Microfibrillar Blends Research Articles

Manufacture and rheological behavior of all recycled PET/PP microfibrillar blends

AbstractFor several years, new plastic bottles made from opaque polyethylene terephtalate (PET) have been on the market. When their waste is mixed to those of recycled clear PET, the obtained material cannot be recycled anymore due to a loss of properties. Moreover, because of an important grade variety, the large number of additives used and poor homogeneity, the processing and recycling of opaque PET appears as a challenge. The way chosen to revalue this recycled opaque PET (r‐OPET) is its microfibrillation in a recycled polypropylene (rPP) matrix. The effects of the concentration of r‐OPET were studied by rheology, supported by scanning electron microscope images and related to the morphology of the mixture. It was demonstrated that (20/80)w r‐OPET/rPP blend was the best ratio to favor microfibrillation, as it offers the appropriate amount of solid filler to obtain a sea‐island morphology.Thereafter, the influence of the temperature of microfibrillation is presented. The thermomechanical curve of the (20/80)w r‐OPET/rPP blend suggests that microfibrillation should be more effective around the Tg of r‐OPET. The optimum temperature was found, where an improvement of rheological and mechanical properties is observed. A Cross model with yield stress is proposed to describe the rheological behavior of this material.

Physical and Mechanical Properties of Wood-Plastic Composites Made with Microfibrillar Blends of LDPE, HDPE and PET

The effect of microfibrillar blends of recycled plastics on selected physical and mechanical characteristics of wood-plastic composites (WPCs) was investigated in this study. The production of wood plastic composites was carried out through a two-step extrusion technique. The plastic blends were drawn after extrusion to obtain microfibrillar morphology. The addition of polyethylene-co-glycidyl methacrylate (E-GMA) enhanced compatibility between the two phases and a homogenous structure was seen in the fracture surfaces by scanning electron microscopy (SEM). The crystallinity of base polymers increased with the addition of polyethylene terephthalate (PET) microfibrils, E-GMA and wood flour. The X-ray diffraction (XRD) patterns were also used to determine the crystallinity of all samples. According to the XRD results, the crystallinity degree of recycled plastics was higher than that of virgin plastics. E-GMA improved the water resistance of wood-plastic composites. The mechanical properties of samples were improved with the addition of PET microfibrils. The microfibrillar blending technique was found to be an effective approach for the production of high quality WPCs from recycled plastic blends.

In situ fibrillation of isotactic polypropylene in ethylene‐vinyl acetate: Toward enhanced rheological and mechanical properties

ABSTRACTIn situ microfibrillar reinforced composites with ethylene‐vinyl acetate (EVA) as matrix and isotactic polypropylene (iPP) as dispersed fibrils were successfully fabricated by multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs). Four types of EVA with different apparent viscosity were utilized to study the influence of viscosity ratio on the morphology and mechanical properties of EVA/iPP in situ microfibrillar blends. The scanning electron micrographs revealed that the dividing–multiplying processes in LMEs could effectively transform the morphology of iPP phase into microfibrils and the morphology of iPP microfibrils strongly depended on the viscosity ratio. Higher viscosity ratio was favorable for formation of finer microfibrils with narrower diameter distribution. The morphology development of iPP with different viscosity ratio greatly affected the rheological and mechanical properties of EVA/iPP blends. The dynamic rheological results shown that the iPP microfibrils were helpful to increase the storage modulus and loss modulus. The tensile test indicated that the mechanical properties of EVA/iPP blends were controlled by the morphology of iPP phase and the polarity of EVA matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47557.

Novel Polyamide 6/Polystyrene In Situ Microfibrillar Blends Prepared by Anionic Polymerization of ε‐Caprolactam via Reactive Extrusion

In this study, polyamide 6/polystyrene in situ microfibrillar blends are prepared via anionic polymerization of ε‐caprolactam in a twin screw extruder. Scanning electron microscope analysis reveals that microfibrillated PA6 dispersed phase, which is continuous and preferentially oriented parallel to the extrusion direction, is in situ formed within polystyrene (PS) matrix during reactive extrusion at the content PS equal to 30 and 40 wt%. Mechanical properties analysis shows that the yield strength and elongation at break of PA6/PS (70/30 and 60/40) microfibrillar blends are remarkably increased with respect to those of pure PS. Also, the in situ fibrillation mechanisms are investigated by the analysis of morphological evolution. This work demonstrates a facile and efficient route to fabricate the microfibrillar blends with relatively high contents of polymer microfibrils.image

Effect of blend ratio on the dynamic mechanical and thermal degradation behavior of polymer–polymer composites from low density polyethylene and polyethylene terephthalate

Microfibrillar polymer–polymer composites (MFCs) based on low-density polyethylene (LDPE) and polyethylene terephthalate (PET) were prepared by cold drawing-isotropization technique. The weight percentage of PET was varied from 5 to 45 %. Microfibrils with uniform diameter distribution were obtained at 15 to 25 wt% of PET as evident from the scanning electron microscopy (SEM) results. Dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) damping behavior (tan δ) were examined as a function of blend composition. The E′ values were found to be increasing up to 25 wt% of PET. An effort was made to model the storage modulus and damping characteristics of the MFCs using the classical equations used for short-fiber reinforced composites. The presence of PET microfibrils influenced the damping characteristics of the composite. The peak height at the β-transitions of loss modulus was lower for MFCs with 25 % PET, showing that they had superior damping characteristics. This phenomenon could be correlated with the PET microfibrils morphology. The thermal degradation characteristics of LDPE, neat blends and microfibrillar blends (MFBs) were compared. The determination of activation energy for thermal degradation was carried out using the Horowitz and Metzger method. The activation energy for thermal degradation of microfibrillar blends was found to be higher than that for the corresponding neat blends and MFCs. The long PET microfibrils present in MFBs could prevent the degradation and enhance the activation energy.

Formation of various crystalline structures in a polypropylene/polycarbonate in situ microfibrillar blend during the melt second flow.

A strong shear flow was imposed on the melt of polycarbonate (PC) microfibrils with β-nucleation agent reinforced isotactic polypropylene (iPP) during the melt second flow process, i.e. gas-assisted injection molding (GAIM). A special shell-core structure was formed in the iPP/PC microfibrils with β-nucleation agent (PP/PC/β-NA) composites. A lot of β-transcrystalline and α-transcrystalline superstructures were observed in the skin and sub-skin regions, whereas β-spherulite structures were formed in the gas channel region. There is no doubt that the distinct hierarchical structure has great potential to significantly improve the mechanical performance of the composites, and the experimental results verify this. The results of the mechanical performance testing show that the yield strength of the PP/PC/β-NA composites reached 61.9 MPa, which is 19.7 MPa higher than that of the iPP parts molded by GAIM (G-iPP) (42.2 MPa). The tensile modulus of the PP/PC/β-NA composites (3.3 GPa) increased by 135%, compared to that of G-iPP (1.4 GPa). The high content of β-crystals improved the elongation at break of the composites compared to the iPP/PC microfibril (PP/PC) composites; the elongation at break of the PP/PC/β-NA composites (13%) is over 3 times greater than that of the PP/PC composites (4%).

Poly(lactic acid)-Based in Situ Microfibrillar Composites with Enhanced Crystallization Kinetics, Mechanical Properties, Rheological Behavior, and Foaming Ability.

Melt blending is one of the most promising techniques for eliminating poly(lactic acid)'s (PLA) numerous drawbacks. However, success in a typical melt blending process is usually achieved through the inclusion of high concentrations of a second polymeric phase which can compromise PLA's green nature. In a pioneering study, we introduce the production of in situ microfibrillar PLA/polyamide-6 (PA6) blends as a cost-effective and efficient technique for improving PLA's properties while minimizing the required PA6 content. Predominantly biobased products, with only 3 wt % of in situ generated PA6 microfibrils (diameter ≈200 nm), were shown to have dramatically improved crystallization kinetics, mechanical properties, melt elasticity and strength, and foaming-ability compared with PLA. Crucially, the microfibrillar blends were produced using an environmentally friendly and cost-effective process. Both of these qualities are essential in guarantying the viability of the proposed technique for overcoming the obstacles associated with the vast commercialization of PLA.

Relationship between dye sorption and morphology in polypropylene/poly (butylene terephthalate) microfibrillar blend nanocomposite fibers

In this research work, the relation between microstructural enhancement and dyeing behavior of immiscible blend nanocomposite fibers was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction patterns, and rheometric mechanical spectrometer along with quantitative analysis of dye sorption. A novel microfibrillar morphology blend fiber, in which poly (butylene terephthalate) nanocomposite fibrils uniformly distributed in the cross section of polypropylene matrix, was successfully developed using melt compounding process. Preferred location of nanoclay had improving effect on poly (butylene terephthalate) fibril formation such that there was an organoclay concentration above that fiber with fine microfibrillar morphology could hardly be produced. It was demonstrated that nanoclay melt intercalation and partitioning controlled the activation energy of dyeing. The maximum sorption rate was achieved by utilizing compatibilizer to transfer part of nanoclay platelets into the polypropylene matrix.

Effect of compatibilizer on the morphology development, static and dynamic mechanical properties of polymer-polymer composites from LDPE and PET

The morphology development and mechanical properties of low density polyethylene (LDPE)/ poly ethylene terephthalate (PET) blends and microfibrillar composites (MFC) at varying concentrations of a compatibilizer polyethylene grafted with maleic anhydride (PE-g-MA) were analyzed in this study. The microstructure of the microfibrillar blends (MFBs) and composites during the various stages of their preparation was characterized using scanning electron microscopy (SEM). The aspect ratio of the PET microfibrils was found to increase with compatibilizer loading up to an optimum level. The presence of 4 wt% PE-g-MA affected the dimensions of the PET fibrils differently in 75/25 and 85/15 w/w% microfibrillar blends. The variation in the length of the microfibrils was found to influence the static and dynamic mechanical properties of the microfibrillar composites. The studies pointed towards the necessity of optimizing the compatibilizer concentration to achieve enhanced properties for the MFCs.

Macromol. Mater. Eng. 11/2012

Cover: Composite design is a complex task because the desired effects of a component or a processing step may be accompanied by side effects. Monitoring the nanostructure under service conditions may accelerate the design by guiding the focus of the designer. The front cover illustrates nanostructure evolution mechanisms during slow load-cycling of oriented HDPE/PA microfibrillar blends studied as a function of composition. Further details can be found in the article by A. Zeinolebadi, N. Stribeck,* M. Ganjaee-Sari, N. Dencheva, Z. Denchev, and S. Botta on page 1102.

Nanostructure Evolution Mechanisms During Slow Load‐Cycling of Oriented HDPE/PA Microfibrillar Blends as a Function of Composition

AbstractOriented precursors of MFCs consisting of HDPE and PA6 or PA12 are studied during strain‐controlled slow load‐cycling. In the PA6‐containing blends a strongly retarded nanostrain response is detected. Compatibilization induces nanostrain heterogenization. Stress fatigue is lower in the PA12 blends, but hardly decreased by the compatibilizer. Selective migration of the compatibilizer into a disordered semi‐crystalline fraction of the HDPE matrix can explain the findings. The semi‐crystalline HDPE entities in PA6 blends appear more disordered than in PA12‐blends. An analysis of the HDPE nanostructure evolution during cycling reveals epitaxial strain crystallization. Uncompatibilized PA6 blends cycled about high pre‐strain show plastic flow but nanoscopic shrinkage in the semi‐crystalline stacks. magnified image

Effect of blend ratio on the mechanical and sorption behaviour of polymer–polymer microfibrillar composites from low-density polyethylene and polyethylene terephthalate

The morphology of the neat blends, microfibrillar blends and the corresponding microfibrillar composites based on low-density polyethylene and polyethylene terephthalate was analyzed. As the polyethylene terephthalate concentration increased, an increase in the diameter of polyethylene terephthalate spheres/fibrils was observed. The fibrils with relatively uniform diameter distribution were obtained in the range of 15–25 wt% polyethylene terephthalate concentration. The tensile properties of the blends and microfibrillar composites increased with polyethylene terephthalate concentration up to an optimum level. The neat blends exhibited inferior tensile properties in comparison with the microfibrillar composites. As the polyethylene terephthalate concentration increased, the solvent uptake reduced. The diffusivity and permeability of the microfibrillar composites were lower than the corresponding blends. The solvent uptake was found to be lowest for the composite with 25 wt% polyethylene terephthalate concentration. The polyethylene terephthalate microfibrils in the microfibrillar composites offered a tortuous path for the diffusion of the solvent.

Morphology and Mechanical Properties of Normal Blends and In-Situ Microfibrillar Composites from Low-Density Polyethylene and Poly(ethylene terephthalate)

In this work, normal blends, microfibrillar blends and composites were prepared from low density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) in 85/15 and 75/25 w/w% ratio in the presence and absence of a compatibilizer polyethylene grafted with maleic anhydride (PE-g-MA). The microfibrillar composites (MFCs) were prepared using extrusion – drawing – isotropization technique. The morphology development of the microfibrillar blends and composites was studied using scanning electron microscopy (SEM). The presence of 5 wt% PE-g-MA compatibilizer affected the continuity of the fibrils differently in 75/25 and 85/15 w/w% microfibrillar blends. In the case of normal blends the addition of compatibiliser reduced the size of the dispersed PET phase. The presence of PET microfibrils improved the tensile properties of the microfibrillar composites. The normal blends exhibited a relatively ductile failure during tensile loading in comparison with the microfibrillar composites. The microfibrillar nature of the dispersed phase was found to improve the stiffness of the composite rather than their impact strength.

Wood plastic composites based on microfibrillar blends of high density polyethylene/poly(ethylene terephthalate)

High-melting-temperature poly(ethylene terephthalate) (PET) was successfully introduced into wood plastic composites through a two-step reactive extrusion technology. Wood flour was added into pre-prepared PET/high density polyethylene (HDPE) microfibrillar blends (MFBs) in the second extrusion at the temperature for processing HDPE. Addition of 25% in situ formed PET microfibers obviously increased the mechanical properties of HDPE, and more significant enhancement by the in situ formed recycled PET microfibers was observed for the recycled HDPE. Adding 2% E-GMA improved the compatibility between matrix and microfibers in MFBs, resulting further enhanced mechanical properties. The subsequent addition of 40% wood flour did not influence the size and morphology of PET microfibers, and improved the comprehensive mechanical properties of MFBs. The wood flour increased the crystallinity level of HDPE in the compatibilized MFB in which PET phase did not crystallize. The storage modulus of MFB was greatly improved by wood flour.

In situ microfibrillar blends and composites of polypropylene and poly (ethylene terephthalate): Morphology and thermal properties

Microfibrillar blends were prepared from polypropylene and poly (ethylene terephthalate) by extrusion followed by cold drawing. The draw ratio employed had a prominent effect on the aspect ratio of the microfibrils produced, as revealed by scanning electron microscopy. The subsequent isotropization step between the Tm of the polymers created microfibrillar composites with randomly oriented short microfibrils of poly (ethylene terephthalate). The X ray diffraction patterns of the microfibrillar blends were different from those of corresponding composites although the polypropylene phase in both exhibited predominantly the presence of α crystallites. The crystallization of the polypropylene phase was affected by the orientation and diameter of the poly (ethylene terephthalate) microfibrils. The short microfibrils in the microfibrillar composites were not effectual in hastening the crystallization of polypropylene. The thermal decomposition studies revealed the capability of microfibrillar blends to delay the degradation better than the microfibrillar composites.

Morphology and properties of isotactic polypropylene/poly(ethylene terephthalate) in situ microfibrillar reinforced blends: Influence of viscosity ratio

In situ microfibrillar reinforced blends based on blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were successfully prepared by a “slit extrusion–hot stretching–quenching” process. Four types of iPP with different apparent viscosity were utilized to investigate the effect of viscosity ratio on the morphology and mechanical properties of PET/iPP microfibrillar blend. The morphological observation shows that the viscosity ratio is closely associated to the size of dispersed phase droplets in the original blends, and accordingly greatly affects the microfibrillation of PET. Lower viscosity ratio is favorable to formation of smaller and more uniform dispersed phase particles, thus leading to finer microfibrils with narrower diameter distribution. Addition of a compatibilizer, poly propylene-grafted-glycidyl methacrylate (PP-g-GMA), can increase the viscosity ratio and decrease the interfacial tension between PET and iPP, which tends to decrease the size of PET phase in the unstretched blends. After stretched, the aspect ratio of PET microfibrils in the compatibilized blends is considerably reduced compared to the uncompatibilized ones. The lower viscosity ratio brought out higher mechanical properties of the microfibrillar blends. Compared to the uncompatibilized microfibrillar blends, the tensile, flexural strength and impact toughness of the compatibilized ones are all improved.

Crystallization of oriented isotactic polypropylene (iPP) in the presence of in situ poly(ethylene terephthalate) (PET) microfibrils

The present article reports the nonisothermal crystallization process and morphological evolution of oriented iPP melt with and without in situ poly(ethylene terephthalate) (PET) microfibrils. The bars of neat iPP and PET/iPP microfibrillar blend were fabricated by shear controlled orientation injection molding (SCORIM), which exhibit the oriented crystalline structure (shish–kebab), especially in the skin layer. The skin layer was annealed at just above its melting temperature (175°C) for a relatively short duration (5min) to preserve a certain level of oriented iPP molecules. It was found that the existence of ordered clusters (i.e. oriented iPP molecular aggregates) leads to the primary nucleation at higher onset crystallization temperature, and formation of the fibril-like crystalline morphology. However, the overall crystallization rate decreases as a result that the relatively high crystallization temperature restrains the secondary nucleation. With the existence of PET microfibrils, the heterogeneous nucleation distinctly occurs in the unoriented iPP melt and results in the increase of crystallization peak temperature and overall crystallization rate, for the first time, we observed that the onset crystallization temperature has been enhanced further with addition of PET microfibrils in the oriented iPP melt, indicating the synergistic effect of row nucleation and heterogeneous nucleation under quiescent condition.

Application of In Situ Microfibrillization to Recycling Ultraviolet‐Aged Poly(Ethylene Terephthalate) (PET) and High Density Polyethylene (HDPE)

The potential of in situ microfibrillization for recycling ultraviolet‐aged high density polyethylene (HDPE) and poly(ethylene terephthalate) (PET) mixtures was investigated. The photodegradation of HDPE and PET was conducted through accelerated irradiation in an ultraviolet (UV) chamber. The ultraviolet‐aged HDPE and PET was melt blended (in 80/20 wt. ratio) and rectangular slit die extruded, followed by hot stretch and quenching; thus the in situ microfibrillar PET/HDPE blends were fabricated. Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and contact angle measurements indicate that HDPE and PET suffered photodegradation. There is an increase in yield strength and tensile modulus as well as Vicat softening temperature (VST) tests for in situ microfibrillar blends with increasing UV exposure time, while there is a decrease in these properties for conventional blends, indicating that the in situ microfibrillar blend process has promising potential for recycling plastic mixtures.

Rheological behavior of PET/HDPE in situ microfibrillar blends: Influence of microfibrils' flexibility

AbstractPoly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) in situ microfibrillar reinforced blends were prepared via a slit die extrusion‐hot stretch‐quenching process. The in situ PET microfibrils contain various contents of a segmented thermoplastic elastomer, Hytrel 5526 (HT), hence having different flexibility as demonstrated by dynamic mechanical analysis. It is interesting that the simple mixing leads to nanoscale particles of the HT phase in PET phase, and the size of the HT particles is almost independent of the HT concentration, as observed from the scanning electron microscope micrographs which show that the microfibrils with different HT concentrations have almost the same diameter and smooth surfaces. The static rheological results by an advanced capillary rheometer show that the entrance pressure drop and the viscosity of the microfibrillar blends both reduced with increasing the microfibrils' flexibility. Furthermore, the data obtained by the temperature scan of the PET/HT/HDPE microfibrillar blends through a dynamic rheometer indicates that the more flexible microfibril leads to lower melt elasticity and slightly decreases the viscosities of blends, presenting a consistent conclusion about influences of the microfibrils' flexibility on the rheological behavior from the static rheometer measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1205–1216, 2007

Recyclability of In Situ Microfibrillar Poly(ethylene terephthalate)/High‐Density Polyethylene Blends

AbstractRepetitive processing was employed to assess the recyclability of in situ microfibrillar poly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) blends which were fabricated through a “rectangular slit die extrusion–hot stretching–quenching” process. For comparison, the conventional PET/HDPE blends were also obtained using the same processing operation but without hot stretching. The morphological observation indicated that slit die extrusion and hot stretching successfully made the dispersed PET phase deform in situ into well‐defined microfibrils. The average diameter of the microfibrils increased with the processing cycles. The rheological properties obtained from the parallel‐plate dynamic rheometer suggested that the microfibrillar blends have higher viscosity and viscoelastic moduli (storage and loss moduli) as well as better flow stability than the conventional PET/HDPE blend. More importantly, with the increase in the processing cycles, an increase in yield strength and unchanged tensile modulus were observed for in situ microfibrillar blends, while a decrease in these properties for conventional blend, indicating that the in situ microfibrillar PET/HDPE blends have promising recycling potential.magnified image