Rafael L. Quirino

Matrices from vegetable oils, cashew nut shell liquid, and other relevant systems for biocomposite applications

The partial replacement of petroleum-derived plastics and composites by novel bio-based materials from inexpensive, renewable, natural resources has the potential to greatly impact the plastics, coatings, and composites industries. Natural starting materials are usually abundant and renewable on a time scale many orders of magnitude smaller than petroleum. These characteristics, in combination with good mechanical properties, make the design of bio-based composites an interesting strategy for lowering the environmental impact of the plastics and composites industries while maintaining economical competitiveness. The present review will focus on the progress made over the last decade in the development of a select group of bio-based matrices for biocomposite applications. The text is organized into sections that describe a matrix system and its many reinforcements. The matrices covered in this review include composites from vegetable oils, cashew nut shell liquid, and a brief overview of other currently academically relevant bio-based matrix systems, such as polysaccharides, polylactide (PLA), polyhydroxyalkanoates (PHAs), proteins, and lignin.

Oxidation behavior of multiwalled carbon nanotubes fluidized with ozone.

Multiwalled carbon nanotubes (MWCNTs) were simultaneously fluidized and oxidized with gaseous ozone in a vertical reactor. Two different varieties of MWCNTs were compared to determine the versatility of the treatment and to elucidate the effect of defects on the oxidation behavior of MWCNTs. The extent of oxidation and nature of functional groups introduced on the nanotube surfaces were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Boehm titration, and structural changes were monitored with Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). After only a few minutes of treatment, nongraphitic impurities were removed from the MWCNTs, and significant levels of oxidation (∼8 atom % O) were achieved with very little damage to the nanotube sidewalls. Short O3 exposure resulted in primarily hydroxyl functionalities, whereas longer exposure led to the formation of mainly carboxylic acid groups. Aliphatic defects present in the commercially produced MWCNTs were found to play an important role in the oxidation mechanism. Because of its ability to remove impurities and to evenly oxidize the sidewalls of nanotubes without the use of any solvents, the fluidized O3 reaction developed in this study was found to be an attractive option for industrial-scale MWCNT functionalization.

Bio-Based Polymers with Potential for Biodegradability

A variety of renewable starting materials, such as sugars and polysaccharides, vegetable oils, lignin, pine resin derivatives, and proteins, have so far been investigated for the preparation of bio-based polymers. Among the various sources of bio-based feedstock, vegetable oils are one of the most widely used starting materials in the polymer industry due to their easy availability, low toxicity, and relative low cost. Another bio-based plastic of great interest is poly(lactic acid) (PLA), widely used in multiple commercial applications nowadays. There is an intrinsic expectation that bio-based polymers are also biodegradable, but in reality there is no guarantee that polymers prepared from biorenewable feedstock exhibit significant or relevant biodegradability. Biodegradability studies are therefore crucial in order to assess the long-term environmental impact of such materials. This review presents a brief overview of the different classes of bio-based polymers, with a strong focus on vegetable oil-derived resins and PLA. An entire section is dedicated to a discussion of the literature addressing the biodegradability of bio-based polymers.

Vegetable Oils as a Chemical Platform

As dwindling crude oil reserves around the planet bring uncertainty about the supply of energy and raw materials to mankind, many scientists are focusing their efforts in developing inventive solutions to diminish our dependency on petroleum. Besides appeasing concerns related to a very vulnerable economy strongly tied to crude oil markets, alternative technologies and sources of chemicals have the potential to provide more environmentally friendly solutions, including lower CO2 emissions, improved atom economy, and the use of renewable resources. In that context, vegetable oils can be used as a chemical platform, leading to a variety of products through chemical modifications. This chapter covers the use of vegetable oils for the preparation of various materials, including polymers, composites, coatings, gels, emulsions, binders in ink formulations, and other minor applications.

Cardanol-Based Supramolecular Gels

With the increasing interest in the development of new materials from bio-renewable resources seen in the last couple of decades, great emphasis has been put in the use of bio-renewable materials as building blocks for the preparation of bio-based polymers and composites. Lately, cardanol, a phenol derived from extracts of cashew nut shells, has gained attention due to its abundance, lack of competing applications, and great potential for the preparation of supramolecular structures through various routes. In this chapter, an initial overview of supramolecular gels is presented, covering background information on the terminology, chemical structure, properties, and the starting materials used in their synthesis. A section is dedicated to the latest advancements of cardanol-based gels, followed by a section describing applications involving cardanol-based gels and related self-assembled materials.

Plant Oil-Based Polyhydroxyurethanes

The development of novel bio-based polymers from inexpensive and renewable materials has the potential to greatly impact our current economy, the environment, and our energy matrix. The replacement of petroleum-based materials with bio-based counterparts can be greatly advantageous. The advantages of bio-based materials are the ready availability of large quantities of renewable starting materials at insignificant costs, the potential of producing more bio-degradable materials than the virtually indestructible petroleum-based polymers, the possibility of obtaining properties not currently available in commercial petroleum-based products, and their overall intrinsic low toxicity. This chapter presents the reader with an overview of the major accomplishments in bio-based polyurethane research, with a special focus on polyhydroxyurethanes (PHUs). Alternative polyurethane (PU) systems from nonisocyanate sources are briefly described in this chapter, and concluding remarks give a perspective on the future of bio-based PHUs.

Experimental study of thermopower of SWCNTs and SiC nanoparticles with B–P (born–phosphorus) sol–gel dopants

Seebeck coefficients of randomly distributed single-walled carbon nanotubes (SWCNTs) combined with Silicon Carbide (SiC) nanoparticles were experimentally determined. The Seebeck coefficients of pristine SiC/SWCNT samples were compared with those of SiC/SWCNT samples doped with P-type (Boron) and N-type (Phosphorous) sol–gel dopants. Pristine SiC/SWCNT samples were prepared by depositing SiC nanoparticles and SWCNTs on a non-conductive glass substrate. Doped SiC/SWCNT samples were prepared by coating each half of the samples alternately with B and P sol–gel dopants. Thermoelectric circuits were prepared by creating hot and cold junctions on the P and N-doped ends of the SiC/SWCNT samples with conductive Silver epoxy and Alumel (Ni–Al) wire. Voltage, current and resistance were measured across the samples against temperature difference. The SWCNTs used were approximately 60% semiconducting and 40% metallic. The Seebeck coefficient for pristine SWCNTs was 0.10 ± 0.006 mV per degree Celsius. When diffused with B–P, the Seebeck coefficient increased to 0.308 mV per degree Celsius. Pristine SiC nanoparticles showed no presence of thermoelectric (TE) effect, but substantial TE effects were observed upon inclusion of SWCNTs. Although the samples with various SWCNT compositions showed similar Seebeck coefficients, the current, resistance and power factor (PF) changed accordingly. Resistance of the pristine SWCNTs slightly decreased with increase in temperature. Structure–property relations were determined using scanning electron microscopy (SEM) and Raman spectroscopy. It was revealed that fibre-like SWCNTs created randomly distributed networks with nano-contact junctions inside the SiC matrix. Diffusion of dopants into CNTs in the doped samples increased the charged carrier concentration enhancing the thermopower of SWCNTs. Analysis of the Raman spectra showed an upshift in the tangential vibrational G-band modes of SWCNTs when doped with an electron-acceptor dopant (Boron), and a downshift in the case of an electron-donor dopant (Phosphorus). Incorporation of the dopant materials in the SWCNT structure was also evidenced by the presence of disorder induced D-band peaks in the doped SWCNTs.

Enhanced Charge Carrier Concentration of SiC/CNT with N and P Type Doping Agents

Single-walled Carbon nanotubes (SWCNTs) have been shown to have excellent conductive properties. SWCNTs were dispersed in a SiC nanoparticle matrix to form a homogeneous mixture that is both mechanically durable and conductive. The SWCNT amount has been varied. SiC/SWCNT mixtures were then doped with various N- and P-type agents, and the resulting samples were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Raman spectra of the samples were also measured for evidence of structural changes. Seebeck coefficients were measured for the doped samples demonstrating the change in thermoelectric properties. Shifts in the G peak (1580.6 cm-1) of the Raman spectra of the samples provides evidence of an increase in charge carrier concentration in the doped samples, correlating well with the Seebeck coefficient results.Copyright