Synthesis of poly-methyl methacrylate -Zinc composites and Study Electrical Properties 

 

                          ⁽¹⁾Bahaa H. Rabee,  ⁽²⁾ Majeed Ali Habeeb , ⁽³⁾Ahmed Hashim

 

                     

 

                            ^(1,2)Babylon University, College of Education , Department of physics,  Iraq.

 

                            ⁽³⁾Babylon University, College of Science , Department of physics,  Iraq.

 

E-Mail:dr_bahaa19@yahoo.com

 

E-Mail: ahmed_taay@yahoo.com

 

 

Abstract

 

      In this paper, samples of(PMMA-Zn) composites were prepared using Hot Press method. The effect of Zinc content and temperature on the D.C electrical conductivity have been investigated. Results show that the  D.C conductivity of such composites increases suddenly by several order of magnitude at a critical weight concentration.                       

 

     The D.C electrical conductivity changed with increasing of temperature. Also the activation energy change with increasing filler concentration.

 

Keywords: Composites, electrical conductivity, poly-methyl methacrylate.

 

 

Introduction

 

        Polymer Matrix Composite is material consisting of polymer matrix combined with a fibrous reinforcing agent. Polymer matrix composites are very popular due to their low cost, high strength to weight ratio, non-corrosive and simple fabrication methods. Polymer matrix composites reinforcement by strong fibrous network is characterized by the high tensile strength, high stiffness, high fracture toughness, good abrasion resistance, good puncture resistance, good corrosion resistance and low cost [1]. Electrical properties of polymers are the responses when an electric field applied and the subject of electrical properties of polymers covers a diverse range of molecular phenomena. In contrast to metals, when the electrical response is one of electronic conduction polymers display a much less striking response. These absences of any over riding conduction dose allow, however, a whole set of more suitable electrical effects to be observed more easily, for example, polarization phenomena resulting from distortion and alignment of molecules under the influence of the applied field becomes apparent. Examination of such polarization not any gives valuable insight into the nature of the electrical response itself, but it also provides an effective way to probe molecular dynamics. For this, reassign electrical studies form a desirable supplement to studies of purely mechanical properties aimed at reaching an understanding of the behavior of polymers on a molecular level. The study of electrical properties will also facilitate the fundamental understanding of the thermal and optical properties of polymer[2]

 

 

Experimental work

 

     The materials used in this paper is poly-methyl methacrylate as matrix and Zinc  as a filler. The weight percentages of Zinc are (0,25,35,45 and 55).  The Hot Press method used to press the powder mixture. The mixture  of  different Zinc percentages has been compacted at temperature 160^oC under a pressure 100 bar for 10 minutes . Its cooled to room temperature , the samples were disc shape of a diameter about 15mm and thickness ranged between (1.38-1.52)mm. The resistivity was measured over range of temperature from (30 to 80)^oC using Keithly electrometer type (616C) .The volume electrical conductivity defined by :

 

  

 

                                                                                                           

 

Where :

 

A = guard electrode effective area.

 

R = volume resistance (Ohm) .

 

L = average thickness of sample (cm) .

 

In this model the electrodes have circular area A= D²?/4 where    D= 0.5 cm² .          

 

          The activation energy was calculated using equation : 

 

   ? = ?_o exp(-E_a/k_BT)…………..(2)

 

Where:

 

 ? = electrical conductivity at T temperature

 

?₀ = electrical conductivity at absolute zero of temperature

 

K_B = Boltzmann constant

 

E_act = Activation Energy

 

 

 

Results and Discussion                                                                                               

 

       Figure(1) shows the electrical conductivity enhancement of the composite by increasing the concentration of the Zinc filler at T=303k. At lower concentration of the filler [?<40wt.%], the electrical conductivity of the composite increases slightly; while at higher concentration [??40wt.%], the conductivity increases sharply where the composite becomes a good conductive substance. The source of the conductivity enhancement is the electrical contacts generated from the filler networks. At high filler content, the amount of the interconnecting networks is increased and the contact resistance between the filler is decreased, and hence a good electron conduction is achieved resulting in transformation of the polymer insulator to a good conductive polymer composite[3].

 

 

 

 

 

 

 

 

 

 

 

 

     

 

 

        The variation of the electrical conductivity of composites as a function of temperature  is shown in figure(2). The figure shows that the electrical conductivity increase with increasing  temperature(?<?c), this attributed to the polymeric chains and Zinc particles act as traps the charge carriers which transited by hopping process. on increasing the temperature, segments of the polymer being to move, releasing the trapped charges.  The released of trapped charges is intimately associated with molecular motion . The increase of current with temperature is attributed to two main parameters , charge carriers and mobility of these charges. The increase of temperature will increase the number of charge carriers exponentially. The mobility depends on the structure and the temperature[4]. The electrical conductivity decreases with increasing  temperature(?>?c)  that any of this material has a positive thermal coefficient of resistance(conductive material).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                      

 

 

 

      Figure(3) shows the variation of the ln(conductivity) as a function of  inverted absolute temperature of the PMMA-Zinc composites, it can be seen that there are high values of activation energy these high values are attributed to the existence of free ions in the  polymer. By adding low concentrations of Zinc, the values of the activation energy are decreasing for composites as a result of the impact of space charge [5].

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                  The addition of low concentrations creates local energy levels in the forbidden energy gap which act as traps for charge carriers, which move by hopping among these levels. By increasing the Zinc concentrations, the activation energy decreases as a result of the increase of local centers [4], as shown in figure(4) .

 

 

 

 

 

 

 

 

 

 

 

 

Conclusions

 

1.                The D.C electrical conductivity of the poly-methyl methacrylate increases by increasing the Zinc concentrations and its changed with increase the temperature.

 

2.                The activation energy of D.C electrical conductivity decreases by increasing Zinc concentrations.

 

 

References

 

 [1] Alvarez M. P. and Poblete V.H., 2008, “ Submicron Copper- Low- Density                                                                                             polyethylene conducting composites : Structural, Electrical and percolation                                                        Threshold” ,Chile

 

[2] A.R.Blyth, 1979, “Electrical Properties of Polymers”, London-NewYork

 

[3] Younis Khalaf, 2008, “The dielectric properties of polyvinylchloride-nickel                                    composites”, J. of physics, No.3, P.(529-536).

 

[4] Majdi. K.S  and Fadhal H .J,1997,”Electrical conduction of PMMA and the effect                                               of Graphite addition” , Uni. Of Basra, Iraqi of Polymers. , Vol.1, No. 1 , pp(15-20).

 

[5] Ahmed M. S.  and Zihilif A. M.  , 1992, “ The electrical conductivity of                                   polypropylene and Nickel- Coated carbon Fiber composite” ,J. Mater. Sc.                                                                 Vol. 25 , No. 706, Uni. of Jordan ,  Amman , Jordan.