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Flax fiber has emerged as a promising, eco‐friendly alternative to traditional synthetic reinforcement in polymer composites. However, manufacturing biocomposites using three‐dimensional (3D) printing technology is typically accompanied by significant processing challenges and weak product performance under dynamic loading conditions. This study aims to unlock the potential of 3D‐printed polylactic acid (PLA) by incorporating chemically modified chopped flax fibers and thermoplastic polyurethane elastomer to improve impact strength and processability. To achieve this, we employed the fused deposition modeling (FDM) technique to prepare composite specimens for the study. The crystallization behavior, tensile and impact properties, as well as the fracture behavior of the composites were investigated. The findings suggest that our approach stands out because it not only facilitates the challenging task of 3D printing PLA with fiber additives of high weight fraction and high aspect ratio but also results in a remarkable 120% enhancement in impact strength and an around 31.2% increase in tensile elongation compared to neat PLA, without compromising the elastic modulus. Highlights: Flax fibers were modified through alkalization and silanization.Alkalization significantly enhanced printing quality.Silanization reduced fiber attrition and doubled the fiber aspect ratio.TPU particles facilitated the 3D printing of biocomposites.For the first time, the hybrid strategy doubled the impact strength of PLA. [ABSTRACT FROM AUTHOR]

The objective of this investigation is to enhance the compatibility between the poly (styrene-co-acrylonitrile) (SAN) and ethylene-propylene-diene monomer rubber (EPDM) in the presence of organically modified montmorillonite (OMMT) to achieve better impact strength of this hybrid material by utilizing styrene-ethylene-butylene-styrene grafted with maleic anhydride (SEBS-g-MAH) as a compatibilizer. The effectiveness of (SEBS-g-MAH) as a compatibility agent is based on the analysis of the rheological, mechanical, and morphological properties of the final products. Mixtures were produced through melt blending using Brabender mixer. X-ray diffraction (XRD), scanning electron microscopy (SEM), tensile and impact tests were used to examine the structural, morphological, and mechanical characteristics of SAN/EPDM composites with and without OMMT and SEBS-g-MAH. According to the SEM analysis and XRD patterns, the SEBS-g-MAH reduced the EPDM phase's domain size, exfoliated structure and homogeneous dispersion of the OMMT silicate layers was observed. Based on the ATG results, the addition of SEBS-g-MA did not substantially alter the thermal stability of SAN/EPDM/OMMT nanocomposites. The stiff clay's competing effect, along with the tough effects of the EPDM and SEBS-g-MAH elastomers, have a significantly impact on the modulus and impact strength, resulting in balanced properties. [ABSTRACT FROM AUTHOR]

In this paper, we report the high-temperature and high-voltage (HV) insulation characteristics of the polypropylene (PP) blend with highly packed elastomeric domains that showed excellent mechanical toughness in our previous study to find its suitability as insulation material for power cable applications. The main focus lies on tensile properties with thermal aging, thermomechanical behavior corresponding to the thermal transition, high-temperature volume resistivity and DC dielectric strength, and space charge accumulation behavior of the PP blend in comparison to the crosslinked polyethylene (XLPE). Our PP blend having low elastic modulus of approximately 266.9 MPa exhibited high tensile strength and elongation at break, and high-temperature stability as well. Using this PP blend, not only good HV insulating performances in volume resistivity and DC breakdown strength (BDS) were obtained similar to XLPE, but also adequate values were obtained at high temperature, even at 110 °C, which was not possible with XLPE. However, there was space charge accumulation and electric field distortion in the PP blend like XLPE, which needs to be suppressed. Therefore, our PP blend is expected to have the potential to replace existing XLPE as insulation materials for future HV power cables.

In this research, poly(lactic acid) (PLA) was toughened and improved the crystallinity by rubber particles and inorganic filler. CaCO3 was employed as a filler and nucleating agent while poly(methyl methacrylate)-poly(butadiene-styrene) (MBS) core-shell impact modifier was added as a toughening agent. Overall, the enhancements of both the toughness and crystallization of PLA with CaCO3 and MBS were successfully achieved. The tensile modulus and strength of PLA increased with increasing CaCO3 content from 10 to 30wt%. However, they decreased slightly when CaCO3 loading reached 40 wt% due to particles agglomerations. With the addition of MBS rubber, the tensile modulus and strength of the PLA/CaCO3 composites became lower than those observed for PLA/CaCO3 composites due to the softening effect. Furthermore, the compositions with MBS showed superior toughness in terms of the tensile elongation at break and impact strength. CaCO3 nucleated the PLA crystal which reflected as the increase in the degree of crystallinity (Xc) by at least 2 times for all formulations studied. The crystallization half-time (t1/2) of PLA with 40 wt% CaCO3 was dramatically reduced, from 26 min, in neat PLA, to 0.9 min. With the addition of MBS, it did at 2.7 min for the same CaCO3 content. The maximum increment of heat distortion temperature (HDT), around 8 °C, was found for the PLA with 20 wt% CaCO3.

In order to toughen Poly(lactic) acid and binary blends with low PBAT content while maintaining a high biodegradability of the final material, poly(lactic) acid (PLA)/poly(butylene-adipate-co-terephthalate) (PBAT)/ polyolefin elastomer grafted with glycidyl methacrylate (POE-g-GMA) extruded ternary blends have been investigated in this work from a thermal, mechanical, and rheological point of view. The two elastomers have been added in different amounts as dispersed phases into the PLA matrix, paying attention to the final objective: the design of a 90% biodegradable formulation according to EN 13432. These ternary blends exhibited improved impact properties but still low elongation at break. Consequently, to the ternary composition with the best compromise of PLA quantity, biodegradability and thermo-mechanical properties (81 wt.% PLA, 9 wt.% PBAT, and 10 wt.% POE-g-GMA) a small quantity (10 wt.%) of a biobased plasticizer was added in order to further increase the impact properties in parallel with the tensile flexibility. Two types of plasticizers were investigated, one not reactive [Acetyl Tributyl Citrate (ATBC)], and one reactive [Glycidyl ether (EJ-400)]. A micromechanical study, in order to investigate the toughening mechanism of these systems, was carried out on the final formulations. They were also examined by dilatometric tests and elasto-plastic fracture mechanics correlating the data obtained to the morphology and to the rheological properties. In conclusion, the best compromise between impact, tensile properties and biodegradability content was achieved using the reactive plasticizer (EJ-400) whose interaction with the matrix is confirmed by the FT-IR analysis.

In this research, poly(lactic acid) (PLA) was toughened and improved the crystallinity by rubber particles and inorganic filler. CaCO3 was employed as a filler and nucleating agent while poly(methyl methacrylate)-poly(butadiene-styrene) (MBS) core-shell impact modifier was added as a toughening agent. Overall, the enhancements of both the toughness and crystallization of PLA with CaCO3 and MBS were successfully achieved. The tensile modulus and strength of PLA increased with increasing CaCO3 content from 10 to 30wt%. However, they decreased slightly when CaCO3 loading reached 40 wt% due to particles agglomerations. With the addition of MBS rubber, the tensile modulus and strength of the PLA/CaCO3 composites became lower than those observed for PLA/CaCO3 composites due to the softening effect. Furthermore, the compositions with MBS showed superior toughness in terms of the tensile elongation at break and impact strength. CaCO3 nucleated the PLA crystal which reflected as the increase in the degree of crystallinity (Xc) by at least 2 times for all formulations studied. The crystallization half-time (t1/2) of PLA with 40 wt% CaCO3 was dramatically reduced, from 26 min, in neat PLA, to 0.9 min. With the addition of MBS, it did at 2.7 min for the same CaCO3 content. The maximum increment of heat distortion temperature (HDT), around 8 °C, was found for the PLA with 20 wt% CaCO3. [ABSTRACT FROM AUTHOR]

The focus of our study is to identify physical properties of different impact-resistant/toughened structural adhesives and identify/develop an elastic-viscoelastic-plastic model as a function of loading rate by using Ludwik-type equations to be able to predict adhesive behavior at higher loading rates and to make cars more crashworthy. For this purpose, we first characterized eight different commercial toughened epoxy structural adhesives to provide detailed information about their constituents using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS). Most (but not all) of the model adhesives contained organic tougheners in the form of carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, as well as polyurethane adducts. The main crystalline inorganic phases were found as calcite (CaCO3), wollastonite (CaSiO3) or calcium silicate (CaSiO3), talc (Mg3Si4O10 (OH)2), zeolite which is an alumina silicate based mineral and has many different elements in its composition (M2/nO⋅Al2O3⋅xSiO2⋅yH2O, M can be Mg, Na, Ca, K, Li). The total amount of inorganic fillers was found to be different in each adhesive. Material behavior of the model adhesives were determined via tensile tests and Single Lap Joint (SLJ) tests in shear. Split Hopkinson pressure bar (SHPB) was also used to measure the strain and stress values at higher strain rates in the order of 10² s-1, which is generally encountered in impact related loading situations. Toughness values in the range ~0.5 to ~1.35 MJ/m³ were observed with the model adhesives tested in tensile mode within the ~3 x 10-3 to 0.18 m/m/s strain rate range. The softening behavior of the elastic moduli at higher strain rates observed during tensile testing was also observed with SHPB testing. It is remarkable that, overall, the modulus magnitudes seem to be similar between the tensile test and SHPB specimens within this softening range of the initial bilinear elastic behavior observed. When the results from bulk (tensile) and bonded (shear) specimens were compared, it was clearly seen that the toughness responses of the adhesives to (tensile/shear) strain rates in the bulk and bonded forms, respectively, were different, with the bonded shear toughness values in the ~25 to ~120 MJ/m³ range within ~1.25 to ~25 mm/mm/s shear strain range. The model adhesive which included just inorganic fillers had the lowest tensile toughness at the lowest tensile strain rate, but the highest slope in its tensile toughness regression line, exhibited the second highest bonded shear toughness. When tested at the extension rates of 25 mm/min and 100 mm/min in bonded lap shear, the same adhesive exhibited limited interfacial failure areas, however the dominant failure mode was cohesive failure. When the extension rate increased further, transition to interfacial (adhesive) failure was observed revealing that interfacial failures do not necessarily diminish adhesive bond toughness. Our observations point to the fact that cohesive deformation/failure processes indicating interfacial separations, inter-particle interactions as well as polymer matrix deformation in high deformation loading scenario as in bonded shear loadings may provide the highest toughness. Apparently, a large inorganic filler weight fraction is not necessary to obtain high shear toughness in bonded form since the highest bonded shear toughness was obtained with the adhesive which had the least amount of inorganic fillers among the model adhesives with 14.72 wt %. [ABSTRACT FROM AUTHOR]

In rubber-toughened mixtures, the rubber is intended to dissipate the stress so that the blend shows ductility and plastic deformation. But poor interfacial adhesions, high interfacial tension, differences in polarity and structure between rubber and thermoplastic phases are the main reasons for incompatibility of these systems. The present work deals with the study of nanocomposites based on poly(styrene–acrylonitrile) (SAN) and ethylene–propylene–diene monomer (EPDM) blends with and without an organically modified montmorillonite (O-Mmt) filler as a compatibilizer. These blends are prepared by melt compounding using an internal mixer (Brabender). The dispersion of O-Mmt layers and the morphology of the nanocomposites, were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The effects of EPDM amount and O-Mmt on the rheological, mechanical properties and thermal stability of the nanocomposites were also investigated. All molten blends containing nanoclay particles exhibit higher viscosity than those of neat SAN/EPDM binary blends. XRD patterns and SEM examination revealed that silicate layers were exfoliated and well dispersed in the blend and the presence of nanoclay has reduced the domain size of EPDM phase. Thermogravimetric analysis (TGA) results showed that the incorporation both of EPDM and O-Mmt increased the thermal stability of SAN material. In binary blends, addition of EPDM has reduced the stiffness and tensile strength; however it improved the impact toughness and ductility of SAN. But, on adding nanoclay, results display the reverse trend: the stiffness of SAN/EPDM/O-Mmt nanocomposites increases in comparison to neat SAN and SAN/EPDM blends. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene-methyl-acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl-methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1–5 µm sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness andGICfracture toughness values of PLA were as much as 160, 320 and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values. [ABSTRACT FROM AUTHOR]

While vinyl-terminated butadiene acrylonitrile is frequently used for the toughening of vinylester and polyester, very limited research has been conducted on modification of epoxy with this oligomer. Herein, the effect of vinyl-terminated butadiene acrylonitrile addition to epoxy in bulk and glass reinforced composite is systematically investigated. Thermo-physical behavior and mechanical characteristics of the samples are determined. To interpret the test results, the void content of reinforced samples is measured and fracture surface of the specimens is investigated. It is found that vinyl-terminated butadiene acrylonitrile improves the toughness with slight negligible effects on other characteristics. Incorporation of 15 phr of vinyl-terminated butadiene acrylonitrile increases theKICof epoxy from 0.6 MPa to 2.3 MPam0.5. Similarly, addition of 15 phr vinyl-terminated butadiene acrylonitrile leads to 67% enhancement in the interlaminar fracture toughness of composites. The toughening mechanisms and toughness transfer from bulk to composite are discussed. [ABSTRACT FROM PUBLISHER]

In this work we present a reversible and toughened thermoset system based on the covalent incorporation of a furane functionalized ethylene–propylene rubber (EPM-Fu) into a thermoset furane functionalized polyketone (PK-Fu) via Diels–Alder (DA) reversible cross-linking with bismaleimide (b-MA). FT-IR and DSC analyses proved the reversible interaction between PK-Fu and EPM-Fu with b-Ma via DA and r-DA sequence. Likewise, thermo-mechanical experiments (DMTA) indicated the re-workability of the material with no evident differences in elastic and loss modulus after several heating cycles and recycling procedures. Moreover, a considerable increase in the softening point (tangent δ ) was also found for the higher toughened system containing 12 wt% of EPM-Fu (neat thermoset T = 137 °C whereas toughened thermoset T = 155 °C). A two-fold increase in IZOD impact strength compared to the neat thermoset (up to 27 J/m) was also recorded by the toughened system. Overall, this approach clearly indicates that fully thermally reversible and toughened thermosets can be realized starting from mixtures of furan functionalized polyketone and EPM rubber, cross-linked via reversible Diels–Alder chemistry. [ABSTRACT FROM AUTHOR]

Friedel-Crafts alkylation reaction was employed to reactively compatibilize the polypropylene (PP)/acrylonitrile- butadiene-styrene (ABS) blends, using AlCl as a catalyst. Rheology, morphology and mechanical properties of the reactive compatibilized blends along with the reference un-compatibilized samples were studied. Scanning electron microscopy (SEM) observations showed that blends containing catalyst exhibited an improvement in the dispersion state of ABS rubber particles. The results of mechanical tests revealed that reactive compatibilization partly increased the ultimate strength and Izod impact strength of the blends with a loss in tensile ductility. The change in these properties was explained in terms of different chemical reactions including grafting and degradation. Occurrence of these reactions was confirmed using different viscoelastic properties of the compatibilized blend samples. A great improvement in ultimate strength and impact toughness to levels much higher than those of neat PP was achieved in reactively compatibilized PP/ABS blends containing PP- g-MA. These findings were justified by morphological and rheological analyses. The formation of graft copolymer was also confirmed using Fourier transform infrared spectroscopy (FTIR) measurements. The results of impact toughness data were in agreement with the interfacial tension values measured via contact angle analysis. The deformation behavior of the different compatibilized samples was rationalized via fractographic study of the impact-fractured surfaces. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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, G Ιc , from 100 J/m 2 for the neat epoxy to 2015 J/m 2 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. [ABSTRACT FROM AUTHOR]

This work was aimed at improving essential work of fracture (EWF) toughness of Polyamide 6 (PA6) without sacrificing the mechanical properties, whereby two different kinds of terpolymer were incorporated into the PA6 matrix. Furthermore, 1.1′-carbonyl-bis-caprolactam (CBC), as a chain extender, was added into PA6/Lotader blends to reveal the effect of chain entanglement on fracture behavior of the blends. Tensile test results indicated that incorporation of Lotader and CBC did not cause a significant reduction on mechanical properties of the blends, on the contrary caused an enhancement of yielding strength. It was observed that the incorporation of Lotader in to PA6 matrix gave rise to a remarkable enhancement on the EWF toughness especially in presence with CBC. Energy partitioning concept was also employed for further analysis and inference on the effect of additive type and ratio on fracture toughness of PA6 blends. [ABSTRACT FROM AUTHOR]

The focus of our study was to determine the mixed-mode fracture behavior and the governing fracture (failure) criteria for different impact-resistant/toughened structural adhesives. Four of the five model adhesives used contained organic tougheners in the form of carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, as well as polyurethane adducts. The main crystalline inorganic phases were calcite (CaCO 3), wollastonite (CaSiO 3) or calcium silicate (CaSiO 3), talc (Mg 3 Si 4 O 10 (OH) 2), zeolite which is an alumina silicate based mineral and has many different elements in its composition (M 2 /nO.Al 2 O 3.xSiO 2.yH 2 O., M can be Mg, Na, Ca, K, Li). The total amount of inorganic fillers was different in each adhesive. Independently Loaded Mixed-Mode Specimen (ILMMS) was used for independent measurement of P I (opening) and P II (in-plane shear) loads which were necessary to determine the strain energy release rate values, G I and G II without using a finite element analysis. Two versions of the ILMMS specimen geometry (a, b) were used: monotonic in opening and static in shear loads, and monotonic in shear and static in opening loads, respectively. Elliptical energy balance failure criterion and parabolic principal stress criterion were used for curve fitting. The experimental data revealed that all but one of the adhesives were more accurately represented by the energy balance criterion except for one that was more accurately represented by the principal stress criterion indicating more brittle behavior. Results obtained from ILLM specimen a showed that ranking varied as related with the G Ic and G IIc values and, also, the applied static load. For example, while Adhesive 2 was in the first rank based on G Ic value, it became third in the ranking based on G II c value. Thus, it can be suggested that ranking as well as the fracture behavior (i.e., cohesive vs. adhesive failure; interfacial separations) change with the extent of the mode mixity present in loading of toughened epoxy adhesives. [ABSTRACT FROM AUTHOR]

Abstract: Epoxy resins are inherently brittle. Thus they are toughened with reactive liquid rubbers or core–shell elastomers. Surface-modified silica nanoparticles, 20 nm in diameter and with a very narrow particle size distribution, are available as concentrates in epoxy resins in industrial quantities since 10 years. Some of the drawbacks of toughening, like lower modulus or a loss in strength can be overcompensated when using nanosilica together with these tougheners. Apparently there exists a synergy as toughness and fatigue performance are increased significantly. In this article the literature published in the last decade is studied with a focus on mechanical properties. Results are compared and the mechanisms responsible for the property improvements are discussed. [Copyright &y& Elsevier]

Poly (lactic acid) (PLA) was melt blended in a twin screw extruder using an ethylene-methyl acrylate-glycidyl methacrylate rubber as a toughener. PLA/rubber blends were immiscible as observed by scanning electron microscopy. Impact strength and ductility of PLA were improved by the addition of the rubber at the expense of strength and stiffness. An organo-montmorillonite (OMMT) was used at 2 wt % to counteract the negative effect of the rubber on modulus, and balanced properties were observed at 10 wt % rubber content. X-ray diffraction and transmission electron microscopy revealed the formation of intercalated/exfoliated structure in the ternary nanocomposites. Thermal behavior analysis indicated that the degree of crystallinity is slightly affected by the clay and the rubber. Both the clay and the rubber decreased the crystallization temperature of PLA and acted as nucleating agents for PLA. The viscosity of the mixtures as measured by melt flow index was highly influenced by the rubber and the OMMT. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1-1000 mm/min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1-10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10-1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Abstract: The present research aims to utilize ultrafine elastomeric particles to reduce the problem of brittleness in poly(lactic acid) (PLA). Particles of acrylate rubber were added to PLA at the range from 0.1 to 10wt%. Maximum reduction of the flexural modulus and the tensile modulus was achieved by 20 and 45% respectively when the acrylate rubber was applied at 10wt%. The tensile elongation at break of the rubber-modified PLA was also raised around 50 times from the 3.5% observed in the neat PLA to 200%. The toughening efficiency of the ultrafine rubber particles was also reflected through the significant increase in the impact strength by fourfolds. Fractographs of the acrylate rubber-modified PLA verified plastic deformation and good dispersion of the rubber particles in the PLA. Microscopic observation revealed that the ultrafine acrylate rubber played an important role inducing numerous crazes as the mechanism for energy absorption. The introduction of the ultrafine acrylate rubber particles by only 0.5wt% helped increasing the degree of crystallinity. [Copyright &y& Elsevier]

Abstract: Poly(butyl acrylate) was prepared by the free radical polymerization of butyl acrylate as an initiator in the presence of 2,2′-Azoisobu-tyronitrile (AIBN) and the average molecular weight, polydispersity and thermal stability were evaluated. PLA and PBA were melt blended using a Haake Rheometer, and the light transmission, thermal properties, dynamic rheological properties, mechanical properties, phase morphology of blends and toughening mechanism were investigated. Dynamic rheology, SEM and DSC results show that the PLA is partial miscible with PBA. The PBA component improved the crystallization ability of PLA and the crystallinity of PLA increased with content of PBA (<15wt.%). With the increase of PBA, the tensile strength and modulus of the blend decreased slightly while the elongation at break and toughness were dramatically increased. With the addition of PBA, the failure mode changes from brittle fracture of neat PLA to ductile fracture of the blend. Rheological results revealed the complex viscosity and melt elasticity of the blends decreased with increasing content of PBA and phase segregation occurred at loading above 11wt.% PBA. UV–vis light transmittance showed that PLA/PBA blends with a high transparency, and the transmittance decreased with the amount of PBA. [Copyright &y& Elsevier]

Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility, rubber concentration, blend morphology, particle cavitation, and particle/matrix interface. It has been tried to provide an in-depth view of the state-of-the-art knowledge in the field and to direct future studies towards exploring new approaches for toughening of epoxy polymers. [ABSTRACT FROM AUTHOR]

Abstract: A bisphenol A-based epoxy was modified with an amphiphilic poly(ethylene-alt-propylene)–b-poly(ethylene oxide) (PEP–PEO) block copolymer as a toughening agent. PEP–PEO molecules self-assemble into spherical micelles in epoxy with an average diameter of 15nm and give rise to 180% improvement in fracture resistance. The fracture and tensile behaviors of the PEP–PEO-modified epoxy were investigated at loading rates ranging from 0.51 to 508mmmin−1. The toughened epoxy exhibits mechanical properties that are significantly more rate dependent than the neat epoxy material. As expected, a higher test rate leads to a more brittle behavior of the material and a lower fracture toughness value. With careful systematic study of their micromechanical deformation processes, the observed strain rate dependence is explained. The implications of the current findings on nano-sized rubber toughening of epoxy are also discussed in detail. [Copyright &y& Elsevier]

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Abstract: The aim of this study was to investigate rubber toughening of resol type phenol–formaldehyde resin. For this purpose, phenolic resin was first modified by acrylonitrile butadiene rubber alone, and then by using nitrile rubber together with 3-aminopropyltriethoxysilane. Test specimens were prepared by mixing and casting of liquid phenolic resin in three groups. In the first one, neat phenolic resin specimens were produced. In the second group, phenolic resin was modified with 0.5, 1, 2, and 3wt% nitrile rubber, while in the last group modification was carried out by using 0.5wt% nitrile rubber together with 1, 2, and 4wt% amino silane (with respect to nitrile rubber). All specimens were heat cured in an oven. In order to observe behavior of the specimens, three-point bending, Charpy impact, plane-strain fracture toughness, and dynamic mechanical analysis tests were conducted according to the related ISO standards for all specimen groups. Scanning electron microscopy (SEM) was also used for the fractographic analysis of some samples. It was concluded that although there were problems in mixing and casting of liquid resol type phenolic resin, its toughness could be improved by using nitrile rubber and amino silane. Modification by using nitrile rubber and amino silane together was much more effective than by using only nitrile rubber. For instance, in this synergistic case Charpy impact strength and fracture toughness values of the neat phenolic specimens were increased 63 and 50%, respectively. SEM studies indicated that the main rubber toughening mechanism was shear yielding observed as deformation lines, especially initiated at the domains of nitrile rubber and amino silane. [Copyright &y& Elsevier]

Abstract: Syntactic foams having low-density microballoons (220–320kg/m3) have compressive strengths of 30–40MPa and fracture strains of around 15–20%, demonstrating adequate compressive damage tolerance. However, high-strength foams (60–70MPa), with high-density microballoons (380–460kg/m3), demonstrate less than 10% fracture strain and poor damage tolerance. The present study deals with increasing the fracture strain of high-density syntactic foams without a significant decrease in strength. An approach of modifying the matrix resin with incorporation of rubber particles is adopted. Such highly damage tolerant hybrid foams will be useful for aerospace and marine structures. This approach effectively increases the fracture strain of syntactic foams without a significant decrease in strength. All types of hybrid foams could be compressed to about 40% strain without any signs of failure. This study also focuses on using waste industrial materials in developing high-performance composites. Therefore, rubber particles obtained from waste tires have been used for fabricating the hybrid foams. [Copyright &y& Elsevier]

Abstract: A common method for toughening thermoset resins is the addition of butadiene-acrylonitrile based rubber modifiers. A difficulty experienced by diglycidyl ether of bisphenol-A (DGEBA) vinyl esters (VE) compared to other thermosets is the solubility of the butadiene-acrylonitrile modifier. In this study, a miscible system was prepared by reducing the VE monomer molecular weight to 540g/mol from industrially used monomers possessing molecular weights greater than 700g/mol. A main objective of this study was to toughen the vinyl ester while limiting plasticization by varying rubber reactivity and concentration. All modified samples experienced a significant increase in fracture toughness with some degree of plasticization, as shown by losses in modulus and glass transition temperature (Tg). Epoxy terminated rubber (ETBN) yielded a higher toughness than vinyl terminated rubber (VTBN) due to the difference in rubber particle formation and resulting morphology. Chemical linkage of VTBN to the vinyl ester matrix hindered complete phase separation, but helped the retention of mechanical properties when compared to ETBN. [Copyright &y& Elsevier]

Fatigue crack growth measurements have been made on blends of polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-acrylonitrile) (PSAN) and poly(vinyl chloride) (PVC) with two impact modifiers. In one modifier, the particles have a polybutadiene core and a PMMA shell; in the other, there is a PMMA core, a poly(butyl acrylate-styrene) inner shell and a PMMA outer shell. The overall pattern of fatigue crack growth is similar in all eight blends, but there are significant quantitative differences in ΔKth, the threshold value of the cyclic range of stress intensity factor, and in the growth rate characteristics above ΔKth. These are related to various features seen on the fracture surfaces under the scanning electron microscope, and hence to the mechanisms of deformation and fracture near the crack tip, which include crazing, particle–matrix debonding, and ductile drawing. [ABSTRACT FROM AUTHOR]

Dart drop, Charpy impact and single edge notched bending fracture tests were conducted over a range of temperatures on blends of polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC) with two core–shell impact modifiers, which were based, respectively, on polybutadiene and poly(butyl acrylate-co-styrene). The Tg values of the two rubbers were -75 and -8°C, respectively. The transition from fully brittle to partially or fully ductile behaviour occurred at various temperatures TBD depending upon a number of factors, which included the Tg of the rubber phase, the choice of thermoplastic matrix, and the type of test. In disc specimens subjected to dart drop impact, ductility was observed at lower temperatures than in sharply-notched specimens tested in slow three-point bending. It is concluded that the Tg of the rubber phase generally marks a lower limit for ductility in rubbertoughened blends, but that other factors can shift the brittle–ductile transition to higher temperatures. [ABSTRACT FROM AUTHOR]

Rubber toughening of an amorphous polyamide (Zytel 330) using combinations of triblock copolymers of the type SEBS and a maleic anhydride functionalized version, SEBS-g-MA, was investigated and the results compared with those of nylon 6 and nylon 66. The effects of rubber content and the type of extruder on the morphology, Izod impact behavior and the ductile–brittle transition temperature were explored. The shape and sizes of the rubber particles in blends with this amorphous polyamide were found to be more similar to those in nylon 6 than in nylon 66 blends. The twin screw extruder produced smaller particles with a more narrow distribution of sizes than the single screw extruder. Higher rubber contents generally yielded tougher blends; there is a critical rubber particle size above which the ternary blends are brittle at 20 wt% total rubber. The ductile-to-brittle temperature was found to decrease with increased rubber content and decreased rubber particle size. In general, the trends for this amorphous polyamide are rather similar to those reported earlier for semi-crystalline nylon 6 and nylon 66. [Copyright &y& Elsevier]

The deformation mechanisms of rubber toughened polyethylene terephthalate (PET) are studied with fractography of impact fractured samples and tensile dilatometry. The dispersed phase consists of a mixture of an ethylene-co-propylene rubber (EPR) and a compatibilising agent (E-GMA8: copolymer of ethylene and 8 wt% of glycidyl methacrylate). It is found that the ductile fracture behaviour, above the brittle–ductile transition temperature (Tbd), consists of a high degree of rubber cavitation and extensive matrix shear yielding, both in the fracture plane and the stress whitened zone surrounding the crack. A steep increase in the volume strain upon tensile loading confirms the presence of the rubber voiding mechanism in the PET/(EPR/E-GMA8) blend system. It is seen that the stress whitened zone below the impact fracture surface consists of different zones, depending on the test temperature. Below Tbd, a layer of a highly deformed structure is followed by a cavitation layer containing only a limited number of cavitaties. Increasing the temperature, causes the deformation layer to be replaced by a zone lacking structure. It is believed that part of the fracture energy has been dissipated in the form of heat inducing a relaxation in the structure. Dynamical mechanical analysis under superimposed axial stresses reveals that the dispersed rubber particles internally cavitate in the presence of volume strain. At increased volume strains, the biaxial stress state in the cavitated particle is disturbed, resulting in the rupture of the rubber chains closest to the void by a tearing mechanism; revealing that the rubber particle is damaged upon cavitation. [Copyright &y& Elsevier]

A comparative fundamental study was performed regarding the notched impact toughening performance of various rubber modified semicrystalline polyethylene terephthalate (PET) systems. Various modifiers with and without functional groups were evaluated: ethylene-co-propylene rubber (EPR), maleic anhydride grafted EPR (EPR-g-MA), glycidyl methacrylate grafted EPR (EPR-g-GMAx) and ethylene–glycidyl methacrylate copolymers (E–GMAx). Both binary and ternary blends (consisting of a preblend of EPR and a functionalised modifier) were examined. The most effective toughening route for PET is provided by dispersing a preblend of EPR and a low amount of E–GMAx. A minimum dispersed phase concentration of 30 wt% is needed to obtain a pronounced improvement of the impact strength and to induce a brittle–ductile transition of the fracture mode. The impact behaviour of the rubber toughened PET is primarily controlled by the morphological characteristics, i.e. the interparticle distance. An equal critical interparticle distance (IDc) of 0.1 μm was established experimentally for the different GMA compatibilised systems. This IDc is found to be independent of the amount of GMA functionalities present, the way of incorporation in the chain (grafting or copolymerisation) and the nature of the compatibiliser. The ternary PET/(EPR/E–GMA8) blends provided the best ultimate mechanical properties, displaying highly (15-fold) increased impact strengths and reasonable elongations at break. [Copyright &y& Elsevier]

In this study, a transparent acrylonitrile–butadiene–styrene polymer alloy was tested in a range of biaxial stress states and a yield locus was generated. The onset of microscopic damage was detected by in situ light transmission measurements. The macroscopic yield locus followed a linear behavior on an octahedral shear stress vs. mean stress plot and the onset of microscopic damage was dependent on both shear and mean stresses. Our findings indicate that macroscopic ductility arises from damage in the polymer at two distinct length scales. On the scale of the rubber particle (0.1–0.2 um), damage occurs via particle debonding from the matrix. At a length scale intermediate between the particle size and macro scale, damage occurs through the formation of micro crack arrays with a well-defined pattern. [ABSTRACT FROM AUTHOR]

The equivalent inclusion method (EIM) assuming linear elasticity is used to calculate the mechanical interactions between spherical rubber particles in an amorphous matrix, as in a rubber toughened polymer. The influences of the various calculation parameters are examined and it is shown that the method can provide reliable results with regard to the level of hydrostatic stress in the particles. Damage of the material is simulated by replacing the most stressed particles by voids. Numerical simulations for several hundreds of interacting particles give information on the kinetics and spatial organisation of the damage. It appears that, as the volume fraction of particles increases from 10 to 20%, the spatial configuration of the damage evolves from a localised to a diffuse mode. These results are discussed in relation to the efficiency of rubber toughening. [Copyright &y& Elsevier]

The properties of three different adhesive pastes J-101, J-114, and EA9309.3N/A are evaluated. These adhesives are two-part thermosetting pastes which can be cured at 80-90°C and are designed for inlay or dowel bonding application, and thus are especially suitable for a bondline thickness from 0.8 to 1.6 mm. The compositions are based on CTBN-modified DGEBA and multicomponent polyamine curing agent systems. Durability and fatigue life tests are also discussed. The microstructure and fracture behavior of these adhesives is studied by scanning electron microscopy (SEM). Different toughening mechanisms are proposed to account for the toughness of these adhesives. The experimental results show that both J-101 and J-114 adhesives develop good mechanical properties when cured at 80-90°C. Furthermore, their durability performance compares favorably with, or even exceeds, that of commercially-available EA9309.3N/A adhesive. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to increasing the lap joint strength, different from the traditional methods of either increasing the lap joint area or altering the joint geometry. This is accomplished by the selective use of rubber toughening in epoxy to optimize lap joint strength. This was accomplished in three stages. In the first stage an adduct was prepared, this was used to make bulk tensile specimens to calculate the bulk properties for various concentrations of rubber, i.e. 0, 10, and 20 parts per hundred parts of resin (epoxy). In the second stage finite element models were developed using the bulk properties previously obtained. Interfacial stresses were used to access the trends obtained by the selective use of rubber toughening at different locations of the overlap in different configurations. The modeling of adhesive joints was done using ALGOR 2-D, linear and nonlinear finite element analyses (FEA). In the third stage, tensile shear tests conducted on the lap joints validated the trends from the finite element models. Finite element modeling and meshing of the lap joints having 25.4 and 50.8 mm adhesive overlap lengths were completed. Different configurations of rubber toughened and untoughened adhesive were tried in these two overlaps. The validation was done by lap joint tests conducted on an Instron mechanical tester coupled with an extensometer. Comparable strengths were obtained for completely toughened overlap and the configuration where only the edges of the adhesive overlap were toughened and the region in-between was untoughened. Also, the nonlinear FEA was shown to represent the experimental results more closely than the linear approach. [ABSTRACT FROM AUTHOR]

The toughening mechanisms of poly(lactic acid; PLA) blended with two different elastomers, namely poly (butylene adipate-co-terephtalate; PBAT) and polyolefin elastomers with grafted glycidyl methacrylate (POE-g-GMA), at 10 and 20 wt.%, were investigated. Tensile and Charpy impact tests showed a general improvement in the performance of the PLA. The morphology of the dispersed phases showed that PBAT is in the form of spheres while POE-g-GMA has a dual sphere/fibre morphology. To correlate the micromechanical deformation mechanism with the macroscopical mechanical behaviour, the analysis of the subcritical crack tip damaged zone of double-notched specimens subjected to a four-point bending test (according to the single-edge double-notch four-point bend (SEDN-4PB) technique) was carried out using several microscopic techniques (SEM, polarized TOM and TEM). The damage was mainly generated by shear yielding deformation although voids associated with dilatational bands were observed. [ABSTRACT FROM AUTHOR]

Single crazes in transparent glassy thermoplastics are measured by means of optical interferometry. Applying numerical or analytical methods to measured creaze shapes, also their micromechanics has been evaluated. These data can be transferred to rubber-modified species of the respective thermoplastics to predict craze-governed toughening. Such predictions can be verified by comparison with results of electron microscopic investigations. [ABSTRACT FROM AUTHOR]

There are many methods widely applied in the engineering of biomaterials to improve the mechanical properties of the dental composites. The aim of this study was to assess the effect of modification of dental composites with liquid rubber on their mechanical properties, degree of conversion, viscosity, and cytotoxicity. Both flow and packable composite consisted of a mixture of Bis-GMA, TEGDMA, UDMA, and EBADMA resins reinforced with 60 and 78 wt.% ceramic filler, respectively. It was demonstrated that liquid rubber addition significantly increased the fracture toughness by 9% for flow type and 8% for condensable composite. The influence of liquid rubber on flexural strength was not statistically significant. The addition of the toughening agent significantly reduced Young's modulus by 7% and 9%, respectively, while increasing deformation at breakage. Scanning electron microscopy (SEM) observations allowed to determine the mechanisms of toughening the composites reinforced with ceramic particles. These mechanisms included bridging the crack edges, blocking the crack tip by particles and dissipation of fracture energy by deflection of the cracks on larger particles. The degree of conversion increased after modification, mainly due to a decrease in the matrix resin viscosity. It was also shown that all dental materials were nontoxic according to ISO 10993-5, indicating that modified materials have great potential for commercialization and clinical applications. [ABSTRACT FROM AUTHOR]

It has been already pointed out that one of the best ways to increase toughness of the inherently brittle polylactide (PLA) without sacrificing strength and modulus is the use of thermoplastic elastomer toughening approach; but what happens under outdoor conditions was not explored. Therefore, the objective of this study was to explore the degree of losses especially in fracture toughness of PLA when blended with thermoplastic polyurethane (TPU) elastomer or thermoplastic polyester elastomer (TPE) after weathering. For this purpose, neat PLA, its 10 phr TPU and TPE blends were exposed to accelerated weathering conditions of both ultraviolet‐irradiation cycles and moisture cycles as described in the standard of ISO 4892‐3 for various periods. In general, due to the significant molecular weight reduction via chain scission reactions, drastic losses in the strength and toughness of the specimens were observed. On the other hand, in terms of %retention in the properties after weathering periods, it could be suggested that, rather than use of neat PLA, the use of its TPU or TPE blends would be still advantageous for both "indoor use" and also for "outdoor use." © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47177. %Retention in the strength (σFlex) and fracture toughness (KIC and GIC) of polylactide and its thermoplastic polyurethane and thermoplastic polyester elastomer blends after each accelerated weathering period. [ABSTRACT FROM AUTHOR]