Rubber Particle Size Research Articles

Use of rubberized engineered cementitious composite in strengthening flexural concrete beams

This study aimed to investigate the flexural behavior of reinforced concrete beams strengthened with high-performance rubberized engineered cementitious composite (RECC) at different cross-sectional positions (compression and tension zones). The RECC material was developed with different sizes of rubber particles, including 4.75 mm crumb rubber (CR) and 0.4 mm powder rubber (PR). The investigation tested conventional normal concrete (NC) and two full RECC beams with CR and PR as reference beams for comparison. A four-point bending test was conducted to evaluate the flexural strength, ductility, energy absorption, deformability, first cracking load, and cracking behavior of the strengthened beams compared to the reference beams. The study also compared the experimental results and their theoretical predictions calculated by design code equations and proposed model from the literature. The results revealed that using a RECC layer in the compression side exhibited a significantly higher deformability, cracking behavior, ductility, and energy absorption compared to the reference NC beam. Meanwhile, placing a RECC layer in the tension side showed lower ductility and energy absorption capacity compared to counterpart beams strengthened in the compression side, but still higher than the NC reference beam. The results also indicated that strengthening the beam in the compression side with a RECC layer developed with PR showed better enhancement in the energy absorption and ductility compared to a RECC layer developed with CR.

Influence of Non-Rubber Components on the Properties of Unvulcanized Natural Rubber from Different Clones.

Natural rubber from different Hevea braziliensis clones, namely RRIM600, RRIT251, PB235 and BPM24, exhibit unique properties. The influences of the various fresh natural rubber latex and cream concentrated latex on the non-rubber components related properties were studied. It was found that the fresh natural rubber latex exhibited differences in their particle size, which was attributed to the non-rubber and unique signature of clones which affect various properties. Meanwhile, the cream concentrated latex showed the protein contents, surface tension, and color of creamed latex to be lower than the fresh natural latex. However, TSC, DRC, viscosity, particle size and green strength of concentrated latex were found to be higher than the fresh natural latex. This is attributed to the incorporation of HEC molecules. Also, the rubber particle size distribution in the RRIM600 clone exhibited a large particle size and uniform distribution, showing good mechanical properties when compared to the other clones. Furthermore, the increased green strength in the RRIM600 clone can be attributed to the crystallization of the chain on straining and chain entanglement. These experimental results may provide benefits for manufacturing rubber products, which can be selected from a suitable clone.

Optimization of Cement–Rubber Composites for Eco-Sustainable Well Completion: Rheological, Mechanical, Petrophysical, and Creep Properties

To ensure well integrity, wellbore must be strongly cased using durable cement slurries with essential additives during downhole completion. The rubber materials that come from industrial waste are becoming extremely encouraged in the use as an additive in preparing cement slurries due to their growing environmental footprint. However, the proper design of cement slurry strongly depends on its rheological, mechanical, petrophysical, and creep properties, which can be altered by changing additives. This study aimed to examine the cement properties under alteration in different chemical admixtures to create efficient binding properties, and to estimate the optimum cement–rubber slurry composition for eco-sustainable completion. Three cement samples with different mesh sizes of the crumb rubber particles were prepared. This study examined the variation in rheological behaviors, elastic and failure characteristics, permeability, and creep behavior of the cement–rubber composites for petroleum well construction. The experimental study showed that the addition of 15% or more crumb rubber to the cement resulted in very thick slurries. Moreover, it was shown that the addition of crumb rubber with various particle sizes to the cement reduced the strength by more than 50%, especially for a higher amount of rubber added. It was also revealed that the addition of a superplasticizer resulted in an 11% increase in compressive strength. The results showed that cement–crumb-rubber composites with 12% by weight of cement (BWOC) represented the optimum composite, and considerably improved the properties of the cement slurry. Water-permeability tests indicated the addition of 12% BWOC with 200-mesh crumb rubber decreased the permeability by nearly 64% compared to the base cement. Creep tests at five different stress levels illustrated that the neat cement was brittle and did not experience strain recovery at all stress levels. Cement slurries with the largest rubber-particle size were elastic and demonstrated the highest amount of strain recovery. Finally, a relationship was established between the permeability, average strain, and mesh size of the rubber particles, which offered the strain recovery, satisfied the zonal isolation, and consequently reduced the microannulus problem to ensure the cement’s integrity.

Experimental investigation on the impact resistance of rubber self-compacting concrete

Stiffness degradation and micro-cracks are commonly observed in the self-compacting concrete subjected to long-term vibration and impact loading. Adding rubber particles to the concrete is a universal approach to improve impact resistance. Exploiting the dynamic mechanical properties of the rubber self-compacting concrete under impact loading is of great significance. Herein, a comprehensive investigation of rubber self-compacting concrete under impact loading was carried out using a split Hopkinson pressure bar. The influence of rubber replacement rate, rubber particle size, and strain rate on impact resistance was considered. 108 rubber self-compacting concrete specimens along with 36 ordinary self-compacting concrete ones were designed. As a result, the dynamic stress–strain relationship of rubber self-compacting concrete was proposed. The results show that rubber self-compacting concrete's dynamic peak strain and peak stress were higher than ordinary self-compacting concrete with similar static compressive strength. The dynamic compressive strength and DIF-σ and DIF-ε of rubber self-compacting concrete can be increased with strain rate. The sensitivity of growth rates of DIF-σ and DIF-ε to strain rate decreases with the strain rate. DIF-σ and DIF-ε showed a positive linear correlation with rubber content. The increase of rubber content reduces the dynamic compressive strength of rubber self-compacting concrete. Compared with other sizes, the dynamic compressive strength and DIF-σ and DIF-ε of 12 mesh (1 ∼ 2 mm) rubber particles are generally higher.

Effect of solid-state shear milled natural rubber particle size on the processing and dynamic vulcanization of recycled waste into thermoplastic vulcanizates

Natural rubber (NR) and crosslinked polyethylene (XLPE) waste streams were devulcanized by solid state shear milling (S3M), producing a fine powder that may be more easily reprocessed. Understanding devulcanization and the nature of decrosslinked thermoset materials is of utmost importance for turning these waste steams into functional products. It was found that the devulcanized powders contained significant concentrations of radicals, which may be active in the subsequent revulcanization process. The produced devulcanized powders were converted into recyclable thermoplastic vulcanizates (TPVs) by twin screw extrusion. Reprocessing of these powders into value-added products is an important step in recycling and the use of extrusion allows for high throughput and industrial viability. Herein, we demonstrate that the optimal conditions for reprocessing are dependent upon the particle size of the devulcanized powder. Furthermore, dynamic vulcanization is affected by the nature of these recyclate powders. The successfully prepared TPVs showed similar properties to virgin materials, with a high elongation to failure. Therefore, the conversion of waste rubber into the rubber phase of a TPV shows significant promise in moving towards sustainable products, providing the revulcanization step can be well controlled.

Axial compressive behavior of square steel tube confined rubberized concrete stub columns

An innovative square steel tube confined rubberized concrete column is proposed in this study to alleviate the pollution from waste rubber and improve the mechanical properties of conventional concrete. The axial compressive behavior of square steel tube confined rubberized concrete (Ru-STCC) stub column is experimentally studied. A total of thirty-two specimens, including four square steel tube confined concrete (STCC) stub columns and twenty-eight Ru-STCC stub columns, were fabricated and tested. The variables included rubber particle volume replacement ratio, steel tube thickness, rubber particle size and concrete strength grade. The failure mode, axial ultimate compressive strength, rigidity, ductility, strain characteristics, and confinement effects were analyzed. The results show that the failure modes of Ru-STCC specimens were the core concrete shear failure and steel tube buckling. Ultimate axial compressive strength and rigidity were found inversely proportional to the volume replacement ratio, When the volume replacement ratio reached 20%, the ultimate axial compressive strength and rigidity reduced by more than 20%. With the increase of steel tube thickness, the ultimate axial compressive strength increased by more than 10%. Concrete strength grade and rubber particle size have significant effects on rigidity and ductility, respectively. In addition, the differences between square concrete-filled in steel tube (CFST), rubberized concrete-filled in steel tube (Ru-CFST), STCC, and Ru-STCC stub columns were discussed by compressive strength and deformation capacity. The axial ultimate compressive strength of square Ru-STCC specimens was evaluated using various calculation models. The simplified formulae for the prediction of axial ultimate compressive strength were also presented.

In-situ observation of spatial organization of natural rubber latex particles and exploring the relationship between particle size and mechanical properties of natural rubber

Natural rubber (NR), an important source of elastomeric material, has superior comprehensive properties compared to synthetic high cis-1, 4-polyisoprene, which are attributed to its peculiar architecture. However, it is a challenge to identify the precise structure of NR, especially the structure of NR particles, as there are no direct characterization methods to perform in-situ investigation of structure of NR particles at an intact state. In this study, we used cryogenic transmission electron microscopy (cryo-TEM) to directly explore the morphology of NR particles existing in the latex without drying or chemical fixation. Then, the spatial organization of proteins and phospholipids on the surface of NR particles was visualized by stochastic optical reconstruction microscopy (STORM). The results show that NR particles are spherical particles with an average particle size of 88 ± 15 nm, and the exterior of NR particles is a mixed monolayer of proteins and phospholipids (ca. 4.6 ± 0.77 nm in thickness). Thus, a more complete model for the Hevea brasiliensis rubber particles was proposed. Moreover, we explicated the relationship between the particle size of NR particles, molecular characteristics, and mechanical properties of NR. The Mnand Mw of small rubber particles (SRPs) with a particle size of 106 nm are (1.56 ± 0.06) × 106 g/mol and (2.21 ± 0.07) × 106 g/mol respectively, which are much larger than those of the large rubber particles (LRPs) with a particle size of 628 nm (Mn: (0.41 ± 0.05) × 10 6 g/mol; Mw: (1.63 ± 0.10) × 106 g/mol). After vulcanization, the SRPs have better mechanical properties. Compared with LRPs, SRPs exhibit a 4.3-fold increase in tensile strength (from 5.7 to 24.6 MPa) and a 3.5-fold increase in toughness (from 12.9 to 44.9 kJ/m2). This work not only provides rational design for the new biomimetic synthetic rubber with unique hierarchical structures and excellent properties, but also offers a new possibility for tuning the mechanical properties of NR by preparation of LRPs/SRPs blend of various ratios.

Poly (Lactic Acid) (PLA)/Recycled Styrene Butadiene Rubber (rSBR) Composites

Recycled styrene butadiene rubber (rSBR) from waste car tires was used as a filler in poly(lactic) acid (PLA) to modify its properties. The compounds were prepared via twin-screw extrusion and molded by injection with different rSBR contents (0 to 25% wt.). Additionally, recycled rubber particle size was controlled between 125 and 1000 μm to determine the effect of this parameter. From the samples produced, a series of morphological, physical and mechanical characterizations were performed. As expected, rSBR addition decreased the PLA stiffness. Up to 5% rSBR, the flexural and elastic moduli were unchanged, but the tensile strength, elongation at break and impact toughness were decreased. The highest tensile strength, elongation at break and impact toughness were achieved for PLA/rSBR blends filled with small rubber particles (125-250 μm). According to the morphological analysis, this behavior was associated to better interfacial interactions between smaller rSBR particles (higher specific surface area) and PLA resulting in a more uniform filler distribution and better stress transfer from PLA to rSBR. Finally, to complete the mechanical properties of the materials, fatigue tests were carried out on different blends and the results were related to instrumented indentation to get some more local information.

Composition Optimization and Damping Performance Evaluation of Porous Asphalt Mixture Containing Recycled Crumb Rubber

Composition optimization of the asphalt mixture of pavement is one effective measures to reduce the harm of traffic noise. To improve the noise reduction effect of porous asphalt mixture (PAM) and promote the recycling of crumb rubber in highway engineering, the preparation parameters of high-viscosity modified asphalt for PAM were optimized in this study, and the mixture gradation was optimized based on the unbalance force and contact force of mixed aggregate. The effects of crumb rubber content and particle size on the damping performance and dynamic shear modulus of the mixture were studied. The effects of different preparation parameters on the performance of the PAM were comprehensively evaluated based on the orthogonal test, and preparation parameters of PAM were recommended. The results show that with the increase of crumb rubber content, the damping ratio of the mixed aggregate increases gradually. The addition of crumb rubber is conducive to improving the damping performance and toughness of the PAM, but it has an adverse impact on the bearing capacity. Under the condition of low strain, the damping ratio of the mixed aggregate containing 2–5 mm crumb rubber is 1.2–5 times that of the mixed aggregate containing 0.6–1 mm crumb rubber. The recommended optimum content of crumb rubber in PAM is 4%, and the optimum particle size of alternative aggregate is 2.36–4.75 mm. The significant factors affecting Marshall stability are rubber particle content, asphalt aggregate ratio, mixing temperature, compaction times, and forming temperature. The rational utilization of crumb rubber in PAM is of positive significance to promoting the green development of highway construction and the harmless treatment of waste resources.

Retraction Note to: Influence of crumb rubber particle sizes on rutting, low temperature cracking, fracture, and bond strength properties of asphalt binder

Retraction Note to: Influence of crumb rubber particle sizes on rutting, low temperature cracking, fracture, and bond strength properties of asphalt binder

Preparation of diene-based nanoparticles by semibatch microemulsion polymerization and their catalytic hydrogenation

Poly(acrylonitrile-co-butadiene) nanoparticles were synthesized by semibatch microemulsion polymerization. The microstructure of the polymers was characterized by 1H NMR and FT-IR. The particle size of the nitrile butadiene rubber (NBR) latex could be well controlled by reaction temperature, surfactant concentration, and feeding time of monomer. The minimum particle size of 34.2 nm could be achieved by using the surfactant/monomer mass fraction of 7.9 wt%. The latex can be directly catalyzed for hydrogenation using Wilkinson's catalyst (RhCl(PPh3)3) and second generation Grubbs catalyst (Grubbs II), respectively. The hydrogenated products (HNBR) with a degree of hydrogenation above 95 mol% were obtained. The fast rate of hydrogenation demonstrates the unique advantages of small particle size.

Effect of acids and freeze–thaw on the durability of modified rubberized concrete with optimum rubber crumb content

AbstractInvestigations of the effect of acids and freeze–thaw on pozzolanic cement‐based rubberized concrete after surface treatment of rubber crumbs are limited. Rubberized concrete's mechanical and durability properties (water absorption, acid attack resistance, and freeze–thaw attack resistance) are evaluated. Six rubber crumbs content (0%, 10%, 15%, 20%, 25%, and 30%) and particle size 0.6–2.36 mm are used to replace fine aggregate in concrete partially, and 15% replacement level of rubber crumb is found to be the optimum quantity in concrete. Structural analyses show that the specimens remain in the crystalline phase after being submerged in H2SO4 and HCl acid. When rubberized concrete is immersed in H2SO4 and HCl solution with equal concentrations and duration, specimens immersed in HCl solution have been found to have less surface erosion, less weight loss, and lower compressive strength loss. When the conventional concrete mix is immersed in H2SO4 and HCl solution, the losses in compressive strength are 74.56% and 30.34%, but in rubberized concrete, the losses are 60.01% and 24.22% only. No apparent microcracks and no spalling on the surfaces of the specimens are found up to 90 freeze–thaw cycles. Rubberized concrete's ultrasonic velocity decreases slightly up to 90 freeze–thaw cycles, but it still has good concrete quality.

Experimental investigation on bond-slip behavior of self-compacting rubberized concrete-filled steel tubes

The bond strength between materials is the basis of the cooperative work of composite structures. This study aims to investigate the bonding performance of push-out tests conducted on self-compacting rubberized concrete-filled steel tubes (SCRCFST). The rubber content, particle size, interface bonding length, and water–cement ratio were varied to evaluate their impact on bond strength. The failure mode and failure mechanism were analyzed. The bond damage and energy consumption capacity were investigated. Moreover, this study reveals the characteristics of the stress–slip curve and derives the characteristic equations from reviewing the different points. Test results indicate that rubber particles enhance the energy dissipation capacity of specimens after reaching ultimate bond strength. Furthermore, bond strength decreases with the increase of rubber particles size and water–cement ratio, while the bonding length is barely impacted. It is worth noting that the bonding strength increases slightly at 10% rubber content. The main contribution of this work is to fill the gap in the bonding performance of SCRCFST and guide engineering utilization. HIGHLIGHTS Seventeen cylindrical specimens of SCRCFST performed a push-out test by monotonous loading. Bond damage degree and energy dissipation capacity were investigated. Increasing rubber-related parameters negatively affected the bond properties of the structure. Bond strength equations were proposed.

Damage Characteristics of Uniaxial Compressed Concrete Embedded Different Aging Rubber by 3D Mesoscale Model

Rapid development of the automobile industry has brought the disposal problem of waste rubber tires. Mixing waste rubber tires into concrete can not only solve environmental problems but also improve the mechanical properties of concrete. Rubber aging is one of the main factors to affect the mechanical properties of rubberized concrete. Therefore, an FEM model of rubberized concrete in mesoscale is established in this paper. The influence of rubber aging on the uniaxial compression damage of rubberized concrete is u;studied. The results show that (1) the elastic modulus and compressive strength of rubberized concrete are negatively correlated with the aging level and content of rubber and positively correlated with the particle size of rubber. (2) After uniaxial compression of concrete enters the softening section, the crack resistance of concrete is positively correlated with the aging level and content of rubber and negatively correlated with the particle size of rubber. (3) Compared with the elastic modulus, the compressive strength of rubberized concrete is more sensitive to the change of parameters of rubber, that is, the change range of the compressive strength of rubberized concrete is always greater than the change range of its elastic modulus, when the aging level, content, and particle size of rubber change.

Feasibility study of compressed bricks utilizing rubber glove manufacturing residue

The demand of the rubber glove had increased significantly since early of the year 2020 due to the COVID-19 virus breakout especially in the medical and healthcare sector. Rubber Glove Manufacturing Residue (RGMR) is the by-product from the effluent treatment by coagulation process in the manufacturing procedure. Non-recyclable RGMR are disposed to landfill after treated. This research is aimed to reuse the RGMR in cemented interlocking bricks to address the natural resources depletion issues and greenhouse gases released from the burnt brick production. The comparison in terms of physical and mechanical properties was conducted in between RGMR and crumb rubber interlocking bricks (RIB). RGMR and crumb rubber were used as partial fine aggregate replacement by 10% while fly ash was used as a cement replacement material by 56%. Four mixes were tested, and the interlocking bricks were categorized as medium weight bricks. However, only control mix and RGMR-2 mix fulfilled the loadbearing masonry requirement of a minimum of 13.8 MPa. RGMR-2 utilizing 10% fine aggregate replacement using RGMR without cement replacement. As for the mixes utilizing fly ash and fine aggregate replacement, RGMR-1 mix and RIB mix show compressive strength of 12.15 MPa and 11.64 MPa respectively. Besides that, the use of RGMR reduced the water absorption compared to RIB mix due to the larger particle size of crumb rubber. The water absorption rate for RIB mix has exceeded the limit of water absorption for the medium weight bricks of 240 kg/m3. The finding indicates that the RGMR exhibited a better performance as compared to the crumb rubber.

Reducing the emission of climate-altering substances in cementitious materials: A comparison between alkali-activated materials and Portland cement-based composites incorporating recycled tire rubber

Low carbon or near-zero carbon concrete technology is in line with the pillars of sustainable development, where industrial waste or low-carbon binders can reduce or eliminate consumption of Portland cement and natural resources, leading to less environmental pollution. This work presents an experimental study on the comparison between alkali-activated materials (also recognized as geopolymers) and a traditional cementitious matrix (Portland cement) incorporated with rubber particles, deriving from end-of-life tires, as replacement of raw mineral aggregates. To explore the potential of rubber-geopolymer compounds, an experimental comparative analysis with rubber-Portland mortars was performed. Initial investigations (microstructural/compositional analysis, porosity and water absorption measurements, and mechanical tests) were conducted on rubberized samples obtained by varying the binder, the sand-rubber replacement ratio (0 vol%, 50 vol%, and 100 vol%) and the rubber particle size (0–1 mm rubber fine aggregate and 1–3 mm rubber granules). The results revealed a greater compatibility of the alkali-activated matrix with tire rubber aggregates, resulting in better performance in terms of interfacial adhesion, reduced porosity rate, flexural strength, and toughness. However, compressive strength results showed a weaker mechanical performance of rubber-geopolymer mixes compared to Portland counterparts. As also verified by Si/Al elemental analysis, the structural quality and mechanical development of the geopolymer matrix was strongly influenced by the removal of sand as a Si-source. The potential embodied carbon emission performance and cost analysis were also estimated to evaluate the economic and environmental impact related to the use of recycled rubber as complete aggregate in Portland and geopolymer mixes. Sustainability analysis revealed the greater environmental friendliness of geopolymer formulations compared to those in ordinary cement, but higher production costs. The total addition of rubber aggregates induced an increase in emissions and costs (variable according to the type of matrix) which, however, does not directly correlate with the processing/price of the polymer fraction. Deepening the research on cleaner matrices and promoting the use of recycled materials in concrete applications could lead to a gap levelling between Portland and geopolymer rubber-based composites. Building on these findings, future study will focus on the optimization of the mix design as a function of rubber aggregates.

Creep deformation characteristics of rubberised structural concrete

The influence of replacement of fine mineral aggregates with crumb tyre rubber of different particle sizes (2.36, 1.18 and 0.425 mm) on creep and shrinkage of structural rubberised concrete (rubcrete) is investigated. Rubcrete specimens were made using plain Portland cement (PC), 0.60 w/b ratio, crushed andesite coarse aggregate and a 90/10 blend of, respectively, crushed fine andesite and crumb rubber aggregate. The crumb rubber sizes were not blended in the concrete, resulting in three rubcrete mixes. Drying shrinkage and creep was monitored for approximately 1 year. The results show that compared to mineral aggregate concrete (MAC) both drying shrinkage and creep of the rubcretes increased, respectively, by up to 20% and 10% with decrease in crumb rubber particle size. Minimal differences were observed between the drying shrinkage and creep of the rubcretes made with the 1.18 and 2.36 mm crumb rubber aggregates. The results also showed that the introduction of crumb tyre rubber in concrete did not alter the micro-cracking potential of the rubcretes. Ultimately, the findings clearly show that structural rubcrete has similar creep and shrinkage deformation characteristics to that of MAC of similar strength.

The use of recycled elastomeric materials for sustainability in circular economy

AbstractThe use of scrapped elastomeric goods primarily service failed or worn‐out tires is a challenging task for the rubber society. To address this issue, recycling and reusing of these tires by different technique bring major relief toward environmental concern. Recycling technology generates secondary raw materials, which are important resources for manufacturing industries and contribute significantly for the sustainability in circular economy. In this work, an effort was made to understand the retention of physical properties as a function of crumb rubber loading and particle size. Four different sizes of cryogenically shredded crumb rubber particles (120, 140, 200, and 270 mesh) were physicochemically characterized and incorporated by 10 phr of each in two different grades of carbon black–filled, natural rubber–based tread compound. The mixed compounds were characterized and compared with the control one. Optical microscope and scanning electron microscope analyses concluded that the finer the particle size, the better is the dispersion of crumb rubber particles which provide superior mechanical, extrusion, and wear properties. Tensile properties were retained around 95%–97% for both 270‐mesh loaded compounds, which indicates that reduction in particle size can increase the volume of recycled product utilization.

Preparation and Properties of Sustainable Brake Pads with Recycled End-of-Life Tire Rubber Particles.

Sustainable composite brake pads were processed by employing recycled end-of-life tire (ELT) rubber particles obtained by means of cryogenic grinding and ambient grinding. The effect of the grinding mechanism and concentration of ELT rubber particles was then reported. From the friction result test, better behavior in terms of coefficient of friction (COF) was obtained when 3% of ELT rubber particles were introduced into the composite. It was demonstrated that the size of the particles is not as determinant as the friction mechanism in the wear properties of the sustainable brake pads. Whereas, while increasing the ELT rubber particle size acts as detrimental to the COF either in the ambient or cryogenic grinding, at high friction distances, the better adhesion of the particles because of the rough surface of the particles subjected to ambient grinding enhances the long-life behavior of the composite brake pads.

Characterization of Mechanical of CTBN Liquid Rubber‐Modified Epoxy Cured by Anhydride- and Amine-Based Agent

The main purpose of this work is to reveal the effects of carboxyl-terminated butadiene–acrylonitrile (CTBN) rubber particles on the fracture and tensile behavior of anhydride-and amine-cured epoxy/CTBN blends. In this study, 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, 10 wt.% and 15 wt.% CTBN were added to two different epoxy-hardener systems. The CTBN/epoxy blends were prepared by ultrasonic mixing device and curing processes were determined by DSC analysis. As CTBN fraction by weight increased in both epoxy systems, a decrease in tensile strength and modulus was detected, but deformation ability improved. The fracture toughness of CTBN/epoxy blends cured with amine-based hardener increased up to 10 wt.% CTBN addition and then decreased. The average rubber particle size was found to have a significant effect on the fracture toughness of CTBN/epoxy blends. Compared to pure epoxy, fracture toughness increased approximately 3.5-fold in amine-cured 10% CTBN / epoxy blend. In CTBN/epoxy blends cured by amine-based curing agent, CTBN shifted the reaction rate and thus it was provided better control over CTBN particle size in the cured CTBN/epoxy. The toughening mechanisms induced by CTBN, such as rubber cavitation and matrix shear banding, contributed to the enhanced fracture toughness of the amine-cured CTBN/epoxy.