Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
  • C08F255/02—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00 on to polymers of olefins having two or three carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F222/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
  • C08F222/04—Anhydrides, e.g. cyclic anhydrides
  • C08F222/06—Maleic anhydride
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/001—Removal of residual monomers by physical means
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/02—Neutralisation of the polymerisation mass, e.g. killing the catalyst also removal of catalyst residues

Definitions

• the present invention relates to a process for the preparation of polyolefins having particular rheological and compatibilization properties, as well as the resulting polyolefins and their use.
• the problems posed by polymers in general, and polyolefins in particular, concern their insufficient melt strength during their use by extrusion.
• melt strength of polyethylene (PE) and polypropylene (PP), defined by a high elongational viscosity, is insufficient for certain types of processing, such as foam extrusion, blow molding, thermoforming and blowing, in particular 3D blowing.
• the objective of the present invention is to provide a process for the preparation of polyolefins having improved properties with regard in particular to the melt strength.
• the present invention therefore relates to a process for the preparation of polyolefins comprising the steps of a) grafting of acid groups on polyolefins by means of a graftable monomer carrying at least one functional group chosen from a carbonyl and an acid anhydride , optionally in the presence of another graftable monomer carrying vinyl unsaturation and optionally of one or more aromatic rings, b) purification consisting in removing at least part of the graftable monomer carrying at least one functional group chosen from a carbonyl and an acid anhydride, which has not reacted with the polyolefins c) neutralization of the acid groups with at least one neutralizing agent.
• the polymers obtained by the process according to the present invention have improved properties, in particular as regards the melt strength, thanks to the introduction of an additional purification step b).
• an additional purification step b there remains in the final product always a more or less significant part of functional graftable monomers which have not reacted with the polyolefins.
• the presence of these functional graftable monomers which have not reacted with the polyolefins, that is to say which have not been grafted onto the polyolefins after step a) may be responsible, inter alia, for a melt strength insufficient and coloring problems.
• This purification step b) therefore has the objective of eliminating at least part of the functional graftable monomers which have not reacted with the polyolefins.
• An advantageous embodiment of the present invention provides that the purification step b) is carried out by one of the current and known methods, preferably by entrainment with acetone, by stripping with hot air, by stripping with water vapor, by stripping with an inert gas or by degassing.
• the grafting of the acid functions is carried out, for example by the radical route, on polyolefins.
• the polyolefins which can be used in the process according to the invention are polymers of linear olefins containing from 2 to 8 carbon atoms such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene and 1-octene.
• the linear olefins preferably contain from 2 to 6 carbon atoms, more particularly from 2 to 4 carbon atoms.
• the polyolefins can be selected from the homopolymers of the abovementioned olefins and from the copolymers of these olefins, in particular copolymers of ethylene or propylene with one or more comonomers.
• the comonomers are advantageously chosen from the olefins described above, from diolefins comprising from 4 to 18 carbon atoms, such as 4-vinylcyclohexene, dicyclopentadiene, methylene- and ethylidene-norbornene, 1,3- butadiene, isoprene and 1,3-pentadiene.
• the polyolefins are chosen from polymers of propylene and polymers of ethylene.
• the polyolefins are chosen from the ethylene homopolymer, the propylene homopolymer, the ethylene copolymers, the propylene copolymers, the ethylene and propylene copolymers and their mixtures.
• the polymers of propylene are most often chosen from homopolymers and copolymers of propylene whose melt index (MFI), measured at 230 ° C, under a load of 2.16 kg according to standard ASTM D 1238 (1986) is between 0.1 and 2000 dg / min, preferably between 0.1 and 500 dg / min, particularly preferably between 0.1 and 50 dg / min.
• MFI melt index
• the polymers of ethylene are most often chosen from homopolymers and copolymers of ethylene having a standard density of between 860 and 996 kg / m-, preferably between 915 and 960 kg / nv *, particularly preferred between 936 and 953 kg / m- and a melt index (measured at 190 ° C under a load of 5 kg according to ISO 1133 (1991)) between 0.01 and 2000 dg / min, preferably between 0 , 1 and 200 dg / min, particularly preferably between 1 and 40 dg / min.
• Propylene polymers are very particularly preferred.
• the graftable monomer carrying at least one functional group chosen from a carbonyl and an acid anhydride can be chosen, for example, from unsaturated mono- or dicarboxylic acids and their derivatives and unsaturated mono- or dicarboxylic acid anhydrides and their derivatives.
• the graftable monomer preferably comprises from 3 to 20 carbon atoms. Mention may be made, as typical examples, of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, maleic anhydride, itaconic anhydride. , crotonic anhydride and citraconic anhydride. Maleic anhydride is most particularly preferred.
• the amount of graftable monomer carrying at least one functional group chosen from a carbonyl and an acid anhydride, used for grafting depends inter alia on the properties which it is intended to obtain for the product, the quantity of radical generator used and therefore the grafting yield and desired grafting rate, as well as the reaction time. It is generally sufficient to allow an improvement in the properties of the finished product and will generally be between 0.01 to 10% by weight, preferably between 0, 1 and 5% by weight relative to the polyolefins.
• the graftable monomer carrying vinyl unsaturation and optionally one or more aromatic rings preferably comprises from 3 to 20 carbon atoms. As typical examples, 1-dodecene, styrene, vinylpyridine, divinylbenzene, 1,4-hexadiene and their mixtures can be cited. Most preferred is styrene.
• this graftable monomer carrying vinyl unsaturation and optionally one or more aromatic rings makes it possible in certain cases in particular to increase the degree of grafting of polyolefins.
• the necessary proportion of this monomer depends on the properties targeted and is generally 0.01 to 10% by weight, preferably 0.1 to 5% by weight, relative to the polyolefins.
• a particularly preferred form of the process of the present invention provides that it is carried out in the absence of graftable monomer carrying vinyl unsaturation and optionally of one or more aromatic rings.
• Another embodiment of the present invention therefore relates to a process in which the grafting of acid groups is carried out in the presence of a radical generator.
• an organic peroxide is preferably used, and more particularly an alkylperoxide.
• an organic peroxide there may be mentioned t-butylcumyl peroxide, 1,3-di (2-t-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di (t-butyl) peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) -3 -hexyne.
• 2,5-dimethyl-2,5-di-t-butylperoxyhexane (DHBP) is particularly preferred.
• the radical generator is generally used in the process according to the invention in an amount sufficient to allow grafting to be carried out. Furthermore, it is desirable that the quantity does not exceed the minimum quantity necessary since any excess of radical generator can cause degradation of the polyolefin.
• the quantity is usually at least 0.0005% by weight relative to the polyolefins, it is in particular at least equal to 0.001% by weight, the values of at least 0.005% by weight being the most advantageous. In general, the amount does not exceed 3% by weight relative to the polyolefins, preferably not 0.5% by weight, the values of at most 0.15 being the most recommended.
• the step for neutralizing the acid groups is preferably carried out with at least one neutralizing agent which includes a cationic part comprising one or more cations chosen from the group consisting of alkali cations, alkaline earth cations and transition metals such as for example Zn + , Al 3+ and Zr 4+ .
• a neutralizing agent which includes a cationic part comprising one or more cations chosen from the group consisting of alkali cations, alkaline earth cations and transition metals such as for example Zn + , Al 3+ and Zr 4+ .
• the neutralizing agent preferably includes an anionic part comprising one or more anions chosen from the group consisting of alcoholates, carboxylates, hydroxides, oxides, alkyls, carbonates and hydrogen carbonates.
• neutralizing agents are sodium hydroxide, calcium oxide, sodium carbonate, sodium hydrogencarbonate, sodium methoxide, sodium acetate, magnesium ethoxide, acetate zinc, diethylzinc, aluminum butoxide, zirconium butoxide, and the like.
• Sodium hydroxide and zinc acetate are particularly preferred.
• the amount of neutralizing agent added depends on the intended use and therefore on the desired properties of the polyolefins.
• the neutralizing agent is used in an amount of 10% to 300% of the stoichiometric value relative to the acid groups, preferably in an amount close to the stoichiometry.
• the amount of neutralizing agent added will be between 0.1 and 1000 meq / kg of polyolefin grafted with acid groups, preferably between 1 and 450 meq / kg of grafted polyolefin, more preferably between 5 and 300 meq / kg, very particularly preferably between 10 and 100 meq / kg depending on the grafting rate of the polyolefin.
• a further improvement in the properties of the finished product can be achieved by following step c) of a purification step d) consisting in eliminating the products of the neutralization reaction of the grafted acid functions.
• This purification step can be carried out by all current and known methods, preferably by stripping with steam, by stripping with hot air or by degassing, preferably by degassing under vacuum. This purification is often essential because it allows to shift the balance of the neutralization reaction.
• all the devices known for this purpose can be used. Thus one can work indifferently with mixers of external or internal type. Internal type mixers are the most suitable and among them are BRABENDER® batch mixers and continuous mixers, such as extruders.
• An extruder in the sense of the present invention comprises at least the following parts: a feed zone and at its outlet a discharge zone preceded by a compression zone, the latter forcing the molten mass to pass through the evacuation area.
• Reactive extrusion is a known and practiced method for grafting functional groups and therefore, in a preferred embodiment of the method according to the present invention, the grafting step is carried out in an extruder, a technique generally called “grafting" by reactive extrusion “or” reactive extrusion ".
• steps a) and c) of the process are carried out in an extruder.
• a particularly preferred extruder for carrying out the process according to the invention consists of an alloy resistant to corrosion.
• a particularly preferred alloy is an alloy mainly consisting of nickel or cobalt.
• all the stages are carried out according to a continuous process comprising a single melting of the polyolefins and in a more than preferred manner all the stages can be carried out in a single extrusion in an extruder which generally comprises , in addition to the areas mentioned above, optionally, one or more batch feeders for the separate introduction of the polyolefin (s), graftable monomers carrying at least one functional group chosen from carbonyl and anhydride of acid, of the radical generator and / or of the stabilizer, one or more screw elements allowing the propagation of the material to be extruded, one or more heating zones allowing the melting of the constituents and, if necessary, one or more degassing zones for the purification step (s).
• degassing zones must be isolated from the reagent injection zones by a plug of molten material which is generally produced via pairs of left-hand screw elements with respect to the direction of transport.
• the evacuation zone can also be followed by a granulating device or a device giving the extruded material a profiled shape, such as a film, a pipe, a sheet, etc. or a device giving the extruded material an expanded profiled shape by the addition of an expanding agent.
• the expanding agent used for the purposes of the present invention, is chosen from the expanding agents usually used to generate cells in plastics, as described in the work entitled Encyclopedia of Polymer Science and Engineering, second edition, vol. 2, 1985, p. 434 - 446.
• the expanding agent can be a chemical type or a physical type expanding agent.
• the expanding agent is of the physical type such as, for example, alkanes (butane, propane, isobutane, pentane), hydrofluorocarbons, carbon dioxide or their mixtures.
• a particularly preferred process in accordance with the present invention, can comprise the steps of i) introduction and fusion of the polyolefin (s) ii) introduction of the graftable monomers carrying at least one functional group chosen from a carbonyl and an acid anhydride, of the radical generator and optionally of the graftable monomer carrying vinyl unsaturation and optionally of one or more aromatic rings, iii) grafting of the graftable monomers carrying at least one selected functional group from a carbonyl and an acid anhydride iv) elimination of the graftable monomers carrying at least one functional group chosen from a carbonyl and an unreacted acid anhydride, in excess v) optional introduction of a stabilizer vi ) introduction of the neutralizing agent vii) elimination of the pennant from the neutralizing agent, and viii) granulation or extrusion of a profiled form, optionally expanded.
• the process temperature is higher than the melting temperature and lower than the decomposition temperature of the polyolefin and of the grafted polyolefin, if necessary at an optimal temperature for the radical generator.
• the temperature therefore depends on the nature of the constituents of the reaction mixture and will generally be at least 100 ° C, most often at least 130 ° C, in particular at least 140 ° C. Generally one works at a temperature not exceeding 400 ° C, most often not 300 ° C and more particularly not 250 ° C.
• the time required to carry out the various stages of the process according to the present invention, in this case the grafting and / or the preliminary purification, the neutralization and / or the final purification depends on the quantities used of the reagents, on the temperature, the nature of the reactants used, the type of reactor (for example the extradeuse) used. It is generally from 1 second to 1 hour, preferably from 5 seconds to 30 minutes, more particularly from 10 seconds to 10 minutes.
• one or more usual additives of polyolefins can be incorporated at any time, such as for example stabilizers, antioxidant additives, antistatic agents, organic or inorganic dyes and fillers, etc. . as long as they do not interfere with the grafting of the acid groups.
• At least one stabilizer is added during the process.
• the stabilizer used in the process of the present invention is chosen from compounds comprising a sterically hindered phenol group, from phosphorous compounds and from their mixtures.
• substances such as 1,3,5-trimethyl-2,4,6-tris (3,5-t-butyl-4-hydroxybenzyl) benzene, pentaerythrityl tetrakis- (3,5 -di-t-butyl-4-hydroxyphenylpropionate), tris- (2,4-di-t-butylphenyl) phosphite or a mixture of pentaerythrityl tetrakis- (3,5-di-t-butyl-4-hydroxyphenylpropionate) and tris- (2,4-di-t-butylphenyl) phosphite, preferably in equal amounts.
• the preferred stabilizer is 1,3,5-trimethyl-2,4,6-tris (3,5-t-butyl-4-hydroxybenzyl) benzene.
• the invention also relates to the polyolefins resulting from the process according to the invention.
• the invention further relates to polyolefins having partially neutralized acid groups having a melt flow index of 0.001 to 1000 dg / min and improved melt strength characterized by an exponential increase in elongational viscosity and by an increase in viscosity dynamic at low shear frequencies.
• the polyolefins are those identified above.
• the melt melt index of polyolefins having partially neutralized acid groups is usually 0.001 to 1000 dg / min, preferably between 0.01 and 100 dg / min, particularly preferably between 0.1 and 50 dg / min , the melt index being measured at 230 ° C under a weight of
• the polyolefins according to the invention are characterized by ionic aggregates having a shape analogous to that of a bunch of grapes whose size is between 10 and 500 nm and whose grapes have a dimension of less than 50 nm.
• the bunches of grapes are usually larger than 10 nm, preferably greater than 50 nm.
• the bunches of grapes are usually less than 500 nm in size, preferably less than 200 nm.
• the grapes constituting the cluster usually have a dimension of less than 50 nm, preferably less than 25 nm, particularly preferably less than 10 nm.
• Polyolefins find an interesting application in the preparation of foams, in particular polypropylene foams and high density polyethylene foams produced by foam extrusion.
• polyolefins find an interesting application in the production of shaped objects by foam extrusion, thermoforming or blowing, in particular by 3D blowing.
• Another area of application is the improvement of adhesion in compatibilization, multilayer and sealing applications.
• the invention also relates to the foaming extrusion process according to which the foaming extrusion is carried out consecutively to the process for preparing polyolefins.
• Example 1 serves to illustrate the present invention without limiting its scope.
• Example The resin used is a random copolymer of propylene and ethylene sold under the trademark ELTEX® P KS 001 PF and it is characterized by: an MFI (melt flow index measured according to standard ASTM D 1238 (1986) at 230 ° C under a load of 2.16 kg) of 4.5 dg / min, a melting temperature of 134 ° C (measured by the DSC technique (Differential Scanning Calorimetry) according to ISO standard FDIS 11357-3
• the resin feed rate in the extender is 5 kg / h.
• the extruder is a CLEXTRAL BC21 with double co-rotating screws. The diameter of the screws is 25 mm and their length is 1200 mm. The screw rotation speed is 300 rpm (rotations per minute).
• the sheath is made up of 12 sheath elements (zones) each with a separate temperature regulation.
• the 12 zones are respectively:
• the introduction rate is 200 ml / h and the temperature of the zone is 180 ° C.
• mixing zone temperature: 240 ° C
• additional degassing zone for the removal of water and acetic acid temperature: 240 ° C
• compression zone to force the material through the die (temperature: 200 ° C).
• a die After these 12 sheath zones, a die allows the transformation of the melt into a rod which is cooled and transformed into granules.
• the final polymer is characterized by an MFI of 7.4 dg / min. It is also characterized by the RME, ARES and transmission electron microscopy techniques as indicated below.
• the elongational viscosity of the polymer considered is determined using a rheometer marketed by RHEOMETRICS under the name RME (RHEOMETRICS ELONGATIONAL RHEOMETER FOR MELTS).
• the sample (55x9x2 mm) is obtained by extrusion and is subjected to a relaxation procedure before the measurements.
• the curve shown in Figure 1 (RME diagram) represents the variation, at 190 ° C of the elongational viscosity in the molten state (expressed in kPa.s) as a function of time (expressed in s) for an elongation gradient (expressed in s "1 ) of 1.
• the polymer produced in the example exhibits an exponential increase in the elongational viscosity as a function of the time characteristic of a structural hardening under stress (melt resistance).
• the dynamic viscosity is determined using an imposed deformation rheogoniometer marketed by RHEOMETRICS under the name ARES (ADVANCED RHEOLOGICAL EXPANSION SYSTEM).
• ARES ADVANCED RHEOLOGICAL EXPANSION SYSTEM
• the measurements are carried out on the sample, placed between 2 parallel plates and subjected to a deformation, with a diameter of 25 mm and a thickness of 2 mm cut in a pressed plate.
• the curve shown in Figure 2 represents the variation, at 170 ° C, of the dynamic viscosity expressed in Pa.s as a function of the frequency expressed in rad / s.
• the polymer produced in the example is characterized by an increase in dynamic viscosity at low frequencies.
• Transmission electron microscopy is carried out using a ZEISS EM 910 microscope. The examination was carried out on ultramicrotomic sections of approximately 90 nm.
• FIG. 3 represents the photograph obtained by transmission electron microscopy.
• ionic aggregates having a shape analogous to that of a bunch of grapes whose size is of the order of 100 to 200 nm and the grapes have a dimension of the order of 10 nm.
• Analyzes carried out by microanalysis using a LINK eXL II system attached to the ZEISS EM 910 microscope clearly show the presence of zinc in the ionic aggregates, in particular in the grapes constituting the bunch.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Graft Or Block Polymers (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Sealing Material Composition (AREA)

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