Pratheep Kumar Annamalai

Easily deconstructed, high aspect ratio cellulose nanofibres from Triodia pungens; an abundant grass of Australia's arid zone

The production of high aspect ratio cellulose nanofibres without resorting to very harsh mechanical and/or chemical processing steps remains a challenge that hinders progress in the fast-moving nanocellulose field. In response to this challenge, herein we report the preparation of high aspect ratio (>500) and small diameter (<8 nm) cellulose nanofibrils through the deconstruction of Australian native ‘spinifex’ grass (Triodia pungens) by applying very mild pulping conditions combined with only one pass of high pressure homogenization. Spinifex grass has an unusually high hemicellulose content, which facilitates this easy fibrillation process. Tensile measurements of the nanopaper produced by vacuum filtration indicated a high toughness of about 12 MJ m−3, a tensile strength of 82 MPa and a high elongation at break of 18%. The transverse elastic modulus of single nanofibrils analysed by AM-FM is in the range of 19–24 GPa. Under these mild processing conditions, Triodia pungens nanofibrils retained their crystallinity.

Understanding the ageing aspects of natural ester based insulation liquid in power transformer

Cellulose based insulation materials and mineral oils have widely been used in liquid filled transformers. Environmental and fire-safety concerns have accelerated the use of Natural Esters (NE) as a sustainable alternative to mineral oil. There is a rapid growth of their application for distribution level transformers. To ensure a safe and long-term operation of the vegetable oil filled transformers, it is necessary to clarify the knowledge gaps with respect to the ageing of vegetable oil impregnated cellulose and insulation diagnostic methods. The condition monitoring of mineral oil filled transformers has been well characterised, due to the numerous laboratory and field studies conducted during the past several decades. The application of these available condition monitoring techniques for NE filled transformers is yet to be validated as the use of NE for power transformers is in the evaluation stage. In this paper the performance of NE as insulation in transformers by evaluating the ageing of NE impregnated cellulose pressboard is presented. For this purpose, an accelerated ageing experiment has been carried out in sealed tubes at 120 °C. The ageing of oil impregnated pressboard has been characterised by decrease in the degree of polymerisation (DP) of pressboard, and the formation of both 2-furfuraldehyde and dissolved carbon dioxide (CO2) in the oil. The structural changes of cellulose have been supported by Fourier Transform Infrared (FTIR) spectra. Moreover, the results have been compared with cellulose insulation samples aged under similar conditions in conventional mineral oil. Acidity value, dissipation factor and viscosity measurements have been used to compare the stability of NE in a transformer operating environment to mineral oil.

Production of cellulose nanocrystals via a scalable mechanical method

The production of rigid rod-like cellulose nanocrystals (CNC) via more scalable methods is necessitated by an increasing demand for CNC in various industrial sectors over the last few years. Contemporary protocols involve the consumption of large amounts of strong acids, enzymatic treatments, ultra-sonication and combinations thereof. In an attempt to address this scalability challenge, we aimed to isolate CNC via a scalable mechanical method i.e. high energy bead milling (HEBM). An aqueous dispersion of commercially available microcrystalline cellulose (MCC) was micronized through a HEBM process. This process was optimised by varying the concentration (0.5–2 wt%) and time (15–60 min) parameters, in order to obtain a high yield of well-separated CNCs as characterised by transmission electron microscopy (TEM). Micronisation of cellulose via the HEBM method under mild conditions resulted in cellulose nanocrystals with an average aspect ratio in the range of 20 to 26. The nanocrystals also retained both their crystallinity index (ICr) (85 to 95%) and thermal stability described in terms of onset degradation temperature (Tonset) (230–263 °C). The production yield of CNC from MCC via this process ranged between 57 and 76%. In addition, we found that micronisation of the MCC in the presence of dilute phosphoric acid also resulted in CNC with an average aspect ratio ranging from 21 to 33, high crystallinity (88–90%) and good thermal stability (Tonset 250 °C). In this study, we demonstrate the micronisation of commercially available MCC into CNC and describe their dimensions and properties after acid treatment and HEBM. Furthermore, we are able to recommend the use of this scalable milling process to produce rod-like cellulose nanocrystals having a thermal stability suitable to withstand the melt processing temperatures of most common thermoplastics.

Spinifex nanocellulose derived hard carbon anodes for high-performance sodium-ion batteries

The selection of an appropriate anode material is a critical factor in dictating the effectiveness of sodium-ion batteries as a cost-effect alternative to lithium-ion batteries. Hard carbon materials sourced from biomass offer the potential for a more sustainable anode material, while also addressing some of the thermodynamic issues associated with using traditional graphite anodes for sodium-ion batteries (NIBs). Herein, we report the preparation of carbon electrode materials from low-cost cellulose nanofibers derived from an Australian native arid grass ‘spinifex’ (Triodia pungens). This nanocellulose derived carbon produced by a fast, low temperature carbonization protocol showed superior performance as an anode for NIBs with a specific capacity (386 mA h g−1 at 20 mA g−1) on par with that of the graphite based anode for lithium-ion batteries, and is one of the highest capacity carbon anodes reported for NIBs. The excellent electrochemical performance is attributed to the large interlayer spacing of the carbon (∼0.39 nm). Superior cycling stability and high rate tolerance (326 mA h g−1 at 50 mA g−1 and 300 mA h g−1 at 100 mA g−1) suggest that hard carbons derived from sustainable precursors are promising for next generation rechargeable batteries.

Can clay nanoparticles accelerate environmental biodegradation of polyolefins

Abstract Synthetic polyolefins have been used in an enormous array of applications in the modern society, due to a combination of reliable raw materials, low cost processing, tailorable mechanical properties, low density and inertness or stability towards environmental factors. In the last two decades, with the concern of sustainable development, these polyolefins have necessitated further research into: i) finding alternative or renewable raw materials resources, ii) developing polymeric materials from renewable feedstocks that are capable of giving rise to comparable performance to the petrochemical based polymer counterparts and iii) triggering the biological degradation of polyolefins. In order to overcome the issues associated with waste accumulation and disposal, the biological recycling or degradation in the landfill or soil burial, composting and sewage have all been considered as less energy consuming, less toxic and environmentally friendly ways of sustainably managing the life cycle of high volume commodity polymers. It has also been well accepted that an abiotic oxidation (photo-, thermo-oxidation) is a prerequisite for enhancing the biodegradability or biological accessibility of polyolefins. For this purpose, several pro-oxidant approaches have been reported. The present paper reviews how the natural or synthetic clay nanoparticles, which are potential nanoscale fillers recently used for reinforcing polymers, can affect or enhance the biodegradability of polyolefins. They have also been discussed from the perspective of nanocomposite materials with controlled degradability and their associated applications.

Biopolymeric Nanocomposites as Environment Benign Materials

In the twenty-first century, major changes are coming and materials will be a key enabling technology. Fuel economy, consumption, and demand for high-performance light-weight materials are pressurizing the industrialists. The maximum possible use of renewable resources is gaining attention as an alternative to petroleum resources. On the other hand, reinforcement of polymers with nanoscale particulates has gained a massive attraction from the researchers in academia and industries, because of the exponential improvement in physical, mechanical, and thermal properties with smaller amount of incorporation. For a global commercialization of these materials, the environmental concerns such as raw materials, energy use, recycling, and disposal (especially via biodegradation) are also to be envisioned. Thus, this chapter is intended to review the recent research activities in the area of nanocomposites using biopolymers that include polymers derived from renewable resources. General preparation methods, structure–property relationships, and biodegradability of these nanocomposites have been discussed in the context of environmental benignness.

Effect of pressboard ageing on power transformer mechanical vibration characteristics

Power transformer winding clamping pressure is a critical parameter, which is directly related to transformer short circuit ride through capability. Mechanical impacts generated on the winding structure during short circuit faults, switching surges and other high current faults have a significant impact on the winding clamping structure and could lead to reduce the clamping pressure. The change in clamping pressure influences the vibration behaviour of winding structure. Hence, variations in clamping pressure can be assessed by monitoring the transformer vibrations. However, it has been observed that, not only progressive loss of clamping pressure but also solid insulation ageing has a significant influence on the winding vibration characteristics. Therefore, for a proper analysis of transformer vibration a clear understanding of the effect of solid insulation ageing on vibration behaviour of transformer winding structure is essential. This study aims to investigate the sensitivity of the transformer winding vibration characteristics to ageing of solid insulation material. Variations in modal parameters of winding structure with solid insulation ageing is studied using Finite Element Modelling (FEM). Results are used to discuss the sensitivity of winding vibrations to solid insulation ageing.

Polymers from biomass: characterization, modification, degradation, and applications

1DBT-IOC Centre for Advanced Bioenergy Research, Indian Oil R&D Center, Sector 13, Faridabad 121007, India 2Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia 3Chemical Engineering Department, University of Louisiana at Lafayette, Lafayette, LA 70504, USA 4Department of Food Engineering, Mokpo National University, Jeonnam 534-729, Republic of Korea

Synthesis and characterization of cellulose nanocrystals as reinforcing agent in solely palm based polyurethane foam

The increasing awareness of the environment and the economy of petroleum resources has driven the development of alternative processes and raw materials based on sustainable and renewable biomaterials with excellent properties. This study is aimed to use biologically renewable cellulose nanocrystals (CNC) as reinforcing agent to enhance the properties of polyurethane foams (PUF) based on solely palm-polyol. Rod-like shape cellulose nanocrystals (CNC) was successfully isolated from cotton based resources via strong acid hydrolysis with the average width, length and aspect ratio about 14.7 ± 4.9 nm, 167.7 ± 23.2 nm and 11.4, respectively. The crystallinity of CNC was confirmed by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) and was found at 82.8% and 83.8%, respectively. This obtained cellulose nanocrystals (CNC) at a loading of 0.4 wt. % was then incorporated via solvent-free sonication method in the model of palm based polyurethane foam. The preliminary results showed that the effect of CNC on the mechanical properties afforded a significant improvement on the compressive strength and modulus without affecting much their tensile strength. The results on thermal stability and thermal transitions were found unchanged whereas the storage modulus revealed substantial improvement with the presence of CNC with almost two fold from 0.7 MPa to 1.3 MPa (∼86 %).

Influence of moisture dependency of pressboard on transformer winding clamping pressure

Short circuit (SC) strength of a power transformer is influenced by its winding clamping pressure. The required level of clamping pressure is selected at the design stage based on the maximum allowable SC current level of the transformer. Progressive loss of clamping pressure is a common problem in power transformers. Shrinkage and fading of the stiffness of solid insulation due to thermal degradation are the most common causes of this problem. It has also been identified that changes in the moisture content and repetitive compression cycles on pressboard during high current faults tend to change the winding clamping pressure. This study aims to investigate the effects of moisture and compression cycles on winding clamping pressure through a set of laboratory experiments and finite element analyses. Thickness change and compressive stress-strain curves of pressboard were measured under different moisture conditions. The results were then used to calculate changes in winding geometry and clamping pressure of a 100 kVA three phase, disc type transformer winding.