SOLID STABILIZER COMPOSITION FOR SYNTHETIC POLYMERS

Abstract: A solid stabilizer composition for synthetic polymers is formed by a solid, continuous phase and by a solid dispersed phase in said continuous phase, wherein the continuous phase is constituted by amorphous 2,2′-­ oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-­ propionate] and the dispersed phase is constituted by an amorphous, or crystalline, or partially amorphous and partially crystalline organic phosphite, with the weight ratio of said continuous phase to said dispersed phase being comprised within the range of from 9:1 to 1:9. The process for preparing said solid composition and its use in the stabilization of synthetic polymers are disclosed.

Description: The present invention relates to a solid stabilizer composition for synthetic polymers, to the processes for preparing it and to its use in the stabilization of the synthetic polymers. In the art, it is usual to stabilize the synthetic polymers against the oxidative degradation caused by light and heat, by means of the addition of small amounts of stabilizers, such as sterically hindered phenols, and organic phosphites, sometimes used in combination with one another. For such a technique known from the prior art, reference is made to the specification of GB-A- 803,557, US-A- 3,516,963, US-A- 4,187,212, US-A- 4,360,617 and EP-B- 48,562. A drawback relevant to some organic phosphites is their tendency to hydrolysis, in particular during their storage under warm and moist conditions, with the consequent loss of stabilizing activity, and danger of corrosion of the equipment used for processing the organic polymers incorporating said hydrolysed phosphites. Therefore, it is usual in the art to stabilize the organic phosphites by means of the addition of organic bases which act by buffering the acidity which is formed during the hydrolysis, and therefore slow down the hydrolysis rate. However, this operating way does not make it possible satisfactory results to be achieved, in particular in case of the organic phosphites derived from pentaerythritol, whose sensitivity to hydrolysis remains high even in the presence of an organic base. On the other side, in the use of mixtures of sterically hindered phenols and of organic phosphites in the stabilization of the organic polymers, difficulties exist in accomplishing a complete mutual homogenizing of the two stabilizers, and then of these with the organic polymer. Often, this fact, combined with the phenomena of hydrolysis the phosphite can undergo, does not allow a so high as desirable stabilizing effect to be obtained. A sterically hindered phenol used in the art in order to stabilize the synthetic polymers is 2,2′-oxamido-bis[ethyl-3-(3.5-di-tert.-butyl-4-hydroxyphenyl)-propionate]: disclosed, e.g., EP-A- 21,596 and in US-A- 4,145,556 and US-A- 4,263,446. Mixtures of this hindered phenol with phosphite esters are described in EP-B- 48,562 The present Applicant found now that when said 2,2′-oxamido-bis[ethyl-3-(3.5-di-tert.-butyl-4-hydroxyphenyl)-propionate] is molten and then rapidly cooled down to ambient temperature values, takes a solid and amorphous form, and is capable of stably maintaining such an amorphous state when it is maintained at temperatures lower than approximately 50°C. The present Applicant found also that when a liquid and homogeneous mixture of said 2,2′-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate] with an organic phosphite, solid at ambient temperature, is rapidly cooled, a solid composition can be obtained in which such 2,2′-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate] constitutes the solid, continuous and amorphous phase, and the organic phosphite constitutes the solid, amorphous and/or crystalline phase dispersed in said continuous phase, and that such a composition is capable of stably maintaining said characteristics within the above specified range of temperatures. The present Applicant found finally that the organic phosphite, in said composition, acquires exceptionally high characteristics of resistance to hydrolysis, and that the same composition constitutes a stabilizer which is easily homogenizable with the synthetic polymers, and is capable of endowing these polymers excellent characteristics of stability to the action of degradation caused by light and heat. In accordance with the above, a purpose of the present invention is a solid composition resistant to hydrolysis, stabilizer for the organic polymers. Another purpose of the present invention is the process for preparing such a composition. A further purpose of the present invention is the use of the composition in the stabilization of the synthetic polymers. Still further purposes of the invention will be clear for those skilled in the art from the following disclosure. In particular, the solid composition, resistant to hydrolysis and stabilizer for synthetic polymers, according to the present invention, is formed by a solid continuous phase and a solid phase dispersed in said continuous phase, wherein the continuous phase is constituted by amorphous 2,2'-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate], and the dispersed phase is constituted by an either amorphous, or crystalline, or partially amorphous and partially crystalline organic phosphite or phosphonite, with said organic phosphite or phosphonite being solid at ambient temperature, and being selected from those definable by the following general formulae: or or wherein: the R radicals independently represent either substituted or non-substituted alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicals; the weight ratio of said continuous phase to said dispersed phase, in said composition, being furthermore comprised within the range of from 8:2 to 2:8. The sterically hindered phenol, 2,2'-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propion ate], is normally available as a crystalline solid having a melting point of 175-178°C. When this phenol is heated to a temperature higher than its melting temperature, and is then rapidly cooled to ambient temperature values (20-25°C), or to temperature values approximately equal to ambient temperature, turns into a solid amorphous on X-ray analysis, with the following characteristics, detected by DSC (Differential Thermal Analysis): a glass transition at approximately 40°C; an exothermic peak at approximately 131°C, relevant to crystallization of a portion of the product. an endothermic peak at approximately 176°C, relevant to the melting of the crystallized portion of the product. Examples of organic phosphites falling within the scope of above formula (I), useful for the purposes of the present invention are: diphenyl 2-ethylhexyl- phosphite, triphenyl phosphite, tris(2,5-di-tert.-butyl-phenyl)-phosphite, tris(2-tert.-butylphenyl)-phosphite, tris(2-phenylphenyl)-phosphite, tris[2-(1,1-dimethylpropyl)-phenyl]phosphite, tris(2-cyclohexylphenyl)-phosphite, tris(2-tert.-butyl-4-phenylphenyl)-phosphite, tris(2-tert.-butyl-4-methylphenyl)-phosphite, tris(2,4-di-tert.-amylphenyl)-phosphite and tris(2,4-di-tert.-butylphenyl)-phosphite. Examples of organic phosphites falling within the scope of above formula (II), useful for the purposes of the the present invention are: bis(2,4-di-tert.-butylphenyl)pentaerythritol diphosphite and distearyl-pentaerythritol diphosphite. An example of organic phosphonite, falling within the scope of formula (III), is tetrakis(2,4-di-tert.-butylphenyl)-4,4′-biphenylene diphosphonite. In the preferred form of practical embodiment, the organic phosphite or phosphonite is present in the composition in the form of particles having a particle size of the order of from 50 to 500 µm, and the weight ratio of the continuous phase to the dispersed phase in the composition is comprised within the range of from 3:7 to 7:3. The composition of the present invention is prepared by blending 2,2′-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate] powder with the selected organic phosphite powder. By operating under nitrogen, or under another inert gas, the mass is molten to a temperature which typically is of the order of from 180 to 200°C, the molten mass is homogenized and is then submitted to a rapid cooling down to ambient temperature values (20-25°C), or to temperature values close to ambient temperature. The rapid cooling, suitable for causing the molten material to rapidly solidify, can be carried out by any methods known in the art. The preferred methods consist in pouring the molten material on a cool metal plate, maintained, e.g., at a temperature equal to, or lower than, ambient temperature; in pouring the molten mass into water, or another non-reactive, cold liquid, e.g., maintained at a temperature equal to, or lower than, ambient temperature; and in cooling the molten, or partially molten, material in an inert gas, (e.g., nitrogen), in the form of droplets, by means of a technique similar to prilling. In any case, a stabilizer composition resistant to hydrolysis is obtained, wherein the organic phosphite is in the form of a solid phase, as particles having a particle size comprised within such range of values as above specified, with said particles being dispersed inside a continuous and amorphous solid phase of 2,2′-oxamido-bis[ethyl-3(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate]. The phosphite, in said composition, will be in the form of an amorphous, or crystalline, or partially amorphous and partially crystalline solid, as a function of the characteristics of the particular phosphite selected and, above all, as a function of the concentration of phosphite in the composition, in the meaning that at higher concentrations of the same phosphite, the crystalline form is favoured. Furthermore, the process for the preparation of the above disclosed composition makes it possible a solid composition to be prepared as a mass which can be submitted to scaling and/or to grinding, or as free-flowing granules, having the desired particle size, which can be directly used in the stabilization of the synthetic polymers. By means of the composition of the present invention, synthetic polymers and copolymers can be stabilized, such as polyolefins, EPDM resins, elastomers, ABS resins, polymeric alloys, polyesters, polycarbonates, and still others. The particularly good results which can be obtained by means of the composition of the present invention probably derive from the absence, or the substantial absence, of phenomena of hydrolysis of the phosphite, and from the optimum distribution of the two components of the same composition, which facilitates a good homogenizing and distribution inside the synthetic polymer. Example 1 In this example, compositions formed by the (A) component: 2,2′-oxamido-bis[ethyl-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionate]; and by the (B) component: bis(2,4-di-tert.-butylphenyl)pentaerythritol diphosphite are prepared and characterized. In particular, compositions containing the (A) and (B) components in various proportions, are prepared. The process used for preparing the compositions is as follows. To a glass reactor having a capacity of 0.5 litres, equipped with a mechanical stirrer, and with a jacket for heating fluid circulation, (A) and (B) component powders are charged under nitrogen, according to the weight ratios specified in tables 1 to 3. The powders are molten by heating to 190°C; the molten mass is maintained at this temperature for a few minutes, in order to homogenize it, and this latter is then poured onto an aluminum plate of 50x50 cm, maintained at ambient temperature. On the plate a this transparent layer is formed, which solidifies soon into a glass-like mass. When all the solid has reached ambient temperature, the solid is ground inside a mortar with a pestle, until a powder is obtained, whose average particle size is of approximately 10 to 500 microns. The so-obtained compositions are submitted to the following analytical checks: HPLC (High Pressure Liquid Chromatography) analysis: the sample, dissolved in acetone and analysed by high pressure liquid chromatography, shows the presence of the two components in their respective starting amounts, and does not show any presence of foreign substances as compared to the initial substances; DSC (Differential Scanning Calorimetry) analysis: the sample is sealed inside an aluminum dish, and the dish is charged to the sample-holder of the instrument (Mettler TA 3000, with Mettler TC 10 Processor), and is heated under nitrogen, at a temperature increase rate of 15 degrees Celsius/minute, up to 200°C. The behaviour of the sample shows the presence of a continuous amorphous phase of the (A) component, and of the dispersed phase of the (B) component. The stability to hydrolysis of the phosphite in said compositions is measured by storing the samples inside a sealed chamber, under controlled conditions of temperature and moisture. Samples are drawn over time, and the drawn samples are submitted to HPLC analyses, which make it possible the presence of unaltered (A) and (B) components, and the presence of the 2,4-di-tert.-butylphenol possibly formed due to the hydrolytic decomposition, to be determined. This test makes it possible to conclude for the high stability to hydrolysis of the compositions. Example 2 The experimental procedure is the same as of Example 1, with compositions being prepared, which are formed by the (A) phenolic component, and by the (C) component: tris-(2,4-di-tert.-butylphenyl) phosphite, in various proportions. The so obtained compositions were submitted to HPLC and DSC analyses, as reported in Example 1, with results similar to those as obtained in said Example 1 being obtained. Example 3 The action of the stabilizer compositions according to the present invention is verified, during the processing step, both by means of measurements of Melt-Flow Index (MFI - ASTM D 1238) after a plurality of extrusions of a polymeric composition constituted by an organic polymer and a stabilizer composition, and by means of measurements of Yellow Index carried out on slabs of 1.5 mm of thickness, obtained by press-moulding the granules corresponding to the various extrusions. Furthermore on the slabs, relating to the first-extrusion granules, the long-term stability is determined by thermal ageing inside a forced-air circulation oven at 140°C, until the first degradations symptoms appear at the edges of the sample. Commercial polypropylene marketed by Montedison company under the trade-name MOPLEN® FL 20F is blended with the stabilizer compositions containing the (A) phenolic antioxidant, and the (B) phosphite, with various ratios of (A)/(B) in the stabilizer composition. In all cases, the amount of stabilizer composition is fixed at the value of 0.1% by weight. In particular, stabilizer compositions are used, which contain the (A) and (B) components in the following proportions, as % by weight: 80%A-20%B; 60%A-40%B; 50%A-50%B; 40%A-60%B; 20%A-80%B. For comparative purposes, also the (A) and (B) stabilizers are separately used in an amount of 0.1% by weight in the composition with the polymer. The blending of the polymer with the stabilizer compositions, or the individual stabilizers, is carried out by a 30-minute blending inside a planetary mixer. The so obtained homogeneous powders are extruded, for 7 successive passages, through an extruder of 19 mm of diameter, with a barrel length approximately 5 times as long as the barrel diameter, equipped with a screw and with a nozzle of 2 mm, with a compression ratio of 1:4, at the speed of 50 revolutions per minute, and with a temperature profile along the extruder of 190°C; 235°C; 270°C; 270°C. After each extrusion, the filament is chopped into granules. A portion of the so-obtained granules are analysed for Melt Index according to ASTM-D 1238, by operating at 230°C, and under a pressure of 2.16 kg. A second portion of the granules are used for preparing slabs. The balance are used for the successive extrusions. The results obtained as to the change in Melt Index, after the 1st, 3rd, 5th and 7th extrusion, are summarized in Table 1. In said table, also the values are reported, which are obtained with virgin polypropylene. The granules put aside after each extrusion are press-moulded so as to obtain slabs of 1.5 mm of thickness, by operating at 200°C, for 3 minutes under 4 kg/cm², and for the following 3 minutes under 130 kg/cm², and subsequently cooling the so obtained slabs in water at ambient temperature. On these slabs, measurements of Yellow Index are carried out by a reflection method. The results of these tests are reported in Table 2, relatively to the slabs corresponding to the granules obtained after the odd-numbered extrusions. Finally, for all samples, the slabs obtained after the first extrusion are submitted to an accelerated thermal ageing, at 140°C, inside a forced-air circulation oven, equipped with a rotary carousel as the sample-holder. The stability over time is verified until symptoms of degradation at slab edges first appear. In Table 3, the observed degradation induction times are reported. The same commercial polypropylene MOPLEN® FL 20F was used for preparing commercial samples containing 0.1% by weight of the stabilizer composition formed by the (A) phenolic stabilizer and by the (C) phosphite in various proportions. On these samples, tests are carried out, which are at all similar to the above described tests, and the results are reported in Tables 4, 5 and 6, which respectively contain the values of change in polymer Melt Index measured after multiple extrusions; the values of the Yellow Indexes of the slabs obtained from the granules produced in the various extrusions; and the induction times at the incipient degradation symptoms, relevant to the slabs obtained from the granules from the first extrusion and submitted to accelerated ageing.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, GR, LI, LU, NL, SE A solid composition, resistant to hydrolysis and stabilizer for synthetic polymers, consisting of a solid continuous dispersant phase and a solid phase dispersed in said solid continuous dispersant phase, in which the solid continuous dispersant phase consists of amorphous 2,2'-oxamido-bis[ethyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate], and the dispersed phase consists of an either amorphous, or crystalline, or partially amorphous and partially crystalline organic phosphite or phosphonite, said organic phosphite or phosphonite being solid at a temperature of from 20°C to 25°C, and selected from those having the general formulae: or or wherein: the R radicals independently represent either substituted or unsubstituted alkyl, cycloalkyl, aryl, alkaryl, or aralkyl radicals, the weight ratio of said continuous dispersant phase to said dispersed phase, in the composition, being from 8:2 to 2:8. Composition according to Claim 1, wherein the organic phosphite of formula (I) is selected from: diphenyl-2-ethylhexyl phosphite, triphenyl phosphite, tris(2,5-di.tert.butylphenyl) phosphite, tris(2-tert.butylphenyl) phosphite; tris(2-phenylphenyl) phosphite, tris[2-(1,1-dimethylpropyl)phenyl] phosphite, tris(2-cyclohexylphenyl)-phosphite, tris(2-tert.butyl-4-phenylphenyl) phosphite, tris(2-tert.butyl-4-methylphenyl) phosphite, tris(2,4-di.tert.amylphenyl)phosphite, and tris(2,4-di.tert.butylphenyl) phosphite. Composition according to Claim 1, wherein the organic phosphite of formula (II) is selected from: bis(2,4-di.tert.butylphenyl)pentaerythritol diphosphite, and distearyl-pentaerythritol diphosphite. Composition according to Claim 1, wherein the phosphonite defined in formula (III) is : tetrakis(2,4-di.tert.butylphenyl)-4,4'-biphenylene diphosphonite. Composition according to Claim 1, wherein the weight ratio of said solid continuous dispersant phase to said dispersed phase is of from 3:7 to 7:3. Composition according to Claim 1, wherein the size of the particles of said dispersed phase is from 50 µm to 500 µm. Process for preparing the composition according to Claim 1, comprising the steps of: blending powdered 2,2'-oxamido-bis[ethyl-3-(3,5-di.tert.butyl-4-hydroxyphenyl)-propionate] with a powdered organic phosphite (I) or (II), or a powdered organic phosphonite (III); melting the blend at a temperature of from 180°C to 200°C; homogenizing the molten mass, and subjecting the homogenized molten mass to rapid cooling to a temperature of from 20°C to 25°C by pouring said mass onto a cold metal plate, or into water, or into another nonreactive cold liquid, or by contacting said homogenized molten mass with nitrogen or another inert gas. Use of the composition according to Claims 1 to 5 as a stabilizer for an organic polymer. Claims for the following Contracting State : ES Process for preparing a solid composition,resistant to hydrolysis and stabilizer for synthetic polymers, consisting of a solid continuous dispersant phase and a solid phase dispersed in said solid continuous dispersant phase, in which the solid continuous dispersant phase consists of amorphous 2,2'-oxamido-bis[ethyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate], and the dispersed phase consists of an either amorphous, or crystalline, or partially amorphous and partially crystalline organic phosphite or phosphonite, said organic phosphite or phosphonite being solid at a temperature of from 20°C to 25°C, and selected from those having the general formulae: or or wherein: the R radicals independently represent either substituted or unsubstituted alkyl, cycloalkyl, aryl, alkaryl, or aralkyl radicals, the weight ratio of said continuous dispersant phase to said dispersed phase, in the composition, being from 8:2 to 2:8, comprising the steps of: blending powdered 2,2'-oxamido-bis[ethyl-3-(3,5-di.tert.butyl-4-hydroxyphenyl)-propionate] with a powdered organic phosphite (I) or (II), or a powdered organic phosphonite (III); melting the blend at a temperature of from 180°C to 200°C; homogenizing the molten mass, and subjecting the homogenized molten mass to rapid cooling to a temperature of from 20°C to 25°C by pouring said mass onto a cold metal plate, or into water, or into another nonreactive cold liquid, or by contacting said homogenized molten mass with nitrogen or another inert gas. Process according to Claim 1, characterized in that the organic phosphite of formula (I) is selected from: diphenyl-2-ethylhexyl phosphite, triphenyl phosphite, tris(2,5-di.tert.butylphenyl) phosphite, tris(2-tert.butylphenyl) phosphite; tris(2-phenylphenyl) phosphite, tris[2-(1,1-dimethylpropyl)phenyl] phosphite, tris(2-cyclohexylphenyl)-phosphite, tris(2-tert.butyl-4-phenylphenyl) phosphite, tris(2-tert.butyl-4-methylphenyl) phosphite, tris(2,4-di.tert.amylphenyl)phosphite, and tris(2,4-di.tert.butylphenyl) phosphite. Process according to Claim 1, characterized in that the organic phosphite of formula (II) is selected from: bis(2,4-di.tert.butylphenyl)pentaerythritol diphosphite, and distearyl-pentaerythritol diphosphite. Process according to Claim 1, characterized in that the phosphonite defined in formula (III) is : tetrakis(2,4-di.tert.butylphenyl)-4,4'-biphenylene diphosphonite. Process according to Claim 1, characterized in that the weight ratio of said solid continuous dispersant phase to said dispersed phase is of from 3:7 to 7:3. Process according to Claim 1, characterized in that the size of the particles of said dispersed phase is from 50 µm to 500 µm.

Inventors: NERI, CARLO, NODARI, NEREO, SANDRE, GIOVANNI
Applicants: ENICHEM SYNTHESIS S.P.A.
Application year: 1988
Main classification: C08K5
IPC codes: C08K5, C08L101