CS267179B1 - Synergic mixture of substances for isotactic polypropylene stabilization - Google Patents

Abstract

Desired isotactic stability polypropylene is achieved by a synergistic effect a mixture of compounds containing dia-alkyl pentaeritritol diphosphites and arylalkylphenyl phosphites, which are represented by weight 1: 1 to 1: 4, preferably 1: 1.5 to 1: 3, wherein the concentration of dialkylpentaeritrotoldiphosphites is 0.01 to 0.5 wt. preferably about 0.05 up to 0.3 wt. % and arylalkylphenyl phosphite concentration is 0.01 to 0.5 wt. % preferably but 0.05 to 0.3 wt. %, based on stabilized polypropylene. This mixture provides at the same time high whiteness of polypropylene granulate and the resistance of polypropylene of fibers against the phenomenon known as gas fading. The synergistic mixtures can be used in production isotactic polypropylene intended for fibers and foils.

Description

The present invention relates to a synergistic mixture of organic phosphite-based substances which are added to isotactic polypropylene to stabilize against thermo-oxidative degradation, improve the whiteness of polypropylene granulate and reduce the tendency to gas yellow fading of white and light colored polypropylene fibers. ,

Isotactic polypropylene drawn by stereospecific polymerization on Ziegler-Natta catalysts is easily subject to oxidation in the granulation process, in subsequent processing processes and in the long-term use of the product. Polypropylene products are subject to thermo-oxidative and light aging, which leads to deterioration and loss of performance. In order to stabilize them, additives are added to the polypropylene which eliminate the above-mentioned disadvantages of pure polypropylene. The basic components of the mixture of added additives are processing antioxidants and heat stabilizers, which prevent the polymer from oxidizing during granulation and protect the polymer during processing. Together with light stabilizers, they protect polypropylene products against the effects of the weather. Phenol groups, organic phosphites, thiodipropionic acid esters and others are commonly used for this purpose. From the point of view of efficiency and affordability, a sterically hindered low-molecular-weight 2,6-ditert-butyl-4-methylphenol is commonly used, which is combined, for example, with sterically unprotected phenols and thiodipropionic acid esters (No. AO 229 766, No. AO 239 187). In addition to its advantages, the additive mixture based on sterically hindered phenol is characterized by an increased sensitivity to trace amounts of substances occurring in the technological process of solvent preparation of polypropylene and substances acting on products, most often polypropylene fibers. The result of this action is a color change of polypropylene in the direction of the shade. The presence of trace amounts of Al and Ti compounds from the catalyst system and Na ⁺ ions from NaOH used to adjust the pH of the polypropylene suspension leads to the undesired conversion of phenol to rye-colored products, degrading the polypropylene granulate.

When polypropylene (POP) fibers are stored in the absence of light, the hindered phenols are oxidized by N ₂ oxides and atmospheric oxygen, leading to a lemon-fed gas fading.

Organic phosphite-based substances effectively eliminate gas fading, do not react with residues of catalytic systems to form lived transformation products and are characterized by differentiated activity as processing antioxidants and heat stabilizers. The patent literature describes the use of a wide range of phosphorus-based compounds, for the purpose of documenting the advantage of the process according to the invention, the use of chemically related or identical substances is mentioned. ^r

The use of pentaerythritol diphosphite compounds is described in combinations:

a) pentaerythritol diphosphite + sterically hindered HALS (EP 155 912),

b) bis (2,4-ditert-butylphenyl) pentaerythritol diphosphite + hindered phenol + Na 2 PO 4 (JP 127 744/86):

c) distearylpentaerythritol diphosphite (EP 186 628)

d) pentaerythritol-tetrakis [3,5-ditert-butyl-4-hydroxy] hydrosilicate + hydroxylamine (EP 138 761).

Alkylphenyl phosphite derivatives are also protected as components of stabilizing mixtures of polyolefins (FR 2 019 209), JP 2 643/72, DE 3 000 745 FR 2 573 084, JP 127 744/86, FR 2 103 681 JP 964/84).

In these patents, pentaerythritol diphosphite-based substances and alkylphenylphosphites are protected in the presence of a component of a different chemical nature - most often hindered and unprotected phenols, or used without co-stabilizers, only in combination with light stabilizers.

The combination of phosphorus compounds with hindered phenols is always a potential source of storage yellowness in polypropylene fibers, on the other hand the protection of polypropylene and

The fiber prepared from it does not guarantee sufficient thermostability of the products, especially when using alkylphenyl phosphites alone.

Compounds based on pentaerythritol diphosphite prevent reactions leading to coloration of the polymer both in the granulation process and in the case of fibers during storage, but on the other hand they do not provide! sufficient protection of the polymer during granulation and processing, therefore they are most often combined with phenols.

These disadvantages of individual groups of antioxidants are eliminated by the process according to the invention, which uses a combination of arylalkylphenyl phosphites and dialkyl pentaerythritol diphosphites, which guarantees sufficient antioxidant efficiency in polypropylene granulation, good thermostability in polypropylene fiber processing, good whiteness of polypropylene granules and phenomenon of gas fading due to the observed synergistic effect. In combination with light stabilizers, the combination of phosphorus compounds guarantees sufficient light stability of the polypropylene fibers.

For stabilization, a mixture of phosphites is used in an amount of 0.01 to 0.5 wt.%, Preferably 0.05 to 0.3 wt.%. % of dialkyl pentaerythritol diphosphate and 0.01 to 0.5 wt. %, however, preferably 0.05 to 0.3 wt. % of tris (1-phenylethylphenyl) phosphite, based on stabilized polypropylene, the weight ratio of phosphites being 1: 1 to 1: 4, but preferably 1: 1.5 to 1: 3, which is added to the powdered polypropylene before granulation. In the preparation of polypropylene for the production of fibers, said mixture can be supplemented with light stabilizers of the hydroxybenzophenone type or of the sterically hindered piperidine type. The mixture of phosphitic stabilizers according to the invention provides:

1. Elimination of the effect of Na ⁺ ions present on the polypropylene powder and prevention of the formation of a vivid coloration of the granulate when the critical concentration is exceeded.

2. Sufficient protection of polypropylene against oxidation in the granulation process.

3. Increasing the processing stability of polypropylene during processing into fibers.

4. Long-term thermostability of POP fiber.

5. Elimination of causes leading to storage yellowness (gas fading) in white and pastel-colored POP fibers.

Polypropylene with a mixture of phosphitic stabilizers can be prepared by granulation on conventional single-thread and twin-screw extruders.

The examples below document the advantages of using a synergistic mixture of phosphitic stabilizers. The examples document the synergistic effect of the components of the mixtures and their advantages over the stabilization system based on low molecular weight sterically hindered phenol and sulfur costabilizer used today. The examples describe a process for the preparation of granules and a process for the preparation of polypropylene fibers. The properties of granules and fibers are given in a separate table, including a commentary on individual determined quantities.

Example 1

99.05 parts by weight of polypropylene powder with an IT value = 9.8 g / 10 min and a sodium ion content of 160 ppm (determined by atomic absorption spectroscopy) are mixed with 0.1 part of 2,6-ditert-butyl-4-methylphenol in a low-speed mixer. 0.55 parts by weight of distearyl thiodipropionate, 0.2 parts of light stabilizer 2-hydroxy-4-n-octyloxybenzophenone and 0.1 part of calcium stearate. After stirring for 20 minutes, the mixture is subjected to plasticization by intensive kneading in a twin-screw kneader with opposite rotation of the screws at a temperature of 200 ° C. The molten polypropylene is extruded by a single-screw extruder and granulated at 230 ° C.

CS 267 179 Bleaches by extrusion into water. Polypropylene fibers are prepared from granulated polypropylene by spinning on a 35 mm single-screw extruder at temperatures of individual zones 310, 315, 315 and 315 ° C. A spinning head with a 33-hole nozzle with a hole diameter of 0.5 mm is used. The fiber is wound at a speed of 400 m / min. After elongation to a deformation degree of 3.3 at 110 ° C, a polypropylene fiber with a unit length weight of 6.4 dtex is obtained. The light stability of the fiber is determined (decrease in fiber strength after 920 hours of irradiation in the Xenotest) and the tendency of the fiber to gas fading, which is assessed visually after one month of storage of the fiber wound on a spool without access to light. The characteristics of the polypropylene granulate and the fiber are given in the table.

Example 2

By the procedure as in Example 1, a granular polypropylene and a polypropylene fiber containing 99 ', 5 wt. % of polypropylene powder with IT value = 9.8 g / 10 min and Na content ⁺ 160 ppm, 0.15 wt. % distearylpentaerythritol diphosphite, 0.25 wt. % of light stabilizer 2-hydroxy-4-n-octyloxybenzophenone and 0.1 part of calcium stearate.

The characteristics of the polypropylene granulate and fibers are given in the table.

Example 3

By the procedure as in Example 1, a granular polypropylene and a polypropylene fiber containing 99.5 wt. % of PP powder with IT value = 9.8 g / 10 min and Na content ⁺ 160 ppm, 0.15 wt. % tris (1-phenylethylphenyl) phosphite, 0.25 wt. % of a light stabilizer of 2-hydroxy-4-n-octyloxy benzophenone and 0.1 part of calcium stearate. The characteristics of the polypropylene granulate and fibers are given in the table.

Example 4

By the procedure as in Example 1, a granular polypropylene and a polypropylene fiber containing 99.475 wt. % of PP powder with IT value = 9.8 g / 10 min and Na content 160 ppm, 0.075 wt. % distearylpentaerythritol diphosphite, 0.1 wt.% tris (1-phenylethylphenyl) phosphite, 0.25 wt.% 2-hydroxy-4-n-octyloxybenzophenone light stabilizer and 0.1 wt. % calcium stearate. The characteristics of the polypropylene granulate and fibers are given in the table.

Example 5 '

By the procedure as in Example 1, a granular polypropylene and a polypropylene fiber containing 99.470 wt. % polypropylene powder, 0.1 wt. % distearylpentaerythritol diphosphite, 0.25 wt. % tris (1-phenylethylphenyl) phosphite, 0.13 wt. % of a light stabilizer of the group of sterically hindered amines of the piperidine type under the trade name Chimessorb 944 and 0.05 wt.% of calcium stearate. The characteristics of the polypropylene granulate and fibers are given in the table.

Prí, klad6

Proceeding as in Example 1, the prepared granule polypropylene and polypropylene containing ^ 9.22 parts of polypropylene powder having a IT = 9.8 g / 10 min and containing 160 ppm of Na ^+, 0.25 wt. % bis (2,4-ditert-butylphenyl) pentaerythritol diphosphite, 0.3 wt. % tris (1-phenylethylphenyl) phosphite, 0.13 wt. % of a light stabilizer with the trade name Chimassorb 944 and 0.1 wt. % calcium stearate. The characteristics of the polypropylene granulate and the fibers ¹ are given in the table.

CS 267 179 Bl

Table 1

Properties of polypropylene granules and fibers prepared according to Examples no. 1 ač. 6.

Example no. IT g / 10 min ID Yellowness. % IP days P 920% Gas fading 1 10.1 1.82 17.8 8 67 slightly yellowish fiber 2 11.4 2, 17 5.4 6 57 without color change 3 10.7 1.85 8.6 5 82 very faint kidney observable yellowing 4 9.8 1.47 2.17 12 55 without color change 5 9.5 1.42 2.21 61 17 without color change 6 9.3 1.36 2.03 112 13 without color change

IT .... melt flow index g / 10 min, evaluated according to ČSN 64 0861

ID .... degradability index, evaluated according to ČSN 64 3050

Yellowness .... evaluated by trichromatic colorimeter, given as Yellow index in%

IP .... induction period at 150 ° C evaluated as the number of days to damage the sample in the form of a plate

P920 ···· decrease in fiber strength after 920 hours of irradiation in Xenotest, expressed in% of flood

Gas fading .... color effect on the fiber after 1 month of storage without access to light.

Claims (2)

Synergistic mixture of substances for stabilizing isotactic polypropylene, characterized in that it comprises dialkyl pentaerythritol diphosphite (I) and arylalkylphenyl phosphite (II), which are represented in a weight ratio of I: II - 1: 1 to 1: 4, preferably 1: 1.5 to 1 : 3, wherein the concentration (I) is 0.01 to 0.5 wt. % preferably 0.05 to 0.3 wt. % and the concentration (II) is 0.01 to 0.5 wt. % preferably 0.05 to 0.3 wt. %, based on stabilized polypropylene. 2. A synergistic mixture of substances according to claim 1, characterized in that the dialkylpentaerythritol diphosphite is distearylpentearitrile diphosphite and bhis (2,4-ditert-butylphenyl) pentaerythritol diphosphite and the arylalkyl phosphite are tris (1-phenylethylphenyl) phosphite.