WO2013181705A1

WO2013181705A1 - Impregnated polymer granules, processes for preparation and polymer products thereof

Info

Publication number: WO2013181705A1
Application number: PCT/AU2013/000600
Authority: WO
Inventors: Gary Toikka; Con Filippou; Katherine Dean; Long Yu; Qiang Yuan
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 2012-06-05
Filing date: 2013-06-05
Publication date: 2013-12-12

Abstract

The present invention relates to processes for preparing CO₂ impregnated polymer granules The present invention also relates to processes for preparing pre-expanded polymer beads or foamed polymer products using the CO₂ impregnated polymer granules. The present invention also relates to CO₂ impregnated polymer granules, pre-expanded polymer beads and foamed polymer products. The process for preparing CO₂ impregnated polymer granules may comprise contacting polymer granules with pressurised CO₂ comprising liquid CO₂ to absorb CO₂ into the polymer granules, and contacting the CO₂ absorbed polymer granules with pressurised CO₂comprising gaseous CO₂ to obtain CO₂ impregnated polymer granules.

Description

IMPREGNATED POLYMER GRANULES, PROCESSES FOR PREPARATION AND POLYMER PRODUCTS THEREOF FIELD

The present invention relates to processes for preparing C0₂ impregnated polymer granules. The present invention also relates to processes for preparing pre- expanded polymer beads or foamed polymer products using the C0₂ impregnated polymer granules. The present invention also relates to C0₂ impregnated polymer granules, pre-expanded polymer beads and foamed polymer products.

BACKGROUND

Products made from foamed, or pre-expanded, polymer beads have many uses including as packing materials, insulation products and foam drinking cups.

Foamed or pre-expanded polymer beads can be made by foaming, or expanding, polymer granules. Polymer granules can be expanded by use of physical blowing agents such as nitrogen, air, propane, butane, C0₂ and the like. Moulded polymer products can then be prepared from pre-expanded polymer beads.

A commonly used polymer for producing foamed polymer products is polystyrene. However, polystyrene is not biodegradable and therefore, in view of environmental concerns, attempts have been made to find alternative biodegradable polymers which can be foamed to provide foamed products. One such biodegradable polymer is polylactic acid (PLA). However, it has been found to be difficult to form foamed PLA beads and associated moulded foamed products, in a manner analogous to current polystyrene processes.

One process for preparing foamed PLA beads can involve the use of liquid C0₂ as a blowing agent. In such a process, once the liquid C0₂ has been absorbed into the polymer granule, it can act to plasticise the granule to nucleate the foaming process. However, under this process, although C0₂ is absorbed into the PLA granule, it does not distribute evenly throughout the granule and can result in beads with hard, or un- foamed, centres. Furthermore, under this process, the granules may begin to foam under ambient conditions as soon as the beads have been removed from the liquid C0₂, which results in beads with poor surface quality, poor cell formation and a high density. Various processes involving lengthy storage and refrigeration techniques have been used in an attempt to address the processing problems encountered. Supercritical C0₂ (scC0₂) has also been used in relation to producing pre- expanded polymer beads. However, scC0₂ is not practical for commercial production of pre-expanded polymer beads as it is expensive and cannot easily be undertaken on a commercial scale. Furthermore, the high pressures required for scC0₂ and its ability to plasticise polymers (i.e. lower the melt temperature) can result in polymer granules fusing together during absorption of C0₂.

Accordingly, there is a need for providing improved methods and processes of producing C0₂ impregnated polymer granules and pre-expanded polymer beads, which may also be applied on a commercial scale for forming foamed polymer products.

SUMMARY

In view of the limitations of the prior art, processes were evaluated to identify improved methods and processes for preparing C0₂ impregnated polymer granules. In various embodiments, processes were identified for preparing C0₂ impregnated polymer granules in which the granules could be pre-expanded following a C0₂ impregnation step without requiring additional processing, such as refrigerated storage. In various embodiments, C0₂ impregnated polymer granules were obtained from a C0₂ impregnation process with C0₂ content and distribution suitable for pre- expansion. Pre-expansion of the C0₂ impregnated polymer granules may be initiated directly after C0₂ impregnation or after extended times where the C0₂ impregnated polymer granules are held or stored under ambient conditions.

In a first aspect, there is provided a process for preparing C0₂ impregnated polymer granules, wherein the process comprises the steps of:

i) contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules; and

ii) contacting the C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂ to obtain C0₂ impregnated polymer granules.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressurised C0₂ may consist of, or consist essentially of, liquid C0₂. In an embodiment, the step i) of contacting polymer granules with liquid C0₂ to absorb C0₂ into the polymer granules comprises contacting polymer granules with liquid C0₂ in a pressure vessel. The parameters in the pressure vessel are sufficient to initiate absorption or impregnation of C0₂ into the polymer granules. The parameters may involve at least one of temperature, pressure and duration.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the temperature may be between the triple point and critical point for a C0₂ system. The temperature may be about - 20 °C to 31 °C, about -10 °C to 25 °C, about 0 °C to 15 °C, or about 5 °C to 10 °C. In one embodiment, the temperature is below about 20 °C, below about 15 °C, or below about 10 °C. In one embodiment, the temperature is about 0 °C to 15 °C. In a particular embodiment, the temperature is about 5 °C to 10 °C.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressurised C0₂ comprising liquid C0₂ may be operated to be at or above the saturated liquid-vapour phase line for C0₂. It will be appreciated that for polymer granules to be in contact with liquid C0₂, operation at about or above the saturated liquid-vapour phase line between the triple point and critical point is required. Operation at about or above the saturated liquid- vapour phase line may require at least one of higher pressures to be applied and variation in temperature application. In one embodiment, the pressurised C0₂ comprising liquid C0₂ is provided at about the saturated liquid-vapour phase line for C0₂. For example, in the step i) of contacting polymer granules with liquid C0₂ to absorb C0₂ into the polymer granules, the polymer granules may be contacted with liquid C0₂ in a pressure vessel for a duration without applied temperature or pressure increase into the vessel. The temperature and pressure in the pressure vessel may be allowed to reduce generally on the saturated liquid-vapour phase line for C0₂.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressure may be less than the critical point pressure for a C0₂ system. The pressure may be less than about 7.3 MPa, less than 7.0 MPa, less than 6.5 MPa, or less than 6 MPa. The pressure may be about 4 to 7 MPa, about 5 to 7 MPa, or about 6 MPa.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the duration may be at least about 5 minutes, at least about 15 mins, at least about 30 mins, or at least about 60 mins. The duration may be up to about 2 hours, up to about 4 hours, or up to about 6 hours. It will be appreciated that the duration for absorption of C0₂ will depend significantly on the size of the polymer granules being used, with smaller granule sizes typically requiring a shorter C0₂ absorption duration. ln the step ii) of contacting C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂, the pressurised C0₂ may consist of, or consist essentially of, gaseous C0₂. In an embodiment, the step ii) of contacting C0₂ absorbed polymer granules with gaseous C0₂ comprises contacting polymer granules with gaseous C0₂ in a pressure vessel. The parameters in the pressure vessel enable C0₂ to distribute in the polymer granules. The parameters may involve at least one of temperature, pressure and duration.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the temperature may be between the triple point and critical point for a C0₂ system. The temperature may be about -20 °C to 31 °C, about -10 °C to 25 °C, about 0 °C to 15 °C, or about 5 °C to 10 °C. In one embodiment, the temperature is below about 20 °C, below about 15 °C, or below about 10 °C. In another embodiment, the temperature is about 0 °C to 15 °C, or about 5 °C to 10 °C.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the pressurised C0₂ may be operated below the saturated liquid-vapour equilibrium for C0₂. The pressure may be less than 6 Pa, or about 1 to 5 MPa, or about 1 .5 to 3 MPa. In another embodiment, the pressure is about 2 MPa.

A pressure vessel comprising liquid C0₂ may be vented to release C0₂ and reduce pressure in the vessel such that operation is below the saturated liquid-vapour line for C0₂. After the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂ may comprise isothermally reducing pressure, such as by venting of C0₂ from a pressure vessel. In one embodiment, the process for step i) and step ii) occurs in a pressure vessel and wherein the pressure vessel is vented after step i) for initiating step ii) by releasing C0₂ from the pressure vessel and reducing pressure in the pressure vessel such that operation is below the saturated liquid-vapour line for C0₂.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the duration may be at least about 15 mins, at least about 30 mins, or at least about 60 mins. The duration may be up to about 2 hours, up to about 4 hours, up to about 8 hours, or up to about 16 hours. The duration for contacting the C0₂ absorbed polymer granules with gaseous C0₂ will also depend significantly on the size of the polymer granules being used, with smaller granule sizes typically requiring a shorter duration. The polymer may be any polymer suitable for foaming or moulding in which C0₂ is used as a nucleating agent and plasticiser. The polymer may be a

biodegradable polymer. In one embodiment, the polymer comprises a polylactic acid. The polymer granules may comprise, or be formulated to comprise, one or more additives. The one or more additives may be selected from nucleating agents, lubricants, plasticisers, and antioxidants. In one embodiment, the one or more additives comprise a nucleating agent selected from at least one of sodium benzoate, talc, calcium carbonate, silica, silicates, fluorohectorites, hectorites, titania, phosphate ester salts, organic pigments, inorganic pigments, micro or nano sized organic particulates and micro or nano sized inorganic particulates. In another embodiment, the one or more additives may be selected from lubricants, plasticisers, and antioxidants. In a particular embodiment, the one or more additives are selected from lubricants.

The polymer granules may have a diameter up to about 10 mm. The polymer granules may have a diameter of about 0.1 to 10 mm, about 0.2 to 7 mm, about 0.3 to 5 mm. In one embodiment, the polymer granules have a diameter of about 0.1 to 1 .0 mm, about 0.2 to 0.9 mm, about 0.3 to 0.8 mm, about 0.4 to 0.7 mm, or about 0.5 mm. The sizing of the granules for this embodiment may provide further advantages of improved impregnation of C0₂. It will be appreciated that the polymer granules may be provided in various shapes, for example spherical or oval shaped.

The polymer granules may be coated with one or more external lubricants. The external lubricants are applied to the polymer granules before contact with liquid C0₂. The external lubricant may be selected from at least one of waxes such as

polyethylene waxes and oxidized polyethylene waxes, paraffins, metal soaps, esters, amides, fatty acids, and fatty esters. In one embodiment, the external lubricant is a paraffin wax. The external lubricant can be particularly advantageous for use with polymer granules of smaller diameter, such as diameters of about 0.5 mm. The process of coating the polymer granules may comprise the use of one or more solvents in combination with the lubricant. The one or more solvents may be selected from one or more organic solvents. The coating of the granules can provide further advantages such as improved impregnation of C0₂ and facilitation of further processing of the granules.

The C0₂ wt % in the C0₂ impregnated polymer granules may be less than 30%, or about 5% to 25%, or about 10% to 20%. In a further embodiment, the polymer granules may have a substantially homogenous distribution of C0₂. The distribution of C0₂ in the polymer granules can enable the impregnated polymer granules to be pre- expanded or foamed without further processing. For example, the polymer granules may be pre-expanded or foamed without lengthy refrigerated storage. In one embodiment, the polymer granules are pre-expanded or foamed directly after impregnation. In another embodiment the polymer granules are pre-expanded or foamed after storage under ambient conditions. The storage may be for a duration of up to about 6 hours, up to about 4 hours, up to about 3 hours, or up to about 2 hours. In one embodiment, the storage is about 5 minutes to 4 hours. In another embodiment, the storage is about 15 minutes to 2 hours.

In a second aspect, there is provided C0₂ impregnated polymer granules prepared by the process according to the first aspect or embodiments thereof.

In a third aspect, there is provided a process of preparing pre-expanded or foamed polymer beads comprising a step of pre-expanding or foaming the C0₂ impregnated polymer granules prepared according to the first aspect or embodiments thereof.

In one embodiment, there is provided a process of preparing pre-expanded or foamed polymer beads comprising:

i) and ii) preparing C0₂ impregnated polymer granules according to the first aspect;

iii) optionally storing the C0₂ impregnated polymer granules at about ambient conditions; and

iv) pre-expanding or foaming the C0₂ impregnated polymer granules to obtain pre-expanded or foamed polymer beads.

In an embodiment, the process of preparing pre-expanded or foamed polymer beads comprises:

impregnating polymer granules with C0₂ by contacting the polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, and contacting the C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂, to obtain C0₂ impregnated polymer granules, and

pre-expanding or foaming the C0₂ impregnated polymer granules.

In an embodiment, the pre-expanding or foaming is carried out by heating C0₂ impregnated beads using convective, conductive or radiation methods. The convective method may involve the use of an oven or heated air. The conductive method may involve the use of steam or hot water. The radiation may involve the use of IR lamps. In one embodiment, the pre-expanding of the C0₂ impregnated polymer granules comprises the use of steam. A further advantage in using steam is the absence of hydrostatic pressure encountered in water and a reduction or elimination in the agglomeration or grouping together of beads, particularly for beads of about 0.5 mm in diameter.

The C0₂ impregnated polymer granules may be pre-expanded and/or foamed directly after absorption of C0₂ or may be stored before pre-expanding and/or foaming. In one embodiment, the C0₂ impregnated polymer granules are stored at ambient temperature prior to pre-expanding or foaming. For example, the C0₂ impregnated polymer granules may be pre-expanded without stored refrigeration. Prior to pre- expanding or foaming, the C0₂ impregnated polymer granules may be stored at ambient temperature for up to about 6 hours, up to about 4 hours, up to about 2 hours, or about 5 to 120 minutes, about 10 to 100 minutes, or about 20 to 60 minutes.

In an embodiment, the process of preparing pre-expanded or foamed polymer beads consists of:

impregnating polymer granules with C0₂ by contacting the polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, and contacting the C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂, to obtain C0₂ impregnated polymer granules;

optionally storing the C0₂ impregnated polymer granules at ambient conditions before pre-expanding; and

pre-expanding or foaming the C0₂ impregnated polymer granules.

The pre-expanding of the C0₂ impregnated polymer granules may comprise heating to obtain pre-expanded polymer beads. The heating may be at a temperature of about 50 °C to 120 °C. In one embodiment, the impregnated polymer granules are heated to a temperature of about 85 °C to 95 °C. The impregnated polymer granules may be heated for about 3 seconds to 120 seconds. It will be appreciated that smaller polymer granules generally expand at a faster rate and require less heating, for example C0₂ impregnated polymer granules of 0.5 mm diameter may require heating in water of about 1 -5 seconds.

The pre-expanding of the C0₂ impregnated polymer granules may comprise a process for the separation or removal of pre-expanded polymer beads by applied air flow process. This air flow process can facilitate reducing the grouping together of beads. ln a fourth aspect, there is provided pre-expanded or foamed polymer beads. The pre-expanded or foamed polymer beads may be prepared from the process according to the third aspect or embodiments thereof.

The polymer beads may comprise an outer shell and a core. The polymer beads may have a homogeneous cell structure, such as a homogeneous cell size and distribution. The polymer beads may comprise an intermediary area disposed between the outer shell and core having a substantially homogeneous cell size and distribution. The core may be of a lower density than the average density of the bead.

The core may have a density of less than 30 g/L. In one embodiment, the core has a density of less than 25 g/L, less than 20 g/L, or less than 15 g/L. It will also be appreciated that a homogeneous nucleation and cell growth can enable the formation of beads with an outer shell, which can have an excellent surface finish or high surface smoothness. It will also be appreciated that an advantage of the process as described herein is that beads can be formed having an outer shell and a core, wherein the outer shell has a high surface smoothness and the core has a substantially homogenous shell structure.

In a fifth aspect, there is provided a process for preparing a foamed polymer product comprising:

foaming the polymer beads prepared according to the third aspect or embodiments thereof, or the C0₂ impregnated polymer granules prepared according to the first aspect or embodiments thereof.

In one embodiment, the process for preparing a foamed polymer product comprises the steps of:

i) and ii) preparing C0₂ impregnated polymer granules according to the process of the first aspect or embodiments thereof;

iii) optionally storing the C0₂ impregnated polymer granules at about ambient conditions;

iv) optionally pre-expanding or foaming the C0₂ impregnated polymer granules according to the third aspect or embodiments thereof to obtain pre-expanded or foamed polymer beads;

v) optionally coating the C0₂ impregnated polymer granules or pre-expanded polymer beads;

vi) optionally treating the beads with liquid C0₂;

vii) foaming the beads or granules into a polymer product.

In another embodiment, the process may comprise the steps of: i) and ii) preparing C0₂ impregnated polymer granules according to the process of the first aspect or embodiments thereof;

iv) pre-expanding the C0₂ impregnated polymer granules according to the third aspect or embodiments thereof to obtain pre-expanded polymer beads;

v) coating the pre-expanded polymer beads to form coated beads;

vi) optionally treating the coated beads with liquid C0₂; and

vii) foaming the beads into a polymer product.

The process may comprise moulding the polymer beads or granules to obtain a moulded polymer product. For example, the polymer beads may be moulded by fusion or post-expansion processes.

The coating may comprise one or more fusion agents. In one embodiment, the coating comprises a fusion agent selected from at least one of polyvinyl acetate, polyvinyl-acetate-based polymer, polyvinyl alcohol, polycaprolactone, polyester, polyester amide, protein-based material, polysaccharide, natural wax or grease, and acrylate. In a further embodiment, the fusion agent is selected from at least one of a polyvinyl alcohol and vinyl acetate-ethylene copolymer based coating. The coating of the beads can provide further advantages such as improved uniform foaming or facilitation of further processing of the beads. The coating, when present, can facilitate post-expansion fusion.

In one embodiment, the process comprises treating the pre-expanded or foamed polymer beads with a coating to form coated beads, and treating the coated beads with liquid C0₂ prior to being placed in the mould.

It will be appreciated that the mould can be provided in a pre-determined shape and size. In one embodiment, the filling of the mould with polymer beads comprises crack filling the mould. The crack filling may comprise opening the mould sufficiently to incorporate an excess amount of coated beads, such that when the mould is closed, the beads are compacted.

The heat treatment of the mould may comprise a convective heating method. The convective heating method may comprise application of at least one of heated air, heated gas, heated vapour, and oven treatment. BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be further described and illustrated, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a pressure-temperature phase diagram for C0₂;

Figure 2 is a schematic illustration showing the process of one embodiment of the invention;

Figures 3a and 3b show foamed beads having a substantially homogenous cell structure produced according to a process of the present invention; and

Figure 4 shows variation in foamed bead density as a function of 'lag time' for foamed beads produced according to a process of the present invention.

DETAILED DESCRIPTION

Processes were evaluated to identify improved methods for preparing C0₂ impregnated polymer granules. In various embodiments, processes were identified for preparing C0₂ impregnated polymer granules in which the granules could be pre- expanded following a C0₂ impregnation step without requiring lengthy refrigerated storage. In various embodiments, C0₂ impregnated polymer granules can be obtained directly from a C0₂ impregnation process with C0₂ content and distribution suitable for pre-expansion.

In the following, particular features and embodiments of the claimed processes and products are described, including features of the C0₂ impregnated polymer granules, beads, and foamed or moulded polymer products. All features below may apply independently to the processes and products of the invention.

For convenience of reference, the following terms are used to generally define the different polymer materials at various stages of the process. In the C0₂ impregnation step, the term "granule" generally refers to a polymer particulate, and can apply to polymer particulates either before or after C0₂ impregnation. The term "polymer granule" generally refers to the polymer granule before any C0₂ absorption or impregnation step. During C0₂ impregnation the polymer granule is contacted with pressurised C0₂ comprising liquid C0₂ and the resulting product is referred to as "C0₂ absorbed polymer granules". The "C0₂ absorbed polymer granules" are then contacted with pressurised C0₂ comprising gaseous C0₂ and the resulting product is referred to as "C0₂ impregnated polymer granules". The C0₂ impregnated polymer granules can then be pre-expanded or foamed, such as by heating, and at that stage are generally referred to as "beads" or "pre-expanded beads" or "pre-expanded polymer beads". The C0₂ impregnated polymer granules, or pre-expanded polymer beads, can then be foamed or moulded into products which are generally referred to as "polymer products" or "foamed polymer products". Impregnated granules

A process for preparing C0₂ impregnated polymer granules comprises contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, and contacting the C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂.

The use of pressurised C0₂ comprising liquid and then gaseous C0₂ enables the C0₂ to absorb and impregnate into the polymer granules, and can provide a substantially homogenous distribution of C0₂ within the polymer granules. A substantially homogeneous distribution of the C0₂ following absorption and impregnation allows the C0₂ impregnated granules to be pre-expanded or foamed directly after impregnation. The C0₂ impregnated granules can also be stored at ambient conditions, such as ambient temperature and pressure, for a number of hours prior to foaming. The C0₂ impregnated granules can also be stored in sealed C0₂ bags or containers. This allows the C0₂ impregnated granules to be shipped and pre- expanded at a later date.

A substantially homogeneous distribution of C0₂ in the C0₂ impregnated polymer granules can also enable the production of pre-expanded polymer beads having a substantially homogeneous cell structure and low density core. Pre-expanded polymer beads may also be obtained having consistent, smooth, glossy surface quality, including a strong and robust outer shell.

Pressurised C0₂

The process of the present invention involves contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, and contacting the C0₂ absorbed polymer granules with pressurised C0₂ comprising gaseous C0₂.

The term "pressurised C0₂" generally refers to a C0₂ system capable of adsorption or impregnation of C0₂ into polymer granules. The pressurised C0₂ comprising liquid C0₂ may also comprise gaseous C0₂ where liquid-gas phase equilibrium conditions are achieved. To provide liquid C0₂, liquid C0₂ can be used and the system could operate at or above the saturated liquid-vapour equilibrium, for example at about 6 MPa. To provide gaseous C0₂ the system could operate at a pressure below the saturated liquid-vapour equilibrium, for example at about 2 MPa. The pressurised C0₂ may comprise a solvent. Examples of suitable solvents include, but are not limited to, a co-solvent such as a second gas, for example N₂, or other solvent such as a polar or polar protic solvent.

Figure 1 shows a pressure-temperature phase diagram for C0₂. C0₂ may exist as a solid, liquid, gas or supercritical fluid. The temperatures and pressures at which these phases exist are shown in the phase diagram of Figure 1 . With reference to the phase diagram of Figure 1 , pressurised C0₂ containing liquid or gaseous C0₂ may be below the critical point and above the triple point. Pressurised C0₂ containing gaseous or liquid C0₂ that is below the critical point may be referred to as "subcritical C0₂".

The use of pressurised C0₂ comprising liquid and gaseous C0₂ can enable the

C0₂ to be absorbed into the polymer granule with a substantially homogeneous distribution. The substantially homogeneous distribution of C0₂ in the polymer granule can allow the production of foamed or pre-expanded polymer beads, having a substantially homogeneous cell structure and low density core.

The pressurised C0₂ comprising liquid C0₂ may be at any pressure which allows the C0₂ to be absorbed into the polymer granules, with the pressurised C0₂ comprising gaseous C0₂ enabling distribution, equilibration or further impregnation of C0₂ in the polymer granules. For example, C0₂ impregnated polymer granules may be produced according to various embodiments of invention having a substantially homogenous distribution of C0₂. The pressure of the pressurised C0₂ does not need to remain constant throughout the absorption step. The pressure may be varied intentionally or may vary as a result of C0₂ being absorbed into the polymer granules. Preferably the pressurised C0₂ is provided such that there is a substantially homogeneous distribution of C0₂ in the polymer granules. The pressurised C0₂ may be at a pressure above the triple point and below the critical point (31.1 °C and

7.4 MPa). In the step of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressurised C0₂ may consist of, or consist essentially of, liquid C0₂. In an embodiment, the step of contacting polymer granules with liquid C0₂ to absorb C0₂ into the polymer granules comprises contacting polymer granules with liquid C0₂ in a pressure vessel at parameters sufficient to initiate impregnation or absorption of C0₂ into the polymer granules. The parameters may involve at least one of temperature, pressure and duration.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the temperature may be between the triple point and critical point for a C0₂ system. The temperature may be about - 20 °C to 31 °C, about -10 °C to 25 °C, about 0 °C to 15 °C, or about 5 °C to 10 °C. In one embodiment, the temperature is below about 20 °C, below about 15 °C, or below about 10 °C. In another embodiment, the temperature is about 0 °C to 15 °C, or about 5 °C to 10 °C. For example, the temperature may be at about or between about any one of the following amounts: -10, -9, -8, -7, -6, -5, -4, -3, -2, -1 , 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25 °C. It will be appreciated that to provide and maintain liquid C0₂ in a pressure vessel, for example operating at the saturated liquid vapour phase line, higher temperatures require higher pressures.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressurised C0₂ comprising liquid C0₂ may be operated to be at or above the saturated liquid-vapour phase equilibrium line for C0₂. It will be appreciated that for polymer granules to be in contact with liquid C0₂, operation at about or above the saturated liquid-vapour phase line between the triple point and critical point is required. Operation at about or above the saturated liquid-vapour phase line may require at least one of higher pressures to be applied and variation in temperature application. In one embodiment, the pressurised C0₂ comprising liquid C0₂ is provided at about the saturated liquid-vapour phase equilibrium line for C0₂. For example, in the step of contacting polymer granules with liquid C0₂ to absorb C0₂ into the polymer granules, the polymer granules may be contacted with liquid C0₂ in a pressure vessel for a duration without applied temperature and/or pressure increase into the vessel. The temperature and pressure in the pressure vessel may be allowed to reduce generally with the saturated liquid- vapour phase equilibrium for C0₂. The temperature in the pressure vessel may be reduced by cooling the vessel such that the pressure is reduced along the saturated liquid-vapour phase line for C0₂.

In the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the pressure may be less than the critical point pressure for a C0₂ system. The pressure may be less than about 7.3 MPa, less than 7.0 MPa, less than 6.5 MPa, or less than 6 MPa. The pressure may be about 4 to 7 MPa, about 5 to 7 MPa, or about 6 MPa. For example, the pressure may be at about or between about any one of the following amounts 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 MPa, including any increments of 0.1. It will be appreciated that to provide and maintain liquid C0₂ in a pressure vessel, for example operating at the saturated liquid vapour phase line, higher temperatures require higher pressures. ln the step i) of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the duration may be at least about 5 minutes, at least about 15 mins, at least about 30 mins, or at least about 60 mins. The duration may be up to about 2 hours, up to about 4 hours, or up to about 6 hours. It will be appreciated that the duration for absorption of C0₂ will depend significantly on the size of the polymer granules being used, with smaller granule sizes typically requiring a shorter C0₂ absorption duration. For example, a suitable duration for 0.5 mm polymer granules may be about 30 minutes to 6 hrs, or about 1 to 4 hrs, although an absorption duration could be as low as about 5 minutes. For example, the duration may be at about or between about any one of the following amounts: 5 mins, 15 mins, 30 mins, 45 mins, 1 hr, 2hrs, 3hrs, 4hrs, 5hrs, 6hrs.

In the step ii) of contacting polymer granules with pressurised C0₂ comprising gaseous C0₂, the pressurised C0₂ may consist of, or consist essentially of, gaseous C0₂. For example, all the liquid C0₂ from the absorption step may be converted into gaseous C0₂. The step of contacting polymer granules with gaseous C0₂ typically comprises contacting polymer granules with gaseous C0₂ in a pressure vessel. The parameters in the pressure vessel enable C0₂ to distribute in the polymer granules. The parameters may involve at least one of temperature, pressure and duration.

The pressurised C0₂ initially comprises liquid C0₂, for example pressurised C0₂ provided at the saturated liquid-vapour equilibrium. In the step of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the gaseous C0₂ may be provided by reducing at least pressurised C0₂ such that the liquid C0₂ is converted into gaseous C0₂. In an embodiment, the step of contacting the C0₂ absorbed polymer granules with gaseous C0₂ comprises contacting the C0₂ absorbed polymer granules with gaseous C0₂ in a pressure vessel at parameters sufficient to enable distribution, equilibration or further impregnation of C0₂ into the C0₂ absorbed polymer granules, for example substantially homogeneous distribution of C0₂. Further impregnation may comprise an increase, decrease or no change in total C0₂ content in the granules, although advantages can be obtained from further impregnation in that further distribution or equilibration of C0₂ in the granule can be achieved.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the temperature may be between the triple point and critical point for a C0₂ system. The temperature may be about -20 °C to 31 °C, about -10 °C to 25 °C, about 0 °C to 15 °C, or about 5 °C to 10 °C. In one embodiment, the temperature is below about 20 °C, below about 15 °C, or below about 10 °C. In another embodiment, the temperature is about 0 °C to 15 °C, or about 5 °C to 10 °C. For example, the temperature may be at about or between about any one of the following amounts: -10, -9, -8, -7, -6, -5, -4, -3, -2, -1 , 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25 °C.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous

C0₂, the pressurised C0₂ may be operated below the saturated liquid-vapour equilibrium for C0₂. The pressure may be less than 6, less than 5, less than 4, less than 3, or less than 2 MPa. The pressure may be about 1 .5 to 3 Pa. For example, the pressure may be at about or between about any one of the following amounts 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 MPa, including any increments of 0.1 . In one embodiment, a pressure vessel comprising liquid C0₂ may be vented to release C0₂ and reduce pressure in the vessel such that operation is below the saturated liquid- vapour equilibrium for C0₂. In another embodiment, after the step of contacting polymer granules with pressurised C0₂ comprising liquid C0₂ to absorb C0₂ into the polymer granules, the step of contacting the C0₂ absorbed polymer granules with gaseous C0₂ comprises isothermally reducing pressure, such as by venting of C0₂ from a pressure vessel.

In the step ii) of contacting the C0₂ absorbed polymer granules with gaseous C0₂, the duration may be at least about 15 mins, at least about 30 mins, or at least about 60 mins. The duration may be up to about 2 hours, up to about 4 hours, up to about 8 hours, or up to about 16 hours. The duration may be less than about 14 hours, less than about 10 hours, less than about 6 hours, less than about 2 hours, or less than 1 hour. The duration for contacting the C0₂ absorbed polymer granules with gaseous C0₂ will also depend significantly on the size of the polymer granules being used, with smaller granule sizes typically requiring a shorter duration. For example, a suitable duration for 0.5 mm polymer granules may be about 1 to 8 hours, or about 2 to 4 hours, although the duration may be as low as about 15 minutes. For example, the duration may be at about or between about any one of the following amounts: 15 mins, 30 mins, 45 mins, 1 hr, 2 hrs, 3 hrs, 4 hrs, 5 hrs, 6 hrs, 7 hrs, 8 hrs, 9 hrs, 10 hrs, 1 1 hrs, 12 hrs, 13 hrs, 14 hrs, 15 hrs, 16 hrs.

Absorption and Impregnation of C0₂

In various embodiments, C0₂ may be absorbed into the polymer granules with a substantially homogeneous distribution. The homogeneous distribution of the C0₂ in the impregnated granules can provide pre-expanded beads with a substantially homogeneous cell structure, low density core and good surface quality.

The time required for the polymer granules to absorb C0₂ varies depending on the size of the polymer granules. The process may comprise an absorption step comprising contacting the polymer granules with liquid C0₂, followed by an

equilibration step to distribute and further impregnate C0₂ into the granules. The equilibration (or further impregnation) step comprises contacting the polymer granules with pressurised C0₂ comprising gaseous C0₂. The equilibration step can allow C0₂ to distribute and impregnate the granule core, or can enable a substantially homogenous distribution of C0₂ within the granules.

In embodiments where the pressurised C0₂ comprises gaseous and liquid C0₂ and the process comprises converting all liquid C0₂ to gaseous C0₂, the time sufficient for the polymer granules to absorb C0₂ may be referred to as including an equilibration time or further impregnation time leading to further distribution and equilibration. The equilibrium or further impregnation time, as a percentage of the total impregnation time (i.e. initial absorption time and equilibration/further impregnation time), may be up to about 80%, up to about 75%, up to about 70%, up to about 65%, or up to about 60%.

The absorption of C0₂ into the polymer granules results in a content or amount of C0₂ in the polymer granules. The equilibration step can facilitate providing a content range of C0₂ in the polymer granules that is suitable for pre-expansion or foaming without lengthy refrigeration storage. The polymer granules may be pre-expanded or foamed immediately after impregnation or stored at ambient pressure and temperature. The C0₂ content of the impregnated granules may be about 5% to 30%, about 10% to 25%, or about 15% to 20%, or up to about 30%, up to about 25%, or up to about 20%. The C0₂ content of the beads may be at least about 5%, at least about 10%, or at least about 15%.

Although the C0₂ impregnated granules produced by the process of the present invention can be pre-expanded directly after absorption of C0₂, the granules may also optionally be stored at ambient temperature and pressure for a number of hours prior to foaming or pre-expansion. For example, ambient temperature may be a

temperature in the range of about 18 to 25 °C. As another alternative, the C0₂ impregnated granules can be stored for several months in sealed C0₂ bags or containers. This allows the C0₂ impregnated granules to be transported or stored and pre-expanded at a later date. It will be appreciated that different sized beads may require different storage conditions. When the C0₂ impregnated granules are stored at ambient conditions, the storage time, which may also be referred to as "lag-time", may be up to about 8 hours, up to about 4 hours, up to about 2 hours, or up to 1 hour. The storage time may be at least 30 mins, at least 1 hour, at least 2 hours, at least 4 hours, or 6 hours or more. In one embodiment, the storage is about 5 minutes to 4 hours. In another embodiment, the storage is about 15 minutes to 2 hours.

When the C0₂ impregnated granules are stored in sealed C0₂ bags or containers, the storage time, or lag-time, may be several days, several weeks or several months.

The impregnated granules can provide advantages including homogeneous cell structure intermediary area between the core and outer shell, a low density core and good surface quality or high surface smoothness. For example, the homogeneous cell structure may provide a size ratio of a large to small cells that is at least about 5: 1 . For example, the density of the core may be about a third or less of the average density of the impregnated granule. For example, good surface quality or high surface smoothness may be provided by observation of substantially few or no collapsed cells, which can be observed under SEM using X100 times.

Polymer

The polymer granule may be formed from any polymer which is capable of being impregnated with C0₂ and foamed into a pre-expanded bead.

The polymer may be any weight average molecular weight or number average molecular weight or molecular weight distribution that can be impregnated with C0₂ and pre-expanded. The polymer may have a weight average molecular weight of less than about 1 10,000, less than about 105,000, less than about 100,000, or less than about 95,000. The polymer may have a weight average molecular weight of up to about 1 10,000, up to about 105,000, up to about 100,000, or up to about 95,000. The polymer may have a number average molecular weight of less than about 75,000, less than about 70,000, less than about 65,000, or less than about 60,000. The polymer may have a number average molecular weight of up to about 75,000, up to about 70,000, up to about 65,000, or up to about 60,000.

In one embodiment, the polymer is a biodegradable polymer, or a partially biodegradable polymer. Suitable examples of biodegradable polymers or partially biodegradable polymers include, but are not limited to, polybutylene succinate (PBS), poybutylene succinate-co-adipate (PBSA) copolymers, polybutyrate adipate terephthalate (PBAT), adipic acid aliphatic/aromatic copolyesters (AAC), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxy alkanoates (PHAs) including poly-β- hydroxybutyrate (PHB) and its copolymer with hydroxyvaleric acid (PHB/v), modified polymers of polyterephthalate, polytetramethylene adipate-co-terephthalate and combinations or blends of the above.

In a preferred embodiment, the polymer is polylactic acid, or a blend of one of the aforementioned polymers with polylactic acid (PLA). PLA is a polymer or copolymer comprising, or consisting essentially of, lactic acid monomer units. Polylactic acid may include an L-isomeric lactic acid, a D-isomeric lactic acid, a L, D-isomeric lactic acid or combinations, blends and various proportions thereof. For example, the D-isomer may be provided in an amount to enable a particular degree of crystallinity or

amorphousness, and various blends can enable modification of characteristics including Tg and melt temperatures.

A polymer usually has a distribution of crystalline (ordered) and amorphous (disordered) regions, and the fraction of the ordered molecules in a polymer can be characterized by the degree of crystallinity (% of mass of c rysta 11 i n ity/tota I mass). A well known method for measuring the degree of crystallinity in a polymer is differential scanning calorimetry (DSC).

In one embodiment, the degree of crystallinity in the polymer may be low, for example (in % of mass of crystal linity/total mass when measured by DSC) less than about 5%, 4%, 3%, 2%, 1.5%, 1 %, 0.5%, or 0.1 %. In a preferred embodiment, the degree of crystallinity in the polymer is less than about 1 %. Further advantages may be provided by a polymer with low crystallinity, for example good impregnation or pre- expansion or foaming properties.

The polymer granules used in the process of this invention may be of any size suitable for pre-expansion. For example, the polymer granules may have a diameter of up to about 10 mm. The polymer granules may have a diameter of up to about 5 mm, up to about 3 mm, up to about 1 mm, up to about 0.7 mm, or up to about 0.5 mm. The polymer granules may have a diameter of at least about 0.1 mm, at least about 0.3 mm, or at least about 0.5 mm. The polymer granules may have a diameter of about 0.1 to 5 mm, about 0.2 to 2 mm, about 0.3 to 1 mm, or about 0.5 mm. In one embodiment, the polymer granules have a diameter of about 0.1 to 1 .0 mm, about 0.2 to 0.9 mm, about 0.3 to 0.8 mm, about 0.4 to 0.7 mm, or about 0.5 mm. The sizing of the granules for this embodiment may provide further advantages of improved impregnation of C0₂. In one particular embodiment, the polymer granules have a diameter of about 0.3 to 1 mm, and more preferably 0.3 to 0.9 mm, which may provide further advantages when using the granules to produce moulded products. It will be appreciated that the polymer granules may be provided in various shapes, for example spherical or oval shaped.

The polymers may also be modified. For example, the polymers may be modified by inclusion of groups such as peroxides, anhydrides, oxazoline, acetates, citrates or formats. The polymers may also be modified by varying the catalyst used in the polymerisation process. Additional modifications may for example include grafting maleic anhydride onto the PLA chains, which can be used to change the free volume and intermolecular forces,

The polymer may also include one or more additives. Suitable additives include, but are not limited to, nucleating agents, lubricants, plasticisers, anti-oxidants and chain extenders.

Nucleating agents provide nucleation sites for gas cells to be built upon during the pre-expansion step. Use of nucleating agents as additives can assist in providing foamed beads with improved cell structure. The nucleating agents used in the present invention may be any nucleating agents suitable for use in pre-expanding polymer granules. For example, the nucleating agent may be selected from the group consisting of sodium benzoate, talc, calcium carbonate, silica, silicates,

fluorohectorites, hectorites, titania, phosphate ester salts, organic pigments, inorganic pigments, micro or nano sized organic particulates and micro or nano sized inorganic particulates.

Other nucleating agents may include azodicarbonamide (ADC, which is also a blowing agent), titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Suitable organic nucleation agents may also be used.

In one embodiment, the one or more additives in the polymer granules, if present, do not include a nucleating agent (other than the presence of C0₂).

Lubricants can be used to minimise the frictional forces between polymer molecules, or between polymer molecules and other components in the polymer granule (if present). Lubricants can be subdivided into external and internal lubricants. External lubricants typically provide lubrication between the polymer and external factors, such as other polymer granules. Examples of external lubricants include, but are not limited to, waxes, paraffins, esters, amide and fatty acids. An example of where it may be advantageous to include an external lubricant in a polymer granule is when the polymer granules are of smaller diameter. In this case, the external lubricant can assist in preventing the polymer granules from sticking together. Preferred for this purpose is paraffin wax although other waxes may also be used.

In an embodiment, the polymer granules may be coated with one or more external lubricants before the C0₂ impregnation process. The one or more external lubricants may be selected from at least one of waxes, paraffins, esters, amides and fatty acids. In one embodiment, the external lubricant is a wax. The external lubricant may be selected from at least one of polyethylene waxes, oxidized polyethylene waxes, paraffin, metal soaps, esters, amides, fatty acids, and fatty esters. The external lubricant may be a paraffin wax. The external lubricant can be particularly advantageous for use with polymer granules of smaller diameter, such as diameters of about 0.5 mm. The process of coating the polymer granules may comprise the use of one or more solvents in combination with the lubricant. The one or more solvents may be selected from organic solvents. The organic solvents may be, for example, acetone, dichloromethane, hexane, benzene, and ethyl acetate. The organic solvent may be selected from saturated, unsaturated, or aromatic hydrocarbons. Saturated hydrocarbons may be selected from cyclic and non-cyclic compounds, and branched or straight chained compounds. The saturated hydrocarbons may be selected from alkanes, for example from at least one of pentane, hexane, heptane, octane, nonane, and decane.

Internal lubricants typically provide lubrication between polymer molecules.

Examples of suitable internal lubricants include, but are not limited to, fatty alcohols, esters, waxes, fatty acids, fatty acid ester, fatty acid ester of polyol, fatty acid amines and metallic stearates such as zinc, calcium, magnesium, lead and lithium stearate, steric acid, low molecular weight polyethylene.

Plasticisers can be added to polymers to lower the glass transition of the polymer and soften the polymer. Examples of suitable plasticisers include, but are not limited to, citric acids like tributyl citrate, triethyl citrate, and poly(caprolactone).

Rubber tougheners can also be added to polymers to modify physical properties of pre-foamed beads and ultimately moulded products. For PLA, biodegradable polymers based on polyesters include BioMax, Bionolle and Paraloid BPM 250.

Anti-oxidants can be added to polymers to increase stability of the polymer to degradation when exposed to oxygen. In one embodiment, the anti-oxidant is trisnonylphenyl hosphate (TNPP). TNPP may also be used to lower the activation energy of oxazoline if it is used to chain extend PLA (i.e. to increase PLA melt strength).

Antioxidants include ferrous/iron powders, ascorbic acid, photosensitive dyes, enzymatic oxidation (e.g. glucose oxidase/catalase and alcohol oxidase), ferrous salts or unsaturated fatty acids (e.g. oleic and linoleic acids) sulfites, boron, palladium catalysts, glycols, unsaturated fatty acids such as oleic, linoleic or linolenic acid and hydrocarbons (Brody et al. 2001 ; Day, 2003), BHA or butylhydroxyanisole and BHT or butylhydroxytoluene food antioxidants are vitamins A, C, and E; β-carotene; selenium and lycopene. The International Food Information Council [http://www.ific.org] provides excellent comprehensive listings of functional food components.

Antioxidants are generally not directed to PLA, as hydrolysis is usually the main chemical break down process and PLA is preferred to bio-degrade after its use has expired.

Chain extenders can be added to polymers to increase the melt strength of the polymer and to reduce the amount of open cells in the foamed polymer bead.

Examples of suitable chain extenders include, but are not limited to, ethylene carbonate, heterocyclic compounds and diisocyanate, 4,4-methylene diphenyl diisocyanate, 1 ,4-butanediol and 1 ,4-butane diisocyanate, bis-cyclic imino-ethers, pyromellitic dianhydride oxazoline).

Pre-expansion process

The process for preparing polymer beads may include a pre-expansion or foaming process. The pre-expansion or foaming process may comprise the step of heating the C0₂ impregnated polymer beads prepared by the process described herein. In various embodiments, a substantially homogeneous distribution of the C0₂ impregnated granules can be obtained, which can provide polymer beads with a substantially homogeneous cell structure, low density core and good surface quality.

The pre-expanding or foaming may be carried out by heating C0₂ impregnated beads using convective, conductive or radiation methods. The methods may be batch or continuous processes. The convective method may involve the use of an oven or hot air. The conductive method may involve the use of steam or hot water. The radiation may involve the use of IR lamps. In one embodiment, the pre-expanding of the C0₂ impregnated polymer granules comprises the use of steam. An advantage of using steam is that there is no hydrostatic pressure present and a reduction or elimination in the agglomeration or grouping together of beads may be obtained, particularly for beads of about 0.5mm in diameter.

The C0₂ impregnated polymer granules may be pre-expanded and/or foamed directly after absorption of C0₂ or may be stored before pre-expanding and/or foaming. In one embodiment, the C0₂ impregnated polymer granules are stored at ambient temperature prior to pre-expanding or foaming. For example, the C0₂ impregnated polymer granules may be pre-expanded without stored refrigeration. Prior to pre- expanding or foaming, the C0₂ impregnated polymer granules may be stored at ambient temperature for up to about 6 hours, up to about 4 hours, up to about 2 hours, up to about 1 hour, up to about 30 mins, up to about 15 mins, or about 5 to

120 minutes, about 10 to 100 minutes, or about 20 to 60 minutes.

The process of preparing pre-expanded or foamed polymer beads may consist of:

optionally storing the C0₂ impregnated polymer granules at ambient temperature and pressure before pre-expanding; and

pre-expanding or foaming the C0₂ impregnated polymer granules.

The pre-expanding of the C0₂ impregnated polymer granules may comprise a process for the separation or removal of pre-expanded polymer beads by applied air flow process. This air flow process can facilitate reducing the grouping together of beads.

Different heating methods may be used depending on the size of the bead and the amounts that are desired to be pre-foamed. For example, water can be particularly suitable to pre-foam 0.5 mm granules to obtain larger amounts of pre-expanded beads, although ovens or IR for 3-4 mm granules may be suitable to moderate batch amounts.

One advantage of the present invention is that the C0₂ impregnated beads prepared by the process of the invention can be pre-expanded in existing EPS

(Expanded Polystyrene) equipment. Some modification of the equipment may be preferred. Pre-expanding in hot water may produce beads with reduced size and increased density due to the hydrostatic pressure of the water. Furthermore, the use of water may prevent the foaming of large numbers of beads as production is limited by the size of the water bath. Another advantage of not using hot water to pre-expand the C0₂ impregnated polymer granules is that the complete pre-expanded beads can be separated from the partially pre-expanded beads by density. For example, by blowing a stream of air through the pre-expanded beads, the lower density, complete, pre- expanded beads will be carried with the air and separated from the higher density, partially pre-expanded beads.

Pre-expansion temperature

The C0₂ impregnated polymer granules may be heated to any temperature which enables the beads to pre-expand. In one embodiment, the C0₂ impregnated polymer granules are heated to a temperature of about 50 °C to 120 °C. For example, the temperature may be about 60 °C to 1 10 °C, such as about 70 °C to 100 °C, or about 85 °C to 95 °C.

The C0₂ impregnated polymer granules may be heated to a temperature of up to about 120°C. For example, the temperature may be up to about 1 10°C, such as up to about 100°C, or up to about 95°C. The C0₂ impregnated polymer granules may be heated to a temperature of at least about 50°C. For example, the temperature may be at least about 60°C, such as at least about 70°C, or at least about 80°C, or at least about 90°C.

In various embodiments, the temperature to pre-expand the C0₂ impregnated polymer granules, or the pre-expansion temperature, is typically above ambient temperature. This means that the C0₂ impregnated granules can be obtained that are stable at ambient temperature, and may not require lengthy refrigerated storage before pre-expansion or foaming. Pre-expansion time

The C0₂ impregnated polymer granules may be heated for a period of time sufficient for a portion of the granules to at least partially expand or pre-expand. The pre-expansion time may be as short as a few seconds, or may be up to several minutes. A suitable pre-expansion time will depend on a range of factors including size of the granules, temperature and heating method used (e.g. water or air).

The pre-expansion heating time may be up to about 120 seconds, up to about 100 seconds, up to about 80 seconds, up to about 40 seconds, up to about 20 seconds, or up to about 10 seconds. For example, the pre-expansion heating time may be at about or between about any one of the following amounts (seconds): 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 150, 200. Polymer beads

In one embodiment, the present invention provides polymer beads. The polymer beads may be formed by pre-expanding the C0₂ impregnated polymer granules as described herein.

The pre-expanded or foamed polymer beads may comprise an outer shell and a core, with an intermediary area disposed between the outer shell and core. The bead may comprise a cell structure with a substantially homogeneous cell size and distribution. The polymer beads, or pre-expanded polymer beads, may have low density cores. The polymer beads, or pre-expanded polymer beads, may comprise a hard shell and a low density core.

In one embodiment, the core has a density of less than about 30g/L. For example, the core may have a density of less than about 25g/L, less than about 20g/L, or less than about 16g/L. In some embodiments, the core has a density of about 16g/L to 30g/L. For example, the core may have a density of about 10g/L to 15g/L.

The intermediary area disposed between the outer shell and core may have a substantially homogeneous cell size and distribution. The beads may be produced with both open and closed cells. The cells may typically have a size of about 10μηι to 1000 pm, more typically about 300pm to 800 pm. For example, the size of the cells may be at about any one of the following amounts: 10, 20, 30, 40, 50, 75, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 pm. The beads may exhibit various properties including being spongy, rubbery, substantially resilient, and good impact resistance.

Figures 3a and 3b show C0₂ impregnated polymer beads pre-expanded by the process according to one embodiment of the invention. The pre-expanded beads as shown in Figure 3a have homogeneous cell structures typically about 300 pm in size.

Larger cells (e.g. 500-800 pm) may be present in the centre of bead with thinner walls.

Open cells can be found and are generally indicative of a low melt strength material.

Cell walls in the beads may also be substantially homogeneous. Figure 3b shows beads produced by three methods, namely (i) PLA in heated water, (ii) polystyrene in steam, (iii) PLA in steam.

The beads may be obtained with good surface quality or high surface smoothness. For example, good surface quality or high surface smoothness may be provided by observation of substantially few or no collapsed cells, which can be observed under SEM using X100 times. As mentioned above, the C0₂ impregnated granules may be stored at ambient conditions before pre-expansion or foaming into beads. The storage time or "lag-time" before pre-expansion or foaming may involve about a few minutes to one or more hours. For example, the storage time or "lag-time" may be at about or between about any one of the following amounts: 15 mins, 30 mins, 45 mins, 1 hr, 2 hrs, 3 hrs, 4 hrs, 5 hrs, 6 hrs, 7 hrs, 8 hrs, 9 hrs, 10 hrs, 1 1 hrs, 12 hrs, 13 hrs, 14 hrs, 15 hrs, 16 hrs. The density of beads and C0₂ content in the beads are typically inversely correlated for increasing storage times, for example as storage time increases density of beads produced generally increases while C0₂ content decreases. Figure 4 shows this correlation where the density and C0₂ content of beads produced by the process were about 20 g/L and 15 wt% C0₂, respectively, at about 30 mins lag time, and about 40 g/L and 12 wt% C0₂, respectively, at about 180 mins lag time. Further advantages may be provided by providing various lag times relative to the size of granules, such that the C0₂ content decreases to an advantageous amount that provides lower densities. In a preferred embodiment, the lag time is about 30 mins to 2 hours for granules of about 0.3 to 0.5 mm. It will be appreciated that smaller sized granules typically require shorter lag times.

Foamed polymer product

In one embodiment, there is provided a process for preparing a foamed polymer product from the polymer beads.

The process for preparing a moulded polymer product may include the step of foaming the impregnated polymer granules, polymer beads, or pre-expanded polymer beads, within a mould. The moulding process involves foaming the impregnated polymer granules or pre-expanded polymer beads, typically achieved by heating in a mould.

It will be understood that the polymer beads, or pre-expanded polymer beads, may be moulded by any moulding process known in the art. In one embodiment, the pre-expanded polymer beads are moulded by a fusion including a post-expansion process.

Fusion moulding is well known to those skilled in the art, and generally involves ensuring foamed beads are placed under temperatures and induced post-expansion exerting pressures that lead to adequate levels of fusion between the pre-foamed beads. It is important to eliminate or minimise shrinkage in the process, and post expansion is an ideally favoured method (analogues to EPS) In the absence of post- expansion and subsequently adequate fusion, additional agents may be required, e.g. post C0₂ treatment, solvents, bead coating (including adhesives).

In another embodiment, the process for preparing a foamed polymer product comprises:

optionally treating the pre-expanded or foamed polymer beads with a coating to form coated beads;

optionally treating the beads with liquid C0₂;

filling a mould with the polymer beads; and

applying heat treatment to the mould to form a foamed polymer product.

The foamed polymer product can be formed by contacting steam or air with pre- expanded/foamed beads.

A coating may also be applied to the pre-expanded or foamed beads. The coating of the beads can provide further advantages such as improved uniform foaming or facilitation of further processing of the beads. The coating, when present, can facilitate post-expansion fusion. The coating may comprise or consist of one or more fusion agents, such as acetone. The coating agent may comprise one or more other additives. The fusion agent can assist in reducing tool temperatures and heating times while improving fusion. While many suitable coatings are available (e.g.

acetone), PVA [polyvinyl alcohol or) or PVA [polyvinyl acetate)] alone or as mixture is a biodegradable option that is suitable as a coating for producing foamed polymer products. Co-polymerisation with ethylene blocks can also be used and provides typically moisture resistance, elasticity amongst other properties. Foamed polymer products with good water resistance can also be obtained using VINNAPAS 320 from Wacker [polyvinyl alcohol) stabilised vinyl acetate-ethylene copolymer dispersion].

In one embodiment, the coating may be selected from at least one of polyvinyl acetate, polyvinyl-acetate-based polymer, polyvinyl alcohol, polycaprolactone, polyester, polyester amide, protein-based material, polysaccharide, natural wax or grease, and acrylate. In a further embodiment, the coating is selected from at least one of a polyvinyl alcohol stabilised vinyl acetate-ethylene copolymer based coating.

The process may also comprise treating the uncoated or coated beads with liquid C0₂ prior to being placed in the mould. In a further embodiment, at least one of the processes of i) optionally treating the pre-expanded or foamed polymer beads with a coating to form coated beads, and ii) optionally treating the beads with liquid C0₂, is conducted within the mould prior to post expansion heating. It will be appreciated that the mould can be provided in a pre-determined shape or size. In one embodiment, the filling of the mould with polymer beads comprises 'crack filling' the mould. Crack filling may comprise of opening the mould sufficiently to incorporate an excess amount of coated beads, such that when the mould is closed, the beads are compacted.

The heat treatment of the mould may comprise a convective and/or conductive heating method. The convective heating method may comprise application of at least one of heated air, heated gas, heated vapour, and oven treatment. For example, the beads can be placed in a mould and exposed to heat in the form of heated air or steam. Air at 75°C is particularly suitable for post-expansion of PLA beads. Preferred processing conditions can be provided near the glass transition (Tg) temperature for the type of polymer. A temperature too high above Tg may lead to an undesirable degree of shrinkage, while a temperature significantly below Tg may not achieve a sufficient degree of fusion between the beads.

Post expansion moulding is well known to those skilled in the art, and may generally involve placing a plurality of pre-expanded polymer beads into a mould and treating the polymer beads with steam. The steam promotes post-expansion (in the presence of residual or otherwise added blow/foaming agents) and causes the polymer beads to fuse together (under processing conditions conducive to the thermo- mechanical and physical properties of the polymer) thus forming a moulded polymer product.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

The invention will now be described with reference to the following non-limiting Examples. EXAMPLES

General Protocol

Unless stated otherwise, the following general protocol was followed.

Polymer granules were placed in a pressurised vessel and pressurised C0₂ comprising liquid C0₂ was introduced into the vessel for a time sufficient for the polymer granules to absorb C0₂. The pressure was reduced to provide gaseous C0₂ for a time sufficient to enable C0₂ to distribute in the polymer granules (or equilibrate or further impregnate). The C0₂ impregnated polymer granules were optionally stored at ambient temperature and pressure or were pre-expanded immediately. The C0₂ impregnated polymer granules were pre-expanded in an oven (although as mentioned various heating modes possible) pre-heated to a suitable pre-expansion temperature to form pre-expanded beads. The pre-expanded beads were then removed from the oven and cooled to ambient temperature. The pre-expanded beads were optionally formed into moulded polymer products.

In the Examples provided below, the polylactic acid material used was

NatureWorks LLC, USA D6302. This polylactic acid comprises >99% polylactic acid and has a isomeric D/L - PLA ratio that makes it amorphous.

A general schematic of the process of one embodiment of the invention is shown in Figure 2. As can be seen in Figure 2, step 1 involves providing polylactic acid granules. Step 2 involves modifying the polylactic acid granules as desired. Step 3 involves contacting the polylactic acid granules with pressurised C0₂ comprising liquid and then gaseous C0₂ to obtain C0₂ impregnated polylactic acid granules. Step 4 involves optionally storing the C0₂ impregnated polylactic acid granules before step 5 involves pre-expanding the C0₂ impregnated polylactic acid granules in an oven (others as mentioned above) to form pre-expanded beads. Step 6 involves forming a moulded polymer product from the pre-expanded polylactic acid beads.

Example 1 : Pre-foaming of PLA granules, 3 mm elliptical shaped beads

Approximately 250 g of commercially available PLA granules were placed in a pressure vessel. Liquid C0₂ was introduced into the vessel at 6MPa until the PLA granules were fully submerged. The vessel was cooled to 10°C and absorption was left to take place over one hour. The pressure reduced over the one hour to 4.8-5.1 MPa. Following absorption, the pressure was further reduced to 2MPa to introduce gaseous C0₂, by venting off excess C0₂, and allowed to equilibrate C0₂ for three hours.

Following the three hours equilibrium, the pressure was reduced to ambient conditions and the C0₂ impregnated polymer granules were removed from the pressure vessel. The C0₂ impregnated polymer granules were weighed to determine a C0₂ content of 15.1-16.4%. The C0₂ impregnated polymer granules were subsequently kept under ambient conditions for (lag) times between 0-240 min before being pre-expanded in an oven kept at 90 °C. Pre-expansion times in the oven were varied between 30s and 90s. The density of the pre-expanded beads varied between 20-100 g/L depending on the lag-time conditions

Low density pre-expanded beads were obtained with lag times between 5-120 min, pre-expansion times of 50-80 sec, resulting in substantially homogeneous cell structure. Some beads were also obtained with even lower density (hollow) centres, no hard, or white, core and excellent surface finish including a shell. Both open and closed cells in the 300-800 μηι range were obtained.

Example 2: Pre-foaming of PLA granules, 3 mm elliptical shaped beads

The C0₂ impregnated polymer granules were prepared as per Example 1 above with the exception that absorption was left to take place over two hours. The two hour absorption led to a C0₂ content of 21 .9%. Low density pre-expanded beads were obtained with lag times between 5-120 min, pre-expansion times of 50-80 sec, resulting in substantially homogeneous cell structure. Some beads were also obtained with even lower density (hollow) centres, no hard, or white, core and excellent surface finish including a shell. Both open and closed cells in the 300-800 μηι range were obtained.

Example 3: Pre-foaming of PLA granules, 0.5 mm spherical shaped beads

210g of 0.5mm PLA granules were coated with 5% paraffin wax. The PLA granules were placed in a pressure vessel. Liquid C0₂ was introduced into the vessel at 6MPa until the PLA granules were fully submerged. The vessel was cooled to 5°C and absorption was left to take place over 30 minutes. The pressure reduced over the 30 minutes to 3.7MPa. Following absorption, the pressure was further reduced to 2MPa to introduce gaseous C0₂, by venting off excess C0₂, and allowed to equilibrate and further impregnate C0₂ for 90 minutes. Following the 90 minutes further impregnation process, the pressure was reduced to ambient conditions and the C0₂ impregnated PLA granules were weighed to determine a C0₂ content of 12.3-13.1 %. The C0₂ impregnated PLA granules were subsequently kept under ambient conditions for times between 0-30 minutes before being pre-expanded in hot water kept at 90°C. Pre-expansion times in hot water varied between 1 -8 seconds. The bulk density of the pre-expanded beads was approximately 40g/L and provided less homogenous cell structures, which was largely due to processing granules with a reasonably inhomogeneous size distribution in larger pilot scale equipment. The pre-expansion conditions can be optimised further to produce beads with substantially more homogeneous cell structure, although processing at more controllable small scale conditions provided more homogenous cell structures and densities consistently < 30 g/L. Example 4: Pre-foaming of PLA granules, 0.5 mm spherical shaped beads

200g of 0.5mm PLA granules were coated with 5% paraffin wax in octane. The coated PLA granules were placed in a pressure vessel. Liquid C0₂ was introduced into the vessel at 6MPa until the PLA granules were fully submerged. The vessel was cooled to 5°C and absorption was left to take place over 60 minutes. The pressure was reduced over the 60 minutes to 3.7MPa. Following absorption, the pressure was further reduced to 2MPa to introduce gaseous C0₂, by venting off excess C0₂, and allowed to equilibrate for 180 minutes. Following the 180 minutes equilibrium, the pressure was reduced to ambient conditions and the C0₂ impregnated PLA granules were weighed to determine a C0₂ content of 15.5-16.1 %. The C0₂ impregnated PLA granules were subsequently kept under ambient conditions for times between

0-30 minutes before being pre-expanded in steam vapour produced by boiling water. Pre-expansion times in steam varied between 1 -5 seconds. The bulk density of the pre-expanded beads was approximately 35g/L. Example 5: Moulding of pre-foamed EPLA beads to make prototype bar

Pre expanded beads were prepared as per Example 3. A moulded product was produced using a prototype bar tool with dimensions 100 x 50 x 25mm. The tool was optionally heated with steam to a temperature of between 22-60°C. The tool was crack filled with pre-expanded beads and sealed. Steam was introduced at 100KPa for times between 3-15 seconds. Products were dried to eliminate excess moisture following the moulding process. The products density was determine gravimetrically and found to vary between 40-55g/L.

Excessive steam times and high tools temperatures were found to attribute to excessive product shrinkage. Low steam times and low tool temperatures attributed to minimal shrinkage but compromised bead fusion. A balance between steam time and tool temperature yielded acceptable product appearance with minimal bead fusion. Preferred processing conditions are provided near the glass transition (Tg) temperature of the polymer, which in this case is PLA. A temperature too high above Tg may lead to an undesirable degree of shrinkage, while a temperature significantly below Tg may not achieve a sufficient degree of fusion between the beads.

Example 6: Moulding of pre-foamed EPLA beads to make prototype bar

Pre expanded beads were prepared as per Example 3. A moulded product was produced using a prototype bar tool with dimensions 100 x 50 x 25mm. The tool was optionally heated with steam to a temperature of between 22-60°C. The tool was crack filled with pre-expanded beads and sealed. Steam was introduced at 100KPa with the inclusion of a fusion agent (acetone, 1-3mls) via a specially designed venturi for times between 3-15 seconds. Products were dried to eliminate excess moisture following the moulding process. The products density was determined gravimetrically and found to vary between 40-55g/L. The use of acetone allowed for a reduction in tool temperature and steam time to produce a product with considerable increased fusion compared to the process used in Example 5.

Example 7: Moulding of pre-foamed EPLA beads to make prototype bar

Pre expanded beads were prepared as per Example 3. A moulded product was produced using a prototype bar tool with dimensions 90 x 60 x 25mm. Pre-expanded beads were coated with polyvinyl alcohol) stabilised vinyl acetate-ethylene copolymer by immersing them in a 5% solution, and subsequently dried. To promote post- expansion the coated beads were placed in a pressure vessel with liquid C0₂ held at 6MPa until the beads were fully submerged. The vessel was left at room temperature with absorption to take place over 45 minutes. The pressure was reduced to ambient conditions and the C0₂ impregnated pre-expanded beads were removed from the pressure vessel. The C0₂ impregnated pre-expanded beads were weighed to determine a C0₂ content of 30.4-34.5%. The impregnated pre-expanded beads were subsequently placed in an aluminium mould and sealed. Hot air was introduced at 75°C for between 60-160 seconds. The product was removed and then weighed to determine the density. The density of the product varied between 50-60g/L.

The introduction of post expansion within the mould allowed for improved fusion between the beads. The moulded product was found to have smoother surfaces and an increased level of mechanical strength. Example 8: Moulding of pre-foamed EPLA beads to make prototype box

Pre-expanded beads were prepared as per Example 3. A moulded prototype box was produced using an industrially designed and manufactured steam tool for 5 making prototype boxes. The dimensions of each side of the boxes produced were 140mm x 1 15 mm with a 1 10 x 1 10 mm base and 20mm wall thickness. The tool was heated with steam to temperatures between 25-60°C. The tool was pneumatically crack filled with the pre-expanded beads and sealed. Steam was first introduced to the inside of the box (venting outside) at 100KPa for times between 10-80 seconds. Steam l o was then introduced from the outside of the box (venting inside) again at 100KPa for times between 10-25 seconds. Following the dual steam injection procedure, the tool was subsequently cooled to 40°C prior to removing the moulded box. Optimum conditions were obtained with tool temperatures less than 35°C and steam times of 15 seconds for both inside and outside steam injection directions.

15

Example 9: Moulding of pre-foamed EPLA beads to make prototype box

Pre-expanded beads were prepared as per Example 3. A moulded prototype box was produced using an industrially designed and manufactured steam tool for making prototype boxes. The dimensions of each side of the boxes produced were

20 140mm x 1 15 mm with a 1 10 x 1 10 mm base and 20mm wall thickness. The tool was heated with steam to temperatures between 25-29°C. The tool was pneumatically crack filled with the pre-expanded beads and sealed. Steam was first introduced, with 10-15 ml acetone included as a fusion agent via venturi, from both the inside of the box (venting outside) at 100KPa for 10-15 seconds and outside of the box (venting inside)

25 at 100KPa for 10-15 seconds. Following the dual steam/fusion agent injection

procedure, the tool was subsequently cooled to 40°C prior to removing the moulded box. Good quality was obtained for the boxes moulded under the conditions described above, although less than EPS boxes moulded under EPS optimised conditions.

Preferred conditions were obtained with tool temperatures less than 35°C and

30 steam times of 15 seconds for both inside and outside steam injection directions.

Claims

CLAIMS:

1 . A process for preparing C0₂ impregnated polymer granules, wherein the process comprises the steps of:

2. The process according to claim 1 , wherein for step i) the pressurised C0₂ consists of liquid C0₂.

3. The process according to claim 1 or claim 2, wherein at least step i) occurs in a pressure vessel having parameters of temperature, pressure and duration, for initiating absorption of C0₂ into the polymer granules.

4. The process according to claim 3, wherein the parameters of temperature and pressure in step i) provides operation at about or above the saturated liquid-vapour phase line for a C0₂ system.

5. The process according to claim 4, wherein for step i) the temperature is about -20 °C to 31 °C, preferably about -10 °C to 25 °C, or more preferably about 0 °C to 15 °C.

6. The process according to any one of claims 3 to 5, wherein for step i) the pressure is less than about 7.0 MPa, preferably about 4 to 7 MPa, or more preferably between about 6 MPa.

7. The process according to any one of claims 1 to 6, wherein for step i) the duration is at least about 15 mins or up to about 6 hours, or more preferably at least about 30 mins or up to about 2 hours.

8. The process according to any one of claims 1 to 7, wherein for step ii) the pressurised C0₂ consists of gaseous C0₂.

9. The process according to any one of claims 1 to 8, wherein step ii) occurs in a pressure vessel having parameters of temperature, pressure and duration, for facilitating distribution of C0₂ in the polymer granules.

10. The process according to claim 9, wherein the parameters of temperature and pressure in step ii) provides operation below the saturated liquid-vapour equilibrium for C0₂.

1 1. The process according to claim 9 or claim 10, wherein for step ii) the temperature is about -20 °C to 31 °C, preferably about -10 °C to 25 °C, or more preferably about 0 °C to 15 °C. .

12. The process according to any one of claims 9 to 1 1 , wherein for step ii) the pressure is less than 6 MPa, preferably about 1 to 5 MPa, or more preferably about 1.5 to 3 MPa.

13. The process according to any one of claims 9 to 12, wherein for step ii) the duration is at least about 15 mins or up to about 16 hours, or more preferably at least about 30 mins or up to about 4 hours.

14. The process according to any one of claims 1 to 13, wherein the process for step i) and step ii) occurs in a pressure vessel and wherein the pressure vessel is vented after step i) for initiating step ii) by releasing C0₂ from the pressure vessel and reducing pressure in the pressure vessel such that operation is below the saturated liquid-vapour line for C0₂.

15. The process according to any one of claims 1 to 14, wherein the polymer granules comprise biodegradable type polymers selected from the group consisting of polybutylene succinate (PBS), poybutylene succinate-co-adipate (PBSA) copolymers, polybutyrate adipate terephthalate (PBAT), adipic acid aliphatic/aromatic copolyesters (AAC), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxy alkanoates (PHAs) including poly-p-hydroxybutyrate (PHB) and its copolymer with hydroxyvaleric acid (PHB/v), modified polymers of polyterephthalate, polytetramethylene adipate-co- terephthalate, and combinations or blends thereof.

16. The process according to claim 15, wherein the polymer granules comprise polylatic acid.

17. The process according to any one of claims 1 to 16, wherein the polymer granules comprise one or more additives selected from the group consisting of nucleating agents, lubricants, plasticisers, and antioxidants.

18. The process according to any one of claims 1 to 17, wherein the polymer granules have a diameter between about 0.1 to 10 mm, preferably about 0.1 to

1 .0 mm, and more preferably about 0.4 to 0.7 mm.

19. The process according to any one of claims 1 to 18, wherein the polymer granules are coated with one or more external lubricants selected from the group consisting of waxes such as polyethylene waxes or oxidized polyethylene waxes, paraffins, metal soaps, esters, amides, fatty acids, and fatty esters.

20. The process according to claim 19, wherein the one or more external lubricants is a paraffin wax.

21. The process according to any one of claims 1 to 20, wherein the C0₂ wt % in the C0₂ impregnated polymer granules is less than 30 wt%, preferably about 5 wt% to 25 wt%, or more preferably about 10 wt% to 20 wt%.

22. C0₂ impregnated polymer granules prepared by the process according to any one of claims 1 to 21.

23. A process of preparing pre-expanded or foamed polymer beads comprising: i) and ii) preparing C0₂ impregnated polymer granules according to the process of any one of claims 1 to 21 ;

24. The process according to claim 23, wherein the pre-expanding or foaming step iv) is carried out by heating the C0₂ impregnated polymer granules using convective, conductive or radiation methods.

25. The process according to claim 24, wherein the heating of the C0₂ impregnated polymer granules involves a convective method comprising steam.

26. The process according to any one of claims 23 to 25, wherein the pre- expanding or foaming step iv) occurs directly after step ii) and without the optional storage step iii).

27. The process according to any one of claims 23 to 25, wherein the storage step iii) is for up to about up to about 4 hours, preferably about 5 to 120 minutes, or more preferably about 20 to 60 minutes.

28. The process according to any one of claims 23 to 27, further comprising the separation or removal of pre-expanded polymer beads during or after formation thereof in step iv) using an air flow process.

29. Pre-expanded or foamed polymer beads prepared by the process according to any one of claims 23 to 28.

30. The pre-expanded or foamed polymer beads according to claim 29, wherein the beads comprise an outer shell and a core, with an intermediary area disposed between the outer shell and core having a substantially homogeneous cell size and distribution.

31. The pre-expanded or foamed polymer beads according to claim 30, wherein the density of the core is less than 30 g/L, preferably less than 25 g/L, or more preferably less than 15 g/L.

32. The pre-expanded or foamed polymer beads according to claim 30 or claim 31 , wherein the outer shell has a high surface smoothness.

33. A process for preparing a foamed polymer product comprising the steps of: i) and ii) preparing C0₂ impregnated polymer granules according to the process of any one of claims 1 to 21 ;

iv) optionally pre-expanding or foaming the C0₂ impregnated polymer granules according to any one of claims 23 to 28 to obtain pre-expanded or foamed polymer beads;

vi) optionally treating the beads with liquid C0₂;

vii) foaming the beads or granules into a polymer product.

34. The process according to claim 33 comprising the steps of:

i) and ii) preparing C0₂ impregnated polymer granules according to the process of any one of claims 1 to 21 ;

iv) pre-expanding the C0₂ impregnated polymer granules according to any one of claims 23 to 28 to obtain pre-expanded polymer beads;

v) coating the pre-expanded polymer beads to form coated beads;

vi) optionally treating the coated beads with liquid C0₂; and

vii) foaming the beads into a polymer product.

35. The process according to claim 34, comprising the step vi) of treating the coated beads with liquid C0₂ prior to the foaming step vii).

36. The process according to any one of claims 33 to 35, wherein the step vii) of foaming the beads or granules into the polymer product comprises filling a mould with the polymer and applying heat treatment to the mould to form a moulded polymer product.

37. The process according to any one of claims 33 to 36, wherein the coating in step v) comprises one or more fusion agents selected from at least one of polyvinyl acetate, polyvinyl-acetate-based polymer, polyvinyl alcohol, polycaprolactone, polyester, polyester amide, protein-based material, polysaccharide, natural wax or grease, and acrylate.

38. The process according to claim 37, wherein the one or more fusion agents are selected from at least one of a polyvinyl alcohol and vinyl acetate-ethylene copolymer based coating.