Effect of Silanes on Mechanical Properties of Alkali-resistant Glass FRC

Objectives: The study aims at comparing mechanical properties of alkali-resistant (AR) glass fibre-reinforced composites (AR-GFRC) containing one of three silanes: 3-methacryloxypropyltrimethoxysilane (3-MPS), 8-methacryloxypropyltrimethoxysilane (8-MOS) and 3-acryloxypropyltrimethoxysilane (3-APS), with and without plasma treatment before silanization.
Methods: Continuous unidirectional AR glass fibres (ARcoteX® 5326 2400tex, Owen Corning), that were used in all 12 groups of AR-GFRCs, were cleaned ultrasonically and divided into two groups: with or without cold plasma (Piezobrush® PZ2, Relyon Plasma, Germany) treatment. Both groups were further randomly and equally divided into three groups, which were silanized by immersion in hydrolysed silane mixtures containing one of the three silanes for 10 min, hung dry for 24 h and then placed in vacuum oven (80°C, 5000 Pa, 2 h).
The silanized glass fibres were laminated with a resin matrix (UDMA:TEGDMA at 60:40 weight ratio, CQ 0.7wt%, DMAEMA 0.7wt%) for 10 min. They were grouped in bundles of two in stainless steel moulds (2×2×25mm³) (n=16). All specimens were irradiated for 60 s from the top and bottom (Elipar S10, 3M ESPE). Eight specimens from each subgroup underwent artificial ageing by immersion in boiling water (100°C, 16 h).
All test specimens were subjected to three-point bending test with the upper surface (facing the curing lamp) towards the crosshead. Statistical analysis was performed with three-way ANOVA and Tukey post hoc test at α=0.05.
Results: Ageing lowered the fracture strength of AR-GFRCs by almost half. AR-GFRC containing 8-MOS exhibited statistically higher fracture strength and lower modulus compared with those containing shorter chain silanes. Plasma treatment before silanization reduced the modulus of AR-GRFCs (p=0.001).
Conclusions: The three silanes provided comparable mechanical properties when incorporated into AR-GFRCs. 8-MOS might impart improved strength and lower stiffness to AR-GFRC compared with other shorter chain silanes. Future studies are required to further understand how the choice of silane might improve mechanical properties of FRCs.