WO2019155398A1

WO2019155398A1 - Biodegradable plastic

Info

Publication number: WO2019155398A1
Application number: PCT/IB2019/050991
Authority: WO
Inventors: Sudhakar MUNIYASAMY; Osei OFOSU; Asanda MTIBE; Rajesh D ANANDJIWALA
Original assignee: Csir
Priority date: 2018-02-07
Filing date: 2019-02-07
Publication date: 2019-08-15
Also published as: GB201801978D0

Abstract

This invention relates to a biodegradable plastic and a process for producing the biodegradable plastic from bio-based polymers and agricultural by-products renewable resource based. The biodegradable plastic is produced in a process comprising melt blending a polymer blend comprising or consisting of polybutylene succinate (PBS); and at least one other bio-based polymer. The other bio-based polymer may be a biopolyester such as polybutylene adipate co-terephthalate (PBAT) or polylactic acid (PLA) or poly hydroxy butyrate (PHB) or thermoplastic starch which may be modified.

Description

BIODEGRADABLE PLASTIC

BACKGROUND TO THE INVENTION

This invention relates to a biodegradable plastic and more particularly to a process for producing the biodegradable plastic from bio-based polymers and agricultural by-products renewable resource based.

The current consumable plastics products for single- and short-time uses are derived from petroleum based feedstock, therefore, they are non- biodegradable when disposed in natural environments, persisting in landfill for many decades, thus causing serious environmental damage as well as harmful to terrestrial and aquatic habitats [1 -3].

To overcome this global challenge and managing the plastic wastes, many countries have prohibited the use of plastic bags, for example, Tanzania, Ivory Coast, Kenya and many others [4-6]. Also, there are commercially available bio-based polymers, such as polylactic acid (PLA), starch, cellulose and other microbial bio-based polymers polyhydroxy butyrate (PHB), succinic acid and others, being used to meet ecological requirements, however, there are major drawbacks in that they cannot be used directly for bioplastic products due to their low thermal stability, slow crystallization behaviour, poor impact resistance, low rate of biodegradation and difficulties in conventional processing, which prevent their applications in a wide range of industrial products [7-26].

There are biodegradable plastic technologies available commercially, particularly in the developed countries like Italy, France, USA and Australia. However, the post-consumer plastic waste of these technologies are mainly suitable for industrial composting facilities (at 60-70°C), since they don’t have enough landfill sites. Majority of commercially available biodegradable plastic technologies are not suitable for developing countries like India, China and African countries including South Africa, where most plastic waste are still dispose in landfill sites [7,15, 23, 26].

It is an object of the invention to provide a biodegradable plastic that will, at least partially, alleviate the above disadvantages.

It is also an object of the invention to provide a biodegradable plastic which will be a useful alternative to existing biodegradable plastic.

SUMMARY OF THE INVENTION

According to the invention there is provided a process for producing a biodegradable plastic, comprising melt blending a polymer blend comprising or consisting of:

• polybutylene succinate which may be derived partially from a bio based source (PBS), or derived 100% from a bio-based source (Bio-PBS); and

• at least one other bio-based polymer, preferably a biopolyester such as polybutylene adipate co-terephthalate (PBAT) or ploylactic acid (PLA) or poly hydroxy butyrate (PHB) or thermoplastic starch which may be modified. The polybutylene succinate and at least one other bio-based polymer/s may be blended at a weight ratio of 1 :0.25 to 1 :2, typically 1 :0.4 to 1 :1 .

In one embodiment of the invention, the at least one other bio-based polymer is polybutylene adipate co-terephthalate (PBAT), and the polybutylene succinate and polybutylene adipate co-terephthalate are blended at a weight ratio of 1 :0.25 to 1 :1 , for example 1 :0.3 to 1 :0.8, typically 1 :0.4 to 1 :0.7, or 1 :0.5 to 1 :0.6, or an amount of 55-75% to 25- 45%, preferably 60-70% to 30-40%, for example 65-70% to 30-35%, by weight.

The polymer blend may include 1 to 10%, preferably 3 to 7.5%, most preferably about 5% by weight natural polymer/s such as cellulose (60-70% crystalline content) or starch (above amylose 70% content) or protein (above 60%), which is preferably plasticized with a plasticizer such as glycerol, for example plasticized microcrystalline cellulose.

The polymer blend may include 0.5 to 2%, typically 0.5 to 1 % by weight of an additive such as epoxy polyester, chain extender with alkyl side groups different lengths or a styrene-acrylate co-polymer with epoxy functionality, or a combination thereof.

In another embodiment of the invention, at least one other bio-based polymer is polylactic acid, preferably modified polylactic acid such as starch blended polylactic acid (cPLA), and the polybutylene succinate and cPLA are blended at a weight ratio of 1 :3 to 1 :1 , typically 1 :2.3 to 1 :1.5, or an amount of 30-40% to 70-80%, by weight.

Preferably the melt blending of bio-based polymers occurs in a melt twin screw extruder, typically in a single step co-rotating melt extrusion process. Further the melted bio-based polymers, preferably bio-based polymers pellets, produced from the melt extrusion may be sent to an injection moulding or blown film to produce biodegradable plastic products (films/or injection moulded parts).

The temperature of the melt blending occurs with a melt temperature in the range of about 130 to 160°C, typically about 135 to 155 °C.

In a preferred embodiment of the invention, melt blending occurs with a feeding temperature - in a Zone I of 125 - 160°C; in a Zone II of 140- 185°C, in a Zone 111:145-190°C, in a Zone IV of 150-195°C; Zone V of 140- 195°C; Zone VI of 140-190°C and Melt temperature 135-155 °C.

The melt blending may occur at a feeding speed of 25-35 rpm, typically about 30 rpm; and a residential time of 1 -2 min.

The invention further comprises a biodegradable plastic produced by the process as defined above.

According to the invention there is provided a biodegradable plastic, comprising or consisting of:

• polybutylene succinate which may be derived partially from a bio based source (PBS), or derived 100% from a bio-based source (Bio-PBS);

• polybutylene adipate co-terephthalate (PBAT);

• optionally a natural polymer; and

• optionally an additive; wherein:

the biodegradable plastic has a tensile strength greater than 20 MPa, preferably greater than 30 MPa and an elongation break at greater than 800%, preferably greater than 900%.

According to another embodiment of the invention there is provided a biodegradable plastic, comprising or consisting of:

• polybutylene succinate which may be derived partially from a bio based source (PBS), or derived 100% from a bio-based source (Bio-PBS); • polylactic acid (PLA) which may be modified

• optionally a natural polymer; and

• optionally an additive; wherein:

the biodegradable plastic has a tensile strength greater than 30 MPa, preferably greater than 35 MPa and an elongation break at greater than 50%, preferably greater than 100%.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood from the detailed description given herein and from the accompanying drawing and results which are given only as an illustration and that is not limit the intended scope of invention.

Figure 1 is a flow diagram of a process for producing bioplastic materials of the present invention using a co-rotation twin screw extrusion and injection moulding, and using an extruder and blown film/injection moulding;

Figure 2 is a graph of thermal properties of developed bioplastic materials of the present invention by thermalgravimetric analysis;

Figure 3 is a graph of biodegradation (%) versus incubation time

(days) for a neat biopolymer, a referenced cellulose and a bioplastic bag of the present invention;

Figure 4 is a graph showing the results bioplastic of the invention tested for biodegradation in industrial compost, soil and marine water as per ASTM standards;

Figure 5 is photographs of bioplastic material of the present invention under composting conditions at 0 day, 17 days and 30 days; Figure 6 is photographs of the bioplastic material in the present invention on soil incubation at day 0, 60 days and 90 days;

Figure 7 is photographs of the bioplastic of the present invention in a marine water medium in the presence of sewage microbial inoculum after 30 days, after 60 days and after 140 days; and

Figure 8 is a photograph of a prototype of blown film plastic bag produced from the developed bioplastic biodegradable material of the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Definition

“Additive” refers to plastic materials which are a group of compounds with a variety of applications such as adhesion promotors, bonding agents, Ultra violet light stabilizers, plasticizers, chain extenders, stabilizers.

“Blend” is a mixture of two or more different polymers/plastics to give a homogeneous material.

“Bioplastic” means a plastic material derived from renewable resource based including plants, starch, microorganisms.

“Bio-based polymers” are defined as polymers made from biological sources. Some of these polymers are formed directly in the polymeric form within the producing organisms such as microorganisms, algae, or plants, while others are manufactured ex vivo from bio-based monomers. “Compatibilizers” refers to any polymeric interfacial agent that facilitates formation of uniform plastic blends with desirable end properties.

“Biodegradable plastic” means plastics that undergo degradation by action of microorganisms (bacteria/fungi/algae) in natural environmental conditions (soil/compost and water).

“Recyclable plastic” refers to a plastic - containing product that can be reprocessed into another, similar or often different, plastic - containing products.

“Compostable plastic” refers to a plastic that undergoes degradation by biological processes during composting to yield C0₂, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and leaves no visible, distinguishable or toxic residue.

Materials

PBS - Polybutylene succinate is a bio-based polymers derived partially biobased sourced from Showa Polymer Inc, Japan.

BioPBS - Polybutylene succinate derived from 100% biobased sourced from PTTMCC, Thailand.

PBAT - Polybutylene adipate terephthalate sourced from BASF, Germany.

MCC - Microcrystalline cellulose extracted from maize stalk residues.

nPLA - Polylactic acid sourced from Nature works, USA.

cPLA - starch blended polylactic acid sourced from Cereplast, USA.

Glycerol used as plasticizer obtained from Sigma Aldrich, South Africa.

Additives - Epoxy polyester trade named as JONCRYL^® ADR-4368-C,

BASF.

Abbreviations

PBS - Polybutylene succinate PBAT - Polybutylene adipate co-terephthalate

pMCC - Plasticized microcrystalline cellulose

PLA - Polylactic acid

HDPE - High densily polyethylene

LLDPE - Linear low density polyethylene

DSC - Differential scanning colorimetry

TGA - Thermogravimetric analysis

Tcc - cold crystallization temperature

AH_C- enthalpy of crystallization

J/g - Joule per gram

Tm - Melting temperature

AH_m- Enthalpy of melting

MFI - Melt flow index

MPa - Mega pascal

PDI - Poly dispersion index

Mw - molecular weight

The present invention provides a biodegradable and compostable plastic produced from agricultural (agro) by-products and bio-based polymers.

The major drawbacks of commercially available bio-based polymers can be effectively addressed by melt blending bio-based polymers with fillers and additives. The melt processing technique is fast, economical and a convenient approach compared to developing a new material through synthetic polymerization. Agriculture by-products, such as starch and cellulose are widely available natural polymers from renewable resources which can be used to develop thermoplastic hybrid materials by melt processing technique with the addition of suitable plasticizers such as glycerol. With this approach, stiffness, melt viscosity and barrier properties of the bio-based polymers can be improved with the help of reactive agents and natural fillers, respectively. The present invention consists of a bioplastic formulation which utilizes agricultural by-products blended with bio-based polymers to produce a biodegradable plastic for applications in flexible plastic packaging products. The present invention may be designed using low cost agricultural by products and bio-based polymers. This biobased biodegradable plastic achieves good mechanical properties that are similar to conventional non- biodegradable low density polyethylene (LDPE) films. The development of this biodegradable bioplastic does not need a separate melt processing equipment, instead existing conventional processing equipment, such as melt extrusion, melt blowing and injection moulding can be used. This processed bioplastic is reusable and mechanically recyclable. After the end-of-life of this bioplastic product can undergo, preferably complete, biodegradation in natural environmental conditions including landfill, compost (such as municipal home compost or industrial compost) or aqueous media, in a timely and efficient manner within 3-6 months without any toxic residues. In addition to that the raw materials utilized in developing the product are derived from naturally renewable resources, therefore, the technology is sustainable.

The biodegradation of plastic is a chemical degradation process mediated by natural microorganisms such as bacteria, fungi and algae. The biodegradation process can be affected by various physical-chemical properties as well biological properties such as molecular weight, thickness, crystallinity and microorganisms. Therefore, the biodegradable plastic technology is designed for the product to meet the necessarily functionalities similar to conventional plastics but after its end-of-life, when disposed into natural environments, it will undergo biological degradation in a timely and efficient manner.

In the present invention, a single step co-rotating melt extrusion processing technique is employed, where the bio-based polymers were blended with agriculture by-products using natural plasticizer. The characterization results of the compounded bioplastic showed that the incorporation of agro by-products provided a bioplastic with improved properties and added advantage of biodegradability and can become an alternative to conventional non-biodegradable LDPE plastic. The amount and form of the agro by-products acts as a nucleating agent in the transesterification reaction. This approach resulted in the development of bioplastic products for flexible packaging applications with improved mechanical and thermal properties and addresses the processing draw backs of bio-based polymers.

With reference to Figure 1 , an embodiment of the invention comprises a bio-based polymer 10 comprising biopolyesters 14 melt blended at a temperature between 130-140 °C 18 together with an agricultural by product 12 comprising starch and cellulose using glycerol as plasticizer and/or additive 16 in a co-rotation twin screw extrusion and injection moulding 20 to produce a bioplastic test specimen 22. The bioplastic test specimen 22 undergoes characterization 24.

Another embodiment of the invention comprises a bio-based polymer 10 comprising biopolyesters 14 melt blended at a temperature between 130- 140 °C 18 together with an agricultural by-product 12 comprising starch, cellulose using glycerol as plasticizer and/or additive 16 in an extruder 26. Extruded pellets 28 is produced from the extruder 26 and the extruded pellets 28 is sent to a blown film or injection moulding 30 to produce a biodegradable plastic bags or films 32.

Numerous feedstocks (biomass) such as sugarcane (molasses and bagasse), agricultural residues (maize and wheat) and other biomass may be utilized as raw material feedstocks for biobased polymers. The present invention is easily scalable using laboratory validated optimization parameters and it can be processed on existing processing technologies (extrusion, injection molding, and blown film).

• Biodegradable in soil, compost and aqueous medium.

• Recyclable (mechanical).

• Renewable resource based and non-toxic.

• Suitable for flexible film applications (plastic carrier bag).

Some of the properties of the biodegradable plastic bags are:

• Retain excellent properties and ease of processing similar to conventional LDPE.

• Affordable.

• Resource efficient compared to conventional plastic.

• Adds value to customer’s brand.

• Reduce the environmental impact of short term disposable plastic wastes.

The biodegradable plastic is mechanically recyclable. However, the hetero chain biodegradable plastic cannot be mixed with conventional petroleum based carbon-chain plastics. It is advised that a separate recycling system is needed to avoid contamination of recyclability of thermoplastic biopolyester/biodegradable polymers.

This bioplastic material must be stored at room temperature, away from sunlight and less exposure to high humidity conditions.

Melt extrusion of BioPBS with starch modified PBAT and plasticized microcrystalline cellulose (60-70/30-40/1 -3 % w/w) was found to be an optimum amount to modify the inherent properties of PBS matrix such as thermal processability, brittability, elongation properties through transesterification reactions to meet physical properties of conventional PE plastic films with added advantages of virtually 100% biodegradability and compostability. The blend does not contain any CaC0₃ as filler or amide as lubricants.

Preferred processing parameters:

Feeding temperature - Zone l:125°C; Zone ll:140°C, Zone 111:145°C, Zone IV: 150°C; Auxiliary feeder: 155°C and Melt temperature 135 °C

Feeding Speed - 30 rpm ; Residential time 1 -2 min

Mechanical properties:

Ultimate tensile strength (MPa) - 30.08 ± 0.4

Tensile modulus (MPa) - 232 ± 6.05

Elongation at break (%) - 756 ± 20.38

Thermal - Physical properties:

Melt flow index (MFI) g/10 min - 3.71

Rheology (Mw g/mol) - 3.6

Differential scanning colorimetry - crystallization temperature (AHc (J/g) - 40.8

Melting temperature - 1 1 1 °C

Thermogravimetric analysis - weight degradation temperature - 230-250°C (single peak)

Biodegradation properties:

Soil - virtually 100% biodegradable within six months (ASTM D5988-18) Compost - virtually 100% biodegradable within 3 months (ASTM D6400- 12)

Marine water - virtually 100% biodegradable within 6 months (ASTM D6691 - 17).

Examples

Preferred processing parameters of the bio-based polymers blending process used in the present invention as shown in Table 1 below.

Table 1 . Processing parameters for development bioplastic blends in a twin screw extruder into pellets.

The optimized parameters for the injection moulding of the bio-based polymers and blended bioplastics used in the present invention as shown in Table 2 below.

Table 2. Processing parameters for development bioplastic materials in injection moulder into test specimen/products.

0-30% of PBAT was used as an optimum amount to modify the physical, mechanical and thermal properties of PBS as shown Table 3 below. Above 30% PBAT content, the mechanical properties of PBS/PBAT blends drops drastically. Table 3. Mechanical and thermal properties of the developed bioplastic materials: PBS, PBAT and PBS-PBAT blends in comparison with HDPE and LLDPE.

A preferred combination is with a tensile strength greater than 30 MPa and an elongation break at greater than 900%.

0-10% of pMCC which contains 30% glycerol was used as an optimum amount to modify the physical, mechanical and thermal properties of PBAT in the present invention as shown Table 4 below

Table 4. Mechanical and thermal properties of the developed bioplastic materials: PBAT and PBAT-pMCC.

0-50% PBS was used to modify the mechanical properties of cPLA in the present invention as shown Table 5. PLA is very brittle material but the starch blended PLA (cPLA) with PBS, it improves from brittle to non-brittle (non-breakable), which can be used for rigid packaging applications (cutlery items, crates and others).

Table 5. Mechanical and thermal properties of the developed bioplastic materials: cPLA-PBS blends.

0-1 % of chain extender was used to increase melt strength and thermal stability of bio-based polymers PBS-PBAT blends as referred Table 6 and 7 below.

Table 6. Mechanical and thermal properties of the developed bioplastic materials: PBS, PBAT, PBS-PBAT blends, PBS-PBAT-chain extender

Table 7. Thermal-physical properties of the developed bioplastic and blends determined by rheology

Table 8 provides DSC results of developed bioplastic materials indicating that below 0-30% PBAT content the enthalpy of crystallinity and enthalpy of melting drops drastically. Enthalpy of crystallinity and enthalpy of melting are major factors for determining the maximum PBAT content.

Table 8. Thermal properties of developed bioplastic materials by differential scanning colorimetry.

A preferred crystallinity is above 30 AH_C (J/g)

Figure 2 shows the TGA results of developed bioplastic materials indicating that the compatibility of PBS-PBAT blends showing single step degradation.

Figure 3 shows the developed bioplastic material tested percentage biodegradation under industrial composting conditions in comparison to a neat biopolymer PBS, a referenced cellulose of the present invention (70% PBS/30%PBAT/1 %chain extender). The results indicate the developed bioplastic material undergoes compost biodegradation as similar like cellulose (positive reference).

Figure 4 is the developed bioplastic material (70% PBS/30%PBAT/1 %chain extender) tested for biodegradation in industrial compost, soil and marine water as per ASTM standards. This indicates that biodegradability of the developed bioplastic materials in the present invention.

Figure 5 is the fragmentation (as the first step of biodegradation) of the developed bioplastic materials (70% PBS/30%PBAT/1%chain extender) under composting conditions at 0 day, 17 days and 30 days. The results indicate after 30 days incubation time the fragmented bioplastic materials were not visually distinguishable

Figure 6 is the fragmentation (as the first step of biodegradation) of the bioplastic material in the present invention (70% PBS/30%PBAT/1%chain extender) on soil incubation at day 0, 60 days and 90 days. The results indicate after 90 days incubation time the fragmented bioplastic materials were not visually distinguishable

Figure 7 is the fragmentation (as the first step of biodegradation) of the bioplastic of the present invention (70% PBS/30%PBAT/1 %chain extender) in a marine water medium in the presence of sewage microbial inoculum after 30 days, after 60 days and after 140 days. The results indicate after 140 days the developed bioplastic material is completely soluble.

Figure 8 is the prototype of blown film plastic bag produced from the developed bioplastic biodegradable material of the present invention (70% PBS/30%PBAT/1 %chain extender) on lab scale validated technology.

References

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Claims

1 . A process for producing a biodegradable plastic, comprising melt blending a polymer blend comprising or consisting of:

• polybutylene succinate; and

• at least one other bio-based polymer, preferably a biopolyester such as polybutylene adipate co-terepthalate (PBAT) or ploylactic acid (PLA) or poly hydroxy butyrate (PHB) or thermoplastic starch which may be modified.

2. The polybutylene succinate and at least one other bio-based polymer/s may be blended at a weight ratio of 1 :0.25 to 1 :2, typically 1 :0.4 to 1 :1 .

3. The process claimed in claim 2, wherein at least one other bio based polymer is a biopolyester.

4. The process claimed in claim 3, wherein the biopolyester is polybutylene adipate co-terephthalate (PBAT) or ploylactic acid (PLA) or poly hydroxy butyrate (PHB) or thermoplastic starch which may be modified.

5. The process claimed in claim 1 , wherein the at least one other bio based polymer is polybutylene adipate co-terephthalate, and the polybutylene succinate and polybutylene adipate co-terephthalate are blended at a weight ratio of 1 :0.25 to 1 :1 .

6. The process claimed in claim 5, wherein the and the polybutylene succinate and polybutylene adipate co-terephthalate are blended at a weight ratio of 1 :0.4 to 1 :0.7.

7. The process claimed in claim 1 , wherein the at least one other bio based polymer is polybutylene adipate co-terephthalate, and the polybutylene succinate and polybutylene adipate co-terepthalate are blended in an amount of 55-75% to 25-45%, by weight.

8. The process claimed in claim 7, wherein the polybutylene succinate and polybutylene adipate co-terephthalate are blended in an amount of 60-70% to 30-40%, by weight.

9. The process claimed in any one of the preceding claims, wherein the polymer blend includes 1 to 10%, by weight natural polymer/s.

10. The process claimed in claim 9, wherein the polymer blend includes 3 to 7.5%, by weight natural polymer/s.

1 1. The process claimed in claim 0, wherein the polymer blend about 5% by weight natural polymer/s.

12. The process claimed in claim 9, wherein the natural polymer/s are selected from cellulose, starch or protein.

13. The process claimed in claim 12, wherein the natural polymer/s are plasticized.

14. The process claimed in claim 9, wherein the natural polymer is microcrystalline cellulose plasticised with glycerol.

15. The process claimed in any one of the preceding claims, wherein the polymer blend includes 0.5 to 2%, by weight of an additive.

16. The process claimed in claim 15, wherein the polymer blend includes 0.5 to 1% by weight of an additive.

17. The process claimed in claim 15 or 16, wherein the additive is a epoxy polyester, chain extender with alkyl side groups different lengths or a styrene-acrylate co-polymer with epoxy functionality, or a combination thereof.

18. The process claimed in claim 1 , wherein the at least one other bio based polymer is modified polylactic acid (cPLA), and the polybutylene succinate and polylactic acid are blended at a weight ratio of 1 :3 to 1 :1.

19. The process claimed in claim 18, wherein the at least one other bio based polymer is modified polylactic acid (cPLA), and the polybutylene succinate and polylactic acid are blended at a weight ratio of 1 :2.3 to 1 :1 .5.

20. The process claimed in claim 1 , wherein the at least one other bio based polymer is modified polylactic acid (cPLA), and the polybutylene succinate and polylactic acid are blended in an amount of 30-40%, by weight.

21. The process claimed in claim 20, wherein the at least one other bio based polymer is modified polylactic acid (cPLA), and the polybutylene succinate and polylactic acid are blended in an amount of 70-80%, by weight.

22. The process claimed in any one of the preceding claims, wherein the melt blending of bio-based polymers occurs in a melt twin screw extruder.

23. The process claimed in claim 22, wherein the melt blending of bio based polymers occurs in a single step co-rotating melt extrusion process.

24. The process claimed in claim 1 , wherein the temperature of the melt blending occurs with a melt temperature in the range of 130 to 160 °C.

25. The process claimed in claim 24, wherein the temperature of the melt blending occurs with a melt temperature in the range of 135 to 155 °C.

26. The process claimed in claim 25, wherein the melt blending occures with a feeding temperature - in a Zone I of 125 - 160°C; in a Zone II of 140-185°C, in a Zone 111:145-190°C, in a Zone IV of 150-195°C; Zone V of 140-195°C; Zone VI of of 140-190°C and Melt temperature 135-155 °C.

27. The process claimed in claim 26, wherein the melt blending occurs at a feeding speed of 25-35 rpm; and a residential time of 1 -2 min.

28. A biodegradable plastic produced by a process as defined in any one of the preceding claims.

29. A biodegradable plastic, comprising or consisiting of:

• polybutylene succinate;

• polybutylene adipate co-terephthalate;

• optionally a natural polymer; and

• optionally an additive; wherein:

the biodegradable plastic has a tensile strength greater than 20 MPa and an elongation break at greater than 800%%.

30. The biodegradable plastic claimed in claim 29, with a tensile strength greater than 30 MPa and an elongation break at greater than 900%.

31. A biodegradable plastic, comprising or consisting of:

• polybutylene succinate; • ploylactic acid (PLA) which may be modified

• optionally a natural polymer; and

• optionally an additive; wherein:

the biodegradable plastic has a tensile strength greater than 30 Mpa and an elongation break at greater than 50%.

32. The biodegradable plastic claimed inclaim 31 , that has a tensile strength greater than 35 MPa and an elongation break at greater than 100%.