Extrusion reactive

In general, reactive extrusion is the term applied to chemical modification of polymers in the presence of an initiator such as peroxides. During chemical modification, there can be other undesired side reactions taking place, for example, cross-linking, degradation into low MW fractions and so on. Good process control is an essential requisite for attaining a balance of desired properties. 

Grafted copolymers can be prepared with up to 10-15% comonomer content successfully during extrusion. The grafted or modified polymers are prepared in order to achieve specific properties such as  

Another type of reactive extrusion is controlled degradation of PP in the presence of a peroxide initiator to give controlled rheology grade product for film applications. Typical examples of grafting reactions are  

The use of REX for the modification of TPS has been reviewed recently by Xie et al. [63], Kalambur and Rizvi [64, 65], and Raquez et al. [66]. The reactive blending of thermoplastic starch has been successfully used for TPS compatibilization with several polymers [63, 64, 67-69]. Examples of reactive blending of TPS have been described recently for PLA [68-72], PHB [73, 74], polyethylene [74-77], polyurethanes [78] and polyesters [79, 80]. 

Reaction with vinyl acetate [81], hydroxypropylation [82], reactions with styrene [83], with ethylene glycol and other glycols giving rise to glucosides [63,84] or with acrylamide monomer [85,86] have also been described. Reactive extrusion is also used to decrease the melt viscosity and decrease the interfacial tension of TPS-based blends [76]. Ning et al. [74] studied the effect of adding citric acid on TPS and LLDPE, via a single-step reactive extrusion. The authors showed improvements in the compatibilization and the mechanical properties and shifts of polyethylene peaks observed by FTIR. 

Miladinov et al. reported the preparation of starch-fatty acid esters by reactive extrusion of plasticized starch and acid anhydrides (acetic, propionic, heptanoic and palmitic anhydrides) in the presence of sodium hydroxide as a catalyst [87]. Starch esters have been prepared by REX using maleic anhydride (MA) as a cyclic dibasic acid anhydride in the presence of 20 wt% glycerol as plasticizer. This material was melt-blended with biodegradable polyester. 

Shujum et al. described compatible TPS/LLDPE blends, produced by one-step reactive extrusion in a single-screw extruder. Maleic anhydride (MAH), and dicumyl peroxide (DCP) were used to graft MA onto the LLDPE chain [88]. 

A maleated ester of low density polyethylene, prepared by the reaction of LDPE and dibutyl maleate in solution, was blended with TPS by reactive extrusion. Mechanical properties of the blends were similar to those of the LDPE due to the compatibilization of these dissimilar components [75]. 

The replacement of the usual batch reactors by twin-screw extruders is highly desirable in order to make the process continuous and economically viable (Jacobsen et al, 1999). Moreover, after reactive extrusion, aliphatic polyesters can be further extruded into films, fibres, bottles and various shaped articles in a continuous process. The interest of industries in reactive extrusion aimed at producing aliphatic polyesters is testified by several patents dealing with ringopening polymerisation of eCL (Wautier, 1995 Narayan et al, 1998) and lactides (Fritz et al, 1998). 

The faster kinetics is aceounted for the coordination of the Lewis base onto the metal, which polarises the metal alkoxide bond and makes the monomer insertion easier (Fig. 4.12). An excess of triphenylphosphine is however not beneficial to polymerisation. Worse, this excess can compete with the monomer for coordination to aluminium, which is detrimental to the kinetics. 

Thermal stability of the as-polymerised PLLAs (at a [LLA]q/ [Sn(Oct)2.PPh3]o ratio of 5000), thus contaminated by the residual tin-based catalyst, has been analysed by Thermal Gravimetric Analysis. Table 4.2 shows that the degradation rate is decreased by PPhs when the monomer-to catalyst molar ratio is higher than 5000. 

13 Twin-screw extruder for ring-opening polymerisation of LA by Sn(0ct)2.PPh3. 

It thus appears that the addition of an equimolar amount of PPh3 onto Sn(Oet)2 has a twofold beneficial effect. It increases the polymerisation rate and it delays noxious transesterification reactions. An acceptable balance between propagation and side reactions is then reached, and polymerisation is fast enough to be conducted in an extruder. 

There are numerous examples of the use of extruders to carry out chemical reactions in polymeric systems (Xan-thos, 1992). In genial, two types of reactions are carried out in extruders polymerization or depolymerization and polymer modification. In this section we illustrate the approach to modeling reactive extrusion by considering the stepwise polycondensation reaction of two species A and B in a singlescrew extruder. 

PLA properties and price can be changed by combining PLA with other biocompatible polymers, fillers, or reinforcements [111, 112]. 

Jacobsen et al. [90] compared the properties of PLA samples produced in a glass ampoule and the single-stage continuous reactive extrusion (Table 11.2). The resulting conversions, 98.5% and 99%, show that in both cases the polymerization reaction has 

Source. Reproduced from ref. 90 with permission of Elsevier. 

Screw speed (rpm) Mass flow rate (kg/h) Extruder head pressure (har) Mw/M Conversion (%) 

High viscosities and low diffusion rates in polymers make polymerization or modification reactions significantly different from the reactions of smaller molecules. When a batch reactor is used for bulk polymerizations, mixing and heat transfer are only efficient during the initial reaction period. When the conversion increases the viscosity also increases following increase in the molecular weight of polymer during the polymerization reactions. The addition of solvents 

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Reactive extrusion Reactive groups Reactive ion etching (RIE)... 

M. Xanthos, ed.. Reactive Extrusion Erinciples andEractice, Hanser PubHshers, Munich, Germany, 1992. 

Blends based on polyolefins have been compatibilized by reactive extrusion where functionalized polyolefins are used to form copolymers that bridge the phases. Maleic anhydride modified polyolefins and acrylic acid modified polyolefins are the commonly used modified polymers used as the compatibilizer in polyolefin-polyamide systems. The chemical reaction involved in the formation of block copolymers by the reaction of the amine end group on nylon and anhydride groups or carboxylic groups on modified polyolefins is shown in Scheme 1. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

Moore, S., Innovative Reactive Extrusion Technologies bring Added Value to Recycled Plastics, MP, Jan. 2000. 

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

A major challenge is then to devise conditions so as to maximize grafting and minimize or control these side reactions. Some discussion of many of these parameters is provided in the reviews mentioned above. It is significant that many recent publications and patents in the area of reactive extrusion relate, not to the development of new reactions or processes, hut to the selection of operating parameters. 

Example 3. Hydrolysis in an Extruder.69 PET reactive extrusion experiments were carried out on a 25-mm Berstorff ZE25 corotating twin-screw extruder with a barrel length-to-screw ratio of 28 1. The extruder consisted of six barrel sections equipped for heating, cooling, and controlling the temperature of each section of the extruder. Initially reaction extrusion of PET and water was performed with cold water at room temperature injected into the extruder. Typical operating conditions were reaction temperatures of 230-265° C, extruder speeds... 

Atlanta, Ga., 26th-30th April 1998, p.2942-5. 012 FEEDSTOCK RECYCLING OF POLYMETHYL METHACRYLATE (PMMA) BY DEPOLYMERISING IN A REACTIVE EXTRUSION PROCESS Breyer K Michaeli W IKV (SPE)... 

REACTIVE EXTRUSION FOR THE HYDROLYTIC DEPOLYMERISATION OF POLYETHYLENE TEREPHTHALATE... 

Xanthos, M. (Ed.), Reactive Extrusion Principles and Practice, Hanser Puhhshers, Munich, 1992. 

Elucidation of degradation kinetics for the reactive extrusion of polypropylene is constrained by the lack of kinetic data at times less than the minimum residence time in the extruder. The objectives of this work were to develop an experimental technique which could provide samples for short reaction times and to further develop a previously published kinetic model. Two experimental methods were examined the classical "ampoule technique" used for polymerization kinetics and a new method based upon reaction in a static mixer attached to a single screw extruder. The "ampoule technique was found to have too many practical limitations. The "static mixer method" also has some difficult aspects but did provide samples at a reaction time of 18.6 s and is potentially capable of supplying samples at lower times with high reproducibility. Kinetic model improvements were implemented to remove an artificial high molecular weight tail which appeared at high initiator concentrations and to reduce step size sensitivity. 

Reactive extrusion is the chemical modification of polymer while it is being transported in an extruder. In this work, polypropylene is intentionally degraded by the addition of a free radical initiator (a peroxide) during extrusion. The product has improved flow properties because of the removal of the high molecular weight tail and the narrowing of the molecular weight distribution. 

Obtaining Kinetic Samples for Reactive Extrusion. To develop and test kinetic models, homogeneous samples with a well defined temperature-time history are required. Temperature history does not necessarily need to be isothermal. In fact, well defined nonisothermal histories can provide very good test data for models. However, isothermal data is very desirable at the initial stages of model building to simplify both model selection and parameter estimation problems. 

Results of Method A The agitated ampoule method proved to have too many constraints to be useful as a method for obtaining kinetic samples for this reactive extrusion. The constraints were as follows o High initiator concentrations (>0.04 wt %) and high temperatures (e.g. 

Reverse-flow reactors Reactive distillation Reactive extraction Reactive crystalization Chromatographic reactors Periodic separating reactors Membrane reactors Reactive extrusion Reactive comminution Fuel cells... 

Homopolymers and copolymers from amido-sulfonic acid or salt containing monomers can be prepared by reactive extrusion, preferably in a twin screw extruder [1660]. The process produces a solid polymer. Copolymers of acrylamide, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methyl-propane sulfonate have been proposed to be active as fluid loss agents. Another component of the formulations is the sodium salt of naphthalene formaldehyde sulfonate [207]. The fluid loss additive is mixed with hydraulic cements in suitable amounts. 

Thermal quenching of the crosslinking reaction In an actual reactive extrusion process, the degree of crosslinking can be controlled by adjusting the residence time at elevated temperature. 

Reactive dyes, 9 173-178, 242, 463-500 26 397. See also Modern reactive dyes anthraquinone, 9 319-320 antisetting agents and, 9 493-498 development history, 9 463-470 Reactive extrusion (REX), 10 364 ... 

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