Plasma treated AR-glass fibres in experimental reinforced composites with three silanes: a study on mechanical properties

Purpose: To compare and contrast mechanical properties of experimental alkali-resistant (AR) glass fibre-reinforced composites (FRCs) silanised with one of three functional trialkoxy silanes: 3-methacryloxypropyltrimethoxysilane (3-MPS), 8-methacryloxypropyltrimethoxysilane (8-MOS) and 3-acryloxypropyltrimethoxysilane (3-APS). The experimental AR-FRCs were silanised with or without plasma pretreatment. Materials: and methods Continuous unidirectional AR-glass fibres (ARcoteX ® 5326 2400tex, Owen Corning) were cleaned ultrasonically, treated either with or without cold plasma (Piezobrush ® PZ2, Relyon Plasma, Germany), then silanised by immersion for 10 min in activated, hydrolysed silane solution containing either 3-MPS, 8-MOS or 3-APS. The fibre bundles were next air-dried (24 h), and dried in vacuum oven (80 °C, 5 kPa, 2 h), producing 6 types of silanised AR-glass fibres. Next, silanised AR-glass fibres were laminated with a resin matrix, bis -GMA:TEGDMA at 60:40 wt%, CQ at 0.7 wt%, DMAEMA at 0.7 wt%) for 10 min and paired randomly in rovings of two in stainless steel moulds (2 mm × 2 mm × 25 mm) to prepare an AR-FRC beam specimen (n = 16). All specimens were light-cured from the top and bottom directions for 60 s (Elipar S10, 3M ESPE). Half of the samples (n = 8) underwent accelerated artificial ageing by immersion in boiling water (100°C, 16 h). Finally, 12 experimental AR-FRC groups were produced. All specimens were subjected to the three-point bending test with the upper surface (facing curing light) towards the cross-head. After testing, fibres, silanised and non-silanised, were inspected under scanning electron microscopy (SU1510, Hitachi, Tokyo, Japan). Statistical analysis was performed with three-way ANOVA and the Tukey post hoc test at α = 0.05. Results: The flexural modulus, flexural strength and fracture work of the materials were significantly affected by silane type (p < 0.05) and artificial ageing (p < 0.001). Plasma treatment on AR-glass fibres significantly reduces flexural modulus of FRC (p<0.001) and slows the plasticising effect of artificial ageing on FRC. Conclusion: Long chain silanes impart higher flexural strength and lower flexural modulus to AR-FRCs. While artificial ageing halves flexural strength and plasticises them, plasma surface pre-treatment of AR-glass fibres before silanisation reduces the plasticising effect.