Plastics are now an inseparable element of the world around us. Due to their properties, i.e. the relatively low production cost and ease of processing, they accompany us in virtually all areas of everyday life and technology. We find them, among others, in household goods, sports equipment, office products, electronics or even packaging. Without modern plastics, such major development in the automotive, aerospace, and medical industries would not be possible.
Most plastics are produced as a result of the processing of basic non-renewable raw material – crude oil – and are not biodegradable, which is their main disadvantage. Looking from a global perspective, the continuous exploitation of crude oil leads directly to the depletion of its resources. This is a significant problem, although not as noticeable at the moment as the problem of the amount of waste generated after using plastics. You should be aware that their decomposition time in the natural environment can be up to several generations.
Research indicates that 75% of plastics that have been introduced to the market since the start of their production have already become waste. This is 6.3 billion tons, of which less than 10% has been recycled, and 12% subjected to energy recovery. This means that around 5 billion tonnes of plastics are collected in landfills, but also discarded in forests, waters, beaches and illegal landfills scattered around the world. It is the waste that occurs in the marine environment that has the greatest impact on the natural environment and man.
Currently, the biggest problem is municipal waste, including one-off packaging. Although it constitutes approximately 8% of the total weight of all garbage, due to the low specific weight it occupies a significant volume, constituting almost 30% of the volume of all waste. This group includes mainly bottles made of polyethylene terephthalate (PET) and shopping bags, breakfast bags or foil packaging made of polyethylene (PE) or polypropylene (PP). The largest recipient of packaging is the food industry, which consumes about 60% of all packaging.
Due to the growing problem with the management of plastic waste, research is being conducted to develop new biodegradable polymer materials, colloquially referred to as bioplastics. Such materials should have useful properties comparable to those obtained by conventional methods. They are obtained on an industrial scale from both renewable and petrochemical raw materials.
Compared to traditional plastics produced from fossil sources, bio-plastics have a number of valuable advantages. First of all, they allow raw materials to be saved thanks to the use of cyclically renewing biomass. In addition, their production and use are carbon-neutral, which means that their processing does not contribute to the production of carbon dioxide. Moreover, some types of bioplastic are biodegradable.
Bioplastics can be divided into three groups depending on the source of origin and biodegradability:
• plastics derived from renewable raw materials, but not biodegradable – e.g. polyamide (PA), polyethylene terephthalate (PET),
• biodegradable plastics, but not from renewable raw materials – e.g. 1,4-butylene 1,4-butylene 1,4-butadiene terephthalate (PBAT) or polycaprolactone (PCL),
• bio-based materials derived from renewable raw materials (biodegradable polymers), biodegradable – e.g. polylactide, i.e. polylactic acid-based material (PLA), polyglycolide based on glycolic acid (PGA) or modified starch.
Among the aforementioned materials, the dominant role is played by PLA (polylactide), which quantitatively accounts for approximately 40% of all biodegradable polymers. It is often called ‘double green’ as it is both biodegradable and derived from renewable raw materials. Polylactide is a polymer with properties similar to polystyrene, as it is stiff and brittle. It is characterized by a glass transition temperature of approx. 57°C and a melting point in the range of 170-180°C. It also possesses good strength properties (60 MPa strength module).
A group of bio-based plastics based on biodegradable polymers found application in two areas. The first of them is a highly specialized branch of medicine and tissue engineering, where this type of plastics is used to produce such elements as bioresorbable surgical threads, braces, clips, implants, capsules for controlled dosing of medicines, etc. The second area is related to mass production of packaging, foils dedicated to food products, thermoforming foils, waste bags, trays, cups, bottles, cutlery, garden foils, disposable products, interior design elements, paper coating materials and for printing. Replacement of packaging produced from conventional plastics with biodegradable substitutes is part of the trend of the economy of sustainable development and reduction of waste.
Despite many advantages, it should be remembered that biodegradable polymer materials also have drawbacks that limit their widespread use. For this reason, they still lose in many areas to their non-biodegradable counterparts. First of all, biodegradable bioplastics are more expensive than those currently on the market, although it is worth noting that their price is constantly decreasing. It is predicted that in the coming years it may be equal to the price of classic polymer materials of petrochemical origin. Many of them are inferior to conventional materials also in terms of mechanical properties, i.e. they are too brittle or stiff or they have too low tensile strength.
Due to the frequent use of these materials for the production of food packaging, appropriate barrier properties are also required. They are important because of the permeability of oxygen, carbon dioxide and water vapor, which can adversely affect the packed product.
In addition, due to the sensitivity of biodegradable polymers to heat, humidity and shear stresses, they are more demanding in the manufacturing process than their non-biodegradable counterparts. For these reasons, bio-plastics may be partially degraded already at the stage of the processing. The mentioned disadvantages of biodegradable polymeric materials are the basis for conducting research in the field of improving their properties or limiting unfavourable functional features.
Bioplastics contain, in addition to polymers, other materials and additives that together determine the processing possibilities and the final product characteristics. These can be additives used to stabilize materials, pigments, various fillers or plasticizing additives (plasticizers). Although plasticizing additives represent a small percentage of all components in the plastic, it is extremely important for biodegradable plastics that all of them are also biodegradable. Additives introduced during processing do not change the structure of the biopolymer, but only react with its structure. This changes the physicochemical properties of the materials, giving the products the required usable properties.
In parallel with the dynamic development of bioplastics dedicated to specialist packaging, there is a growing need for plasticizing additives that will be compatible with biodegradable polymers and will give the plastics the desired properties.
As a result of joint work of research departments of PCC MCAA and PCC Exol, a new product group is being developed as part of the CITREX project. These are plasticizing products dedicated to specialist packaging, films, food laminates, but also of potential use in toys production. The development of products meeting market requirements and at the same time being a product innovation is a major research challenge. Both the synthesis of such products and their application require thorough recognition in many areas, including those concerning the synthesis path, methods of analysis, possible applications and information on consumers and competitors on the target market. Therefore, the basic goal of the project is not only to develop plasticizing additives, but above all to gain knowledge of the properties and applications of these products.
The key criteria to be met by plasticizing additives dedicated to biodegradable polymers are:
• no plasticizer migration from bioplastics under the influence of high temperature and storage time
Reducing the migration of plastic additives is a key aspect in developing their structures. The phenomenon of migration can colloquially be defined as the “leakage” of plastic plasticizer. In the case of a finished product, it may result in the loss of the material’s properties and deterioration of its aesthetics – a discolouration of the product or distortion of its form.
In practice, the migration can be limited by adjusting the appropriate molecular weight of the plasticizer (its mass) and modifying its chemical structure towards a more branched or linear one.
The plasticizing additive added to the bioplastic must meet the biodegradability criterion. This means that it should easily undergo a natural decomposition process, e.g. by composting, which does not result in the formation of harmful substances. One of the ways to increase the biodegradability of products is the use of raw materials of natural origin, such as carboxylic acids and other biodegradable raw materials in chemical synthesis.
The criteria described above refer to both the modification of the chemical structure and the selection of raw materials used, while maintaining the appropriate molecular weight of the compound being synthesized. Their fulfilment is a huge research challenge from the point of view of designing appropriate plasticizing additives and conducting their synthesis. Therefore, the implementation of the project requires many laboratory tests to obtain compounds of repeatable quality and structure.
The attractiveness of the new product on the market also results from its innovativeness. Plasticizing additives developed within the CITREX project are characterized by an innovative combination of natural carboxylic (amber and citric) bio acids, polyols produced by PCC Rokita and lauryl alcohol used in cosmetic products, and therefore non-toxic. At the same time, the manufactured products have a strictly defined molecular weight, which is intended to limit the migration of additives from the final product. The main goal in the design of new molecular structures was to create such a molecule that would interact with the biopolymer contained in bioplastics (on the “like attracts like” principle), which also has an impact on reducing the migration process and will contribute to meeting the requirements for plasticizing additives.
Obtaining a laboratory sample of the product is the first, preliminary stage of research carried out as part of the CITREX project. At the same time, it is the beginning of the next stage, that is testing the application properties of the given products. A thorough examination of the properties of these products is the basis in the selection of the targeted applications.
The bioplastics and bio-additives market is certainly a promising and rapidly growing market, which is particularly noticeable in recent times. This is due, inter alia, to increasing consumer awareness of the negative impact of plastics on the environment. Conscious consumers are increasingly turning to ecological substitutes for packaging and disposable products made of conventional plastics. As a result, there is a continuing increase in demand for various elements made of bioplastics, such as containers or cutlery made of PLA.