Search

Polylactide (PLA) is one of the most important bioplastics worldwide and thus represents a good potential substitute for bead foams made of the fossil-based Polystyrene (PS). However, foaming of PLA comes with a few challenges. One disadvantage of commercially available PLA is its low melt strength and elongation properties, which play an important role in foaming. As a polyester, PLA is also very sensitive to thermal and hydrolytic degradation. Possibilities to overcome these disadvantages can be found in literature, but improving the properties for foaming of PLA as well as the degradation behavior during foaming have not been investigated yet. In this study, reactive extrusion on a twin-screw extruder is used to modify PLA in order to increase the melt strength and to protect it against thermal degradation and hydrolysis. PLA foams are produced in an already known process from the literature and the influence of the modifiers on the properties is estimated. The results show that it is possible to enhance the foaming properties of PLA and to protect it against hydrolysis at the same time., Deutsche Forschungsgemeinschaft

Increasing requirements are leading to new developments in bead foam materials. Engineering thermoplastics such as polybutylene terephthalate (PBT) outperform standard bead foams in thermal stability. In order to obtain molded parts, beads are fused together using steam chest molding. Classical theories for the fusion mechanism, explaining the molding of amorphous EPS (expandable polystyrene) or semi-crystalline EPP (expanded polypropylene), cannot be applied to E-PBT (expanded polybutylene terephthalate). In previous studies, sufficient time for polymer interdiffusion during molding is identified as crucial and requires adjusted crystallization kinetics. This study consequently examines to which extent the crystalline properties and the bead fusion behavior of E-PBT can be influenced by the bead foaming process. By varying the underwater granulation (UWG) water temperature, different cooling rates of the expanding melt are generated. The foamed beads show different cell morphologies, thermal and dynamic mechanical properties depending on the UWG water temperature. Those beads that show a pronounced shrinkage behavior in the thermomechanical analysis, caused by an increased open cell content and a pronounced cold-crystallization, exhibit a reduced bead fusion quality. The bead fusion quality is examined by the fracture surface. The shrinkage phenomenon causes a reduced bead to bead contact and partially separation between the beads.

Expanded polymeric beads offer the advantage of being able to produce parts with complex geometries through a consolidation process. However, established polymeric beads are made of thermoplastics, deform and melt beyond their temperature services. In this manuscript, a new technique is proposed to fabricate expandable epoxy beads (EEBs), then expand and fuse them to produce epoxy particle foams (EPFs). This technique is called solid-state carbamate foaming technique. For production of EEBs, a mixture of epoxy, carbamate and hardener is prepared and poured into a 10 mL syringe. The mixture is manually extruded into 60 °C water to obtain a cylindric shape. The extrudate is then further cured to obtain an epoxy oligomer behaving rheological tan delta 3 and 2 at 60 °C. The extrudate is cut into pellets to obtain EEBs. The EEBs are then loaded into an aluminum mold and placed in an oven at 160 °C to expand, fuse to obtain EPFs of 212 kg/m3 and 258 kg/m3. The obtained EPFs provide a Tg of 150–154 °C. The fusion boundaries in EPFs are well formed. Thus, the produced EPFs exhibit a compressive modulus of 50–70 MPa, with a torsion storage modulus at 30 °C of 34–56 MPa.

Environmental stress cracking (ESC) is one of the most prominent failure mechanisms for polymer components. The high sensitivity of plastics in regard to environmental influences has always meant that plastics as materials have been viewed very critically in outdoor applications. Recently, the massive occurrence of microplastics in the environment means that questions about the long-term stability of plastic parts and the studies of plastic fragmentation are of great scientific interest. ESC behavior also plays an important role in connection with the formation of microplastics. In this work, the influence of two different sample wetting methods on ESC behavior was investigated. In case A, the sample was in situ wetted with the medium during the measurement by using a sponge. In case B, the sample was wetted by storage in the medium prior to measurement. Different stress cracking agents (SCA) were examined for polymethylmethacrylate (PMMA). Fracture-mechanical fatigue crack propagation (FCP) tests were carried out to quantitatively determine the sensitivity to ESC. Correlations between the absorption behavior and the ESC behavior of the SCA and the resulting morphological phenomena were established. Depending on the wetting method, significant differences in FCP were observed. The in situ wetting of the samples (case A) during the FCP measurement with ethylene glycol (EG) and with deionized water (DI) led to a significant shift in the crack propagation curves to higher ∆K—compared to the PMMA reference. In the case of n-heptane (NH), a more brittle crack propagation behavior was observed due to the chemical interaction with PMMA. The previously immersed samples (case B) give different results. Storage in NH and EG showed no influence on the crack propagation behavior. Samples immersed in DI showed a completely different course of crack growth. At a certain load, a sudden deceleration of the crack propagation and thus a horizontal curve could be seen. Above a certain ∆K value, crack growth began again. Depending on the immersion time (14, 30, or 60 days), this so-called stepped behavior shifted to lower da/dN values.

Expandable polystyrene (EPS) and expanded polypropylene (EPP) dominate the bead foam market. As the low thermal performance of EPS and EPP limits application at elevated temperatures novel solutions such as expanded polybutylene terephthalate (E-PBT) are gaining importance. To produce parts, individual beads are typically molded by hot steam. While molding of EPP is well-understood and related to two distinct melting temperatures, the mechanisms of E-PBT are different. E-PBT shows only one melting peak and can surprisingly only be molded when adding chain extender (CE). This publication therefore aims to understand the impact of thermal properties of E-PBT on its molding behavior. Detailed differential scanning calorimetry was performed on neat and chain extended E-PBT. The crystallinity of the outer layer and center of the bead was similar. Thus, a former hypothesis that a completely amorphous bead layer enables molding, was discarded. However, the incorporation of CE remarkably reduces the crystallization and re-crystallization rate. As a consequence, the time available for interdiffusion of chains across neighboring beads increases and facilitates crystallization across the bead interface. For E-PBT bead foams, it is concluded that sufficient time for polymer interdiffusion during molding is crucial and requires adjusted crystallization kinetics.

The use of amine-based carbamates with their dual function, acting as amine curing agents and CO2 blowing agents after their decomposition without by-products, are promising for ecofriendly epoxy foams as high-performance materials. However, controlling cell morphology requires a proper adjustment of the viscosity at the foaming step. The viscosity is altered not only by blending neat amine and its derived carbamate at a fixed pre-curing time, but also by changing the pre-curing time at a fixed blend ratio. Within this study, diglycidylether of bisphenol A (DGEBA) epoxy resin is mixed with different blend ratios of isophorone diamine (IPDA) and its derived carbamate (B-IPDA). The systems are characterized by DSC and rheology experiments to identify the pre-curing effects on the derived epoxy foams. Epoxy foams at a blend ratio of 30/70w IPDA/B-IPDA showed the best foam morphology and an optimum Tg compared to other blend ratios. Furthermore, it was found that both pre-curing times, 2 h and 3 h, for the 30/70w IPDA/B-IPDA system reveal a more homogeneous cell structure. The study proves that the blending of neat amine and carbamate is beneficial for the foaming performance of carbamate systems.

With macroscopic litter and its degradation into secondary microplastic as a major source of environmental pollution, one key challenge is understanding the pathways from macro- to microplastic by abiotic and biotic environmental impact. So far, little is known about the impact of biota on material properties. This study focuses on recycled, bottle-grade poly(ethylene terephthalate) (r-PET) and the degrading enzyme PETase from Ideonella sakaiensis. Compact tension (CT) specimens were incubated in an enzymatic solution and thermally and mechanically characterized. A time-dependent study up to 96 h revealed the formation of steadily growing colloidal structures. After 96 h incubation, high amounts of BHET dimer were found in a near-surface layer, affecting crack propagation and leading to faster material failure. The results of this pilot study show that enzymatic activity accelerates embrittlement and favors fragmentation. We conclude that PET-degrading enzymes must be viewed as a potentially relevant acceleration factor in macroplastic degradation.

In this study, an empirical correlation between the tack of phenolic prepregs and the rheological state of the base resin was established. Multivariable analyses were carried out to investigate the determining mechanisms of the prepreg tack along with the temperature- and time-dependent state of the resin. The material storage stability in terms of the degree of cure (DoC) was monitored within 150 days. Furthermore, the DoC at gelation was determined so discussion could be made over the morphological state of the base resin. Rheological properties of the resin such as storage and loss moduli were evaluated as a function of the DoC and temperature, thus describing the flow and cohesive behaviour towards the final prepreg tackiness. A maximum tack plateau was found when conditions of ageing and temperature were balanced within a suitable viscosity and DoC range. Indicators suggest that the interaction between resin and filler effectively changes the resin viscosity, therefore regulating the prepreg tackiness level. For the first time, inherent phenolic resin properties were thoroughly determined by systematically varying the conversion state and operating temperature, in order to gain an in-depth understanding of the effects on the final composite tack property.

Reactive compounding of terminally phenolic OH-functionalized polycarbonate (PC) with epoxy-functionalized polymethylmethacrylate (PMMA) prepared by copolymerization with glycidyl methacrylate was investigated. It was spectroscopically demonstrated that a PC/PMMA copolymer was formed during the melt reaction of the functional groups. Zirconium acetylacetonate could catalytically accelerate this reaction. Correlations of the phenomenological (optical and mechanical) properties with the molecular level and mesoscopic (morphological) structure were discussed. By the investigated reactive compounding process, transparent PC/PMMA blends with two-phase morphologies were obtained in a continuous twin-screw extruder, which, for the first time, combined the high transmission of visible light with excellent mechanical performance (e.g., synergistically improved tensile and flexural strength and high scratch resistance). The transparency strongly depended on (a) the degree of functionalization in both PC and PMMA, (b) the presence of the catalyst, and (c) the residence time of the compounding process. The in-situ-formed PC/PMMA copolymer influenced the observed macroscopic properties by (a) a decrease in the interphase tension, leading to improved and stabilized phase dispersion, (b) the formation of a continuous gradient of the polymer composition and thus of the optical refractive indices in a diffuse mesoscopic interphase layer separating the PC and PMMA phases, and (c) an increase in the phase adhesion between PC and PMMA due to mechanical polymer chain entanglement in this interphase.

The aging behavior of a fast-curing epoxy resin (EP) was examined over three months in unidirectional carbon fiber prepregs for the first time. The semi-latent, 120 °C curing one-pot formulation was developed based on industry-grade diglycidyl ether of bisphenol A (DGEBA) resins without the necessity of B-staging, to fully monitor the property change by aging without any post-processing influence. To extend the shelf-life compared to standard wet EP systems, the latent dicyandiamide (DICY) and a semi-latent urea-based catalyst were used, leading to full conversion within 15 min. The conversion was monitored by increasing Tg0 and rheology. High quality unidirectional carbon prepregs were manufactured and then investigated over three months regarding tackiness and resin flow. In parallel, laminates were autoclave-manufactured to evaluate the aging influence on the interlaminar properties. Thus, a correlation between decreasing gel-time, interlaminar adhesion and resulting multiple crack growth was observed via GIC and interlaminar shear strength (ILSS) testing. The investigations show a clear influence of the consolidation quality of the prepregs based on ILSS values and GIC values. A decrease of 19% in ILSS and combined with an erroneous increase of 63% of the GIC due to multiple delamination was observed in the worst case.

Multi-wall carbon nanotubes were dispersed homogeneously throughout a poly(ether ether ketone) matrix by melt processing. The influence of nanotube content on both rheological and electrical properties was analysed. The dynamic storage modulus, G ′ , shows a characteristic solid-like behavior above 1 wt% nanotubes. A sharp transition from an electrically insulating to a conductive composite was observed between 1 and 1.5 wt%. By applying a power-law relation, the rheological and electrical percolation thresholds were found to be 0.9 wt%, and 1.3 wt%, respectively. Considering this data, Guth’s filler reinforcement theory provides a valuable estimation of the aspect ratio of the nanotubes after processing and indicates substantial length degradation during the dispersion process.

BACKGROUND: Charge storage capability is a fundamental property of polymers used in electromechanical transducer applications. In this work, the charge retention of ternary blends of poly(phenylene ether) and polystyrene modified with poly(styrene-co-acrylonitrile), polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene or polystyrene-block-polyisobutylene-block-polystyrene (SIBS) triblock copolymers was correlated with the blend composition, final morphology and the chemical structure of the components. RESULTS: It was determined that the charge storage capability is favoured by a finely dispersed and non-interconnected phase and can be reduced by high polarity or low molecular weight of the blend components. Additionally, the molecular weight and the amount of styrene of the copolymers also determined the phase morphology, which in turn affected the charge retention. The use of SIBS for the ternary blends, especially in small quantities, significantly improved the charge storage. As such, 100 µm films with a surface potential of about 400 V were able to retain up to 240 V (60%) after 24 h at 130 °C. CONCLUSION: The electret behaviour of the polymer blends was influenced by a complex relationship between chemical structure, molecular weight and phase morphology. Copyright © 2009 Society of Chemical Industry

Immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) were batch-foamed using CO2 as a blowing agent as a function of foaming temperature, foaming time, and blend composition. Evaluation of the resulting cellular morphology revealed an enhanced foamability of SAN with PPE contents up to 20 wt% as indicated by a similar volume expansion but a significantly reduced mean cell size. This behavior is related to a heterogeneous nucleation activity by the dispersed PPE phase. A further increasing PPE content, however, leads to increasing foam densities as well as nonuniform foam morphologies. The changes in the foaming behavior can be correlated with the melt rheological properties and the corresponding blend morphology. Shear-rheological investigations revealed an onset of percolation of the dispersed PPE phase between 20 and 40 wt%, and a transition towards cocontinuity at 60 wt%. The materials response under uniaxial elongational flow, as assessed by Rheotens measurements, revealed an increase in elongational viscosity scaling with the PPE content, similar to the shear data. However, the strain hardening behavior was reduced by increasing PPE contents and, at 20 wt%, the drawability revealed a significant drop-both phenomena limiting the foamability of polymers. In summary, the present study discusses fundamental aspects of foaming immiscible PPE/SAN blends. POLYM. ENG. SCI., 48:2111–2125, 2008. © 2008 Society of Plastics Engineers

The potential of fatigue crack growth experiments to sensitively analyze the anisotropic mechanical behavior of injection-molded, multiphase polymer blends is presented. The properties of immiscible blends based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) is investigated, both in perpendicular and in parallel to the injection-direction. As a result of the limited interfacial adhesion and the orientation of the blend phases, the direction in parallel to flow revealed to be the weaker link. In order to enhance the toughness behavior, the PPE/SAN blends were systematically modified by the addition of different polystyrene-b-polybutadiene-b-poly(methyl methacrylate) triblock terpolymers (SBM), potentially acting as a compatibilizing and toughening agent. Such a compatibilization step of PPE/SAN blend leads to the formation of nanostructured morphologies. Depending on the composition of the triblock terpolymer, the resistance to crack growth was either further degraded or, in the case of high interfacial presence and compatibilization efficiency, significantly improved. The results were correlated to the fracture mechanisms of the blends as analyzed by scanning electron microscopy of the fracture surfaces. In contrast to poorly-compatibilized blends, a significant plastic deformation, an enhanced phase adhesion and a strongly reduced anisotropy could be detected in case of well-compatibilized blends. In summary, the presented study of the fatigue crack growth behavior revealed a detailed insight into the mechanical property profile of the selected multiphase blends and, moreover, demonstrated the potential of this method to sensitively analyze the anisotropy of such materials.

Due to the establishment of common thermoplastics such as polyethylene, polypropylene and polytetrafluoroethylene as substrates for modern electrets, research in this field has seen significant progress in recent decades. However, there still is a need for new substrate materials in order to boost modern-day electret applications. Important targets for a further development are electret substrates with a tailored balance between cost and performance especially at elevated temperatures. In this study, experimental results concerning the charge storage behaviour of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) films and its blends with polystyrene (PS) are presented. As demonstrated, the good electret performance of neat PPE can be further enhanced by the addition of suitable weight fractions of PS, a synergistic electret behaviour that is related to morphological blend parameters such as the packaging density and the presence of PS micro-heterogeneities in the PPE/PS matrix. Most importantly, the results highlighted in this study clearly demonstrate the potential of blending as a promising approach towards satisfying the demands of tomorrows’ electret applications.

The mechanical performance of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) and the subsequent influence of compatibilisation by tailored polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) on the mechanical performance under static and dynamic loads is analysed in detail. A PPE/SAN 60/40 blend was selected as a base system for the compatibilisation experiments. The observed static tensile behaviour is described by micromechanical models and correlated to the blend microstructures as observed by transmission electron microscopy. In most cases, the addition of the SBM triblock terpolymers further enhances the ductility of the blend while only leading to a minor reduction of modulus and strength. Triblock terpolymers with symmetric end blocks, mainly located at the interface between PPE and SAN, led to nearly isotropic specimens. In contrast, SBM materials with a longer polystyrene block predominantly formed micelles in the PPE phase and the blends revealed a highly anisotropic morphology. Comparative investigations of the fatigue crack growth behaviour parallel to the direction of injection also reflected this variation in mechanical anisotropy of the compatibilised blends. A poor toughness and a predominant interfacial failure were observed in the case of the SBM with a long polystyrene block. In contrast, a considerable improvement in properties as a result of pronounced plastic deformations was observed for blends compatibilised by triblock terpolymers with symmetric end blocks. The systematic correlation between morphology and mechanical performance of compatibilised PPE/SAN blends established in this study provides an efficient way for the desired selection of suitable and effective compatibilising agents, ensuring both a superior multiaxial toughness as well as a high strength and modulus of the overall system.

There is enormous scientific and economic interest in the development and evaluation of polymer nanocomposites due to the fact that the properties of a material become increasingly insensitive to flaws at the nanoscale, enabling the exploitation of the unique physical and mechanical properties of very small objects in large-scale components. However, the successful industrial implementation of such novel materials poses unique challenges which are not only related to the small size of the reinforcements. Decades of intensive research have shown that polymer nanocomposites differ from their counterparts based on traditional reinforcements in many ways and a fundamental understanding of the structure-propertyrelationships of such novel materials is only slowly emerging. Although issues such as the intrinsic properties of the nanoscale constituent as well as the degree of dispersion and orientation of individual filler particles clearly appear to be important factors, molecular interactions between the filler and the matrix during processing can lead to pronounced variations in the matrix microstructure. These variations in themselves lead to pronounced changes in the micro- and macromechanical deformation behaviour of the nanocomposites. A detailed investigation of fatigue crack growth behaviour of such novel materials for example is essential in order to understand the fracture mechanical performance and the transition from a ductile to a brittle behaviour which is often observed experimentally, especially in the case of amorphous matrices. However, as the size of the filler particles approaches the molecular level, the novel interactions at the interface or even in the interphase can lead to significant changes in the micromechanical deformation behaviour. Significant work has been carried out regarding the fracture mechanical investigation of polymer blends with both micro- and nanoscale morphologies and much can be learned by comparing the results of polymer nanocomposites to these more established polymer blends.

Carbon nanofibre (CNF)-reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites containing up to 10 wt % of nanofibres were prepared by a novel solvent-assisted extrusion process using short chain oligomers to tailor the melt viscosity of the UHMWPE matrix. A detailed investigation of the resulting nanocomposite microstructure and of the static mechanical properties revealed that the carbon nanofibres lead to improved mechanical properties of the UHMWPE related to the wear performance of such systems. Unidirectional sliding tests against a 100Cr6 steel under dry conditions verified the significant potential of dispersed carbon nanofibres to reduce the wear rate of this polymer. In light of the promising results, a further optimization of the processing conditions of such UHMWPE nanocomposites is expected to yield interesting future nanocomposite materials even for demanding applications such as artificial knee implants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4173–4181, 2007

Immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) with a weight composition of 60/40 were compatibilised by polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) using a two-stage melt-processing approach. In order to investigate the influence of the SBM composition on the compatibilisation efficiency, the block lengths of the triblock terpolymers were systematically varied. The resulting morphological features of the blend systems as function of SBM composition and processing parameters are correlated with the resulting thermal and thermo-mechanical properties. In the ideal case, SBM should be located at the interface as PS is miscible with PPE while PMMA is miscible with SAN. The elastomeric middle block as an immiscible component should remain at the interface. This particular morphological arrangement is known as the ‘raspberry morphology’. A detailed TEM analysis of the blend morphologies following initial extrusion-compounding revealed a high compatibilisation efficiency of the SBM types with equal lengths of the end blocks and, furthermore, the desired raspberry morphology was achieved. In contrast, high PS contents in comparison to the other blocks led to a pronounced micelle formation in the PPE phase. Further evaluation of the blend structures following injection-moulding indicated that the morphologies remain relatively stable during this second melt-processing step. A detailed thermal analysis of all blend systems supports the interpretation of the observed morphological features. The fundamental correlation between SBM composition and blend morphology established in this study opens the door for the controlled development of interfacial properties of such compatibilised PPE/SAN blends during melt-processing.

In the context of establishing novel polymer nanocomposites for successful industrial use, this chapter is aimed at providing a fundamental overview of comprehensive research regarding carbon nanofiber (CNF)-reinforced poly(ether ether ketone) (PEEK) composites for demanding tribological applications. Following a summary overview describing the potential of nanoscale additives for tribological systems in general, the intrinsic structure–property relationships of CNFs are discussed in order to set the frame for the subsequent experimental results regarding their use in PEEK. As demonstrated, successful PEEK–nanofiber composites have been developed, showing a clear enhancement in mechanical properties while minimizing other detrimental effects commonly observed with such nanocomposites. These nanocomposites also reveal a significant beneficial effect on the wear behavior of PEEK under dry sliding conditions. In addition to relating the observed enhancements in the tribological performance to the underlying microstructures and properties of the nanocomposites, evidence for a further optimization of such systems by combining the nanoscale filler with conventional tribological additives and reinforcements such as carbon fibers is provided. Lastly, based on the promising results regarding the wear behavior of such hybrid systems, the performance of advanced nanocomposite hybrid materials for an intended industrial tribological application is introduced and discussed.

Foaming of multiphase blend systems can be identified as a promising approach to satisfy the steadily growing demand for cellular materials with enhanced properties. However, combining the sophisticated fields of polymer blends and polymer foams not only offers great chances, but also poses a significant challenge, as the multiphase characteristics of blends and the complexity of foam processing need to be taken into account. Therefore, the foaming behavior of polymer blends is systematically analyzed, correlating the blend structure and the physical characteristics of reference systems to their foam processability and resulting foam morphology. The cellular materials are prepared via batch-foam processing, using carbon dioxide as a blowing agent. Starting with an immiscible poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) blend, pathways to tailor the foaming behavior via controlling the micro- and nanostructure of such blends are developed; strategies aiming at reducing the cell size, enhancing the foam homogeneity, and improving the density reduction. As a result of adjusting the blend structure over multiple length scales, cooperative foaming of all blend phases and cell sizes down to several hundred nanometers can be achieved. In the light of the results presented, a general understanding of foaming multiphase blends is developed and guidelines for the selection of blend systems suitable for foaming can be deduced.

The microstructure of melt-processed, immiscible poly(2,6-dimethyl-1,4- phenylene ether)/poly(styrene-co-acrylonitrile) blends (PPE/SAN) was controlled by systematically adjusting the viscosity ratio between both phases. For this purpose, low-viscous polystyrene (PS) was added as a third component, as it shows selective miscibility with PPE and thus allows the varying of the shear viscosity of PPE over a broad range. In order to theoretically predict the phase morphology, a model following Utracki was applied taking into account the viscosity ratio and the respective volume contents of each phase. Detailed transmission electron microscopic investigations of the blend morphologies demonstrated excellent agreement with theory. Moreover, quantitative evaluation of the observed microstructures allowed further description of the degree of blend co-continuity. Thus, desirable compositions of the ternary blend systems could be identified which potentially show enhanced properties such as a high heat deflection temperature, an elevated strength, stiffness, and ease of processing. Finally, a optimum (PPE/PS)/SAN blend system that has been optimised regarding the aforementioned properties was compatibilized by polystyrene-b-poly(1,4-butadiene)-b-poly(methyl methacrylate) triblock terpolymers. Due to the interfacial enrichment of the block copolymer, nanostructured blend morphologies were observed. In the view of these results, pathways to control both the micro- and the nanostructure of PPE/SAN blends are derived, potentially useful to enhance the mechanical as well as thermomechanical property profile.

The foaming behaviour of polymer blends was systematically investigated using carbon dioxide as a blowing agent. Two batch-processing techniques were used to prepare specimens of different size. Various binary mixtures over a wide compositional range were selected as reference materials, in particular including immiscible (poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) blends. Moreover, the influence of a compatibilization with block copolymers was investigated for PPE/SAN blends. The resulting foam morphology was characterised by evaluating the density, the cell size distribution, the cell wall morphology and the compression behaviour. Besides the commonly accepted key criteria for foaming neat polymers, our study identified significant factors determining the foamability of blends such as the blend morphology, the rheological and the thermal properties. Interestingly, the compatibilization of these PPE/SAN blends by block copolymers was identified as a technique to establish micro- and submicrocellular foam morphologies with nanostructured cell walls. In view of these results, new pathways for the tailoring of cellular materials are derived.