Mohd Nashrul Mohd Zubir

Basic effects of pulp refining on fiber properties—A review

The requirement for high quality pulps which are widely used in paper industries has increased the demand for pulp refining (beating) process. Pulp refining is a promising approach to improve the pulp quality by changing the fiber characteristics. The diversity of research on the effect of refining on fiber properties which is due to the different pulp sources, pulp consistency and refining equipment has interested us to provide a review on the studies over the last decade. In this article, the influence of pulp refining on structural properties i.e., fibrillations, fine formation, fiber length, fiber curl, crystallinity and distribution of surface chemical compositions is reviewed. The effect of pulp refining on electrokinetic properties of fiber e.g., surface and total charges of pulps is discussed. In addition, an overview of different refining theories, refiners as well as some tests for assessing the pulp refining is presented.

Transformer oil based multi-walled carbon nanotube–hexylamine coolant with optimized electrical, thermal and rheological enhancements

In a one-pot microwave-assisted method, multi-walled carbon nanotubes (MWNT) are functionalized with hexylamine (HA). Based on FT-IR, TGA-DTG, Raman, EDS, CHNS/O and TEM results, the functionalization of MWNT with HA was confirmed . The effect of microwave-assisted functionalized MWNT with HA charged transformer oil at different concentrations was experimentally investigated for electrical, thermal and rheological properties. According to the breakdown voltage, flash point, density, electrical conductivity, thermal parameters and viscosity results of the synthesized transformer oil-based coolants they could be an appropriate alternative for different transformers operating at a nominal voltage less than 170 kV.

Mass production of highly-porous graphene for high-performance supercapacitors

This study reports on a facile and economical method for the scalable synthesis of few-layered graphene sheets by the microwave-assisted functionalization. Herein, single-layered and few-layered graphene sheets were produced by dispersion and exfoliation of functionalized graphite in ethylene glycol. Thermal treatment was used to prepare pure graphene without functional groups, and the pure graphene was labeled as thermally-treated graphene (T-GR). The morphological and statistical studies about the distribution of the number of layers showed that more than 90% of the flakes of T-GR had less than two layers and about 84% of T-GR were single-layered. The microwave-assisted exfoliation approach presents us with a possibility for a mass production of graphene at low cost and great potentials in energy storage applications of graphene-based materials. Owing to unique surface chemistry, the T-GR demonstrates an excellent energy storage performance, and the electrochemical capacitance is much higher than that of the other carbon-based nanostructures. The nanoscopic porous morphology of the T-GR-based electrodes made a significant contribution in increasing the BET surface as well as the specific capacitance of graphene. T-GR, with a capacitance of 354.1 Fg−1 at 5 mVs−1 and 264 Fg−1 at 100 mVs−1, exhibits excellent performance as a supercapacitor.

Development of novel hybrid flexure-based microgrippers for precision micro-object manipulation

This paper describes the process of developing a microgripper that is capable of high precision and fidelity manipulation of micro-objects. The design adopts the concept of flexure-based hinges on its joints to provide the rotational motion, thus eliminating the inherent nonlinearities associated with the application of conventional rigid hinges. A combination of two modeling techniques, namely, pseudorigid body model and finite element analysis was utilized to expedite the prototyping procedure, which leads to the establishment of a high performance mechanism. A new hybrid compliant structure integrating cantilever beam and flexural hinge configurations within microgripper mechanism mainframe has been developed. This concept provides a novel approach to harness the advantages within each individual configuration while mutually compensating the limitations inherent between them. A wire electrodischarge machining technique was utilized to fabricate the gripper out of high grade aluminum alloy (Al 7075T6). Experimental studies were conducted on the model to obtain various correlations governing the gripper performance as well as for model verification. The experimental results demonstrate high level of compliance in comparison to the computational results. A high amplification characteristic and maximum achievable stroke of 100 microm can be achieved.

Investigation on the use of graphene oxide as novel surfactant to stabilize weakly charged graphene nanoplatelets

This paper presents a unique synergistic behavior between a graphene oxide (GO) and graphene nanoplatelet (GnP) composite in an aqueous medium. The results showed that GO stabilized GnP colloid near its isoelectric point and prevented rapid agglomeration and sedimentation. It was considered that a rarely encountered charge-dependent electrostatic interaction between the highly charged GO and weakly charged GnP particles kept GnP suspended at its rapid coagulation and phase separation pH. Sedimentation and transmission electron microscope (TEM) micrograph images revealed the evidence of highly stable colloidal mixtures while zeta potential measurement provided semi-quantitative explanation on the mechanism of stabilization. GnP suspension was confirmed via UV-vis spectral data while contact angle measurement elucidated the close resemblance to an aqueous solution indicating the ability of GO to mediate the flocculation prone GnP colloids. About a tenfold increase in viscosity was recorded at a low shear rate in comparison to an individual GO solution due to a strong interaction manifested between participating colloids. An optimum level of mixing ratio between the two constituents was also obtained. These new findings related to an interaction between charge-based graphitic carbon materials would open new avenues for further exploration on the enhancement of both GO and GnP functionalities particularly in mechanical and electrical domains.

Sustainability and environmental impact of ethanol as a biofuel

Abstract Biofuels are acting as a renewable replacement for petroleum fuels due to some environmental and economic benefits. They are prepared by blending a major portion of diesel fuel and a certain minor percentage of bio-oils, which provides less greenhouse gas (GHG) compared to pure diesel. Recently, bioethanol has been the most widely used biofuel for transportation. Bioethanol can be produced from different kinds of agricultural raw materials classified into three categories: simple sugars, starch, and lignocellulose. Use of bioethanol-blended gasoline fuel for automobiles can significantly reduce petroleum use and exhaust GHG emission. Bioethanol from sugar cane, produced under the proper conditions, is essentially a clean fuel and has several clear advantages over petroleum-derived gasoline in reducing GHG emissions and improving air quality in metropolitan areas. However, there remains a compromise between GHG emission and saving of fossil fuel energy by introducing bioethanol either totally or as a blending component of engine fuel. Thus, considering biofuel as a replenishable energy source, the future pathway of energy management could be planned.

Experimental investigation on the use of highly charged nanoparticles to improve the stability of weakly charged colloidal system

The present work highlighted on the implementation of a unique concept for stabilizing colloids at their incipiently low charge potential. A highly charged nanoparticle was introduced within a coagulated prone colloidal system, serving as stabilizer to resist otherwise rapid flocculation and sedimentation process. A low size asymmetry of nanoparticle/colloid serves as the new topic of investigation in addition to the well-established large size ratio nanoparticle/microparticle study. Highly charged Al2O3 nanoparticles were used within the present research context to stabilize TiO2 and Fe3O4 based colloids via the formation of composite structures. It was believed, based on the experimental evidence, that Al2O3 nanoparticle interact with the weakly charged TiO2 and Fe3O4 colloids within the binary system via absorption and/or haloing modes to increase the overall charge potential of the respective colloids, thus preventing further surface contact via van der Waals attraction. Series of experimental results strongly suggest the presence of weakly charged colloids in the studied bimodal system where, in the absence of highly charged nanoparticle, experience rapid instability. Absorbance measurement indicated that the colloidal stability drops in accordance to the highly charged nanoparticle sedimentation rate, suggesting the dominant influence of nanoparticles to attain a well-dispersed binary system. Further, it was found that the level of colloidal stability was enhanced with increasing nanoparticle fraction within the mixture. Rheological observation revealed that each hybrid complexes demonstrated behavior reminiscence to water with negligible increase in viscosity which serves as highly favorable condition particularly in thermal transport applications.

Heat transfer enhancement of water-based highly crumpled few-layer graphene nanofluids

Backward-facing step heat transfer of transitional and turbulent flows occurs in many industrial applications. The heat transfer performances of different multiphase working fluids over a backward-facing step in the transitional and turbulent flow regimes, however, have not been fully investigated experimentally. Recently, highly crumpled few-layer graphene (HCFLG) with a high surface area has been introduced as a promising additive for preparing nanofluids for high performance heat transfer applications. In this work, the heat transfer properties of the HCFLG nanofluids were studied experimentally. The HCFLG was prepared by exfoliation of graphite in the presence of liquid-phase using microwave-assisted methods, which was shown to be industrially-scalable, cost-effective, and simple. Then the HCFLG was used for fabricating a new class of water-based graphene nanofluid for use in large-scale heat transfer equipment. The prepared water-based HCFLG nanofluids were shown to be stable with less than 2% sedimentation after 30 days. In addition, the measured thermophysical properties indicated that the water-based HCFLG nanofluids have huge potential for high performance heat transfer applications. Finally, the water-based HCFLG nanofluids were shown to be significantly more effective in the duct with a backward-facing step in terms of overall thermal performance including the local Nusselt number (Nu), convective heat transfer coefficient, performance index, pumping power, and rheological properties such as effective viscosity in comparison to distilled water.

Investigation on the Use of Graphene Oxide as Novel Surfactant for Stabilizing Carbon Based Materials

The present work reported on the use of graphene oxide (GO) as effective dispersant to isolate different carbon allotropes. The nature of its chemical structure which consists of hydrophobic and hydrophilic components enables GO to behave as surfactant, paving routes for dissolution of graphitic materials and achieving surfactant free all-carbon solutions. Two additional carboneous materials under the family of fullerene (carbon nanofiber—CNF) and graphite (graphene nanoplatelets—GnP) were introduced within the present study to form a new GO based hybrid complexes on top of the commonly investigated carbon nanotube (CNT) based GO hybrid. Investigation on GO stability with respect to particle size and zeta potential measurements showed that the strength of its dispersibility was highly dependent on its morphological size and less affected by the pH. Rheological study revealed that GO shear–strain relationship is highly sensitive to the particle size. The GO viscosity experienced dramatic changes from Newtonian toward shear thinning behaviors as the particle size increases. Thermal conductivity measurement highlighted as high as 8% increase in magnitude with the addition of CNT, CNF, and GnP carbon constituents, indicating that the enhancement may be attributed to the much efficient thermal transport along the conducting path of pristine carbon allotropes. GRAPHICAL ABSTRACT

Experimental investigation of heat transfer performance and frictional loss of functionalized GNP-based water coolant in a closed conduit flow

The convective heat transfer coefficient and friction factor for fully developed turbulent flow of trimethylolpropane tris[poly(propylene glycol), amine terminated] ether-treated graphene nanoplatelet (TMP-treated GNP)-based water coolants are experimentally determined at constant velocity flowing through a horizontal copper tube with uniform heat fluxes. The TMP-treated GNP was first analyzed in terms of structure and morphology to confirm the GNP functionalization with TMP. The colloidal stability of TMP-treated GNP-based water coolant shows the high potential of the coolants for using in heat transfer equipment. Then, the experiments were conducted at a Re range of 3900–11700 at constant velocity flow (1–3 m s−1) and concentrations of 0.025 wt% to 0.1 wt%. The enhancement in thermal conductivity for TMP-treated GNP-based water coolants was between 20% and 31% compared to the basefluid. The convective heat transfer coefficient for the TMP-treated GNP-based water coolant was found to be up to 107% higher than the basefluid. The Nusselt number increased up to 72% at a heat flux of 23870 W m−2. However, the friction factor drop increases simultaneously in the range 4–10%. The results suggest that TMP-treated GNP-based water coolants could function well as working fluids in heat transfer applications and provide good alternatives to conventional working fluids.