Special Issue "Synthesis and Applications of Eco-Friendly Polymers"

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Materials Processes".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 10635

Special Issue Editors

Dr. Marco Valente
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Guest Editor
Department of Chemical Engineering Materials and Environmental, Faculty of Industrial Engineering, University of Rome Sapienza, 00185 Rome, Italy
Interests: biodegradation of polymers; reuse of waste in composites; biofriendly materials; compound and additives for polymer processes; production of alternatives to plastic single-use objects
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Carlo Santulli
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Guest Editor
School of Sciences and Technologies, University of Camerino, via Gentile III da Varano 7, 62032 Camerino, Italy
Interests: biopolymers; biocomposites; natural fibers; mechanical and thermal characterization; agrowaste
Special Issues, Collections and Topics in MDPI journals
Dr. Loris Giorgini
E-Mail Website
Guest Editor
Department of Industrial Chemistry, University of Bologna - Alma Mater, 40126 Bologna, Italy
Interests: biopolymers; composite materials; recovery and reuse of polymers; synthesis and characterizations of polymers; chemical recycling of composite and plastic materials; functional materials and polymers; sustainable polymers

Special Issue Information

Dear Colleagues,

During the last decades, environmental protection has become one of the most important issues, especially concerning plastic waste. Plastic consumption has grown during recent years, creating a problem regarding disposal. Attempts to reduce the impact of plastic involve three main approaches: the reduction of waste; reuse of products; and the production of polymers and composites with less impact on the environment. The new regulations of the European community have severely limited the use of disposable plastic objects. Considering both the process of production and the optimization of materials and polymeric technological solutions, the scientific world has been moving towards solutions lessen the impact of plastic. One interesting strategy is the use of polymeric matrix composites filled with natural waste product. In this class of materials, wood plastic composites (WPCs) are strengthened, thanks to their potential recyclability and the possibility to use waste materials for their production. WPCs could substitute virgin wood in many applications, such as automotive, nautical, construction like windows and doorframes, and outdoor furniture. Moreover, WPCs can be modeled using the same methods as in traditional woodworking, and processed through traditional thermoplastic methods. Other important properties of WPCs are low moisture absorption, low density, low price, and less abrasion of wood than mineral filler during processing.

Possible naturally induced degradation is a typical phenomenon of polymer materials, leading to fragmentation and significant changes in the structure of the material characterized by the loss of some properties (e.g., mechanical properties, viscosity, molecular weight, etc.). Degradation can occur through different processes including thermal degradation, photodegradation, oxidative degradation, mechanical degradation, hydrolysis reactions with water (hydrolytic degradation), and the action of microorganisms such as bacteria, fungi, or algae (biodegradation). The increasing consumption of polymer materials and the attention to environmental problems have directed research towards the reduction of oil-based consumption. In fact, the disposal of polyolefins has highlighted important problems related to the low degradation rate in environmental conditions. The use of oil-based/bioderived polymer blends is an effective way to reduce oil-based consumption, increasing, at the same time, bioderived polymer properties. One of the main features of bioderived polymers is their desirable high eco-friendly footprint.

Prof. Marco Valente
Assoc. Prof. Dr. Carlo Santulli
Dr. Loris Giorgini
Guest Editors

Manuscript Submission Information

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Published Papers (8 papers)

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Research

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Article
Abrasive Wear Behavior of CNT-Filled Unidirectional Kenaf–Epoxy Composites
Processes 2021, 9(1), 128; https://doi.org/10.3390/pr9010128 - 08 Jan 2021
Cited by 3 | Viewed by 619
Abstract
Kenaf (Hibiscus Cannabinus) fibers have received significant attention for replacing the usage of synthetic fibers, especially glass fiber, in the fabrication of fiber-reinforced polymer (FRP) composites. The aim of this research was to study the change in wear behavior of kenaf-epoxy [...] Read more.
Kenaf (Hibiscus Cannabinus) fibers have received significant attention for replacing the usage of synthetic fibers, especially glass fiber, in the fabrication of fiber-reinforced polymer (FRP) composites. The aim of this research was to study the change in wear behavior of kenaf-epoxy fiber composites by filling them with multiwall carbon nanotubes (MWCNT). In particular, the effect of untreated MWCNT (PMWCNT), acid-treated MWCNT (AMWCNT), and silane-treated MWCNT (SMWCNT) was studied, using three different MWCNT loadings, i.e., 0.5, 0.75, and 1 wt.%. The abrasive wear test was conducted to measure the wear properties of the composites. A thermal infrared camera was also used to measure the punctual contact temperature during the abrasive wear test, while the abraded surfaces were analyzed using the stereomicroscope. Starting from the considerable reduction of wear rate with the introduction of kenaf fibers, it was observed that PMWCNT provided some further, yet modest, reduction of wear rate only at the higher loadings. In contrast, the inclusion of AMWCNT proved to increase the specific wear rate of the epoxy-kenaf composites, an effect worsened at higher loadings. This may be due to the weakened interfacial bonding between the AMWCNT and epoxy. On the other hand, the presence of SMWCNT improved the interfacial bonding between CNT and epoxy, as shown by an increase in contact temperature. However, the increase in bonding strength was stipulated to have caused the rougher worn debris, thus inducing a three-body abrasive wear effect. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Evaluation of Novel Bio-Based Amino Curing Agent Systems for Epoxy Resins: Effect of Tryptophan and Guanine
Processes 2021, 9(1), 42; https://doi.org/10.3390/pr9010042 - 28 Dec 2020
Viewed by 879
Abstract
In order to obtain an environmentally friendly epoxy system, L-tryptophan and guanine were investigated as novel green curing agents for the cross-link of diglycidyl ether of Bisphenol A (DGEBA) as a generic epoxy resin model of synthetic and analogous bio-based precursors. In particular, [...] Read more.
In order to obtain an environmentally friendly epoxy system, L-tryptophan and guanine were investigated as novel green curing agents for the cross-link of diglycidyl ether of Bisphenol A (DGEBA) as a generic epoxy resin model of synthetic and analogous bio-based precursors. In particular, L-tryptophan, which displays high reaction temperature with DGEBA, was used in combination with various bio-based molecules such as urea, theobromine, theophylline, and melamine in order to increase the thermal properties of the epoxy resin and to reduce the crosslinking reaction temperature. Later, in order to obtain similar properties using a single product, guanine, a totally heterocyclic molecule displaying amine functional groups, was tested as hardener for DGEBA. The thermal behavior of the precursor mixtures was evaluated by dynamic differential scanning calorimetry (DSC) leading to a preliminary screening of different hardening systems which offered a number of interesting hints in terms of bio-based compounds able to provide high Tg resins. These encouraging results pave the way for a further study of a new class of renewable, low-toxic, and sustainable curing agent systems for the production of fully bio-based epoxy resins. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Characterization of Licorice Root Waste for Prospective Use as Filler in more Eco-Friendly Composite Materials
Processes 2020, 8(6), 733; https://doi.org/10.3390/pr8060733 - 24 Jun 2020
Cited by 4 | Viewed by 1257
Abstract
The extraction of glycyrrhizin from licorice root and stolon with ethanol/water solutions leaves a lignocellulosic residue, which could be potentially applied in biocomposites. This process proved difficult in principle, given the considerable hardness of this material as received, which impedes its use in [...] Read more.
The extraction of glycyrrhizin from licorice root and stolon with ethanol/water solutions leaves a lignocellulosic residue, which could be potentially applied in biocomposites. This process proved difficult in principle, given the considerable hardness of this material as received, which impedes its use in polymer resins in large amounts. After ball milling, up to 10% of this fibrous residue, which shows very variable aspect ratio, was introduced into an epoxy matrix, to investigate its possible future application in sustainable polymers. Of the three composites investigated, containing 1, 5 and 10 wt% of licorice waste, respectively, by performing flexural testing, it was found that the introduction of an intermediate amount of filler proved the most suitable for possible development. Thermal characterization by thermogravimetry (TGA) did not indicate large variation of degradation properties due to the introduction of the filler. Despite the preliminary characteristics of this study, an acceptable resin-filler interface has been obtained for all filler contents. Issues to be solved in future study would be the possibility to include a larger amount of filler by better compatibilization and a more uniform distribution of the filler, considering their orientation, since most of it maintains an elongated geometry after ball milling. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Preparation and Characterization of Environmentally Friendly Controlled Release Fertilizers Coated by Leftovers-Based Polymer
Processes 2020, 8(4), 417; https://doi.org/10.3390/pr8040417 - 01 Apr 2020
Cited by 6 | Viewed by 1196
Abstract
In this work, a novel bio-based polyurethane (PU) was synthesized by using a leftovers (SF)-based polyol and isocyanate for controlled release fertilizers (CRFs). Its chemical structure, surface elemental compositions and distribution were examined by Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDX) and [...] Read more.
In this work, a novel bio-based polyurethane (PU) was synthesized by using a leftovers (SF)-based polyol and isocyanate for controlled release fertilizers (CRFs). Its chemical structure, surface elemental compositions and distribution were examined by Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDX) and a multifunctional imaging electron spectrometer (XPS). The microstructure morphology of CRFs were examined by SEM. The nutrient release behaviors of CRFs were observed in water. The results demonstrated that SF-based PU-coated urea (FPU) had a denser structure and better nutrient releasing ability. Findings from this work indicated that the use of SF as a coating material of environment-friendly CRFs had great potential, and would hopefully be used for horticultural and agricultural applications. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Ecofriendly Preparation and Characterization of a Cassava Starch/Polybutylene Adipate Terephthalate Film
Processes 2020, 8(3), 329; https://doi.org/10.3390/pr8030329 - 11 Mar 2020
Cited by 6 | Viewed by 1351
Abstract
Composite films of polybutylene adipate terephthalate (PBAT) were prepared by adding thermoplastic starch (TPS) (TPS/PBAT) and nano-zinc oxide (nano-ZnO) (TPS/PBAT/nano-ZnO). The changes of surface morphology, thermal properties, crystal types and functional groups of starch during plasticization were analyzed by scanning electron microscopy, synchronous [...] Read more.
Composite films of polybutylene adipate terephthalate (PBAT) were prepared by adding thermoplastic starch (TPS) (TPS/PBAT) and nano-zinc oxide (nano-ZnO) (TPS/PBAT/nano-ZnO). The changes of surface morphology, thermal properties, crystal types and functional groups of starch during plasticization were analyzed by scanning electron microscopy, synchronous thermal analysis, X-ray diffraction, infrared spectrometry, mechanical property tests, and contact Angle and transmittance tests. The relationship between the addition of TPS and the tensile strength, transmittance, contact angle, water absorption, and water vapor barrier of the composite film, and the influence of nano-ZnO on the mechanical properties and contact angle of the 10% TPS/PBAT composite film. Experimental results show that, after plasticizing, the crystalline form of starch changed from A-type to V-type, the functional group changed and the lipophilicity increased; the increase of TPS content, the light transmittance and mechanical properties of the composite membrane decreased, while the water vapor transmittance and water absorption increased. The mechanical properties of the composite can be significantly improved by adding nano-ZnO at a lower concentration (optimum content is 1 wt%). Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Sustainable Jatropha Oil-Based Membrane with Graphene Oxide for Potential Application in Cu(II) Ion Removal from Aqueous Solution
Processes 2020, 8(2), 230; https://doi.org/10.3390/pr8020230 - 17 Feb 2020
Cited by 1 | Viewed by 1546
Abstract
More recent attention has been focused on the utilization of Jatropha curcas in the field of water treatment. The potential of Jatropha oil in the synthesis of membrane for water filtration had been explored, its performance compared to the addition of graphene oxide [...] Read more.
More recent attention has been focused on the utilization of Jatropha curcas in the field of water treatment. The potential of Jatropha oil in the synthesis of membrane for water filtration had been explored, its performance compared to the addition of graphene oxide (GO) in the polymer matrix. Jatropha oil was modified in a two-step method to produce Jatropha oil-based polyol (JOL) and was blended with hexamethylene diisocyanate (HDI) to produce Jatropha polyurethane membrane (JPU). JPU was synthesized in different conditions to obtain the optimized membrane and was blended with different GO loading to form Jatropha/graphene oxide composite membrane (JPU/GO) for performance improvement. The synthesized pristine JPU and JPU/GO were evaluated and the materials were analyzed using fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), contact angle, water flux, and field emission scanning electron microscopy (FESEM). Results showed that the ratio of HDI to JOL for optimized JPU was obtained at 5:5 (v/v) with the cross-linking temperature at 90 °C and curing temperature at 150 °C. As GO was added into JPU, several changes were observed. The glass transition temperature (Tg) and onset temperature (To) increased from 58 °C to 69 °C and from 170 °C to 202 °C, respectively. The contact angle, however, decreased from 88.8° to 52.1° while the water flux improved from 223.33 L/m2·h to 523.33 L/m2·h, and the pore distribution in JPU/GO became more orderly. Filtration of copper ions using the synthesized membrane was performed to give rejection percentages between 33.51% and 71.60%. The results indicated that GO had a significant impact on JPU. Taken together, these results have suggested that JPU/GO has the potential for use in water filtration. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Article
Effect of Cellulosic Waste Derived Filler on the Biodegradation and Thermal Properties of HDPE and PLA Composites
Processes 2019, 7(10), 647; https://doi.org/10.3390/pr7100647 - 21 Sep 2019
Cited by 5 | Viewed by 1262
Abstract
Composites with high density polyethylene (HDPE) and poly(lactic) acid (PLA) matrix have been tested to analyze the effect of natural fillers (wood flour, recycled wastepaper and a mix of both fillers) and temperature on polymer degradation. Composting tests have been performed in both [...] Read more.
Composites with high density polyethylene (HDPE) and poly(lactic) acid (PLA) matrix have been tested to analyze the effect of natural fillers (wood flour, recycled wastepaper and a mix of both fillers) and temperature on polymer degradation. Composting tests have been performed in both mesophilic (35 °C) and thermophilic (58 °C) conditions. Degradation development has been evaluated through mass variation, thermogravimetric analysis and differential scanning calorimetry. HDPE, as expected, did not display any relevant variation, confirming its stability under our composting conditions. PLA is sensibly influenced by temperature and humidity, with higher reduction of Mw when composting is performed at 58 °C. Natural fillers seem to influence degradation process of composites, already at 35 °C. In fact, degradation of fillers at 35 °C allows a mass reduction during composting of composites, while neat PLA do not display any variation. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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Review

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Review
A Critical Review on the Synthesis of Natural Sodium Alginate Based Composite Materials: An Innovative Biological Polymer for Biomedical Delivery Applications
Processes 2021, 9(1), 137; https://doi.org/10.3390/pr9010137 - 11 Jan 2021
Cited by 19 | Viewed by 1975
Abstract
Sodium alginate (Na-Alg) is water-soluble, neutral, and linear polysaccharide. It is the derivative of alginic acid which comprises 1,4-β-d-mannuronic (M) and α-l-guluronic (G) acids and has the chemical formula (NaC6H7O6). It shows water-soluble, non-toxic, biocompatible, biodegradable, and [...] Read more.
Sodium alginate (Na-Alg) is water-soluble, neutral, and linear polysaccharide. It is the derivative of alginic acid which comprises 1,4-β-d-mannuronic (M) and α-l-guluronic (G) acids and has the chemical formula (NaC6H7O6). It shows water-soluble, non-toxic, biocompatible, biodegradable, and non-immunogenic properties. It had been used for various biomedical applications, among which the most promising are drug delivery, gene delivery, wound dressing, and wound healing. For different biomedical applications, it is used in different forms with the help of new techniques. That is the reason it had been blended with different polymers. In this review article, we present a comprehensive overview of the combinations of sodium alginate with natural and synthetic polymers and their biomedical applications involving delivery systems. All the scientific/technical issues have been addressed, and we have highlighted the recent advancements. Full article
(This article belongs to the Special Issue Synthesis and Applications of Eco-Friendly Polymers)
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