WO2012168261A1

WO2012168261A1 - Solid composition comprising a radical forming compound and a flame retardant

Info

Publication number: WO2012168261A1
Application number: PCT/EP2012/060631
Authority: WO
Inventors: Bart Fischer; Boen Ho O; Andreas Herman Hogt
Original assignee: Akzo Nobel Chemicals International BV
Current assignee: Nouryon Chemicals International BV
Priority date: 2011-06-09
Filing date: 2012-06-06
Publication date: 2012-12-13
Anticipated expiration: 2013-12-09

Abstract

Solid composition comprising a radical forming compound and a flame retardant and not comprising a polymer or polymeric resin other than a flame retardant, said flame retardant being present in an amount of at least 25 wt%, based on the weight of the total composition. The radical forming compound acts as dust suppressant for the flame retardant.

Description

SOLID COMPOSITION COMPRISING A RADICAL FORMING COMPOUND AND A FLAME RETARDANT

The present invention relates to a solid composition comprising a radical forming compound and a flame retardant, a process for preparing such a solid composition, and a process for preparing polystyrene using such a solid composition.

Foamed polystyrene materials that are used in the building, construction and transport industry must in general be fire resistant. To establish this, flame retardants - in particular halogenated flame retardants - are commonly used in the production of foamed polystyrene materials.

In US 6,340,713, for instance, particulate, expandable styrene polymers have been described which contain graphite particles for reducing the thermal conductivity of foams to be produced from these polymers. In addition, the polymers contain 0.6 to 5% by weight of a brominated flame retardant and 0.1 to 1 .0% by weight of an organic bromine compound as a flame retardant synergist, based on polymer, which compounds are applied as separate powders. Said compounds are added to the polymers to ensure that the graphite-containing foams prepared from the polymers pass the burning tests required for use in building and construction (B1 and B2 in accordance with DIN 4102). A problem with the use of flame retardants in the form of powders is that during the handling and dosing of these materials, especially in the case of halogenated flame retardants, much dust is generated, which is highly undesirable from both health and environmental perspective. In order to deal with the problem of dust formation of flame retardant powders that are used in the production of polystyrene, the flame retardant powders can be coated with a so-called dust suppressant. Suitable dust suppressants include for instance salts, fats, oils or polymeric structures that immobilize the dust by binding it to the powder.

A drawback of such known dust suppressants is, however, that they disturb the often delicate suspension stability in a suspension polymerization process for producing expandable polystyrene (EPS), or that they have adverse effects in the final polymer product.

Object of the present invention is to provide an improved dust suppressant system which does not disturb the delicate suspension stability in a suspension process for producing polystyrene, and which does not have adverse effects in the polystyrene to be produced.

Surprisingly, it has now been found that this can be established when use is made of a dust suppressant system comprising a solid composition that comprises a radical forming compound and a relatively high amount of a flame retardant; at least 25 wt%, based on the weight of the total composition.

The flame retardant might be of polymeric nature. An example of such a flame retardant is brominated polystyrene (co) polymer.

The solid composition is not a so-called masterbatch or polymerizable or curable composition. Therefore, the composition according to the invention does not contain a polymer or polymeric resin other than a flame retardant. In other words, the only polymer or polymeric resin present in the composition can be a polymeric flame retardant. If the composition does not contain a flame retardant of polymeric nature, the solid composition does not contain any polymer or polymeric resin.

Accordingly, the present invention provides a solid composition comprising a radical forming compound and a flame retardant and not comprising a polymer or polymeric resin other than a flame retardant, the flame retardant being present in an amount of at least 25 %wt, based on the weight of the total composition.

The radical forming compound is preferably an organic radical forming compound, also known as organic initiator. More preferably, the organic radical- forming compound is a C-C initiator or an organic peroxide.

The radical-forming compound preferably has a one hour half life time of more than 120°C, as measured by differential scanning calorimetry-thermal activity monitoring (DSC-TAM) of a 0.1 M dilute solution of the radical forming compound in monochlorobenzene, as is known in the art. Half-life data determined in this way are listed in the Akzo Nobel's brochure "Initiators for high polymers" with code 2161 , June 2006.

More preferably, the radical forming compound is also a suitable flame retardant synergist, because that would allow it to function as dust suppressant and at the same time improve the activity of the flame retardant.

Even more preferably, the radical forming compound is selected from the group consisting of dicumyl peroxide, di-(t-butylperoxyisopropyl)benzene, 2,3- dimethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane and poly(1 ,4- diisopropyl benzene). Most preferably, the radical forming compound is dicumyl peroxide.

Preferably, the flame retardant is present in an amount of at least 30 wt%, based on the weight of the total composition. More preferably, the flame retardant is present in an amount of at least 40 wt% based on the weight of the total composition. Most preferably, the flame retardant is present in the range of from 50-95 wt%, based on the weight of the total composition.

In the solid composition according to the present invention, the radical forming compound is suitably present in an amount of at least 5 wt%, based on the weight of the total composition. Preferably, the radical forming compound is present in an amount in the range of from 10-70 wt%, based on the weight of the total composition.

The flame retardant to be used in accordance with the present invention can be any flame retardant known in the art. Suitable examples of flame retardants include phosphor and/or nitrogen-containing compounds, like melamine and derivatives and halogenated flame retardants. Preferably, the flame retardant to be used is a halogenated flame retardant, more preferably a brominated flame retardant. The brominated flame retardant can suitably be selected from the group consisting of hexabromocyclododecane, pentabromobenzylbromide, tetrabromobisphenyl A bis(allylether), tetrabromobisphenyl A bis(2,3- dibromopropyl ether), dibromohexahydrophtalimide, N-methyl- dibromohexahydrophtalimide, N, 2-3-dibromopropyl-4,5- dibromohexahydrophtalimide, bis(2,3-dibromopropyl)tetrabromophtalate, tris(2,3-dibromoisopropyl)isocyanurate, tribromophenyl allyl ether, and brominated polystyrene (co) polymer.

Brominated polystyrene (co) polymers and their preparation are known and disclosed in, e.g., US 4,975,496.

Preferably, the brominated flame retardant is pentabromobenzylbromide, tetrabromobisphenyl A bis(allylether) or tetrabromobisphenyl A bis(2,3- dibromopropyl ether). Most preferably, the brominated flame retardant is tris(2,3-dibromoisopropyl)isocyanurate.

The solid composition according to the present invention will preferably be in the form of particulates. These particulates may have any suitable shape including well-defined shapes such as globular, oblate or prolate spheroids, rodlike, disc-like or less well defined granules. The granules may suitably have an average diameter in the range of from 100 μιτι - 5 cm, preferably in the range of from 300 μιτι - 3 cm, and more preferably in the range of 500 μιτι - 1 cm. The present invention also relates to a process for preparing the solid composition according to the present invention, comprising mixing at an elevated temperature the flame retardant in solid form with the radical forming compound in fluid form (e.g. as a melt or in suspension), and subsequently cooling down the temperature of the mixture so obtained to form the solid composition. In the solid composition so obtained the flame retardant is retained, and hence dust formation is attractively avoided. The radical forming compound can be mixed with the flame retardant powder in the desired ratio in any suitable mixing unit followed by particle shaping and sizing. Examples of suitable particle shaping equipments are pelleting and tabletting presses, extruders and roll compactors, optionally combined with moulding to the desired size. Examples of sizing techniques are milling, crushing, breaking and granulation. Alternatively, processes including dumping the solid composition in fluid state on a cold plate or belt, or spraying through a cold tower also allow making the solid composition without a sizing step. To reach the required elevated temperature the composition can be heated by any form of heating or as a result of ordinary heat dissipation during the mechanical action.

When use is made of brominated flame retardants, such as for instance hexabromocyclododecane, hydrogen bromide is often formed as a result of the thermal decomposition of the brominated flame retardant during the processing/foaming of polystyrene, which will adversely affect the physical properties of the foamed polymer product. In addition, the hydrogen bromide formed may cause corrosion of the metal equipment with which the hot blend comes into contact during the process. Therefore, in a preferred embodiment of the present invention the solid composition according to the present invention also contains a HBr scavenger, such as dibutylmaleate.

In addition, the composition may also contain additives including scavengers such as EDTA, adsorbents such as activated carbon, absorbents such as micro porous particulates, and pH buffers such as balanced mixtures of carboxylic acids and their counter salts, metal oxides or hydroxides, and the like.

Furthermore, the present invention relates to a process for preparing polystyrene wherein use is made of the solid composition according to present invention.

Preferably, the polystyrene is an expandable or expanded polystyrene. Suitable processes for preparing polystyrene wherein use can be made of the solid composition according to the present invention include suspension polymerization processes and extrusion processes that are known in the art. Beads of expandable polystyrene to be obtained with a suspension polymerization process will generally contain blowing agents such as aliphatic or cycloaliphatic hydrocarbons or halogenated hydrocarbons such as (iso- )butane, (iso-)pentane, hexane, heptane, cyclohexane, methyl chloride and dichlorodifluoronnethane. The concentration of blowing agent will normally range from 3 to 15 percent by weight based on the weight of polystyrene polymer. The present invention relates, however, also to polymerization processes for preparing polystyrene wherein no use is made of a blowing agent. The process for preparing the polystyrene is preferably a suspension polymerization process, more preferably a suspension polymerization process wherein use is made of a blowing agent. Suitable extrusion processes include those wherein polystyrene is molten and compounded with additives and blowing agent and foamed into sheets.

EXAMPLES

Example 1

A solid composition of 70 pbw hexabromocyclododecane (bromine content: 75%) and 30 pbw dicumyl peroxide (99.7% purity) in accordance with the present invention was made in a three step process. Agglomerates were made by mixing the solids using a Nauta mixer at 55°C and subsequently cooling down to room temperature. By compacting the agglomerates using a Herzog tablet press at 100kN, 4cm tablets were obtained. These tablets were crushed and treated by a friction sieve. The resulting material was characterized in terms of particle size, size distribution, and dust level. Particle size and size distribution were determined by passing the end product through an array of sieves with decreasing sieve holes and subsequent determining the weight fractions in the sieves. The dust levels were determined applying a standard Heubach Attrition test equipment (Heubach, 38685 Langelsheim, Germany), according to DIN 55992-1 . In a 15 minutes test run an air flow of 25 liter/min was chosen and the filter was replaced every 5 minutes. In Table 1 the properties of the end product are shown.

Table 1

Example 2 (Comparative Example)

For reasons of comparison, the amount of dust as expressed by the DIN 55992- 1 test was also determined for unformulated hexabromocyclododecane. The test result is shown in Table 2. Table 2

It will be clear from Tables 1 and 2 that the solid composition according to the present invention has superior dust properties in comparison to the pure flame retardant.

Example 3 (Comparative Example)

Polyvinyl acetate (PVA) is a known dust suppressant. The present Example however shows its negative effect on the suspension stability in polystyrene production. The dust suppressant system according to the present invention, which does not require PVA and still provides good dust suppression, does not negatively influence the suspension stability.

A 1 -litre stainless steel reactor equipped with a baffle, a three-bladed impeller, a pressure transducer, and a nitrogen purge, was used to test the suspension polymerization of styrene. A water/styrene ratio of 1 :1 was applied, 250 g styrene and 250 g water. The recipe further comprised tricalciumphosphate (0.5% on styrene), ammoniumpersulfate (0.001 %), benzoyl peroxide (Perkadox® L-W75; 0.38%) as first stage initiator, t-butyl peroxybenzoate (Trigonox® C; 0.08%) as 2^nd stage initiator, hexabromocyclododecane (0.67%), and dicumyl peroxide (Perkadox® BC; 0.22%). The mixture was stirred and heated to 90°C for 6 hrs. Polyvinylacetate (PVA, Mowiol® 26-88) was added (2%) as a 5% solution in water. After 4 hrs the mixture was further heated, after 5 hrs pentane was added (7%), and after 6.5 hrs the mixture had reached a temperature of 1 12°C and showed large lumps of polystyrene indicating that suspension failure had occurred. Repeating the same experiment without the addition of PVA did not result in the formation of large lumps of polystyrene. Hence, no suspension failure occurred.

Claims

1 . A solid composition comprising a radical forming compound and a flame retardant and not comprising a polymer or polymeric resin other than a flame retardant, the flame retardant being present in an amount of at least

25 wt%, based the weight of the total composition.

2. A solid composition according to claim 1 , wherein the flame retardant is present in an amount of at least 40 wt%, based on the weight of the total composition.

3. A solid composition according to claim 1 or 2, wherein the radical forming compound is present in an amount of at least 5 wt%, based on the weight of the total composition.

4. A solid composition according to any one of the preceding claims, wherein the flame retardant is a halogenated flame retardant.

5. A solid composition according to claim 4, wherein the flame retardant is a brominated flame retardant.

6. A solid composition according to claim 5, wherein the flame retardant is selected from the group consisting of hexabromocyclododecane, pentabromobenzylbromide, tetrabromobisphenyl A bis(allylether), tetrabromobisphenyl A bis(2,3-dibromopropyl ether), dibromohexahydrophtalimide, N-methyl-dibromohexahydrophtalimide, N, 2-3-dibromopropyl-4,5-dibromohexahydrophtalimide, bis(2,3- dibromopropyl)tetrabromophtalate, tris(2,3-dibromoisopropyl)isocyanurate, tribromophenyl allyl ether, and brominated polystyrene (co) polymer.

7. A solid composition according to any one of the preceding claims, wherein the radical forming compound is a C-C initiator or organic peroxide.

8. A solid composition according to any one of the preceding claims wherein the radical forming compound has a half life of one hour at more than 120°C as measured in 0.1 M monochlorobenzene solution.

9. A solid composition according to any one of claims 7 or 8 claims, wherein the radical forming compound is selected from the group consisting of dicumyl peroxide, di-(t-butylperoxyisopropyl)benzene, 2,3-dimethyl-2,3- diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane and poly(1 ,4-diisopropyl benzene).

10. A solid composition according to claim 9 wherein the radical forming compound is dicumyl peroxide.

1 1 . A solid composition according to any one of the preceding claims in the form of particulates.

12. A process for preparing the solid composition according to any one of the preceding claims, comprising mixing at an elevated temperature the flame retardant in solid form with the radical forming compound in fluid form, and subsequently cooling down the temperature of the mixture so obtained to form the solid composition.

13. A process for preparing polystyrene wherein use is made of the solid composition according to any one of claims 1 -1 1 .

14. A process according to claim 13, wherein the polystyrene is an expandable or expanded polystyrene.

15. A process according to claim 13 or 14, wherein the process is a suspension polymerization process.