Process for making stabilized non-colored rubber

Details Process for making stabilized non-colored rubber Process for making stabilized non-colored rubber

1999-06-29

2001-01-16

Cain, Edward J. (Department: 1714)

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

Synthetic resins

Treating polymer containing material or treating a solid...

C528S491000, C528S499000, C523S328000, C523S332000, C523S335000

Reexamination Certificate

active

06174991

ABSTRACT:

TECHNICAL FIELD
This invention relates to a process for making stabilised, non-coloured polymer products of anionic polymerisation. In particular, this invention relates to a process for making stabilised, non-coloured rubber by using epoxidised soya bean oil and neodecanoic acid during the polymer recovery process.
BACKGROUND ART
Polymerisation processes for the manufacture of polymer products of anionic polymerisation, such as lithium butadiene rubber, styrene-butadiene rubber and butadiene-styrene-isoprene rubber are well known. It is also well known that stabilisers, such as antioxidants, may be added to the polymer cement following polymerisation to reduce the natural degradation and resulting discolouration of the polymer. The desire to sustain colourless product is particularly important to butadiene rubber or styrene-butadiene rubber in HIPS (high impact polystyrene) applications. A commonly used antioxidant system in the manufacture of lithium-butadiene rubber, for example, is tris(nonylphenol) phosphite (TNPP) in combination with phenolic antioxidants, such as Irganox 1076. However, as part of efforts to improve the manufacturing processes to reduce or eliminate health hazardous materials, alternative antioxidant systems are being sought and tested. It is known that Irganox 1520, a hindered phenol, provides desirable properties in the polymer and reduces degradation to a degree comparable to current antioxidant systems. However, it has been recognized in the past (U.S. Pat. No. 3,658,743) that hindered phenols used as antioxidant may cause discolouration. Byproducts of low purity Irganox 1520 can form colour bodies during the recovery process, which can result in a coloured rubber product. Polymer treated and recovered using low purity grades of Irganox 1520 alone does not provide a product which remains colourless after thermal aging (herein referred to as “sustained colourlessness”).
Iganox 1520 is available in three grades, which differ in degree of purity. Energy consuming distillation is used to purify or reduce impurities in the crude Irganox 1520 product to remove higher and lower boiling byproducts. A product with a relatively lower proportion of byproducts (such as odour causing mercaptans) was available as Irganox 1520 L grade. A product with relatively higher proportion of byproducts has been offered as Irganox 1520 D and may be further purified to produce Irganox 1520 L. The Irganox 1520 L grade is additionally reacted with epoxidised soya bean oil for further removal of byproducts such as mercaptans to reduce odour. This product is available as Irganox 1520 LR grade.
DISCLOSURE OF THE INVENTION
We have found an improved polymer recovery process which will produce a sustained colourless polymer product of anionic polymerisation, such as polybutadiene polymer, solution butadiene-styrene copolymer, or butadiene-styrene-isoprene copolymer. The recovered polymer has the preferred physical characteristics of known polymers, is stabilised against degradation including discolouration, in accordance with industry and commercially preferred standards.
In the preferred process for the recovery of a polymer from a cement produced in a lithium alkyl initiated polymerisation process, the polymer cement is shortstopped, washed, stabilised, coagulated, stripped and dried. The recovery comprises adding a short stop to the polymer in the cement, washing catalyst residue from the polymer with water, adding an antioxidant Irganox 1520 to the cement to stabilise the polymer, adding epoxidised soya bean oil to the polymer to stabilise the polymer against colour degradation, coagulating, stripping and drying the polymer. The pH of the cement is regulated in the range of from about 3 to about 7, or preferably from about 6 to about 7, during the catalyst wash and the coagulation steps of the recovery process. In an alternative process, instead of adding the epoxidised soya bean oil to the polymer cement, the epoxidised soy bean oil may be reacted with the Irganox 1520 before adding to the polymer cement.
A product of an anionic polymerisation process is also provided. The polymer is removed from the product of the polymerisation process by a recovery process with a short stop addition step, a catalyst wash step, an antioxidant addition step, a coagulation and a stripping step. The pH is controlled in the range of from about 3 to about 7 and preferably from about 6 to about 7 during the catalyst wash step and the coagulation step. The shortstop step is the addition of an organic acid of formula R—COOH, where R is an organic moiety, and preferably a C
3
-C
30
, more preferably a C
3
-C
20
and most preferably a C
3
-C
15
. The preferred short stop is neodecanoic acid. The anti-oxidant is Irganox 1520 and epoxidised soya bean oil, the Irganox 1520 containing byproducts that have not been removed and that without the addition of epoxidised soya bean oil would produce a coloured polymer product. The Irganox 1520 is available in different grades of purity. It should be noted that impurities are removed by the manufacturer, and “removal” or “removed” in relation to the impurities in Irganox 1520 herein is intended to mean reduced levels of by-products or impurities and not necessarily a product from which all by-products or impurities have been removed.
The polymer recovered according to the recovery process of the invention is substantially colourless and maintains a colourless state after thermal aging for an acceptable polymer shelf life. A sustained colourless product in the context of the invention has stability and shelf life including colourlessness after thermal aging comparable to the colourlessness achieved for polybutadiene polymer recovered using the currently preferred Irganox 1076 (hindered phenolic stabiliser of Ciba Geigy) and TNPP tris(nonylphenyl) phosphite system. The process will be described with reference to the lithium butadiene polymerisation process and the solution styrene/butadiene polymerisation process, although it is not intended to restrict the invention to recovery of polymer from these processes.
The polymer cement produced by anionic polymerisation, such as in the lithium butadiene polymerisation process or in the solution styrene-butadiene polymerisation process contains initially a “living” polymer. A short stop is added to the living polymer cement to stop the polymerisation process.
The preferred short stop is neodecanoic acid to an amount of greater than or equal to the molar amount of lithium initiator used for the polymerisation. The molar ratio of neodecanoic acid to lithium is preferably 1.5.
A catalyst washing and neutralisation step is conducted to wash the lithium residues from the polymer. This step is performed by (1) the addition of 5-100 wt. % (relative to the cement) of demineralised water, (2) intensive mixing and (3) the addition of a water soluble acid, of which non-limiting examples are H
2
SO
4
, HCl or, preferably, citric acid. The amount of acid added is selected according to the pH in order to keep the catalyst washing step in a slightly acidic to neutral environment at a pH in the range of from about 3 to about 7 and preferably from about 6 to about 7. The molar amount of HCl is 1-1.5 times the molar amount of lithium initiator being used for the polymerisation, the molar amount of H
2
SO
4
is 0.5-0.75 times the molar amount of lithium initiator, the molar amount of citric acid is 0.3-0.5 times the molar amount of lithium initiator. In step (1), alternatively, the addition of demineralised water may be in the range of 5-50 wt. %, or 5-25 wt. % (relative to the cement).
The antioxidant addition consists of adding any Irganox 1520 grade and epoxidised soya bean oil to the polymer:
Irganox 1520 D or commercially available Irganox 1520 L plus, for example, about 200 wt. % epoxidised soya bean oil (relative to the anti-oxidant) may be added to the polymer cement. The epoxidised soya bean oil may be added as a blend together with the Irganox 1520 D or Irganox 1520 L or separately. The amount of epoxidised soya bean oil required wi

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