High-density Polyethylene Phase Research Articles

Influence of phase morphology on the sliding wear of polyethylene blends filled with carbon nanofibers

AbstractIn this work, phase separation in carbon nanofiber (CNF) composites with a blend of ultrahigh molecular weight polyethylene (UHMWPE)/high‐density polyethylene (HDPE) was revealed, and its effects on tribological properties were investigated. Results from morphological analysis by optical and scanning electron microscopy indicated two distinct microstructures: a dispersed UHMWPE phase and a continuous microstructure containing HDPE and CNFs. The addition of CNFs into the UHMWPE/HDPE blend induced a decreased steady‐state torque indicative of a decreased dissolution and improved processability. Because CNFs predominantly resided into the HDPE phase, neat HDPE, a HDPE/CNF composite, and neat UHMWPE samples were also prepared for comparison. Wear results, determined by a pin‐on‐disk apparatus, showed that both initial run‐in and steady‐state wear rates of the UHMWPE/HDPE/CNF nanocomposites were reduced with an increasing concentration of CNFs. The wear resistance of the UHMWPE/HDPE blend was more strongly influenced than neat HDPE by the addition of CNFs, which may have been affected by a reduced dissolution and improved interfacial interaction between the two phases. Results from this study suggested that HDPE may not be appropriate for processing UHMWPE composites, as CNFs reside in the HDPE phase, and HDPE diminishes the wear resistance of the material. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Effect of nanoclay on the morphology and properties of poly(methyl methacrylate)/high‐density polyethylene blends

AbstractThe effect of nanoclay on the morphology and properties of poly(methyl methacrylate) (PMMA)/high‐density polyethylene (HDPE) blends was studied. A scanning electron microscopy study of the PMMA/HDPE (70/30 w/w) blends with nanoclay indicated a reduction in the average domain sizes of the dispersed HDPE phase and, hence, a better extent of mixing compared to that of the blends without any nanoclay. An X‐ray diffraction study and transmission electron microscopy revealed the localization of intercalated nanoclay in the PMMA matrix of the PMMA/HDPE (70/30 w/w) blend. However, the same effect of clay was not observed in the PMMA/HDPE (30/70 w/w) blend when HDPE became the matrix. In the PMMA/HDPE (30/70 w/w) blend, the addition of nanoclay increased the domain size of the dispersed PMMA domains by preferential location of the clays inside the PMMA domains. The addition of polyethylene‐grafted maleic anhydride in both compositions of the PMMA/HDPE blend effectively reduced the domain size of the disperse phases in the blend. However, the presence of clay increased the tensile strength and storage modulus of the PMMA/HDPE blends in both blend compositions. Thus, in the PMMA/HDPE blend, the clay platelets acted as a effective compatibilizer as long as they were dispersed mainly in the matrix phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Development of isotropic compatible HDPE/PP blends for structural applications

AbstractIn 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

Fabrication and characterization of multi-filament copper matrix–polyethylene fibres composite wire

In this work, the process of co-drawing followed by bundling and restacking was used to fabricate composite wires with a metallic copper matrix and High Density Polyethylene (HDPE) polymer fibres. After processing, copper matrix composite wires with 3770 polymer domains of approximately 20 μm in diameter were obtained. Differential Scanning Calorimetry analysis, optical microscopy and microhardness measurements were performed on the polymer and the copper components of the composites. The volume fraction and the degree of crystallinity of the polymer remain constant during the drawing. This procedure leads to a lamellar reorganization and fragmentation of the crystalline HDPE phase.

Shear-induced crystallization in a blend of isotactic polypropylene and high density polyethylene

Shish–kebab morphologies were observed with relatively low shear rate and low temperature in the phase-separated isotactic polypropylene (iPP) and high density polyethylene (HDPE) blend. Both components are crystallizable polymers. In our experiments, relatively low shear rates and low temperatures were used, so that the entangled network chains cannot be broken up or disentangled, and the shish nuclei must be formed from oriented and stretched network chains instead of a bundle of pulled-out chains. The effects of shear rate, shear time and temperature on the formation and morphology of shish–kebabs were studied by in situ optical microscopy and shear hot stage under various thermal and shear histories. Optical microscopic measurement showed that the length of iPP cylindrites is much longer than the dimension of phase domains, which implies that iPP cylindrites grow through both iPP and HDPE phase domains. An unexpected ‘core–shell’ structure was observed in the melting procedure, which could be explained by the difference of crystallinity between ‘core’ and ‘shell’. It is most important that two kinds of shish–kebabs, the interface morphology and transcrystallites were observed by scanning electron microscopy (SEM). SEM observation also revealed that the width of iPP shish is about 1–2μm and the width of HDPE shish is about 100nm. The difference in the shish width probably resulted from the lower molecular weight, higher polydispersity, less inter-chain interaction force, and faster nucleation and growth rate of HDPE relative to the iPP chains.

Reometria de torque, propriedades mecânicas e morfologia de blendas compatibilizadas de PA6/PEAD

Neste trabalho investigamos o efeito de diferentes compatibilizantes na reometria de torque, propriedades mecânicas e morfologia das blendas de PA6/PEAD. As blendas foram preparadas em uma extrusora dupla-rosca contra-rotativa com filetes totalmente interpenetrantes, a 240 °C em todas as zonas e velocidade de 50 rpm. A composição das blendas foi de 80/20 (% em peso) para as blendas binárias de PA6/PEAD e de 80/10/10 (% em peso) para as blendas ternárias de PA6/Compatibilizante/PEAD. Os resultados mostraram que houve um aumento no torque das blendas de PA6/PEAD com a adição dos compatibilizantes. O compatibilizante PEgAA foi o que apresentou maior reatividade com a PA6. Entretanto, foi observada uma redução no torque devido à degradação. Os resultados de propriedades mecânicas mostraram que houve aumento considerável na resistência ao impacto das blendas de PA6/PEAD quando os compatibilizantes foram adicionados. Estes resultados foram corroborados pelos dados de deformação na ruptura sob tração. Os resultados de MEV mostraram que a adição dos compatibilizantes às blendas de PA6/PEAD reduziu significativamente o tamanho médio das partículas de PEAD, e melhorou a adesão entre as fases desses polímeros, resultando principalmente, em um aumento da resistência ao impacto.

Compatibilized polyamide 6/polyethylene blend–clay nanocomposites: Effect of the degradation and stabilization of the clay modifier

Blends of polyamide 6 (PA6) and high-density polyethylene (HDPE) were compatibilized using an already investigated method and a sample of Cloisite 15A, a montmorillonite modified with ammonium quaternary salts was added. The blends were prepared in a twin screw extruder and characterized from a morphological, rheological and mechanical point of view. The results indicated that, despite a good morphology achieved in the filled blends and a moderate intercalation of the clay, the mechanical properties are far from being good, especially the ultimate properties. In order to investigate the possible influence of the inhibition of the crystallization and of the degradation of the organic modifier of the clay, DSC measurements and FTIR–ATR were carried out. The results confirm that the clay causes a slight decrease of the crystallization, particularly in the HDPE phase. In addition, in the preparation conditions, the clay modifier is sensitive to thermo-oxidation. Both features can, therefore, explain the bad mechanical performance, even if the degradation effects seem to be more important. In order to prevent, or at least to reduce, the thermo-oxidation, a stabilizing system was added to the filled blends. In this case, the mechanical properties are improved for the entire compatibilized blend set.

Effects of crystallization on dispersion of carbon nanofibers and electrical properties of polymer nanocomposites

AbstractPolymer nanocomposites filled with low volume fractions of carbon nanofibers (CNFs) were prepared by melt‐compounding. Three types of polymers with different crystallization behavior, i.e., weakly‐crystallized low density polyethylene (LDPE), strongly crystallized high density polyethylene (HDPE) and amorphous polystyrene (PS), were selected as matrices for the nanocomposites. The effects of polymer crystallization on the dispersion of CNFs were examined. Optical and electron microscopic examinations revealed that the dispersion of CNFs in the nanocomposite matrices was strongly depended on the crystallization behavior of polymer matrices. The CNFs were found to disperse uniformly in weakly crystallized LDPE and amorphous PS matrices, but agglomerated in HDPE due to its strong crystallization tendency. Such a distinct dispersion behavior of CNFs in polymers had a profound effect on the electrical properties of the nanocomposites investigated. The PS/CNF nanocomposites exhibited the lowest percolation threshold. The HDPE/CNF nanocomposites showed the largest percolation threshold due to the CNF agglomeration within the amorphous phase of HDPE. POLYM. ENG. SCI., 48:177–183, 2008. © 2007 Society of Plastics Engineers

Study of Mechanical Properties and Morphology of PA 6/PO Blends Compatibilized by PO Grafted with Itaconic Acid

AbstractTwo different types of polyolefine (PO) grafted with itaconic acid as a reactive compatibilizer, polypropylene (PP) grafted with itaconic acid (PP-g-ITA) and high density polyethylene (HDPE) grafted with itaconic acid (HDPE-g-ITA), PP and HDPE grafted with copolymer of itaconic acid and styrene (PP-g-(ITA-St) and HDPE-g-(ITA-St)) were prepared by melt graft technique through reactive type twin-screw extruder. FT-IR and thermal analysis were used to characterize the structure of the graft copolymer. The graft ratio (GR) and melt flow rate (MFR) were determined by non-aqueous titration and melt flow rate analyzer. The effect of the concentration of monomer and initiator dosage on GR and MFR of graft copolymer were studied. Then polyamide 6 (PA 6) blends, PA 6/PP (PA 6/HDPE), that compatibilized with PP-g-ITA (HDPE-g-ITA) were prepared. The morphology of the blends was analyzed by SEM, DSC and Molau tests and the mechanical properties of which were characterized by tensile, impact, and bend tests. The results of mechanical property showed that the impact strength of blends was increased by 50% and 70% after PP-g-ITA and HDPE-g-ITA was used as compatibilizer, but the MFR of blends was decreased. The SEM photographs indicated that the accession of compatibilizer obviously improved binding state between two phases in blends, the size of dispersed phase was reduced evidently and the interface became indistinct. DSC results demonstrated that in the case of PP-g-ITA, glass temperature (Tg) of PA 6 matrix in blends was ascended, melt point (Tm) was improved a little, crystallinity (Xc) was decreased, Tm and Xc of PP phase was increased; With the accession of HDPE-g-ITA, Tm of PA 6 matrix and HDPE phase had almost no change, Xc of PA 6 matrix was decreased and Xc of HDPE phase was increased.

Effect of EPDM on Morphology, Mechanical Properties, Crystallization Behavior and Viscoelastic Properties of iPP+HDPE Blends

AbstractSummary: Blends of isotactic polypropylene (iPP) and high density polyethylene (HDPE) with and without ethylene‐propylene‐diene (EPDM) terpolymer as compatibilizer were systematically investigated to determine the influence of the EPDM on blends properties. The morphology was studied by Scanning Electron Microscopy (SEM). Mechanical properties of investigated systems: tensile strength at break, elongation at break, yield stress and Izod impact strength were determined. Crystallization behavior was determined by Differential Scanning Calorimetry (DSC). Dynamic Mechanical Analysis (DMA) was used to determined the storage modulus (E′), loss modulus (E″), and loss tangent (tan δ). The PP+HDPE blend revealed poor adhesion between PP and HDPE phases. Finer morphology was obtained by EPDM addition in PP+HDPE blends and better interfacial adhesion. Addition of HDPE to PP decreased tensile strength at break, elongation and yield stress. Decrease of tensile strength and yield stress is faster with EPDM addition in PP+HDPE blends. Elongation at break and impact strength was significantly increased with EPDM addition. The addition of EPDM in PP+HDPE blends did not significantly change melting points of PP phase, while melting points of HDPE phase was slightly decreased in PP+HDPE+EPDM blends. The EPDM addition increased the percentage of crystallization (Xc) of PP in PP+HDPE blends. The increase of Xc of HDPE was found in the blend with HDPE as matrix. Dynamical mechanical analysis showed glass transitions of PP and HDPE phase, as well as the relaxation transitions of their crystalline phase. By addition of EPDM glass transitions (Tg) of HDPE and PP phases in PP+HDPE blends decreased. Storage modulus (E′) vs. temperatures (T) curves are in the region between E′/T curves of neat PP and HDPE. The decrease of E′ values at 25 °C with EPDM addition in PP+HDPE blends is more pronounced.

Effects of electron-beam irradation on some structural properties of granulated polymer blends

The aim of this article was to show the effects of the electron radiation dose and presence of a compatibiliser on the peak melting temperature ( T pm) of the crystalline phase, crystallinity ( X c), and melt flow rate (MFR) of granulated blends of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) as well as of blends of LDPE, HDPE, and PP. The purpose of applying the high-energy electron radiation with doses up to 300 kGy and of adding a compatibiliser was to enhance mechanical properties of the studied blends and, at the same time, to investigate the possibility of using this technique in the processes of recycling polymeric materials. As the compatibilisers, the styrene–ethylene/butylene–styrene elastomer grafted with maleic anhydride (SEBS- g-MA) and trimethylol propane trimethacrylate (TMPTA) were utilised; they were added at the amounts of 5, 10, and 15 wt% and 1, 2, and 3 wt%, respectively. The enhancement of mechanical properties was accompanied by the following effects, discussed in this article: (i) a decrease in the peak melting temperature upon the electron radiation for the crystalline phase of LDPE, HDPE, and PP that constituted the studied granulated blends and (ii) changes in MFR upon both the electron radiation and the addition of compatibilisers.

Rapid manufacturing of PA/HDPE blend specimens by selective laser sintering: Microstructural characterization

The structure and properties of parts made by selective laser sintering (SLS) depend on the process parameters and the characteristics of the powder material to be processed. The use of polymeric blends can increase the range of structures and properties of SLS parts. This study investigates the processing of blends of polyamide (PA2200) and high-density polyethylene (HDPE) by SLS using a CO 2 laser. Powder properties of undiluted polymers, mixture composition, processing parameters and their influence on the microstructure of the specimens manufactured, were evaluated. PA2200 showed higher absorption of laser energy than HDPE during the sintering of blend specimens, with subsequent thermal energy transfer to the melting of the HDPE phase. The microstructures of PA2200/HDPE blend specimens were heterogeneous with co-continuous and disperse phases depending on the quantity of HDPE. The porosity and crystallinity also changed as a function of the component proportions. These results suggest that it is feasible to manufacture blend parts using SLS, with control over the structure and properties being achieved through selecting the polymer properties (laser absorption and melt flow), powder characteristics (form and size distribution) and the optimum process parameters according to the blend composition.

Rheological and Mechanical Properties of LDPE/HDPE Blends

Melt rheology and mechanical properties of binary blend of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated. Four different wt fractions of blends containing LDPE/HDPE (20/80, 40/60, 60/40, and 80/20) were prepared. Cole-Cole plots [storage melt viscosity (η′) vs. loss melt viscosity (η″)] and relation between storage melt viscosity (η′) with frequency (ω) and blend composition were constructed. Miscibility of blends was established from rheological data. Impact strength of the blends increased with increasing LDPE concentration, whereas tensile strength shows the opposite trends. Percentages of the crystallinity of the blends were calculated by both the differential scanning calorimetry and wide-angle X-ray scattering methods, which show that the percentage of crystallinity decreased with increasing LDPE concentration, but the rate of crystallization of HDPE phase was unaffected.

Small‐angle X‐ray scattering investigation of the deformation processes in the amorphous phase of high density polyethylene

AbstractIn situ small‐angle X‐ray scattering of high density polyethylene under uni‐axial tensile test was used for investigating the deformation at the scale of the periodic crystalline–amorphous nano‐structure. The more or less uniform elastic straining of the rubbery amorphous layers is discussed in terms of mechanically active intercrystalline tie chains. Correlation is made with the long‐term use properties. It is concluded that this approach is a powerful means to assess the mechanical efficiency of tie molecules. Copyright © 2004 Society of Chemical Industry

A lithium ionomer of poly(ethylene‐co‐methacrylic acid) copolymer as compatibilizer for blends of poly(ethylene terephthalate) and high density polyethylene

AbstractBlends of 75/25 poly(ethylene terephthalate) (PET)/high density polyethylene (HDPE) containing poly(ethylene‐co‐methacrylic acid) partially neutralized with lithium (PEMA‐Li) were obtained by direct injection molding in an attempt (i) to ameliorate the poor performance of the binary blend and (ii) to find the best compatibilizer content. The presence of PEMA‐Li caused a nucleation effect on PET, and a decrease in the crystalline content of HDPE. The compatibilizing effect of PEMA‐Li was due to the combined effects of interaction at the interface and chemical reactions. The ternary blends showed a complex morphology, with two dispersed HDPE and PEMA‐Li phases that contained a small internal dispersed phase, probably of PET. The compatibilizing effect of PEMA‐Li was clearly shown by means of an impressive increase in the ductility and to a minor extent in the impact strength. The highest property improvement (ductility increase 1450%) appeared upon the addition of 45% PEMA‐Li with respect to the HDPE phase, but taking into account the recycling interest, the ternary blend with the addition of roughly 22.5% PEMA‐Li appears to be the most attractive.

Adhesion between semi-crystalline polymers: grafted PE/EVOH copolymer

Amongst modern polymeric materials, the use of multi-layer structures is becoming popular. This study deals specifically with a five-layer system composed of two outer strata of high-density polyethylene (HDPE) with an inner layer of an ethylene/vinyl alcohol copolymer (EVOH). The further two layers consist of an “adhesive” between the HDPE and EVOH phases: a grafted polyethylene (PE *). We study here the adhesion between EVOH and PE * by means of peel tests. Rate- and temperature-dependent behaviour is described by time–temperature superposition. High values of peel energy are partly attributable to considerable dissipation during elasto-plastic deformation of the peel arm, yet the intrinsic, local adhesion energy is also large. The latter can be partially explained using the Dugdale model, but a second mechanism related to shear would also seem important.

Carbon black‐filled PET/HDPE blends: Effect of the CB structure on rheological and electric properties

AbstractThe rheological and electric properties of blends of poly(ethylene terephthalate) (PET) and high‐density polyethylene (HDPE) filled with various types of carbon black (CB) were analyzed in detail in this project. Four types of CB samples with available values of surface area, particle size, porosity, density, and maximum packing fraction were considered. Blends were prepared using an internal mixing chamber at two different rotational speeds, prior to mold compression of the samples. The rheological properties of the blends with varying polymer composition and a constant amount of CB were recorded in terms of torque variation with time for two shear rates (in terms of rotational speed). Rheological data were related to the resistivity of blends. Results show that the CB structure (porosity, surface area, apparent bulk density, and particle size) largely determine the resulting equilibrium torque and electrical properties. Furthermore, since CB is preferentially located in the HDPE phase, higher conductivity is observed as the PET content decreases, since the relative CB content in this phase increases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 562–569, 2001

Positive and negative temperature coefficient effects of an alternating copolymer of tetrafluoroethylene–ethylene containing carbon black-filled HDPE particles

A conductive polymer composite was prepared by melt-mixing of an immiscible semicrystalline polymer blend of an alternating copolymer of tetrafluoroethylene–ethylene (ETFE), high density polyethylene (HDPE), and carbon black (CB). The optical microscopy and time-of-flight secondary mass spectrometry results indicated that the CB particles were selectively localized in the HDPE phase. In addition, it was found that the CB-filled HDPE particles formed a dispersed phase in the ETFE matrix. A double-positive temperature coefficient (PTC) effect was observed in the composite, caused by the large thermal expansion due to the consecutive melting of HDPE and ETFE crystallites. The negative temperature coefficient (NTC) that was observed in this system could not have been caused by the formation of flocculated structures because the size of the CB-filled HDPE particles is significantly large, so that their mobility is extremely limited even at high temperatures. This conclusion was confirmed by observing the morphology of the composite at temperature ranging from 25 to 250°C. These results suggest that new mechanisms need to be uncovered to explain the NTC effect of conductive polymer composites.

Blend compatibility study by solid-state 13C nuclear magnetic resonance

The application of proton spin–lattice relaxation time in the rotating frame and carbon-13 cross-polarization/magic-angle spinning to investigate the compatibility of a polymeric blend formed by high-density polyethylene (HDPE) and a synthetic petroleum resin of low molecular weight showed that this system presents a range of compatibility varying up to 40% (w/w) of the petroleum resin. The blends showed a shift of the NMR lines to short contact time—i.e., a rigid region. The 60/40 blend clearly displays the presence of domains of distinct mobility: one rigid (short contact time) and the other flexible (long contact time), indicating phase separation. Thus, besides the crystalline phase of HDPE, the blends show two amorphous phases: one rich in the polyolefin and the other rich in the low-molecular-weight component.

Effects of Thermal History on the Interfacial Layer of PS/HDPE/SBS Blends

Polystyrene (PS), high-density polyethylene (HDPE), and a triblock copolymer of styrene, butadiene, and styrene (SBS) were melt-mixed and quenched from the melt state into liquid nitrogen, ice water, room-temperature water, and boiling water. Several specimens quenched into liquid nitrogen were annealed at elevated temperatures. The samples that underwent different thermal histories were examined with TEM, and the effects of cooling rate, annealing time, and annealing temperature on the interfacial layer structure were investigated. In the melt-mixed PS/HDPE/SBS blend a mixture of SBS and PS was situated between the PS and PE phases, forming an interfacial layer encapsulating the PE particles. In the sample prepared by quenching the melt into liquid nitrogen, the interfacial layer between the PS and HDPE phases was about 200 nm thick. Two thin SBS layers on the both sides of the interfacial layer were observed. The SBS separated from the PS and PE phases, forming a thinner interfacial layer under slow coo...