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All issues / Volume 8 (2014) / Issue 2 (February)

The ongoing impact of carbon (allotropic forms)/polymer composites
G. C. Psarras
Vol. 8., No.2., Pages 73-73, 2014
DOI: 10.3144/expresspolymlett.2014.9
This is an editorial article. It has no abstract.
Graphene reinforced ultra high molecular weight polyethylene with improved tensile strength and creep resistance properties
A. Bhattacharyya, S. Chen, M. Zhu
Vol. 8., No.2., Pages 74-84, 2014
DOI: 10.3144/expresspolymlett.2014.10
Reduced graphene oxide or graphene was dispersed in ultra high molecular weight polyethylene (UHMWPE) using two methods to prepare nanocomposite films. In pre-reduction method, graphite oxide (GO) was exfoliated and dispersed in organic solvents and reduced to graphene before polymer was added, while reduction of graphene oxide was carried out after polymer addition for in situ reduction method. Raman spectroscopic study reveals that the second method results in better exfoliation of graphene but it has more amorphous content as evident from selected area electron diffraction (SAED) pattern, wide angle X-ray and differential scanning calorimetry (DSC). The nanocomposite film produced by prereduction method possesses higher crystallinity (almost the same as that of the pure film) as compared to the in situ method. It shows better modulus (increased from 864 to 1236 MPa), better strength (increased from 12.6 to 22.2 MPa), network hardening and creep resistance (creep strain reduced to 9% from 50% when 40% of maximum load was applied for 72 h) than the pure film. These findings show that graphene can be used for reinforcement of UHMWPE to improve its tensile and creep resistance properties.
Preparation and characterization of biopolymers comprising chitosan-grafted-ENR via acid-induced reaction of ENR50 with chitosan
M. R. H. Mas Haris, G. Raju
Vol. 8., No.2., Pages 85-94, 2014
DOI: 10.3144/expresspolymlett.2014.11
This paper describes the first detailed tailored-approach for the preparation of biopolymers comprising chitosan (CTS) grafted onto the backbone of epoxidized natural rubber (CTS-g-ENR). In a typical experiment, appropriate amount of CTS and AlCl3•6H2O was added to a specified amount of ENR50 (ENR with about 50% epoxy content) dissolved in a dual-solvent consisting of 1,4-dioxane and water (97.5:2.5% v/v) and the resulting mixture refluxed with continuous stirring for 6 hours. Nuclear magnetic resonance (NMR) spectral analysis of a biocomposite, CTS-g-ENR-P1, revealed that its epoxy content is 22.36% which is considerably lower than 44.93% as determined for ENR50-control (ENR50 derivative obtained under similar experimental condition but in the absence of CTS). This means that the grafting of CTS onto the backbone of ENR had occurred. The revelation is affirmed by the presence of the characteristic absorption bands of CTS and ENR, and the appearance of new bands at 1219, 902 and 733 cm–1 in the Fourier transform infrared (FTIR) spectrum of CTS-g-ENR-P1. Further evidence that CTS had been successfully grafted onto the backbone of ENR can be deduced and described in this paper from the data obtained by means of Differential Scanning Calorimetric analysis, Thermogravimetric analysis and Variable Pressure Scanning Electron Microscopy.
Curing kinetics, mechanism and chemorheological behavior of methanol etherified amino/novolac epoxy systems
S. F. Zhao, G. P. Zhang, R. Sun, C. P. Wong
Vol. 8., No.2., Pages 95-106, 2014
DOI: 10.3144/expresspolymlett.2014.12
The curing kinetics and mechanism of epoxy novolac resin (DEN) and modified epoxy novolac resin (MDEN) with methanol etherified amino resin were studied by means of differential scanning calorimetry (DSC), Fourier transforminfrared (FT-IR) spectroscopy and chemorheological analysis. Their kinetics parameters and models of the curing were examined utilizing isoconversional methods, Flynn-Wall-Ozawa and Friedman methods. For the DEN mixture, its average activation energy (Ea) was 71.05 kJ/mol and the autocatalytic model was established to describe the curing reaction. The MDEN mixture exhibited three dominant curing processes, termed as reaction 1, reaction 2 and reaction 3; and their Ea were 70.05, 106.55 and 101.91 kJ/mol, respectively. Besides, Ea of reaction 1 was similar to that of DEN mixture, while Ea of reactions 2 and 3 corresponded to that of the etherification reaction between hydroxyl and epoxide group. Moreover, these three dominant reactions were nth order in nature. Furthermore, their curing mechanisms were proposed from the results of DSC and FTIR. The chemorheological behavior was also investigated to obtain better plastics products via optimizing the processing schedules.
Percolated conductive polyaniline-clay nanocomposite in polyvinyl chloride through the combined approach porous template and self-assembly
J. D. Sudha, S. Sivakala, C. K. Chandrakanth, K. S. Neethu, K. N. Rohini, R. Ramakrishnan
Vol. 8., No.2., Pages 107-115, 2014
DOI: 10.3144/expresspolymlett.2014.13
In this paper, we are reporting a novel strategy for the preparation of conductive polyaniline-clay nanocomposite in Polyvinylchloride (PVC) matrix by admicellar emulsion polymerization using a low cost renewable resource based surfactant cum dopant. The highly oriented percolated network of polyaniline-clay nanocomposite in PVC matrix was revealed from the studies made by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FTIR) results suggested that porous template was formed by the noncovalent interactions among the hydroxyl groups present in the nanoclay edges and the chloride ions present in PVC matrix. Here, the bio-based surfactant, 4-hydroxy-2-pentadecyl benzene-1-sulphonic acid (PDPSA) performed multiple roles of dopant, emulsifier and soft template during the polymerization of anilinium+PDPSA (An+PDPSA) in PVC-clay matrix. The prepared composite exhibited electrical conductivity (σdc) of 4.8•10–2 S/cm and electromagnetic interference shielding efficiency (EMI SE) of 55.2 dB suggesting it as a prospectable candidate for the encapsulation of electronic devices in high technological applications.
Fast curing ethylene vinyl acetate films with dual curing agent towards application as encapsulation materials for photovoltaic modules
H-Y. Xue, W-H. Ruan, M-Q. Zhang, M-Z. Rong
Vol. 8., No.2., Pages 116-122, 2014
DOI: 10.3144/expresspolymlett.2014.14
To speed up curing of ethylene vinyl acetate (EVA) films as encapsulation materials for photovoltaic modules, a dual curing agent of benzoyl peroxide (BPO) and butylperoxy 2-ethylhexyl carbonate (TBEC) was introduced in this work. The experimental results indicated that for the weight ratio of BPO/TBEC of 0.6/2.4, over 80% gel content of EVA was yielded after curing at 130°C for 12 min. Compared with the case of single curing agent, the present one obviously operated at much lower temperature with faster rate. By carefully studying the influence of curing agent proportion and curing conditions on gel content of EVA films, as well as rheology and curing kinetics, the mechanism involved was analyzed and verified. The results are believed to be useful for developing new curing system of EVA encapsulation films with improved processability.
Preparation and characterization of novel thermoset polyimide and polyimide-peo doped with LiCF3SO3
M. H. Ugur, R. D. Toker, N. Kayaman-Apohan, A. Gungor
Vol. 8., No.2., Pages 123-132, 2014
DOI: 10.3144/expresspolymlett.2014.15
This paper deals with the synthesis and characterization of a new type of anhydrous ionic conducting lithium doped membranes consist of polyimide (PI), poly (ethylene oxide) (PEO) and lithium trifluoromethanesulfonate (LiCF3SO3) for solid polymer electrolyte (SPE). For this purpose, different molar ratios of lithium salt (Li-salt) solution are added into poly (amic acid) (PAA) intermediate prepared from the reaction of 3,3',4,4'-benzophenon tetracarboxylic dianhydride (BTDA) and 4,4'-oxydianiline (ODA). PEO is incorporated into PAA since it forms more stable complexes and possess high ionic conductivities. Then, Li-salt containing PAA solutions are imidized by thermal process. The effect of interaction between host polymer and Li-salt is characterized by FT-IR (Fourier Transform Infrared) spectroscopy and SEM (scanning electron micrsocopy). The conductivities of Li-salt and PEO containing PI composite membranes are in the range of 10–7–10–5 S•cm–1. The conductivity increases with incorporation of PEO. Thermogravimetric analysis results reveal that the PI/PEO/LiCF3SO3 composite polymer electrolyte membranes are thermally stable up to 500°C.
Effect of a new surface-grafting method for nano-hydroxyapatite on the dispersion and the mechanical enhancement for poly(lactide-co-glycolide)
L. X. Jiang, L. Y. Jiang, L. J. Xu, C. T. Han, C. D. Xiong
Vol. 8., No.2., Pages 133-141, 2014
DOI: 10.3144/expresspolymlett.2014.16
In this paper, a new surface-grafting D, L-lactide (DLLA) for nano-hydroxyapatite (n-HA) with the assist of citric acid was designed. The dispersion of new surface modified n-HA was characterized by Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and dispersion test, and the mechanical enhancement effect for poly(lactide-co-glycolide) (PLGA) was evaluated by scanning electron microscopy (SEM), differential scanning calorimeter measurements (DSC) and electromechanical universal tester. The results showed that citric acid played a critical role in surface-grafting, which could greatly increase grafting amount and improve dispersion of n-HA, so that it resulted in better interfacial adhesion throughout PLGA matrix, higher crystallinity and better mechanical enhancement for PLGA than the surface-grafting method for n-HA without citric acid, whose bending strength and tensile strength were both over 20% higher than those of pure PLGA when 3 wt% n-HA was added, and it still enhanced 8 and 6% higher than those of pure PLGA even the introduction of 15 wt% n-HA, respectively. The above results suggested that the surface-grafting for n-HA with the aid of citric acid was an ideal novel surface modification method, which could greatly improve the dispersion of n-HA and exhibit excellent mechanical enhancement effect for PLGA, suggesting it has a great potential in the bone fracture internal fixation application in future.
Published by:

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