Silane Treatment Effects on Glass/Resin Interfacial Shear Strengths Subir Debnath 1 , Stephanie L. Wunder 1 , John I. Mc

1. O - Schematic diagram of the bottom grip used on the tensile testing machine for pullout tests. - Sample Load-Displacement curve for unsoaked 5% MPS treated specimen. Silane Treatment Effects on Glass/Resin Interfacial Shear Strengths Subir Debnath1,Stephanie L. Wunder1,John I. McCool2, George R. Baran3 1Department of Chemistry, Temple University, Philadelphia, PA 2Department of Industrial Engineering, Penn State Great Valley, Malvern, PA 3College of Engineering, Temple University, Philadelphia, PA Preparation & Testing of Microbond Shear Strength Samples : - Place fine resin (60/40 BisGMA/TEGDMA) beads of about 0.1 to 0.4 mm embedded length on the fibers. - Cure the beads for 4 min in a light curing oven, let sit overnight. - Attach one end of fiber to a cardboard tab inserted in the top grip of a tensile testing machine. - A special bottom grip (figure below), consisting of two glass slides that could be moved horizontally, was used. The top grip was used to position the bead just below the slides, which were closed until they just touched the outer surface of the fiber. - The load was measured at a crosshead speed of 1 mm/min. - The peak debonding load (F) from the load-displacement curve was recorded and used to calculate the interfacial shear strength () from the following equation : = (F/dl), where d is the fiber diameter and l is the embedded length of the resin bead. Results Abstract Silane coupling agents are used to improve adhesion between a polymer matrix and the filler. Objective: to measure interfacial shear strengths of glass fiber/resin interfaces following seven glass surface treatments. Methods: glass fibers approximately 30 mm in diameter and 8 cm long were silanated using various concentrations (1%, 5% and 10%) of either 3-methacryloxypropyl-trimethoxysilane (MPS) or glycidoxypropyltrimethoxysilane (GPS) in acetone (99.8%). Rubber (poly(butadiene/acrylonitrile), amine terminated, MW = 5,500) was also attached to the fiber surface via GPS molecules to observe the effect of an elastomeric interface on shear bond strength. A bead of resin (60/40 BisGMA/TEGDMA) approximately 0.2 to 0.4 mm in length was cured onto the treated fibers. Approximately half of the specimens were soaked in 50:50 ethanol:water for one month. Sample sizes ranged from 13 to 20. The load required to dislodge the resin bead was converted to shear bond strength. Results: interfacial shear strengths ranged from 12 MPa for untreated fibers to 20 MPa for fibers treated with 5% MPS. Tukey’s multiple comparison test showed that the 5% MPS treatment yielded a significantly higher fiber-resin shear strength than all others. After soaking, the shear strengths of all except untreated interfaces were lowered. Conclusions:silanated interfaces are more susceptible to the deleterious effect of soaking than non-silanated interfaces. This work was supported by USPHS DE 09530. Conclusions -   For unsoaked fibers, interfacial strength is poorest, and similar for the “as is” fibers, 5% GPS and control rubber treated fibers as in these cases, at least one of the surfaces has no covalent linkage, either to silica (control rubber) or the matrix (“as is” and 5% GPS). -   5% MPS treated samples exhibited highest interfacial strength. -  A rubbery interface had only minimal effect on the interfacial strength. - Soaking decreases the interfacial shear strength for all the samples, with 10% MPS showing the largest drop before and after soaking. Future Work   - Correlation of interfacial strength values with elastic modulus and fracture toughness for composite samples prepared using same filler surface treatments. - Average shear bond strengths of treated glass fibers before and after soaking. Introduction Inorganic fillers in dental composites are typically coated with silanes in order to improve the bond to the resin matrix and increase the service life of the composite1; an attendant benefit is the improved dispersability of silanated fillers in matrix monomers2. The resulting materials possess superior mechanical properties and wear resistance, and increased resistance to water sorption3 when compared with composites containing non-silanated fillers. In general, the stronger the filler-resin interface, the greater the improvement in static4, impact5, and fatigue properties6. Numerous methods have been developed for evaluating the quality of the filler-resin interface, and these have been recently reviewed7. The microbond test was developed for fibers with small diameters, and relies on the ability to displace a small resin droplet that has been cured around a fiber8. The effectiveness of silanation protocols has been indirectly assessed, usually by subjecting composites to soaking or boiling water treatments, then measuring the strength of the composite9,10. The implied assumption has been that weaker, or more readily degraded interfaces, will result in lower composite strengths. In this study, we employ the microbond test to evaluate the shear strength of the interface between glass fibers and a BISGMA/TEGDMA matrix following fiber surface treatment by various silanating protocols, both before and after soaking in 50:50 (v/v) methanol-water mixture. Reaction Scheme : Silane Treatment Measure load at crosshead speed of 1 mm/min Failed Interface Si OH OMe Si OH O Movable glass slides Si Si OH Si MeO Fiber O Si O O OMe Silane coated Fiber Glass Fiber Surface MPS References 1. Chen, T.M. and G.M. Brauer, Solvent Effects on Bonding Organo-Silane to Silica Surfaces. Journal of Dental Research, 1982. 61: p. 1439-1443. 2. Mohsen, N.M. and R.G. Craig, Effect of Silanation of Fillers on their Dispersability by Monomer Systems. Journal of Oral Rehabilitation, 1995. 22: p. 183-189. 3. Wang, J.-W. and H. Ploehn, Dynamic Mechanical Analysis of the Effect of Water on Glass Bead-Epoxy Composites. Journal of Applied Polymer Science, 1996. 59: p. 345-357. 4. Zhao, F. and N. Takeda, Effect of Interfacial Adhesion and Statistical Fiber Strength on Tensile Strength of Uniderctional Glass Fiber/Epoxy Composites. Part I: Experimental Results.Composites: Part A, 2000. 31: p. 1203-1214. 5. Kessler, A. and A. Bleddzki, Correlation Between Interphase-Relevant Tests and the Impact-Damage Resistance of Glass/Epoxy Laminates with Different Fibre Surface Treatments. Composites Science and Technology, 2000. 60: p. 125-130. 6. Keusch, S., H. Queck, and K. Gillespie, Influence of Glass Fibre/Epoxy Resin Interface on Static Mechanical Properties of Unidirectional Composites and on Fatigue Performance of Cross Ply Composites.Composites Part A, 1998. 29: p. 701-705. 7. Pitkethly, M., A Round-Robin Programme on Interfacial Test Methods. Composite Science and Technology, 1993. 48: p. 205-214. 8. Miller, B., P. Muri, and L. Rebenfield, A Microbond Method for Determination of the Shear Strength of a Fiber/Resin Interface. Composites Science and Technology, 1987. 28: p. 17-32. 9. Craig, R. and E. Dootz, Effect of Mixed Silanes on the Hydrolytic Stability of Composites. Journal of Oral Rehabilitation, 1996. 23: p. 751-756. 10. Mohsen, N. and R. Craig, Hydrolytic Stability of Silanated Zirconia-Silica-Urethane Dimethacrylate Composites. Journal of Oral Rehabilitation, 1995. 22: p. 213-220. Resin bead Rubber Treatment Interfacial area OMe Si OH NH2 Peak debonding load (F) O Si MeO NH2 O Si OH OMe Rubber [Poly(butadiene/acrylonit-rile), amine terminated] ( MW : 5,500 ) GPS Glass Fiber Surface H2N NH HO O Si O SiO2 - Raman spectra of A380 fumed silica silanated with GPS (), the rubber attached via method II (), and the neat GPS () and rubber (). Bands characteristic of the GPS, in particular the CH stretching and bending vibrations are observed on the silanated beads. In addition, the double bond and cyano groups from the rubber, at 1660 cm-1 and 2225 cm-1, respectively, are also observed on the rubber coated beads. Materials and methods Various Fiber Treatments : • Methods • - Glass fibers were treated by various methods to vary the nature of the fiber/resin interface. Fibers were coated with various concentrations (1%, 5% and 10%) of MPS (for which there exists coupling between the silane and matrix) or GPS (for which there is chemical attachment to the silane but none to the matrix). • - Rubber treatment of fibers included coating the fibers nonspecifically with rubber (for which there is no chemical attachments to the fiber), and coating fibers with silane and rubber (for which there is chemical attachment to the silica). • - The load required to dislodge the bead from the treated fiber was converted to shear bond strength. • - Samples soaked in 50:50 (v/v) mixtures of ethanol and distilled water at 37 0C for a period of one month were also tested. Rubber Treatment of Fibers : Acknowledgements This investigation was supported by Research Grant DE09530 from the National Institute for Dental and Craniofacial Research, Bethesda, Maryland, USA. All the materials used for making the dental resins were kindly donated by ESSTECH, Essington, Pa. Silane Treat-ment of Fibers : Method I Method II Control Silanate fibers Silanate fibers Stir fibers and React GPS with 1% GPS in , 5%,10% Rubber for 2 with 1% with Rubber EtOH days in CHCl3 GPS in MPS/ in CHCl3 Acetone Centrifuge, evacuate and heat cure at 110oC Centrifuge, evacuate Evacuate for 2 hrs React with and heat cure at 110 oC after Fibers for 2 hrs washings React with rubber in CHCl3 Evacuate Evacuate after after washings washings Evacuate after washings