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This work is licensed under a Creative Commons Attribution 4.0 International License. 

 

   

 

 

 

 

 

  

             

 

 
 

 

 

Abstract   

In this study, polyester composites reinforced with pistachio shells powder (P.) with an average 

diameter (150 – 200 μm) with different weight ratios (0.5%, 1%, 1.5%, 2%, and 2.5%) were 

prepared to the resin. The Shore D hardness, thermal conductivity (K), and the glass transition 

temperature (Tg) of the samples were examined. The results showed that the Shore D hardness 

increases with the increase of the reinforcement ratio and its maximum value is (87.55) at (2.5% 

P.) While the value of hardness at (0%) is (86.5). The thermal conductivity increases slightly with 

the increase in the percentage of reinforcement and its maximum value is (0.213253 W/ m. K) at 

(2.5% P.), while the value of K at (0% P.) is (0.170264W/ m. K), but with this slight increase in 

thermal conductivity, polyester composites remain from the insulating materials.  The minimum 

(Tg) of (UPE/ P.) composites was the value (113.898°C) at (2.5% P.). Polyester composites are 

used in wood paints, either in primitive finishes or final finishes. 

 

Keywords: pistachio husks, Shore D hardness, composites, Thermal conductivity. 
 

1. Introduction 

Solid wastes resulting from agricultural and industrial wastes were of limited use due to the lack 

of cost-effective fillers in the manufacture of polymeric composites. Plus, natural materials are 

eco-friendly, plentiful, and renewable. Nutshells, peanuts, olive stone, coconut and palm trees, rice 

husks, jute, stalk fibers, bagasse and hulled sugar [1-9] are used as reinforced fillers in polymer 

matrix composites to improve physical and mechanical properties and to reduce production cost 

[1]. Polymers are inert and lightweight materials that possess a high degree of Coated and have a 

low density, low stiffness and high resistance to corrosion. They are also characterized by ease of 

manufacture and processing, which made them widely used in the field of civil and construction 

engineering [10]. The composite material consists of matrix material and reinforcement [5] and 

these materials are characterized by high toughness, lightweight, low density, low-cost 

manufacturing, does not rust or corrode [11]. Polymer-based composites are one of the best and 

most common composite materials. Due to its high mechanical properties, the reinforced polymer 

doi.org/10.30526/36.2.3055 

Article history: Received 2 October 2022, Accepted 1 November 2022, Published in April 2023. 

 

 

 

Ibn Al-Haitham Journal for Pure and Applied Sciences 

Journal homepage: jih.uobaghdad.edu.iq 

 

Effect of Pistachio Husks Powder Additive on Unsaturated Polyester Composites 

 
Shatha H. Mahdi 

Department of Physics, College of 

Education for Pure Science Ibn Al-Haitham, 

University of Baghdad, Baghdad, Iraq. 

shatha.h@ihcoedu.uobaghdad.edu.iq 

Rihab Nassr Fadhil 
Department of Physics, College of 

Education for Pure Science Ibn Al-Haitham, 

University of Baghdad, Baghdad, Iraq. 

rihab.n@ihcoedu.uobaghdad.edu.iq 

 

 

https://creativecommons.org/licenses/by/4.0/
mailto:shatha.h@ihcoedu.uobaghdad.edu.iq
mailto:rihab.n@ihcoedu.uobaghdad.edu.iq


IHJPAS. 36(2)2023 

192 
 

has been used in various industries [12] [13]. The materials used in the reinforcement, are in 

different shapes, such as fibers, particles, scales, or Flakes, depending on the type of use [14] [15]. 

Polyester resin is a type of thermosetting resin [16]. It is prepared by reaction with a dibasic 

unsaturated acid and it is required that one or both of the monomers have a double bond in its 

composition,  After the linear polymer is formed, it is mixed with an effective vinyl monomer such 

as styrene plus a catalyst that breaks down into free cracks. Thus, the vinyl monomer is 

polymerized with the double bonds along the polymer chain, thus forming polyester [17]. Polyester 

resin has good thermal properties as it withstands high temperatures (for resins) up to 260°C, but 

suffers spontaneous disintegration at a temperature of about (300°C) even in the absence of oxygen 

[18]. It is also characterized by excellent chemical and electrical resistance to acids, solvents, wear, 

salts and environmental influences, in addition to being low in cost, but characterized by weakness 

and fragility [19]. The importance of particle-supported polymeric materials prompted scientists 

And researchers to do many studies and research. In 2018, the researcher Mohammed Al-Saadi 

and others used pistachio husks and their effect on the mechanical properties of polyester matrix. 

It obtained the dispersion of the pistachio husks particles in the polymer matrix and it obtained the 

highest tensile strength, flexural strength and impact strength. [1]. In 2021, the researchers Zaynab 

N. and Samah M. conducted an experimental study of the effect of food trash powder on FWP, 

Compressive and abrasion behaviour of polyester composite The results showed that FWP 

improved the tribological and mechanistic behaviour of the UPE composites with a slight 

difference. FWP acts as reinforcement and increases abrasion resistance [20]. In 2021, the 

researcher Yahya Hısman Celik and others used the effect of adding hazelnut shells, pistachio 

skins, and Apricot kernel peel on unsaturated polyester composites. It was concluded that 

increasing the reinforcements added to polyester increases the compressive strength, stiffness, 

specific weight and thermal conductivity properties [21]. The study aims to prepare composites of 

unsaturated polyester, to obtain a new material with qualified physical properties in the 

manufacture of paint for wooden furniture through the use of fillers of pistachio shells that can be 

exploited and clear the environment from it by recycling.  

 

2.  Materials and Methods 

2.1 Matrix Material 

Unsaturated polyester resins (UPE) were supplied from Saudi Industrial Resins Limited. And it is 

converted to a solid state by adding a hardener in a ratio of (98:2). The viscosity was average.  

Table 1 shows the chemical and physical properties of UPE. 

Table 1. The Chemical  and Physical Properties of (UPE).  

Properties UPE 

Physical State Liquid 

Colour Transparent 

Density at (25°C) 1 To 1.3 g/cm3 

Odor Pungent 

Vapor Density 3.6 (Air = 1) 

 

 



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2.2 Reinforcement materials 

Pistachio husk powder (P.) is used as Reinforcement material. Some of the basic properties of (P.) are 

shown in Table 2. 

 

Table 2: basic properties of (P.).  

Properties Pistachio husk waste powder (P.) 

Form  powder 

Colour light yellow 

Purity  99.9%  

average diameter   (150 - 200 µm)  

 

2.3  Method   

The unsaturated polyester resin was prepared with a hardening ratio (98:2) and then different weight 

percentages of pistachio shells powder (P.) (0, 0.5, 1, 1.5, 2 and 2.5%) were added. Six samples of (UPE/P.) 

composites were prepared according to (ASTM-E 10) using the Hand lay-up modeling process [22]. Figure 

(1) is a photograph of the samples. 

 

Fig. 1. A photograph of the samples for UPE/ P. composites at (0, 0.5, 1, 1.5, 2 and 2.5) %     

 

3.  Results and Discussion 

3.1. Thermal conductivity (K) 

Fig. 2 and Table .3 show the results of the thermal conductivity of the (UPE/ P.) composites. The 

thermal conductivity increases slightly with the increase of the reinforcement ratio. It is (0.213253 

W/ m. K) at the ratio (2.5% P.) however; composites (UPE/ P.) of insulating materials remain. 

Heat in polymeric materials is transmitted in the form of an elastic wave [23] [24]. The wave loses 

part of its energy at the interface area between the matrix and the reinforcing material [25] [26]. 

Pistachio shell powder is an insulating material, but it slightly increased the thermal conductivity 

in unsaturated polyester composites. The reason for this may be due to the properties of the 

unsaturated polyester used in this research in terms of the glass transition temperature, which are 

equal to (125.5 °C) for pure unsaturated polyester and its high melting point. 



IHJPAS. 36(2)2023 

194 
 

 
Fig. (2) Thermal conductivity V.s P. weight percentage for UPE/ P. composites. 

 

Table (3) Thermal Conductivity for UPE/ P. composite 

P.% K(W/ m. K) 

0 0.170264 

0.5 0.173773 

1 0.181237 

1.5 0.189365 

2 0.189371 

2.5 0.213253 

 

3.2. Hardness Tests 

Figure 3 and Table 4 show the results obtained from the Shore D hardness test for (UPE/P.) 

composites. It is observed that the Shore D hardness values increase with the increase of the 

reinforcement ratio. The highest value was (87.55) with a rate of (2.5%). The reason for the 

increase in hardness is due to the homogeneous distribution of pistachio shell powder among the 

unsaturated polyester resin chains and the cohesion strength between the matrix material and the 

reinforcement material [27] [28]. Thus, we obtained a compound that is more resistant to 

environmental factors than pure unsaturated polyester.  

 

 
Fig. (3) Shore D hardness of polymer composites as a Function of pistachio husk powder. 

 

 

k
 (

w
/m

.k
)

weight % P.

86.4

86.6

86.8

87

87.2

87.4

87.6

87.8

0 1 2 3

H
a
r
d

n
e
ss

Weight% P.



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Table (4) Shore D hardness for UPE /P. composite. 

P.% Shore D hardness  

0 86.5  

0.5 87.2  

1 87.37  

1.5 87.45  

2 87.52  

2.5 87.55  

 

3.3. Glass-transition Temperature 

The Tg is the temperature at which the polymer changes from a solid to a soft state. Figure 4 and 

Table 5 show the obtained values for (Tg) for (UPE/ P.) composites. Figures (5, 6, 7, 8, 9 and 10) 

show the results obtained from the (DSC131 EVO) device, which shows the relationship between 

heat flow and the sample temperature, through which the values of (Tg) were found. It was noticed 

in Figure (4) that the values of (Tg) decrease with the increase in the percentage of reinforcement. 

The lowest value was (113.898°C) at the ratio (2.5% P.). The reason for this is that the value of 

(Tg) depends on several factors, including the chemical composition, as the hardness of the 

polymeric chains depends on the presence of compensated groups or chemical bonds that increase 

the flexibility of the chains and reduce Tg. Structural factors such as molecular weight, as the value 

of Tg, increases with increasing molecular weight. The degree of branching decreases Tg because 

with the increase of Tg, the ends of the chains increase, which leads to an increase in the free 

volume [29].   

 
Fig. (4) Tg vs. P. weight percentage for UPE /P. composites. 

Table (5) Tg for UPE /P. composite.  

P.% Tg (°C) 

0 125.5 

0.5 125.313 

1 125.1 

1.5 124.039 

2 122.086 

2.5 113.898 

112
114
116
118
120
122
124
126
128

0 1 2 3

Weight% P.

T
g

(°
C

)



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196 
 

 
Fig. )5( Heat Flow vs.  Sample Temperature for weight percentage 0%. 

 
Fig. (6) Heat Flow vs.  Sample Temperature for weight percentage 0.5 %. 

 
Fig. (7) Heat Flow vs.  Sample Temperature for weight percentage 1 %. 

-5

0

5

10

15

20

25

30

0 50 100 150 200 250

H
e
a
tF

lo
w

(µ
V

)

Sample Temperature (°C)

-10

-5

0

5

10

15

20

0 50 100 150 200 250

H
e
a
tF

lo
w

(µ
V

)

Sample Temperature (°C)

Tg:125.313(°C)
Tig:124.958(°C)
Teg:126.575(°C)

-5

0

5

10

15

20

0 50 100 150 200 250

H
e
a
tF

lo
w

 (
µ

V
)

Sample Temperature 

(°C)

Tg:125.1(°C)
Tig:124.642(°C)
Teg:125.114(°C)

Tg: 125.5 (°C) 

Tig: 124 (°C) 

Teg: 127 (°C) 



IHJPAS. 36(2)2023 

197 
 

 
Fig. (8) Heat Flow vs.  Sample Temperature for weight percentage 1.5 %. 

 

 

 

 

 

 
Fig. (9) Heat Flow vs.  Sample Temperature for weight percentage 2 %. 

-5

0

5

10

15

20

25

0 50 100 150 200 250

H
e
a
tF

lo
w

(µ
V

)

Sample Temperature (°C)

-5

0

5

10

15

20

0 50 100 150 200 250

H
e
a
tF

lo
w

(µ
V

)

Sample Temperature (°C)

Tg: 124.039(°C) 

Tig: 122.889(°C) 

Teg: 145.106(°C) 

Tg: 122.086(°C) 

Tig: 122.465(°C) 

Teg: 122.677(°C) 



IHJPAS. 36(2)2023 

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Fig. (10) Heat Flow vs.  Sample Temperature for weight percentage 2.5 %. 

 

5. Conclusion 

We concluded Thermal conductivity increases slightly with the increase in the percentage of 

reinforcement and its maximum value is (0.213253 W/ m. K) at (2.5% P.). The Shore D hardness 

increases with the increase of the reinforcement ratio and its maximum value is (87.55) at (2.5% 

P.). Glass transition temperature (Tg) decreasing with the increase of the reinforcement ratio, and 

its minimum (Tg) value is (113.898°C) at (2.5% P.). Polyester composites are used in wood paints, 

either in primitive finishes or final finishes. 

   

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http://dx.doi.org/10.1504/PIE.2019.099357