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The addition of well-dispersed nanoparticles can significantly increase the mechanical properties and toughness of epoxy polymers. In this study, an epoxy resin was modified by addition of silica nanoparticles, (CTBN) rubber microparticles and a combination of both. An in-situ orthogonal cutting rig combined with high magnification and high-speed imaging system was used to determine the effects on the chip formation mechanism and machining induced damage to the material. This study indicates that chip formation in silica-modified epoxy is governed by a fracture process with large cracks both at the machined surface level and subsurface within the chip formation zone. The presence of rubber enables larger plastic deformation within the epoxy-modified polymer as the toughening mechanism of the rubber deflects the generated cracks within the primary deformation zone. The magnitude of machining induced damage was found to be lower for rubber microparticles and was correlated with a rubber toughening mechanism observed during cutting. The higher magnitude of machining induced damage of silica-modified epoxy was linked to the material’s poor resistance to crack initiation and growth. These findings of the effect of rubber microparticles and silica nanoparticles on chip formation process will give engineers a greater ability to create a trade-off between filler properties vs material properties vs machining induced damage during Design for Manufacturing (DFM) stages of a product design.

This study describes the toughening of poly(lactic acid) (PLA) through blending it with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers (EPE, Pluronic®) at loadings less than 10 wt%. The miscibility of EPE copolymers in PLA was examined by thermal, morphological, and rheological analysis. Copolymers with low molecular weight and low poly(propylene oxide) (PPO) content were more miscible with PLA but less efficient as a toughening agent. In contrast, copolymers with high PPO content and high molecular weight formed droplets in the PLA and significantly increased the ductility of PLA at 5 wt% loading. More importantly, it was found that the toughening mechanism in those toughened PLA/EPE blends is similar to “rubber toughening of brittle plastics” rather than plasticization. Since the refractive indices of PLA and EPE are nearly matched, the blends were transparent. For the first time, the rheological properties of PLA/EPE blends are studied. Both the miscible and immiscible blends exhibited lower viscosity than neat PLA on account of different mechanisms. The low viscosity of the miscible blends resulted from the plasticization effect of the molecularly dissolved EPEs while the low viscosity of the immiscible blends resulted from the lubrication effect of the phase-separated EPE liquids. This lubrication effect also led to low adhesion on metal surfaces.

In this work, the mechanism behind rubber toughening of poly(lactic acid)/cellulose nanocrystal-g-rubber-g-poly( d -lactide) (CNC-rDx-PDLA) composites was elucidated through systematic study of the effects of rubber segment content (length) in CNC-rDx-PDLA nanofillers and the nanofiller concentrations on the deformation behavior of the nanocomposites. It was shown that with an increase of rubber segment length and rubber filler concentration, the elongation at break of the resulting composites increased. Moreover, a dramatic increase in elongation at break (from 20% to 200%) was observed when the rubber segment content (length) in the CNC-rDx-PDLA nanofillers was increased from 52 to 68%. Cavitation mechanism was found dominant when the rubber segment content in the nanofillers was 52% and below, whereas, stable crazes were formed and followed by fibrillation when the rubber segment content in the nanofillers was increased to 68%, which was evident by small angle X-ray scattering (SAXS) study and scanning electron microscopy (SEM) analysis. The existence of a transition from cavitation to crazing in the composite systems could be attributed to a more mobile rubber phase because of longer rubber chain length. Our study suggests that the effective toughening mechanism for thermoplastics such as PLA is crazing induced plastic deformation.

The purpose of this study was to investigate how optimum mechanical properties (strength-modulus-toughness) of inherently very brittle polylactide (PLA) could be obtained by reinforcing with E-glass fibers (GF) and blending with thermoplastic polyurethane elastomer (TPU). Composites and blends were compounded by twin-screw extruder melt mixing, while specimens were shaped by injection molding. SEM analyses revealed that 15 wt% GF and 10 wt% TPU domains, alone and together, could be uniformly distributed in the PLA matrix leading to significant improvements in properties. Mechanical tests indicated that use of TPU blending alone resulted in enormous increases in the ductility and fracture toughness values, while GF reinforcements led to significant increases in strength and elastic modulus values. When GF and TPU were added together, it was observed that crack deflection, debonding and fiber pull-out toughening mechanisms of GF reinforcements were as effective as the rubber toughening mechanism of TPU blending.

Mechanical stress exerted upon impact-modified polycarbonate (PC) and poly(ethylene terephthalate) (PET) blends has been reported to generate microscopic voids via rubber-toughener (RT) particle cavitation which can macroscopically manifest to visibly whiten the material. Previous work has revealed a whitening phenomenon in collegiate American football helmet outer shells after a single season and in helmet-grade plaques following linear impact testing. The purpose of this research was to quantify the effects of repetitive linear drop exposures on the (i) impact performance; (ii) physical and thermal properties; and (iii) surface and tensile mechanical properties of a stress-whitened American football helmet outer shell material. Statistically significant changes in plaque impact performance corresponded to substantial stress-whitening that penetrated up to 40–45% into the plaque thickness and elicited shifts in surface and tensile mechanical properties. Nanoscale microscopy revealed elongation of the PC/PET matrix and delamination at the RT-matrix interface. Thermal property analysis suggested the concomitant occurrence of RT cavitation and strain-induced PET crystallization. Overall, the research identified a battery of diagnostic tools to characterize material property changes of stress-whitening in rubber-toughened helmet outer shell materials.

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

Maleation of ethylene–octene copolymer (EOC) with incorporation of styrene as a comonomer was investigated. Maleated EOC thus obtained was compounded with polyamide-6 (PA6) and its efficiency as an elastomer in PA6 matrix was evaluated. Maleated EOC incorporated with styrene provides higher impact strength than the conventional maleated EOC. By various investigations, it was proved that the incorporation of the styrene increases the graft degree of MA onto EOC and the maleated EOC thus obtained shows higher performance as an elastomer in the rubber toughening of PA6 due to enhanced interfacial strength and stability.

This work aimed at investigating the thermal mechanical behavior of recycled polypropylene (PP)-based composites under dynamic loading. PP was blended by extrusion with different fractions of ethylene octene copolymer (EOC) as soft rubber toughening agent and talc as rigid reinforcing agent. To simulate mechanical recycling, the composites were grinded and re-extruded up to 6 times. The dynamic behavior was studied by means of a split Hopkinson pressure bar at various strain rates and temperatures. We found that neat PP and PP/talc composites presented a brittle behavior at low temperatures. The addition of EOC inclusions markedly improved the impact resistance of PP and PP/talc. The results also indicated that the impact resistance of PP/talc was improved with the recycling numbers due to a fragmentation of the talc particles during the reprocessing inducing a self-reinforcement. However, the impact resistance of PP/EOC decreased with the recycling due to chain scission mechanisms. Concerning PP/EOC/talc composite, its dynamic behavior was almost constant with the recycling number possibly induced by equilibrium between self-reinforcement and chain scission mechanisms. Complementary information about the dynamic behavior of the materials was deduced from optical microscopy investigation of the morphology after dynamic compression testing.

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. The lack of substantial toughness in these polymers limits their use in practical engineering applications. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and act to toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer. Here a variety of two-phase polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Fracture mechanics experiments demonstrate that a small reduction in the inclusion's Young's modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). The finite element method and digital image correlation are utilized to study this toughening mechanism. Optical strain measurements confirm the numerical simulation results and possible toughening and strengthening mechanisms.

Many polymer materials are brittle and hence susceptible to fracture, especially in the presence of notches, scratches, or internal defects. This limits the application of polymer-based materials across a wide range of technological fields. The toughening of polymer materials by developing a two-phase structure with the use of soft rubber as the dispersed phase has gained considerable attention because of their commercial importance. Over the past several decades, homogeneous rubber microparticle toughening and related toughening mechanisms have been extensively investigated. Currently, rubber toughening is being developed considering the design and control of rubber structures for improving the toughness, and realizing the rigidity-toughness balance with minimal loss of heat resistance of polymer materials. This paper reviews the state-of-the-art research progress of polymer materials toughened by structured rubbers. To provide a general understanding on rubber toughening, we first briefly introduce the classification of polymer materials that require toughening, common strategies for improving the interfacial adhesion between rubber particles and polymer matrices, and homogeneous rubber microparticle toughening of polymer materials. Further, four categories of structured rubber toughening are discussed in detail, which includes heterogeneous rubber microparticle toughening, oriented anisotropic rubber microparticle toughening, rubber nanoparticle toughening and bimodal size distributed rubber particle toughening. Furthermore, the relationship between the structure of rubbers and the properties of modified polymer materials, such as toughness, modulus and heat resistance, is discussed. The influence of the interface or interphase on these properties is highlighted. Finally, future research endeavors and possible directions for further progress in this field are outlined.

A series of dynamically vulcanized isotactic polypropylene (PP)/ethylene–propylene–diene rubber thermoplastic vulcanizates (TPVs) containing different content of β-nucleating agent (β-NA) were prepared and introduced into isotactic PP matrix as a toughening agent. The effect of β-nucleated TPVs (β-TPVs) on the toughness and other properties of PP were studied. Differential scanning calorimetry and wide-angle X-ray diffraction results indicated that the β-crystallinity and the relative content of β-phase in β-TPVs samples and the toughened blends increased with the content of β-NA increasing. The notched impact strength of PP toughened by β-TPVs, with limited loss in the tensile strength and rigidity, showed an almost linear increase with increasing β-NA content. Especially when the content of β-NA was 0.5 wt%, the impact strength of the toughened blends was ten times more than that of pure PP. The toughening mechanism based on classical rubber toughening mechanisms was discussed and a synergic toughening mechanism was proposed.

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.

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 10 wt%. Maximum reduction of the flexural modulus and the tensile modulus was achieved by 20 and 45% respectively when the acrylate rubber was applied at 10 wt%. 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 0.5 wt% helped increasing the degree of crystallinity.

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 (

Open-faced asymmetric double cantilever beam (ADCB) specimens of toughened epoxy-aluminum adhesive joints were aged either in a constant humidity environment or a cyclically changing environment to study the mixed-mode fatigue behavior. Under constant humidity environments, the fatigue threshold strain energy release rate initially decreased with aging time until it reached a constant minimum value for long times. In contrast, the crack growth rates continued to increase with aging time. It is hypothesized that at crack growth rates close to threshold the fatigue behavior is governed by the epoxy matrix, whereas at relatively high crack growth rates the fatigue behavior is governed by the loss of the rubber toughening mechanism. Increasing the aging temperature accelerated the degradation of the joints leading to a reduction in the time to reach the constant minimum value and increased the crack growth rates. Under a cyclic aging environment with intermittent salt spray, neither the threshold strain energy release rate nor the crack growth rates degraded until four weeks of aging. The superior fatigue performance of these joints compared to joints aged in constant humidity environments was due to the lower water concentrations in the adhesive while aging. This conclusion was supported by moisture uptake measurements of the adhesive in deionised and salt water environments that showed simple Fickian behavior at room temperature and dual-Fickian behavior at higher temperature. The salt water environment produced osmotic pressure that decreased the moisture concentration in the second stage of diffusion.

Poly(lactic acid) (PLA) was toughed by blending hydrogenated styrene-butadiene-styrene block copolymer (SEBS) with the aid of reactive compatibilizer, poly(ethylene-co-glycidyl methacrylate) (EGMA). The high temperature property and thermal aging resistance were improved by further incorporating polycarbonate (PC), the ductile polymer with high glass transition temperature. On the basis of transmission electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis, the outstanding toughness and aging resistance of the 4 component alloy; e.g., PLA/PC/SEBS/EGMA = 40/40/5/5 (wt. ratio), seems to come from the negative pressure effect of SEBS that dilates the plastic matrix consisting of PLA and PC to enhance the local segment motions.

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 15 nm 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 508 mm min −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.

Various compositions of maleated ethylene-propylene-rubber (EPR-g-MA) toughened polyamide 6 without and with short glass fiber, i.e. 5–20 wt.% rubber and 5–20 wt.% fiber, are prepared using an industrial twin-screw extruder at different levels of feed rate (100–250 kg/h), screw speed (200–450 rpm) and barrel temperature (230–260 °C). Trial runs designed based on the Taguchi’s orthogonal arrays are subjected to tensile, impact, scanning electron microscopy (SEM) and optical microscopy tests; and the results are used to perform the analysis of variance (ANOVA). It is shown that the rubber particle size decreases significantly by increasing the rubber content for the unreinforced blend. The results also indicate that the composition of the compounds is the most influential factor on the phase morphology and mechanical properties of both the unreinforced and reinforced blends compared to the extrusion variables. But the processing parameters can also influence the performance characteristics slightly. The most important processing parameter, among the others, is shown to be the mixing temperature, which decreases the fiber length greatly and leads to the thermo-mechanical degradation of the polymers above 240 °C.

Rubber toughening of poly(ether imide) (PEI) has been elusive up to now due to the high processing temperature of PEI, which leads to degradation of the rubber. In this study, by profiting from the miscibility between PEI and poly(butylene terephthalate) (PBT), and the low T g of PBT, we prepared a blend by melt extrusion with 20 wt% PBT in an attempt to render it toughenable by decreasing its T g and processing temperature. The PEI-rich blend was subsequently mixed with maleic anhydride (0.9 wt%) grafted poly(ethylene-octene) copolymer (mPEO) up to 30 wt%. The decrease in T g and processing temperature resulted in no observable degradation of the mPEO, and to the formation of a homogeneous morphology of rubber particles with a fine particle size, indicating that compatibilization was achieved. Upon rubber addition, stiffness decreased, while a very large toughness increase occurred with only 15% mPEO (impact strength more than 10-fold that of the PEI–PBT matrix). Upon observation of the fracture surface, the increase in impact strength was attributed partially to the cavitation and debonding of the rubber particles, and mostly to the deformation and yielding of the PEI–PBT matrix.

This paper focuses on the use of epoxidized natural rubber (ENR) as a toughening agent for nylon 6 (PA6). Natural rubber (NR) was used to compare with ENR. Polymer blends were prepared by using a twin-screw extruder and pressing as a sheet in a compression molding machine. It was found that NR and ENR decreased yield stress and tensile strength but slightly increased elongation at break of PA6. NR slightly decreased impact strength of PA6, whereas this property increased up to sixfold by blending with ENR. This phenomenon could be explained in terms of blend morphology. Too large a particle diameter of NR was a cause of the premature failure. The impact strength of the blends increased with increasing ENR content. Rubber particle diameter also increased but was still much smaller than natural rubber particles. Phenolic resin was employed for crosslinking ENR. Compounded ENR increased tensile properties but decreased impact strength of the blends. This was because the morphology of ENR was changed from small particles to large patches of rubber after vulcanization.

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.

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.

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 3 wt% nitrile rubber, while in the last group modification was carried out by using 0.5 wt% nitrile rubber together with 1, 2, and 4 wt% 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.

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.

Syntactic foams having low-density microballoons (220–320 kg/m 3 ) have compressive strengths of 30–40 MPa and fracture strains of around 15–20%, demonstrating adequate compressive damage tolerance. However, high-strength foams (60–70 MPa), with high-density microballoons (380–460 kg/m 3 ), 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.

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 540 g/mol from industrially used monomers possessing molecular weights greater than 700 g/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 ( T g ). 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.

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.

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.

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.

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.

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 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.

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 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 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.

Dynamic mechanical measurements were carried out on rubber-toughened poly(methyl methacrylate) (RT-PMMA) under superimposed static tensile and compressive stresses, in the temperature range −40 to 10°C, which includes the glass transition of the rubber phase. Under compression, where the dynamic loss curves were very reproducible, the tan δ peak due to the rubber particles shifted to higher temperatures with increasing superimposed stress. Under tension, by contrast, the loss curves were much more variable, in some cases splitting into two peaks, and the peak temperature was no longer a function of the superimposed stress. This behaviour is consistent with incipient cavitation in a proportion of rubber particles under tensile stress. It is concluded that the transition from reproducible to variable dynamic mechanical behaviour marks the onset of cavitation in the rubber phase. The specimen-to-specimen variations observed under superimposed tension appear to be due to differences in strain distributions within and between rubber particles. The procedure provides a method for measuring the resistance of rubber particles to cavitation in response to mechanically and thermally generated stresses, and for distinguishing the cavitation event from subsequent dilatational yielding.

Carbon-fibre/polybenzoxazine composites were fabricated in order to examine the toughening effect of amine-terminated butadiene acrylonitrile rubber (ATBN) and carboxyl-terminated butadiene acrylonitrile rubber (CTBN) modifications of polybenzoxazine. The mode II delamination toughness of carbon-fibre/polybenzoxazine composites was measured as a function of rubber content. Transmission optical microscopy (TOM) and scanning electron microscopy (SEM) were used to investigate the fracture mechanism and toughening effect in the carbon-fibre/polybenzoxazine composites. Delamination toughness of the carbon-fibre/polybenzoxazine composites increased by ATBN modification as a result of the enhancement of the toughness of polybenzoxazine and interfacial bonding in the composites with increasing ATBN content. The better interfacial bonding in the ATBN-modified system induced the growth of some cracks allowing the intrinsic resin toughness to be fully extracted during composite delamination. In the case of CTBN modification, the delamination toughness of the composite was hardly increased because of the weak interfacial bonding.

We have investigated the microdeformation mechanisms in thin films and bulk samples of impact-modified PMMA over a range of experimental conditions by TEM. The extent of cavitation of the modifier particles and the competition between crazing and simple shear deformation are discussed, as well as the extent to which the thin film behaviour is representative of that of the bulk. In both cases cavitation and crazing tend to dominate at intermediate strain rates and low temperatures, but are suppressed as the strain rate is decreased and/or the temperature is raised. However, cavitation is also suppressed at impact speeds in both thin films and bulk samples tested at room temperature, this being reflected by macroscopically brittle failure via propagation of single unstable cracks/crazes across the whole sample.

The effects of morphological parameters, especially rubber particle size distribution, on the brittle ductile transition of poly(vinyl chloride) (PVC)/nitrile rubber (NBR) blends with the morphology of well-dispersed NBR particles have been studied. PVC has been supertoughened with well-dispersed NBR particles. A master curve of the brittle ductile transition of PVC/NBR blends is obtained by plotting impact strength versus average matrix ligament thickness. The relationships of critical particle size and critical rubber volume fraction to rubber particle size distribution are discussed. It is argued that rubber particle size distribution is one of the morphological parameters dominating the toughness and the toughening mechanisms of PVC/NBR blends, in addition to the average rubber particle size, rubber particle volume fraction and average matrix ligament thickness. A narrow rubber particle size distribution favours the rubber toughening of PVC.

A programme of experiments is used to test the validity of the energy-balance model for rubber particle cavitation 1,2 . The yield behaviour of a transparent grade of rubber-toughened poly(methyl methacrylate) (RTPMMA) is investigated over a range of temperatures, in tension, compression and flexure. Differences between yield in tension and yield in compression are shown to affect flexural yield behaviour, and in particular the position of the neutral plane, which shifts towards the compression surface when the material cavitates in tension. The energy-balance model is used to calculate when cavitation is energetically possible, and the experimental observations at each temperature are compared with the predictions of the model. It is found that the release of energy is a necessary but not sufficient condition for cavitation, and that a small energy barrier at small void sizes exerts a controlling influence upon the cavitation process.

Rubber toughening of a series of blends constituted by a polypropylene (PP) matrix added with talc, and modified by ethylene–propylene (EPR) and/or ethylene–butene rubber (EBR), with different molecular weights, was investigated. The fracture toughness was measured by an elasto-plastic fracture mechanics approach, applying the methodology of the essential work of fracture, and by conventional testing. It was found that: (i) EBR has a higher toughening efficiency than EPR; and (ii) the fracture toughness increases by increasing the molecular weight of the dispersed elastomeric phase. Measurements of volume change and temperature increase in specimens stretched during tensile tests indicated that the presence of EBR in the blends reduces cavitation and crazing, and induces a large amount of shear yielding. Some difference in the microcavitation mechanisms induced by each of the two elastomers was shown by electron microscopy analysis. An explanation of this behaviour on the basis of structural changes within the matrix or at the rubber–matrix interface was sought. Dynamic thermomechanical analysis indicated that EBR has a stronger interaction than EPR with the PP matrix.

Blends of d,l -lactide/glycolide copolymers were synthesized and their properties and in vitro degradation behaviour were evaluated as a function of chain architecture and blend composition. Tensile and impact properties of the blends are hardly influenced by matrix composition and chain architecture, but predominantly vary with the amount of rubber. In vitro degradation showed that hydrolytic degradation is enhanced by the incorporation of glycolide into the poly( d,l -lactide) matrix. Surprisingly, blends based on 6-arm star-shaped poly( d,l -lactide- co -glycolide) retain their mechanical properties for a longer period than blends with linear matrices of comparable composition. Physical aging of the linear copolymers is more severe and faster than that of star-shaped copolymers. © 1997 Elsevier Science Ltd.

Poly(ethylene terephthalate) (PET) was blended with up to 5% of an SEBS elastomer. The elastomer was functionalized with 0 to 4.5 wt% maleic anhydride grafted onto the ethylene-butylene midblock. Graft copolymer formed by reaction of PET hydroxyl end groups with the anhydride in situ was thought to act as an emulsifier to decrease interfacial tension and promote adhesion. All the elastomers increased the melt viscosity of PET, however the amount and functionality of the elastomer did not have a large effect on blend rheology. In contrast, particle size was strongly dependent on the elastomer functionality: the higher the functionality, the smaller the particle size and the narrower the particle size distribution. Furthermore, elastomer content had less effect on the particle size as the functionality increased, and the tendency toward increasing particle size with increasing elastomer content diminished. These trends were attributed to an increase in the degree of grafting on the in situ graft copolymer. Particles of functionalized SEBS were primarily spherical in injection moulded blends in contrast to the highly elongated particles of unfunctionalized SEBS. In un-notched tensile tests, blending PET with any SEBS elastomer enhanced the stability of the propagating neck. Notched tensile tests differentiated among the blends in terms of their toughness. The least effective elastomer was the unfunctionalized SEBS. The most effective was the SEBS with only 1 % anhydride. The decrease in toughness with increasing functionality was attributed to decreasing particle size.