茂金属聚乙烯宽幅吹塑棚膜的研究

了mLLDPE与LDPE共混树脂吹塑宽幅棚膜的优异力学，光学性能及其覆盖棚室的光温效应。阐明了解决mLLDPE熔体粘度大，熔体强度低，熔体易破裂等关键问题的工艺技术要点，介绍了高效6911／B215耐老化体系在薄型mLLDPE棚膜中的良好应用效果，报导了外涂型流滴消雾剂应用情况并提出了发展建议。     

Effects of ultrasonic oscillations on processing behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene/low‐density polyethylene blends

The influences of ultrasonic oscillations on rheological behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene (mLLDPE)/low‐density polyethylene (LDPE) blends were investigated. The experimental results showed that the presence of ultrasonic oscillations can increase the extrusion productivity of mLLDPE/LDPE blends and decrease their die pressure and melt viscosity during extrusion. Incorporation of LDPE increases the critical shear rate for sharkskin formation of extrudate, crystallinity, and mechanical properties of mLLDPE. The processing behavior and mechanical properties of mLLDPE/LDPE blends were further improved in the presence of ultrasonic oscillations during extrusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2522–2527, 2004     

mLLDPE性能及mLLDPE/LDPE共混物吹膜性能研究

研究了茂金属线型低工聚乙烯的基础性能,包括密度、熔体流动指数、熔流比、分子量及其分布、熔点、屈服强度、断裂强度、伸长率、等。利用吹膜机研究了ｍＬＬＤＰＥ／低密度聚乙烯共混物的吹膜性能,讨论了共混物中ｍＬＬＤＰＥ的含量与力学性能及光学性能的关系,雾度、透光度与薄膜厚度的关系。     

Properties of films made from ternary blends of metallocene and conventional polyolefins

Thin films were blown from a composition of 75% linear low density polyethylene (LLDPE) and 25% LDPE. The LLDPE content was made up of different % of metallocene‐based and conventional octene‐based LLDPE. Tensile strength, dart impact strength, hot tack strength, heat seal strength, and the barrier properties of these films were measured. All the properties showed significant improvement when conventional LLDPE (cLLDPE) was replaced by metallocene‐based LLDPE (mLLDPE), even to the extent of only 25%. The blends of 50% mLLDPE and 50% LDPE showed attractive properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 53–57, 2001     

mLLDPE及mLLDPE／LDPE共混物薄膜性能研究

研讨了茂金属线型低密度聚乙烯（ｍＬＬＤＰＥ）薄膜和ｍＬＬＤＰＥ与低密度聚乙烯（ＬＤＰＥ）共混物薄膜的物理性能和光学性能,并与传统的ＬＬＤＰＥ薄膜和ＬＬＤＰＥ／ＬＤＰＥ共混物薄膜进行了比较,表明ｍＬＬＤＰＥ薄膜和ｍＬＬＤＰＥ／ＬＤＰＥ共混物薄膜的性能优于传统的ＬＬＤＰＥ薄膜和ＬＬＤＰ／ＬＤＰＥ共混物薄膜,指出在ｍＬＬＤＰＥ中混合１０％ＬＤＰＥ,对薄膜性能影响不大。     

Study of the Effects of Gamma Irradiation on the Structure and Physical Properties of Low Density Polyethylene Films Containing Hindered Amine Stabilizers

The effect of gamma‐irradiation on the structure, rheology, and mechanical properties of low density polyethylene (LDPE) films containing some new hindered amine stabilizers (HAS) has been investigated and the results obtained were compared to additive free samples. The HAS used involved various structures such as an alkoxyamine, a polymer bound HAS and a HAS modified with siloxane; these are commercially known as Tinuvin 123, Sanduvor PR 31 and Uvasil 299, respectively. It was found that the carbonyl index values measured by FTIR spectroscopy increased linearly with the radiation dose for all the samples studied, however this increase was less pronounced for the stabilized samples. The formation rates of carbonyls followed the order LDPE > LDPE/Uvasil 299 > LDPE/PR 31 > LDPE/Tinuvin 123. The second order derivative UV analysis showed the formation of vinyl groups in the irradiated samples at higher doses (812 kGy), while vinylidene groups were detected only in the films stabilized with PR 31 and Tinuvin 123. The curves of the melt flow rate (MFR) exhibited a fast increase for the unstabilized sample after 67 kGy, indicating the occurrence of chain scission. The stabilized samples on the other hand showed an evident increase in MFR from almost 300 kGy. The contribution of different HAS for the durability of LDPE films under γ rays was evaluated by determining the half‐value‐dose, which is related to the radiation resistance of the material. The results indicated that the presence of HAS in LDPE films improves the half‐value‐dose of those stabilized with Tinuvin 123 by 2.5 times against 2.4 and 2 for PR 31 and Uvasil 299, respectively. These data correlate well with the results obtained by FTIR and MFR measurements. Finally, the higher efficiency of Tinuvin 123 could be assigned to its appropriate oxidation state to enter the stabilization mechanism directly.

An example of the new HAS.     

mLLDPE薄膜的光氧化及热力学降解

茂金属线型低密度聚乙烯(mLLDPE)和传统线型低密度聚乙烯(LLDPE)薄膜经紫外灯照射不同时间后,用红外光谱和差示扫描量热法对薄膜跟踪测试。发现mLLDPE的羰基指数及不饱和碳碳双键的变化快于LLDPE;mLLDPE的氧化初始温度及熔融热焓的变化也明显低于LLDPE。     

Critical insights into ethylene-1-alkene copolymers and long-chain branched polyethylene microstructure on thermo-rheological and sealing behavior of multicomponent systems

The microstructure-property relationships in multicomponent ethylene-1-alkene copolymers with different branching in the microstructures are demonstrated. The metallocene catalyzed linear low density polyethylene (mLLDPE), was miscible with both autoclave grade low density polyethylene (LDPE-A) and/or tubular grade low density polyethylene (LDPE-T). For these multicomponent systems, the rheological response was distinctly differentiating and sensitive to the microstructure of LDPE, at higher shear regimes. The thicker lamellae of LDPE-T and/or LDPE-A might co-crystallize if there is a high density polyethylene-like fraction present in the mLLDPE. Even though the macro parameters like density and melt index (MI) of the investigated multicomponent systems are comparable, the subtle differences in the microstructure manifested by type and distribution of comonomer and/or branching affected the sealing performance. Both high comonomer content and comonomer distribution in the mLLDPE matrix affording a higher fraction of material melting below 120°C were found to be critical for the heat sealing. The fraction of material melting at lower temperatures, attributed to the tertiary branches present in the hyper-branched microstructure of LDPE-A, participate in the sealing process, and lower the sealing temperature. It was evident that mLLDPE with asymmetric distribution of lamellae is more sensitive to the microstructure of the LDPE used.     

Properties of mLLDPE/LDPE blends in film blowing

We evaluated the inline birefringence of two blend systems in film blowing. The first system consisted of a metallocene catalyzed linear low density polyethylene (mLLDPE‐1) and a low density polyethylene (LDPE‐1); the second one was made of a metallocene catalyzed polyethylene containing sparse long chain branches (mLLDPE‐2) and another low density polyethylene (LDPE‐2). Experimental data show that before the crystallization starts, the birefringence of the mLLDPE‐2/LDPE‐2 blends is a linear function of blend composition, suggesting miscibility of the mLLDPE‐2/LDPE‐2 blends. However, the birefringence of the mLLDPE‐1/LDPE‐1 blends shows positive deviations with respect to a linear function of blend composition. This is caused by the existence of form birefringence, suggesting immiscibility of the mLLDPE‐1/LDPE‐1 blends. The nonuniform biaxial elongational viscosity (NUBEV) at the reference temperature of 175°C for LDPE‐1 was evaluated for different operating conditions. The results show that NUBEV is approximately a unique function of the deformation rate, confirming the validity of the assumptions and technique used for the NUBEV calculation. The NUBEV and the nonuniform biaxial Trouton ratio (NUTR) of the mLLDPE‐2/LDPE‐2 blends was also evaluated using the same technique. The NUBEV of all mLLDPE‐2/LDPE‐2 blends shows a strain‐thinning behavior within the deformation rates investigated. Furthermore, the NUTR results show that LDPE‐2 deviates largely from the Newtonian fluid behavior, whereas mLLDPE‐2 is quite close to the Newtonian behavior. Nevertheless, the NUTR of the mLLDPE‐2/LDPE‐2 blends is almost a linear function of blend composition. POLYM. ENG. Sci., 45:343–353, 2005. © 2005 Society of Plastics Engineers     

Natural weathering,artificial photo‐oxidation,and thermal aging of low density polyethylene: Grafting of acrylic acid onto aged polyethylene films

The photo‐oxidation and thermal initiation changes of commercial low density polyethylene (LDPE) films used in greenhouse covering, in the presence or absence of ultraviolet (UV) stabilizer, were monitored by infrared (IR) spectroscopy, by mechanical tests and by applying the grafting of acrylic acid onto the aged films. It was found that the resistance of PE films to UV irradiation and heat initiation as proved by tensile strength and elongation at break % was better for stabilized PE films compared with the unstabilized ones. A simple correlation was not observed between the fall in mechanical properties and the rate of film oxidation. On the other hand, an almost linear relation was obviously noticed between the degree of PE oxidation (C?O) measured by IR spectroscopy and the grafting level. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2365–2371, 2003     

茂金属线性低密度聚乙烯树脂的结构与性能

对国产和进口茂金属线性低密度聚乙烯树脂(mLLDPE)的分子量及分布、支化程度、基本性能与流变行为进行了对比分析,研究表明国产mLLDPE与进口同类产品相比,分子量分布宽,支化程度高,加工性能更好,可以通过流变测试的各种参数如黏流活化能、剪切变稀指数、松弛谱分布宽度对其结构进行剖析。同时对两者薄膜制品的性能进行了研究,结果表明,国产mLLDPE树脂生产的薄膜力学性能更为优异,但鱼眼稍多,外观略差。     

Optical properties of blown and cast polyethylene films: Surface versus bulk structural considerations

In this article we report on some surprising, and we believe new, findings regarding the factors affecting the optical properties (haze) of polyethylene blown and cast films. A comprehensive investigation of blown and cast films made from conventional Ziegler‐Natta catalyzed linear low density polyethylene (LLDPE) as well as metallocene‐catalyzed LLDPE (mLLDPE) resins was conducted. The large majority of the contribution to the total haze in the blown and cast films was observed to come from the surface roughness of the films, with the bulk (internal) contribution being relatively minor. Using a variety of analysis and characterization methods, including atomic force microscopy, small angle light scattering, and wide angle X‐ray scattering, we determined that the surface roughness in these films was a result of the development of distinct spherulitic‐like superstructures formed during the blown or cast film processing. Furthermore, these superstructures were observed only in the mLLDPE blown films, and not in the LLDPE blown films processed at similar conditions. Analysis of the rheological and molecular characteristics of these various mLLDPE and LLDPE resins revealed that the mLLDPE resins exhibited considerably lower molecular weight, narrower molecular weight distribution, lower zero shear viscosity, and lower melt elasticity compared with the LLDPE resins of similar melt index. These observations support our general finding and primary conclusion from this work that in polyethylene blown and cast films made using typical processing conditions, the optical haze properties are adversely affected because of enhanced surface roughness caused by the formation of spherulitic‐like superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2845–2864, 2000     

Melt Rheological and Impact Properties of Thermally Stable PP/mLLDPE Blends

Effect of the heat stabilizer on the melt rheological properties of the blends of polypropylene (PP) with mLLDPE (mettalocene linear low density polyethylene), after thermal degradation in an air oven, was studied. Study carried out is presented to describe the effect of blending ratio and presence of stabilizer on shear stress, shear rate, melt viscosity and melt elasticity parameters. In general, blending of PP with mLLDPE results in an increased viscosity. The viscosity of PP abruptly decreases after the thermal degradation. Interestingly the melt viscosity PP/mLLDPE blend does not show such a marked decrease. This shows that mLLDPE not only acts as an impact modifier but also acts as a thermal stabilizer. The presence of stabilizer in both materials has not shown much difference in melt viscosity thereby suggesting adequate stabilization of the blend system.     

Crystalline structure and phase structure of mLLDPE/LDPE blends

The crystalline structure and phase structure of metallocene linear low density polyethylene (mLLDPE) and low density polyethylene (LDPE) blends were investigated, using a combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) techniques. The samples displayed cocrystallization phenomenon for LDPE of 80 wt% in the blends, indicating good compatibility between the two components under this circumstance; as LDPE content decreased, phase separation arose whereas partial cocrystallization still existed in the blends. Over the whole range of weight fractions, the intrinsic crystal structure of mLLDPE does not change with the addition of LDPE, while enhanced orthorhombic crystalline phase were observed as LDPE content increased. The changes in the thickness of interface layer σ_b, dispersed phase size a_c and integral invariant Q further indicate the existence of partial compatibility between the two phases. Irrespective of the phase inversion, the morphology of the dispersed phase is deduced to be in a transitional state from rod-like shape to flakes within the whole proportional range investigated.     

Electron beam irradiation of low-density polyethylene filled with metal hydroxides for wire and cable applications

The effects of electron beam irradiation for crosslinking of polymers used for wire and cable insulations are still being researched. In this research, the influence of electron beam irradiation on the different blends of low-density polyethylene (LDPE) filled with aluminum trihydrate and magnesium hydroxide (ATH, MH) were studied. It was revealed by melt flow index, tensile strength, and elongation at break tests that addition of MH to LDPE increases the adhesion forces inside polymer matrices more efficient than similar ATH/LDPE compounds. Field emission scanning electron microscopy test showed that MH is platy in structure and more homogenous mixed than ATH with LDPE. The results on thermogravimetric analysis and limiting oxygen index tests revealed that the thermal stability and incombustibility properties of MH blends are more efficient than similar ATH blends. Meanwhile, it was observed by smoke density test that MH blends produce the lowest smoke density compared with virgin LDPE and similar ATH blends. It was also observed that increasing irradiation by electron beam had impressive affections on the density, gel content, and mechanical properties for all the polymeric samples in this study.     

Application of chemiluminescence to probe miscibility in metallocene‐catalyzed polyethylene blends

Chemiluminescence (CL) monitoring has successfully been applied to the study of the oxidative degradation of two‐component polyethylene blends made with commercially available low‐density polyethylene, linear low‐density polyethylene, high‐density polyethylene, and metallocene‐catalyzed linear low‐density polyethylene (mLLDPE) formulations. The emphasis in the analysis of the results is placed on blends containing mLLDPE to address the lack of CL information on these blends. The CL data are consistent with the thermal and physicomechanical properties of the blends, with a decreased blend miscibility being reflected in the CL data as a departure from the idealized behavior observed for more miscible blends. Furthermore, the results suggest that immiscibility in the solid state is reflected to some extent in the behavior of the melt. Preliminary experiments conducted to determine the level of consistency of CL results with respect to both variability between instruments and variability between techniques indicate a high degree of correlation in each case. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3006–3015, 2003     

Comparative effects of cobalt carboxylates on the thermo‐oxidative degradation of LDPE films

This article reports the effect of three cobalt carboxylates—cobalt stearate (CoSt₃), cobalt palmitate (CoPal₃), and cobalt laurate (CoLau₃)—on the thermo‐oxidative degradation of low‐density polyethylene (LDPE) films prepared by sheeting process. The carboxylates were blended with LDPE in the concentration range of 0.05–0.2% (w/w). The degradation was monitored by techniques such as FTIR spectroscopy, change in the mechanical properties (tensile strength and elongation at break), viscometry, surface electron microscopy, melt flow index measurements, and apparent density measurements. Studies indicate that films containing these additives are highly susceptible to thermo‐oxidative degradation. Oxygen containing functionalities such as carbonyl and vinyl species are generated on the surface of polyethylene because of thermo‐oxidation, as indicated by FTIR studies. This oxidative process is accelerated in the presence of cobalt carboxylates. The degradation of LDPE was found to increase proportionally with concentration as well as with increasing chain length of the cobalt carboxylate, and follow the order CoSt₃ > CoPal₃ > CoLau₃. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3758–3765, 2007     

mLLDPE流变与加工特性的研究

主要研究国产mLLDPE加工特性,通过流变试验确定mLLDPE的临界剪切速率范围,并在mLLDPE中加入加工助剂,消除mLLDPE的熔体破裂现象,利用mLLDPE与LDPE共混,增强mLLDPE熔体强度,提高膜泡稳定性。     

Enhanced flow behaviors of metallocene‐catalyzed linear low‐density polyethylene during ultrasound‐assisted extrusion

The effect of ultrasound on flow behaviors of metallocene‐catalyzed linear low‐density polyethylene (mLLDPE) melt in capillary‐like die during the extrusion is investigated in this article. The rise in die temperature is found with increasing ultrasound power, especially at lower initial die temperature. At the same die temperature, the presence of ultrasound can decrease the apparent viscosity and the viscous flow activation energy of mLLDPE melt then increase its slip velocity at the capillary wall in the die. The flow behavior of mLLDPE melt is enhanced during ultrasound‐assisted extrusion as the presence of ultrasound can enhance the mobility and the orientation of entangled segments. It is also found that ultrasound can break the dispersed phase of mLLDPE/polyolefin elastomer (POE) blend into small pieces thus improve the homogeneous dispersion of POE phase in mLLDPE matrix. A possible mechanism for enhanced flow behaviors of mLLDPE melt because of the presence of ultrasound is also proposed. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

茂金属线型低密度聚乙烯的结构与性能

利用傅里叶变换红外光谱、凝胶渗透色谱、差式扫描量热法和力学性能测量等手段表征了茂金属线型低密度聚乙烯(mLLDPE)和传统线型低密度聚乙烯(LLDPE)的结构及性能,用热分级法表征了LLDPE的片晶厚度多散性,测试了mLDPE薄膜的相关性能。结果发现,mLLDPE的片晶厚度分布指数为1.1347,小于传统LLDPE,表明其具有更好的支化均匀性,但其相对分子质量分布窄;mLLDPE薄膜具有较高的落镖冲击强度、撕裂强度、热封强度和突出的光学性能。