Deposition of Carbon Nanotubes Onto Aramid Fibers Using as-received and Chemically Modified Fibers

Multiwall carbon nanotubes (MWCNTs) oxidized by an acid treatment were deposited on the surface of as-received commercial aramid fibers containing a surface coating (“sizing”), and fibers modified by either a chlorosulfonic treatment or a mixture of nitric and sulfuric acids. The surface of the aramid fiber activated by the chemical treatments presents increasing density of CO, COOH and OH functional groups. However, these chemical treatments reduced the tensile mechanical properties of the fibers, especially when the nitric and sulfuric acid mixture was used. Characterization of the MWCNTs deposited on the fiber surface was conducted by scanning electron microscopy, Raman spectroscopy mapping and X-ray photoelectron spectroscopy. These characterizations showed higher areal concentration and more homogeneous distribution of MWCNTs over the aramid fibers for as-received fibers and for those modified with chlorosulfonic acid, suggesting the existence of interaction between the oxidized MWCNTs and the fiber coating. The electrical resistance of the MWCNT-modified aramid yarns comprising ∼1000 individual fibers was in the order of MΩ/cm, which renders multifunctional properties

Review of nanomaterials in dentistry: interactions with the oral microenvironment, clinical applications, hazards, and benefits.

Interest in the use of engineered nanomaterials (ENMs) as either nanomedicines or dental materials/devices in clinical dentistry is growing. This review aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. The flow rate and quality of saliva are likely to influence the behavior of ENMs in the oral cavity, but how the protein corona formed on the ENMs will alter bioavailability, or interact with the structure and proteins of the pellicle layer, as well as microbes in the biofilm, remains unclear. The tooth enamel is a dense crystalline structure that is likely to act as a barrier to ENM penetration, but underlying dentinal tubules are not. Consequently, ENMs may be used to strengthen dentine or regenerate pulp tissue. ENMs have dental applications as antibacterials for infection control, as nanofillers to improve the mechanical and bioactive properties of restoration materials, and as novel coatings on dental implants. Dentifrices and some related personal care products are already available for oral health applications. Overall, the clinical benefits generally outweigh the hazards of using ENMs in the oral cavity, and the latter should not prevent the responsible innovation of nanotechnology in dentistry. However, the clinical safety regulations for dental materials have not been specifically updated for ENMs, and some guidance on occupational health for practitioners is also needed. Knowledge gaps for future research include the formation of protein corona in the oral cavity, ENM diffusion through clinically relevant biofilms, and mechanistic investigations on how ENMs strengthen the tooth structure

Effect of morphology and particle size on the mechanical properties of SAN composites

The effect of morphology (core-shell and three-layer) and particle size on the mechanical properties of a SAN composite was investigated. The-core-shell (CS) and three-layer (TL) particles with same global composition (60PBA/40PS) were both obtained by emulsion and microemulsion polymerization to obtain particles with different size. The composites with particles obtained by emulsion, independently of the morphology (CS or TL) and particle size (170 and 220 nm); have at maxima in impact resistance at a 20% of particles content. A different behaviour, however, was observed when particles obtained by microemulsion were used. The composites with TC particles obtained by microemulsion polymerization show a maximum in impact resistance at 10% particles, but impact resistance of composites with CS particles obtained by microemulsion polymerization did not show a maximum and increases with particles content

Preparation and characterization of henequen cellulose grafted with methyl methacrylate and its application in composites

The grafting polymerization of methyl methacrylate (MMA) and cellulose from henequen (Agave fourcroydes) is investigated as a function of the initiator concentration (cerium-and-ammonium nitrate) and the monomer/cellulose ratio. The formation of cellulose-g-PMMA is confirmed by IR spectroscopy, DSC, and TGA. Both the initiator concentration and the MMA/cellulose ratio have a strong influence over the grafting parameters and over the molecular weight of the grafted PMMA. A higher initiator concentration and a lower monomer/cellulose ratio result in a lower molecular weight of the grafted polymer. Increasing the amount and the molecular weight of the grafted PMMA increases the compatibility of the fibers with SAN and PVC, as demonstrated by a mechanical test and scanning electron microscopy. SAN and PVC composites made with grafted cellulose exhibit higher flexural and tensile moduli, respectively, than those produced with the ungrafted fibers. Both moduli increase as the amount of reinforcement increases. © 1997 John Wiley & Sons, Inc

Preparation and characterization of henequen cellulose grafted with methyl methacrylate and its application in composites

The grafting polymerization of methyl methacrylate (MMA) and cellulose from henequen (Agave fourcroydes) is investigated as a function of the initiator concentration (cerium-and-ammonium nitrate) and the monomer/cellulose ratio. The formation of cellulose-g-PMMA is confirmed by IR spectroscopy, DSC, and TGA. Both the initiator concentration and the MMA/cellulose ratio have a strong influence over the grafting parameters and over the molecular weight of the grafted PMMA. A higher initiator concentration and a lower monomer/cellulose ratio result in a lower molecular weight of the grafted polymer. Increasing the amount and the molecular weight of the grafted PMMA increases the compatibility of the fibers with SAN and PVC, as demonstrated by a mechanical test and scanning electron microscopy. SAN and PVC composites made with grafted cellulose exhibit higher flexural and tensile moduli, respectively, than those produced with the ungrafted fibers. Both moduli increase as the amount of reinforcement increases. © 1997 John Wiley & Sons, Inc

Flexural, impact and compressive properties of a rigid-thermoplastic matrix/cellulose fiber reinforced composites

The mechanical behavior of rigid-thermoplastic matrix-cellulose fiber reinforced composites is investigated. These materials exhibit a brittle behavior, that is, they possess a high modulus and therefore, a very limited amount of deformation to fracture. Such behavior makes the characterization of interfacial properties difficult to evaluate. In this paper, the flexural, impact and compressive behavior of cellulose fibers reinforced polymeric matrices, such as poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) are investigated and special attention is given to the effect of fiber surface treatment on the effective properties. The flexural strength of the composites remains constant when the fiber is grafted with PMMA and a brittle interface is formed around the cellulose fibers, regardless of fiber content. This behavior is not observed in composites reinforced with untreated cellulose fibers or poly(butyl acrylate)-grafted fibers, which show a low flexural strength at higher fiber contents. In the case of impact loading, the presence of an elastomeric type material, in this case, poly(butyl acrylate)-grafted cellulose fibers seems to provide an alternative mechanism for energy dissipation in the composite, thus, showing a better impact behavior than the composites with the other fiber surface treatments. The impact behavior seems to be improved by the mechanical properties of the cellulose fibers. Specifically, the low elastic modulus of the cellulose fiber resulting from the attack of the grafting process, contributes to decrease the rigidity of the composite. Using the fact that glassy materials such as PMMA and SAN are able to yield when they are loaded under compression, even at room temperature, compression experiments were performed using two different sample geometries. The first was the typical rectangular sample and the other was the hourglass shaped specimen. Due to the compressive state of stress induced at the middle portion of the last specimen, a better indication of fiber matrix adhesion could be evaluated as compared to the other sample geometry that induced mixed stress component signs in the test area. The fiber-matrix interfacial properties are assessed from scanning electron microscope photographs. © 2002 Elsevier Science Ltd. All rights reserved

Effect of tallow and rice polishings in feedlot rations on growth and carcass characteristics of lambs

Morphology, mechanical properties and crystallinity of foamed and unfoamed composites polypropylene (PP) and cellulose from Agave tequilana were studied. The PP-cellulose composite with PP-g-MA as coupling agent was obtained using a twin-screw extruder. Foamed composite was obtained by blending the composite with a blowing agent and moulding by compression. The morphology of the foamed composite, observed by SEM, shows that the bubble diameters were smaller when cellulose content increased. Young's modulus and impact of foamed and unfoamed PP/PP-g-MA composites were higher than the pure PP matrix, and they increase with the cellulose content. An increment of the crystallization percent was observed with respect at XRD analysis. This indicates that the cellulose acts as a nucleation agent, favouring the crystallization in the composites. " 2012 Springer-Verlag Berlin Heidelberg.",,,,,,"10.1007/s00289-012-0878-8",,,"http://hdl.handle.net/20.500.12104/41023","http://www.scopus.com/inward/record.url?eid=2-s2.0-84878593383&partnerID=40&md5=7b18b5b09909e01e62bc545c7212b1e0",,,,,,"3",,"Polymer Bulletin",,"83

Effect of the cellulose of Agave tequilana Weber onto the mechanical properties of foamed and unfoamed polypropylene composites

Morphology, mechanical properties and crystallinity of foamed and unfoamed composites polypropylene (PP) and cellulose from Agave tequilana were studied. The PP-cellulose composite with PP-g-MA as coupling agent was obtained using a twin-screw extruder. Foamed composite was obtained by blending the composite with a blowing agent and moulding by compression. The morphology of the foamed composite, observed by SEM, shows that the bubble diameters were smaller when cellulose content increased. Young's modulus and impact of foamed and unfoamed PP/PP-g-MA composites were higher than the pure PP matrix, and they increase with the cellulose content. An increment of the crystallization percent was observed with respect at XRD analysis. This indicates that the cellulose acts as a nucleation agent, favouring the crystallization in the composites. © 2012 Springer-Verlag Berlin Heidelberg

Mechanical properties of acrylate-grafted henequen cellulose fibers and their application in composites

The properties of cellulose fiber and PMMA- or PBA-grafted cellulose fibers are investigated as a function of the initiator (ceric-ammonium nitrate) concentration and the amount of grafted polymer onto cellulose fiber. The molecular weight of cellulose decreases while the crystallinity increases with an increment of initiator concentration because of the partial degradation of the amorphous zone of the fibers exposed to the oxidation by the initiator. This results in a reduction of the elastic modulus and tensile strength at high initiator concentrations. Degradation of cellulose is partially inhibited during the grafting process and, therefore, the effect of initiator on the mechanical properties is less notorious in the grafted cellulose fiber. The grafting of PMMA or PBA on the fiber results in lower mechanical properties than those of the ungrafted cellulose fiber. The reduction of the elastic modulus is independent of the amount of grafted PMMA or PBA, but the tensile strength decreases with the PBA content on the PBA-grafted fiber. Either the grafted or the ungrafted cellulose fibers improve the mechanical properties of plasticized PVC composites, and the best results are obtained for PMMA-grafted cellulose fibers because of the better fiber-matrix adhesion. The Halpin-Tsai equation seems to better agree with the experimental data when there is a good fiber-matrix adhesion. In contrast, for poor fiber-matrix adhesion the experimental data has a better agreement with the parallel arrangement equation. © 1999 Elsevier Science Ltd

Mechanical properties of acrylate-grafted henequen cellulose fibers and their application in composites

The properties of cellulose fiber and PMMA- or PBA-grafted cellulose fibers are investigated as a function of the initiator (ceric-ammonium nitrate) concentration and the amount of grafted polymer onto cellulose fiber. The molecular weight of cellulose decreases while the crystallinity increases with an increment of initiator concentration because of the partial degradation of the amorphous zone of the fibers exposed to the oxidation by the initiator. This results in a reduction of the elastic modulus and tensile strength at high initiator concentrations. Degradation of cellulose is partially inhibited during the grafting process and, therefore, the effect of initiator on the mechanical properties is less notorious in the grafted cellulose fiber. The grafting of PMMA or PBA on the fiber results in lower mechanical properties than those of the ungrafted cellulose fiber. The reduction of the elastic modulus is independent of the amount of grafted PMMA or PBA, but the tensile strength decreases with the PBA content on the PBA-grafted fiber. Either the grafted or the ungrafted cellulose fibers improve the mechanical properties of plasticized PVC composites, and the best results are obtained for PMMA-grafted cellulose fibers because of the better fiber-matrix adhesion. The Halpin-Tsai equation seems to better agree with the experimental data when there is a good fiber-matrix adhesion. In contrast, for poor fiber-matrix adhesion the experimental data has a better agreement with the parallel arrangement equation. © 1999 Elsevier Science Ltd