Available online at www.icemme.com

Proceedings of the

1st International Conference on Engineering Materials and Metallurgical Engineering

22- 24 December, 2016 Bangladesh Council of Scientific and Industrial Research (BCSIR)

Dhaka, Bangladesh STUDY OF THE THERMAL AND ELECTRICAL PROPERTIES OF COCONUT SPATHE

FIBER REINFORCED OBSOLETE POLYMER COMPOSITES

Rabeya Akter1*, M. A. Gafur2, Nafis Ahmed2, Budrun Neher1, Md. Mahbubur Rahman Bhuiyan1, Farid Ahmed

1Department of Physics, Jahangirnagar University, Savar, Dhaka. 2Pilot Plant And Process Development Centre, Bangladesh Council Of Scientific And Industrial Research (BCSIR), Dhaka, Bangladesh

1rrabeya1306@gmail.com, 2d_r_magafur@yahoo.com, budrunneher@gmail.com, fahmed@juniv.edu

ABSTRACT This study aims at leading to a recycling and reuse approach to conserve the materials resources and to reduce the waste disposal problem it was explored that the possibility of developing coconut spathe fiber as a new engineering material. The objective of this study was to investigate the properties of the coconut spathe fiber reinforced HDPE composite so that it can be used as a new engineering material and also reuse of HDPE plastic materials. Coconut spathe fiber reinforced HDPE (from HDPE can as obsolete polymer) were prepared by hot press molding method at 1500C under 60 KN load by varying fiber weight percentage from 0 to 20 to the total weight of the composite. Two layer of spathe fiber was used for 15, 20% composite and one layer for 5, 10% composite. Electrical analysis (electrical resistivity, electrical conductivity), thermal analysis (TG, DTG, TMA, thermal conductivity) were carried out. From TG curve, thermal stability for coconut spathe fiber reinforced HDPE composites was maximum for 5% composite. Thermal conductivity of the composite was increased with the addition of fiber in the composite up to 20% composite. Electrical resistivity of the composite was high, in the order of 106ohm.m, it reveals the coconut spathe fiber reinforced HDPE behaves like an insulator. Keywords: coconut spathe fiber, obsolete polymer (recycled HDPE), matrix, TG, DTG, DTA, resistivity, conductivity.

1. INTROUCTION

Recent environmental concerns have triggered the use of natural fibers because they fulfil the sustainability criteria for development and are readily available from renewable sources at a low price. Natural fibers are favored over synthetic fibers as reinforcement [1-3]. Several researchers came up with ideas of reinforcing different natural fibers in polymers to produce eco-friendly composites for several applications [4] Natural fibers like henequen, sisal, jute, coir, etc. possess physical and mechanical properties that make them attractive as reinforcing materials for the substitution of engineering manmade fibers [5-8] which are neither biodegradable nor renewable. Additionally, their hollow tubular structure enhances their acoustic and thermal insulating properties, which could lead to energy saving in several industrial applications [9–13]. Among natural fibers coconut wastes abound throughout the year, an estimated 12.75t dry lignocelluloses residues are generated annually from husks, spathes, peduncles, petioles, leaves. This provides bright prospects for utilizing farm residues and panels production for the construction industry [14]. Coconut spathe, the covering of the coconut inflorescence, is an under-exploited material with considerable potential in this respect. Although substantial research has been carried out on other tissue-types of the coconut palm (Cocosnucifera), e.g., different part from coconut palm tree, e.g., rachis, rachilla, spathe, root, coir have been examined and concluded that all parts can be used for composite, leaf bud sheath, coir, shell [15-18], reports on the use of coconut spathe as a source of fiber in composite materials are scarce. In recent years, the demand for renewable materials for the development of polymer composites has been growing, at the annual rate of 15-20% in automotive applications and 50% or more in construction applications, the rest being in the manufacture of tiles, furniture, sea platforms, etc. [19]. On the other hand, a continued increase in the use of plastics has led to increase the amount of plastics ending up in the waste stream, which motivated to more interest in the plastic recycling and reusing [20]. High density polyethylene (HDPE) is one of the highly requested plastic in the world and common plastic waste. Plastic consumption has increased significantly in the urban areas - from 5.56 kg per person in 2005 to 14.9 kg per person in 2014 and increased the volume of wastes [21]. The understanding of the benefit of natural fiber and availability of coconut spathe fiber has stimulated the current work in which coconut spathe fiber are being developed as new engineering material and recycled

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HDPE as obsolete polymer is used for leading reusing approach. Coconut spathe fiber reinforced HDPE composite was prepared and TG, DTA, TMA was used to analyze the thermal stability of the composite, Thermal conductivity was also studied for the composite.

1. EXPERIMENTAL

2.1 MATERIALS Waste material was employed in this investigation, viz., recycled HDPE as matrix and coconut spathe fiber as reinforcement. The commercially available raw material for matrix was recycled high density polyethylene (HDPE) from colorless HDPE can from local market with a density of 960-970 kg/m3. Coconut Spathe fiber was collected from local sources by hand from coconut tree.

2.2 FABRICATION OF THE COMPOSITE

Composites were prepared by hot press molding method at 150◦C under 60 KN pressure by varying fiber weight percentage from 0 to 20 to the total weight of the composite. The extracted coconut spathe fibers were washed with distilled water in order to remove inclusions and foreign particles and then dried in sunlight for 2 days in daylight. After that, the dried fibers were cut into a size of 14 cm×12cm mat. They were dried in oven for 24 hours to remove moisture and to improve bonding. HDPE sheet of equal size of fiber was taken and these pellets were thoroughly cleaned with water and dried for at least 2 days under the sun in open air before they were used as composite matrix. Two open molding plates of 21cm × 16cm were used for the hot press. By inserting spathe fiber in between HDPE sheet spathe fiber reinforced HDPE composites were prepared. For 5, 10% composite, one layer of spathe fiber in between HDPE, and for 15, 20% composite, two fiber layers were used. Two molding papers were used to cover and compress the composite and let the matrix flow into the fiber uniformly. Figure 1 shows (a) raw coconut spathe fiber and (b) HDPE sheet from colorless HDPE can. Composites for different ratio of HDPE and spathe fiber were made by Paul-Otto Weber Press machine.

(a) (b)

FIG. 1: (A) RAW COCONUT SPATHE FIBER, (B) HDPE SHEET FROM HDPE CAN

The mold was then compressed with 60KN pressure at 150ºC for 20 min and allowed to cool at room temperature. The composition of composites samples are given in table1 below:

Table 1: Composition of different percentages of HDPE and coconut spathe fiber in composites

Composites (coconut spathe fiber layer:

HDPE sheet)

Composition (weight (%) HDPE (wt%)

Coconut spathe fiber (wt%)

C1 (0:2) 100 0 C2 (1:4) 95 5 C3 (1:2) 90 10 C4 (2:4) 85 15 C5 (2:2) 80 20

After the hot press molding operation, the specimen was cut according to ASTM standard and characterized

in terms of density, thermal, mechanical and flexural properties. Table 2 summarizes the property tests performed on each composite sample.

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Table 2: Property tests conducted on sample composites

Property Test Physical Measurement of bulk density

Water absorption of composites

Mechanical Tensile strength at yield of composites % of elongation at break. Flexural test Hardness of composites Impact Strength Test

Thermal Thermo gravimetry analysis Thermo Mechanical analysis Differential thermal analysis Thermal Conductivity

Structural X-Ray Diffraction Test

The dimensions and geometric characteristics of the maximum amount of 25 wt. % spathe fiber

incorporated into the HDPE matrix did not allow the recommended standard specimen thickness to be used. Hence, possible and practically allowable thickness of the composite sample was employed. To measure bulk density and water uptake 50 mm x 10 mm samples were cut.

3. CHARACTERIZATION OF COMPOSITES

3.1 INVESTIGATION of THERMAL PROPERTIES

Thermal Gravimetry (TG) and Derivative Thermo-Gravimetry (DTG) were carried out by a coupled

Differential thermal analyzer (DTA) and Thermo gravimetric analyzer (TGA) to investigate the therrmal stability of the spathe fiber, HDPE and composites. The thermal stability of the composites were observed by EXSTAR TG/DTA 6300.The test was performed at a heating rate of 20o C/min from 30ºC to 600ºC with an inert environment of nitrogen.

The coefficient of thermal conductivity was determined by Lee’s disc apparatus. The procedure is to place the specimen of the samples which were cut equal to the disc, between a steam chamber and two good conductivity metal discs (of the same metal) and allow the setup to come to equilibrium, so that the heat lost by the lower disc to convection is the same as the heat flow through the poorly conducting disc. Thermal conductivity can be determined by the formula,

푘 = (1)

Where, k- Coefficient of thermal conductivity of the sample, A= Area of the sample in contact with the metallic disc, x= Thickness of the sample, T1-T2= Temperature difference across the sample thickness, m= Mass of the metallic disc, c= The heat capacity of the metallic disc, dT/dt= Rate of cooling of the metallic disc at T2

3.2 INVESTIGATION OF ELECTRICAL PROPERTIES

Electrical properties like resistance, resistivity, conductivity was measured by electrometer with source ASTM 6517B. The test specimen was about18mm for every composite. By varying voltage from 0 to 50 volt, current was recorded and from I-V (current-voltage) curve resistance, hence conductivity was calculated by the formula

휎 =⍴

(2)

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Where, = resistivity

4. RESULTS AND DISCUSSION 4.1 THERMAL PROPERTIES

4.1.1 TG, DTA AND DTG OF RECYCLED HDPE PELLETS

The TGA was carried out to investigate the thermal stability of pure recycled HDPE and HDPE/spathe fiber composites samples. Figure 2 shows the TG, DTA and DTG curves for recycled HDPE pellets. The top (blue) one is the TG, bottom (red) one is the DTG and middle (green) one is the DTA curves for HDPE sheet under air environment. The onset temperature which refers to the degradation of a sample are important in determining thermal stability of the composites. Table 3 summarizes the onset and decomposition temperatures of the pure recycled HDPE and HDPE/spathe fiber composites.

Thermal degradation of pure recycled HDPE shows at maximum degradation temperature, the decomposition was faster owing to the increased thermal conductivity of the HDPE.

The TG curve reveals that the onset temperature of recycled HDPE, 50% degradation occurs at 455.9°C, 473.9°C and maximum slope at 479.5°C. The total degradation loss is 91.7%%. DTA yields the two endothermic peaks at 139.1ºC and 481.2ºC respectively. The first one is due to the melting and the second one is due to the degradation of polymer. The DTG curve shows the maximum degradation rate was obtained at 480.6°C with the rate of 5.07 mg/min.

7. LENGTH OF PAPER

FIG. 2: TG, DTG AND DTA CURVES OF 0% RECYCLED HDPE/SPATHE FIBER COMPOSITE

Temp Cel550.0500.0450.0400.0350.0300.0250.0200.0150.0100.050.00.0

DTA

uV

200.0

150.0

100.0

50.0

0.0

-50.0

-100.0

TG %

0.0

-50.0

-100.0

-150.0

-200.0

-250.0

-300.0

DTG

mg/

min

16.00

14.00

12.00

10.00

8.00

6.00

4.00

2.00

0.00

139.1Cel4.3uV

119.1Cel26.9uV

481.2Cel20.5uV

480.6Cel5.07mg/min

332.0Cel-2.3%

455.9Cel-4.2%

491.7Cel-95.9%

524.0Cel-96.2%

473.9Cel-50.0%

91.7%479.5Cel-64.7%

27.9Cel0.0%

196.4Cel-1.1%

1.1%

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FIG. 3: TG, DTG AND DTA CURVES OF 5% AND 10% RECYCLED HDPE/SPATHE FIBER COMPOSITES

FIG. 4: TG, DTG AND DTA CURVES OF 15% (LEFT) AND 20% (RIGHT) RECYCLED HDPE/SPATHE FIBER COMPOSITES

From Fig. 3 and Fig. 4, the TG curve shows the major degradation occurs in one step for spathe-HDPE

composites. The onset temperature i.e., 50% degradation temperature and maximum slope are summarized in TABLE 3. The DTA curve shows the two endothermic peaks which are due to removal of moisture and thermal degradation respectively. The DTG curve also reveals that there are two peaks for 10% and 20% recycled HDPE/spathe fiber composite. DTG curve of spathe-HDPE composites depicts a predominant peak at maximum degradation rate which corresponds to heavier material and the first one for lighter material.

Table 1 TGA, decomposition temperature, onset temperature and the weight lose (%) at maximum

degradation temperature for pure recycled HDPE and its composites incorporating Coconut spathe fiber evaluated in air.

Composite

(wt%) Onset temp. (°C)

50% degradation

(°C)

Max. slope

at (°C)

Weight lose (%)

DTG peak (ºC)

Max. deg. rate

(mg/min)

DTA peak (ºC)

0% 455.9 473.9 479.5 91.7 480.6 5.07 139.1, 481.2 5% 460.6 475.7 481.3 88.6 476.5 12.01 143.8, 476.5 10% 458.1 476.6 480.7 87.4 482.4 5.16 137.9, 482.4 15% 459.4 478.3 484.3 85.4 485.3 6.72 141.5, 483.2 20% 454.5 474.1 478.6 64.7 481.4 2.74 135, 482

Temp Cel550.0500.0450.0400.0350.0300.0250.0200.0150.0100.050.00.0

DTA

uV

150.0

100.0

50.0

0.0

-50.0

-100.0

TG %

50.0

0.0

-50.0

-100.0

-150.0

-200.0

-250.0

DTG

mg/

min

18.00

16.00

14.00

12.00

10.00

8.00

6.00

4.00

2.00

0.00

-2.00

-4.00

143.8Cel-33.5uV 476.5Cel

-37.0uV

29.4Cel0.0%

200.2Cel-1.1%1.1%

198.4Cel-1.1%

381.5Cel-5.6%

4.4%

380.9Cel-5.5%

460.6Cel-8.7%

490.5Cel-97.3%516.0Cel

-102.3%

475.7Cel-52.9%

88.6%

Temp Cel600.0550.0500.0450.0400.0350.0300.0250.0200.0150.0100.050.00.0

DTA

uV

200.0

150.0

100.0

50.0

0.0

-50.0

-100.0

-150.0

TG %

50.0

0.0

-50.0

-100.0

-150.0

-200.0

-250.0

-300.0

-350.0

DTG

mg/

min

14.00

12.00

10.00

8.00

6.00

4.00

2.00

0.00

-2.00

137.9Cel-4.7uV

482.4Cel11.7uV

371.0Cel0.34mg/min

482.4Cel5.16mg/min

35.5Cel0.0%

199.4Cel-1.2%

1.2%

248.1Cel-1.5%

398.9Cel-10.8%

9.3%

398.9Cel-10.8%

458.1Cel-13.8%

494.8Cel-101.2%

524.5Cel-101.5%

476.6Cel-57.5%

87.4%480.7Cel-67.7%

Temp Cel550.0500.0450.0400.0350.0300.0250.0200.0150.0100.050.00.0

DTA

uV

200.0

150.0

100.0

50.0

0.0

-50.0

-100.0

-150.0

TG %

0.0

-50.0

-100.0

-150.0

-200.0

-250.0

-300.0

DTG

mg/

min

35.00

30.00

25.00

20.00

15.00

10.00

5.00

0.00

-5.00

141.5Cel-9.2uV

483.2Cel-4.9uV

485.3Cel6.72mg/min

27.7Cel0.1%

200.3Cel-1.3%

1.4%199.2Cel-1.3%

400.1Cel-9.7%

8.4%

400.2Cel-9.7%

459.4Cel-12.1%

497.1Cel-97.6%

524.0Cel-98.0%

478.3Cel-54.8%

85.4% 484.3Cel-68.7%

Temp Cel550.0500.0450.0400.0350.0300.0250.0200.0150.0100.050.00.0

DTA

uV

140.0

120.0

100.0

80.0

60.0

40.0

20.0

0.0

-20.0

-40.0

-60.0

-80.0

TG %

0.0

-50.0

-100.0

-150.0

-200.0

-250.0

DTG

mg/

min

12.00

10.00

8.00

6.00

4.00

2.00

0.00

-2.00

135.0Cel11.2uV

482.0Cel33.0uV

406.1Cel42.5uV

481.4Cel2.74mg/min

368.2Cel0.28mg/min

50.2Cel-0.1%

113.1Cel-0.8%

0.7%

113.1Cel-0.8%

200.1Cel-1.4%

0.5%200.1Cel-1.4%

400.3Cel-15.3%

13.9%

400.1Cel-15.3%

454.5Cel-18.3%

493.6Cel-83.0%

521.7Cel-83.5%

474.1Cel-50.7%

64.7%

478.6Cel-58.1%

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4.1.2 Thermal Conductivity Measurement

Fig. 5 shows the thermal conductivity of the composites has decreased with increase in volume fraction of fibers. At maximum volume fraction of fiber, the thermal conductivity of the composites has varied from 0.117 W/ºC.m to 0.147 W/ºC.m in the temperature range 40-80ºC. The thermal conductivity of composites increases with increase in fiber angles. The spathe fiber reinforced HDPE composite possess good thermal insulating properties.

FIG. 5 THERMAL CONDUCTIVITY OF DIFFERENT WT% OF SPATHE FIBER REINFORCED HDPE COMPOSITES AT DIFFERENT TEMPERATURE.

4.2 ELECTRICAL PROPERTIES

4.2.1 I-V CURVE CHARACTERISTIC CURVE

The graph of current versus voltage for different wt% of spathe fiber- recycled HDPE composites are

shown in fig. 15. This graph shows linear curve within certain range which means all composites following Ohm’s law of current at some voltages.

Fig. 6: I-V characteristic curves of different wt % of spathe fiber-HDPE composites.

4.2 Electrical Resistivity Measurement The resistivity of fiber reinforced composites depend on the moisture content, crystalline and amorphous component present, present of impurities, chemical composition, cellular structure, microfibrillar angle etc.

00.00010.00020.00030.00040.00050.00060.00070.00080.0009

40 60 80

Ther

mal

Con

duct

ivity

(W

/ºC.m

)

At Temperature in degree

20% composite15% composite10% composite5 % composite0 % composite

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From I-V characteristic curve the resistance was calculated, hence resistivity. The shapes of reinforcement determine the interparticle contact, which affect the conductivity [22]. The moisture content in fibers increased the conductivity i.e. decreased resistivity [23]. Fig. 7 shows volume resistivity of recycled HDPE, after incorporating fiber the resistivity decreased at 5% recycled HDPE/spathe fiber composites, hence resistivity again increased for 10% and 20 % recycled HDPE/spathe fiber composites. The hydroxyl group in the hydrophilic fiber can absorb moisture and hence the presence of the natural fiber decreases the resistivity.

Fig. 7 Resistivity of the different wt% of recycled HDPE/spathe fiber composites

5. CONCLUSION

The performance of an engineering material is essential for selecting the proper material in a given application as well as for designing a composite structure with the selected material. The objective of this work was to fabricate and study the effect of addition of Coconut spathe fiber in composites with recycled high-density polyethylene matrix reinforced with different amounts of spathe fiber pieces, with a view to examine the possibility of spathe fiber as a new engineering material with HDPE. The effect of addition of coconut spathe fiber in HDPE polymer composite has been studied by evaluating the thermal and electrical properties. Thermal analysis of the composites revealed that the thermal stability of recycled HDPE/spathe fiber composites is higher than that of recycled HDPE pellets. It would be nice to produce the samples by using injection molding machine instead of hot press machine. Because in hot press machine made samples presence of air bubbles are almost inevitable. The surface electrical resistivity was decreased with the incorporation of fiber in the HDPE pellets. But the surface resistivity of the composites had higher values in the order of 106, behaving like good insulator. Additionally, studies on the durability, biodegradation, and long term behavior of the composites are necessary if they are to be used in load bearing applications.

6. ACKOWLEDGEMENT I am thankful to National Science and Technology (NST) Fellowship, Ministry of Science and Technology, Government of the People’s Republic of Bangladesh. This research work has done under the technical support of Pilot Plant and Process Development Centre laboratory, BCSIR, Dhaka under the co-supervision of Dr. M. A. Gafur.

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