de gruter v k singh

DOI 10.1515/secm-2013-0318 Sci Eng Compos Mater 2014; aop

Vinay K. Singh *

Mechanical behavior of walnut ( Juglans L.) shell particles reinforced bio-composite Abstract: In the present work walnut particle reinforced

composite material was developed. Ten wt%, 15 wt%,

20 wt% and 25 wt% (weight percentage) of walnut parti-

cles were mixed with epoxy resin (CY-230). Scanning elec-

tron microscopy (SEM) shows that the walnut particles

were well dispersed in the epoxy resin matrix. Addition

of walnut particles increased the modulus of elasticity

of the bio composite. Addition of walnut particles in bio

composite decreased the ultimate strength both in com-

pression and tension. However, addition of walnut par-

ticles in bio composite increased the hardness. Flexural

modulus of elasticity also increased with increasing wal-

nut particles weight percentage, whereas flexural strength

and strain decreased with increased weight percentage of

walnut particles.

Keywords: composite material; environment; polymer;

walnut particles.

*Corresponding author: Vinay K. Singh, College of Technology,

G. B. Pant University of Agriculture and Technology, Pantnagar,

Uttarakhand-263145, India, e-mail: [email protected]

1 Introduction Composite is a material formed with two or more compo-

nents, combined as a macroscopic structural unit with

one component as a continuous matrix, and other as rein-

forcements with significantly different physical or chemi-

cal properties, which remain separate and distinct on a

macroscopic level within the finished structure. Normally,

the matrix is the material that holds the reinforcements

together and has lower strength than the reinforcements.

Most commercially produced composites use a polymer

matrix material called as resin solution [1] .

Composite resin technology has continuously evolved

since its introduction by Bowen [2] as a reinforced Bis-GMA

system. A major breakthrough in composite technology

was the development of photo-curable resins [3] . Con-

tinued development resulted in materials with reduced

particle size and increased filler loading that significantly

improved the universal applicability of light-cured com-

posite resins [4] .

As epoxy resins are a good solvent they are widely used

in industrial applications because of their high mechani-

cal and adhesion characteristics and chemical resistance

together with their curability in a wide range of tempera-

tures without the emission of any volatile byproducts.

The properties of epoxy-based organic/inorganic filled

composites can be finely tuned by an appropriate choice

of the structures of epoxy pre-polymer and hardener, type

and amount of inorganic filler. The composites have many

advantages over traditional silica powder or inorganic

mineral filled materials, including lower cost, lighter

weight, environmental friendliness and recyclability.

With growing environmental awareness, ecologi-

cal concerns and new legislation, bio particle reinforced

plastic composites have received increasing attention

during recent decades. Particleboards are of very recent

origin. The important aspect that has impacted favorably

on the development of these composite materials is the

possibility of incorporating waste agro-waste (agricul-

tural residues including stalks of most cereal crops, rice

husks, coconut fibers, bagasse, maize cobs, peanut shells,

and other wastes) product and recycled plastics with the

advantage of a positive eco-environmental impact. Due to

a worldwide shortage of trees and environmental aware-

ness, research on the development of composite prepa-

rations using various waste materials is being actively

pursued [5 – 7] . Based on a literature search [6, 8 – 10] ,

among the possible alternatives, the development of com-

posites using agricultural byproducts or agro-waste mate-

rials are currently the center of attention.

Particleboards are among the most popular materials

used in interior and exterior applications such as floor,

wall and ceiling panels, office dividers, bulletin boards,

cabinets, furniture, counter tops and desk tops [11] . The

production of particleboard can be related to the decided

economic advantage of low cost raw wood material,

inexpensive agents and simple processing. Therefore,

agro-waste instead of wood is widely used in the manu-

facturing of particleboard. Among the raw materials are

almond shell [12] , wheat straw [13] , bamboo [14] , cotton

seed hulls [15] , flax shiv [16] , rice straw-wood [17] , vine

prunings [18] , coir pith [19] and wood flour [20] . Polymers

such as urea-formaldehyde, phenol-formaldehyde, mela-

mine formaldehyde, polyethylene and polyvinylidene are

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2 V.K. Singh: Mechanical behavior of walnut shell particles reinforced bio-composite

commonly used as binders. Urea formaldehyde is the most

economic and useful adhesive among these binders.

The aim in the preset investigation with the objectives

was to develop a composite material containing different

percentages of walnut particle as the filler material and

investigate the mechanical behavior of different composites.

2 Materials and methods

2.1 Matrix material

2.1.1 Epoxy resin CY-230

Epoxy resin is widely used in industrial applications

because of its high strength and mechanical adhesiveness

characteristic. It is also a good solvent and has good chem-

ical resistance over a wide temperature range. Araldite

CY-230 purchased from M/s Petro Araldite Pvt. Limited

(Chennai, India) was used in the present investigation.

2.1.2 Hardener HY951

Hardener HY-951 purchased from M/s Petro Araldite Pvt.

Limited (Chennai, India) was used as the curing agent. In

the present investigation 8 wt% hardener HY-951 with epoxy

resin (CY-230) was used in all the material developed. The

weight percentage of hardener used in the present investi-

gation was as per recommendation of Singh and Gope [21] .

2.2 Reinforcing element

2.2.1 Walnut particles

The walnut particles are residues widely generated in

high proportions in the agro-industry by the grinding of

walnut shell. It is generally light to dark brown in color.

The walnut shells are underutilized, renewable agricul-

tural material. In the present study weight fraction (V f ) of

walnut particles varied from 10 – 25. Walnut particle pur-

chased from Allied Buss., Haldwani, India.

2.3 Optimization of weight percentage

2.3.1 Hardener (HY-951)

According to Misra and Singh [22] the per cent elongation,

yield strength and Young modulus reached the maximum

at 8 wt% of hardener (HY-951) when mixed with resin (CY-

230). Therefore in the present study 8 wt% of HY-951 has

been used.

2.3.2 Walnut particles

It was mixed with the resin up to the limits and the flow-

ability of the mixture was maintained for the purpose of

pouring the mixture into the vertical mould. No compres-

sion load was applied in this arrangement. The size of the

walnut particles was controlled by sieving with ASTM 40

and ASTM 80.

2.4 Method

Epoxy resin (CY-230), hardener (HY-951), and walnut par-

ticles with different weight percentages were used. Differ-

ent weight percentage (wt%) of walnut particles (15, 20,

25, 30 wt%) and epoxy resin were mixed by mechanical

stirring at 3000 rpm. Based on the curing curve [23] , the

solution obtained by mixing of walnut particles with resin

was kept in the furnace at a temperature of 90 ± 10 ° C for

2 h [21] . At intervals of 30 min the solution was taken out

of the electric furnace and remixed by a mechanical stirrer

at the same speed. After 2 h the whole solution was taken

out and allowed to cool to 45 ° C. When a temperature of

45 ° C was attained the hardener HY-951 (8 wt%) was mixed

immediately [21] . Due to the addition of hardener a highly

viscous solution was obtained which was remixed at high

speed by the mechanical stirrer. The viscous solution so

obtained was poured into different moulds for sample

preparation. Tensile, compression and bending tests were

conducted on a 100 kN servo hydraulic universal testing

machine (ADMET, USA) under displacement mode of

control of 1 mm/min. The results are presented and dis-

cussed in subsequent sections.

3 Results

3.1 Density

Density is one of the most important properties of the par-

ticle board material. The density of walnut particles rein-

forced composite for various weight percentages along

with density of epoxy resin are presented in Table 1 .

Table 1 reveals that increase in weight percentage of

reinforced particles, i.e., the walnut particles in the resin



V.K. Singh: Mechanical behavior of walnut shell particles reinforced bio-composite 3

solution decreases the density. This decrease in density of

25 wt% is about 1% of 10 wt%. The decrease in density can

be related to the fact that the walnut particles are light but

occupy a substantial amount of space. Hence there is a

general decrease in the density of all the composite mate-

rials with regard to the epoxy resin.

3.2 Water absorption capacity

Water absorption capacity is another crucial factor to be

taken into account when considering the effect of water

on the composite material developed. The soaking period

is 24 h taken as constant for all combinations of material.

The effect is presented in Table 2 .

The effect of water absorption was important in case

the material that has been developed when used for appli-

cations comes in contact of water. The water absorption

capacity was found to be higher for 25 wt% of walnut par-

ticle reinforced composite as compared with lower weight

percentage of walnut particles. This substantial increase

with regard to the epoxy resin could be because the

walnut particles here have maximum capacity for water

absorption compared to the resin particles.

3.3 Scanning electron microscope (SEM)

The state of dispersion of particles into the resin matrix

plays a significant role with regard to the mechanical

properties of the composite. In the present investiga-

tion SEM was carried out on LEO435V6 instrument and

voltage was kept 20 kV for bio composite containing dif-

ferent weight percentage of walnut particles to evaluate

the particle size, particle matrix interface and dispersion

of walnut particles in the epoxy resin matrix.

Figure 1 (A) and 1(B) show the SEM micrographs of dif-

ferent bio composite material investigated in the present

work. In all cases, good dispersion of walnut particles in

the resin matrix has been observed. Figure 1(A) and 1(B)

show the SEM micrograph of composite containing 10

wt% and 25 wt% of walnut particles, respectively. It is

seen in the figures that walnut particles are well dispersed

in the epoxy resin matrix in a preferred orientation.

Hence, from the above micrographs it is can be con-

cluded that due to uniform dispersion of walnut particles

in epoxy resin, a remarkable effect on the mechanical

properties may be obtained.

3.4 Mechanical properties

3.4.1 Tensile stress-strain curve

The mechanical properties of the walnut particles filled

epoxy resin bio composite materials were determined

by a 100 kN ADMET Servo hydraulic Universal Testing

Machine at 1 mm/min strain rate under displacement

control mode. The tensile stress-strain curve for walnut

particles reinforced composite materials containing

Table 1 Density of walnut particle reinforced composite.

S. no.

Walnut particle (10 wt%)

(g/cm 3 )


(g/cm 3 )


(g/cm 3 )


(g/cm 3 )

Epoxy (g/cm 3 )

1 1.169 1.161 1.159 1.157 1.179

2 1.172 1.167 1.164 1.156 1.184

3 1.168 1.163 1.159 1.157 1.186

Mean 1.168 1.161 1.159 1.156 1.179

SD 0.0020 0.0031 0.0029 0.0006 0.0036

Table 2 Water absorption capacity.

S. no.





Epoxy resin

1 0.554% 0.573% 0.581% 0.613% 0.543%

2 0.557% 0.579% 0.583% 0.629% 0.549%

3 0.548% 0.569% 0.582% 0.619% 0.546%

Mean 0.553% 0.573% 0.582% 0.620% 0.546%

SD 0.000045 0.00005 0.00001 0.00008 0.00003




10 wt%, 15 wt%, 20 wt% and 25 wt% of walnut particles

reinforced composite is shown in Figure 2 . All tests were

conducted as per ISO in 100 kN Servo hydraulic Univer-

sal Testing Machine. Brittle behavior can be seen in the

stress strain diagram due to addition of walnut parti-

cles in the epoxy resin matrix for all weight percentages

of walnut particles. However, it is seen that beyond 10

wt% of walnut particle the stress strain behavior does

not increase, therefore there is no improvement in load

bearing capacity.

3.4.2 Tensile properties

Tensile tests were carried out at strain rates of 1 mm/min.

The properties of the walnut particle of 10, 15, 20 and

25 wt% reinforced composite are presented in Table 3 .

The results of the ultimate tensile strength, percent-

age elongation in length and modulus of elasticity are

shown in the Table 3 for strain rate of 1 mm/min. Remark-

able differences can be seen on the ultimate tensile

strength of the bio composite material between 10 wt%

and over 10 wt% of walnut particles. It can be noticed that

for all specimens the ultimate tensile strength is highest

for the 10 wt% of walnut reinforced composite and is

163 MPa. Also, 10 wt% of walnut reinforced composite is

shown as maximum percentage elongation from amongst

the composite materials. It is seen that addition of walnut

particles significantly affects the ultimate strength and

180

160

140

120

100

Str

ess

(MP

a)

80

60

40

10 wt% walnut powder



25 wt% walnut powder20

00.00 0.01 0.02 0.03 0.04 0.05

Strain0.06 0.07 0.08 0.09

Figure 2 Stress-strain diagram under tension for different wt% of walnut particles.

A

B

Figure 1 (A) 10 wt% of walnut particles. (B) 25 wt% of walnut

particles.




percentage elongation. The ultimate tensile strength and

the modulus of elasticity of 10 wt% of walnut board are

almost 1.37 and 1.45 times higher than 15 wt% walnut

board, 1.43 and 1.51 times higher than 20 wt% walnut

board and 1.57 and 1.52 times higher than 25 wt% walnut

board. It is true for all particulate composite material;

no material can be fabricated which has more ultimate

strength from matrix material if reinforced material is

mixed at macro level. These behaviors are also shown in

Figure 3 .

On the basis of results obtained the effect of weight

fraction (V f ) on modulus of elasticity and ultimate strength

are shown in Equations 1 and 2 with a correlation coeffi-

cient greater than 0.99.

3 2

f f

f

Modulus of elasticity (MPa) -0.69V 42.44V

-858.1V 7040.0

= ++

(1)

3 2

f f

f

Ultimate strength (MPa) -0.058V 3.42V

-66.43V 544

= ++

(2)

3.4.3 Compressive strength

The compressive strength properties of the walnut particle

filled epoxy resin composite materials were determined

by 100 kN ADMET Servo controlled Universal Testing

machine at 1 mm/min strain rate under displacement

control mode.

The results of the compressive test are shown in

Table 4 . All tests were conducted under displacement

control mode. Stress strain diagram obtained from com-

pressive test is shown in Figure 4 .

A remarkable difference can be noticed in the value of

the compressive strength with different weight percentage

Table 3 Tensile properties of the composite materials.

Property





Ultimate tensile strength (MPa) 163.00 119.00 114.00 104.00

% Elongation in length 8.49 7.29 6.93 6.85

Modulus of elasticity (MPa) 2013.00 1388.00 1333.00 1328.00

205 9.0

8.5

Ultimate strength, MPa

Ulti

mat

e st

reng

th, M

odul

us o

f ela

stic

ity

Modulus of elasticity/10 MPa

% Elongation

Elo

ngat

ion

(%)

8.0

7.5

7.0

6.5

190

175

160

145

115

130

10010 12 14 16 18

Walnut particles (wt%)20 22 24

Figure 3 Variation of ultimate tensile strength, modulus of elasticity and elogation for different weight percentage of walnut reinforced

composite.

Table 4 Compressive properties of the composite materials.

Property





UTS (MPa) 261.00 231.00 191.00 135.00

% Reduction in length 49.95 46.61 45.69 31.48

Modulus of elasticity (MPa) 1578.00 1668.00 2321.00 2391.00




fUltimate strength (MPa)=-8.36V +350.8.

(4)

3.4.4 Hardness

As known, hardness implies a resistance to indentation,

permanent or plastic deformation of material. In a bio

composite material, filler weight fraction significantly

affects the hardness value of the hybrid composite mate-

rial. Hardness values measured on the Rockwell M-scale

showing the effect of weight percentage of walnut par-

ticles on the hardness values of hybrid composite are

presented in Table 5 . Variation of hardness with walnut

particles weight percentage is shown in Figure 6 .

It is found that hardness of neat epoxy resin (CY-230

+ 8 wt% of HY-951) is 56.4 MRH. The hardness of the fab-

ricated composite made of epoxy resin and 25 wt% is the

maximum and is 89.8 MRH. The hardness increases with

increase in walnut particles weight percentage. Figure 7

shows that with increasing of hardness, ultimate strength

in compression as well tension deceases and material

behaved in a brittle manner.

Table 5 Rockwell hardness values on M-scale for various filled

hybrid composites.

S. no

Walnut (10 wt%)

Walnut (15 wt%)

Walnut (20 wt%)

Walnut (25 wt%)

Resin

1 R-63 R-67 R-77 R-90 R-57

2 R-64 R-65 R-81 R-87 R-55

3 R-61 R-66 R-79 R-89 R-58

4 R-60 R-68 R-80 R-91 R-57

5 R-63 R-64 R-78 R-92 R-55

Mean R-62.2 R-66 R-79 R-89.8 R-56.4

SD 1.6431 1.5811 1.5811 1.9235 1.3416

050

55

60

65

70

Har

dnes

s (M

RH

)

75

80

90

85

5 10 15Walnut particles (wt%)

20 25

Figure 6 Hardness (MRH) for different weight percentage of walnut

reinforced composite.

300

250

200

Str

ess

(MP

a)

150

100

50

00 0.1 0.2 0.3

Strain

10 wt% of walnut particle15 wt% of walnut particle20 wt% of walnut particle25 wt% of walnut particle

0.4 0.5

Figure 4 Stress-strain diagram under compression for different

wt% of walnut particles.

310

280

250

220

190

160

13010 15 20

Walnut particles (wt%)25

30

35

40

50

45

Ultimate strength, MPa

% Reduction in length

Mod

ulus

of e

last

icity

, Ulti

mat

e st

reng

th

Modulus of elasticity/10 MPa

Red

uctio

n in

leng

th (

%)

Figure 5 Ultimate strength for different weight percentage of

walnut reinforced composite.

composition of walnut particle. It can be noticed that

addition of walnut particle improves the modulus of elas-

ticity of composite materials. It is found that ultimate com-

pressive strength of 10 wt% of walnut is about 261.0 MPa.

But increase in weight percentage of walnut particles, the

ultimate strength decreases considerably. Hence, taking

into consideration the requirement and the cost effective-

ness various composition of the reinforced material can be

taken. Variation in ultimate strength, percentage reduc-

tion in length and modulus of elasticity with respect to

different weight percentage walnut reinforced composite

are shown in Figure 5 .

On the basis of results obtained the effect of weight

fraction (V f ) on modulus of elasticity and ultimate strength

are shown in Equations 3 and 4 with a correlation coeffi-

cient >0.9.

fModulus of elasticity (MPa)=61.84V +907.3

(3)




The present result shows that a linear relation between

hardness and ultimate strength in tension and compres-

sion exists. The following correlation between hardness

and ultimate strength has been developed (Equations 5

and 6) with a correlation coefficient >0.9, where H is hard-

ness in MRH scale.

Ultimate compressive strength (MPa) -4.280H 522.3= +

(5)

Ultimate tensile strength (MPa)=-1.648H 247.3.+

(6)

3.4.5 Flexural strength

The flexural strength of the walnut particle filled epoxy

resin composite materials were determined by 100 kN

ADMET make servo controlled universal testing machine

at 1 mm/min strain rate under displacement control mode

using three point bend test. The results are presented in

Table 6 .

As depicted by the test data, amongst the composite

materials developed the 25 wt%, walnut reinforced com-

posite shows the best results with regard to the flexural

modulus of elasticity (1560 MPa) and also it is better than

10 wt% walnut reinforced composites with regard to the

flexural modulus of elasticity. But flexural stress and flex-

ural strain was found to be higher for 10 wt% walnut filled

composites as compared with others investigated in this

report.

4 Conclusions Epoxy bio composites reinforced with walnut particles

were prepared. Such bio composites were experimentally

characterized by means of microscopy, tensile, compres-

sion, hardness and bending test. Remarkable changes

in the mechanical properties have been noticed due to

addition of walnut particles in bio composite. Addition

of walnut particles increased the hardness, which is very

important property for particles board with sustainable

tensile and compressive properties.

Acknowledgments: The author expresses his gratitude

and sincere thanks to Department of Science and Technol-

ogy, India, for providing finance to carry out this research

work smoothly.

Received December 16 , 2013 ; accepted January 2 , 2014

280

260

240

Ultimate strength (compression)

Ultimate strength (tension)

220

200

Ulti

mat

e st

reng

th (

MP

a)

180

160

140

120

10060.0 70.0 80.0

Hardness (MRH)90.0

Figure 7 Variation of ultimate strength with hardness (MRH).

Table 6 Flexural strength properties for resin and composites materials.

Properties





Flexural modulus (MPa) 1360.0 1450.0 1500.0 1560.0

Flexural stress (MPa) 769.0 614.0 603.0 439.0

Flexural strain 0.057 0.042 0.040 0.028




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de gruter v k singh

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