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ScienceDirect Procedia Materials Science 6 (2014) 1696 – 1702

3rd International Conference on Materials Processing and Characterisation (ICMPC 2014)

Tensile and flexural behavior of hemp fiber reinforced virginrecycled HDPE matrix composites Sukhdeep Singha, Dharmpal Deepakb, Lakshya Aggarwalc, V.K. Guptab* a

Department of Mechanical Engineering, RIEIT, Railmajra, SBS Nagar-144533, India b Department of Mechanical Engineering, Punjabi University, Patiala-147002, India c Department of Mechanical Engineering, M.M. University, Sadhopur, Ambala, India

Abstract Hemp fibre reinforced polyethylene (fresh and recycled) composite is manufactured by injection moulding technique for varying fiber contents from 10% to 30%. Tensile and flexural tests are conducted on composite specimens in accordance to ASTM D638 and ASTM D790 standards respectively. The results obtained are compared with specimens made of 100% fresh HDPE and mixture of virgin and recycled HDPE (50% each). The tensile strength of hemp fiber composite decreases respectively by 0.53 MPa to 2.20 MPa with the increase in hemp content from 10% to 30% when compared with specimen made of 50% fresh and 50% recycled HDPE. The flexural strength of composite containing 10% and 30% hemp fiber are reduced respectively by 3.82 MPa and 4.99 MPa when compared with specimen made of 50% fresh and 50% recycled HDPE. Investigation of tensile fractured surface reveals that the fiber delamination, fiber tensile fracture and poor interfacial adhesion between hemp fiber and HDPE matrix are mainly responsible for poor tensile strength of the composite. © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

© 2014 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET). Selection and peer review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET) Keywords: HDPE; Injection Moulding; Hemp Fiber; Recycled HDPE

* Corresponding author. Tel.: +91-175-3046338; fax: +91-175-3046333. E-mail address: [email protected]

2211-8128 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET) doi:10.1016/j.mspro.2014.07.155

Sukhdeep Singh et al. / Procedia Materials Science 6 (2014) 1696 – 1702

1.

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Introduction

The development of high-performance materials made from natural resources is increasing worldwide due to their abundant source in the nature, low cost, light weight and high specific modulus in contrast to the synthetic fibers (Kabir et al. 2011; Faruka et al. 2012). In addition, they are biodegradable, renewable, have low specific weight, high specific strength and stiffness than glass fibers, ease of processing, reduced wear, good thermal and acoustic insulating properties (Bledzki et al. 1996; Liu et al. 2009; Khalil et al. 2012). Hemp fiber (Cannabis sativa) is recently gaining attention as diversified reinforcing applications in composite industry, housing, railways and aerospace applications due to its high specific strength and stiffness. Hemp offers excellent mechanical strength and Young’s modulus (Shahzad, 2011; Hassan et al. 2012). However, the foremost limitation of natural fibers used as reinforcement is the poor interfacial adhesion between polar hydrophilic natural fibers and non-polar hydrophobic polymers. Different coupling agents have been used to increase compatibility between natural fibers and thermoplastic matrices, thereby augmenting the composite’s performance (Xi et al. 2007; Xue et al. 2007). The increasing use of polyethylene in number of applications is posing a serious environmental threat and thus the researchers are motivated to undertake studies concerning recycling of polymer waste. The literature consulted so far reveals that the studies pertaining to mechanical characterization of hemp fiber reinforced polyethylene (PE) composites, especially containing recycled PE, are rather scant. In the light of these facts, it is decided to investigate the mechanical behavior of hemp fiber-recycled PE composites. In the present study natural fiber composites, containing 10%, 20% and 30% hemp fibers as reinforcement and mixture of virgin and recycled high density polyethylene (HDPE) as matrix, have been fabricated. The tensile and flexural properties of the composites are evaluated and compared with samples made of 100% virgin HDPE and 50-50 mixture of virgin and recycled HDPE. 2. 2.1

Experimental details Material and method

In this study, we have used hemp fiber as reinforcement and High Density Polyethylene (HDPE) as matrix. Both virgin and recycled HDPE are employed for preparation of composites. Hemp fibers are procured from Chandra Prakash & Company from Jaipur, (Rajasthan) and HDPE (virgin and recycled) of moulding grade is purchased from Goyal Polymers, Chandigarh. The hemp fiber reinforced HDPE composites are fabricated by injection moulding technique. 2.2

Chemical treatment of hemp fibers

To improve interfacial adhesion between hemp fibers and HDPE matrix, chemical treatments of the hemp fibers was carried out. Before treatment, hemp fibers were washed with distilled water at 80°C for 1 hour and thereafter dried in an oven at 100°C for 5 hours (Favaro et al. 2010). The fibers were then treated with NaOH solution (5wt. %) for 24 hours at 50°C. The fibers were then washed several times with fresh water to remove traces of NaOH sticking on the surface of hemp fibers. Final washing of the fibers was carried out with distilled water till a pH of 7 was achieved. The fibers were then dried at room temperature for 48 hours, followed by oven drying at 80°C for 10 hours (Oza et al. 2011). A total of 200 gm of hemp fibers, with an initial pH of 10.0, were subjected to chemical treatment. However, due to removal of moisture and fiber loss during washing, the weight of the treated hemp fibers decreased to around 150 gm. 2.3

Fabrication of tensile and flexural specimens

In order to investigate the influence of varying the content of hemp fibers on tensile and flexural properties of hemp fiber-reinforced HDPE composite, the samples for tensile and flexural testings were prepared by taking hemp content as 10%, 20% and 30% (wt. %) in a matrix of HDPE (50% virgin+50% recycled). For the purpose of

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comparison, the tensile and flexural specimens were also prepared for 100% virgin HDPE and 50-50 mixture of virgin and recycled HDPE. The details of composite specimens are given in Tables 1-2 below. Table 1: Description of Tensile Specimens Fiber (wt. %)

Sample Density* (gm/cc)

Wt. of Tensile specimen (gm)

Total Fiber wt (gm)

10

0.991

8.859

0.886

20

1.042

9.315

1.863

30

1.093

9.771

2.931

Table 2: Description of Flexural Specimens Fiber (wt. %)

Sample Density* (gm/cc)

Wt. of Flexural specimen (gm)

Total Fiber Wt. (gm)

10

0.991

5.113

0.511

20

1.042

5.376

1.075

30

1.093

5.639

1.692

* [Density of Hemp fiber = 1.45 gm/cc (Aziz and Ansell, 2004), Density of HDPE = 0.94gm/cc (Chong et al. 2010; Kumar et al. 2011)].

The tensile and flexural specimens were fabricated by putting mixture of hemp fibers and HDPE, corresponding to details mentioned in Table-1 and Table-2, into the injection moulding machine (Model-BH100, Make-J.B. Industries Pvt. Ltd.). Five similar specimens, both tensile and flexural, were fabricated corresponding to each composition (i.e. 10, 20 and 30%). The geometry and dimensions of the tensile and flexural specimens were kept in accordance to ASTM D638 and ASTM D790 standards respectively. 2.4

Testing of samples

Tensile and flexural tests were conducted on universal testing machine (Model-SS UTM 1205, Capacity-250kN, Make-P.S.I. Sales Pvt. Ltd.) available at CIPET, Amritsar. Before testing, the conditioning of specimens was done according to ASTM standards in an environmental test chamber maintained at 23°C (± 2°C) and 50 RH (± 5%). During tensile test, the ASTM D638 standard was followed and dumbbell shape specimens were subjected to uniaxial tensile load by gripping their ends in UTM and keeping a gauge length of 50 mm. Flexural test was also performed on universal testing machine (50kN load cell) at a cross-head speed of 2 mm/min, according to ASTM D790 standard, while keeping a span to depth ratio of 16:1. Corresponding to each composition, five similar specimens were tested and the average flexural strength was taken. The results obtained by testing five similar samples, corresponding to each composition, were averaged to estimate the tensile and flexural strength of a particular sample. 3. 3.1

Results and discussion Surface topography of jute fibers

To reveal surface topography of the treated and untreated hemp fibers, both the fibers were cut into small sizes of 4 to 5 mm along the longitudinal section. Optical examinations were carried out on the untreated and alkali treated hemp fibers to study the morphological changes that occurred during the course of chemical treatment of fibers, Fig. 1. The surface of 5% NaOH treated hemp fiber appears to be uneven and serrated as compared to untreated hemp fiber. The surface topography of the treated fibers shows the absence of surface impurities, which were present in the untreated hemp fiber. The surface of treated fiber gets roughened by NaOH treatment. The diameter of treated fiber ranges from 250 to 275μm and the aspect ratio ranges from 15 to 18.

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Fig. 1. Optical micrograph of untreated and 5% NaOH treated hemp fibers.

3.2

Mechanical characterization

The injection moulded specimens were tested to evaluate their tensile and flexural strength. The results obtained from tensile and flexural tests are summarized in Table 3. Table-3. Tensile and Flexural Strength of Specimens Tensile Strength

Flexural strength

(MPa)

(MPa)

100% fresh

17.39

16.39

S2

50% fresh + 50% Recycled HDPE

12.27

22.56

S3

10% hemp + 90% HDPE (fresh + Recycled)

17.39

16.39

S4

20% hemp + 80% HDPE (fresh+ Recycled)

12.27

22.56

S5

30% hemp + 70% HDPE (fresh + Recycled)

17.39

16.39

Notation of Sample

Composition of Sample

1

The tensile strength of sample S2 decreases as compared to sample S1 by 1 MPa owing to mixing of 50% recycled HDPE in 50% fresh HDPE (Fig. 2). By increasing the content of hemp fibers from 10% to 30% in a matrix of recycled and virgin (50% each) HDPE, the tensile strength is observed to decrease, except for composite sample S4 with 20% hemp fibers. The sample S4 exhibits a slightly higher tensile strength compared to sample S2 consisting of HDPE matrix with equal proportions of virgin and recycled HDPE. It is also evident from Fig 2 that the tensile strength of sample S1 containing 100% virgin HDPE is the highest among all the samples. It appears that due to poor adhesion between the matrix and the hemp fibers in composite samples S3 and S5, the tensile strength is reduced as compared to sample S2. But the higher tensile strength of sample S4 than S2 could be attributed to good adhesion between hemp fiber and HDPE matrix. The other possible reason for lower tensile strength of composite specimens as compared to specimen S2 could be due to fiber orientation during the preparation of composite whereby it was impossible to align the fibers in a straight manner. The flexural strength of composite samples (S3-S5) and sample S2 is higher than the sample S1 consisting of 100% virgin HDPE alone (Fig. 3). The flexural strength of sample S2 with 50-50 mixture of recycled and virgin HDPE is 10.29 MPa higher than the sample S1 made of 100% fresh HDPE . With the addition of 10 and 20% hemp fibers in HDPE matrix (50% fresh + 50% recycled), the flexural strength decreases, as evident from the comparison

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Tensile strength (Mpa)

of samples S2, S3 and S4 (Fig. 3). However, with further increase in hemp fiber to 30%, the flexural strength increases a little. Aziz and Ansell (2004) also noticed that flexural strength of the composites increases with the addition of natural fibers (kenaf fibers).

20 18 16 14 12 10 8 6 4 2 0

17.39

16.39

16.67

15.86

14.19

S2 S3 S4 Fiber volume fraction (% )

S1

S5

Fig. 2. Tensile strength of various specimens

22.56

Flexural strength (Mpa

25

18.72

20 15

16.71

17.57

S4

S5

12.27

10

5 0 S1

S2

S3

Fiber volume fraction(% )

Fig. 3. Flexural strength of various specimens

3.3

SEM analysis of fractured surface

SEM images of tensile fractured surface of hemp fiber reinforced PE composite samples are depicted in Figs. 4 to 6. The SEM image of 10% hemp composite shown in Fig. 3 reveals the presence of dimpled morphology, depicting brittle mode of fracture in composite sample from regions, which do not contain hemp fibers. The SEM image also reveals that hemp fibers are not uniformly distributed in HDPE matrix. As a result of which the fiber could not play a positive role in improving the performance of composite, especially for tensile strength, as observed in this study.


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Fig. 4: SEM of tensile fractured surface of 10% hemp composite

SEM images shown in Fig 5(a) and 5(b) reveal that fiber delamination and fiber tensile failure are prevalent failure mechanisms in 10% hemp fiber composite. In addition, a poor adhesion between HDPE matrix and hemp fiber is also evident from this image. These fractures are also evident for 20% hemp fiber composite in Fig. 6.

Fig.5: SEM of 10% hemp fiber composite showing delamination and tensile fracture

Fig. 6: SEM of 20% hemp fiber composite showing delamination and tensile fracture

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4.

Conclusions The present study has led to the following conclusions: ‚ Reinforcement of hemp fibers in HDPE matrix reduces the tensile strength. Tensile strength of the composite decreases by 0.53 MPa to 2.20 MPa with the increase in hemp content from 10% to 30% respectively when compared with specimen made of 50% fresh and 50% recycled HDPE. However, the composite with 20% hemp fibers is observed to have tensile strength higher by 0.28 MPa as compared to HDPE sample containing 50-50 mixture of fresh and recycled HDPE. ‚ Flexural strength decreases with the addition of hemp fibers in HDPE matrix containing equal proportions of virgin and recycled HDPE. Flexural strength of the composite containing 10% and 30% hemp fibers are respectively lower by 3.82 MPa and 4.99 MPa when compared to specimen made of 50-50 mixture of virgin and recycled HDPE. ‚ Fiber delamination, fiber tensile fracture and poor interfacial adhesion between hemp fibers and HDPE matrix are mainly responsible for poor tensile strength of the composite as compared to specimen having equal proportions of virgin and recycled HDPE.

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