Cocrystallization and miscibility studies of blends of ultrahigh molecular weight polyethylene with conventional polyethylenes (original) (raw)
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Journal of Applied Polymer Science, 2005
Various blend ratios of high-density polyethylene (HDPE) and ultrahigh-molecular-weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. Although the presence of HDPE in the blends enabled melt processing, the presence of UHMWPE helped to improve the toughness of the resulting blends. The processability of the blends was investigated with the Brabender torque, which was used as an indication of the optimum blend conditions. The blends were characterized with differential scanning calorimetry. The mechanical tests performed on the blends included tensile, flexural, and impact tests. A 50:50 (w/w) blend yielded optimum properties in terms of the processability and mechanical properties. The tensile property of the 50:50 blend was intermediate between those of HDPE and UHMWPE, but the strain at break increased 200% in comparison with that of both neat resins. The energy at break of the 50:50 blend revealed an improvement in the toughness. The fracture mechanism was also investigated with scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 413–425, 2005
Journal of Applied Polymer Science, 2002
This article presents the tensile properties and morphological characteristics of binary blends of the high-density polyethylene (HDPE) and a linear low-density polyethylene (LLDPE). Two constituents were melt blended in a single-screw extruder. Injection-molded specimens were evaluated for their mechanical properties by employing a Universal tensile tester and the morphological characteristics evaluated by using a differential scanning calorimeter and X-ray diffractometer. It is interesting to observe that the mechanical properties remained invariant in the 10 -90% LLDPE content. More specifically, the yield and breaking stresses of these blends are around 80% of the corresponding values of HDPE. The yield elongation and elongation-at-break are around 65% to corresponding values of HDPE and the modulus is 50% away. Furthermore, the melting endotherms and the crystallization exotherms of these blends are singlet in nature. They cluster around the corresponding thermal traces of HDPE. This singlet characteristic in thermal traces entails cocrystallization between these two constituting components. The clustering of thermal traces of blends near HDPE meant HDPE-type of crystallites were formed. Being nearly similar crystallites of blends to that of HDPE indicates nearness in mechanical properties are observed. The X-ray diffraction data also corroborate these observations.
Journal of Applied Polymer Science, 2012
The dynamic rheological behavior of low‐density polyethylene (LDPE)/ultra‐high‐molecular‐weight polyethylene (UHMWPE) blends and linear low‐density polyethylene (LLDPE)/UHMWPE blends was measured in a parallel‐plate rheometer at 180, 190, and 200°C. Analysis of the log–additivity rule, Cole–Cole plots, Han curves, and Van Gurp curves of the LDPE/UHMWPE blends indicated that the blends were miscible in the melt. In contrast, the rheological properties of LLDPE/UHMWPE showed that the miscibility of the blends was decided by the composition of LLDPE. The differential scanning calorimetry results and scanning electron microscopy photos of the LLDPE/UHMWPE blends were consistent with the rheological properties, whereas with regard to the thermal and morphological properties of LDPE/UHMWPE blends, the results reveal three endothermic peaks and phase separation, which indicated a liquid–solid phase separation in the LDPE/UHMWPE blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Thermorheology and processing of polyethylene blends : macromolecular structure effects
2008
Rheological and processing behavior of a number of linear low-density polyethylene (LLDPE)/low-density polyethylene (LDPE) blends was studied with emphasis on the effects of long chain branching. First, a linear low-density polyethylene (LL3001.32) was blended with four LDPE's having distinctly different molecular weights. At high LDPE weight fractions, DSC melting thermograms have shown three different polymer phases; two for the pure components and a third melting peak of co-crystals. Different rheological techniques were used to check the thermorheological behavior of all blends in the melt state and the effect of long chain branching. It was found that all blends are miscible in the melt state at small LDPE concentrations. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, SER. The blends exhibit strain hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branchi...
Polymer international, 2005
The influence of M w of LLDPE on the rheological, thermal and mechanical properties of m-LLDPE/ HDPE blends of low and high branch content (BC) was studied. Melt rheology of m-LLDPE blended with linear HDPE revealed strong influence of M w on melt miscibility at both branching levels. Low M w m-LLDPE/HDPE blends are suggested to be miscible at all compositions, while viscosity of high M w m-LLDPE/HDPE blends showed negative deviation from log additivity suggesting layered morphology of these blends. The DSC results suggest that compatibility in the solid state is independent of M w and BC. For all blends studied, the HDPE-rich blends were found to contain single crystal populations suggesting high degree of cocrystallization, whereas, m-LLDPE rich phase showed separate crystallization. The melt miscibility and the crystallization of high BC m-LLDPE blends with HDPE are suggested to be controlled by different factors. Small strain mechanical properties of these blends were found to be a strong function of blend compatibility and the specific properties of the blend components.
Polypropylene–polyethylene blend morphology controlled by time–temperature–miscibility
Polymer, 2000
Isotactic polypropylene (PP) has been blended with various types of polyethylene, high density (HDPE), low density (LDPE), linear low density (LLDPE), very low density (VLDPE) and ultra low density (ULDPE). Each blend contained 20% by mass PP. The blends were cooled from the melt to temperatures where PP could crystallise, but not the polyethylene. When the two polymers were immiscible, or immiscible at the crystallisation temperature where liquid-liquid phase separation occurred on cooling, then the two phases crystallised independently. Under these conditions the crystallisation rate (half-time) for PP was very similar to that of pure polypropylene. When the polymers were miscible, crystallisation of PP took place from a solution in the molten polyethylene. Under these conditions the crystallisation rate of PP was greatly decreased since it was in dilute solution. The significant change in rate of crystallisation of PP was a detection of miscibility. After PP had crystallised the blend was cooled to ambient temperature and the polyethylene quickly crystallised in the intervening spaces.
Properties of polyethylene-polypropylene blends
Journal of Materials Science, 1980
High-density polyethylene (PE)-isotactic polypropylene (PP) blends have been characterized by a number of techniques such as wide-angte X-ray scattering, differential scanning calorimetry, picnometry, swelling in n-hexane and finally stress-strain tensile elongation. All the measurements have been performed on cilindrical shaped specimens, obtained directly by extrusion. The specimens show a complete random orientation of the crystallites of both the components. No co-crystallization phenomenon are observed. The melting point of both PE and PP decreases slightly with increasing concentration of the second component. The fractional crystallinity of PE decreases and that of PP increases with respect to the corresponding homopolymer values with increase in the concentration of the companion polyolefin. Such an effect is related to morphological kinetic effects and to different rates of crystallization of the two components, during the non-isothermal crystallization process following extrusion. Young's modulus, E is proportional to the overall fractional crystallinity. The ultimate properties show a synergistic effect due to the strong interactions between the crystallites and their tie molecules of the twoPE and PP distinct phases. Finally, it is to be remarked that the results obtained in this paper, especially with respect to the ultimate properties, are quite different from those reported by other authors. This can be attributed to the different processing conditions used for obtaining the present blend specimens. Such conditions are certainly very important in determining particular blend morphologies which will determine in turn the properties of the analysed samples.
Materials Science, 2011
Blends of high-density polyethylene (HDPE), moderate and hyper-branched LLDPEs (LLDPE and HbPE, respectively) have attained widespread commercial applications, though the understanding of the mechanical and melt-flow properties of such blends has been handicapped by the absence of a consensus concerning the degrees of mixing of the components. Moreover, usually the blends are obtained by melt blending, which may not ensure the initial homogeneity of the components. In our work the mixtures were prepared by dissolving the conventional LLDPE having branching content 7.2 wt% with HbPE with comonomer content 17.8 wt% in xylene at 130 °C and stirring for 2 hours. The same procedure was applied for the blending of HDPE with HbPE. After dissolving the mixtures were cooled in liquid nitrogen and after that freeze dried in vacuum line. The ratio of components in the blends was varied. Differential scanning calorimetry has been used to investigate the miscibility and thermal behavior of the blends. For this purpose isothermal and non-isothermal treatment of prepared blends were conducted. By preliminary study the double melting peaks in non-isothermal endotherms have been observed in all the studied blends. The presence of two peaks in DSC scan can be attributed to the formation of separated crystals from both the high density/linear low density and highly branched components. However, certain limited degree of co-crystallization
Journal of Applied Polymer Science, 2003
The phase behavior and the crystallization kinetics of blends composed of isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE) were investigated by differential scanning calorimetry. The phase behavior indicates the formation of separate crystals of iPP and LLDPE at each investigated blend composition. The crystallization trace reveals that iPP crystallizes in its normal range of temperatures (i.e., at temperatures higher than that of LLDPE), when its content in the blend is higher than 25% by weight. In the blend whose iPP content is as high as 25%, at least a portion of iPP crystallizes at temperatures lower than that of LLDPE. This behavior has been proposed by Bassett to be attributed to a change in the kind of nucleation from heterogeneous to homogeneous. From the Avrami analysis of the isothermal crystallization of iPP in the presence of molten LLDPE, n values close to 2 are always obtained. According to our previously proposed interpretation of the Avrami coefficient, it can be related to the crystallite fractal dimension, through d ϭ n ϩ 1, which gives values close to 3, according to the spherulitic observed morphology. The kinetics parameter, i.e., the half-time of crystallization, and the kinetic constant k show that a decrease in the overall rate of crystallization of iPP occurs on blending. Optical microscopy photographs, taken during the cooling of the samples from the melt, confirm the above results and show increasingly less resolved spherulite texture on increasing LLDPE content in the blend. The diffusion parameters evaluated for the neat polymers and for the blends in dichloromethane, which give information on the miscibility in the amorphous state, show that the diffusional behavior of the blends is governed by iPP, suggesting a two-phase amorphous state.
Polymer International, 2004
In this paper, the implications of melt compatibility on thermal and solid-state properties of linear low density polyethylene/high density polyethylene (LLDPE/HDPE) blends were assessed with respect to the effect of composition distribution (CD) and branch content (BC). The effect of CD was studied by melt blending a metallocene (m-LLDPE) and a Ziegler-Natta (ZN) LLDPE with the same HDPE at 190 • C. Similarly, the effect of BC was examined. In both cases, resins were paired to study one molecular variable at a time. Thermal and solid-state properties were measured in a differential scanning calorimeter and in an Instron mechanical testing instrument, respectively. The low-BC m-LLDPE (BC = 14.5 CH 3 /1000 C) blends with HDPE were compatible at all compositions: rheological, thermal and some mechanical properties followed additivity rules. For incompatible high-BC (42.0 CH 3 /1000 C) m-LLDPE-rich blends, elongation at break and work of rupture showed synergistic effects, while modulus was lower than predictions of linear additivity. The CD of LLDPE showed no significant effect on thermal properties, elongation at break or work of rupture; however, it resulted in low moduli for ZN-LLDPE blends with HDPE. For miscible blends, no effect for BC or CD of LLDPE was observed. The BC of LLDPE has, in general, a stronger influence on melt and solid-state properties of blends than the CD.