A look inside the extruder: evolution of chemistry,morphology and rheology along the extruder axis during reactive processing and blending

A simple device was recently developed for fast sampling (within a few seconds) of representative melt samples (about 2 g) on a running extruder. An array of such devices has been mounted on a twin‐screw extruder. The goal of this study was to de‐black‐box reactive processing of polymers by studying some typical examples. ‐ Processing of polyolefins in the presence of peroxides: when the polymer is molten and the melt temperature is sufficiently high branching/cross‐linking of PE and degradation of PP occurs; the conversion follows a convex profile along the screw axis, which profile is similar to the exponential profile calculated for peroxide decomposition. ‐ Free‐radical grafting of maleic anhydride (MA) onto polyolefins: MA grafting onto PE and PP also follows a convex profile with branching/cross‐linking as parallel side reaction for PE and degradation for PP; for PE degradation of the formed grafted/cross‐linked gel is observed at the end of the extruder. ‐ Reactive blending of PA‐6 with EPM‐g‐MA: within a few seconds the in‐situ compatibilization reaction, resulting in PA‐6/EPM graft copolymers, is completed and the degree of rubber dispersion has changed from the mm to the sub‐μm range, regardless of the MA content of EPM‐g‐MA and the EPM‐g‐MA content of the blend; PA degradation occurs along the whole extruder.     

The Effect of the Compatibilization Route of PA/PO Blends on the Physico-chemical Phenomena Developing Along a Twin-screw Extruder

The effect of the compatibilization method (ex-situ, in-situ, cross linking) on the chemical conversion, morphological and rheological evolution of polyamide/polyolefin blends along a twin screw extruder is investigated. For this purpose, samples were quickly collected from the extruder at specific barrel locations, quenched and subsequently characterized off-line. While significant changes occur very quickly in the melting zone for the ex-situ and in-situ routes, changes of the cross linking system could be detected along all the extruder. Correlations between chemical conversion, particle size and linear viscoelastic response could be established.     

Compatibilized PP/EPDM/PA6 ternary blends: extended morphological studies

Polypropylene (PP)/polyamide6 (PA6)/ethylene propylene diene monomer (EPDM) (70/15/15) ternary polymer blends compatibilized with maleic‐anhydride‐grafted EPDM (EPDM‐g‐MA) were prepared by melt blending using a twin‐screw extruder (TSE) in different processing conditions (barrel temperature profile, screw speed, and mixing sequence). The microstructures of prepared ternary blends were studied and compared to the predictions of spreading coefficient, minimum relative interfacial energy (RIE), and dynamic interfacial energy phenomenological models. The observed morphologies were somehow different from the model predictions. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical and morphological evolution of PA‐6/Epm/Epm‐g‐MA blends in a twin screw extruder

Chemical conversion and morphological evolution of PA‐6/EPM/EPM‐g‐MA blends along a twin screw extruder were monitored by quickly collecting small samples from the melt at specific barrel locations. The results show that the MA content of all blends decreases drastically in the first zone of the extruder, i.e., upon melting of the blend components. Significant changes in morphology are also observed at this stage. A correlation between chemistry and morphology could thus be established. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1311–1320, 1999     

Morphology of PC/SAN blends: effect of reactive compatibilization,SAN concentration,processing, and viscosity ratio

This article examines the effects of dispersed phase concentration, processing apparatus, viscosity ratio, and interfacial compatibilization using an SAN–amine compatibilizer on the morphology of blends of bisphenol A–polycarbonate (PC) with styrene–acrylonitrile (SAN) copolymers. For uncompatibilized blends, the dispersed phase particle size increased significantly with SAN concentration, and was found to exhibit a minimum at a viscosity ratio of approximately 0.35 for a fixed concentration of 30% SAN in the blend. Although the morphology of uncompatibilized PC/SAN blends mixed in a Brabender mixer, single‐ and twin‐screw extruders were quite similar, the twin‐screw extruder produced significantly finer morphologies in blends containing SAN–amine. The average particle size for blends compatibilized with the SAN–amine polymer was approximately half that of uncompatibilized blends and was relatively independent of viscosity ratio and dispersed phase composition. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 71–82, 1999     

A study on melt grafting of maleic anhydride onto low‐density polyethylene and its blend with polyamide 6

Graft copolymerization of low‐density polyethylene (LDPE) with a maleic anhydride (MAH) was performed using intermeshing corotating twin‐screw extruder in the presence of benzoyl peroxide (BPO). The LDPE/polyamide 6 (PA6) and LDPE‐g‐MAH/PA6 blends were prepared in a corotating twin‐screw extruder. The melt viscosity of the grafted LDPE was measured by a capillary rheometer. The grafted copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microcopy (SEM). The influence of the variation in temperature, BPO and MAH concentration, and temperature on the grafting degree and on the melt viscosity was studied. The grafting degree increased appreciably up to about 0.45 phr and then decreased continuously with an increasing BPO concentration. According to the FTIR analysis, it was found that the amount of grafted MAH on the LDPE chains was ～5.1%. Thermal analysis showed that melting temperature of the graft copolymers decreases with increasing grafting degree. In addition to this, loss modulus (E″) of the copolymers first increased little with increasing grafting and then obviously decreased with increasing grafting degree. Furthermore, the results revealed that the tensile strength of the blends increased linearly with increasing PA6 content. The results of SEM and mechanical test showed that the blends have good interfacial adhesion and good stability of the phase structure, which is reflected in the mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 267–275, 2010     

Influence of Reactive Compatibilization on the Melt Flow Properties and Morphology of Polyamide 6/Styrene-Acrylonitrile Blends

Summary: In this study, we investigate the influence of reactive compatibilization on the rheological properties of polyamide 6/styrene-acrylonitrile (PA 6/SAN) blends in the melt. Linear viscoelastic shear oscillations, simple elongation to a large stretch ratio and subsequent recovery experiments were performed. The morphology of the blends was examined by atomic force microscopy. We prepared three PA 6/SAN blends with different composition ratios of PA 6 and SAN (70/30, 50/50, 30/70) and a constant concentration of the reactive agent. Our experiments revealed that reactive compatibilization significantly increases the complex modulus of PA 6/SAN blends at low frequencies. In particular, the data of the PA 6/SAN 50/50 blend and the PA 6/SAN 30/70 blend indicated that an elastic network between neighbouring PA 6 domains was formed. In simple elongation, the transient elongational viscosity of the blends exceeded the values of the single components. In recovery, the recovered stretch of all blends was larger than the recovered stretch of the pure components. The differences of the blend morphology and of the linear viscoelastic behaviour were qualitatively explained by the asymmetric properties of the reactively compatibilized interface.     

Reactive blending of PE‐GMA/PA6 effect of composition and processing conditions

Blends of ethylene‐glycidyl methacrylate copolymer (PE‐GMA) and polyamide 6 (PA6) were prepared in a corotating twin screw extruder. Two processing temperatures were used in order to disperse PA6 in two forms: at high temperature in the molten state in molted PE‐GMA Matrix (emulsion type mixture) and at lower temperature as fillers in molted PEGMA matrix (suspension type mixture). Processed blends were analyzed by scanning electron microscopy and dynamic mechanical experiments to probe the reactivity in the extruder and the compatibilization phenomena. The dependence of the morphology and the rheological properties of PE‐GMA/PA6 blends on blend composition and screw rotational speed was also investigated and is discussed in the paper. The results show that dispersion of the two polymers in the molten state leads to a higher level of interfacial reaction. They also show that whatever the screw rotational speed and the temperature of extrusion are, the rate of interfacial reaction in PE‐GMA/PA6 blends is higher for 50/50 PE‐GMA/PA blends than for 70/30 PE‐GMA/PA blends. Copyright © 2015 John Wiley & Sons, Ltd.     

聚丙烯/尼龙6/聚丙烯接枝物原位复合材料的形态与力学性能——共混过程对体系的影响

聚丙烯／尼龙６／聚丙烯接枝物原位复合材料的形态与力学性能———共混过程对体系的影响黎学东陈鸣才黄玉惠丛广民（中国科学院广州化学研究所广州５１０６５０）关键词原位复合材料，成纤，相容性原位成纤复合材料是指在加工过程中增强相在基体中就地形成微纤，不...     

Use of maleic anhydride compatibilization to improve toughness and other properties of polylactide blended with thermoplastic elastomers

Polylactide (PLA) being a very brittle biopolymer could be toughened by blending with thermoplastic elastomers such as thermoplastic polyurethane elastomer (TPU) and thermoplastic polyester elastomer (TPE); unfortunately, these blends are immiscible forming round domains in the PLA matrix. Therefore, the purpose of this study was to investigate the effects of using maleic anhydride (MA) compatibilization on the toughness and other properties of PLA blended with TPU and TPE. MA grafting on the PLA backbone (PLA‐g‐MA) was prepared separately by reactive extrusion and added during melt blending of PLA/thermoplastic elastomers. IR spectroscopy revealed that MA graft might interact with the functional groups present in the hard segments of TPU and TPE domains via primary chemical reactions, so that higher level of compatibilization could be obtained. SEM studies indicated that PLA‐g‐MA compatibilization also decreased the size of elastomeric domains leading to higher level of surface area for more interfacial interactions. Toughness tests revealed that Charpy impact toughness and fracture toughness (K_IC and G_IC) of inherently brittle PLA increased enormously when the blends were compatibilized with PLA‐g‐MA. For instance, G_IC fracture toughness of PLA increased as much as 166%. It was also observed that PLA‐g‐MA compatibilization resulted in no detrimental effects on the other mechanical and thermal properties of PLA blends. Copyright © 2014 John Wiley & Sons, Ltd.     

Morphologies and properties of plasticized starch/polyamide compatibilized blends

A new sodium carboxymethylcellulose (CMC) compatibilized glycerol-plasticized starch/polyamide PA11 blend having improved mechanical properties was realized in a one step extrusion process. Blends were prepared in internal mixer and twin screw extruder. Mechanical properties (stress and strain at break) are improved by adding 1 wt% of CMC. Rheological characterization and scanning electron microscopy show that a co-continuous morphology is observed on a wide range of TPS amount.     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Long-Range Processing Correlation and Morphological Fractality of Compatibilized Blends of PS/ HDPE/ SEBS Block Copolymer

Summary: Processing and compatibilization effects of a commercially available styrene/ ethylene-butylene/ styrene (SEBS) compatibilizer on the morphological structure, rheological and mechanical properties of blends of polystyrene (PS) and high density polyethylene (HDPE) were investigated. The rheological behaviour of the blends melt during processing was followed by measuring torque; extrusion capacity output and melts back-pressure in a twin screw extruder. The processing parameters were decreased with the HDPE content. The results show that SEBS compatibilizer can yield compatibilization by substantially reducing torque and increasing the back-pressure. However, the Hurst indices of melt processing parameters are increased with compatibilization. Near-infrared spectra had been described by the Hurst index H_NIR which is then related to HDPE content in the blends. The correlation between the blend compositions, morphological structure, mechanical and rheological properties and processing parameters was established and discussed on base of correlation with the fractal indices obtained from the SEM microphotographs of PS/HDPE/SEBS blends.     

Monitoring polyolefin modification along the axis of a twin‐screw extruder. II. Maleic anhydride grafting

The physico‐chemical phenomena developing along the screw axis of a twin‐screw extruder during the grafting of maleic anhydride (MA) onto polyolefins [polyethylene (PE), ethylene–propylene rubber (EPM), and polypropylene (PP)] were investigated. For this purpose, sampling devices located along the extruder barrel were used to collect polymer samples that were subsequently characterized to follow the degrees of grafting and crosslinking or degradation. A similar evolution of MA grafting was observed regardless of the polyolefin type or MA and peroxide concentration when grafting was performed under identical conditions, that is, the same peroxide type and set temperature. A correlation between the MA grafting and the calculated peroxide decomposition was established. Chemical reactions occurred along the extruder axis until the peroxide was fully converted. More detailed quantitative measurements of the peroxide decomposition and MA grafting would allow the development of accurate process models. The final MA content depended on the polyolefin composition (PE > EPM ≫ PP). As expected for PE, crosslinking occurred in addition to grafting, but after a certain residence time, the PE network degraded. The PP viscosity reduction after MA grafting was due to the conversion of tertiary PP radicals into primary PP radicals after grafting. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3919–3932, 2000     

Effect of maleic anhydride-grafted ethylene-propylene rubber on the mechanical, rheological and morphological properties of organoclay reinforced polyamide 6/polypropylene nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were compatibilized with maleic anhydride-grafted ethylene-propylene rubber (EPRgMA). The blends were melt compounded in twin screw extruder followed by injection molding. The mechanical properties of PA6/PP nanocomposites were studied by tensile and flexural tests. The microstructure of the nanocomposite were assessed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The dynamic mechanical properties of the PA6/PP blend-based nanocomposites were analyzed by using a dynamic mechanical thermal analyzer (DMTA). The rheological properties were conducted from plate/plate rheometry via dynamic frequency sweep scans. The melt viscosity in a high shear rate region was performed by using a capillary rheometer. The strength and stiffness of the PA6/PP-based nanocomposites were improved significantly with the incorporation of EPRgMA. Adding EPRgMA to the PA6/PP blends resulted in a finer dispersion of the PP phase. TEM and XRD results revealed that the organoclay was dispersed more homogeneously in the presence of EPRgMA, however, mostly in the PA6 phase of the blends. DMTA results showed that EPRgMA worked as an effective compatibilizer. The storage (G′) and loss moduli (G″) assessed by plate/plate rheometry of PA6/PP blends increased with the incorporation of EPRgMA and organoclay. Furthermore, the apparent shear viscosity of the PA6/PP blend increased significantly for the EPRgMA compatibilized PA6/PP/organoclay nanocomposite. This was traced to the formation of an interphase between PA6 and PP (via PA6-g-EPR) and effective intercalation/exfoliation of the organoclay.     

Poly(lactic acid)/coplasticized thermoplastic starch blend: Effect of plasticizer migration on rheological and mechanical properties

Polylactic acid (PLA) and thermoplastic starch (TPS) are known as bio‐based and biodegradable thermoplastic polymers that can be used in different applications owing to their inherent physical and mechanical properties. In order to reduce the higher costs of PLA and tuning its physical and mechanical properties suitable for short life packaging applications, blending of PLA with the TPS, more economical biodegradable polymer, has been considered in academic and industrial researches. However, melt blending of PLA with TPS without compatibilization process caused some drawbacks such as coarsening morphology and declining mechanical properties and ductility because of thermodynamic immiscibility, which may restrict its usage in packaging applications. Subsequently, our approach in this research is compatibilization of PLA/TPS blends by utilization of primary well tuning of TPS formulation with a combination of sorbitol and glycerol plasticizers. In this work, the wide composition range of melt mixed PLA/TPS blends was prepared using a laboratory twin screw extruder. The effects of microstructure on the rheological and mechanical properties of PLA/TPS blends were studied using different methods such as scanning electron microscopy (SEM) images, contact angle, oscillatory shear rheological measurements, and tensile and impact strength mechanical tests. The rheological and mechanical properties were interpreted according to the morphological features and considering the possibility of plasticizer migration from TPS to PLA phase during melt blending. Reduction in complex viscosity and storage modulus of PLA matrix samples indicates the improved melt processability of blends. Finally, in comparison with mechanical results reported in literature, our simple approach yielded the blends with elastic modulus and ductility comparable with those of chemically compatibilized PLA/TPS blends.     

Effects of different types of polyethylene on the morphology and properties of recycled poly(ethylene terephthalate)/polyethylene compatibilized blends

Recycled poly(ethylene terephthalate) (R‐PET) was blended with four types of polyethylene (PE), linear low density polyethylene (LLDPE; LL0209AA, Fs150), low density polyethylene (LDPE; F101‐1), and metallocene‐LLDPE (m‐LLDPE; Fv203) by co‐rotating twin‐screw extruder. Maleic anhydride‐grafted poly(styrene‐ethylene/butyldiene‐styrene) (SEBS‐g‐MA) was added as compatibilizer. R‐PET/PE/SEBS‐g‐MA blends were examined by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), and mechanical property testing. The results indicated that the morphology and properties of the blends depended to a great extent on the miscibility between the olefin segments of SEBS‐g‐MA and PE. Due to the proper interaction between SEBS‐g‐MA and LDPE (F101‐1), most SEBS‐g‐MA, located at the interface between two phases of PET and LDPE to increase the interfacial adhesion, lead to better mechanical properties of R‐PET/LDPE (F101‐1) blend. However, both the poor miscibility of SEBS‐g‐MA with LLDPE (LL0209AA) and the excessive miscibility of SEBS‐g‐MA with LLDPE (Fs150) and m‐LLDPE (Fv203) reduced the compatibilization effect of SEBS‐g‐MA. DSC results showed that the interaction between SEBS‐g‐MA and PE obviously affected the crystallization of PET and PE. DMA results indicated that PE had more influence on the movement of SEBS‐g‐MA than PE did. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactive compatibilization of blends of PET and PP modified by GMA grafting

The melt radical grafting of glycidyl methacrylate (GMA) onto isotactic polypropylene (PP) was carried out in Brabender internal mixer and the influence of reaction procedure, radical initiator concentration and addition of co-monomer (styrene) on the grafting efficiency was examined. The viscosity, the thermal behaviour and melt rheology of PP-g-GMA samples was then analysed as a function of grafted GMA content. Blends of poly(ethylene terephthalate) (PET) with PP and PP-g-GMA (5.2 wt% GMA), prepared in internal mixer, were characterised by SEM, DSC and melt viscosimetry. The morphological analysis of PET/PP-g-GMA blends (80/20, 50/50 w/w) pointed out a marked improvement of phase dispersion (with particle size of about 0.6 μm for 80/20 blend) and interfacial adhesion, as compared to non-compatibilized PET/PP blend. The results of mixing torque and thermal analysis supported the occurrence of in-situ compatibilization reaction between epoxy groups of GMA modified PP and carboxyl end-groups of PET in the melt.     

CHEMICAL MODIFICATION OF STYRENE/ETHYLENE-BUTHYLENE/STYRENE COPOLYMERS

The chemical modification of two thermoplastic elastomer styrene/ethylene-buthylene/styrene copolymers (SEBS) with diethylmaleate (DEM) as functionalizing agent was carried out in a corotating twin screw extruder and in an internal mixer. The residence time distribution of the extruder was studied due to its great influence on the grafting chemical reaction, the degree of functionalization, and the viscoelastic properties of the obtained modified polymers. The influence of copolymer melt viscosities, and DEM and initiator concentration ratio on the grafting degrees was studied as well. In this case, an internal mixer was used.

Optimal processing conditions were established to obtain grafted polymers characterized by good processability and an absence of crosslinking. The grafting degree achieved in the internal mixer was the same for both copolymers with different viscosities and it increased as the DEM and initiator concentrations and concentration ratios were increased.     

Reactively and physically compatibilized immiscible polymer blends: stability of the copolymer at the interface

This paper reports on the interfacial behaviour of block and graft copolymers used as compatibilizers in immiscible polymer blends. A limited residence time of the copolymer at the interface has been shown in both reactive blending and blend compatibilization by preformed copolymers. Polystyrene (PS)/polyamide6 (PA6), polyphenylene oxide (PPO)/PA6 and polymethylmethacrylate (PMMA)/PA6 blends have been reactively compatibilized by a styrene-maleic anhydride copolymer SMA. The extent of miscibility of SMA with PS, PPO and PMMA is a key criterion for the stability of the graft copolymer at the interface. For the first 10 to 15 minutes of mixing, the in situ formed copolymer is able to decrease the particle size of the dispersed phase and to prevent it from coalescencing. However, upon increasing mixing time, the copolymer leaves the interface which results in phase coalescence. In PS/LDPE blends compatibilized by preformed PS/hydrogenated polybutadiene (hPB) block copolymers, a tapered diblock stabilizes efficiently a co-continuous two-phase morphology, in contrast to a triblock copolymer that was unable to prevent phase coarsening during annealing at 180°C for 150 minutes.