Fully biodegradable sustainable biocomposite material and production method with improved performance properties for use in automotive industry

Abstract

The invention relates to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposites with improved performance properties by using biodegradable polymer blends reinforced with natural fibers, which are lighter than synthetic fibers such as glass fiber, in the presence of epoxy POSS molecules for use in the production of battery packs, especially in electric vehicles, and production method.

Description

[0001] DESCRIPTION

[0002] FULLY BIODEGRADABLE SUSTAINABLE BIOCOMPOSITE MATERIAL AND PRODUCTION METHOD WITH IMPROVED PERFORMANCE PROPERTIES FOR USE IN AUTOMOTIVE INDUSTRY

[0003] Technical Field

[0004] The invention relates to a fully biodegradable and sustainable biocomposite material with improved performance characteristics for use in the automotive industry and to a production method.

[0005] The invention relates to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposites with improved performance properties by using biodegradable polymer blends reinforced with natural fibers, which are lighter than synthetic fibers such as glass fiber, in the presence of epoxy POSS molecules for use in the production of battery packs, especially in electric vehicles, and production method.

[0006] State of the Art

[0007] Electric vehicles have gained great momentum in recent years as an environmentally friendly and sustainable transportation alternative. One of the main reasons for this rise is the positive environmental impact and energy efficiency of electric vehicles. Electric vehicles produce less greenhouse gas emissions than gasoline and diesel vehicles and play an important role in protecting air quality and combating climate change. This is why the use of electric vehicles is being increasingly promoted around the world. Batteries play a vital role in the success of electric vehicles. Conventional battery packs used in electric vehicles are usually made of heavy materials such as aluminum. These materials increase vehicle weight, reduce energy efficiency and complicate recycling processes. Moreover, being heavy metals, they cause long-term negative environmental impacts. In addition, their high density leads to increased vehicle weight and disadvantages such as high CO2 emissions and poor performance.

[0008] Due to these negative impacts, in recent years, the automotive industry has sought lighter, sustainable, and recyclable materials to reduce fuel consumption and produce high- performance materials for battery packs. For this purpose, the leading compounding companies in the sector offer different materials to automotive manufacturers. For example, SABIC, one of the world's most important polymer suppliers, manufactures products for use in the battery packs of electric vehicles. One of the most prominent of these products is the poly(phenylene ether) (PPO) / polystyrene (PS) blend that they launched under the name NORYLTM RESIN. Although this product is an ideal electric vehicle battery case material due to its high dimensional stability and low hydrolytic resistance, its low solvent resistance and sensitivity to environmental stress cracking are among its disadvantages. In addition, its very high glass transition temperature (Tg), around 215-220eC, makes it very difficult to process, although it has a high heat deflection temperature (HDT) and high dimensional stability. The products to be used in under-hood parts in the automotive sector must have sufficient strength, stiffness and HDT value in order to be widely used industrially. The increase in thermo-mechanical properties is achieved by increasing their dimensional stability. For this reason, it is known that in the industry, polymeric materials are often used in combination with synthetic fibers such as glass fiber (GF) or talc as a reinforcing agent in order to provide sufficient requirements to be used in under-hood applications (Kodal et aL, 2015). For this reason, other materials recommended by SABIC are glass fiber-reinforced polyamide 6 (PA6) or polypropylene (PP) composite materials. The fact that such products have high dimensional stability due to their glass fiber content, have a sufficient HDT value and are easier to process than PPO-based products makes them one step ahead.

[0009] However, as previously discussed, battery packs for electric vehicles are primarily composed of synthetic polymers or polymer blends, including polypropylene (PP), polyamide 6 (PA6), and polyphenylene oxide / polystyrene (PPO / PS), which are not generally considered environmentally sustainable materials Investigating the use of environmentally friendly polymers instead of such materials has recently become one of the most frequently studied topics due to the fact that their recycling is very long, they are not biodegradable and their carbon footprint is high starting from the production processes. Considering that 40% of the world's solid waste comes from polymers, the need to increase the adoption of environmentally sustainable materials becomes even more apparent..

[0010] Furthermore, as mentioned in detail earlier, synthetic polymers used in the battery packs of electric vehicles are reinforced with synthetic fibers to improve their dimensional stability. For this purpose, glass fiber is the most widely used synthetic fiber in the industry. However, the low recyclability of glass fiber and its high risk of causing health problems have triggered the use of more environmentally friendly and sustainable composite materials. The use of glass fiber as a reinforcing agent in polymeric products is disadvantageous in many respects.

[0011] Burial in the soil (landfilling) is one of the leading methods used in the recycling processes of synthetic fibers, especially glass fibers. For example, in the UK, 67% of end-of-life glass fiber composites are disposed of by landfilling. Furthermore, 13% of glass fiber can be recycled and only 6% can be reused. Therefore, new regulations have recently banned the burial of glass fiber composites in developed countries such as Germany and the UK due to their negative impact on the environment.

[0012] Another method used to recover synthetic fibers such as glass fiber from composite structures is incineration. In this method, since polymeric compounds have certain calorific values, the waste composite can be converted into heat to generate electricity. However, the major disadvantage of incineration is the ash by-product, which can only be landfilled as inert waste. This incineration and recycling process has many disadvantages. One of the disadvantages is that it is a costly process. For example, the cost of recycling through incineration in France is reported to be €92 per 1 ton of product. Furthermore, it is only possible to achieve an efficiency rate of 35% when converting heat into electricity. In addition, greenhouse gases released during the incineration process cause serious environmental damage. Moreover, like any other recycling process, pyrolysis has its limitations and the possibility of char formation on the surface of the resulting fiber is the most challenging. There is a significant decrease in the mechanical properties of recovered fibers due to coal formation. Methods such as chemical treatment and postheating of fibers only reduce char formation to a certain extent. All of these situations undermine the progress of the circular economy.

[0013] Other recycling methods that are not frequently applied include mechanical and chemical recycling processes. However, the fact that the mechanical performance of the glass fiber after the mechanical recycling process is far behind the mechanical performance of the glass fiber when it is first used and the use of large amounts of solvents in the chemical recycling process distracts these methods from environmentally friendly and industrially applicable methods.

[0014] In addition to all these, surface modification of fibers is performed by chemical processes such as "silanization and alkalization" or physical processes such as "plasma" to improve the insufficient interfacial interaction between synthetic fibers and polymer matrices. However, these processes are both environmentally unfriendly and costly as they require further modification.

[0015] In the present art, the materials used in the battery packs of electric vehicles involve processes that are far from being sustainable and environmentally friendly, from the production process to the final product and after the end of their useful life.

[0016] As a result, due to the above-mentioned drawbacks and the inadequacy of the existing solutions, a development in the relevant technical field has become necessary.

[0017] Purpose of the Invention

[0018] The invention is inspired by existing situations and aims to solve the above-mentioned problems.

[0019] The main purpose of the invention is to provide products and a production method with improved performance characteristics for use in the battery packs of innovative electric vehicles that are completely environmentally friendly and have a high potential to contribute to a sustainable economy. For this purpose, lightweight, low carbon footprint poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) biocomposites reinforced with natural fibers were prepared. In order to improve the interfacial interaction / adhesion performance between all components in the prepared biocomposites, polyhedral oligomeric silsesquioxane (POSS) nanoparticles containing epoxy functional groups, a hybrid nanoparticle, were used.

[0020] A purpose of the invention is to provide competitive products and a manufacturing method that are sustainable and environmentally friendly for use in battery packs for electric vehicles. Considering the environmental sensitivities within the scope of Euro 7 norms, the polymers used in automotive parts must have sufficient thermal stability and mechanical properties in order to provide low CO2 emissions along with high performance requirements. The Euro 7 regulation aims to reduce total NOXemissions from cars and vans by 35% by 2035 compared to Euro 6. This makes it inevitable to make lighter and higher quality parts in vehicles. In addition, with increasing environmental sensitivity, developed countries have made a rapid transition to electric vehicle production and started to encourage their citizens to buy these vehicles. This has led to a very rapid growth in the electric vehicle sector. According to Marketsandmarkets Research, the global electric vehicle market size of 388.1 billion dollars in 2023 is expected to increase to 951 .9 billion dollars by 2030 with an annual growth rate of 13.7%.

[0021] By year of 2016, the automotive sector is the 4th largest economy in the world, accounting for approximately 5% of the world economy with 4 trillion dollars. In the recent past, Turkiye has been one of the countries with the highest share in automotive production with a growth of 16.1% in the automotive sector. Moreover, the automotive sector is the sector with the highest R&D expenditure in Turkiye. This has made the development of materials with high performance characteristics inevitable. In recent years, many automotive parts have been made using naturally reinforced composite materials, mostly based on polypropylene and reinforcing natural lignocellulosic fibers such as jute, flax, hemp and wood. For example, Mercedes and BMW use hemp fiber for composites such as door panels, dashboards, etc. In our country, the importance given to hemp cultivation and production increased with the introduction of hemp in 2019 at the "Symposium on Local Governments in the Presidential Government System" and the preparation of the "Report and Action Plan on Industrial Hemp Cultivation in Turkiye" immediately afterwards. According to Demirbek and Bulut's 2021 publication, the global market size for industrial hemp announced in 2019 is USD 4.71 billion, and it is estimated that the industrial hemp market size will reach USD 10.6 billion by 2025. More recently, the hemp industry in Europe has started to be used in industrial fields such as automobiles and construction materials. It is aimed to expand the use of hemp, whose production has become a state policy in our country, in the automotive sector and future studies in this field with this invention.

[0022] In addition, investments in biopolymers are increasing today. As a solution to reduce the impact of plastic materials on environmental pollution, the use of biodegradable materials, especially in the packaging and automotive sectors, is becoming widespread, especially in developed countries. In Europe, several pieces of legislation have been introduced to promote the use of biodegradable polymers. For example, in Germany, companies using biodegradable plastic materials are not subject to the environmental tax known as "green tax". In Japan, the use of biodegradable plastic materials is regulated and encouraged. In our country, there is not yet an official regulation on the use of biodegradable materials, but new regulations are expected to be made within the scope of the European Union harmonization process, especially for packaging and automotive materials. In this respect, the outputs of this invention in the field of biodegradable plastic materials, which is quite new for our country, may guide our domestic industrialists as a result of the said regulations, and for this reason, it is also important. It is also thought that the invention will contribute to the competitiveness of our country in this new technological field.

[0023] A purpose of the invention is to provide an industrially applicable production method. When planning the invention, special care was taken to ensure that all the implemented steps could be adapted to the industrial scale. For this reason, extrusion process was preferred when preparing the samples and standard test samples were prepared by injection molding. In this way, it is possible to scale-up the outputs of the invention so that they can be easily applied by companies operating in the food and beverage packaging, textile and electrical-electronics industries in Turkiye.

[0024] In order to fulfill the aforementioned objects, the invention relates to poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposites for use in the automotive industry, fully biodegradable and sustainable, with improved performance properties in the presence of epoxy POSS molecules.

[0025] Preferred embodiments of the invention provide biocomposites with tensile strength 38-85 MPa, elongation at break 1-13%, Young's modulus 4500-6200 MPa and HDT between 160-183eC.

[0026] In order to fulfill the aforementioned purposes, the invention relates to a method of manufacturing said biocomposites, in its most basic form, comprises the following process steps;

[0027] (i) Mixing PHBV and PBS in certain proportions by melt blending method and adding epoxy POSS to the blend in certain proportions to improve interfacial interaction between PHBV and PBS;

[0028] (ii) In order to increase the HDT value, adding of the hemp fiber to the PHBV / PBS / Epoxy POSS blend and compounded by melt blending method, adding of Epoxy POSS again at a determined rate to improve the interfacial adhesion between the PHBV / PBS / Epoxy POSS blend and hemp fiber. According to preferred embodiments of the invention, (i) in the melt blending step, the amount of PHBV is 60-90% by weight and the amount of PBS is 5-40% by weight, and 1- 20 wt.% epoxy POSS is added in proportion to the total mixture.

[0029] According to preferred embodiments of the invention, (ii) in the melt blending step, 5-40% by weight of hemp fiber is added to the PHBV / PBS / Epoxy POSS blend and again 1-20% by weight of epoxy POSS is added to the total blend.

[0030] In order to fulfill the aforementioned objects, the invention also is electric vehicle battery cases for use in the automotive industry made of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposite with improved performance properties in the presence of epoxy POSS molecules.

[0031] The structural and characteristic features and all advantages of the invention will be more clearly understood with the detailed description given below; therefore, the evaluation should be made by taking this detailed description into consideration.

[0032] Detailed Description of the Invention

[0033] In this detailed description, the preferred embodiments of the use of the inventive POSS nanoparticles containing multiple epoxy functional groups in the polymer industry are described only for a better understanding of the subject matter and in a non-limiting manner.

[0034] The invention relates to biocomposite products and production methods for use in the battery boxes of electric vehicles, which are completely environmentally friendly, have a high potential to contribute to a sustainable economy and have innovative, improved performance characteristics.

[0035] With the invention, lightweight, low carbon footprint, poly(3-hydroxybutyrate-ko-3- hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) biocomposites reinforced with natural fibers were prepared. In order to improve the interfacial interaction / adhesion performance between all components in the prepared biocomposites, polyhedral oligomeric silsesquioxane (POSS) nanoparticles containing epoxy functional groups, a hybrid nanoparticle, were used. The low recyclability of glass fiber used as a reinforcement material in the battery cases of electric vehicles and the high risk of causing health problems have triggered the use of more environmentally friendly and sustainable composite materials. The high density of glass fiber causes the weight of the final products to increase. Compared to synthetic fiber additives such as glass, carbon and kevlar, natural fibers have a lower density and the ability to impart high specific mechanical properties in performance demanding applications such as automotive and aerospace. They are also recyclable and biodegradable, making them sustainable materials compared to glass and carbon fiber. Therefore, in recent years, automotive manufacturers have begun to widely investigate the use of composite materials containing natural fibers due to their low density and environmental friendliness. Recently, leading companies in the sector have started to use natural fiber reinforced polymeric composites in various parts of the vehicle (for example, Audi uses natural fibers in seat backs, rear door panels, side door panels, trunk linings and spare tire storage in A series vehicles), which provide lightness and therefore contribute to both low emission values and fuel consumption.

[0036] Tablel . Characteristics of various natural fibers and glass fibers

[0037] The main reason for the widespread use of lignocellulosic fibers is to avoid the use of non- recyclable and non-renewable reinforcements such as glass and carbon fiber. Natural fibers are not only lightweight and biodegradable, but also have advantages in terms of energy consumption and price compared to synthetic fibers. While the energy consumption required in the production process of glass fiber is 30 GJ / ton, this figure is 4 GJ / ton for natural fiber. Natural fibers such as kenaf, hemp, flax, jute, sisal have many advantages such as lightness, cost, reduction in CO2 emission, less dependence on petroleum resources and recyclability as well as being environmentally friendly. In addition, while CO2, SOXand NOXemissions in the production of 1 kg of natural fiber are 0.64 kg, 1.2 g and 0.95 g, respectively, this increases to 20.4 kg, 8.8 g and 2.9 g during glass fiber production.

[0038] As explained in the present technique, the unsustainability of synthetic fibers such as glass fiber and the difficulties in recycling processes make them less environmentally friendly materials. On the other hand, the biodegradability, recyclability, low density, low energy requirements during their production and high strength-to-weight ratio of natural fibers make them an ideal additive material for the automotive industry. It was decided to use hemp fiber as natural fiber in this invention. The reason for choosing hemp fiber as a lignocellulosic fiber type is that it has relatively the highest mechanical properties among natural fibers, as can be seen in Table 1. The mechanical properties of hemp fiber such as modulus are comparable to glass fiber. In addition, hemp fiber is known to have many advantageous properties when used in automotive applications, such as affordable cost, high tensile strength and stiffness, an ideal substitute material for glass fiber, reduction in molding time, weight reduction in the final product, easy processing and recyclability. For example, in Kaya and Oner's study in 2020, it was reported that the durability of cars whose body is made of hemp is ten times higher than those made of steel. In addition, hemp production has become a state policy in our country in recent years. For this purpose, Hemp Research Institutes were established at Samsun Ondokuz Mayis University in 2019 and Yozgat Bozok University in 2020 for research and development studies in hemp production. Samsun Ondokuz Mayis University started its activities and in cooperation with the Black Sea Agricultural Research Institute, Narhsaray hemp variety with low tetrahydrocannabinol (THC) content and high fiber and stem yield was developed. Therefore, hemp fiber was preferably used due to its advantageous properties mentioned above, the fact that its use in textile products has become very common in our country; therefore, it is easy to obtain, and with the studies carried out within the scope of the invention, its use in areas such as the automotive sector has been investigated and its use in products with high added value has become widespread.

[0039] As mentioned in the present art, battery packs for electric vehicles are made of synthetic polymers or polymer blends such as PR, PA6 and PPO / PS, which are not typically regarded as environmentally sustainable materials. Investigating the use of environmentally friendly polymers instead of such materials has recently become one of the most frequently studied topics due to the fact that their recycling is very long, they are not biodegradable and their carbon footprint is high starting from the production processes. Poly(lactic acid) (PLA), thermoplastic starch (TPS), poly(butylene-adipate-co- terephthalate) (PBAT), poly(butylene succinate) (PBS), poly(caprolactone) (PCL) and poly(3-hydroxybutyrate-ko-3-hydroxyvalerate) (PHBV) are among the most widely used biodegradable polymers recently. Polymeric products used in under-the-hood applications in the automotive sector, such as battery packs for electric vehicles, must have sufficient HDT. One of the most basic criteria for increasing the HDT value of polymeric products is to have sufficient crystallinity. Products with increased crystallinity exhibit high thermomechanical properties such as HDT. Therefore, high HDT value is directly related to crystallinity. Among the biodegradable polymers mentioned above, PHBV has the highest HDT value. The HDT of pure PHBV is known to be 143eC. Due to its high HDT value, for example, the lids of commercial hot coffee containers are made of PHBV. From this point of view, PHBV is one of the polymers that promises potential for use in battery packs of electric vehicles. PHBV, one of the most important members of polyhydroxyalkalkonates, is known to be a semi-crystalline thermoplastic polymer synthesized by bacteria. The high HDT value is due to its high crystallinity and can be processed by conventional polymer processing techniques such as extrusion and injection molding. It has a tensile strength ranging from 22-34 MPa and in this respect its mechanical properties are similar to PP. Therefore, the use of PHBV instead of PP matrix is preferred in this invention study. However, the high crystallinity of PHBV makes it a brittle polymer and hinders its widespread use. For this purpose, one of the methods used to reduce the brittleness and increase the toughness of PHBV is to blend PHBV with another biodegradable polymer that is flexible and has a low glass transition temperature (Tg). Blending two polymers is a widely used method to obtain cheaper materials without significant changes in the properties of both polymers compared to synthesizing new polymer materials. However, polymer blends also play an important role in eliminating or minimizing the disadvantageous properties of one polymer by mixing it with another polymer. Therefore, the brittle feature of PHBV is eliminated by blending it with a more flexible biodegradable polymer within the scope of the invention. This gives PHBV flexibility without compromising its biodegradability. For this purpose, blends of PHBV with PBS were created. PBS is a fully biodegradable aliphatic thermoplastic polyester with easy processability, high chemical resistance and thermal stability obtained by polycondensation reaction of succinic acid and 1 ,4 butanediol. In addition, the low glass transition temperature leads to high toughness and flexibility. In addition, PBS is a polymer with high crystallization ability and has high crystallinity. Therefore, in order to obtain both flexible material from PHBV and not to compromise the crystallization behavior, blends of PHBV and PBS were prepared within the scope of the invention.

[0040] In the studies carried out within the scope of this invention, PHBV / PBS blends were prepared and then reinforced with hemp fiber and completely environmentally friendly products were produced and the usability of these products as battery boxes in electric vehicles was investigated. First, PHBV blends containing different ratios of PBS were obtained and the PHBV / PBS blend giving optimum properties was reinforced with hemp fiber at different concentrations. There are two disadvantages here.

[0041] The first is that PHBV and PBS are thermodynamically immiscible, as is the case with many polymer blends. PHBV / PBS blends also have an unstable phase morphology and poor interfacial interaction. The fact that PHBV / PBS blends do not exhibit sufficient interfacial interaction causes phase separation between the components and adversely affects the performance properties, especially the mechanical and rheological properties of the final product. For example, Kennouche et al. formed PHBV and PBS blends by melt blending method in their 2016 study and stated that poor interfacial adhesion between the components negatively affected the mechanical properties of the blend. Therefore, in order to obtain the desired properties in polymer blends, the interaction between the components should be increased. There are studies on this in the literature. In studies carried out by Ma et al. in 2014 dicumyl peroxide (DCP) was used to increase the level of interaction between PHBV and PBS. DCP was used in these studies to obtain free radicals and subsequently branched structures. The results obtained showed that in the presence of DCP, PHBV-g-PBS copolymers were formed and the impact strength and elongation at break of the PHBV / PBS blend were significantly improved as a result of increased interfacial interaction between the components. However, the formation of cross-linked structures was shown as a negative side of these studies in terms of processability. One of the most effective methods for the compatibilization of polymer blends is to obtain stable phase morphologies in polymer blends by reactive compatibilization using compatibilizers during melt blending.

[0042] Polymers with functional groups such as hydroxyl, carboxylic acid, anhydride, amine, epoxy, etc. can be compatibilized by reactive compatibilization technique. Reactive compatibilization uses polymeric or non-polymeric compounds that have the ability to bind to the end (or sometimes main chain) groups of the polymers to be compatibilized, or that can bind reactively with both blended polymers, or that can bind reactively with one and be compatible with the other. The block or graft copolymers formed in this way settle between both phases and create a surfactant activity. All this formation takes place in-situ as the two polymers are blended in the melt phase. In addition, for the purpose of compatibilization, di / poly-functional and non-polymer small molecules that can react with the chain end groups of the polymer pairs to be compatibilized can be used. Reactions using chain extenders are more economical than the copolymer addition technique. Chain extenders are usually added in very small quantities during melt blending and do not require any separation or cleaning at the end of the process. Isocyanates, anhydrides, epoxies, oxazolines, etc. are examples of chain extenders. While this technique is very effective, the type of reagent to be selected should be determined specifically considering the characteristics of the final product to be used.

[0043] In the study by Chikh et al. in 2016, a reactive compatibilization technique was used to ensure compatibility between PHBV and PBS and for this purpose, maleic anhydride grafted PHBV (PHBV-g-MA) was used together with DCP as a compatibilizer. The authors found that by using PHBV-g-MA, the interfacial interaction between PHBV and PBS was significantly increased and mechanical and rheological properties were improved. In the study by Feijoo et al. 2022, Joncryl® ADR - 4468, an epoxy-based chain extender, was used as a compatibilizer for a blend of PHBV and poly(butylene succinate-ko-butylene adipate) (PBSA). In the study, it was determined that the interaction between the components was significantly improved and increases in mechanical, dynamic-mechanical and rheological properties were obtained through the graft and / or copolymer formed in the interphase as a result of the reaction of the epoxy groups of Joncryl and the hydroxyl and carboxylic acid groups of the polymers. However, the lack of a study on the HDT values of the products in this study and the fact that the thermal stability could not be improved were considered as the shortcomings of this study.

[0044] Polyhedral oligomeric silsesquioxane (POSS) nanoparticles, which have recently emerged as an alternative to conventionally used compatibilizers, are nanoscale molecules with a cage(lattice) structure. The general formula for POSS is (RSiO1 .5)n, where n is usually 6, 8 or 10 and the ratio of Si to O is 1.5. The R group in the structure is hydrogen, alkyl, alkylene, arylene or any derivative of these groups, reactive and / or non-reactive (Kannan et aL, 2005; Ghanbari et aL, 2011). Composed of organic and inorganic parts, the inorganic silicon oxide structure of POSSs is surrounded by organic chains, which ensures excellent compatibility with other polymers. They are also odorless and environmentally friendly. Thermal stability, mechanical strength, gas permeability and flame retardancy properties of the polymer to which they are added can be improved due to the selection of the R group in the structure of POSS to be compatible with the polymer matrix and the nanosize of POSS.

[0045] POSSs, whose molecular structure is shown above, can be dispersed in the polymer matrix at the molecular level if they are compatible (soluble) with the matrix in which they will be used and can interact with the matrix (chemical or physical), in which case a nanocomposite is literally obtained. Although such a situation is ideal, it is generally observed in the literature that POSSs exhibit a dispersion in the 100 - 500 nm band. In polymer / POSS composite systems dispersed at the nano-level and interacting with the polymer matrix, mechanical properties are increased, thermal properties and thermal resistance are improved. There are studies in the literature on the use of POSS molecules as effective compatibilizers for polymer blends. In Kodal's study in 2016, the effect of POSS types with and without functional groups was investigated in order to increase the interfacial interaction between PA6 and PP. The findings showed that in the presence of POSS nanoparticles, the melt viscosity of PP / PA6 blend and the particle size of the dispersed phase decreased and the percent crystallinity of PA6 increased. In the studies of KIIIQ et al. in 2019 and 2020, the effect of POSS nanoparticles on the compatibility of immiscible PLA / poly(butylene adipate-co-terephthalate) (PBAT) and partially miscible PLA / thermoplastic polyurethane (TPU) blends was investigated. The results obtained showed that the mechanical properties improved and the particle size of the dispersed phase decreased as a result of increasing the interfacial interaction between the components in the presence of POSS nanoparticles. As a general conclusion, POSS nanoparticles were found to act as effective compatibilizers for biodegradable polymer blends.

[0046] The fact that POSSs can be more easily physically dispersed in a polymer matrix than nanoclays or nanotubes and can carry different side reactive groups makes these hybrid nanostructures a good nanocompatibilizer candidate for polymer blend systems. In the literature, some studies can be found in which POSS structures are used as nanocompatibilizers. In the 2014 study by Monticelli et al. two POSS species, one with hydroxyl functionality and one without functional groups, and one POSS species grafted with PCL-b-PLA diblock copolymer were used for the compatibilization of PLA and poly(8- caprolactone) (PCL) biodegradable polymer blends. The results of the study showed that POSS structures have a compatibilization effect, especially in POSS type with the functional group and diblock copolymer grafted POSS type, and highly homogeneous blend morphologies were obtained. Li et al. in 2010 investigated the compatibilizing effect of POSS in polystyrene (PS) / poly(methyl methacrylate) (PMMA) blend. It was reported in the study that compatibilization between components was achieved with the use of POSS. In their 2002 study, Zhang et al. synthesized methyl methacrylate grafted POSS (POSS-g- MMA) and used this POSS as a compatibilizer in PS / PMMA blend. From the contact angle measurements, it was determined that the interfacial tension decreased with the increase in the amount of POSS-g-MMA compatibilizer and the phase sizes decreased from SEM analysis.

[0047] As can be seen from the studies summarized above, there are no studies using POSS nanoparticles in the compatibilization of PHBV / PBS biodegradable polymer blends.

[0048] Unlike the studies in the literature, POSS nanoparticles with aliphatic and cycloaliphatic multiple reactive epoxy functional groups and also containing three aliphatic reactive epoxy functional groups were used within the scope of this invention to compatibilize thermodynamically immiscible PHBV / PBS blends. PBS and PHBV have hydroxyl (-OH) and carboxylic acid (-COOH) reactive end groups. The POSS molecules used within the scope of the invention are capable of forming block copolymer structures by interacting with the reactive end groups of PBS and PHBV in PHBV / PBS blends, and these copolymers acted as compatibilizers at the interface.

[0049] In the first stage of the studies carried out within the scope of the invention, PHBV / PBS polymer blends were compatibilized with POSS nanoparticles. For this purpose, POSS molecules were added as compatibilizers to PHBV / PBS blends, containing between 5-40 wt.% of PBS, at ratios ranging from 1 -20% by mass during the melt blending process. The mechanical, thermo-mechanical, rheological, thermal and morphological properties of the samples were then investigated. After evaluating the results obtained in terms of structure-property relationship, the PHBV / PBS blend ratio compatibilized with POSS giving optimum properties was determined.

[0050] In the second stage of the studies carried out within the scope of the invention, the PHBV / PBS - POSS samples obtained from the first stage and showing the highest performance characteristics were reinforced with hemp fiber in order to increase the HDT value and enable their use in the battery boxes of electric vehicles.

[0051] A review of the literature reveals a very limited number of studies in which natural fibers were added to PHBV / PBS blends. For example, in the study of Chilali et al. in 2019, flax fiber was added to the PHBV / PBS / PLA ternary blend and composite materials were obtained in layered structure and their properties were examined, it was stated that the compatibility between the polymer matrix and flax fiber was not sufficient and the flax fiber could not adhere to the structure and caused delamination. In the literature, there are studies in which PHBV / natural fiber and PBS / natural fiber composites were prepared and their properties were investigated. For example, in the 2008 study by Sing et aL, PHBV was reinforced with bamboo fiber. The authors stated that there is a very weak interfacial interaction between bamboo fiber and PHBV and this negatively affects the mechanical properties. Similar findings are also found in the literature for PBS composites reinforced with elephant grass or different natural fibers. In PBS - natural fiber and also PHBV - natural fiber composites, the insufficient interfacial interaction between the matrix and natural fibers is due to the polarity difference between the highly polar lignocellulosic fibers and the biodegradable polymers with low polarity. In order to obtain the desired mechanical performance in fiber reinforced polymer composites, it is very important to improve the fiber - matrix interfacial interaction. The most commonly used method is to increase the level of interaction between natural fibers and biodegradable polymers by surface modification of fiber surfaces by methods such as silanization and alkalization. However, the use of large amounts of solvents in chemical surface modification processes makes these methods less environmentally friendly. Another method is in situ compatibilization with materials with reactive groups such as polymeric diphenyl isocyanate (PDMI). However, PDMI is toxic, causing environmental damage. Moreover, none of these methods are environmentally friendly. For example, the use of large quantities of chemicals and solvents in the chemical modification process generates waste that is difficult to dispose of, leading to extra costs for the industry and environmental problems. Physical methods, on the other hand, are time-consuming and energy-consuming, making them unsuitable for low-cost production.

[0052] For these reasons, a sustainable and environmentally friendly method will be developed if the interfacial adhesion between hemp fiber and PHBV / PBS matrix can be achieved directly during blending in the presence of POSS.

[0053] In the second stage of the studies carried out within the scope of the invention, hemp fiber was added to the PHBV / PBS blends obtained from the first stage and having optimum properties and compatibilized with POSS molecules, while POSS nanoparticles were added to the system again in the melt blending stage to improve the interfacial adhesion between hemp fiber and PHBV / PBS matrix. Thus, the interfacial interaction between PHBV and PBS was improved while at the same time the interaction between hemp fiber and polymer matrix was enhanced. The POSS molecules used within the scope of the invention contain reactive epoxy functional groups that have the potential to react with the reactive end groups -COOH and -OH groups of PBS and PHBV, as well as the functional - OH groups of hemp fiber. Thus, an efficient and environmentally friendly interfacial adhesion between hemp fiber and PHBV / PBS was also achieved. The water absorption resistance of hemp fiber, which is known to be highly hydrophilic, was also increased by depleting the -OH groups after the reaction with epoxy POSS, thus providing long-term resistance to environmental conditions.

[0054] In the literature, there is also no study comparatively investigating the potential of POSS molecules on the interfacial adhesion of PHBV / PBS - hemp fiber systems. The originality of the invention has the potential to contribute significantly to the literature in this respect.

[0055] In addition, as mentioned earlier, polymeric materials must have sufficient strength, stiffness and heat deflection temperature (HDT) to be widely used industrially, especially in the automotive sector. In the studies within the scope of the invention, by increasing the fiber matrix interfacial adhesion, the already high HDT value of PHBV was further improved and a fully biodegradable and environmentally friendly biocomposite material that can be used in the battery boxes of electric vehicles was developed.

[0056] Inventive Methods and Experimental Studies The invention covers the production of sustainable, completely environmentally friendly, high-added value and qualified products that can be used in the battery boxes of electric vehicles.

[0057] Within the scope of the invention, at least one epoxy POSS selected from POSS comprising triple and multiple epoxy reactive groups in aliphatic structure (T-POSS, IM- POSS) and POSS comprising multiple epoxy groups in cycloaliphatic structure (S-POSS), whose chemical structures are given below, was used as POSS type. With the studies carried out within the scope of the invention using POSS molecules, the interfacial interactions between both PHBV - PBS and PHBV / PBS - hemp fiber were significantly improved and biocomposite products with performance characteristics that can be used in battery boxes of electric vehicles were obtained.

[0058] Molecular structure of, a) POSS comprising triple epoxy groups (T-POSS), b) POSS comprising multiple epoxy groups in aliphatic structure (M-POSS), c) POSS comprising multiple epoxy groups in cycloaliphatic structure (S-POSS).

[0059] In the inventive method, POSSs comprising reactive epoxy functional groups were used directly in PHBV / PBS blends in the first stage of the study and then in PHBV / PBS - hemp fiber biocomposites in the second stage of the study.

[0060] PHBV / PBS and PHBV / PBS - hem fiber materials were produced without a change in the production processes, In these products, the interfacial interaction between the components is significantly improved, increasing their molecular weight and improving their mechanical, morphological and thermo-mechanical properties,

[0061] The thermal stability and HDT values of these products increase.

[0062] The materials used within the scope of the invention and their quantities are shown in Table 2.

[0063] Table 2. Materials and quantities used within the scope of the invention

[0064] The inventive method consists of two steps. In the first step, POSS molecules are added to the PHBV / PBS blend while the samples are prepared by melt blending method to improve the interfacial interaction between PHBV and PBS. Then, in the second step, hemp fiber is added to PHBV / PBS blends whose interfacial interaction is improved with POSS molecules. POSS molecules are added to the system again in the second stage of the study to ensure interfacial adhesion between hemp fiber and PHBV / PBS.

[0065] Preparation of Samples by Melt Blending Method (Extrusion)

[0066] In the first step of the method, PHBV and PBS are compounded in specific proportions in an extruder using the melt blending method. While obtaining PHBV / PBS blends, the amount of PHBV varies between 60-90 wt.% and the amount of PBS varies between 5-40 wt%.

[0067] Epoxy POSS nanoparticles are then added to the extruder at ratios ranging from 1 -20% by weight to improve the interfacial interaction between PHBV and PBS. Before compounding, PHBV and PBS were dried in a vacuum oven at 60-80'C for 12 hours.

[0068] Extruder screw speed varies between 25-200 rpm, mixing time between 2-5 minutes and barrel temperature between 170-200'C.

[0069] At this stage, the extruder barrel is purged with an inert gas, preferably argon gas, to minimize thermo-oxidative degradation.

[0070] After the melt blending process is completed, the samples are molded using the injection molding process to obtain standard test samples.

[0071] Injection pressure ranges between 4-10 bar and injection mold temperature between 25- 80'C.

[0072] Then, after the samples are evaluated in terms of rheological, mechanical, thermal and morphological properties, the PHBV / PBS / Epoxy POSS composition that gives optimum performance characteristics is determined.

[0073] In the second step of the method, the PHBV / PBS / Epoxy POSS blend with optimum performance characteristics is fed back into the extruder. Then, hemp fiber is added to the blend to increase the HDT value of PHBV / PBS / Epoxy POSS samples.

[0074] Before blending, the PHBV / PBS / Epoxy POSS blend and hemp fiber are dried in a vacuum oven at 60-80'C for 12 hours.

[0075] Extruder screw speed varies between 25-200 rpm, mixing time between 2-5 minutes and barrel temperature between 170-200'C.

[0076] At this stage, the extruder barrel is purged with an inert gas, preferably argon gas, to minimize thermo-oxidative degradation.

[0077] Epoxy POSS is added back to the extruder during melt blending to improve the interfacial adhesion between the PHBV / PBS / Epoxy POSS blend and the hemp fiber in proportions ranging from 1-20% by weight.

[0078] The hemp fiber utilized in the study is in a chopped form, with fiber lengths ranging from 5 to 20 mm. At the end of the melt blending process, samples are molded using the injection molding process to produce standard test samples.

[0079] Injection pressure ranges between 4-10 bar and injection mold temperature between 25- 80‘C.

[0080] Tests applied to the samples

[0081] Density, tensile, rheology, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), heat deflection temperature (HDT) and Fourier transform infrared spectroscopy (FTIR) tests are applied to the samples in accordance with the relevant standards.

[0082] Evaluation:

[0083] All samples are evaluated for changes in physical and mechanical properties.

[0084] Results

[0085] The results of tensile and heat deflection temperature (HDT) tests performed to investigate the ability of POSS nanoparticles, T-POSS and M-POSS containing triple and multiple epoxy reactive groups in aliphatic structure and S-POSS containing multiple epoxy groups in cycloaliphatic structure used within the scope of the invention, to work as an effective interfacial adhesion agent in PHBV / PBS / Hemp fiber biocomposites and to be used in under-hood parts of electric vehicles are shown in Table 3.

[0086] Table 3. Changes in mechanical and thermo-mechanical properties of PHBV, PHBV / PBS / Hemp and PHBV / PBS / Hemp biocomposites containing epoxy POSS nanoparticles

[0087] As can be seen from Table 3, tensile strength and elongation at break values of PHBV decreased with the addition of PBS and hemp fibers at varying ratios to PHBV. This indicates a weak interfacial interaction between the components. The increase in Young's modulus value is due to the fact that the modulus value of hemp fiber is higher than PHBV and PBS. The addition of PBS and hemp fiber to PHBV did not cause a significant increase in HDT values.

[0088] However, significant increases in both mechanical properties and HDT values were obtained with the addition of POSS molecules to PHBV / PBS / Hemp fiber biocomposite at ratios ranging from 1-20% by weight, regardless of the epoxy POSS type. These findings indicate that epoxy POSSs act as an effective interfacial adhesion agent for the PHBV / PBS / Hemp fiber system.

[0089] These results are promising in terms of epoxy POSS molecules contributing to the industrial usability of PHBV / PBS / Hemp fiber biocomposites and ensuring their transformation into qualified products, especially by using them in the battery boxes of electric vehicles.

[0090] As a result of the invention, biocomposites obtained in the extrusion process can be transformed into the desired end product by injection molding and compression molding.

[0091] As a result of the invention, PHBV / PBS - hemp fiber biocomposites, which are transformed into products with superior performance properties in the presence of POSS molecules, can be used in the automotive industry.

Claims

CLAIMS1. Poly(3-hydroxybutyrate-ko-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposites with improved performance properties in the presence of epoxy POSS molecules, with fully biodegradable and sustainable properties for use in the automotive industry.

2. The biocomposite according to claim 1 , characterized by comprising; at least one epoxy POSS selected from the group consisting of POSS (T-POSS) comprising a triple epoxy group, POSS (M-POSS) comprising multiple epoxy groups in aliphatic structure, POSS (S-POSS) comprising multiple epoxy groups in cycloaliphatic structure.

3. The biocomposite according to claim 1 , characterized in that; has tensile strength of 38-85 MPa, elongation at break of 1 -13%, Young's modulus of 4500-6200 MPa and HDT of 160-183eC.

4. The biocomposite according to claim 2, characterized in that; has tensile strength of 38-70 MPa, elongation at break of 1-13%, Young's modulus of 4500-5250 MPa, HDT of 160-172eC and contains T-POSS.

5. The biocomposite according to claim 2, characterized in that; has tensile strength of 50-85 MPa, elongation at break of 2-8%, Young's modulus of 4930-6200 MPa and HDT of 170-183eC and contains M-POSS.

6. The biocomposite according to claim 2, characterized in that; has tensile strength of 46-79 MPa, elongation at break of 1 -10%, Young's modulus of 4900-5750 MPa and HDT of 160-180eC and contains S-POSS.

7. A production method poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposites with improved performance properties in the presence of epoxy POSS molecules, with fully biodegradable and sustainable for use in the automotive industry, characterized by comprising the following;(i) Compounding PHBV and PBS in certain proportions by melt blending method and adding epoxy POSS to the blend in certain proportions to improve interfacial interaction between PHBV and PBS;(ii) In order to increase the HDT value, adding of hemp fiber to the PHBV / PBS / Epoxy POSS blend and compounded by melt blending method, and adding of epoxy POSS again at a determined rate to improve the interfacial adhesion between the PHBV / PBS / Epoxy POSS blend and hemp fiber.

8. The method according to claim 7, characterized in that (i) in the melt blending step, the amount of PHBV is 60-90% by weight and the amount of PBS is 5-40% by weight, and 1-20 wt.% epoxy POSS is added relative to the total compound.

9. The method according to claim 7, characterized in that; (ii) in the melt blending step, 5-40% by weight of hemp fiber is added to the PHBV / PBS / Epoxy POSS blend and 1 -20 wt.% epoxy POSS is added relative to the total compound.

10. The method according to claim 7, characterized in that; adding at least one epoxy POSS selected from the group consisting of POSS (T-POSS) containing a triple epoxy group, POSS (M-POSS) containing multiple epoxy groups in aliphatic structure, POSS (S-POSS) containing multiple epoxy groups in cycloaliphatic structure.

11. The method according to claim 7, characterized in that; the raw materials are vacuum dried at 60-800 before compounding.

12. The method according to claim 7, characterized in that; each melt blending step in the extrusion process is carried out with extruder screw speed between 25-200 rpm, mixing time between 2-5 minutes and barrel temperature between 250- 2800.

13. The method according to claim 7, characterized in that; the extruder barrel is swept with an inert gas to minimize thermo-oxidative degradation at each melt blending step in the extrusion process.

14. The method according to claim 7, characterized in that; the biocomposite material obtained in the extrusion process is transformed into the desired end product by injection molding and compression molding.

15. The method according to claim 7, characterized in that; the biocomposite obtained in the extrusion process is molded by the injection molding process.

16. The method according to claim 15, characterized in that; it is molded at 4-10 bar injection pressure and 25-800 injection mold tempe rature.

17. The method according to claim 7, characterized in that; (ii) in the melt blending step, hemp fibers are added in chopped form with fiber lengths of 5-20 mm.

18. An electric vehicle battery case for use in the automotive industry made of poly(3- hydroxybutyrate-ko-3-hydroxyvalerate) (PHBV) / poly(butylene succinate) (PBS) - hemp fiber biocomposite with improved performance properties in the presence of epoxy POSS molecules.

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