465 research outputs found

    Theoretical evaluation of the melting efficiency for the single-screw micro-extrusion process : the case of 3D printing of ABS

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    One of the challenges for single-screw micro-extrusion or additive manufacturing (AM), thus 3D printing, of polymers is controlling the melting efficiency so that energy and equipment costs can be minimized. Here, a numerical model is presented for AM process design, selecting acrylonitrile-butadiene-styrene (ABS) as viscoelastic reference polymer. It is demonstrated that AM melting is different compared to conventional melting due to variation in extrusion dimensions, leading to a different balance in heating by conduction and viscous heat dissipation as caused by the shearing between the melt layers in the associated film layer near the barrel. The thickness of this melt film layer is variable along the screw length, and it is shown that simplified models assuming an overall average value are too approximate. It is highlighted that the screw frequency, pitch angle and compression ratio are important process parameters to control the point of melt finalization. In addition, the power-law index reflecting the shear thinning nature of the polymer melt is showcased as a key parameter. Moreover, AM process results assuming constant and temperature dependent specific heat capacities and thermal conductivities are compared. The current work opens the door for on-line AM process control, addressing all relevant operating and material parameters

    The compounding of short fibre reinforced thermoplastic composites

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    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique

    Modelling of flow and heat transfer, mixing and morphology development in plasticating single screw extrusion of polymer systems

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    Models for flow and heat transfer, morphology development of liquid-liquid and solids-liquid systems and mixing assessment in conventional single screw estruders are introduced. Their computer implementation and interdependence are explained. Representative predictions are discussed with the aim of illustrating the capability of these models as wells as showing the typical response of single screw extruders

    Characterization of dispersive and distributive mixing in a co-rotating twin-screw compounding extruder

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    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A new design of closely intermeshing co-rotating twin-screw compounding extruder, developed at Brunel University, has been utilized in the development of quantitative techniques for characterization of dispersive and distributive mixing in thermoplastics materials prepared by extrusion compounding. Image analysis procedures were used to quantify mixing of polypropylene composites containing calcium carbonate filler using reflected light microscopy on polished surfaces, and transmitted light microscopy of microtomed pigmented sections. Stereological statistics have been applied to raw sample data; results are discussed in relation to mechanistic phenomena influencing particle agglomeration, dispersion and distribution of fillers in thermoplastics. Dispersive or intensive mixing determined from calcium carbonate filled polypropylene specimens showed that processing parameters had no significant influence except when filler was added midway along the machine although the melting zone was highlighted as having a marked effect on the rate of filler dispersion. Premixing of filler and polymer introduced additional agglomeration into the filler. A series of model experiments were undertaken to assess the influence of specific parameters. In this context moisture content emerged as having the single most important effect on filler compaction. Distributive or extensive mixing of carbon black pigmented specimens was very significantly affected by the presence of segmented disc elements at the end of the screws. These elements produced more than a six-fold increase in distributive mixing in the extrudate.Polymer Engineering Directorate of the Science and Engineering Research Council; Croxton and Garry Ltd

    Chemistry, morphology and rheology evolution along the extruder

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    Tese de Doutoramento em Ciência e Engenharia de Polímeros.In this work an investigation of the evolution of physico-chemical phenomena along a co-rotating twin-screw extruder was carried out in order to enhance the understanding of reactive extrusion. A new sampling device, which allows the collection in a few seconds of small amounts of material from the melt during processing, was tested using a reactive system and an immiscible blend. PA-6/EPM blending and SMA imidation experiments are reported in terms of morphology development and evolution of the chemical conversion along the extruder, respectively. Comparison of the results obtained using the new sampling technique with those of classical screw pulling experiments evidenced the potential erroneous conclusions than can be drawn from the latter. Subsequently, a number of these sampling devices was used at various locations of the extruder to study in more detail polyolefin modification and compatibilization of blends of polyamide-6 and MA-containing polymers. Polyolefin modification (degradation, crosslinking and grafting of MA) along the extruder axis was investigated. The main conclusions are that the degree of branching/crosslinking and/or degradation depends on the ethene/propene ratio, on the original polymer molecular weight and on the amount of peroxide added. A similar evolution of the MA grafting content for PE, EPM and PP was observed, but the final MA contents were different. A good correlation between MA grafting and peroxide decomposition was established. The MA graft content is low for polyolefins with high propene content, increases as the propene content decreases and reaches a plateau at propene levels below 50 wt.%. Branching/crosslinking occurs for polyolefins with low propene content, while degradation is the main side reaction for polyolefins with high propene content. A detailed chemical mechanism is proposed in order to explain these results. Since one of the main applications of maleated polyolefins is their use as compatibilizers for polymers blends, the development of chemistry, morphology and rheology of blends of PA-6 and MA containing polymers was studied. The chemical conversion and morphological evolution of PA-6/EPM/EPM-g-MA blends were monitored along the extruder. The results show that the MA content of the MA containing polymer in all blends decreases drastically in the first zone of the extruder, i.e., upon melting of the blend components. Dramatic changes in morphology are also observed in this stage. The processing conditions, particularly temperature profile and screw speed, affect both the chemical conversion and the morphological evolution. Using low temperatures and low screw speeds it became possible to observe in real time the evolution of morphology development of a reactive blend.Como uma das aplicações principais das poliolefinas modificadas com MA é o seu uso como compatibilizadores em misturas de polímeros, foi realizado um estudo sobre desenvolvimento químico, morfológico e reológico de misturas de PA-6 e polímeros que contêm MA. A conversão química e a evolução morfológica de misturas de PA-6/EPM/EPM-g-MA foram monitorizadas ao longo da extrusora. Os resultados mostraram que em todas as misturas a quantidade de MA dos polímeros que contêm MA diminui drasticamente na primeira zona da extrusora, i.e., durante a fusão dos componentes da mistura. Durante esta fase observam-se alterações drásticas de morfologia. As condições de processamento, particularmente perfil de temperatura e velocidade de rotação dos fusos, afecta a conversão química e a evolução da morfologia. A observação da evolução do desenvolvimento da morfologia para uma mistura reactiva foi possível utilizando baixas temperaturas e baixas velocidades de rotação dos fusos. Como uma das aplicações principais das poliolefinas modificadas com MA é o seu uso como compatibilizadores em misturas de polímeros, foi realizado um estudo sobre desenvolvimento químico, morfológico e reológico de misturas de PA-6 e polímeros que contêm MA. A conversão química e a evolução morfológica de misturas de PA-6/EPM/EPM-g-MA foram monitorizadas ao longo da extrusora. Os resultados mostraram que em todas as misturas a quantidade de MA dos polímeros que contêm MA diminui drasticamente na primeira zona da extrusora, i.e., durante a fusão dos componentes da mistura. Durante esta fase observam-se alterações drásticas de morfologia. As condições de processamento, particularmente perfil de temperatura e velocidade de rotação dos fusos, afecta a conversão química e a evolução da morfologia. A observação da evolução do desenvolvimento da morfologia para uma mistura reactiva foi possível utilizando baixas temperaturas e baixas velocidades de rotação dos fusos. Como uma das aplicações principais das poliolefinas modificadas com MA é o seu uso como compatibilizadores em misturas de polímeros, foi realizado um estudo sobre desenvolvimento químico, morfológico e reológico de misturas de PA-6 e polímeros que contêm MA. A conversão química e a evolução morfológica de misturas de PA-6/EPM/EPM-g-MA foram monitorizadas ao longo da extrusora. Os resultados mostraram que em todas as misturas a quantidade de MA dos polímeros que contêm MA diminui drasticamente na primeira zona da extrusora, i.e., durante a fusão dos componentes da mistura. Durante esta fase observam-se alterações drásticas de morfologia. As condições de processamento, particularmente perfil de temperatura e velocidade de rotação dos fusos, afecta a conversão química e a evolução da morfologia. A observação da evolução do desenvolvimento da morfologia para uma mistura reactiva foi possível utilizando baixas temperaturas e baixas velocidades de rotação dos fusos. Como uma das aplicações principais das poliolefinas modificadas com MA é o seu uso como compatibilizadores em misturas de polímeros, foi realizado um estudo sobre desenvolvimento químico, morfológico e reológico de misturas de PA-6 e polímeros que contêm MA. A conversão química e a evolução morfológica de misturas de PA-6/EPM/EPM-g-MA foram monitorizadas ao longo da extrusora. Os resultados mostraram que em todas as misturas a quantidade de MA dos polímeros que contêm MA diminui drasticamente na primeira zona da extrusora, i.e., durante a fusão dos componentes da mistura. Durante esta fase observam-se alterações drásticas de morfologia. As condições de processamento, particularmente perfil de temperatura e velocidade de rotação dos fusos, afecta a conversão química e a evolução da morfologia. A observação da evolução do desenvolvimento da morfologia para uma mistura reactiva foi possível utilizando baixas temperaturas e baixas velocidades de rotação dos fusos

    Novel Application of Twin Screw Extruder on Production of Diverse Formulations

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    Twin-screw extruder has attracted considerable attention in the pharmaceutical industry as an alternative processing instrument due to its advantages compared to other conventional equipment, such as economical processing, small footprint, reduced in-process times, solvent-free and continuous processing. These superiorities have led to the application of twin-screw extruder to produce numerous dosage forms, including pellets, tablets and films. Many other formulations production can also be beneficial from the introduction of twin-screw extruder to the process. Nanocrystal formulations are promising drug delivery systems owing to their ability to enhance the bioavailability and maintain the stability of poorly water-soluble drugs. However, conventional methods of preparing nanocrystal formulations, such as spray drying and freeze-drying, have some drawbacks, including high cost, time and energy inefficiency, traces of residual solvent. In this study, twin-screw extruder was combined with high pressure homogenizer to successfully produce nanocrystal solid dispersions (NCSDs). The process could successfully overcome the limitation of conventional methods. Dry granulation process is necessary for some moisture sensitive APIs. However, the widely applied dry granulation technologies, slugging and roller compaction, have some limitations: single batch operation, low manufacturing throughput, high amounts of fines and dust, inferior tensile strength of final tablet and loud operation. The previously unreported study of applying twin screw extruder to the dry granulation process was successfully conducted. The continuous processing nature, simplicity of operation and easiness of optimization made (twin-screw dry granulation) TSDG quite competitive compared to other conventional dry granulation techniques. Kollidon® SR is a polyvinyl acetate (PVAc) and polyvinyl pyrrolidone (PVP) based polymer. The plastic PVAc and sticky PVP make Kollidon® SR an extraordinary option for direct compression of high hardness and low friability tablet. In addition, the low glass transition temperature (Tg) of about 35 oC should make Kollidon® SR a perfect candidate for twin screw extruder. But this application is rarely reported. This study demonstrated Kollidon® SR could be successfully processed by twin-screw extruder to produce tablets, which is compared to the direct compressed counterpart. The physicochemical properties of both products were analyzed. The drug release mechanism was determined

    Evaluation of particle and fibre degradation during processing of wood plastic composites (WPC) using dynamic image analysis

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    Die vorliegende Arbeit wurde im Rahmen des DFG Graduiertenkollegs 1703 „Ressourceneffizienz in Unternehmensnetzwerken – Methoden zur betrieblichen und überbetrieblichen Planung für die Nutzung erneuerbarer Rohstoffe“ durchgeführt. Es wurde der Einfluss verschiedener Prozessparameter auf die Morphologie der Holzkomponente von Holz-Kunststoff-Kompositen (Wood Plastic Composites – WPC) untersucht. Die Ergebnisse wurden bereits anderswo publiziert bzw. zur Publikation eingereicht (insgesamt vier Publikationen) und werden innerhalb individueller Kapitel der vorliegenden Arbeit wiedergegeben. WPC vereinen die Eigenschaften von Holz als Füllstoff mit den Eigenschaften von Polymeren als Matrixmaterial. Aktuelle Literatur und Forschungsarbeiten wurden gesichtet, um Möglichkeiten zu identifizieren, wie WPC zu einer effizienten Ressourcennutzung beitragen kann. Die Ergebnisse zeigen, dass eine Vielzahl von Abfall- und Nebenprodukten aus Holz- und Agrarwirtschaft zur Herstellung von WPC verwendet werden kann, z.B. Sägespäne, Reststoffe aus der Plattenproduktion und Schlämme aus der Faserstoffproduktion. Darüber hinaus können auch Kunststoff-Rezyklate und Biokunststoffe als Rohstoff dienen. Für die Eigenschaften von WPC spielt die Morphologie der Holzkomponente – Fasern oder Partikel – eine entscheidende Rolle. Während der Verarbeitung von WPC treten hohe Temperaturen und Scherkräfte auf, welche zur Zerkleinerung der Holzkomponente führen. Um die Zerkleinerung während der Verarbeitung analysieren zu können, wurde die Eignung der Partikel¬charakterisierung mittels dynamischer Bildanalyse zur Größenbestimmung von WPC-Füllstoffen geprüft. Dafür wurden Holzpartikel aus der Polymermatrix gelöst und ihre Morphologie vor und nach der Verarbeitung verglichen. Es zeigte sich, dass eine Auswertung bezüglich der längenbasierten Größenverteilung am besten geeignet ist, um Prozess-Effekte zu analysieren, da Partikel an beiden Enden der Größenverteilung gut abgebildet werden. Die Effekte von Prozessparametern wie Holzanteil, Beschickungsmethode, Vorwärmen des Holzes, Polymerviskosität, Rotor-/Schneckendrehzahl, Förderrate und Schneckenkonfiguration auf die Holzzerkleinerung wurden untersucht. Dazu wurden Fichtenholz-Partikel (Picea abies) entweder unter Verwendung eines Innenmischers oder eines Doppelschnecken-Extruders mit Polypropylen (PP) compoundiert. Zur Bestimmung des Einflusses der Polymerviskosität wurden verschiedene Sorten PP und schwachverzweigtes Polyethylen (HDPE) verwendet, welche sich in ihrem Schmelzflussindex (melt flow rate – MFR) unterscheiden. Nach dem Compoundieren betrug die Partikelgröße nur noch < 3 % der ursprünglichen Größe. Bei den PP-Kompositen nahm die Partikelzerkleinerung sowohl im Innenmischer als auch im Extruder mit zunehmendem Holzanteil zu. Auch eine zunehmende Anzahl an Knetelementen im Schneckenprofil führte zu einer stärkeren Partikelzerstörung. Bei den HDPE-Kompositen war der Einfluss des Holzanteils nur gering. Wurden die Holzpartikel und das Polymer dem Prozess gleichzeitig zugeführt, war die Partikelzerstörung intensiver als wenn die Partikel dem bereits geschmolzenen Polymer zugegeben wurden. Auch ein Vorwärmen der Partikel führte zu einer stärkeren Zerkleinerung. Die Zerkleinerung konnte unter Verwendung eines Matrixpolymers mit hohem MFR reduziert werden. Zum einen variierte der Einfluss der Förderrate mit der Schneckendrehzahl, zum anderen variierte der Einfluss von Förderrate und Schneckendrehzahl auch mit dem Holzanteil. Da die Bedingungen des Compoundierprozesses im Labormaßstab üblicherweise nicht mit Bedingungen im Industriemaßstab vergleichbar sind, wurden die Prozessparameter an einem Labor-Extruder so gewählt, dass sie industrielle Bedingungen imitieren. Die Einkürzung von Kiefernholzfasern (Pinus radiata) wurde mit der Einkürzung von Glasfasern verglichen, da diese ein Standardmaterial in der industriellen Kompositfertigung darstellen. Mittels sogenannter „Dead-stop“-Versuche und Probennahme entlang der Extruderschnecken wurde der Einfluss von Schneckenkonfiguration, Schneckendrehzahl und Förderrate analysiert. Prozesseinstellungen, die einen geringeren Anteil an spezifischer mechanischer Energie ins Material eintrugen, sowie eine schonende Schneckenkonfiguration verzögerten die Fasereinkürzung entlang der Extruderschnecken. Für eingangs längere Glasfasern war dieser Effekt ausgeprägter als für eingangs kürzere Holzfasern. Die Faserlänge im Endprodukt zeigte jedoch keine Unterschiede bezüglich der Prozesseinstellungen. Glasfasern zeigten deutlichere Unterschiede in der Faserlänge aufgrund der Schneckenkonfiguration als Holzfasern. Diese spiegelten sich auch in den mechanischen Eigenschaften wieder: ein aggressiveres Schneckenprofil resultierte in geringeren Festigkeiten bei den Glasfaser-Kompositen, jedoch nicht bei den Holzfaser-Kompositen

    PP/clay nanocomposites: compounding and thin-wall injection moulding

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    This research investigates formulation, compounding and thin-wall injection moulding of Polypropylene/clay nanocomposites (PPCNs) prepared using conventional melt-state processes. An independent study on single screw extrusion dynamics using Design of Experiments (DoE) was performed first. Then the optimum formulation of PPCNs and compounding conditions were determined using this strategy. The outcomes from the DoE study were then applied to produce PPCN compounds for the subsequent study of thin-wall injection moulding, for which a novel four-cavity injection moulding system was designed using CAD software and a new moulding tool was constructed based upon this design. Subsequently, the effects of moulding conditions, nanoclay concentration and wall thickness on the injection moulded PPCN parts were investigated. Moreover, simulation of the injection moulding process was carried out to compare the predicted performance with that obtained in practice by measurement of real-time data using an in-cavity pressure sensor. For the selected materials, the optimum formulation is 4 wt% organoclay (DK4), 4 wt% compatibiliser (Polybond 3200, PPgMA) and 1.5 wt% co-intercalant (erucamide), as the maximum interlayer spacing of clay can be achieved in the selected experimental range. Furthermore, DoE investigations determined that a screw speed of 159 rpm and a feed rate of 5.4 kg/h are the optimum compounding conditions for the twin screw extruder used to obtain the highest tensile modulus and yield strength from the PPCN compounds. The optimised formulation of PPCNs and compounding conditions were adopted to manufacture PPCN materials for the study of thin-wall injection moulding. In the selected processing window, tensile modulus and yield strength increase significantly with decreasing injection speed, due to shear-induced orientation effects, exemplified by a significantly increased frozen layer thickness observed by optical microscopy (OM) and Moldflow® simulation. Furthermore, the TEM images indicate a strong orientation of clay particles in the flow direction, so the PPCN test pieces cut parallel to the flow direction have 36.4% higher tensile modulus and 13.6 % higher yield strength than those cut perpendicular to the flow direction, demonstrating the effects of shear induced orientation on the tensile properties of thin-wall injection moulded PPCN parts. In comparison to injection speed, mould temperature has very limited effects in the selected range investigated (25-55 °C), in this study. The changes in moulding conditions show no distinctive effects on PP crystallinity and intercalation behaviour of clay. Impact toughness of thin wall injection moulded PPCN parts is not significantly affected by either the changes in moulding conditions or clay concentration (1-5 %). The SEM images show no clear difference between the fracture surfaces of PPCN samples with different clay concentrations. TEM and XRD results suggest that higher intercalation but lower exfoliation is achieved in PPCN parts with higher clay content. The composites in the thin sections (at the end of flow) have 34 % higher tensile modulus and 11 % higher yield strength than in the thicker sections, although the thin sections show reduced d001 values. This is attributed to the significantly enhanced shear-induced particle/molecular orientation and more highly oriented frozen layer, according to TEM, OM and process simulation results. In terms of the reduced d001 values in the thin sections, it is proposed that the extreme shear conditions in the thin sections stretch the PP chains in the clay galleries to a much higher level, compaction of clay stacks occurs as less interspacing is needed to accommodate the stretched chains, but rapid cooling allows no time for the chains to relax and expand the galleries back. Overall, data obtained from both actual moulding and simulation indicate that injection speed is of utmost importance to the thin-wall injection moulding process, development of microstructure, and thus the resulting properties of the moulded PPCN parts, in the selected experimental ranges of this research

    Vacuum compression molding as a screening tool to investigate carrier suitability for hot-melt extrusion formulations

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    © 2020 by the authors. Licensee MDPI, Basel, Switzerland. Hot-melt extrusion (HME) is the most preferred and effective method for manufacturing amorphous solid dispersions at production scale, but it consumes large amounts of samples when used for formulation development. Herein, we show a novel approach to screen the polymers by overcoming the disadvantage of conventional HME screening by using a minimum quantity of active pharmaceutical ingredient (API). Vacuum Compression Molding (VCM) is a fusion-based method to form solid specimens starting from powders. This study aimed to investigate the processability of VCM for the creation of amorphous formulations and to compare its results with HME-processed formulations. Mixtures of indomethacin (IND) with drug carriers (Parteck® MXP, Soluplus®, Kollidon® VA 64, Eudragit® EPO) were processed using VCM and extrusion technology. Thermal characterization was performed using differential scanning calorimetry, and the solid-state was analyzed via X-ray powder diffraction. Dissolution studies in the simulated gastric fluid were performed to evaluate the drug release. Both technologies showed similar results proving the effectiveness of VCM as a screening tool for HME-based formulations

    Mechanical And Electrical Properties Of Short Carbon Fibre Reinforced Polycarbonate Composites

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    A series of composites was prepared using polycarbonate (PC) as the matrix, reinforced with short carbon fibre (SCF) at different weight fractions. The composites were compounded by single screw extruder and specimens were prepared by injection moulding machine. The effect of fibre weight fractions on the mechanical and electrical properties of SCF reinforced polycarbonate composite was studied. The test specimens were fabricated in accordance to the ASTM specifications. The mechanical properties of the composites were characterized by tensile, flexural and fracture toughness tests, while the morphological properties were characterized by scanning electron microscope (SEM). In addition, electrical properties were evaluated by surface resistivity test. Cox-Krenchel and rule of mixtures (RoM) were used to predict theoretical tensile moduli of the composites. Experiment results revealed that density of the composites increased with the addition of SCF. Fibre length was found to be greatly reduced during processing the of composites. Higher mean fibre length tends to provide better reinforcement effect, thus enhanced mechanical properties. Incorporation of SCF improved the strength of the composite, and the effect was more prominent at higher weight fraction of SCF. With increasing SCF content, the surface resistivity reduced drastically with the percolation threshold lie in between 10% - 14% of SCF weight fraction. Cox-Krenchel model showed to be a good approximation to predict the composites’ tensile modulus. 14% SCF reinforced PC composite which was obtained from commercial compound proved the effective extrusion compounding of these self-compounded composites (5%, 10% and 15% SCF), by possessing intermediate properties in between 10% and 15% SCF reinforced PC composites as expected
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