Prof. Stoyko Fakirov, PhD, DSc, Dhc, was born in January 1936, in a small village at the foot of the Balkan Mountains in Bulgaria. He went to elementary school there and attended high school in the neighboring town. In 1959, he earned a Master of Science degree in chemistry from Sofia University (Bulgaria), where he was immediately appointed as an assistant professor. Two years later, he started his PhD studies at the Lomonosov State University in Moscow (Russia). In 1987 he was nominated as a full professor of polymer chemistry at Sofia University. Currently he acts as an Honorary Academic in the Department of Mechanical Engineering of the University of Auckland, New Zealand. He has a world-wide reputation in polymer science and technology. According to Google Scholar he has 8000+ citations, H-index = 48 and is on position 21 in the world-wide list of the topic “Polymer Composites”. Stoyko has 350+ publications, of which 220 are listed in Web of Science.  He wrote 16 books on polymers with Wiley, Springer, Hanser, Cambridge University Press and others (some of the edited books are of 1000 pages). The book list also includes the textbook “Fundamentals of Polymer Science for Engineers” (Wiley-VCH, 2017), which consists of 25 chapters. He got 9 US Patents and delivered 120+ invited research seminars world-wide. Besides, he acts as an Editorial Board member of 16 international polymer journals.

His important contributions to polymer science and technology consist of the formulation, demonstration and naming the phenomena of “Chemical healing”, “Chemically released diffusion”, “Sequential reordering in condensation copolymers”, and “Melting of polymer crystals below the glass transition temperature of the same polymer”. Stoyko derived also an equation known as “Fakirov equation”, created a new type of polymer composites known as “Microfibrillar composites (MFC)”, which he further developed to “Nanofibrillar composites (NFC)”, including the Nanofibrillar single polymer composites, and formulated and demonstrated the “Concept of converting instead of adding” (a technology for converting practically any bulk polymer into a nano-size material).

Back in the 1980s he has been an Alexander von Humboldt Fellow, and in 2000 he received the most prestigious award in Germany for scientific achievements, the “Alexander von Humboldt Research Award”. The International Association of Advanced Materials (IAAM) honoured him with the Medal of the Year 2017 for his notable and outstanding contribution in the field of advanced materials science and technology, and in 2018 he got the degree “Doctor honoris causa of Sofia University”, Bulgaria.

Professor Stoyko Fakirov is still active and will definitively continue to do so beyond his 85^th birthday, which is on January 19, 2021. For this we congratulate him very much and wish him good health for many more years in the field of polymer science as well as good luck in his fishing hobby.

Some 70 – 80 years ago, when the first synthetic polymers were brought to the market, they were named “artificial” (in Europe) or “man-made” (in USA) materials in order to stress on the fact that they are not “natural” materials, that is, not of the same excellent qualities. Step by step, in the next years, they found wider and wider applications reaching in the last decades the situation of not only extremely large applications but also in many cases being non-replaceable by any other material. This is because the synthetic polymers as materials have many attractive advantages as compared with the classic materials as wood, metals, ceramics, and glass. They are noticeably light (with density around or below 1), quite easy processable (usually one-step manufacturing of articles with complex shape), unlimited opportunities for coloring in mass, harmless for the environment during their use because of their chemical resistance against environmental and atmospheric factors. In this respect the synthetic materials overcome all other materials. Strange enough, just this inherent advantage of plastics materials is converted in their most serious disadvantage when they become waste or litter – they do not oxidize as metals or chemically degrade as cellulose- and protein-based materials.

The popular hope that chemists will create biodegradable plastics for mass production turned out to be illusive – the few example in this respect are irrelevant economically. This is demonstrated by the recent decision of the European Union to ban the manufacturing of 10 plastics one-way articles, since they are the main component of the sea waters littering. EU comprises 27 countries, some of them belonging to the world industrial and scientific lieders and nevertheless they could not offer a better solution except the drastic reduction of packaging products creating the main plastics litter. This mean further that the solution of the negative environmental problem which arises from the plastic waste is not a task of scientists only but of the whole society. People must be educated about the proper collection of plastic waste and the governments must financially support the recycling industry since the recycling is not a profitable business because of the small difference in the prices of fresh and recycled plastics.

Attempts for reducing of the amount of the fresh synthesized polymers are hardly the appropriate solution since the needs of them are continuously increasing. For example, the annual growth of PET for bottles manufacturing is currently 10%! The production of plastics for packaging purposes will also increase since in poor countries 50% of food is spoiled because of bad packaging (in India it is 50% while in UK – 2-3%).

Today over 300 million tons of plastic are produced each year, of which 8 million end up in the oceans. If we continue polluting the seas in this way, it has been estimated that by 2050, the mass of plastic in the oceans will exceed the mass of fish. It has also been reported that one in three species of marine life have been found entangled in marine litter, and 90% of all seabirds have plastic in their stomachs. Plastic packaging is the largest end-use market segment accounting for almost 40% of the total worldwide plastic usage. Over 500 billion plastic bags are used worldwide annually, and the average working life of a plastic bag is 15 min.

Again: a proper solution of the problem could be expected if, in addition to the efforts of the scientists, legal steps of all governments will be undertaken regulating the proper handling of plastics waste.

It must be stressed that the recycling does not solve the problem of the negative impact of plastics on the environment, it only postpones this solution. This is because after the end-of-life of the recycled plastics they are converted again in waste or litter. Applications of fresh or recycled plastics assuming a “burring” as mixing with concrete, manufacturing of articles which are incorporated in buildings, road constructions, hydroengineering or other similar applications with warranted no further reappearance of these materials in our life, are the proper solution of the problem. Another similar solution is the incineration of fresh or recycled plastics materials when the bulk polymers are converted in gases. In both cases the plastics “disappear” from our life and do not pollute any more our Nature.

The contributions collected in the Special Issues (Part 1 and Part 2) are prepared by polymer scientists with world-wide reputation (the number of citations of some of them is between 10 000 and 50 000 and their h-index between 50 and 100, respectively). Nevertheless, they do not offer solutions of the pandemic problems created by the plastics wastes, they only suggest ways for reduction the amount of plastics litter via recycling of the plastics wastes.

The contributions are grouped in two separate publications: (i) Recycling of Polymer Blends and Composites (Part 1), and (ii) Recycling of Neat Polymers (Part 2). This is done because the two groups of materials have some specific characteristic features which make the recycling approaches rather different. A good example in this respect is the present of glass fibers (up to 30%) in the glass fibers reinforced polymer composites.

Plastics have been widely used nowadays because of their low unit cost and balanced performance that other materials don’t have. However, a huge amount of waste plastics, which are difficult to handle and non-degradable, are followed. These wastes used not to be put in the right place after consumption, resulting in enormous environmental pressure. According to a report by the United Nations Environment Program, there are 9 billion tons plastic products produced worldwide, and only 9% are recycled.

There is an old Chinese saying that it is better for the doer to undo what he has done, implying the solution to the above problem may come from itself. It is well known that thermoplastics have an obvious advantage. That is, they can be molded repeatedly at a relatively low temperature (below 300 °C) compared with metals and ceramics. In this context, whether they are new, old or discarded, they can be recycled and reused so long as they are properly treated. In particular, when waste plastics are recycled in a safe, efficient and eco-friendly way, we can provide a powerful strategy for reducing carbon emissions, carbon peaking and carbon neutrality. This will be a promising way for the future development of plastics.

From an industrial perspective, LyondellBasell, Dow, SABIC, BASF as well as Adidas, Nike, IKEA, Coca-Cola, Pepsi, Unilever, Procter & Gamble, Danone, Nestlé and other industry giants have developed plastic recycling technologies or purchased recycled plastic products. In terms of policy, the United States launched the green electronic product evaluation tool EPEAT as early as 2004, which clearly requires the use of recycled plastics. In 2019, the European Green Deal proposed to promote the transformation of industry to a clean circular economy. By 2030, for example, all EU products will use reusable or recyclable plastic packaging, thereby contributing to its 2050 goal of achieving carbon neutrality. In September 2020, President Xi Jinping indicated at the UN General Assembly that China would adopt strong policies to achieve a carbon peak by 2030 and a carbon neutral by 2060. As the largest country in production and consumption of plastics, China is being challenged by how to manage, utilize and recycle waste plastics. So far, Chinese government and companies have been aware of the significance of the green recycle of plastics for sustainable development. Kingfa Sci. & Tech. Co., Ltd. will also actively follow the national policy and actively devote itself to this business.

As a matter of fact, Kingfa Sci. & Tech. Co., Ltd. has utilized recycled plastics as raw materials in the products since 2003. Kingfa has produced more than 1.2 million tons of high-quality recycled plastics, helping partners to reduce carbon by about 1.5 million tons over the past fifteen years. Now we have an annual production capacity of 285,000 tons of recycled plastics, including high-quality packaging recycled PE, recycled PP and PA for vehicles, high-performance recycled PC and alloys, and recycled flame retardant HIPS. Kingfa achieved 30% sales growth of recycled plastics in 2020. In the future, we will continue to upgrade our recycled plastics production bases in Qingyuan city, Guangdong province and Xuzhou city, Jiangsu province and strive to achieve a production capacity of 1 million tons per year in total by 2025.

The contributions appearing in the Special Issue are led by Professor Stoyko Fakirov. It introduces the latest achievements and research progress of recycling of plastics and composites. Readers must be able to be benefited from the papers for building up sustainable "carbon" chain of the plastics industry. I would like to take this opportunity to express my heartiest congratulations to Professor Stoyko Fakirov.

The growing need of multifunctional materials with tailor made properties led in the last decades to the development of novel commercial polymer blends, possessing superior physical properties with respect to traditional matrices and showing economical advantages with respect to the synthesis of new plastics. Due to the progressive increase of the environmental concerns on the management of plastic wastes, the difficulties in the sorting technologies and the limited chemical compatibility between the greatest part of polymer pairs, the technical potential of polymer blends often remains unexploited when the recycling stage is considered. In some cases, also the addition of compatibilizers to recycled blends does not represent a satisfactory solution to retain and/or tailor their properties.

The aim of this review is that to perform a critical analysis of the potentialities of polymer blends recycling. After an introductive section on the problems and the definitions of plastics recycling, some basic concepts about the physical behaviour of polymer blends are reported. The third section of the review is focused on the analysis of the mechanical recycling of polymer blends, and a general distinction between recycling techniques applied to compatible and un-compatible polymer blends is performed. In this chapter, also the analysis of the recycling potential of commingled plastics deriving from unsorted wastes and of the effect of the thermal reprocessing on the morphological and thermo-mechanical behaviour of polymer blends is reported. Considering the increasing importance of bioplastics in the modern society, the fourth chapter of this review is focused on the mechanical and chemical recycling of blends containing bioplastics, with particular attention to polylactic acid (PLA) and thermoplastic starch (TPS) based blends. The key aspects of the recycling technologies applied to polymer blends and the future perspectives are summarized in the last section of the review.

Carbon fiber reinforced polymers (CFRP) offer outstanding lightweight potential and can play a key role for modern energy and mobility concepts. However, production of carbon fibers is energy- and cost-intensive, while at the same time waste rates of common manufacturing technologies are quite high and repair possibilities for damaged parts still limited. Therefore, holistic recycling approaches are urgently required in order to reach acceptable cost-efficiency and sustainability. What makes the recycling so challenging, is the fact that true recycling, i.e. re-usage of fibers in high-performance composites, requires preservation of a high fiber length and enabling of accurate fiber orientation. This generates a trade-off between the best possible exploitation of the fiber properties and the effort to minimize the recycling costs. Hence, this paper does not only give a brief overview of technologies to recover carbon fibers from waste and to process them to new CFRP components. In addition, different approaches are presented, that exploit the specific characteristics of semi-finished products based on recycled carbon fibers, in order to achieve process- or material-related multifunctionality. This includes quasi-plastic deformation behavior (enables deep-drawing or curved tow placement), improved surface quality through reduced fiber print-through, robust resin impregnation through supersaturated nonwovens, and high energy absorption.

The recycling of carbon fibres is a critical step in the reutilization of carbon fibres in a closed-loop economy. Evaluation of the recovered fibres regarding their mechanical properties, purity of the fibre surfaces and thermal stability are key points when exploring new high performance applications. This publication reports about the investigation of the thermal stability of pyrolysed carbon fibres and virgin fibres alone and in composite materials using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).

A commercial pyrolysed woven fabric (unaltered in length) was processed like virgin high tenacity carbon fibre to investigate the recycling potential of unchopped fibres and demonstrate their recycling without further down-cycling. Identical components of virgin and pyrolysed fibres were manufactured. These composite materials as well as the fibres solely were compared regarding their thermal degradation behaviours as a function of heating rates as well as temperature ranges in different gas environments. For further analysis of the data a kinetic study was performed. In addition, light microscopy and SEM imaging was used to visualize and investigate the samples.

A slight shift to lower temperatures in thermal decomposition behaviour of the pyrolysed carbon fibres was observed. The decomposition of the matrix was similar in the TGA measurements but possibly, due to the missing sizing and lower fibre orientation a higher mass fraction of resin as well as higher activation energy values were calculated. The degradation of the carbon fibre fraction showed the largest variation. This is assumed to be due to the carbon fibre crystal structure but for verification, additional work needs to be performed.