Adsorptive ethylene recovery from LDPE off-gas

The objective of this study was to verify experimentally the recovery of high-purity ethylene from LDPE off-gas by a vacuum swing adsorption process. Adsorbent for this purpose was prepared by the impregnation of AgNO₃ on Montmorillonite clay. The prepared adsorbent with an original substrate-shaped form shows high adsorption selectivities of light olefins to the corresponding paraffins. A 4-bed vacuum swing adsorption process using the above adsorbent, in which steps comprise adsorption (feeding), cocurrent rinse with ethylene product, countercurrent desorption (production) of ethylene by vacuum pump, pressurization-1 with paraffin stream, pressurization-2 with the rinse off-gas from the other bed and pressurization-3 with paraffin stream, was experimentally applied to recover ethylene from LDPE off-gas. Ethylene product purity of 99.95% could be obtained with the recovery of over 93%. The ethylene productivity of prepared adsorbent was 1.98 mol/kg-hr. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

LDPE熔体在双螺杆挤出机中流动的有限元分析

利用大型有限元分析软件包ANSYS分析了低密度聚乙烯(LDPE)在双螺杆挤出机三头常规螺纹元件中的流动情况,讨论了整个流道的速度分布、压力分布、粘度分布及螺杆挤出特性曲线。计算结果表明：LDPE熔体在双螺杆挤出机中得到了充分的混合。     

Study of the relationship between shear modification and melt fracture in extrusion of LDPE

Successive passes through an extruder can modify the melt morphology of low-density polyethylene (LDPE) by applying a shearing process. The major effects of shear modification are to decrease the elastic properties, as evidenced by the decrease in extrudate swell at the exit of a capillary and in melt viscosity at a low-frequency region. The effect of shear modification is also shown by the delay in the onset of melt fracture upon extrusion. The critical shear stress resulted from extrudate appearance, and apparent discontinuity in the flow curve of LDPE shows a similar value with polypropylene rather than those of LLDPE and HDPE. The shearing histories experienced by these materials did not result in any measurable change in molecular weight, so that the chemical modification process such as degradation and crosslinking may be ruled out. These behaviors were also confirmed to the fact that the extrudate swell was fully reversible by annealing in a molten state. The effects of shear modification on rheological properties could be explained by the changes in melt morphology owing to the disentanglement of temporary couplings between long branches. Also, a reduction in melt elasticity by shear modification of LDPE can be used as an effective tool to improve the surface roughness of extrudates in the cable-making process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2187–2195, 1998     

熔融纺丝法研究LDPE的拉伸流变性能

采用熔融纺丝法研究了低密度聚乙烯(LDPE)熔体的拉伸流变性能。LDPE熔体强度随温度升高而下降;适当降低拉伸黏度可提高熔体的可拉伸性;随拉伸应变速率升高拉伸应力上升,而拉伸黏度下降;拉伸应力和拉伸黏度都随温度的升高呈下降趋势;提高挤出速率可得到较低的拉伸应力和拉伸黏度。     

高MFR的LDPE在聚烯烃色母粒中的应用

将熔体流动速率(MFR)分别为20,40,80,200g/10 min的低密度聚乙烯(LDPE)分别与MFR为7g/10 min的LDPE以质量比为1:1共混,制备颜料质量分数为30%的蓝色母粒。采用毛细管流变仪研究该系列色母粒的加工流变性能、着色性能及制品的力学性能,并与经典的聚乙烯蜡色母粒配方对比。结果表明:将高MFR的LDPE应用于聚烯烃色母粒体系,在不使用聚乙烯蜡的情况下,可制备出综合性能优良的新型色母粒。     

服装低密度聚乙烯热熔胶化学粉碎的研究

服装粘合衬布的生产需要低密度聚乙烯热熔胶的微细粉末,介绍了对该热熔胶的化学粉碎技术所进行的实验研究,表明采用适当的助剂种类和用量以及适宜的工艺过程,通过化学粉碎可以得到合格的粉末产品。     

LDPE熔体在挤出口模流动时入口区流型的观测

应用毛细管流变仪测量了在接近实际挤出工艺条件下低密度聚乙烯熔体的流变性质,应用流动可视化技术,观测了试样熔体流经突然收缩的轴对称口模时的入口收敛流型,发现,在口模入口前区的两侧存在明显的环流区,环流区长度随着挤出速率和流道收缩比的增加而增大,而随着温度的升高而减小,采用环流区长度的公式估算了实验条件下试样的环流区长度值,结果表明,预测值与实测值之间有较好的一致性。     

Influence of molecular architecture and melt rheological characteristic on the optical properties of LDPE blown films

A systematic investigation on the origin of the haze of LDPE blown films was conducted, aiming to correlate the film haze with the molecular architecture and melt rheological properties. First of all, the haze measurement indicated that the surface haze, rather than the bulk haze, is the dominating factor for the total haze of the investigated films. No spherulitic crystals or other superstructures were observed for the LDPE blown films, implying that the crystallites formed in the film-blowing process are too small to be responsible for the optical haze. Rheological study revealed that the surface roughness was originated from the irregular flow of LDPE melt during the extrusion process. NMR, GPC and parallel-plate rheology were applied to study the molecular architecture of the LDPE resins. It was found that the LDPE sample with higher haze value exhibits distinctly larger portion of higher molecular weight component, broader molar mass distribution, significantly higher side chain branch density.     

Nitroso labeling in electron-irradiated LDPE

Summary The nitroso labeling method (1) has been used to demonstrate its possibilities for the characterization of irradiated polyethylene (LDPE) with respect to its crosslinkings and oxygen functionalities.ESR spectra of nitroso labeled LDPE consist of the superposition of the signals resulting from three different radicals.It has been shown that a relative estimation of the ketone content is possible in irradiated LDPE samples even at low concentrations thus giving a sensitive method for this functional group in polyethylene.     

熔融结晶法回收硝基氯苯精馏废液的研究

采用熔融结晶法对精馏塔处理过的硝基氯苯废料回收进行了研究。考察了指定进料组成下,降温速率、结晶终温、结晶时间等操作条件对对硝基氯苯(p-NCB)和间硝基氯苯(m-NCB)结晶过程的影响,以及对位结晶与间位结晶的差异。给出了2种典型进料组成的最优操作分离条件:进料质量分数w(p-NCB)=89.31%、w(m-NCB)=10.69%时,降温速率0.049 1℃/min、结晶时间480 min、结晶终温60℃;进料质量分数w(m-NCB)=76.03%、w(p-NCB)=23.97%时,降温速率0.015 8℃/min、结晶时间440 min、结晶终温27℃。实验表明,硝基氯苯间位结晶提纯比对位结晶提纯困难得多,采用实验中获得的最佳分离条件,w(p-NCB)≥90%的原料经单级结晶就可以得到纯度99%以上的产品,w(m-NCB)≥90%的原料通过二级结晶也可得到纯度99%以上的产品,而进料质量分数较低时经过多级结晶也能得到纯度99%以上的产品。     

LDPE细粉产生的原因及控制措施

分析了低密度聚乙烯(LDPE)细粉产生的可能原因:LDPE在生产过程中挤出切粒不良,颗粒脱水干燥,气力输送碰撞摩擦,颗粒外观不良等。通过加强相关设备管控,控制LDPE颗粒外观,选择合适的气力输送系统,增加除尘设备等措施,可以减少和降低最终产品中的细粉含量,对LDPE质量提升有一定借鉴意义。     

The measurement of melt flow and melt stability

The melt flow of a plastic as measured by the standard method (ASTM D-1238) is at a high enough stress so that the flow is non-Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.     

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。     

LDPE生产工艺中的相平衡

运用相平衡理论分析了低密度聚乙烯(LDPE)工艺流程及LDPE在不同压力、温度、相对分子质量状态下的相分离特性,优化了工艺操作方案,使LDPE熔融产品在分离系统中能够有效地分离,降低了聚合物在装置设备上的结垢速度,避免了因聚合物结垢带来的安全隐患。     

LDPE熔融接枝MAH及其增容PA6/LDPE合金的研究

以过氧化二异丙苯(DCP)为引发剂,马来酸酐(MAH)为接枝单体,采用熔融法制备了MAH接枝低密度聚乙烯(LDPE-g-MAH)。研究了不同DCP和MAH配比对接枝反应的影响,并以相对接枝率较高的LDPE-g-MAH作为增容剂,讨论了其用量对尼龙6(PA6)/LDPE合金力学性能的影响。结果表明:LDPE/DCP/MAH质量比为100/0.2/2时,相对接枝率较高,该种配方的接枝物可显著改善PA6/LDPE体系的相容性,在PA6/LDPE(质量比50/50)和PA6/LDPE(质量比80/20)两种体系中,增容剂的最佳用量分别为4~5 phr和2~3 phr。     

Investigations of environmental stress cracking resistance of LDPE/UHMWPE and LDPE/EVA blends

Abstract

Low density polyethylene (LDPE)/ultrahigh molecular weight polyethylene (UHMWPE) and LDPE/poly(ethylene-co-vinylacetate) (EVA) blends were tested and compared with respect to their environmental stress cracking resistance (ESCR) using the Bell telephone test. The time to failure in the ESCR test improved with increasing UHMWPE and EVA content, and considerable improvements were produced when an UHMWPE weight fraction of 0.4 and EVA weight fraction of 0.03 were used. Thermal and morphological studies were conducted, and a relationship between morphological features and composition was established. Furthermore, the failed specimens were further characterised by scanning electron microscopy and fractographic methodology to investigate the failure mechanism for ESCR samples.     

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     

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     

开口爽滑剂在低密度聚乙烯薄膜中的应用

介绍了目前我国低密度聚乙烯薄膜发展现状,开口剂和爽滑剂在低密度聚乙烯薄膜开口爽滑性方面的作用,分析了薄膜提高开口爽滑性的同时,如何兼顾较好光学性能,对国内低密度聚乙烯生产企业今后牌号升级及细化提出了建议。     

挤出涂层级LDPE树脂1C7A-1的结构与性能

研究了涂层级低密度聚乙烯1C7A-1的相对分子质量及其分布,甲基支化度及羧基、碳碳双键含量,熔胀比及加工性能。结果表明:1C7A-1的相对分子质量及其分布为15～17、熔胀比为1.71,均与国外试样相当;甲基支化度、双键数、羰基含量适中;具有优良的高速加工性能。