Synthesis and Multiscale Characterization of Toughened Epoxy Incorporating Nanoparticles
Mona Abd_Elsabour Ahmed;
Abstract
While epoxy resin is the most used adhesive in structural applications, it suffers from brittle behaviour at failure and relatively low energy absorption (toughness). The main objective of this work is to examine the effect of incorporating a mixture of reactive rubber nanoparticles (RRNP) and organically modified nanoclay (Cloisite-30B) into the epoxy matrix with the aim of improving material toughness without altering its desired strength and stiffness. The functionalized RRNP and Cloisite-30B have been impregnated in the epoxy matrix using ultrasonic homogenization technique targeting to create tough and stiff epoxy nanocomposites. Each nanomaterial has been studied separately and this was followed by combining the optimal percentage of each to form hybrid. Morphological information of hybrid materials is important for perfect understanding of the relationship between the structure and mechanical properties.
Firstly, SBR elastomer is dissolved in a low boiling point solvent, then emulsified in an aqueous solution through a soap-in-situ procedure and then homogenized by sonification. After forming uniform latex particles with sub-micron size, most of the solvent was stripped off, and
SUMMARY AND CONCLUSIONS
131
cross-linking reaction was performed by simply increasing the emulsion temperature to form crosslinked rubber particles that are insoluble yet completely dispersible. Overall, during the cross-linking reaction to form stable styrene-co-butadiene (SBR) rubber nanoparticles; the internal double bond units reacted with each other by the enhancement of a crosslinking agent (p-divinylbenzene DVB) via radical addition reaction. However, most of external double bond units on or near the surfaces are much more difficult to find each other and remained on the surfaces. As a result the presence of these unreacted double bonds is valuable in the subsequent epoxidation reactions. The epoxidized (RRNP) was characterized by 1H-NMR spectrum where the formation of epoxy groups is assured by the appearance of two new signals corresponding to the protons of the epoxy group (at 2.45 and 2.7 ppm )with the reduction in area of the signal of vinyl double bond protons(at δ = 4.9 ppm). In addition; FT-IR spectrum of epoxidized SBR showed the bonds of stretching and contracting in phase of all epoxy rings observed at about 1258 and 842 cm−1
After functionalization, the epoxy groups created on RRNP surface have been chemically connected into the .
SUMMARY AND CONCLUSIONS
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epoxy matrix. The incorporation of the surface epoxy groups of the particles during the epoxy curing reaction enhanced the adhesive force between the epoxy matrix and the particles and exceeds the matrix cohesive force. Consequently, the resulting core-shell reactive rubber nanoparticles (RRNP) are homogeneously embedded in the epoxy matrix with chemical interfacial interactions. All of these are assured by complete morphological study via SEM&TEM.
Secondly, Cloisite30B/epoxy nanocomposite specimens have been prepared by treating the epoxy base with different percentages of clay (2, 4, 6, 8 and 10 wt %). Epoxy resin monomer readily entered into the gallery of Cloisite30B by the help of organically modified clay surface. Morphological studies for all specimens having these Cloisite30B percentages have been performed using XRD and TEM. In XRD, almost disappearance of the nanoclay main peak (at 2θ=4.62°) was observed, this is an evidence of complete dispersion of the nanoclay in the epoxy matrix. As the wt% of clay increases from 2 wt% to 10 wt. %; there is a noticeable increase in 2θ and consequently an obvious decrease in d-spacing values. In TEM, it can be concluded that most of the clay platelets have been dispersed in the exfoliation mode for nanoclay
SUMMARY AND CONCLUSIONS
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percentage up to 6wt%. Up to this weight percentage, nanoclay has fully delaminated to silicate layers giving rise to mostly exfoliated nanocomposites with partial intercalated nanoplatelts, which is in consistent with XRD results. On the other hand, increasing the weight percentage of nanoclay in the epoxy matrix resulted in the difficulty of dispersion. This can be noticed from the TEM image of the epoxy–clay nanocomposite (10 wt. % specimen), where intercalated clay nanoplatelets were observed with some agglomerates.
Finally, the mechanical properties were studied by 3-d bending test (flexural test) to obtain stress –strain curve for epoxy nanocomposites. Epoxy with different percentages of RRNP (5, 7, and 10) wt. % give higher flexural strain than neat epoxy with lower flexural strength due to plastic effect of rubber nanoparticles. The best performance was normally achieved with 5 wt% of RRNP which gives higher strain than neat epoxy. As a result, it was found that the optimal wt. % of RRNP is 5wt. % .This percentage shows the highest toughness value (area under the curve), compared with all other wt. % of RRNP specimens. This could be attributed to the fact that, at higher RRNP percentage, the rubber particles agglomerate and consequently reduce their toughening effect.
SUMMARY AND CONCLUSIONS
134
Flexural (3-d bending) test had also been performed
Firstly, SBR elastomer is dissolved in a low boiling point solvent, then emulsified in an aqueous solution through a soap-in-situ procedure and then homogenized by sonification. After forming uniform latex particles with sub-micron size, most of the solvent was stripped off, and
SUMMARY AND CONCLUSIONS
131
cross-linking reaction was performed by simply increasing the emulsion temperature to form crosslinked rubber particles that are insoluble yet completely dispersible. Overall, during the cross-linking reaction to form stable styrene-co-butadiene (SBR) rubber nanoparticles; the internal double bond units reacted with each other by the enhancement of a crosslinking agent (p-divinylbenzene DVB) via radical addition reaction. However, most of external double bond units on or near the surfaces are much more difficult to find each other and remained on the surfaces. As a result the presence of these unreacted double bonds is valuable in the subsequent epoxidation reactions. The epoxidized (RRNP) was characterized by 1H-NMR spectrum where the formation of epoxy groups is assured by the appearance of two new signals corresponding to the protons of the epoxy group (at 2.45 and 2.7 ppm )with the reduction in area of the signal of vinyl double bond protons(at δ = 4.9 ppm). In addition; FT-IR spectrum of epoxidized SBR showed the bonds of stretching and contracting in phase of all epoxy rings observed at about 1258 and 842 cm−1
After functionalization, the epoxy groups created on RRNP surface have been chemically connected into the .
SUMMARY AND CONCLUSIONS
132
epoxy matrix. The incorporation of the surface epoxy groups of the particles during the epoxy curing reaction enhanced the adhesive force between the epoxy matrix and the particles and exceeds the matrix cohesive force. Consequently, the resulting core-shell reactive rubber nanoparticles (RRNP) are homogeneously embedded in the epoxy matrix with chemical interfacial interactions. All of these are assured by complete morphological study via SEM&TEM.
Secondly, Cloisite30B/epoxy nanocomposite specimens have been prepared by treating the epoxy base with different percentages of clay (2, 4, 6, 8 and 10 wt %). Epoxy resin monomer readily entered into the gallery of Cloisite30B by the help of organically modified clay surface. Morphological studies for all specimens having these Cloisite30B percentages have been performed using XRD and TEM. In XRD, almost disappearance of the nanoclay main peak (at 2θ=4.62°) was observed, this is an evidence of complete dispersion of the nanoclay in the epoxy matrix. As the wt% of clay increases from 2 wt% to 10 wt. %; there is a noticeable increase in 2θ and consequently an obvious decrease in d-spacing values. In TEM, it can be concluded that most of the clay platelets have been dispersed in the exfoliation mode for nanoclay
SUMMARY AND CONCLUSIONS
133
percentage up to 6wt%. Up to this weight percentage, nanoclay has fully delaminated to silicate layers giving rise to mostly exfoliated nanocomposites with partial intercalated nanoplatelts, which is in consistent with XRD results. On the other hand, increasing the weight percentage of nanoclay in the epoxy matrix resulted in the difficulty of dispersion. This can be noticed from the TEM image of the epoxy–clay nanocomposite (10 wt. % specimen), where intercalated clay nanoplatelets were observed with some agglomerates.
Finally, the mechanical properties were studied by 3-d bending test (flexural test) to obtain stress –strain curve for epoxy nanocomposites. Epoxy with different percentages of RRNP (5, 7, and 10) wt. % give higher flexural strain than neat epoxy with lower flexural strength due to plastic effect of rubber nanoparticles. The best performance was normally achieved with 5 wt% of RRNP which gives higher strain than neat epoxy. As a result, it was found that the optimal wt. % of RRNP is 5wt. % .This percentage shows the highest toughness value (area under the curve), compared with all other wt. % of RRNP specimens. This could be attributed to the fact that, at higher RRNP percentage, the rubber particles agglomerate and consequently reduce their toughening effect.
SUMMARY AND CONCLUSIONS
134
Flexural (3-d bending) test had also been performed
Other data
| Title | Synthesis and Multiscale Characterization of Toughened Epoxy Incorporating Nanoparticles | Other Titles | "تحضير ودراسة الخصائص المتعددة النطاقات لراتنجات الايبوكسي المقواة ميكانيكيا باستخدام جسيمات نانونية الحجم ونشطة السطح كيميائيا" | Authors | Mona Abd_Elsabour Ahmed | Issue Date | 2015 |
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