Search

Often, fillers are added to polymers in order to improve stiffness and inadvertently reduce toughness. This is not unexpected, as it is almost impossible to have a stiff material and still retain considerable level of toughness, especially in a poorly dispersed system. However, if the particles are well dispersed, it is quite possible to have a “win-win” situation, whereby the process will simultaneously improve toughness and stiffness. Fillers can be well dispersed and on a micro-scale agglomerate. If they are well dispersed, they will be well attached to the matrix and will remain so, even at large deformations. Of course agglomerated fillers will be prone to debonding, causing an internal fracture, leading to the formation of voids and hence, eventual deformation. However, brittle polymers can be toughened, significantly, by the addition of miscible amorphous polymers and/or a thermoplastic elastomer. In this chapter, the various mechanisms suitable for toughening nanostructured polymer blends will be succinctly reviewed. The interparticle distance and the interfacial adhesion of the filler to the polymer account for the extent of toughening achievable in the system. By far, toughening (with particulate fillers) immiscible blends has been more successful with semicrystalline than with amorphous polymers. Quite obviously, the toughening mechanism synonymous to conventional polymer blends is expected to be different from the mechanisms based on the nanophase-separated structures, since the latter represents a specific morphology-toughness correlation. This is because; toughness modification in polymer blends results in a specific toughness-morphology correlation and this is even more so, when nano-additives are factored into the system.

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 mu m 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 and G(IC) fracture 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.

Mechanical rejuvenation is known to dramatically alter the deformation behavior of amorphous polymers. Polystyrene (PS)—for example, typically known as a brittle polymer—can be rendered ductile by this treatment, while a ductile polymer like polycarbonate (PC) shows no necking anymore and deforms homogeneously in tensile deformation. The effects are only of temporary nature, as because of physical aging the increasing yield stress, accompanied by intrinsic strain softening, renders PS brittle after a few hours, while for PC necking in tensile testing returns in a few months after the mechanical rejuvenation treatment. In this study, it is found that physical aging upon rejuvenation in both PS and PC can be delayed in two different ways: (1) by reducing the molecular mobility through antiplasticization and (2) by applying toughening agents (rubbery core-shell particles). For the first route, even though progressive aging is found to decrease with increasing amounts of antiplasti- cizer added, dilution of the entanglement network results in enhanced brittleness. Besides antiplasticization effects, also some typical plasticization effects are observed, like a reduction in matrix Tg. For the second route, traditional rubber toughening using acrylate core-shell modifiers also results in a reduced yield stress recovery, and ductile tensile deformation behavior is observed even 42 months after mechanical rejuvenation. V C 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 134-147, 2008

Under certain conditions, such as sufficiently low temperatures, high loading rates and/or highly triaxial stress states, glassy polymers display an unfavorable characteristic—brittleness. A technique used for reducing the brittleness (increasing the fracture toughness) of these materials is rubber toughening. While there is significant qualitative understanding of the mechanical behavior of rubber-toughened polymers, quantitative modeling tools for the large-strain deformation of rubber-toughened glassy polymers are largely lacking. In this paper, we develop a suite of numerical tools to investigate the mechanical behavior of rubber-toughened glassy polymers, with emphasis on rubber-toughened polycarbonate. The rubber particles are modeled as voids in view of their deformation-induced cavitation early during deformation. A three-dimensional micromechanical model of the heterogeneous microstructure is developed to study the effects of initial rubber particle (void) volume fraction on the underlying elasto-viscoplastic deformation mechanisms in the material, and how these mechanisms influence the macroscopic response of the material. A continuum-level constitutive model is developed for the large-strain elasto-viscoplastic deformation of porous glassy polymers, and it is calibrated against micromechanical modeling results for porous polycarbonate. The constitutive model can be used to study various boundary value problems involving rubber-toughened (porous) glassy polymers. As an example, the case of an axisymmetric notched bar is simulated for the case of polycarbonate with varying levels of initial porosity. The quality of the constitutive model calibration is assessed using a multi-scale modeling approach.

This study focuses on the tensile behavior of fiber-reinforced polymer (FRP) composites in a concrete-based alkaline environment. Because basalt/glass FRP (BFRP/GFRP) composites exhibit relatively poor alkaline resistance compared with carbon FRP (CFRP) composites, a rubber toughening modification method has been proposed to mitigate microcracking and decrease the diffusion of the alkaline solution in the resin matrix. Different proportions of liquid rubber toughening agents were added into the epoxy resin, on the basis of which different FRP composites were made and then subjected to tensile tests after alkaline exposure. Test results indicated that the rubber toughening modification approach can significantly reduce the tensile strength degradation of the BFRP and GFRP composites in the alkaline solution. Moreover, no degradation of the elastic modulus for the FRP composites was observed. The weight gain and microstructure of the FRP composites were also investigated before and after the alkaline exposure to determine the corrosion mechanisms of the FRP composites in the alkaline environment and interpret the mechanical test results.

Composite material has attracted increasingly remarked interest over the last few decades and set it apart in its own class due to its distinct properties. This paper is a review on the matrix toughness of thermoplastic polymer composites. Toughness of thermoplastics has been actively studied since the 1980s.the main advantage in using thermoplastics to toughen resins is that their incorporation need not result in important decreases in desirable properties such as modules and yield strengths. However, the predominant criteria for achieving optimum toughness enhancement in the thermoplastic toughening of epoxy resins are still not all that clear from the literature. Epoxy and polyester resins are commonly modified by introducing carboxyl-terminated butadiene-acrylonitrile copolymers (ctbn). A tough elastomeric phase, for example, a silicone rubber with good thermal resistance in a polyimide resin, produced a tough matrix material. It summarizes what the authors believe are the important requirements for good thermoplastic toughening.

At present, the rubber toughening of plastics has become an attractive field of study in polymer science and technology because brittleness is known to be a drawback in many engineering plastics; it can cause premature failure during application. Among existing rubber materials, epoxidized natural rubber (ENR) has been widely used as an impact modifier or toughening agent in a large number of engineering plastics; in particular, it enhances the impact strength, which deteriorates with the incorporation of other additives, such as fillers and flame retardants. ENR is a modification product from natural rubber produced via an epoxidation reaction. ENR also has good chemical resistance. In this review, we aim to provide a concise current status in the field of ENR toughening agents for plastics with a brief discussion of their associated problems and potential applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42270.

The classical method of toughening polymethylmethacrylate (PMMA) is to incorporate composite rubber particles into the homopolymer matrix. This approach has been extended in the present work by (i) combining rubber toughening with chemical modification of the matrix or (ii) introduction of the rubber modifier via PMMA–b-polybutylacrylate (PBA)–b- PMMA triblock copolymers. Significant improvements in fracture toughness at low speeds were observed in notched compact tension tests when the ductility of the rubber toughened PMMA matrix was improved by copolymerization, and comparable levels of toughness were achieved in the block copolymers. However, both types of material showed a transition to more brittle behavior at impact speeds, associated with increased localization of the crack tip deformation. Physical interpretations for this behavior and the scope for further optimization of the fracture response are discussed.

Abstrtact In this study, the effectiveness of short glass fibre (SGF) reinforcements in poly(ethylene terephthalate) (PET) and blends of maleic anhydride grafted styrene-ethylene-butadiene-styrene/PET (MA-g-SEBS/PET) matrices have been investigated. One of the drawbacks for rubber toughening of polymers is the severe reduction in tensile properties (i.e. tensile modulus and tensile strength). With the incorporation of SGF into ternary SGF/rubber/PET blends, the resulting blends may possess attractive tensile and impact characteristics. From this research, it was observed that SGF is effective in improving the tensile modulus, tensile strength and notched impact strength in the SGF/PET binary blends. However, the presence of MA-g-SEBS rubber in the SGF/rubber/PET blends did not improve the notched impact strength, while the tensile properties were adversely affected. Scanning electron microscopy (SEM) examination observed that in the ternary blends, a layer of MA-g-SEBS/PET matrix was coated onto the glass fibres. These coatings reduced the interfacial shear strength between the fibre and matrix, which gave rise to the severe reduction in tensile strength with increasing rubber content.

Core-shell polybutadiene-graft-polystyrene (PB-g-PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB-g-PS blends with a constant rubber content of 20 wt%. PB-g-PS particles with a lower PB/PS ratio (

When compounding engineering thermoplastics with glass fibers for reinforcement purposes, a tremendous amount of polymer-containing waste is generated. However, the polymer of interest is usually commingled with the polymer used to purge the extruder. Reclaiming valuable polymer from this waste is hindered by the incompatibility with the purging material since this leads to a blend system that has poor mechanical properties and low economic value. For this reason, this potentially valuable post-industrial polymer-waste is normally land filled. The current research is directed at the characterization and reuse of a post-industrial PA66 filled with glass fibers; this was separated from LDPE purge material and its impact resistance was modified through rubber toughening. Styrene-Ethylene-Butylene-Styrene and Ethylene-Propylene elastomers grafted with maleic anhydride (SEBS-g-MA and EP-g-MA respectively) were used as the toughening agents in this study due to their compatibility with PA. Izod impact strength, tensile strength and modulus, flexural strength, and elongation at break were used to characterize mechanical properties of the rubber-toughened recycled glass-filled PA66. The morphology of the fracture surfaces of the composites was examined by Scanning Electron Microscopy (SEM). It was found that both impact strength and elongation at break increase with increasing rubber content while flexural strength and tensile strength suffer upon incorporating rubber; however, by adding moderate amounts of rubber to the recycled glass-fiber-reinforced PA66 a balance between stiffness and toughness of the material could be obtained. For example, the addition of 10 wt.% of SEBS-g-MA to the recycled PA66 with 23.62 wt.% glass fiber loading resulted in a 27% and 151% increase in tensile strength and impact strength respectively of the blends when compared with neat PA66. This suggests that compounding both glass fibers and elastomers with PA66 is a useful strategy to recycle PA66, especially for reuse in under-the-hood automotive applications.

The rubber toughening of nylon 6 nanocomposites prepared from an organoclay was examined as a means of balancing stiffness/strength versus toughness/ductility. Nine different formulations varying in montmorillonite, or MMT, and maleated ethylene/propylene rubber or EPR-g-MA rubber content were made by mixing of nylon 6 and organoclay in a twin screw extruder and then blending the nanocomposites with the rubber in a single screw extruder. In this sequence, the MMT platelets were efficiently dispersed in the nylon 6 matrix. The MMT platelets did not penetrate into the rubber phase. The addition of clay affected the dispersion of the rubber phase resulting in larger and more elongated rubber particles. The tensile properties and impact strength of these toughened nanocomposites are discussed in terms of the MMT and rubber contents and morphology. There is a clear trade-off between stiffness/strength versus toughness/ductility.

Rubber toughening of polyamide 6 (PA6)/ layered-silicate nanocomposites was investigated. Different systems were prepared via melt blending according to different formulations. Wide-angle X-ray diffraction and transmission electron microscopy analyses showed that the nanocomposites had an appreciable degree of exfoliation. A linear elastic fracture mechanics approach was applied to characterize the material fracture behavior in dry conditions, whereas, because of the considerable ductility exhibited by the samples in the wet state, an elastic-plastic approach based on the essential work of fracture methodology was employed. In the absence of rubber, the presence of silicate layers makes the material fracture resistance decrease relative to neat polymer, depending on the degree of humidity. The results showed that the toughening action of rubber strongly depends on the degree of humidity of the material, at least for the rubber contents considered in this study (lower than 10 wt %). In particular, in slightly wet conditions, it was found that the addition of small amounts of rubber increased the fracture resistance of PA6/layered-silicate nanocomposites without appreciably impairing the material stiffness. Thus, the results indicated that, for the given humidity conditions, a good balance between stiffness and toughness was obtainable by employing a suitable ratio of rubber to layered-silicate content.

Ethylene-octene random copolymer (EOC) is one of the most commonly employed elastomers for PP, and as such its rubber toughening efficiency has been extensively studied. However, most existing studies employ EOC containing an octene comonomer of about 8 mol %. Therefore, in this study, we investigated the effect of EOC octene comonomer content on the morphology and thermal and mechanical properties of PP-ethylene random copolymer (PP-CP)/EOC (80/20 wt %/wt %) blends. It was clearly shown that the properties of the blends are significantly affected by the octene content. The rubber particle size of the blends decreased as the octene content in the EOC was increased, which was a consequence of the reduced interfacial tension between PP-CP and EOC. Impact strength of the blends as a function of octene content displayed a brittle-ductile transition. The tensile yield strength and modulus of the PP-CP/EOC blends were decreased by addition of EOC, owing to incorporation of the soft EOC into the hard PP-CP. The tensile yield strength and modulus of PP-CP/EOC blends decreased monotonically with the octene content in the EOC. The melting temperature as well as the crystallinity of the PP-CP phase were not affected significantly by the addition of EOC whereas a notable shift in melting and crystallization temperatures was observed for the EOC phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1133–1139, 2007

In the present study two series of isotactic polypropylene (iPP)/SiO2 nanocomposites containing 1, 2.5, 5, 7.5, and 10 wt % SiO2 nanoparticles were prepared by melt-mixing on a twin-screw corotating extruder. In the first series untreated fumed silica nanoparticles were used, whereas in the second nanoparticles were surface-treated with dimethyldichlorosilane. In both cases, the average size of the primary nanoparticles was 12 nm. Tensile and impact strength were found to increase and to be affected mainly by the type and content of silica nanoparticles. A maximum was observed, corresponding to samples containing 2.5 wt % SiO2. These findings are discussed in light of the SEM and TEM observations. By increasing the amount of nanoparticles, large aggregates of fumed silica could be formed, which may explain the reduction of mechanical properties with higher concentrations of SiO2. However, it was found that surface-treated nanoparticles produced larger aggregates than did those derived from untreated nanoparticles, despite the increased adhesion of the iPP matrix, as was postulated from yield strength. This behavior negatively affected mechanical properties. In addition, an effort was made to determine if toughening theories, mainly the critical interparticle distance for rubber toughening or composites, also might be applicable in nanocomposites. From DSC measurements it was demonstrated that silica nanoparticles acted as effective nucleating agents, increasing the crystallization rate and the degree of crystallinity of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2684–2696, 2006

In this paper, the effect of two-phase structure on the mechanism of rubber-toughening of epoxy resins was studied. Three types of hydroxyl-terminated polyesters with different molecular weights were synthesized in order to modify epoxy resins to obtain single-phase (P-1), critical phase separation (P-2) and two-phase (P-3) structures. The results of dynamical mechanical analysis and scanning electron microscopy distinguished the dissolved and phase-separated polyesters in the epoxy matrix. The P-1 system showed the highest dissolved content of polyester in the epoxy matrix, while the P-3 system exhibited the lowest content. Both dissolved and phase-separated polyesters proved to be capable of increasing the toughness of modified epoxy resins. The phase-separated polyester was found to contribute much more to the improvement of toughness.  2005 Society of Chemical Industry

The influence of sample thickness on the fracture behaviour of an aliphatic polyketone and a blend of this polymer and 10 wt% core–shell rubber was studied. The sample thickness was varied from 0.1 to 8 mm. The skin morphology was studied by SEM. The fracture behaviour was studied on single edge notch specimen at a high strain rate (30 sK1) in the temperature range of K40 to 120 8C. The fracture stress, fracture strain and fracture energies were determined. The temperature development in the notch area was followed with an Infra Red camera. The cavitation of the rubber particles was studied on tensile bars with a laser setup. With decreasing specimen thickness the fracture energies increased strongly and the brittle-ductile transition shifted to lower temperatures this both for the aliphatic polyketone and the polyketone-rubber blend. The deformation in these materials in accompanied with a strong temperature increase in the deformation zone. The addition of rubber particles decreases the sensitivity towards the thickness. However, in very thin samples the cavitation of the rubber particles is more difficult and the rubber toughening effect decreases. The strong thickness effects on the fracture toughness indicate for both the homo polymer and the blend indicate that data from a standard test with 4 mm thick samples are not representative for thin walled applications.

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 ΔK th, the threshold value of the cyclic range of stress intensity factor, and in the growth rate characteristics above ΔK th. 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.

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 T g 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 T BD depending upon a number of factors, which included the T g 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 T g of the rubber phase generally marks a lower limit for ductility in rubbertoughened blends, but that other factors can shift t...

Styrenic polymers and copolymers are often impact modified with rubber particles. The efficiency of rubber toughening depends mainly on the size of the rubber particles and the degree of cross-linking. The deformation rate, the temperature, the orientation of the polymer molecules and the efficiency of rubber grafting also influence rubber toughening. It is thought that on impact, cavitation inside the rubber particles occurs which reduces the detrimental dilatational stress in the bulk polymer without forming cracks in the brittle matrix or at the rubber-matrix interface. Crazing and shearing are facilitated if the rubber particles can easily cavitate. This can be achieved by either avoiding too much cross-linking or by adding oil (silicone oil in the case of ABS) into the rubber particles, which acts as nuclei for void formation. An electron spectroscopic imaging method is described which allows visualizing the location of the oil. Already after cooling silicone oil modified ABS samples down to liquid nitrogen temperature rubber cavitation is observed. This cavitation is caused by the thermal stress developing due to the differences in thermal expansion coefficient between the rubber phase and the SAN-matrix and is facilitated by silicone oil. Voiding also leads to an increase of light scattering, which can be detected by an optical microscope using dark field illumination.

The fracture behaviors of α-zirconium phosphate (α-ZrP) based epoxy nanocomposites, with and without core-shell rubber (CSR) toughening, were investigated. The state of exfoliation and dispersion of α-ZrP nanofiller in epoxy were characterized using X-ray scattering and various microscopy tools. The level of enhancement in storage moduli of epoxy nanocomposite against neat epoxy is found to depend on the state of exfoliation of α-ZrP as well as the damping characteristics of the epoxy matrix. The fracture process in epoxy nanocomposite is dominated by preferred crack propagation along the weak intercalated α-ZrP interfaces, and the presence of α-ZrP does not alter the fracture toughness of the epoxy matrix. However, the toughening using CSR can significantly improve the fracture toughness of the nanocomposite. The fracture mechanisms responsible for such a toughening effect in CSR-toughened epoxy nanocomposite are rubber particle cavitation, followed by shear banding of epoxy matrix. The ductility and toughenability of epoxy do not appear to be affected by the incorporation of α-ZrP. Approaches for producing toughened high performance polymer nanocomposites are discussed.

Toughening of epoxy resins for improvement of crack resistance has been the subject of intense research interest during the last two decades. Epoxy resins are successfully toughened by blending with a suitable liquid rubber, which initially remains miscible with epoxy and undergoes a phase separation in the course of curing that leads to the formation of a two-phase microstructure, or by directly blending preformed rubbery particle. Unlike the situation for thermoplastics, physical blending is not successful for toughening epoxy resins. Recent advances in the development of various functionalized liquid rubber-based toughening agents and core-shell particles are discussed critically in this review.

Tensile tests on high-impact polystyrene (HIPS) show that a 60 Mrad dose of γ-radiation raises the yield stress from 11.5 to 19.8 MPa, and the flow stress from 10.0 to 19.6 MPa, while reducing the elongation at break from 50 to 4%. Similar reductions in fracture resistance are observed in irradiated Charpy impact specimens. The Tg of the rubber phase shifts from −70 to −57 °C, and its estimated shear modulus increases from 0.1 to 0.5 MPa. It is concluded that the observed changes in mechanical properties are due almost entirely to crosslinking of the polybutadiene. This not only inhibits cavitation and fibrillation in the rubbery membranes of the “salami” particles, thereby delaying yield, but also makes the fibrillated membranes more resistant to further dilatation, so that rates of craze thickening in the polystyrene matrix are reduced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2168–2180, 2004

The microhardness, H, of PMMA/natural rubber blends, prepared following the solution method has been investigated by means of the microindentation technique. Hardness changes are correlated with the variation of the glass transition temperature. The influence of temperature and degree of deformation on H were additionally examined. The inclusion of rubber particles in the PMMA matrix is shown to soften the blends. The variation of the micromechanical property at the phase boundary of polymer/rubber particle has been studied. Results reveal that H drastically drops at the interphase. In the case of the drawn materials, the indentation anisotropy (ΔH) is shown to gradually increase with the draw ratio, where ΔH is found to be higher for the PMMA/rubber blend than for the original PMMA. This result is explained by the higher orientation of the PMMA molecules near the periphery of stretched rubber particles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 205–210, 2004

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 ( T bd ), 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 T bd , 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.

When researching the effect of rubber toughening in acrylonitrile-butadiene-styrene (ABS) copolymer and high-impact polystyrene (HIPS) and also toughening methods used in other materials, then, often comparisons are needed between materials with and without the toughening agents over the full crack velocity range. This is from the threshold stress to just maintain crack propagation up to the limiting crack velocity conditions. However, the toughening of materials can change other material properties including, for example, the onset of yield in the material under static stress. The result can be that a crack velocity versus stress curve cannot be obtained by experiment over the full crack velocity range for some toughened materials. However, as used in this study, combined experimental and computer simulations can provide for a meaningful and informative comparison between crack velocity versus stress curves for materials with and without toughening agents over the full crack velocity range.

In this study, improvements in mechanical and thermal behavior of short glass fiber (GF) reinforced diglycidyl ether of bisphenol-A (DGEBA) based epoxy with hydroxyl terminated polybutadiene (HTPB) modification have been studied. A silane coupling agent (SCA) with a rubber reactive group was also used to improve the interfacial adhesion between glass fibers and an epoxy matrix. 10, 20, and 30 wt% GF reinforced composite specimens were prepared with and without silane coupling agent treatment of fibers and also HTPB modification of epoxy mixture. In the ruber modified specimens, hardener and HTPB were premixed and left at room temperature for 1 hr before epoxy addition. In order to observe the effects of short glass fiber reinforcement of epoxy matrix, silane treatment of fiber surfaces, and also rubber modification of epoxy on the mechanical behavior of specimens, tension and impact tests were performed. The fracture surfaces and thermal behavior of all specimens were examined by scanning electron microscope (SEM), and dynamic mechanical analysis (DMA), respectively. It can be concluded that increasing the short GF content increased the tensile and impact strengths of the specimens. Moreover, the surface treatment of GFs with SCA and HTPB modification of epoxy improved the mechanical properties because of the strong interaction between fibers, epoxy, and rubber. SEM studies showed that use of SCA improved interfacial bonding between the glass fibers and the epoxy matrix. Moreover, it was found that HTPB domains having relatively round shapes formed in the matrix. These rubber domains led to improved strength and toughness, due mainly to the “rubber toughening” effect in the brittle epoxy matrix.

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 -GMA x ) and ethylene–glycidyl methacrylate copolymers (E–GMA x ). 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–GMA x . 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.

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile-brittle (D-B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear-induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D-B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler-dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening.

Various experimental techniques and finite element modelling (FEM) were employed to assess mechanical and chemical properties of vinyl-ester (VE)/poly(acrylonitrile–butadiene–styrene) (ABS) blends with different ABS particle content. The blends were to be used as a toughening agent for interlayer toughened VE/glass composite material. Firstly, the materials' fracture toughness and tensile properties were examined, the results showing excellent toughening potential of the blends as well as a non-linear trend for fracture toughness as a function of ABS weight content. The tensile testing of the blends served to define the yield point of the materials and to obtain their stress–strain curves, which were then used as input into finite element analysis models. The mechanical testing results suggested that a chemical reaction may have occurred between the constituents of the blends. Based on the Raman spectroscopy results and mechanical testing data, 7% of ABS was believed to be the critical ABS content where significant changes in the materials' chemical composition and consequently in mechanical properties occurred. Finally, FEM was undertaken to further verify the existence of this sudden variation in material's properties.

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.

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.

The toughening of glass fiber reinforced nylon-6,6 (PA-6,6) by using the functionalized triblock copolymer styrene-(ethylene-co-butylene)-styrene, grafted with maleic anhydride (SEBS-g-MA) was examined. Blends containing 2.5, 5, 7.5, 10, and 12.5 wt% copolymer were prepared by melt blending in a single-screw extruder. Emphasis was given to the study of mechanical properties in comparison with morphology and thermal properties of the aforementioned samples. Although the amount of SEBS-g-MA that was added in PA-6,6 was not enough to produce a super-tough material, a significant increase in the resistance to crack propagation and impact strength was observed in all blends. This behavior was proportional to the amount of SEBS-g-MA that was added for samples having up to 10%, rubber, while additional amounts seem to have no further effect. A small decrease in tensile strength was also observed. From FTIR spectroscopy and DSC analysis it was shown that the grafting extent of SEBS-g-MA to PA-6,6 was very low. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 153–163, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/adv.10023

The toughening behavior of short glass fiber reinforced toughened polymers was studied using fracture mechanics and microscopic techniques. The essential work of fracture (EWF) analysis shows that the inclusion of short glass fibers not only provided a stiffening effect but also a toughening influence. It was observed that rubber-related toughening and fiber-related toughening were competitive in nature for the reinforced, toughened nylon 6,6. When the matrix stress was substantially reduced by the presence of short fibers via the load-shedding mechanism, rubber toughening was severely curtailed. At higher fiber volume fractions, fiber pull-out work contributed significantly to the enhancement of the specific essential fracture work. Fiber-end plasticity was evident under microscopic examination.

The rigid nano-silica and soft nano-rubber toughening effects on neat epoxy under impact loading in a range of −50 to 80 °C were investigated. Nanosilica particles (20 nm) toughened neat epoxy at all temperatures with a maximum toughening efficiency at −50 °C and lower efficiency at elevated temperatures. In contrast, except at −50 °C, nano-rubber particles (100 nm) showed the deterioration effect on the impact fracture toughness of epoxy resin. Scanning electron microscopy examinations revealed that the crack pinning and local epoxy deformation induced by rigid particles in term of nano-silica/epoxy and nano-rubber/epoxy interfacial debonding (at −50 °C) led to positive toughening efficiency on neat epoxy. However, at 20 and 80 °C, the rubber cavitations/void plastic growth was significantly suppressed under the impact loading, which led to the negative toughening efficiency on epoxy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45319.

Poly(lactic acid)/2 wt % organomodified montmorillonite (PLA/OMMT) was toughened by an ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) rubber. The ternary nanocomposites were prepared by melt compounding in a twin screw extruder using four different addition protocols of the components of the nanocomposite and varying the rubber content in the range of 5–20 wt %. It was found that both clay dispersion and morphology were influenced by the blending method as detected by X-ray diffraction (XRD) and observed by TEM and scanning electron microscopy (SEM). The XRD results, which were also confirmed by TEM observations, demonstrated that the OMMT dispersed better in PLA than in E-MA-GMA. All formulations exhibited intercalated/partially exfoliated structure with the best clay dispersion achieved when the clay was first mixed with PLA before the rubber was added. According to SEM, the blends were immiscible and exhibited fine dispersion of the rubber in the PLA with differences in the mean particle sizes that depended on the addition order. Balanced stiffness-toughness was observed at 10 wt % rubber content in the compounds without significant sacrifice of the strength. High impact toughness was attained when PLA was first mixed with the clay before the rubber was added, and the highest tensile toughness was obtained when PLA was first compounded with the rubber, and then clay was incorporated into the mixture. Thermal characterization by DSC confirmed the immiscibility of the blends, but in general, the thermal parameters and the degree of crystallinity of the PLA were not affected by the preparation procedure. Both the clay and the rubber decreased the crystallization temperature of the PLA by acting as nucleating agents. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41518.

Melt blending thermoplastic polymers with various elastomers have been considered as the most economical and effective route to toughen these polymers. Yet, the underlying mechanisms controlling such toughening are controversial. We demonstrate here that differences in elastomer morphology can induce dramatically changes in toughening efficiency. In this study, the brittle poly(ethylene terephthalate) (PET) was toughened by poly(ethylene-octene) (POE) elastomer with maleic anhydride grafted POE (mPOE) as compatibilizer. Depending on the shearing action from the nozzle during injection molding, special sample with elongated elastomer particle but almost isotropic and amorphous PET matrix was prepared by injection molding. The toughening efficiency for elongated or spherical elastomer particles, therefore, could be evaluated without the influence of matrix resin. Most interestingly, compared to spherical elastomer particle, the occurrence of brittle-ductile transition (BDT) of the elongated-elastomer-toughened PET was delayed. SEM micrographs of the impact fracture surface suggested that the matrix shear yielding could not be effectively initiated in the oriented blends until the elastomer content increased up to 40 wt.%.

The impact fracture parameters of blends of nylon 6 and maleated ethylene–propylene rubber (EPR- g -MA) reinforced with glass fibers as a function of glass fiber and EPR- g -MA content were examined. Both the linear elastic fracture mechanics (LEFM) model and a modified essential work of fracture (EWF) model were used to analyze the data. It was found that the addition of EPR- g -MA to unreinforced nylon 6 increased the EWF parameters u o and u d defined by U / A = u o + u d l, where U / A is the total fracture energy per unit area and l is the ligament length. Beyond a critical rubber content, which coincided with the ductile-to-brittle transition, there was a large increase in u d . When glass fiber reinforcement was used without rubber toughening, the EWF model was unable to model the observed fracture response. On the other hand, the LEFM model adequately described the fracture behavior, and it was found that the critical strain energy release rate, G IC , increased with increasing glass fiber content. When both glass fiber reinforcement and rubber toughening were used, the u o increased with increasing EPR- g -MA or glass fiber content; whereas, u d increased with increasing ERR- g -MA content or decreasing glass fiber content.

This study is a fractographic examination of epoxy resin modified with scrap car tyre regrinds used as toughening phase. Five different surface treatment techniques, used to improve the compatibility at the interface between the rubber particles and the epoxy matrix, were: oxygen plasma, two silane coupling agents, acrylic acid and acrylic acid/benzoylperoxide mixture. Rubber parts of ground scrap car tyres with a size range of 355–500 μm after surface treatment were mixed with epoxy. This mixture was poured into molds to obtain fracture toughness test specimens. After curing, plane strain fracture toughness tests were performed and the fractured surfaces of the specimens were examined under the scanning electron microscope. Fractographic studies indicated that the increase in fracture toughness values were due to the improved interface leading to crack deflection as the main rubber toughening mechanism. Secondary rubber toughening mechanisms observed were shear deformation and some debonding initiated at the interface.

Rubber toughening usually involves the addition of rubber particles to a rigid polymer in order to promote energy absorption through the initiation of local yielding, which takes the form of multiple crazing and/or extensive shear yielding. In addition to these classic mechanisms, recent studies of deformation mechanisms in various rubber modified polymers, using a range of electron microscopy techniques, have revealed two new mechanisms of energy absorption. Direct observations of micromechanical processes in high impact polystyrene and copoly(styrene/acrylonitrile)–acrylate blends, carried out in situ on the stage of a transmission electron microscope have shown that the rigid, glassy subinclusions found in both ‘salami’ and hard–soft–hard ‘core–shell’ rubber particles respond to high tensile stresses by cold drawing. Fibrillation begins in the rubber phase and then draws fibrils of glassy polymer from the subinclusions, causing initially spherical inclusions to become flattened discs before fin...

The effect of the elastomer stiffness on brittle–tough transition in elastomer toughening thermoplastics was quantitatively studied. A correlation between brittle–tough transition temperature and the elastomer stiffness was obtained. The calculation from this correlation showed that the brittle–tough transition temperature (Tbt) of elastomer toughening thermoplastics slowly increased up to one tenth of the modulus of matrix, thereafter it increased rapidly with increasing the modulus of elastomer. The results indicated that the modulus of the elastomer must be one-tenth or less of that of the matrix in order to be effective at low temperature.

The influence of interfacial adhesion on the tensile properties, including toughness, of poly(vinyl chloride) (PVC)–nitrile rubber (NBR) blends with the morphology of well-dispersed rubber particles has been investigated using two types of blends. The first type, which contains NBR26 (NBR with 26 wt% acrylonitrile (AN)), has a higher interfacial adhesion strength than the second type that contains NBR18. The secant modulus and yield stress of the blends were found to be independent of interfacial adhesion. On the other hand, the elongation-at-break and toughness (defined as the area under the stress–strain curve to break) depend strongly on the interfacial strength. The effects of rubber particle size, size distribution and rubber volume fraction on the tensile properties have been combined into the effect of a single morphological parameter, the matrix ligament thickness T. Both the elongation-at-break and toughness increase as T decreases. At T μm the blends with stronger interfacial adhesion (PVC–NBR26) have much higher elongation-at-break and toughness. Stress whitening was observed in all deformed PVC–NBR18 blends. For PVC–NBR26 blends, however, stress whitening occurred only at T>0.06 μm . Transmission electron microscopy studies revealed that debonding at the PVC–NBR interface is the sole microvoiding mechanism that causes stress whitening.

Toughened epoxy resin composites have been prepared by resin-transfer moulding by using a range of toughening agents. Two types of epoxy-functional preformed toughening particles were investigated and have a three-layer morphology in which the inner core is crosslinked poly(methyl methacrylate), the intermediate layer is crosslinked poly(butyl acrylate) rubber and the outer layer is a poly[(methyl methacrylate)-co-(ethyl acrylate)-co-(glycidyl methacrylate)]. The presence of glycidyl groups in the outer layer facilitates chemical reaction with the matrix epoxy resin during curing. Comparisons were made with acrylic toughening particles that have a similar structure, but which do not have the epoxy functionality in the outer shell, and with a conventional carboxy-terminated butadiene acrylonitrile (CTBN) liquid rubber toughening agent. The composites were characterised by using tensile, compression and impact testing. The fracture surfaces and sections through the moulded composites were examined by means of optical and scanning electron microscopy. Short-beam shear tests and fragmentation tests were used to investigate the interfacial properties of the composites. In general, use of the epoxy-functionalised toughening particles gave rise to superior properties compared with both the non-functionalised acrylic toughening particles and CTBN.

The influence of interfacial adhesion on the impact toughness of poly(vinyl chloride) (PVC)–nitrile rubber (NBR) blends with the morphology of well-dispersed rubber particles has been investigated. The blend containing NBR 18 (NBR with 18 wt% acrylonitrile (AN)) has medium interfacial adhesion strength, and exhibits a brittle–ductile transition at a critical matrix ligament thickness T c =0.059 μm while the blend containing NBR 26 (NBR with 26 wt% AN) and having stronger interfacial adhesion exhibits the transition at T c =0.041 μm. The difference can be understood in terms of the deformation mechanisms. Debonding at the interface of the PVC–NBR 18 blend takes place upon impact, and this induces shear yielding of the matrix. For the PVC–NBR 26 blend, however, no microvoid is formed, so the occurrence of matrix shear yielding is delayed. In the investigated rubber particle size range (0.04−0.12 μm ), debonding followed by matrix shear yielding is a much more important toughening mechanism than internal cavitation of rubber particles.

The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, K IC , measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber-rich domains and the structure of the rubber-rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy-residing dispersed rubber phase and the rubber-dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process.

The high temperature application of styrenic polymers was extended beyond the glass transition temperature of amorphous PS by the two following modifications: 1. Increasing the syndiotactic portion, producing crystallites, which act as physical cross-links in the temperature region between the glass transition and the melting point. 2. Copolymerisation with DPE leading to an increase in the glass transition temperature with increasing DPE-content. In both materials crazing prevails. Toughness has been successfully improved by rubber modification, by which the initiation and stabilisation of the deformation processes—mostly voiding and crazing—are enhanced. Due to the higher stiffness of the molecules in S/DPE and the mutual interaction between the propagating crazes and the crystalline lamellae in sPS, the rubber toughening in these two types of products is likely to be reduced compared to an amorphous PS.

The recent advances in the studies of the toughening methods and theories of polypropylene (PP)–elastomer blends are reviewed in the present article. Inclusions are key to toughening PP; they can play the role of agent-induced crazing, cause shear yielding of the matrix around them, and end the propagation of cracks. The major theories interpreting the toughening mechanisms of the blends are: multiple crazing, damage competition theory, shear-yielding theory, microvoids, and cavitation theories. The factors affecting the toughening effect are relatively complicated. Therefore, these theories have been verified only in some cases when they have been applied in relevant conditions. To achieve the objective of better toughening, it is important to improve the uniform distribution of dispersed-phase particle size and suitable filler size, as well as improving the dispersion of the inclusions formed in the matrix; in addition the matrix materials or fillers must be functional with suitable modifier in order to enhance the interfacial adhesion or to improve the interfacial morphological structure between the filler and matrix. However, the exact toughening mechanisms for PP–rubber blends have to be studied further because of complications resulting from the crystallinity of the matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 409–417, 2000

The toughening mechanisms and their sequence in rubber modified plastics is determined experimentally through the use of a multi-axial testing combined with and a rubber-modified material with favorable properties. The multi-axial testing was achieved by internally pressurizing and uniaxially loading hollow cylinders. This test allows independent control of the mean stress (volume change) and octahedral shear stress (shape change) between regions of uniaxial compression and equal biaxial tension. The rubber-modified material consists of a methacrylate–butadiene–styrene (MBS) core-shell modifier dispersed in polyvinylchloride (PVC). The whitening behavior of this material during deformation is favorable, since it provides optical verification of cavitation or debonding. In situ light transmission measurements of the MBS modified PVC in the multi-axial stress state test allows the mechanics associated with rubber particle cavitation to be evaluated. The onset of whitening in these systems occurs at a constant octahedral shear stress under a positive mean stress prior to yielding. This behavior is in disagreement with recent models, which predict cavitation occurring at a constant positive mean stress in MBS modified PVC.