Polymer matrix of fiber-reinforced composites: Changes in the semi-interpenetrating polymer network during the shelf life

• Published in: Journal of the mechanical behavior of biomedical materials 2018-02, Vol.78, p.414-419
• Main Authors: Khan, Aftab A, Al-Kheraif, Abdulaziz A, Al-Shehri, Abdullah M, Säilynoja, Eija, Vallittu, Pekka K
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Elastic Modulus; Hardness; Materials Testing; Mechanical Phenomena; Polymethyl Methacrylate - chemistry; Surface Properties; Temperature; Time Factors
• ISSN: 1751-6161; 1878-0180
• DOI: 10.1016/j.jmbbm.2017.11.038

This laboratory study was aimed to characterize semi-interpenetrating polymer network (semi-IPN) of fiber-reinforced composite (FRC) prepregs that had been stored for up to two years before curing. Resin impregnated prepregs of everStick C&B (StickTech-GC, Turku, Finland) glass FRC were stored at 4°C for various lengths of time, i.e., two-weeks, 6-months and 2-years. Five samples from each time group were prepared with a light initiated free radical polymerization method, which were embedded to its long axis in self-curing acrylic. The nanoindentation readings on the top surface toward the core of the sample were made for five test groups, which were named as "stage 1-5". To evaluate the nanohardness and modulus of elasticity of the polymer matrix, a total of 4 slices (100µm each) were cut from stage 1 to stage 5. Differences in nanohardness values were evaluated with analysis of variance (ANOVA), and regression model was used to develop contributing effect of the material's different stages to the total variability in the nanomechanical properties. Additional chemical and thermal characterization of the polymer matrix structure of FRC was carried out. It was hypothesized that time of storage may have an influence on the semi-IPN polymer structure of the cured FRC. The two-way ANOVA test revealed that the storage time had no significant effect on the nanohardness of FRC (p = 0.374). However, a highly significant difference in nanohardness values was observed between the different stages of FRC (P