EYSI-EIER
`
`Prog. Polym. Sci. 27 (2002) 1195 1282 :-
`www.elsevier.comI|ocatelppolysci
`
`
`
`Radical reactions on polypropylene in the solid state
`
`Manfred Riitzsch”’*, Manfred Amoldb, Eberhard Borsig°,
`Hartmut Bucka“, Norbert Reichelt”
`
`'Borealis AG, St Peterstr. 25, A-4021 Linz. Austria
`bIPW Martin-Luther-University. Halle/Wittenburg, Geusaer Str., Geb. I31, 06217 Merseburg, Gennany
`‘Polymer Institute SAS, Dubravska cesta 9, 84226 Bratislava, Slovak Republic
`
`Received 21 July 2000; revised 5 Augrrst 2001; accepted 5 November 2001
`
`Abstract
`
`The chemical modification initiated by radicals and the grafting of isotactic polypropylene (i-PP) in the solid
`state are reviewed.
`
`The attack of a radical onto the polypropylene mainchain is led by abstraction of a hydrogen atom to a tert-
`carbon radical. The tert-carbon radical of the polypropylene mainchain is rmstable and overcomes with the so-
`called B-scission-reaction.
`During the B-scission-reaction, the mainchain is broken into two parts with a double bound on the one and a
`primary radical on the other chain end.
`The resulting degradation of the molecular weight is one limitation of the radical modification of i-PP in the melt
`and is the main reason for the development of radical reactions in the solid state.
`It is well known that the B-scission-reaction depends strongly on the temperature. Below 60 °C, the recombina-
`tion reactions of the i-PP-radicals predominate so that a cross-linking results.
`Above 60 °C, the B-scission-reaction increases and the molecular weight of the i-PP decreases in a logarithmic
`scale.
`
`The first pan of our paper deals with the mechanism of the grafting reactions of different monomers onto i-PP
`below the melting point of i-PP and the special processing conditions related to it.
`To start the grafting at low reaction temperatures, -y or electron-ray scattering or special peroxides are used. As
`monomers difierent methacrylates, acrylates, acrylonitrile, styrene, divinylbenzene, maleic anhydride, butadiene,
`dimethylbutadiene, vinyltrimethoxysilane and other silanes to PP-graft copolymers are investigated.
`The influence of the resonance stability (Q-value of the Qe-schema) of the monomer radicals in the process will
`be discussed. From this knowledge, we will further discuss a special process for the long chain br'anching of the
`melting temperature of i-PP in an extruder. The properties of the resulting materials are an important part of our
`review. © 2(X)2 Elsevier Science Ltd. All rights reserved.
`
`Keywords: Polypropylene; Radical reactions; Solid state; Grafting; Branching; Cross linking
`
`* Corresponding author. Tel.Ifax: +43 732 698].
`E-mail address: m.ratzsch@borealisgroup.com (M. Riitzsch).
`
`0079 6700I0?J$ see front matter © 2002 Elsevier Science Ltd. All rights reserved.
`PH: S0079 6700(02)00006 0
`
`PAGE 1 OF 88
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`BOREALIS EXHIBIT 1015
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`

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`1196
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`M. Ratzsch et al. / Prog. Polym. Sci. 27 (2002) 1195 1282
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`Contents
`
`5.
`
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1197
`1.
`2. Diffusion and sorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1198
`2.1. Morphology of PP powder
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1198
`2.2. Diffusion in PP particle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1200
`2.3. Equilibrium sorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1201
`2.3.1. Results of the experimental examinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1202
`3. Process for the modi®cation of polypropylene in the solid state . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1204
`3.1. Description of the process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1206
`3.2. The heating of the solid particle and the sorption of monomers as well as peroxide . . . . . . . . ..1206
`3.3.
`Increase of the temperature for the start of the peroxide degradation . . . . . . . . . . . . . . . . . . . ..1207
`3.4.
`Increasing the temperature by the application of microwaves
`. . . . . . . . . . . . . . . . . . . . . . . . ..1208
`3.5.
`Increase of the temperature due to back mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1209
`4. Mechanism and kinetic of radical reactions on PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1210
`4.1. Peroxide degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1210
`4.2. Polypropylene degradation by b scission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1213
`4.3. Radical reactions in the solid state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1214
`4.3.1. Termination reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1214
`4.3.2.
`Investigation of physical diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1215
`4.3.3.
`Investigation of reaction diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1215
`In¯uence of different POs on the b scission of PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1218
`5.1. General course of the effect of peroxide on PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1218
`In¯uence of the type of peroxide on the b scission of PP chains . . . . . . . . . . . . . . . . . . . . . . ..1220
`5.2.
`5.3. The ef®ciency of peroxides on PP degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1223
`6. Grafting of monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1224
`6.1. Grafting of PP with maleic anhydride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1224
`6.2. Grafting of PP with styrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1226
`6.3. Cografting of styrene and maleic anhydride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1232
`6.3.1. Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1232
`6.3.2. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1232
`6.4. Grafting of PP with acrylates and methacrylates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1235
`6.5. Grafting of PP with further monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1237
`6.5.1. Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1237
`6.5.2. Discussion of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1239
`6.5.3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1244
`7. Cross linking of PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1245
`7.1. Cross linking of PP by peroxide alone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1245
`7.2. Cross linking of PP in the presence of polyfunctional monomers . . . . . . . . . . . . . . . . . . . . . . ..1249
`7.3. Cross linking of PP in the presence of sulphur and its compounds . . . . . . . . . . . . . . . . . . . . . ..1253
`8. High melt strength PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1254
`8.1. Mechanisms and technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1255
`8.2. Long chain branched polypropylene based polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1257
`8.3. Function of melt drawability and melt strength from HMS content in blends . . . . . . . . . . . . . ..1259
`8.4. Rheological properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1260
`8.5. Shear sensitivity of melt strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1260
`9. Properties and application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1261
`9.1. The properties of high melt strength PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1261
`9.1.1. The Daploy process for manufacturing HMS PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1263
`9.1.2. Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1264
`9.1.3. Applications of long chain branched polypropylene based polymers (HMS PP) . . . . . . .1265
`9.1.4. HMS PP in foam extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1265
`
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`1197
`
`9.1.5. Properties and product bene®ts of HMS PP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1267
`9.1.6. HMS PP in blown ®lm with air cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1267
`9.1.7. HMS PP in direct coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1268
`9.1.8. HMS PP in thermoforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1270
`9.2. The properties of the PP alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1272
`9.2.1. Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1273
`9.2.2. Morphology of the graft polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1273
`9.2.3. Thermomechanical properties
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1274
`9.2.4. Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1275
`9.2.5. Surface properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1279
`References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1279
`
`1. Introduction
`
`The synthesis of polyole®ne graft copolymers by reactive extrusions is excellently reviewed by Moad
`[1] so that it is not necessary to discuss the radical grafting reactions under melt conditions in this review.
`One important basis of the possibility to modify isotactic polypropylene (i-PP) in the solid state is the
`morphology of the native powder from the polymerization reactor. The porous macroparticles have a
`diameter of 1±3 mm inside of the holes with a summary density between 0.87 and 0.856 g/cm3 in
`comparison with the compact material (granulate) with 0.91 g/cm3. An exact densitometric measure-
`ment of the porosity is not possible because of a closing ®lm on the surface. The crystallinity of the i-PP
`in the powder particles is between 40.5% (82.7 J/g) and 43.3% (86.9 J/g) (by DSC-measurements)
`depending on the polymerization technology and the reaction conditions in comparison with the crystal-
`linity after melting and re-cooling with 48.1% (98.2 J/g).
`The measurements of the density and the crystallinity of the powders would be carried out by
`Gierlinger [2] of Borealis GmbH, Linz, Austria. The knowledge of the crystallinity is of interest for a
`chemical modi®cation because there is every reason to believe that the initiator and monomers are only
`condensed in the holes and dissolved in the amorphous phase, so that the crystallinity can be neglected.
`The second important factor for the use of the native reactor granule is their inertness. The role of
`oxygen in all radical reactions is well known. The native reactor granules absorb the oxygen and react in
`high rates to hydroperoxides and build up all the well-investigated following oxidation products. This
`reaction is accelerated by the residues of the polymerization-catalysts [5].
`So, the best way of modifying i-PP in the solid state is to transport the powder under inert conditions
`directly from the polymerization reactor(s) into the modi®cation reactor.
`One of the ®rst research groups recognizing the possibilities and chances of the i-PP powder modi-
`®cation was from Montecatini/Himont/Montell [3,4] in the beginning of the 1990s. They developed the
``HIVALLOY' reactor alloy process of i-PP by activating the powder by e-beam radiation or with special
`peroxides. 1996 PCD/Borealis Linz published [6] as the second company the results of an i-PP powder
`modi®cation development into the own `DAPLOY'-process.
`Previous modi®cation of i-PP in the solid state was done by grafting of acrylic monomers on poly-
`propylene (PP) ®bres of Russian scientists in the `Baumwoll-Institute of Moscow' by g-radiation
`activation at 30±60 8C and in different other research groups f.e. by ultraviolet initiation of hydroxy-
`ethylacrylate [7] at 50 8C.
`The targets are changing the surface properties (adhesion, dyability) of the PP-®bres.
`
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`The third important basis for the solid state modi®cation of i-PP is the reduction of the b-scission-
`reaction by the temperature.
`In Part 4, we will demonstrate that below 60 8C the cross-linking reactions and above the degradation
`reactions dominate.
`The grafting of monomers reduces the decrease in the molecular weight in different amounts. Lambla
`and co-workers [8,9] found a reduction of the molecular degradation by adding styrene (S) to a free
`radical grafting of glycidyl methacrylate on i-PP at .200 8C in an extruder.
`To reduce the b-scission-reaction during the grafting in the extruder, the initiator was selected so that
`this main decomposition range is between 160 and 180 8C, which means before or during the melting of
`the i-PP crystallites [10].
`A mechanochemical initiation of grafting i-PP with maleic anhydride (MAH) at 180 8C is published
`by Russian scientists [11].
`The chemistry of free radical graft copolymerization, initiated with t-butoxy radicals, has been
`investigated using 3-methylpentane and 2,4-dimethylpentane as models for LLDPE and PP, respec-
`tively, by Dokolas et al. [17].
`Mitsutani and co-workers published the development of microporous ®lms and ®bres containing
`®nally dispersed cross-linked vinylpolymers on i-PP-powder in n-Hexan at 70±80 8C with AIBN as
`an initiator [12], without solvent at 90±95 8C and with BPO as initiator [13] and at 170±200 8C in a twin
`screw extruder with 1,1-bis(t-butylperoxy)cyclohexane as the initiator [14]. In this case, the bifunctional
`monomer divinylbenzene (DVB) compensates the degradation reactions by coupling reactions.
`Hawker and co-workers [15] reported a synthesis of PP grafted PS by an interesting combination of a
`metallocene catalyst co-polymerization and the living free radical polymerization.
`Mirawa et al. [16] reported the living radical grafting of S on a modi®ed i-PP-chain. The nitroxide
`stable free radical polymerization leads to a controlled grafting with a uniform PS chain-length.
`
`2. Diffusion and sorption
`
`2.1. Morphology of PP-powder
`
`The idea for a model, ®rst developed by Yermakov et al. [18], contents that the catalysts consist of
`particles which break up fast into small parts at the beginning of the polymerization. During the
`polymerization reaction, the small catalyst parts grow to the microparticle, which form macroparticles
`by the interpenetration of the polymer chains of the microparticles.
`This idea has been acknowledged by the practical results and is now the basis of the multigrain model
`[19,20]. Electron microscopic examinations con®rm the correctness of these ideas. In Figs. 1 and 2, the
`multigrain structure of PP-synthesis products is demonstrated.
`The size of microparticles and the extensions of the holes can be estimated from Fig. 2. The diameter
`of the microparticles is between ca. 0.5 and 1.0 mm, the visible hole measures about 0.8 mm. These
`dimensions are only examples and not valid for all products.
`The following processes determine the transport of the components to the place of reaction:
`² diffusion in porous regions of the PP-grain (macroparticle)
`² mass transfer from the gas to the surface of the microparticles
`
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`1199
`
`Fig. 1. Electron micrograph of PP particle (multigrainstructure).
`
`² absorption in the amorphous phase
`² diffusion in the amorphous phase.
`
`These processes are demonstrated in Fig. 3.
`The diffusion coef®cient determines the rate to obtain the equilibrium conditions. The sorption
`determines the concentration of the modi®ers in the solid phase.
`Basic examinations of different authors [21] indicated that sorption and diffusion in crystalline areas
`can be ignored, i.e. according to the process of solid state grafting, the reactive modi®cation can be
`realized only in the amorphous areas.
`The in¯uence of crystallinity on the equilibrium concentration of styrene in PP-®lms is demonstrated
`in Fig. 4.
`The equilibrium concentration of styrene increases from about 16% with a crystallinity of approxi-
`mately 63% (129.4 J/g) to about 35% with a crystallinity of 53% (108.7 J/g).
`The experiments demonstrate that the higher the crystallinity of the i-PP the lower is the absorbed
`styrene. From these results, the conclusion is that the radical initiated grafting reaction of i-PP with
`styrene (and the other monomers) in the solid state can only take place in the amorphous regions.
`
`Fig. 2. PP particle (part of macroparticle and microparticle).
`
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`
`Fig. 3. Salience of diffusion processes in porous polypropylene particles.
`
`2.2. Diffusion in PP-particle
`
`The diffusion coef®cients were found by analysing the sorption measurements by Kietz [22], Pape
`[23] and RaÈtzsch [24,147].
`The measurements were carried out in vacuum conditions or under normal pressure at various
`temperatures.
`PP-powder as well as PP-granulate were used as absorbents. The design of the device used and the
`results are described in Ref. [25].
`For the interpretation, it was assumed that the PP-particle is homogeneous. Under this precondition,
`an effective diffusion coef®cient for the homogeneous PP-particle can be calculated. This diffusion
`coef®cient includes the mass transfer in the pores and in the amorphous phase.
`A `one parameter model' already describes the measurements in a very exact way with an error of
`
`Fig. 4. Weight content of styrene in dependence on time (in ®lms with different crystallinity), temperature ˆ 100 8C.
`
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`1201
`
`Table 1
`Diffusion coef®cients of different unsaturated molecules into the i PP powder at different temperatures
`
`Component
`
`Molecular weight
`
`i PP
`
`Temperature (8C)
`
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Isoprene
`Divinylbenzene
`Dimethylbutadiene
`Styrene
`Styrene
`
`54.09
`54.09
`54.09
`54.09
`54.09
`54.09
`54.09
`54.09
`82.16
`130.19
`82.15
`104.15
`104.15
`
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`Powder
`
`25
`40
`60
`80
`26
`40
`60
`80
`100
`100
`100
`100
`100
`
`Diffusion coef®cients (m2/s)
`2.5 £ 10212
`7.0 £ 10212
`2.5 £ 10211
`6.5 £ 10211
`1.5 £ 10212
`4.0 £ 10212
`1.0 £ 10211
`5.0 £ 10211
`3.58 £ 10210
`5.44 £ 10211
`1.32 £ 10210
`1.19 £ 10212
`1.94 £ 10212
`
`,2%, but an exact physical interpretation of the measurements or the separation of the particular
`transport resistances is not possible. The experimental diffusion coef®cients can be found in Tables 1
`and 2.
`The dependence of the diffusion coef®cients on the molecular weight and the temperature can be
`
`described by the following relationship:
`D…i† ˆ A
`M…i† exp 2
`
`…1†
`
`
`
`E
`8:315 £ T
`
`The constant A and the activation energy E were determined by using Eq. (1) as adaption function with
`the experimental data (Tables 1 and 2).
`We found a good adaption by using a constant A of 40 for granules and 100 for powder, assuming an
`activation energy of diffusion of E ˆ 70:000 (see Figs. 5 and 6).
`
`2.3. Equilibrium sorption
`
`For the sorption of polymers a detailed description is given in Ref. [25]. The chain-of-rotators (COR)
`equation of state is used for polymers. The COR equation is broadened in relation to the use of group
`
`Table 2
`Diffusion coef®cients of butadiene and vinyltrimethoxysilane in i PP granular at different temperatures
`
`Component
`
`Molecular weight
`
`i PP
`
`Temperature (8C)
`
`Butadiene
`Butadiene
`Butadiene
`Butadiene
`Vinyltrimethoxysilane
`
`54.09
`54.09
`54.09
`54.09
`148.23
`
`Granular
`Granular
`Granular
`Granular
`Granular
`
`27
`40
`60
`80
`100
`
`Diffusion coef®cients (m2/s)
`4.00 £ 10213
`2.30 £ 10212
`9.00 £ 10212
`3.50 £ 10211
`1.15 £ 10211
`
`PAGE 7 OF 88
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`M. Ratzsch et al. / Prog. Polym. Sci. 27 (2002) 1195 1282
`
`Fig. 5. Calculated results of diffusion coef®cients in comparison with experimental results of diffusion coef®cients (powder).
`
`assignments. Regener [26] was the ®rst who proposed this method. The applicability of this method to
`monomer/polymer mixtures is shown by Fink et al. [27]. Binary interaction parameters can be calculated
`from HENRY-coef®cients, which are experimentally determined. The determination of HENRY-coef®-
`cients is carried out by the inverse gas/liquid chromatography or by the measurement of the sorption
`equilibrium under vacuum conditions. The proof of the exactness of the equations was carried out by
`isopiestic measurements of the system ethylbenzene/polypropylene.
`
`2.3.1. Results of the experimental examinations
`The Henry-constant (weight per weight), H, is from the reduced, corrected retention-volume (on
`273.15 K), Vg0,
`
`Hi…T† ˆ R £ 273:15
`M £ Vg0
`
`…2†
`
`Fig. 6. Calculated results of diffusion coef®cients in comparison with experimental results of diffusion coef®cients (granules).
`
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`1203
`
`Table 3
`Coef®cients a1, a2 and a3 of styrene, MMA, BMA and butadiene
`
`Component
`
`Styrene
`MMA
`BMA
`Butadiene
`
`a1
`
`45.652
`50.425
`66.749
`43.205
`
`a2
`
`6284.85
`6017.18
`8528.16
`4257.40
`
`a3
`
`5.1544
`5.8674
`7.8966
`4.9385
`
`The dependence of the experimentally determined Henry-constant on the temperature can be described
`directly by the empirical relationship.
`
`
`Hi…T† ˆ exp a1 2
`
`a2
`T
`
`
`2 a3 £ ln…T†
`
`…3†
`
`In Table 3, the coef®cients of the empirical relationship are collected for typical grafting monomers. The
`results agree well with the results from the literature (for instance with the extensive measurements of
`Horak [28]).
`The adaption of the COR model and the Henry law with the exponential equation for the systems
`styrene/homopolymer and butadiene (BD)/homopolymer is depicted in Fig. 7.
`From the comparison, it follows that the description of the sorption equilibrium in the area of low
`solubilities is only possible through the Henry law.
`In Fig. 8, the dependence of the weight-part of the butadiene on the weight-part of the styrene in PP is
`shown. One recognizes that the solubility of styrene increases with the growth of the weight-part of
`butadiene. The increase in the solubility is nearly linear. This means that at the conditions of 0.04 MPa
`and 393 K in the mixture of styrene and butadiene in PP, we have the feature that a mutual rise and not a
`regression of a solubility takes place.
`
`Fig. 7. Comparison of calculated data acc. COR model with calculated data acc. Henry law (temperature ˆ 100 8C) for Sli PP
`and BD/i PP.
`
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`
`Fig. 8. Dependence of solubility of styrene on solved butadiene in i PP.
`
`3. Process for the modi®cation of polypropylene in the solid state
`
`Saturated hydrocarbons are relatively stable organic compounds. The modi®cation requires an
`abstraction of the hydrogen atom from the mainchain. The reaction of hydrocarbons with reactive
`especially proton active radicals can abstract a hydrogen atom to generate a radical on the mainchain.
`The polypropylene macromolecule has tert-C-atoms in the mainchain:
`
`The hydrogen atoms at the tert-C-atoms are easy to abstract by primary-radicals from the decom-
`position of peroxides or by the in¯uence of the e-beam radiation technique. The radiation process is not
`selective, but at low temperatures stable macroradicals can be created.
`As discussed in Section 1, the tert-C-radical in the i-PP mainchain is under normal condition not
`stable; it degradated during the b-scission reaction into two polymer parts: one with a chained radical,
`the other with an unsaturated end group.
`In Fig. 9 the relative rate of degradation-, combination-, and termination-reactions of an iPP-radical in
`dependence on the temperature is represented. The relative rate is de®ned by the following operation:
`…4†
`
`rrel;i ˆ riXn
`jˆ1
`
`rj
`
`One recognizes that the grafting of polypropylene with monomers after radical generations is signi®cant
`due to radical-reactions in a narrow temperature range from 80 to 150 8C. In the temperature range up to
`180 8C, branching and cross-linking are predominant with special additives (f.i. bi- and tri-functional
`monomers) and at temperatures above 180 8C, the degradation reaction is dominating.
`
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`1205
`
`Fig. 9. Dependence of modi®cation reactions of i PP radicals on temperature.
`
`A prerequisite for the chemical modi®cation is the transport of the monomers to the `reaction place',
`the amorphous phase.
`The b-scission reaction can be in¯uenced outside of the temperature by the monomers.
`The possibility to reduce the b-scission reaction by grafting of a monomer implies that the concen-
`tration of the C-radicals are reduced and stabilized by the addition of the monomer. Later in the review,
`we will discuss the effectiveness of the different monomers as b-scission blocker.
`In the technological process, we have to combine the absorption of the radical generator and the
`monomer into the i-PP powder or granulate and parallel heat up the mixture to the decomposition
`temperature of the peroxide. This means that there are two problems which need to be solved. First,
`the diffusion (mass transfer) of the monomer and peroxide has to be ®nished before or at the same time
`the decomposition of the peroxide has reached its maximum rate.
`The second problem concerns the way how the i-PP-particles can be heated up to the reaction
`temperature within a very short period of time because the heat transfer to and into the particles is
`relatively low.
`The speed of the mass transfer depends on the characteristic value (Kmas).
`The characteristic value of the mass transfer is de®ned by the equation:
`
`Kmas ˆ D1…i†
`R2
`1
`where R is the radius of the particles (powder ˆ granulate).
`The measurements of the diffusion coef®cients, D, in Section 2.2 result in a relationship of the rate of
`the mass transfer of the granulate and the powder:
`
`…5†
`
`granulate
`powder
`
`ˆ from 3 £ 1024 to 6 £ 1024
`
`…6†
`
`The rate of the mass transfer to the reaction place is in the granulate about four magnitudes smaller
`than in the powder. Therefore, only powder is effective in a technical process for the solid state
`modi®cation.
`
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`
`Fig. 10. Block ¯ow sheet of the chemical modi®cations of i PP powder in the solid state and extrusion with granulation.
`
`3.1. Description of the process
`
`The modi®cation takes place in several steps:
`² heating of the solid particle and sorption of monomers as well as peroxides
`² increasing the temperature for the start of the peroxide degradation
`² chemical modi®cation of PP due to radical-reactions
`² ®nishing of the reaction and removal of the rest of the modi®ers
`
`In Fig. 10, the block-¯ow-sheet of solid state grafting technology is shown.
`
`3.2. The heating of the solid particle and the sorption of monomers as well as peroxide
`
`The heating of the powder and the sorption of the modi®ers in the powder take place in a one step
`process.
`As it has been described before, the diffusion-rate is strongly dependent on the temperature and
`increases with higher temperatures. Therefore, the sorption can be accelerated by the increase in the
`temperature.
`The heating of the polyole®n particles is done by the direct heat transfer of a ¯uid, for example by
`adding the heated gaseous modi®ers in the cycle as well as by the indirect heat transfer during a hot
`surface of the reactor wall.
`
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`1207
`
`Fig. 11. Typical process ¯ow sheet of process stage `sorption'.
`
`The sorption from the gaseous phase guarantees the necessary homogeneous distribution of the
`modi®ers.
`The temperature for the sorption under technical conditions is restricted because of the strong
`temperature dependence of the peroxide degradation on 60±120 8C.
`Modi®ers with high molecular weight sorption can be absorbed under vacuum conditions.
`The time for a homogeneous distribution (sorption) of the modi®ers in the particles depends on the
`process conditions and the vapour pressure of the modi®er.
`In Fig. 11, the typical process-¯ow-sheet of the sorption step is represented.
`
`3.3. Increase of the temperature for the start of the peroxide degradation
`
`For the modi®cation reaction, it is important that after the sorption of the modi®ers, the temperature of
`the polyole®ne particles has to be raised to the reaction temperature (peroxide degradation temperature)
`within a short period of time.
`Concerning the heating of powders, the following techniques have proved to be favourable:
`
`² direct and indirect heating by the powder during intensive mixing
`² increase in the temperature by application of microwaves.
`
`The energy for heating of the PP-powder by intensive mixing results from the rebound of the particles
`with the high speed rotating mixer plates and with the mixer wall. The strong movement of the particles
`makes an increased indirect heat transport through the heated mixer wall possible.
`
`PAGE 13 OF 88
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`
`Fig. 12. Labour plant for heating by microwaves.
`
`3.4. Increasing the temperature by the application of microwaves
`
`The heating in a microwave ®eld is a typical dielectrical heating technique. A prerequisite for heating
`in the microwave ®eld is an asymmetrical molecular structure.
`The dipole induces rotations and vibrations of the molecules in the electric changing ®eld. Through
`the intermolecular friction of the molecules, high frequency energy gets transformed into heat.
`The polyole®ne molecules have no dipoles so that they are theoretically inactive, which means they
`are not heatable in the microwave ®eld. Dissolved polar substances in polypropylene can act as heat
`generator for PP.
`To proof the functional ability of microwave heating as well as of the continuous chemical modi®ca-
`tion in the microwave ®eld, investigations of the grafting of MMA on PP-powder were carried out in a
`small technical installation.
`In Fig. 12, the construction of the labour plant for the microwave heating is represented.
`The PP-powder, saturated with modi®ers, ¯ows from a storage bin into a quartz-tube. For a low
`energy absorbing media as i-PP, we developed a special adjustable applicator of the type (H10). The PP-
`powder ¯ows through a quartz-tube and was heated by the microwave effect.
`The special dosing unit regulates the ¯ow of mass. The temperature was measured before and after the
`quartz-tube with thermoelements.
`The energy consumption of the microwave process can be measured by the performance of the
`adjustable magnetron.
`The experimental results corresponds with the calculated values from the theoretical model on the
`condition that the quartz-tube behaves like an ideal tubular reactor under adiabatical conditions.
`
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`1209
`
`Fig. 13. Incr