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All issues / Volume 14 (2020) / Issue 10 (October)

Repeatedly self-healing of wider cracks in polymers
M. Q. Zhang
Vol. 14., No.10., Pages 895-895, 2020
DOI: 10.3144/expresspolymlett.2020.73
This is an editorial article. It has no abstract.
Eco-friendly surface hydrophobization of all-cellulose composites using layer-by-layer deposition
O. Korhonen, N. Forsman, M. Osterberg, T. Budtova
Vol. 14., No.10., Pages 896-907, 2020
DOI: 10.3144/expresspolymlett.2020.74
All-cellulose composites were prepared by dispersing kraft fibers in a matrix made from pulp dissolved in NaOH-water. To hydrophobize the composite surface while maintaining the material fully bio-based and biodegradable, layer-by-layer deposition of cationic starch and carnauba wax was performed. Various options of surface coating, drying, and curing were tested, including partial and complete melting of the wax. The composite surface was characterized by water contact angle, roughness and scanning electron microscopy, and material properties by adsorption and absorption of water (in vapor and liquid form) and tensile testing. The highest water contact angle was obtained when the layer-by-layer deposition was performed by dipping the dry composite into cationic starch solution, then in wax dispersion, and partially melting the wax after coating. However, it was demonstrated that the dipping approach was detrimental to material tensile properties, due to heterogeneous swelling of cellulose during the treatment and multiple drying sequences. Process optimization via spraying resulted in composites with Young’s modulus of 6 GPa and hydrophobic surface with water contact angle 122 °C.
A phosphorus/boron-containing triazine-trione derivative endowing epoxy resin with excellent flame retardance
H. J. Duan, J. F. Cao, Y. S. Chen, J. S. Wang, S. Ji, H. R. Ma
Vol. 14., No.10., Pages 908-923, 2020
DOI: 10.3144/expresspolymlett.2020.75
A novel flame retardant containing boron and phosphorus, based on triazine-trione sturcture (TDB) was successfully synthesized, via substitution and esterification reaction between 1,3,5-tris(2-hydroxyethyl)isocyanurate (THEIC), diphenyl phosphoryl chloride (DPCP) and boric acid (BA), and then blended into DGEBA to prepare flame-retardant composites. The structure of TDB was characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR). The thermal and flame-retardant properties of epoxy thermosets were systematically investigated. The results showed that the Tg, T5% and Tmax values of EP samples were gradually decreased with the increasing content of TDB, while the char yields at 700 °C increased. With the introduction of 10 wt% TDB, the LOI value of the thermoset was 27.5%, and the UL-94 rating reached V-0. Furthermore, compared with pure EP, the peak heat release rate (pk-HRR) decreased by more than half, as well as the lower total heat release (THR) and total smoke production (TSP) were obtained. The flame retardant mechanism was studied by analyzing the char residue after cone calorimeter (CC) test and the pyrolysis products via scanning electronic microscopy (SEM), laser Raman spectroscopy (LRS), FTIR and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). It revealed that on account of the existence of triazine-trione structure and phosphorus/boron elements, the intumescent and compact phosphorus/boron-rich char layer was formed, meanwhile, the non-flammable gases and phosphorus-containing free radicals from triazine-trione and DPCP structure can develop the flame retardancy in the gas phase.
Poly(lactic acid)-silkworm silk fibre/fibroin bio-composites: A review of their processing, properties, and nascent applications
O. S. Akintayo, J. L. Olajide, O. T. Betiku, A. J. Egoh, O. O. Adegbesan, O. O. Daramola, E. R. Sadiku, D. A. Desai
Vol. 14., No.10., Pages 924-951, 2020
DOI: 10.3144/expresspolymlett.2020.76
The past few decades have witnessed an upsurge in the utilization of natural fibres in green materials advancement. This rise can be linked to calls from stakeholders, around the world, on the issue of sustainability and eco-friendliness. A shift from the utilization of non-biodegradable sources to renewable sources is a current area of intense research, which also stimulates industrial attention. Amongst the creations of nature, silkworm silk fibres have attracted considerable interest from materials science researchers. Inferable from its amazing biocompatibility, bioresorbability, and biodegradability, silkworm silk strands have been used in the improvement of polylactic acid/silk fibre biocomposites. Hence, with the continued use of these biocomposites in industrial and biomedical applications, it has become necessary to look at the systematic progress made in its processing, overall property improvements, and various applications. This review article also presents the challenges facing the advancement of this biocomposite, the suggested solutions and concludes with anticipated future trends.
Joint effects of long-chain branching and specific nucleation on morphology and thermal properties of polypropylene blends
L. Gajzlerova, J. Navratilova, A. Ryzi, T. Slabenakova, R. Cermak
Vol. 14., No.10., Pages 952-961, 2020
DOI: 10.3144/expresspolymlett.2020.77
The influence of long-chain branching and specific β-nucleation on polymorphic composition, melting and crystallization, and morphology of polypropylene blends were investigated by wide-angle X-ray scattering, differential scanning calorimetry, and scanning electron microscopy. Linear polypropylene and long-chain branched polypropylene were used for the preparation of blends in various proportions. N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide was introduced (0 or 0.03 wt%) as a β-specific nucleating agent into prepared blends. It was found that LCB-PP strongly induces γ-phase formation in the blends and suppresses the nucleation activity of a β-specific nucleating agent. Blends containing a predominant amount of α- and γ-phases showed higher thermodynamic stability within melting, as compared to the samples rich in β-phase. During crystallization, LCB-PP in the blends increases nucleation density by self-seeding effect, manifesting itself in the shift of crystallization temperature. β-phase in the blends is distinctly separated in spherulites, while α- and γ-phases coexist on the lamellae level.
A facile approach for grafting bi-functional groups terminated branched polyphosphazene on carbon fibers
Z. J. He, J. H. Liu, S. H. Liu, X. Q. Zhang, C. H. Lei
Vol. 14., No.10., Pages 962-969, 2020
DOI: 10.3144/expresspolymlett.2020.78
We explored a facile method for grafting bi-functional groups terminated branched polyphosphazene on carbon fibers via direct epoxy amination with an aqueous ammonia solution. The branched polyphosphazene with abundant β-hydroxyl groups and amino groups significantly changes the chemical composition of carbon fibers surface. A significant improvement in interfacial shear strength was obtained from 43.6 MPa for virgin carbon fibers (C.F.) composites to 89.6 MPa for branched polyphosphazene grafted C.F. composites.
Piezoresistive carbon-based composites for sensor applications: Effects of polarity and non-rubber components on shape recovery
Y. Nakaramontri, C. Kummerloewe, C. Nakason, S. Pichaiyut, S. Wisunthon, F. Clemens
Vol. 14., No.10., Pages 970-986, 2020
DOI: 10.3144/expresspolymlett.2020.79
Natural rubber (NR) composites filled with carbon nanotubes (CNT), and carbon black (CB) were prepared. Also, other rubber matrices were tested, namely epoxidized-NR (ENR) and isoprene rubber (IR). The aim was to examine the effects of polarity and non-rubber constituents in rubber on mechanical and piezoresistive sensor properties. Thus, the relative resistances during extension were determined under static (stepwise) and dynamic (cycling) deformation of the composites. It was found that ENR-CNT/CB exhibited mechanical properties superior to NR-CNT/CB and IR-CNT/CB. This is attributed to the chemical ENR-CNT/CB linkages and physical interactions of non-rubber components with CNT/CB surfaces. This also helps the recovery of resistivity to the original value after 20 extension cycles. After 10 000 cycles, the resistivity had changed by 2 orders of magnitude before showing the constant resistivity. Thus, ENR-CNT/CB composites can serve in sensors for health monitoring, motion sensors, and other related products, being cost-effective and easy-to-process materials.
Large-scale electrospinning of poly (vinylalcohol) nanofibers incorporated with platelet-derived growth factors
B. Koprivova, M. Lisnenko, K. Solarska-Sciuk, R. Prochazkova, V. Novotny, J. Mullerova, P. Mikes, V. Jencova
Vol. 14., No.10., Pages 987-1000, 2020
DOI: 10.3144/expresspolymlett.2020.80
Nanofibrous materials have great potential for use in tissue engineering due to their structure, which mimics the extracellular fibrous matrix. Increasing their biological activity is currently the main goal in the development of these scaffolds. From the standpoint of promoting healing and tissue regeneration, the use of human platelets containing hundreds of biologically active molecules is promising. The present work deals with the preparation of PVA-based nanofibrous material containing native platelet-derived proteins that are released in a sustained manner. The needleless electrospinning process of preparation of material that does not affect the activity of incorporated proteins has been optimized, and the resulting material can be produced on a large scale with a protein loading efficiency of 0.64%. The reasonable fiber diameter distribution (370±150 nm) with low defects ensures a homogeneous distribution of proteins. The use of high molecular weight PVA (125000 g/mol) with a high degree of hydrolysis (98–98.8%) resulted in a 40% reduction in PVA solubility without the need for subsequent covalent crosslinking. This, in turn, results in a sustained release of proteins, where after an initial burstrelease of 90% of the proteins, 10% is gradually released over the next 7 days. Our results demonstrate the potential use of the platelet-lysate loaded PVA material in tissue engineering.
Published by:

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