Effect of novel nanocrystalline polyhedral oligo silesquioxanes (POSS) on the hybrid acrylate composites performance

Abstract

The aim of this study is to investigate the in uence of the polyhedral oligo silsesquioxanes (POSS) structure obtained by facile synthesis on the improvement in mechanical properties of acrylate composite lms. The composite lms consist of UV cured Bisphenol A glycidylmethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) as matrix and reactive POSS structures as reinforcement. Introduced functionalities considering hydroxyl, both hydroxyl and allyl, and methacrylate groups in POSS-M, POSS-M-A and POSS-M-Cl, respectively, enabled optimization of system compatibility. Composites were made with 1, 3 and 5 wt. % of POSS particles. A morphology of hybrid composites was examined by transmission electron microscopy (TEM). Cross-linking density (3), storage modulus (G'), damping factor (tanδ) and Tg of the composites were determined from the dynamic-mechanical analysis (DMA). A higher amount of methacrylate groups contributed to the increased cross-linking points and thus to increased storage modulus for composites with POSS-M-Cl. Micro Vickers hardness (HV) of hybrid composites showed incompatibility of POSS-M particles with Bis-GMA/TEGDMA matrix that led to a decrease of composite hardness when compared to neat polymer matrix. The highest hardness improvement was obtained by the addition of POSS-M-A reinforcement (increase by 50%). Brazilian test was used to estimate the elastic modulus by the indirect test method and it indicated a decrease in mechanical properties with the POSS addition higher than 1 wt.%. Methods used in this paper for estimation of reinforcing e ect clearly indicate that the incompletely condensed POSS-M-A exhibit the optimal performance of composites based on Bis-GMA/TEGDMA matrix due to the presence of both hydroxyl and allyl functional group.