Hardening induced by gamma irradiation in poly(methyl methacrylate): Poly(chlorotrifluoroethylene) blends

01423418(95)00032-0 ELSEVIER

Polymer Testing 15 (1996) 291-296 0 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0142-9418/96/$15.00

MATERIAL PROPERTIES Hardening Induced by Gamma Irradiation in Poly(methy1 methacrylate): Poly(chlorotrifluoroethylene) Blends P. Agrawal,

R. Bajpai & S. C. Datt*

Department of Postgraduate Studies and Research in Physics, Rani Durgavati University, Jabalpur (M.P.)-482 001, India (Received 25 January 1995; revised version received 18 June 1995; accepted 27 July 1995)

ABSTRACT Specimens of poly(methy1 methacrylate) (PMMA) and poly(chloro trifluoroethylene) (PCTFE)

polyblends with different weight percentage

ratios were irradiated with

various doses of gamma irradiation (I-100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using the Vicker’s microhardness research

microscope.

tester attached to a Carl Zeiss NU 2 Universal

The value of Vicker’s hardness number, H,, was found to

increase up to 5 wt% of PCTFE,

beyond which decrease

in hardness level was

observed. Thus the maximum value of H, was observed in the blends having 5 wt% of PCTFE. Also, a general increase in the microhardness level was observed in the irradiated specimens as compared to the untreated blends. The blends became brittle after the irradiation dose of 100 Mrad and indentation testing resulted in the cracking of the specimens.

1 INTRODUCTION The formation of intermolecular chemical bonds and the degradation of polymers are irreversible radiation chemical processes. These processes produce *Address for correspondence: 482 001, India.

Prof. S. C. Datt, 500/A, Napier Town, Howbagh, Jabalpur (M.P.)-

291

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P. Agrawal, R. Bajpai, S. C. Datt

most marked changes in the structure and properties of polymers as a result of the irradiation. ‘7’Depending on the conditions of irradiation and the chemical structure of the polymer, one obtains either crosslinking or degradation; the net effect3 is determined by the process which predominates. The change in molecular weight of polymers due to crosslinks has been thoroughly investigated.- On the other hand, many polymers suffer main-chain scission7 and a loss in mechanical properties such as strength8v9 when exposed to radiation. The influence of gamma irradiation on various mechanical properties of polymers has also been studied by several workers.1S’5 PMMA is a well known degradative polymer,“j whose main chains are found to suffer random degradation as a result of exposure to radiation. PCTFE is an example of scission polymers. 3 The blending of PMMA with typical fluoro polymers like poly(vinylidene fluoride) (PVF,) and poly(viny1 fluoride) (PVF) is already known. ‘7.‘8The blending of PMMA with poly(chlorotrifluoro ethylene) has also been reported. I9 The study of the effect of electron irradiation on the surface microhardness of the PMMA:PCTFE polyblends has been reported.*O However, the study of the effect of gamma irradiation on the PMMA:PCTFE blends has not yet been carried out. It is, therefore, interesting to study the effect of gamma irradiation on the surface microhardness of this polymer blend. For this purpose different doses of gamma radiation were utilized ranging from 1 to 100 Mrad (1, 20, 30,50, 75 and 100 Mrad). Microhardness testing of materials is being very widely utilized, nowadays, for the knowledge of the toughness of the polymeric materials.21-23 The Vicker’s microhardness testing was utilized to study the effect of gamma irradiation on these blends due to its relative simplicity and nondestructive nature of testing.

2 EXPERIMENTAL

2.1 Preparation of blends For preparation of the blends, the commercially available polymers PMMA and PCTFE were used. The polymer granules were supplied by M/s Chemical Agencies, Bombay, India. Both the polymers were low molecular weight substances. The specific gravity, melting point and glass transition temperature of PMMA and PCTFE were 1.17-1.20, 498 and 378 K, and 2.08-2.20, 493 and 338-373 K, respectively. The solution casting*9*20technique was utilized for preparing the blends of different compositional ratios of the two polymers. PCTFE was added in 1, 3, 5, 8 and 10 wt% ratio in the PMMA matrix for preparing the blends. Increasing concentration of PCTFE beyond 10 wt% ratio produced separation

Hardening induced by gamma ivadiafion

293

of phases of the two polymers in the blend which caused loss of transparency and clarity in the blend specimens, Samples of size 1x1 cm and thickness 0.04 cm were taken for the irradiation work. 2.2 Gamma i~diation Gamma irradiation was carried out at the University Science Instrumentation Centre, Nagpur University, Nagpur. “@Co Gamma Chamber-900”24 was used as the irradiation source. Samples were irradiated with various doses ranging from 1 to 1OOMrad (1, 10, 20, 30, 50, 75 and 1OOMrad). 2.3 ~~roha~n~

testing

The irradiated specimens were indented at room temperature by a mhp- 160 ~croh~dness tester with a Vicker’s di~ond pyramid indenter having a square base and 136” pyramid angle, attached to a Carl Zeiss NU 2 Universal Research Microscope. Vicker’s hardness number, H,, was calculated from the relation: 1.854”L

Hv=-& _

kg/mm2

where L is load (kg) and d is the diameter of indentation (mm). The indenting load was ranged from 60 to 100 g as it was the saturation load range for the PMMAPCTFE polymer blend. The diameter of inden~tions were measured by a micrometer eyepiece with an objective of magnification 12.5x. For each test the duration of indentation was kept at 30 s. For each load at least five indentations were made at different points of the specimen, and the average H, was computed. Usually, the value of H,,ranged &5% from the average value. During the test the specimens were kept strictly horizontal and rigid.

3 RESULTS AND DISCUSSION Figure 1 illustrates the effect of gamma irradiation on the value of H,, of the PMMA:~~ blends. It can be observed that the gamma irradiation is giving rise to a larger value of H, for the irradiated blends except the one having 1 wt% of PCTFE. However, almost 100% increment in the value of H, is observed for the blend having 5 wt% of PCTFF irradiated with the radiation dose of 1 Mrad as compared to the u&radiated blend. It can also be observed that the value of surface microhardness increases with increasing PCTFE con-

P. Agrawal, R. Bajpai, S. C. Datt

294

6.5 7 0

I

I

t

1

10

2.0

Gamma

irradiation

I 30

t

I

50

75

I 100

dose (mrad)

Fig. 1. Variation of H, with different doses of gamma irradiation at 100 g: O-1, +-3, O-5, A-8 and x-10 wt% of PCTFE in PMMA matrix.

tent up to 5 wt% in PMMA matrix and thereafter it decreases with increasing wt% of PCTFE. Hence, the polyblend having 5 wt% of PCTFE in PMMA matrix exhibits the maximum value of H, after irradiation. Gamma irradiation is found to reverse the nature of PMMA:PCTFE polyblends if compared with the untreated ones. The value of H, is reported20 to be decreasing with increasing wt% concentration of PCTFE up to 5 wt% whereas the post irradiation value of H, is observed to be increasing with increasing wt% of PCTFE up to 5 wt%. Again for untreated blends the value of H, is increasing with increasing concentration of PCTFE beyond 5 wt%. On the other hand decrease in the value of H, could be observed after irradiation with increasing concentration of PCTFE beyond 5 wt%. The general increase in the level of surface microhardness could be a consequence of radiation crosslinking4-6 imparted due to gamma irradiation. This radiation crosslinking may be taking place due to the presence of PCTFE in the PMMA matrix as suggested by the increasing post-irradiation value of H, with increasing PCTFE content up to 5 wt%. The three dimensional network density after irradiation may be less for the blends having PCTFE content more than 5 wt%. The peak in the H,-gamma irradiation dose profile at 30 Mrad for the blends having PMMA:PCTFE concentration ratio of 95:5 suggests that this is the

Hardening induced by gamma irradiation

295

optimum set of conditions for imparting maximum surface microhardness to the polyblend. The decrease in the value of & beyond 30 Mrad which continues up to 50 Mrad may be due to the scissioning phenomenon taking place as a result of irradiation in this dose range. Beyond 50 Mrad increase in the value of H, could be observed which continues up to 100 Mrad. The increasing nature of H, could be due to the higher radiation doses because the probability of dissociation of molecules is higher. Probably, the ionic radicals are being generated which are giving rise to a larger density of crosslinks between polymeric molecules.

4 CONCLUSIONS It can, therefore, be concluded that gamma irradiation produces hardening in the polymer blends and hence the values of & for the irradiated specimens are higher than the Unix-radiated samples. Maximum hardness level is exhibited by the blends incorporating 5 wt% of PCTFE. It is also observed that the results obtained for gamma irradiation on the surface microhardness of the blend is almost similar to that obtained for electron i~adiation21 in the same dose range.

ACKNOWLEDGEMENTS The authors are grateful to Shri S. G. Hussain, Scientific Officer, University Science Ins~mentation Centre, Nagpur University, Nagpur for carrying out the gamma irradiation work. The authors P. A. and R. B. are also grateful to Madhya Pradesh Council of Science and Technology, Bhopal for sanctioning a research project under which this work has been carried out.

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