Special Issue "Sustainable Polymer Technologies for a Circular Economy"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Applied Industrial Technologies".

Deadline for manuscript submissions: 10 July 2022 | Viewed by 9592

Special Issue Editor

Prof. Dr. Sergio Torres-Giner
E-Mail Website
Guest Editor
Research Institute of Food Engineering for Development (IIAD), Universitat Politècnica de València (UPV), Camino de Vera s/n, 46022 Valencia, Spain
Interests: bio-based and biodegradable polymers; green composites; polymerization of biopolymers; processing of bioplastics; nanofibers obtained by electrospinning; sustainable polymer technologies for food preservation; controlled release of active compounds in plastic formulations; biopolymers for food packaging; bioeconomy; circular economy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We live in a defining moment in history, a moment where the scientific community has come together to agree on an ambitious framework to resolve the environmental issues associated with plastic waste. Plastics are the “workhorse” material of the modern economy, with multiple functions that help to tackle a number of the challenges facing our society. Plastic production has increased from 15 million tons in the sixties to 311 million tons in 2014 and is expected to triple by 2050, as plastics come to serve increasingly more applications. Plastic packaging is and will remain the dominant sectoral use of plastics globally, representing nearly 40% of the plastic market. However, after a first short use cycle, most of its value is lost to the economy. Furthermore, hundreds of millions of tons of plastics escape collection systems, ending up in the environment whether as microscopic particles or surviving in a recognizable form for hundreds of years. Therefore, it is high time to implement the Circular Economy principles in the plastic sector. The game-changing strategy is to promote sustainable polymer technologies that decouple plastics from fossil feedstocks, drastically reduce the leakage of plastics into natural systems, and increase the quality and uptake of plastic recycling. This Special Issue focuses on recent research studies devoted to enabling better economic and environmental advances in the plastic packaging value chain that can successfully accelerate the transition of the plastic industry from its traditional linear economy to a more valuable and sustainable model.

Prof. Dr. Sergio Torres-Giner
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2300 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Plastics towards a Circular Economy
  • Biopolymers
  • Green composites
  • Natural additives for plastic formulations
  • Waste management of plastics
  • Biorefinery system design
  • Reduction of plastic packaging leakage
  • Chemical and physical recycling
  • Compostable plastic articles
  • Sustainable packaging

Published Papers (9 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Article
The Investigation of Key Factors in Polypropylene Extrusion Molding Production Quality
Appl. Sci. 2022, 12(10), 5122; https://doi.org/10.3390/app12105122 - 19 May 2022
Viewed by 197
Abstract
This study took food-grade polypropylene packaging products as the research project and discussed how to control the polypropylene extrusion sheet thickness and vacuum thermoforming quality and weight. The research objective was to find the key factors for reducing costs and energy consumption. The [...] Read more.
This study took food-grade polypropylene packaging products as the research project and discussed how to control the polypropylene extrusion sheet thickness and vacuum thermoforming quality and weight. The research objective was to find the key factors for reducing costs and energy consumption. The key aspects that may influence the polypropylene extrusion molding quality control were analyzed using literature and in-depth interviews with scholars and experts. These four main aspects are (1) key factors of polypropylene extrusion sheet production, (2) key factors of the extrusion line design, (3) key factors of polypropylene forming and mold manufacturing, and (4) key factors of mold and thermoforming line equipment design. These were revised and complemented by the scholar and expert group. There are 49 subitems for discussion. Thirteen scholars and experts were invited to use qualitative and quantitative research methods. A Delphi questionnaire survey team was organized to perform three Delphi questionnaire interviews. The statistical analyses of encoded data such as the mean (M), mode (Mo), and standard deviation (SD) of various survey options were calculated. Seeking a more cautious research theory and result, the K-S simple sample test was used to review the fitness and consistency of the scholars’ and experts’ opinions on key subitem factors. There are ten key factors in the production quality, including “A. Main screw pressure”, “B. Polymer temperature”, “C. T-die lips adjustment thickness”, “D. Cooling rolls pressing stability”, “E. Cooling rolls temperature stability”, “F. Extruder main screw geometric design”, “G. Heating controller is stable”, “H. Thermostatic control”, “I. Vacuum pressure”, and “J. Mold forming area design”. The key factors are not just applicable to classical polypropylene extrusion sheet and thermoforming production but also to related process of extrusion and thermoforming techniques in expanded polypropylene (EPP) sheets and polylactic acid (PLA). This study aims to provide a key technical reference for enterprises to improve quality to enhance the competitiveness of products, reduce production costs, and achieve sustainable development, energy savings, and carbon reductions. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Atomization of Microfibrillated Cellulose and Its Incorporation into Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Reactive Extrusion
Appl. Sci. 2022, 12(4), 2111; https://doi.org/10.3390/app12042111 - 17 Feb 2022
Viewed by 544
Abstract
The present study focuses on the preparation and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films that were reinforced with cellulose microstructures to obtain new green composite materials for sustainable food packaging applications. The atomization of suspensions of microfibrillated cellulose (MFC) successfully allowed the [...] Read more.
The present study focuses on the preparation and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films that were reinforced with cellulose microstructures to obtain new green composite materials for sustainable food packaging applications. The atomization of suspensions of microfibrillated cellulose (MFC) successfully allowed the formation of ultrathin cellulose structures of nearly 3 µm that were, thereafter, melt-mixed at 2.5, 5, and 10 wt % with PHBV and subsequently processed into films by thermo-compression. The most optimal results were attained for the intermediate MFC content of 5 wt %, however, the cellulose microstructures showed a low interfacial adhesion with the biopolyester matrix. Thus, two reactive compatibilizers were explored in order to improve the properties of the green composites, namely the multi-functional epoxy-based styrene-acrylic oligomer (ESAO) and the combination of triglycidyl isocyanurate (TGIC) with dicumyl peroxide (DCP). The chemical, optical, morphological, thermal, mechanical, and barrier properties against water and aroma vapors and oxygen were analyzed in order to determine the potential application of these green composite films in food packaging. The results showed that the incorporation of MFC yielded contact transparent films, whereas the reactive extrusion with TGIC and DCP led to green composites with enhanced thermal stability, mechanical strength and ductility, and barrier performance to aroma vapor and oxygen. In particular, this compatibilized green composite film was thermally stable up to ~280 °C, whereas it showed an elastic modulus (E) of above 3 GPa and a deformation at break (ɛb) of 1.4%. Moreover, compared with neat PHBV, its barrier performance to limonene vapor and oxygen was nearly improved by nine and two times, respectively. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Valorization of Rice Straw into Cellulose Microfibers for the Reinforcement of Thermoplastic Corn Starch Films
Appl. Sci. 2021, 11(18), 8433; https://doi.org/10.3390/app11188433 - 11 Sep 2021
Cited by 2 | Viewed by 816
Abstract
In the present study, agro-food waste derived rice straw (RS) was valorized into cellulose microfibers (CMFs) using a green process of combined ultrasound and heating treatments and were thereafter used to improve the physical properties of thermoplastic starch films (TPS). Mechanical defibrillation of [...] Read more.
In the present study, agro-food waste derived rice straw (RS) was valorized into cellulose microfibers (CMFs) using a green process of combined ultrasound and heating treatments and were thereafter used to improve the physical properties of thermoplastic starch films (TPS). Mechanical defibrillation of the fibers gave rise to CMFs with cumulative frequencies of length and diameters below 200 and 5–15 µm, respectively. The resultant CMFs were successfully incorporated at, 1, 3, and 5 wt% into TPS by melt mixing and also starch was subjected to dry heating (DH) modification to yield TPS modified by dry heating (TPSDH). The resultant materials were finally shaped into films by thermo-compression and characterized. It was observed that both DH modification and fiber incorporation at 3 and 5 wt% loadings interfered with the starch gelatinization, leading to non-gelatinized starch granules in the biopolymer matrix. Thermo-compressed films prepared with both types of starches and reinforced with 3 wt% CMFs were more rigid (percentage increases of ~215% for TPS and ~207% for the TPSDH), more resistant to break (~100% for TPS and ~60% for TPSDH), but also less extensible (~53% for TPS and ~78% for TPSDH). The incorporation of CMFs into the TPS matrix at the highest contents also promoted a decrease in water vapor (~15%) and oxygen permeabilities (~30%). Finally, all the TPS composite films showed low changes in terms of optical properties and equilibrium moisture, being less soluble in water than the TPSDH films. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Torrefaction of Coffee Husk Flour for the Development of Injection-Molded Green Composite Pieces of Polylactide with High Sustainability
Appl. Sci. 2020, 10(18), 6468; https://doi.org/10.3390/app10186468 - 17 Sep 2020
Cited by 8 | Viewed by 1283
Abstract
Coffee husk, a major lignocellulosic waste derived from the coffee industry, was first ground into flour of fine particles of approximately 90 µm and then torrefied at 250 °C to make it more thermally stable and compatible with biopolymers. The resultant torrefied coffee [...] Read more.
Coffee husk, a major lignocellulosic waste derived from the coffee industry, was first ground into flour of fine particles of approximately 90 µm and then torrefied at 250 °C to make it more thermally stable and compatible with biopolymers. The resultant torrefied coffee husk flour (TCHF) was thereafter melt-compounded with polylactide (PLA) in contents from 20 to 50 wt% and the extruded green composite pellets were shaped by injection molding into pieces and characterized. Although the incorporation of TCHF reduced the ductility and toughness of PLA, filler contents of 20 wt% successfully yielded pieces with balanced mechanical properties in both tensile and flexural conditions and improved hardness. Contents of up to 30 wt% of TCHF also induced a nucleating effect that favored the formation of crystals of PLA, whereas the thermal degradation of the biopolyester was delayed by more than 7 °C. Furthermore, the PLA/TCHF pieces showed higher thermomechanical resistance and their softening point increased up to nearly 60 °C. Therefore, highly sustainable pieces were developed through the valorization of large amounts of coffee waste subjected to torrefaction. In the Circular Bioeconomy framework, these novel green composites can be used in the design of compostable rigid packaging and food contact disposables. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Low Temperature Decomposition of Polystyrene
Appl. Sci. 2020, 10(15), 5100; https://doi.org/10.3390/app10155100 - 24 Jul 2020
Cited by 2 | Viewed by 1071
Abstract
Styrene oligomers (SOs), of styrene (styrene monomer, SM), 1,3-diphenylpropane (styrene dimer, SD1), 2,4-diphenyl-1-butene (styrene dimer, SD2) and 2,4,6-triphenyl-1-hexene (styrene trimer, ST), had been detected in the natural environments far from industrial area. To confirm SOs formation through thermal decomposition [...] Read more.
Styrene oligomers (SOs), of styrene (styrene monomer, SM), 1,3-diphenylpropane (styrene dimer, SD1), 2,4-diphenyl-1-butene (styrene dimer, SD2) and 2,4,6-triphenyl-1-hexene (styrene trimer, ST), had been detected in the natural environments far from industrial area. To confirm SOs formation through thermal decomposition of polystyrene (PS) wastes in the nature, purified polystyrene (SO-free PS) has been shown to decompose at 30 to 150 °C. The SO ratio of SM:SD:ST was about 1:1:5 with ST as the main product. Mass spectrometry with selected ion monitoring was used for the quantitative analysis of the trace amounts of SOs. The rate of PS decomposition was obtained as k(year1)=5.177 exp(5029/T(K)) based on the amount of ST. Decomposition kinetics indicated that not only does drifting lump PS break up into micro/nano pieces in the ocean, but that it also subsequently undergoes degradation into basic structure units SO. According to the simulation at 30 °C, the amounts of SOs in the ocean will be over 400 MT in 2050. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Manufacturing and Characterization of Green Composites with Partially Biobased Epoxy Resin and Flaxseed Flour Wastes
Appl. Sci. 2020, 10(11), 3688; https://doi.org/10.3390/app10113688 - 26 May 2020
Cited by 5 | Viewed by 964
Abstract
In the present work, green-composites from a partially biobased epoxy resin (BioEP) reinforced with lignocellulosic particles, obtained from flax industry by-products or wastes, have been manufactured by casting. In this study, the flaxseed has been crushed by two different mechanical milling processes to [...] Read more.
In the present work, green-composites from a partially biobased epoxy resin (BioEP) reinforced with lignocellulosic particles, obtained from flax industry by-products or wastes, have been manufactured by casting. In this study, the flaxseed has been crushed by two different mechanical milling processes to achieve different particle sizes, namely coarse size (CFF), and fine size (FFF) particle flaxseed flour, with a particle size ranging between 100–220 µm and 40–140 µm respectively. Subsequently, different loadings of each particle size (10, 20, 30, and 40 wt%) were mixed with the BioEP resin and poured into a mold and subjected to a curing cycle to obtain solid samples for mechanical, thermal, water absorption, and morphological characterization. The main aim of this research was to study the effect of the particle size and its content on the overall properties of composites with BioEP. The results show that the best mechanical properties were obtained for composites with a low reinforcement content (10 wt%) and with the finest particle size (FFF) due to a better dispersion into the matrix, and a better polymer-particle interaction too. This also resulted in a lower water absorption capacity due to the presence of fewer voids in the developed composites. Therefore, this study shows the feasibility of using flax wastes from the seeds as a filler in highly environmentally friendly composites with a wood-like appearance with potential use in furniture or automotive sectors. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Pine Resin Derivatives as Sustainable Additives to Improve the Mechanical and Thermal Properties of Injected Moulded Thermoplastic Starch
Appl. Sci. 2020, 10(7), 2561; https://doi.org/10.3390/app10072561 - 08 Apr 2020
Cited by 14 | Viewed by 1393
Abstract
Fully bio-based materials based on thermoplastic starch (TPS) were developed starting from corn starch plasticized with glycerol. The obtained TPS was further blended with five pine resin derivatives: gum rosin (GR), disproportionated gum rosin (dehydroabietic acid, RD), maleic anhydride modified gum rosin (CM), [...] Read more.
Fully bio-based materials based on thermoplastic starch (TPS) were developed starting from corn starch plasticized with glycerol. The obtained TPS was further blended with five pine resin derivatives: gum rosin (GR), disproportionated gum rosin (dehydroabietic acid, RD), maleic anhydride modified gum rosin (CM), pentaerythritol ester of gum rosin (LF), and glycerol ester of gum rosin (UG). The TPS–resin blend formulations were processed by melt extrusion and further by injection moulding to simulate the industrial conditions. The obtained materials were characterized in terms of mechanical, thermal and structural properties. The results showed that all gum rosin-based additives were able to improve the thermal stability of TPS, increasing the degradation onset temperature. The carbonyl groups of gum rosin derivatives were able to interact with the hydroxyl groups of starch and glycerol by means of hydrogen bond interactions producing a significant increase of the glass transition temperature with a consequent stiffening effect, which in turn improve the overall mechanical performance of the TPS-resin injected moulded blends. The developed TPS–resin blends are of interest for rigid packaging applications. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Influence of Temperature on the Composition and Calorific Value of Gases Produced during the Pyrolysis of Waste Pharmaceutical Blisters
Appl. Sci. 2020, 10(3), 737; https://doi.org/10.3390/app10030737 - 21 Jan 2020
Cited by 5 | Viewed by 869
Abstract
Waste pharmaceutical blisters (WPBs) are a type of multimaterial waste that contain layers of plastic and metal connected permanently. The separation of those materials with the application of mechanical methods is impossible. One of the methods that can be used to recover metal [...] Read more.
Waste pharmaceutical blisters (WPBs) are a type of multimaterial waste that contain layers of plastic and metal connected permanently. The separation of those materials with the application of mechanical methods is impossible. One of the methods that can be used to recover metal from WPBs is pyrolysis—a thermal decomposition process performed in the absence of oxygen. The products are a solid fraction that contain char and metal, liquid fraction, and gases. The gases produced during the process can be used as a fuel, either alone or mixed with another gaseous fuel such as natural gas. The presented research was focused on the determination of the influence of the process temperature on the composition of gases produced during the pyrolysis of two types of pharmaceutical blister waste: pre- and postconsumer. The postconsumer waste contains trace amounts of pharmaceutical products. One of the goals was to determine whether those compounds influence the gas properties. The method of neutralizing these materials can be part of the circular economy, the idea of which is to strive to maximize the use of natural resources and bring them back into circulation. The presented method allows not only to recover char, oil, and metal that can be easily separated from the solid fraction, but also to reuse the process gases as a fuel and, possibly, to form HCl during the decomposition of PVC. The paper includes the analysis of the input material, as well as a detailed chemical analysis of the produced gases. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Article
Preparation and Characterization of Electrospun Pectin-Based Films and Their Application in Sustainable Aroma Barrier Multilayer Packaging
Appl. Sci. 2019, 9(23), 5136; https://doi.org/10.3390/app9235136 - 27 Nov 2019
Cited by 17 | Viewed by 1490
Abstract
Pectin was first dissolved in distilled water and blended with low contents of polyethylene oxide 2000 (PEO2000) as the carrier polymer to produce electrospun fibers. The electrospinning of the water solution of pectin at 9.5 wt% containing 0.5 wt% PEO2000 [...] Read more.
Pectin was first dissolved in distilled water and blended with low contents of polyethylene oxide 2000 (PEO2000) as the carrier polymer to produce electrospun fibers. The electrospinning of the water solution of pectin at 9.5 wt% containing 0.5 wt% PEO2000 was selected as it successfully resulted in continuous and non-defected ultrathin fibers with the highest pectin content. However, annealing of the resultant pectin-based fibers, tested at different conditions, developed films with low mechanical integrity, high porosity, and also dark color due to their poor thermal stability. Then, to improve the film-forming process of the electrospun mats, two plasticizers, namely glycerol and polyethylene glycol 900 (PEG900), were added to the selected pectin solution in the 2–3 wt% range. The optimal annealing conditions were found at 150 °C with a pressure of 12 kN load for 1 min when applied to the electrospun pectin mats containing 5 wt% PEO2000 and 30 wt% glycerol and washed previously with dichloromethane. This process led to completely homogenous films with low porosity and high transparency due to a phenomenon of fibers coalescence. Finally, the selected electrospun pectin-based film was applied as an interlayer between two external layers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by the electrospinning coating technology and the whole structure was annealed to produce a fully bio-based and biodegradable multilayer film with enhanced barrier performance to water vapor and limonene. Full article
(This article belongs to the Special Issue Sustainable Polymer Technologies for a Circular Economy)
Show Figures

Figure 1

Back to TopTop