MXPA00011529A - Process for pelletizing elastomeric anionically polymerised polymers - Google Patents

Abstract

A process for pelletizing elastomeric anionically polymerized polymers which comprises subjecting the polymer to solid state extrusion in a single screw extruder with a length to diameter ratio of 10:1 or less wherein the barrel of the extruder has longitudinal grooves and transversally extending pins to increase mixing wherein the temperature in the extruder is sufficient to agglomerate or melt the polymer but lower than the degradation temperature of the polymer and the speed of the extruder screw is from 30 to 100 rpm.

Description

PROCESS TO FORM PELES OF ANIONICALLY POLYMERIZED ELASTOMERIC POLYMERS FIELD OF THE INVENTION This invention relates to a process for forming pellets of anionically polymerized elastomeric polymers.

BACKGROUND OF THE INVENTION The elastomeric polymers of styrene and butadiene or of isoprene are anionically polymerized in an organic solvent. Such polymers are also frequently hydrogenated while in the solvent. The final step in the production of these polymers requires the removal of the solvent from the polymer / solvent / dispersion / suspension mixture, usually referred to as polymer cement, to produce dry material that can be packaged. This final processing step is frequently referred to as the "finishing" of the polymer. These polymers are generally produced as a lump that is sometimes difficult to handle and is often ft_ £: 125033 undesirably also sticky. The problems associated with the adhesive nature of this sticky material impose limitations on whether it can be manufactured in a realistic or profitable manner. It is even possible to manufacture these products, which are often sold in bags as lumps, the shape of the product can be difficult for the end users to handle it and put it in their desired use. The particle size of the lump is often fine and tends to coat the equipment, particularly in the case of sticky grades, creating fouling and waste. Some products are blocked in the bags, forming a polymer "pillow" of 13.6-18.1 kg (30 to 40 pounds). The polymer bags must be cut by hand to open and the block material has to be fed to a mechanical crusher before mixing it with other ingredients. Many polymers, especially polymers; thermoplastic but not elastomeric, sor. conveniently manufactured in the form of pellets. This form is very easy to handle and the problems of agglomeration can be easily solved by sprinkling the polymer with anti-adhesion agents.

The pellets of these commercial thermoplastic polymers are formed with melt extruders, often twin screw extruders, which perform their function by melting the polymer and extrude it through a die or die where it is crumbled into small pellets. Many of the polymers of this invention are high molecular weight materials and highly elastic materials. When these polymers are processed in the twin screw melt extruders, they tend to generate sufficient cutting heat to cause significant degradation. The degradation causes the properties of the polymer to be altered and this is a significant disadvantage. It is clear therefore that it would be highly advantageous to be able to finish the sticky elastomeric polymers of this invention in such a way that they could be produced in the form of pellets. It could be more advantageous if this process is capable of being carried out without significant degradation of the polymer.

BRIEF DESCRIPTION OF THE INVENTION This invention solves the problems discussed above. The styrene and butadiene or isoprene elastomeric polymers, including the polyisoprene star polymers, are polymerized as in the past. This processing may also incorporate hydrogenation, if desired. The polymer is produced in the form of lumps. The dry polymeric lump is then converted to pellets via extrusion in the solid state. The polymeric lump is extruded into a single screw extruder, which has a longitudinally fluted barrel and has spikes extending into the barrel transverse to the polymer flow. The extruder has a length to diameter ratio (L / D) of 10: 1 or less, preferably 8: 1 or less, and is operated at 30 to 100 rpm, preferably 40 to 60 rpm. The temperature of the polymer in the extruder must be sufficient to agglomerate the polymer, but the temperature must not exceed the degradation temperature of the polymer. Preferably, extrusion in the solid state is carried out at 200 ° C or less, and more preferably at 160 ° C or less.

DETAILED DESCRIPTION OF THE INVENTION It is necessary to use a simple screw extruder in this extrusion process in solid state in order to minimize the cutting of the polymer. Excessive cutting can cause an undesirable increase in polymer temperature which, as discussed above, can cause significant degradation. The twin screw extruders increase the cutting of the polymer and thus can not be used in the present invention. In this process, sufficient mechanical heat is generated by the extrusion of the polymer without auxiliary heating of the equipment or preheating of the lumps, which is necessary. Sufficient heat must be generated in order to agglomerate the polymer, sufficiently so that it can be extruded and then cut into pellets. By agglomerate is meant that the polymer is sufficiently soft and sufficiently tacky to adhere to each other, but has not yet passed through the glass transition temperature which is the point at which the polymer melts. Polymers of the type described herein are known to degrade at temperatures of 300 ° C and above, so it is important that the temperature in the single screw extruder be less than that. However, it is possible that higher localized temperatures may occur in the extruder, so it is highly preferred that the temperature in the extruder be 200 ° C or lower. It is more preferred that the temperature be 160 ° C or lower to minimize localized temperature peaks that can cause degradation of the polymer at those sites. The use of a simple screw (as opposed to the twin screw) is necessary to achieve agglomeration without high temperature, but it is important that sufficient mixing of the polymer occurs. In order to ensure that this occurs, the barrel of the single screw extruder has longitudinal channels and spikes that extend in the barrel transversely to the flow of the polymer. These characteristics increase the mixing without dramatically increasing the cut of the polymer.

The longer the polymer is processed in the extruder, the more likely it is that polymer degradation will occur. In this way, it is preferred that long extruders are not used. It is preferred that the length to diameter ratio (L / D) be 10: 1 or less, preferably 8: 1 or less, more preferably 4: 1 or less. In order to obtain sufficient mixing, the speed of the extruder screw should be 30 e. 100 rpm for extruders with an L / D ratio of 2: 1 to 10: 1. If the L / D ratio is smaller, then the screw speed may be lower. Again, the goal is to provide sufficient mixing without heating the polymers to a temperature where they degrade. Polymers suitable for finishing by the process of this invention include hydrogenated homopolymers and copolymers of diolefins containing from 4 to 12 carbon atoms, hydrogenated copolymers of one or more conjugated diolefins and one or more monoalkeni aromatic hydrocarbons containing from 8 to 16 carbon atoms. The base polymer may be of a star or linear structure. The hydrogenated polymers can be selectively hydrogenated, completely or partially. The hydrogenated polymers of conjugated diolefins and copolymers of. Conjugated diolefins and monoalkenyl arenes are preferably hydrogenated such that more than 90% of the initial ethylenic unsaturation is removed by hydrogenation. Preferably, the hydrogenated polymers are substantially free of ethylenic unsaturation. Selective hydrogenation refers to processes that hydrogenate a substantial portion of the ethylenic unsaturation and a substantial portion of the initial aromatic unsaturation is left unhydrogenated. As used herein, a hydrocarbon polymer substantially free of ethylenic unsaturation will be a hydrocarbon polymer that contains, on average, less than 10 carbon-carbon ethylenic double bonds per polymer chain. Polymers containing more than this amount of ethylenic unsaturation, under certain conditions, will show excessive crosslinking during a functionalization reaction when functionalization is completed in a mixing apparatus capable of imparting high mechanical shear.

Useful hydrocarbon polymers include those prepared in bulk, e: a suspension, in solution or in emulsion. As is well known, the polymerization of the monomers to produce hydrocarbon polymers can be achieved by using free radical, cationic and anionic initiators, or polymerization catalysts. A wide range of polymers of various molecular weights can be processed as described herein. In general, the higher the molecular weight of the polymer, the greater the probability that polymer degradation will occur in conventional processing in molten form. Thus, this invention is especially advantageous for higher molecular weight polymers. In general, polymers with weight average molecular weights of between 100,000 and 1,200,000 can be processed according to this process. The weight average molecular weights, as used herein, for the linear anionic polymers refer to the weight average molecular weight as measured by Gel Permeation Chromatography ("GPC") with a polystyrene standard. For star polymers, the weight average molecular weights are determined by light scattering techniques.

EXAMPLES Comparative Example 1 To better understand the operation of the melt extruder, several typical rheological tests were performed on a laboratory scale. First of all, an attempt was made to measure the melt flow rate (MFI) of Polymer A, which is a star polymer, of hydrogenated polyisoprene, containing 6% by weight of polystyrene, at temperatures up to 270 ° C. Even at these high temperatures and with a weight as high as 9.9 kg, the material was extremely difficult to press through the hole of the melt flow matrix, 0.2 mm (0.008 inch matrix). Additional testing using a capillary rheometer at equally high temperatures produced poor results. An attempt was made to extrude Polymer B, another hydrogenated polyisoprene star polymer, containing 6% by weight of polystyrene, using a 19 mm (0.75 inch) Brabender single screw melt heated to 200-220 ° C and of course Some degradation seemed to occur. Twin screw extruders with their high cut mixing capabilities can produce even greater degradation.

Example 2 Several different polymer grades were agglomerated and pelletized in a 57 mm (2.25 inch) single screw extruder with eJ. Bodine motor coupled, adapted with cutter blades. The extruder had 6 channels or notches of 9.5 mm (3/8 inches) in width and longitudinal channels of 1.6 mm (1/6 inch) in depth in the barrel, and 10 spikes extending transversely to the flow. The details of the extruder designs are shown in Table 1. This extruder was used to determine if it was possible to agglomerate different elastomeric polymer lump materials. Surprisingly enough, the extruder was easily able to produce pellets of many different materials. In all tests, there was no evidence of polymer degradation in this type of extrusion.

Table 1: Simple Screw Extruders Contrary to typical plastics (melt) extruders, no additional heating of the extruder parts was used to achieve agglomeration. The L / D ratio of the extruder is generally low in contrast to the typical L / D 's of the molten material extruders that are in the range of 15 to 30. In addition, these single screw extruders distribute high torque at low rpm , which minimizes the degradation due to heating by cutting. The high torsional capacities allow them to easily process these highly elastic materials.

The tested extruders have barrels and pins with channels or notches. These two characteristics ensure that the material is uniformly cut and therefore heated for agglomeration. Additional tests without channels and spikes were not as successful. The 57 mm (2.25 inch) extruder was adjusted with a variable speed cutter to form pellets of the extruded strands. Runs were carried out at 35 rpm. No heating or external cooling was applied. The temperature of the polymer due to frictional heating was 150 ° C. All the tested materials were successfully extruded without degradation. It was more difficult to achieve a homogeneous strand with Polymer C which is a linear hydrogenated block copolymer of styrene and isoprene. Some strands appeared to have a "dust" of the lumps along the outer edge, indicating the possible sliding along the barrel cavity and insufficient mixing. This disappears as the extruder temperatures rise. Several KRATON materials were also extruded using the 57 mm (2.25 inch) unit (KRATON is a trademark). The research polymers KRATON GRP-6919 and GRP-6912, and the commercial materials SHELLVIS 50, 90, 260, 300 worked well (SHELLVIS is a trademark). The commercial polymers KRATON G1651, G1650, G1652, and those of research grade GRP-6917 were successfully formed into pellets after experimentation with different matrix designs. All these polymers are manufactured by Shell Chemical Company and are block copolymers of styrene and / or hydrogenated isoprene and / or butadiene.

Example 3 After the success of the 57 mm (2.25 inch) tests, a larger 102 mm (4 inch) extruder was used. The details of the design of the extruder can be found in Table 1. This extruder also had pins and channels in the barrel. The results proved to be equally successful. A large pellet test was run with approximately 1361 kg (3000 pounds) of Polymer A, which was successfully performed.

The typical conditions of the run were 35 rpm, 11. 5 amps, and a production speed of 1.36 kg / inuto (3 pound / minute). The die or die of 254 orifice size holes of 3.18 mm (1/8 inch) was fixed with a pelletizer of two blades to cut the material as it was extruded. The pellets then fell into a small fluidized cooler. The cooler was equipped with a fan that distributed air at room temperature at a speed of up to 71 mVminute (2500 cubic feet / minute). A temperature probe was placed approximately in the middle of the barrel. The process appeared to reach the resting state with a measured barrel temperature of 150 ° C. This temperature is due to heating by cutting the material. No external heating or cooling was applied. The pellets that left the cooler were at a temperature of about 80 ° C. No degradation of the polymer was observed in the samples taken throughout the run.The analysis of gel permeation chromatography of the clumps and of the polymers Extruded A and B of both extruders show no signs of degradation Polymer A and Polymer B were also tested in their intended use as an additive in motor oils.The shapes of crumb and pellet were used. The rheological concentrations of the oil concentrates with lumps and pellets showed no change in the fundamental properties of the polymers with extrusion.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (4)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A process for forming pellets of elastomeric polymers, characterized the process because it comprises fastening the polymer to extrusion in solid state in a single screw extruder with a length to diameter ratio of 10: 1 or less, wherein the barrel of the extruder has longitudinal channels and spikes that extend transversely, to increase mixing, where the temperature in the extruder is sufficient! to agglomerate the polymer, but less than the. Polymer degradation temperature and extruder screw speed is 30 to 100 rpm.

2. The process according to claim 1, characterized in that the temperature in the extruder is 200 ° C or less.

3. The process according to claim 2, characterized in that the temperature in the extruder is 160 ° C or less.

4. The process according to claim 1, characterized in that the length-to-diameter ratio of the extruder is 8: 1 or less, and the speed of the extruder screw is 40 to 60 rpm.