Rheology of LLDPE,LDPE and LLDPE/LDPE blends and its relevance to the film blowing process

The relevance of polymer melt rheology in film blowing process for linear low‐density polyethylene (LLDPE) and its blends with three different low‐density polyethylenes (LDPEs) has been discussed. The effect of different LDPE components as well as their concentration on shear and elongational viscosity has been investigated. A good correlation has been observed between the extensional rheological parameters of LDPEs measured by different experimental techniques. The molecular structure of parent polymers as well as blend composition play an important role in the rheology of these blends and consequently their performance in the film blowing process. © 2000 Society of Chemical Industry     

Linear low density polyethylenes and their blends: Part 4 shear flow of LLDPE blends with LLDPE and LDPE

The steady state and dynamic shear behavior of linear low density polyethylenes (LLDPE) blended with low density polyethylene (LDPE) and with another LLDPE resin were measured in capillary and parallel plate geometries at T = 150, 190, and 230°C. The extrudate swell and the Bagley correction were determined. It was observed that the pressure correction plays a significant role in capillary flow of LLDPE/LDPE blends–an indication of immiscibility. Several other rheological functions also suggested a phase separation for the system. Nevertheless, the blend behaved as a “compatible” mixture of emulsion type. By contrast, blends of two LLDPE resins show expected miscibility. However, even in this case additivity was not always observed. A new simple method of calculating the relaxation spectrum was developed. The method is analytical and its accuracy depends on adequacy of the semiempirical relation (proposed previously) to describe dynamic viscosity dependence on the test frequency. For all samples the spectrum allowed computation of storage modulus in good agreement with experimental findings.     

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     

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     

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     

Effect of EPDM on LDPE/LLDPE blends: mechanical properties

Blends of two polyethylenes and an elastomer were prepared to investigate the effect of the latter polymer. The blends contain equal parts of low density (LDPE) and linear low density polyethylene (LLDPE), and ethylene–propylene–diene rubber (EPDM) with variable content ranging from 0 to 17.5%. Melt-mixed blends were prepared using a single-screw extruder. The influence on the mechanical properties of the following factors were analyzed: EPDM content, stretching rate in the range from 10 to 750 mm/min, and two cooling conditions. From the equilibrium torque the miscibility was analyzed. The structure exhibited by the stress–strain (–) curve of the polyethylenes blend is reduced with the addition of the elastomeric phase, and the ultimate properties increase because the amorphous phase becomes softer and reduces its capability to transmit the applied stress to the crystalline particles. The slope of the – curve in the strain hardening region shows a maximum value at the stretching rate ∼ 50–80 mm/min, which is explained partially in terms of the strain-induced crystallization of the polyethylene components. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 677-683, 1997     

Melt strength and film bubble instability of LLDPE/LDPE blends

The relevance of measuring the melt strength of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blends to their performance in terms of bubble stability in the film blowing process has been investigated. A good correlation between the melt strength values for two series of LLDPE/LDPE blends and the size of the operating window for stable film bubble formation has been established. Both the macromolecular structure of the parent polymers, and melt morphology play an important role in the performance of these blends in the film blowing process. © 1999 Society of Chemical Industry     

Rheological study of the miscibility of LLDPE/LDPE blends and the influence of Tmix

The miscibility of LLDPE and LDPE blends and the influence of mixing temperature (T_mix) are discussed. Adequate amounts of antioxidants were added during melt blending. Dynamic and steady shear measurments were carried out at 190°C in a Rheometrics Mechanical Spectrometer 800.The dependence of rheological properties on blend composition indicated that blends of LLDEPE (butene) and LDPE mixed at 190°C and 220°C are only partially miscible; immiscibilty is likely to occur around the 50/50 composition and in the LDPE‐rich blends. Blends at 190°C are likely miscible in the LLDPE‐rich range. Tncreaasing T_mix did improve the miscibility of LLDPE/LDPE blends at 190°C or influence the dynamic sher properties (η′ or G′) of the “pure” resins of blends. Suggested that the molecular order [see Hussein and Williams, J. Non‐Newt. Fluid Mech., 86 105 (1999); Hussein and Williams, Macromol. Rapid Commun., 19 , 323 (1998)] and mismatch of the molecular conformations of different polyethylene structures provide an explanation for the immiscibility of polyethylenes. Agreement was observed between themeasured dynamic properities and theortical predictions of Palierne and Bousmina‐Karner emulsion models.     

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     

Mechanical strengths of molten and solidified LLDPE/LDPE blends and wood/LDPE composites under tensile deformation

The mechanical strengths of neat low‐density polyethylene (LDPE), a blend of LDPE with linear low‐density polyethylene (LLDPE), and a composite of LDPE with wood flour (wood/LDPE) were investigated in molten and solidified states under tensile deformation. The results are discussed in terms of the effects of LLDPE and wood contents, roller speed, and volumetric flow rate. In LLDPE/LDPE blends, incorporating LLDPE from 0 to 30 wt% into LDPE caused a slight increase in drawdown force, a larger fluctuation in drawdown force, and a reduction of maximum roller speed to failure. The mechanical properties of the solidified LLDPE/LDPE corresponded to those of the molten LLDPE/LDPE with regard to the effect of LLDPE content. For wood/LDPE composites, increasing the wood flour content in molten LDPE caused considerable reductions in drawdown time and maximum roller speed to failure. The drawdown force increased with increasing wood flour up to 10 wt% before it decreased at the wood loading of 20 wt%. A number of voids and pores on the extrudate surfaces became obvious for the composites with 20 wt% of wood content. Increasing wood content enhanced the tensile modulus for the solidified LDPE but decreased its tensile strength. Unlike those of LLDPE/LDPE blends, the changes in tensile modulus and strength of solidified wood/LDPE composites with wood content did not correspond to those of the molten composites. In all cases, the drawdown force increased with increasing roller speed. The effect of volumetric flow rate from the extruder on the mechanical strengths of the solidified blends was more pronounced than on those of the molten ones. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

LLDPE/LDPE共混熔体不稳定流动性的研究

采用恒速型双毛细管流变仪对比研究了LDPE/LLDPE不同组分含量共混物在较宽速率范围内的流变行为,通过研究共混物的黏度、弹性、挤出压力振荡、流动曲线、挤出畸变的差异,分析讨论了共混组成对黏弹性,进而对挤出压力振荡、鲨鱼皮等不稳定流动现象的影响。结果表明,共混使熔体的非线性黏性、弹性均增加,挤出畸变现象加重;少量LDPE的混入可消除LLDPE的挤出压力振荡现象,但鲨鱼皮畸变加重;而少量LLDPE的混入却不能消除LDPE熔体在毛细管入口处的压力振荡现象。     

硅烷接枝交联LDPE、LLDPE及其共混物的结构研究

利用红外光谱、凝胶渗透色谱、热延伸试验、差示扫描量热法、扫描电子显微镜等方法研究了低密度聚乙烯（LDPE）、线型低密度聚乙烯（LLDPE）及其共混物的乙烯基硅烷接枝及交联产物的分子结构、熔融行为和形态。结果表明：硅烷接枝后,LDPE、LLDPE的重均摩尔质量小幅增加;硅烷接枝交联能力为：LLDPE〉LDPE／LLDPE共混物〉LDPE;接枝和交联使LDPE、LLDPE及其共混物的结晶度降低,晶粒变得不均匀;硅烷接枝和交联能增加LDPE／LLDPE共混物的相容性;交联结构提高了LDPE、LLDPE及其共混物的抗冲性。     

Transient elongational viscosity of LLDPE/LDPE blends and its relevance to bubble stability in the film blowing process

Transient elongational viscosity of linear low density polyethylene (LLDPE) and its blends with 10% and 20% of low density polyethylene (LDPE) was measured at two temperatures by a constant strain rate elongational rheometer. In addition, the performance of the blends in the film blowing process was assessed in terms of bubble stability at two processing temperatures. An operating window for stable bubble production was determined. The elongational viscosity measurements on blends revealed stronger strain hardening characteristics at a higher temperature of testing. These results correlate favorably with findings from a bubble stability investigation where it was found that the size of the operating window for stable bubble production increased with increasing extrusion temperature. This work seems to indicate that increasing processing temperature during the film blowing of LLDPE-rich blends could lead to a processability improvement of these blends as far as bubble stability is concerned.     

Studies on binary and ternary blends of polypropylene with ABS and LDPE. I. Melt rheological behavior

Studies are presented on melt rheological properties of binary blend of polypropylene (PP) and acrylonitrile–butadiene–styrene terpolymer (ABS), and ternary blend of PP, ABS, and low-den-sity polyethylene (LDPE). Data obtained in capillary rheometer are presented to describe the effect of blending ratio, shear stress, and shear rate on flow properties, melt viscosity, and melt elasticity. At a blend composition corresponding to 10 wt % ABS content, both binary and ternary blends show maximum in melt viscosity accompanied by minimum in melt elasticity. Pseudoplasticity of the melt decreases with increasing ABS content. In ternary blends, LDPE facilitates the flow at low LDPE contents and obstructs the flow at high LDPE contents. Scanning electron microscopic studies are also presented to illustrate the state of dispersion and its variation with blend composition.     

A study on PVC/LLDPE blends with solid-state-chlorinated polyethylene as compatibilizer

Chlorinated polyethylene (CPE) prepared by solid-state chlorination was used as compatibilizer for poly(vinyl chloride) (PVC)/linear low-density polyethylene (LLDPE) blends. Effects of CPE molecular structure on stress-strain behaviors, dynamic mechanical properties, and morphologies of PVC/LLDPE blends were studied by using SEM, TEM, DMA, and testing mechanical properties. The results showed that the compatibility of PVC/LLDPE blends was improved with the addition of CPE. Also, adhesion strength between the two phases and mechanical properties of the blends were increased. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2535–2541, 1997     

Development of nanofibrous morphology in LDPE/LLDPE/PP blends and its effect on mechanical properties of blend films

Nanofibrous morphology has been observed in ternary blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) when these were melt‐extruded via slit die followed by hot stretching. The morphology was dependent on the concentration of the component polymers in ternary blend LDPE/LLDPE/PP. The films were characterized by wide angle X‐ray diffraction (XRD), scanning electron microscopy (SEM), and testing of mechanical properties. The XRD patterns reveal that the β phase of PP is obtained in the as‐stretched nanofibrillar composites, whose concentration decreases with the increase of LLDPE concentration. The presence of PP nanofibrils shows significant nucleation ability for crystallization of LDPE/LLDPE blend. The SEM observations of etched samples show an isotropic blend of LDPE and LLDPE reinforced with more or less randomly distributed and well‐defined nanofibrils of PP, which were generated in situ. The tensile modulus and strength of LDPE/LLDPE/PP blends were significantly enhanced in the machine direction than in the transverse direction with increasing LLDPE concentration. The ultimate elongation increased with increasing LLDPE concentration, and there was a critical LLDPE concentration above which it increased considerably. There was a dramatic increase in the falling dart impact strength for films obtained by blow extrusion of these blends. These impressive mechanical properties of extruded samples can be explained on the basis of the formation of PP nanofibrils with high aspect ratio (at least 10), which imparted reinforcement to the LDPE/LLDPE blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

LDPE接枝聚氨酯对TPU/LDPE共混物流变行为的影响

以低密度聚乙烯(LDPE)接枝聚氨酯(LDPE-g-PU)为增容剂,利用旋转流变仪研究了热塑性聚氨酯弹性体(TPU)/LDPE/LDPE-g-PU共混物的流变行为,分别以温度和增容剂用量为变量研究了共混物的储能模量、耗能模量、损耗角正切以及复数黏度与剪切速率的关系。结果表明:TPU/LDPE/LDPE-g-PU共混物为假塑性流体;加入LDPE-g-PU后,共混物的复数黏度先降低后升高,当w(LDPE-g-PU)为1%时,共混物的复数黏度降至最低;升高温度对共混物复数黏度的影响根据角频率的不同有所差异,低频率时复数黏度升高,高频率时复数黏度降低。     

Shear induced shish-kebab structure in PP and its blends with LLDPE

In order to better understand the effect of shear stress on the crystal morphology and orientation of polyolefins, dynamic packing injection molding was used to prepare oriented pure polypropylene (PP) and its blends with linear low density polyethylene (LLDPE). The obtained samples were characterized via 2d-SAXS, 2d-WAXD and AFM. Macroscopically, shear induced morphology with surface skin, central core and oriented layer between the skin and the core was observed in the cross-section areas of the samples. For pure PP, a highly oriented structure was seen in the sheared layer but much less oriented structure exists in the core. The orientation in the skin lies in between. The shish-kebab structure, composed of stretched chains (shish) and layered crystalline lamellae (kebabs), was found in the sheared layer. Shish structure exists mainly in the skin layer and oriented spherulits dominates in the core. For PP/LLDPE (50/50) blends, a change of phase morphology from less-phase-separated structure (homogeneous) in the skin, to co-continuous structure in the sheared layer and sea-island structure in the core was observed. PP formed a shish-kebab structure in all the three layers. And on the other hand, a very unique crystal morphology and lamellar orientation of LLDPE were obtained, with the lamellar stack oriented either perpendicularly or 45-50° away from the shear flow direction.     

LLDPE/LDPE为载体的母粒应用性能探讨

以不同共混比的LLDPE/LDPE为载体树脂,制成不同浓度的白色母粒,研究该载体树脂的共混比对不同浓度母粒在塑料中色彩性能、遮盖力,以及母粒加工流变性的影响。     

LLDPE／LDPE共混物熔体挤出流动性的研究

应用毛细管流变仪，考察了挤出条件下ＬＬＤＰＥ／ＬＤＰＥ共混物熔体的流动性及其影响因素。结果表明，末端压力损失随着ＬＬＤＰＥ质量百分含量ＬＬ的增加而有所增大；熔体的剪切流动基本上服从指数律，其非牛顿性随着ＬＬ的改变而发生波动。