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     

CHARACTERIZATION OF MICROCELLULAR FOAMED POLYOLEFIN BLEND COMPOSITES WITH WOOD FIBER

The effects of wood fiber content on the void fraction, cell morphology, and notched Izod impact strength of microcellular foamed HDPE/PP blend composites with wood fiber were studied. The influence of wood fiber content on the carbon dioxide adsorption and desorption in the samples was also examined. Adsorption of carbon dioxide decreased with increased wood fiber content. Gas diffusion rates were faster as wood fiber content increased. The void fraction decreased dramatically when wood fiber was introduced in the blend. Environmental scanning electron microscopy (ESEM) was used to investigate the effects of wood fiber content on cell morphology. The 30:70 HDPE/PP polymer blend without wood fiber resulted in a high void fraction, with a uniform and well-developed microcellular structure, but when wood fiber was introduced, a uniform and well-developed microcellular structure could not be produced. The effects of foaming on Izod impact strength were dependent on wood fiber content.     

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。     

Relationship between cell morphology and impact strength of microcellular foamed high‐density polyethylene/polypropylene blends

Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher‐value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell‐population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well‐developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well‐developed microcellular morphology. Polym. Eng. Sci. 44:1551–1560, 2004. © 2004 Society of Plastics Engineers.     

Microcellular foaming of PE/PP blends

Three different polyethylene/polypropylene (PE/PP) blends were microcellular foamed and their crystallinities and melt strengths were investigated. The relationship between crystallinity, melt strength, and cellular structure was studied. Experimental results showed that the three blends had similar variation patterns in respect of crystallinity, melt strength, and cellular structure, and these variation patterns were correlative for each blend. For all blends, the melt strength and PP melting point initially heightened and then lowered, the PP crystallinity first decreased, and then increased as the PE content increased. At PE content of 30%, the melt strength and PP melting point were highest and the PP crystallinity was least. The blend with lower PP crystallinity and higher melt strength had better cellular structure and broader microcellular foaming temperature range. So, three blends had best cellular structure at PE content of 30%. Furthermore, when compared with PE/homopolymer (hPP) blend, the PE/copolymer PP (cPP) blend had higher melt strength, better cellular structure, and wider microcellular foaming temperature range, so it was more suited to be microcellular foamed. Whereas LDPE/cPP blend had the broadest microcellular foaming temperature range because of its highest melt strength within three blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4149–4159, 2007     

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) blends using supercritical carbon dioxide

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) (PPS/PES) blends presents a promising approach to produce high‐performance cellular materials with tailored microstructures and enhanced properties. This study investigated the effects of multiphase blend composition and process conditions on the foaming behaviors and final cellular morphology, as well as the dynamic mechanical properties of the solid and microcellular foamed PPS/PES blends. The microcellular materials were prepared via a batch‐foam processing, using the environment‐friendly supercritical CO₂ (scCO₂) as a blowing agent. The saturation and desorption behaviors of CO₂ in PPS/PES blends for various blend ratios (10 : 0, 8 : 2, 6 : 4, 5 : 5, 4 : 6, 2 : 8, and 0 : 10) were also elaborately discussed. The experimental results indicated that the foaming behaviors of PPS/PES blends are closely related to the blend morphology, crystallinity, and the mass‐transfer rate of the CO₂ in each polymer phase. The mechanisms for the foaming behaviors of PPS/PES blends have been illustrated by establishing theoretical models. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42634.     

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。     

Processing and characterization of microcellular foamed high-density polythylene/isotactic polypropylene blends

In this paper, a study on the batch processing and characterization of microcellular foamed high-density polyethylene (HDPE/iPP) blends is reported. A microcellular plastic is a foamed polymer with a cell density greater than 10⁹ cells/cm³ and fully grown cells smaller than 10 µm. Recent studies have shown that the morphology and crystallinity of semicrystalline polymers have a great influence on the solubility and diffusivity of the blowing agent and on the cellular structure of the resulting foam in microcellular batch processing. In this research, blends of HDPE and iPP were used to produce materials with variety of crystalline and phase morphologies to enhance the subsequent microcellular foaming. It was possible to produce much finer and more uniform foams with the blends than with neat HDPE and iPP. Moreover, the mechanical properties and in particular the impact strength of the blends were significantly improved by foaming.     

Improving polypropylene microcellular foaming through blending and the addition of nano‐calcium carbonate

This article reports an attempt to improve polypropylene (PP) microcellular foaming through the blending of PP with high‐density polyethylene (HDPE) as a minor component and the incorporation of nano‐calcium carbonate (nano‐CaCO₃) into PP and its blends with HDPE. Three HDPEs were selected to form three blends with a viscosity ratio less than, close to, or greater than unity. Two concentrations of nano‐CaCO₃, 5 and 20 wt %, were used. The blends and nanocomposites were prepared with a twin‐screw extruder. The foaming was carried out by a batch process with supercritical carbon dioxide as a blowing agent. The online shear viscosity during compounding and the dynamic rheological properties of some samples used for foaming were measured. The cell structure of the foams was examined with scanning electron microscopy (SEM), and the morphological parameters of some foams were calculated from SEM micrographs. The rheological properties of samples were used to explain the resulting cell structure. The results showed that the blend with a viscosity ratio close to unity produced a microcellular foam with the minimum mean cell diameter (0.7 μm) and maximum cell density (1.17 × 10¹¹ cells/cm³) among the three blends. A foamed PP/nano‐CaCO₃ composite with 5 wt % nano‐CaCO₃ exhibited the largest cell density (8.4 × 10¹¹ cells/cm³). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Foam extrusion of high density polyethylene/wood‐flour composites using chemical foaming agents

A one‐way analysis of variance and thermal analysis were performed in this study to examine the influences of the contents, types (exothermic vs. endothermic), and forms (pure vs. masterbatch) of chemical foaming agents (CFAs), as well as the use of coupling agents, on the density reduction (or void fraction) and cell morphology of extrusion‐foamed neat high density polyethylene (HDPE) and HDPE/wood‐flour composites. The CFA types and forms did not affect the void fractions of both the neat HDPE and HDPE/wood‐flour composites. However, a gas containment limit was observed for neat HDPE foams whereas the average cell size achieved in the HDPE/wood‐flour composite foams remained insensitive to the CFA contents, irrespective of the foaming agent types. The experimental results indicated that the use of coupling agent in the formulation was required to achieve HDPE/wood‐flour composite foams with high void fraction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3139–3150, 2003     

Influence of composition on the linear viscoelastic behavior and morphology of PP/HDPE blends

In this paper the influence of temperature and composition on the dynamic behavior and morphology of polypropylene (PP)/high-density polyethylene (HDPE) blends were studied. The blend composition ranged from 5 to 30 wt% of dispersed phase (HDPE) and the temperatures ranged from 180 to 220 °C. The interfacial tension between PP and HDPE at temperatures of 180, 200 and 220 °C was obtained from fitting Palierne's emulsion model [1] to the experimental data of PP/HDPE blends with different compositions and from the weighted relaxation spectra of PP/HDPE blends with different compositions, following Gramespacher and Meissner [2] analysis. The interfacial tension between PP and HDPE as inferred from the rheological measurements was shown to depend on PP/HDPE blend composition. However, the results indicated that there is a range of PP/HDPE blend composition for which interfacial tension between PP and HDPE is constant. Considering these values, it was shown that interfacial tension between PP and HDPE decreases linearly with increasing temperature.     

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.     

Effects of compatibilizers on the physico‐mechanical and foaming properties of polyproylene/wood‐fiber composites

Polypropylene (PP)/wood‐fiber (WF) composites were prepared by intermeshing co‐rotating twin screw extruder, and microcellular closed cell PP/WF composite foams were prepared by using pressure‐quenched batch process method. The effect of various compatibilizers on the mechanical properties, morphology, crystallinity, rheological properties, and foamability of PP/WF composites were investigated. The results showed that PP/WF composite with addition of PP‐g‐MA as compatibilizer had the highest tensile strength, stiffness, and crystallinity, after foaming, it showed highest relative density and cell density, as well as the smallest cell size. Higher crystallinity of PP/WF composites, showed higher stiffness and higher relative density. J. VINYL ADDIT. TECHNOL., 19:250–257, 2013. © 2013 Society of Plastics Engineers     

Structure and properties of rubber-modified polypropylene impact blends

The state of dispersion of poly(ethylene-co-propylene) (PEP) rubber and high-density polyethylene (HDPE) in polypropylene (PP) blends was investigated using scanning electron microscopy to examine solvent-etched microtomed surfaces cut at low temperatures. The validity of the method was established by comparing the areal fraction of dispersed particles in micrographs with the volume fraction of PEP and HDPE in PP-rich blends. When small amounts of PEP and HDPE were added to PP, they combined to form composite PEP–HDPE particles with characteristic internal structures in a PP matrix. Changes in impact strength and flexural modulus with changes in mixing conditions and blend composition were determined and interpreted in terms of the size, composition, and internal structure of the dispersed particles. Particle growth in the melt limited the impact strength level achieved in molded articles. A simple model proposed for screening rubbers for toughening of brittle plastics successfully predicts that PEP rubber should be an excellent impact modifier for PP.     

Microhardness of ternary blends of polyolefins with recycled polymer components

Microhardness tests, Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) measurements were performed on melt‐pressed films of multicomponent blends based on low‐density polyethylene (LDPE), linear LDPE (LLDPE), high‐density polyethylene (HDPE), and polypropylene (PP), and their recycled homologues. Some of the PE blends also contained ethylene‐propylene‐diene monomer (EPDM) as compatibilizer. In all cases, the variation of microhardness as a function of content of the recycled component follows the additivity law of components. Thus, the range of hardness values of polyolefin blends can be controlled by choice of both components and their relative content in the blend. The hardness of the components increases from LDPE, to LLDPE, to HDPE, to PP and increases from 20 to 84 MPa. For recycled components, the hardness values are reduced by ～15%. According to DSC results, all the blends are immiscible. Results are discussed in terms of the levels of crystallinity reached for the different blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2046–2050, 2003     

The effects of nanoclay on the extrusion foaming of wood fiber/polyethylene nanocomposites

This article presents the foaming behaviors of wood fiber/high density polyethylene (HDPE) composites with small amounts of nanoclay. Melt compounding is used to prepare two types of clay‐filled wood fiber composites: intercalated and exfoliated clay composites. Their respective morphologies are determined using wide‐angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM). We subsequently conduct an extrusion foaming experiment of the composites using N₂ as the blowing agent. Varying the wood fiber content, as well as the processing parameters, such as temperature and pressure, the effects of different amounts of clay and the degree of exfoliation on the final cell morphology and the foam density of the wood fiber/HDPE/clay nanocomposite foams are studied. The results suggested that the addition of nanoclay improved the cell morphology of the wood fiber/HDPE composite foams as its content and degree of dispersion increased. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

The development of laminar morphology during extrusion of polymer blends

Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-induced morphology to generate discontinuous overlapping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high density polyethylene and polyamide-6 (HDPE/PA-6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems.     

Structure and properties of PP/POE/HDPE blends

This work was aimed to counteract the effect of ethylene‐α‐olefin copolymers (POE) by reinforcing the polypropylene (PP)/POE blends with high density polyethylene (HDPE) particles and, thus, achieved a balance between toughness and strength for the PP/POE/HDPE blends. The results showed that addition of HDPE resulted in an increasing wide stress plateau and more ductile fracture behavior. With the increase of HDPE content, the elongation at break of the blends increased rapidly without obvious decrease of yield strength and Young's modulus, and the notched izod impact strength of the blends can reach as high as 63 kJ/m² at 20 wt % HDPE loading. The storage modulus of PP blends increased and the glass transition temperature of each component of the blends shifted close to each other when HDPE was added. The crystallization of HDPE phase led to an increase of the total crystallinity of the blend. With increasing HDPE content, the dispersed POE particle size was obviously decreased, and the interparticle distance was effectively reduced and the blend rearranged into much more and obvious core‐shell structure. The fracture surface also changed from irregular striation to the regularly distant striations, displaying much obvious character of tough fracture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process

Use of supercritical carbon dioxide (scCO₂) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO₂ process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO₂ solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO₂ concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO₂ can be achieved through judicious polymer blending.     

PP/COPET/ZnO三元共混物的结构与性能研究

以氧化锌(ZnO)为抗菌剂、水溶性聚酯(COPET)为成孔剂,通过共混纺丝和碱处理,制备了具有多孔结构的、具有吸湿和抗菌功能的聚丙烯(PP)纤维。研究发现,PP/COPET/ZnO三元共混物的密度和结晶度随COPET含量增加而增大;COPET质量分数为9%的共混物的结晶特性略优于3%的;COPET质量分数为6%时纤维的保水率最大;共混纤维对大肠杆菌、枯草杆菌、八叠球菌均有抗菌敏感性。