Cavitation Of Rubber Particles Research Articles

Toward Largely Enhanced Toughness and Balanced Strength in PA1012/EPDM Blends via Synergistic Effect of Sacrificial Bonds and Network Structure

AbstractHere, zinc‐neutralized ethylene propylene diene monomer (EPDM) ionomers with different neutralization levels are prepared through melt blending, and are then incorporated with polyamide 1012 (PA1012) to fabricate PA1012/EPDM ionomer blends. Interestingly, complex crosslinking networks are formed in the blends due to the construction of sacrificial bonds (Zn2+‐carboxyl, Zn2+‐amide). The as‐formed network structure and sacrificial bond endow the PA/EPDM blends with largely enhanced toughness (16 times higher than that of neat PA), as well as balanced strength and stiffness. Meanwhile, the rheological behaviors of PA1012/EPDM ionomer blends indicate their relative low melting viscosity, which can avoid the processing shortcomings of plastics toughened with rubber. Moreover, PA1012/EPDM ionomer blends show obvious gelation behavior, and a maximum notched Izod impact strength exhibited at the gel point, in which unique double network structure can be observed obviously, indicating that there is a corresponding correlation between the rheological and mechanical parameters. Furthermore, the supper‐toughening mechanism of PA1012/EPDM ionomer blends at gel point is explored, which origins from the large deformation and cavitation of rubber particles and the destruction of special double network morphologies. This study provides a novel and effective strategy to fabricate PA materials with outstanding toughness and excellent strength simultaneously.

Preparation and toughening of mechanochemically modified lignin-based epoxy

In this work, succinylated lignin (SA-KL) was prepared by reacting a kraft lignin and succinic anhydride (SA) through a solvent-free ball milling process. A bisphenol A/F epoxy resin (DER 353) cured with a commercial alicyclic anhydride and SA-KL (~38 wt% in the composition) exhibited a flexural strength of 48.8 MPa and modulus of 3.62 GPa but a low impact strength of 6.7 kJ/m2 which were comparable to the properties of many anhydride cured epoxies. Toughening of the lignin-based epoxy resin with a carboxyl-terminated butadiene acrylonitrile (CTBN) liquid rubber was investigated. Introduction of the CTBN rubber significantly increased the impact strength and fracture toughness but resulted in reduction of flexural strength. A ductile-brittle transition was observed at 5–12 wt% CTBN rubber. Examination of the fracture surfaces by scanning electron microscopy suggests that rubber particle cavitation and massive shear yielding of the epoxy matrix were the dominant toughening mechanisms. Incorporation of CTBN had little change to the thermal stability of the lignin-based epoxy. This study introduces a green method for synthesis of lignin-derived polyacid and a viable approach for achieving balanced mechanical and thermal properties for lignin-based epoxy materials.

Effect of reactive group types on the properties of poly(ethylene octane) toughened poly(lactic acid)

In this work, maleic anhydride (MA) and glycidyl methacrylate (GMA) grafted poly(ethylene octane) (MPOE and GPOE) were used to toughen poly(lactic acid) (PLA). Results exhibited that the MA and GMA strongly influenced the morphology and mechanical properties of PLA. The stronger interfacial reactions between the carboxyl and/or hydroxyl of PLA and epoxy groups of GPOE induced smaller dispersed phase sizes and higher impact strength than that of PLA/MPOE blends. SEM results showed that the shear yielding properties of the PLA matrix and cavitation of rubber particles were major toughening mechanisms. Rheological investigation indicated that the PLA/GPOE blends had higher storage modulus and complex viscosity at low angular frequencies range due to the high interfacial adhesion between PLA and GPOE. The results of DMA showed that all the PLA blends had lower storage modulus due to the low stiffness of the elastomers. Compared MPOE, the addition of GPOE significantly decreased the cold crystallization and melting temperature which indicated that GPOE could enhance the crystalline ability of PLA.

Preparation of binary and hybrid epoxy nanocomposites containing graphene oxide and rubber nanoparticles: Fracture toughness and mechanical properties

ABSTRACTBinary and hybrid epoxy nanocomposites modified with graphene oxide (GO) and core–shell rubbers (CSR) were synthesized via the solvent‐exchange method. X‐ray diffraction analysis and scanning electron microscopy of the samples showed a homogeneous dispersion of GO and CSR in the epoxy matrix. The tensile modulus and tensile strength of the samples modified with CSR decreased continuously with increasing CSR content; however, with the addition of only 0.05 phr GO to the neat epoxy and rubber‐modified epoxy, these properties significantly increased. The use of GO and CSR individually improved the fracture toughness, but the impact of GO was greater. The simultaneous use of GO and CSR improved both the fracture toughness and the mechanical properties. Our investigation of the toughening mechanism indicated that crack deflection–bifurcation, crack pinning, and particle debonding–pullout in the presence of GO nanosheets and limited rubber particle cavitation contributed to fracture toughness improvement in the hybrid systems. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46988.

Phase morphology, fracture toughness and failure mechanisms in super-toughened PLA/PB-g-SAN/PMMA ternary blends: A quantitative analysis of crack resistance

The effect of poly(methyl methacrylate) (PMMA) content on the fracture resistance, failure mechanisms and micromechanical deformation of poly(lactic acid) (PLA)/polybutadiene-g-poly(styrene-co-acrylonitrile) (PB-g-SAN) blend was studied. The fracture toughness of samples was characterized by the essential work of fracture (EWF) method. The specific EWF (we) linearly increased with PMMA content up to 30 wt%, indicating improved fracture toughness of ternary blends with PMMA content. The specific plastic work (βwp) increased at first with PMMA content up to 15 wt% and then decreased at higher loadings of PMMA. The energy dissipated during yielding (we,y) and subsequent tearing (we,t) stages was determined by the energy partitioning approach. Both we,y and we,t components monotonically increased with PMMA content in ternary blends, suggesting enhanced material resistance against crack initiation and subsequent crack propagation. Fracture behavior and toughening mechanisms were studied. Suitable interfacial adhesion, cavitation of rubber particles and irreversible plastic growth of micro-voids caused massive shear yielding of matrix material in the super-toughened blends.

Fracture behaviour of rubber- and silica nanoparticle-toughened glass fibre composites under static and fatigue loading

The crosslinked polymers used in fibre composites are very brittle, and require toughening for structural applications. Research over many years has increased the fracture energy, but the fatigue resistance of these toughened polymers is very poor, limiting the optimisation of structures. This work reports the first successful use of hybrid toughening to increase both the quasi-static interlaminar fracture energy, GIC, and the fatigue threshold strain-energy release-rate, Gth. Amine-cured epoxy glass-fibre composites were toughened using carboxyl-terminated butadiene-acrylonitrile (CTBN) which forms micron-sized rubber particles and 20 nm-diameter silica nanoparticles. The toughening mechanisms were identified as cavitation of rubber particles and debonding for the silica nanoparticles, followed by plastic void growth. The CTBN greatly increases GIC, and the nanoparticles increase Gth. Combining both particles as a hybrid has a synergistic effect on the fatigue resistance. This demonstrates the effectiveness of hybrid toughening, enabling the design of optimised composites by combining micro- and nanoparticles.

Toughening of polyamide 12/nanoclay nanocomposites by incompatible styrene‐butadiene‐styrene rubber through tailoring interfacial adhesion and fracture mechanism

AbstractThe main drawback of polyamide 12 (PA 12)/nanoclay nanocomposites in their wide range of potential engineering applications known as diminished toughness was overcome using incompatible styrene‐butadiene‐styrene block copolymer (SBS) rubber. Applying optimal processing parameters for co‐rotating twin‐screw extrusion resulted in strong interfacial adhesion of matrix and rubber and intercalated and delaminated nanoclay stacks confined in the matrix. The formulation of compatibilized PA 12/SBS/nanoclay nanocomposites was optimized by employing response surface Box–Behnken methodology. A combination of microscopic methods, that is, atomic force microscopy, transmission and scanning electron microscopy, and transmission optical microscopy, along with single‐edge‐double‐notch four‐point‐bending technique, was exploited to exhaustively explore the toughening mechanisms and microstructure. The findings verify that by tailoring the rubber/matrix interfacial strength and nanocomposite morphology, the Izod impact strength of PA 12/nanoclay nanocomposites is noticeably improved even by incorporating an incompatible rubber and tough fracture mechanisms including rubber particle cavitation and large‐scale shear yielding are attained.

Addition of nanoclay and compatibilized EPDM rubber for improved impact strength of epoxy glass fiber composites

Epoxy-glass fiber reinforced nanocomposites containing compatibilized ethylene propylene diene monomer (EPDM) rubber were processed for improved impact strength. Nanocomposites were reinforced with 1.0 wt% of nanoclay and 2.5–10.0 wt% of EPDM (both untreated and compatibilized). Compatibilization was done using two treatments: silane treatment and UV-assisted maleic anhydride grafting (MAH). SEM-EDS and FTIR confirmed EPDM treatment. SEM of fractured impact specimens was done to study effect of compatibilization on interfacial adhesion of nanocomposite constituents. XRD and TEM determined clay morphology in nanocomposites. EPDM concentration of 5.0 wt% resulted in maximum impact strength. For nanocomposites reinforced with silane treated EPDM, maximum improvement in impact strength was 68%, with a small drop in tensile properties. For MAH grafted EPDM, improvement in impact strength was 26%, but tensile properties recovered. Cavitation of rubber particles and improved interfacial adhesion of nanocomposite constituents were the main reasons for improved impact strength.

Fracture behavior of silica nanoparticles reinforced rubber/epoxy composite

Hybrid composites consisting of soft rubber (carboxyl-terminated butadiene acrylonitrile, CTBN) and silica nanoparticles with average particle size of 20 nm were studied for improving toughness of epoxy resins (diglycidyl ether of bisphenol A, DGEBA). The hybrid carboxyl-terminated butadiene acrylonitrile /silica nanoparticles epoxy systems exhibited improvements in the Young’s modulus, and more importantly, fracture toughness (KIC), which can be explained by synergistic impact from the inherent characteristics of each filler. In this study, the highest KIC was reached with addition of small amounts of silica nanoparticles (5 vol.%) to the epoxy containing 15 vol.% carboxyl-terminated butadiene acrylonitrile, where the KIC was distinctly higher than with the epoxy containing carboxyl-terminated butadiene acrylonitrile or silica nanoparticles alone. Cavitation of rubber particles with matrix dilation and particle debonding with subsequent void growth were determined as the toughening mechanisms responsible for the toughness improvements for epoxy. The evidence indicates that debonding of the silica nanoparticles causes a weakening of the matrix–particle interface. The toughness enhancement in hybrid nanocomposites involves an increase in silica nanoparticles particle debonding an increase in plastic zone size, which allows the epoxy matrix to dissipate more fracture energy.

Toughening of epoxy hybrid nanocomposites modified with silica nanoparticles and epoxidized natural rubber

Silica nanoparticles (SN) and epoxidized natural rubber (ENR) were used as binary component fillers in toughening diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine. For a single component filler system, the addition of ENR resulted in significantly improved fracture toughness (KIC) but reduction of glass transition temperature (Tg) and modulus of epoxy resins. On the other hand, the addition of SN resulted in a modest increase in toughness and Tg but significant improvement in modulus. Combining and balancing both fillers in hybrid ENR/SN/epoxy systems exhibited improvements in the Young’s modulus and Tg, and most importantly the KIC, which can be explained by synergistic impact from the inherent characteristics associated with each filler. The highest KIC was achieved with addition of small amounts of SN (5 wt.%) to the epoxy containing 5–7.5 wt.% ENR, where the KIC was distinctly higher than with the epoxy containing ENR alone at the same total filler content. Evidence through scanning electron microscopy (SEM) and transmission optical microscopy (TOM) revealed that cavitation of rubber particles with matrix shear yielding and particle debonding with subsequent void growth of silica nanoparticles were the main toughening mechanisms for the toughness improvements for epoxy. The fracture toughness enhancement for hybrid nanocomposites involved an increase in damage zone size in epoxy matrix due to the presence of ENR and SN, which led to dissipating more energy near the crack-tip region.

Preparation of core-shell structured particle and its application in toughening PA6/PBT blends

Combining the excellent mechanical strengths of polyamide 6 (PA6) with the low water absorption of poly(butylene terephthalate) (PBT) was supposed to be a feasible way to prepare a high comprehensive performance material. However, the poor compatibility between PA6 and PBT resulted in low-notched impact strength of PA6/PBT blends. Poly(n-butyl acrylate)/poly(methyl methacrylate-co-methacrylic acid) (PBMMA), a core-shell structured modifier with controlled particle sizes, was prepared by seed emulsion polymerization and confirmed by Transmission electron microscope (TEM). The PBMMA particles as toughening modifier and compatilizer were employed to toughen PA6/PBT blends. The notched impact strength of the PA6/PBT blends was significantly increased and the water absorption was reduced with the addition of PBMMA particles. With 23.0 wt% modifier loading, the notched impact strength of the blends was 25.66 kJ/m2, which was 4.04 times higher than that of pure PA6/PBT. Meanwhile, the water absorption of the blends was only 1.3%, dropping 53.6% compared with pure PA6 and reducing by 26.6% than PA6/PBT. Scanning electron microscope results showed that the PBMMA particles were dispersed in the PA6/PBT blends homogeneously, and the toughening mechanism was the cavitation of rubber particles and shear yielding of the matrix. Thermo-gravimetric analysis analysis demonstrated that the compatibility between PA6 and PBT was improved with the addition of core-shell PBMMA particles. The core-shell particles could be used as an effective modifier to achieve the high toughness and low water absorption for PA6/PBT blends. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation of the Role of Rubber Particle Cavitation Resistance on the Toughening Mechanisms of Epoxy Resins

The occurrence of rubber particle cavitation in rubber modified epoxy resins has generated some controversy in the literature and role of cavitation resistance in toughening mechanisms has remained an enigma. In this study, hydroxyl terminated polybutadiene (HTPB) and synthesized epoxy terminated polybutadiene (ETPB) have been used to toughen an epoxy resin. FTIR and titration techniques were used to monitor the ETPB synthesis. Mean fracture toughness, KIC, of 0.65 MPa.m0.5 was measured for unmodified epoxy polymer. The measured toughness was increased by the addition of HTPB to 1.23 MPa.m0.5 and ETPB to 1.80 MPa.m0.5. The cavitation zone of the HTPB modified sample was bigger than that of ETPB modified sample which showed the higher cavitation resistance of ETPB particles. SEM studies showed volumetric expansion of rubbery phase in slow crack growth region of both samples which proved the plastic void growth. The results showed that the elevated cavitation resistance of ETPB did not suppress plastic void growth. The optical microscopy of crack tips showed shear banding which was more significant in ETPB modified sample. SEM micrographs of fracture surface of HTPB modified samples showed no tail formation while pinning tails were present in ETPB modified samples. The results showed that higher cavitation resistance activated crack pinning process and induced larger shear banding zone in ETPB modified samples. Deflection and forking of the main crack into secondary cracks was also observed in ETPB modified samples while these phenomena were not present in HTPB modified samples.

Effect of matrix chain entanglement on toughening mechanism evolution of acrylic impact modifier toughened methyl methacrylate-N-phenylmaleimide copolymers

The toughening mechanism evolution of acrylic impact modifier (AIM) toughened methyl methacrylate-N-phenylmaleimide copolymers (PMMA-PMI) was investigated in terms of matrix chain entanglement density (νe), especially within the range of matrix νe ≈ 0.1 mmol/cm3. After respectively blended the PMMA-PMI having designed νe with the same content preformed AIM, it was showed that the notched impact strength of the blends increase with PMMA-PMI νe enhancement. The morphological analyses revealed that the extent of shear yielding gradually enlarged when matrix νe is higher than 0.1061 mmol/cm3. Whereas, in the AIM/PMMA-PMI blend with lower matrix νe, the toughening mechanism transformed into matrix crazing triggered by PBA cavitation. The results suggest that the response of the matrix with different νe to the rubber particle cavitation dominate toughening mechanism and mechanical performance of AIM/PMMA-PMI blends, and it is believed that matrix νe is an inherent factor to toughening mechanism evolution.

Fracture behavior and deformation mechanisms of polypropylene/ethylene-propylene-diene blends

Abstract The fracture behavior and deformation mechanism of polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) were studied by scanning electron microscopy and transmission electron microscopy analyses. The deformation mechanism was investigated under different conditions. Voids were seen under all the conditions because of matrix shear yielding, indicating that rubber particle cavitation took place during the blend fracture process; moreover, the void size and density increased as the fracture surface was approached. However, the void density and extent of elongation of the rubber particles in the deformation zone decreased with increasing test speed rate. Many voids were positioned in the rubber particles, confirming that matrix shear yielding initiated by rubber particle cavitation was the main deformation mechanism during ductile fracture in the matrix.

Impact behavior of CNT-filled PP/EPDM blends: effect of dynamic vulcanization and PP-g-MA compatibilizer

The impact strength and crystallite structure of un-vulcanized and dynamically vulcanized polypropylene/ethylene-propylene terpolymer (PP/EPDM) blends and polypropylene/ethylene-propylene terpolymer/carbon nanotube (PP/EPDM/CNT) blend nanocomposites with and without maleic anhydride-grafted polypropylene (PP-g-MA) were studied. The results showed that incorporation of EPDM increased the impact toughness of PP matrix by promoting debonding and cavitation of rubber particles. Dynamic vulcanization increased the interfacial adhesion leading to superior impact strength. Incorporation of CNT into PP/EPDM blends changed the crystallization behavior of the PP matrix and further increased the impact resistance. Morphological observations on impact-fractured surfaces indicated that dominant failure modes of CNTs in blend nanocomposites with and without PP-g-MA are pulling out and breakage of nanotubes, respectively. While the PP-g-MA had a negative effect on the impact strength of PP, the results demonstrated that its presence enhanced the impact strength of the blends and blend nanocomposites mostly via enhancing the adhesion between the PP and EPDM particles and improving the dispersion of CNTs in the matrix, respectively. The former decreases the rubber particle size and the latter decreases the size of CNT aggregates and crystallites.

Computational modeling of rubber-toughening in amorphous thermoplastic polymers: a review

The fracture behavior of rubber-toughened polymers is governed by two dissipative microscopic deformation and damage mechanisms: matrix shear yielding and crazing. These mechanisms are strongly interconnected with the eventual cavitation of the fine dispersed rubber particles. The present work summarizes and discusses a variety of micromechanical–computational modeling approaches undertaken over the past twenty years aiming at an improved understanding of the relation between microstructure and toughening in this class of materials. The focus is on materials such as ABS where both mechanisms are prevalent.

Synergic effects of poly(vinyl butyral) on toughening epoxies by nanostructured rubbers

Synergic effects of poly(vinyl butyral) (PVB) on rubber toughening of epoxies have been examined in detail using two different liquid rubbers. The PVB is seen to be miscible with the epoxy used. Incorporation of the PVB into liquid rubber/epoxy blends lowers the rubber particle size from 0.76 μm to 28 nm, leading to a tremendous increase in fracture toughness, represented by the critical strain energy release rate, GΙc, from 100 J/m2 for the neat epoxy to 2015 J/m2 for the ternary blend of PVB/liquid rubber/epoxy (14/14/72 by weight). Such an enormous improvement in toughness is largely ascribed to the unique nanostructure of the rubber phase and enhanced deformability of the epoxy. Rubber particle cavitation and shear yielding of the matrix are found to be the main toughening mechanisms. This study provides a novel approach to achieving nano-dispersion of a typical liquid rubber in toughening epoxies which conventional routes fail to deliver. Such an approach serves as first direct evidence about that nano-sized rubber particles other than block copolymers considerably toughen epoxies by over 20 fold.

Relationship between fracture toughness and temperature in epoxy coatings

Relationship between fracture toughness and temperature in epoxy coatings

Mechanical and Morphological Properties and Deformation Mechanisms of Acrylonitrile-Butadiene-Styrene/Poly(ϵ-Caprolactone) Blends with Varied Matrix Composition

Acrylonitrile-butadiene-styrene and poly(ϵ-caprolactone) blends (ABS/PCL) were prepared by mixing styrene-co-acrylonitrile (SAN), polybutadiene-g-SAN (PB-g-SAN), and PCL with varied SAN and PCL composition. PCL is miscible with SAN and can improve the matrix toughness. The impact strength and elongation at break of the ABS/PCL blends increased with the PCL content. When the PCL content was lower than 20 wt%, the improvement of impact strength for the blends was not obvious. A significant increase of impact strength took place when the PCL content was between 20 and 25 wt%. When PCL content was more than 20 wt%, the impact strength was higher than 800 J/m which shows the super toughness. The addition of PCL improved the dispersed phase morphology of PB-g-SAN in the matrix and the interfacial adhesion increased. Deformation observations showed that, when the PCL content was lower than 20 wt%, crazing was the major deformation mode. When the PCL content was 20 wt%, crazing and slight shear yielding could be found. When the PCL content was more than 20 wt%, cavitation of rubber particles and shear yielding of the matrix were the major deformation modes. The cause of the change of the deformation mode lies in the varied matrix composition which modifies the crazing and yielding stresses of the matrix and the final fracture mode and impact toughness.

OS1736 ゴム強化エポキシ接着剤の疲労き裂伝ぱ特性

Epoxy resins are utilized in many industrial areas as matrix of composite materials and adhesives because of high strength and stiffness. Fatigue properties are important in terms of the long time reliability. To enhance the fatigue life of the epoxy adhesives, the fracture mechanism of the resin between rigid substrates under cyclic loading should be clarified. In this study, the fatigue crack propagation behavior of toughened epoxy adhesive was investigated and was compared with that of bulk resin. The fatigue crack propagation behaviors of adhesives are similar to those of the bulk resins. As the results of fractographic observation, the fracture surface for the adhesive layer are very flat and was different from that of bulk resin where the plastic deformation was popular. The deformation around the crack tip was restrained by the rigid metal substrates and the tri-axial stress was kept in spite of the rubber particle cavitation.