Use of polyalcohols as polymer stabilizers

Details Use of polyalcohols as polymer stabilizers Use of polyalcohols as polymer stabilizers

1999-08-04

2001-11-06

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S310000, C524S732000, C525S253000, C526S200000, C526S202000

Reexamination Certificate

active

06313203

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
The present application is the national stage under 35 U.S.C. 371 of PCT/NL97/00709, filed Dec. 18, 1997.
The present invention relates to the use of polyalcohols for stabilising polymers, in particular vinyl chloride polymer and to polymers stabilised with polyalcohols.
The manufacture of plastic articles from organic thermoplastic polymers requires high temperatures (160° C. and higher), which leads to partial degradation of the polymer and hence to lower mechanical performance and discoloring of the product. The problem is especially serious for vinyl halide polymers such as PVC. Stabilisers and co-stabilisers are commonly used for preventing such thermo-oxidative degradation of polymers. Such stabilisers also protect finished polymer-based articles against degradation processes resulting from the action of heat, oxygen and/or (UV) light. Suitable stabilisers should not only prevent degradation of the polymer, but must also be compatible with the various other compounds of the polymer blend, avoiding the release of volatile or other components as a result of dehomogenising, which components may limit the utility of the polymer or may be detrimental to health.
Until now the so-called primary PVC stabilisers have often been based on heavy metal containing compounds, such as cadmium, barium, tin and lead compounds. These primary stabilisers are capable of irreversibly binding hydrogen chloride. More recently inorganic stabilisers based on e.g calcium, zinc, aluminium and magnesium layered structures have been developed. However, their performance is still insufficient to fully replace the heavy metal stabilisers. Further stabilisation is achieved by means of metal-free secondary stabilisers such as epoxy compounds, organic phosphites, antioxidants and light stabilisers. It has been known that hydrogen chloride, but also certain metal chlorides such as zinc chloride, catalyst the degradation of PVC. This unfavourable effect of metal chlorides may be reduced by a reaction with metal compounds such as calcium stearate or e.g. by complexing with polyalcohols and/or organic phosphites or &bgr;-diketo compounds. Polyalcohols, such as sorbitol, mannitol, lactitol, (di)pentaerythritol and tris(2-hydroxyethyl) isocyanurate (THEIC) have been proposed as (co)stabilisers for organic polymers.
Various patents describe the use of polyalcohols as stabilises for PVC. Examples of these are DE-A-2728865 which describes the use of mannitol, sorbitol or xylitol, together with calcium and zinc stearates and stearoylbenzoylmethane for stabilising PVC. WO 93/07208 discloses a PVC stabiliser system formed from zinc oxide and penta-erythritol. The use of maltitol and lactitol as stabilisers is described in EP-A-677549. Long-chain fatty acid partial esters of polyols such as polyglucose or sorbitol have been proposed as PVC stabilisers in DE-A-3536936 and DE-A-3643968, respectively. SU patent 863602 teaches the use of xylitan for improving the thermal and mechanical stability of butadiene/styrene latex and similar latices.
Known stabilisers such as sorbitol, mannitol and xylitol show disadvantages in that, although they give a good heat stability, they have a negative effect on the discolouring of the polymer during processing. The more effective ones, such as THEIC, are rather expensive.
It has been found now that thermoplastic polymers, as vinyl chloride polymers, can be effectively stabilised by the addition of certain natural cyclic polyalcohols. These cyclic polyalcohols increase the heat-stability of the polymers and at the same time do not substantially contribute to discolouration. The cyclic polyalcohols are especially non-toxic, food-compatible carbohydrates. Suitable carbohydrates include non-reducing oligo- and poly-saccharides, di- and oligo-saccharides the reducing unit of which has been reduced, acid-catalysed dehydration products of sugar alcohols. Non-reducing polysaccharides preferably have chain lengths of less than 100 monosaccharide units. Examples of cyclic polyalcohols are polyfructoses such as inulin, and levan, and the cyclic mono-dehydration products of sugar alcohols including xylitol, arabinitol, sorbitol (glucitol), galactitol (dulcitol), mannitol, iditol, and higher analogues. The mono-dehydrated products of the hexitols are typically 2-(1,2-dihydroxyethyl)-3,4-dihydroxy-oxolanes or (less commonly) the isomeric 2,5-bis(hydroxymethyl)-3,4-dihydroxy-oxolanes or 2-hydroxymethyl-3,4,5-trihydroxy-oxanes and of the pentitols they are usually 2-hydroxymethyl-3,4-dihydroxy-oxolanes. The anhydrohexitols are preferred. The mono-dehydration products of xylitol, sorbitol, and galactitol are also known as xylitan, sorbitan and galactitan, respectively. Where reference is made hereafter to anhydro-polyols or sorbitan, these terms also include the anhydro-derivatives of the other sugar alcohols, especially galactitan. Mixtures of anhydropolyols can also be used advantageously, as such components often have complementing stabilising effects.
Preferably at last one of the components is an anhydrohexitol. Examples of useful mixtures are sorbitan/xylitan sorbitan/anhydrolactitol, mannitan/galactitan, sorbitan/inulin, and in particular a mixture of sorbitan and galactitan, e.g. in ratios between 1:3 and 3:1.
The cyclic, non-reducing carbohydrates such as inulin and sorbitan can be used in polymer compounds in a manner known per se. The stabilisers can be mixed with other additives, such as impact modifiers for rigid formulations (for example chlorinated polyethylene or butadiene/styrene/(acrylonitrile) co or ter-polymers), plasticisers for flexible formulations (for example phthalic esters such as dibutyl phthalate or dioctyl phthalate, aliphatic monobasic or dibasic esters such as butyl oleate, epoxidised soybean oil, dioctyl adipate), fillers, pigments, flow modifiers (for example acrylates), lubricants (for example calcium stearate, zinc stearate, fatty esters and amides), flame retardants (for example aluminium hydroxide, antimony trioxide), phosphites (for example triaryl phosphites or aryl-alkyl phosphites), antioxidants (for example hindered phenols), HALS (hindered amine light stabiliser) compounds, UV absorbers (for example benzophenones such as 2-hydroxy-4-methoxybenzophenone, benzotriazoles, salicylates), keto esters and ketones such as N-phenyl-3-acetyl-2,4-pyrrolidine-2,4-dione; other stabilisers such as &bgr;-diketones and &bgr;-keto esters, &bgr;-aminocrotonates including dihydropyridine-3, 5-dicarboxylic esters, uracils, other polyol co-stabilisers such as pentaerythritol, tris-(hydroxyethyl isocyanurate), mannitol and the like may also be used at reduced levels. Examples of suitable formulations are given as compounds A, B and C below. The formulations are then processed into a shaped article by means of calendering, rotational moulding, spread coating, slush moulding, extrusion, injection moulding, blow-moulding or other conventional technique.
Preferentially, the polyol stabilisers are used in combination with a calcium salt such as calcium stearate and/or zinc compounds, such as zinc stearate or zinc oxide. Inulin and the anhydropolyols are preferably used at a level of 0.001-5%, especially 0.01-2%, most preferably 0.05-1% with respect to the thermoplastic polymer. Another class of (co)stabilisers to be used advantageously in combination with the present polyols are the anionic clays, such as alkali metal alumosilicates and other zeolyte-type compounds, and layered multimetal salts commonly referred to as hydrotalcites. The hydrotalcites are considered as an anionic clay with an overall chemical composition of: M
2+
x
M
3+
y
(OH)
2x+3y−2
CO
3
, in which M
2+
is a bivalent cation like Mg, Zn, Ni etc. and M
3+
is a trivalent cation, in particular Al. The carbonate group can be exchanged by other anions or anionic complexes such as hydroxide, nitrate, sulphate, iodide, bromide, chloride, fluoride, oxalate and other (di)carboxylates, oxide, perchlorate and silicate. Typical examples are Al
2
Mg
6
(OH)
16

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