A H, Bhuiyan

A, Razzak

IACS Institutional Repository

Indian J. Phys. 77A (4). 353-357 (2003)/U P  A \DC electrical conduction mechanism in polypropylene~Bijoypurwhite clay (PI^BWC) compositesA Ra/zak tml A H Bhuiyan"^Department ol‘ Physics, Bangladesh University of Engineering and I'eehnology tBU Ii'D , Dliakn KHM). BangladeshE-mail . ab||Miyan<«>phy hue! ac hdReceived 5 September 2002, au cpicd 2d Matdi 200 iAbstract : Polypropylene-Bijoypur white clay (PP-BWC) composites were prepared at dilfereni compositions ol PI* and BWC ol Bangladesh by extrusion technique. Structural change was investigated using X-ray dilfractonietiy (XRD) The dc eleciiical coiuliietioii mechanism of different PP-BWC composites was studied by current-voltage (I V) characteristic mcasuremems It is observed that Poole- Frenkel type of mechanism is operative in these materials The dc conductivity measurement of the dillerent samples was performed m the temperature range 29H K to 400 K. The temperature dependence of electrical conductiviiy indicates that the conduction is due to thermally activated hopping of charge carriers.Keywords : Polypropylene-Bijoypur white clay composites. X-ray diffractomctry, dc electrical propeilics PACSNos. : 61.41+e, 72m T in , 6l.IO.Nz1. IntroductionPolymer composites have attracted much attention of the researchers in recent years because of their application in a variety of areas such as electrostatic charge dissipation, electromagnetic inlerferencc/radio frequency (EMI/RF) shielding, electrodes for polymer-based batteries and intermediate layers of high-voltage cable [1-5]. Many reports have appeared both on the theory of electrical conduction [b,7| and experimental finding in a number of such composites [8,9]. Radhakrishnan and Saini [1()| carried out an investigation on dc and ac conduction of polyester elastomer filled with various metallic and ferrite fillers as a lunclion of temperature, frequency and filler concentration. The results have been explained on the basis of Schottky barrier formation and the depiction regions formed near the polymer-metal interface. There are also reports on the electrical properties of ceramic/polymer composites [II], mixed rubber composites [ 1 2 ], polyethylcne-carbon-fiber composites [13], carbon black-filled  high densityCorresponding Authorpolyethylene (HDPE) composites 114), polyanilinc/ polypropylene (PANI/PP) composites [15]. The dielectric loss of the ccramic/polymcr composites is observed to dominate by those of the polymer, whereas the ceramic phase may have a significant contribution on the steady- state electrical conduction and low-frequency dielectric loss at high temperature |I1]. The activation energy decrease observed in mixed rubber composites may he associated with gradual decrease in the temperature coefficient of conductivity [ 1 2 ].Shan Ren and Hon (16] prepared composite from a newspaper fiber-rein forced polypropylene (NPF/PP) and intcrfacial modification on the mechanical properties were investigated. Natural fibers, such as recycled corrugated board, chemical wood pulp, ihcrmomcchanical pulp, and cotton pulp were also found to have reinforcing properties for polypropylene. The mechanical properties have been improved by blending of carbon fiber with the NPF/PP composites. Ahmad e t a l  [17] have investigated the electricalO 2003 lACS354 A Razzak and A H Bhuiyanproperties of polypropylene-tale (PP-talc) composites. It was found that electromagnetic waves interact with the material via the impurities, inclusions and voids existing in the bulk composites. The impedance, return loss and insertion loss shows relatively low Ircqucncy dependence. These results suggest that this composite material may find some microwave applications.Bijoypur white clay (BWC) is being u.scd m ceramics, insulators and sanitary industries of Bangladesh. Chowdhury and Bhuiyan earned out investigations on the structural [ 18| and dc electrical [19] properties of BWC on heal treatment at high temperature. Bui so lar, no study of the electrical properties of PP-BWC composites has been appeared in the literature.TItis work is an attempt to elucidate the dc electrical properties of PP-BWC composites from the current-voltage (I”V) characteristics and temperature dependence of dc electrical conductivity. 7'he XRD analysis ol’ the composites is also included.2. Experimental details2. /. Sam f)lc p re p a ra tio n  :Composites used m this work were prepared from PP (NOVOLRN MOOL 2310025, BASP\ Germany, density = 9(X) kg/m\ melting temperature = 338 K, glass transition temperature = 270 K, refractive index /i = 1.3, molecular weight A/„. = 184700 g/mole) and uncompressed hard and solid BWC collected from mine at Bijoypur, Nctrakona, Bangladesh. Collected BWC lumps were manually crushed into powder using mortal and pestle and then sieved through a 200 mesh sieve. At first, five batches with different composition.s (wt^ iJf) of PP and BWC powder were prepared according to the formula lOPP : xBWC where a = I, 2, 3, 4, 5. The samples arc represented asSampledc,signation A B C, C4 c ,Composition(wt%) PP BWC 10 : 1 K) : 2 10 ; 3 10 : 4 10 5The different mixtures were mixed during passingthrough an extrusion machine. The molten material was collected through the die in the form of rod. The rod shape composite samples were cut into pellets. The samples were then placed inside a die punch of internal diameter 0.019 m. The pellet ,shapc samples were pressed using a hydraulic pressing unit at a pressure of 34 MPa at 398 K for five minutes. After removing the sample from the die punch, its upper and lower faces were polished.and then thin coating of conducting silver paste was applied on both sides which act ils. electrode for electrical measurements.2.2. M e a su re m en t te ch n iq u es  :2.2. L  X -ra y  d iffra c tio nAn X-ray diffractometer (Model JDX-8P JEOL Ltd., Tokyo, Japan) was used to record the XRD patterns of all ih^  samples. The target is and the wavelength of X-ra\radiation is 1.5418 A . The XRD patterns of the sampk s mentioned in Section 2.1 were recorded as a function nj 2 6  from 3 to 73^2.2.2. D C  e lec tr ic a l m ea su rem en tThe dc current was measured using a digital Kcithky Electrometer (model 614, Kcilhley Instrument liu Cleveland, Ohio, USA). A pressure contact .specimen lioklcr housed in a steel chamber, with an in-built heater was employed for the measurement. A transistorized powei supply, model 6181C of Hewlett Packard was used loi voltage supply across the samples. The dc conductivity was calculated from the measured dc current through the saiujik and effective .sample dimensions. Thickness of the sample is 4.25 X 10"^  m and diameter is 6.35 x 1(>-^  m. The I V characteristic measurement was performed from 10-160 V at room temperature. The temperature dependence ol ik current was measured from 298 K to 420 K with a conslani (k applied voltage of 1(X) V. The temperature was rccouktl by a Cr~Al thermocouple by measuring the emf with a micro voltmeter (model 197A of Kcithlcy Instrument Inc Cleveland, Ohio, USA). All the measurement wcic performed in vacuum (« IO~Uorr ).3. Results and discussion3.1. X R D  a n a ly s is  :X-ray diffraction patterns of the samples A, B, C|, C2, Cu C4 and C^  are presented in Figure 1. These diffractionFigure 1. The XRD patterns of all the samples represented by ko A (PP), (b> : B (BWC). (c) : C,, (d) : Cj. (e) : C,, (0  : C4 and (g) ODC electrical conduction mechanism etc 355paticrns are represented respectively by diffractograms a, h, ( i  e. A and g . The details of the X-ray scans (20 and dhki) arc depicted in Table 1.Tabic 1. 29 and r/|,ki values of samples A (PP) and B (BWC),BWCPP20 (degree) 1.2 14 017 018 6 21 9 25 6 29 4 3T8 43.4 47 8 4S.8duk\ (A) 12 277 6 325 5.215 4.770 4 058 3 479 3 038 2.652 2 085 1 903 1.86629 (degree)9.2 12.6 20 0 21.025.0 26 8 36 638.039.442.4 45.8dm  (A) 9612 7 030 4.440 4 230 3.560 3.320 2 455 2 370 2 286 2.1.32 1 981These variations in the XRD reflections indicate a definite effect of BWC in the PP structure.3.2. C urren t vo ltage ( l - V )  ch a ra c te r is tic s  :Figure 2 shows I-V characteristic curves for sample A, Ci, C2, C3, C4 and C5 measured at room temperature. It is observed that current increases non-linearly within the voltage range used. It is also seen that current increases as BWC concentration in PP increases. The non-lincanty in I~V characteristics of PP and composites implies different conduction mechanisms in different voltage regions.In the XRD pattern of sample A (PP), it is observed that the intense diffraction maxima appear at the 2 6  values of 14", I T \  18.6“, 21.9°, 25.6°, 29.4°, These values are niaiched very closely with the values reported by several authors [20,21] indicating that the PP used in this experiment is isoiactic. The X-ray scans of PP indicate monoclinic a  lorm  crystallites with some peaks absent. The absence of s o m e  peaks could be due to orientation of the crystalline p h a se  [22J.The XRD pattern of the sample B (BWC) shows the main position of diffraction peaks at the 2 6  values of 1 2 .6 *^* 20", 21°, 25°, 26.8°, 36.6°, 38°, 39.4°, 42.4°, 45.8°, 55°. The XRD analysis shows the presence of kaolinilc (7.03, 3.56 and 1.45 A), silicon oxide (4.44, 2.44 and 1.45 A), iron oxide (1.67, 1.38 and 1.28 A), potassium aluminium silicate hydroxide (4.93, 3.56, 2.53 and 2.37 A), aluminium silicate (9.61 and 4.44  A), etc. Very small amount of oxides fd potassium, calcium, sodium, e tc  may also be present as reported by Biswas and Basak [23] and Chowdhury and Bhuiyan [I 8 j.The XRD patterns of samples C, to Cs containing different amount of BWC shown in Figure 1, exhibit mostthe major characteristic reflections present in the XRD patterns of PP and BWC. It is observed that the intensity of the characteristic reflections (20 = 12.6°, 20°, 21°, 25°, 26.8°, e tc )  of BWC is increasing and that of PP (20 = 14°, 17°, 18.6°, 21.9°, 25.6°, 29.4°, e tc )  is decreasing gradually tts the BWC proportion increases. The apparent doublet at 20 = 21.9° in the XRD pattern of PP becomes a clear doublet and appears as two distinct intense reflections ta case o f composites with high BWC concentrations.Figure 2. Variation of log,,,/ with log,,, V (applied voltage in V) for different samples.It is observed that the dependence of / on V  can be fitted to a relation /  «= V'*, where n is the power factor. Various conduction mechanisms arc characterized by different values of n. The case of n = 1 represents Ohmic conduction and is usually the re.sull of the field-independent values of the carrier concentration and the mobility. The carriers may be ions, holes or electrons, but must be intrinsic to the material. If the value of n is more or less than unity, then the conduction mechanism is other than Ohmic. Here, there are two slopes : one at low voltage region 10-110 V, and the other at high voltage region 110-160 V, for all the samples. The n values arc depicted in the Table 2. It is seen that the n values arc close to unity in the lower voltage region andTabic 2. n values for different voltage regions for the samples A and C, to C5.Samples Region 10-110 V Region no-A 0.75 1.66c, 0,75 1.45Cl 0.75 1.40Cy 0.75 1.25C4 0.80 1.20c, 0.80 I.IO356 A Razzak and A H Bhuiyanth a t  a r c  m u c h  a b o v e  u n ity  a t h ig h e r  v o lta g e  re g io n . T h e  n o n - l in e a r i ty  o f  l o g io /  v e rs u s  lo g jo V  c u rv e s  c a n  b e  d u e  to  th e  s p a c e  c h a rg e  b u ild -u p  g iv in g  r is e  to  th e  n o n -u n ifo rm ity  o f  th e  f ie ld  d is t r ib u t io n  b e tw e e n  th e  e le c tro d e s  a n d /o r  m a y  a ls o  b e  r e la te d  to  th e  g e n e ra t io n  o f  c a r r ie rs  in  th e  b u lk  o f  th e  m a te r ia ls .  T h e  a b o v e  r e s u lt  s u g g e s ts  th a t th e  c o n d u c tio n  m e c h a n is m  in  th e s e  m a te r ia ls  m a y  b e  sp a c e  c h a rg e  l im ite d  c o n d u c tio n  (S C L C ), S c h o ttk y  o r  P o o le -F re n k e l ty p e  [2 4 ,2 5 ] , It is  s e e n  th a t a s  th e  B W C  c o n c e n tra t io n  in c re a s e s ,  th e  d if fe re n c e  in  s lo p e  d e c re a s e s . T h is  m e a n s  th a t th e  c o n d u c tio n  m e c h a n is m  te n d s  to  b e  in d e p e n d e n t  o f  v o lta g e  a t  h ig h  B W C  c o n c e n t ra t io n s .  I t  is in te re s t in g  to  n o te  th a t  c o m p o s ite s  w ith  h ig h  B W C  c o n te n t  s h o w  v e ry  c lo s e  to  O h m ic  b e h a v io u r  in  th e  e x p e r im e n ta l  v o lta g e  re g io n .T h e  I - V  d a ta  a re  p lo t te d  a s  l o g io /  v e rs u s  in  F ig u re  3 fo r  fu r th e r  a n a ly s is .  It is  s e e n  th a t  th e  c u rv e s  a re  l in e a r  in th e  h ig h e r  v o lta g e  ra n g e . I t is  a ls o  o b s e rv e d  th a t  th e  lo g io /  v e rs u s  c u rv e  b e c o m e s  l in e a r  w ith  th e  in c re a s e  o f  B W C  c o n te n t  th r o u g h o u t  th e  v o lta g e  ra n g e . T h is  s u g g e s ts  th a t  th e(voltagc)‘'2v>'2 “Figure 3. Variation of logio f with (applied voltage in V) for different samples.conduction is bulk limited. These results indicate the possibility of presence of Poole-Frenkel type of mechanism in these materials.3.3. Temperature dependence of dc electrical conductivity( a ) :Figure 4 shows the plots of logio (T versus 1/T curves for samples A, Ci, Cj, Cj, C4 and C5. It is seen that there are two temperature regions, namely, region I (298-360 K) and region II (above 360 K). The dc conductivity increases slowly in region I and that in region II increases rapidly with temperature.The increase of cr with temperature may be due to the increased movement of the adventitious ions and/or electrons. The carriers experience a thermal velocity due to the increase in temperature in addition to the ^plied electric field whichw a s  k e p t  c o n s ta n t  a t  1 0 0  V . S o  th e  r e s u l t a n t  v e lo c iu  e x p e r ie n c e d  b y  th e  c a r r ie r s  is  th e  s u m  o f  th e  d r if t  vclocitv d u e  to  th e  a p p l ie d  f ie ld  a n d  th e  th e rm a l v e lo c ity , in ihis s tu d y , th e  th e rm a l v e lo c ity  is  c h a n g e d  d u e  to  th e  in c rease  m te m p e ra tu re .T h e  a c t i v a t i o n  e n e r g y  ( E r )  f o r  t h e  s a m p le s  w as d e te rm in e d  f ro m  F ig u re  4 . T h e  v a lu e s  o f  a c t iv a t io n  energy a s s o c ia te d  w ith  th e  tw o  te m p e r a tu r e  r e g io n s  o f  all ihc s a m p le s  a re  d e p ic te d  in  T a b le  3 . T h e  a c t iv a t io n  en e rg y  o[ a ll th e  .sam p les h a s  h ig h e r  v a lu e  in  h ig h  te m p e ra tu re  region th a n  th o s e  a t  lo w  te m p e ra tu re  r e g io n . In  b o th  lo w  an d  high 400K 368K 3.33K 308KFigure 4. Variation of logi^ or with \/T  for different siunples.Table 3. Activation energy (£V) values for the samples A and Cj to (VActivation energy, £V (eV)Samples Region 1 (298-360 K) Region II (above 360 K)A 0.09 0.15c, 0.06 0.16Ci 0.08 0.16C'K 0.07 0.20C4 0.05 0.10Cs 0.04 0.11temperature regions, the activation energy decreases with increasing percentage of BWC. The existence of the shallow trap levels in the materials, is supported by the existence of different small values of activation energies at low and high temperatures. With the increase in temperature, carriers ot respective trap levels take part in the conduction process.The low activation energy as obtained from the temperature dependence of conductivity, indicates the existence of thermally activated hopping conduction in theseDC electrical conduction mechanism etc 357materials [26]. In  th is  k in d  o f  c o n d u c t io n  p ro c e s s ,  th e  c a r r ie r  may b e  b o u n d  to  th e  a g g lo m e r a te s  i ts e lf .  As a  re s u lt ,  th e  carriers m a y  n o t  ta k e  p a r t  in  th e  c o n d u c t io n  th ro u g h o u t th e  bulk o f  th e  m a te r ia l .4, ConclusionsThe X R D  in v e s t ig a t io n  s h o w s  a  d e f in i te  c h a n g e  in  th e  P iV  B W C  s t r u c tu re  w ith  B W C  c o n c e n t r a t io n .  I t m a y  b e  in fe r re d  from  th e  I - V  c h a r a c te r i s t i c s  th a t  th e  P o o le - F r e n k c l  ty p e  m ech an ism  m a y  b e  o p e ra t iv e  in  th e s e  m a te r ia ls .  T h e  in c rc a s^  of dc  e le c tr i c a l  c o n d u c t iv i ty  w i th  te m p e r a tu re  is  d u e  IE) in creased  m o v e m e n t  o f  th e  a d v e n ti t io u s  io n s  a n d /o r  e lec tro i]^  within th e  m a te r ia l .  T h e  lo w  a c t iv a t io n  e n e rg y  in d ic a te s  that th e  th e rm a l ly  a c t iv a te d  h o p p in g  c o n d u c t io n  is o p e ra t i^ ^  m th e se  m a te r ia ls .AcknowledgmentTire a u th o rs  a rc  th a n k fu l  to  th e  a u th o r i ty  o f  B a n g la d e s h  U n iv e rs ity  o f  E n g in e e r in g  a n d  T e c h n o lo g y ,  D h a k a  fo r  p ro v id in g  th e  f in a n c ia l  s u p p o r t .References[II S K Bhattacharya Metal Filled Polymer (New York : Dekkcr) (1986)121 D A  Scanor Electrical Properties of Polymers (New York . Academic) (1982)n j  IZ K Sickel Carbon Black Polymer Composites (New York : Dekkcr) (1982)[41 A Slcrnfield Modern PlastUs Ini 48 (1982)D M  Bipg Polym. Compos 8 1 (1987)16] S K Bhattacharya and A C D Chaklader Polym Plast. TechnoL i (1982)[7] R D Sherman, L M Middleman and S M Jacobs Polym, Enftfi. Sci. 23 36 (1983)18] S Radhakrishnan J Mater Sci U tt 4 1445 (1985)19] Z Q Q Baker and M K Abdcla/cc/ ./ Mater Sn  23 2995 (1988)[10] S Radhakrishnan and R D Saini J Mater Sn  26 5950 (1991)f l l]  M J Abdullah and D K Das Gupta J. IEEE Trans Electrical Insulation 25 605 (1990)(12| M Amin, G M Nusr and M S Sobhy J Mater Sci 26 4615 (1991)[13] F J Balta Callcja, R K Bayer and T A E/.querra J Mater Sci. 23 1411 (1988)[14] Gun Joo Lee, Kyung Do Suh and Scung Soon Im J Polym Ettftfi S (i 38 471 (1998)[15] Jiping Yang, Chunttan Zhao, Di Cui Jianan Hou. Meixiang Wan and Mao Xu J. Appl Polym Sn  56 831 (1995)[16] Shan Ren and David N S Hon J. Reinforced Plastic and Composites 12 1311 (1993)[17] M S Ahmad, M K Abdelazcez and A M Zihlif J Mater. Sci 24 1795 (1989)[18] F-U-Z Chowdhury and A H Bhuiyan Indian J Phys. 71A 569(1997)[19] F-IJ-Z Chowdhury and A H Bhuiyan Indian J Phys. 71A 635 (1997)[20] A K Gupta and S N Purwar J Appl Polym. Sn. 25 24 (1980)[21] S N Maiti and P K Mahapatro J. Polym Mater. 6 107 (1989)[22] A T Jones, J M Ai/elwood and D R Deckett Makromol. Chem. 74 134 (1964)[23] M A Biswas and A K Basak Pak. J. Sci Indus Res. 4 118 (1961)[24] J G Simmons Phys Rev 155 657 (1967)[25] 1 M Talwar and D R Bhawalkar Indian J Pure Appl. Phys 1 681 (1969)[26] S L Wu and I C Tung ./ Mater Sci 31 2177 (1996)

DC Electrical Conduction Mechanism in Polypropylene-Bijoypur White clay (PP-BWC) Composites

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DC Electrical Conduction Mechanism in Polypropylene-Bijoypur White clay (PP-BWC) Composites

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