WO2005026254A1

WO2005026254A1 - Biodegradable thermoplastic material

Info

Publication number: WO2005026254A1
Application number: PCT/EP2004/010320
Authority: WO
Inventors: Antonio Fochesato
Original assignee: Deca S.R.L.
Priority date: 2003-09-17
Filing date: 2004-09-14
Publication date: 2005-03-24
Also published as: EP1664184A1; ITPD20030213A1

Abstract

A biodegradable thermoplastic material comprises a physical mixture of olefin-based and/or styrene-based polymeric matrix, a starch consisting of a mixture of rice starch and corn starch and an effective fraction of poly(epsilon-caprolactone) (PCL).

Description

BIODEGRADABLE THERMOPLASTIC MATERIAL

The present invention concerns a biodegradable thermoplastic material, according to the characteristics outlined in the preamble of the main claim.

In particular, the present invention falls within the field of so-called compostable materials, i.e. those materials that can be biodegraded into compost when subjected to certain temperature and relative humidity conditions for a certain period of time.

Due to known problems inherent to management of waste and pollution control, materials of this type have in recent years received an increasing amount of attention.

As known, the biodegrading into compost of a material is a controlled oxidisation process, carried out by microorganisms, which leads to the formation of carbon dioxide, water, minerals and a stabilised organic substance (actual compost) .

In the technical field identified above it is known that there is a requirement to make a polymer-based material that, as well as responding to the requirements of biodegradability necessary to be classified as compostable, has good mechanical characteristics and low production cost. For this purpose, different materials comprising a polymeric matrix combined with a natural polymer of vegetable origin, typically starch, have been perfected and released onto the market. This type of solution is, indeed, indicated as preferred, for the purposes of compostability, by various national and international regulations, including those of the European Community. A first class of materials comprising a polymeric matrix in combination with polymers of vegetable origin is made up of materials in which a thermoplastic polymer is chemically bonded with starch, through a suitable reaction in a chemical reactor.

This class includes, for example, materials comprising a polymeric matrix based upon biodegradable thermoplastic polymers and water-soluble products, by themselves or in mixture, such as poly (epsilon- caprolactone) (hereafter, for the sake of brevity, PCL) , or poly vinyl alcohols (PVA) , in which organic chains deriving from corn starch, wheat starch and potato starch are integrated, with covalent bindings.

Materials of this type, however, have a series of limitations, including unsuitable mechanical properties and a very high production cost, which substantially limit its use, in particular in applications of a lesser technical profile.

Moreover, this class of materials is negatively characterised in that they are not very thermally stable, which substantially limits recycling (also of production discards and waste) with a consequent worsening of the overall costs. Indeed, recycled material has totally insufficient resistance to traction and resistance to collisions for its actual practical application.

Further examples of materials of this type, particularly in which the polymeric matrix is formed from polyethylene and/or its derivatives or else from polystyrene, are described in US patents nos . 5.496.895, 5.461.094, 6.090.863 and 5.412.005. A second class of materials is formed from compounds substantially consisting of a physical mixture of olefin-based, or else styrene-based, polymers, and starch (possibly pre-treated) , together with other substances the function of which is that of making the (non-polar) polyolefin polymer and the (polar) starch compatible . Examples of this second class of materials are described in US patent application no. 2003/0100635, as well as in US patents nos. 4337181 and 5292782. These materials, however, have proven unsuitable for requirements of mechanical resistance and low production costs.

The problem forming the basis of the present invention is that of making a biodegradable thermoplastic material structurally and functionally conceived to overcome the limitations outlined above with reference to the quoted prior art . In this problem a primary purpose of the finding is that of making a thermoplastic material that responds to the requirements laid down by current standards for being classified as compostable. This problem is solved and this purpose is achieved by the present finding through a biodegradable thermoplastic material made in accordance with the following claims.

According to a first aspect of the present invention, the material object of the finding comprises a physical mixture of an olefin and/or styrene-based polymeric matrix, a starch of vegetable origin, in turn consisting of a suitable mixture of rice starch and corn starch, and an effective fraction of poly (epsilon- caprolactone) (PCL) . The polymeric matrix preferably consists of linear polyethylene (LLDPE) , or else low-density polyethylene (LDPE) , high-density polyethylene (HDPE) , polypropylene homopolymer, block or statistical polyethylene- polypropylene copolymer, high-impact polystyrene (HIPS) or polystyrene crystal (PS) .

The primary function of the polymeric matrix is that of giving the material the required mechanical properties. Moreover, the selection of the compounds indicated above is also determined by their low price on the market . The starch used is a suitably dosed mixture of rice starch and corn starch. The starch, in the same way as the other materials of this technical field, is the component that by decomposing causes the degradation process of the thermoplastic material. Indeed, in certain temperature and humidity conditions, it hydrolyses forming dextrin and glucose which are in turn converted, following the oxidising action of thermophiles (fermentation process) , into ethanol and carbon dioxide . The degradation of the starch inevitably leads to the decay of the entire material (and therefore to its degradation) since the starch is intimately connected with the polymer constituting the base matrix. The PCL used preferably has a medium or medium-high viscosity index.

Amongst the components of the thermoplastic material of the invention, the PCL in the mixture is the one that decomposes most quickly and at the lowest temperatures, in this way promoting the start of the hydrolysis reaction of the starch.

According to a further aspect of the invention, the rice starch and the corn starch are in a ponderal ratio of between 1:1 and 1:4, synergically exploiting the different characteristics of the two types of starch. Rice starch, indeed, possesses greater mechanical resistance at low temperatures and tends to ferment at lower temperatures with respect to corn starch. This means, first of all, greater mechanical resistance of the entire thermoplastic material at low temperatures (measured at -20°C, according to a known standard) . Such a positive characteristic of rice starch, indeed, proves particularly important for those materials whose polymeric matrix is styrene-based, which would have, per se, a rather high glass transition temperature, with a consequent tendency of the material to become fragile.

Secondly, the presence of rice starch promotes faster biodegradation of the entire material at the end of its life, since, fermenting at lower temperatures, substantially acts as initiator of the fermentation of the corn starch.

According to a further aspect of the invention, the material can comprise a hydrophilic agent, preferably siloxane-based, the purpose of which is that of promoting the hydrolysis reaction of the starch. According to a further aspect of the invention, the material has a range of compositions in which the ponderal fraction of the polymeric matrix is between 40% and 50%, the PCL between 3% and 10%, the rice starch between 10% and 20% and the corn starch between 20% and 40%. A preferred composition within this range has also been identified, shown in greater detail in the examples described hereafter, thanks to which the different properties of the material have been optimised. The material according to the finding can also comprise mineral or organic loads, preferably selected from calcium carbonate, talc and pumice, or else fossil flour and wood flour. In particular, the addition of pumice gives the material a high mechanical resistance to traction and compression, whereas the addition of wood flour improves the material in terms of dimensional stability.

The material object of the present invention has particular application in the production of containers such as pots, boxes and in the field of packaging in general.

The characteristics and advantages of the invention shall become clearer from the detailed description of some preferred embodiments thereof, illustrated for indicating and not limiting purposes with reference to the attached drawings, in which: figure 1 is a graph representing the progression through time of the degradation of a first example of thermoplastic material made according to the present invention, figures 2 and 3 are graphs analogous to that of figure 1, in which the progression through time of the degradation of a second and third thermoplastic material made according to the present invention. In order to evaluate the mechanical and biodegradabability characteristics of the material of the present invention, four different samples have been prepared, made according to the following formulations. Example 1

Corn starch 40%

Rice starch 10% PCL 5%

Polypropylene-ethylene copolymer 43% Hydrophilic agent 2%

The material having the composition shown above was prepared in the following way. The polypropylene copolymer (in this example ethylene and propylene have been block copolymerised) was mixed with PCL in a vertical screw mixer for 15 minutes, whereas the rice starch, the corn starch and the hydrophilic agent were mixed apart for 15 minutes in a rotating mixer (sifting machine) .

After this first mixing, the polypropylene copolymer and the PCL are loaded at the mouth of a co-rotating twin-screw extruder equipped with 2 degassers and dispensers, preferably of the gravimetric type, whereas the starch and the hydrophilic agent were entered into the extruder after the first degasser through forced lateral feeding.

The mixture (compound) was extruded at a temperature of 215-220°C, cooled in a water tank at 15°C and then cut into the shape of cylindrical granules. The possible organic load (fossil flour and/or wood flour) or mineral load (talc, calcium carbonate and/or pumice) can be inserted into the extruder through a second forced lateral dispenser, before the second degasser. Examples 2-4

Further samples of material were prepared by using the same formulation of example 1, in which instead of the polypropylene-ethylene copolymer, on various occasions low-density polyethylene, linear polyethylene and high- impact polystyrene were used.

The preparation of the samples took place according to the same methods as the previous example, apart from the extrusion temperature that was, respectively, 185- 200 °C for the formulation with low-density polyethylene 200-205° for the formulation with linear polyethylene and 210-220°C in the formulation with polystyrene. The granules formed from the samples obtained according to examples 1 to 4 were subsequently dried for 6 hours at 105°C in a ther ostatted stove with forced air circulation and then injection moulded into the shape of multi purpose test specimens (MPTS) , according to standard ISO R527.

Thereafter, all of the samples were subjected to mechanical resistance tests and biodegradability tests. As far as the mechanical resistance tests are concerned, the samples were subjected to mechanical resistance tests under traction (according to standard ISO 178) and impact resistance tests (according to standard ISO 180) , highlighting properties up to 50% greater with respect to the analogous materials produced in the chemical reactor.

As far as the biodegradability aspect is concerned, the samples were tested according to standard ISO/CD 14852, so as to verify the possibility of classifying the material in question as compostable. This test foresees the arrangement of the samples for 56 days at a temperature of 58°C (+/-2°C) in an area with a relative humidity of more than 65%. The material is classified as compostable if at the end of the test period it has disintegration equal to or greater than 90%.

In the attached figures 1, 2 and 3 the respective average progression through time of the disintegration of the samples relative to example 1, 2 and 4 (that of example 3 being practically identical to that of example 2) is shown in a graph. It should be noted that all of the tested samples could be classified as compostable, having the samples made according to examples 1, 2 and 3 having highlighted a disintegration index of 95% after just 45 days and the sample made according to example 4 a disintegration index of 92% after 56 days foreseen by the test.

The present invention thus solves the aforementioned problem with reference to the quoted prior art, at the same time offering numerous other advantages, including the possibility of recycling the material and of washing it even after its first production. This material, indeed, can be thermally treated without causing particular drawbacks, since the triggering of the degrading process requires, as well as temperature, the presence of water. Moreover, the material according to the invention has good mechanical characteristics and a low production cost (estimated to be about 50%less with respect to the cost of the most common materials currently on the market . Moreover, the material according to the invention can normally be worked in normal transformation plants used in the field, such as plants for the production of blown film, with a flat head, or injection moulding plants or thermoforming plants, without any need to make mechanical changes.

Claims

1. Biodegradable thermoplastic material, comprising a physical mixture of olefin-based and/or styrene-based polymeric matrix and a starch, characterised in that said starch consists of a mixture of rice starch and corn starch and in that it comprises an effective fraction of poly (epsilon-caprolactone) (PCL).

2. Material according to claim 1, wherein said olefin- based and/or styrene-based polymeric matrix is selected from the group consisting of linear polyethylene, low- density polyethylene, high-density polyethylene, polypropylene, block or statistical polyethylene- polypropylene copolymer, high-impact polystyrene or polystyrene crystal .

3. Material according to claim 1 or 2 , wherein said rice starch and said corn starch are present in a ponderal ratio of between 1:1 and 1:4.

4. Material according to one or more of the previous claims, wherein said polymeric matrix is present with a ponderal fraction of between 40% and 50%, said PCL with a ponderal fraction of between 3% and 10%, said rice starch with a ponderal fraction of between 10% and 20% and said corn starch with a ponderal fraction of between 20% and 40%.

5. Material according to one or more of the previous claims, wherein an effective fraction of a hydrophilic agent is further foreseen.

6. Material according to claim 5, wherein said hydrophilic agent is polysiloxane-based.

7. Material according to claim 6, wherein said polymer- based matrix is present with a ponderal fraction of about 43%, said PCL of 5%, said rice starch of about 10%, said corn starch of about 40% and said hydrophilic agent of about 2%.

8. Material according to one or more of the previous claims, wherein a mineral and/or organic load is further foreseen.

9. Material according to claim 8, wherein said mineral or organic load is selected from the group consisting of talc, calcium carbonate, pumice, fossil flour and wood flour.

10. Use of the material according to one or more of the previous claims for the production of pots, boxes, containers in general, as well as articles in the field of packaging.