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     

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     

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.     

Effects of the viscosity ratio on polyolefin ternary blends

Polyolefin binary and ternary blends were prepared from polypropylene (PP), an ethylene–α‐olefin copolymer (mPE), and high‐density polyethylene (HDPE) on the basis of the viscosity ratio of the dispersed phase to the continuous phase. In PP/mPE/HDPE blends, fibrils were observed when the dispersed‐phase (mPE/HDPE) viscosity was less than that of PP, or when the viscosity of mPE was less than that of PP, although the viscosity of mPE/HDPE was greater than that of PP. The notched impact strength and mechanical properties such as the yield strength, flexural modulus, and hardness of PP/mPE binary blends further increased with the addition of HDPE according to the type of HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4027–4036, 2004     

Effects of dispersed phase composition on thermoplastic polyolefins

Ternary blends of polypropylene (PP), ethylene–octene copolymer (mPE), and high‐density polyethylene (HDPE) were prepared based on the phase behavior and physical properties of mPE/HDPE binary blends, and the results were interpreted in terms of morphology and both rheological and mechanical properties of the ternary blends as well as the binary blends. It was found that when mPE encapsulates HDPE in the PP matrix, compared to the encapsulation of mPE by HDPE, better blend properties were obtained, presumably because of the compatibilizing effect of mPE between PP and HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 179–188, 2004     

PP／HDPE／SBS三元共混物的研究——形态结构与性能

研究了PP/HDPE/SBS三元共混物的性能及形态结构特征。研究结果表明,PP三元共混物的冲击韧性除与SBS的含量密切相关外,还与HDPE的含量有关,HDPE起到了与SBS相似的增韧作用。由于HDPE的掺入,减少了SBS的含量,制成了一种力学性能均衡的超高韧性PP三元共混材料。形态结构的研究表明,共混物中,SBS呈颗粒状分布,另外SBS还与HDPE组成了具有包藏结构的复合粒子。     

Thermal properties and crystallization behavior of polyolefin ternary blends

Crystallization behaviors, spherulite growth and structure, and the crystallization kinetics of polypropylene (PP)/ethylene‐α‐olefln copolymer (mPE)/high‐density polyethylene (HDPE) ternary blends and of mPE/HDPE binary blends have been studied using polarizing optical micrography (POM) and differential scanning calorimetry (DSC). In mPE/HDPE blends, large pendant groups of mPE disturbed spherulite growth of HDPE, leading to a different crystallite morphology and isothermal kinetics. Non‐isothermal properties, morphology, and isothermal crystallization kinetics of PP in ternary blends were significantly influenced by the composition and crystallization behavior of the mPE/HDPE binary blends as well as the crystallization condition. Polym. Eng. Sci. 44:1858–1865, 2004. © 2004 Society of Plastics Engineers.     

Compatibilization efficiency of styrene–butadiene triblock copolymers in polystyrene–polypropylene blends with varying compositions

The compatibilization efficiency of two styrene‐butadiene‐styrene triblock copolymers with short (SB1) and long (SB2) styrene blocks was studied in polystyrene (PS)–polypropylene (PP) blends of composition 20, 50, and 80 wt % PS. The supramolecular structure of the blends was determined by small‐angle X‐ray scattering, and the morphology was studied with transmission electron microscopy and scanning electron microscopy. Structural changes in both the uncompatibilized and compatibilized blends were correlated with the values of tensile impact strength of these blends. Even though the compatibilization mechanisms were different in blends with SB1 and SB2, the addition of the block copolymers to the PS–PP 4/1 and PS–PP 1/4 blends led to similar structures and improved the mechanical properties in the same way. These block copolymers had a very slight effect on the impact strength in PS–PP 1/1 blends, exhibiting a nearly cocontinuous phase morphology. The strong migration of SB2 copolymers to the interface and of SB1 copolymers away from the interface were detected during the annealing of compatibilized PS–PP 4/1 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2431–2441, 2004     

The effect of matrix toughness and dispersed elastomer phase on the brittle-ductile transition in PP/HDPE/SBS blends

In this paper the sbrittle-ductile transition of polypropylene, high density polyethylene, and a styrene-butadiene-styrene triblock copolymer (PP/HDPE/SBS) ternary blends is investigated for fixed compositions and prepared under various conditions. The morphology of the SBS dispersed phase particles and impact strength of the PP ternary blends is closely related to the processing conditions. There is a sharp Brittle-Ductile transition for the ternary blends when interparticle distance T becomes less than the critical interparticle distance T_c. Both the impact strength in general and more specifically, T_c depend upon the toughness of the PP/HDPE composite matrix.     

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.     

Study of injection molded microcellular polyamide‐6 nanocomposites

This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The microcellular nanocomposite processing was performed on an injection‐molding machine equipped with a commercially available supercritical fluid (SCF) system. The molded samples produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscope (SEM) analyses. Molding conditions and nano‐clays have been found to have profound effects on the cell structures and mechanical properties of polyamide‐6 (PA‐6) base resin and nanocomposite samples. The results show that microcellular nanocomposite samples exhibit smaller cell size and uniform cell distribution as well as higher tensile strength compared to the corresponding base PA‐6 microcellular samples. Among the molding parameters studied, shot size has the most significant effect on cell size, cell density, and tensile strength. Fractographic study reveals evidence of different modes of failure and different regions of fractured structure depending on the molding conditions. Polym. Eng. Sci. 44:673–686, 2004. © 2004 Society of Plastics Engineers.     

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.     

Development of isotropic compatible HDPE/PP blends for structural applications

In an attempt to provide superior products for the structural applications, this study aimed at preparing isotropic compatible high density polyethylene (HDPE)/ polypropylene (PP) blends without the use of the expensive compatibilization technique. Morphological and structural characterizations of the homopolymers and blends were carried out. In addition, some of the structurally important mechanical and thermal properties were characterized. Such characterizations were performed to investigate whether or not the blends are compatible and therefore acceptable for the structural applications. Scanning electron microscope (SEM) micrographs of the blend samples indicate that the interfacial adhesion between HDPE and PP phases is intimate in the 5/95 HDPE‐PP, good in the 85/15 HDPE‐PP and 95/5 HDPE‐PP, fair in the 30/70 HDPE‐PP and very poor in the 50/50 HDPE‐PP. Similarly, mechanical and thermal responses of the first three blends are remarkable. The 30/70 HDPE‐PP blend displays a fairly good performance. Whereas, the properties of the 50/50 HDPE‐PP blend are very poor. This decides that the first three blends are compatible and, therefore, structurally attractive materials. The fourth is partially compatible and, as a consequence, can be rather acceptable for the structural applications. However, the fifth is incompatible and, of course, is not acceptable for such applications. On the other hand, SEM micrographs and differential scanning calorimetry results indicate that the crystalline structures of individual polymers are appreciably affected by blending. Additionally, the study reveals that the end use performance of blends is strongly dependent on the crystalline structure changes occurring in each component due to blending as well as the compatibility between the blend components. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PP／PE复合基材及其增韧研究

研究了PP/PE共混复合基材的力学性能和形态结构与组成配比的关系.结果表明,PP/HDPE/EPDM和PP/LLDPE共混体系可以制成具有高抗冲击性能的复合基材,且其他力学性能均衡,加工性能良好。弹性体SRS对复合基材的力学性能及形态有较大影响.实验结果表明,LLDPE具有分割、插入、细化PP球晶的作用,并与PP有较好的相容性;EPDM对PP/HDPE共混体系具有良好的增容效果。     

Mechanical behaviors of ethylene/styrene interpolymer compatibilized polystyrene/polyethylene blends

In this study, ethylene/styrene interpolymer was used as a compatibilizer for the blends of polystyrene (PS) and high‐density polyethylene (HDPE). The mechanical properties including tensile and impact properties and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Tensile tests showed that the yield strength of the PS/HDPE/ESI blends decreases considerably with increasing HDPE content. However, the elongation at break of the blends tended to increase significantly with increasing HDPE content. The excellent tensile ductility of the HDPE‐rich blends resulted from shield yielding of the matrix. Izod and Charpy impact measurements indicated that the impact strength of the blends increases slowly with HDPE content up to 40 wt %; thereafter, it increases sharply with increasing HDPE content. The impact energy of the HDPE‐rich blends exceeded that of pure HDPE, implying that the HDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI compatibilizer. The correlation between the impact property and morphology of the blends is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4001–4007, 2007     

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology,mechanical properties and mechanism

As linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m^?2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry     

Compatibilizers for recycling of the plastic mixture wastes. II. The effect of a compatibilizer for binary blends on the properties of ternary blends

In this article, we discuss the effect of a compatibilizer for binary blends on the properties of ternary blends composed of high‐density polyethylene (HDPE), polypropylene (PP), or polystyrene (PS) and poly(vinyl chloride) (PVC) virgin polymers with a simulated waste plastics fraction. Chlorinated polyethylene (CPE), ethylene–propylene rubber (EPR), and their 1/1 (w/w) mixture were tested as compatibilizers for the HDPE/PP/PVC ternary blend. CPE, styrene‐ethylene‐propylene block copolymer (SEP), or their 1/1 (w/w) mixture were tested as compatibilizers for the HDPE/PS/PVC ternary blend. The composition of the ternary blends were fixed at 8/1/1 by weight ratio. The amount of the compatibilizer was 3 phr. Rheological, mechanical, and thermal properties were measured. For the 8/1/1 HDPE/PP/PVC ternary blends, the tensile strength was slightly decreased, but the impact strength was significantly increased by adding EPR, CPE, or their mixture. EPR exhibited the most significant impact modification effect for the ternary blends. In a similar way, for 8/1/1 HDPE/PS/PVC ternary blends, on adding SEP, CPE, or their mixture, the tensile strength was slightly decreased, but the impact strength was noticeably increased. It was found that the SEP worked much better as an impact modifier for the ternary blends than CPE or the SEP/CPE mixture did. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1048–1053, 2000     

Processing‐improved properties and morphology of PP/COC blends

The aim of this study was to improve mechanical properties of polypropylene/cycloolefin copolymer (PP/COC) blends by processing‐induced formation of long COC fibers. According to the available literature, the fibrous morphology in PP/COC blends was observed just once by coincidence. For this reason, we focused our attention on finding processing conditions yielding PP/COC fibrous morphology in a well‐defined, reproducible way. A number of PP/COC blends were prepared by both compression molding and injection molding (IM). Neat polymers were characterized by rheological measurements, whereas phase morphology of the resulting PP/COC blends was characterized by means of scanning electron microscopy (SEM). The longest COC fibers were achieved in the injection molded PP/COC blends with compositions 75/25 and 70/30 wt %. Elastic modulus and yield strength of all blends were measured as functions of the blend composition using an Instron tensile tester; statistically significant improvement of the yield strength due to fibrous morphology was proved. Moreover, two different models were applied in the analysis of mechanical properties: (i) the equivalent box model for isotropic blends and (ii) the Halpin‐Tsai model for long fiber composites. In all PP/COC blends prepared by IM, the COC fibers were oriented in the processing direction, as documented by SEM micrographs, and acted as a reinforcing component, as evidenced by stress–strain measurements. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Recycling of commingled plastics waste containing polypropylene,polyethylene, and paper

Polymer waste recycling is a major technical problem, because large amounts of synthetic polymers are produced every day and polymeric wastes are gathered from municipal solid wastes. There are a few polyolefins, such as polyethylene (PE) and polypropylene (PP) with huge amounts of paper in the waste materials. In order to recycle the commingled plastics waste that contains paper, hydrolytic treatment is needed prior to conventional processing. In this project, the optimum conditions of hydrolytic treatment of paper and the mechanical properties and morphological state of different compositions of PP high‐density PE (HDPE) blends with paper were studied. Ethylene‐propylene‐diene copolymer (EPDM) was added to improve the mechanical properties of blends. The results show that the hydrolytic treatment of paper improves the mechanical properties, such as the tensile strength and modulus of the PP/HDPE/paper composites relative to the untreated samples, and up to 30% paper can be added to commingled PP and HDPE blends. The EPDM was used as an impact modifier. The plastics waste containing paper can be used in applications such as artificial wood. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2573–2577, 2001     

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.