FR2574083A1 - DOLOMITE-BASED LOAD HAVING A DELAYING EFFECT ON COMBUSTION OF ORGANIC POLYMERS - Google Patents

Abstract

THE INVENTION CONCERNS A PULVERULENT FILLER FOR PLASTIC MATERIAL, WITH A GRANULOMETRY LESS THAN OR EQUAL TO 20 MM, BASED ON HYDROXIDES AND CARBONATES OF MAGNESIUM AND CALCIUM. THE CHARGE IS PREPARED BY HYDRATION OF DOLOMITIC LIMESTONE, CALCINE DOLOMITE, NATURAL AND CALCINATED DOLOMITIC DOLOMITES AND MAGNESITES, WITH AQUEOUS SOLUTIONS OF ANIONIC AND NON-IONIC SURFACTANTS. CATALYTIC IMPURITIES IN NATURAL RAW MATERIAL ARE PASSIVE DURING CALCINATION, AND COMPOSITE MATERIALS HAVE GOOD MECHANICAL PROPERTIES AND ARE IN PARTICULAR INCOMBUSTIBLE.

Description

DOLOMITE-BASED LOAD HAVING A DELAYING EFFECT ON

  COMBUSTION OF ORGANIC POLYMERS.

  The invention relates to a filler based on a calcined dolomite hydrate, which makes it possible to prepare polyolefins and other organic polymers with reduced combustibility.

  It is known that it is possible, by the addition of concentra-

  inorganic fillers to polyolefins, to increase the modulus of elasticity while maintaining, and possibly increasing viscosity, the moment of

  satisfies certain conditions of granulometric distribution

the load.

  Among the most important inorganic fillers on an industrial scale are calcium carbonate, on the one hand in the form of micro-milled limestone, on the other hand

  in the form of chemically precipitated calcium carbonate.

  In composites made of polyolefins and carbonates

  of calcium, one obtains, compared to the non-polyolefins

  loaded, an improvement of some properties at the level of the implementation and the mechanical characteristics, but, noe when the concentration of calcium carbonate is high,

  these composites remain always combustible.

  Recently, a filler has been known that plays the role of a flame retardant for polyolefins. It is magnesium hydroxide, the use of which makes it possible to obtain non-flammable and self-extinguishing polyolefins without

  formation of fumes or toxic products.

  Magnesium hydroxide, which to date was obtained exclusively by precipitation of magnesium salts (at

  from seawater or solutions obtained by dissolu-

  of magnesium-containing mineral products), has a fundamental disadvantage: its high price, due to an expensive preparation process, to which it is often necessary to add a

insufficient purity.

  This insufficient impurity is at the origin of a catalytic activity of the charges, an activity which manifests itself by a

  faster degradation by thermo-oxidation and photo-

  oxidation, polyolefins. In the case of micro-charges

  crushed, it is different transition metals (Cu, Mn, Fe, etc.) which are at the origin of the catalytic activity, and which is always found in natural mineral raw materials. In the chemically precipitated charges, the removal of these metals is usually carried out by expensive processes, but the residues are nevertheless found in the form of extremely reactive salts (chlorides, nitrates, sulphites, sulphates, etc.), of which catalytic action

is particularly strong.

  Another disadvantage of the above-mentioned magnesium hydroxide

  The reason lies in its tendency to form aggregates, which makes it more difficult to mix with plastic. It is therefore necessary to use necessarily high shear forces to obtain a good homogenization of the composite material.

  One of the methods for simplifying the homogeneity

  The use of magnesium hydroxide in the plastics material is in the use of mixtures of magnesium hydroxide and calcium carbonate, according to various mixing ratios, according to the Czechoslovak PV patent application.

  754-84. Microbrilled calcium carbonate destroys

  dyes of microcrystals regnesium hydroxide, which then facilitates the homogenization of the mixed charge in the plastic. The elementary analysis of such a mixed charge presents between the different constituents a relation analogous to that

  that one has in a hydrated dolomite or a dolomitic limestone

  that with the difference that these hydrates, which were prepared

  by known methods, contain only a small percentage

carbonates.

  The known hydration processes of calcined dolomites apply essentially to magnesia mortars, in which the presence of Ca (OH) 2, which forms the constituent

  principal, is necessary. Therefore, during the preparation

  In the case of dolomitic lime, supercalination of magnesium oxide is most often carried out, since the calcination temperature depends on the calcination conditions of the calcium oxide. A magnesium oxide thus calcined can not be

that hardly hydrated.

  If the calcination of a dolomite is carried out at a low temperature, for example at 800 ° C, what is called semi-calcined dolomite, which, in addition to undecomposed calcium carbonate, contains magnesium oxide, which is used for example for the treatment of water. according to

  Hungarian patent N 13 564 of 28.7.1977, the addition of

  Activators (eg calcium chloride, triethanolamine, fatty acids) facilitate the hydration of a semi-calcined dolomite. Kaminskas (Z. nerog Chem 18, 3144 (1973)) has previously described the interesting influence of various salts (eg calcium chloride) on the acceleration of hydration of magnesium oxide. and

dolomitic lime.

  Although the process described gives a hydrated dolomite consisting of individual particles of high surface area and small diameter, the drying of the hydrates thus prepared leads to the formation of solid aggregates, which can not be dispersed in the polymer melt and which, when used as fillers, undesirably affect the mechanical properties of organic polymers. It is therefore

  necessary for the waterproofing of

  individual cells, already during the hydration process, with the formation of a homogeneous protective layer on the individual particles. For magnesium hydroxide,

  which releases water above 340 C, acts as a delay

  effective combustion date, a necessary condition lies in a homogeneous and complete dispersion of the different

charge particles.

  The object of the invention is therefore to create a powder

  Slug based on dolomites or dolomitic limestones, which contains a mixture of magnesium hydroxide and calcium with calcium carbonate, and having a particle size less than or equal to 20 Dm, the surface of which has been treated

  by waterproofing substances.

  The invention also aims to create a process for the preparation of a powdery filler, by calcination and hydration of dolomites or dolomitic limestones, in which dolomites or dolomitic limestones are first calcined at lower or equal temperatures at 1100 C, then hydrated, preferably with solutions

  anionic or nonionic surfactants.

  The invention also aims to create an appropriate process

  for the preparation of a pulverulent filler, wherein the surfactants used are ammonium salts of fatty acids having 12 to 20 carbon atoms, as well as mixtures of fatty acid salts and esters

  of fatty acids having at least two free alcohol groups.

  Finally, the invention also aims to create composite materials based on polyolefins and a powdery filler

according to the invention.

  Dolomitic limestones, limestone dolomites, dolomite

  dolomitic mites and magnesites are raw materials

  defined by their magnesium carbonate content.

  The latter is the weakest in dolomite limestone.

  ticks, in which the MgCO3 content is at least 4.6%

  in mass. This content is 22.9% by mass in the Dolomites

  limestone mites, 41.2% by mass in the dolomites and

  can reach 45.7% by mass in dolomitic magnesites.

  The filler prepared according to the invention from these natural raw materials eliminates the defects mentioned above by bringing together the advantages that result from the possibility of simultaneous use of CaCO3 and Mg (OH) 2. The preparation of the filler according to the invention is relatively simple and inexpensive, since none of the constituents

  is prepared by precipitation from solutions. The effi-

  The capacity of the filler according to the invention as a non-toxic combustion retardant opens up numerous possibilities for using polyolefins on a large scale in many industrial branches, for example in the building, transport and electrical engineering sectors. etc. The filler according to the present invention is derived from dolomite, or else from dolomitic magnesites or dolomitic limestones, that is to say that the starting raw material contains either an equimolar ratio MgCO3: CaCO3, an excess of MgCO3, or a slight excess of CaCO3. It is clear that the composition of the starting raw material will have a decisive influence on the efficiency of the filler as a fire retardant. The degree of purity of the raw material influences the degree of whiteness of the load and the composite. An important advantage of the feedstock according to the invention, compared to mixtures of fillers of similar composition and prepared by precipitation, is a reduction in the final catalytic activity, without elimination.

  expensive impurities present.

  The calcination of dolomite can be carried out at temperatures of 750 to 1100 C; if the temperature is lower, only decomposition of MgCO3 into MgO occurs, with a partial conversion of CaCO3 present in CaO; if the temperature is higher, MgO.CaO is created. In addition to these main chemical reactions, the calcination is accompanied by a conversion of the active salts of the transition metals into inert oxides, that is to say that calcination removes

  the catalytic activity of natural dolomite. Calcina

  The dolomite can be preferably produced in rotary kilns and, in order to maintain the chemical purity, it is advantageous to use a fuel having a minimum sulfur content, for example natural gas. The calcined and passivated dolomite is then subjected to hydration. Since the hydration of MgO is much slower than that of CaO, it will be advantageous to proceed with hydration

  in hydration reactors under pressure at temperatures of

  from 150 to 220 C. Given that the compounds

  obtained have different crystalline networks, hydra-

  tation causes a spontaneous decomposition of the material, with the formation of very small particles. Thanks to an appropriate control of the hydration process, we can obtain a

  product with a particle size distribution allows it to

  both to be directly used in the intended application, or else it is enough for a simple sieving of the product, without subsequent grinding. If the specifications to be met by the fineness of the load are particularly severe, the hydrated product can be crushed, before sieving, with much lower energy conditions

  only when grinding the basic raw material.

  The filler according to the invention can be surface-treated with fatty acids, their salts, esters or partial esters.

  glycerol and fatty acids, possibly other

  anionic or nonionic active agents, which treatment may preferably be carried out directly during hydration, using solutions or emulsions of these substances

in water.

  A substance suitable for surface treatment must satisfy the following conditions: 1) It must be soluble in water, 2) It must form a hydrophobic film on the surface of the load, 3) It must not lower the stability of the surface. oxidation, or the photooxidation stability, of polyolefins

loaded.

  With regard to 1), the substance intended for the treatment must form in aqueous medium a true solution or a micellar solution. As for condition 2), we must take into account

  the fact that we use micellar solutions of

  these containing not only a hydrophilic functional group,

but also a hydrophobic chain.

  The hydrophilic functional groups may have an ionic or nonionic character. The ionic functional groups form carboxylic acid (organic) salts R-COO X, in which the cation X can be either an ion

  of alkali metal (Na +, K +), an ion (NH4 +).

  The use of ammonium salts of organic acids is particularly interesting, given that, during the chemisorption on the basic surface of the charge, it is released from ammonia, which is released during hydration

  of the charge. Conversely, when using metal salts

  the ions of these metals remain sorbed by the surface of

the load, which is undesirable.

  Examples of functional groups

  nonionic telomers of ethylene oxide and ethylene-

  glycol. To obtain the necessary solubility in water, it is necessary that the hydrophilic functional group contains at least

ethylene oxide units.

  About 2). So that the surface of the load presents

  a hydrophobic character, it is necessary that the hydro-

  The phobe of the charge treating substance has a sufficient number of hydrophobic units. If this group consists of hydrocarbons, the number of carbon atoms in the chain must be at least 12. This means that, among the fatty acids from natural, vegetable or animal fats, it is possible to use the following acids, alone or as a mixture: lauric acid (C12H2402), myristic acid (C14H2802), palmitic acid (C16H3202), stearic acid (C18H3602), arachidic acid (C20H4002), behenic acid (C22H4402), oleic acid (C18H3402 )

  linoleic acid (C18H3202) and erucic acid (C22H4202).

  The three acids mentioned last are examples of unsaturated acids, the double bonds of which can be advantageously used to form chemical bonds between the filler and the polyolefins, which has favorable consequences, in composite mineral products, in the form of a decrease in creep. Instead of natural fatty acids, straight-chain or branched synthetic acids can also be used, as long as they have at least 12

carbon atoms.

  About 3). The transition metal salts (Fe,

  Mn, Cu, Cr, Ti) act as catalysts for the degradation of

  polyolefins by heat oxidation and

  oxidation. Even if we use for the preparation of the dolomitic load very pure raw materials (such as

  in Example 2) and for the preparation of composite materials

  In the case of pure polyolefin, no complete absence of transition metals can be guaranteed in the feedstock or in the polymer, where excess residues of the polymerization catalysts are always present. It is known that only those compounds of these metals in which the transition metal is in a low valence state and in a form such that it can form active complexes with the oxygen of the air, have catalytic activity (see Zahradnickova A., Vesely K .: Chemicky Prumysl 32, 533 (1982), Lunak S., Lederer P., Stopka F., Veprek-Siska J .: Czech Commun., Chem., 46, 2455 (1981); Vesely K., Petruj J. and Zahradnickova A .: 28th Microsymposium of IUPAC, Prague 8-11.7.1985). Fatty acids react on the oxides present in transition metals by forming catalytically active salts, which not only catalyze oxidation

  polyolefins themselves, but also

  phenolic oxidants used, which not only leads

  to a severe degradation of the stability of

  sites, but still to an undesirable color change, caused by oxidation products of antioxidants

  phenolic. We found that it was possible to improve

  significantly increase oxidation stability by addition of

  with transition metals forming stable complexes. This is why it is advantageous to add to the ammonium salt of a fatty acid acting as an emulsifier, an ester of a fatty acid and a polyalcohol, in which at least two of them remain free. OH groups. As examples of suitable esters, mention may be made of monostearate

  glycerol, pentaerythritol distearate and mono-

  sorbitol stearate. The esters mentioned can be

  easily dispersed in aqueous solutions of an emulsifier

  such as ammonium salts of fatty acids. The amount of the aqueous solution or emulsion of the treatment substance used for the hydration of dolomites

  totally or partially calcined can be very variable.

  It is advantageous to use only a slight excess of water (approx.

  50% molar) relative to the stoichiometric amount required for hydration. In this case, the hydration is carried out "dry", ie the heat of hydration of MgO (34.3 kJ / mol) or CaO (64.9 kJ / mol) is sufficient for

  evaporation of excess water, and we obtain direct

  a free-flowing powder that is no longer needed

to dry.

  The quantity of concretely optimal water required for hydration therefore depends on the composition of the raw material, its degree of calcination and the progress

  technique of the hydration process.

  The invention will be better explained with reference to the examples below, in which the parts and percentages are by weight.

Example 1

  Dolni Rozinka dolomite having the composition

  following: MgO 18.8% CaO 30.2% Fe203 0.18% SiO2 1.10%

A1203 0.31%

  Loss on ignition 49.41% The dolomite was calcined for 3 hours in a laboratory muffle furnace at a temperature of 1000 ° C. An X-ray diffraction analysis revealed that the calcined material contained 34.1% of MgO, 40.4% CaO and 25.5% CaCO3. So there was a decarboxylation

  complete MgCO3 and decarboxylation of 74% CaCO3.

  The calcined material was hydrated in a laboratory autoclave for 6 hours at 200 ° C in the presence of excess water and 0.4% potassium stearate (calculated on calcined dolomite). Screening on a 40 Am mesh screen, the larger particles were separated from the resulting suspension, and the remaining slurry was evaporated to dryness before drying for one hour.

  at 150 C. A fine, free-flowing, non-free-flowing powder was obtained

  wettable with water, a microscopic observation showed that it had a particle size of between 1 and

  4 gm. A differential thermal analysis made it possible to

  that the dry hydrate had the following composition: Mg (OH) 2

  38.5%, Ca (OH) 2 41.7%, CaCO 3 19.8%.

  In a laboratory kneader, the mixture was kneaded at a temperature of

  at 220 C a mixture of polypropylene (Mosten 58,412)

  and charges. From the material, it was prepared by

  4mm thick plates, which were used firstly to assess the combustibility by the Oxygen Index Method (LOI) according to ASTM D 2863, and secondly to assess the limit. of creep (ak) and impact resistance

  on notched bar (ak) according to DIN 53 453.

  The properties of the polypropylene loaded with the treated dolomite (D) and with a micro-milled limestone (V) are compared in the following table: Test specimen PP DV LOI ak (%) (%) (M (% O2) ( MPa) (kJ.m) a 60 40 - 21.9 24, 5 5.2 b 50 50 - 23.3 22.7 5.8 c 40 60 - 25.1 20.8 6.5 d 60 - 40 19.6 24.7 5.2 e 50 - 50 20.5 23.1 6.0 f 40 - 60 21.7 21.0 7.0 It should be noted in this connection that a material with an index of Oxygen greater than 22.5 can be considered as self-extinguishing.It is clear that the new filler according to the invention gives practically the same properties as a microbrushed limestone, with, however, in addition, a strong

reduction of combustibility.

Example 2

  A Varin dolomite having the following composition was used: MgO 21.19% CaO 31.19% SiO 2 + Al 2 O 3 0.22% Fe 2 3 0.044% The dolomite was calcined for 3 hours at 850 ° C. in a laboratory muffle furnace . X-ray diffraction analysis revealed that the calcined material

  contained 29.2% MgO, 7.7% CaO and 63.1% CaCO3.

  To 100 g of the calcined material was added 25 g of an aqueous solution containing 4% ammonium stearate. After stirring, a lumpy and moist product was obtained, which was introduced into a laboratory autoclave with stirring and heated for 2 hours at a temperature of 120 ° C. After opening the autoclave, a hydrophobic hydrate was obtained,

  dry and free flowing, which has been shown by thermal analysis

  that differential have the following composition: Mg (OH) 2

  36.6%, Ca (OH) 2.8.8%, CaCO3 54.6%.

  An air screen was used to separate a fraction of particle size greater than 10 gm, the fines were

  as filler in the following mixtures with different

  Polyolefin rents, mixtures obtained by kneading in a Brabender Plasticorder at 220-230 ° C, and from which test specimens were prepared by pressing at 2300 ° C. The table below gives an overview of the prepared mixtures

and their properties.

TABLE: PROPERTIES OF COMPOSITES

  Polymer Charge Additive LOI Index Number Modulus (MPa) a (kJ.m2 (%) (%) melting, 21N melting, 49N (% 02) elasticity k (GPa) PP 40 CaSt 2 0.38 1, 30 21.8 2.53 24.5 2.9

  PP 40 GM 2 0.35 1.47 21.7 2.41 22.8 5.0

PP 60 GM 2 24.5 15.6 2.0

  1PE 40 GM 2 0.05 0.36 22.0 18.1 18.8

  RPE 40 GM 2 0.08 0.50 22.0 1.4 8.5 Ex2lications: PP: Polypropylene MOSTEN 55212, manufacturer CHZ Litvinov 1PE: Linear polyethylene LITEN FB 29, manufacturer CHZ Litvinov rPE: Polyethylene branched BRALEN RB 03-23 , manufacturer Slovnaft Bratislava CaSt: Calcium Stearate GM: Glycerol Monostearate

Claims (5)

claims   1. Powdery fillers for plastics, in particular for polyolefins, based on hydroxides and   magnesium and calcium carbonates and with a   trie less than or equal to 20 Dm, characterized in that it was obtained by hydration of dolomitic limestone, dolomite limestone, dolomite or dolomitic magnesite   calcined in the presence of impermeable substances   cient. 2. Process for the preparation of a pulverulent filler according to claim 1, characterized in that calcine   at a temperature up to 1100 C of limestone dolomite   ticks, dolomite limestones, dolomites and magnesites dolomiti-   natural resources, and then hydrate them with   anionic or nonionic surfactants.   3. Process for the preparation of a pulverulent filler according to claim 2, characterized in that the surfactants used are ammonium salts of fatty acids having 12 to 20 carbon atoms.   4. Process for the preparation of a powdery filler   according to one of claims 2 or 3, characterized   in that mixtures of fatty acid salts and fatty acid esters having at least two fatty acids are used as surfactants. free alcohol groups.   5. Composite materials based on polyolefins and a   pulverulent filler according to claim 1.