Rubber Toughened and Nanoparticle Reinforced Epoxy Composites

Epoxy resins have achieved acceptance as adhesives, coatings, and potting compounds, but their main application is as matrix to produce reinforced composites. However, their usefulness in this field still limited due to their brittle nature. Some studies have been done to increase the toughness of epoxy composites, of which the most successful one is the modification of the polymer matrix with a second toughening phase. Resin Transfer Molding (RTM) is one of the most important technologies to manufacture fiber reinforced composites. In the last decade it has experimented new impulse, due to its favorable application to produce large surface composites with good technical properties and at relative low cost. This research work focuses on the development of novel modified epoxy matrices, with enhanced mechanical and thermal properties, suitable to be processed by resin transfer molding technology, to manufacture Glass Fiber Reinforced Composites (GFRC’s) with improved performance in comparison to the commercially available ones. In the first stage of the project, a neat epoxy resin (EP) was modified using two different nano-sized ceramics: silicium dioxide (SiO2) and zirconium dioxide (ZrO2); and micro-sized particles of silicone rubber (SR) as second filler. Series of nanocomposites and hybrid modified epoxy resins were obtained by systematic variation of filler contents. The rheology and curing process of the modified epoxy resins were determined in order to define their aptness to be processed by RTM. The resulting matrices were extensively characterized qualitatively and quantitatively to precise the effect of each filler on the polymer properties. It was shown that the nanoparticles confer better mechanical properties to the epoxy resin, including modulus and toughness. It was possible to improve simultaneously the tensile modulus and toughness of the epoxy matrix in more than 30 % and 50 % respectively, only by using 8 vol.-% nano-SiO2 as filler. A similar performance was obtained by nanocomposites containing zirconia. The epoxy matrix modified with 8 vol.-% ZrO2 recorded tensile modulus and toughness improved up to 36% and 45% respectively regarding EP. On the other hand, the addition of silicone rubber to EP and nanocomposites results in a superior toughness but has a slightly negative effect on modulus and strength. The addition of 3 vol.-% SR to the neat epoxy and nanocomposites increases their toughness between 1.5 and 2.5 fold; but implies also a reduction in their tensile modulus and strength in range 5-10%. Therefore, when the right proportion of nanoceramic and rubber were added to the epoxy resin, hybrid epoxy matrices with fracture toughness 3 fold higher than EP but also with up to 20% improved modulus were obtained. Widespread investigations were carried out to define the structural mechanisms responsible for these improvements. It was stated, that each type of filler induces specific energy dissipating mechanisms during the mechanical loading and fracture processes, which are closely related to their nature, morphology and of course to their bonding with the epoxy matrix. When both nanoceramic and silicone rubber are involved in the epoxy formulation, a superposition of their corresponding energy release mechanisms is generated, which provides the matrix with an unusual properties balance. From the modified matrices glass fiber reinforced RTM-plates were produced. The structure of the obtained composites was microscopically analyzed to determine their impregnation quality. In all cases composites with no structural defects (i.e. voids, delaminations) and good superficial finish were reached. The composites were also properly characterized. As expected the final performance of the GFRCs is strongly determined by the matrix properties. Thus, the enhancement reached by epoxy matrices is translated into better GFRC´s macroscopical properties. Composites with up to 15% enhanced strength and toughness improved up to 50%, were obtained from the modified epoxy matrices

The accuracy, smoothness and porosity of the segmentation results averaged across subjects for Dataset I (Subject 2–20, left column), Dataset II (Head 2 and 3, middle column), and Dataset III (Head 1–5, right column).

<p>The red error bars indicate standard deviations across subjects. The inset in (d) shows tissue-averaged quantities. All the colors refer to the legend in (i). (***: significant with <i>p</i> < 0.001)</p

The truth data of Head 3 in Dataset II (first row) and Head 1 in Dataset III (second row).

<p>As a comparison, the third row shows the results from the proposed algorithm using global TCM on Head 1 in Dataset III. The columns correspond to axial slices of GM, 3D rederings of the CSF and skull, respectively.</p

The 3D renderings of the results using different methods on Head 3 in Dataset II.

<p>From the first row to the last row: GM, WM, CSF, skull and scalp. The first column is the results by eUS, the second column is after the MRF-based clean-up, and the third and fourth column corresponds to the proposed algorithm using different TCMs (global, regional).</p

The optimal values for the parameters in Eq 6, learned from prior data.

<p>The optimal values for the parameters in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125477#pone.0125477.e015" target="_blank">Eq 6</a>, learned from prior data.</p

Rhodopsin levels and the integrity of photoreceptor cells using Rh1-GFP.

<p>Representative images of the GFP fluorescence in intact eyes are shown. (A-E) The green fluorescing deep pseudopupil of flies with different genotypes expressing Rh1-GFP (upper panel). (A’-E’) GFP-fluorescence was detected in intact eyes after cornea optical neutralization by water immersion. (A, A’) wild type (<i>Rh1</i>::<i>GFP</i>), (B, B’) <i>Rh1</i>::<i>GFP</i> flies raised in vitamin A-free food, (C, C’) <i>ninaA</i>^<i>1</i> (<i>Rh1</i>::<i>GFP;ninaA</i>^<i>1</i>), (D, D’) <i>rdgA</i>^<i>BS12</i> (<i>rdgA</i>^<i>BS12</i><i>Rh1</i>::<i>GFP</i>), (E, E’) <i>rdgA</i>^<i>BS12</i> 5 day-old. With the exception of the <i>rdgA</i>^<i>BS12</i> flies in E and E’, flies depicted in this figure were 1 day old. Scale bar on upper panels, 50 μm; on lower panel, 2 μm.</p

<i>roh</i> mutation results in Rh1 decrease.

<p>(A) GFP fluorescence of one-day old wild-type (left panel) and <i>roh</i>^{<i>EY04039</i>} (right panel) flies showing a reduction in Rh1-GFP. Scale bar, 50 μm. (B) Western blotting showing decreased Rh1 levels in the <i>roh</i>^{<i>EY04039</i>} mutant (<i>ey-flp Rh1</i>::<i>GFP; FRT42D roh</i>^{<i>EY04039</i>}<i>/ FRT42D GMR-hid CL</i>); the INAD and TRP levels are not affected compared to the wild-type. The reduction of Rh1 levels could be rescued in <i>roh</i>^<i>ex</i> (<i>ey-flp Rh1</i>::<i>GFP; FRT42D roh</i>^<i>ex</i><i>/FRT42D GMR-hid CL</i>) and <i>roh</i>^{<i>EY04039</i>};<i>GMR>roh</i> (<i>ey-flp Rh1</i>::<i>GFP; FRT42D roh</i>^{<i>EY04039</i>}<i>/ FRT42D GMR-hid CL;GMR-gal4/UAS-roh</i>) flies. Flies less than 1 day old were used. (C) Quantification of relative Rh1 level in various genotypes: wt, <i>ninaA</i>^<i>1</i>, <i>roh</i>^{<i>EY04039</i>}, <i>roh</i>^<i>ex</i> and <i>roh</i>^{<i>EY04039</i>};<i>GMR>roh</i>. The Rh1 levels were normalized to tubulin. (D) Quantitative real-time PCR of wild-type (<i>ey-flp Rh1</i>::<i>GFP; FRT42D/ FRT42D GMR-hid CL</i>) and <i>roh</i>^{<i>EY04039</i>} fly head with <i>rh1</i>-specific primers. The results are normalized to the expression level of <i>gpdh</i>. The graphs represent the means ± SD of three independent experiments. Error bars represent the SD. (E) Average rhabdomere numbers per ommatidia of the <i>roh</i>^{<i>EY04039</i>} mutant under the indicated conditions. Each data point was based on examination of >60 ommatidia from >3 flies. Error bars represent the SDs. Asterisks indicate statistically-significant differences (one-way ANOVA and post-hoc Dunnett’s test; ns: not significant, **p < 0.01).</p

The <i>scox</i> and <i>porin</i> mutations lead to light-dependent photoreceptor cell degeneration.

<p>(A-B) Average rhabdomere numbers per ommatidia of (A) the <i>scox</i> mutant flies and (B) the <i>porin</i> mutant flies under the indicated conditions. Each data point was based on examination of >60 ommatidia from >3 flies. Error bars represent the SD. Asterisks indicate statistically-significant differences (one-way ANOVA and post-hoc Dunnett’s test, **p < 0.01). (C-K) Transmission electron microscopy sections of single ommatidia of fly compound eyes with the indicated genotype and conditions. (C) 10 day-old wild-type, (D) 1 day-old <i>scox</i>^{<i>EY05333</i>}<i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; scox</i>^{<i>EY05333</i>}<i>FRT40A/GMR-hid CL FRT40A</i>), (E) 10 day-old <i>scox</i>^{<i>EY05333</i>}<i>/hid</i>, (F) 10 day-old <i>scox</i>^{<i>EY05333</i>}<i>/hid</i> under dark condition, (G) 10 day-old P-element excised <i>scox</i>^<i>ex</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; scox</i>^<i>ex</i><i>FRT40A/GMR-hid CL FRT40A</i>), (H) 1 day-old <i>porin</i>^{<i>k05123</i>}<i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; porin</i>^{<i>k05123</i>}<i>FRT40A/GMR-hid CL FRT40A</i>), (I) 10 day-old <i>porin</i>^{<i>k05123</i>}<i>/hid</i>, (J) 10 day-old <i>porin</i>^{<i>k05123</i>}<i>/hid</i> under dark condition, (K) 10 day-old p-element excised <i>porin</i>^<i>ex</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; porin</i>^<i>ex</i><i>FRT40A/GMR-hid CL FRT40A</i>). Scale bar, 2 μm. With the exception of the dark-reared (F) <i>scox</i>^{<i>EY05333</i>}<i>/hid</i> and (J) <i>porin</i>^{<i>k05123</i>}<i>/hid</i> flies, flies were maintained under a 12 hr light/12 hr dark cycle. (L) ERG responses of wild-type, <i>scox</i>^{<i>EY05333</i>}<i>/hid</i>, <i>scox</i>^<i>ex</i><i>/hid</i>, <i>porin</i>^{<i>k05123</i>}<i>/hid</i>, and p-element excised <i>porin</i>^<i>ex</i><i>/hid</i> flies in response to a 10-s orange light stimulus as indicated. Flies used were less than 2 days old.</p

Analysis of mutants of rhodopsin homeostasis, retinal degeneration, and phototransduction with the <i>Rh1</i>::<i>GFP ey-flp/hid</i> method.

<p>(A-E) Detection of fluorescence in the deep pseudopupil (left panels) and by cornea optical neutralization (right panel). (A) <i>FRT40A/hid</i>, (B) <i>ninaA</i>^<i>1</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP;ninaA</i>^<i>1</i><i>FRT40A/GMR-hid CL FRT40A</i>), (C) <i>trp</i>^<i>P343</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP;FRT82B trp</i>^<i>P343</i><i>/ FRT82B GMR-hid CL</i>), (D) <i>trp</i>^<i>P343</i><i>/hid</i> 10 day-old. 1 day-old flies were used, with the exception of the <i>trp</i>^<i>P343</i><i>/hid</i> flies, which were 10 day-old (D). Scale bar in right panels, 50 μm; in the left panels, 2μm. (E-H) ERG recordings of (E) wild type and (F) <i>ninaA</i>^<i>1</i><i>/hid</i> flies. Flies were exposed to 5 s pulses of orange light (O) or blue light (B), interspersed by 7 s, as indicated. A PDA was induced in the wild-type by blue light and terminated by orange light (arrows). (G-J) ERG response of (G) wild-type, (H) <i>Hdc</i>^<i>P217</i><i>/hid</i>, (I) <i>trp</i>^<i>P343</i>, and (J) <i>trp</i>^<i>P343</i><i>/hid</i> flies in response to a 5-s orange light stimulus.</p

Reduced on- and off-transients in <i>dmn</i> and <i>rab6</i> mutants.

<p>ERG response of (A) control, (B) <i>dmn</i>^{<i>K16109</i>}<i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; FRT42D dmn</i>^{<i>K16109</i>}<i>/ FRT42D GMR-hid CL</i>), (C) precise p-element excised <i>dmn</i>^<i>ex</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; FRT42D dmn</i>^<i>ex</i><i>/ FRT42D GMR-hid CL</i>), (D) <i>dmn</i>^{<i>K16109</i>}<i>/hid;GMR>dmn</i> (<i>ey-flp Rh1</i>::<i>GFP; FRT42D dmn</i>^{<i>K16109</i>}<i>/ FRT42D GMR-hid CL;GMR-gal4/UAS-dmn</i>), (E) <i>rab6</i>^{<i>EP2397</i>}<i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; rab6</i>^{<i>EP2397</i>}<i>FRT40A/GMR-hid CL FRT40A</i>), (F) precise p-element excised <i>rab6</i>^<i>ex</i><i>/hid</i> (<i>ey-flp Rh1</i>::<i>GFP; rab6</i>^<i>ex</i><i>FRT40A/GMR-hid CL FRT40A</i>) flies in response to a 2-s orange light stimuli.</p