Search results for "Thermal Stability"

1990

New monomers are described for the synthesis of rod-like poly(1,4-phenyleneethynylene)s with long flexible aliphatic side chains. By palladium catalyzed polycondensation soluble polymers with melting points around 100°C could be obtained. The molecular weight was estimated by GPC, VPO and elemental analysis: GPC showed a multimodale distribution with Pn = 9–15. NMR spectra were found to be in agreement with the assumed polymer structure, but signals of the acetylenic carbons could not be detected. A broad, structureless absorption with a maximum at λ = 410 nm is seen in the UV-VIS-spectra. The thermal decomposition of the substituted PPE's starts at about 400°C and is comparable to that of …

Effect of the Biopolymer Charge and the Nanoclay Morphology on Nanocomposite Materials

2016

This work represents a contribution to the design, preparation, and characterization of nanocomposite materials based on biocompatible components. The effects of composition, filler geometry, and polymer charge were highlighted, and their role on the final properties of the nanocomposites was revealed. We combined some biopolymers (methylcellulose, alginate, chitosan) with two nanoclays (kaolinite sheets and halloysite nanotubes) to prepare nanocomposites by means of the casting method from water. The thermal stability, the surface wettability, and the mechanical properties of the obtained films were studied. SEM micrographs highlighted the surface morphology of the biocomposite materials. …

Impact of non-functionalized and ionic liquid modified carbon nanotubes on mechanical and thermal properties of ethylene- octene copolymer nanocompos…

2016

In this article the development and characterization of composites made from metallocene based ethylene-octene copolymer (EOC) with 38% octene content, non-modified or modified multi walled carbon nanotubes (MWCNTs), covalently functionalised with long chain hexadecyl moiety imidazolium ionic liquid (IL-f-MWCNTs), is presented. The procedure of MWCNTs functionalization is discussed. In order to obtain a good dispersion of the filler, composites with MWCNTs and IL-f-MWCNTs in the concentration range of 0.5-12 wt.% were made by ultrasonication / thermoplastic mixing method. The results indicated improvement in mechanical properties with increase of the filler content. The methodology of the d…

Selective photocatalytic oxidation of 3-pyridinemethanol on platinized acid/base modified TiO2

2021

TiO2 catalysts, modified with acidic or alkaline solutions and then platinized, were used for the partial photocatalytic oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B-3 under environmentally friendly conditions. The reaction took place in water under UVA light and air oxygen. Catalysts were characterized by TEM, photoluminescence, DRIFT-IR, Raman, DRS, XPS, and photocurrent measurements. The photocatalytic activity results show that Pt loading of untreated samples leads to a significant activity improvement (hence product yield) as much as acid and alkaline treatments do. Moreover, the alkaline treated TiO2 samples exhibit a further increase in activity after loading w…

Synthesis and properties of aromatic ionenes

1993

Cationic polyelectrolytes with aromatic segments can be synthesized by a repetitive alkylation reaction. The structure of the products, their synthesis and their solubility are described. All ionenes are not, or only in small amounts, water soluble. The best solubility can be achieved by mixtures of polar protic and aprotic solvents. Variations of the counterion produces sufficient solubility in THF. All ionenes show a typical polyelectrolyte effect. The thermal stability of aromatic ionenes and the glass transition temperature is dominated by the nature of the counterion. The molecular weight of oligomers can be described by using a combination of a conductive titration method and an ion s…

Electrically conductive TCNQ complexes of aromatic ionenes

1995

New types of complex salts of 7,7',8,8'-tetracyanoquinodimethane with aromatic ionenes and their model compounds were prepared. The electrical conductivity and the activation energy were measured and discussed in relation to their structure. The effects of the nature of the aromatic unit, and the flexibility and rigidity of the polymer backbone were compared with the corresponding model compounds. The effects of frequency and temperature are discussed in terms of the molecular structure of the complex. The electroconductivity at room temperature of the 1 :1 polymer complex salts was found to be between 2 x 10 -4 and 7 x 10 -5 S/cm, while that of the model complex salts was between 1.3 x 10 …

PBI-based composite membranes for polymer fuel cells

2010

Abstract In the present study poly(2,2-(2,6-pyridin)-5,5-bibenzimidazole) was used for the preparation of novel MEAs for high-temperature polymer fuel cells (HT-PEMFCs). We prepared hybrid materials with two types of silica fillers in order to increase the MEA performances using this polymer. The membranes were characterized in terms of their microstructure and thermal stability. Cell operation tests and Electrochemical Impedance Spectroscopy were used for the characterization of the MEAs. A maximum power density of about 80 mW cm−2 was obtained at 300 mA cm−2 by using an imidazole-modified silica filler. The EIS technique showed that the fillers chiefly help to reduce the charge transfer r…

The influence of counterions and hydrophobic moieties on the thermostability of Langmuir-Blodgett multilayers

1994

Abstract Langmuir-Blodgett (LB) multilayers with various counterions and different organic moieties (one- and two-chain fatty acids, polymeric acid) are prepared to investigate on line temperature-dependent structural changes and desorption by small-angle X-ray scattering (SAXS), interference-enhanced reflection and Nomarsky microscopy. On temperature increase a sequence of phase transitions can be observed. A crystalline LB film melts to a fluid phase and eventually desorbs either from droplets or from a homogeneous film. The phase sequence depends on the counterion: nickel stearate and magnesium stearate melt while the layered structure is conserved; SAXS measurements reveal a continuous,…

Sustainable nanocomposites based on halloysite nanotubes and pectin/polyethylene glycol blend

2013

Abstract This study was focused on the preparation and characterization of biofilms based on pectin/polyethylene glycol 20000 (PEG) blend and halloysite nanotubes (HNTs). The obtained blends loaded with a natural nanoclay are proposed as sustainable alternative to the polymers produced from non-renewable resources such as fossil fuels. Properties of technological interest have been monitored and they were correlated to the structural features of the nanocomposites. It turned out that the wettability of the films can be tuned by changing the composition and the distribution of HNTs into the material as well as the surface roughness. The tensile properties of the blend are enhanced by the pre…

Effect of small amounts of poly(lactic acid) on the recycling of poly(ethylene terephthalate) bottles

2011

Abstract Poly(ethylene terephthalate) (PET) is one of the most used commodity polymers, especially for food and beverage applications, and its recycling is of great importance because of the possible use in the textile and construction industries. On the other hand, the interest in biodegradable polymers has led, in recent years, to the use of materials such as poly(lactic acid) (PLA) also in the food and beverage industry. The presence of small amounts of PLA in the PET waste can significantly affect the post-consumer recycling process. In this work, the effect of the presence of small amounts of PLA on the recycling of PET bottles is investigated by rheological, mechanical, morphological …