PSI - Issue 13

Mark Kopietz et al. / Procedia Structural Integrity 13 (2018) 143–148 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

146

4

25

25

20

20

5 shear strength  [MPa] 10 15

5 shear strength  [MPa] 10 15

Matrix

Matrix

3P 2P-15ELO 2P-15ELO-1WE3110

3P 2P-15ELO 2P-15ELO-1WE3110

Interlaminar

Interlaminar

Media

Media

Air H 2 O

Air 1N HCl 1N NaOH

0 15 30 45 60 75 0

0 15 30 45 60 75 0

Time t [d]

Time t [d]

Fig. 1. Progress of interlaminar shear strength τ of GFRP while stored in deionized water (H 2 O, left) and acid and alkaline solutions (HCl/NaOH, right), respectively, compared to non-stored samples (Air)

It was found that 3P reference composites reach their final ILSS right at the beginning of storage, whereas both, the neat and the surfactant modified 2P systems still undergo a post-curing process. Thus, the ILSS achieves its final stage after several days. After reaching their maxima it is clear to see that 2P composites, further enhanced by the use of the surfactant, achieve higher ILSS than 3P composites and as a consequence higher fiber/matrix adhesion. Deionized water turned out to generally decrease the ILSS, while the 2P composites remain at a nearly constant level, the 3P composites still loose ILSS after several days due to storage. Negative impact of both media, acid and alkaline solutions, respectively, is clearly seen on all tested composites. While the 3P composites directly result in decreased ILSS, 2P composites’ post -curing hides possible loss of ILSS in the first 14 days. The ILSS of the 3P composites was strongly impacted by both solutions, whereby alkaline media had a stronger effect than the acid solution. For both 2P composites also decreased ILSS as a consequence of media storage was detected, however, the type of media was within statistical tolerances not crucial. 3.2. Gravimetric media uptake Furthermore, both test runs were accompanied with gravimetric measurements. Detection of mass uptake or loss (Δ m ) during media storage was investigated. It is important to mention that the 3P Resin® includes chemically non bonded organic phosphates which are able to diffuse into the media. Due to recent developments the 2P matrices are made with chemically bonded emulsifiers, hence, an unfavorable diffusion was not expected. In the first run samples were stored in deionized water (H 2 O), see Fig. 2, left. In the second run the samples were stored in aqueous acid (HCl) and alkaline (NaOH) solutions, respectively, see Fig. 2, right. The progress under water-storage clearly indicates that the 3P composites loose mass, and thus, the organic phosphates unfavorably diffused into the media and contaminated it. The 2P composites exhibited slight media uptake, whereby the modified system took up less media than the non-modified version. Therefore, a stronger fiber/matrix adhesion and thus a lower capillary action are attributed. Clearly, the 3P composites exhibited an increased loss of mass due to the unfavorable diffusion of organic phosphates. However, it should be noted that the impact of alkaline media was much greater than that if the acid solution. In the case of the unmodified 2P composites no clear dependence on the storage media was identifiable. With surfactant modified 2P composites the degradation was stronger in acid solution. After storage in acid and alkaline media, respectively, all tested composites showed a mass loss over time. Scanning electron microscopy For further qualitative analysis the morphologies of the non-stored composites were investigated with scanning electron microscopy (SEM), see Fig. 3. The morphology of 3P composites exhibited nearly neat glass fibers where only small amounts of the hybrid resin seem to adhere on the fibers (Fig. 3, left). Compared to that, the morphology

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