CS269396B1 - A method of stabilizing a polyolefin blend with a phenolic antioxidant with sulfur costabilizers - Google Patents

Abstract

The solution relates to the stabilization of polyolefins against oxidation of a mixture of a phenolic antioxidant with sulfur costabilizers. The essence of the solution is a method of stabilizing polyolefins against oxidation of a mixture of a phenolic antioxidant and a sulfur costabilizer, consisting in using a mixture formed by an alkyl-substituted 4,4-isopropylidenebisphenol of the general formula I, where R1 is methyl, tert-butyl and R2 is a hydrogen atom, methyl, tert-butyl, and a sulfur stabilizer selected from the group consisting of dialkyl sulfide, dialkyl disulfide and dialkyl-3,3-thiodipropionate, where alkyl is θηΗ2η+1 8 n ~ =8, 10, 12, 14, 16, 18, wherein the concentration of bisphenol of formula I is 0.025 to 1.5 wt. % and the sulfur costabilizer is 0.05 to 2 wt. % calculated on the weight of the polyolefin.

Description

The invention relates to the stabilization of polyolefins against oxidation by mixtures of a phenolic antioxidant with sulfur co-stabilizers.

Polyolefins must be protected from external influences such as atmospheric oxygen, heat, radiation or mechanical stress. The choice of stabilizers depends on the extent of their practical application. Stabilizers protecting polyolefins from autoxidation belong, by their nature, either to the so-called preventive antioxidants that deactivate hydroperoxides, or to compounds that interrupt the chain mechanism of oxidation. The use of a combination of these two mechanisms often leads to an increase in the overall stabilizing effect by applying a heterosynergistic effect.

Due to the high temperatures used in polyolefin processing and the aggressive environments to which polymer products are exposed in applications, antioxidants need to be as volatile as possible and well-compatible with the polymer. Phenolic antioxidants with a suitable molecular structure meet these conditions.

Variously alkylated 4,4'-isopropylidenebisphenols have been studied for the stabilization of hydrocarbon substrates (Pospíšil □., Kotulák L., Kahovec Eur. Polym. 3. 6, 841 (1970)). In the patent literature, some of them have been proposed separately for the stabilization of polyethylene (Brit., patent no. 793 430), transparent polyolefins (US pat. no. 2 706 189), rubber and petroleum products (US pat. no. 2 745 726 and US pat. no. 2 877 209). Phenolic antioxidants are commonly used in mixtures, for example, with sulfur stabilizers. The stabilization of hydrocarbon substrates using 4,4'-isopropylidenebisphenols in a mixture with a sulfur co-stabilizer and other additives is known from the patent literature. For example, a three-component stabilizing mixture consisting of (a) 4,4-isopropylidenebisphenols, (b) dialkyl sulfides, dialkyl disulfides, or dialkyl thiodipropionates, and (c) epoxides or organic phosphites has been proposed for the stabilization of EPDM rubbers (U.S. Patent No. 3,658,743). A mixture of these phenols with dialkyl thiodipropionate has also been proposed for the stabilization of polyolefins (U.S. Patent No. 67,19171).

Effective non-volatile phenolic antioxidants include variously sterically hindered alkyl-substituted 4,4'-isopropylidenebisphenols, which were prepared according to Czechoslovak patents No. 129,886 and 153,757 (Kahovec 3., Pospíšil 3., Collect. Czech. Chem. Commun. 33, 1709 (1968)).

We have now found that the effectiveness of these phenolic antioxidants in stabilizing polyolefins can be substantially increased in admixture with the sulfur co-stabilizers of the present invention.

The subject of the invention is a method of stabilizing polyolefins against oxidation with a mixture of a phenolic antioxidant and a sulfur co-stabilizer, the essence of which consists in using a mixture formed by alkyl-substituted 4,4 ^- isopropylidenebisphenol of general formula I.

2 k<is R is methyl, tert, butyl and R is a hydrogen atom, methyl, tert, butyl, and a sulfur stabilizer selected from the group consisting of dialkyl sulfide, dialkyl disulfide and dialkyl-3,3-thiodipropionate, where alkyl is ^c _n ^H 2n+1 ^{and n = 8} < i ^{1 2} » 14, 16 » 18, wherein the concentration of the bisphenol of formula I is 0.025 to 1.5 wt.%, and the sulfur costabilizer 0.05 to 2 wt.%, calculated on the weight of the polyolefins.

Polyolefins stabilized with this mixture were heated in an oxygen atmosphere to the processing temperature (high-density polyethylene = HOPE - to 150 °C, polypropylene = PP - to 180 °C), while the course of oxygen consumption by the sample was monitored. The stability of the polyolefin was assessed according to the length of the initial interval in which there is no oxygen consumption, the so-called induction period. To compare the effectiveness of the proposed stabilizing mixtures, an effective synergistic mixture of 2,6-ditert. butyl-4-methylphenol (0.005 mol/kg polymer, i.e. 0.11 wt.%) and dioctadecyl-3,3-thiodipropionate (0.0075 mol/kg polymer, i.e. 0.49 wt.%) was taken as a standard. Stability A _pe j expresses the ratio of the length

CS 269396 Bl induction periods of the measured sample and standard.

It has been shown that the addition of dialkyl disulfides and dialkyl-3,3-thixo-propoxonates to the variously sterically shielded alkyl derivatives of 4,4'-isopropylidenebisphenol always leads to a substantial (synergistic) increase in the stabilizing efficiency of bisphenols in both PP and HOPE. When dialkyl sulfides were used, this synergistic increase was not evident in both highly sterically shielded 2,6-ditert.butyl and 2,6,2',6'-tetratert.butyl, 4'-isopropylxenedebisphenols, while the synergistic effect was greatest in derivatives containing only one tert.butyl group in the ortho position to the hydroxyl group or two methylene groups in both ortho positions or a combination of methyl and tert.butyl groups (these phenols belong to the partially shielded, so-called cryptophenols).

The addition of a sulphide hydroperoxide decomposer to variously sterically shielded 4,4'-isopropylidenebisphenols therefore always leads to an increase in their stabilization efficiency, which is higher, usually significantly, than the efficiency of the commonly used mixture of 2,6-ditert.butyl-4-methylphenol with dioctadecyl-3,3-thiodxpropionate. In the case where the sulfur costalizer is internally activated, for example, by a carbonyl group in the -position to the sulfur atom (dioctadecyl,3,3-thiodoxypyroxonate) or by a bond between sulfur atoms (disulfides), the most effective structure of the 4,4'-isopropylidenebisphenolic antioxidant is given by the substitution of the phenolic nuclei by a combination of methyl and tert-butyl groups in the ortho positions of each hydroxyl group. The unactivated sulfur costalizer (dialkyl sulfide) forms the most effective mixtures with less sterically hindered 4,4'-isopropylidenebisphenols, resulting in a structure in which only one ortho position of each hydroxyl group is substituted, namely by a tert-butyl group.

The invention is further explained by means of examples and a table.

Example 1

Polypropylene containing 2-tert.-butyl-4,4'-isopropylidenebisphenol as a phenolic antioxidant (0.0025 mol/kg PP, i.e. 0.07% by weight) and polypropylene (PP) containing the same amount of the above-mentioned phenolic antioxidant in a mixture with dioctadecyl-3,3-thiodipropionate (0.0075 mol/kg PP, i.e. 0.49% by weight) were heated in an oxygen atmosphere to 180 °C. From the measurement of oxygen consumption, the value A _pe y for stabilization of PP by phenol alone was calculated to be A _pe j = 0.61 and for its mixture with dioctadecyl,3,3-thiodipropionate = 2.56, ' re 1

Example 2

For polypropylene (PP) stabilized with 2,2'-ditert.butyl-4,4'-isopropylidenebisphenol (0.0025 mol/kg PP, i.e. 0.08 wt. %) the value of A _re ^ = 0.86 was found at 180 °C. When PP was sterilized with a mixture of this phenol with didodecyl sulfide (0.075 mol/kg PP, i.e. 0.28 wt. %) the value of A _re j reached 3.30.

Example 3

For polypropylene (PP) stabilized with 2,2'-dxmethyl-6,6'- tert. butyl-4,4'-isopropylidenebisphenol (0.0025 mol/kg PP, i.e. 0.09 wt. %) at 180 °C, the value of A _rei = 0.74. When PP was stabilized with a mixture of this phenol with dioctyl disulfide (0.0075 mol/kg PP, i.e. 0.22 wt. %), the value of A _rel reached 3.64.

Example 4

For high-density polyethylene (HDPE) stabilized with 2,6-ditert.butyl-4,4'-xisopropylidenebisphenol (0.0025 mol/kg HOPE, i.e. 0.08 wt. %) A _pe ^ value of 0.79 was found at 150 °C. When HDPE was stabilized with a mixture of this phenol with didecyl-3,3-thiopropionate (0.0075 mol/kg HOPE, i.e. 0.17 wt. %) A _pe j reached a value of 2.15.

Example 5

For high-density polyethylene (HDPE) stabilized with 2,2'-dimethyl-4,4'-isopropylidenebisphenol (0.0025 mol/kg HDPE, i.e. 0.06 wt. %) at 150 °C, the value of ^A r _e i ~ 0/56 was found. When stabilizing HDPE with a mixture of this phenol with dihexadecyl disulfide

CS 269396 B1 (0.0075 mol/kg HOPE, i.e. 0.39 wt.%) achieved an A _re j value of 2.42.

Table Examples of stabilization efficiency of proposed stabilization systems in polypropylene.

Stabilization system ^{and And} the 2-tert-butyl-4,4'-isopropylidenebisphenol 0.61 + dioctadecyl-3,3'-thiodipropionate 2.56 + dioctadecyl disulfide 3.32 + dioctadecylsulfide 1.91 2,2'-di-tert-butyl-4,4'-isopropylidenebisphenol 0.86 + dioctadecy1-3,3'-thiodiprop ionate 3.78 + dioctadecyl disulfide 4.15 + dioctadecylsulfide 4.34 2, 2'-Dimethyl-4,4 ^Z -isopropylidene bisphenol 0.51 ^points + dioctadecyl-3,3'-thiodipropionate 3.47 + dioctadecyl disulfide 3.58 + dioctadecylsulfide 2.23 2,6-di-tert-butyl-4,4'-isopropylidenebisphenol 0.78 ^°C + dioctadecyl1-3,3'-thiodipropionate 2.20 + dioctadecyl disulfide 3.47 + dioctadecylsulfide 1.66 2,2'-dimethyl-6,6'-di-tert-butyl-4,4'-isopropylidenebisphenol 0.74 + dioctadecyl1-3,3'-thiodipropionate 4.16 + dioctadecyl disulfide 4.51 + dioctadecyl sulfide 3.04 2,2'-6,6'-tetratert-»butyl 1-4,4'-isopropyl idenbisphenol 0.67 + dioctadecyl1-3,3'-thiodipropionate 2.76 + dioctadecyl disulfide 3.46 + dioctadecylsulfide 1.59

^and Phenols were used at a concentration of 0.0025 mol/kg PP, sulfur co-stabilizers at a concentration of 0.0075 mol/kg PP.

^b A _rel in HDPE equal to 0.56, in combination with dihexadecyl sulfide A _rel = 2.42.

^C A , in HOPE equal to 0.79, in combination with didecyl-3,3-thiodipropionate A 2.15.

Claims (1)

SUBJECT OF THE INVENTION A method of stabilizing polyolefins against oxidation by a mixture of a phenolic antioxidant with sulfur co-stabilizers, characterized in that a mixture consisting of alkyl-substituted 4,4 ^- isopropylidenebisphenol of the general formula I is used. 1 2 where R is methyl, tert, butyl and R is a hydrogen atom, methyl, tert, butyl, and a sulfur costabilizer selected from the group consisting of dialkyl sulfide, dialkyl disulfide and dialky 1.-3,3-thiodipropionate, where alkyl is ^c _n H2n+l ^{8 n = 8/} whereby the concentration of bisphenols of formula I is 0.025 to 1.5 wt.%, and the sulfur costabilizer 0.05 to 2 wt.%, calculated on the weight of the polyolefin.