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

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 40012

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Special Issue Editors

Dr. Gergely Kali

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Guest Editor

Center for Chemistry and Biomedicine, Department of Pharmaceutical Technology, Institute of Pharmacy, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria
Interests: green polymer chemistry; monomers from renewable resources; macromolecular engineering

Prof. Dr. Anil K. Bhowmick

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Co-Guest Editor

Department of Chemical and Biomolecular Engineering, The University of Houston, Houston, TX 77204-4004, USA
Interests: sustainable polymers from renewable sources; polymer nanocomposites and nanomaterials; thermoplastic elastomers and polymer blends; polymer modification; rubber technology; failure and degradation of rubbers; adhesion and adhesives; waste rubber recycling

Special Issue Information

Dear Colleagues,

In recent decades, as a result of chemophobia and rising prices in oil, there has been an increase in the application of naturally occurring materials from renewable instead of fossil resources. This trend has been even more significant in the field of synthetic macromolecular chemistry since polymers are large scale, widely used products, and even small changes in the synthesis procedures may have globally noticeable effects. This Special Issue will focus on the green synthesis possibilities in polymer chemistry, including environmentally favorable initiation/catalysis, the use of monomers/polymers from renewable resources, and low energy consumption reactions. These new conditions deliver more sustainable polymer chemistry, which is essential for future sustainability, but also increases the level of trust in this field. The issue will also compare green polymers with the known commercial ones and try to forecast some application possibilities for them.

Dr. Gergely Kali
Prof. Anil K. Bhowmick
Guest Editors

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. Processes is an international peer-reviewed open access monthly 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 2400 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

green polymers
monomers from renewable resources
natural polymers
environmentally friendly conditions
biodegradability
green macromolecular engineering

Published Papers (11 papers)

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Editorial

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2 pages, 168 KiB

Open AccessEditorial

Special Issue “Green Synthesis Processes of Polymers & Composites”

by Gergely Kali and Anil K. Bhowmick

Processes 2021, 9(4), 628; https://doi.org/10.3390/pr9040628 - 02 Apr 2021

Viewed by 1150

Abstract

Undoubtedly, polymers and composites are the most important materials in the late XXth and early XXIst century [...] Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

Research

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9 pages, 2330 KiB

Open AccessArticle

Environmental Method for Synthesizing Amorphous Silica Oxide Nanoparticles from a Natural Material

by Vahid Zarei, Mojtaba Mirzaasadi, Afshin Davarpanah, Alireza Nasiri, Majid Valizadeh and Mohammad Javad Sarbaz Hosseini

Processes 2021, 9(2), 334; https://doi.org/10.3390/pr9020334 - 12 Feb 2021

Cited by 26 | Viewed by 3347

Abstract

Numerous studies have been performed on the generation of several silicon-based engineering materials that often have used chemical materials that have high risks for health and the safety of the environment. Generally, in the synthesis of Nano-silica, tetramethoxysilane, tetraethoxysilane, and tetraethyl orthosilicate (TEOS) are used as precursor materials; however, these materials are toxic and expensive for the production of Nano-silica. This paper presents an environmentally friendly short method (EFSM) with high efficiency for the synthesis of amorphous silica oxide Nanoparticles by using agricultural waste called rice husks (RHs). Use of the EFSM method as an alternative to the chemical methods would have the advantages of fast and simple operation, controllability, great pureness of the Nanoparticles, and low manufacturing cost. A Nanoparticles (NPs) evaluation was conducted with energy-dispersive spectroscopy (EDS), field emission scanning electron microscope (FESEM) and X-ray fluorescence (XRF). By applying the EFSM method, non-toxic amorphous silica nanoparticles with a purity of 94.5% and particle size less than 100 nm was synthesized without using any chemical material. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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17 pages, 8519 KiB

Open AccessArticle

Itaconate Based Elastomer as a Green Alternative to Styrene–Butadiene Rubber for Engineering Applications: Performance Comparison

by Liwei Li, Haijun Ji, Hui Yang, Liqun Zhang, Xinxin Zhou and Runguo Wang

Processes 2020, 8(12), 1527; https://doi.org/10.3390/pr8121527 - 24 Nov 2020

Cited by 9 | Viewed by 3182

Abstract

In response to increasingly stringent requirements for the sustainability and environmental friendliness of the rubber industry, the application and development of bio-based elastomers have received extensive attention. In this work, we prepared a new type of bio-based elastomer poly(dibutyl itaconate-butadiene) copolymer (PDBIB) nanocomposite using carbon black and non-petroleum-based silica with a coupling agent. Using dynamic thermodynamic analysis (DMTA) and scanning electron microscope (SEM), we studied the effects of feed ratio on dynamic mechanical properties, micro morphology, and filler dispersion of PDBIB composites. Among them, silica-reinforced PDBIB60 (weight ratio of dibutyl itaconate to butadiene 40/60) and carbon black-reinforced PDBIB70 (weight ratio of dibutyl itaconate to butadiene 30/70) both showed excellent performance, such as tensile strength higher than 18 MPa and an elongation break higher than 400%. Compared with the widely used ESBR, the results showed that PDBIB had better rolling resistance and heat generation than ESBR. In addition, considering the development of green tires, we compared it with the solution polymerized styrene–butadiene rubber with better comprehensive performance, and analyzed the advantages of PDBIB and the areas to be improved. In summary, PDBIB prepared from bio-based monomers had superior performance and is of great significance for achieving sustainable development, providing a direction for the development of high-performance green tire and holding great potential to replace petroleum-derived elastomers. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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17 pages, 4888 KiB

Open AccessArticle

Solid-State Compounding for Recycling of Sawdust Waste into Green Packaging Composites

by Rula M. Allaf and Mohammad Futian

Processes 2020, 8(11), 1386; https://doi.org/10.3390/pr8111386 - 30 Oct 2020

Cited by 6 | Viewed by 2889

Abstract

The present study explores solid-state cryomilling for the compounding of green composites. Herein, wood plastic composites (WPCs) composed of sawdust (SD) and poly(ε-caprolactone) (PCL) with various compositions were prepared. Two compounding techniques, namely, extrusion and cryomilling, were utilized to prepare WPC raw material pellets and powders, respectively, for comparison purposes. Flat pressing was further utilized to prepare WPC films for testing. Morphological, structural, thermal, mechanical, and surface wettability properties were investigated. Results indicate the advantages of cryomilling in producing WPCs. Scanning electron microscopy (SEM) along with optical micrographs revealed well ground SD particles and uniform distribution in the PCL matrix. Tensile strength and elongation at break of the composites declined with increasing SD content, however, the modulus of elasticity significantly increased. Water contact angles averaged less than 90°, implying partial wetting. Visual observations and thermo-gravimetric analysis (TGA) indicated thermal stability of composites during processing. In conclusion, PCL/SD WPC is a potential candidate to replace conventional plastics for packaging applications. This would also provide a much better utilization of the currently undervalued wood waste resources. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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13 pages, 1664 KiB

Open AccessFeature PaperArticle

Post-Polymerization Heat Effect in the Production of Polyamide 6 by Bulk Quasiliving Anionic Ring-Opening Polymerization of ε-Caprolactam with Industrial Components: A Green Processing Technique

by Zsófia Osváth, Anita Szőke, Szabolcs Pásztor, Györgyi Szarka, László Balázs Závoczki and Béla Iván

Processes 2020, 8(7), 856; https://doi.org/10.3390/pr8070856 - 17 Jul 2020

Cited by 7 | Viewed by 3902

Abstract

Bulk, solventless anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) with high yields, without side products and with short reaction times, initiated by caprolactamate-carbamoylcaprolactam initiating systems belong to green polymerization processes, leading to poly(ε-caprolactam) (Polyamide 6, PA6, Nylon 6). However, the effect of post-polymerization heat (i.e., slow, technically feasible cooling) on the fundamental characteristics of the resulting polymers such as yield and molecular weight distributions (MWDs) have not been revealed thus far. Significant post-polymerization effect was found by us in terms of both monomer conversions and MWDs by carrying out CPL polymerization with industrial components under conditions mimicking thermoplastic reaction transfer molding (T-RTM). Remarkably, higher monomer conversions and molecular weights (MWs) were obtained for Polyamide 6 samples prepared without quenching than that for the quenched polymers at the same reaction times. Independent of quenching or non-quenching, M_n of the resulting polymers as a function of conversion fell in the theoretical line of quasiliving AROP of CPL. At high monomer conversions, significant increase of the MW and broadening of the MWDs occurred, indicating pronounced chain–chain coupling. These findings have fundamental importance for designing processing conditions for in situ polymerization processes of ε-caprolactam by various techniques such as T-RTM, reaction injection molding (RIM), and other processing methods of Polyamide 6. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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16 pages, 6708 KiB

Open AccessFeature PaperArticle

Sustainable Water Responsive Mechanically Adaptive and Self-Healable Polymer Composites Derived from Biomass

by Pranabesh Sahu and Anil K. Bhowmick

Processes 2020, 8(6), 726; https://doi.org/10.3390/pr8060726 - 22 Jun 2020

Cited by 5 | Viewed by 2552

Abstract

New synthetic biobased mechanically adaptive composites, responding to water and having self-healing property, were developed. These composites were prepared by introducing plant-based cellulose nanofibrils (CNFs) at 10, 20, and 25% (v/v) concentration into a biobased rubbery poly (myrcene-co-furfuryl methacrylate) (PMF) matrix by solution mixing and subsequent compression molding technique. The reinforcement of CNFs led to an increase in the tensile storage modulus (E’) of the dry composites. Upon exposure to water, water sensitivity and a drastic fall in storage moduli (E’) were observed for the 25% (v/v) CNF composite. A modulus reduction from 1.27 (dry state) to 0.15 MPa (wet state) was observed for this composite. The water-sensitive nature of the composites was also confirmed from the force modulation study in atomic force microscopy (AFM), revealing the average modulus as 82.7 and 32.3 MPa for dry and swollen composites, respectively. Interestingly, the composites also showed thermoreversibility and excellent healing property via Diels-Alder (DA) click chemistry using bismaleimide as a crosslinker, when the scratched samples were heated at 120 °C (rDA) for 10 h and then cooled down to 60 °C (DA) followed by room temperature. The healing efficiency was obtained as about 90% from the AFM 3D height images. Thus, the composites exhibited dual stimuli-responsive behavior as mechanically adaptive water sensitive polymers with water as the stimulus and self-healing polymer using bismaleimide as an external stimulus. Therefore, this study provides guidance and new frontiers to make use of composite materials based on biopolymers for various potential smart and biomedical applications. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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11 pages, 1760 KiB

Open AccessArticle

Synthesis, Characterization of sym-2,4,6-trisubstituted-s-Triazine Derivatives and Their Effects on Flame Retardancy of Polypropylene Composites

by Ali Aldalbahi, Bander Alotaibi and Ayman El-Faham

Processes 2020, 8(5), 581; https://doi.org/10.3390/pr8050581 - 14 May 2020

Cited by 5 | Viewed by 2815

Abstract

Polypropylene (PP) is flammable material, which brings latent danger to the environment and human society. Therefore, developing new environmentally friendly and effective flame-retardant is one of the most important ways to improve the flame retardancy of PP and improve safety during its lifetime. Herein, we describe the synthesis of five sym-2,4,6-trisubstituted-s-triazine derivatives, namely, N²,N⁴,N⁶-triphenyl-1,3,5-triazine-2,4,6-triamine (TAT), N²,N⁴,N⁶-tris(4-bromophenyl)-1,3,5-triazine-2,4,6-triamine (TBAT), N²,N⁴,N⁶-tris(4-chlorophenyl)-1,3,5-triazine-2,4,6-triamine (TCAT), 4,4′,4″-((1,3,5-triazine-2,4,6-triyl) tris(azanediyl)) triphenol (THAT), and N²,N⁴,N⁶-tris(4-methoxyphenyl)-1,3,5-triazine-2,4,6-triamine (TMAT), from the reaction of cyanuric chloride and p-substituted aniline employing conventional heating or microwave irradiation. The prepared compounds characterized by different techniques, such as Fourier-transform infrared (FTIR), Ultra-Violet and Visible (UV-Vis), Nuclear Magnetic Resonance spectroscopy (¹H-NMR and ¹³C-NMR), Thermogravimetric Analysis (TGA), and differential scanning calorimetry (DSC). The effect of substituent on the aniline moiety has great impact on its thermal stability, as observed from the TGA and DSC data. Based on the TGA and DSC results, three triazine derivatives TAT, TBAT, and TMAT were used as charring agents in the presence of different proportions of ammonium polyphosphate (APP) to form an intumescent flame-retardant (IFR) system, to improve the flame retardancy of PP. The flammability property of PP was investigated by a vertical burning test (UL94). The results of UL94 revealed that the TXAT/APP (IFR) system influence the PP and could improve the flame retardancy of PP. Best results were obtained with the mass ratio of APP and TXAT 2:1. When the IFR loading was 25 wt%, it displayed great influence and passed V-0 with TMAT, and V-1 with both TAT and TBAT in the UL94 test. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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9 pages, 2400 KiB

Open AccessArticle

Formulation and Functional Properties of Whey Protein-Based Tissue Adhesive Using Totarol as an Antimicrobial Agent

by Yifan Hou, Xiaonan Zhang, Cuina Wang and Mingruo Guo

Processes 2020, 8(4), 496; https://doi.org/10.3390/pr8040496 - 24 Apr 2020

Cited by 4 | Viewed by 2661

Abstract

Tissue adhesives have been widely used in surgical procedures. Compared to traditional surgical sutures, tissue adhesives provide fast bonding experiences and full closure of wounds. However, current tissue adhesives are mostly fossil-based synthetic products. Therefore, it is of great significance to explore the use of natural materials in tissue adhesives. Whey is a low-end byproduct of cheese manufacturing. Whey protein, a group of small globular proteins, can exhibit adhesive properties if their structures are modified by physical or chemical means. The objectives of this study were to investigate the functional and structural properties of whey protein-based tissue adhesive, along with the antibacterial effect of totarol, a natural antimicrobial agent. Whey protein isolate (WPI) solutions (25%–33% protein) were mixed with different levels (0.1%–0.3% w/w) of totarol. The mixtures were analyzed for total plate count and yeast and mold count. The lap-shear bonding strength was tested after the WPI-totarol solutions were mixed with a crosslinking agent, glutaraldehyde (GTA). The lap-shear bonding strength of the tissue adhesive was about 20 kPa, which is comparable to that of a commercial BioGlue^®. The microstructures of the mixtures were analyzed by scanning electron microscopy (SEM). Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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13 pages, 2089 KiB

Open AccessArticle

Preparation of Sawdust-Filled Recycled-PET Composites via Solid-State Compounding

by Rula M. Allaf, Esraa Albarahmieh and Mohammad Futian

Processes 2020, 8(1), 100; https://doi.org/10.3390/pr8010100 - 11 Jan 2020

Cited by 12 | Viewed by 5428

Abstract

Recently, consumer markets have shown great interest in sustainable products. Considerable research efforts are headed towards developing biodegradable and recyclable polymers and composites. In this study, the fabrication of a wood–plastic composite (WPC) via solid state compounding has been examined. Polyethylene terephthalate (PET) and wood sawdust waste as major components of waste and challenging materials for the manufacturing of WPCs have been explored. Furthermore, the addition of poly(ε-caprolactone) as a biodegradable plasticizing agent was investigated. Composite powders were prepared by cryogenic solid-state milling (cryomilling) according to a statistical mixture design. Mechanical and water absorption properties were inspected on film samples obtained by hot pressing. Different formulations resulted in a variety of colors, textures, water interactions and mechanical properties. A sawdust content of approximately 25 vol.% was optimal for the best combination of properties. The results indicated that cryomilling is technically advantageous in the production of WPCs. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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6 pages, 1572 KiB

Open AccessCommunication

Investigations on Novel Ternary Green Polymer Composite

by Ting-Chia Hsu, Li-Ting Lee and Xin-Yun Wu

Processes 2020, 8(1), 31; https://doi.org/10.3390/pr8010031 - 27 Dec 2019

Cited by 2 | Viewed by 2268

Abstract

In this study, the novel ternary green polymer composites of poly(l-lactic acid) (PLLA)/poly(ethylene adipate)/hexagonal boron nitride (PLLA/PEA/h-BN) were synthesized and prepared. The crystallization rate of the biodegradable polymer PLLA in the composite was significantly increased with the addition of PEA and functional h-BN. In ternary PLLA/PEA/h-BN composites, PEA can be used as a plasticizer, while h-BN is a functional nucleation agent for PLLA. The analysis of the isothermal crystallization kinetics by the Avrami equation shows that the rate constant k of the ternary PLLA/PEA/h-BN composite represents the highest value, indicating the highest crystallization in the ternary composite. Adding h-BN in the composite can further increase the k value and increase the crystallization rate. Polarized optical microscopy (POM) images reveal that h-BN is an effective nucleation agent that increases the nucleation density of composites. Analysis of wide-angle X-ray diffraction (WAXD) further confirmed that the crystalline structures of PLLA were unchanged by the addition of PEA and h-BN. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the h-BN particles are uniformly distributed in the composite. The distribution of h-BN having a particle size of a few hundred nm causes an effective nucleation effect and promotes the crystallization of the ternary composites. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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Review

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21 pages, 6628 KiB

Open AccessFeature PaperReview

Terpene Based Elastomers: Synthesis, Properties, and Applications

by Pranabesh Sahu, Anil K Bhowmick and Gergely Kali

Processes 2020, 8(5), 553; https://doi.org/10.3390/pr8050553 - 08 May 2020

Cited by 50 | Viewed by 8334

Abstract

The limited source of fossil-fuel and the predominance of petroleum-based chemistry in the manufacturing of commodity polymers has generated tremendous interest in replacing the fossil source-based polymers with renewable counterparts. The field of sustainable elastomers has grown in the past three decades, from a few examples to a plethora of reports in modern polymer science and technology. Applications of elastomers are huge and vital for everyday living. The present review aims to portray a birds-eye view of various sustainable elastomers obtained from the wide family of acyclic terpenes (renewable feedstocks from different plant oils) via various polymerization techniques and their properties, as well as plausible developments in the future applications of sustainable polymers. Not only the homopolymers, but also their copolymers with both green and commercial fossil based comonomers, are reviewed. Full article

(This article belongs to the Special Issue Green Synthesis Processes of Polymers & Composites)

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