Production processes and equipment for processing polyvinyl alcohol

Abstract

The present invention describes a method for making a plasticized polyvinyl alcohol polymer mixture, the method comprising the steps of: introducing a polyvinyl alcohol polymer comprising at least 98 wt% polyvinyl alcohol or a blend of the polymers into a mixing reactor; wherein the mixing reactor comprises a mixing chamber having a main inlet, a main outlet and at least two mutually engaging parts extending between the main inlet and the main outlet, the at least two mutually engaging parts being arranged to apply shear forces to the polymer as the polymer is transported from the inlet through a reaction zone to the outlet by the parts; one or more auxiliary inlets, the one or more auxiliary inlets The auxiliary inlet is located downstream of the main inlet, and is used to deliver reactants including a processing aid and a plasticizer to the chamber to form a reaction mixture; wherein the blending chamber includes multiple heating zones, and the multiple heating zones are arranged so that the mixture is subjected to a controlled temperature distribution; the auxiliary outlet is located between the reaction zone and the main outlet, and the main outlet is arranged to allow the processing aid to be removed from the chamber; the reaction mixture including the processing aid, the plasticizer and the polymer is reacted in the reaction zone to form a plasticized polymer; wherein when the processing aid is water, the amount of water is from 3wt% to 18wt%; and the plasticized polymer is allowed to pass through the main outlet.

Description

Technical Field

[0001] The present invention relates to a process for producing polypolymers, in particular polyvinyl alcohol. The present invention also relates to an apparatus for carrying out the process. The present invention further relates to a process for producing polyvinyl alcohol pellets in a suitable physical manner for processing into films or other extruded products. The present invention further relates to a novel processable polyvinyl alcohol composition that can be produced by the process. Background Art

[0002] Polyvinyl alcohol is usually made from hydrolyzed polyvinyl acetate. The degree of hydrolysis affects the properties of the polymer. Polyvinyl alcohol with a low degree of hydrolysis (LD) of 88% or less is widely used in the industry.

[0003] Highly hydrolyzed polyvinyl acetate, i.e., having a degree of hydrolysis greater than 98%, is a copolymer comprising primarily homopolyvinyl alcohol. Like many carbohydrates, the polymer decomposes before reaching its melting point of about 250°C. This makes melt processing difficult, and for this reason, highly hydrolyzed polymers are generally processed as aqueous solutions. Partially hydrolyzed polyvinyl acetate is readily melt processed. For example, 80% hydrolyzed polyvinyl acetate, specifically polyvinyl alcohol copolymers, can be extruded or converted into films by blow molding more easily than highly hydrolyzed polyvinyl alcohol. Typically, highly hydrolyzed polyvinyl alcohol can have a crystallinity of up to about 50%, depending on the thermal history of the material.

[0004] The significant difference between highly hydrolyzed (highly hydrolyzed, HD) polyvinyl alcohol and partially hydrolyzed (lowly hydrolyzed, LD) polyvinyl alcohol is the degree and quality of crystalline order because the chain structure is different. Polyvinyl alcohol with less than 2% non-hydrolyzed acetate groups can easily crystallize to form strong hydrogen-bonded domains. These domains have substantially the same structure as the domains present in polyethylene. The reason can be attributed to the tiny hydroxyl groups. However, because of hydrogen bonding, the melting point of highly hydrolyzed polyvinyl alcohol is about 150°C higher than that of polyethylene. Polyhydroxy compounds have been used as plasticizers, but it is not easy to achieve efficient production of plasticized polyvinyl alcohol with high hydrolysis. Summary of the invention

[0005] According to a first aspect of the present invention, there is provided a method for producing a plasticized polyvinyl alcohol polymer mixture, the method comprising the steps of:

[0006] introducing a polyvinyl alcohol polymer or a blend of polymers comprising at least 98 wt% polyvinyl alcohol into a mixing reactor;

[0007] wherein the mixing reactor comprises a blending chamber having a main inlet, a main outlet and at least two interengaging components extending between the main inlet and the main outlet, the components being arranged to exert shear forces on the polymer as the polymer is conveyed by the components from the inlet through the reaction zone to the outlet;

[0008] one or more auxiliary inlets, the one or more auxiliary inlets located downstream of the main inlet, for introducing reactants including a processing aid and a plasticizer into the chamber to form a reaction mixture;

[0009] wherein the blending chamber comprises a plurality of heating zones arranged so that the mixture is subjected to a controlled temperature profile;

[0010] an auxiliary outlet located between the reaction zone and the primary outlet, the primary outlet being arranged to allow removal of a processing agent from the chamber;

[0011] reacting a reaction mixture comprising a processing aid, a plasticizer and a polymer in a reaction zone to form a plasticized polymer; wherein when the processing aid is water, the amount of water is from 3 wt % to 18 wt %; and

[0012] The plasticized polymer is allowed to pass through the main outlet.

[0013] A processing aid and a plasticizer are reacted with polyvinyl alcohol or a blend thereof using a reaction mixer according to the present invention, followed by removal of all or most of the processing aid from an auxiliary outlet to provide plasticized polyvinyl alcohol or a blend thereof.

[0014] The mixing of plasticizer and polyvinyl alcohol can be accomplished in a variety of reactors, including well-mixed batch reactors. In such reactors, a large exotherm of reaction associated with the mixing process is readily seen. The temperature of the reaction mixture can rise 100 to 150°C above the start-up temperature, which means that if the initial temperature of the mixture is above 100°C, the temperature of the reaction mixture can exceed the degradation temperature of the polyvinyl alcohol. A high start-up temperature is desirable for starting the process and reaching completion quickly. The exotherm of reaction in a batch process is difficult to control when the volume of reactants in the reaction vessel is large relative to the cooling surface area of ​​the reactor. The temperature increase can not only discolor and degrade the polymer, but can also carbonize it and cause it to burn.

[0015] For these reasons, preferred embodiments include fully mixed flow reactors. Reactors of this type should be constructed to control the exothermic heat of reaction. A convenient embodiment is a twin screw extruder reactor in which there is good mixing and good cooling capacity along the length of the barrel. Typically, the extruder should have an L:D greater than 25:1 and preferably 40:1 or greater. The extruder can be equipped with a screw configuration that provides good mixing. There are many different types of commercially available screw configurations, but the preferred screw configuration is a co-rotating, closely meshed type. The screw components should provide gentle mixing and material delivery at a rate that, together with the selected barrel temperature profile, allows the reaction to be completed in a controlled manner before the product is discharged from the die. The throughput rate should be balanced with the complete removal of the processing aid.

[0016] An electrically driven screw can be used to convey the reaction mixture to a die, which in a simple configuration produces strands that pass directly to a pelletizer. It is convenient to support the strands with a conveyor belt as they are discharged from the die, as this can be used to apply a withdrawal force to the strands. This allows the diameter of the strands to be controlled. Multiple strand dies can be used, limited by the ease of strand handling and the pelletizing capacity of the pelletizer. Advantageously, the strands can be cooled on the conveyor belt and / or during transport from the conveyor belt to the pelletizer. The chipping rate of the pelletizer can be adjusted, and this rate can be used to control the pellet size relative to the strand throughput rate.

[0017] This configuration is particularly well suited to small scale manufacturing using extruders having barrel diameters of 10-40 mm diameter.

[0018] The preferred embodiment is an extrusion process to make highly hydrolyzed PVOH pellets for blown film. If a superior product is to be produced from a specific formulation of PVOH blend, processing aids and plasticizers, the exothermic reaction can be controlled by varying the screw configuration.

[0019] Another preferred embodiment is a method for preparing highly hydrolyzed thermoplastic PVOH pellets for use as blown film by melt reaction extrusion, the method comprising: (1) melting polyvinyl alcohol; (2) destroying the crystallinity of polyvinyl alcohol with water; (3) melt blending polyvinyl alcohol with a plasticizer; (4) removing excess water through a vacuum port located just before the metering section to the end of the extruder to produce a bubble-free strand extrudate; (5) extruding through a die; and (6) cooling and pelletizing.

[0020] Polyvinyl alcohol can be prepared by hydrolyzing polyvinyl acetate, wherein the degree of hydrolysis is 98% or more.

[0021] The processing aid can be water. As an option, the processing aid can include a mixture of water and one or more C1-C4 alcohols or other hydroxyl compounds having a boiling point lower than the boiling point or melting point of the plasticizer. Water can be used for cost and environmental reasons.

[0022] The amount of water in the reaction mixture may be from 3 wt% to 18 wt%, alternatively 3 wt% to 15 wt%, alternatively 3 wt% to 12 wt%, alternatively 5 wt% to 10 wt%.

[0023] The plasticizer may be selected from the group consisting of polyols, polyethylene glycols, glycerol, diols or triols, for example, propylene glycol, ethylene glycol, polyethylene glycol, glycerol, sorbitol (melting point 94-98° C.).

[0024] Exemplary plasticizers are mannitol (melting point 164-169° C.), erythritol (melting point 275° C.), pentaerythritol (melting point 198-210° C.), dipentaerythritol (melting point 212-220° C.), trimethylolpropane (melting point 63° C.), and mixtures thereof.

[0025] Mixtures of pentaerythritol and dipentaerythritol may be employed. Polyols that may be used include alkoxylated derivatives. The degree of alkoxylation may be varied to alter the extent of hydrogen bonding of the plasticizer to the polyvinyl alcohol, which in turn affects the effectiveness of the plasticizer as a processing aid. For any given polyol plasticizer, the degree of alkoxylation can vary from 1% to 99%, but is generally most effective when within the range of 5%-50%. Alkoxylation of polyols that are liquid at or near ambient temperature may be particularly advantageous.

[0026] Glycerol is an effective plasticizer. It is easy to obtain at low cost and provides high energy output in the anaerobic digestion waste treatment of polyvinyl alcohol. Glycerol is environmentally safe. For the case of a plasticizer that is liquid at ambient temperature, such as glycerol, boiling point (295°C) and steam pressure at processing temperature, such as 190-220°C, can be considered because the plasticizer must be contained in the mixing reactor. The mixing reactor can also contain superheated water that can be discharged during processing. The loss of glycerol when the auxiliary reactor outlet discharges water vapor can cause a change in the formula and requires, for example, the use of a condenser with appropriate capacity to recover the plasticizer, thereby coping with the amount of volatiles removed depending on the scale of the reactor used. The disadvantage of the glycerol / water mixture is that it can be volatilized from the reactor together during processing.

[0027] Exemplary formulations may contain no glycerol.

[0028] Processing temperatures may be up to about 220°C and are a function of reactor design, agitation and containment capabilities.

[0029] Solid plasticizers with high melting temperatures relative to ambient temperature can be used. At processing temperatures, solid plasticizers are often volatile. Exemplary plasticizers have a melting point of about 150°C to about 300°C, typically about 150°C to about 275°C. Solid plasticizers that can be used include: erythritol, pentaerythritol, sorbitol and trimethylolpropane and mixtures thereof, particularly mixtures of pentaerythritol and dipentaerythritol, for example comprising 90-95wt% pentaerythritol and 10-5wt% dipentaerythritol, particularly comprising 93% pentaerythritol and 7% dipentaerythritol.

[0030] Exemplary plasticizers have the property of being non-volatile at processing temperatures so that they remain in the formulation when the important step of removing processing aids is performed.

[0031] For specific applications, in addition to the solid plasticizer, a liquid polyol, for example glycerol, may be used in an amount of 1 to 5 wt %.

[0032] Plasticizers and processing aids can be added to the reactor individually or in various combinations. For example, a solution of glycerol or other plasticizers in water or other processing aids C1-C4 can be injected through a single auxiliary inlet.

[0033] The solid plasticizer may be fed into the reactor independently or together with one or more polymeric materials in the formulation.

[0034] In a preferred embodiment, the mixing reactor comprises a twin screw extruder with counter-rotating, closely meshing screws. Alternatively, the mixing reactor may comprise a jacketed batch reactor useful for smaller scale processing. The mixing reactor should have a large internal surface area per unit mass of reactants to allow efficient heat dissipation.

[0035] The extruder reactor chamber may consist of 5-20, typically 10-15, for example about 12 heating zones. The temperature profile may be increased from ambient temperature at the first zone to about 200° C. adjacent the secondary outlet. The reaction zone may have a temperature of at least about 200° C.

[0036] The location of the reaction zone is controlled by selecting and / or adjusting one or more of the following parameters: screw configuration, formulation, temperature profile, rotational speed of one or more screws (depending on the reactor type), and the rate at which the reaction mixture is fed into the apparatus. Screw configuration can play an important role in ensuring that any desired reaction is completed within a portion or a proportion of the length of the extruder barrel. Any selected screw configuration should be effective in the particular size of the extruder employed. Extruders having a ratio of length (L) to barrel diameter (D), i.e., L:D in the range of 20:1 to 50:1 or even greater, can be employed. In order to make a twin-screw extruder with a barrel diameter in the range of 15 mm to 95 mm or greater effective, the selected configuration can have significant material conveying capacity relative to the intensive mixing component or back-mixing component in the length of the barrel. The intermeshing nature of the conveying screws can provide sufficient mixing capacity along a certain proportion of the length of the screw without introducing too much internal heating or shear heating of the material. The reaction exotherm can be significant and very rapid, and the control of heat removal from the reaction mixture is an important consideration in the overall screw design.

[0037] For an extruder of 55 mm diameter with an L:D of 48, which is divided into, for example, 12 heating zones of equal length from zone 0 adjacent to the main feed opening for feeding solid powdered polymer and solid plasticizer to zone 11 immediately before the main outlet of the extruder, closely meshing screw elements may be used from zone 0 to zone 5. Intensive paddle mixing screw elements may be used in zone 6, followed by further conveying screw elements in zones 7 and 8. A second intensive mixing zone may be located in zone 9, with further conveying screws located in zones 10 and 11. The very rapid and exothermic reaction of the reaction mixture transition between a mixture of polystyrene, water or other processing aids and a plasticizer is difficult to control when it occurs and can only be achieved with appropriate screw construction, screw speed and barrel heating and cooling schedules.

[0038] The position of the reaction zone can be determined by monitoring the temperature. A temperature sensor can be located at each zone along the length of the reaction vessel. Typically, in the reaction zone, the temperature can be between 1°C and 7°C higher than the set point temperature of the zone. In an embodiment, by appropriately adjusting the above parameters, the position of the reaction zone when most of the reaction is completed is controlled so that it is located upstream of the auxiliary outlet, zones 5 and 6. The position of the reaction zone can be adjusted so that the reaction is completed before discharge, that is, in the first discharge zone of the discharge zone (7), the reaction mixture can be completely in a viscoelastic state that allows the removal of the processing aid.

[0039] Energy can be provided by the shearing force produced in the reaction mixture, but for exemplary screw configurations, compared with the heat that can be introduced or removed by the wall of the reactor using the electric heating belt on the barrel of the extruder and the tubular water cooling system, this energy should be small. In the reaction zone, the main heat source of reactant can be to be derived from the reaction exothermic, and this reaction exothermic is caused by the chemical energy of the reaction between the hydrogen-bonded crystalline domain of the processing aid and the polymer and the plasticizer participated in. Cannot affect the chemical reaction that can cause the main chemical bond in each reactant and not to involve auxiliary hydrogen bonds. When the temperature can be raised to the temperature point where combustion can occur, this can cause polymer decomposition in the extruder, produce brown and even polymer mixture sharply carbonization in the product.

[0040] In an exemplary embodiment, the screw configuration of a twin-screw extruder, which typically rotates a twin screw that meshes closely with each other, has been disclosed above. When using extruder reactors produced by different companies, the specific configuration of the screw design may change, but in an exemplary system that can be used, the conveying section is arranged at the throat or inlet of the extruder in zone 0 to advance the solid powder that forms part of the reaction mixture, and zone 0 is kept at a temperature close to the surrounding. The feed rate of the ingredients should be adjusted so that the throat is not overfed. When the main recycled material is also added to the formulation, the same solid feed port can be used, but the type of conveying screw used in this zone should be able to convey both hard thermoplastic recycled materials and raw powder. Liquid processing aids and any liquid plasticizers used can be fed downstream of the solid feed port in zone 0. The temperature of the conveying section in zones 1 to 5 can be increased to ensure that the reactants are well mixed, affected and react to begin to form a viscous slurry, and in zone 5, the viscous slurry undergoes rapid exothermic conversion to a fully viscoelastic molten state. When all processing variables are properly controlled, the reaction can begin at the interface between the flights of the co-rotating screws in zones 2 to 4, but only reaches a rapid rate that propagates through the entire reaction mixture in zone 5.

[0041] The intensive mixing screw employed in zone 6 ensures that the desired reaction is substantially complete in this zone. There may be a pressure drop in zones 7 and 8, which are equipped with conveying screws, and these zones are only partially filled with material. This allows one or more of these zones to be equipped with a discharge port, which is provided with a filler valve to ensure that solid material is not lost, and the discharge port is arranged so that most of the processing aid is removed. The latent heat of volatilization when removing the processing aid can be an important part of the cooling mechanism at this stage to ensure that the viscoelastic polymer is not overheated. The intensive mixing zone of the screw installed in zone 9 ensures that any residual unreacted polymer is converted to the desired viscoelastic state. The paddle mixer can also act as a seal to allow vacuum assistance to be applied to the filler discharge ports located in both zones 7 and 10. Zone 10 can be equipped to provide a water content of the reaction mixture when it exits the main outlet that is typically between about 0.05 and about 0.5%. The screw elements installed in zones 10 and 11 allow further mixing, conveying, discharge and compression of the melt through an auxiliary outlet to a mold of the melt or another pumping system.

[0042] In an embodiment with 12 temperature zones, the zones may have the following exemplary zones with average set temperatures:

[0043]

[0044] The actual set temperature used may vary slightly depending on the size of the extruder barrel. In extruders with a barrel diameter in the range of 15-95 mm and larger, the temperature of each zone shown may vary by 5-20°C or more.

[0045] The process may further include an intensive mixing zone downstream of the reaction zone.

[0046] In an embodiment, the intensive mixing zone may include a paddle mixer located between the reaction zone and the secondary outlet.The mixing zone may be a kneading zone including one or more pairs of interengaging rotor blades or paddles.

[0047] The auxiliary outlet may be a drain port configured to allow removal of the processing aid from the mixing reactor.

[0048] Twin screw extruder reactors can be directly equipped with a variety of different dies for pellet manufacturing. For small extruders with barrel diameters <35 mm or when the output rate requirements are low, for example, 1-20 kg per hour, the number of strands is limited by ease of handling, and a simple strand die with 1-5 holes is appropriate. Air cooling of the strands can be used. This is important because polyvinyl alcohol is too hydrophilic to use a traditional water bath. Air cooling can include using a forced air cooler or simply using a strand length before pelletizing by any readily available pelletizing device. Conveyor belts are appropriate means of gathering tension and applying tension to the strands before pelletizing to control the diameter of the strands. In order to overcome die expansion, it may be necessary to draw the strands, which may be between 10% and 60% depending on the type of formulation, the pressure drop between the extruder and the die, and the material throughput rate.

[0049] For large twin-screw extruders that can use multi-hole dies, air-cooled dry face cutters can be used.

[0050] The auxiliary outlet of the twin screw reactor is advantageously equipped with a metering system to smoothly transfer the formulated viscoelastic polyvinyl alcohol product to the granulation device. This can be a simple strand cutter, or a dry face granulator. An exemplary metering pump is a single screw extruder mounted orthogonally or at another convenient angle other than 90° to the auxiliary outlet of the extruder reactor, but any other pump capable of quantitatively handling thermo-viscoelastic polymers can be used, for example, a gear pump.

[0051] When a single screw extruder is used, the single screw extruder may have appropriate physical dimensions and throughput required to match the physical dimensions and throughput of the extruder reactor. The mechanical structure or mechanical connection box connecting the two extruders may have one or more of the following characteristics.

[0052] (i) Minimum dead volume possible.

[0053] (ii) a port to allow discharge with or without a filler valve and with or without vacuum assistance.

[0054] (iii) Mixing should also be good within the combined volume. This can most easily be achieved by extending the screw elements in zone 12 of the extruder reactor described above into the volume within the connecting box structure without contacting the screw of the single screw extruder.

[0055] (iv) The structure of the mechanism for coupling the two extruders should be able to be heated and cooled in a controlled manner when the extruder system is large, ie when the diameter of the twin screw reactor barrel is >50 mm.

[0056] If the single screw extruder has the desired advantageous features, the single screw extruder itself can be of standard type with an electrically heated barrel that can reach a temperature similar to that in zone 12 of the exemplary twin screw system. The single screw extruder can provide some additional reaction time, but there is almost no further mixing. Since the main purpose is to deliver the viscoelastic reaction product to the die so that it can be cut in a quantitative manner, conventional screw designs can provide increased forward movement of the material and increase the melt pressure until it approaches the die or it will be appropriate. The only significant requirement may be to properly design the screw near the junction between the two extruders. At this junction, the following is necessary:

[0057] (i) The viscoelastic melt is transferred unimpeded to the flights of a single screw which must convey the material along the screw at a rate that should allow discharge to occur at the junction.

[0058] (ii) The screw design at the junction between the two extruders should not create stagnation zones.

[0059] The mixing reactor should be self-cleaning during and after use. The specific twin screw components disclosed herein are particularly suitable for self-cleaning. Single screw extruders are not self-cleaning, and the junction area between two extruders is also not self-cleaning. Traditional cleaning of extruder systems is to use a purge material after use, which also makes it easier to start the system the next time it is used.

[0060] Experience has shown that conventional clean-up processes for exemplary reactor configurations may not be effective because:

[0061] (i) Conventional scavenging materials, whether or not they contain abrasive additives, do not clean well because they are typically formulated with hydrophobic polymers such as polyethylene. Hydrophobic materials or hydrophilic polymers cannot be removed from the walls and crevices of the system. This problem can be exacerbated by the significant difference in melting points of the scavenging materials and the product materials, which have melting points significantly higher than those of the cleaning materials.

[0062] (ii) Because of the environmental requirements for polyvinyl alcohol, an exemplary scavenging material may be another biodegradable material. Experience has shown that it is difficult to make scavenging materials from polyvinyl alcohol or other biodegradable polymers, or when used, they are ineffective.

[0063] For this reason, the present protocol was developed for rapid cleaning, startup, and shutdown of an exemplary reactor system.

[0064] Regarding starting, a completely empty and clean twin-screw extruder barrel and a single-screw extruder barrel are the best starting points. In the case where the twin-screw system is separated from the single-screw system and the single-screw extruder is separated from the mold and the merging unit is attached to the single-screw extruder, everything is clean and empty, and the extruder barrel is heated to the selected barrel temperature profile. The powder feed of the polymer (and solid plasticizer when used) is started, followed by the simultaneous or successive supply of water or processing aids (and liquid plasticizers when used). The initial feed rate and screw speed of the twin-screw extruder are lower than the steady-state speed used when the production rate is, for example, 50% of the full rate and between 100 and 150 rpm, respectively. The feeding is continuous until the viscoelastic product is stably discharged from the extruder.

[0065] When the polymer coming out of the extruder is flowing smoothly, the two extruders are quickly coupled, the single screw extruder has been heated to the operating temperature required for the formulation being used, and the screw speed is selected, which is necessary to match the rate at which the material is fed to the twin screw extruder. The coupling of the extruders can be facilitated by one of the following:

[0066] (i) The two extruders are connected by a hinged connection so that the connection can be made by simply swinging the single screw extruder into position, using a quick-action connection mechanism or traditional bolts for final connection.

[0067] (ii) A single screw system may be mounted on one or more tracks so that it can be rotated directly into position, with the final mechanical linkage arranged as described in (i) above.

[0068] When the viscoelastic polymer is discharged smoothly and at a steady rate from the single screw extruder, the multi-hole die, which has been heated to the selected temperature, is quickly assembled to the auxiliary outlet of the single screw extruder. The die can be hinged to the extruder or mounted on a track system for precise movement. The die can be manually fixed in place.

[0069] When multiple polyethylene strands are discharged independently and smoothly from all die holes, the dry face cutter unit is quickly installed together with the cooling cabinet and drive motor. The cutter unit installed on the track system can help this process, so that it can be quickly moved to the appropriate position and mechanically fixed. The cutter blade can start immediately and produce pellets. When the cutter runs at the correct speed, pellets of appropriate size can be produced. The pellets can be pneumatically transported to a suitable storage tank, from which the pellets can be quantitatively distributed in bags or other containers in a conventional manner. When the pellets are transported to the storage tank or storage tank and / or then when the pellets are in the storage tank or storage tank, the pellets can be cooled.

[0070] Once the start-up procedures are completed and the system is in steady state and at a low throughput rate, it is a routine task for a skilled operator to increase the throughput rate of material to an economical production rate.

[0071] In order to provide a clean extruder for the next start-up after a production run, a specific procedure is usually required to bring all parts of the exemplary complex system to a clean state again. Simply flushing the extruder using traditional purge methods is ineffective. A procedure that can be effective is as follows:

[0072] (i) The first step is to maintain the temperature profile for both the twin screw extruder and the single screw extruder and stop all feeds.

[0073] (ii) The dry face cutter can be quickly removed and subsequently cleaned manually while inspecting the blade for wear.

[0074] (iii) The mold can be removed quickly and, after wiping off any surface polymer, placed in an autoclave at 300-450°C until the polymer is reduced to ash that can be blown off the mold or mold holes.

[0075] (iv) The single screw extruder can then be quickly separated from the twin screw reactor and as much polymer as possible pumped out of the system before the screw is removed from the extruder. There are two options for removing any residual polymer stuck to the screw: (a) the hot polymer cleanly breaks away from the screw as a continuous spiral wrap as the screw is slowly pulled out of the barrel (or lifted in the case of a clamshell extruder), or (b) the screw can be allowed to cool after being pulled from the extruder and the polymer allowed to cool completely to allow crystallization and embrittlement. The cold polymer can then be cleanly broken away from the screw mechanically. In both cases, the barrel is cleaned mechanically while still hot using a standard cleaning rod.

[0076] (v) Any polymer remaining in the chamber of the coupling may be mechanically removed once separated from the twin screw extruder while the chamber itself is still hot.

[0077] (vi) Once separated from all attachments, the twin screw extruder can be allowed to cool to 100-110°C along the length of the barrel and the screw speed can be reduced to 100 rpm. The exemplary screw configuration can easily eject any residual polymer, which is initially molten and, as the barrel cools, is in the form of crumbs, which are usually brown in color because of the long residence time of the material in the barrel. Finally, in order to flush the screw and barrel, dry polyvinyl alcohol powder is fed to the extruder, which is discharged as a white powder when the cleaning is complete, i.e., at the point where the barrel heat can be turned off.

[0078] When the shutdown process is complete, the individual components of the system are ready to start.

[0079] When water is used as a processing aid, the water content of the finished plasticized polymer pellets may be less than 5 wt%, alternatively less than 2 wt%, alternatively less than 0.5 wt%, and as a further alternative in the range of 0.1-0.5 wt%.

[0080] Without wishing to be bound by theory regarding the mechanism of conversion of the reaction mixture from a paste to a thermoplastic melt, it is believed that molecules of a plasticizer such as glycerol can slowly become crystalline domains of the polyvinyl alcohol used alone. The energy provided by the application of shear forces to control the temperature of the polymer mixture can allow control of the chemical energy of the exothermic reaction between the polymer and the processing aids, especially water, which destroy the crystalline domains of the polymer and the rate of destruction of the crystalline domains of the polymer after the exothermic reaction begins is very fast and locally at achievable high temperatures. Failure to fully effectively control this may result in polymer degradation or even carbonization.

[0081] The rotational speed of the twin screws can be adjusted to control the specific energy per unit length of the reaction mixing chamber per unit mass of reacting material, so that the screws act as energy input devices. It is believed that such mechanical influx of energy into the material is used to initiate the slow destruction of crystalline domains in the polymer, but such mechanical influx of energy into the material is not necessary once the reaction of the bulk material begins to take off.

[0082] In a typical embodiment, the chamber of the extruder reactor providing mixing can be 30%-70% filled with the polymer mixture, while the remaining volume is empty or used as a lower pressure zone to facilitate the removal of volatile components. The distribution of the reaction mixture along the length of the twin screw extruder barrel can depend on the screw configuration used in each of the 12 zones of this example, but is not limited to the reactor system disclosed herein.

[0083] Partially filled twin screw extruders are often due to the pulsations seen in the material leaving the reactor. A set of screws for compaction can be employed in zone 12, thereby providing a continuous output, which is particularly advantageous when the reactor extruder is not coupled to a pump such as a single screw extruder or another device for dampening any pulsations and thus allowing more precise control of pellet size, especially when a dry face cutter is used for pellet production.

[0084] A pump may be located downstream of the main outlet. The pump may comprise a single screw extruder unit.

[0085] In an embodiment, the mixing reactor can be a twin screw extruder and can have a length to diameter ratio in the range of 20: 1 to 50: 1 or greater, alternatively about 25: 1 to 45: 1, and further alternatively about 40: 1. For example, a typical mixer reactor can have two screws with a length of 4.8 meters and a diameter of 95 mm.

[0086] The onset of the exothermic reaction can be controlled by selecting the temperature profile and shear rate applied to the twin screws. The extent of the exothermic reaction can be controlled by the rate at which heat is removed from the mixer, by utilizing the composition of the reaction mixture and the feed rate, and by adjusting the shear energy input and the location of the reaction zone. The location of the reaction zone where the exothermic reaction occurs can be controlled by appropriate control of the temperature profile and the rotation rate. The zone where the reaction occurs can also vary with the nature of the reactants used and the composition of the formulation used.

[0087] The average residence time in the mixing vessel can be about 2-10 minutes, and when processing at a temperature close to the melting point of a polymer, time and temperature all affect the yellowing of polyvinyl alcohol. For the extruder reactor type as disclosed herein, the residence time distribution measurement (RTD) of the reactor using pulsation feeding dye has been described that the RTD cloth type can be the Poisson distribution (Gaussian modified Poisson distribution) of Gaussian modification in fact, in about 2 minutes, the first exposure color occurring from the exemplary reactor configuration, and distribution reaches a peak in about 2.5 minutes. Dyeing intensity declines exponentially and becomes insignificant after about 9 minutes. This pattern of RTD is seen in the system of 20,25,30,55mm and larger exemplary types in screw diameter. Using the screw configuration of poor design can greatly increase overall RTD, causing poor product quality.

[0088] The residence time in the reactor can be selected to be sufficient to allow completion of the reaction so that a viscoelastic melt is obtained with a minimum amount of unreacted polyvinyl alcohol.

[0089] It has been clearly demonstrated that polyvinyl alcohol degrades before the melting point of about 250° C. Thermogravimetric analysis shows that under oxidative conditions, the degradation of polyvinyl alcohol can be very rapid at processing temperatures below 200° C. In preferred embodiments, by properly designing and controlling the entire reaction system, the destruction of the crystalline structure of the polymer occurs rapidly relative to thermal degradation.

[0090] The reaction mixture or recipe may determine the properties of the final product and also determine the settings that may be required for controlled operation of the pellet manufacturing system and may include:

[0091] Polyvinyl alcohol (degree of hydrolysis at least 98%), 87-92%, alternatively 85%;

[0092] Plasticizer, 5-20%, as an option 10%;

[0093] Water or other processing aids, 3-20%, as an option 5%.

[0094] Optional additives to the formulation are anti-caking agents such as stearates to aid processing or such as chalk, fumed silica and many others of each type. If these optional additives are necessary for a particular end use, they can be used in small amounts in the formulation, typically 0.1-5.0 wt%.

[0095] The percentages referred to in this specification may be selected from any indicated range relative to the total of 100%. The percentages or other amounts used in this specification are by weight unless otherwise specified.

[0096] In certain embodiments, the polyvinyl alcohol is composed of a blend of two or more polyvinyl alcohol polymers, each polyvinyl alcohol polymer having a degree of hydrolysis of at least 98%, optionally, one polyvinyl alcohol having a higher molecular weight, and at least one polyvinyl alcohol having a lower molecular weight. The high molecular weight polymer has a higher molecular weight than the low molecular weight polymer. In embodiments, the polymer may include 80% high molecular weight polyvinyl alcohol and 20% low molecular weight polyvinyl alcohol. The ratio of high molecular weight polyvinyl alcohol to low molecular weight polyvinyl alcohol may be 2:1 to 10:1, optionally 3:1 to 7:1, alternatively 6:1 to 4:1, and alternatively about 5:1.

[0097] Manufacturers of highly hydrolyzed polyvinyl alcohol produce a number of series of products with different molecular weights. Some typical properties are shown in Table 1.

[0098] Table 1 Typical properties of polyvinyl alcohol

[0099]

[0100] *Measured using a 4% polymer solution in water at 25°C

[0101] The dispersity index (DI = Mw / Mn) of the polymers varies significantly in this table because of rounding of the molecular weight range numbers cited. If the polymerization of the vinyl acetate monomers conforms to an ideal free radical initiated polymerization mechanism, the theoretical value should be 2.0. Mw, Mn and DI are measured by aqueous gel permeation chromatography (GPC) method (ASTM D6666). For the materials used in GPC, the Mn measured for high molecular weight polymers can range from about 60,000 to about 120,000, and for low molecular weight polymers, the number average molecular weight (Mn) can be about 5000 to about 30,000.

[0102] Alternatively, molecular weight may be defined by solution viscosity of a 4% solution at a known temperature, in accordance with polymer manufacturing practices and industry practice.

[0103] The blend of polymers of different molecular weights used can be selected based on the physical properties desired in the final product. This may require the use of materials of different molecular weights. It may be advantageous to use polymers of two or more different molecular weights. The use of a single molecular weight polymer is not excluded.

[0104] Since a water bath cannot be used with polyvinyl alcohol, an air cooling chamber can be located downstream of the die. This can include a system of moving rollers housed in a controlled atmosphere, arranged so that the polymer strands emerging from the die are maintained at the appropriate tension as they cool and solidify prior to pelletization.

[0105] According to a second aspect of the present invention, there is provided a polyvinyl alcohol polymer component, comprising:

[0106] A polyvinyl alcohol polymer or a blend of the polyvinyl alcohol polymers, the polyvinyl alcohol polymer or the blend of the polyvinyl alcohol polymers having a degree of hydrolysis of 98% or more;

[0107] a plasticizer, the plasticizer being in the range of 6 to 15 wt %;

[0108] wherein the plasticizer is selected from the group consisting of polyols, polyethylene glycols, glycerol, diols, triols and mixtures thereof; and

[0109] having a water content in the range of 0.1 to 0.5 wt %;

[0110] Among the polymers are viscoelastic thermoplastic materials.

[0111] Exemplary polymers and plasticizers are disclosed above.

[0112] According to a third aspect of the present invention, an apparatus for reactively mixing a polyvinyl alcohol polymer having a polyvinyl alcohol content of 98 wt % or more, the apparatus comprising a mixing reactor;

[0113] wherein the mixing reactor comprises a blending chamber having a main inlet, a main outlet and at least two interengaging components extending between the main inlet and the main outlet, the components being arranged to apply shear forces to the polymer as the polymer is conveyed by the components from the inlet through the reaction zone to the outlet;

[0114] wherein the reactor chamber includes a plurality of heating zones, the plurality of heating zones being arranged such that the mixture is subjected to a temperature profile that increases in temperature from an inlet to an outlet;

[0115] one or more auxiliary inlets, the one or more auxiliary inlets located downstream of the main inlet, for introducing reactants including a processing aid and a plasticizer into the chamber to form a reaction mixture;

[0116] This temperature profile causes the processing aid and plasticizer to react with the polymer in the reaction zone to form a plasticized polymer.

[0117] In an alternative embodiment, the apparatus comprises an auxiliary outlet located between the reaction zone and the main outlet.

[0118] An exemplary apparatus is as disclosed above. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] The invention is further described by way of example, without any limiting meaning, with reference to the accompanying drawings, in which:

[0120] Figure 1 Shown are typical torque changes and temperature changes when polyvinyl alcohol is reacted with a processing aid (water) and glycerol (plasticizer) by reaction mixing in a Brabender batch reactor at ~60°C;

[0121] Figure 2 Shows typical torque changes and temperature changes when polyvinyl alcohol (85%) (including different grades) reacts with water and glycerol by reaction mixing in a Brabender batch reactor;

[0122] Figure 3 Shown is the effect of initial mixing temperature when polyvinyl alcohol is reacted with a processing aid (water) and glycerol (plasticizer) by reaction mixing at ~60°C in a Brabender batch reactor;

[0123] Figure 4 It is a diagrammatic representation of a twin screw extruder system;

[0124] Figure 5 is a diagrammatic representation of a twin screw extruder coupled to a single screw extruder equipped with multiple female dies and a dry face pelletizer;

[0125] Figure 6 is a diagrammatic representation of a twin screw extruder having prominently marked heating zones and coupled to a single screw extruder equipped with a dry face cutter;

[0126] Figure 7 The polymer containing 12% glycerol in D2O is shown in 1 HNMR spectrum;

[0127] Figure 8 A typical thermogram obtained by thermogravimetric analysis is shown. DETAILED DESCRIPTION

[0128] The processing issues associated with the control of either disintegrating or reactive blending in a twin screw extruder of polyvinyl alcohol with different molecular characteristics (such as molecular weight and degree of hydrolysis or blends of the same polymer having different characteristics) with processing aids and plasticizers (of the types previously defined) under different processing conditions (such as formulation ingredients, temperature, mixing level and time) can be most easily seen by conducting batch experiments.

[0129] An understanding by one skilled in the art of reactive extrusion that the compounding process produces an unexpectedly large and rapid exothermic reaction should lead to the correct design of a twin-screw extruder reactor for the continuous manufacture of polyvinyl alcohol pellets suitable for use in other thermoplastic manufacturing processes such as blown film, injection molding, or contour molding using non-reactive extrusion methods.

[0130] The essence of the continuous pellet manufacturing process is to avoid the well-known degradation of polyvinyl alcohol, which occurs at temperatures close to its melting point, by producing plasticized pellets at temperatures well below the melting point.

[0131] Any batch reactor can be used, provided that it is temperature controlled and equipped with a good mixing device equipped with a torque meter and means for measuring the temperature of the reaction mixture. A convenient commercial device for such measurements is the measuring Brabender Plastogram mixer.

[0132] Figure 1 Shown is the typical output of a batch mixing process carried out in a metering and well mixing mixer using mono highly hydrolyzed (>98%) polyvinyl alcohol with water as a processing aid (5%) and glycerol as a plasticizer when mixing is carried out at a nominal temperature of 60°C.

[0133] With the intermeshing agitator blades running at a constant speed of 100 rpm, the temperature and torque remain essentially constant for about 12 minutes. During the induction period, the viscosity (represented by the torque) is low because the slurry formed when the formulation components are first introduced into the preheated mixing chamber in the batch reactor used in the exemplary embodiment changes only slowly, and the heat generated is consumed in the steel walls of the container. After 12 minutes, the viscosity can be seen to increase slowly as the processing aid begins to expand the polymer. Until 17 minutes, the expansion and mixing process increases rapidly, and the temperature rises almost instantly within a few seconds, which also causes a very rapid increase in viscosity. After reaching the peak torque, the temperature continues to rise as the torque begins to decrease. In further experiments conducted over a longer period of time, it was observed that the temperature of the mixture will stabilize at the temperature value of the reactor set point of 60°C. The viscosity properties will also settle at a stable level, which depends on many factors, including the amount of residual crystals in the fluid, and also on whether crystallization is still occurring when the temperature is reduced.

[0134] The rapid exotherm can be attributed to a complex series of reactions involving secondary bonding interactions (primary hydrogen bonds) between all components of the mixture introduced into the batch reactor. In fact, during the reaction, if all the crystalline domains of the polymer are destroyed by the processing aids and plasticizers, the multiphase slurry is converted into a single-phase thermoplastic viscoelastic fluid of high viscosity. In the viscoelastic state, whatever the degree of disruption of the crystalline structure of the polymer (initially ~50%), the disruption of the crystalline structure has been achieved at a temperature far below the melting point of the crystalline domains of the polymer (in the case shown, the highest temperature reached is 105°C, which is important because the polymer degrades before reaching its melting point by simple heating.).

[0135] Unless the process is performed in a true calorimetric reactor and the torque measurements can be calibrated, the data generated will always be qualitative. Furthermore, no direct quantitative relationship can be made between what is measured in a batch reactor and what can occur in a continuous flow twin screw extruder reactor for the same reaction. However, for those skilled in the art of reaction processing, the observations made using the calorimetric batch reactor are sufficiently instructive to allow definition of screw configurations, temperature profiles and feed conditions for the effective production of thermoplastic pellets of polyvinyl alcohol in extruder reactors of varying sizes.

[0136] Figure 2 Shows that when all conditions are Figure 1 The sensitivity of the method is shown in Figure 2, but with a melt of two different polymer grades. The general pattern of viscosity change and temperature change is similar, but the sharp onset of the phase transition from a slurry to a viscoelastic melt occurs earlier and both the temperature rise and the viscosity level reached are higher.

[0137] Figure 3 All other conditions are shown with Figure 1 The pattern of change of both viscosity and temperature is similar, but occurs much faster.

[0138] There are many different configurations and sizes of twin screw extruder reactors that, when equipped with the appropriate screws, are capable of producing acceptable pellets for downstream processing, particularly blown film.

[0139] Figure 4 It is a diagrammatic representation of a twin screw extruder system. The co-rotating screw extruder (1) is equipped with closely meshing screws with an L:D ratio greater than 40:1. The barrel is equipped with both a heating device and a refrigeration device. The screw is driven by an electric motor (2). The solid raw material feed port (3) is located vertically or laterally on the extruder barrel (1). The liquid feed port (4) is located either vertically or laterally downstream of the solid feed port (3). A single or multiple female molds (5) deliver a strand of reacted polymer material to a rotating cutter blade in a pelletizer unit (6). The strand can be transported between the mold and the pelletizer by means of an electric conveyor belt, the speed of which controls the stretch ratio of the strand and the diameter of the pellets entering the pelletizer. The pellet length is controlled by the speed of the pelletizer blade relative to the speed of the strand.

[0140] The configuration shown is advantageous for smaller extruder reactors with barrel diameters in the range of 10-40 mm.

[0141] Figure 5 A twin screw system is shown, which is attached to a single screw extruder equipped with a dry flour granulator unit. The extruder motor and feed port of the twin screw extruder reactor are connected to the single screw extruder equipped with a dry flour granulator unit. Figure 4 Similar to what is seen in . A single screw extruder (7) or other pump is capable of conveying a pulsation-free thermoviscoelastic polymer. It is orthogonally attached to the twin screw extruder via a coupling zone (8), but may be attached at other convenient angles within the range of 95-150°. This part of the system is driven by an electric motor (9). The single screw extruder (7) delivers the reacted polymer to a plurality of female dies (10) to form a plurality of strands. The strands are delivered to a pelletizer unit (11) which is equipped with an independently controlled electric drive unit (13). The cutter blade is located in a conduit (12) and is in close contact with the die face under the action of a controlled contact pressure. A cooling airflow directed upward in a conduit (13) equipped with an observation port carries the pellets away from the cutter unit and is collected in a silo for subsequent packaging and distribution. The airflow is indicated by a hollow arrow.

[0142] Figure 6A twin screw extruder is shown coupled to a single screw extruder equipped with a dry face cutter, wherein all items of the system are connected to Figure 5 The heating zones of the twin screw extruder are numbered from 0 to 11. The discharge zone is marked with the symbol O.

[0143] Zone 1 with a temperature of 100-150°C, optionally with a temperature of 120°C, is a feed zone with a screw conveyor for conveying the material to an intensive mixing zone (2) with a temperature of 120-180°C, optionally with a temperature of 160°C. Zone 3 with a temperature of 170-220°C, optionally with a temperature of 190°C, is a reaction zone with a screw conveyor with or without backmixing. Zone 4 with a temperature of 190-220°C, optionally with a temperature of 200°C, is an intensive mixing zone, which is arranged so that the reaction reaches at least partial completion. Zone 5 with a temperature of 190-220°C, optionally with a temperature of 195°C, is a low pressure zone, which removes volatiles by controlled exhaust. Zone 6 with a temperature of 190-220°C, optionally with a temperature of 195°C, is a conveying zone, which is pumped into a die or into a single screw extruder. If a single screw extruder is used, zone 7 having a temperature of 190-220°C, alternatively 195°C, provides additional residence time to complete the reaction and convey the material through a die for pelletization. Zone 8 includes a die having a temperature of 180-220°C, alternatively 195°C.

[0144] Raw materials and finished products are analyzed using a variety of techniques including gel permeation chromatography (GPC), proton nuclear magnetic resonance spectroscopy (pNMR), differential scanning calorimetry (DSC), dynamic thermal analysis (DMA) and other laboratory methods. The defining test for the quality of the pelletized product is the ability to easily blow film from it using standard commercial film blowing equipment. This quality test just mentioned is completed under defined pellet production conditions without introducing defects such as gels, fish eyes, voids and other defects that often occur when pellets are not produced properly.

[0145] Figure 7 The polymer containing 12% glycerol in D2O is shown in 1 H NMR Spectroscopy. NMR spectroscopy has been used to verify the copolymer composition of the material supplied to make the pellets and, more importantly, a method has been developed for estimating the amount of plasticizer in the pellets and in the finished product made from the pellets.

[0146] NMR measurements are typically performed using a JEOL ECA400 or ECA600 MHz NMR spectrometer with a 5 mm broadband tunable solution probe, but any suitable instrument may be used. The NMR instrument is calibrated using known concentrations of the plasticizer in deuterated water D2O.

[0147] Calibration was accomplished by making solutions of glycerol and polymer in D2O (2%-12% wt / wt), as shown in Table 2. Approximately 10 mg of each glycerol solution and polymer solution were diluted in 1 mL of D2O and transferred to a field-matched 5 mm NMR tube heated to 50°C and locked to the spectrometer using pulsed field gradient (PFG) averaging. Eight scans with an increased relaxation delay of 10 seconds (vs. 1 second in the standard experiment) were acquired for each sample using the 8 scans embedded in the experiment. 1 H spectroscopy to ensure complete relaxation, thus allowing for the acquisition of quantitative NMR data.

[0148] Samples of the pellets or finished product (approximately 10 mg) were dissolved in D2O by heating to 60°C for 12 hours or until completely dissolved and then submitted to the same analytical procedure as used for the calibration standards.

[0149] Table 2 is a list of solutions used to calibrate the NMR instrument.

[0150] serial number Calibration samples GLU010715-001 <![CDATA[2% glycerol in D2O]]> GLU010715-002 <![CDATA[4% glycerol in D2O]]> GLU010715-003 <![CDATA[6% glycerol in D2O]]> GLU010715-004 <![CDATA[8% glycerol in D2O]]> GLU010715-005 <![CDATA[10% glycerol in D2O]]> GLU010715-006 <![CDATA[12% glycerol in D2O]]> GLU010715-007 Pellet samples

[0151] For each calibration curve of different concentration solutions, the CH resonance of glycerol was integrated with the polymer resonance at 4.25 ppm. Analysis of the prepared pellets and finished solutions in the same manner as the calibration standards provides a reliable measure of the glycerol (or other) plasticizer content.

[0152] Table 3 lists the peak area integration of glycerol standard sample and pellet sample

[0153]

[0154]

[0155] For the example described, the amount of glycerol in the pellets was 6.88 wt%. The level of glycerol in the pellets and the finished product affects the physical properties of the pellets and the amount of water absorbed. Typically, in the finished product, the absorbed water content is in the range of 0.1-5.0 wt%. This varies with the indoor humidity level. Typically, film-grade products quickly reach an equilibrium moisture level of ~2.0%. In order to achieve the desired properties in the film-grade product, the glycerol content is required to be in the range of 6.0-15.0 wt%, but as an option is in the range of 8.0-10.0 wt%.

[0156] NMR is used to establish pellet formulations and pellet manufacturing processes to achieve optimal properties for controlled manufacture of end products with specific physical properties for downstream use.

[0157] The NMR method employed is not specific to the exemplary plasticizers, but is general to the preferred class of polyhydroxy materials.

[0158] By examining typical thermograms obtained from thermogravimetric analysis of polyvinyl alcohol in air, e.g. Figure 8 As shown, we can understand the importance of keeping the processing temperature controllable.

[0159] Figure 8 A typical thermogram obtained from thermogravimetric analysis is shown. The thermogram was obtained when pellets made using the method described in Example 1 were examined. The weight loss shown was obtained in air. The main features that can be seen in this analysis are when water (0.1-5.0%) and liquid plasticizer (~5-15%) are present. The loss of water becomes significant at 100°C, while the plasticizer slowly decomposes and is lost at 1800°C and above. Above 210°C, along with the loss of water, the sharp loss of plasticizer and the decomposition of the polymer are very rapid. Near 300°C, carbonization of the polymer begins, and above 400°C, the final combustion of the carbonized polymer residue is rapid. The thermogram also shows any inorganic residues (0.1-4.0%) that may be present in the ingredients used in the polymerization process and hydrolysis process to make the polyvinyl alcohol used in the manufacture of the pellets.

[0160] Example

[0161] The following reactive extrusion process was employed.

[0162] The melt extruder used in this extrusion operation is designed to perform several operations in the preparation of pellets. Highly hydrolyzed polyvinyl alcohol is fed into the initial part of the extruder. Water and plasticizer are fed to the molten polyvinyl alcohol through the side flow (auxiliary inlet) of the extruder. Water is fed into the liquid feed zone to destroy the highly crystalline structure of the highly hydrolyzed polyvinyl alcohol. The formation of hydrogen bonding between the hydroxyl groups of the polyvinyl alcohol and the hydroxyl groups of the plasticizer due to the highly exothermic reaction and the temperature increase recorded in the batch blender (Brabender) up to 150°C. In the twin-screw extruder, the release of this high exothermic heat is controlled by the designed screw configuration disclosed above. Water cooling is also used at the reaction zone of the twin-screw extruder to control the heat generated from the exothermic hydrogen bonding between the hydroxyl groups of the polyvinyl alcohol and the hydroxyl groups of the plasticizer. After the thermoplastic polyvinyl alcohol blend is melt-consolidated, a vacuum port is used to remove the water used to destroy the crystalline structure of the highly hydrolyzed polyvinyl alcohol. Optionally, when a low boiling point plasticizer is used, additional polyvinyl alcohol plasticizer can be pumped into the extruder after the vacuum port during the removal of water to make up for any polyvinyl alcohol plasticizer that has been devolatile. The resulting reaction melt blend is extruded through a die located at the end of the extruder and pelletized using a dry face cutter. As an option, the extruded strands are cooled on an air cooling belt and pelletized.

[0163] Twin screw extruders (Rondol extruder, APV extruder and Zepplin extruder) are set up to perform the operations disclosed in the following examples. The polyvinyl alcohol blend is delivered to the extruder using a conventional solid feeder designed to provide a uniform flow rate. Water and liquid plasticizer are delivered as liquids to the extruder at a position downstream of the polyvinyl alcohol blend (i.e., at a position lower than the barrel of the extruder). The mixture of polyvinyl alcohol blend, water and plasticizer is gently mixed to reduce the risk of overheating due to the high reaction exotherm generated by hydrogen bonding between the hydroxyl groups of polyvinyl alcohol and the plasticizer. A strong mixing zone is used towards the end of the extruder and in front of the devolatilization zone to ensure that the exothermic reaction is completed. The polyvinyl alcohol mixture is dehydrated by a vacuum port to remove excess water for destroying the crystallinity of the polyvinyl alcohol. The product is extruded through a die onto an air cooling belt and granulated.

[0164] Example 1

[0165] Formulation F9 included a polyvinyl alcohol blend (SELVOL EH 6210313 (59.5%), EH 4109645 (25.5%) from Sekisui Specialty Chemicals Europe, SL) in a series of runs using water (5%) and glycerol (10%). Feed rate to extruder (Rondol orthogonal system, twin screw 25 mm; L:D 20:1; discharge only at the junction of twin and single screw extruder); total throughput rate 1.5 kg / h; die temperature 175°C; torque developed 60%. Extruder equipped with strand pelletizer. The extrusion temperature profile along the barrel of the extruder was: Zone 0, ambient temperature; Zone 1, 20°C; Zone 2, 40°C; Zone 3, 80°C; Zone 4, 90°C; Zone 5, 150°C; Zone 6, 200°C; Zone 7, 200°C; Zone 8, 200°C; Zone 9, 200°C; Zone 10, 200°C; Zone 11, 200°C. The properties of the pellet samples produced from these runs are given by 1 H NMR, DSC, GPC and other experimental methods were tested, but the key test was to produce a good film from the pellets using a standard commercial film blowing process.

[0166] Example 2

[0167] Formulation K1-010 was used as a polyvinyl alcohol blend (SELVOL EH 6210313 (59.5%), EH 4109645 (25.5%) from Sekisui Specialty Chemicals Europe Ltd. in a series of runs using water (5%) and pentaerythritol (10%). Feed rate to extruder (Zeppelin RHC 25 twin screw extruder, L:D 40:1; discharge in zones 8 and 9); total throughput rate 10 kg / h; die temperature 195°C; torque developed 52 + / - 2.0%. The extruder was equipped with a strand pelletizer. Across the barrel of the extruder, the extrusion temperature profile was: Zone 0, ambient temperature; Zone 1, 20° C.; Zone 2, 40° C.; Zone 3, 80° C.; Zone 4, 90° C.; Zone 5, 150° C.; Zone 6, 200° C.; Zone 7, 200° C.; Zone 8, 200° C.; Zone 9, 200° C.; Zone 10, 200° C.; Zone 11, 200° C. As in Example 1, the properties of the pellet samples produced by these runs were tested, and good films were produced from the pellets using a standard commercial blown film process.

[0168] Example 3

[0169] Formulation L1-010 was used as a polyvinyl alcohol blend (SELVOL EH 6210313 (56%), EH 4109645 (24%) from Sekisui Specialty Chemicals Europe Ltd. in a series of runs using water (10%) and dipentaerythritol (10%). Total feed rate to extruder (Zeppelin RHC 25 twin screw extruder, L:D 40:1; discharge in zones 8 and 9) 5.0 kg / h; die temperature 195°C; torque generated 44 + / - 4.0%. The extruder was equipped with a strand pelletizer. The extrusion temperature profile along the barrel of the extruder was: Zone 0, ambient temperature; Zone 1, 20° C.; Zone 2, 40° C.; Zone 3, 80° C.; Zone 4, 90° C.; Zone 5, 150° C.; Zone 6, 200° C.; Zone 7, 200° C.; Zone 8, 200° C.; Zone 9, 200° C.; Zone 10, 200° C.; Zone 11, 200° C. As in Example 1, the properties of the pellet samples produced by these runs were tested and good films were produced from the pellets using a standard commercial blown film process.

[0170] Example 4

[0171] Formulation M1-010 was used as polyvinyl alcohol blend (SELVOL EH 6210313 (56%), EH 4109645 (24%) from Sekisui Specialty Chemicals Europe Ltd. in a series of runs using water (10%) and a mixture of pentaerythritol and dipentaerythritol (10%). Total feed rate to extruder (Zeppelin RHC 25 twin screw extruder, L:D=40:1; discharge in zones 8 and 9) 10 kg / h; die temperature 195°C; torque developed 55%+ / -5.0%. The extruder was equipped with a strand pelletizer. The extrusion temperature profile along the barrel of the extruder was: Zone 0, ambient temperature; Zone 1, 20° C.; Zone 2, 40° C.; Zone 3, 80° C.; Zone 4, 90° C.; Zone 5, 150° C.; Zone 6, 200° C.; Zone 7, 200° C.; Zone 8, 200° C.; Zone 9, 200° C.; Zone 10, 200° C.; Zone 11, 200° C. As in Example 1, the properties of the pellet samples produced by these runs were tested, and good films were produced from the pellets using a standard commercial blown film process.

[0172] Example 5

[0173] Formulation F9 was used as a polyvinyl alcohol blend (SELVOL EH 6210313 (% 6%), EH 4109645 (24%) from Sekisui Specialty Chemicals Europe Ltd.) in a series of runs using water (5%) and glycerol (10%). The total feed rate to the extruder (Zeppelin RHC 55 twin screw extruder with L:D=48:1 coupled to a single screw; discharge at zones 7, 9 and the junction between the two extruders) was 200 kg / h; die temperature 195°C; torque 45%+ / 1 3.0%. The single screw extruder was equipped with a multi-hole die to which a dry face granulator was attached. The extrusion temperature profile along the barrel of the extruder was: Zone 0, ambient temperature; Zone 1, 20°C; Zone 2, 40°C; Zone 3, 80°C; Zone 4, 90°C; Zone 5, 150°C; Zone 6, 200°C; Zone 7, 200°C; Zone 8, 220°C; Zone 9, 220°C; Zone 10, 230°C; Zone 11, 210°C. As in Example 1, the characteristics of pellet samples produced from these runs were described, and good films were produced from the pellets using a standard commercial blown film process using DSC.

Claims

1. A method for producing a plasticized polyvinyl alcohol polymer, the method comprising the steps of: introducing a homopolyvinyl alcohol polymer or a blend of said homopolyvinyl alcohol polymers into a mixed flow reactor, said homopolyvinyl alcohol polymer being prepared by hydrolysis of homopolyvinyl acetate, wherein the degree of hydrolysis is above 98%; wherein the mixed flow reactor comprises a blending chamber having a main inlet, a main outlet and at least two interengaging components extending between the main inlet and the main outlet, the components being arranged to apply shear forces to the polymer as the polymer is conveyed by the components from the inlet through a reaction zone to the outlet; one or more auxiliary inlets, the one or more auxiliary inlets being located downstream of the primary inlet for delivering reactants including a processing aid and a plasticizer to the chamber to form a reaction mixture; wherein the plasticizer is selected from the group consisting of mannitol, pentaerythritol, dipentaerythritol and mixtures thereof; wherein the blending chamber comprises a plurality of heating zones arranged so that the mixture is subjected to a controlled temperature profile of up to 220° C.; wherein the position of the reaction zone is controlled by varying one or more of: the temperature profile, the rotational speed of one or more screws, and the rate at which the reaction mixture is fed into the mixed flow reactor; an auxiliary outlet located between the reaction zone and a primary outlet, the primary outlet being arranged to allow removal of a processing aid from the chamber; reacting a reaction mixture comprising the processing aid, the plasticizer, and the polymer in the reaction zone to form a plasticized polymer; wherein the processing aid is water, and the amount of water in the reaction mixture is from 3 wt % to 18 wt %; and The plasticized homopolymerized polyvinyl alcohol polymer is allowed to pass through the main outlet.

2. The method according to claim 1, wherein the boiling point of the processing aid is lower than the boiling point of the plasticizer.

3. The method of claim 1, wherein the amount of water is 3 wt% to 15 wt%, alternatively 3 wt% to 12 wt%, and yet alternatively 5 wt% to 10 wt%.

4. A process according to any one of the preceding claims, wherein the temperature profile increases from ambient temperature at the first zone to 200°C adjacent the auxiliary outlet, and wherein the reaction zone has a temperature of at least 200°C.

5. A process according to any one of the preceding claims, comprising an intensive mixing zone located downstream of the reaction zone, wherein the intensive mixing zone comprises a paddle mixer located between the reaction zone and the auxiliary outlet.

6. A method according to any one of the preceding claims, wherein the mixing zone comprises a kneading zone comprising one or more pairs of interengaging rotor blades or paddles.

7. A method according to any one of the preceding claims, wherein the auxiliary outlet is a drain outlet configured to allow removal of a processing aid from the mixing reactor.

8. A method according to any one of the preceding claims, wherein the plasticising polymer has a water content of less than 5 wt%, alternatively less than 2 wt%, alternatively less than 0.5 wt%.

9. A method according to any one of the preceding claims, wherein a pump is located downstream of the main outlet, and wherein the pump comprises a single screw extruder unit.

10. A method according to any one of the preceding claims, wherein the polyvinyl alcohol polymer comprises a blend of two or more polyvinyl alcohol homopolymers, each homopolymer being prepared by hydrolysis of polyvinyl acetate, wherein the degree of hydrolysis is above 98%; wherein the blend comprises a higher molecular weight homopolymer polyvinyl alcohol and at least one lower molecular weight homopolymer polyvinyl alcohol, the higher molecular weight polymer having a higher molecular weight than the lower molecular weight polymer.

11. The method of claim 10, wherein the ratio of high molecular weight polyvinyl alcohol to low molecular weight polyvinyl alcohol in the polyvinyl alcohol blend is in the range of 2:1 to 10:1, alternatively in the range of 3:1 to 7:1, alternatively in the range of 4:1 to 6:1, and alternatively about 5:

1.

12. The method of claims 10 to 11, wherein the high molecular weight polymer has a molecular weight in the range of 60,000 to 120,000, and wherein the low molecular weight polymer has a molecular weight in the range of 5,000 to 30,000.

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