Polylactic acid / polycarbonate polymer alloy and method of formation

Abstract

This invention relates to the field of polymer technology and discloses a polylactic acid / polycarbonate polymer alloy and a method for forming the same. The polylactic acid / polycarbonate polymer alloy is disclosed to include polylactic acid / glycidyl methacrylate, acrylate, an initiator, polylactic acid, and polycarbonate. The material characteristics of the polylactic acid / polycarbonate polymer alloy of this invention will resemble those of polycarbonate, which possesses high toughness, heat resistance, and durability.

Description

1. Specification of Polylactic Acid / Polycarbonate Polymer Alloy and Formation Method Thereof Technical Field This invention relates to polylactic acid (PLA) / polycarbonate (PC) polymer alloys, which can be used to manufacture electronic appliances and household appliances. Bio-based PLA provides environmentally friendly properties and PC provides protection to achieve the desired high toughness, heat resistance and durability. The formulation of the polymer alloy, the formation method and the biphasic plasticizer used to manufacture the polymer alloy are all parts of this invention. Background Art Due to the increasing concern for environmental sustainability, lower-carbon bio-based alternatives are being used to replace petroleum-based plastic materials. Polylactic acid (PLA) is one of the most popular bio-based polymers derived from carbon-renewable resources such as corn, which can be naturally recycled through biological processes, thereby reducing fossil fuel consumption and greenhouse gas emissions. PLA is a suitable environmentally friendly polymer alternative to traditional plastics due to its excellent properties, such as high tensile strength, high flexural strength and high stiffness. Although PLA is widely used in disposable products, such as plastic 15 bags, it is not suitable for tough and durable applications, such as electronic and household appliances, automotive interior trim components, etc., due to its inherent limitations. Table 1. Comparison between polylactic acid (PLA) properties and tough and durable application requirements Property Requirements PLA Tensile Strength (MPa) ≥ 60 50 Flexural Strength (MPa) ≥ 95 60 Impact Strength (IZOD) (kJ / m2) ≥ 15 1.3 Heat Resistance: Vicat Softening Temperature (°C) ≥ 110 60 Aging Resistance (GB / T 7141) After accelerated testing at 90 °C for 1,000 hours, the above failure characteristics are met. HK 30134880 A 2 Property Pass Requirements As can be seen from Table 1 above, in general, PLA: (i) Poor toughness: PLA is brittle. PLA has an impact strength of only 1.3 kJ / m², which is only 8.7% of the required value of 15 kJ / m²; (ii) low heat resistance: the Vicat softening temperature is low, approximately 60°C; and (iii) poor durability: because PLA is (bio)degradable, its properties deteriorate easily under environmental stress, and it is generally considered to have a durability of no more than two years. To improve this, researchers have attempted to form polylactic acid / polycarbonate (PLA / PC) alloys, aiming to utilize polycarbonate (PC) to protect PLA and remedy its inherent limitations. PC (as a typical engineered plastic) is commonly used in the automotive and electrical industries due to its high thermal stability and impact resistance. However, PC is a petroleum-based plastic with a high carbon footprint. Therefore, there is an urgent need to develop new materials with excellent PC properties and a low carbon footprint.Due to the inherent excellent toughness and thermal flexural temperature of PC, incorporating PLA into PC is a promising method for preparing polymer alloys with excellent mechanical properties. However, due to the different polymer characteristics, the amorphous polymer chains of PC are difficult to disrupt the crystalline phase of PLA. Even if some additives can be added to reduce the crystallinity of PLA and prepare polymer chains of PLA and PC, a large amount of PC is still required to ensure sufficient protection and provide better mechanical and thermal properties. It has been reported that a large amount of PC (about 90% by weight) is required to form polymer alloys, which hinders the use of bio-based PLA for carbon reduction purposes. The present invention provides a method for forming a polylactic acid (PLA) / polycarbonate (PC) polymer alloy with the desired high toughness, heat resistance and durability, possessing the environmentally friendly properties of PLA and the protective effect on PC. Specifically, an effectively interpenetrating biphase plasticizer is used to achieve a cluster-induced phase transformation, which favors PC being in the continuous phase and providing protection. According to a first aspect of the invention, a polylactic acid (PLA) / polycarbonate (PC) polymer alloy is provided, comprising polylactic acid / glycidyl methacrylate (PLA / GMA), acrylate, an initiator, PLA, and PC. According to a second aspect of the invention, a biphase plasticizer is provided, comprising polylactic acid (PLA), glycidyl methacrylate (GMA), and acrylate. According to a third aspect of the invention, a method for forming a polylactic acid (PLA) / polycarbonate (PC) polymer alloy is provided, comprising (a) mixing PLA and glycidyl methacrylate (GMA) to form polylactic acid / glycidyl methacrylate (PLA / GMA), and (b) mixing said PLA / GMA, acrylate, initiator, PLA, and PC. The accompanying drawings illustrate embodiments of the invention by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an exemplary route for synthesizing the biphase plasticizer PLA / GMA-co-EHA according to the invention; and Figure 2 shows the steps for forming the PLA / PC polymer alloy according to the invention by clustering-induced phase transformation according to the invention. Detailed Description 15 To promote efficient blending of PLA and PC, interpenetration of polymer chains at the interface of the two polymers is achieved by a biphase plasticizer (i.e., polylactic acid / glycidyl methacrylate-co-acrylate (e.g., 2-ethylhexyl acrylate), PLA / GMA-co-EHA). It is designed to incorporate two different phase behaviors (PLA phase and EHA phase, respectively) onto a single plasticizer.The PLA phase is miscible with the PLA polymer chains, while the EHA phase can penetrate and loosen the 20 PC polymer chains, allowing the PLA polymer chains to permeate into them and thus produce well-blended PLA / PC polymer alloys. After modifying the continuous phase PLA into the aforementioned biphase plasticizer (e.g., PLA / GMA-co-EHA), the initiator, PLA, and PC are mixed together by melt blending in a second step (HK 30134880 A 4). Due to the strong affinity between similar PLA phase groups in the PLA / GMA-co-EHA molecules, they aggregate to form micellar spherical PLA clusters, with the core constructed by the "tail" of the PLA phase groups and the outer surface covered by the "head" of the EHA phase groups. Furthermore, as PLA loses its fluidity after aggregation, the highly fluid PC becomes the continuous phase to fill the gaps between the PLA / GMA-co-EHA clusters. Therefore, a phase transformation occurs to form a PLA / PC polymer alloy with PC5 as a continuous phase to protect PLA. The material characteristics of this PLA / PC polymer alloy will resemble those of PC, which exhibits high toughness, heat resistance, and durability. As shown in Figures 1 and 2, the biphase plasticizer and PLA / PC polymer alloy can be prepared as follows: a) PLA and PC are dried in ovens at 60-80 °C and 100-120 °C, respectively, for 3-6 hours; b) PLA and GMA are mixed in a twin-screw extruder at 160-180 °C to obtain PLA / GMA. PLA / GMA comprises 85-99 wt% PLA and 1-15 wt% GMA; c) PLA / GMA (0.1-15 wt%), acrylates (such as butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate or lauryl acrylate; 0.01-1 wt%), initiators (e.g., dicumyl peroxide, tert-butyl peroxybenzoate, benzoyl peroxide, di-tert-butyl peroxide or hydrocumyl peroxide; 0.001-0.1 wt%), PLA (10-90 wt%) and PC (10-90 wt%) are mixed in a twin-screw extruder at 210-240°C. PLA / GMA reacts with acrylates (such as 2-ethylhexyl acrylate (EHA)) via a 20-radical polymerization process to form a biphase plasticizer PLA / GMA-co-EHA; and d) thereafter, with the assistance of the biphase plasticizer, a PLA / PC polymer alloy is formed.Examples 1, 3, and 5 illustrate polylactic acid (PLA) / polycarbonate (PC) polymer alloys and methods for forming biphase plasticizers and PLA / PC polymer alloys according to the present invention, while Examples 2, 4, 6, and 7 are for comparative purposes. Example 1 HK 30134880 A 5 The polymer blend was prepared as follows. First, PLA and PC were dried in ovens at 70 °C and 110 °C, respectively, for 4 hours. Then, PLA (85 wt%) and GMA (15 wt%) were mixed in a twin-screw extruder at 170 °C to obtain PLA / GMA. Next, PLA / GMA (2 wt%), 2-ethylhexyl acrylate (0.095 wt%), dicumyl peroxide (0.005 wt%), PLA (48.3 wt%), and PC (49.6 wt%) were mixed in a twin-screw extruder at 230 °C. Test samples of the polymer blends thus prepared were prepared by injection molding at 220 °C. The properties of the sample from Example 1 are shown in Table 2, which met the requirements for tough and durable applications. Example 2: A polymer blend was prepared using the exact same formulation as in Example 1, but instead of premixing PLA and GMA, all components were mixed together in one step. Test samples of the polymer blends thus prepared were prepared by injection molding at 220 °C. The properties of the sample from this example are shown in Table 2. Compared to Example 1, direct mixing without synthesizing a PLA-based plasticizer resulted in much lower mechanical properties in the sample, which did not meet the requirements for tough and durable applications. Example 3: A polymer blend was prepared as follows. First, PLA and PC were dried in ovens at 70 °C and 110 °C, respectively, for 4 hours. Then, PLA (85 wt%) and GMA (15 wt%) were mixed in a twin-screw extruder at 170 °C to obtain PLA / GMA. Next, 20 PLA / GMA (2 wt%), 2-ethylhexyl acrylate (0.095 wt%), dicumyl peroxide (0.005 wt%), PLA (58.3 wt%), and PC (39.6 wt%) were mixed in a twin-screw extruder at 230 °C. Test samples of the polymer blends thus prepared were prepared by injection molding at 220 °C. The properties of the sample from Example 3 are shown in Table 2, which met the requirements of 25 for tough and durable applications.HK 30134880 A 6 Example 4 A polymer blend was prepared using the exact same formulation as in Example 3, but instead of premixing PLA and GMA, all components were mixed together in one step. Test samples of the polymer blend thus prepared were prepared by injection molding at 220 °C. The properties of the samples are shown in Table 2. Compared to Example 3, direct mixing without synthesizing the 5-PLA-based plasticizer resulted in much lower mechanical properties in the samples, which did not meet the requirements for tough and durable applications. Example 5 A polymer blend was prepared as follows. First, PLA and PC were dried in ovens at 70 °C and 110 °C, respectively, for 4 hours. Then, PLA (85 wt%) and GMA (15 wt%) were mixed in a twin-screw extruder at 170 °C to obtain PLA / GMA. Next, PLA / GMA (2 wt%), 2-ethylhexyl acrylate (0.095 wt%), dicumyl peroxide (0.005 wt%), PLA (38.3 wt%), and PC (59.6 wt%) were mixed in a twin-screw extruder at 230 °C. Test samples of the polymer blend thus prepared were prepared by injection molding at 220 °C. The properties of the resulting samples are shown in Table 2, which meet the requirements for tough and durable applications. Example 6 A polymer blend was prepared using the exact same formulation as in Example 3, without premixing PLA and GMA, but by mixing all components together in one step. Test samples of the polymer blend thus prepared were prepared by injection molding at 220 °C. The properties of the resulting samples are shown in Table 2. Compared to Example 5, direct mixing without synthesizing a PLA-based plasticizer resulted in much lower mechanical properties in the samples, which do not meet the requirements for tough and durable applications. HK 30134880 A 7 Example 7 A polymer blend was prepared by mixing PLA (50 wt%) and PC (50 wt%) in a twin-screw extruder at 230 °C. Test samples of the polymer blend thus prepared were prepared by injection molding at 220 °C. The properties of the samples are shown in Table 2. Compared with the examples above, the direct blending of PLA and 5% PC without the application of any compatibilizer resulted in poor toughness of the samples, which does not meet the requirements for toughness and durability applications.Table 2. Comparison of the characteristics of the examples with the requirements of tough and durable applications. Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Tensile strength (MPa) ≥ 60 68.7 64.4 67.2 65.8 68.9 67.4 67.1 Flexural strength (MPa) ≥ 95 101 85.1 95 80.2 103.8 89.1 84.6 Impact strength (IZOD) (KJ / m2) ≥ 15 86.7 17.2 48.8 7.9 113.2 25.2 6.7 Heat resistance: Vicat softening temperature (°C) ≥ 110 130.2 115 116 100.7 142.3 130.0 114.8 Anti-aging (GB / T 7141) After 1,000 hours of accelerated testing at 90 °C, the above-mentioned properties passed the requirement through failure through failure through failure HK 30134880 A 8 It should be understood that the above only shows examples of how the invention can be implemented, and various modifications and / or changes can be made thereto without departing from the spirit of the invention. It should also be understood that some features of the invention described in the context of individual embodiments for clarity may also be provided in combination in a single embodiment. Conversely, for brevity, various features of the invention described in the context of individual embodiments may also be provided individually or in any suitable sub-combination. HK 30134880 A 1 Claims 1. A polylactic acid (PLA) / polycarbonate (PC) polymer alloy comprising polylactic acid / glycidyl methacrylate (PLA / GMA), acrylate, initiator, PLA and PC. 2. The polymer alloy of claim 1, wherein the PLA / GMA is 0.1-5 15 by weight. 3. The polymer alloy of claim 1, wherein the acrylate is 0.01-1% by weight. 4. The polymer alloy of claim 1, wherein the initiator is 0.001-0.1% by weight. 5. The polymer alloy of claim 1, wherein the PLA is 10-90% by weight. 6. The polymer alloy of claim 5, wherein the PLA is greater than 50% by weight. 7. The polymer alloy of claim 1, wherein the PC is 10-90% by weight. 8. The polymer alloy of claim 1, wherein the acrylate is butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, or lauryl acrylate.9. The polymer alloy of claim 1, wherein the initiator is dicumyl peroxide, tert-butyl peroxybenzoate, benzoyl peroxide, di-tert-butyl peroxide, or cumyl hydroperoxide. 10. A biphase plasticizer comprising polylactic acid (PLA), glycidyl methacrylate (GMA), and acrylates. 11. The biphase plasticizer of claim 10, wherein the acrylate is butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, or lauryl acrylate. 12. The biphase plasticizer of claim 10, wherein the biphase plasticizer comprises polylactic acid / glycidyl methacrylate-co-2-ethylhexyl acrylate (PLA / GMA-co-EHA). HK 30134880 A 1 Drawings of the specification HK 30134880 A 2 HK 30134880 A.