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All issues / Volume 17 (2023) / Issue 11 (November)

Challenges and opportunities of polymer recycling in the changing landscape of European legislation
Andrea Toldy
Vol. 17., No.11., Pages 1081-1081, 2023
DOI: 10.3144/expresspolymlett.2023.81
This is an editorial article. It has no abstract.
Four-dimensional printing of acrylonitrile butadiene styrene – thermoplastic polyurethane shape memory polymers with excellent material and interfacial adhesion performance
Kianoosh Soltanmohammadi, Mohammad Aberoumand, Davood Rahmatabadi, Elyas Soleyman, Sogol Ghasemi, Ismaeil Ghasemi, Majid Baniassadi, Karen Abrinia, Mahdi Bodaghi, Mostafa Baghani
Vol. 17., No.11., Pages 1082-1095, 2023
DOI: 10.3144/expresspolymlett.2023.82
There are a limited number of thermoplastics with intrinsic shape memory effect (SME) that are four-dimensional (4D) printable. Development of other shape memory polymers (SMPs) entails synthesis with a complicated chemical experimental lab effort. In this paper, for the first time, a novel layered multi-material structure is developed based on a deep comprehension of SMEs’ macromolecular requisites. The fused deposition modeling (FDM) method is used for the four-dimensional printing of layered structures whose base materials show no SME. Commercial acrylonitrile butadiene styrene (ABS), toughened ABS-thermoplastic polyurethane (TPU) blend, and TPU, all with no SME, are used to fabricate bi-layers of ABSTPU blends and TPU with different volumetric proportions. Different thermo-mechanical tests, including dynamic mechanical thermal analysis (DMTA), and constrained and free shape recovery, are conducted. Also, the interfacial properties of the layered 4D printed structure are assessed by the mean of shear testing and scanning electron microscopy (SEM). Experimental results reveal that the 4D printed bi-layer composites possess a high level of programmability, SME (90–96%), and perfect interfaces without any porosity and detachment between layers. The results of this research can potentially eliminate the desperate need for SMPs for 4D printing and broaden the opportunity to have smart parts using commercial thermoplastics.
Bio-based composites of sago starch and natural rubber reinforced with nanoclays
Jareerat Ruamcharoen, Ruszana Munlee, Lapporn Vayachuta, Polphat Ruamcharoen
Vol. 17., No.11., Pages 1096-1109, 2023
DOI: 10.3144/expresspolymlett.2023.83
Sago starch (SS) was blended with natural rubber (NR) using nanoclays, namely montmorillonite (MMT), kaolinite (KAO), and kaolinite modified by dimethyl sulfoxide (KAO-D) to enhance its physical and mechanical properties. Each nanoclay was incorporated at 2, 4, 6, and 8 wt%, respectively. The SS80NR20 (80 wt% of sago starch and 20 wt% of natural rubber) biocomposites were characterized by solubility of water, water vapor transmission, mechanical and thermal properties. The constituent interaction and morphology of the SS80NR20 biocomposites were also presented by using X-ray diffraction (XRD) technique and scanning electron microscope (SEM). The findings demonstrated that the inclusion of clays significantly improved both the water resistance and tensile properties when compared to the SS80NR20 blend. In the SS80NR20 biocomposites, MMT at 6 wt% exhibited the lowest moisture content, solubility in water, and water vapor transmission. As the amount of nanoclay in the biocomposites increased, their tensile strength dramatically increased whilst their strain at break had a tendency to diminish. Strong interaction by establishing the intercalated structure of MMT, and KAO within SS80NR20 biocomposites were attributed to both physical and mechanical properties, while the weak interaction at the interface of SS and NR was attributed to KAO-D.
The competition between self-seeding and specific nucleation in crystallization of long-chain branched polypropylene
Sona Zenzingerova, Michal Kudlacek, Jana Navratilova, Lenka Gajzlerova, David Jaska, Lubomir Benicek, Roman Cermak
Vol. 17., No.11., Pages 1110-1120, 2023
DOI: 10.3144/expresspolymlett.2023.84
The main purpose of this work is to present the effect of long-chain branching and specific α-nucleation on the optical properties, crystallization and supermolecular structure of polypropylene (PP). Commercially available α-nucleating/clarifying agent 1,3;2,4-bis(3,4-dimethylbenzylidene)sorbitol (Millad 3988) was mixed into linear PP and long-chain branched PP (LCB-PP) in the concentration of 0.2 wt%. For the study of polymorphic composition, crystallinity, and crystallization process under isothermal conditions in the temperature range of 130–150 °C, differential scanning calorimetry and wide-angle X-ray scattering were used. Although the used nucleating/clarifying agent appears to have a slight effect on the optical properties of long-chain branched polypropylene, it does not appear to affect the crystallization kinetics significantly. LCB-PP exhibited self-nucleation, favored over nucleation by a specific nucleating agent.
Synthesis and characteristics of α-carboxylic, ω-hydroxyl natural rubber toughened poly(lactic acid)
Abdulhakim Masa, Varaporn Tanrattanakul, Ruedee Jaratrotkamjorn
Vol. 17., No.11., Pages 1121-1134, 2023
DOI: 10.3144/expresspolymlett.2023.85
This work presented the synthesis of α-carboxyl, ω-hydroxyl natural rubber (CHNR) for use as an alternative toughening agent for poly(lactic acid) (PLA). The proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) analyses verified the chemical structure of CHNR consisting of the hydroxyl and carboxyl end groups. The molecular weights of CHNR were set from 5000 to 15 000 g·mol–1 which were determined by gel permeation chromatography (GPC) and 1H-NMR. The PLA and CHNR were prepared by reactive blending using a twinscrew extruder. It was found that the reaction between PLA and CHNR proceeded through transesterification without a catalyst. The formation of copolymer (PLA-co-CHNR) at the interface of PLA and CHNR increased the interfacial adhesion between the two phases. Differential scanning calorimetry (DSC) analysis revealed that CHNR was more compatible with PLA than natural rubber (NR). The compatibilization affected the blend morphology by reducing the interfacial tension. It resulted in a reduction of rubber particle size. The CHNR with a molecular weight of 5000 g·mol–1 showed the greatest improvement in the toughness and ductility of PLA.
A comparison of the mechanical behaviour of natural rubber-based blends using waste rubber particles obtained by cryogrinding and high-shear mixing
Nicolas Candau, Rachel LeBlanc, Maria Lluisa Maspoch
Vol. 17., No.11., Pages 1135-1153, 2023
DOI: 10.3144/expresspolymlett.2023.86
The influence of the type of mechanical recycling of waste rubber particles on the tensile properties of waste/natural rubber blends has been investigated. The wastes originating from ground tyre rubber (GTR) had been treated by two distinct processes: cryo-grinding and high shear mixing (HSM). For both processes, the resulting composites show enhanced stiffness and strength for all strain rates and temperatures tested. This is attributed to both the reinforcing effect of the waste as well as the nucleation ability of the wastes on strain induced crystallization (SIC) in the natural rubber (NR) matrix. Cryo-grinding was shown to provide the finest particle size with an average diameter of 34 μm, while the HSM process was found to show an elastic modulus of aggregated GTR powder of 7 MPa at 1 Hz at room temperature. Within these characteristics, the NR/GTR blends using the HSM process show the best tensile performance under single loading, with the highest strength and highest ability to crystallize under strain. Under cyclic loading, NR/GTR blends using cryo-ground GTR particles show the best performance, which we ascribed to their ability to better distribute and accommodate the stress from one cycle to another owing to their finest size. Both explored recycling techniques provide the natural/waste rubber blends interesting properties such as mechanical reinforcement and strain-induced crystallization ability under various testing conditions.
In situ catalyzed poly(ε-caprolactone)/organic rectorite nanocomposites with excellent electrochemical performance
Limin You, Shifan Zhang, Zhuoxiong Huang, Wanle Pi, Jiaqi Liu, Rui Ma
Vol. 17., No.11., Pages 1154-1165, 2023
DOI: 10.3144/expresspolymlett.2023.87
In recent years, solid polymer electrolytes (SPE) has attracted much attention because of its good safety and environmental stability, among which poly(ε-caprolactone) (PCL) based solid electrolyte film is one of the most potential materials. We have adopted the method of synthesizing polymer nanocomposites with natural clay, which can effectively meet the needs of electrolytes. In this study, cetyl trimethyl ammonium bromide (CTAB) was used to modify rectorite (REC), and the ε-CL monomer is inserted between the rectorite silicate layers. PCL/organic rectorite (OREC) nanocomposites were synthesized by in situ intercalation polymerization. The yield of the polymer nanocomposite could reach 93.6% when the molecular weight of the polymer nanocomposite was 39 000. The effects of OREC addition on the morphology, thermal stability, and electrochemical properties of PCL/OREC nanocomposites were investigated by various characterization methods. The temperature can be increased by 50 °C when the thermal decomposition is 50 wt%, and the crystallinity decreases by 4.6%. Composite polymerelectrolytes (CPEs) (PCL/OREC) showed a good electrical conductivity of 1.13·10–4 S·cm–1 at 60 °C and an excellent capacity retention rate of 96.7% after 100 cycles at 0.5 C current density. This study has important guiding significance for the development of polymer nanocomposites as solid electrolytes.
How introduction of deposit-refund system (DRS) changes recycling of non-drinking bottle PET wastes
Janka Bobek-Nagy, Róbert Kurdi, András Kovács, Lilla Simon-Stőger, Márton Szigeti, Csilla Varga
Vol. 17., No.11., Pages 1166-1179, 2023
DOI: 10.3144/expresspolymlett.2023.88
Under the era of circular economy, the deposit-refund system (DRS) for e.g. polyethylene terephthalate (PET) is thought to be a good choice to achieve a more structured plastic recycling. The present research has the aim to make a comprehensive description and a practical guideline in order to evaluate how collection and separation system influence the quality and efficiency of mechanical recycling of PET. The DRS has been symbolized by manually collected bottles with (BCL) and without (B) caps and labels. Samples have been given from the selective income (SI) and the sorting residue (SR) of a manual selective waste sorting plant and PET fraction of refuse derived fuel (RDF). Based on preliminary qualification results such as melt flow indices (MFI), PET bottles are worth selecting into the main colours like water clear, blue, and all the others together, referred to as PET-A, PET-B, and PET-D fractions of the sorting plant. The SR seemed to be a beneficial raw material for PET recycling as both mechanical and rheological properties were proper enough. PET separated from the Mechanical Biological Treatment (MBT) plant as RDF showed the worst processing and mechanical properties, but both can be improved with deeper precleaning. X-ray tomography (CT) scans have shown a correlation between the source of waste and the gas void structure which influence the macroscopic mechanical properties.
Published by:

Budapest University of Technology and Economics,
Faculty of Mechanical Engineering, Department of Polymer Engineering