The Microcellular Injection Molding of Low-Density Polyethylene (LDPE) Composites

This paper reports the study of microcellular injection molding of low-density polyethylene- (LDPE) based composites. The effects of adding nanoclays and polymer additives in LDPE as well as rheological property of materials on the cell morphology, mechanical properties and surface properties of microcellular injection molded LDPE based composites are presented. For the microcellular injection molding process, when 3 wt% of nanoclays are added into LDPE-based polymers, the cell morphology can be significantly improved due to the nucleating effects resulting from the broad interface areas between polymer and nanoclays. Also, the addition of low melt flow LDPE into high melt flow LDPE could achieve smaller and denser bubbles in the polymer matrix than neat high melt flow LDPE.     

Computational study of particle in-flight behavior in the HVOF thermal spray process

A computational framework is developed for the multiphase flow in a high velocity oxygen-fuel (HVOF) thermal spray coating process with steel powders as the feedstock. The numerical model includes continuum-type differential equations that describe the evolution of gas dynamics and multi-dimensional tracking of particle trajectories and temperature histories in the turbulent reacting flow field. The numerical study shows that the particle temperature is strongly affected by the injection position while the particle velocity is less dependent on this parameter. Moreover, both particle velocity and temperature at impact are strongly dependent on particle size, although the spatial variation of these two variables on the substrate is minimal. It is also found that not all the particles are deposited on the substrate perpendicularly (even if the spray angle is 90°), due to substantial radial fluid velocities near the stagnation point. A statistical distribution of particle velocity, temperature, impinging angle and position on the substrate as well as particle residence time is obtained in this work through independent random tracking of numerous particles by accounting for the distributed nature of particle size in the feedstock and injection position as well as the fluctuations in the turbulent gas flow.     

基于实验数据的湍流扩散POD模态分析

采用粒子成像测速（PIV）和激光诱导荧光（LIF）技术同时测量了水平通道中湍流扩散过程的流速和荧光剂浓度的瞬时分布,并利用实验数据,通过本征正交分解（POD）模态分析方法,实现了湍流条件下荧光剂扩散过程中浓度分布的数值重构。该方法应用于瞬时浓度分布的特征分析中,得到了瞬时分布的各阶模态,并分析各阶模态空间分布特征及其所含能量。结果表明,浓度分布在距离荧光剂入口较近的区域具有较强的周期性,且低阶POD模态能量占主导地位。应用POD分析得到的模态可以较准确地重构距离荧光剂入口较近区域的浓度分布的基本特征,相对误差主要集中于距离荧光剂入口较远的区域,表明本文提出的基于POD模态分析的湍流条件下浓度场的数值重构更适用于周期性较强的系统,为预测未知时刻的湍流扩散浓度分布提供了基础。     

硅烷交联聚乙烯电力电缆绝缘料的研制

采用两步法制备了硅烷交联聚乙烯（PE）电力电缆绝缘料。以双螺杆挤出机为反应器,以低密度聚乙烯（LDPE）和线型低密度聚乙烯（LLDPE）为基础树脂,考察了影响PE接枝交联的主要因素（如基础树脂的配比,交联剂的用量及种类,引发剂、抗氧剂的用量等）,得出了具有良好性能的硅烷交联PE电力电缆绝缘料的配方（质量份数）：LDPE为85．00phr,LLDPE为15．0H0phr,硅烷W为0．60phr,硅烷Q为1．40phr,引发剂为0．12phr,抗氧剂为0．20phr。     

亚甲基丁二酸接枝LDPE

利用反应挤出技术制备了低密度聚乙烯(LDPE)/亚甲基丁二酸接枝物。研究了引发剂种类及用量对接枝率和接枝物熔体流动速率(MFR)的影响。结果表明：采用引发剂L-101的接枝率最高,添加ω(L-101)为0．2％时．接枝率即可接近90％,接枝的同时伴有交联,接枝物的MFR从LDPE的16g／10min下降到2g／10min左右。     

管式法LDPE产品浊度影响因素及改进措施

通过在管式法低密度聚乙烯装置上控制反应压力和各反应区压降、调整反应温度器分布、合理设定引发剂注入压力、优化反应器流量分配和比例控制、调整添加剂用量等,降低了树脂薄膜制品的浊度值。提高了膜制品的光学性能,改进了高档膜料树脂的质量,其中控制引发剂注入压力比对应点反应压力高25MPa,反应器流量分配调整为正面进料为41．8％,第一侧流为28．7％,第二侧流为29．5％。     

线性锥形衣架机头流率分布数值模拟

给出了预测线性锥形歧管衣架机头出口流率分布的计算程序,研究了影响出口流率分布的相关因素。模拟结果表明:衣架机头的出口流率分布与机头的几何参数和材料的物性参数都有关系,其中调节块区的缝隙高对出口流率分布的影响最大;基于流动指数n为常数而设计的衣架机头,如果没有调节块的调节作用是很难满足实际生产需要的。     

Graft copolymerization of oleic acid onto low‐density polyethylene in the molten state

A graft copolymer of oleic acid (OA) onto low‐density polyethylene (LDPE) was prepared using dicumyl peroxide (DCP) as an initiator in the molten state. The grafting was carried out in a Haake rheometer. The effects of the reaction time and the amount of DCP and the monomer on the percentage of grafting were studied. The rheological behavior and the melt‐flow rate of the graft copolymer (LDPE‐g‐OA) were also investigated. FTIR spectroscopy and a mass spectrum were used to characterize the structure of LDPE‐g‐OA. The experimental results showed that when the OA amount was 10 wt % and the DCP amount was 0.4 wt % based on the LDPE the percentage of grafting of LDPE‐g‐OA, prepared by maintaining the temperature at 170°C and the roller speed at 80 rpm, was about 6 wt %. It was found that both LDPE and LDPE‐g‐OA were pseudoplastic fluids. OA was grafted onto LDPE in the form of a monomer and a dimer. The grafted LDPE is expected to act as a compatibilizer between starch and polyethylene. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3299–3304, 2003     

Mixing in High-Pressure Polymerization Reactors: A Combined Experimental and Modeling Approach

Mixing in low-density polyethylene (LDPE) reactors is crucial regarding process safety as well as process efficiency. The extreme process conditions of pressures up to 3000 bar make it difficult to get an insight into LDPE reactors. This problem is tackled by a combined experimental and modeling approach. A poly(methylmethacrylate) duplicate of a laboratory high-pressure reactor is set up to measure residence times and visualize flow lines. Experimental results are then compared to a computational fluid dynamics model.     

聚乙烯熔融挤出接枝α—甲基丙烯酸

通过聚乙烯熔啧挤出接枝甲基丙烯酸（MAA）,研究了各种因素对LDPE接枝率及熔体流动速率的影响,研究表明,MAA用量对接枝率影响较大,而引发剂用量对接枝率影响不大;丙烯酸（AA）的加入提高了接枝率和熔体流动速率,而另入马来酸酐（MAH）接枝率则反而下降;DCP／BOP为4／1时接枝率最高,阻交联剂的加入提高了熔体流动速率,但降低了接枝率。     

Numerical simulation of polymer foaming process in extrusion flow

Computer simulations of polymer foaming processes in extrusion flow have been carried out in order to improve current understanding of viscoelasticity and bubble growth effects on die-swelling in the production of polymer foam. The linear and non-linear viscoelastic materials functions of a commercial low density polyethylene (LDPE) melt have been extracted by fitting its rheometric data with constitutive models including a simple viscoelastic model (SVM), the exponential Phan-Thien–Tanner (EPTT) model and the double convected pom–pom (DCPP) model. Simulations of LDPE melt under extrusion flow without foaming show that the predictions of the die-swell by the SVM are in reasonably good agreement with the results obtained from the EPTT and DCPP models. By comparison of the simulation results of LDPE foaming in extrusion flow using the Bird–Carreau model and the SVM, a cooperative effect of polymer viscoelasticity and bubble growth on the die-swell has been quantified. The numerical results also show that the density of polymeric foam decreases significantly with the increasing concentration of foaming agent, and that the combination of the SVM and bubble growth model can account for some essential physics of polymer foaming process in extrusion flow.     

The study of melt grafting mechanism of acrylic acid and butyl acrylate onto low density polyethylene and its application as internal plasticizer

Melt grafting of acrylic acid (AA) and butyl acrylate (BA) (equal molar ratios) onto low‐density polyethylene (LDPE) was carried out in Haake internal mixter by free radical grafting copolymerization. The graft degree of AA and BA in the grafted LDPE (LDPE‐g‐(AA+BA)) was determined by FTIR. The influences of initiator on the graft degree of AA and BA, melt flow rate (MFR), and gel content were investigated, and the optimum conditions were obtained. The successive self‐nucleation/annealing (SSA) thermal fraction method was used to characterize the molecular structure and polydispersity of LDPE‐g‐(AA+BA) with various graft degrees. The effects of thermal fraction parameters on fraction of LDPE‐g‐(AA+BA) were investigated. On the basis of the results of SSA, the grafting reaction mechanism of AA and BA onto LDPE was proposed, i.e., grafting reaction preferentially occurred on the tertiary carbons of LDPE. The grafted LDPE possessed suitable reactivity and rheological property. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

活性硅油对LDPE的改性作用的研究

本文研究活性硅油对ＬＤＰＥ的化学改性作用。红外光谱（ＩＲ）和熔体指数（ＭＩ）的测定结果表明，用过氧化物为引发剂，在熔融状态下，活性硅油分子可接枝到聚乙烯分子链上。经硅油接枝改性后的聚乙烯而环境应力开裂能力大大增强；树枝引发示性电压和工频击穿电压也得到明显提高。     

通信电缆屏蔽专用树脂的研究

采用熔融挤出法，在引发剂和分散剂的作用下，将马来酸酐（ＭＡＨ）单体接枝到低密度聚乙烯（ＬＤＰＥ）分子，制备马来酸酐接枝聚乙烯（ＭＡＨ－ｇ－ＰＥ），用以替代进口的通信电缆屏蔽层专用树脂。并研究了引发剂用量、分钐剂种类和用量及螺杆转速对接杆率、熔体流动速率和与铝箔之间剥离强度的影响，从而得出最佳配方。其性能基本接近进口产品，有很大的应用价值。     

高速挤出涂覆专用树脂的工业开发

结合市场需求和低密度聚乙烯（LDPE）装置特点,开发了LDPE高速挤出涂覆专用树脂1C7A-1。确定了反应压力、反应温度、引发剂消耗量及链转移剂加入种类。生产的1C7A-1各项指标可满足市场需求,涂覆过程中的膜边缘稳定性得到提高,挤出复合时缩幅较小,且加工速度较高（大于280m/min）,最小涂覆厚度达到6μm,填补了国内无菌包装高速挤出涂覆树脂生产的空白。     

注塑模具概念设计的CAE应用

为研究注塑过程模拟技术捕助模具概念设计和工艺设计结合实例分析了 CAE在概念设计阶段的作用,及其进行模具流道系统和冷却系统设计方案的评估和优化的途径,提出了在模具概念设计阶段利用CAE技术捕助助塑工艺设计的方法。结果表明,该方法可以在模具概念设计阶段有效顶测填充模式的合理性、预测特定模具结构及其注塑材料注射成型可能存在的缺陷、确定合理的排气槽位置、对冷却系统的布局和设计合理性进行评价等,是缩短模具开发周期、提高设计品质的有效措施。     

二烯基双酚A醚接枝低密度聚乙烯的制备

介绍了二烯基双酚Ａ醚（ＤＢＡＥ）与低密度聚乙烯（ＬＤＰＥ）在Ｈａａｋｅ转矩流变仪的混炼器中进行熔融接枝反应,采用红外光谱（ＦＴ－ＩＲ）分析证实了接枝共聚物（ＬＤＰＥ－ｇ－ＤＢＡＥ）并通过对ＬＤＰＥ－ｇ－ＤＢＡＥ的接枝率（ＧＲ）和熔体流动速率（ＭＦＲ）测试,考察了制备条件（反应温度,引发剂用量和ＤＢＡＥ用量）对接枝反应及产物的影响,ＬＤＰＥ－ｇ－ＤＢＡＥ的最终目的是作为高密度聚乙烯／聚碳酸酯共混体系     

Modeling of the production of ultra fine Aluminium particles in rapid quenching turbulent flow

A two-dimensional axi-symmetric turbulent model of a particle generator with radial injection of a quenching gas was developed to gain a better understanding of the particle forming process. The model uses the Jones–Launder Low Reynolds Number (LRN) Turbulence model to calculate the fluid flow field. The evolution of the particle size distribution is calculated using the method of moments (MOM) assuming a lognormal particle size distribution and no coagulation when the gas temperature is lower than the melting point of Aluminium. The model provides information on distributions of flow, temperature and concentration fields and particle generation within the reactor as well as mixing cup data as a function of reactor length. The effect of the injection flow rate on the characteristics of the final product was studied. The model can be used to study laminar, turbulent and systems where both regimes are present.     

Efforts to decrease crosslinking extent of polyethylene in a reactive extrusion grafting process

Grafting of acrylic acid and glycidyl methacrylate onto low density polyethylene (LDPE) was performed by using a corotating twin‐screw extruder. The effects of residence time and concentration of initiator and monomers on degree of grafting and gel content of grafting LDPE were studied systematically. Paraffin, styrene, p‐benzoquinone, triphenyl phosphite, tetrachloromethane, and oleic acid were added to try to decrease the extent of crosslinking of LDPE. 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (4‐hydroxyl‐TEMPO) and dipentamethylenethiuram tetrasulfide were also tried to inhibit crosslinking reaction of LDPE during its extruding grafting process. It was found that p‐benzoquinone, triphenyl phosphite and tetrachloromethane were good inhibitors for crosslinking of LDPE. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 535–543, 2001     

Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.