86
Australian Dental Journal, April, 1975
Silane coupling agents in stainless steel and polymethyl methacrylate systems K. D. B. Faulkner AND
J. K. Harcoutl
Department of Dental Prosthetics, University of Melbourne ABSTRACT--Smooth stainless steel rods coated with silanes were embedded in acrylic resin dough. The strength of the bond between treated rods and polymerized resin was improved compared with that found in the untreated rods under all conditions of the tests. The strength increased with age when specimens were left in air; immersion in water lessened the increase in strength. (Received for publication November, 1973) Introduction
A considerable amount of research is being directed towards the development of truly adhesive dental materials. These efforts are concerned mainly with pit and fissure sealants and luting materials that will bond t o enamel and dentine. Another facet of adhesion which would be useful in dentistry is the bonding of metals to acrylic resin. The designing of partial dentures would be greatly simplified if true adhesion could be achieved between stainless steel or cobaltchromium alloys and polymethyl methacrylates. The study was designed to evaluate the use of adhesion promoting substances to produce clinically acceptable acrylic-metal interfaces without the need for mechanical retention. This report I . G.-Theory of mechanisms of s i l h e coupling agents in glass reinforced and filled thermoplastic and thermosetting resin systems. New york, Union Carbide Corporation, 1968 (pp. 1-61.
deals with the effects of various silane adhesion promoters on bonding between polymethyl methacrylate and stainless steel. A typical silane coupling agent may be symbolised thus: R-Si(-OR’)3 R is an organofunctional group which is capable of reaction with a polymer. This reaction is a typical condensation reaction. OR’ is a hydrolysable group which is capable of reaction with other hydroxyl radicals’. Silanes may be described as bifunctional materials, and are monomeric silicon chemicals. Those used as adhesion promoters in this study were manufactured and coded by the Union Carbide Corporation, and had the following compositions?
1 Sterman S., and Marsden,
2
Adhesion promoters. New York, Union Carbide Corporation. 1971 (pp. 15-16).
87
Australian Dental Journal, April, 1975
I a . -
m
u'O.3
i '
0.2
t:: Y)
4 0.1
n
0 I~WDIATE
nrm iomwnw mu TWEMTTUIC (4 m k a )
LEGENDS
Fig. 1.-Mean
(3 mtka)
ImEtsto IN WATER AT 37% (1 m k )
I~WISEDIN UTtR AT 37.c (4 m k i )
values and standard deviations for a control and each material tested under five conditions.
AP 131 A 189 mercapto ( H S ) A 174
CH.0 methacryloxy I )I (CHI = C-C--O-)
A 1100 amino (NHr)
methoxy (-0Ca) methoxy (-0CHs) ethoxy (-0cJ-I.)
Covalent chemical bonding occurs with both organic polymer and inorganic substrate. Sterman and Marsden' claim that the alkoxy groups hydrolyse to form silanols which condense with metal oxides. At the other end of the molecule, the organic radicals are able to react by condensation with various resins.
Fig. 2.-Typical specimens of test pieces after impact testing showing fracture through the acrylic rod in three cases.
(i) AP 131 a mercaptosilane of unknown formula (ii) A 174 7 - methacryloxypropyltrimethoxysilane CHaO
I
II (iii) A 189 .--, 7 - mercaptopropyltrimethoxy silane HS-CHEHCHfii(-OCH& (iv) A 1100 7 - aminopropyltriethoxysilane CH2=C-C-O-CHCH9CH-Si(-OCH& ~~
~
NHA.!HEH~H,SiC~d8 The functional groups in each of these materials are:
Mothods and matorirls Composite test pieces of acrylic rod and stainless steel rod were prepared for impact testing. Each specimen was 9.5 mm in diameter. The stainless steel rod was prepared by sandblasting a surface which had been previously machined flat, with grade 60 aluminium oxide for 5 seconds. Two minutes after sandblasting, the surface was coated with the silane under test and allowed to stand for 15 minutes. A piece of 9.5 mm acrylic rod was slid into a PTFE mould with a 9.5 mm bore, and a constant volume of freshly mixed acrylic resin dough (L/P ratio 1:3 by volume) was added to the mould from an open ended syringe and packed down. A silane coated stainless steel rod was placed in firm contact with the acrylic dough and the specimen was immediately put in an air
88
Australian Dental Journal, April, 1975
chamber and the pressure raised to 690 kPa. After standing for 15 minutes, the pressure chamber was placed in water at room temperature and was then raised to 100°C over 1 hour, and maintained at that value for two hours. The chamber was allowed to cool, pressure released, and the specimen was removed from the FTFE mould avoiding a n y force on the junction between the metal and acrylic resin. Twelve specimens of each silane and twelve controls without silane coating were prepared for each test. The specimens were tested for impact strength of the metal-polymer bond at the following time intervals:(i) Immediately after cooling. (ii) After standing in air at room temperature (approximately 21°C) for 4 weeks. (iii) After standing in air at room temperature (approximately 21°C) for 3 months. (iv) After immersion in water at 37°C for 1 week. (v) After immersion in water at 37°C for 4 weeks. All specimens were gripped in an Avery Impact Tester by the stainless steel rod so that the metalpolymer junction was 22 mm below the point of impact of the pendulum. Results
Figure 1 shows the mean values together with the standard deviations for the impact strength of the 12 specimens in each test group. In the immediate testing of the interface, the silane treatment increased the bond strength in all cases, the A 189 being the most effective. In specimens allowed to stand in air at room temperature for 4 weeks and 3 months, there is a gradual further increase in bond strength with D. J., MacDonald. N. C., and Walker, P.-The effect of high humidity environments on the strength of adhesive joints. Chemistry and Industry, 27: 1230. 123! (July 4) 1964.
3 Falconer,
time, but little change in the untreated controls. Specimens immersed in water at 37°C for 1 week showed marked decreases in strength of the specimens bonded with A 189 and A 174,but only slight drops in strength with the other two treatments and little change in the controls. When the specimens were immersed in water at 37°C for 4 weeks, further strength losses were apparent in all test samples, the strength in all cases being less than for samples tested immediately after curing, but they were still stronger than the controls. The greatest reduction in strength was noticed in specimens treated with A 189. Discussion
Analyses of results showed that improvements in adhesion were highly significant in every series. The strength of the bond between acrylic resin and stainless steel treated with coupling agents increases with time when stored in air, but the increased strength falls with storage in water at 37°C. However, the bond remains stronger in all cases than when n o adhesion promoter is used. In many cases fracture was through the acrylic resin rod rather than along the interface, leaving acrylic adhering to the stainless steel rod (Fig. 2). In immediate testing and in specimens tested after standing at room temperature for 4 weeks and 3 months, this phenomenon was the rule, indicating in these cases that the joint was stronger than the organic polymer. The results of the tests on specimens after immersion in water support the work of Falconer, MacDonald, and Walkers who studied the effects of high humidity on coupled epoxy resin and stainless steel in which strength decreases of 30 per cent were observed after 17 days. Department of Dental Prosthetics, University of Melbourne, 71 1 Elizabeth Street, Melbourne, Vic., 3000.
Australian Dental Journal, April, 1975
Silane coupling agents in stainless steel and polymethyl methacrylate systems K. D. B. Faulkner AND
J. K. Harcoutl
Department of Dental Prosthetics, University of Melbourne ABSTRACT--Smooth stainless steel rods coated with silanes were embedded in acrylic resin dough. The strength of the bond between treated rods and polymerized resin was improved compared with that found in the untreated rods under all conditions of the tests. The strength increased with age when specimens were left in air; immersion in water lessened the increase in strength. (Received for publication November, 1973) Introduction
A considerable amount of research is being directed towards the development of truly adhesive dental materials. These efforts are concerned mainly with pit and fissure sealants and luting materials that will bond t o enamel and dentine. Another facet of adhesion which would be useful in dentistry is the bonding of metals to acrylic resin. The designing of partial dentures would be greatly simplified if true adhesion could be achieved between stainless steel or cobaltchromium alloys and polymethyl methacrylates. The study was designed to evaluate the use of adhesion promoting substances to produce clinically acceptable acrylic-metal interfaces without the need for mechanical retention. This report I . G.-Theory of mechanisms of s i l h e coupling agents in glass reinforced and filled thermoplastic and thermosetting resin systems. New york, Union Carbide Corporation, 1968 (pp. 1-61.
deals with the effects of various silane adhesion promoters on bonding between polymethyl methacrylate and stainless steel. A typical silane coupling agent may be symbolised thus: R-Si(-OR’)3 R is an organofunctional group which is capable of reaction with a polymer. This reaction is a typical condensation reaction. OR’ is a hydrolysable group which is capable of reaction with other hydroxyl radicals’. Silanes may be described as bifunctional materials, and are monomeric silicon chemicals. Those used as adhesion promoters in this study were manufactured and coded by the Union Carbide Corporation, and had the following compositions?
1 Sterman S., and Marsden,
2
Adhesion promoters. New York, Union Carbide Corporation. 1971 (pp. 15-16).
87
Australian Dental Journal, April, 1975
I a . -
m
u'O.3
i '
0.2
t:: Y)
4 0.1
n
0 I~WDIATE
nrm iomwnw mu TWEMTTUIC (4 m k a )
LEGENDS
Fig. 1.-Mean
(3 mtka)
ImEtsto IN WATER AT 37% (1 m k )
I~WISEDIN UTtR AT 37.c (4 m k i )
values and standard deviations for a control and each material tested under five conditions.
AP 131 A 189 mercapto ( H S ) A 174
CH.0 methacryloxy I )I (CHI = C-C--O-)
A 1100 amino (NHr)
methoxy (-0Ca) methoxy (-0CHs) ethoxy (-0cJ-I.)
Covalent chemical bonding occurs with both organic polymer and inorganic substrate. Sterman and Marsden' claim that the alkoxy groups hydrolyse to form silanols which condense with metal oxides. At the other end of the molecule, the organic radicals are able to react by condensation with various resins.
Fig. 2.-Typical specimens of test pieces after impact testing showing fracture through the acrylic rod in three cases.
(i) AP 131 a mercaptosilane of unknown formula (ii) A 174 7 - methacryloxypropyltrimethoxysilane CHaO
I
II (iii) A 189 .--, 7 - mercaptopropyltrimethoxy silane HS-CHEHCHfii(-OCH& (iv) A 1100 7 - aminopropyltriethoxysilane CH2=C-C-O-CHCH9CH-Si(-OCH& ~~
~
NHA.!HEH~H,SiC~d8 The functional groups in each of these materials are:
Mothods and matorirls Composite test pieces of acrylic rod and stainless steel rod were prepared for impact testing. Each specimen was 9.5 mm in diameter. The stainless steel rod was prepared by sandblasting a surface which had been previously machined flat, with grade 60 aluminium oxide for 5 seconds. Two minutes after sandblasting, the surface was coated with the silane under test and allowed to stand for 15 minutes. A piece of 9.5 mm acrylic rod was slid into a PTFE mould with a 9.5 mm bore, and a constant volume of freshly mixed acrylic resin dough (L/P ratio 1:3 by volume) was added to the mould from an open ended syringe and packed down. A silane coated stainless steel rod was placed in firm contact with the acrylic dough and the specimen was immediately put in an air
88
Australian Dental Journal, April, 1975
chamber and the pressure raised to 690 kPa. After standing for 15 minutes, the pressure chamber was placed in water at room temperature and was then raised to 100°C over 1 hour, and maintained at that value for two hours. The chamber was allowed to cool, pressure released, and the specimen was removed from the FTFE mould avoiding a n y force on the junction between the metal and acrylic resin. Twelve specimens of each silane and twelve controls without silane coating were prepared for each test. The specimens were tested for impact strength of the metal-polymer bond at the following time intervals:(i) Immediately after cooling. (ii) After standing in air at room temperature (approximately 21°C) for 4 weeks. (iii) After standing in air at room temperature (approximately 21°C) for 3 months. (iv) After immersion in water at 37°C for 1 week. (v) After immersion in water at 37°C for 4 weeks. All specimens were gripped in an Avery Impact Tester by the stainless steel rod so that the metalpolymer junction was 22 mm below the point of impact of the pendulum. Results
Figure 1 shows the mean values together with the standard deviations for the impact strength of the 12 specimens in each test group. In the immediate testing of the interface, the silane treatment increased the bond strength in all cases, the A 189 being the most effective. In specimens allowed to stand in air at room temperature for 4 weeks and 3 months, there is a gradual further increase in bond strength with D. J., MacDonald. N. C., and Walker, P.-The effect of high humidity environments on the strength of adhesive joints. Chemistry and Industry, 27: 1230. 123! (July 4) 1964.
3 Falconer,
time, but little change in the untreated controls. Specimens immersed in water at 37°C for 1 week showed marked decreases in strength of the specimens bonded with A 189 and A 174,but only slight drops in strength with the other two treatments and little change in the controls. When the specimens were immersed in water at 37°C for 4 weeks, further strength losses were apparent in all test samples, the strength in all cases being less than for samples tested immediately after curing, but they were still stronger than the controls. The greatest reduction in strength was noticed in specimens treated with A 189. Discussion
Analyses of results showed that improvements in adhesion were highly significant in every series. The strength of the bond between acrylic resin and stainless steel treated with coupling agents increases with time when stored in air, but the increased strength falls with storage in water at 37°C. However, the bond remains stronger in all cases than when n o adhesion promoter is used. In many cases fracture was through the acrylic resin rod rather than along the interface, leaving acrylic adhering to the stainless steel rod (Fig. 2). In immediate testing and in specimens tested after standing at room temperature for 4 weeks and 3 months, this phenomenon was the rule, indicating in these cases that the joint was stronger than the organic polymer. The results of the tests on specimens after immersion in water support the work of Falconer, MacDonald, and Walkers who studied the effects of high humidity on coupled epoxy resin and stainless steel in which strength decreases of 30 per cent were observed after 17 days. Department of Dental Prosthetics, University of Melbourne, 71 1 Elizabeth Street, Melbourne, Vic., 3000.
