Polycarbonate-poly(butyleneterephthalate) (pc-pbt) blends with recycled content, process for producing the same and use thereof

Abstract

The disclosure relates to the technical field of polymer materials, and particularly to a blend based on polycarbonate (PC) and poly(butyleneterephthalate) (PBT), which is at least partly recycled. The present disclosure further concerns the process for manufacturing the blend as well as the use of the PC-PBT blend in automotive structural parts and electrical vehicles.

Description

[0001] POLYCARBONATE-POLY(BUTYLENETEREPHTHALATE) (PC-PBT) BLENDS WITH RECYCLED CONTENT, PROCESS FOR PRODUCING THE SAME AND USE THEREOF

[0002] FIELD OF THE DISCLOSURE

[0003] The disclosure relates to the technical field of polymer materials, and particularly to a blend based on polycarbonate (PC) and poly(butyleneterephthalate) (PBT), which is at least partly recycled. The present disclosure further concerns the process for manufacturing the blend as well as the use of the PC-PBT blend in automotive structural parts and electrical vehicles.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] Different polymer materials are essential for a number of industries worldwide such as building and construction, packaging, consumer goods, electronics and automotive industry.

[0006] There are three different types of polymers, which are thermoplastics, thermosets and elastomers. Thermoplastics have many different applications and there is a high demand for this type of polymers. Thermosets cannot be melted and reshaped, and elastomers are sensitive to fluids, but the lifespan of thermoplastic polymers can be practically limitless since in theory they can be melted and reshaped repeatedly. Examples of thermoplastics are polycarbonate, poly (butyleneterephthalate), polystyrene and polyethylene, and they can be used to make toys, sports equipment, car parts, bottles, containers and grocery bags, for example.

[0007] Especially polycarbonate (PC) and poly(butyleneterephthalate) (PBT) blends are widely used engineering plastics in automotive industry for moulded automobile parts. PC is a versatile material with attractive processing and physical properties, and it has various applications. In engineering, PC is strong, tough, a good electrical insulator with heat and flame-retardant properties and it may be optically transparent. PC also has low weight and high impact resistance, and it can produce smooth surfaces. PBT is a mechanically strong, semi-crystalline polymer that resists solvents, shrinks very little during forming and is heat resistant up to 150 °C or up to 200 °C with glass fiber reinforcement.

[0008] PC and PBT blends have been studied rather extensively due to their unique properties. PC has hardness and dimensional stability while PBT has a high thermal and mechanical stability providing resistance to impact and heat, as well as a low absorption of water. PC- PBT blends usually contain reinforcing agents such as metals and / or inorganic mineral fillers in order to obtain material with high enough mechanical properties. The blends further usually comprise auxiliary substances such as impact modifiers, stabilizers, compatibilizers and colorants.

[0009] Despite the ongoing research and development of reinforced polymer blends, especially from PC and PBT, there is still a need to overcome the challenges associated with recyclability and other properties of the materials.

[0010] BRIEF DESCRIPTION OF THE DISCLOSURE

[0011] An object of the present disclosure is to provide a polymer blend based on PC and PBT, which is at least partly recycled, a method of manufacture, and use of the obtained blend in automotive structural parts and electrical vehicles.

[0012] A problem with current state of the art is that metallic and inorganic additives affect negatively on the recyclability of the material. The challenge is to have a PC-PBT blend with high impact properties that can be repeatably mechanically recycled.

[0013] The object of the disclosure is to alleviate current challenges, which is achieved by a process, method and use which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

[0014] The PC-PBT blend as such has poor miscibility, which means that it has poor mechanical properties. Thus, additives for reinforcement are usually needed. However, inorganic additives such as glass fiber limits further mechanical recycling steps since it breaks down in the extruder and the formed short fibers act as a filler, not improving mechanical properties efficiently when recycled. The inventors of this disclosure surprisingly noticed that leaving the inorganic additives, including glass fibers, out of the blend of the disclosure, creates a blend composed essentially of polymers with properties comparable and superior to commercial PC-PBT blends comprising reinforcement compounds. With a composition consisting essentially of polymers, typically comprising no newly added inorganic additive such as glass fiber and / or organic fiber-formed additives, making the product of this disclosure fully mechanically recyclable without the side effects of reinforcing additives losing impact properties under mechanical grinding during the compounding process.

[0015] The disclosure is based on the idea of using at least partly recycled PC, typically obtained as post-industrial waste or post-consumer waste, mixing it with PBT, which optionally is at least partly recycled, and a certain combination of auxiliary substances, excluding or minimizing the amount of fillers, inorganic additives and / or metals, to yield a blend having comparable and superior impact strength properties to commercial virgin blends. The aim of the disclosure is to provide an essentially polymer-based PC-PBT blend with low ash content. The advantage of the disclosure is thus the provision of a fully recyclable polymer blend, which for example enables further mechanical recycling steps of the same plastic part in automotive application, for instance. This is a both economical and environmentally friendly approach to the industry’s needs.

[0016] An advantage of the disclosure is that it enables high recycled polymeric content with comparable and / or higher impact properties compared to the commercially available resins based on virgin materials. More in detail the advantage of the disclosure is providing a formulation in which no or less inorganic additives, such as glass fiber or metals are used and substantially no catalyst(s) for transesterification.

[0017] Usually, high molecular weight polycarbonate needs harsher compounding conditions, which causes degradation of the polycarbonate, resulting in diminish in mechanical properties, for instance the impact strength. In this disclosure, the compounding process for manufacturing the blend is quite mild and does not cause significant degradation. Thus, another advantage of the disclosure is provision of a compounding process in which the high impact properties of the polycarbonate are retained.

[0018] Another advantage of the disclosure is the provision of a PC-PBT blend that has superior tensile strength and elastic modulus properties compared to commercial PC-PBT blends, which makes it especially suitable for use in safety components in automotive parts such as crash box.

[0019] The blend according to the disclosure has an inter-penetrating network (IPN) blend structure, which typically results in a combination of properties from the individual polymers and for example one transition temperature due to the reactions between the polymers. Without being bound to any specific theory, the highly cohesive nano-scale polymer morphology of the blends of the disclosure is considered to be the factor explaining the extraordinary elastic properties and mechanical ductility of the PC / PBT blend of the disclosure achieved without the addition of f iller(s) and / or catalyst(s) for transesterification. The polymer blend comprises substantially no filler(s) and / or no added catalyst(s) promoting transesterification. Typically, also the total amount of added auxiliary substance(s) such as the total amount of compatibilizer(s), impact modifier(s), stabilizer(s) and viscosity modifier(s) is less than 15 wt-% and preferably 10 wt-% or less of the total weight of the blend. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

[0021] Figure 1 shows a schematic flow diagram representing the manufacturing process;

[0022] Figure 2 shows a chart of the Charpy notched impact measurements for the prepared blend examples and comparative examples;

[0023] Figure 3 shows Charpy notched impact, ultimate tensile strength and tensile modulus measurements compared to the total amount of impact modifier;

[0024] Figure 4 shows DSC heating curves of a commercial blend and blends according to the invention: a) 1stheating curve and b) 2ndheating curve;

[0025] Figure 5 shows DMA measurements of a commercial blend, rPC, and blends according to the invention: (a) Storage Modulus (G') (b) tan 5; and

[0026] Figure 6 illustrates the blend morphology of Osmium tetroxide-stained samples by STEM and TEM EDS.

[0027] DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] The disclosure relates to a polymer blend which comprises more than 85 wt-% of polycarbonate (PC) and poly(butyleneterephthalate) (PBT), a PC to PBT ratio of 1 :1 -5:1 , and more than 40 wt-% of recycled PC and / or recycled PBT of the total weight of PC and PBT, and wherein the ash content of the blend is less than 4 wt-% of the total weight of the blend, the storage modulus of the blend is at least 1 .5 GPa at 80 °C and the blend is formed by adding to the blend 3-7 wt-% of one or more impact modifier(s) of the total weight of the blend.

[0029] According to embodiments of the disclosure, the disclosure comprises a polymer blend, wherein at least part of the PC and / or PBT is recycled, preferably over 40 wt-% of the total weight of PC and PBT is recycled PC and / or recycled PBT, more preferably over 55 wt-% and most preferably over 60 wt-% of the total weight of PC and PBT is recycled PC and / or recycled PBT.

[0030] According to some embodiments, the polymer blend of the disclosure is formed by further adding 2-5 wt-% of compatibilizer and 0.1 -1 wt-% of stabilizer to the PC-PBT blend.

[0031] Typically, the polymer blend according to the disclosure is substantially free of added catalyst and / or f iller(s) . In the context of this disclosure, the terms “additive” and “filler” refer to materials added to polymers to enhance or modify their physical properties and processability, such as mineral fillers, metal fillers, fibrous fillers or particulate fillers. The polymer blend of this disclosure does not need these kinds of externally added modifiers. Catalysts are typically added to polymer blends to enable / ensure transesterification. In this disclosure, no such catalyst for transesterification is needed. The polymer blend of the disclosure as such is such that the properties are improved and superior to currently commercially available blends.

[0032] The disclosure relates to a polymer blend which has a storage modulus of at least 1 .5 GPa at 80 °C. The storage modulus is determined by dynamical mechanical analysis, measured using Mettler DMA SDTA 861 e in tensile mode. Tension was applied in the direction of melt flow orientation. 10 Hz test frequency was used, and temperature range from room temperature to +180°C was investigated.

[0033] The disclosure further relates to a process for manufacturing PC-PBT blend and to the use of this blend.

[0034] In embodiments of the disclosure the ratio of PC and PBT is typically 1 :1 -5:1 PC:PBT, preferably 2:1 -4:1 PC:PBT, more preferably 3:1 -1.5:1 PC:PBT by weight.

[0035] In the context of this disclosure, the term “compatibilizer” refers to material that is added to a mixture of incompatible polymers to suppress their phase separation and promote interfacial adhesion. In the context of this disclosure, the compatibilizer is typically reactive with polyesters and polycarbonates and may be an acrylate or methacrylate-containing polymer. In general, compatibilization is the addition of a substance to a polymer blend, to improve the stability and phase morphology of the blend by creating interactions between the immiscible polymers, which will improve the miscibility of the polymers. There are three major methods of compatibilization, which are addition of pre-synthesized block or graft polymers, in situ compatibilization using reactive groups in both polymers which creates block polymers at the interface during blending, and dynamic vulcanization commonly known as crosslinking. In the context of this disclosure, the compatibilization method of choice is the addition of a pre-synthesized block polymer, and typically the compatibilizer comprises acrylate or methacrylate and / or epoxy functional groups, preferably glycidyl methacrylate functional group.

[0036] In the context of this disclosure, the term “impact modifier” refers to an auxiliary substance added to compounded polymer materials to improve the durability and toughness of the plastic product. The mechanism typically relies on compounds that elastomeric or rubbery in nature, which can absorb the energy of an impact or dissipate it. Impact modifiers can be incorporated through polymerization in the reactor or as auxiliary substances in the compounding step. Sometimes impact modifier and host polymer are naturally compatible, but often chemical modification is required to compatibilize the polymers. Impact modifiers can be categorized in modified polyolefins, core-shell impact modifiers, thermoplastic elastomers and bulk elastomeric impact modifiers. In the context of this disclosure, the impact modifiers typically belong to core-shell impact modifiers, structures like methacrylate-butadiene-styrene (MBS) and acrylic and / or methacrylic impact modifiers, and / or to bulk elastomeric impact modifiers. Typical suitable impact modifiers can be conjugated dienes and high molecular weight elastomeric materials derived from olefins, monovinyl aromatic monomers, acrylic and methacrylic acid and their ester derivatives, for example.

[0037] Due to the similarity in the structures of some compatibilizers and impact modifiers, an impact modifier can also act as a compatibilizer. In this disclosure, typically one or two impact modifiers can be added into the blend. Different types of impact modifiers have different challenges. For example, reactive impact modifiers tend to reduce flow and acrylic modifiers tend to have poor low impact resistance. Thus, when choosing impact modifiers one must consider the balance of impact resistance, flow, stiffness, weatherability, low- temperature toughness and thermal stability. For example, using a combination of reactive and non-reactive impact modifiers can improve the impact-flow balance, and using coextrusion with either all-acrylic or acrylic-modified cap layer over a core layer containing an impact modifier with good low temperature performance. Thus, in some embodiments in this disclosure, two impact modifiers are used. Typically, both impact modifiers have core shell structures.

[0038] In the context of this disclosure, the term “stabilizer” refers to an auxiliary substance added to polymer blends that inhibit or retard common polymer degradation processes such as oxidation, UV-damage, thermal degradation, ozonolysis or biodegradation or combinations thereof. Typically, in the context of this disclosure the stabilizer is an acid scavenger, thermostabilizer and / or phenolic antioxidants, and provides heat-stability, processing rejuvenation and / or impurity neutralization.

[0039] In the context of this disclosure, the term “viscosity modifier” refers to a processing aid, hydrocarbon polymeric additives that acts as a flow enhancer by decreasing the viscosity at high temperatures while not increasing the viscosity too much at low temperatures. In the context of this disclosure, the viscosity modifier can typically be polyalkyl methacrylate, hydrogenated styrene-diene, olefin copolymer or polyisobutene.

[0040] In the context of this disclosure, the term “ash content” refers to the total content of the blend of inorganic noncombustible material, such as glass fibers, glass spheres, glass flakes, carbon fibers, minerals or other inorganic matter whether added or present in the raw material.

[0041] In the context of this disclosure, the term “recycled PC” (rPC) material typically refers to post industrial waste or post-consumer waste high-viscosity polycarbonate and it is used as obtained from the source. The term “post industrial waste” refers to material that is separated from the waste stream in any industrial manufacturing process, which, in the context of the disclosure, can typically be material from automotive industry.

[0042] PC-PBT blends are usually reinforced with further materials like talc, glass fibers / spheres / flakes and / or carbon fibers. Glass fibers and their role as nanoparticle fillers, flowability enhancers and crystallization adjustors have been extensively studied. Their use, however, limits the recyclability of the product. In practise it prevents the mechanical re-compounding of the material since for example the glass fibers break in the extruder. Glass fibers are short in fiber forms and when they are compounded again in the extruder, they do not melt but are crushed into pieces, like powder, and the fibers become shorter. This causes them to lose their reinforcing function and the material loses its good mechanical properties, and the short fibers become just fillers in the recycled material. Usually at least 6-7 wt-%. of the total weight of the blend of glass fiber is needed for it to be effective.

[0043] In this disclosure, glass-based additives such as glass fibers, glass spheres and glass flakes, mineral based additives such as talc and wollastonite, and fiber-based additives, such as carbon fibers, are typically not added to the PC-PBT blend. However, a small amount of them might be added, typically below 2 wt-%, or be present as residues in the raw material PC and / or PBT. For the purpose of this disclosure, it is not necessary to remove the residues as long as the total ash content in the blend is low, typically below 4 wt-%. If a feedstock, however, has more than 4 wt-% of above-mentioned additives, it can be processed with commonly known methods to remove excess additives, after which it can be used in the disclosure. In this disclosure, virgin feedstock, the direct resin produced from a petrochemical feedstock which has never been used or processed before, can also be used as a feedstock. Recycled PBT is typically chemically recycled but alternatively it is mechanically recycled.

[0044] Polymer blends typically also contain at least a little bit of other functional fillers such as pigments such as TiO2and carbon black. When the inorganic residue is less than 4 wt-% of the total weight of the blend, it does not affect the recyclability, or the properties of the blend. Inorganic residues constitute the total ash content of the blend and can also originate from compatibilizer, impact modifier(s), stabilizer and / or viscosity modifier. In some embodiments of the disclosure the ash content is less than 4 wt-%, preferably less than 3 wt-%, more preferably less than 2 wt-%, most preferably less than 1 wt-% of the total weight of the blend.

[0045] Embodiments of the disclosure relates to a polymer blend wherein the blend comprises,

[0046] • more than 85 wt-% of polycarbonate (PC) and poly(butyleneterephthalate) (PBT),

[0047] • a PC to PBT ratio of 1 :1 -5:1 , preferably 3:1 -1 .5:1 PC:PBT by weight, wherein more than 40 wt-%, preferably over 55 wt-% and most preferably over 60 wt-% of the total weight of PC and PBT is recycled PC and / or recycled PBT, and

[0048] • wherein the ash content of the blend is less than 4 wt-%, preferably less than 3 wt- %, more preferably less than 2 wt-%, most preferably less than 1 wt-% of the total weight of the blend,

[0049] • wherein the storage modulus of the blend is at least 1 .5 GPa at 80 °C, and

[0050] • wherein the blend is formed using 3-7 wt-%, preferably 3-5 wt-% of one or more impact modifier(s) of the total weight of the blend for compounding.

[0051] According to some embodiments of the disclosure, the polymer blend further comprises 2- 5 wt-%, preferably 2-4 wt-%, most preferably 2-3 wt-% of compatibilizer of the total weight of the blend and / or 0.1-1 wt-%, preferably 0.2-0.8 wt-%, most preferably 0.4-0.6 wt-% of stabilizer of the total weight of the blend,

[0052] According to some embodiments of the disclosure the polymer blend comprises more than 85 wt-% of polycarbonate (PC) and poly (butyleneterephthalate) (PBT), a PC to PBT ratio of 1 :1 -5:1 PC:PBT by weight and more than 40 wt-%, preferably over 55 wt-% and most preferably over 60 wt-% of recycled PC and / or recycled PBT of the total weight of PC and PBT, an ash content of less than 4 wt-%, preferably less than 3 wt-%, more preferably less than 2 wt-%, most preferably less than 1 wt-% of the total weight of the blend, a storage modulus of at least 1.5 GPa at 80 °C and the blend is formed by adding during compounding 3-7 wt-% of one or more impact modifiers, 0.1-1 wt of stabilizer and 2-5 wt- % of compatibilizer of the total weight of the blend.

[0053] The blend of the disclosure further typically comprises 0.1 -1 wt-%, preferably 0.2-0.8 wt- %, most preferably 0.4-0.6 wt-% of viscosity modifier of the total weight of the blend.

[0054] According to some embodiments, the disclosure comprises a polymer blend comprising in total 3-7 wt-%, preferably 3-6 wt-%, more preferably 4-6 wt-% of one or more impact modifier(s) of the total weight of the blend. Typically, the total amount of compatibilizer, impact modifier, stabilizer and viscosity modifier is less than 15 wt-%, preferably 10 wt-% or less of the total weight of the blend, more preferably 3 - 10 wt-% of the total weight of the blend during compounding.

[0055] According to some embodiments of the disclosure, the impact modifier is selected from a group consisting of core-shell impact modifiers and / or bulk elastomeric impact modifiers comprising acrylate and / or methacrylate functional groups such as acrylate-styrene- acrylonitrile, styrene-butadiene-styrene, styrene-butadiene rubber, styrene-isoprene- styrene, methyl methacrylate-butadiene-styrene, methacrylate-butadiene-styrene and acrylonitrile-styrene-acrylonitrile or a combination thereof. According to some embodiments of the disclosure, the impact modifier is preferably methacrylate-butadiene- styrene (MBS).

[0056] According to some embodiments of the disclosure, the compatibilizer is selected from a group consisting ofstructures comprising acrylate, methacrylate functional groups, diene functional group, epoxy functional group such as methyl methacrylates, glycidyl methacrylates and ethyl acrylates, and may be styrene-methyl methacrylate-glycidyl methacrylate random copolymer, maleic anhydride-styrene-methyl methacrylate terpolymer, styrene-ethylene / butadiene-styrene, ethylene-acrylic ester copolymer, acrylonitrile-butadiene-styrene, or a combination thereof.

[0057] According to some embodiments of the disclosure, the stabilizer is selected from a group consisting of organic phosphates, alkylated monophenols or polyphenols, stearates, calcium-based stabilizers, zinc-based stabilizers, or a combination thereof.

[0058] According to some embodiments of the disclosure, the viscosity modifier is selected from a group consisting of polyalkyl methacrylate, hydrogenated styrene-diene, olefin copolymer or polyisobutene or a combination thereof. Typically, in embodiments of the disclosure a high molecular weight polycarbonate is used. In general, the higher the molecular weight, the higher the impact properties that can be achieved. Polycarbonate with a molecular weight of at least 52 000 g / mol can be considered a high molecular weight polycarbonate.

[0059] According to some embodiments of the disclosure, a process for manufacturing PC-PBT blend is provided, comprising the steps of i) drying of a mixture of PC and PBT until the moisture content is below 200 ppm, ii) compounding the mixture in an extruder, wherein the temperature during the compounding is kept between 220-280 °C, preferably 240-265 °C, wherein vacuum is applied to remove the degradation gases, and wherein inert gas is purged in the extruder feeding zone. The temperature of the feeding zone is typically kept at 20-50 °C to prevent the degradation of the processing aid that typically is a vegetablebased processing aid which degrades at higher temperatures.

[0060] According to some further embodiments of the disclosure, the extruder may be a twin- screw extruder.

[0061] The temperature in the compounder should be high enough to enable the processability of PC but low enough to prevent degradation of PBT. According to some embodiments of the disclosure, the temperature during compounding is kept between 220 and 280 °C, preferably 230-270 °C, more preferably 240-265 °C.

[0062] According to some embodiments of the disclosure, the extruder screw speed is typically 20-300 rpm, preferably 100-120 rpm.

[0063] According to some embodiments, the compounding is typically continued for 60-600 s, preferably 80-300 s, more preferably 90-110 s.

[0064] According to some embodiments, the Charpy notched impact value of the PC-PBT blend is at least 60 kJ / m2, preferably at least 65 kJ / m2. In the context of this disclosure, the Charpy notched impact test is performed according to the ISO 179 standard. The test is a single point test that measures material’s resistance to impact, and it is defined as the kinetic energy needed to initiate fracture and continue the fracture until the specimen is broken.

[0065] The disclosure also relates to the use of PC-PBT blend of the disclosure as structural parts in automotive industry and electrical vehicles. Some examples of these are door handles, body panels, tailgates, spoilers, front grilles, roof cladding, energy absorbers, housing, trunk lids, tank flaps, luggage racks and interior low-gloss parts such as glove boxes. The disclosure can also be used in outdoor power equipment such as tractor or lawn mower tools and equipment parts, appliances, and consumer goods such as oven handles, vacuum cleaner housing and nozzles, fluid containers and transport bins for food, telecommunications such as radio housing and speakers, and building and construction such as outdoor enclosure and building supplies.

[0066] In the context of this disclosure, the processing method for the PC-PBT blend is extrusion using a twin-screw extruder. Polymer extrusion refers to a manufacturing technique where raw plastic material is melted and formed in a continuous profile. The screw design can be varied by methods known in the art depending on the used material and desired final product design. High molecular weight PC has good impact resistance, dimensional stability, and heat resistance, but due to its high viscosity the processing of high molecular weight polycarbonate is demanding. In this disclosure, a processing aid may be added in the blend in the feeding zone at 20-50 °C. At higher temperatures, the processing aid can degrade.

[0067] In Figure 1 recycled feedstock 10 comprising inorganic or non-melting contents, such as glass fibers, is fed to a drying step 100. The dried recycled feedstock 10 is fed to an extruder 200 for an optional pretreatment process to remove excess residues. After the optional pretreatment extruder, the feedstock is fed to a compounding extruder 400 in which the process described in this disclosure takes place.

[0068] The recycled feedstock 20 without excess residues, and / or virgin feedstock 30, can each be optionally dried in step 300, after which the optionally dried feedstock 20 and / or 30 is fed to the compounding extruder 400. Impact modifier 40, optionally a second impact modifier 50, optionally stabilizer 60, optionally compatibilizer 70 and optionally viscosity modifier 80 each optionally dried in step 500, are fed to the compounding extruder 400. The product obtained in step 400 is optionally fed to pelletizing step 600, after which the obtained granules are optionally dried in step 700.

[0069] EXAMPLES

[0070] Example 1 : Preparing PC-PBT blend

[0071] PC and PBT, in a ratio of 3:1 PC:PBT, were dried in the oven at 120 °C for 2 hours, until the moisture content of PC and PBT was below 200 ppm. Compatibilizer, impact modifier A, impact modifier B, stabilizer and viscosity modifier were added, and the mixture was compounded in a twin-screw extruder with a screw speed of 100 r / min for 0.15 hours. The temperature profile of the extruder had a range of between 240-265 °C increasing continuously towards the die of the extruder. Only the temperature of the feeding zone was kept at 20-50 °C. Extrudate was cooled down in water bath and pelletized to granule form. The granules were dried to ensure the moisture content was below 200 ppm before the injection molding to produce standard test bars. Twin-screw extruder with length / diameter (L / D) ratio between 25-65 was utilized. Vacuum was applied to facilitate the removal of degradation gases as a by-product of the process. The extruder was purged with inert gas starting from the feeding zone of the extruder and the gravimetric feeders were kept under continuously purged inert gas blanket to avoid moisture update of the input materials. Water bath temperature was kept at room temperature to cool down the polymer blend strand before pelletizing. After pelletizing the granules were dried for 2 hours at 100°C.

[0072] Blends were made according to the process described above. The total amount of recycled content, the ratio of PC:PBT, as well as used compatibilizer, impact modifier(s), stabilizer and viscosity modifier as well as their amounts are presented in Table 1 . Table 1 . Examples of PC-PBT blends.

[0073] Comparative examples of blends, where no impact modifiers were added, were prepared according to the same process described above. The total amount of recycled content, the ratio of PC:PBT, as well as used compatibilizer, stabilizer and viscosity modifier as well as their amounts are presented in Table 2.

[0074] Table 2. Examples of comparative blends. Example 2: Mechanical properties

[0075] Tensile measurements were performed with 10 mm / min strain rate with Instron 4505 universal material tester (Instron Corp. Norwood, Massachusetts, USA) with an Instron 2665 Series high-resolution digital extensometer. Charpy notched impact measurements were done with V-notch shape with 2 mm depth of notch and 4mm thickness of sample rod and with Ceast Resil 5.5 equipment. 10 repetitions for each impact test and 5 repetitions for tensile tests were measured for each test run sample.

[0076] Standard test bars were produced with an injection molding equipment. The tensile tests were performed according to the ISO 527 standard. The Charpy notched impact test was performed according to the ISO 179 standard. The results are presented in Table 3 for the test samples according to Table 1 and for the commercial blend as well as the comparative formulations according to Table 2, without any impact modifier, the Charpy Notched impact test results are presented in Table 4. Figure 2 shows the measured Charpy notched impact tests for the blends according to the disclosure, the commercially available blend, and the comparative blends in which no impact modifiers were used. The Charpy notched impact for a 100 w-% recycled PC sample was 11 .9 kJ / m2.

[0077] Table 3. Results for measurements for blend examples. Table 4. A PC-PBT blend without impact modifier.

[0078] As can be seen from the measurement results presented in Tables 3 and 4 and Figure 3, the impact modifier is essential to the PC-PBT formulation, and best impact properties were observed when the blend contains preferably at least 3 wt-% of impact modifier. All of the examples show that the disclosed PC-PBT blend has either comparable or better mechanical properties compared to commercial PC-PBT blend. In Figure 3 the total amount of impact modifier (wt-%) is shown on the x-axis, the Charpy Notched Impact (kJ / m2) as well as the Ultimate Tensile strength (MPa) on the primary y-axis and Tensile Modulus (MPa) on the secondary y-axis.

[0079] Example 3: Differential scanning calorimetry (DSC)

[0080] Differential scanning calorimetry (DSC) characterization of test samples according to Table 1 was done using a NETZSCH DSC 204F1 Phoenix instrument with the parameters 20°C / min heating and cooling rates, over two heating-cooling cycles and under N2gas (50 mL / min flow). The second heating and cooling curves were recorded and analyzed to observe the effect of exothermic reactions observed during the first heating cycle.

[0081] Differential scanning calorimetry (DSC) data for the commercial virgin PC-PBT blend (Xenoy), and the PBT and PC blends according to Table 1 are shown in Table 5 and Figure 4.

[0082] The data of the PC-PBT blends demonstrate the effect of exothermic reactions observed during the first heating cycle. There is a clear decrease in the degree of crystallinity during the first heat cycle and the DSC data implies strong interactions between the PBT and PC polymer chains, leading to hindered crystallization of PBT.

[0083] Nearly complete amorphization of the blend took place during the second heating cycle in DSC, which is a hallmark of highly cohesive nano-scale polymer morphology and hence the factor explaining the extraordinary elastic properties and mechanical ductility of the studied PC / PBT blends. Table 5. DSC measurements

[0084] Example 4: Dynamical mechanical analysis (DMA)

[0085] The viscoelastic properties of the polymer blends according to Table 1 were studied using dynamical mechanical analysis (DMA). Storage modulus (G') can be considered as elastic modulus that is measured continuously as a function of temperature, frequency or time. In this disclosure, storage modulus was measured as a function of time where constant frequency and force were applied. Damping coefficient (tan(6)) represents the energy loss due to increasing mobility of polymer chains and irreversible conformational changes occurring at a given thermal and mechanical stress. The peak temperature on tan(b) indicates the relaxation time of the polymer matrix and sudden loss of energy due to this conformational change of polymer chains that is also reflected as sudden damping of storage modulus curve.

[0086] DMA analysis of the samples was done using Mettler DMA SDTA 861 e in tensile mode. Samples were 9 mm x 4 mm x 2 mm (length x width x thickness). Tension was applied in the direction of melt flow orientation. Constant test frequency of 10 Hz was used, and temperature sweep was between 25 °C to 175 °C. The results for the commercial reference and blends 2, 3, 6 and 7 are presented in Figure 5. Figure 5A shows the storage modulus (G') and Figure 5B tan 5 results for the commercial reference, the rPC, blend 2 (S2), blend 3 (S3), blend 6 (S6) and blend 7 (S7).

[0087] The storage modulus of blends 2, 3, 6 and 7 and the commercial PC-PBT blend are in the range of 2-2.4 GPa at +40 °C. In comparison, the neat PC has a higher modulus of about 3 GPa at this temperature. The clear difference between the studied samples and the commercial reference is the better retention of stiffness (elastic modulus) of studied PC- PBT blend samples up to temperatures around +80°C. This is in alignment with the corresponding (intermediate) glass transition temperatures shown in the tanS signal, and partly in line with the transitions seen in the DSC data presented in the Example 3 and Table 5.

[0088] The PC-PBT blends have roughly 20 °C higher useful maximum service temperature range as compared to the commercial Xenoy blend, which rapidly loses elastic storage modulus onsetting at the glass transition of PBT at around +50°C. The PC-PBT blend of this disclosure stays rigid under elevated temperatures. The temperature of the structural parts in cars can increase to 60-80 °C especially in countries where the average temperature is high, such as South European, South American, and African countries.

[0089] Example 5: Morphology and structure of the polymer blends by STEM , EDS, electron and XRD diffraction

[0090] The microstructure was studied with transmission electron microscope (TEM) and scanning TEM using FEI Talos F200X equipped with 4 Super-X EDS detectors. The morphology was revealed with TEM and STEM bright field (BF) and high angle annular dark field (HAADF) images of Osmium tetroxide-stained samples. The crystallinity was studied with selected area electron diffraction (SAED) and the chemical elemental information was investigated by EDS mapping of Osmium, Carbon and Oxygen.

[0091] The fine nanoscopic morphology of the r-PC / PBT blends was revealed by EDS elemental mapping of Osmium-stained samples, while the nanoscopic detail of the blend was only faintly visible by the mass density contrast under TEM / STEM. Especially the Osmium and Oxygen elemental contrast images showed inter-penetrating network (IPN) structures in the nanoscale. Partial crystallization and continued trans-esterification reactions of PBT were observed by differential scanning calorimeter (DSC) data from the first heating cycle, but electron- and x-ray diffraction analyses implied mesomorphic poorly crystallized morphology consisting of randomly oriented nodular nanoscopic PBT networks, which was supported by the elemental contrast image of the STEM-EDS mappings. Nearly complete amorphization of the blend took place during the second heating cycle in DSC, which is a hallmark of highly cohesive nano-scale polymer morphology and hence the factor explaining the extraordinary elastic properties and mechanical ductility of the studied PC / PBT blends. Figure 6 shows in (a) a STEM HAADF image with inverse contrast for better illustration of different phases and SAED pattern with its radial profile and in (b) a STEM HAADF image and elemental mapping (at%) of Carbon (C), Oxygen (O) and Osmium (Os) of blend 2 according to Table 1 .

[0092] The transesterification and favorable melt viscosity ratio led to extremely fine nanoscopic blend morphology with high cohesion between PC and PBT phases without added catalyst or filler(s).

Claims

CLAIMS1 . A polymer blend characterized in that it comprises more than 85 wt-% of polycarbonate (PC) and poly(butyleneterephthalate) (PBT), a PC and PBT ratio of 1 :1 - 5:1 , more than 40 wt-% of recycled PC and / or recycled PBT of the total weight of PC and PBT, and wherein the ash content of the blend is less than 4 wt-% of the total weight of the blend, the storage modulus of the blend is at least 1 .5 GPa at 80 °C, and the blend is formed by adding 3-7 wt-% of one or more impact modifier(s) of the total weight of the blend.

2. The blend of claim 1 , characterized in that the blend is formed by adding 2-5 wt-% of compatibilizer and 0.1-1 wt-% of stabilizer(s) of the total weight of the blend.

3. The blend according to any one of the preceding claims, characterized in that the blend does not comprise added catalyst and / or inorganic filler.

4. The blend according to any one of the preceding claims, characterized in that the polymer blend has an inter-penetrating network (IPN) blend structure.

5. The blend according to any one of the preceding claims, characterized in that the blend is formed by adding 2-5 wt-%, preferably 2-4 wt-%, more preferably 2-3 wt-% of compatibilizer of the total weight of the blend.

6. The blend according to any one of the preceding claims, characterized in that the blend is formed by adding 0.1 -1 wt-%, 0.2-0.8 wt-%, more preferably 0.4-0.6 wt-% of viscosity modifier of the total weight of the blend.

7. The blend according to any one of the preceding claims, characterized in that the ash content is less than 3 wt-%, preferably less than 2 wt-%, more preferably less than 1 wt-% of the total weight of the blend.

8. The blend according to any one of preceding claims, characterized in that over 55 wt-% and most preferably over 60 wt-% of the total weight of PC and PBT is recycled PC and / or recycled PBT.

9. The blend according to any one of the preceding claims, characterized in that the ratio of PC to PBT is 2:1 -4:1 PC:PBT, preferably 3:1 -1.5:1 PC:PBT.

10. The blend according to any one of the preceding claims, characterized in that the blend is formed by using in total 3-7 wt-%, preferably 4-6 wt-% of one or more impact modifier(s) of the total weight of the blend during compounding.11 . The blend according to any one of the preceding claims, characterized in that the impact modifier is a core-shell impact modifier and / or a bulk elastomeric impact modifier, preferably the impact modifier is selected from a group consisting of structures comprising acrylate functional groups such as methacrylate, conjugated dienes and high molecular weight elastomeric materials derived from olefins, monovinyl aromatic monomers, acrylic and methacrylic acid and their ester derivatives or combinations thereof.

12. The blend according to any one of the preceding claims, characterized in that the impact modifier is methacrylate-butadiene-styrene (MBS).

13. The blend according to any one of the preceding claims, characterized in that the blend is formed by adding 0.1 -1 wt-%, preferably 0.2-0.8 wt-%, more preferably 0.4- 0.6 wt-% of stabilizer of the total weight of the blend.

14. The blend according to any one of the preceding claims, characterized in that the stabilizer is selected from a group consisting of organic phosphates, alkylated monophenols or polyphenols, stearates, calcium and zinc-based stabilizers or combinations thereof.

15. The blend according to any one of the preceding claims, characterized in that the compatibilizer is selected from a group consisting of structures comprising acrylate functional group, glycidyl functional group, diene functional group, epoxy functional group or combinations thereof.

16. The blend according to any one of the preceding claims, characterized in that the viscosity modifier is selected from a group consisting of polyalkyl methacrylate, hydrogenated styrene-diene, olefin copolymer or polyisobutene or combinations thereof.

17. The blend according to any one of the preceding claims, characterized in that the Charpy notched impact value of the blend is at least 60 kJ / m2, more preferably at least 65 kJ / m2.

18. The blend according to any one of the preceding claims, characterized in that the total amount of compatibilizer, impact modifier, stabilizer and viscosity modifier is less than 15 wt-% and preferably 10 wt-% or less of the total weight of the blend.

19. A process for manufacturing polymer blend according to any of the claims 1 -18, characterized in that the process comprises: i) drying of a mixture of PC and PBT until the moisture content is below 200 ppm; ii) adding 2-5 wt-% of compatibilizer, 3- 7 wt-% of impact modifier(s) and 0.1 -1 wt-% of stabilizer(s) of the total weight of the blend; iii) compounding the blend in an extruder, wherein the temperature during the compounding is kept between 220-280 °C, wherein vacuum is applied to remove the degradation gases, and wherein inert gas is purged in the extruder feeding zone.

20. The process according to the claim 19, characterized in that the extruder is a twin- screw extruder.

21. The process according to any one of claims 19-20, characterized in that the temperature during compounding is kept between 220 and 280 °C, between 230 and 270 °C, or between 240 and 265 °C, preferably between 240 and 265 °C.

22. The process according to any one of claims 19-21 , characterized in that the extruder screw speed is 20-300 r / min, preferably 100-120 rpm.

23. The process according to any one of claims 19-22, characterized in that the compounding is continued for 60-600 s, preferably 80-300 s, more preferably 90-110 s.

24. Use of the polymer blend of any one of the preceding claims as structural parts in automotive industry such as door handles, body panels, tailgates, spoilers, front grilles, roof cladding, energy absorbers, housing, trunk lids, tank flaps, luggage racks and interior low-gloss parts such as glove boxes, and electric vehicles, outdoor power equipment, appliances and consumer goods, telecommunications and building and construction.

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