The present invention is concerned with a composition of matter based on polyethylene terephtalate (PET), preferably but not necessarily waste PET in the form of used PET bottles, and with a method of making rigid foam products from this composition.

For some years the accumulation of PET scrap, notably used beverage bottles, has become a serious problem for the authorities responsible for the disposal of solid wastes. The use of recycled PET for the manufacture of beverage bottles is not permitted by the health regula¬ tions, whereas other applications for recycled PET such as fibres for filling anoraks and duvets are not sufficiently large to absorb the available wastes.

However, it is generally considered that PET cannot be made into rigid foam because its melt viscosity is too low and that in consequence it will not retain the bubbles of an expanding gas. A first object of the present invention thus consists in making a composition based on PET, which can be used for the manufacture of stable foams, that is to say, a composition with a melt viscosity considerably higher than that of unmodified PET bottle grade; it is especially wished to provide a method for the chemical modification of PET, so as to make it suitable for the manufacture of closed cell foams.

This purpose is obtained by means of a composition resulting from the reaction of PET with a polyfunctional

carboxylic acid anhydride, more particularly at a tempera¬ ture between 250° and 300°C.

A further object of the invention consists in making foamed articles, such as an insulating board usable in the building industry, treating a mixture of dried PET and of the anhydride of a polyfunctional carboxylic acid in a quantity between 0.05% and 2% by weight of the PET, at a temperature between 250° and 300°, to obtain a composition of modified PET with a higher viscosity. It is then pos¬ sible to foam this material by methods known to those skilled in the art, especially in an extruder or injection moulding machine, in order to manufacture an insulating board, which is stronger, particularly in respect to im¬ pact strength, than the conventional expanded polystyrene board, and given the low price of the waste raw material, which is considerably cheaper to manufacture than expanded polystyrene board.

It is known that PET is a linear condensation polymer which behaves as typical thermoplastic material with a very low melt viscosity. However, the present inventors have stated that in reacting the PET with a very small amount of a polycarboxylic acid anhydride a composition is obtained with an unexpectedly higher melt viscosity than that of the unmodified PET, probably due to the formation a reticulated three-dimensional structure by reaction of the terminal hydroxyl groups, present in the PET, with the anhydride.

It has also been stated that, under certain condi¬ tions, a further increase in the viscosity can be obtained by the subsequent or simultaneous addition of a polyfunc-

tional alcohol, such as, for example, pentaerythritol (in an amount of about 0,1 - 2 wght %) .

Better results as regards the even structure of the foam were obtained by adding a nucleating agent, such as a powdered mineral or polymeric material, for example 2% of a master batch of 40% activated talc dispersed in polystyrene. This also serves to accelerate the crystal¬ lisation of the modified PET after extrusion, which reduces the time necessary to achieve a solid and stable foam structure.

Finally, it is essential to note that the PET must first be very carefully dried, using for example the methods used in preparing PET for bottle manufacture, to a level of not more than 0.01% water. PET is hygroscopic and, at the temperature of the reaction with an anhydride, it is readily hydrolysed by the presence of water. Such hydrolysis results in chain scission and hence in a reduc¬ tion of molecular weight. This, of course, reduces the viscosity, which is the opposite of the purpose of the in¬ vention.

One of the essential aspects of the invention is the possibility of making foam articles in a single operation, the chemical modification of the PET being effected directly in an extruder or an injection moulding machine, using waste PET bottles which have been comminuted and dried, or similarly dried virgin PET polymer, and then mixed with the anhydride and fed to said extrusion or in¬ jection moulding machine. Alternatively, the reactants may be fed through a port in the cylinder of the extrusion

machine .

Examples of the polycarboxylic acid anhydrides include pyromellitic acid dianhydride and trimellitic acid an¬ hydride. These may be used in amounts between 0.05% and 2.5% of the weight of the PET, preferably between 0.1 and 0.5 wght %.

For the extrusion of rigid foam, usual blowing agents may be employed, such as 5-phenyl indole and azodicar- bonamide, volatile liquids such as pentane, chlorofluoro- hydrocarbons such as "Freon 12", or hydrochlorofluorocar- bons such as CHC1F2(HCFC - 22).

Examples of the invention will be described as fol¬ lows. The percentage in the compositions refers to the per cent by weight in relation to the weight of PET.

Preparation of dried PET

Bottle scrap, film or fibre is comminuted in a rotary granulator, the ground material passing through a 5 mm screen. It is then dried in a standard drying equipment such as a "Conair Churchill D06H" for four hours at 180°C, to reach a water content not greater than 0.01%.

Example 1

Dried PET, as obtained above, is fed to an L.M.P. type RC2L twin screw co-rotating intermeshing extruder fitted with a 4 mm die. The temperatures indicated (starting from the feed end) were 259°, 268°, 273°, 274° and 260°. At a pressure of 3 bars, the extrudate diameter was 4 mm.

A quantity of PET was mixed, in a tumbler mixer, with 0.25% of pyromellitic dianhydride, and fed to the ex-

truder. Extruding at the same temperatures as in the previous run, the pressure in the die head had risen to 30 bar and the diameter of the extrudate was 10.5 mm. The in¬ crease in pressure and the increase in diameter of the ex¬ trudate indicated a considerable rise in the intrinsic viscosity of the PET.

A further quantity of PET was mixed in a tumbler mixer with 0.25% of pyromellitic dianhydride and 2% of a nucleating agent comprising 40% activated talc dispersed in polystyrene. The mixture was fed to the extruder and "Freon 12" gas was introduced at the discharge end of the screws at a pressure of 50 bar. Foam was extruded having a diameter of 14.5 mm at an extruder head pressure of 20 bar. The foam obtained has a specific gravity of 0.21.

Example 2

A mixture of dried PET with 0.2% pyromellitic acid dianhydride and 2% nucleating agent (40% activated talc in polystyrene) was mixed in tumbler mixer and fed to an L.M.P. RC2L extruder, fitted with an 8 mm die. Temperature settings were (from the feed end) 262°, 269°, 273°, 274° and the die was held at 259°. "Freon 12" was introduced at 50 bar. The die head pressure was 30 bar and a foamed ex¬ trudate of 35 mm diameter was obtained. The foam obtained had a specific gravity of 0.2.