Laminating-multiplying Elements Research Articles

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.

A high‐barrier PP/EVOH membrane prepared through the multistage biaxial‐stretching extrusion

ABSTRACTThe polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) membranes were prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). A biaxial‐stretching occurred when polymer melts flowing through a LME. The morphology development of PP/EVOH blends and its effect on gas‐barrier property, solvent‐absorption property and mechanical properties were characterized by scanning electron microscope (SEM), polarized optical microscope (POM), gas‐permeability test, immersion experiment, differential scanning calorimetry (DSC), and tensile test. With the introduction of LME and the increasing of its number, morphology of EVOH phase in PP matrix gradually changed from zero‐dimension spherical particles to one‐dimension fibers, and then to two‐dimension sheets. As a result, the nitrogen permeability coefficient decreased nearly by two orders of magnitude and the permeability coefficient of toluene‐PP/EVOH system declined by almost four times. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45016.

In situ polyolefin elastomer/poly(trimethylene terephthalate) microfibrillar composites fabricated via multistage stretching extrusion

The in situ polyolefin elastomer (POE)/poly(trimethylene terephthalate) (PTT) microfibrillar composites (MFCs) sheets were successfully prepared by multistage stretching extrusion with the assembly of laminating-multiplying elements (LMEs). The morphology of PTT phase was greatly influenced by the composition. The tensile strength of the sheets and the products which were some sheets secondary processing by compression molding were similar, when the weight ratio of POE/PTT was 90/10, the tensile strength was the highest. At this blend ratio, the diameters distribution of PTT microfibers was relative uniformity by scanning electron microscopy (SEM) studies, which was good to reinforce the POE. When the PTT content was higher, the distribution more scatter. Dynamic rheology studies showed that compared with the neat POE, when PTT content was 20 %, the storage modulus, loss modulus values and the complex viscosity were the highest while the tanδ was the lowest for the MFCs, especially at low frequency (ω 100 rad/s), the differences became negligible.

In situ fibrillation of poly(trimethylene terephthalate) in polyolefin elastomer through multistage stretching extrusion

ABSTRACTPolyolefin elastomer (POE)/poly(trimethylene terephthalate) (PTT) microfibrillar composites (MFCs) were successfully fabricated by multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs). The morphologies of these novel materials were greatly influenced by the compositions. The number of microfibrils increased with increasing PTT concentration, as revealed by scanning electron microscopy. The tensile strength was the highest along the extrusion direction at the weight ratio of 85/15. Moreover, dynamic rheological results showed that the storage modulus, loss modulus, and complex viscosity were the highest while the tan δ was the lowest for MFCs prepared at the weight ratio 85/15 compared with the neat POE, especially at low frequency (ω < 1 rad/s). In addition, the PTT microfibrils had more effect on the rheological properties compared to the PTT particles. However, the differences became negligible at high frequency (ω > 100 rad/s). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43797.

Analysis of crystalline structure and morphology of isotactic polypropylene under the coexistence of organic montmorillonite particles and shear flow

In this work, the different effects of organic montmorillonite (OMMT) particles and shear flow on the crystallization behavior of isotactic polypropylene (iPP) were discussed. While neat iPP and OMMT filled iPP were treated using the multistage stretching extrusion technology, changing the number of laminating-multiplying elements (LMEs) can obtain samples with different dispersion degree of OMMT particles and different orientation degree of molecular chains. With the increase of LME number, the content of β-crystal in neat iPP increased. But for OMMT/iPP composites, decreasing LME number caused the increase of content of β-crystal. The experimental results showed that the shear flow and large OMMT aggregations were essential factors for the formation of β-crystal in composites, and the crystalline morphology strongly depended on the size of OMMT particles. The scanning electron microscope (SEM) images of sample with 3 wt% of OMMT particles and without LME illustrated that β-transcrystallinity, fan-shaped β-crystal and α-spherulite were induced by different size of OMMT particles, respectively. A schematic was proposed to describe the formation mechanism of α-crystal and β-crystal under the coexistence of OMMT particles and shear flow.

Exfoliation of organic montmorillonite in iPP free of compatibilizer through the multistage stretching extrusion

Polypropylene (PP)/organic montmorillonite (OMMT) nanocomposites were first prepared through twin-screw extruder and then subjected to multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs, which divide and recombine polymer melts). The exfoliated efficiency of LMEs on OMMT dispersed in PP matrix was investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and X-ray diffraction. Because of the absence of compatibilizer, molecular chains of PP were not intercalated into the galleries of OMMT during the multistage stretching extrusion. The exfoliation of OMMT was induced by the strong force occurred in LMEs, which can destruct van der Waal’s interaction between the laminate OMMT platelets. The exfoliation degree of OMMT has been improved with the increase of number of LMEs used. The dispersion morphology of OMMT was thermodynamically stable after secondary melt processing. As a result, the mechanical properties of composites have been enhanced with increasing LME number. We realized the exfoliation of OMMT by the function of strong shear field without the incorporation of compatibilizer.

Effect of multistage tensile extrusion induced fiber orientation on fracture characteristics of high density polyethylene/short glass fiber composites

Abstract The high density polyethylene (HDPE)/short glass fiber (SGF) composites were prepared by multistage tensile extrusion with an assembly of laminating-multiplying elements (LMEs) connecting with an extruder. The strong shear and elongational force field in LME could make the fibers orientated along the melt flow direction. The degree of fiber orientation could be controlled by the number of LMEs. The SEM morphological observations illustrated that the fiber orientation degree was gradually increased by increasing the number of LMEs. However, the fiber length distribution and crystallinity of composites did not change much with increasing the LMEs, and would not affect the mechanical properties. The essential work of fracture (EWF) analysis at quasi-static rate of loading showed that the fracture toughness along the melt flow direction increased with the number of LMEs increasing because of the change of the fiber related damage mechanism. An opposite trend was found if samples were stretched perpendicular to the melt flow direction.

Morphologies and properties of polycarbonate/polyethylene in situ microfibrillar composites prepared through multistage stretching extrusion

ABSTRACTThe sheets of polycarbonate (PC)/polyethylene (PE) in situ microfibrillar composites are successfully prepared directly through multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs) instead of the secondary processing. The morphological development of the PC dispersed phase in PE matrix with increasing the number of LMEs during multistage stretching extrusion investigated by scanning electron microscope shows that core‐skin structure of the microfibrillar PC/PE composites during multistage stretching extrusion with 4 LMEs is weakened, and the diameter of the PC microfibrils is relatively more uniform, indicating that the shear field in LMEs greatly affects the morphology of PC dispersed phase in PE matrix. The tensile, crystalline, melting, orientation and rheological behavior of the PC/PE microfibrillar composites are also investigated. The results show that the PC microfibrils are helpful to increase complex viscosity and yield stress of the PE/PC composites. In addition, it is found that the glass transition temperature of PC in PE matrix reduced with increasing the number of LMEs during dynamic rheological testing. It is coincided with the results of DSC analysis of the PC/PE composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40108.

In situ microfibrillar morphology and properties of polypropylene/polyamide/carbon black composites prepared through multistage stretching extrusion

Isotactic polypropylene/polyamide/carbon black (PP/PA/CB) composites with microfibrillar morphology were designed and prepared using a multistage stretching extruder with an assembly of laminating-multiplying elements (LMEs). CB was selectively located in PA. With the increase of LME number from zero to seven, the conductive PA/CB phase was found to experience an elongating-breaking-elongating process. This morphological development resulted in the strong dependence of electrical resistivity on the LME number. When no LME was used, PP/PA/CB materials with 2.0, 3.0, or 4.0 wt% (1.0, 1.6, and 2.1 vol%) CB employed were insulators (resistivity: 1010 Ω cm) due to their droplet morphology. With the introduction of LMEs, a conductive network was formed because of the microfibrillation of the conductive PA/CB phase; these materials became conductors (resistivity: 104–106 Ω cm). The percolation threshold can lower to 1.5 wt% (0.9 vol%). The low resisticity and percolation threshold cannot be obtained through the conventional method.

The distribution and morphological evolution of dispersed phase in laminating‐multiplying elements during extrusion

AbstractThree kinds of polymeric blends: nylon 6/isotactic polypropylene, talc/ethylene 1‐octene copolymer, and carbon black (CB)/propylene–ethylene copolymer are prepared by applying an assembly of laminating‐multiplying elements (LMEs) connecting with an extruder. The morphological observations illustrate that those LMEs may not only provide biaxial stretching force on the melt, leading to the orientation of dispersed phase, but also make the distribution of those particles become more even. The tensile, barrier, or electrical properties are also investigated, respectively, and demonstrate the development of morphologies in LMEs. Results suggest that the laminating‐multiplying extrusion system is a useful tool to obtain polymeric composites with specific morphologies and distribution. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

The electrical conductivity of carbon nanotube/carbon black/polypropylene composites prepared through multistage stretching extrusion

We reported the design of a grape-cluster-like conductive network in a polypropylene (PP) matrix, where oriented multi-walled carbon nanotubes (MWCNTs) served as branches and provided charge transport over large distances while grape-like carbon black (CB) aggregates enriched around MWCNTs and linked these conductive tubes through charge transport over small distances. The key for construction of this grape-cluster-like conductive network was the extension and orientation of MWCNTs, which was achieved in this work by multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs, which divide and recombine polymer melts). The highest efficient grape-cluster-like conductive network was obtained at a CB:MWCNT weight ratio of 6. The experimental results showed that this novel grape-cluster-like conductive network provided a low percolation threshold for PP/CB/MWCNT composites due to the synergistic effect of CB and oriented MWCNTs. When the combined CB and MWCNT content was about 6.9vol%, the electrical resistivity of PP/CB/MWCNT composites prepared by multistage stretching extrusion with 6 LMEs decreased to only 0.63Ωcm.

In situ fibrillation of polyamide 6 in isotactic polypropylene occurring in the laminating‐multiplying die

AbstractThe polyamide 6 (PA6)/isotactic polypropylene (iPP) in situ fibrillation composites are prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). The scanning electron micrographs illustrate that the dividing‐multiplying processes in LMEs elongate, break, and stabilize the dispersed PA6 phase in the iPP matrix along the flowing direction (FD). The morphology development of PA6 with different LME numbers greatly affects the rheological properties, crystalline behaviors, and mechanical properties. The dynamic rheological test performed at 195°C shows that the increased spatial restriction of the high‐aspect‐ratio PA6 particles increases the viscoelastic moduli, complex viscosity, and relaxation time. The crystalline analysis reveals that the heterogeneous nucleation becomes predominant and the transcrystalline morphology is observed in those samples produced by more LMEs. The tensile tests indicate that both, breaking strength and elongation, enhanced simultaneously because of the fibrillation of dispersed phase and the improvement in interfacial adhesion between the fibers and the matrix. Copyright © 2009 John Wiley & Sons, Ltd.