Effect of Polyethylene Molecular Architecture on the Dynamic Viscoelastic Behavior of Polyethylene/Polyhexene-1 Blends and Its Correlation with Morphology

In the present work, the rheology, morphology, and interfacial interaction of polyethylene/polyhexane-1 (PE/PH-1) blends with various polyethylene types with different molecular architectures are investigated. The scanning electron microscopy (SEM) images showed a droplet-matrix morphology in all percentage of PH-1 for all blend systems and the size of droplets increased proportionally with PH-1 content. The minimum droplet size is observed for high-density polyethylene (HDPE)/PH-1 blends. The homogeneity of the blends at various compositions is assessed by using viscoelastic parameters determined by dynamic oscillation rheometry in the linear viscoelastic region. A distinct Newtonian plateau at low frequencies is perceived and the variations of complex viscosity (η*) versus angular frequency (ω) for all blend systems are in good agreement with Carreau-Yasuda model. The complex viscosity of samples at various percentages of PH-1 showed the negative deviation from mixing rule in low and high frequencies for all blend systems. The Cole-Cole plots deviated from semi-circular shape at higher percentages of PH-1 than 10wt% in the blends of low-density polyethylene (LDPE)/PH-1 and linear low-density polyethylene (LLDPE)/PH-1. By using emulsion theoretical model, the lowest interfacial tension is found for HDPE/PH-1 blends comparing with its counterparts based on LDPE and LLDPE and the best fitting with experimental data was observed for this blends system.     

Effect of nitrocellulose (NC) on morphology,rheological and mechanical properties of glycidyl azide polymer based energetic thermoplastic elastomer/NC blends

As a new kind of propellant binder, energetic thermoplastic elastomer (ETPE ) can improve propellant recyclability and environmentally friendly disposal. The rheological behavior of the ETPE binder can be beneficial to identify suitable and safe conditions for processing ETPE propellants. In this paper, ETPE /nitrocellulose (NC ) blends with different mass ratios of NC to ETPE were prepared by the physical mixing method. The heat of explosion and the morphological, thermal, mechanical and rheological properties of the resulting blends were studied systematically. It was found that the heat of explosion of ETPE /NC blends increased with increasing NC content. SEM images showed that the NC domains in the blends changed from tiny pieces to fibers with increasing NC mass ratio, which indicates phase separation in the blends. The tensile mechanical properties of the blends had a peak value when the NC content was 10 wt%, and then increased with the increasing addition of NC . The thermal behavior made clear that the ETPE and NC were partially miscible. Rheological studies on dynamic strain sweep and frequency sweep demonstrated that the content of NC in the blends had a monotonic effect on their rheological properties at 130 °C. Rheological studies also showed that the rheology of the blends is dependent on temperature. The Cole ? Cole and Han plots confirmed phase separation in the blends. © 2016 Society of Chemical Industry     

Rheological and mechanical properties in polyethylene blends

Melt rheology and mechanical properties in linear low density polyethylene (LLDPE)/low density polyethylene (LDPE), LLDPE/high density polyethylene (HDPE), and HDPE/LDPE blends were investigated. All three blends were miscible in the melt, but the LLDPE/LDPE and HDPE/LDPE blends exibiled two crystallization and melting temperatures, indicating that those blends phase separated upon cooling from the melt. The melt strength of the blends increased with increasing molecular weight of the LDPE that was used. The mechanical properties of the LLDPE/LDPE blend were higher than claculated from a simple rule of mixtures, whiele those of the LLDPE/HDPE blend conformed to the rule of mixtures, but the properties of HDPE/LDPE were less than the rule of mixtures prediction.     

The impact of viscoelastic behavior and viscosity ratio on the phase behavior and morphology of polypropylene/polybutene‐1 blends

In this study, the influence of the viscosity ratio on the rheology, morphology, and interfacial interaction of polypropylene and polybutene‐1 (PB‐1) resins with various melt flow behaviors in the blend are investigated. A droplet‐matrix morphology is observed in the scanning electron microscope images for all formulations and the size of particles increased proportionally by increasing the viscosity ratio. Viscoelastic parameters of blends at various viscosity ratios and compositions are measured by small‐amplitude oscillation rheometry in the linear viscoelastic region. The Cole‐Cole plots showed a nearly semicircular arc for all compositions. This semicircular arc is observed while the viscosity ratio is lower than 1, and the Cole‐Cole plots deviated from the semicircular shape at PB‐1 content higher than 10 wt%. It is emphasized that, in addition to compatibility, the semi‐circularity of Cole‐Cole plots affects the size of the dispersed particles, which is under the influence of the viscosity ratio. It is found that the interfacial tensions of polypropylene and PB‐1 are not significantly different when changing the viscosity ratio and coarsening the morphology. The form relaxation times in the blends with lower viscosity ratios are shorter than the form relaxation times of the blends with higher viscosity ratios. J. VINYL ADDIT. TECHNOL. 21:94–101, 2015. © 2014 Society of Plastics Engineers     

Rheological,thermal, and morphological properties of low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene and linear low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene blends

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     

Thermoplastic elastomers from rubber and recycled polyethylene: chemical reactions at interphases for property enhancement

Recycled low density polyethylene (R‐LDPE) has been reactively compatibilized with butadiene rubber (BR) by using small additions of reactive polyethylene copolymers and reactive BRs to produce thermoplastic elastomers (TPEs). TPEs were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), rheology measurements, wide‐angle X‐ray scattering (WAXS) and mechanical testing. WAXS results show that the presence of BR and reactive modifiers does not completely prevent the crystallization of R‐LDPE during the TPE formation. Depression of the melting point has been found in all cases. Also in all cases, compatibility is provided by formation of interfacial layers. The best mechanical characteristics are obtained for R‐LDPE + BR blends compatibilized with poly(ethylene‐co‐acrylic acid) (PE‐co‐AA) and polybutadiene terminated with isocyanate groups (PB‐NCO) for PB‐NCO = 7.5 wt% per PB and COOH/NCO ratio = 1/1. The stress at break and elongation at break are respectively improved by 31 % and 63 %. The PB‐NCO modifier participates in co‐vulcanization with BR in the rubber phase and reacts at the interface with the PE‐co‐AA dissolved in the polyolefin phase. As a result, the amorphous phase of R‐LDPE is dissolved by the rubber phase and a morphology with dual phase continuity is formed, assuring an improvement of mechanical properties of TPEs. Copyright © 2004 Society of Chemical Industry     

Degradation behavior of poly (caprolactone)–poly(ethylene glycol) block copolymer/low–density polyethylene blends

Blends of poly(carprolactone)-poly(ethylene glycol) block polymer (PCE) with low-density polyethylene (LDPE) were prepared by extrusion followed by compression molding into thin film specimens. The morphology, thermal properties, degradation, and mechanical behavior of the blends were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), water immersion, static tensile testing, and dynamic mechanical analysis (DMA). The LDPE/PCE blends were immiscible for all chemical compositions. A LDPE/PCE (75/25 wt%) blend exhibited small reductions in weight and tensile strength after immersion in a buffer solution (pH = 5.0) at 50°C for extended periods of time. However, grafting maleic anhydride onto the LDPE/PCE blends improved the compatibility between the LDPE and PCE phases. Consequently, a 75/25 wt% blend of maleated LDPE/PCE exhibited significant losses in weight and tensile strength after immersion in the buffer solution. For comparison, blends of poly(caprolactone) (PCL) with LDPE were fabricated by similar techniques. The effect of compatibilizer on the degradation of LDPE/PCE and LDPE/PCL is discussed.     

Processability of LLDPE/LDPE blends: Capillary extrusion studies

The processing behavior of a number of linear low‐density polyethylenes/low density polyethylene (LLDPE/ LDPE) blends with emphasis on the effects of long chain branches is presented. A Ziegler‐Natta linear low‐density polyethylene was blended with four low‐density polyethylene LDPE's having distinctly different molecular weights. The weight fractions of the LDPEs used in the blends were 1, 5, 10, 20, 50, and 75 wt%. Capillary extrusion reveals that the onset of sharkskin and gross melt fracture are slightly influenced with the addition of LDPE into LLDPE. However, the amplitude of the oscillations in the stick‐slip flow regime was found to scale well with the weight fraction of LDPE. Amounts as low as 1 wt% LDPE have a significant effect on the amplitude of pressure oscillations. These effects are clearly due to the presence of long chain branching (LCB); furthermore, it was observed that the onset of this flow regime was shifted to higher shear rates with increase of LDPE content. On the other hand, shear rheology is not sensitive to detect addition of small levels of LDPE up to 20 wt%. Extensional rheology can detect levels of LDPE as small as 1 wt% only at high Hencky strain rates (typically greater than 5s^?1) and only for certain blends, typically those that contain LDPE of high molecular weight. It is suggested that the magnitude of oscillations in the oscillating melt fracture flow regime is a sensitive method capable of detecting low levels of LCB. POLYM. ENG. SCI., 47:1317–1326, 2007. © 2007 Society of Plastics Engineers     

Co‐crystallization in ternary polyethylene blends: tie crystal formation and mechanical properties improvement

Understanding the co‐crystallization behavior of ternary polyethylene (PE) blends is a challenging task. Herein, in addition to co‐crystallization behavior, the rheological and mechanical properties of melt compounded high density polyethylene (HDPE)/low density polyethylene (LDPE)/Zeigler ? Natta linear low density polyethylene (ZN‐LLDPE) blends have been studied in detail. The HDPE content of the blends was kept constant at 40 wt% and the LDPE/ZN‐LLDPE ratio was varied from 0.5 to 2. Rheological measurements confirmed the melt miscibility of the entire blends. Study of the crystalline structure of the blends using DSC, wide angle X‐ray scattering, small angle X‐ray scattering and field emission SEM techniques revealed the formation of two distinct co‐crystals in the blends. Fine LDPE/ZN‐LLDPE co‐crystals, named tie crystals, dispersed within the amorphous gallery between the coarse HDPE/ZN‐LLDPE co‐crystals were characterized for the first time in this study. It is shown that the tie crystals strengthen the amorphous gallery and play a major role in the mechanical performance of the blend.© 2016 Society of Chemical Industry     

Poly(allylammonium acrylate) as a drug-releasing matrix

A large increase in the crystallization temperature of low density polyethylene (LDPE) when blended with high density polyethylene (HDPE) is reported. Such behavior is observed for quenched LDPE rich blends when the low melting component is cooled from 119 °C under controlled conditions in the differential scanning calorimeter. It is suggested that the presence of the most linear LDPE methylene segments within the HDPE-rich crystals (cocrystallization phenomenon) facilitates the nucleation of the more branched LDPE segments on cooling. On reheating, a depression in the low melting temperature component (LDPE) is observed with increasing HDPE content in the blend. Received: 29 December 1996/Revised: 11 March 1997/Accepted: 14 March 1997     

Elongational rheology of LLDPE / LDPE blends

The objective of this study is to investigate the effect of low density polyethylene (LDPE) content in linear low density polyethylene (LLDPE) on the crystallinity and strain hardening of LDPE / LLDPE blends. Three different linear low density polyethylenes (LL‐1, LL‐2 and LL‐3) and low density polyethylenes (LD‐1, LD‐2 and LD‐3) were investigated. Eight blends of LL‐1 with 10, 20, 30 and 70 wt % of LD‐1 and LD‐3, respectively, were prepared using a single screw extruder. The elongational behavior of the blends and their constituents were measured at 150°C using an RME rheometer. For the blends of LL‐1 with LD‐1, the low shear rate viscosity indicated a synergistic effect over the whole range of concentrations, whereas for the blends of LL‐1 with LD‐3, a different behavior was observed. For the elongational viscosity behavior, no significant differences were observed for the strain hardening of the 10–30% LDPE blends. Thermal analysis indicated that at concentrations up to 20%, LDPE does not significantly affect the melting and crystallization temperatures of LLDPE blends. In conclusion, the crystallinity and rheological results indicate that 10–20% LDPE is sufficient to provide improved strain hardening in LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3070–3077, 2003     

Miscibility analysis in LLDPE/LDPE blends via thermorheological analysis: Correlation with branching structure

This article describes correlation between thermorheological properties and the miscibility of LLDPE/LDPE blends. Samples of LLDPE/LDPE with the blending ratio of 5/95, 10/90, 25/75, 50/50, 75/25, and 90/10 were prepared via melt mixing in a twin screw extruder. Both applied polyethylenes are varying in their long‐chain branches. Five methods including the time–temperature superposition (TTS) principle, van Gurp–Palmen plot, Cole–Cole curve, zero‐shear viscosity as a function of concentration, and relaxation spectrum were employed to examine the miscibility behavior of the samples. The results obtained by these methods indicated the immiscibility of the LLDPE/LDPE blends except the one with 10 wt% LLDPE content. Moreover, Scholz and Einstein models used for further checking of miscibility of the blends showed consistent results. Also, by using the Scholz model, the value of α/R, ratio of interfacial tension to droplet radius, for the blend with 95 wt% LLDPE content was estimated as 876 N m^?2 that was comparable with prior values found for LLDPE/LDPE blends. The potential of thermorheological approach as an alternative powerful tool for analyzing LCB and miscibility issues in PE blends could be highlighted. POLYM. ENG. SCI., 54:1081–1088, 2014. © 2013 Society of Plastics Engineers     

Multiple melting and partial miscibility of ethylene‐vinyl acetate copolymer/low density polyethylene blends

Multiple melting behaviors and partial miscibility of ethylene‐vinyl acetate (EVA) copolymer/low density polyethylene (LDPE) binary blend via isothermal crystallization are investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). Crystallization temperature T (°C) is designed as 30, 50, 70, 80°C with different crystallization times t (min) of 10, 30, 60, 300, 600 min. The increase of crystallization temperature and time can facilitate the growth in lateral crystal size, and also the shift of melting peak, which means the completion of defective secondary crystallization. For blends of various fractions, sequence distribution of ethylene segments results in complex multiple melting behaviors during isothermal crystallization process. Overlapping endothermic peaks and drops of equilibrium melting points of LDPE component extrapolated from Hoffman–Weeks plots clarify the existence of partial miscibility in crystalline region between EVA and LDPE. WAXD results show that variables have no perceptible influence on the predominant existence of orthorhombic crystalline phase structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

湿热老化对LDPE/POE结晶行为和力学性能的影响

在温度(40±2)℃,相对湿度93%条件下,研究了湿热老化对低密度聚乙烯(LDPE)与乙烯-辛烯共聚物(POE)共混物结晶行为和力学性能的影响。结果表明,随着湿热老化时间的延长,纯LDPE的拉伸强度以及POE用量分别为30%和70%共混物的断裂伸长率稍有增加。湿热老化对共混物的结晶行为产生了显著影响,且结晶行为的变化主要在老化前期完成。在老化中,POE的熔融峰和LDPE的低温熔融峰向高温方向漂移,并提高了共混物中LDPE在高温位置结晶的完善性和均一性。纯LDPE在老化过程中,小尺寸的晶体逐渐长大,结晶度逐渐增大,提高了LDPE结晶的完善性,且主要对LDPE(110)晶面产生明显的影响。     

Isothermal crystallization, melting behavior and crystalline morphology of syndiotactic polystyrene blends with highly-impact polystyrene

Syndiotactic polystyrene (sPS) blends with highly-impact polystyrene (HIPS) were prepared with a twin-screw extruder. Isothermal crystallization, melting behavior and crystalline morphology of sPS in sPS/HIPS blends were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). Experimental results indicated that the isothermal crystallization behavior of sPS in its blends not only depended on the melting temperature and crystallization temperature, but also on the HIPS content. Addition of HIPS restricted the crystallization of sPS melted at 320 °C. For sPS melted at 280 °C, addition of low HIPS content (10 wt% and 30 wt%) facilitated the crystallization of sPS and the formation of more content of α-crystal. However, addition of high HIPS content (50 wt% and 70 wt%) restricted the crystallization of sPS and facilitated the formation of β-crystal. More content of β-crystal was formed with increase of the melting and crystallization temperature. However, α-crystal could be obtained at low crystallization temperature for the specimens melted at high temperature. Addition of high HIPS content resulted in the formation of sPS spherulites with less perfection.     

LLDPE/LDPE blends. I. Rheological,thermal, and mechanical properties

Structure and mechanical properties were studied for the binary blends of a linear low density polyethylene (LLDPE) (ethylene‐1‐hexene copolymer; density = 900 kg m⁻³) with narrow short chain branching distribution and a low density polyethylene (LDPE) which is characterized by the long chain branches. It was found by the rheological measurements that the LLDPE and the LDPE are miscible in the molten state. The steady‐state rheological properties of the blends can be predicted using oscillatory shear moduli. Furthermore, the crystallization temperature of LDPE is higher than that of the LLDPE and is found to act as a nucleating agent for the crystallization of the LLDPE. Consequently, the melting temperature, degree of crystallinity, and hardness of the blend increase rapidly with increases in the LDPE content in the blend, even though the amount of the LDPE in the blend is small. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3153–3159, 1999     

The Influence of Blend Ratio on the Morphology,Mechanical, Thermal,and Rheological Properties of PP/LDPE Blends

This paper reports on how the blend ratio and morphology influence the mechanical, thermal, thermomechanical, and rheological properties of poly(propylene) (PP)/low density polyethylene (LDPE) blends. The blend morphology is composed of the major matrix phase and the minor phase, with subinclusions of the major matrix existing within the minor phase. Blends containing low amounts (<20 wt%) of either phase exhibit partial miscibility but the phases are immiscible at higher contents. Partial miscibility of the blends is revealed by scanning electron microscopy studies showing fibril‐like structures and confirmed by rheology. The tensile modulus of the blends decreases with increasing amounts of LDPE, but low LDPE contents exhibit positive deviation from the mixing rule of mixture due to partial compatibility. The crystallinity of PP is affected less than that of LDPE in the blends. Thermomechanical and rheological properties of neat polymers are significantly influenced by blending. The blend ratio and morphology influence impact strength and elongation at break, and the result demonstrates that the 80/20 PP/LDPE blend offers a balance among the mechanical and material properties that are essential for flexible packaging applications.

     

LLDPE／EPO共混体系相容性及结晶结构的研究

利用DSC、WAXD两种方法系统研究了LIDPE／EPO（线型低密度聚乙烯／乙烯丙烯辛烯－1共聚物）共混体系的相容性及结晶结构，通过DSC上（熔融峰，结晶峰）呈现单峰确定了此共混体系在水晶水平上共晶；用WAXD方法，计算了共混体系的结晶度，晶胞参数及微晶大小随组成不同而变化的关系，进一步证实了LLDPE／EPO共混体系的相容性。     

PTT／纳米CaCO3复合材料流变行为及结晶性能研究

以毛细管流变仪研究了聚对苯二甲酸丙二酯(PTT)/纳米CaCO3复合材料的流变行为,讨论了复合材料的组成、剪切应力和剪切速率及温度对熔体流变行为、熔体黏度的影响,测定了不同配比的复合材料熔体的非牛顿指数 n。结果表明,PTT/纳米CaCO3复合材料熔体为假塑性流体,表观黏度随着剪切速率增加而降低。纳米CaCO3的加入量较少(1％)时,熔体黏度较纯PTT迅速下降;随着纳米CaCO3含量增加(2％-20％),熔体黏度随之上升,但都小于纯PTT的;直到含量为30％时,熔体黏度才超过纯PTT的。差示扫描量热仪测定复合材料的结晶和熔融性能发现,复合材料的熔体结晶温度Tpc和熔融温度Tm较纯PTT、都有所升高,说明纳米CaCO3的加入对PTT的结晶起到了异相成核作用。     

Compatibility of reactively compatibilized polyamide 11 (nylon 11)/polyethylene (PE) alloys

The compatibility of nylon 11/polyethylene (PE) alloys on addition of reactive maleated ethylene‐propylene‐diene copolymer (EPDM‐graft‐MAH) was investigated by differential scanning calorimetry, morphological observations and rheology. The decrease in the differential volume of the melting temperature of nylon 11 and PE with increasing compatibilizer suggests that the addition of EPDM‐graft‐MAH affects the crystalline behavior of nylon 11 and PE. The decreased particle size of the dispersed phase also confirmed the improvement in the compatibility. The rheological behavior revealed that the addition of the compatibilizer enhanced the apparent viscosity of the melting blends, which resulted from the increasing interaction between the chains due to the improvement in compatibility of nylon 11 and PE. Copyright © 2004 Society of Chemical Industry