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Externally bonded wet-layup carbon fiber-reinforced polymer (CFRP) strengthening systems are extensively used in concrete structures but have not found widespread use in deficient steel structures. To address the challenges of the adhesive bonding of wet-layup CFRP to steel substrates, this study investigated the effect of core–shell rubber (CSR) nanoparticles on the curing kinetics, glass transition temperature ( T g ) and mechanical properties of ambient-cured epoxy/CSR blends. The effects of silane coupling agent and CSR on the adhesive bond properties of CFRP/steel joints were also investigated. The results indicate that CSR nanoparticles have a mild catalytic effect on the curing kinetics of epoxy under ambient conditions. The effect of CSR on the T g of epoxy was negligible. Epoxy adhesives modified with 5 to 20%wt. of CSR nanoparticles were characterized with improved ductility over brittle neat epoxy; however, the addition of CSR nanoparticles reduced tensile strength and modulus of the adhesives. An up to 250% increase in the single-lap shear strength of CFRP/steel joints was accomplished in CSR-modified joints over neat epoxy adhesive joints. [ABSTRACT FROM AUTHOR]

The dispersion of nanoparticles plays a key role in enhancing the mechanical performance of polymer nanocomposites. In this work, one hybrid epoxy nanocomposite reinforced by a well dispersed, zinc oxide functionalized, multi-wall carbon nanotube (ZnO-MWCNT) and core-shell rubber (CSR) was prepared, which possesses both high modulus and fracture toughness while maintaining relatively high glass transition temperature (Tg). The improved fracture toughness from 0.82 ​MPa ​m1/2 for neat epoxy to 1.46 ​MPa ​m1/2 for the ternary epoxy nanocomposites is resulted from a series of synergistic toughening mechanisms, including cavitation of CSR-induced matrix shear banding, along with the fracture of MWCNTs and crack deflection. The implication of the present study for the preparation of high-performance polymer nanocomposites is discussed.

Externally bonded wet-layup carbon fiber-reinforced polymer (CFRP) strengthening systems are extensively used in concrete structures but have not found widespread use in deficient steel structures. To address the challenges of the adhesive bonding of wet-layup CFRP to steel substrates, this study investigated the effect of core–shell rubber (CSR) nanoparticles on the curing kinetics, glass transition temperature (Tg) and mechanical properties of ambient-cured epoxy/CSR blends. The effects of silane coupling agent and CSR on the adhesive bond properties of CFRP/steel joints were also investigated. The results indicate that CSR nanoparticles have a mild catalytic effect on the curing kinetics of epoxy under ambient conditions. The effect of CSR on the Tg of epoxy was negligible. Epoxy adhesives modified with 5 to 20%wt. of CSR nanoparticles were characterized with improved ductility over brittle neat epoxy; however, the addition of CSR nanoparticles reduced tensile strength and modulus of the adhesives. An up to 250% increase in the single-lap shear strength of CFRP/steel joints was accomplished in CSR-modified joints over neat epoxy adhesive joints.

Stiffness–toughness balance is an important issue in rubber toughened polymer blends. In this work, a facile and effective route to simultaneously toughen and reinforce polylactide (PLA) by regulating the distribution of core–shell rubber (CSR) nanoparticles with carbon black (CB) is reported. The PLA/CSR/CB nanocomposites are prepared via direct melt‐blending PLA, CSR, and CB nanoparticles with different self‐aggregate capabilities. The FTIR and DFT calculation results reveal that the interactions between CB and CSR are stronger than those between CB and PLA. Thus, CB nanoparticles with high self‐aggregate capability (HCB) can drive CSR nanoparticles to join into the HCB network structures and form CSR‐HCB network structures in the PLA/CSR/HCB nanocomposites. However, for the CB nanoparticles with low self‐aggregate capability (LCB), uniform dispersion of both CSR nanoparticles and small‐sized CB clusters in the PLA/CSR/LCB nanocomposites is observed. Compared to the network structures, the uniform dispersion structure can endow PLA/CSR/CB nanocomposites with much better stiffness–toughness balance performances. Additionally, the distribution of CSR nanoparticles on the rheological properties of PLA/CSR/CB nanocomposites are studied. This work reveals significant correlations between distribution of CSR nanoparticles and properties of PLA nanocomposites, which is helpful to prepare high‐performance PLA materials. [ABSTRACT FROM AUTHOR]

This study investigated simultaneous improvement in both toughness and heat resistance of polylactic acid (PLA) by incorporating core-shell rubber (CSR), poly D-lactic acid (PDLA), and nucleating agents. CSR was found to provide almost 25 folds increase in the impact strength of PLA with a slight decrease in thermal resistance. PDLA at 5 wt% and three commercial nucleating agents including talc, LAK301, and NAV101 at 0.5–5 wt% were investigated to further improve the thermal properties of the PLA/CSR blend. It was found that heat resistance of the blend strongly correlated with the % PLA/PDLA stereocomplex crystals (Xc,sc). LAK301 was found to be the most effective in improving the heat resistance as it could induce the highest Xc,sc, followed by talc. Their optimal content was 1 wt%. On the other hand, NAV101 not only failed to improve but also worsened both the impact strength and thermal resistance of the blends. [ABSTRACT FROM AUTHOR]

This study investigated the performance of two acrylic rubbers on the improvement of mechanical and thermal properties of polylactic acid (PLA)/ poly(D-lactide) (PDLA) stereocomplex. The selected acrylic-based rubbers consisted of a commercial acrylic rubber (ACM) and acrylic core–shell rubber (CSR). In this work, 5 wt% PDLA was melt-blended with PLA to form PLA/PDLA stereocomplex (ST) in the presence of a 15 wt% acrylic-based rubber in an internal mixer at 180 °C and 50 rpm. It was found that the small amount of PDLA could successfully form stereocomplex crystals with PLA during melt mixing. The addition of acrylic-based rubbers not only increased the impact strength of the blends but also assisted PLA in forming more perfect crystals. This is because the rubbers could act as nucleation sites for PLA crystallization leading to smaller spherulite size than that of neat unmodified PLA. Comparatively, CSR could provide much higher %crystallinity with quicker nucleation onset than ACM in both PLA and ST systems, even though the crystallization rate was lower. In terms of mechanical properties, CSR also contributed to the highest impact strength due to the smaller size of CSR than ACM in both PLA and ST systems. [ABSTRACT FROM AUTHOR]

Automotive structural adhesives must show a steady toughness performance in the temperature range of −40 °C to 80 °C, considering their actual usage environments. Core-shell rubber (CSR) nanoparticles are known to enhance the toughness of epoxy systems. In this study, a CSR, pre-dispersed, diglycidyl epoxy of bisphenol A (DGEBA) mixture at 35 wt % (KDAD-7101, Kukdo Chemical, Seoul, Korea) was used as a toughener for an automotive structural epoxy adhesive system. A simple, single-component, epoxy system of DGEBA/dicyandiamide with a latent accelerator was adopted, where the CSR content of the system was controlled from 0 to 50 phr by the CSR mixture. To determine the curing conditions, we studied the curing behavior of the system by differential scanning calorimetry (DSC). Modulus variations of the cured bulk epoxies were studied using a dynamic mechanical analyzer (DMA) in the dual cantilever mode. The flexural modulus of the cured epoxies at various temperatures (−40, −10, 20, 50, and 80 °C) showed the same tendency as the DMA results, and as the flexural strength, except at 0 phr. On the other hand, the strain at break exhibited the opposite tendency to the flexural modulus. To study the adhesion behavior, we performed single-lap joint (SLJ) and impact wedge-peel (IWP) tests. As the CSR content increased, the strength of the SLJ and dynamic resistance to the cleavage of the IWP improved. In particular, the SLJ showed excellent strength at low temperatures (32.74 MPa at 50 phr @ −40 °C (i.e., an 190% improvement compared to 17.2 MPa at 0 phr @ −40 °C)), and the IWP showed excellent energy absorption at high temperatures (21.73 J at 50 phr @ 80 °C (i.e., a 976% improvement compared to 2.07 J at 0 phr @ 80 °C)). The results were discussed in relation to the changes in the properties of the bulk epoxy depending on the temperature and CSR content. The morphology of the fracture surface was also provided, which offered useful information for composition studies using the CSR/epoxy system.

Epoxy foam adhesives are widely used for weight reduction, watertight property, and mechanical reinforcement effects. However, epoxy foam adhesives have poor impact resistance at higher expansion ratios. Hence, we prepared an epoxy composite foam adhesive with core–shell rubber (CSR) particles to improve the impact resistance and applied it to automotive structural adhesives. The curing behavior and pore structure were characterized by differential scanning calorimetry (DSC) and X-ray computed tomography (CT), respectively, and impact wedge–peel tests were conducted to quantitatively evaluate the resistance to cleavage of the CSR/epoxy composite foam adhesives under impact. At 5 and 10 phr CSR contents, the pore size and expansion ratio increased sufficiently due to the decrease in curing rate. However, at 20 phr CSR content, the pore size decreased, which might be due to the steric hindrance effect of the CSR particles. Notably, at 0 and 0.1 phr foaming agent contents, the resistance to cleavage of the adhesives under the impact wedge–peel condition significantly improved with increasing CSR content. Thus, the CSR/epoxy composite foam adhesive containing 0.1 phr foaming agent and 20 phr CSR particles showed high impact resistance (EC = 34,000 mJ/cm2) and sufficient expansion ratio (~148%).

To simultaneously address the lower toughness and the build-up of internal heat for fast-curing epoxy matrices, the influence of nominal 100 nm and 300 nm core-shell rubber (CSR) particles on the properties and rheo-kinetics were studied. The fracture energy was enhanced by a factor of 14.5, up to 2572 ± 84 J m −2 with 14.5 wt% of the nominal 300 nm diameter CSR particles, with evidence of cavitation and plastic void growth of the rubber core combined with shear band yielding of the epoxy matrix. These toughening mechanisms were modelled with an approximately linear increase up to 10 wt% for both particle types. At higher concentrations, deviation between the measured and modelled data was observed due to insufficient epoxy to dissipate additional energy. The CSR particles were not filtered out or damaged during the manufacturing of composites and reduced the total heat of reaction with a linear correlation, demonstrating a multi-functionality of simultaneous toughening and reduction of the exothermic peak. [ABSTRACT FROM AUTHOR]

Ultra-tough and heat-resistant poly(l -lactide)/core-shell rubber (PLLA/CSR) blends were fabricated by utilizing stereocomplex (SC) crystallites to effectively regulate the CSR distribution in PLLA matrix. Linear and 3–11 armed poly(d -lactide)s (PDLAs) were synthesized and then melt-mixed with PLLA/CSR blend. Interestingly, the incorporated PDLA chains could collaborate with PLLA chains to form dense SC crystallites network in PLLA/PDLA/CSR blends, thus inducing the CSR particles to transform from uniform distribution structure to network-like structure. With increasing the PDLA arm numbers, the size of CSR clusters in the network-like structure first increased and then decreased, and the continuity of the network-like structure first remained at a high level and then decreased obviously. The formation of CSR network-like structure could remarkably improve the impact strength of PLLA/PDLA/CSR blends without deteriorating their strength and modulus (compared with PLLA/CSR blend), and the CSR network-like structure with larger-sized CSR clusters and higher continuity could help obtain higher impact strength (78.3 kJ/m2). Moreover, the heat resistance of PLLA/PDLA/CSR blends could also be significantly improved (the highest Vicat softening temperature was 131 °C) by the SC crystallites network and CSR network-like structure. This work provides an effective strategy for controlling the rubber network-like morphology and thereby preparing high-performance PLLA materials. [ABSTRACT FROM AUTHOR]

Epoxy systems containing flexible epoxy and nano-sized particles were prepared and mechanical properties, such as lap-shear and impact-peel strengths were measured. Core-shell rubber (CSR), CaCO3, and SiO2particles were used as nano sized particles. Polyurethane- and polyamide-modified epoxies were used to form flexible epoxy matrix. As curing agents, DDS (4,4-diaminodiphenyl sulfone) and DICY (dicyandiamide) were used, and 2E4MZ-CNS(1-cyanoethyl-2-4-metylimidazole) was used as catalyst. As an adhesion promoter, zirconate coupling agent was used. CSR has significantly improved impact-peel strengths especially at low temperature, −40°C, due to the presence of highly flexible segments in epoxy backbones. Furthermore, nano-sized inorganic particles, CaCO3, and SiO2, have improved the impact-peel strengths of the epoxy systems. However, the lap-shear strength was decreased as the content of flexible epoxy was increased in epoxy systems. [ABSTRACT FROM AUTHOR]

Epoxy polymers, although often used in fiber-reinforced polymeric composites, have an inherent low toughness that further decreases with decreasing temperatures. Second-phase additives have been effective in increasing the toughness of epoxies at room temperature; however, the mechanisms at low temperatures are still not understood. In this study, the deformation mechanisms of a diglycidyl ether of bisphenol-A epoxy modified with MX960 core-shell rubber particles were investigated under quasi-static tensile and impact loads at room temperature and liquid nitrogen temperature. Overall, the core-shell rubber had little effect on the tensile properties at room temperature and liquid nitrogen temperature. The impact strength decreased from neat to 1 wt% and 3 wt% but increased from neat to 5 wt% at room temperature and liquid nitrogen temperature, with a higher impact strength at room temperature at all core-shell rubber loadings. While a large toughening effect was not seen in this study, the mechanisms analyzed herein will likely be of use for further material investigations at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

In the present work, epoxy/polyamide/CSR (core-shell rubber)/anhydride blends were prepared to investigate the effects of soluble polyamide and core-shell rubber particles on the impact peel strength of the cured blends at room temperature and low temperature, 23°C and −40°C, respectively. A cure accelerator, 1-(2-cyanoethyl)-2-ethyl-4- methylimidazole (2E4MZ-CN), has reduced cure time up to 10 sec at 200°C. Soluble polyamide and nano-sized CSR particles in epoxy systems had no influence on the cure kinetics. Both CSR particles and soluble polyamide significantly contributed to increasing the peel strength at room temperature. Soluble polyamide provided no impact resistance properties at low temperature, −40°C while CSR particles played a key role to improve impact optimized performance of epoxy systems at low temperature. Higher peel strength and impact resistance properties are strongly recommended for high performance structural adhesives in the various fields of industries. [ABSTRACT FROM AUTHOR]

This paper presents the effects of processing parameters and submicron core-shell rubber particle filler on the mechanical properties and cell morphology of microcellular injection molded polyamide-6 (PA-6) composites. Three types of materials are studied, namely, neat PA-6 resin, and 0.5 wt% and 3.1 wt% core-shell rubber polybutylacrylate-polymethylmethacrylate-filled PA-6 composites. This study shows that the addition of a small amount (0.5%) of core-shell rubber particles improved the ductility and impact strength of microcellular injection molded PA-6 samples. In comparison to the microcellular injection molded PA-6 polymer-clay nanocomposite, the samples with a small amount (0.5%) of core-shell rubber had much higher impact strength and ductility. The small addition of core-shell rubber also reduced cell size and increased cell density of the microcellular injection molded PA-6 parts, in comparison to their neat resin counterparts. On the other hand, at higher core-shell rubber loading, the cell size and density were found to be similar to that of the neat resin. [ABSTRACT FROM AUTHOR]

[Display omitted] • Core-shell rubbers (CSRs) with two core polymers have been used to toughen epoxy asphalt (EA). • 2 wt% CSR with polybutadiene (PB) core alters the phase separation mechanism of EA. • Both swollen polymer and asphalt particles form in the continuous epoxy phase of EA. • The area fraction of swollen PB particles is higher that of swollen SB particles. • EA modified by CSR with PB core exhibits higher damping and mechanical properties. Core-shell rubber (CSR) is a good candidate for toughening epoxy asphalt binders. However, the knowledge of the effect of the core polymer on the performance of CSR modified hot-mix epoxy asphalt binder (HEAB) is not completed and systematic yet. In this paper, CSR modified HEABs were prepared by the incorporation of 2 wt% CSR particles with different core polymers, which were in turn subjected to viscous measurements, confocal microscopy, thermogravimetric analysis, dynamic mechanical analysis and tensile tests. The results revealed that the viscosity of CSR with styrene-butadiene copolymer (SB) core (CSR SB) modified HEAB is higher than that of CSR with polybutadiene (PB) core (CSR PB) modified HEAB during curing. The shell destruction of CSR particles resulted in the swelling of the core polymers and dispersion of swollen core polymer particles in the epoxy phase in the micron scale along with asphalt particles. The phase separation of CSR PB modified HEAB occurred in the spinodal decomposition mode, which was different from the nucleation and growth mechanism of the neat and CSR SB modified HEABs. The area fraction of swollen PB particles in the CSR modified HEAB was greater than that of swollen SB particles. The core polymer had a negligible effect on the thermal stability of CSR modified HEABs. The glass transition temperatures of epoxy and asphalt, damping ability and mechanical properties of the neat HEAB were increased with the addition of CSR particles. Especially, CSR PB modified HEAB had higher tensile strength and toughness than CSR SB modified HEAB. With 2 wt% CSR PB particles being adding, the tensile strength, elongation at break and toughness of the neat HEAB were increased by 53%, 42% and 110%, respectively. [ABSTRACT FROM AUTHOR]

The fatigue resistance of epoxy polymer blends incorporating different types of preformed polymer particles was evaluated in terms of fatigue threshold and fatigue crack propagation (FCP). The fatigue thresholds of epoxies modified with polyamide-12 (PA12) particles were associated with higher stress intensity factor ranges (ΔK) than those of pure epoxies, irrespective of the molecular weights between cross-links (Mc). In contrast, the fatigue thresholds of epoxy blends with core-shell rubber (CSR) particles were affected by Mc. The FCP curve for a highly crosslinked CSR-toughened epoxy with Mc of 1110 g/mol was located at higher ΔK values compared with data for the corresponding pure epoxy. In contrast, the fatigue threshold of a moderately cross-linked CSR-modified epoxy with Mc of 2360 g/mol appeared in the lower ΔK range relative to the pure epoxy. Both cavitation of the CSR particles and plastic deformation of the latter epoxy were localized in a narrow area. [Display omitted] • Fatigue thresholds of epoxies with varying cross-link densities (Mc) were compared. •Fatigue thresholds of epoxies with polyamide-12 particles increased regardless of Mc. •Fatigue thresholds of epoxy blends with rubber particles depended highly on Mc. [ABSTRACT FROM AUTHOR]

Automotive structural adhesives must show a steady toughness performance in the temperature range of −40 °C to 80 °C, considering their actual usage environments. Core-shell rubber (CSR) nanoparticles are known to enhance the toughness of epoxy systems. In this study, a CSR, pre-dispersed, diglycidyl epoxy of bisphenol A (DGEBA) mixture at 35 wt % (KDAD-7101, Kukdo Chemical, Seoul, Korea) was used as a toughener for an automotive structural epoxy adhesive system. A simple, single-component, epoxy system of DGEBA/dicyandiamide with a latent accelerator was adopted, where the CSR content of the system was controlled from 0 to 50 phr by the CSR mixture. To determine the curing conditions, we studied the curing behavior of the system by differential scanning calorimetry (DSC). Modulus variations of the cured bulk epoxies were studied using a dynamic mechanical analyzer (DMA) in the dual cantilever mode. The flexural modulus of the cured epoxies at various temperatures (−40, −10, 20, 50, and 80 °C) showed the same tendency as the DMA results, and as the flexural strength, except at 0 phr. On the other hand, the strain at break exhibited the opposite tendency to the flexural modulus. To study the adhesion behavior, we performed single-lap joint (SLJ) and impact wedge-peel (IWP) tests. As the CSR content increased, the strength of the SLJ and dynamic resistance to the cleavage of the IWP improved. In particular, the SLJ showed excellent strength at low temperatures (32.74 MPa at 50 phr @ −40 °C (i.e., an 190% improvement compared to 17.2 MPa at 0 phr @ −40 °C)), and the IWP showed excellent energy absorption at high temperatures (21.73 J at 50 phr @ 80 °C (i.e., a 976% improvement compared to 2.07 J at 0 phr @ 80 °C)). The results were discussed in relation to the changes in the properties of the bulk epoxy depending on the temperature and CSR content. The morphology of the fracture surface was also provided, which offered useful information for composition studies using the CSR/epoxy system. [ABSTRACT FROM AUTHOR]

• Core-shell rubber (CSR) nanoparticle toughened epoxy asphalt (EA) has been developed. • The toughness of the pure EA increases by 2-fold with only addition of 1 wt% CSR. • The shell of CSR is broken and the core of CSR swells in the EA. • Newly micro-scale CSR phase uniformly disperses in the epoxy phase of the EA. • CSR nanoparticles alters the mechanism of phase separation of the pure EA. Core-shell rubber (CSR) has been widely applied in the improvement of the toughness for the brittle epoxy resin. In this study, an epoxy asphalt (EA) binder has been toughened by the inclusion of CSR nanoparticles with approximately 100–200 nm in diameter. The incorporation of CSR nanoparticles significantly increased the viscosity of the pure EA during curing. Even with 5 wt% CSR, the EA blend exhibited extremely long operational lifetime (more than 2.5 h) for mixture pavements. The glassy shell of CSR nanoparticles was broken and the rubbery core of CSR nanoparticles swelled in the EA. New micro-scale CSR domains formed and uniformly dispersed in the epoxy phase of the cured EA. The inclusion of CSR nanoparticles altered the phase separation mechanism of the pure EA. The sea-island morphology of the pure EA took place through the nucleation and growth (NG) mechanism, while co-continuous microstructures in the EA blends with 3 wt% and 5 wt% CSR formed through the spinodal decomposition (SD) mechanism. Both sea-island and co-continuous microstructures via combined the NG and SD mechanisms were observed in the EA blend containing 1 wt% CSR. The glass transition temperature and thermal stability of the pure EA was improved by the inclusion of higher CSR loadings. The incorporation of CSR greatly enhanced the mechanical properties of the pure EA. In the case of 1 wt% CSR inclusion, 29% increase in the tensile strength, 60% improvement in the elongation at break and 2-fold increment in the toughness were obtained. [ABSTRACT FROM AUTHOR]

• Durability of CFRP-concrete bond was evaluated with three-point bending test. • Epoxy modified with core-shell rubber (CSR) nanoparticles improved CFRP-concrete bond durability. • Silane surface functionalization of concrete substrate enhanced CFRP-concrete bond durability. • Combined use of CSR nanoparticles and silane does not offer additional benefits. • CFRP with CSR-modified epoxy matrix exhibited better durability than CFRP with neat epoxy matrix. The adhesive bond between externally bonded fiber-reinforced polymer (FRP) repairs and the concrete substrate can significantly deteriorate under hygrothermal conditions. The present study evaluated the epoxy adhesive toughening with core–shell rubber (CSR) nanoparticles and concrete surface functionalization with an epoxy-functional silane coupling agent as a means of improving the bond durability under hygrothermal exposure. To determine the effect of environmental degradation, beam bond test specimens were subjected to control conditions (standard laboratory conditions: 23 ± 2 °C and RH 50 ± 10%) and a hygrothermal accelerated conditioning protocol (ACP) (water immersion at 45 ± 1 °C) for 8 weeks. Bond test results indicate that CSR toughening and silane coupling agent can improve FRP-concrete adhesive bond strength retention following accelerated conditioning by up to 15% over that of neat epoxy. Following accelerated conditioning, CFRP coupons prepared with CSR-modified epoxy retain their mechanical properties, while the CFRP prepared with the neat epoxy exhibited a significant reduction in strength (40%) and elongation (54%). CSR nanoparticles demonstrated good compatibility with the base epoxy resin, as evidenced by differential scanning calorimetry (DSC) glass transition temperature measurements. [ABSTRACT FROM AUTHOR]

Alpha-zirconium phosphate (Zr(O 3 POH) 2 ·H 2 O, α-ZrP) nanoplatelets were exfoliated using tetra- n -butylammonium hydroxide (TBA) and cured through the anionic phosphonate on the surface of the exfoliated α-ZrP-TBA. α-ZrP-TBA can both initiate an anionic polymerization of epoxy monomers and serve as reinforcing agents for epoxy matrix. The epoxy/α-ZrP-TBA nanocomposites exhibit greatly increased Young's modulus of 4.3 GPa, while maintaining a relative high glass transition temperature of 110 °C. In addition, epoxy/α-ZrP-TBA nanocomposites are highly toughenable. With an addition of 3 vol% core-shell rubber particles, the K IC value is improved from 0.55 to 1.55 MPa m1/2. The usefulness of the present study for preparation of high-performance thermosetting polymers is discussed. Transparent epoxy/α-ZrP-TBA bulk sample, showing the exfoliation and toughening mechanisms using core-shell rubber particles. Image 1 • Epoxy/α-ZrP-TBA nanocomposites with attractive mechanical properties were prepared. • α-ZrP-TBA in epoxy serves both as a reinforcing agent and as a curing agent with a good latency. • The Young's modulus is increased by over 70% with 4 vol% addition of α-ZrP-TBA in epoxy. • With an additional incorporation of 3 vol% of rubber particles, K IC is increased by 180%. [ABSTRACT FROM AUTHOR]

Epoxy foam adhesives are widely used for weight reduction, watertight property, and mechanical reinforcement effects. However, epoxy foam adhesives have poor impact resistance at higher expansion ratios. Hence, we prepared an epoxy composite foam adhesive with core–shell rubber (CSR) particles to improve the impact resistance and applied it to automotive structural adhesives. The curing behavior and pore structure were characterized by differential scanning calorimetry (DSC) and X-ray computed tomography (CT), respectively, and impact wedge–peel tests were conducted to quantitatively evaluate the resistance to cleavage of the CSR/epoxy composite foam adhesives under impact. At 5 and 10 phr CSR contents, the pore size and expansion ratio increased sufficiently due to the decrease in curing rate. However, at 20 phr CSR content, the pore size decreased, which might be due to the steric hindrance effect of the CSR particles. Notably, at 0 and 0.1 phr foaming agent contents, the resistance to cleavage of the adhesives under the impact wedge–peel condition significantly improved with increasing CSR content. Thus, the CSR/epoxy composite foam adhesive containing 0.1 phr foaming agent and 20 phr CSR particles showed high impact resistance (EC = 34,000 mJ/cm2) and sufficient expansion ratio (~148%). [ABSTRACT FROM AUTHOR]