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Conduction Mechanism and Conductivity Behaviour of Pure Polypropylene (pp) and Polypropylene-banana Fiber (pp-b) Composites

Md. Nazrul Islam*
Department of Physics, Primeasia University, Bangladesh

M.A Gafur
P. P& PDC, BCSIR, Bangladesh

Md. Amir Hossain Khan
Department of Physics, Jahangir Nagar University, Bangladesh

Abstract/ Executive Summary:

Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials. The research on natural fiber based composite materials fit well into this ecological image. This paper reports the conduction mechanism and ac conductivity, activation energy behavior of Polypropylene and banana fiber reinforced thermoplastic composites. Polypropylene [-CH2-CH2-CH2-]n and different fiber content (wt. %) of polypropylene-banana fibers (natural fiber) composites were fabricated using a hot-press molding system. The optimum fabrication parameters were established (initial pressure, temp. etc.). These composite test samples were fabricated so the short fibers were randomly oriented in the matrix. The detail investigation of the a. c. conductivity and conduction mechanism of polymer composites would provide information about the relaxation processes, activation energy etc. which are dependent on frequency, temperature and time. The activation energy involved in the above processes can also be estimated from this study. The measurements were performed over a wide range of frequency of 60 Hz to 3 MHz and temperature range from 30°C (303°K) to 110°C (383°K). Experimental results of the ac properties of pure polypropylene and polypropylene-natural banana fiber composites were compared. It has been established that the fabricated composition changes its insulating property after adding the natural fibers and gives the better conductivity properties.

Keywords: Composites, Ac conductivity, Dielectric constant, Hopping conduction, Interfacial polarization, Activation energy

Location: Department of Physics, Primeasia University, Bangladesh

Start Date:

End Date:

Program Area: Comparative study

Commodity: Banana

Objectives:

The polymers usually behave as insulating materials having resistivity of the order of 108 -1014 Ω-m. They have high degree of toughness flexibility and can be molded at higher temperature. Due to this reason some polymers have high resistivity, high dielectric breakdown strength. So, the study was undertaken to justify it.

Methodology:

2.1 Materials PP was collected from local market. Banana fibers were collected locally. All these fibers were chopped and kept at 3830 K for 24 hours for moisture free. For getting uniform length, all these fibers were sieved by 2 mm sieve. PP matrix materials were also taken as moisture free at the same procedure. 2.2 Sample Preparation 2.2.1 Fiber Cutting and Mixing All the fibers were collected locally and chopped by a sharp knife and sieve by 2 mm sieve to get uniform fiber. This fiber kept at a dry environment (oven) for 24 hours at 383°K. Fiber and polymer were thoroughly mixed using a blender. The mixing time and blade speeds were 2 minutes and 400 rpm respectively. For uniform mixing this process was repeated 3 times and the intermingled fibers are separated manually.

2.2.2 Casting, Molding and Demolding A steel device is made to very close tolerance for the molding process. The mixture of fiber and matrix is cast by simply pouring the mixture into the mold and leveling it to the desired thickness. Only slight stamping or hammering on the mold is required for sufficient compaction. Both mixed fibers and polymer were taken in a mold. An initial of 50 KN pressure over the sample area was given to top of the mold and then the mold was kept in a P/O/ Weber Pressen Hydraulic Machine. The applied pressure is measured by using a load cell, set in the device. Heating was done electrically and the temperature set at 453°K. Only 25-30 minutes were required to reach such temperature. The temperature was kept at 453°K for 20 minutes. After completion of heating the final pressure of 50 KN over the sample area was set to avoid the kind of voids and have a desired thickness. This additional pressure was kept for one hour. An attempt has been made to prepare PP- fiber composite of different proportion of PP and fiber according to (100-X) PP: X Fiber [X= 0, 10,20,25]. Four batches of different mixing ratios (100:0), (90:10), (80:20), (75:25) were used. The percentage (%) of fibers was taken as 0, 10, 20, and 25 of total 100 gm of composites for the fabrication of PP & banana fiber composites. Cooling was done by water flow through the outer area of the heating plates of the hydraulic press machine for 25 minutes. When the Weber Pressen hydraulic machine is made the specimen. The specimen was cooling, the specimen adheres very strongly with the mold; the makeshift device did require removing by a set up device, which is made as a makeshift device. After separation of the composites from the device. After cooling and de-molding, the prepared samples were then made in a circular shape to form compact pellets of diameter 8 mm to.01m by cork-borer with heavy pressure.

2.3 Testing Procedure For ohomic contact both sides of the prepared samples were polished by sand paper and coated with silver paste. The ac. conductivity and dielectric properties have been measured using a Wayne Keer B224 Universal (transformer ratio arm) bridge. The ac conductivity with frequency and frequency of PP and PP-B are calculated from the measured data. These parameters have been measured at temperatures of 303, 343,363K as a function of frequencies of 60Hz 10 KHz, 1 MHz and 3 MHz. The sample temperature, during the experiment PID thermostatic Oven (SE-70, electrode AS 20438) containing the sample holder which is connected with proper screening to the measuring electrodes. in instruction manual. All these measurements were taken 4 times for each batch and average values were considered. In this measurement there were no major variations with in individual data. Here the value of conductance G0 was obtained initially by adjusting the conductance ratio arms and after connecting the sample a final value of conductance G¤ was obtained by adjusting the conductance ration arms. Finally, the conductance Gx was obtained conductance ration Gr and (G¤-G0). AC conductivity were performed at different frequencies and temperatures by using the following formulae: ac conductivity = sac = (d/A) Gx where, d is the thickness, A is the area of sample and e0 is permittivity of free space.

Source of Information: Journal of Building Material Science | Volume 02 | Issue 02 | December 2020

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The ac electrical conductivity of the composites increases as the concentration of banana fiber increases in PP. It is also observed that ac conductivity decreases with the increase of temperature up to 363K and then remains almost constant in the composites at all frequencies. The frequency and temperature dependence of sac may be attributed to the increases of relaxation times dominated by interfacial type of mechanism. This feature can be attributed to the dominating contribution of interfacial polarization in the composites with higher fiber concentration. which indicates that fiber act as an intermediate plasticizer in the composites. The differences in activation energies become less with the increase of concentration of fiber in the matrix. Experimental observations suggest that it is possible to make PP-banana fiber composites by the hotpress molding method and these composites can be used in the manufacture of high frequency electrical device. This fabrication technique may also be applied to prepare the dielectric material for the preparation of capacitor and other electrical devices.

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