DE19921277A1 - Preparation of prefoamed polymer granulate useful for production of packaging, insulation and molded articles comprises growth of starch granules at below gelatinization temperature - Google Patents

Abstract

A process for the production of a prefoamed polymer granulate (I) comprises accumulation of starch at below the gelatinization temperature from a seed and expansion of the resulting starch granulate at a pressure above atmospheric pressure and at above the gelatinization temperature. Independent claims are included for (i) the granulate (I), (ii) a process for the production of a foamed molded article by addition of a preferably prefoamed starch granulate in a hermetically sealed mold and irradiation with microwave energy to effect foaming of the granulate and (iii) the resulting molded article.

Description

The invention relates to a pre-expanded polymer granules that especially as a starting material for the production of molded parts for the packaging industry, as insulation and for the production of Models (molded parts) is useful for full mold casting. It affects also a foamed molded part made from such a pre-expanded polymer granules. Finally, the invention also relates to methods of manufacture of the pre-expanded polymer granulate and the foamed molded part.

Under a "pre-expanded polymer granulate" in the context of existing documents understood a polymer granulate, the individual Grains at least essentially of a polymeric material with zel lular structure exist and are further foamable.

Pre-expanded polymer granules made of polystyrene, Polymethyl methacrylate or its copolymers, but also others In individual cases, polymers of petrochemical origin come during manufacture of pre-expanded granules for use. Since all in Pre-expanded polymer granules used in practice to a greater extent are of petrochemical origin, they pollute natural resources and are not biological, incomplete or insufficiently fast degradable. The expanded polymers can moreover only in certain Borders are recycled. However, there are alternatives to recycling only the ecologically undesirable landfill and disposal measures burning on.

Methods for making pre-expanded polymer granules include in  usually a suspension polymerization in the presence of a blowing agent (e.g. pentane), followed by pre-foaming in stirred tanks Heat supply and conditioning of the expanded granulate foreskin to compensate for the negative pressure in the pearls.

Molded parts for the packaging industry, for insulation materials and as Models for full mold casting are pre-expanded with pre-expanded foam Polymer granules (in particular polystyrene, polymethyl methacrylate and their Copolymers) produced in automatic foam machines. The ecological disadvantages the use and disposal of these molded parts correspond to the disadvantages the polymer granules on which they are based.

It was therefore the object of the invention to produce both polymer granules Raw materials of non-petrochemical origin as well as a corresponding one pre-expanded polymer granules of non-petrochemical origin available molding.

In particular, molded parts should be provided that are structured rell are designed so that they (a) indu in the packaging strie, (b) as insulation materials or (c) in the foundry industry (as a model for full mold casting). All are advantageous Process substances are biodegradable and harmless to the environment Lich.

With regard to the pre-expanded polymer granulate, the question is posed Task by providing granules based on a biopolymer solved, which can be prepared by starch below the gelatin temperature (or gelatinization temperature) is attached to germs and the granules thus forming starch at one print above atmospheric pressure and a temperature above gelation tion temperature (usually a temperature above 75 ° C) expan be dated. The granules are usually placed in an autoclave expands.

A pressure between 4 and 20 is advantageously used for the expansion bar and a temperature between 120 ° C and 200 ° C set.  

Typically, the starch is added before being attached to the germs suspended in a suspending agent and then the starch suspension contacted the germs that the starch attaches to the germs.

The starch suspension is usually carried out in the usual way Introducing starch (and possibly other substances) into one Suspending agent (e.g. deionized water) is produced. The suspension tion can take place in the presence of a dispersing agent which Wetting the starch (and / or other substances) with the suspension promotes. It can also be done by stirring the starch (and the other substances) in the suspension medium and / or by application of the starch-suspension agent mixture are supported with ultrasound.

The method according to the invention is advantageously designed in this way tet that before and / or during the addition of the starch to the germs too a propellant is deposited. The goal is pursued here To form granules, the granules of which comprise a blowing agent. Preferably the blowing agent is contained in the starch suspension. The germs too can contain a blowing agent.

The blowing agent advantageously comprises a water of crystallization inorganic salt. A preferred orphan is a salt, which at least part of its crystal water at normal pressure already at Gives warming to a temperature above 75 ° C.

Inorganic salt used as a blowing agent (whether it contains water or not) should be as environmentally compatible as possible and therefore should essentially only comprise Na +, K + and / or Al ³⁺ as cations. As anions, it should essentially only comprise hydrogen carbonates, hydrogen sulfates, hydrogen phosphates, carbonates, sulfates and / or phosphates.

Examples of particularly suitable inorganic salts are sodium hydrogen carbonate NaHCO ₃ , aluminum sulfate Al ₂ (SO ₄ ) ₃ , sodium hydrogen sulfate NaHSO ₄ , the mixed salt potassium sulfate-aluminum sulfate K ₂ SO ₄ . Al ₂ (SO ₄ ) ₃ and tetrasodium diphosphate Na ₄ P ₂ O ₇ and their derivatives containing water of crystallization. Mixtures of the salts mentioned with one another and with other inorganic salts are sometimes useful in order to ensure crystal or water release over a wide temperature range. Examples include mixtures of (a) sodium hydrogen carbonate and aluminum sulfate, (b) sodium hydrogen sulfate and sodium hydrogen carbonate, (c) potassium sulfate aluminum sulfate and sodium hydrogen carbonate, (d) oxalic acid dihydrate and sodium hydrogen carbonate, and (e) tetrasodium diphosphate and sodium hydrogen carbonate, the individual components preferably Contain crystal water.

In addition to or instead of inorganic salts, a blowing agent can be added to the germs and / or the starch, which comprises an organic salt, which preferably releases CO ₂ , NH ₃ and / or water when heated. Examples of such organic salts are ammonium oxalate (NH ₄ ) ₂ (COO) ₂ , ammonium oxalate monohydrate (NH ₄ ) ₂ (COO) ₂ .H ₂ O and ammonium acetate NH ₄ (CH ₃ COO); when heated, these salts completely decompose into gases such as CO ₂ , NH ₃ and H ₂ O and are therefore absolutely harmless with regard to environmental compatibility.

The above-mentioned inorganic and organic salts (blowing agents) set zen the water contained in them or the said gases in one certain temperature, but free in a wide temperature range. The The type and amount of the blowing agent to be used or a Blowing agent mixture taking into account the gas release temperature Select areas so that the blowing agents expand (pre-expand) of the starch granules, and he will go through the pre-foaming process result in a surplus expansion capacity for a later one Finished foaming of a molded part remains.

In addition to native starch, the starch suspension is preferably one Commercially available pre-pasted (pre-gelatinized) starch added. Before pasted (pre-gelatinized) starch can bind additional water.

A starch suspension can also contain proteins such as zein or lipids such as containing palmitic acid. Starch-protein mixtures can do additional things Bind water. Starch-lipid mixtures can reduce the viscosity of water enlarge films of the foam during pre- and finished foaming and so that Difficulty escaping the propellant gases.  

A starch suspension can advantageously be polyfunctional Contain alcohols such as glycerin. Polyfunctional alcohols work with Foaming up as a plasticizer.

Typically comprise the germs to which the starch attaches should, even strength itself. As a rule, the germs essentially exist or entirely from native, pre-pasted or pre-gelatinized starch or a mixture of native and / or pre-pasted and / or before gelatinized starch.

The germs can be removed by sieving or another mechanical Separation process obtained from commercially available products of native starch become. Fluidizable germs, which are preferably a have average particle size in the range between 40 and 50 microns. Out of them are preferably granules with a medium in the addition of starch particle size in the range between 300 and 1000 microns.

The germs advantageously have a composition that the Composition of the material to be added (to be pelletized) at least essentially corresponds. Then the compositions according to one Regulation above - related to the manufacture of starch suspensions - has already been explained and a subsequent freeze-drying manufactured. So there is a suspension for freeze drying appropriate composition (suspending agent, starch, if appropriate other components).

The starch is advantageously deposited on the germs (granulation) by thermal or mechanical means. A thermi The accumulation is spray granulation in a fluidized bed system; a mechanical attachment can be in an intensive mixer or a plate granulation system. Also a combination of several systems for gradual granulation is possible and useful in some cases. Granules with a medium size are typically used for granulation Particle size in the range between 300 and 1000 microns generated. The middle Particle size is dependent on the molded part and its geometry set. The thermal or mechanical way produced (non-foamed) granules are storage and trans  portable.

The (non-foamed) produced in the first process step Granules are advantageously used to facilitate pre-foaming (the Expansion) moistened or moistened with water and / or ethanol.

Typically, the expansion of the starch according to the invention comprehensive granules (starch particles) to a pre-expanded starch granule lat carried out in an autoclave. By defining a setting Certain pressure-temperature-time regimes allow pre-expanded starch granuiate with different bulk densities. The specialist will based on a few preliminary tests for every desired application find suitable pressure-temperature-time regimes.

Advantageously, a pressure above the Atmospheric pressure and a temperature above 75 ° C.

The pre-expanded granules according to the invention can also be used with a Coating based on disaccharides (such as cane sugar / sucrose), Oligosaccharides, polysaccharides or mixtures of these saccharides be provided. Such a coating conveys one when finished foaming pre-expanded granules to a molded part welding the individual pre-expanded granules with each other.

The shelf life of the pre-expanded starch granules according to the invention lats can be increased by conditioning treatment. In the Conditioning diffuses condensed water from the cells of the starch foam of the granules into the surrounding atmosphere and air into the cells of the starch foam. When the exchange is complete, that's it pre-expanded polymer granulate can be stored.

For foaming the pre-expanded starch granules into the molded part, So for ready foaming, the starch granules are preferably included Moisturized water and / or ethanol.

With regard to the foamed molded part that is pre-foamed Based on polymer granulate, the task is performed by a molded part  solved, which is obtainable by a process in which a pre-expanded Starch granules (for example, one produced according to the invention Starch granules) placed in a hermetically sealed form and there is exposed to microwave energy to cause foaming (finished foam) of the granules.

The prefoamed granulate is preferably passed through in the mold Vibration compresses. The pre-expanded granulate can be in a mold be shaken out of a fixed part and from one or consists of several movable moldings. The fixed part of the form and the moving parts of the mold close the pre-expanded starch granules then hermetically. Shaking the foamed polymer granules pursues the goal of realizing the densest spherical packing and can on reached a one, two or three-dimensional excitable vibration table become.

The fixed part of the mold and the moving parts of the mold consist at least essentially of what is transparent to microwaves Material such as teflon or polyethylene. To achieve a hermetic Completing the form, its moving parts are preferably single movable. Individual or all parts of the mold are equipped with heating elements, e.g. B. incorporated heating coils, equipped to heat the mold allow.

Microwave energy is preferably applied to the mold in order to a temperature increase and thus a softening of the pre-expanded To cause starch granules. The remaining capacity of the blowing agent causes then a further enlargement of the starch granules. Weld them together flat, so that there is a honeycomb-like shape for the resulting molded part Structure results.

Advantageously, at least one wall part of the mold (but preferably the entire inner wall of the mold) shortly before Demoulded heated to the adjacent surface of the finished foam Smooth the molded part.

The moving parts of the mold are taken back for demolding,  and the finished foamed, optionally with smooth surfaces see molded parts are removed from the mold, for. B. ejected.

The pre-expanded starch granules can be used before the microwave treatment in an intermediate step at a pressure above atmospheric pressure and a temperature above 75 ° C, for example in an autoclave be preformed, for example to specify simple geometries. Doing so ensures that there is a residual expansion capacity for the finished foaming remains present.

The shelf life of the finished foamed molding according to the invention can be increased by conditioning treatment. At the Kon ditioning ensures that condensed water from the cells of the starch foam of the granules into the surrounding atmosphere and air into the Starch foam cells diffuse. A high shelf life of the pre-foamed starch granules is reached when the mass transfer is completed.

To the resistance of the molded part according to the invention against environmental Rivers can increase the surfaces of the molded parts by dipping modified in solutions of certain substances. Often he Desired hydrophobization can be achieved, for example, by dipping the Molding in a starch acetate solution. Surface treatment can, however not only by immersing the molded part in a liquid but also can be achieved by another form of application, for example by spraying or applying.

The invention will now be described with reference to the accompanying Drawings explained in more detail. They represent:

Fig. 1 shows a fluidized bed installation for the production of starch granules by means of spray granulation,

Fig. 2 an autoclave for prefoaming of the starch granules,

Fig. 3 is a molding system (automatic foaming machine) with a vibrating table for pre-foaming pre-foamed starch granules and

Fig. 4 shows a microwave heating system.

To produce a pre-foamed starch granulate in a first process stage starch germs in a fluidized bed below the gelati temperature with a finely divided, droplet-shaped starch suspension contacted. Starch is stored from the suspensions droplets on the germs and granules are formed in this way.

The more precise process sequence of the first process stage will now be explained with reference to FIG. 1.

In a reservoir 2 there is a suspension of starch in water; the suspension is stirred to prevent starch from being deposited. The suspension comprises a mixture of native and pre-cloned starch and a blowing agent, namely a crystal water containing the inorganic salt.

By means of a pump 1 , the starch suspension is brought out of the container 2 and through a spray arrangement 3 into a fluidized bed apparatus 4 (injected). Finely distributed suspension droplets form.

The fluidized bed apparatus currently contains the Injection of the suspension already a batch of fluidisable starch germs, each comprising a mixture of native and pre-pasted starch. The germs have an average size in the range between 40 and 50 µm and were made by freeze drying.

Hit the suspension droplets injected into the fluidized bed on the starch germs and most of the water they contain evaporates. There is a continuous accumulation of starch on the Germs, which form granules that contain starch in their interior and include starch accumulated around it. Because the droplet-shaped In addition to starch, starch suspension also includes blowing agents, is also stored this propellant to the starch germs and is found accordingly also in the granules formed.

The accumulation (granulation) is stopped when an average particle size of about 500 μm (the predetermined target size) is reached, and the granules obtained are discharged from the fluidized bed apparatus 4 .

The granules so produced, ie the granules comprising the starch thus formed, are expanded in a second process stage at a pressure above atmospheric pressure and a temperature above the gelation temperature (5 bar; 150 ° C.). This takes place in an autoclave, as will be explained in more detail with reference to FIG. 2.

The starch granules are placed in a container 11 of an autoclave 12 . This has a water reservoir 13 . By means of not shown heaters, the temperature in the autoclave 12 is increased to a temperature of about 70 ° C, whereby - in the presence of water - the internal pressure of the autoclave increases considerably. The starch granules start to foam; however, this foaming process is terminated in good time, so that a residual expansion capacity remains for later finished foaming of a molded part.

The product of the second process stage is therefore a pre-expanded one Preserve starch granules.

These pre-expanded starch granules can be further processed into a molded part in a further process step, as will be explained in more detail with reference to FIG. 3.

A mold 21 shown in FIG. 3 consists of a fixed part 22 and a plurality of movable parts 23 . The fixed part of the mold and the movable parts of the mold are made of transparent material for microwaves, namely Teflon.

The mold 21 is clamped in a box or frame 27 of a three-dimensionally excitable vibrating table 24 and thereby securely fastened to it. The vibrating table can be excited electrically or pneumatically in a first spatial direction by only indicated vibrators 25 ; for the vibration in the second and third spatial directions, additional vibrator elements (not shown in FIG. 3) are additionally provided (piston vibrators, roller vibrators). The vibrating table 24 is connected via a spring with springs 26 to a fixed base 28 .

In operation, the moving parts of the mold 21 are first moved up to the fixed part of the mold in such a way that a filling opening for the pre-expanded starch granules remains free.

The pre-expanded granulate is then filled into the mold through this opening after it has been moistened with water and ethanol. There is then a vibration compression by actuation of the vibration table 24 to ensure a tight packing of the pre-expanded starch granules. If necessary, granulate is refilled after the vibration (shaking).

Then the mold 21 is hermetically sealed and removed from the vibrating table.

Through the walls of the mold which are transparent to microwaves, the granulate is subjected to microwave energy in order to cause the granules to foam, for example in a microwave heating system, as will be explained in more detail below with reference to FIG. 4.

After foaming (ready foaming) of the polymer granules into one The molded part is ventilated for the purpose of pressure equalization. After this The pressure inside the mold is not reduced by means of illustrated heating elements heated to the adjacent surface of the to smooth the foamed molding.

The molded part is then removed from the mold and becomes hydrophobic undergo treatment. To do this, it is placed in a solution of starch acetate immersed.

Series production of molded parts from foamed starch granules can take place in a microwave heating system shown in FIG. 4. Molds 31 with filled and compressed starch granules are moved one after the other on a conveyor belt 35 in the direction of the arrow into the heating tunnel of a microwave apparatus 32 . One or more microwave modules 33 in a heating tunnel 34 of the apparatus 32 generate microwaves which are directed towards the molds 31 located in the tunnel. Through their walls, which are transparent to microwaves, the microwaves penetrate into the molds and cause the starch granules to foam in the manner described above. The conveyor belt 35 transports the molds with the finished foamed molded parts out of the microwave apparatus 32 . This is followed by the further process steps described above.

The microwave apparatus 32 is protected against microwave leakage by microwave absorbers 36 , which are arranged both in the region of the tunnel inlet and in the region of the tunnel outlet. Field unification is achieved in the microwave apparatus by field stirrers, not shown.

Claims (30)

1. A process for producing a pre-expanded polymer granulate, characterized in that

• - Starch is deposited on germs below the gelation temperature and
• - The granules comprising starch thus formed are expanded at a pressure above atmospheric pressure and a temperature above the gelation temperature.

2. The method according to claim 1, characterized in that the starch before the attachment to the germs is suspended in a suspension medium and the starch suspension is contacted with the germs so that the Starch attaches to the germs. 3. The method according to claim 2, characterized in that the starch suspension supported by a dispersing aid and / or supported by stirring the starch in the suspending agent and / or under supports the starch suspension through the action of ultrasound medium mixture is produced. 4. The method according to claim 2 or 3, characterized in that the Starch suspension a protein and / or a lipid and / or a polyfunction contains light alcohol. 5. The method according to any one of the preceding claims, characterized records that before and / or during the addition of the starch to the germs a blowing agent is also added to form a granulate, the Granules include a blowing agent. 6. The method according to any one of claims 2-4, characterized in that a blowing agent is contained in the starch suspension and / or the germs.   7. The method according to claim 5 or 6, characterized in that the Blowing agent comprises an inorganic salt containing water of crystallization. 8. The method according to claim 7, characterized in that the inorganic salt as cations essentially comprises only Na ⁺ , K ⁺ and / or Al ³⁺ . 9. The method according to claim 7, characterized in that the inorganic cal salt as anions essentially only hydrogen carbonates, hydrogen sulfa te, hydrogen phosphates, carbonates, sulfates and / or phosphates. 10. The method according to claim 5 or 6, characterized in that the blowing agent comprises an organic salt which releases CO ₂ , NH ₃ and / or H ₂ O when heated. 11. The method according to any one of the preceding claims, characterized indicates that the germs include starch. 12. The method according to any one of the preceding claims, characterized indicates that the germs are essentially or entirely from native, pre-pasted or pre-gelatinized starch or a mixture of native and / or pre-pasted and / or pre-gelatinized starch best hen. 13. The method according to any one of the preceding claims, characterized records that the germs from a starchy suspension by freezing drying are available. 14. The method according to any one of the preceding claims, characterized records that the germs have an average size in the range between 40 and 50 µm and / or the granules have an average particle size in the range between Own 300 and 1000 µm. 15. The method according to any one of the preceding claims, characterized records that the addition of starch to the germs on thermal or mechanical way. 16. The method according to claim 15, characterized in that the An  Storage of the starch on the germs (a) by spray granulation in a Fluid bed system, (b) in an intensive mixer or (c) in a plate granulation plant is effected. 17. The method according to any one of the preceding claims, characterized records that the granules before prefoaming with water and / or ethanol be moistened. 18. The method according to any one of the preceding claims, characterized records that the granules are expanded in an autoclave. 19. The method according to any one of the preceding claims, characterized records that the pre-foamed starch granules with a coating based of disaccharides (such as cane sugar / sucrose), oligosaccharides, polysac charides or mixtures of these saccharides is provided. 20. The method according to any one of the preceding claims, thereby secenn records that the pre-expanded granules by a conditioning treatment is made storable. 21. A process for producing a foamed molding, thereby characterized in that a preferably pre-expanded starch granules in a hermetically sealed form introduced and there with microwave energy is applied to cause the granules to foam. 22. The method according to claim 21, characterized in that the before foamed granules are compacted in the mold by vibration. 23. The method according to claim 20, characterized in that the before foamed starch granules before microwave treatment at one pressure above atmospheric pressure and a temperature above gelation temperature is further foamed. 24. The method according to any one of claims 21-23, characterized in that the pre-foamed starch granules with before being introduced into the mold Water and / or ethanol and / or a polyfunctional alcohol moistened become.   25. The method according to any one of claims 21-24, characterized in that at least one part of the wall of the mold after lowering the pressure in is heated in the mold or after foaming of the granules in the mold, to smooth the adjacent surface of the foamed molding. 26. The method according to any one of claims 21-25, characterized in that the granules of the starch granules are provided with a coating that you Promotes welding together. 27. The method according to any one of claims 21-26, characterized in that at least one surface of the molded part (a) a hydrophobization undergoes treatment or (b) is treated with a substance that the Foamed starch of the molded part superficially modified or derivatized siert. 28. The method according to any one of claims 21-27, characterized in that the starch granules according to a method according to any one of claims 1 to 20 is manufactured. 29. Starch granules, characterized in that it is by a method can be produced according to one of claims 1 to 20. 30. molded part, characterized in that it according to a method one of claims 21-28 can be produced.