LU84200A1 - PROCESS FOR IMPROVING THE TREATMENT OF POLYMERS AND POLYMER COMPOSITIONS THUS OBTAINED - Google Patents

Description

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The present invention relates to polypropylene polymer pellets having better processing characteristics for spinning, extrusion and the like, as well as methods for obtaining such pellets. A polypropylene polymer having good processability for processing Advantageously, the formation of fibers or films has the following characteristics: l) the ability to be thinned without breaking when it is melted, thus making it possible to manufacture, with a high throughput, fine filaments and thin films having a high resistance to unthinned products; and 2) the ability to be pumped through conduits and capillaries and / or to be thinned in the form of fibers or films requiring a minimum of energy, which implies lower shear viscosities and extension for the polymer melt ”20 It has been shown that the first characteristic (high slenderness) can be obtained with a polypropylene polymer having a narrow molecular weight distribution (i.e. the weight weight average molecular weight divided by 25 number average molecular weight of polymer) "

The second characteristic (low shear and extension viscosities) is obtained with a polymer with a lower average molecular weight by weight * 30 The Ziegier-Natta catalysts currently used in the industrial manufacture of polypropylene give polymers which, at the output of the polymerization reactor, have a molecular weight distribution too wide for the manufacture of fine fibers or thin films. Thus, a polymer having a low average molecular weight by weight at the outlet of a reactor of this type would have the low viscosity desired for the treatment, but could not be thinned to the desired degree. Consequently, the polypropylene manufacturers have found it necessary to manufacture a polymer of an H molecular weight at very high weight, then carrying out a disorderly molecular scission step (thermal or chemical degradation) which , Inherently, narrows the molecular weight distribution, while at the same time reducing the weight average molecular weight to the desired degree.

Polypropylene is chemically degraded by the addition of compounds that break down the free radicals that form. Chemical stabilizers added to polypropylene to improve end-use stability can cause disruption with free radical generators.

However, it has been found that certain types of free radical-generating chemicals such as, for example, the specific organic peroxides described in British Patent 1,442,681, are * minimally altered by the stabilizers usually used and that, as soon as therefore, they were preferred prodegraders.

The degree to which the polymer can be degraded, however, is limited because the polymer manufacturers are unable to form pellets from polymers having a very low viscosity. Consequently, in polypropylene processing plants where films and fibers are made, there is the problem of using polypropylene which is not optimally suitable for these applications. * Therefore, it has been demonstrated that it is necessary to have a polymer having a high viscosity for the formation of pellets and a low viscosity for the treatment for the final use.

Currently, low viscosity polypropylene polymers which are desirable for processing facilities cannot be processed into pellets on an industrial scale by polymer manufacturers without an excess of "nets" ( lozenges with long tails) tending to clog equipment in manufacturing and processing facilities *

It has been suggested that the viscosity of the polymers for the formation of pellets could be increased by operating the pelleting machine at a temperature just above the melting point of the polypropylene polymer in order to improve the cutting into pellets. This procedure can only be adopted at a low flow rate to reduce the heat generated by the shearing forces involved in the tableting equipment and / or by cooling the molten polymer, which considerably increases the costs and the complexity. of the process.

It has also been suggested to add, in the treatment plant for the end use, an additional chemical prodegrading agent to the polypropylene pellets in order to reduce the viscosity of the polymer to the desired degree before the formation of fibers or dandruff. However, this method has several drawbacks: 1) peroxide-based prodegrading agents present risks of fire and explosion and they require special equipment and methods for treatment; 5 2) to reach its maximum efficiency, the peroxide must be dispersed uniformly in the polymer before its decomposition and its reaction, otherwise there is a risk of obtaining a polymer having a variable viscosity and having an even greater molecular weight distribution than that initial polymer * The polymer manufacturer who has access to specialized equipment and who, at the outlet of the reactor, obtains fine flakes instead of pellets, is clearly better able to obtain this uniform distribution; 3) the treatment equipment risks being damaged by a polymer having a variable viscosity i 15 4) the peroxide is more effective as a degrading agent if it is dispersed properly. before the reaction} and 5) the peroxide added to or on the pellets rather than inside them acts as a lubricant in the feed sections of the former extruder, thereby reducing the flow for a given number of revolutions per minute.

In the treatment plant, it is also possible to reduce the molecular weight by adopting very high temperatures so as to cause thermal degradation of the polypropylene. However, these very high temperatures give rise to the consequences— | following quences:! l) reduced service life of the equipment; 2) flow restrictions due to constraints resulting from sudden cooling; • 3) excessive energy consumption j i 4) hazardous work environments; and 5) problems with additives.

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Among the problems posed by the additives are: 1) excessive degradation of the additives, which requires the addition of a greater amount of additives to the polymer than in the final product; 2) limited range of additives that can be used, so that more expensive or non-optimal additives must be used; and 3) clogging of conduits, capillaries, dies and the like for polymers, due to degradation products.

Additional information can be obtained by referring to earlier patents. In British Patent 1.44-2.681 in the name of Chemie Linz, a process for the preparation of polypropylene is described in which degradation is carried out with peroxide-degrading agents to obtain a polypropylene polymer having a narrow distribution. molecular weight. In US patent 3 * 867 * 534 in the names of Baba et al., The use of aliphatic peroxides as prodegrading agents for polypropylene is described and the problems which arise arise in 1 However, it is suggested that an unreacted prodrug be avoided. In US Patent No. 3 * 144 * 436 in the names of Greene et al., A method of degrading stereoregular polymers is described using free radical initiators. In one embodiment, a two-step process is described in which the injection of the prodrug is controlled in the area of the extruder where the! melt. In U.S. Patents 3,849 * 241 to Buntin et al. and 35 * 978 * 185 also, in the names of Buntin et al., are described / / 7 melt blowing processes which are improved by controlled degradation of the polymers. Similarly, in the patent of the United States America No. 3 · 755 · 527 in the names of Keller et al ·, 5 the advantages of degradation of polymers are described.

The present invention relates to: 1) a multi-step process for the degradation of polypropylene by initially obtaining a polymer which is easily transformed into pellets which, when heated, undergo further degradation by forming a polymer of low viscosity which can be easily processed to be made into high quality fibers and films; and 2) a polypropylene polymer containing a degrading agent and made into pellets and the like as a result of this process.

The present invention results from the following discovery: when certain free radical-forming chemicals which act as prodegraders from polypropylene to the polymer and in pelletizing equipment operating under specified conditions are added, a fraction of the product chemical remains unaltered following the pitch-twisting process · After extrusion in order to form pellets, the reaction is stopped and the rest of the prodegrading agent then reacts during re-extrusion to form a polymer having a good behavior during processing and forming films and fibers having excellent properties. The exact residual percentage of the degrading agent remaining after the pelletizing carried out by the manufacturer will vary depending on the pelletizing temperature, the residence time of the degrading agent at this temperature, as well as the type of agent of prodégrada- i /! / o L- \ δ tion but, preferably, it will be more than half the quantity originally added and it may go up to 901 of the latter. Ideally, for pelletizing, no environmental degradation but, in practice, a certain amount of the prodegrading agent will initially react during the pelletizing * The small amount initially reacting (amount as small as about 10%) does not reduce as a minimum the viscosity of the polymer in the pelleting machine, thus making it possible to obtain well-formed and freely flowing pellets. After pelletizing, if acceptable results are to be obtained, the residual amount of the prodegrading agent must be at least 0.01%, calculated on the weight of the polymer. In this way, the advantages of a two-step addition degradation method of the type described above with respect to the prior art are preserved, while the disadvantages are practically eliminated.

The only appended figure is a graph illustrating the relation between the reaction time and the viscosity at the extrusion temperatures of polypropylene with two types of prodegradants according to the invention, Although the invention is described with reference to preferred embodiments, it is understood that it is in no way limited thereto. To the con! milk, it is understood that the invention encompasses all variants, all modifications and all 30 equivalents which may fall within the spirit and the scope of the invention as defined in the claims below.

The invention is applicable to the manufacture and processing of polypropylene. It is also applicable to the treatment of a waste material at /

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v 9 polypropylene base in order to be able to reuse it during the formation of films and fibers. Of course, as will be understood by a person skilled in the art, the optimum concentrations and operating conditions will vary according to the properties of the polymer used and the final properties desired for the treatment.

Polypropylene generally has a high weight average molecular weight in the range of from about 250 M to 500 M after its manufacture, as well as a molecular weight distribution of about 10 to 15. high-speed spinning, the weight average molecular weight distribution is about 2.5 to 4.55 · However, when the molecular weight is reduced below about 130 M, the polypropylene resin cannot be easily transformed into pellets on an industrial scale. The low viscosity polymer rather gives poorly formed pellets which are difficult to transport and handle.

As a result, manufacturers prefer that the de—! gradation of the polypropylene before delivery is limited to obtain a molecular weight not falling below about 160 M. A large number of prodegradants are used to obtain this degree of degradation in the pelletizing equipment and most of these agents react completely under conditions in which the peroxide-based prodreating agents decompose at different rates depending on the temperature and the; ambient. The rates of decomposition are! defined in terms of half-life.

! According to the invention, to a polymer in flakes of high molecular weight coming from a reactor for manufacturing polypropylene, there is added, as

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10 source of free radicals, a prodrug having, in polypropylene, a half-life of more than half a minute at 190.56 ° C and this, in an amount sufficient to confer on the polymer the properties 5 desired endpoints for its treatment. If one wishes to use a prodegrading agent having a shorter half-life or if one wishes to subject a larger quantity of the prodegrading agent to the tableting stage without reacting, one can also injecting the prodegrading agent into the stream of the molten polymer. Since, in order to reach its maximum efficiency, the prodegrading agent must be dispersed uniformly, the injection must be carried out and followed by a mixing step. As a general rule, the prodegrading agent must not be altered or must not alter the stabilizers usually used for polypropylene and it must effectively form free radicals which, upon decomposition, initiate the degradation of polypro-pylene . However, the prodegrading agent must have, at the re-extrusion temperatures of the polymer processing installation, a half-life short enough to react essentially completely before leaving the reactor; its half-life in polypropylene must be less than 9 seconds at 288 ° C so that at least 99% of this prodrug in the pellets react before the expiration of a residence time of 1 minute in the extruder at this temperature. By way of example and without any limitation, among these prodegrading agents, there are: 2,5-dimethyl-2,5-bis- (t-butylperoxy) -hexyne-3 and 4-methyl -4-t-butyl-peroxy-2-pentanone (for example ,, Lupersol 130 "and" Lupersol 120 "sold by" Lucidol Division Penwalt 35 Corporation "), 3i6,6,9,99-pcntamethyl-3- (acetate / I 11 ί ethyl) —1,2,4,5-tetroxy — cyclononane ("USP — I38" from "Witco Chemical Corporation”), 2,5-dimethyl-2,5-bis- (t- butylperoxy) -hexane (for example, "Lupersol 101”) and 1,3-bis- (tert-butylperoxyisopropyl) -benzene 5 ("Vulcup R" from "Hercules, Inc # 1 ') · Among these prodegrading agents, "Witco USP-I38" and "Lupersol 130" are highly preferred. The preferred concentrations of the generators constituting the source of free radicals are in the range 10 ranging from about 0.01 to $ 0.4 * calculated on the weight of the polymers. Preferably, the pelletizer is put into service to retain at least 75 ^ of the prodegrading agent added to the pellets. When the user of the polymer subjects the latter to extrusion temperatures, the degradation of the polymer begins again and proceeds to the desired degree with an essentially complete reaction in the process of! re-extrusion.

Typically, these extraction temperatures are in the range of about 238 to 288 ° C. As a variant, these conditions can be obtained for degradation in the assembly of dies of the extruder.

In the following examples, the melt indices were determined using an apparatus for determining these indices (ASTM 1238 standard) operating at 80.56 ° C with a weight of 2,160 g.

Before testing, the samples are allowed to warm up for 5 minutes to equilibrium temperature.

30 The melting point is the number of grams leaving a capillary with a diameter of 2.0955 mm in a period of 10 minutes.

EXAMPLE 1 At the outlet of a reactor, polypropylene flakes are obtained having a melt index 12 of less than 1. To these flakes, $ 0.275 by weight of "Lupersol 130! 1 is added and a mixture is formed. This mixture is transformed into pellets in equipment operating at a temperature of 5 190.56 ° C., the residence time being approximately 2 minutes. Calculations reveal that approximately 22 $ of the peroxide have reacted. the pellets under test and it is found that they have a melt index of about 55 · About 10 $ of the prodrug 10 contained in the pellets react in the apparatus for determining the melt index so that, for the pellets, it can be considered that the real melting index is in the range from 40 to 45 · This polymer is easily transformed into 15 pellets equivalent to normal pellets commercially available.

Then, these pellets are re-extruded at 237.78 ° C., the residence time in the extruder then being approximately 3 minutes. The extrusion product is then subjected to tests and it is found that it has a melt index of approximately 550. In order to demonstrate that the extrusion step carried out at a temperature of 237.78 ° C. does not significantly alter the melting index, the extrusion product is re-extruded and the melting index then rises from 550 to 580. Consequently, approximately $ 95 of the increase in the melting index are due to the prodrug contained in the pellets, while about $ 5 of this increase is due to the action of the extruder.

30 Example 2

The same flakes and the same equipment are used as in Example 1, with the exception that 0.3 $ of rLupersol 130 "is added to the flakes. It is found that the pellets have a melt index 35 of 45 During re-extrusion, it is found that / is' 13 the extrusion product has a melt index of approximately 660. As in Example 1, cutting into pellets is acceptable from the point of view Example 3 The product "Witco Chemical USP-13Sn is applied to the flakes in a concentration of 0.35% by weight. The mixture is extruded at a temperature of 190 ° C. to 56 ° C., the residence time in the extruder being approximately 2 minutes. It is found that the melt index of the extruded sample is approximately 15. The sample is re-extruded at a temperature of 251.67 ° C. over a residence time of 3 minutes and finds that the melt index is 215. The flakes to which no peroxide has been added, but which have been treated as described above, have a melt index of 1.7 ·

Example 4

2% of "Lupersol 130” is mixed with commercially available polypropylene tablets 20 "Hercules PC — 973" · Then this mixture is extruded at 170 ° C with a residence time of one minute. The calculations reveal that 98/0 of the peroxide did not react in the extrusion product Then, with the polypropylene pellets, the extrusion product of the peroxide concentrate was mixed in different percentages.

I To other lozenges, a calculated equivalent amount of pure peroxide is added. We extrude the mixture! of 11 concentrate / polypropylene and the liquid peroxy / polypropylene mixture through a Brabender extruder at 240.5 ° C and with a residence time of 17 minutes. The viscosities at the outlet are determined; the tip of the extruder die; these screws; cosities are indicated in the appended figure. We can see that they are equivalent, j 35 1 /

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: î; 14 The invention therefore encompasses concentrates of prodegrading agents which can be added to tablets which do not contain agents of this type in order to obtain the desired results. Concentrations of up to 5% by weight of prodegrading agent can easily be reached and high concentrations can also be envisaged.

Although it is by no means desired to limit the invention to any particular theory, it may nonetheless be admitted that certain characteristics of the prodegrading agent are important. From the half-life determinations it can be seen that the half-life reaction speed coefficients (k) follow roughly an Arrhenius 15 relation to give: ln k = —19 * 700 + 40.4 for "Lupersol 130”

T

ln k = -19.700 + 4I * 6 for uLupersol 101 “

T

20 where k = coefficient of reaction speed in half-life in polypropylene, min. ** and T = temperature in ° K.

After determining the coefficient k, the following equation can be adopted to determine the quantity of prodrug which has not reacted after a given time: __- kt C e A ° where = concentration of the prodrug 30 unreacted 5 C ^ 0 = initial concentration of prodegrading agent 5 and t = reaction time in minutes.

For example, after 1 minute at 210 ° C (483 ° K), 50% of the initial 35 "Lupersol 130" would not have reacted against / "15 10% only of" Lupersol 101 "under the same conditions ·

Furthermore, it can be seen that the viscosity of the polymer at the outlet of an equipment device can be predicted by the following equation:

1 = 1 + KCD

rf where ji = viscosity of the polymer at the exit of the equipment after chemical degradation 5 10 jl ° = viscosity that the polymer should have had at the exit of the equipment without chemical degradation 5 K = coefficient of efficiency of chemical degradation 5 and 15 = quantity of prodrug having reacted on leaving the equipment.

Since = C ^ 0 - C ^,, by combining the above equations, we obtain the following equation: 20 1 = 1 + K C, (1 - e-kt)

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Therefore, for a constant (KC ^ 0) j the final viscosity of the polymer will be the same after a long reaction time regardless of the agent! 25 prodegradation used. However, the relationship between; viscosity and duration depends on the coefficient of; reaction speed at half-life k. For example, the appended figure is a graph of the viscosity of the polymer; re of polypropylene at its exit, with respect to time on the basis of KC ^ - 0.005 poise "1 (specific value, for example, for" Lupersol 130 or 101 "), the polymer having an initial viscosity of 10,000 poises, while the pelletizing / extrusion processes are carried out at a temperature of 201.67 ° C. This figure 35 demonstrates that the "pelletizing" viscosity of the sample— / / -> —s!: L- 16 tillon of "Lupersol 130" is approximately twice that of the sample of "Lupersol 101” for a [normal pelletizing time in the interval 1 to 3 minutes, although the final viscosities 5 are pretty much the same.

For a prodegrading agent with a short half-life, the viscosity of the polypropylene at the outlet of a pelletizer at 201.67 ° C after a period

The one minute stay is only 67% of that. 10 would be obtained if one used "Lupersol 101", while it was only 30% of what one would have had if one used "Lupersol 130". The latter is therefore preferred, although the other prodegrading agents can be used.

Although in the case of "Lupersol 130" about 50% of the prodregating agent may remain after tableting, since the initial degree of addition is very low, the handling of the polymer has little or no danger. After re-extrusion, there is essentially no further prodegrading agent, since specific processing conditions imply a temperature of at least 237.78 ° C at which the half-life coefficient of "Lupersol 130” is more than 6 min.

25 With a stay time of only two and a half minutes in equipment, for example, only $ 0.000017 of the peroxide in the pellets remains in the extrusion product. For example, yes! the manufacturer supplies polypropylene pellets 30 containing $ 0.2 of “Lupersol 130”, in the extrusion treatment equipment I, we will work at a temperature of 237.78 ° C., the duration of stay in the extruder will be 2.5 minutes and the concentration of "Lupersol 130" in the polymer at the outlet of the extruder will be less than 1 part by 1

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»17 billion.

Therefore, it is found that the present invention provides a polymer composition which can be easily transformed into pellets from the manufacturers of polymers while substantially improving the aptitude for treatment for the use of this composition; the invention also provides a process for manufacturing a material which fully meets the above mentioned aims, objects and advantages. Although the invention has been described with reference to some of its specific embodiments, it is obvious that on reading the description above, the skilled person will recognize many variants, modifications and variations. 15 Consequently, it is understood that all of these variations, modifications and variations fall within the spirit and the broader scope of the claims below.

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Claims (10)

1. A process for the treatment of polypropylene, characterized in that it comprises the steps which consist in: a) forming polypropylene having a high molecular weight average weight, b) adding, to this polypropylene, a prodegrading agent constituting a source of free radicals and having, in polypropylene, a half-life greater than half a minute at 190.56 ° C, c) transforming this polymer into pellets under conditions in which at least about 0.01 $ in weight of prodegrading agent remains available for further degradation after pelletizing * 2. Method according to claim 1, characterized in that it comprises the additional step consisting in extruding this polymer into pellets under conditions in which the residual prodrugant reacts almost completely to form a propylene polymer of low viscosity suitable for the formation of fibers and films. 3 * A method according to claim 1, characterized in that the polypropylene has a weight-average molecular weight in the range of about 250,000 to 500,000 and a molecular weight distribution of about 10 to 15 before 1 * addition of this prodegrading agent. 4. The process as claimed in claim 1, characterized in that the prodrug is added in an amount between about 0.01 and 0.4% by weight of the polymer, while the residual fraction goes up to 75% of the prodegrading agent. 5 * A method according to claim 2, ca-35 characterized in that the propylene polymer has a weight / ζ / Λ v average molecular weight in the range from 11 ranging from about 60,000 to 130,000 with a molecular weight distribution d * about 2.5-4.5 after the substantially complete reaction of the degrading agent. 6 "Process according to claim 1, characterized in that 1 * prodegrading agent is chosen from the group comprising 2,5-dimethyl-2,5-bis- (t-butylperoxy) -hexyne-3 and 3,6 , 6.939-. Pentamethy1-3- (ethyl acetate) -1,2,4,5-tetroxycyclononane. 7 · A method according to claim 4, characterized in that the residual fraction goes up to $ 90 from 1 * prodegrading agent, 8. A process for the treatment of polypropylene, characterized in that it comprises the steps which consist in: a) forming polypropylene having a weight average molecular weight lying in the inter-valle ranging from about 250,000 to 500,000 and a molecular weight distribution of about $ 10 to $ 15. b) add to this polypropylene a prodegrading agent chosen from the group comprising 2,5-dimethyl-2,5-bis- (t-butylperoxy) -hexyne-3 and 25 3 $ 6,6,9 $ 9- pentamethyl-3- (ethyl acetate) —1,2,4,5-tetroxy-cyclononane in an amount ranging between about 0.01 and 0.7 $ by weight of the polymer, c) transforming this polypropyrlene containing the prodegrading agent, in pellets in conditions in which at least about $ 75 of this prodegrading agent remains in the unreacted state after tableting, 9. Polypropylene pellets containing, as a source of free radicals, an unreacted prodigra-35ation agent and having, in the polypropy— f, //.Λ! i! ! i! lène9 a half-life greater than half a minute to! ‘190,956 ° C 10. Polypropylene tablets according to! claim 9 * characterized in that the prodegrading agent is chosen from the group comprising 295-dimethyl-295 * -bis- (t-butylperoxy) ~ hexyne-3 and 396969999-pentamethy1-3- (ethyl acetate) 1929495-tetroxy-cyclononane9 while it is present in an amount of at least 0901% y calculated on the weight of the polymer. VjvXAlk