out.

Swelling Behavior. Swelling behavior of the composite

samples was evaluated by studying the swelling in differ-

ent solvents such as methanol, isobutanol, carbon tetra-

chloride, and water. For the swelling test, the specimens

were dried in an oven for a specified time at a particular

temperature and then cooled in a dessicator. The initial

samples of known weight (Wi) were immersed in 100 ml

of different solvents at room temperature for 15 days. The

samples were filtered and the excess solvent was removed

with the help of filter paper, patted dry with a lint free

cloth, and then final weight (Wf) was noted. The percent

swelling was calculated from the increase in initial weight

in the following manner

Percent swelling PSð Þ ¼ Wf �Wi

Wi

3 100

Moisture Absorbance. Mabs studies onto different sam-

ples were carried out at various humidity levels (varying

from 20 to 100%). Mabs was found out by placing the

known weight (Wi) of dry samples in a humidity chamber

(Swastika make), which was set at a particular humidity

level for about 12 h, and then the final weight (Wf) of the

samples exposed at a particular RH was taken. The per-

cent Mabs was then calculated in the following manner:

%Moisture absorbance %Mabsð Þ ¼ Wf �Wi

Wi

3 100

Chemical Resistance. For the chemical resistance test,

the dried specimens were immersed in 100 ml of 1 N

NaOH and 1 N HCl for different intervals of time (24–

144 h). After this, the samples were filtered out, dried,

and weighed. The percent chemical resistance (Pcr) was

calculated in term of weight loss in the following manner:

Percent chemical resistance Pcrð Þ ¼ Ti �Waci

Ti3 100

where Ti is the initial weight and Waci is the weight after

certain interval.

RESULTS AND DISCUSSION

Evaluation of mechanical properties of polymeric com-

posites materials is one of the most important parameter

which decides their application in various fields. The me-

chanical properties, such as tension, compression, stress–

strain, phase composition of fiber composites have been

studied. These properties depend upon the nature of the

matrix material, nature of the fiber-matrix interfaces, dis-

tribution and orientation of the reinforcing fibers, and of

the interphase region. Hence, the optimization of the

fiber-matrix adhesion is most essential for better physical

and mechanical properties of these natural FRP compo-

sites. To achieve good fiber reinforcement, the interfacial

strength between the fiber and matrix is the most essential

factor [10–12, 16–18]. For a composite to be an effective

load-bearing system, both natural fibers and matrix must

cooperate. This cooperation between the fibers and the

matrix will not exist without the presence of the interface.

The interfacial strength depends on the surface topology

of the fiber. The interface acts as a ‘‘binder’’ and transfers

load between the matrix and the reinforcing fibers. The

interfacial area plays a major role in determining the

strength of composite material because each fiber forms

an individual interface with the matrix. Interfacial bond-

ing is a result of good wetting of the fibers by the poly-

mer matrix as well as the formation of a chemical bond

between the fiber surface and the matrix [10–12, 16–18,

20, 24]. Hence, the interface plays a key role in control-

ling the mechanical properties of cellulosic FRP compos-

ite. The adhesion between cellulosic fiber and polymer

matrix is usually the strongest in polar polymers capable

of forming hydrogen bonds with hydroxyl groups avail-

able on the fiber surface.

Mechanism for Synthesis of Urea–Formaldehyde Resin

The above mechanism involves two important steps

[10, 11]. In the first step, reaction between urea and form-

aldehyde form methylol urea. As urea is tetrafunctional,

therefore, initial reaction in the presence of excess of

formaldehyde (when compared with urea) may lead to the

formation of tetra methylol derivative of urea (Fig. 1A).

The rate at which methylol urea (I) and (II) are formed

depends on the temperature, pH, and the ratio of formal-

dehyde-to-urea (F/U). The controlled formation of dime-

thylol urea can be achieved in slightly alkaline reaction

medium (pH of 7–8) [12]. Further the methylol ureas

being nonadhesive in nature do not undergo condensation

to form polymer molecules. To achieve this condensation,

further reaction is carried out in slightly acidic medium


(pH 5.5–6) at a temperature of 80–908C. The above con-

densation results in the formation of crosslinked polymer

structures (Fig. 1B). After sufficient crosslinking has

taken place, the reaction is stopped by neutralization of

the reaction medium by adjusting the pH level at 7.5–8.

This step is very important because if the reaction is

allowed to continue for a long time, then excessive cross-

linking will lead to the gelatization of the resin.

Optimization of Urea–Formaldehyde Resin

Optimization of UF resin was done by taking into

accounts the mechanical properties such as tensile

strength, compressive strength, flexural strength, wear

resistance, etc.

Tensile Strength. It was observed that UF samples of

ratio 1.0:2.5 were able to sustain more loads when com-

pared with samples of other ratios [10, 11]. This ratio

(1.0:2.5) could bear a maximum load of 128.125 N with

an extension of 1.84 mm (Fig. 2A). On the other hand,

samples of other ratios bore low loads.

Compressive Strength. It is evident from the (Fig. 2B)

that the samples of ratio 1.0:2.5 could bear a maximum

load of 991 N at a compression of 3.51 mm.

Flexural Test. It is evident from the (Fig. 2C) that the

samples of ratio 1.0:2.5 could bear a maximum load of

59 N at a deflection of 0.776 mm.

FIG. 1. A: Formation of methylol derivatives of urea. B: Condensation of methylol urea by elimination.


FIG. 2. Load elongation/deformation/deflection and wear resistance curve of UF resin (A–D). [Color figure

can be viewed in the online issue, which is available at www.interscience.wiley.com.]

FIG. 3. Load elongation/deformation/deflection and wear resistance curve of fiber-reinforced composites

(A–D). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]


Wear Resistance. It was observed that wear rate of

samples of ratio 1.0:2.5 was less when compared with

any other samples (Fig. 2D).

The wear resistance results also support the tensile,

compressive, and flexural results, as brittle materials have

higher wear rate and lower tensile, compressive, and flex-

ural strength. The samples with lower amount of formal-

dehyde have higher concentration of dimethylol urea,

which makes it amorphous in nature but as the ratio of

formalin increases the concentration of dimethylol urea

decrease because of the formation of ether linkage and

two/three-dimensional crosslinking. The ratio (1.0:2.5) of

urea and formaldehyde showing optimum mechanical

properties was taken for further preparation of cellulosic

fiber-reinforced UF composites.

Mechanical Properties of UF Matrix-Based Composites

Tensile Strength. It was observed that tensile strength

of composites increases on reinforcement with G. optivafiber. Composites with 30 wt% loading bear maximum

load followed by 40, 20, and 10% loadings (Fig. 3A). It

was observed that polymer composites with 30, 40, 20,

and10% loading bore loads of 497.0, 435.0, 411.53, and

341.49 N, respectively.

Compressive Strength. The compressive properties of

the composites as a function of load and deformation are

presented in Fig. 3B. From the graph, it is evident that

first compressive force increased with the increase in fiber

content up to 30% and then decreased with further

increase in fiber content. It is clear from the figure that

composites with 30, 40, 20, and 10% loading bore loads

of 3900.00, 3700.0, 3543.5, and 2753.5 N, respectively.

Flexural Strength. Similar trends as obtained in tensile

and compressive strength tests were also observed for

flexural strength results. The flexural properties of sam-

ples as a function of force (in terms of load) and deflec-

tion are shown in Fig. 3C. It is clear from the figure that

composites with 30, 40, 20, and 10% loading bear a load

of 197.0, 177.0, 146.0, and 131.0 N, respectively.

Wear Test. It is evident from Fig. 3D that the wear rate

of UF matrix decreased appreciably as reinforcement with

G. optiva fibers, whereas maximum wear resistance

behavior was shown by a composite with 30% loading,

followed by 40, 20, and 10% fiber loading.

Stress–Strain Analysis

Tensile Stress–Strain Curve. Tensile stress–strain

curves were constructed from the load elongation meas-

urements. The plots of stress vs. strain for FRP compo-

sites are shown in Fig. 4A. From figure, it is clear that in

the elastic region stress was linearly proportional to strain.

When the load exceeded a value corresponding to the

yield strength, the specimen underwent gross plastic de-

FIG. 4. Stress–strain curves of composites under tensile, compressive, and flexural tests (A–C). [Color

figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

TABLE 1. Parameters obtained from tensile stress–strain curve at different loadings.

Fiber

loading (wt%)

Ultimate tensile

stress (N/mm2)

Yield strength

(N/mm2)

Fracture stress

(N/mm2)

Standard

deviation

Tensile modulus

(N/mm2)

UF resin 2.56 1.95 2.27 0.97 87.47

10 6.82 5.37 6.24 1.04 169.62

20 8.02 6.25 7.15 1.19 201.35

30 9.94 8.04 9.32 1.37 263.95

40 8.70 6.96 7.95 1.54 229.46


formation. It was permanently deformed if the load was

released to zero. Different parameters derived from the

stress–strain curve are shown in Table 1.

Compressive Stress–Strain Curve. Compressive

stress–strain curves also were constructed from the load

deformation measurements. The plots of compressive

stress vs. strain for polymer composites are shown in Fig.

4B. Different parameters derived from the stress–strain

curve are shown in Table 2.

Flexural Stress–Strain Curve. Plots of flexural stress

vs. strain for FRP composites are shown in Fig. 4C. Dif-

ferent parameters derived from the stress–strain curve are

shown in Table 3. The deviations from linearity in case

of tensile/compressive and flexural stress–strain curves are

an indication of the beginning of initial matrix cracking.

The first major change in slope in the curves under ten-

sile/compression/flexural tests is the sign of a major crack

in the matrix or the beginning of fiber failure. From the

foregoing results, it is clear that to achieve good fiber

reinforcement, interfacial bonding between the fiber and

polymer matrix is the most essential factor. Aqueous UF

resins can penetrate into the cell wall of cellulosic G.optiva fiber and the amorphous region of cellulose fibers.

Furthermore, UF resins can, at least theoretically, react

with primary OH groups in cellulose and form covalent

bonds by condensation [10]. Whether covalent or hydro-

gen bonds dominate after conditions pertaining to UF

molding compounds is not fully understood. However,

resin penetration will give mechanical interlocking and

thus provide high interfacial strength. Supplementary

from the results, it can be concluded that the tensile

strength of G. optiva/UF composites is mainly dependent

on the strength and modulus of fibers, the strength and

chemical stability of the matrix, and the effectiveness of

the bonding strength between polymer matrix and fibers in

transferring stress across the interface [10, 11, 16, 25]. The

ultimate compressive strength of the composite mainly

depends on the strength of polymeric resin, whereas the

compressive modulus of the composite depends on its rein-

forcement. In general, composite specimens under com-

pression test fail by shear or kinking mechanism [26]. Fur-

ther flexural strength and modulus are controlled by disper-

sion extent. The lower the dispersion extent the higher is

flexural strength. The dispersion extent of fibers determines

how many fibers are neighbored or dispersed. The flexural

strength depends on the fiber types at the compressive side

and dispersion extent of fibers. However, the flexural mod-

ulus depends only on the composite rigidity of the com-

pressive side, but rarely the dispersion extent of fibers.

Normally, the flexural modulus is very sensitive to the ma-

trix properties and matrix/fiber interfacial bonding [27]. It

can be concluded that the flexural properties depend on the

compressive stress at the top region to bear applied load

directly and the tensile stress at the bottom region.

It has been observed that mechanical properties of G.optiva/UF composites increase up to 30% fiber loading

and then decrease. This behavior of polymer composites

can be explained because of fiber–fiber contact at higher

fiber loading. The mechanical strength of UF composites

levels off at high fiber loading. Hence, lower results are

obtained for 40% loading. Because of poor bonding

between fiber and matrix at low % of fiber loading, G.optiva fibers were not capable of transferring load to one

another and hence stress accumulated at certain points of

the composite, which led to lower mechanical properties.

Further during the preparation of polymer composites

with 30% fiber loading, G. optiva fibers acted as carrier

of load and transferred stress from the matrix along the

reinforcement, which resulted in composites with good

mechanical properties.

TABLE 2. Parameters obtained from compressive stress–strain curve at different loading.

Fiber loading

(wt%)

Ultimate compressive

stress (N/mm2)

Yield strength

(N/mm2)

Fracture

stress (N/mm2)

Standard

deviation

Compressive

modulus (N/mm2)

UF resin 19.82 18.07 19.27 1.07 340.00

10 55.07 46.39 53.79 1.48 901.38

20 70.87 62.7 67.48 1.57 1146.00

30 78.00 70.37 75.94 1.29 1287.00

40 74.00 64.28 70.39 1.35 1215.00

TABLE 3. Parameters from flexural stress–strain curve for different % age loading.

Fiber loading

(wt%)

Ultimate flexural

stress (N/mm2)

Yield strength

(N/mm2)

Fracture stress

(N/mm2)

Standard

deviation

Flexural

modulus (N/mm2)

UF resin 17.7 11.35 15.17 1.15 1900.77

10 39.3 29.98 36.13 1.05 2578.74

20 43.8 31.22 39.67 1.26 2874.01

30 59.1 48.87 57.53 1.28 3877.95

40 53.1 45.38 51.07 1.32 3484.25


Swelling, Moisture Absorbance, and Chemical ResistanceBehavior of Polymer Composites

Polymer composites with different loadings show dif-

ferent swelling behavior in different solvents (Table 4)

The swelling behavior of composites in different solvents

follows the trend: H2O [ CH3OH [ C4H9OH [ CCl4.

The swelling behavior of polymer composites increases

with increase in percent loadings because of greater

affinity of water for OH groups present in the FRP

composites.

The Mabs behavior at different humidity levels as a

function of fiber loading has been depicted in Table 5. It

has been found that Mabs increases with increase in hu-

midity level ranging from 20 to 100%.

In case of chemical resistance behavior, it has been

observed that resistance toward chemicals decreases with

the increase in % loading (Table 6). This may be because

of increase in fiber content in the composite, which is vul-

nerable to the chemical attack resulting in decreased re-

sistance toward the chemicals.

Morphological Study of Biocomposites

Morphological results clearly show the difference in

the morphology of the polymer composites when com-

pared with that of fiber and the polymer matrix separately

(Fig. 5A–F). Morphological results clearly show that

when polymer resin matrix was reinforced with the differ-

ent loadings of fiber, morphological changes took place,

depending on the bonding between the varying loading of

fiber and the polymer resin matrix. In case of lower fiber

loading (10 or 20%), the content of polymeric resin being

higher, there was lower bonding between the matrix and

the reinforcement (Fig. 5C and D), and hence mechanical

properties had lower values when compared with 30%

fiber loading. In case of 30% fiber loading, there was inti-

mate mixing of the reinforcement with the resin matrix

(Fig. 5E), and hence resulting polymer composite materi-

als had higher mechanical properties. However, at higher

fiber content (beyond 30%), agglomeration of fibers took

place, which resulted in decreased mechanical properties

(Fig. 5F).

Thermal Analysis of UF Resin and Its Biocomposites

TGA of materials such as raw G. optiva fiber, poly-

meric UF resin, and biocomposites studied was investi-

gated as a function of % weight loss with the increase in

temperature. In case of raw fiber, in the beginning depoly-

merization, dehydration and glucosan formation took

place between the temperature ranges of 26.0–190.08Cfollowed by the cleavage of C��H, C��C, and C��O

bonds. The initial decomposition temperature (IDT) has

been found to be 2008C and the final decomposition tem-

perature (FDT) to be 5018C. On the other hand, in case

of UF resin, it is single-stage decomposition and the

observed IDT is 238.08C and the final decomposition of

the resin took place at 993.08C. It has been observed that

for biocomposites (10%) IDT is 229.08C and the final

decomposition of the composite took place at 810.08C.These results indicate that the presence of cellulose fibers

affects the degradation process of the biocomposites.

The IDT and FDT of resin, fiber, and biocomposite are

presented in the Figs. 6–8. These studies are further sup-

ported by DTA and DTG (Figs. 6–8).

The TG and DTA curves reveal that the G. optivafiber, UF resin, and fiber-reinforced composites decom-

pose in different stages in the temperature range of 200–

501, 238–993, and 22928108C, respectively. Comparison

of magnitude and location of peaks found in the DTA/

DTG curves shows that there is a change in the thermal

behavior of polymer matrix when reinforced with cellu-

losic fibers [10–13, 16–18]. These results are consistent

with results reported earlier [10–12, 16–18, 28].

TABLE 4. Percentage swelling behavior of polymer composites in

different solvents.

% Loading Water Methanol Isobutanol Carbon tetrachloride

0 0.17 0.15 0.12 0.07

10 3.39 3.21 3.14 3.07

20 4.88 4.69 4.58 4.49

30 5.07 4.91 4.83 4.71

40 5.47 5.29 5.26 5.11

TABLE 5. Percentage moisture absorption behavior of polymer

composites at different relative humidity levels.

% Loading Hum ¼ 20 Hum ¼ 40 Hum ¼ 60 Hum ¼ 80 Hum ¼ 100

0 0.00015 0.00027 0.00039 0.00056 0.00073

10 0.00029 0.00043 0.00059 0.00074 0.00089

20 0.00043 0.00067 0.00075 0.00085 0.00096

30 0.00049 0.00073 0.00084 0.00095 0.00102

40 0.00062 0.00085 0.00093 0.00101 0.00109

TABLE 6. A chemical resistances (in terms of wt% loss) of polymer

composites at different time intervals against (a) 1 N HCl and (b) 1 N

NaOH.

% Loading 24 h 48 h 72 h 96 h 120 h 144 h

(a) 1 N HCl

0 1.07 2.12 3.07 4.21 4.67 5.03

10 3.32 4.51 5.34 6.24 7.42 9.05

20 4.64 6.05 7.08 7.53 8.93 10.09

30 5.93 6.78 7.89 8.64 9.47 11.46

40 6.54 7.89 9.05 10.02 10.84 12.49

(b) 1 N NaOH

0 1.47 2.57 3.07 4.57 4.73 5.41

10 3.64 4.75 5.48 6.69 7.67 9.21

20 4.79 6.19 7.19 7.82 9.05 10.23

30 6.05 6.92 8.04 8.79 9.55 11.59

40 6.89 8.04 9.15 10.18 10.93 12.79


CONCLUSIONS

Mechanical characterization of natural FRP biocompo-

sites has been carried out in terms of evaluation of their

tensile, compressive, flexural and wear resistance behav-

ior. These mechanical properties have been investigated

as a function of the chemical nature of matrix polymer

and the content of the reinforcing material. The quantum

of mechanical properties of reinforced UF resin-based

composites has been found to be higher when compared

FIG. 5. SEM images of (A) UF resin, (B) Grewia Optiva fiber, (C–F) composites with 10, 20, 30, and 40% loadings.

FIG. 6. TGA/DTA/DTG analysis of urea–formaldehyde resin.


with parent polymer matrix material (UF resin). This

behavior could be due to penetration of UF resins into

the cell wall of cellulosic G. optiva fibers and the amor-

phous region of cellulose fibers, which results in strong

adhesion between the UF matrix and lignocellulosic G.optiva fibers. Therefore, UF appears to be an interesting

matrix material for fabrication of natural fiber-reinforced

composites. The SEM micrographs show that the fibers

are randomly oriented in uniformally distributed polymer

matrix and are distributed over the whole sample sec-

tion. Thermal studies on composites have revealed that

polymer composites are slightly less stable than the par-

ent resin matrix at elevated temperature. The results of

swelling, moisture, and chemical resistance behavior of

composites are reported and these along with mechanical

properties could be used as determinant for the end

applications of these composites. However, major

restriction in the successful use of natural fibers as rein-

forcement in the fabrication of composite is that these

fibers have been found to increase their swelling, mois-

ture absorption along with reduced chemical resistance

characteristics because of the hydrophilic behavior of the

fiber. In spite of these few limitations, the G. optivafibers have immense scope in the fabrication of natural

FRP composites having vast number of industrial appli-

cations.

FIG. 7. TGA/DTA/DTG analysis of Grewia optiva fiber.

FIG. 8. TGA/DTA/DTG analysis of fiber-reinforced UF composites.


ACKNOWLEDGMENTS

The authors are thankful to Director, National Institute

of Technology, Hamirpur, Himachal Pradesh, India for

providing the basic laboratory facilities. They are also

highly grateful to unknown potential reviewer for health-

ier comments in improving the quality of present research

paper.

REFERENCES

1. J. Chu and J.L. Sullivan, Polym. Compos., 17(4), 556 (1996).

2. P.O. Hagstrand, Polym. Compos., 22(4), 568 (2001).

3. W. Thielemans and R.P. Wool, Polym. Comp., 26(5), 695(2005).

4. J. Andersons, E. Sparnins, and R. Joffe, Polym. Comp., 27,221 (2006).

5. B.N. Misra, I. Kaur, A. Gupta, V. John, and A.S. Singha,

Polym. Compos., 4, 411 (1996).

6. A.S. Singha, A. Shama, and B.N. Mishra, J. Polym. Mater.,25(1), 91 (2008).

7. A.S. Singha, A. Shama, and V.K. Thakur, Bull. Mater. Sci.,31(1), 7 (2008).

8. B.N. Mishra, R.K. Sharma, and A.S. Singha, J. Appl. Polym.Sci., 27, 1321 (1982).

9. G.S. Chauhan, S.S. Bhatt, I. Kaur, A.S. Singha, and B.S.

Kaith, J. Polym. Degrad. Stab., 69, 61 (2002).

10. A.S. Singha and V.K. Thakur, Int. J. Plast. Technol., 11,835 (2007).

11. A.S. Singha and V.K. Thakur, E-J. Chem., 5(4), 782 (2008).

12. A.S. Singha and V.K. Thakur, Bull. Mater. Sci., 31(5), 1

(2008).

13. A.S. Singha and V.K. Thakur, Int. J. Polym. Mater., 57(12),1059 (2008).

14. B.N. Mishra, R. Dogra, I.K. Mehta, and A.S. Singha, Die.Angew. Makromol. Chem., 83, 90 (1980).

15. A.S. Singha, B.S. Kaith, and B.D. Sarwade, Hungar. J. Ind.Chem., VESZPREM 30, 289 (2002).

16. A.S. Singha and V.K. Thakur, Iran. Polym. J., 17(7), 541(2008).

17. A.S. Singha and V.K. Thakur, E-J. Chem., 5(5), 1055

(2008).

18. A.S. Singha and V.K. Thakur, BioResources, 3(4), 1173

(2008).

19. C.A. Boynard and J.R.M. d’Almeida, Polym. Plast. Technol.Eng., 39, 489 (2000).

20. A.K. Bledzki and J. Gassan, Prog. Polym. Sci., 24, 221

(1999).

21. N.E. Marcovich, M.M. Reboredo, and M.I. Aranguren, Ther-mochim. Acta., 372, 45 (2001).

22. Y. Li, Y.W. Mai, and L. Ye, Compos. Sci. Technol., 60,2037 (2000).

23. B.V. Voorn, H.H.G. Smit, R.J. Sinke, and B. Klerk, Compo-sites A, 32, 1271 (2001).

24. B.S. Kaith, A.S. Singha, S. Kumar, and S. Kalia, Int. J.Polym. Mater., 57(1), 54 (2008).

25. Z. Gao and K.L. Reinfshinder, J. Compos. Technol. Res.,14, 201 (1992).

26. L.A. Carlsson and R.B. Pipes, Experimental Characteriza-tion of Advanced Composite Material, Hall, New York, 69

(1987).

27. B.J. Jang, J.Y. Liau, L.R. Hwang, and W.K. Shih, J. Reinf.Plast. Compos., 9, 314 (1990).

28. N. Sgriccia and M.C. Hawley, Compos. Sci. Technol., 67,1986 (2007).


Synthesis and characterization of short Grewia optiva fiber-based polymer composites

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