Carbon nanotube-polycarbonate composites for ultrafast lasers

Carbon nanotube polycarbonate composites with controlled nanotube-bundle size are prepared by dispersion with conjugated polymers followed by blending with polycarbonate. The composite has uniform sub-micrometer nanotube bundles in high concentration, shows strong nonlinear optical absorption, and generates 193 fs pulses when used as passive mode-locker in a fiber laser.

Erbium doped fiber laser mode locked by graphene in carboxymethylcellulose polymer composite

We have presented and demonstrated efficient mode locking of erbium doped fiber laser using graphene carboxymethylcellulose (CMC) polymer composites. The laser gives out soliton pulse with duration of ∼837 fs, and 0.19 nJ pulse energy. © 2014 OSA.

Surface modification of natural fibers using bacteria:depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites

Triggered biodegradable composites made entirely from renewable resources are urgently sought after to improve material recyclability or be able to divert materials from waste streams. Many biobased polymers and natural fibers usually display poor interfacial adhesion when combined in a composite material. Here we propose a way to modify the surfaces of natural fibers by utilizing bacteria (Acetobacter xylinum) to deposit nanosized bacterial cellulose around natural fibers, which enhances their adhesion to renewable polymers. This paper describes the process of modifying large quantities of natural fibers with bacterial cellulose through their use as substrates for bacteria during fermentation. The modified fibers were characterized by scanning electron microscopy, single fiber tensile tests, X-ray photoelectron spectroscopy, and inverse gas chromatography to determine their surface and mechanical properties. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate and poly(L-lactic acid) was quantified using the single fiber pullout test. © 2008 American Chemical Society.

Seismic performance of hybrid fiber reinforced polymer-concrete pier columns

As part of a multi-university research program funded by NSF, a comprehensive experimental and analytical study of seismic behavior of hybrid fiber reinforced polymer (FRP)-concrete column is presented in this dissertation. Experimental investigation includes cyclic tests of six large-scale concrete-filled FRP tube (CFFT) and RC columns followed by monotonic flexural tests, a nondestructive evaluation of damage using ultrasonic pulse velocity in between the two test sets and tension tests of sixty-five FRP coupons. Two analytical models using ANSYS and OpenSees were developed and favorably verified against both cyclic and monotonic flexural tests. The results of the two methods were compared. A parametric study was also carried out to investigate the effect of three main parameters on primary seismic response measures. The responses of typical CFFT columns to three representative earthquake records were also investigated. The study shows that only specimens with carbon FRP cracked, whereas specimens with glass or hybrid FRP did not show any visible cracks throughout cyclic tests. Further monotonic flexural tests showed that carbon specimens both experienced flexural cracks in tension and crumpling in compression. Glass or hybrid specimens, on the other hand, all showed local buckling of FRP tubes. Compared with conventional RC columns, CFFT column possesses higher flexural strength and energy dissipation with an extended plastic hinge region. Among all CFFT columns, the hybrid lay-up demonstrated the highest flexural strength and initial stiffness, mainly because of its high reinforcement index and FRP/concrete stiffness ratio, respectively. Moreover, at the same drift ratio, the hybrid lay-up was also considered as the best in term of energy dissipation. Specimens with glassfiber tubes, on the other hand, exhibited the highest ductility due to better flexibility of glass FRP composites. Furthermore, ductility of CFFTs showed a strong correlation with the rupture strain of FRP. Parametric study further showed that different FRP architecture and rebar types may lead to different failure modes for CFFT columns. Transient analysis of strong ground motions showed that the column with off-axis nonlinear filament-wound glass FRP tube exhibited a superior seismic performance to all other CFFTs. Moreover, higher FRP reinforcement ratios may lead to a brittle system failure, while a well-engineered FRP reinforcement configuration may significantly enhance the seismic performance of CFFT columns.

Seismic Performance of Hybrid Fiber Reinforced Polymer-Concrete Pier Columns

As part of a multi-university research program funded by NSF, a comprehensive experimental and analytical study of seismic behavior of hybrid fiber reinforced polymer (FRP)-concrete column is presented in this dissertation. Experimental investigation includes cyclic tests of six large-scale concrete-filled FRP tube (CFFT) and RC columns followed by monotonic flexural tests, a nondestructive evaluation of damage using ultrasonic pulse velocity in between the two test sets and tension tests of sixty-five FRP coupons. Two analytical models using ANSYS and OpenSees were developed and favorably verified against both cyclic and monotonic flexural tests. The results of the two methods were compared. A parametric study was also carried out to investigate the effect of three main parameters on primary seismic response measures. The responses of typical CFFT columns to three representative earthquake records were also investigated. The study shows that only specimens with carbon FRP cracked, whereas specimens with glass or hybrid FRP did not show any visible cracks throughout cyclic tests. Further monotonic flexural tests showed that carbon specimens both experienced flexural cracks in tension and crumpling in compression. Glass or hybrid specimens, on the other hand, all showed local buckling of FRP tubes. Compared with conventional RC columns, CFFT column possesses higher flexural strength and energy dissipation with an extended plastic hinge region. Among all CFFT columns, the hybrid lay-up demonstrated the highest flexural strength and initial stiffness, mainly because of its high reinforcement index and FRP/concrete stiffness ratio, respectively. Moreover, at the same drift ratio, the hybrid lay-up was also considered as the best in term of energy dissipation. Specimens with glassfiber tubes, on the other hand, exhibited the highest ductility due to better flexibility of glass FRP composites. Furthermore, ductility of CFFTs showed a strong correlation with the rupture strain of FRP. Parametric study further showed that different FRP architecture and rebar types may lead to different failure modes for CFFT columns. Transient analysis of strong ground motions showed that the column with off-axis nonlinear filament-wound glass FRP tube exhibited a superior seismic performance to all other CFFTs. Moreover, higher FRP reinforcement ratios may lead to a brittle system failure, while a well-engineered FRP reinforcement configuration may significantly enhance the seismic performance of CFFT columns.

Evaluation of degree of conversion and hardness of dental composites photo-activated with different light guide tips

Objective: The aim of this study was to evaluate the degree of conversion and hardness of different composite resins, photo-activated for 40 s with two different light guide tips, fiber optic and polymer. Methods: Five specimens were made for each group evaluated. The percentage of unreacted carbon double bonds (% C═C) was determined from the ratio of absorbance intensities of aliphatic C═C (peak at 1637 cm−1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm−1). The Vickers hardness measurements were performed in a universal testing machine. A 50 gf load was used and the indenter with a dwell time of 30 seconds. The degree of conversion and hardness mean values were analyzed separately by ANOVA and Tukey’s test, with a significance level set at 5%. Results: The mean values of degree of conversion for the polymer and fiber optic light guide tip were statistically different (P<.001). The hardness mean values were statistically different among the light guide tips (P<.001), but also there was difference between top and bottom surfaces (P<.001). Conclusions: The results showed that the resins photo-activated with the fiber optic light guide tip promoted higher values for degree of conversion and hardness.

Compressive strength of dental composites photo-activated with different light tips

The aim of this study was to evaluate the compressive strength of microhybrid (FiltekTM Z250) and nanofilled (FiltekTM Supreme XT) composite resins photo-activated with two different light guide tips, fiber optic and polymer, coupled with one LED. The power density was 653 mW cm−2 when using the fiber optic light tip and 596 mW cm−2 with the polymer. After storage in distilled water at 37 ± 2 "C for seven days, the samples were subjected to mechanical testing of compressive strength in an EMIC universal mechanical testing machine with a load cell of 5 kN and speed of 0.5 mm min−1. The statistical analysis was performed using ANOVA with a confidence interval of 95% and Tamhane’s test. The results showed that the mean values of compressive strength were not influenced by the different light tips (p > 0.05). However, a statistical difference was observed (p < 0.001) between the microhybrid composite resin photo-activated with the fiber optic light tip and the nanofilled composite resin. Based on these results, it can be concluded that microhybrid composite resin photo-activated with the fiber optic light tip showed better results than nanofilled, regardless of the tip used, and the type of the light tip did not influence the compressive strength of either composite. Thus, the presented results suggest that both the fiber optic and polymer light guide tips provide adequate compressive strength to be used to make restorations. However, the fiber optic light tip associated with microhybrid composite resin may be an interesting option for restorations mainly in posterior teeth.

Advanced Aerogel Composites for Oil Remediation and Recovery

Oil spills in marine environments often damage marine and coastal life if not remediated rapidly and efficiently. In spite of the strict enforcement of environmental legislations (i.e., Oil Pollution Act 1990) following the Exxon Valdez oil spill (June 1989; the second biggest oil spill in U.S. history), the Macondo well blowout disaster (April 2010) released 18 times more oil. Strikingly, the response methods used to contain and capture spilled oil after both accidents were nearly identical, note that more than two decades separate Exxon Valdez (1989) and Macondo well (2010) accidents.

The goal of this dissertation was to investigate new advanced materials (mechanically strong aerogel composite blankets-Cabot® Thermal Wrap™ (TW) and Aspen Aerogels® Spaceloft® (SL)), and their applications for oil capture and recovery to overcome the current material limitations in oil spill response methods. First, uptake of different solvents and oils were studied to answer the following question: do these blanket aerogel composites have competitive oil uptake compared to state-of-the-art oil sorbents (i.e., polyurethane foam-PUF)? In addition to their competitive mechanical strength (766, 380, 92 kPa for Spaceloft, Thermal Wrap, and PUF, respectively), our results showed that aerogel composites have three critical advantages over PUF: rapid (3-5 min.) and high (more than two times of PUF’s uptake) oil uptake, reusability (over 10 cycles), and oil recoverability (up to 60%) via mechanical extraction. Chemical-specific sorption experiments showed that the dominant uptake mechanism of aerogels is adsorption to the internal surface, with some contribution of absorption into the pore space.

Second, we investigated the potential environmental impacts (energy and chemical burdens) associated with manufacturing, use, and disposal of SL aerogel and PUF to remove the oil (i.e., 1 m3 oil) from a location (i.e., Macondo well). Different use (single and multiple use) and end of life (landfill, incinerator, and waste-to-energy) scenarios were assessed, and our results demonstrated that multiple use, and waste-to-energy choices minimize the energy and material use of SL aerogel. Nevertheless, using SL once and disposing via landfill still offers environmental and cost savings benefits relative to PUF, and so these benefits are preserved irrespective of the oil-spill-response operator choices.

To inform future aerogel manufacture, we investigated the different laboratory-scale aerogel fabrication technologies (rapid supercritical extraction (RSCE), CO2 supercritical extraction (CSCE), alcohol supercritical extraction (ASCE)). Our results from anticipatory LCA for laboratory-scaled aerogel fabrication demonstrated that RSCE method offers lower cumulative energy and ecotoxicity impacts compared to conventional aerogel fabrication methods (CSCE and ASCE).

The final objective of this study was to investigate different surface coating techniques to enhance oil recovery by modifying the existing aerogel surface chemistries to develop chemically responsive materials (switchable hydrophobicity in response to a CO2 stimulus). Our results showed that studied surface coating methods (drop casting, dip coating, and physical vapor deposition) were partially successful to modify surface with CO2 switchable chemical (tributylpentanamidine), likely because of the heterogeneous fiber structure of the aerogel blankets. A possible solution to these non-uniform coatings would be to include switchable chemical as a precursor during the gel preparation to chemically attach the switchable chemical to the pores of the aerogel.

Taken as a whole, the implications of this work are that mechanical deployment and recovery of aerogel composite blankets is a viable oil spill response strategy that can be deployed today. This will ultimately enable better oil uptake without the uptake of water, potential reuse of the collected oil, reduced material and energy burdens compared to competitive sorbents (e.g., PUF), and reduced occupational exposure to oiled sorbents. In addition, sorbent blankets and booms could be deployed in coastal and open-ocean settings, respectively, which was previously impossible.

Natural Fibers for the Production of Green Composites

Development of green composite from natural fibers has gained increasing interests due to the environmental and sustainable benefits when compared with petroleum based non-degradable materials. However, a big challenge of green composites is the diversity of fiber sources, because of the large variation in the properties and characteristics of the lignocellulosic renewable resource. The lignocellulosic fibers/natural fibers used to reinforce green composites are reviewed in this chapter. A classification of fiber types and sources, the properties of various natural fibers, including structure, composition, physical and chemical properties are focused; followed by the impacts of natural fibers on composite properties, with identification of the main pathways from the natural fibers to the green composite. Furthermore, the main challenges and future trend of natural fibers are highlighted.

Green Composites and Their Properties: A Brief Introduction

Green composites are important class of biocomposites widely explored due to their enhanced properties. The biodegradable polymeric material is reinforced with natural fibers to form a composite that is eco-friendly and environment sustainable. The green composites have potential to attract the traditional petroleum-based composites which are toxic and nonbiodegradable. The green composites eliminate the traditional materials such as steel and wood with biodegradable polymer composites. The degradable and environment-friendly green composites were prepared by various fabrication techniques. The various properties of different fiber composite were studied as reinforcement for fully biodegradable and environmental-friendly green composites.

Techno-Economic and Life Cycle Assessment for the Production of Green Composites

Botanically, green composites belong to an economically important seed plant family that includes maize, wheat, rice, and sorghum known as Saccharum offi cinarum. There are so many natural fibers available in the environment such as rice husk, hemp fibers, flax fibers, bamboo fibers, coconut fiber, coconut coir, grawia optiva and many others also. Life Cycle Assessment (LCA) is a process to estimate the environmental feature and potential impacts related to a product, by organizing a directory of pertinent inputs and outputs of a product system, assessing the potential environmental impacts related with the said inputs and outputs, explaining the results of the inventory analysis and impact evaluation phases in connection to the objectives of the study. Particularly Bagasse, an agricultural residue not only becomes a problem from the environmental point of view, but also affects the profitability of the sugarcane industries. This chapter discusses the properties, processing methods and various other aspects including economic and environmental aspects related to green composites.

Glass fibre-reinforced polyethylene composites in rotational moulding

Fibre-reinforced mouldings are of growing interest to the rotational moulding industry due to their outstanding price performance ratio. However, a particular problem that arises when using reinforcements in this process is that the process is low shear and good mixing of resin and reinforcement is not optimum under those conditions. There is also a problem of the larger/heavier reinforcing agents segregating out of the powder to lay up on the inner part surface. In this paper we report on studies to incorporate, short glass fibres into rotationally moulded parts. Four different approaches were investigated; direct addition of fibre in between two powder shots, addition of a layer of pre-compounded polyethylene-glass fibre pellets between two powder shots, addition of a layer of pre-compounded polyethylene-glass fibre powder between two powder shots and a single layer of glass-reinforced, pre-compounded powder. Results indicate that pre-compounding is necessary to gain performance enhancement and the single layer part made from glass-reinforced, pre-compounded powder exhibited the highest tensile and flexural modulus.

Développement de fibres optiques composites pour la génération du supercontinuum dans l’infrarouge

Les sources laser à large bande possédant les caractéristiques requises pour émettre sur la plage spectrale correspondant à la seconde fenêtre de transmission atmosphérique (3 à 5 μm) exercent un attrait considérable pour divers domaines tels que la télédétection de polluants atmosphériques et les contremesures infrarouges. Les supercontinua générés à l’intérieur de fibres optiques représentent une option intéressante pour réaliser ce type de sources laser. En effet, ils possèdent une intensité élevée, un large contenu spectral, une excellente directionnalité de faisceau, ainsi qu’un bon potentiel pour constituer des sources lumineuses compactes et robustes. Toutefois, la génération d’un tel supercontinuum implique certains défis à relever sur le plan de la conception des fibres optiques employées. En fait, ces fibres optiques doivent présenter de faibles pertes de propagation sur la plage spectrale de 3 à 5 μm, posséder un paramètre de non-linéarité élevé et permettre le pompage en régime anomal de dispersion à des longueurs d’onde pour lesquelles des sources laser compactes sont offertes commercialement. En matière de robustesse, ces fibres doivent également démontrer de bonnes propriétés mécaniques ainsi qu’une stabilité chimique appropriée vis-à-vis de la corrosion causée par l’humidité. Dans le cadre de cette thèse, un nouveau type de fibres composites à saut d’indice fortement contrasté a été développé pour atteindre ces objectifs de génération de supercontinuum. Ce type de fibres combine respectivement un verre de tellurite et un verre de germanate pour son coeur et sa gaine permettant ainsi d’atteindre une différence d’indice de réfraction d’environ 0.3 entre ces deux dernières structures. Grâce à cet important saut d’indice, ces fibres peuvent fortement confiner les modes optiques à l’intérieur de leur coeur, ce qui leur donne la possibilité d’atteindre un niveau élevé de non-linéarité et d’optimiser leurs caractéristiques de dispersion chromatique pour la génération du supercontinuum. D’autre part, leur section transversale toute solide leur confère aussi une meilleure stabilité environnementale comparativement à celle démontrée par les fibres optiques microstructurées à base de verres d’oxydes de métaux lourds, de verres de chalcogénure et de verres fluorés. Toutefois, leur fabrication nécessite l’appariement de verres dont les propriétés thermomécaniques concordent suffisamment ensemble pour permettre leur fibrage. Les travaux effectués ici démontrent la production de fibres optiques composites et leur potentiel pour la génération du supercontinuum dans l’infrarouge moyen.

Composites and foams based on polylactic acid (PLA)

Cette étude est destinée à la production et à la caractérisation des composites d’acide polylactique (PLA) et des fibres naturelles (lin, poudre de bois). Le moussage du PLA et ses composites ont également été étudiés afin d’évaluer les effets des conditions de moulage par injection et du renfort sur les propriétés finales de ces matériaux. Dans la première partie, les composites constitués de PLA et des fibres de lin ont été produits par extrusion suivit par un moulage en injection. L’effet de la variation du taux de charge (15, 25 et 40% en poids) sur les caractéristiques morphologique, mécanique, thermique et rhéologique des composites a été évalué. Dans la deuxième étape, la poudre de bois (WF) a été choisie pour renforcer le PLA. La préparation des composites de PLA et WF a été effectuée comme dans la première partie et une série complète de caractérisations morphologique, mécanique, thermique et l’analyse mécanique dynamique ont été effectués afin d’obtenir une évaluation complète de l’effet du taux de charge (15, 25 et 40% en poids) sur les propriétés du PLA. Finalement, la troisième partie de cette étude porte sur les composites de PLA et de renfort naturel afin de produire des composites moussés. Ces mousses ont été réalisées à l’aide d’un agent moussant exothermique (azodicarbonamide) via le moulage par injection, suite à un mélange du PLA et de fibres naturelles. Dans ce cas, la charge d’injection (quantité de matière injectée dans le moule: 31, 33, 36, 38 et 43% de la capacité de la presse à injection) et la concentration en poudre de bois (15, 25 et 40% en poids) ont été variées. La caractérisation des propriétés mécanique et thermique a été effectuée et les résultats ont démontré que les renforts naturels étudiés (lin et poudre de bois) permettaient d’améliorer les propriétés mécaniques des composites, notamment le module de flexion et la résistance au choc du polymère (PLA). En outre, la formation de la mousse était également efficace pour le PLA vierge et ses composites car les masses volumiques ont été significativement réduites.