Nativa, Sinop, v. 9, n. 5, p. 558-562, 2021.

Pesquisas Agrárias e Ambientais

DOI: https://doi.org/10.31413/nativa.v9i5.12830 ISSN: 2318-7670

Mechanical characterization of a polyester matrix composite reinforced

with natural fibers from

Luffa cylindrica

Hoen

Edgley Alves de Oliveira PAULA1, Rafael Bezerra Azevedo MENDES2,

Claudia Yanara Meira da COSTA1, Rafael Rodolfo de MELO3, Alexandre Santos PIMENTA4,

Ramona Rodrigues Amaro de OLIVEIRA3, Joana Alice Galdino de SOUZA3

1 Programa de Pós-Graduação em Ciência e Engenharia dos Materiais, Universidade Federal Rural do Semi-Árido, Mossoró, RN, Brasil.

2 Departamento de Engenharias, Universidade Federal Rural do Semi-Árido, Caraúbas, RN, Brasil.

3 Departamento de Ciências Agronômicas e Florestais, Universidade Federal Rural do Semi-Árido, Mossoró, RN, Brasil.

4 Escola Agrícola de Jundiaí, Universidade Federal do Rio Grande do Norte, Macaíba, RN, Brasil.

*E-mail: edgley.22@hotmail.com

(ORCID: 0000-0002-0258-3209; 0000-0003-3864-2124; 0000-0002-9157-5429; 0000-0001-6846-2496;

0000-0002-2134-2080; 0000-0001-5234-8330; 0000-0002-0640-9574)

Recebido em 09/08/2021; Aceito em 13/12/2021; Publicado em 17/12/2021.

ABSTRACT: The growing demand for renewable products has led to many studies of alternative materials.

The present work describes the production of a composite based in polyester resin reinforced with fibers from

the climber plant Luffa cylindrica and evaluates its mechanical performance. The composite was produced with

two perpendicularly-crossed layers of vegetable fibers. The lamination was performed in a mold with two glass

plates pressed by a hydraulic press. To characterize the properties of the produced composite, density, tensile

and bending strength tests were performed. The final composite had a mean density of 1.16 g cm-3, making it

light due to the reinforcement with vegetable fibers. Tensile and bending strengths were 13.91 and 26.70 MPa,

respectively. The experimental results showed that the composite with vegetable fibers as reinforcement had

lower density than the pure polyester matrix and composites produced with glass fibers. The tensile strength

was higher than the polyester matrix itself, although it was still low. Also, when submitted to bending stress,

the composite presented lower resistance than the matrix. Overall, the composite can be a viable alternative for

non-structural applications where light materials are required such as handicrafts and office partition.

Keywords: sustainable material; vegetable fibers; mechanical properties; technical feasibility.

Caracterização mecânica de um compósito com matriz de poliéster reforçado

com fibras naturais de bucha vegetal (

Luffa cylindrica

Hoen)

RESUMO: A crescente demanda por produtos renováveis tem levado a muitos estudos de materiais

compósitos reforçado com fibras vegetais. A planta trepadeira Luffa cylindrica, conhecida popularmente como

bucha vegetal, também apresenta potencial para este uso. O presente trabalho avalia o desempenho de um

compósito à base de resina de Poliéster reforçado com bucha vegetal. O compósito foi produzido com duas

camadas de fibras vegetais dispostas perpendicularmente entre si. A laminação foi realizada em um molde com

duas placas de vidro prensadas por uma prensa hidráulica. Como propriedade física foi determinada a densidade

e para as propriedades mecânicas, foram realizados ensaios de resistência à tração e flexão. O compósito final

apresentou densidade média de 1,16 g cm-3, tornando-o leve devido ao reforço com fibras vegetais. As

resistências à tração e flexão foram de 13,91 e 26,70 MPa, respectivamente. Os resultados experimentais

mostraram que o compósito com fibras vegetais como reforço apresentou densidade menor que a matriz de

poliéster pura e compósitos produzidos com fibras de vidro. A resistência à tração foi maior do que a própria

matriz de poliéster. Além disso, quando submetido a tensões de flexão, o compósito apresentou menor

resistência do que a matriz. No geral, o composto pode ser uma alternativa viável para aplicações não estruturais

onde materiais leves são necessários, como artesanatos e paredes divisórias.

Keywords: material sustentável; fibras vegetais; propriedades mecânicas; viabilidade técnica.

1. INTRODUCTION

The replacement of unsustainable synthetic raw materials

with natural ones has been a challenge in many industrial

sectors, including the manufacture of composites, where the

search new types of polymeric matrices and reinforcements

stands out. Among the reinforcements targeted for

replacement is fiberglass, which could be substituted

successfully by natural fibers without affecting the strength

of the composite (SANJAY et al., 2015; WAHIT et al., 2012).

This could be a sustainable alternative for a wide variety of

applications, ranging from packaging to the manufacture of

automotive parts. The process of producing composites with

natural fiber reinforcements has found wide application to

make packaging materials (SARIKAYA et al., 2019).

According to Srinivas et al. (2017), polymeric composites

consist of the union of a thermoplastic or thermosetting

polymer reinforced with fibers. There are three types of

polymeric matrix composites: particle-reinforced, fiber-

Paula et al.

Nativa, Sinop, v. 9, n. 5, p. 558-562, 2021.

559

reinforced, and structural composites (SRINIVAS et al.,

2017). Studies of polymeric composites reinforced with

vegetable fibers have been growing rapidly. The use of

natural fibers as reinforcement makes composites totally or

partially recyclable or biodegradable, in addition to being

inexpensive. Among the varieties of lignocellulosic fibers

applied as reinforcements in composites are linen, cotton,

hemp, jute, sisal, kenaf, pineapple, ramie, bamboo, and

banana, among others (ELANCHENZHIAN et al., 2018).

A particularly attractive natural fiber used as

reinforcement in composite materials is that of Luffa cylindrica.

This plant is an herbaceous species of the Cucurbitaceae

family. It is of Asian origin, and arrived in Brazil through

Africans. In the Northeast region of Brazil, this plant can be

found thriving spontaneously in backyards, riverbanks, and

fence borders, where it grows as an annual creeper or

perennial climber, reaching up to 5 meters in height.

(MEDEIROS, 2015; MOTA, 2016).

The fibers of Luffa cylindrica enable the production of

ecological materials that do not harm the environment

(MARTINEZ-PAVETTI et al., 2021). Luffa fiber-based

composite materials, in addition to being environmentally

safe, also provide protection from exposure to various types

of toxic chemicals. The fibers are biodegradable and of high

porosity, forming naturally strong entangled structure,

resulting in high water absorption capacity (BABU;

ARUMUGAN, 2019). The fibers are widely used in the

manufacture of shoes, rugs, sponges, and mops, and also for

the manufacture of value-added products, such as films and

fibers for composites. Due to their lightness in weight and

low cost, Luffa fibers also have uses in the manufacture of

materials for the automotive industry, civil construction and

medical applications, among many others (BABU;

ARUMUGAN, 2019). However, in Brazil, excepting the

eventual use of them as cleaning sponge, there is no large-

scale or industrial utilization for this natural product.

This article reports the development of a composite with

a matrix of polyester resin and reinforcement of Luffa

cylindrica fibers and evaluate the physical and mechanical

properties of the product.

2. MATERIAL AND METHODS

Mats of fibers from Luffa cylindrica fruits (Figure 1A) were

employed for the composite assembly. The fruits were

collected in the municipality of Governador Dix-Sept

Rosado, Rio Grande do Norte State (5° 28′ S and 37° 31′ W),

Brazil. For the production of the composite, the fruits’ seeds

removed and then were washed in running water to remove

the mucilage. The material was oven-dried at 80 ± 2 °C for

24 hours, cut into rectangles and pre-pressed at 0.10 MPa to

obtain the flat mats depicted in Figure 1B.

The mats were placed in a mold together with crystal

orthophtalic polyester resin. After assembling the matrix

reinforcement, the mold was taken to a hydraulic press to

start curing. Thereafter, pressed for 14 hours at 0.15 MPa.

Specimens of dimensions 25 mm width x 2.7 mm thick x 25

mm length were oven-dried at 100 ± 2 ⁰C for about 1 hour

and used to determine the density of the manufactured

composite using ASTM D792 (2008) standard.

The procedures described in the standard ASTM D3039

(2014) were followed for the tensile assays with 5 test

specimens having dimensions of 25 mm width x 2.7 mm

thickness x 240 mm length (Figure 2A).

Figure 1. Fruits of Luffa cylindrica (A); Mats produced after cleaning

(seed and debris removal) and pre-pressing (B).

Figura 1. Frutos de bucha - Luffa cylindrica (A); matéria-prima obtida

após lavagem (remoção de sementes e sujeiras) e pré-pressagem (B).

Figure 2. Test specimens for the tensile (A) and bending (B) assays.

Figura 2. Corpos de prova utilizados para os ensaios de tração (A) e

flexão estática (B).

Mechanical characterization of a polyester matrix composite reinforced with natural fibers from Luffa cylindrica Hoen

Nativa, Sinop, v. 9, n. 5, p. 558-562, 2021.

560

For the bending strength determination, the specimens

were submitted to the procedures described in the standard

ASTM D7264 (2015). These 5 test specimens had

dimensions of 13 mm width x 3.6 mm thickness x 200 mm

length (Figure 2B). The mechanical assays were performed

employing an EMIC DL‑10000 universal testing machine

(São Paulo, Brazil) equipped with a 100 KN load cell.

Loading speeds of 1 and 2 mm min-1 were applied to the test

specimens until complete fracture for the tensile and bending

assays, respectively. With the values of rupture load from the

machine and the dimensions of the test specimens, the

maximum tensile load, deformation, and modulus of

elasticity were obtained.

3. RESULTS

The composite produced with Luffa cylindrica fibers and

polyester resin had mean density of 1.16 ± 0.01 g cm-3 (Table

1).

Table 1. Density of the composite produced with Luffa cylindrica

fibers and polyester resin.

Tabela 1. Densidade dos compósitos produzidos com fibras de

bucha vegetal (Luffa cylindrica) e resina de poliéster.

Panels

Density (g

-3

)

–

1.16

–

1.15

–

1.15

–

1.16

–

1.16

Mean

1.16

Standard deviation

0.01

According to the tensile strength versus strain curves, the

composite produced in this work did not reach the strength

necessary for applications requiring high mechanical

resistance (Figure 3).

Figure 3. Curves obtained for the tensile strength x strain of the

polyester-Luffa fiber composite.

Figura 3. Curvas observadas para os ensaios de tração dos

compósitos confeccionados com fibra de bucha vegetal e resina de

poliéster.

As displayed in Table 2, the tensile strength of the

composite reached a maximum value of 13.91 ± 0.77 MPa

with strain of 0.013 ± 0.002 mm mm-1, and the modulus of

elasticity was 1,076.57 ± 93.70 MPa.

In the bending assays, the five composite test specimens

presented higher resistance compared to the tensile stress.

The behavior of this property indicated by the tension x

strain curves is presented in Figure 4 while the values are in

Table 3. The results indicate that the composite evaluated in

this work had better mechanical performance regarding

bending rather than tensile stress.

The average values determined in the bending assays were

26.70 ± 3.34 MPa for strength, 0.035 ± 0.0005 mm mm-1 for

strain, and 772.99 ± 106.38 MPa for the modulus of elasticity.

The composite reached bending strength and modulus of

elasticity lower than the respective values of 102.02 ± 20.88

MPa and 5,092 ± 58.00 MPa reported by Sapuan et al. (2020).

Therefore, composites of polyester reinforced with Luffa

cylindrica have mechanical properties suitable only for non-

structural applications, such as handicrafts and office

partition.

Table 2. Values of tensile strength of the polyester-Luffa fiber

composite.

Tabela 2. Valores observados para o ensaio de tração dos

compósitos produzidos com bucha vegetal (Luffa cylindrica) e resina

de poliéster.

Panels

Maximum strain

(mm mm-1)

Maximum

strain (MPa)

Modulus of

elasticity (MPa)

CP – 01 0.016 14.23 898.87

CP – 02 0.014 14.34 1,020.02

CP – 03 0.010 12.04 1,186.28

CP – 04 0.014 15.10 1,096.99

CP – 05 0,012 13,85 1,180.67

Mean

0.013

13.91

1,076.57

S. deviation

0.002

0.77

93.70

Figure 4. Curves obtained for the bending strength x strain of the

polyester-Luffa fiber composite.

Figura 4. Curvas observadas nos ensaios de flexão estática para os

compósitos produzidos com bucha vegetal (Luffa cylindrica) e resina

de poliéster.

Table 3. Values determined in bending assays of the polyester-Luffa

fiber composite.

Tabela 3. Valores observados para o ensaio de flexão estática dos

compósitos produzidos com bucha vegetal (Luffa cylindrica) e resina

de poliéster.

Test

Specimen

Maximum strain

(mm mm-1)

Maximum

strength (MPa)

Modulus of

elasticity (MPa)

CP – 01 0.033 28.91 876.35

CP – 02 0.046 27.57 599.14

CP – 03 0.036 31.99 896.22

CP – 04 0.032 25.81 812.35

CP – 05 0.028 19.26 680.88

Mean

0.035

26.70

772.99

S. deviation

0.005

3.34

106.38

0 0,005 0,01 0,015 0,02

Tensile Strength (MPa)

Strain (mm mm-1)

CP - 01

CP - 02

CP - 03

CP - 04

CP - 05

0,00 0,01 0,02 0,03 0,04 0,05

Bending Strength (MPa)

Strain (mm mm-1)

CP - 01

CP - 02

CP - 03

CP - 04

CP - 05

Paula et al.

Nativa, Sinop, v. 9, n. 5, p. 558-562, 2021.

561

4. DISCUSSION

The density results can be considered low compared to

the original density of the polyester resin, of 1.21 g cm-3, as

reported by Sapuan et al. (2020). Pérez et al. (2018), for a

hybrid composite produced with polyester, fiberglass and

cabuya fibers (Agave sp.), the final density was 1.46 g cm-3, and

for one produced with polyester, fiberglass and abaca fibers

(Musa textilis), the density reached 1.48 g cm-3. The final

density determined in the present work for the composite

reinforced with Luffa fibers was lower than the values of 1.30

and 1.21 g cm-3 found by Ferreira et al. (2020) for composites

produced with epoxy-fiberglass and epoxy-fiberglass-jute

fibers (Corchorus capsularis).

Besides the low-density values found here, another

positive characteristic of the composite is the

biodegradability of the Luffa fibers. Furthermore, according

to Dixit et al. (2017), the use of natural vegetable fibers gives

composites other properties that are attractive for industrial

purposes, in particular the low cost of these fibers compared

to synthetic glass, aramid, carbon and steel fibers make them

preferable in the composite industry (AHMAD et al., 2015).

The low tensile strength and the variations of the samples

may have been related to impurities in the fibers causing poor

interaction with the polyester matrix. Other factors

responsible for this poor interaction could have been air

bubbles and voids in the interface areas. In their research,

Faria et al. (2020) show that the lay-up influences the

mechanical properties of the composite, as it provides the

appearance of a greater number of bubbles and voids. In

thermoplastic composites reinforced with natural fibers, the

strength and modulus of elasticity depend on the properties

of the polymeric matrix and the impregnation in the interface

region between matrix and fibers. In composites made with

fragile matrices, the mechanical stresses exerted in the

material may cause high tensions in the fibers, causing low

resistance (WOIGK et al., 2019).

The composite does not have high tensile strength.

However, the result found is superior to the value of 8.14 ±

1.23 MPa found by Sapuan et al. (2020). When compared to

the polyester resin matrix, it was found that the addition of

Luffa fiber reinforcement increased the material's tensile

strength.

According to Patel et al. (2018), the increase in the

percentage of natural fibers in a composite material caused

an initial increase in the tensile resistance. However, after a

critical point is reached, the bonding between the matrix and

the fibers decreases, resulting in higher agglomeration and

consequent loss of strength of the material.

Although the composite reached a better result in the

bending assay, it presented variations in tension x strain

curves and values similar to what was observed in the tensile

assays. As occurred in the tensile assays, the variations might

have been due to impurities in the material and the technique

employed in the production of the composite. The chemical

constituents of the natural fibers (cellulose, hemicellulose,

lignin, waxes, pectin, etc.) could influence the mechanical

properties of the composites including tensile, bending and

impact resistance (LATIF et al., 2019).

As discussed by Latif et al. (2019), this influence arises

from the presence of impurities and the chemical

constituents those materials on the surface of the fibers,

preventing good adherence between the reinforcement and

the polymeric matrix. The interfacial and crystalline bonds

are major factor affecting the mechanical properties of

natural fibers. The mechanical properties are directly

influenced by several factors, such as type of fiber, matrix,

surface treatment and production method. Latif et al. (2019)

further indicate that fibers without treatment tend to have

non-cellulosic constituents and a smooth surface area, factors

that cause lower mechanical interlock and incompatibility

between the reinforcement of the fibers and the matrix

material. SEM (Scanning Electron Micrographs) are highly

recommended here for more detailed analysis of the results.

According to Elanchezhian et al. (2018), the employment

of natural fibers in composites can give these materials low

cost and mechanical properties desirable in civil construction

and for the manufacture of partition panels, false ceilings,

furniture, storage containers, tubes, bags, helmets and car and

boat interior parts, among others.

5. CONCLUSIONS

The use of the Luffa fibers as reinforcement in the

production of the composite provided low density and

reduced the amount of resin used in the manufacturing

process, making it economically feasible to use the material

for various applications. In the tensile strength tests, the

composite was fragile, indicating weak adhesion between the

vegetable fibers and the polyester matrix.

Although the Luffa fibers did not provide the composite

with a flexural strength higher than that of the polyester

matrix, it still presented interesting results that allow the use

of the material in the manufacture of products for non-

structural applications. In general, the addition of Luffa fibers

resulted in good physical and mechanical properties for some

uses.

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