Maleic anhydride modification of polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model

There has been little effort. to quantitatively understand graft copolymerization in batch and continuous mixers. Little information exists on the evolution of grafting reactions with respect to residence time in an internal mixer or along the screw axis in a twin‐screw extruder. In this study, maleic anhydride was grafted onto polypropylene in both an internal mixer and a twin screw extruder. The influence of residence time on degree of grafting in an internal mixer and a twin screw extruder was studied through measuring reaction yields with respect to reaction time in the internal mixer as well as along the screw axis in the extruder. The dependence of the degree of grafting with monomer and peroxide concentration was determined. A free radical kinetic model of the process was developed and compared to experiment. Kinetic parameters were determined.     

Styrene grafting onto a polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model

There has been relatively little effort to quantitatively understand graft copolymerizaution in either batch mixers or twin‐screw extruders. Most efforts have concentrated on grafting maleic anhydride, which does not homopolymerize. In this paper we consider grafting with styrene, which may homopolymerize as well as graft. The influence of residence time on degree of grafting in an internal mixer and a twin‐screw extruder were studied by measuring reaction yields with respect to reaction time in a mixer and along the screw axis in a twin‐screw extruder. The degree of grafting increased with initial monomer and peroxide concentration. Grafting reactions with three different peroxides were also investigated. The degree of styrene grafting in an internal mixer is slightly higher than that in a twin‐screw extruder. The rate of reaction along the screw axis in terms of residence time seems higher than for the batch mixer. The melt viscosity dropped dramatically with addition of peroxide. A kinetic scheme is proposed and the experimental results are critically compared with it.     

Methyl methacrylate modification of polyolefin in a batch mixer and a twin‐screw extruder experiment and kinetic model

Free radical grafting with methyl methacrylate onto molten polypropylene was investigated in both an internal mixer and a modular co‐rotating twin‐screw extruder. There has been little open literature on melt free radical grafting copolymerization of methyl methacrylate. There is also little information on the evolution of grafting reaction with respect to reaction time in an internal mixer and along the screw axes with methyl methacrylate. The influence of residence time on the degree of grafting in an internal mixer and a twin‐screw extruder was studied through measuring reaction yields with respect to reaction time in a mixer and evolution of reaction yield along the screw axis. The degree of grafting increased with initial monomer and peroxide concentration. The grafting reactions with three different peroxides were also investigated. The grafting levels were similar to maleic anhydride and suggested that only an individual methyl methacrylate unit be grafted. The melt viscosity was dramatically reduced with addition of peroxide. A kinetic scheme of our reaction system for methyl methacrylate was proposed and compared with the experimental results.     

The grafting of maleic anhydride on high density polyethylene in an extruder

The grafting of maleic anhydride (MAH) on high density polyethylene in a counter-rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non-linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.     

Simulations of grafting monomers and associated degradation of polypropylene in a modular co‐rotating twin screw extruder

Kinetic models of grafting maleic anhydride (MAH) and methyl methacrylate (MMA) on polypropylene (PP) were developed for screw extrusion. However, the kinetic models were insufficient to explain the grafting reactions along the length of modular co‐rotating twin screw extruders because the rheological properties and the residence time of PP changed owing to degradation of PP during the grafting reaction. In order to model this system for a modular co‐rotating twin screw extruder, the kinetic model of grafting reaction and models for degradation of PP were combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw, the operating conditions, and the physical properties of the polypropylene, the simulations predicted variation of molecular weight and mean residence time due to degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis was also calculated in the simulation. These predictions were compared with experimental data for various operating conditions. J. VINYL. ADDIT. TECHNOL. 11:143–149, 2005. © 2005 Society of Plastics Engineers.     

Experimental study of maleation of polypropylene in various twin‐screw extruder systems

A range of continuous mixing machines were used as continuous reactors for grafting maleic anhydride onto polypropylene. The machines used were (1) a nonintermeshing modular counterrotating twin‐screw extruder, (2) an intermeshing modular corotating twin‐screw extruder, (3) intermeshing modular counterrotating twin‐screw extruder, and (4) a Kobelco Nex‐T continuous mixer. The grafting reaction of maleic anhydride onto polypropylene and degradation of polypropylene during the grafting reaction were investigated as means for comparing these different machines for reactive extrusion. The influence of processing variables such as screw speed and processing temperature on polymer characteristics also was investigated. Generally, in a comparison of the different machines, the intermeshing counterrotating twin‐screw extruder had the lowest levels of grafted maleic anhydride, whereas the Kobelco Nex‐T continuous mixer under the conditions used had the highest levels of grafted maleic anhydride. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1755–1764, 2003     

Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)-poly(ethylene naphthalene 2,6-dicarboxylate), PET-PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET-PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester-ester exchange mechanism for the reaction.     

Kinetics study on melt grafting copolymerization of LLDPE with acid monomers using reactive extrusion method

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide‐induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, ¹H NMR, and ESR. For the first time, the time‐evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate‐controlled step for the graft copolymerization. The results presented here revealed that the relative importance of graft copolymerization compared with homopolymerization mainly depended on the monomer solubility and reactivity, while the process parameters such as reaction temperature also influenced the reaction tendency. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4301–4312, 2006     

EPDM与马来酸酐的反应挤出接枝

用同向双螺杆挤出机,对三元乙丙共聚物（EPDM）进行熔融接枝马来酸酐（MAH）,考察了单体、引发剂（DCP）用量和加工条件对接枝率的影响。结果表明,在EPDM接枝MAH的反应中,随着DCP用量的增加,接枝率增大,随着MAH用量的增加,接枝率趋于一个平衡值,较佳的实验配方为EPDM：MAH：DCP=100：1：0.03。     

Synthesis and characterization of comb‐like polymer PVC–poly(ethylene oxide)

A new series of amphiphilic graft‐copolymers, composed of poly(vinyl chloride) (PVC) backbones and poly(ethylene oxide) side chains, was synthesized by chemical modification of PVC. The synthesis was based on the reaction between chlorine in PVC (polymerization degree 700) and sodium salt of polyethylene glycol (PEG). PEGs with molecular weights of 200 and 600 were used. The graft polymers were characterized by IR and gel permeation chromatography and the molecular parameters such as the average numbers of grafting chains on the PVC backbones were calculated as well as the grafting percent. The molecular weights of PEG were found to influence the rate of the grafting reaction and the final degree of conversion. The maximum grafting percentage of the resulted polymers after the purification was ca. 34%, regardless of the molecular weight of PEG. No gel was observed in the PVC‐g‐PEOs, in spite of the average numbers of grafting chains up to 32. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 475–479, 2000     

Studies on the grafting of methyl methacrylate onto polyacrylonitrile

Grafting of methyl methacrylate onto polyacrylonitrile was carried out using benzoyl peroxide as initiator and dimethylformamide as solvent. The occurrence of grafting was confirmed by IR spectroscopy and SEM analysis. Effects of various parameters such as reaction time, reaction temperature, initiator concentration, and monomer concentration on rate of polymerization, percentage grafting, and grafting efficiency were studied. The graft copolymers were found to have the similar thermal and structural properties like virgin polyacrylonitrile. Decreasing extent of swelling was observed for the polymers of higher percentage graft in polar solvents. © 1993 John Wiley & Sons, Inc.     

Graft copolymerization of methyl methacrylate onto wool by use of ferrous ion–peroxodiphosphate

Polymethyl methacrylate has been graft copolymerized onto wool using a ferrous ion–peroxodiphosphate initiator system in an aqueous methanol medium. Graft copolymerization was carried out at 20°C, 30°C, 40°C, and 50°C. The rate of grafting was found to be dependent on the concentrations of monomer (MMA), ferrous ion (Fe²⁺), peroxodisphosphate (PP), wool (w), and reaction temperature. [Acid], solvent composition and ionic strenghth were also varied to study their effect on grafting. Based on the experimental results, a suitable kinetic scheme was proposed. Rate and thermodynamic parameters were also varied to study their effect on grafting. Based on the experimental results, a suitable kinetic scheme was proposed. Rate and thermodynamic parameters were also evaluated.     

Kinetics of the oxidative dehydrogenation (ODH) of methanol to formaldehyde by supported vanadium-based nanocatalysts

The aim of the present contribution was to develop a detailed kinetic analysis of the oxidative dehydrogenation (ODH) reaction of methanol to formaldehyde on a nano-structured supported vanadium oxide catalyst, selected in a preliminary screening. The chosen vanadium catalyst, supported on TiO₂/SiO₂, has been prepared by grafting vanadyl alkoxide, dissolved in dioxane, and characterized by BET, XRD, Raman, XPS and SEM. An exhaustive set of experimental runs has been conducted in an isothermal packed bed tubular reactor by investigating several operative conditions, such as: temperature, contact time, methanol/oxygen feed molar ratio and water feed concentration. Depending on the operative conditions adopted, the main products observed were formaldehyde and dimethoxymethane while lower amounts of methyl formate and CO₂ were also found. At low contact time, the main reaction product was dimethoxymethane which was then converted into formaldehyde through the reverse equilibrium reaction with water. As a confirmation of this observation, a peculiar behaviour was detected consisting in an increase of selectivity to formaldehyde by increasing methanol conversion. The obtained experimental data of methanol conversion and selectivity towards products were modelled by means of an integral reactor model and the related kinetic parameters were determined by non-linear regression analysis. The adopted reaction rate expressions were of the Mars van Krevelen–Langmuir Hinshelwood type and a good agreement was found between the model theoretical prediction and the experimental data. A reaction mechanism and a detailed reaction scheme (rake-type) were proposed for methanol ODH on a nano-structured catalyst that were able to interpret correctly the collected experimental observations.     

Free radical grafting of glycidyl methacrylate onto polypropylene in a co-rotating twin screw extruder

Free radical grafting of glycidyl methacrylate (GMA) onto molten polypropylene (PP) was studied in a co-rotating twin screw extruder. Grafting yields of GMA obtained under various experimental conditions along the screw length allowed for a good appreciation of the effects of chemical parameters (the presence of styrene and the concentrations of peroxide and monomers) and those of processing parameters (feed rate, screw speed, and specific throughput). Similar to the results obtained in a batch mixer,¹ free radical grafting of GMA carried out in the extruder in the presence or absence of styrene proceeded rapidly, as it was virtually completed half-way down stream of the extruder. Additionally, the presence of styrene as a second monomer increased the GMA grafting yield reatly with reduced PP chain degradation. The ultimate GMA grafting yield increased with increasing concentration of peroxide, 1,3-bis(tert-butylperoxyisopropyl)benzene. This similarity between the batch mixer and the extruder is related to the fact that in both cases it is the concentration of the peroxide and its half lifetime that determine the grafting rate and the ultimate grafting yield. On the othe hand, the GMA grafting yield decreased with increasing screw speed or feed rate. For a particular specific throughput (the ratio of throughput to screw speed), an increase in throughput with a concomitant increase in screw speed brought about a decrease in GMA grafting yield. It was concluded that the GMA grafting yield is affected primarily by the residence time in the zone in which free radicals are not depleted. The effects of screw speed, feed rate, and specific throughput manifest mainly through this local residence time distribution. Specific energy is not a good measure of the performance of the extruder with respect to the free radical rafting of GMA onto PP. © 1995 John Wiley & Sons, Inc.     

熔融挤出接枝法制备粘接性LDPE

用过氧化二异丙苯(DCP)作引发剂,通过双螺杆挤出机将复合接枝单体、低密度聚乙烯(LDPE)、分散剂(ESBO)混合均匀后进行熔融挤出接枝反应,制备粘接性LDPE,并对有关影响因素及熔融接枝反应机理进行讨论。     

Electron spin resonance study and reactive extrusion of polyacrylamide and polydiallyldimethylammonium chloride

In this article we report results from an experimental investigation on reactive extrusion of water‐soluble polymers. A polymer system containing homopolymers of diallyldimethylammonium chloride (PolyDADMAC) and acrylamide (PAM) was chosen for this study. Reactive extrusion was performed in a counter‐rotating, tangential twin screw extruder using glycerol as a plasticizer and 2,5‐dimethyl‐2,5‐di‐(t‐butylperoxy) hexene‐3 (Lupersol 130) as an initiator. The effects of three processing parameters (polyDADMAC/PAM weight ratio, extrusion temperature, and residence time) on grafting efficiency and degree of grafting of polyDADMAC on PAM were examined. We found the grafting efficiency of polyDADMAC onto PAM decreased with increasing extrusion temperature, polyDADMAC/PAM weight ratio, and residence time. The degree of grafting of polyDADMAC increased with increasing polyDADMAC/PAM weight ratio, but decreased with increasing extrusion temperature and residence time. The insoluble gel fraction in the extruded copolymer increased with increasing extrusion temperature and residence time, but decreased with increasing polyDADMAC/PAM weight ratio. The chemistry and free radical mechanism of PAM‐peroxide and polyDADMAC‐peroxide systems were studied for three different peroxides using an electron spin resonance technique. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1154–1164, 2000     

Plastification or melting: A critical process for free radical grafting in screw extruders

This paper shows for the first time that when a monomer is to be grafted onto a polymer backbone by a free radical mechanism in a twin screw extruder, the grafting process occurs mainly, if not exclusively, in the plastification (melting) zone. For this purpose, the free radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) and polyethylene (PE) was chosen as model systems. A co-rotating self-wiping twin screw extruder of type Werner Pfleiderer ZSK-30 (L = 42D) was used to process the grafting. Owing to its modular character in terms of barrel arrangement, screw element combination and barrel temperature, the position and length of the plastification zone can be adjusted virtually at will. This allowed us to follow up the grafting not only at the die exit, but also in the plastification zone under different grafting conditions. Our results clearly show that it is in the plastification (melting) zone that the entire grafting process occurs. This length is usually very short in a co-rotating twin screw extruder like ours. Under the grafting conditions, it varied from 1D to 5D. Thus, any relevant analysis or model of a free radical grafting process carried out in a screw extruder must be based on detailed information generated not only at the die exit, but also and most importantly in the plastification zone. Otherwise, it may lead to incomplete and/or wrong conclusions.     

Modeling of polypropylene degradation during reactive extrusion with implications for process control

This paper presents the development of a model for free radical initiated polypropylene degradation during reactive extrusion that combines a kinetic model of the polypropylene degradation reaction with a simplified model of the melting mechanism in the extruder. The free radical initiated degradation of polypropylene is characterized by a narrowing of the molecular weight distribution (MWD) and a decrease in the molecular weight averages. A high temperature SEC is used to determine MWD's for three different commercially available polypropylenes degraded at various initiator concentrations in a 1.5 inch single screw extruder (L/D = 24:1). The predictions of the kinetic model alone and the combined kinetic-melting model are compared with the experimentally determined MWD's and molecular weight averages for the degraded polypropylenes. The predictions of a modified kinetic model that includes the possibility of termination by combination are also examined. The kinetic-melting model is found to provide significantly improved predictions of the experimentally determined MWD's and molecular weight averages in comparison to the original kinetic model. A viscosity-molecular weight relationship is also developed, which is then used to determine the gain of the degradation process as a function of the initiator concentration from the molecular weight averages predicted by the kinetic-melting model. Earlier work has shown such prior knowledge of the process gain can be used to significantly improve the performance of process control schemes for the degradation process.     

铝塑复合管用接枝型聚乙烯类热熔胶的制备及性能研究

以高密度聚乙烯(HDPE)和线型低密度聚乙烯(LLDPE)为主体树脂,过氧化二异丙苯(DCP)为引发剂,顺丁烯二酸酐(MAH)为主要单体进行接枝反应挤出制取PE-g-MAH接枝物;然后将该接枝物、增黏剂及其它助剂等进行共混挤出,制备出粘接强度高、流动性能好的铝塑复合管用热熔胶。讨论了原料配比、接枝单体、DCP、增黏树脂和乙烯类弹性体等对该热熔胶性能的影响,并采用红外光谱(FT-IR)技术对该接枝物的结构进行了表征。结果表明:以m(HDPE)∶m(LLDPE)=1∶5,适量控制DCP和不饱和单体的用量,并采用MAH/AA混合单体进行接枝改性,在保证热熔胶流动性能较好的前提下,可得到接枝率及剥离强度均较高的热熔胶;另外,加入适量的乙烯类弹性体,热熔胶的剥离强度明显提高。     

Reaction kinetics of graft copolymerization and thermochemical studies of the degradation of poly(vinyl alcohol) graft copolymer

Poly(vinyl alcohol) (PVA) is a water‐soluble and biomedical polymer. 2‐Acrylamido‐2‐methyl‐1‐propanesulfonic acid was grafted onto PVA using ammonium persulfate as radical initiator. The influences of synthesis conditions such as temperature, concentrations of initiator, PVA and monomer were investigated. Both the initial rate of grafting and the final percentage of grafting were increased by an increase in reaction temperature. The reaction kinetics were studied to determine the rate constants of the first‐order reactions. An activation energy of 16.3 kJ mol^?1 was found for the grafting reaction. The graft copolymers were characterized by IR and intrinsic viscosity measurements. A proposed mechanism of the grafting reaction is discussed. Kinetics of the thermal degradation were studied using a thermogravimetric method and the order of thermal stabilities are given. The apparent activation thermodynamic parameters, E_a, ΔH*, ΔS* and ΔG* were determined and correlated to the thermal stabilities of the homo‐ and grafted polymers. © 2001 Society of Chemical Industry