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Poly (methyl methacrylate) (PMMA) network polymer
Polymer Testing 12 (1993) 31-34
A Study of the Microhardness of Ethylene Glycol Dimethacrylate (EGDM)/Poly (methyl methacrylate) (PMMA) Network Polymer R. B a j p a i , M. K r i s h n a K u m a r & S. C. D a t t * Department of Postgraduate Studies and Research in Physics, Rani Durgavati University, Jabalpur-482 001, India (Received 24 January 1992; accepted 7 May 1992)
ABSTRACT The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the stud),' of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (H,,) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of Ho have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged. 1 INTRODUCTION Extensive studies have been carried out by scientists on the networks formed from ethylene glycol dimethacrylate ( E G D M ) and poly (methyl methacrylate) (PMMA). The growing interest in the study of the above networks is currently due to their wide applications, particularly in dentistry and orthopaedics. Mechanical properties such as tensile strength, fatigue, fracture, etc., have been extensively studied by various workers; 1-3 however, the microhardness of such networks has not been studied. The microhardness is found to be a useful tool for * To whom correspondence should be addressed. 31 Polymer Testing 0142-9418/93/$06.00 (~ 1993 Elsevier Science Publishers Ltd, England. Printed in Northern Ireland
32
R. Bajpai, M. Krishna Kumar, S. C. Datt
detecting*-6 changes in various physical properties of polymers. This motivated the authors, and the present paper therefore reports the preparation of and the effect of varying concentration of weight percentage of PMMA on the microhardness of EGDM/PMMA network polymer.
2 EXPERIMENTAL METHOD The chemicals and polymers used for preparation of the network were supplied by Chemical Agencies, Bombay. Different weight percentages ranging from 0.5 to 50 of PMMA were used for preparing different specimens. Azobisisobutyronitrile (0-2 mol%) was dissolved in EGDM. Slurries of PMMA powder and EGDM liquid were heated at 60 °C with stirring until the solution became viscous and apparently uniform. The solution was syringed into moulds made from glass plates. The plates were held together with spring clips and kept in an oven. The thermal treatment was applied in consecutive stages: 5 h at 70 °C, 1 h at 85 °C, 1 h at 100 °C and 2 h at 125 °C. The treatment produced polymerized specimens of size 5 cm x 2.5 cm x 0.2cm, which were slowly cooled down to room temperature. The specimens showed a variation in their whiteness, depending upon the percentage of PMMA; the whiteness of specimens increased with increasing content of PMMA in the network. However, the specimens were opaque at all concentration of PMMA. The whiteness was due to phase separation. The indentations on the specimens were carried out by a mhp 160 microhardness tester (Carl Zeiss, JENA, Germany, model NU 2 No. 659378), with a Vickers diamond pyramidal indenter having a square base and 136° pyramid angle, attached to a Carl Zeiss Universal research microscope (JENA, Germany, Model NU 2 No. 659378). The load was varied from 80 to 160 g. The diameters of the indentations were measured using a micrometer eyepiece. The Vickers hardness number (Hv) is computed by using the relation: Hv = 1.854 x L / d 2 (kg/mm2) where L is the load in kg, and d is the diameter of the indentation in mm. For each test, the duration of the indentation was 30 s. For the same load, at least 10 indentations were made at different points of the specimen and an average hardness number was computed. During indentation the specimens were kept strictly horizontal and rigid.
Microhardess of EGDM /PMMA polymer network
33
3 RESULTS A N D DISCUSSION Figure 1 shows the variation of Hv with weight percentage of P M M A in the network. It reveals that Hv decreases up to 10% P M M A concentration and then increases with further increase in concentration of PMMA. The increase in Hv beyond 10% concentration is attributed to the localized plastic deformation, which accounts for the formation of moderately strong materials. 3 The cross-linking between two polymers increases, which increases the strength of polymer network. The increase of P M M A concentration up to 10% causes complication due to phase separation, which seems to have a decreasing effect on the value of Hr. The increasing and decreasing behaviour is similar for all the loads. However, the level of Hv increases with increase in load. This increase is due to strain hardening, which increases with load. It can, therefore, be concluded that cross-linking density between E G D M and PMMA increases with increase in weight percentage of PMMA beyond 10%, as revealed from the microhardness testing.
14 ^ Z~
o 160g X 140 g
///~"
12
10 E E
8
I
0
1
I
2
I
3
I
4
I
5
I
10
I
20
t
30
I
40
i
50
Weight p e r c e n t a g e of PMMA in m i x t u r e
Fig. 1.
Variation of Hv with weight percentage EGDM/PMMA.
of P M M A
in network
of
34
R. Bajpai, M. Krishna Kumar, S. C. Datt
REFERENCES 1. Atsuta, M. & Turner, D. T., J. Mater. Sci., 18 (1983) 1675-80. 2. Atsuta, M. & Turner, D. T., Polym. Engng Sci., 18 (1982) 1199-1204. 3. Atsuta, M. & Turner, D. T., J. Polym. Sci. (Phys. Edn), 20 (1982) 1609-15. 4. Evans, B. L., J. Mater. Sci., 24 (1989) 173-82. 5. Gonzalez, A., Martin, B., Munoz, M. & Saja, J. A. de, Polymer Testing, 6 (1986) 361-67. 6. Bajpai, R. & Datt, S. C., Indian J. Pure & Appl. Phys., 24 (1986) 254-55.
A Study of the Microhardness of Ethylene Glycol Dimethacrylate (EGDM)/Poly (methyl methacrylate) (PMMA) Network Polymer R. B a j p a i , M. K r i s h n a K u m a r & S. C. D a t t * Department of Postgraduate Studies and Research in Physics, Rani Durgavati University, Jabalpur-482 001, India (Received 24 January 1992; accepted 7 May 1992)
ABSTRACT The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the stud),' of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (H,,) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of Ho have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged. 1 INTRODUCTION Extensive studies have been carried out by scientists on the networks formed from ethylene glycol dimethacrylate ( E G D M ) and poly (methyl methacrylate) (PMMA). The growing interest in the study of the above networks is currently due to their wide applications, particularly in dentistry and orthopaedics. Mechanical properties such as tensile strength, fatigue, fracture, etc., have been extensively studied by various workers; 1-3 however, the microhardness of such networks has not been studied. The microhardness is found to be a useful tool for * To whom correspondence should be addressed. 31 Polymer Testing 0142-9418/93/$06.00 (~ 1993 Elsevier Science Publishers Ltd, England. Printed in Northern Ireland
32
R. Bajpai, M. Krishna Kumar, S. C. Datt
detecting*-6 changes in various physical properties of polymers. This motivated the authors, and the present paper therefore reports the preparation of and the effect of varying concentration of weight percentage of PMMA on the microhardness of EGDM/PMMA network polymer.
2 EXPERIMENTAL METHOD The chemicals and polymers used for preparation of the network were supplied by Chemical Agencies, Bombay. Different weight percentages ranging from 0.5 to 50 of PMMA were used for preparing different specimens. Azobisisobutyronitrile (0-2 mol%) was dissolved in EGDM. Slurries of PMMA powder and EGDM liquid were heated at 60 °C with stirring until the solution became viscous and apparently uniform. The solution was syringed into moulds made from glass plates. The plates were held together with spring clips and kept in an oven. The thermal treatment was applied in consecutive stages: 5 h at 70 °C, 1 h at 85 °C, 1 h at 100 °C and 2 h at 125 °C. The treatment produced polymerized specimens of size 5 cm x 2.5 cm x 0.2cm, which were slowly cooled down to room temperature. The specimens showed a variation in their whiteness, depending upon the percentage of PMMA; the whiteness of specimens increased with increasing content of PMMA in the network. However, the specimens were opaque at all concentration of PMMA. The whiteness was due to phase separation. The indentations on the specimens were carried out by a mhp 160 microhardness tester (Carl Zeiss, JENA, Germany, model NU 2 No. 659378), with a Vickers diamond pyramidal indenter having a square base and 136° pyramid angle, attached to a Carl Zeiss Universal research microscope (JENA, Germany, Model NU 2 No. 659378). The load was varied from 80 to 160 g. The diameters of the indentations were measured using a micrometer eyepiece. The Vickers hardness number (Hv) is computed by using the relation: Hv = 1.854 x L / d 2 (kg/mm2) where L is the load in kg, and d is the diameter of the indentation in mm. For each test, the duration of the indentation was 30 s. For the same load, at least 10 indentations were made at different points of the specimen and an average hardness number was computed. During indentation the specimens were kept strictly horizontal and rigid.
Microhardess of EGDM /PMMA polymer network
33
3 RESULTS A N D DISCUSSION Figure 1 shows the variation of Hv with weight percentage of P M M A in the network. It reveals that Hv decreases up to 10% P M M A concentration and then increases with further increase in concentration of PMMA. The increase in Hv beyond 10% concentration is attributed to the localized plastic deformation, which accounts for the formation of moderately strong materials. 3 The cross-linking between two polymers increases, which increases the strength of polymer network. The increase of P M M A concentration up to 10% causes complication due to phase separation, which seems to have a decreasing effect on the value of Hr. The increasing and decreasing behaviour is similar for all the loads. However, the level of Hv increases with increase in load. This increase is due to strain hardening, which increases with load. It can, therefore, be concluded that cross-linking density between E G D M and PMMA increases with increase in weight percentage of PMMA beyond 10%, as revealed from the microhardness testing.
14 ^ Z~
o 160g X 140 g
///~"
12
10 E E
8
I
0
1
I
2
I
3
I
4
I
5
I
10
I
20
t
30
I
40
i
50
Weight p e r c e n t a g e of PMMA in m i x t u r e
Fig. 1.
Variation of Hv with weight percentage EGDM/PMMA.
of P M M A
in network
of
34
R. Bajpai, M. Krishna Kumar, S. C. Datt
REFERENCES 1. Atsuta, M. & Turner, D. T., J. Mater. Sci., 18 (1983) 1675-80. 2. Atsuta, M. & Turner, D. T., Polym. Engng Sci., 18 (1982) 1199-1204. 3. Atsuta, M. & Turner, D. T., J. Polym. Sci. (Phys. Edn), 20 (1982) 1609-15. 4. Evans, B. L., J. Mater. Sci., 24 (1989) 173-82. 5. Gonzalez, A., Martin, B., Munoz, M. & Saja, J. A. de, Polymer Testing, 6 (1986) 361-67. 6. Bajpai, R. & Datt, S. C., Indian J. Pure & Appl. Phys., 24 (1986) 254-55.