GB2613013A

GB2613013A - Starch grafted co-polymer

Info

Publication number: GB2613013A
Application number: GB2116773.9A
Authority: GB
Inventors: Jahanfar Mehdi
Original assignee: Amir Massoud Amiri
Current assignee: Amir Massoud Amiri
Priority date: 2021-11-22
Filing date: 2021-11-22
Publication date: 2023-05-24
Also published as: GB202116773D0

Abstract

A method for the preparation of starch grafted polyolefin co-polymer granules with biodegradable properties, the method comprising: mixing polyolefin with starch in the presence of a crosslinking agent, reaction initiator and filler, thereby initiating a graft co-polymerization reaction to form a mixture comprising a starch grafted polyolefin co-polymer; and granulating the mixture in a granulator whilst simultaneously heating the mixture in a sequence of heating stages, thereby forming biodegradable starch-polyolefin graft co-polymer granules. The mixture may comprise 10-60 wt.% starch; 20-50 wt.% polyolefin (e.g. polyethylene; polypropylene; polystyrene); 0.1-5 wt.% crosslinking agent (e.g. malonic acid and/or maleic anhydride); and 1-20 wt.% filler (e.g. calcium carbonate, coconut oil and/or palm oil). The reaction initiator (0.01-1 wt.%) may be benzoyl peroxide (BPO), dicumyl peroxide (DCP), and/or azobisisobutyronitrile (AIBN). The mixture may further comprise an oxidisation promotion (e.g. titanium dioxide, 0.5-2 wt.%). Also claimed is a starch grafted polyolefin co-polymer comprising biodegradable properties.

Description

STARCH GRAFTED CO-POLYMER

FIELD OF INVENTION

[1] This invention relates to a starch grafted co-polymer with biodegradable properties, and more specifically to a starch grafted polyethylene, polypropylene, polystyrene or a polyolefin co-polymer and to a process for the production of the biodegradable co-polymer, and to the biodegradable copolymer itself.

BACKGROUND

[2] Biodegradable plastics are plastics that can be decomposed by the action of living organisms such as microbes, into water, carbon dioxide, and biomass.

[3] Biodegradable plastics form a class of plastics including polyhydroxyalkanoate (PHA) plastics, cellulose-based plastics, polyglycolic acid (PGA) plastics, polybutylene succinate (PBS) plastics, polycaprolactone (Pa) plastics, poly(vinyl alcohol) (PVA) plastics, polybutylene adipate terephthalate (PBAT) plastics, and starch blend plastics.

[4] Starch blend plastics are based on starch -a natural polymer which, on its own, can be used to form biodegradable bioplastic films. While fully natural and biodegradable, these films are brittle and have little practical use.

[5] Plasticizers such as glycerol, glycol and sorbitol can be added to starch to provide a biodegradable plastic with improved thermoplastic properties (known as thermoplastic starch (TPS)), which can then be blended with other biodegradable thermoplastic polyesters to obtain desired properties. Such starch blend plastics typically comprise high levels of starch in order to attain biodegradability, for example greater than 50% by weight. However, a downside to this is that the thermal and mechanical properties of starch are not so good and so there is a balance to be struck between increasing the amount of starch, and hence biodegradability, and decreasing the amount of starch in order to improve the thermal and mechanical properties of the plastic. There is also a preference to reduce the amount of starch used as this is a food source in several countries and therefore there is pressure to minimise the use of starch as a biodegradable agent in plastics.

[6] It is desirable to provide a starch based biodegradable plastic with low starch content. It is also desirable to provide a starch based biodegradable plastic with improved mechanical properties.

SUMMARY OF INVENTION

[7] This disclosure relates to a new method of preparing a starch grafted polyethylene, polypropylene, polystyrene or a polyolefin co-polymer from a graft co-polymerization reaction between a starch and polyethylene, polypropylene, polystyrene or a polyolefin. This disclosure also relates to a new starch grafted co-polymer with the polyethylene, polypropylene, polystyrene or a polyolefin. Hereafter when the term polyolefin is used, this will also cover at least the group of polyethylene, polypropylene, polystyrene and polyolefin.

[8] According to one aspect of the invention, there is provided a method for the preparation of starch grafted polyolefin co-polymer granules with biodegradable properties, the method comprising: mixing polyolefin with starch in the presence of a binder or crosslinking agent, a reaction initiator and a filler, thereby initiating a graft co-polymerization reaction to form a mixture comprising a starch grafted polyolefin co-polymer; and granulating the mixture in a granulator whilst simultaneously heating the mixture in a sequence of heating stages, thereby forming starch-polyolefin graft copolymer granules with biodegradable properties.

[9] This method of preparation is a unique method to produce a nanoscale phase of starch between the polymer matrixes which can degrade by the microorganism and in the final stage, because of the last polymer matrix being in the nanoscale particle, it can degrade very easy in nature.

[10] The sequence of heating stages may comprise 2-20 heating stages, preferably 3-10 heating stages and most preferably 7 heating stages.

[11] The temperature of each heating stage may increase along the sequence and within the range 100-250°C, preferably 110-170°C, most preferably 120-170°C.

[12] The temperature of each heating stage may increase in increments of 2-20°C along the sequence, preferably 5-10°C and most preferably 5°C.

[13] The sequence of heating stages advantageously ensures completion of the graft copolymerization reaction and has been found to control viscosity of the mixture to maintain good flowability through the granulator. By having a temperature gradient, and not simply having a single heating stage at a constant temperature, the heating of the starch can be controlled so that it does not burn. Additionally, by gradually increasing the temperature the viscosity of the mixture will decrease and the time for completing the reaction will be shortened.

[14] The mixing step may be carried out at a temperature of 20-100°C, preferably 70-100°C.

[15] The one or more of the heating stages may be subject to a vacuum, and preferably the vacuum subjects a headspace within each heating stage to a vacuum pressure in the range of 1-100Pa. The vacuum advantageously draws away gases from the mixture, thereby preventing formation of gas bubbles within the granules that can detrimentally impact mechanical and physical properties of the granules.

[16] The mixture may comprise 20-50wt% of the polymer, for example polyolefin, preferably 20-40wt%, more preferably 22-35%, for example 25%.

[17] The filler may be selected from calcium carbonate, a vegetable-based oil such as coconut oil or palm oil and/or natural bio based product such as bees wax or any combination thereof. Preferably, the filler is a combination of bee's wax and calcium carbonate [18] The mixture may, for example, comprise 1-25wt% calcium carbonate and/or 1-25wt% bees wax, and preferably the mixture comprises 1-10wt% calcium carbonate and 1-10wt% bees wax. The sum of the amount of calcium carbonate and bees wax should preferably be between 10-25% which preferably includes the calcium carbonate at a level of less than 10%. It has been found that a mixture of calcium carbonate and bees wax imparts the starch grafted polyolefin co-polymer granules with properties beneficial for downstream processing. That is, heat resistance beneficial for extrusion processes and thermomechanical properties for injection moulding processes.

[19] The filler, the binder or crosslinking agent and the reaction initiator are preferably the first components added in the mixing step.

[20] It has been found that adding the calcium carbonate as a filler and maleic anhydride as the crosslinking or binder agent to the starch and polymer mixture first advantageously enables a substantially homogenous mixture thereof prior to initiation of a co-polymerization reaction to produce a substantially homogeneous starch grafted polyolefin co-polymer. BP0 as the initiator is also added and the filler, binder and polymer are then mixed well, and the reaction is initiated.

[21] The Binder or crosslinking agent is preferably maleic anhydride. The mixture may comprise 0.1-5wt% of the Binder agent, and preferably 0.2-2.5wt%. This will be varied to take into account the amount of starch. Increasing the amount of starch will result in higher levels of binder or crosslinking agent being required.

[22] The reaction initiator may be selected from benzoyl peroxide (BPO), dicumyl peroxide (DCP) and/or azobisisobutyronitrile (AIBN). The mixture may comprise 0.01-1wt% reaction initiator, preferably 0.02-0.05wt%. Increasing the amount of the initiator will result in the reaction rate increasing. When using BPO, because of its good reaction rate the 0.02% may be an effective amount but if you are using AIBN it may be necessary to use more [23] The reaction initiator starts the reaction between the polyolefin, the binder or crosslinking agent and the starch.

[24] The mixture may further comprise an oxidation promotor such as titanium oxide. The mixture may comprise 0.5-2wt% titanium dioxide, and preferably 0.6-1wt%. The oxidation will bleach the product and therefore the amount of oxidation promoter used will vary depending on how white the product is. Titanium dioxide advantageously acts as a photocatalyst for controlling oxidation and degradation rate of the starch grafted polyolefin co-polymer and imparts a substantially white colour thereto.

[25] The mixture may further comprise beeswax. Preferably, the mixture may comprise 1-10wt% bees wax, preferably 2-5wt%. Bees wax has been found to act as a lubricant and anti-block agent. Polyethylene wax or paraffin wax may also be used in addition or as an alternative to bee's wax in the same amounts.

[26] The mixture may further comprise calcium stearate. Preferably, the mixture may comprise 0.1-5wt% calcium stearate, preferably 0.2-1wt%. Calcium stearate advantageously coats to the filler (e.g. calcium carbonate) by core shell structure and increases compatibility of the filler with other organic components within the mixture. This helps the mixing of hydrophilic and hydrophobic components in the mixture.

[27] The polymer is preferably polyethylene and may be low density polyethylene and/or high density polyethylene or any suitable combination.

[28] The mixture may comprise 10-60wt% starch, preferably 15-30wt% starch, and most preferably 15-25wt% starch, for example 20-25% starch. The weight ratio between the starch and filler may be 10:1-2:1, and preferably 8:1-4:1. Controlling the ratio between starch and filler advantageously provides control of biodegradation rate.

[29] The granulator may be a twin-screw granulator. The granulator may be configured to form granules with an average diameter of 2-10mm, preferably 3-5mm, and most preferably 3mm.

[30] The Applicants have found that, advantageously, granulating as disclosed herein, and in particular by controlling the speed of granulation it is possible to control the size of the granule and of course the reaction in the granulator. A 3 mm granule is same dimension as the polyethylene raw material granule and in the mixture step they can mix well because of their similarity in size and density. By controlling the size of the granule, it is possible to know whether the reaction has completed or not.

[31] The mixing may be performed for 5-30 minutes before the granulation step, preferably 5-15 minutes, most preferably 10 minutes. This is found to be the optimum time for increasing the speed of the process and cooling down enough [32] According to another aspect of the invention, there is provided starch grafted polyolefin copolymer granules prepared by the method disclosed herein [33] According to another aspect of the invention, there is provided a starch grafted polyolefin copolymer with biodegradable properties comprising 10-60wt% starch, 20-50wt% polyolefin, 0.1-5wt% binder or crosslinking agent, and 1-20wt% filler.

[34] Preferably, the co-polymer (i.e. the starch grafted polyolefin co-polymer) comprises 15-30wt% starch, 15-20wt% polyolefin, 0.2-2.5wt% crosslinking agent, and 10-50wt% filler.

[35] The crosslinking agent may be malonic acid and/or rnaleic anhydride.

[36] The filler may be calcium carbonate and/or a vegetable-based oil such as coconut oil or palm oil, bees wax or combinations thereof. Preferably, the filler is selected from calcium carbonate and coconut oil.

[37] The co-polymer may further comprise an oxidisation promotor such as titanium dioxide. The oxidisation promotor may be present in an amount of 0.5-2wt%, preferably 0.6-1wt%.

[038] The weight ratio between the starch and the filler may be 8:1-4:1.

[39] The co-polymer may be fully biodegradable.

[40] The reaction initiator may be benzoyl peroxide (BPO), dicumyl peroxide (DCP) and/or azobisisobutyronitrile (Al BN).

[41] The product may additionally include calcium stearate.

DETAILED DESCRIPTION OF THE INVENTION

[42] The following example embodiments of the invention are disclosed.

EXAMPLE 1

[43] 10.3 Kg of calcium carbonate is mixed with 1 Kg maleic anhydride and then added to a mixture of 46 Kg polyethylene in powder or granule form, 66 Kg starch, 0.3 Kg calcium stearate, 5 Kg polyethylene wax, 1 Kg titanium oxide, and 0.03 Kg benzoyl peroxide. The ingredients are mixed in a high-speed mixer reactor for 10 minutes at 70-100°C with a mixer rotational speed of 750 rpm.

[44] After mixing for 10 minutes, the mixture is transferred from the high-speed mixer to a separate container where it is rested for 10 minutes to allow for cooling at room temperature (-25°C).

[45] After cooling, the mixture is fed into a twin-screw granulator comprising a sequence of seven heating stages. The mixture is passed through the granulator and seven heating stages, which are configured as follows: ZONE1 ZONE2 ZONE3 ZONE4 ZONES ZONES HEAD 120°C 125°C 130°C 135°C 140°C 145°C 170°C The 'head' corresponds with the discharge zone of the granulator, and the larger temperature increase for the final zone is because the mixture after completing the reaction has good thermal resistance and for exiting the granulator smoothly the head must be warmer.

During the heating and granulating, some air and steam is emitted from the mixture. It is estimated that more than 50% of the co-polymerization reaction occurs in the granulator. A vacuum system is set in Zones 4 and 6 to provide a negative pressure to draw away any gases rising from the mixture during heating.

[046] The grafting co-polymerization reaction occurring during the mixing, cooling and heating stages follows the following mechanism: Elaskt- sAPE' [47] The granulator produces granules of starch grafted polyethylene co-polymer granules with average diameter size 3mm.

EXAMPLE?

[48] An agricultural mulch sheet is formed from a simple mix of 40% of I-IDPE 58% of [LOPE and 2% of master batch code A as described below (and in example 1 above), then the mixture is prepared to be introduced to the blown film producer machine.

[49] A master batch with Code A is produced according to the following process. 10.3 Kg of calcium carbonate is mixed with 1 Kg maleic anhydride and then added to a mixture of 46 Kg polyethylene, 66 Kg starch, 0.3 Kg calcium stearate, 5 Kg polyethylene wax, 1 Kg titanium oxide, and 0.03 Kg benzoyl peroxide. The ingredients are mixed in a high-speed mixer reactor for 10 minutes at 70-100°C with a mixer rotational speed of 750 rpm.

[50] After mixing for 10 minutes, the mixture is transferred from the high-speed mixer to a separate container where it is rested for 10 minutes to allow for cooling at room temperature (-25°C). After cooling, the mixture is fed into a twin-screw granulator comprising a sequence of seven heating stages. The mixture is passed through the granulator and seven heating stages, which are configured as follows: ZONE1 ZONE2 ZONE3 ZONE4 ZONES ZONE6 HEAD 120°C 125°C 130°C 135°C 140°C 145°C 170°C

EXAMPLE 3

[51] A shopping bag is formed from a simple mixing together of 40% of HDPE 56% of LLDPE and 4% of master batch code B made as described below, the mixture is prepared to be introduced to the blown film producer machine.

[52] A master batch with code B is made according to the following process. 10.3 Kg of bee's wax is mixed with 1 Kg maleic anhydride and then added to a mixture of 46 Kg polyethylene, 66 Kg starch, 0.3 Kg calcium stearate, 1 Kg titanium oxide and 0.03 Kg benzoyl peroxide. The ingredients are mixed in a high-speed mixer reactor for 15 minutes at 50°C with a mixer rotational speed of 750 rpm. The mixture is injected to the twin screw extruder for producing the white -milky colour granules.

[53] After mixing for 10 minutes, the mixture is transferred from the high-speed mixer to a separate container where it is rested for 10 minutes to allow for cooling at room temperature (-25°C). After cooling, the mixture is fed into a twin-screw granulator comprising a sequence of seven heating stages. The mixture is passed through the granulator and seven heating stages, which are configured as follows: ZONE1 ZONE2 ZONE3 ZONE4 ZONES ZONE6 HEAD 120°C 125°C 130°C 135°C 140°C 145°C 170°C

EXAMPLE 4

[055] 10.3 Kg of bee's wax is mixed with 1 Kg maleic anhydride and then added to a mixture of 46 Kg polyethylene, 66 Kg starch, 0.3 Kg calcium stearate, 1 Kg titanium oxide and 0.03 Kg benzoyl peroxide. The ingredients are mixed in a high-speed mixer reactor for 15 minutes at 50°C with a mixer rotational speed of 750 rpm. The mixture will inject to the twin screw extruder for producing the white -milky colour granules.

EXAMPLES

[056] 10.3 Kg of polyethylene wax is mixed with 1 Kg maleic anhydride and then added to a mixture of 46 Kg polyethylene, 66 Kg starch, 10 Kg calcium carbonate and 0.3 Kg calcium stearate, 1 Kg titanium oxide, and 0.03 Kg benzoyl peroxide. The ingredients are mixed in a high-speed mixer reactor for 10 minutes at room temperature with a mixer rotational speed of 750 rpm. The mixture will inject to the twin screw extruder for producing the milky creamy colour granules.

TABLE 1 -

Property Units Test method Example 1 Example 2 Example 3 Example 4 Tensile strength (@b, MD) MPa ISIRI 6621 22/23 23/35 Tensile strength (@b, TD) MPa ISIRI 6621 13/59 14/18 Elongation (@b, MD) % 15181 6621 311 269 Elongation (@b, TD) % ISIRI 6621 614 568 Tear Strength (MD) gf ASTM D1922- 48 13 94a Tear Strength (TD) gf ASTM D1922- 354 760 94a Corona mN/m ASTM D5946 Not OK Not OK Thickness micron ISIRI 6231 29 26 Friction coefficient ASTM D1894 0/146 0/149 Degradation (based on chain % ISIRI 14417 12 15 scission of plastic for 9 months)

Claims

CLAIMS1. A method for the preparation of starch grafted polyolefin co-polymer granules with biodegradable properties, the method comprising: mixing polyolefin with starch in the presence of a crosslinking agent, a reaction initiator and a filler, thereby initiating a graft co-polymerization reaction to form a mixture comprising a starch grafted polyolefin co-polymer; and granulating the mixture in a granulator whilst simultaneously heating the mixture in a sequence of heating stages, thereby forming starch-polyolefin graft co-polymer granules with biodegradable properties.
2 The method of claim 1, wherein there is a sequence of 2-20 heating stages, preferably 3-10 heating stages and most preferably 7 heating stages.
3. The method of any preceding claim, wherein the temperature of each heating stage increases along the sequence and within the range 100-250°C, preferably 110-170°C, most preferably 120-145°C.
4. The method of any preceding claim, wherein the temperature of each heating stage increases in increments of 2-20°C along the sequence, preferably 5-10°C and most preferably 5°C.
The method of any preceding claim, wherein the mixing step is carried out at a temperature of 20-100°C, preferably 70-100°C.
6. The method of any preceding claim, wherein one or more of the heating stages are subject to a vacuum, and preferably the vacuum subjects a headspace within each heating stage to a 1-100Pa vacuum pressure
7. The method of any preceding claim, wherein the mixture comprises 20-50wt% of the polyolefin, preferably 30-40wt%.
8. The method of any preceding claim, wherein the filler is selected from calcium carbonate and/or a vegetable-based oil such as coconut oil or palm oil.
9. The method of any preceding claim, wherein the mixture comprises 1-20wt% of the filler.
10. The method of claims, wherein the filler is calcium carbonate and coconut oil.
11. The method of claim 10, wherein the mixture comprises 1-10wt% calcium carbonate and 1-10wt% coconut oil, and preferably the mixture comprises 1-5wt% calcium carbonate and 1-Swt% coconut oil.
12 The method of any preceding claim, wherein the filler and crosslinking agent are the first components added in the mixing step.
13. The method of any preceding claim, wherein the crosslinking agent is selected from malonic acid and/or maleic anhydride.
14. The method of any preceding claim, wherein the mixture comprises 0 5wt% of the crosslinking agent, preferably 0.2-2.5wt%.
15. The method of any preceding claim, wherein the reaction initiator is selected from benzoyl peroxide (BPO), dicumyl peroxide (DCP) and/or azobisisobutyronitrile (AIBN).
16 The method of any preceding claim, wherein the mixture comprises 0.01-1wt% reaction initiator, preferably 0.02-0.05wt%.
17. The method according to any preceding claim, wherein the mixture further comprises an oxidisation promotor such as titanium dioxide.
18. The method of claim 17, wherein the mixture comprises 0.5-2wt% titanium dioxide, preferably 0.6-1wt%.
19. The method of any preceding claim, wherein the polyolefin is polyethylene, polypropylene or polystyrene.
20. The method according to any preceding claim, wherein the mixture further comprises polyethylene wax.
21. The method according to claim 20, wherein the mixture comprises 1-10wt% polyethylene wax, preferably 2-5wt%.
22. The method according to any preceding claim, wherein the mixture further comprises calcium stearate.
23. The method according to claim 22, wherein the mixture comprises 0.1-5wt% calcium stearate, preferably 0.2-1wt%.
24. The method according to any preceding claim, wherein the polyethylene is low density polyethylene and/or high density polyethylene.
The method according to any preceding claim, wherein the mixture comprises 10-60wt% starch, preferably 15-60wt% starch, and most preferably 15-55wt% starch.
26. The method according to any preceding claim, wherein the weight ratio between the starch and filler is 10:1-2:1, and preferably 8:1-4:1.
27 The method according to any preceding claim, wherein the granulator is a twin-screw granulator.
28. The method according to any preceding claim, wherein the granulator is configured to form granules with an average diameter of 2-10mm, preferably 3-5mm, and most preferably 3mm.
29 The method according to any preceding claim, wherein mixing is performed for 5-30 minutes before the granulation step, preferably 5-15 minutes, most preferably 10 minutes.
30. The method according to any preceding claim, wherein the starch-polyolefin graft copolymer granules form a solid additive masterbatch.
31. A starch grafted polyolefin co-polymer comprising biodegradable properties prepared by the method of any preceding claim.
32. A starch grafted polyolefin co-polymer with biodegradable properties comprising 10-60wt% starch, 20-50wt% polyolefin, 0.1-5wt% crosslinking agent, and 1-20wt% filler.
33. The co-polymer according to claim 30, comprising 15-55wt% starch, 30-40wt% polyolefin, 0.2-2.5wt% crosslinking agent, and 1-10wt% filler.
34. The co-polymer according to any one of claims 30-31, wherein the crosslinking agent is selected from malonic acid and/or maleic anhydride.
35. The co-polymer according to any one of claims 30-32, wherein the filler is selected from calcium carbonate and/or a vegetable-based oil such as coconut oil or palm oil or combinations thereof, preferably the filler is selected from calcium carbonate and coconut oil.
36. The co-polymer according to any one of claims 30-33, further comprising an oxidisation promotor such as titanium oxide.
37. The co-polymer according to claim 34, wherein the oxidisation promotor is present in an amount of 0.5-2wt%, preferably 0.6-1wt%.
38. The co-polymer according to any one of claims 30-35 wt.%, wherein the weight ratio between the starch and the filler is 8:1-4:1.
39 The co-polymer according to any one of claims 30-36 wt.%, wherein the co-polymer is fully biodegradable.