Rheology,morphology, and mechanical properties of HMSPP/POE blends and its alternate layered foam

In this article, the multilayered foaming sheet with alternate layered structure was successfully prepared through multilayer co‐extrusion. The high melt strength polypropylene (HMSPP)/poly (ethylene‐co‐octene) (POE) blend and POE were designed as foaming layers and film layers, respectively. POE was added into HMSPP to reduce the crystalline degree and improve the processing performance. The rheological results indicated that the addition of POE had a little effect on relaxation process and the strain hardening behavior of HMSPP when the POE content was lower than 50%. The results of the foam morphology showed that the cell size and its distribution of the multilayered foaming sheet with alternate layers were better than that with single layer. In addition, the cell size reduced and the cell density increased with increasing the number of layers from 4 to 32. The mechanical properties of the multilayered foaming sheet with alternate layers also could be improved through assembling of foaming layers and film layers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41339.     

Strategy for the preparation of lightweight polypropylene/polyethylene-octene elastomer composite foams with different phase morphologies using supercritical carbon dioxide

Polypropylene (PP)/polyethylene-octene elastomer (POE) composites with a “sea-island” structure and a cocontinuous structure were prepared. With the selection of a suitable foaming temperature, the supercritical carbon dioxide foaming of PP/POE composites with different phase morphologies occurred only in the POE phase. The effects of the POE content, foaming temperature, pressure, and number of layers on the cell size, cell density, apparent density, foaming layer density, and foaming ratio under different phase morphologies were investigated by scanning electron microscopy, polarized optical microscopy, differential scanning calorimetry, and dynamic thermomechanical analysis. This article provides a novel approach for foaming PP at a low temperature. For PP/POE-blended composites with a “sea-island” structure, the foaming temperature is as low as 80 °C, and for PP/POE alternating multilayered composites with a cocontinuous structure, foaming can occur at 40 °C. Compared with the conventional methods for foaming PP, this method avoids the problems of a high foaming temperature, a narrow range of the foaming temperature, and a low melt strength of the PP. Thus, the PP foaming method was successfully improved, yielding a new technique for the preparation of lightweight PP. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48157.     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

Enhanced fracture energy during deformation through the construction of an alternating multilayered structure for polyolefin blends

The effects of polymer blend components on the phase morphology, crystallization behavior and mechanical performance of materials processed by high speed thin‐wall injection molding (HSTWIM) and compression molding (CM) processes were investigated. High density polyethylene (HDPE) and polypropylene (PP) containing different ratios of rubber phase (0%, 18% and 21%) were selected to construct different blends. HSTWIM is shown to trigger the formation of a multilayered structure for these blends with oriented polymer crystals and epitaxial growth of HDPE crystals on PP. Such a layered structure is thought to provide a good template for morphological control of various functional polymer composites. Moreover, the addition of rubber in the multilayered structure with the rubber phase partially distributed between layers is observed. These issues are thought to be responsible for the much enhanced fracture energy compared with specimens from CM. The structural details and formation mechanism of these layered structures consisting of different compositions were investigated. Such a study could provide some guidelines for the preparation of high performance bio‐mimic materials or various functional polymer composites with alternating multilayered structure. © 2018 Society of Chemical Industry     

The effect of confined spherulite morphology of high-density polyethylene and polypropylene on their gas barrier properties in multilayered film systems

Confined crystallization of high-density polyethylene (HDPE) in multilayer films is studied in this paper. A new cyclic olefin copolymer (COC), HP030, is co-extruded with HDPE by a layer multiplying technique. The number of layers and layer compositions are changed to study the effect of layer thickness on the crystalline morphology of the HDPE layers under confinement. Atomic force microscopy (AFM) is used to investigate the crystalline morphology of the HDPE layers. MOCON (Minneapolis, MN, commercial instrument) units are employed to measure both oxygen permeability and water vapor transport rate (WVTR) of these co-extruded HDPE/HP030 multilayer films. We report that when the HDPE layer nominal thickness is about 290 nm in the HDPE/HP030 multilayer films, the HDPE layer effective gas barrier property is improved approximately 2 times for oxygen and 5 times for water vapor. This is the result of confined spherulite morphology of HDPE, which increases the tortuosity for gas to diffuse through the films. Similar phenomenon is found for polypropylene (PP), when PP is co-extruded against polycarbonate (PC). The same experiments as for HDPE are conducted to confirm that PP spherulites have been confined by PC in PP/PC multilayer films. We discover that the confined spherulites of PP improve its gas barrier properties as well.     

Structure and properties of electrically conducting composites consisting of alternating layers of pure polypropylene and polypropylene with a carbon black filler

Electrically conducting composites consisting of alternating polypropylene (PP) and carbon black (CB)-filled polypropylene (PPCB) layers were prepared by multilayered coextrusion. The co-continuous structure with selective location of CB in PPCB layers was controllable by changing the number of multiplying elements, and decreased the percolation threshold and electrical resistivity of multilayered composites because of the double percolation effect. This double percolation could be achieved in a single polymer matrix using multilayered coextrusion, whereas it can only be produced in two different polymeric matrices by conventional approaches. Results showed that the dispersion of CB aggregates in PPCB layers was greatly affected by the shearing forces induced by the horizontal spreading flow and vertical recombination occurring during the multilayered coextrusion. The electrical resistivity, positive temperature coefficient effect and mechanical properties of multilayered composites depended strongly on their number of layers. A brittle-ductile transition occurred in PPCB layer compared with the conventional composites. The interesting positive and negative temperature coefficient effects occurred during crystallization and depended on the number of layers. A mechanism is proposed to explain these phenomena.     

Effect of sub-layer thickness on magnetic and giant magnetoresistance properties of Ni-Fe/Cu/Co/Cu multilayered nanowire arrays

Ni–Fe/Cu/Co/Cu multilayered nanowire arrays were electrodeposited into anodic aluminum oxide template by using dual-bath method at room temperature. Scanning electron microscopy and transmission electron micros-copy were used to characterize the morphology and structure of the multilayered nanowire arrays. Vibrating sample magnetometer and physical property measurement system were used to measure their magnetic and giant magnetoresistance (GMR) properties. The effect of sub-layer thickness on the magnetic and GMR proper-ties was investigated. The results indicate that magnetic properties of electrodeposited nanowires are not affect-ed obviously by Cu layer thickness, while magnetic layers (Ni–Fe and Co layers) have significant influence. In addition, GMR ratio presents an oscillatory behavior as Cu layer thickness changes. The magnetic and GMR properties of the multilayered nanowire arrays are optimum at room temperature for the material structure of Ni–Fe (25 nm)/Cu (15 nm)/Co (25 nm)/Cu (15 nm) with 30 deposition cycles.     

Effect of tie-layer thickness on the adhesion of ethylene-octene copolymers to polypropylene

The adhesion of some ethylene-octene copolymers to polypropylene (PP) and high density polyethylene (HDPE) was studied in order to evaluate their suitability as compatibilizers for PP/HDPE blends. A one-dimensional model of the compatibilized blend was fabricated by layer-multiplying coextrusion. The microlayered tapes consisted of many alternating layers of PP and HDPE with a thin tie-layer inserted at each interface. The thickness of the tie-layer varied from 0.1 to 15 μm, which included thicknesses comparable to those of the interfacial layer in a compatibilized blend. The delamination toughness was measured in the T-peel test. Generally, delamination toughness decreased as the tie-layer became thinner with a stronger dependence for tie layers thinner than 2 μm. Inspection of the crack-tip damage zone revealed a change from a continuous yielded zone in thicker tie layers to a highly fibrillated zone in thinner tie layers. By treating the damage zone as an Irwin plastic zone, it was demonstrated that a critical stress controlled the delamination toughness. The temperature dependence of the delamination toughness was also measured. A blocky copolymer (OBC) consistently exhibited better adhesion to PP than statistical copolymers (EO). A one-to-one correlation between the delamination toughness and the reported performance of the copolymers as compatibilizers for PP/HDPE blends confirmed the key role of interfacial adhesion in blend compatibilization.     

HDPE共混PP微孔发泡技术研究进展

介绍了一种用高密度聚乙烯(HDPE)与聚丙烯(PP)共混以改善PP微孔结构的技术,对该技术的研究成果进行了综述性回顾。主要包括结晶度及加工条件对共混体系发泡性能的影响、HDPE熔体流动速率对PP/HDPE共混体系微孔结构的影响。共混发泡技术提高了PP的可发泡性,为解决PP发泡难的问题提供了新方法和新技术。     

Adhesion of propylene–ethylene copolymers to high‐density polyethylene

The adhesion of some propylene–ethylene (P/E) copolymers to polypropylene (PP) and high density polyethylene (HDPE) was studied in order to compare them with other olefin copolymers as compatibilizers for PP/HDPE blends. A one‐dimensional model of the compatibilized blends was fabricated by layer‐multiplying coextrusion. The microlayered tapes consisted of many alternating layers of PP and HDPE with a thin tie‐layer inserted at each interface. The thickness of the tie‐layer varied from 0.1 to 15 μm, which included thicknesses comparable to those of the interfacial layer in a compatibilized blend. In the T‐peel test, the P/E copolymers delaminated at the HDPE interface. An elastomeric P/E with higher ethylene content exhibited substantially higher delamination toughness than a more thermoplastic P/E with lower ethylene content. Inspection of the crack‐tip damage zone revealed that a change from deformation of the entire tie‐layer to formation of a localized yielded zone was responsible. By treating the damage zone as an Irwin plastic zone, it was demonstrated that a critical stress controlled the delamination toughness. The temperature dependence of the delamination toughness was also measured. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Ductile tear behavior of multilayered polypropylene homopolymer/ethylene 1‐octene copolymer sheets

The tear resistance of the polypropylene homopolymer (HPP)/ethylene 1‐octene copolymer (POE) alternating multilayered sheets, which were prepared through multilayered coextrusion, was evaluated. Polarized optical microscope (POM) photographs revealed that HPP and POE layers aligned alternately vertical to the interfaces and continuously parallel to the extrusion direction. Tear results demonstrated the conventional blends had less tear‐resistant than the multilayered samples. Large plastic deformation of HPP layer occurred in the multilayered structure during the stable crack growth, causing the tear energy to increase with the number of layers increasing. The measurements of PCMW2D IR and WAXD revealed that the large plastic deformation had a direct relationship with the crystal structure and termination of micro‐cracks by interface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43298.     

PP/HDPE/滑石粉复合材料微孔发泡实验研究

为了改善聚丙烯(PP)的微孔发泡性能,将PP与高密度聚乙烯(HDPE)共混,提高其熔体强度;然后在PP/HDPE共混体系中加入少量滑石粉,研究滑石粉的用量对共混体系熔体强度及微孔发泡过程的影响。研究结果表明,滑石粉的加入使体系的熔体强度提高,发泡样品的泡孔结构变得更均匀。而且,随着滑石粉用量的增加,泡孔尺寸减小,泡孔密度增加。     

Polymer clay self‐assembly complexes on paper

Layer‐by‐layer (LBL) self‐assembly was used to form polymer/clay complexes on paper to enhance its wet strength properties. Initially, alternating layers of poly(allylamine hydrochloride) (PAH) and Kaolin clay were sequentially deposited on quartz substrate and characterized by UV/Vis/NIR spectroscopy as a model system. The same procedure was then applied to a paper test sheet to form multilayered coatings, which were examined with scanning electron microscopy. The wettability of the LBL coated paper test sheet was shown to change from hydrophilic to hydrophobic with increased number of multilayers and if the terminating layer was Kaolin clay. The wet strength of the coated test sheet was improved by more than 270% over the uncoated test sheet with 16 bilayers of PAH/kaolin complex on the surface. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of ethylene-propylene copolymer with residual PE crystallinity on mechanical properties and morphology of PP/HDPE blends

Morphology and mechanical properties of polypropylene (PP)/high density polyethylene (HDPE) blends modified by ethylene-propylene copolymers (EPC) with residual PE crystallinity were investigated. The EPC showed different interfacial behavior in PP/HDPE blends of different compositions. A 25/75 blend of PP/HDPE (weight ratio) showed improved tensile strength and elongation at break at low EPC content (5 wt %). For the PP/HDPE = 50/50 blend, the presence of the EPC component tended to make the PP dispresed phase structure transform into a cocontinuous one, probably caused by improved viscosity matching of the two components. Both tensile strength and elongation at break were improved at EPC content of 5 wt %. For PP/HDPE 75/25 blends, the much smaller dispersed HDPE phase and significantly improved elongation at break resulted from compatibilization by EPC copolymers. © 1995 John Wiley & Sons, Inc.     

Morphology and electrical conductivity of polyethylene/polypropylene blend filled with thermally reduced graphene oxide and surfactant exfoliated graphene

High‐density polyethylene (HDPE)/polypropylene (PP) composites with graphenes were prepared by melt‐compounding method. Graphene sheets were prepared through thermally reduced graphene oxide (TRG) and surfactant exfoliated graphene (SEG), respectively. Structural characterization showed that the TRG sheets exhibited a few‐layers composition with more defects compared to the SEG sheets. Morphological observations of the composites demonstrated that the graphene was preferentially dispersed in the HDPE phase and the addition of graphene (TRG and SEG) influenced the phase structure of the HDPE/PP composites. The distribution of the TRG sheets in the HDPE phase was better than the SEG sheets, and the obtained HDPE/PP composites exhibited a low electrical percolation threshold with the highly dispersed graphene. The TRG/HDPE/PP composite showed a low electrical percolation threshold of 3 wt% (1.25 vol%). For the SEG/HDPE/PP system, the percolation threshold was 7 wt% (2.98 vol%). Differences in the behavior of the two graphene components (TRG and SEG) in the HDPE/PP composites influenced the formation of percolation networks and electrical properties. POLYM. COMPOS., 38:2098–2105, 2017. © 2015 Society of Plastics Engineers     

Structure and properties of polypropylene/high‐density polyethylene blends by solid equal channel angular extrusion

The solid equal channel angular extrusion (ECAE) process on polypropylene (PP)/high‐density polyethylene (HDPE) blends was carried out. Scanning electron microscopy (SEM) was used to observe the sample structures. Results showed that ECAE process could make PP/HDPE blends to produce orientation structure. Impact performance of ECAE‐PP/HDPE samples after ECAE process improved remarkably, especially for ECAE‐PP/HDPE (90/10)‐O whose impact strength reached 91.91 kJ/m², 18.1 times higher than that of pure PP and 11.2 times higher than that of PP/HDPE (90/10). The mechanism of enhancing between HDPE and PP was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39759.     

Effect of phase morphology and interfacial strength on barrier properties of high density polyethylene/polyamide 6 membranes

A barrier and resistance membrane consisting of alternating layers of high‐density polyethylene (HDPE) and polyamide 6 (PA6) was prepared by microlayered coextrusion. The influence of phase morphology, number of layers, and compatibilizer (CP) content of HDPE/PA6‐microlayered membranes on their gas barrier and water resistance properties were characterized using a scanning electron microscopy, gas in permeability, and water absorption tests. The results suggest that this special‐layered structure led to significant improvement of gas barrier and water resistance properties, compared with conventional membranes. In addition, the barrier and resistance properties of microlayered membranes were obviously enhanced with increased number of layers and CP content. An optimal number of layers and CP content were determined for the improved barrier and resistance properties. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Improving the flame retardancy of polypropylene foam with piperazine pyrophosphate via multilayering coextrusion of film/foam composites

A series of 16-layer polypropylene/flame retardant (PP/FR) film/foam composite structures were produced by microlayer coextrusion. A highly branched PP was used in the foam layers to increase strain hardening and cell stability, while the PP used in the film layers was a high shear viscosity grade to confine bubble growth. In addition to improved tensile properties, the PP/FR composite film/foams exhibited five times the compression modulus of PP/FR composite foams at each FR loading level. The thermal stabilities of the composites were investigated, exhibiting three step decompositions. The FR particles were effective in decreasing flammability by forming intumescent char. The PP/FR-film/foam-20 showed self-extinguishing behavior in a modified vertical burn test, while the PP/FR-foam-20 sample continued to burn. Cone calorimetry demonstrated that PP/FR film/foams had lower heat release than PP/FR foams due to the unique alternating film/foam structure of PP/FR film/foams. Scanning electron microscopy imaging of the residual chars from fire testing that the PP/FR composite film/foams showed a more continuous protective char surface when compared with PP/FR composite foams at each FR concentration. The combined data indicate that the formation of a surface film on top of a foam ensures a robust intumescent fire protective barrier for partly foamed materials and shows a new way toward lightweight materials with improved fire safety performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48552.     

A new method for achieving nanoscale reinforcement of biaxially oriented polypropylene film

Nanolayers of poly(ethylene oxide) (PEO) produced by layer-multiplying coextrusion crystallize as single, high aspect ratio lamellae that resemble large single crystals. The confined crystallization habit imparts two orders of magnitude reduction in the gas permeability. We now demonstrate how the highly oriented lamellar nanolayers can be obtained with biaxial stretching. For this purpose, we chose biaxially oriented polypropylene (BOPP) film for modification and incorporated PEO nanolayers under conditions that mimicked the typical fabrication process. Sheet that contained a center core with 33 alternating layers of polypropylene (PP) and PEO was coextruded and subsequently biaxially oriented at 145 °C. Biaxial stretching reduced the PEO layer thickness from the spherulitic microscale to nanolayers of highly oriented PEO single lamellae. The nanolayers improved the oxygen barrier by an order of magnitude without sacrificing the high clarity and good tear resistance of BOPP film.     

Microcellular foam of polymer blends of HDPE/PP and their composites with wood fiber

In this study, the effects of batch processing conditions (foaming time and temperature) and blend composition as well as the effect of incorporating wood fiber into the blends on the crystallinity, sorption behavior of CO₂, void fraction, and cellular morphology of microcellular foamed high‐density polyethylene (HDPE)/polypropylene (PP) blends and their composites with wood fiber were studied. Blending decreased the crystallinity of HDPE and PP and facilitated microcellular foam production in blend materials. The void fraction was strongly dependent on the processing conditions and on blend composition. Foamed samples with a high void fraction were not always microcellular. The addition of wood fiber inhibited microcellular foaming. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2842–2850, 2003