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Erbas Kiziltas E.,University of Maine, United States | Erbas Kiziltas E.,Scientific and Technological Research Council of Turkey | Erbas Kiziltas E.,Advanced Structures and Composites Center | Kiziltas A.,University of Maine, United States | And 3 more authors.
Carbohydrate Polymers | Year: 2015

The unique micro-nano porous three-dimensional network of bacterial cellulose (BC) can facilitate the incorporation of nanoparticles (NPs) into the BC matrix to create advanced BC-based functional nanomaterials for diverse applications. In this study, novel nanomaterials comprised of bacterial cellulose (BC) synthesized in the presence of different NPs (cellulose nanofibrils (CNF), exfoliated graphite nanoplatelets (xGnP), and nanoclay (NC)) were prepared using an in situ approach. NPs at 0.5 wt.% loading were added into the BC culture medium and their effect on the resulting nanocomposite structure was studied by field emission scanning electron microscopy (FE-SEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). All BC-based nanomaterials produced, exhibited good dispersion of the NPs within the BC matrix and the NPs were found embedded among the voids and microfibrils. The thermal stability and residual mass of BC-xGnP and BC-NC nanomaterials was significantly increased compared with the neat BC. CNF incorporation into the BC matrix did not change the thermal stability and residual mass of the BC matrix. This study also provides novel insights into the properties of the hybrid materials, and shows the approach used to make these materials which results in increased performance for chosen applications. © 2015 Elsevier Ltd. All rights reserved. Source


Silva-Henriquez R.,Advanced Structures and Composites Center | Gray H.,Construction Management Technology | Dagher H.J.,Advanced Structures and Composites Center | Davids W.G.,Civil Structural Engineering | Nader J.,University of Maine, United States
Forest Products Journal | Year: 2010

This article focuses on assessing the strength performance of glued-laminated (glulam) beams with E-glass fiberreinforced polymer (GFRP) prestressing (prestressed GFRP-glulam beams) through bending tests and cross-sectional analysis. In addition to fifteen 6.7-m-long prestressed glulam beams, 15 GFRP-reinforced glulam beams and 15 unreinforced glulam control beams with nominally identical layups and 6.7-m lengths were tested to failure in four-point bending to provide direct performance comparisons. Load-displacement data and strains in the prestressed GFRP were monitored. The results of the tests show that the prestressed GFRP-glulam beams exhibited a 38 percent increase in allowable bending stresses compared with reinforced GFRP-glulam beams without prestress and an approximately 95 percent increase compared with unreinforced glulam beams. Both the prestressed and reinforced specimens exhibited an 8 percent increase in stiffness relative to the control specimens. Loss of prestress due to creep was examined for one specimen by monitoring GFRP strains over a 12-day period following fabrication. The total loss of prestress over this 12-day period was less than 2 percent, and the rate of prestress loss decreased during monitoring. The GFRP stresses predicted by a cross-sectional moment-curvature analysis of the prestressed and reinforced beams agree well with stresses inferred from measured strains. The results of this study show that prestressed GFRP reinforcement of glulam beams shows significant promise for practical applications. © Forest Products Society 2010. Source


Tamrakar S.,Advanced Structures and Composites Center | Lopez-Anido R.A.,Advanced Structures and Composites Center
Forest Products Journal | Year: 2010

Wood plastic composite (WPC) materials are being developed for load-bearing structural applications; therefore, the strain rate-dependent mechanical properties of WPC materials need to be characterized. Extruded WPC Z-section sheet piles composed of 46 percent wood flour, 41 percent polypropylene, and additives were investigated. ASTM D6109 was adopted for assessing flexural properties of plastic lumber in a four-point loading configuration. Coupons were cut from the flanges of the sheet pile section and conditioned for 2 weeks at 21°C and 65 percent relative humidity. The flexural tests were conducted at three different strain rates: 0.55, 1.0, and 5.5 percent per minute. The mode of failure was in tension in the middle third of the bending span. It was found that the mean apparent modulus of elasticity (MOE) increased with the strain rate; e.g., the MOE increased 9.5 percent when the strain rate was increased from 1.0 to 5.5 percent per minute. The variations in mean strain at failure with the strain rate were not statistically significant based on analysis of variance testing. The variation in flexural MOE with the strain rate was compared with the published tensile and compressive MOE values for the same material. The effect of strain rate on the flexural MOE of the polypropylene WPC material was also correlated with the published results for WPC materials with other polymer matrices (high-density polyethylene and polyvinyl chloride). The strain rate effects in the MOE of the WPC material was predicted based on a viscoelastic standard solid model calibrated with the coupon level data. ©Forest Products Society 2010. Source


Duguay A.J.,Advanced Structures and Composites Center | Kiziltas A.,Advanced Structures and Composites Center | Nader J.W.,Advanced Structures and Composites Center | Gardner D.J.,Advanced Structures and Composites Center | Dagher H.J.,Advanced Structures and Composites Center
International SAMPE Technical Conference | Year: 2011

Exfoliated graphite nanoplatelet (xGnP)-filled polymer composites have demonstrated excellent physical, thermal and mechanical properties and are garnering attractiveness as a nanoscale reinforcing filler in academic and industrial R&D activities. The objective of this research was to investigate the effect of particle diameter, filler loading and coupling agent on the thermal behavior of impact modified polypropylene (IMPP) nanocomposites. xGnP-filled IMPP composites were manufactured via melt mixing with and without the addition of polypropylenegraft-maleic anhydride (PP-g-MA). The thermal behavior of the nanocomposites was investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results indicated that the addition of xGnP slightly increased the melting temperature (T m) and increased the crystallization temperature (T c) of IMPP by 2 to 3 °C which is attributed to the heterogeneous nucleation of the xGnP. The TGA results indicated that the degradation temperature of IMPP shifts to a lower temperature with the addition of PP-g-MA, indicative of the poor thermal stability of PP-g-MA. However, the thermal stability of the composites increases with xGnP loading because of the high thermal stability of the xGnP and the hypothesized tortuosity effect of the graphite nanoplatelets inhibiting diffusion of oxygen and volatile products throughout the composites during thermal decomposition. Source


Duguay A.J.,Advanced Structures and Composites Center | Nader J.W.,Advanced Structures and Composites Center | Kiziltas A.,Advanced Structures and Composites Center | Gardner D.J.,Advanced Structures and Composites Center | Dagher H.J.,Advanced Structures and Composites Center
International SAMPE Technical Conference | Year: 2011

In this study, we investigate the effect of particle diameter size, filler loading and coupling agent on the mechanical properties of exfoliated graphite nanoplatelet (xGnP)-filled impact modified polypropylene (IMPP) nanocomposites. xGnP-filled IMPP nanocomposites were prepared at 2, 4, 6, and 8 wt. % xGnP with and without the addition of a coupling agent. The coupling agent used in this study was polypropylene-graft-maleic anhydride (PP-g-MA). The nanoparticles used were xGnP with three different sizes: xGnP 5 has an average thickness of 10 nm, and an average platelet diameter of 5 μm, whereas xGnP 15 and xGnP 25 have the same thickness but average diameters are 15 and 25 μm, respectively. Test results show that nanocomposites with smaller xGnP diameters exhibited better mechanical properties. For composites containing a coupling agent, tensile modulus increased with the addition of xGnP. In the case of neat composites, tensile modulus decreased at higher filler loading levels. Increasing xGnP loading level resulted in reduction of elongation at break for both neat IMPP and IMPP composites with coupling agent. Moreover, unnotched and notched impact strengths were dramatically deteriorated with the introduction of xGnP. Explanation of this brittle behavior is presented using melt flow index, scanning electron microscopy and transmission electron microscopy. Source

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