同向啮合双螺杆挤出机挤出过程的计算机模拟

计算机模拟研究了聚苯乙烯在TSE-35A型同向啮合双螺杆挤出机的挤出过程.计算得到不同喂料速率与不同转速下的停留时间分布,并与在线荧光法测量值对比,二者基本相符.确定了停留时间与螺杆转速及喂料速率之间的函数关系式.模拟结果还预测了喂料速率、螺杆转速等工艺参数对双螺杆内流场变量,如温度、填充率、压力及粘度等的影响.模拟计算有助于了解双螺杆挤出机内部聚合物材料流动状态及停留时间长短,从而指导实际聚合物生产.     

Thermal degradation of high density polyethylene in a reactive extruder

The thermal degradation of high density polyethylene was conducted in a reactive extruder at various screw speeds with reaction temperatures of 400 °C and 425 °C. The residence time of the extruder was estimated and the molecular weight distribution of the fed plastic and reaction products was analysed using gel permeation chromatography. A continuous kinetic model was used to describe the degradation of the high density polyethylene in the reactive extruder. The breakage kernel and the scission rate model parameters were estimated from the experimental data for a variety of cases. It was found that purely random breakage and a scission rate which had a power law dependence on molecular size of 0.474 best described the experimental data.     

On-line monitoring of the residence time distribution along a kneading block of a twin-screw extruder

An on-line Residence Time Distribution (RTD) measuring set-up that enables the characterisation of twin screw extruders at short axial increments is presented. It uses the light emission of a fluorescent tracer (perylene) to generate concentration versus time curves, which are then used to determine the usual RTD parameters, delay time, mean residence time and variance. The system is initially mounted on a rectangular die coupled to a single screw extruder, on-line and off-line measurements being directly contrasted. Then, the optical probe is positioned at several points along the axis of a modular co-rotating twin screw extruder, on-line and off-line data being again compared. Having gained confidence in the measuring technique, an experimental unit utilizing a transparent barrel is used to characterize the evolution of RTD along a kneading block of a twin screw extruder.     

Modeling of L-lactide Polymerization by Reactive Extrusion

The kinetics of L-lactide ring-opening polymerization initiated by stannous octoate and triphenylphosphine was investigated in a batch apparatus (Haake Rheocord Mixer). Based on the experimental data, a kinetic model is developed, considering a coordination-insertion mechanism. Reactive extrusion experiments were further conducted for the same polymerization process, on a co-rotating twin screw extruder. The melted material flow and mixing was described by using the Ludovic® commercial simulator. Based on the developed kinetic model and simulated flow of L-lactide polymerization mixture, a mathematical model of reactive extrusion process is formulated, describing the evolutions of monomer conversion and average molecular weight along the extruder. The model is predicting with a reasonable good accuracy the experimental data.     

Modeling of particle‐dispersed melting mechanism and its application in corotating twin‐screw extrusion

Particle‐dispersed melting is a complex but important melting mechanism in the corotating twin‐screw extruder. In this study, the complex multi‐particle‐dispersed system was simplified into a single‐particle melting model. The finite‐difference method was introduced to solve this problem. The simulation results show that the melting of a particle may involve two steps: the heating stage and melting stage. The heating time and melting time depend on solid concentration, initial melt and solid temperature, and shear rate. Calculations indicate that high solid concentration and solid temperature, low melt temperature and shear rate will result in a more uniform temperature distribution after polymer melting. The model offers valuable information for designing the melting zone in a corotating twin‐screw extruder, especially at high screw speed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2461–2468, 2001     

Modelling non-homogeneous flow and residence time distribution in a single-screw extruder by means of Markov chains

Non-homogeneous velocity distribution of the flow in the channel of a single-screw extruder is taken into account by a new model developed on the basis of the Markov chains. This model allows calculating the Residence Time Distribution (RTD) as well as the influence of the operating conditions on the process at any velocity distribution in the channel. It has been used to represent experimental results on mass flow rate and RTD previously obtained by extrusion of an acrylic polymer, Eudragit E100, at different temperatures and screw rotation speeds. The diffusion coefficient is the only adjusting parameter of the model. It was shown that it does not depend on the screw rotation speed and a correlation between this diffusion coefficient and the barrel temperature was found. The model provides global understanding of the transport kinetics of the flowing material through the extruder according to its behaviour and better describes the progress of the polymer flow all along the barrel from the hopper to the die.     

用反应挤出法制备尼龙6塑料

利用双螺杆挤出机进行了尼龙６阴离子开环聚合反应的研究，通过改变引发剂及活化剂的浓度、螺杆转速、机筒的温度分布以及螺杆元件构型的排布等，研究这些工艺参数对尼龙６反应挤出产物性能的影响。结果表明，反应挤出的尼龙６综合机械性能比水解缩聚法生产，且具有较高的性能价格比。     

CHEMICAL MODIFICATION OF STYRENE/ETHYLENE-BUTHYLENE/STYRENE COPOLYMERS

The chemical modification of two thermoplastic elastomer styrene/ethylene-buthylene/styrene copolymers (SEBS) with diethylmaleate (DEM) as functionalizing agent was carried out in a corotating twin screw extruder and in an internal mixer. The residence time distribution of the extruder was studied due to its great influence on the grafting chemical reaction, the degree of functionalization, and the viscoelastic properties of the obtained modified polymers. The influence of copolymer melt viscosities, and DEM and initiator concentration ratio on the grafting degrees was studied as well. In this case, an internal mixer was used.

Optimal processing conditions were established to obtain grafted polymers characterized by good processability and an absence of crosslinking. The grafting degree achieved in the internal mixer was the same for both copolymers with different viscosities and it increased as the DEM and initiator concentrations and concentration ratios were increased.     

Study on In-Situ Compatibilization of the PP/PA6 Blends in Twin Screw Extruders

The in-situ compatibilization of PP/PA6 blend was studied in a twin screw extruder. The maleic anhydride (MA) content, peroxide concentration, shear rate and feeding order were among the variables investigated. Degree of grafting of samples collected prior to feeding of PA6 into the extruder was measured using titration combined with FTIR technique. From the SEM results it was found that the increasing of initial MA concentration led to larger PA particle size which could be related to secondary reactions between excess MA and PA. The melt linear viscoelastic measurements performed on the blend samples and the obtained relaxation time spectra showed shorter form relaxation time and interfacial relaxation time for one-step compatibilized sample compared to the sample prepared by the two-step method with the same degree of grafting. This was attributed to the stronger interfacial interaction of the one-step compatibilized blend samples which could be resulted from greater efficiency of grafting and/or compatibilization. These results were supported by SEM results which showed smaller particle size for the one-step compatibilized samples. It was demonstrated that melt linear viscoelastic measurement could provide a great insight into understanding the compatibilization process in twin screw extruder.     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

In-Line Monitoring of Bulk Polypropylene Reactors Based on Data Reconciliation Procedures

The main objective of this work is the implementation of a nonlinear dynamic data reconciliation (NDDR) procedure for the in-line monitoring of the bulk propylene polymerization, as performed in a real industrial site. Special attention is given to monitoring of the melt flow index (MI) of the polymer product obtained in an industrial extruder at different operating conditions. In order to do that, a model is developed to describe the polymerization process and the controlled degradation of polypropylene in a reactive extruder. The model is implemented in real time, allowing for in-line and real-time monitoring of the plant operation.     

Emulsion polymerization of styrene in a single continuous stirred-tank reactor

The effects of mean residence time, initiation rate, and emulsifier concentration on particle formation, particle growth, and polymerization rate are examined for the emulsion polymerization of styrene in a completely mixed continuous stirred-tank reactor. Experimental measurements of number of particles, particle size distribution, polymerization rate, and molecular weights are compared with theoretical predictions. A theoretical model which incorporates Stockmayer's modification of the Smith-Ewart theory into the particle growth equation allows reasonably accurate prediction of polymerization rate, particle formation rate, and particle size distribution. Agreement between experimental measurements of number-average and weight-average molecular weights and a theory based on Smith-Ewart case 2 kinetics is also reasonable.     

Ring‐Opening Polymerization of Propylene Oxide by Double Metal Complex in Micro‐Reactor

The ring‐opening polymerization of propylene oxide catalyzed by double metal complex (DMC) is carried out in continuous micro‐reactor (C‐MR). It is found that the monomer conversion at the C‐MR outlet is usually 100% within 2 min of average residence time, which means that the polymerization rate in the C‐MR is faster than that in a traditional semi‐continuous tank reactor. However, the induction period still exists in the polymerization in C‐MR, but can be shortened by increasing the reaction temperature or the micro‐reactor length. The mechanism of monomer coordination and ring opening on DMC during the induction period is confirmed by the ¹H NMR analysis of the samples obtained under very short average residence time. The molecular weight distribution (MWD) of product from C‐MR is generally narrow, which indicates that the process still maintain the characteristics of the “living” polymerization. That is, there is a very high rate ratio of chain transfer to chain propagation provided by the DMC catalyst. However, with the same average residence time, the MWD of product from the longer C‐MR is broader, which can be attributed to the increase of the chain propagation rate caused by rise of pressure.     

Kinetic analysis and modelling of PET macromolecular changes during its mechanical recycling by extrusion

The rheometer cavity has been chosen to analyze, in carefully controlled exposure conditions, the PET macromolecular changes generated during its mechanical recycling by extrusion. Isothermal ageing experiments at 280 °C, under constant or variable oxygen partial pressures (between 0% and 21% of the atmospheric pressure), have allowed us to establish that two types of oxidative macromolecular changes take place successively in an extruder reactor. Chain scissions predominate in the “strongly oxygenated” zones (at the feeder and die), whereas chain couplings (mainly chain branching) predominate in “poorly oxygenated” zones (in the middle of the reactor). Thus, it appears that the relative predominance of both types of modifications is closely related to the extruder geometry and size (in particular, the feeder and die sections and the screw length). A kinetic model of thermal ageing of molten PET has been built to check these assumptions. It describes satisfyingly all the rheometric results obtained in the present study.     

The effect of filler surface modification and processing conditions on distribution behaviour of silica nanofillers in polyesters

Dispersion and distribution of nanosized precipitated amorphous silica particles in poly(ethylene terephthalate) PET and poly(butylene terephthalate) PBT matrices have been studied. The effect of silane coupling agent as well as processing conditions has been analysed on the basis of microscopic analysis of sample morphology. N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (A-1120) has been used as a silica surface modifier. The effect of the extrusion process performance with a single and a twin screw extruder has been tested. It has been found that the processing conditions are more important factors determining fine dispersion and homogenous distributions of filler particles in the matrix than the filler surface modification. The results obtained have revealed that single screw extrusion is preferred only for processing the composites comprising the silica modified with aminosilane, while the application of twin screw extrusion leads to homogenous dispersion and fully deagglomeration of filler particles without silane treatment. It has been established that when the concentration of silica filler increased from 3 up to 7% by weight, the secondary process of particle aggregation occurs.     

Modelling a flow of a highly viscous liquid with the boundary layer of low viscosity in an extruder

Features of the flow of a highly viscous liquid in an extruder with boundary layer of low viscosity liquid at the cylinder wall and at the endless screw surface are considered. The liquid flow is modeled under conditions of isothermal simple shift using cylindrical model of a screw canal. The profiles of rates for the stream of a highly viscous liquid with the ring boundary layer of low-viscous liquid at the cylinder wall and at screw in the both presence and absence of a counter pressure are calculated. Consideration of computer calculations shows that increase in the flow rate is possible when the counter pressure tends to zero and the low-viscous liquid forms a ring boundary layer at the cylinder wall.     

Study of the Alcoholysis of Ethylene-Vinyl Acetate Copolymers with Methanol in the Extrusion Process

Abstract

We investigated the sodium methanolate (NaOMe) catalyzed transesterification of ethylene-vinyl acetate copolymers (EVA) of different compositions with the less compatible methanol (MeOH). The experiments were carried out in a twin-screw extruder with a specially designed reaction zone. The residence time was about 150 seconds. The influence of catalyst quantity on conversion yield was determined for different amounts of added alcohol. Increasing catalyst concentrations accelerated transesterification to such an extent that the state of equilibrium could be achieved during the residence time in the extruder. The dependence of equilibrium conversions on the starting molar ratio MeOH/VA were determined over a broad range, and the equilibrium constant of methanolysis was calculated for K = 3.3. Based on an overall reaction rate derived from the general reaction scheme and which considers a mass transfer for catalyst in the EVA melt, it is possible to calculate the rate constants k ₁ = 33.1 and k _?1 = 8.0 L²˙mol^?2˙min^?1. The methanolysis of EVA in the extrusion process was shown to be a useful method suitable for industrial application. The results of our investigations allow for accurate modification of EVA products.     

Reactive blending of PE‐GMA/PA6 effect of composition and processing conditions

Blends of ethylene‐glycidyl methacrylate copolymer (PE‐GMA) and polyamide 6 (PA6) were prepared in a corotating twin screw extruder. Two processing temperatures were used in order to disperse PA6 in two forms: at high temperature in the molten state in molted PE‐GMA Matrix (emulsion type mixture) and at lower temperature as fillers in molted PEGMA matrix (suspension type mixture). Processed blends were analyzed by scanning electron microscopy and dynamic mechanical experiments to probe the reactivity in the extruder and the compatibilization phenomena. The dependence of the morphology and the rheological properties of PE‐GMA/PA6 blends on blend composition and screw rotational speed was also investigated and is discussed in the paper. The results show that dispersion of the two polymers in the molten state leads to a higher level of interfacial reaction. They also show that whatever the screw rotational speed and the temperature of extrusion are, the rate of interfacial reaction in PE‐GMA/PA6 blends is higher for 50/50 PE‐GMA/PA blends than for 70/30 PE‐GMA/PA blends. Copyright © 2015 John Wiley & Sons, Ltd.     

Increasing molecular weight parameters of a helical polymer through polymerization in a chiral solvent

In this communication, we will demonstrate that polymerization in a chiral solvent can affect the molecular weight distribution of the product by perturbing the balance of the P and M helical screw senses of the growing chains. Specifically, for the Wurtz-type synthesis of polymethylphenylsilane (PMPS) in either (R) or (S)-limonene, the weight-average molecular weight of the products (average Mw = 80 000) was twice that of PMPS synthesized in (R/S)-limonene (average Mw = 39 200). Peturbation of the helical segmentation along the polymer chains leads to a reduction in the rate of occurrence of a key termination step. This the first time that a chiral solvent has been demonstrated to have such an effect on a polymerization process in affecting molecular weight parameters in contrast to affecting tacticity.     

Preparation and evaluation of solid dispersion for nitrendipine-carbopol and nitrendipine-HPMCP systems using a twin screw extruder

In the present study, we prepared solid dispersions of the poorly water-soluble drug nitrendipine (NIT) using the twin screw extruder method with high-molecular-weight substances, hydroxypropylmethylcellulosephthalate (HPMCP) and Carbopol (CAR), as carriers. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) evaluation showed that solid dispersions can be formed when NIT-HPMCP and NIT-CAR mixtures are treated with the twin screw extruder method. Fourier Transformation IR Spectroscopy (FT-IR) obtained with NIT-HPMCP and NIT-CAR solid dispersions indicated the presence of hydrogen bonding between the drug and the carriers. NIT-CAR solid dispersions were found to give somewhat higher dissolution than crystalline NIT and physical mixtures, while the dissolution of NIT-HPMCP solid dispersions was markedly decreased compared with the crystalline NIT and physical mixtures. These findings indicated that CAR has a greater ability to improve the dissolution of NIT than HPMCP when a twin screw extruder was employed to prepare the solid dispersions. The twin screw extruder method can be used as a simple and effective method for the preparation of solid dispersions to improve the dissolution properties of poorly water-soluble drugs when choosing proper polymers as carriers.