An experimental investigation on mechanical and

Journal of Natural Fibers

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An experimental investigation on mechanical and tribological properties of Himalayan nettle fiber composite Mayank Pokhriyal, Lalta Prasad & Himanshu Prasad Raturi To cite this article: Mayank Pokhriyal, Lalta Prasad & Himanshu Prasad Raturi (2017): An experimental investigation on mechanical and tribological properties of Himalayan nettle fiber composite, Journal of Natural Fibers, DOI: 10.1080/15440478.2017.1364202 To link to this article: http://dx.doi.org/10.1080/15440478.2017.1364202

Published online: 20 Sep 2017.

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Date: 20 September 2017, At: 09:51

JOURNAL OF NATURAL FIBERS https://doi.org/10.1080/15440478.2017.1364202

An experimental investigation on mechanical and tribological properties of Himalayan nettle fiber composite Mayank Pokhriyal, Lalta Prasad, and Himanshu Prasad Raturi

Downloaded by [Australian Catholic University] at 09:51 20 September 2017

Department of Mechanical Engineering, G. B. Pant Engineering College, Pauri Garhwal, Uttarakhand, India ABSTRACT

KEYWORDS

The main focus of the present research work was to explore mechanical and tribological properties of Himalayan nettle fiber and unsaturated polyester resin (GP) using hand lay-up method. Four composite laminates were prepared by adding the Himalayan nettle fibers by weight percentage (5%–20%). The various properties (e.g., tensile strength, hardness, impact strength, and abrasion wear) were calculated for the composite laminates. It was found that the significant variation in properties was observed when fiber addition was in the range 15%. The change in the properties was negligible when fiber addition was increased from 15% by weight.

关键词

abrasive wear; composite; hand woven; Himalayan nettle; unsaturated polyester resin 磨料磨损; 复合材料; 手工编织; 喜马拉雅荨麻; 不饱和聚酯树脂

摘要

本课题的主要研究内容是用手糊法研究喜马拉雅荨麻纤维和不饱和聚酯树脂的力学性能和摩擦学性能。通过添加喜马拉雅荨麻纤维重量百分比（5% - 20%）制备了四种复合材料层压板。计算了复合材料层板的各种性能（如拉伸强度、硬度、冲击强度和磨损）。结果发现，纤维加入量在15%范围内，性能有显著变化。当纤维加入量从15%增加到重量时，性能的变化可以忽略不计。

Introduction Natural fibers are being seen in a changed context due to a shift away from synthetic to natural. Remarkable utilization of natural bast fiber (Pokhriyal et al. 2015) composites has been reported in the last few years. Not much work has been reported in the open literature. There is a lot of scope to conduct comprehensive study on natural bast fiber. We know that these fibers are extracted from the outer cell layers of the stem of the plant (Farnfield and Alvey 1975). There are six basic types of natural fibers. They are classified as follows: bast fibers (jute, flax, hemp, ramie, and kenaf), leaf fibers (abaca, sisal, and pineapple), seed fibers (coir, cotton, and kapok), core fibers (kenaf, hemp, and jute), grass and reed fibers (wheat, corn, and rice), and all other types (wood and roots) as reported by Faruk et al. (2012). Natural fibers (e.g., Himalayan nettle, Kenaf, Hemp, Roselle, Rattan, Flax) have various advantages like eco-friendliness, low density, fairly good mechanical properties, non-toxic, low cost, easy availability, renewable, biodegradable, less abrasive, and low energy for processing over traditional synthetic fibers that lead to fabrication of natural fiber composite (Bogoeva-Gaceva et al. 2006). The properties of natural fiber composites are mainly influenced by interfacial adhesion between the matrix and fibers. Now to enhance these properties, the chemical treatment of the fiber needs is required. The tensile strength of natural fiber composite increases with fiber content up to certain value, and after that it drops. The physiographic and climatic diversity makes Uttarakhand state a fertile ground for growing plenty of fibrous plants. Himalayan nettle, which is a short herb about CONTACT Lalta Prasad [email protected] Department of Mechanical Engineering, G. B. Pant Engineering College, Pauri Garhwal, Uttarakhand 246194, India. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/WJNF. © 2017 Taylor & Francis


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2–3 m high, is found upto an altitude of 3,000 meters and belongs to the family Urticaceae locally known by various names of Bhainsya-kandali, Jhir-kandali, Dans-kandali, and Awa in different parts of Uttarakhand. The leaves are stalked, palmately, deeply divided, dendated, and covered with long stinging hairs with hooked protrusions that cause irritation to human skin. The bark fiber peeled off from the stem yields a silky white fiber that is utilized for making thread, ropes, or spun into a yarn. In old days, Himalayan nettle was considered as a waste in Uttarakhand is now a being harvested, processed to make value added products from this fiber. The local communities use the fiber for their domestic or agricultural use (such as shelter, cushions covers, rugs, woven place mats, clothes, ropes, and nets). This process provides them financial support and employment opportunities. However, the collection of Himalayan nettle is seasonal, starting from November to the end of December. Nettle fiber is being used for manufacturing of composite with polymeric matrix that has many applications in textile, cordage industry, and making of aircraft panels, gear wheel, and other machine components (Baiardo et al. 2004; Bodros and Baley 2008; Bogoeva-Gaceva et al. 2006; Deokota and Chhetri 2009; Ochi 2008; Rachchh et al. 2014; Sankari 2000; Shah et al. 2013; Singh and Shrestha 1987; Summerscales et al. 2010; Thiruchitrambalam et al. 2010; Tripathi et al. 2013) Bledzki, Faruk, and Mamun (2008) reported the study on abaca fiber reinforced PP composites and evaluated the mechanical properties. The different length of fibers and different compounding processes were selected for making the composite materials. They found that with an increasing fiber length, the tensile and flexural properties were improved, whereas the mixer-injection molding process showed a better mechanical performance as compared to other compounding coupling processes. Nettle fiber cell wall consists mainly of sugar-based polymers that are combined with lignin with lesser amount of extractives that are distributed throughout primary and secondary cell wall layers. Himalayan nettle fiber contains 85.93% cellulosic structure that is a glucan polymer of D-glucopyranose units that are linked together by beta-(1–4)glycosidic bond, 6.8% hemicelluloses that consists of chains of polysaccharide with a lower degree of polymerization than cellulose and containing sugars D-xylopyranose, D-glucopyranose, D-galactopyranose, L-arabinofuranose, D-mannopyranose, D-glucopyranosyluronic acid with minor amount of other sugars, 5.49% lignin that cotains mainly of guaiacyl, syringyl, and p-hydroxphenyl moieties and other aromatic, 0.08% waxes that are inorganic (Tripathi et al. 2013). Nettle fiber has 50–150 µm diameter and density of 1.452 gm/cm3. Nettle fiber has better mechanical properties such as tensile strength of 86 MPa, Young’s modulus of 62 GPa, and 2% elongation at breaking point as reported by Bajpai et al. (2013). The composites are structured materials made from two or more compatible constituents that combined macroscopically and are insoluble to each other to yield a useful material. The effects of different environments (e.g., river water, diesel water, freezing conditions, sunlight, and soil) on tensile strength of Himalayan nettle polypropylene (PP) composite were reported by Bajpai et al. (2013). They reported that the tensile strength of the composite material decreases in the order of 20% and 13% for river water and diesel water, respectively. The possible reason for this decrease is that the water absorption rate is higher and organic solvent enters into voids and pores. The tensile strength also decreases at freezing conditions (−8°C) with increasing time interval (from 64 h to 512 h). A small decrease (up to 3%) in the tensile strength was reported for exposure time of 512 h. The effect of reinforcement of Himalayan nettle on polypropylene composite material was reported by Paukszta et al. (2013). They found that the mechanical properties of PP composite reinforced with 10% by weight of Himalayan nettle fiber do not differ (e.g., tensile strength, elongation at break, impact strength, and hardness) as compared to that of unfilled polypropylene (Paukszta et al. 2013). The Himalayan nettle is commonly known as Girardinia diversifolia, is found abundantly in open forest land, river sides, and moist habitat in Himalayan regions like Nepal and India (some states of India namely: Uttarakhand, Himachal Pradesh and Jammu and Kashmir). It grows naturally at elevations above 1200 meters (ANSAB 2010; WWE 2007; Friis 1981). It is a perennial herbaceous shrub of Urticaceae family. Whereas, Urtica dioica is another nettle is a herbaceous perennial flowering plant in the family of Urticaceae. It is native to Europe, Asia, northern Africa, and western North America (Schellman and Shrestha, 2008).

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The state of Uttarakhand (India) and other Himalayan regions are rich sources of Himalayan nettle (Girardinia diversifolia) locally named as “kandali” found abundantly on roadside hills. The government of Uttarakhand is providing help to the local community people to make nettle fibers. This nettle fiber is a good substitute for other types of fibers because of various potential advantages like nontoxicity, renewable and biodegradable in nature, cost effectiveness, less weight, and eco-friendliness. Therefore, the authors have selected the Himalayan nettle to explore the potential of this plant fiber as reinforcement in composite material. The objective of the present study was to evaluate the physical, mechanical, and tribological behavior of the composite material. The four bidirectional Himalayan nettle fiber reinforced polyester composite panels have been developed. The various tests were performed on the samples.

Material characterization Himalayan nettle (Girardinia diversifolia) plant as shown in Figure 1(a) is utilized with the present study. The nettle fiber is shown in Figure 1(b). Woven textile is identified by its two main directions (length and width) during the wave of the mat as it is woven. It is typified as a biaxial fabric. It is very important to notice that direction in the textile length is referred as 0° (warp), while the width is referred a 90° (weft) as reported by Soberanis et al. (2012). Nettle fiber was made in the form of hand woven mat produced by the interlacing of warp (0°) fibers and weft (90°) fibers in the weave style to maintain the mat integrity by mechanical interlocking of the nettle fiber as shown in Figure 1(c) In this study, above material (fiber) was procured from Uttarakhand Bamboo and Fiber Development Board (UBFDB), Uttarakhand. The density test on Himalayan nettle fiber was carried out at Northern India Textile Research Association (NITRA), Ghaziabad, and it was found to be 1.452 g/cm3. The density of nettle fiber is half as compared to synthetic fiber. The surface modification of Himalayan nettle fiber was done as per the procedure. The fiber was treated with 6% sodium hydroxide (NaOH) in the water for a period of 24 h. The cured or treated fibers were washed thoroughly with water, and then fibers were air dried (in sunlight) for 2 days at room temperature. The authors have followed the procedure as reported by Mylsamy and Rajendran (2010), before introducing into polymer matrix, which results in a good binding effect and high index of crystalline that is governed by the equation (1) as reported by Mwaikambo and ansell (2002). Fiber OH þ NaOH ! Fiber ONaþ þ H2

(1)

The unsaturated polyester possesses many advantages as compared to other thermosetting resins, namely better mechanical properties, cure capability, and transparency, which make the polyester valuable for manufacturing the large components at relatively low cost. The unsaturated polyester resin can be utilized in wide spectrum of manufacturing process to provide good mechanical properties and good surface profiling. The unsaturated polyester resin was procured from M/s Amtech Esters, New Delhi.

Figure 1. The images of (a) Nettle plant, (b) Nettle fiber, and (c) Hand woven bidirectional nettle mat.

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Composite fabrication Many natural composite like rattan fiber composite has been fabricated by hand lay-up technique (Rachchh et al. 2014). Nettle fiber composites panels were also fabricated by hand lay-up technique. It is the conventional method used extensively as it is easy to operate and costeffective. A wooden mold of 300×210×20 mm3 was used. Firstly, Himalayan nettle fiber in woven style pattern was cut in the size of 290mm×200mm after making in the form of mat by making a setup as shown in Figure 2(a). Polyester resin and methyl-ethyl-ketone-peroxide (MEKP) were used as hardener, and cobalt was used as an accelerator in the ratio of 100:2:2 by weight. All three samples were mixed with the help of mechanical stirrer in the plastic jar. A silicon spray was applied on Mylar sheet (2 mm thickness). It was placed in the wooden mold for easy removal of fabricated laminates. A thin layer of mixture (PR, hardener, and accelerator) was poured followed by nettle fiber mat onto the mixture. The same procedure was repeated to achieve the required thickness. The remaining mixture was poured into the mold. A load of 25 kg was applied from the top of the mold, and the mold was allowed to preserve for 24 h. After 24 h, the laminates were sufficiently hard to remove properly from the mold, one of which is shown in Figure 2(b). Composite panels made with four different weight proportions (5%, 10%, 15%, and 20%) of nettle fiber mat were cut, as per the ASTM standard for mechanical, wear, and water absorption tests by a wire hacksaw blade. The various combinations of fiber and resin for making laminate are shown in Table 1.

Thermo physical test Composite prepared in the present study consists of two constituents: fiber and matrix. The theoretical density of composite materials in terms of weight fractions was calculated as per the equation (2), which is reported by Mahendrakumar et al. (2015).

Figure 2. The image of (a) setup for making bidirectional mat (b) Nettle composite laminate.

Table 1. Detailed designations and composition of Himalayan nettle bidirectional composites. S. No. 1. 2. 3. 4. 5.

Designation C1 C2 C3 C4 C5

Compositions Pure polyester (100%) Polyester (95%) +Himalayan nettle Polyester (90%) +Himalayan nettle Polyester (85%) +Himalayan nettle Polyester (80%) +Himalayan nettle

fiber fiber fiber fiber

(5%) (10%) (15%) (20%)


ρct ¼ W ρf

f

1 þ

Wm ρm

5

(2)

Where W and ρ represent the weight fraction and density, respectively. The ρct is the theoretical density of the composite. The suffix f, m, and ct stand for the fiber, matrix, and the composite materials, respectively. The actual density (ρce) of the composite can be determined experimentally by simple water immersion technique. The volume fraction of voids (Vv) in the composites was calculated by using the equation (3)


Vv ¼

ρct ρce ρct

(3)

Mechanical testing plays a key role in the evaluation of fundamental properties of a new material and in controlling the quality of material for its use in the building and design. For this purpose, engineers have developed a number of experimental techniques like tensile test, hardness test, and impact test, and so on. Laminates made of Himalayan nettle fibers are tested for tensile strength, hardness strength, and impact strength. The tensile tests were performed on computerized universal testing machine [HEICO model (HL-590)] with a cross head speed of 10mm/min. Tensile test samples were cut according to ASTM: 3039–76 having shape like dog-bone. The samples for hardness test were prepared according to ASTM: E92. A computerized Vicker’s hardness tester was used to measure the hardness of the samples. A diamond intender with an apical angle of 136° was allowed to intend on the surface of specimen under a load of 1 kg for 15 s. The impact test specimens were cut under ASTM: E23 with dimension 55×10×10 mm, and depth of notch of 3.33 mm (t/3) with 45° angle was performed on Veekay (Model-I 91) impact tester. Impact specimen is allowed to fracture in charpy testing machine that displays the impact energy (joules) absorbed by the samples. Three body abrasive wear test of composite panels was performed on dry sand and rubber/wheel abrasion tester as per ASTM: G65 test by keeping some parameters constant (i.e., wheel speed: 15 rpm, normal load: 67 N, sliding distance: 1046.15 m, abrasive size: 100µm, counter: 1500). Before conducting the test, the surface of specimen was cleaned with a soft paper soaked in acetone. The specimens were pressed against a rotating wheel with a Chlorobutyl rubber tyre of specified hardness. Figure 3 shows the abraded composite specimen with different fiber loading.

Water absorption test The moisture absorption tests were performed as per ASTM: D 570–98 standards on the specimen as shown in Figure 4. The weights of the samples were taken with the help of electronic balance before

Figure 3. Abraded specimen of nettle fiber composite with different fiber loading.


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Figure 4. Specimen of nettle fiber composites for water absorption test.

subjecting them to normal water. After exposure for 24 h, the specimens were taken out from the moist environment, and all surface moisture was removed with tissue paper. The specimens were reweighed to the nearest 0.001 mg within 1 min of removing them from the environment chamber. The weights of the specimens were measured on regular time intervals (such as 24, 48, 72, 96, 120, 144, 168, and 192 h). The moisture absorption was calculated by the weight difference. The gain in weight percentage of the samples was measured at different time intervals by using the equation (4): ðWw Wd Þ 100 (4) Wd Where Ww is the wet weight of specimen at a given immersion time and Wd is the dry weight of specimen. The theoretical, experimental densities and the corresponding void fraction of the composite material are presented in Table 2. This difference in the theoretical and experimental density of the composites is the measure of voids or pores present in it. The presence of voids in composites significantly affects its mechanical properties directly or indirectly. It was observed that the addition of fiber in the polyester resin led to rise in void fraction of the composites as nettle fiber is hollow in structure and also natural fibers consist of lumens in its cellular structure that acts as void. It means such fiber carries these voids naturally. A maximum of 4.10% void fraction is recorded for composite with 20% fiber loading. A similar trend was also observed by previous researchers (Mahendrakumar et al. 2015). W% ¼

Results and discussion Effect of fiber loading on tensile strength The effect of fiber loading of composite material on tensile strength is shown in Figure 5. It has been seen that the tensile strength increases with increase in fiber loading. This shows an effective and uniform stress transfer within the composite after the incorporation of fibers into matrix up to 15wt % fiber loading. It shows a good fiber-matrix bonding. After that it starts decreasing with further Table 2. Theoretical and experimental densities of the nettle composites with void fractions Composites (% fiber loading) Pure polyester 5 10 15 20

Theoretical density Experimental density (g/cm3) (g/cm3) 1.200 1.211 1.221 1.232 1.243

1.171 1.176 1.183 1.189 1.192

Volume fraction of voids (%) 2.41 2.89 3.11 3.49 4.10


7

33

Tensile Strength (MPa)

31 29 27 25 23 21 19 17 0%

5%

10%

15%

20%

25%

Fiber Loading Figure 5. Effect of fiber loading of Himalayan nettle fiber composite on tensile strength.

increase in fiber loading. The possible reason is that the resin is not sufficient to cover up the fiber (McCrum et al. 1997). It was also observed that the composite with 15 wt% fiber loading exhibits an optimum tensile strength of 31.39 MPa among all composites panels. Effect of fiber loading on hardness test The measured hardness value of the hand woven bidirectional nettle mat composites with different fiber loading is shown in Figure 6. The test results obtained indicate that with increase in fiber loading, the hardness of the composites increases. The maximum hardness (11.33 HV) was recorded for the composite material with 15% by weight fiber loading. The possible reason for maximum hardness is due to the brittle nature of lignocellular fiber. The hardness of pure polyester was obtained 17.2 HV. The hardness is a function of a relative fiber volume and modulus. Effect of fiber loading on impact strength The variation of the impact energy of hand woven nettle with different fiber loading is shown in Figure 7. It was found that the impact energy of composites increases with increases in the fiber 27

Vicker's Hardness (HV)


15

25 23 21 19 17 15

0%

5%

10%

15%

20%

Fiber Loading Figure 6. Effect of fiber loading of Himalayan nettle fiber composite on Vicker’s hardness.

25%

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12

Impact Enegy (Joule)

10 8 6 4 2

0%

5%

10%

15%

20%

25%

Fiber Loading Figure 7. Effect of fiber loading of Himalayan nettle fiber composite on impact energy.

loading up to a certain value, and after that, it starts decreasing. The fiber shows maximum impact energy of 25.9 joules for 20 wt% fiber loading. This is due to better adhesion between fiber and matrix. The possible reason is due to the main factors such as fiber pull out, fiber and/or matrix fracture, and fiber/matrix debonding. Similar trends of impact energy have been reported for curaua fiber polyster composite by Monteiro et al. (2013). Effect of fiber loading on specific wear rate The effect of normal load on the specific wear rate of composites keeping parameters constant (i.e., counter, wheel speed in rpm, sliding distance, normal load, and abrasive size) is shown in Figure 8. Abrasive wear mechanisms are operative, resulting in powdery wear debris. Composites with 20 wt% of fiber loading exhibit minimum specific wear rate at 67 N normal loads. It is generally recognized that abrasive wear is a characteristic of a system and is influenced by various parameters. Generally, hardness of any material plays a key role in enhancing the abrasive wear resistance of the composites. The wear resistance of materials is a function of their hardness and elasticity. It can also be seen from Figure 8 that the addition of fiber leads to decrease in specific wear rate and has a minimum value with 15% fiber loading of 0.0195mm3/N-m for nettle composites, whereas neat polyester shows 0.032 Specific Wear Rate (mm3/min)


0

0.030 0.028 0.026 0.024 0.022 0.020 0.018

0%

5%

10%

15%

20%

Fiber Loading Figure 8. Effect of fiber loading of Himalayan nettle fiber composite on specific wear rate.

25%



9

Figure 9. Effect of immersion time on water absorption properties of nettle fiber composites.

maximum specific wear rate of 0.0302 mm3/N-m. It was observed that the addition of fiber in matrix results in improved wear resistance of the composites. This is attributed to the fact that fiber reinforcement offers better resistance to abrasion and is responsible for the reduced specific wear rate as it was harder than the matrix. Effect of immersion time on water absorption properties of nettle fiber composites The effect of immersion time on nettle fiber composite subjected to different exposure time is shown in Figure 9. It was observed that by increasing the fiber loading, the rate of water absorption of nettle composite increases gradually due to hydrophilic nature of the fibers, and insufficient resin on the fiber leads to poor wetting of fiber. At the end, it approaches to a saturation point. The nettle composite with 20 wt% fiber reinforcement has maximum percentage of water absorption. It was increased at faster rate as compared to other nettle composite. It was evident from Figure 9 that the initial rate of water intake increases with increase in fiber content. The maximum rate of water absorption (6.13% of nettle composite) was recorded for 20 wt% fiber loading. This behavior has been explained on the basis of enhancement of micro void formation in the matrix resin. Because of damage and cracks in the composite materials, the capillarity and transport phenomena via microcracks become very active. The amount of water uptake by polyester resin was almost negligible as it was hydrophobic in nature. The initial rate of water absorption and the maximum water uptake increased for all composite specimens as fiber content increased in the composites.

Conclusions The effects of fiber loading of hand woven bidirectional Himalayan nettle fiber composite on various parameters (like tensile strength, hardness, impact energy, water absorption, and abrasive wear) were experimentally investigated. It was observed that the tensile strength and impact energy of fiber increase on increasing fiber loading but up to a certain limit (i.e., up to 15 wt%) of fiber loading, and after that, a decreasing trend was noticed. It was found that the tensile strength and hardness were increased by 72% and 48%, respectively, for fiber loading of 15 wt% as compared to pure polyester. The impact energy was increased 4.7 times for fiber loading of 15 wt% as compared to pure polyester. The water absorption rate of nettle fiber composite increased gradually on increasing the fiber loading due to the hydrophilic nature of the fibers. After certain time interval, a saturation condition was observed. The specific wear rate decreased with increasing the fiber loading to the composite.

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