Search

This manuscript presents the preparation of polymer layers based on polythiophene (PTh) and its 3-substituted derivatives (substituents 4-(CH3O)C6H4 and 4-(CF3)C6H4 marked as PThOCH3 and PThCF3, respectively) on platinum electrodes by cyclic voltammetry (CV). The polymerization process and the morphology of resulting layers were discussed analysing of CV-voltammograms and scanning electron microscopy (SEM), respectively. Subsequently, the prepared polymers were tested as active/sensitive media of two types of sensors: (i) electrochemical sensor detecting ammonia in aqueous environment, whose response was evaluated by electrochemical impedance spectroscopy (EIS); (ii) chemiresistor detecting NH3 in atmosphere, whose response was evaluated by measurement of resistance. It was found that both the physical (morphology, homogeneity, relative thickness) and receptor properties of the polymer layer deposited on electrode surface are significantly affected by the nature of substituent attached to the thiophene ring. The mutual context of ammonia detection in both environments is discussed. [ABSTRACT FROM AUTHOR]

Polylactide (PLA) is an important biodegradable polymer, used for numerous applications ranging from industrial packaging to tissue engineering. However, its inherent brittleness and limited thermal stability have restricted its penetration to niche markets. In this communication, the authors demonstrate that blending of PLA with castor oil-based polyurethane prepolymer (COPUP), with the addition of COPUP, dispersed in the PLA matrix can overcome the inherent brittleness of the matrix polymer. NCO-terminated COPUP was successfully synthesized and subsequently mixed with variable concentration of PLA matrix using melt blending technique. The interfacial compatibilization between COPUP and PLA phase happened by the reaction of −NCO groups with terminal hydroxyl groups of PLA was confirmed by FT-IR peak deconvolution technique. As indicated by the results of DMA and DSC, the glass transition temperature (Tg) of both PLA and COPUP shifted closer together, indicating that the blend compatibility increased. The tensile properties and notched Izod impact strength of the PLA and toughened PLA are also investigated. With the addition of 30 % COPUP concentration, the elongation at break of the blend reached 377.46 %, and a notched Izod impact 269.62 J m-1. With improved toughness, the PLA/COPUP blends could be used as replacements for some traditional petroleum-based polymers. [ABSTRACT FROM AUTHOR]

This paper investigates the enhancement of fly ash-based geopolymer with chitosan biopolymer. Unconfined compression and split tensile tests were carried out to investigate the effect of addition of small amount of N-carboxymethyl chitosan (0.05, 0.1, 0.15, and 0.2 wt% of fly ash) on the mechanical performance of fly ash-based geopolymer. Scanning electron microscopy (SEM) imaging was also conducted to study the microstructure of the chitosan enhanced fly ash-based geopolymer. The results indicated that the inclusion of N-carboxymethyl chitosan led to slight increase of the unconfined compressive strength and substantial increase of the tensile strength, the displacement at the peak tensile load and the pre-peak toughness, with the maximum increases at 0.1 wt% chitosan content. The SEM imaging indicated that the added N-carboxymethyl chitosan biopolymer coated and bridged the (geopolymerized) fly ash particles and led to the formation of a more condensed geopolymer network structure, thus enhancing the mechanical behavior of the geopolymer-biopolymer composite. However, when too much N-carboxymethyl chitosan was used, the excessive coating and encapsulation of un-reacted and partially hydrolyzed fly ash particles hindered their geopolymerization and adversely affected the mechanical behavior of the geopolymer-biopolymer composite. [ABSTRACT FROM AUTHOR]

Dielectric, thermal, and electrocaloric investigations of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) copolymer, irradiated with high-energy electrons, are reported. While the ferroelectric copolymer is transformed into a relaxor system at high irradiation doses, dielectric investigations, particularly nonlinear dielectric experiments, i.e., temperature dependences of the second and the third harmonic dielectric response, clearly evidence that at lower doses ferroelectric and relaxor states coexist in the P(VDF-TrFE). This is confirmed by the differential scanning calorimetry, which further reveals the influence of irradiation on the copolymer crystallinity and melting point. Finally, it is shown that large electrocaloric response of VDF-TrFE-based polymers is further enhanced in systems with coexisting relaxor and normal ferroelectric states. [ABSTRACT FROM AUTHOR]

The use of native starch as a thermoplastic polymer is limited by its fragility and high moisture absorption. Native potato starch was derivatized using different agents in order to reduce its hydrophobicity. A reduction in starch mechanical properties was also found as a side effect of derivatization treatments. The addition of nanocellulose allows to considerably improve mechanical properties of biopolymers as well as to maintain their inherent biodegradation capability. Cellulose nanofibers were added to native and modified starch in order to improve the mechanical properties. The mechanical properties of starch/cellulose nanocomposite films were evaluated, finding that they considerably improved with the addition of cellulosic nanofibers. This contribution demonstrates a new approach in order to produce bioplastics with combined effect: improved moisture and heat resistance (due to the chemical treatment) and high mechanical properties (after the addition of nanocellulose). [ABSTRACT FROM AUTHOR]

The effects of high energy ball milling (HEBM) on the structure and some key-properties of crosslinked high density polyethylene (PEX) have been thoroughly examined with a combination of X-ray diffraction analysis, IR and Raman spectroscopy, differential scanning calorimetry, gel content measurements, and tensile properties tests. A structure-property relationship, which provides a reasonable explanation for the studied case has been developed based on the experimental results and their analysis. It is proposed that the HEBM provides some of the silane-grafted macromolecular chains, which have a specific orientation, with sufficient energy in order to crosslink and form small crystalline-like areas. The arrangement of chains in the 'reformed' domains leads to a total increase of the overall crystallinity, but also a decrease of the crystalline size. The proposed model can also support the fact that by increasing the milling time, the overall crystallinity of PEX and some important mechanical properties are found to increase. [ABSTRACT FROM AUTHOR]

The impact performance and resistance of toughness-tailored polypropylene (PP) impact copolymer (ICP) blends were examined using a range of microscopic techniques. The double-notch four-point bending (DN-4PB) Charpy impact technique was used to clearly study the impact-enhancement of the ICP blends responsible for the observed toughening effect. The incorporation of ethylene-octene copolymer with a lower molecular weight into the PP matrix induced the formation of massive crazes and shear yielding, leading to a more ductile PP matrix. A detailed investigation showed that well-oriented talc particles act in the PP matrix as stress concentrators to initiate massive crazes by crack deflection and bifurcation. These toughening mechanisms are responsible for the improved impact resistance. The DN-4PB Charpy impact technique used in this study provides an effective methodology for probing the impact fracture mechanisms of toughness-tailored ICP blends. [ABSTRACT FROM AUTHOR]

A series of poly( b-( t-butyl styrene)- b-(ethylene- co-propylene)- b-(styrene- co-styrene sulfonate)- b-(ethylene- co-propylene)- b-( t-butyl styrene)) ionomers were complexed with a series of metal ions. Raman sulfonate group symmetric ν(SO) and asymmetric ν(SO) stretching modes at 1031 and 1127 cm were proportional to ion-exchange capacity. Mono and divalent counter-ions of Li, Na, K, and Ca affected the stretching modes of ν(SO) due to ion size and charge. The gas permeability P and diffusivity D of O, CO, N, and CH decreased with increasing complexation strength between sulfonate group and metal ion. Solubility S was a maximum for ionomers complexed with K and CO, but small changes were observed for other metal ions. Overall, these results suggest that ionomers coordinated with different metal ions influence network physical properties, chain mobility, and gas transport. Graphical abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this study, fatigue damage behavior of (±753) filament wound composite pipes with a surface crack under alternating internal pressure was investigated. The specimens were tested at room temperature and exposed to open ended fatigue tests in which the pipe can be deformed freely in the axial direction. The tests were carried out in accordance with the ASTM D-2992 standard. The alternating internal pressure was generated by conventional hydraulic oil. The low cycle tests were performed with 0.42 Hz frequency and R = 0.05 stress ratio. Glass reinforced polymer pipes (GRP) are made of E-glass/epoxy and have (±753) configuration. Surface cracks were machined in the axial direction of the pipes which have depth-to-thickness ratios a/ t = 0.25–0.38–0.50 and depth to length ratio of a/c = 0.2. Tests were performed at three different loads of 50%, 40%, and 30% of ultimate hoop stress strength of unnotched pipes. The failure behavior of GRP pipes during the test was observed and fatigue test results were presented by means of ( S–N) curves and delamination damage zone area-cycle ( A– N) curves. [ABSTRACT FROM AUTHOR]