Janis G. Matisons

Evaluation of kinetic parameters of thermal and oxidative decomposition of base oils by conventional, isothermal and modulated TGA, and pressure DSC

Abstract Multigrade engine oils used in today’s sophisticated engines are carefully engineered products. Different ingredients, such as viscosity index improvers, dispersants, antioxidants, detergents, antiwear agents, pour point depressants, etc. are added to the base oils to improve their performance as lubricants, significantly. However, the ultimate performance of the lubricant principally depends on the quality of the base oil. Therefore, understanding the degradation behaviour of the base oil is of significant importance. In this study, the kinetic parameters of the decomposition of different types and grades of base oils (all-natural, fully synthetic and semi-synthetic) have been investigated in detail by conventional and isothermal thermogravimetric analyses (TGA) as well as modulated TGA (MTGA ® ). Pressure DSC (PDSC) has been employed to evaluate the spontaneous ignition and oxidative degradation behaviour of the base oils. Base oils with higher viscosity within the same grade tend to degrade at higher temperatures. It appears that the degradation of the oils studied can be modelled by an n th-order mechanism and have similar activation energies of degradation under an inert atmosphere. The all-natural base oil ALOR100 is more resistant to oxidation than the semi-synthetic Yubase4 and fully synthetic PAO4 due to the presence of naturally occurring antioxidants.

Influence of ethylene–propylene ratio on the thermal degradation behaviour of EPDM elastomers

The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene–propylene-diene (EPDM) elastomers was investigated using conventional non-isothermal and isothermal thermogravimetric analysis (TGA) as well as modulated thermogravimetric analysis (MTGA®). Kinetic parameters of degradation were evaluated using single heating rate data under a pseudo-first order assumption; the Flynn–Wall–Ozawa isoconversional method; isothermal methods; and MTGA®. Although the ethylene/propylene ratio influences the onset and peak temperatures of degradation, it appears that not only the ethylene content but microstructure is also a controlling factor in determining the activation energy of degradation. Pseudo-first order analyses show that at least two different first-order degradation reaction mechanisms dominate the degradation process. MTGA® analyses show that the activation energy of degradation increases throughout the reaction. Isothermal TGA confirms that the degradation processes for PE, PP and EPDM are complicated and do not follow an nth order reaction path, rather they follow a random degradation process.

Structural effects on the decomposition kinetics of EPDM elastomers by high-resolution TGA and modulated TGA

Effects of ethylene content and maleated EPDM content on the thermal stability and degradation kinetics of ethylene propylene diene monomer (EPDM) have been studied using high resolution thermogravimetric analysis (Hi-Res TGA) and Modulated TGA (MTGA). Modulated TGA shows that EPDM degradation is complex, with activation energy of degradation increasing throughout the degradation. Values from both dynamic and constant heating rate experiments are in good agreement with each other and with the literature value. However, the dynamic heating rate experiment shows that if the difference of peak temperature of components in a system is less than 5°C, Hi-Res TGA does not resolve them.

Characterization of elastomer compounds by thermal analysis

Abstract Thermal analysis provides very useful tools for the characterization and identification of both, elastomer compound and finished product. This investigation focuses on the use of different thermal techniques for compositional analysis, characterization of thermal, oxidative stability and glass-transition temperature ( T g ) of different components present in the elastomeric systems. Thermogravimetry (TG) is critical for identification of composition. TG analysis of three compositions ( S 1 , S 2 and S 3 ) shows S 1 and S 2 are soft-oil extended compounds and S 3 is a hard compound, all comprising ethylene propylene diene rubber (EPDM). Energy dispersive X-ray analysis (EDAX) of the residues from TGA reveals the presence of mineral filler clay in sample ( S 3 ) besides carbon black. The use of high-resolution TG has been found to give better resolution between overlapping weight loss steps leading to better quantification of various components compared to conventional TG. The coefficient of expansion of the rubber compound (from thermo-mechanical analysis – TMA) above T g is correlated to the hardness of the samples. The use of differential scanning calorimetry (DSC) to determine oxidative stability identifies also the presence of similar antioxidants. Dynamic mechanical analysis (DMA) is found to be very sensitive for characterization of glass-transition temperature, visco-elastic properties and, in particular, the adhesion between the elastomer compound and coating.

Aligned silane-treated MWCNT/liquid crystal polymer films

We report on a method to preferentially align multiwall carbon nanotubes (MWCNTs) in a liquid crystalline matrix to form stable composite thin films. The liquid crystalline monomeric chains can be crosslinked to form acrylate bridges, thereby retaining the nanotube alignment. Further post-treatment by ozone etching of the composite films leads to an increase in bulk conductivity, leading to higher emission currents when examined under conducting scanning probe microscopy. The described methodology may facilitate device manufacture where electron emission from nanosized tips is important in the creation of new display devices.

Weatherability of coated EPDM rubber compound by controlled UV irradiation

Polymeric composites for automotive window seal applications are generally exposed to complex service environment conditions. The fundamental physico-chemical processes that control the durability of such composite systems on a micro and macroscopic level were evaluated in the present case using thermal analysis (TA), elemental mapping and microscopy. Five diAerent EPDM rubber compounds (control, three bulk modified and one surface modified), coated with polyurethane coating were exposed to controlled UV irradiation. The higher the adhesion, the less the extent of UV penetration through the interface. The photo-oxidation mainly takes place from the surface, as the energy gets consumed and the intensity of the UV decreases on its passage through the strongly adhered layers to the rubber compound. The coating layer being on the surface, is more aAected and photodegraded by UV irradiation than the rubber compound. The sample P1cc, being multiphasic in nature and with a strong interface, can scatter the UV strongly and hence shows best weatherability among all the systems. # 2000 Elsevier Science Ltd. All rights reserved.

Deposition characteristics of ureido silane ethanol solutions onto E-glass fibres

The determination of the adsorption and the deposition characteristics of a silane monomer, which does not hydrolyse until it contacts the glass surface can be done by examining the effect of ultra dry solvent carriers. Most of the publications to date concentrate on amine and vinyl silanes. Many industrial processes use silanes with alternative organic functional groups, this study examines an industrial silane monomer with ureido functionality. The determination of how these monomeric, unhydrolysed silane solutions deposit, will improve our knowledge of the deposition behaviour of the much more complicated heterogeneous aqueous solutions. We have shown using diffuse reflectance Fourier transform infra red (DRIFT) how ureido silane deposition from ethanol results in the silane bonding in the OCH3 down orientation, with the ureido amine functions free for reaction with the polymer matrix. Furthermore, treatment with a series of solvents having solubility parameters which match (a) that of the unhydrolysed silane monomer and (b) that of the partially hydrolysed silane monomer can remove different fractions of the deposited silane and result in a certain amount of reorientation of the loosely bound physisorbed layers. X-ray photoelectron spectroscopy (XPS) results show that the silane was deposited in patches. Ultimately, precise control of the deposition conditions will determine the orientation of the silane monomer.

Chiral self-assembly of designed amphiphiles: influences on aggregate morphology.

A series of novel amphiphiles were designed for self-assembly into chiral morphologies, the amphiphiles consisting of a glutamic acid (Glu) headgroup connected through an 11-carbon alkoxy chain to a diphenyldiazenyl (Azo) group and terminated with a variable length alkyl chain (R-Azo-11-Glu, where R denotes the number of carbons in the distal chain). TEM imaging of amphiphile aggregates self-assembled from heated, methanolic, aqueous solution showed that chiral order, expressed as twisted ribbons, helical ribbons, and helically based nanotubes, increased progressively up to a distal chain length containing eight carbons, and then decreased with further increases in distal chain length. TEM and CD showed that the chiral aggregations of single enantiomers were influenced by the molecular chirality of the headgroup. However, the assembly of D,L-10-Azo-11-Glu into nanotubes demonstrated that chiral symmetry breaking effected by the azo group was also relevant to the chiral organization of the amphiphiles. The chiral order of aggregate morphologies was additionally affected by the temperature and solvent composition of assembly in a manner correlated to the mechanism driving assembly; i.e., D,L-10-Azo-11-Glu was sensitive to the temperature of assembly but less so to solvent composition, while L-14-Azo-11-Glu was sensitive to solvent composition and not to temperature. FTIR and UV-vis spectroscopic investigations into the organization of the head and azo groups, in chiral and achiral structures, illustrated that a balance of the influences of the hydrophilic and hydrophobic components on self-assembly was required for the optimization of the chiral organization of the self-assembled structures.

Development of an in vitro reproductive screening assay for novel pharmaceutical compounds

An in vitro reproductive cell‐based toxicity assay was developed using MLTC‐1 (murine Leydig tumour cell line) in order to examine the reproductive toxicity of two novel nanopharmaceutical compounds, namely ethylene glycol mono allyl ether and poly(ethylene glycol) octa‐functionalized polyhedral oligomeric silsesquioxane. Three commonly used cytotoxicity assays, namely the MTT [3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H ‐tetrazolium bromide], MTS [3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H ‐tetrazolium] and Crystal Violet assays, were compared, and the MTT assay proved to be the most accurate and reproducible for the MLTC‐1 cell line. The doubling rate of the MLTC‐1 cells was 30±3.5 h and the optimal seeding density for the MTT assay was 20000 cells per well, and the optimized MTT assay utilized a 4 h cell adherence followed by incubation with 0.5 mg/ml MTT for 1 h. The intra‐ and inter‐assay CV (coefficient of variation) values were 12.3 and 11% respectively. MLTC‐1 cells only produce the reproductive hormone progesterone in response to hCG (human chorionic gonadotropin), which stimulated progesterone production dose‐dependently from 0 to 100 m.i.u. (milliinternational units)/ml (2706±1118 ng/ml). H2O2 as a negative control killed 100% of cells at 1000 μg/ml. The two nanopharmaceutical compounds were cytotoxic at concentrations ≥0.1 μg/ml, but hCG decreased cytotoxicity to ≥1000 μg/ml (P <0.001). hCG‐stimulated progesterone synthesis afforded some protection against the cytotoxic effects of the two novel nanotechnology compounds; therefore doses ≤100 μg/ml and an exposure period of 1 h would be recommended for testing in in vivo animal reproductive assays.

Surface studies on the additive migration and diffusion in the windowseal rubber component influencing adhesion to coating

As rubber formulations are complex mixtures of different additives, many of them often migrate and diffuse to the surface, resulting in poor adhesion of windowseal rubber to coating. The present work was conducted to identify and quantify the diffusion behavior of additives of different rubber samples [masterbatch and final automotive ethylene propylene diene (EPDM) rubber compounds] using different complementary techniques such as contact angle measurements, X-ray photoelectron spectroscopy (XPS), size exclusion chromatography (SEC), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The influence of different methods of processing (milling and extrusion) on the diffusion behavior and change in rubber surface chemistry was investigated. Contact angle measurements using scanning Wilhelmy and sessile drop methods over prolonged time mainly showed an increase in the polar component of the surface energy for the samples, although the total surface energy did not change signi...