FOAM PRODUCTION

Abstract: The manufacture of foamed thermoplastics material making use of polyethersulphone, polysulphone, polyetherimide or polystyrene mixed with a partial solvent such as acetone, methylethylkeytone, or chloroform and a cross-linking agent which is a sulphonylhydrazide compound. The preferred sulphonylhydrazide compound is thiobisbenzenesulphonylhydrazide. The material produced has a high resistance to slumping when burnt.

Description: DESCRIPTION TITLE: FOAM PRODUCTION - TECHNICAL FIELD The present invention concerns the production o foamed materials, in particular foamed thermoplastics materials. BACKGROUND ART Proposals have been made for the production of foamed thermoplastics materials, for example polyethersulphone and polysulphone by which the thermoplastics material in powder or granular form is mixed with a solvent or partial solvent, for example acetone; the mixture then being compressed to form a crepe. After making a crepe in this way it may be foamed in a heated press or mould to produce the foamed thermoplastics material or article. Foamed material produced in this way, and structures made therefrom, have a number of significant advantages over foamed structures formed from other materials. One disadvantage that they have however is that when they are subjected to intense heat, e.g. in radiant panel flame spread tests at 5W/cm a 7 the material melts and slumps; that is to say the material collapses with the possibility of molten, and possibly flaming,material falling from the parent body. This is a significant disadvantage of the known materials and precludes their use in an area where the public are admitted and safety standards are high such as within a commerical aircraft. To increase the resistance of the material to slumping attempts have been made to face the panels with coated glass fibres and such facing . improves the slumping of the material at elevated temperatures. However experiments show that the improvement is of limited application as the foamed thermoplastics polymer material still melts. The fabric coating however retains the burning or melted foam panel in position preventing its slumping. This arrangement is partially successful, however it can lead to problems if the coated fibre facing of the panels is ruptured, which rupture can occur through its mechanical failure caused for example by mechanical stress when subjected to impact - for example in a crash or even possibly delamination of the fibre facing at extremely high temperatures (for example above 800°C) that is to say at temperatures which can occur in a fire following a crash. In any event if the facing ruptures it is possible that molten thermoplastics material may escape therethrough which precludes the use of such an arrangement if safety standards are high. It is possible to have a limited increase in the resistance of a foamed polymer material to melting and burning by the introduction of certain know additives thereto (for example decabromobiphenylene oxide with antimony oxide). However most additives which improve the flamability characteristics is foamed polymer material lead, when the material is heated, to the increased production of toxic smokes (for example the above noted additive leads to the production of Bromine and Hydrogen Bromide vapours) when " the material finally burns. In the context in which articles of foamed plastics materials are often to be used - within the bodies of commercial aricraft - the prevention of toxic smoke is as of great importance as the need to prevent the foamed plastics material melting, burning and slumping. An object of this invention is to provide a foamed plastics polymer material which overcomes the above noted disadvantages and which, when heated, has a high resistance to melting, burning and slumping and produces as little toxic smoke as possible. DISCLOSURES OF THE INVENTION Accordingly one aspect of the invention provides a method of making a foamed thermoplastics * material comprising the steps of; mixing the thermoplastics material with a solvent or partial . solvent to reduce the glass transition temperature thereof, adding to the mixture a suitable cross-linking agent and then foaming the mixture by application • of heat thereto. With advantage the thermoplastics material is one of polyethersulphone, pplysulphone, polyetherimide and polystyrene. The cross-linking agent is preferably a sulphonylhydrazide compound - with advantage thiobisbenzenesulphonylhydrazide. Preferred amounts of polymer material, solvent, and cross-linking agent lie in the ranges of 100: 5 to 100: and 0.1 to 25 parts by weight respectively. Further aspects of the invention provide materials made in accordance with the above methods and articles made of such materials. The partial solvents which may be used differ from the different polymer materials. However, we have found that Keytones are particularly applicable specifically acetone and methylethylkeytone,- and that chloroform and, possibly tetrahydrofuran-may be used as a partial solvent. When preparing the mixture prior to foaming it is possible to add to it one or more of a number of different elastomers, fillers, processing aids or plasticisers in dependence upon the physical characteristic required of the final product. We have found that when making a foamed plastics OMPI material in accordance with the present .invention the material has a substantial resistance to slumping when heated and has no significant increase in toxic smoke production. It is believed that.the reason for this is that the cross-linking agent, the sulphonylhydrazide compound, partially links with the polymer material as foaming takes place. The sulphonylhydrazide compound is however left with some "potential" cross-linking ability which upon the application of higher temperatures (e.g. in a fire) to the foamed material is realised. At this time the foamed material rather than slumping forms a generally fibrous structure which chars but does not slump. It is believed that the sulphonylhydrazide compound decomposes when heated as follows: 2 H 2„N-NH SO2.-R S02--NH-NH2- (S- ,R.-..S)n + (S- /τ R_-SO2 n+4 N +6 ^ H,0 (A) (B) n 2 n 2 It is thought that the two byproducts A and/or B may be formed as an integral part of the thermoplastics polymer chain within the foamed plastics material providing the required cross-linking when the material, in the absence of the cross-linking agent would slump. The particular cross-linking agent that we prefer to use is thiobisbenzenesulphonylhydrazide which appears, from our experimental results, to begin to "partially" cross-link with the polymer materials used at a temperature in the range of 150 to 175°C and to achieve substantially complete cross-linking with that polymer material at a higher temperature - at or about 300°C. Table A illustrates some of the characteristics of polymer materials upon which experiments have been carried out using as the partial solvent acetone or an acetone chloroform mix giving for each material:- 1. Its normal glass transition temperature. 2. The possible range of temperatures. at which foaming can take place with the cross-linking agent included in the 5 mixture. 3. The temperature at which we prefer to foam the polymer material. 1. Glass Transition Temperature 0° 222 174 85- 105 215 Range of Foaming Temperatures (°C) 70 -280 70 - 280 60 - -200 70 - 280 I 3. Preferred Foaming I Temperatures (°C) 140 - 190 160 140 - 190 150 ion o The preparation parameters of three samples of foamed polymer materials embodying the invention will now be given. i AMOUNT (parts by weight) 1. Polymer : Polyethersulphone 100 Partial Solvent: Acetone 60 Cross-linking Thiobisbenzene- 1.5 agent : sulphonylhydrazide Time in mould (Seconds) : 90 Temperature in Mould (°C) : 200 2. Polymer : Polyethersulphone 100 Partial Solvent: Acetone (80)/ 85 Chloroform (5) Cross-linking Thiobisbenzene- 0.5 agent : sulphonylhydrazide Time in mould (Seconds) : 200 Temperature in Mould (°C) : 180 3. Polymer : Polyetherimide 100 Partial Solvent: Acetone 60 Cross-linking Thiobisbenzene agent sulphonylhydrazide 2.0 Time in mould (Seconds) 100 Temperature in Mould (°C) 170 From the results obtained it is suggested that the following operational parameters are usable:- Amount of polymer (by weight) 100 Amount of partial solvent (by weight) 5 to 100 Amount of cross-linking agents (by weight) 0.1 to 25. Time in mould 1 to 30 minutes Temperature in mould 70 to 280°C If desired it is possible to add to the mixture of polymer material, partial solvents and cross-linking agents other agents if desired. Examples of these are Smoke Suppressents:- Ferrocene, Iron Oxide, Alumina Trihydate, Molybdenum Oxide, Vanadium Oxide, a mixture of Iron powder and Copper Oxide, various Alkalynes and Alkalyne Earths, Magnesium Oxide and other known smoke suppressing compounds and mixtures. Elastomers:- Silicone Rubber, Polychloroprene, Nitrile Butadiene Rubber, Ethylene/Acrylic elastomers. Polyester elastomers. Fillers:- Glass or Carbon fibres, Molydbenum Disulphide, Metal particles and fibries, (powdered Bronze, Iron or Tin), Barium Ferrite, Al_0,3H 2 0, Vermiculite Silica, Silicates, Carbon, Calcium, Carbonates, Titanium White, China Clay, Charcoal Powder, Magnesium Carbonate, Mica powder. Talcum powder and the like. If_desired additives enhancing the propensity of the material to char rather than melt may be added, as may be known, suitable plasticisers. Articles may be formed of the material now proposed by injection moulding the polymer/partial solvent/cross-linking agent mixture into a heated mould of the desired shape. It is envisaged that in such an arrangement the liquid gel may be injected rapidly into a cavity in the mould: the release of pressure taking place in the mould allowing the gel to foam, fill the cavity and produce an article of the desirbed shape. An alternative which is envisaged is for the liquid gel material to be injected relatively slowly into a mould but retained at a pressure OMPI ^Zπ preventing it foaming whilst being injected. Such an arrangement could provide, for example, that the injector be fitted in the head of a piston movable away from the inital injection located and by which more gel is passed as the piston moves back. As soon as sufficient gel has been injected into the mould the piston would be rapidly removed to reduce the pressure in the mould allowing the material to foam and fill the mould completely. It enables the continuous extrusion of foamed polyethersulphone and like compositions, blends of polymer materials/solvent mixes with fillers and cross-linking agents (such as described above) which is compounded by passage through an extruder and die heated to a temperature above the foaming temperature of the polymer compound. The gel may be foamed directly from the extruder and die into a hollow tube (e.g. of glass or carbon fibre material) continuously formed on a mandrel surrounding the die. The present material may be utilised to procude a multi-layer structure in which the foamed material is snadwiched between two or more layers of glass or carbon fibre coated materials. In such an arrangement the material is foamed in situ, the surfaces of the fibre coated material having first been treated with a partial solvent such that upon the application of heat a strong bond is formed between the foaming material and the fibre coated -coating. Multi-layer structures may be formed of material embodying the invention by placing quantities of the liquid gel between two or more layers of glass fibres impregnated with a polymer material and coated with a solution of the polymer material, and then allowing foaming to take place. Alternatively it is possible to take one or more layers of foamed polymer material and hold them in contact with layers of fibres reinforced laminates and-heated with a solution of the polymer material (to reduce the glass transistion temperatures of the polymer materials immediately adjacent the interfaces) and then slowly heat the whole composite to a temperature at which joining of the interfaces takes place and then cooling the interfaces. The material produced in accordance with the present invention has good mechanical characteristics. For example a sample of the material foamed to a density of 90 Kg/M 3 is found to have a compressive strength of 500 Kpa. Again the propensity of the material to burn, if formed of a relativelty dense foam, is low. A sample foamed at 60 Kg/M 3 was found not to burn and to have an oxygen index (A.S.T.M.D.2863) of 45. A sample tested in accordance with the Butler Chimney test (A.S.T.M.D. 014) showed that 98% of the original weight of the material was retained. The vertical test procedure in accordance with V.L. 94 after conditioning at 48 hours (at 23°C and 50% relative humidity) disclosed a mean burn time (seconds) for first and second ignition of 0. After conditioning for 168 hours at 70°C the material still retained a V.O. rating. . Another advantage of the material produced in accordance with the present invention is the - . reduction in process time which has been achieved. It is possible when using material * of the present invention to reduce the process time from over 3 hours to 7 minutes. The overall production time of the foamed plastics material has been reduced from approximately 18 days to approximately 1 day. Clearly the addition of additives such as the elastomers, fillers and the like enables material to be obtained which have high flexibility and which are highly resistant to temperatures and flames. Again the material of the present invention enables composite structures to be formed in which a foamed section is bought into intimate contact with a solvent or adhesive coated surface layer to bond the layer of material to the foamed section. In addition to the relatively high density samples noted above it is possible with the present invention to produce extremely low density foams compared with the known methods. Foams with as low density as 8 Kg/M 3 have been produced. Again, the present invention can provide high density foams which form low density charred residues on contact with flame. The plastics materials herein described may therefore be advantageously used in fire sealing applications. Finally it is to be noted that the foams produced in accordance with the present invention have an excellent, smooth, surface finish.

Claims: CLAIMS 1. A method of making a foamed thermoplastics material comprising the steps of? mixing the thermoplastics material with a solvent or partial solvent to reduce the glass transition temperature thereof, adding to the mixture a suitable - cross-linking agent and then foaming the mixture by the application of heat thereto. 2. A method according to Claim 1, in which the thermoplastics material is one of polyethersulphone, polysulphone, polyetherimide and polystyrene and in which the cross-linking agent is a suphonylhydrazide compound. 3. A method according to Claim 2, wherein the cross-linking agent is thiobisbenzenesulphonylhydrazide. 4. A method according to anyone of Claims 1 to 3, wherein the partial solvent.is a keytone or chloroform. 5. A method according to Claim 3, wherein the mixture comprises, by weight: 100 parts of thermoplastics material: 5 to 100 parts of a solvent or partial solvent and 0.1 to 25 parts of a cross-linking agent. 6. A method according to Claim 4, wherein the mixture comprises, by weight, 100 parts of polyethersulphone, 60 parts of acetone, and 1.5 parts of thiobisbenzenesulphonylhydrazide. 7. The foamed theremoplastics material produced by preparing a mixture in accordance with any of one of Claims 1 to 4, wherein the mixture is heated whilst retained under pressure.. 8. A foamed thermoplastics material article made in accordance with Claim 7, wherein the mixture is placed in a mould and heated. 9. A foamed thermoplastics material article made in accordance with Claim 7, wherein the mixture is heated by passage through heated compression rollers 10. A foamed thermoplastics material article made in accordance with Claim 7, wherein the mixture is heated and foamed in passing through an extruder and die. 11. A composite structure formed by foaming a thermoplastics material in accordance with any one of Claims 1 to 7, in contact with one or more layers of fibre material coated with a solution of the polymer material. 12. A composite structure formed by slowly heating one or more layers of foamed thermoplastics materials in accordance with any one of Claims 1 to 7, whilst held in contact with two or more layers of reinforced fibre laminates coated with a solution of the ' polymer material. 13. A method, of making a foamed thermoplastics material substantially as hereinbefore described. 14. An article comprising a foamed thermoplastics material formed as herein described. OMPI

Inventors: SINGH DEVENDRA PAL, SINGH, DEVENDRA, PAL
Applicants: SMITH TECH DEV H R, H.R. SMITH (TECHNICAL DEVELOPMENTS) LIMITED
Application year: 1984
Main classification: C08J9
IPC codes: B32B5, C08J9