振动对mLLDPE加工影响的研究

研究了电磁动态塑化挤出条件下振动力场对茂金属线性低密度聚乙烯(mLLDPE)加工的影响。振动力场有效地降低了模头压力和挤出机消耗的功率,并使mLLDPE的熔体强度得到了提高,从而大大改善了mLLDPE的加工。     

Mathematical and computational modeling of heat transfer and deformation in film blowing process

The blown‐film extrusion process was investigated both experimentally and theoretically. In experimental study, nonisothermal experiments were conducted using low‐density polyethylene. Rheological parameters were studied, considering the polymer melt as a power law fluid in nonisothermal conditions. Axial tension, bubble diameter, and film thickness at a variety of film extrusion conditions, that is, different flow rate, pressure difference across the film, and take‐up speeds were measured. In theoretical study, an analysis was employed to simulate the blown‐film extrusion process by setting up the force‐ and energy‐balance equations on the film bubble moving upward. Four nonlinear complex differential equations were integrated numerically, using an iterative backward shooting method and the fifth‐order Runge‐kutta technique. The program written, based on a mathematical model, predicts the bubble shape, temperature profile, and film thickness as a function of the distance along the machine axis. Furthermore, the model evaluates the elongational viscosity of LDPE in biaxial tension in terms of distance from die axis and take‐up speed. In this simulation, the total stress components in machine and the transverse directions were computed from the die exit up to the freeze line, the knowledge of which is necessary for evaluation of the elastic memory build up in heat‐shrinkable films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2115–2123, 2002     

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。     

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     

Effects of the properties of blowing agents on the processing and performance of extruded starch acetate

The extrusion of polysaccharide‐based polymers, such as starch acetate, is quite different from that of ordinary synthetic polymers. To understand how the physiochemical properties of blowing agents affect plasticization and expansion processes, starch acetate was extruded with water, ethanol, and ethyl acetate. The studied properties and factors were the evaporation rate, surface tension, boiling point, solubility index, latent heat of vaporization of blowing agents, extrusion temperature, and nucleating‐ and blowing‐agent concentrations. The properties of the blowing agents and operating conditions affected the solubility of the matrix polymer, the nucleation process, and cell growth, which affected the foam density and specific volume. A high temperature increased the cell density and specific volume when water and ethanol were used because a high temperature increased the solubility of starch acetate in water and ethanol and promoted nucleation. Ethyl acetate already had high solvency to starch acetate and a high evaporation rate. A high temperature reduced the melting strength, thereby reducing the cell density and specific volume. Water evaporation was greater, despite a high latent heat of evaporation (hr) and boiling point, than the average volumes of ethanol and ethyl acetate that evaporated. The blowing‐agent efficiency was a function of the solvency, blowing‐agent evaporation rate, and operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1880–1890, 2005     

Extrusion of microcellular polysulfone using chemical blowing agents

Microporous polysulfone hollow fibers were developed with the help of chemical blowing agents by means of extrusion. Two chemical blowing agents, azodicarbonamide and 5-phenyltetrazol, were selected, and the foam morphology dependent on the concentration of blowing agent was examined by scanning electron micrograph. By means of changing the processing parameters, e.g., temperature and screw speed, the structures of the foam, usable as membrane, can be controlled. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1753–1760, 1998     

Modeling of nonisothermal film blowing process for non‐Newtonian fluids by using variational principles

In this work, nonisothermal film blowing process analysis for non‐Newtonian polymer melts has been performed theoretically by using minimum energy approach and the obtained predictions were compared with both, theoretical and experimental data (internal bubble pressure, take‐up force, bubble shape, velocity and temperature profiles) taken from the open literature. For this purpose, recently proposed generalized Newtonian model depending on three principal invariants of the deformation rate tensor, D, and its absolute defined as $\sqrt {D \cdot D}$ has been used. It has been found that film blowing model predictions are in very good agreement with the corresponding experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of vibration parameters of electromagnetic dynamic plastics injection molding machine on mechanical properties of polypropylene samples

Dynamic injection processing experiments have been carried out on polypropylene using the self‐made electromagnetic dynamic plastics injection molding machine, and the effects of the vibration force field on mechanical properties of molding samples are studied, namely, the influence of vibration frequency and vibration amplitude on the mechanical properties of samples are researched by using tensile testing, impact testing, differential scanning calorimeter (DSC) and scanning electronic micrograph (SEM) techniques. The results show that the tensile strength and impact strength are both enhanced and the melting point shifts toward the higher temperature, which facilitates the perfection of crystal. The best vibration parameters for processing polypropylene using electromagnetic dynamic plastics injection molding machine are that frequency is from 3 to 9 Hz and amplitude is from 0.1 to 0.4 mm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 972–976, 2006     

Film blowing of silane‐modified polyethylene

The grafting of vinyltriethoxysilane (VTES) onto polyethylene (PE) with the help of small amounts of peroxides was investigated to film‐blow these modified materials. The degree of crosslinking was kept very low to achieve good melt processability and improved mechanical properties. The possibility of obtaining modified PE films with improved properties and regularly distributed crosslinking with a single processing step demonstrates the uniqueness of this study. The additive concentration was established through preliminary studies; with a batch mixer, it was possible to process the modified PE in the film‐blowing operation. Water treatment of the modified films after film blowing allowed for improved properties without the processability being affected. The modification of PE was followed with mechanical, rheological, and extraction tests and with calorimetric analyses. The variations of the main mechanical properties of the films were very important from an application point of view. The elastic modulus and tear strength of the films for both extrusion directions (machine and transverse) increased with the VTES concentration increasing and even more with the addition of a small quantity of a peroxide. Some reductions of the tensile strength and elongation at break were observed, but these reductions were not considerable. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of molecular structure on film blowing ability of thermoplastic zein

The aim of this work was to explore the feasibility of preparing thermoplastic films from commercial zein by film blowing technology. Zein, a cereal protein extracted from maize, was plasticized directly in the extruder, without the time‐consuming and expensive solubilization step, usually utilized in literature for this material. Four different batches of zein were investigated, for it has been observed that properties such as the film‐forming ability of natural polymers strongly depend on several factors such as sources, extraction, and drying conditions. Thermal, rheological, and macromolecular structural characteristics were evaluated for the different materials to establish a correlation among molecular structure, rheological behavior in uniaxial elongation, and film blowing processability. Results indicate that the best films were made by using thermoplasticized zein characterized with a pronounced strain hardening and a large content of α‐helices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Frequency response analysis of nonisothermal film blowing process using transient simulations

Frequency response of the nonisothermal viscoelastic film blowing process to the ongoing sinusoidal disturbances has been investigated using transient simulation techniques. Of the many state variables exhibiting resonant peaks with the input frequency, amplitude ratio of the film cross‐sectional area at the freezeline height has been used as an indicator of the process sensitivity. The effects of operating conditions and viscoelasticity on the sensitivity have been scrutinized around the middle point of three multiple steady states under the given conditions. The sensitivity results have been interpreted through their correlation with results from linear stability analysis. Increasing draw ratio generally makes the system more sensitive to sinusoidal disturbances, whereas the cooling induces more sensitive or less sensitive system, according to the location of a steady state. Also, the viscoelasticity makes the system of extensional thickening fluids more sensitive at low Deborah number and less sensitive at high Deborah number. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

HDPE在振动场中挤出成型时的流变行为

利用自行研制的新型液压振动挤出装置研究了高密度聚乙烯（HDPE）在振动场中挤出成型时的流变行为。研究表明,HDPE熔体在振动场中的表观粘度与振动频率、振幅、口模温度和挤出机螺杆转速均有关,随着振动频率的增加,表观粘度先降至最低值,然后回升到一定程度后基本保持不变,但始终低于未施加振动时的表观粘度;振幅越大,振动场对表观粘度的影响就越大;口模温度超过熔点时,振动场对表观粘度的影响有所增大;螺杆转速越大,振动场对表观粘度的影响就越小。     

Structure and Morphology Development in Films of mLLDPE/LDPE Blends During Blowing

Summary: In this work the analysis of the structure orientation, morphology, relaxation time and optical properties of blown films of mLLDPE, LDPE and their blends were performed by using WAXD, SALS, AFM, DSC and rheological and haze tests. For mLLDPE film, the crystals do not present “a”‐axis orientation along the machine direction; a distinct spherulite like superstructure is seen. The film surface is very rough. The values of bulk and surface haze are higher than LDPE and blends, whereas the relaxation time is lower. For LDPE film the (110) planes are parallel and at same time twisted with respect to the layer of the film with the “a”‐axis well oriented along the machine direction. No spherulite superstructure is observed and the surface of the film is more regular. High values of relaxation time are observed. The surface haze is the predominant contribution to the total haze. For the blend films no clear and distinct spherulite structures are observed. The orientation degree increases with composition never approaching that of LDPE. The surface is very more regular and smooth than that of the pure polymers. The haze values are below the values of pure materials. It was underlined that bulk and surface morphology and orientation degree of the crystalline planes along the machine direction dictate the optical properties of the films. Moreover both orientation and morphology are defined by the PE molecular and melt rheology characteristics, processing conditions and blend composition.

Total, bulk and surface haze of mLLDPE/LDPE blend films as a function of composition.     

Use of Nitrogen as a Blowing Agent for the Production of Fine‐Celled High‐Density Polyethylene Foams

Summary: While many experiments have been performed to examine the effects of administering CO₂ as a blowing agent in the foaming process, very few studies have investigated the use of N₂ for this purpose. In this study, foaming experiments were conducted in extrusion using HDPE as a polymeric material and N₂ as a blowing agent. Talc was used as a nucleating agent, and three different pressure‐drop rates were applied to study the effects of pressure‐drop rates on HDPE foams. The experimental results revealed that the void fraction of high‐density foams blown with N₂ was not affected by the die temperature, contrasting the situation in low‐density foams. Surprisingly, it was the cell density which determined the void fraction of high‐density foams. It was also found that the use of talc significantly increased the cell density and the void fraction of the foams and minimized the role played by the pressure‐drop rate in cell nucleation.

Effect of N₂ content on the cell density of HDPE foams.     

Processing and characterization of LDPE/starch products

Low‐density polyethylene/plastisized starch blends varying in starch content were processed by conventional extrusion, injection‐molding, and film‐blowing techniques. Polyethylene‐g‐maleic anhydride (PE‐g‐MA) was used as a compatibilizer. X‐ray diffraction was used to investigate starch destructurization during extrusion and on subsequent processing. The effect of starch content on the blends was evaluated by mechanical property measurement and scanning electron microscopy. Starch, except for being a biodegradable material, can also act as a reinforcing agent. The reinforcing effect of starch was only realized in injection‐molded materials. Processing–structure–property relationships could explain this behavior. The present study also brought out the effect that the degree of molecular orientation existing in a polymeric matrix may have on the coupling performance of an adhesion promoter. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2548–2557, 2001     

复合拉伸力场挤出HDPE片材的力学性能

利用收敛-发散口模挤出制备了高密度聚乙烯(HDPE)片材,研究了挤出温度对片材力学性能的影响.结果表明:在复合拉伸力场作用下,熔态挤出(140℃)片材的纵、横向屈服拉伸强度分别为28.3,27.0MPa,固态挤出(112℃)片材的纵、横向屈服拉伸强度分别为181.4,51.3 MPa,纵、横向屈服拉伸强度分别增加了540%和90%.与固态挤出相比,熔态挤出片材纵、横向断裂伸长率分别增加了760%和124%.扫描电子显微镜显示,熔态挤出HDPE片材由球晶结构构成;固态挤出片材由大量垂直于挤出方向规整排列的片晶组成,并有少量的串晶生成,片晶厚度增加,这种结构有利于改善制品的双向力学性能.     

吹风气集中回收技术在中型氮肥厂的应用

针对中型氮肥厂的实际情况，结合造气系统工艺流程的改造，论述了适用于中型氮肥厂的吹风气回收技术以及应用该技术所带来的经济效益和社会效益。     

振动力场下填充聚合物挤出过程研究

研究了利用塑料电磁动态塑化挤出机加工ＰＰ／ＣａＣＯ３和ＬＤＰＥ／ＣａＣＯ３时的动态挤出过程,探讨了振动力场对聚合物填充体系挤出过程扣影响规律和作用机理。结果表明,在一定的振动条件下,振动力场的作用使挤出压力减同功率降低,混合分散效果明显提高。     

Extrusion of microcellular open‐cell LDPE‐based sheet foams

In this research, highly open‐cell low‐density polyethylene sheet foams are achieved with an annular die by applying various strategies for cell opening, i.e., (i) creation of a structural nonhomogeneity consisting of hard and soft regions with partial crosslinking, (ii) blending of a hard second‐phase material (i.e., polystyrene phase) into the low‐density polyethylene matrix, (iii) plasticization of the soft region with a secondary blowing agent, (iv) decrease of the cell wall thickness by increasing the cell density, and (v) decrease of the cell wall thickness by increasing the expansion ratio while cell walls are soft. Although the higher surface‐to‐volume ratio of the sheet foams compared with filament foams made it challenging to prevent gas loss, highly open‐cell (up to 99%) and microcellular (up to 3.5 × 10¹⁰ cells/cm³) foam sheets were successfully manufactured with high‐pressure annular dies using the cell‐opening strategies. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3376–3384, 2006