Farhan Ansari- PhD
- PostDoc Position at Stanford University
Farhan Ansari
- PhD
- PostDoc Position at Stanford University
About
26
Publications
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Introduction
Current institution
Publications
Publications (26)
Free standing and strong odor-removing composite films of cellulose nanofibrils (CNF) with a high content of nanoporous zeolite adsorbents have been colloidally processed. Thermogravimetric desorption analysis (TGA) and infrared spectroscopy combined with computational simulations showed that commercially available silicalite-1 and ZSM-5 have a hig...
Nanocomposites with high volume fractions (15–50 vol%) of nanofibrillated cellulose (NFC) were prepared by impregnation of a wet porous NFC network with acetone/epoxy/amine solution. Infrared spectroscopy studies revealed a significant increase in curing rate of epoxy (EP) in the presence of NFC. The NFC provided extremely efficient reinforcement (...
In this study, acetylated rye arabinoxylan (AcAX) films were reinforced with nanofibrillated cellulose from spruce (NFC) ranging from 1-10 weight% of the total composition. Free-standing composite films were casted without the use of any plasticizers. The homogeneous dispersion of NFC in the films was confirmed with scanning electron microscopy. Th...
Polysaccharides guar galactomannan (guar gum), locust bean galactomannan (locust bean gum) and tamarind galactoxyloglucan were selectively oxidized by galactose oxidase. The degrees of oxidation of the products were 18–28% for guar galactomannan, 10–16% for locust bean galactomannan and 12–14% for tamarind galactoxyloglucan, calculated from the rat...
Objectives
Emulsifier molecules, with their amphiphilic character, are ubiquitous in moisturizing creams and primarily serve to disperse the water‐insoluble molecules such as emollients, oils, lipids, and fats in water. The objective of this study was to investigate the effect of emulsifier molecules on the barrier and biomechanical properties of h...
Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle. Many biological materials realize this objective through multiscale (i.e., atomic‐ to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials. Inspired from the architecture of such biological...
Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle. Many biological materials realize this objective through multiscale (i.e., atomic‐ to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials. Inspired from the architecture of such biological...
A new type of high reinforcement content clay−cellulose−thermoset nanocomposite is proposed, where epoxy precursors diffuse into a wet porous clay−nanocellulose mat, followed by curing. The processing concept was scaled to >200 μm thickness composites, the mechanical properties were high for nanocomposites, and the materials showed better tensile p...
A critical aspect in materials design of polymer nanocomposites is the nature of the nanoparticle/polymer interface. The present study investigates the effect of manipulation of the interface between cellulose nanofibrils (CNF) and poly(methyl methacrylate) (PMMA) on the optical, thermal and mechanical properties of the corresponding nanocomposites...
We report on a sustainable route to protective nanocomposite coatings, where one of the components, nanocellulose fibrils, is derived from trees and the glass matrix is an inexpensive sol-gel organic-inorganic hybrid of zirconium alkoxide and an epoxy-functionalized silane. The hydrophilic nature of the colloidal nanocellulose fibrils is exploited...
Nanoscale building blocks of many materials exhibit extraordinary mechanical properties due to their defect-free molecular structure. Translation of these high mechanical properties to macroscopic materials represents a difficult materials engineering challenge due to the necessity to organize these building blocks into multiscale patterns and miti...
Cellulose nanocomposites can be considered for semi-structural load-bearing applications where modulus and strength requirements exceed 10 GPa and 100 MPa, respectively. Such properties are higher than for most neat polymers, but typical for molded short glass fiber composites. The research challenge for polymer matrix biocomposites is to develop p...
Tremendous efforts have been dedicated to developing effective and eco-friendly approaches for separation of oil-water mixtures. Challenges remain in terms of complex processing, high material cost, low efficiency, and scale-up problems. Inspired by the tubular porosity and hierarchical organization of wood, a strong, mesoporous, and hydrophobic th...
Mechanistic behavior and flow properties of cellulose nanofibers (CNFs) in aqueous systems can be described by the crowding factor and the concept of contact points, which are functions of the aspect ratio and concentration of CNF in the suspension. In this study, CNFs with a range of aspect ratio and surface charge density (380–1360 μmol/g) were u...
Polyurethane (PU) nanocomposites utilizing cellulose nanocrystals (CNCs) as nanofiller and amorphous PU matrix were synthesized in a novel solvent-free bulk process. A green nanofiller, CNCs, was studied as reinforcement and was further modified by grafting poly(ethylene glycol) (PEG) on the CNC surface (CNC-PEG). Transmission electron microscopy r...
The nematic structuring of cellulose nanofibers (CNFs) is proposed as a nanostructural engineering tool for exploiting the potential of CNFs in conceptually new “transparent papers”. The nematic-structured CNF papers exhibit...
Although the anisotropy of wood fibers is reasonably well established, the anisotropy of injection molded wood fiber composites is not well understood. This work focuses on chemo-thermomechanical pulp (CTMP) reinforced polypropylene (PP) composites. A kinetic mixer (Gelimat) is used for compounding CTMP/PP composites, followed by injection molding....
The nanocellulose fibril is the major load-bearing component in the wood cell wall. It is readily disintegrated from wood pulp, and of great interest as a component in new materials. It can be used to form 100% cellulose nanofiber (CNF) nanopaper films or polymer matrix nanocomposite films of high cellulose content, where the CNF network controls m...
Wide-spread use of cellulose nanofibril (CNF) biocomposites and nanomaterials is limited by CNF moisture sensitivity due to surface hydration. We report on a versatile and scalable interface tailoring route for CNF to address this, based on technically important epoxide chemistry. Bulk impregnation of epoxide-amine containing liquids is used to sho...
In this work, the problem to disperse cellulose nanocrystals (CNC) in hydrophobic polymer matrices has been addressed through application of an environmentally friendly chemical modification approach inspired by clay chemistry. The objective was to compare the effects of unmodified CNC and modified CNC (modCNC) reinforcement, where degree of CNC di...
Biocomposites reinforced by natural plant fibers tend to be brittle, moisture sensitive and have limited strength. Wood cellulose nanofibers (CNF) were therefore used to reinforce an unsaturated polyester matrix (UP) without the need of coupling agents or CNF surface modification. The nanostructured CNF network reinforcement strongly improves modul...
The morphology of polymer/nanofibrillated cellulose (NFC) composite sheets produced using different techniques and its influence on low strain stiffness were assessed by optical and transmission electron microscopy. Solvent processing led to relatively homogeneous NFC dispersions and significant reinforcement of the in-plane Young's modulus. The co...
The morphology of polymer/nanofibrillated cellulose (NFC) composite sheets produced using different techniques and its influence on low strain stiffness were assessed by optical and transmission electron microscopy. Solvent processing led to relatively homogeneous NFC dispersions and significant reinforcement of the in-plane Young's modulus. The co...
Questions
Questions (4)
If we calculate the strain hardening coefficient using the equation stress=K*strain^n, what do the terms K and n imply. I understand what their definition is and how to calculate them, but what is their physical significance. If we plot standard stress-strain curves on the same graph, is it possible to speculate as to which material has higher n or k? This is in context of polymer composites which show plastic deformation without macroscopic necking.
For ex, from fig 5 of this article
The conventional methods for determining K(IC) values cannot be applied to thin films as the plane strain conditions are not met. What is the next best way to characterize the stress intensity factor of such films in a reliable/repeatable way? Is there a detailed study on the dependance on the K(IC) values on the thickness? By what magnitude will the K(IC) values vary if the plane strain conditions are not met?
Why do properties of some polymers depend on the way in which the specimens are prepared. For ex, the extruded Polyvinyl Acetate sheets are much stronger (at least an order of magnitude) than the solution cast films.
PVAc (M WT 80000 Da), composite with nanocellulose fibrils prepared by solvent casting.
I observe a drastic decrease in the Tg of nanocomposites, 1 day after they are prepared; after which the Tg begins to recover slowly. Could both these phenomenon (sudden decrease and subsequent recovery) be explained by physical ageing? What experiments need to be carried out to ensure this?
The neat PVAc Tg is around 30 C and the composite Tg is 12 C, as measured from DSC. In the first thermal scans, I do not see a significant relaxation enthalpy.
