WO2023135561A1

WO2023135561A1 - A process for preparing a biodegradable polymer composition

Info

Publication number: WO2023135561A1
Application number: PCT/IB2023/050308
Authority: WO
Inventors: Sandanamudi ANUDEEP; Shiva Subramanian; Rani KC
Original assignee: Phitons Bioengineering Private Limited
Priority date: 2022-01-13
Filing date: 2023-01-13
Publication date: 2023-07-20

Abstract

A process for preparing a biodegradable polymer composition is disclosed. Said process comprises processing about 40 % w/w or higher of a modified starch and 30-60 % w/w of polybutylene adipate terephthalate (PBAT) through a twin-screw processor at a barrel temperature ranging between 60-110°C.

Description

A PROCESS FOR PREPARING A BIODEGRADABLE POLYMER COMPOSITION

Field of Invention

The present disclosure relates to a process for preparing a biodegradable polymer composition. Specifically, the present disclosure relates to a process for preparing a biodegradable polymer composition comprising a modified starch and polybutylene adipate co-terephthalate.

Background

Biodegradable materials and environmentally friendly alternatives for plastic are increasingly being adopted in various industries, including for example packaging. Starch is easily available, renewable, biodegradable and generally low cost and has been used for preparing biodegradable plastics. However, starch films are brittle and starch, a hydrophilic material, tends to deteriorate on exposure to humidity. These factors make starch unsuitable for preparing biodegradable plastics especially for food packaging.

To overcome such limitations, starch is modified and blended with other polymers. Modification of starch includes for example plasticization and gelatinization that weaken the inter- molecular hydrogen bonding of the starch molecule. Polymers typically used for blending with starch are polyvinyl alcohol (PVA), polylactic acid (PLA), polycaprolactone (PCL), polybutylene adipate co-terephthalate (PBAT). While PBAT is a completely biodegradable aliphatic -aromatic copolyester with competitive mechanical properties in comparison to low-density polyethylene (LDPE), it is very expensive.

WO 2009/073197 discloses a starch-polyester graft copolymer formed by the reactive blending of a thermoplastic starch with a biodegradable polyester. However, as disclosed by Garalde et al., The effects of blend ratio and storage time on thermoplastic starch/poly(butylene adipate-coterephthalate) films, Heliyon 5 (2019) e01251, such blends of starch and PBAT at 20, 40, and 60 wt% of starch suffer from disadvantages such as low miscibility. Starch-PBAT blends with high starch concentration are also known to result in deterioration of mechanical properties, especially impact strength. Summary

Brief Description of Drawings

Figure 1 shows a comparative study of the solubility of the modified starch used to prepare the biodegradable polymer composition, in accordance with an embodiment of the present disclosure.

Figure 2 shows the Scanning Electron Microscopy (SEM) images of prior art thermoplastic starch /PBAT films (Garalde et al., 2019).

Figure 3 shows the SEM image of a biodegradable polymer composition prepared in accordance with an embodiment of the present disclosure.

Figure 4 shows thermogravimetric analysis of a polymer composition obtained by mixing of starch, glycerol and PBAT.

Figure 5 shows thermogravimetric analysis of a biodegradable polymer composition, prepared in accordance with an embodiment of the present disclosure.

Detailed Description

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

Reference throughout this specification to “one embodiment”, “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms “a,” “an,”, and “the” are used to refer to “one or more” (i.e. to at least one) of the grammatical object of the article.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion and are not intended to be construed as “consists of only”, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described.

The present disclosure relates to a process for preparing a biodegradable polymer composition. Said process comprises processing about 40 % w/w or higher of a modified starch and 30-60 % w/w of polybutylene adipate terephthalate (PBAT) through a twin- screw processor at a barrel temperature ranging between 60-110°C, to obtain the biodegradable polymer composition.

The process conditions, the modified starch and PBAT disclosed herein provide a biodegradable polymer composition which exhibits optimum mechanical properties even at higher percentages (>50%) of starch. The modified starch disclosed herein comprises starch and a compatibilizing agent selected from the group consisting of glycerol, glycerin, sorbitol and a combination thereof in a w/w ratio of 2:1 to 4:1. Said modified starch of the present disclosure is hydrophobic and is substantially insoluble in water such that good physical integrity is maintained even after immersion in water. Said modified starch has a solubility index of less than 15% in water at a temperature of about 80°C. The thermogravimetric analysis of the modified starch shows a characteristic peak at a temperature in the range of 120°C to 180°C.

In accordance with an embodiment, the disclosed modified starch is insoluble in cold water. Cold water refers to water maintained at a temperature of about 10 °C. In accordance with another embodiment, the modified starch has a solubility index in a range of 1%- 5% in water kept at room temperature of about 25 °C and has a solubility index in boiling water (at 100 °C) in a range of 17%- 35%. In accordance with another embodiment, the modified starch has a solubility index in the range of 1%- 5% in chloroform.

In accordance with an embodiment, the modified starch comprises starch and the compatibilizing agent in a w/w ratio of 2: 1-4:1. In some embodiments, the w/w ratio of starch and the compatibilizing agent is 2:1 -3.5:1. In an exemplary embodiment, the w/w ratio of starch and the compatibilizing agent is 3.3:1 to 3.4:1 and in particular 3.34:1. Figure 1 shows a comparative study of the solubility of the modified starch , when the w/w ratio of starch and compatibilizing agent (glycerol) is 3.34:1. The solubility studies were performed in chloroform, cold water at a temperature of 10°C, water at room temperature, water a temperature of 80°C and 90°C, and boiling water.

In accordance with an embodiment, the modified starch has a moisture content in the range of 0.4-0.9%. In some embodiments, the modified starch has the moisture content of 0.6-0.7 %.

Any known source of starch may be used to prepare the modified starch. In accordance with an embodiment, the starch is a natural starch and is selected from the group consisting of potato, wheat, com, cassava, rice, peas starch and a combination thereof. In accordance with an embodiment, the starch is a chemically or physically modified starch, selected from the group consisting of oxidised, carboxymethylated, hydroxyalkylated, enzymatically treated starch, and combinations thereof. In some embodiments, a blend of natural as well as chemically or physically modified starch is used.

The compatibilizing agent is selected from the group consisting of glycerol, glycerin, sorbitol, and combinations thereof. In some embodiments, the compatibilizing agent is glycerol.

The modified starch comprises additives such as fillers, emulsifiers, fragrance, essential oils and fatty acids. Any known fillers may be used. In accordance with an embodiment, the fillers are selected from the group consisting of calcium carbonate, calcium oxides, coco peat, and a combination thereof. Any known emulsifier may be used. In accordance with an embodiment, the emulsifier is selected from the group consisting of tween 20, glycerol monostearate, alcohol ester and a combination thereof.

In accordance with an embodiment, the modified starch is in the form of pellets. Said modified starch is prepared by a process comprising: preparing a blend comprising starch and a compatibilizing agent in a w/w ratio ranging between 2: 1-4:1; processing said blend comprising starch and the compatibilizing agent through a twin-screw processor at a barrel temperature ranging between 60-110°C. The disclosed process conditions subject starch and compatibilizing agent to vigorous mechanical and thermal interaction such that a modified starch, which is substantially insoluble in cold water, water at room temperature as well as chloroform, is obtained.

In accordance with an embodiment, the modified starch and biodegradable polymer composition are prepared in the same twin-screw processor. In some embodiments, said process comprises: feeding the blend comprising starch and the compatibilizing agent to a first inlet of the twin-screw processor; processing the blend through the twin-screw processor at the barrel temperature ranging between 60-110°C to obtain the modified starch; feeding PBAT through a second inlet of the twin-screw processor; processing the modified starch and PBAT through the twin-screw processor at the barrel temperature ranging between 60-110°C; and obtaining the biodegradable polymer composition from a discharge zone of the twin-screw processor. The sequential preparation of the modified starch followed by addition of PBAT to obtain the biodegradable polymer composition, results in a biodegradable polymer composition exhibiting improved properties as compared to a composition resulting from sequential feeding of PBAT through a first inlet followed by the blend of starch and compatibilizing agent, or batch feeding of modified starch and PBAT.

In accordance with an embodiment, the blend comprising starch and the compatibilizing agent is prepared at room temperature of about 25-35 °C. In accordance with an embodiment, the blend comprising starch and the compatibilizing agent is prepared without the addition of water. In accordance with an embodiment, the processing of the blend comprising starch and the compatibilizing agent in the twin-screw processor is carried out without the addition of water. In accordance with an embodiment, the blend comprising starch and the compatibilizing agent is prepared in any known mixer. In some embodiments, said blend is prepared in a ribbon mixer.

In accordance with an embodiment, the blend comprising starch and the compatibilizing agent is processed through the twin-screw processor at the temperature ranging between 60-110°C. In some embodiments, the blend is processed at the temperature ranging between 60-100°C.

In accordance with an embodiment, the modified starch and PBAT are processed through the twin-screw processor at the barrel temperature ranging between 90-110°C.

In accordance with an embodiment, the twin-screw processor for preparing the modified starch as well as the biodegradable polymer composition is operated at a screw speed of 80-140 rpm. In some embodiments, the twin-screw processor is operated at a screw speed of 80-120 rpm. In accordance with an embodiment, the twin-screw processor has a length/ diameter (L/D) in a range of 60/40. In an embodiment, the blend comprising starch and the compatibilizing agent is fed to the twin-screw processor at a feeding rate of 30-100 Kg/ hr. In accordance with an embodiment, PBAT is fed to the twin-screw processor at a feeding rate of 30-100 Kg/ hr. In accordance with an embodiment, the process parameters are varied such that the residence time varies between 1-4 minutes. In accordance with an embodiment, the twin-screw processor is a co-rotating twin-screw processor. In accordance with an embodiment, the co-rotating twin-screw processor is a co-rotating twin-screw extruder. In accordance with an exemplary embodiment, the twin-screw extruder is Omega 40H or Omega 60H (Steer Engineering Pvt. Ltd.).

In accordance with another embodiment, the modified starch and the biodegradable polymer composition are prepared in at least two separate twin-screw processors connected in series. In accordance with an exemplary embodiment, said two twin-screw processors are connected in series, wherein the modified starch is obtained in the form of pellets from the first twin-screw processor and is fed to the second twin-screw processor for processing with PBAT to obtain the biodegradable polymer composition.

In accordance with an embodiment, PBAT is added in an amount ranging between 30-60% w/w of the biodegradable polymer composition. In some embodiments, PBAT is added in an amount ranging between 40-60% w/w of the biodegradable polymer composition. In accordance with an embodiment, PBAT used in the biodegradable polymer composition has a molecular weight in a range of 9 X 10⁴ -15 X 10⁴ Da.

In accordance with an embodiment, a filler is added during the processing of the modified starch and PBAT to prepare the biodegradable polymer composition. Any known filler may be used. In accordance with an embodiment, the filler is selected from a group consisting of calcium carbonate, micronized talc, nano-clay, micro-cellulose and nano-cellulose. The filler is added in a quantity ranging between 0.01-5% w/w of the biodegradable polymer composition.

The biodegradable polymer composition obtained using the above process is also disclosed. Said biodegradable polymer composition comprises 30-60 % w/w of PBAT and at least 40 % w/w of a modified starch, wherein the thermogravimetric analysis of the biodegradable polymer composition shows a characteristic peak at a degradation temperature of 320-340°C. Herein, “characteristic peak” refers to a peak obtained at a certain degradation temperature, and which has a maximum derivative weight loss (%) greater than 1%. The biodegradable polymer composition obtained using the disclosed process comprises PBAT as a continuous phase and the modified starch as a dispersed phase with improved dispersion uniformity and homogeneity, such that SEM images of the biodegradable polymer composition show a homogenous phase. As illustrated in Figure 2, SEM images of prior art TPS/PBAT films (Garalde et al., 2019) show miscibility limitations between PBAT and starch, with micro-fractures. In contrast, referring to Figure 3, SEM images of the biodegradable polymer composition obtained using the disclosed process show a homogenous phase indicating better miscibility between modified starch and PBAT.

In accordance with an embodiment, the biodegradable polymer composition obtained using the disclosed process has a notched izod impact strength of at least 20 KJ/m², measured in accordance with ASTM D256. In accordance with other embodiments, the biodegradable polymer composition has the notched izod impact strength of at least 30 KJ/m².

In accordance with an embodiment, the biodegradable polymer composition obtained using the disclosed process has a melt flow index (MFI) in a range of 4-10 g/10 minutes, measured in accordance with ASTM D1238. In accordance with other embodiments, the biodegradable polymer composition has MFI of 6-11 g/10 minutes.

In accordance with an embodiment, the biodegradable polymer composition obtained using the disclosed process has an elongation at break of at least 150%, measured in accordance with ASTM D638. In accordance with other embodiments, the biodegradable polymer composition has the elongation at break of at least 300%.

Examples:

In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and the exact compositions, methods of preparation and embodiments shown are not limiting of the invention, and any obvious modifications will be apparent to one skilled in the art. Also described herein are method for characterizing the biodegradable polymer compositions in accordance with one or more embodiments of the present invention.

Example 1: Process for preparation of the exemplary biodegradable polymer composition

The biodegradable polymer composition was prepared by first preparing a blend comprising starch and glycerolat room temperature in a ribbon mixer. The blend comprising starch and glycerol was fed and conveyed through a twin-screw extruder. PBAT was fed to the twin-screw extruder through a second inlet. The modified starch and PBAT was conveyed through the twin-screw extruder and the biodegradable polymer composition- BPCI was obtained from the discharge zone of the twin-screw extruder.

The ingredients used to form the exemplary biodegradable polymer composition (BPCI) are listed in Table 1, below.

Table 1: Ingredients for preparing exemplary biodegradable polymer composition

The machine specifications and processing conditions are stated in Table 2, below:

Table 2: Machine specifications and processing conditions

The screw configuration of the twin screw extruder is provided in Table 3, below:

Table 3: Screw Configuration * List of Abbreviations for Elements

The temperature of barrels of the extruder is provided in Table 4, below:

Table 4: Barrel Temperature

The properties of the biodegradable polymer composition (BPCI) obtained are summarized in Table 5, below:

Table 5: Mechanical Properties of Biodegradable Polymer Composition

Example 2: Comparison of the exemplary biodegradable polymer composition with prior art polymer disclosed in Can et al. (PBAT/thermoplastic starch blends: “Effects of oxidized starch and compatibilizer content; AIP Conference Proceedings 1914, 070004 (2017))

The mechanical properties of the exemplary biodegradable polymer composition prepared in Example 1 were compared with that of PBAT/thermoplastic starch blends disclosed in Can et al. Said PBAT/thermoplastic starch blend comprises PBAT and thermoplastic starch in a ratio of 50/50. Table 6 shows a comparison of the mechanical properties of biodegradable polymer composition with said prior art polymer.

Table 6: Comparison of mechanical properties

Observation: It was observed that the biodegradable polymer composition obtained using the disclosed process exhibits significant improvement in mechanical properties when compared with prior known blends of PBAT and starch at same w/w ratio. Example 3: Comparative TGA analysis

Comparative thermogravimetric analysis study of the biodegradable polymer composition (BPCI) obtained in Example 1 and a polymer composition prepared as described below (COMP1), was performed.

Process for preparing CQMP1: COMP1 was prepared by mixing starch, glycerol and PBAT in a ribbon mixer. The quantity of starch, glycerol and PBAT are shown in table 7, below.

Table 7: Ingredients for preparing COMP1

The thermogravimetric analysis of the obtained biodegradable polymer composition was conducted in a thermogravimetric analyser (Perkin Elmer TGA 4000) under a nitrogen atmosphere at a heating rate of 10°C per minute. The change in weight as a function of temperature was recorded.

Observation: Figure 4 shows the thermogravimetric analysis of COMP1. Figure 5 shows the thermogravimetric analysis of BPCI. While three degradation peaks could be seen in Figure 4 at temperature of 195°C, 340.57°C and 415.02°C, two degradation peaks are seen in Figure 5 at temperature of 329.10°C and 414.60°C. The first peak at 195 °C in Figure 4 indicates degradation and release of glycerol suggesting that COMP 1 does not include bound glycerol.

Additionally, the derivative weight loss at around 180°C was observed to be much faster in COMP1 as compared to the derivative weight loss in BPCI at the same temperature. Thus, BPCI demonstrates higher thermal stability as compared to COMP1. It could thus be concluded that while the process of present disclosure results in starch bonded with glycerol via saturated hydrogen bonding, such an effect is not observed in COMP1.

Example 4: Comparative study of mechanical properties of the biodegradable polymer composition with different amounts of modified starch

The process of Example 1 was followed using two commercially available PBAT (from “Ecoworld” and “Xinjiang Blue Ridge Tunhe Polyester Co., Ltd (Tunhe)”) while maintaining the weight percentage of modified starch at 70% and 65% in the biodegradable polymer composition. Table 8, below summarizes the mechanical properties of the biodegradable polymer composition for said weight percentages of modified starch:

*MS: Modified Starch

Table 8: Comparison of mechanical properties

Observation: It was found that the biodegradable polymer composition with up to 70 % w/w of modified starch could be prepared with optimum set of mechanical properties.

Example 5: A comparative study was performed to assess the effect of sequence of addition of the blend comprising starch and compatibilizing agent (glycerol), and PBAT on the mechanical properties of the exemplary biodegradable polymer composition comprising modified starch and PBAT in a w/w ratio of 1:1 (i.e. 50:50).

Table 9 below summarizes the process followed in each experiment and the mechanical properties of the biodegradable polymer composition.

*BMS: Blend of Starch and Glycerol

Table 9: Comparison of Mechanical Properties

Observation: It was observed that when the blend comprising starch and glycerol, and PBAT are fed in a sequence, the process results in a biodegradable polymer composition having optimum set of mechanical properties, as compared to batch feeding where the blend comprising starch and glycerol, and PBAT are fed together. It was further observed that sequential feeding of the blend comprising starch and glycerol followed by PBAT, resulted in improved properties as compared to sequential feeding of PBAT followed by the blend comprising starch and glycerol.

Industrial Application

The disclosed process provides biodegradable polymer compositions which is able to substitute polyethylene in packaging industry, specifically in the food industry where single use plastics are used. The biodegradable polymer composition obtained in the present process is susceptible to both aerobic and anaerobic decomposition.

The process, including the process conditions, the modified starch and PBAT disclosed herein enables preparing biodegradable polymer compositions having a high percentage of modified starch, while achieving optimum mechanical properties and biodegradability. This reduces the cost of manufacturing biodegradable plastics without compromising with the mechanical properties thereof. The disclosed process enables processing the starch, the compatibilizing agent and PB AT at lower barrel temperatures (about 110°C or less) to obtain the biodegradable polymer composition. This allows reducing degradation of material observed at higher temperatures.

The disclosed process of sequential feeding of the blend of starch and the compatibilizing agent followed by PBAT to obtain the biodegradable polymer composition, results in a biodegradable polymer composition exhibiting improved properties as compared to a composition resulting from sequential feeding of PBAT followed by the blend of starch and the compatibilizing agent, or batch feeding of the blend of starch and the compatibilizing agent, and PBAT.

The thermogravimetric analysis of the biodegradable polymer composition obtained using the disclosed process shows a significant derivative weight loss % (greater than 1%) only at temperatures >300°C indicating a stable biodegradable polymer composition. Thus, the obtained biodegradable polymer composition exhibits improved mechanical properties as well as thermal stability.

The SEM images of the obtained biodegradable polymer composition illustrate that the composition shows a homogenous phase indicating better miscibility between modified starch and PBAT. This allows subjecting the disclosed biodegradable polymer composition to different plastic processing technologies like blown film extrusion, blow molding, injection molding and thermoforming.

Claims

We Claim:

1. A process for preparing a biodegradable polymer composition, the process comprising: processing about 40% w/w or higher of a modified starch and 30-60 % w/w of polybutylene adipate terephthalate (PBAT) through a co-rotating twin- screw processor at a barrel temperature ranging between 60-110°C.

2. The process as claimed in claim 1, wherein the modified starch is prepared by a process comprising: preparing a blend comprising starch and a compatibilizing agent selected from a group consisting of glycerol, glycerin, sorbitol and a combination thereof, in a w/w ratio of 2:1-4: 1 ; and processing said blend comprising starch and the compatibilizing agent through a twin-screw processor at a barrel temperature ranging between 60-110°C.

3. The process as claimed in claim 2, wherein the modified starch and the biodegradable polymer composition are prepared in the same twin-screw processor.

4. The process as claimed in claim 3, wherein the process for preparing the biodegradable polymer composition comprises:

- feeding the blend comprising starch and the compatibilizing agent selected from a group consisting of glycerol, glycerin, sorbitol and a combination thereof in the w/w ratio of 2: 1-4:1, to a first inlet of the twin-screw processor;

- processing the blend comprising starch and the compatibilizing through the twin-screw processor at the barrel temperature ranging between 60-110°C to obtain the modified starch;

- feeding PBAT through a second inlet of the twin-screw processor;

- processing the modified starch and PBAT through the twin-screw processor at a barrel temperature ranging between 60-110°C; and

- obtaining the biodegradable polymer composition from a discharge zone of the twin- screw processor.

5. The process as claimed in claim 2 or 4, wherein the blend comprises starch and the compatibilizing agent in the w/w ratio of 3.34:1.

6. The process as claimed in claim 2 or 4, wherein the blend comprising starch and the compatibilizing agent is prepared at room temperature.

7. The process as claimed in claim 2 or 4, wherein the blend comprising starch and the compatibilizing agent is prepared without the addition of water.

8. The process as claimed in claim 2 or 4, wherein processing the blend comprising starch and the compatibilizing agent in the twin-screw processor is carried out without the addition of water.

9. The process as claimed in claim 2 or 4, wherein the blend comprising starch and the compatibilizing agent is processed in the twin-screw processor at the barrel temperature ranging between 60-100 °C.

10. The process as claimed in claim 1, wherein the modified starch comprises starch and the compatibilizing agent selected from the group consisting of glycerol, glycerin, sorbitol and a combination thereof in a w/w ratio of 2: 1 to 4: 1, and wherein the modified starch has a solubility index of less than 15% in water at a temperature of about 80°C and thermogravimetric analysis of the modified starch shows a characteristic peak at a temperature in the range of 120°C to 180°C.

11. The process as claimed in claim 1, wherein the modified starch comprises starch and the compatibilizing agent in the w/w ratio of 3.34:1.

12. The process as claimed in claim 1, wherein PBAT has a molecular weight in the range of 9 X 10⁴ -15 X 10⁴ Da. The process as claimed in claim 1 or 2, wherein the twin-screw processor is operated at a screw speed of 80-140 rpm. The process as claimed in claim 1 or 2, wherein the twin-screw processor has a L/D of 60/40. The process as claimed in claim 1 or 2, wherein the modified starch, the blend of starch and the compatibilizing agent, and PBAT are fed to the twin screw processor at a feeding rate of 30-100 Kg/ hr. The process as claimed in claim 1, wherein the process has a residence time of 1-4 minutes. The process as claimed in claim 1, wherein the twin-screw processor is a co-rotating twin-screw extruder.