N. Roy Choudhury

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.

High-Resolution Solid State NMR Investigation of the Filler-Rubber Interaction: Part III. Investigation on the Structure and Formation Mechanism of Carbon Gel in the Carbon Black-Filled Styrene—Butadiene Rubber

Abstract This investigation describes the elastomer—filler interaction and its formation mechanism using solid state high-resolution, high-speed 1H magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Pulsed NMR measurements were carried out on pure styrene-butadiene rubber (SBR), and solvent extracted carbon gels from freshly prepared and storage matured master batches. The effects of filler loading, storage maturation, severity of extraction and experimental temperature on the elastomer-filler interaction were examined and discussed. High resolution in NMR was achieved by higher temperature/low spinning rate, room temperature/high spinning and combined rotation and multiple-pulse spectroscopy (CRAMPS) techniques. High-speed magic-angle spinning (MAS) was found to be the most suitable method to achieve high resolution. Proton spin—spin relaxation time, T2, was measured successfully for each of the principal resonance species present in the samples. These measurements reveal an insight into...

Surface finish of injection molded materials by micro-thermal analysis

Abstract In typical injection molding processes, surface defects are often encountered, yielding products of inferior part quality. In an effort to identify and eliminate any unwanted finish, surface defects have been created consistently by injection molding and examined via the use of a new technique known as micro-thermal analysis (μTA™). μTA™ is an analytical form of microscopy that combines atomic force microscopy (AFM) and differential thermal analysis (DTA). The experiment was performed on polycarbonate/acrylonitrile-styrene-acrylate (PC/ASA) injection molded parts, using thermal probes. Surface defects, such as variations in gloss level, were produced on injection molded plaques by changing molding parameters including material temperature and packing pressure. μTA™ results reveal that rubber particle aggregation is one of the reasons for lowering the parts surface finish, also that scans performed at elevated temperatures, show that there were no changes in the polymer’s multiphase morphology. Additionally, depth profiling by μTA™ established that PC and ASA are rich at the outermost surface of regions that possess a dull finish, whilst PC is the dominant material in regions of high gloss.

Probing the interface behaviour of injection molded thermoplastics by micro-thermal analysis and temperature-modulated differential scanning calorimetry

Micro-thermal analysis (mTAe) and temperature-modulated differential scanning calorimetry (TMDSC) are emerging as powerful instruments for identifying the existence and quantities of phases in multi-component systems, as well as interfacial properties. In this study, these two complimentary techniques are utilised to probe the interphase behaviour of a polycarbonate/acrylonitrile – styrene – acrylate (PC/ASA) blend as they develop during injection molding. Micro-thermal analysis revealed that parts manufactured at high injection time, pack pressure and melt temperature show a densely packed bulk morphology, a significant amount of particle agglomeration as well as the formation of styrene – acrylonitrile/PC (SAN/PC) interphases. TMDSC qualitatively and quantitatively characterized the PC/ASA’s multiphase morphology and its interfacial properties both before and after injection molding, indicating a greater amount of PC entering the interphase than SAN. q 2003 Elsevier Science Ltd. All rights reserved.

Viscoelastic behaviour of filled, and unfilled, EPDM elastomer

Abstract The viscoelastic behaviour of gum and a highly filled ethylene-propylene terpolymer (automotive windowseal component) at 138 parts carbon black loading was investigated using a dynamic mechanical analyser over a wide range of time, temperature, strain and frequency. The tensile stress relaxation and recovery results of the gum system show time-dependent but strain-invariant behaviour, whereas the filled system shows both strain and time dependence. The relaxation time spectrum of the filled system reveals nonlinear viscoelastic behaviour. The networks of carbon black formed at such a high loading contribute significantly to the relaxation process. The 3D plot of tensile modulus as a function of time and temperature for both the systems follow a similar trend, and even for short-time testing the highly filled system appears to be time–temperature superposable.

Matching cure characteristics of automotive rubber compound and polyurethane coating

The present investigation focuses on matching cure characteristics of EPDM rubber compound and polyurethane (PU) coating using temperature modulated and pressure differential scanning calorimetry (TMDSC, PDSC).TMDSC provides a detailed and better understanding of the curing process of model rubber system as well as complex automotive rubber compounds. The low level of unsaturation present in EPDM, results in the small heat of vulcanization (2–5 J g–1), which is difficult to accurately measure using conventional differential scanning calorimetry (DSC). Thus, curing of highly filled EPDM compound was investigated using TMDSC.The kinetics of PU curing was monitored using pressure DSC (PDSC), and heat of curing was determined as 4.2 J g–1 at 10°C min–1 heating rate. It is found that complex automotive compounds and the PU coating are curing simultaneously.

Prediction of Viscoelastic Behaviour of Thermorheologically Complex Polymeric Materials

A simplified numerical computational technique based on a Gaussian spectral distribution model developed by Dutta and Edward [1] has been used to describe the stress relaxation behavior of polystyrene (PS) and isotactic polypropylene (iPP) over a wide range of time and temperature. An excellent fit between experimental data and the mathematical model is observed. The method may be applied generally for any linear viscoelastic property and for any polymer.

Polymer stabilized noble metal colloids for catalytic and biomedical applications

The nanoparticles of noble metal have attracted enormous interest due to their high catalytic, optical, magnetic and antimicrobial properties. Controlled growth and stabilization of these nanoparticles are essential for their diverse applications. In this work, platinum, and silver nanoparticles are grown onto ordered non-fluoro ionomers and dendrimer for catalytic and antimicrobial applications. This paper thus provides insight on the utilization of dendrimer compartment or ionic domains of non-fluoro ionomers for stabilizing these nanoparticles. UV/vis and TEM results confirm the size and the size distribution of the formed particles. In both cases, ionic domains or the dendrimers result in the stabilization of the colloids. TEM images indicate that platinum nanoparticles grown on ordered non-fluoro ionomers results in highly dispersed particles of small size 2-3 nm, while in dendrimer 8-10 nm silver colloids are formed. All of the synthesized dendrimer based silver complexes are proved to be effective antimicrobial agents in vitro and the platinum nanoparticles exhibit specific electrochemical activities.

APPLICATION OF MICROTHERMAL ANALYSIS AND PULSED FORCE MICROSCOPY TO CHARACTERIZE NANOSTRUCTURED POLYMER

In this investigation, we present the first results of Microthermal analysis (MicroTA) and Pulsed-Force-Mode (PFM) scanning force microscopy employed for visualization and characterization of nanostructured side-chain crystalline polymeric material. PFM was employed to clearly visualize the interesting self-organizing characteristics and the intimate contact of crystalline order as well as amorphous disorder in such polymer. As the sample was heated above the melting point, the well-defined crystalline regions observed at lower temperature no longer exist, and diffused melt boundaries are clearly observed using PFM. The nanophase separated system undergoes a sharp change in its adhesion and stiffness properties with temperature below and above the crystal melting point. Local thermal analyses using MicroTA exhibit consistent rapid crystal melting curves and its lateral homogeneity.