Alfred Tcherbi-Narteh | Tuskegee University (original) (raw)

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Papers by Alfred Tcherbi-Narteh

With the depletion of petrochemical resources, the increase in greenhouse gases emission, and shr... more With the depletion of petrochemical resources, the increase in greenhouse gases emission, and shrinking landfill capacity, the manufacture, use, and disposal of synthetic composites is at an all-time high. This does not lead to any form of sustainable use of composites, let alone allow for growth of the use and supporting industry. Many researchers and industry partners understand the need for sustainable composites and have renewed the research and funding for such progress. One of the particular areas is the expansion into nitroxide mediated polymerization due to the reduction in uncontrolled exothermic reactions during the curing process of thick components. This allows larger and thicker natural composites to be fabricated with a lower cure temperature. The research has expanded from initial work involving the polymerization using a nitroxyl mixed with a conventional initiator like dibenzoyl peroxide [2, p. 422] to chain end functionalization [3], through the development of well...

The objective of this work was to investigate the mitigating effects of montmorillonite nanoclay ... more The objective of this work was to investigate the mitigating effects of montmorillonite nanoclay (MMT) if any, on the properties of carbon fiber reinforced composites (CFRC) infused with different weight percentages of MMT and exposed to UV radiation and condensation. Composites used in this study were control and with 1-3 wt. % of nanoclay. Samples were exposed to 15 days of continuous UV radiation and condensation using QUV/SE accelerated weathering system. Mechanical and thermal properties were characterized by compression tests, thermo-gravimetric analysis (TGA) and dynamic mechanical analyses (DMA) according to ASTM standards. Surface morphology of exposed samples was characterized through Scanning electron microscopy (SEM). These properties were characterized every 120 hours of exposure. Samples exposed to condensation did not follow any specific pattern, although there was a decrease in mechanical properties in all samples.

The objective of this work is to investigate the effect of formic acid, peroxyformic acid and hyd... more The objective of this work is to investigate the effect of formic acid, peroxyformic acid and hydrogen peroxide bleaching on morphology, crystallinity and thermal stability of kenaf fiber as a source of cellulose, and assess the suitability of kenaf fiber for isolation of cellulose nanofibers by acid hydrolysis treatment followed by ultrasonication. Characterization of kenaf fiber after each step of chemical treatments was done using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Extracted cellulose nanofibers had diameters in the nanometer range and showed significant increase in crystallinity, but a decrease in thermal stability.

Open Journal of Composite Materials, 2013

Effects of carboxyl functionalized MWCNTs on the cure behavior of epoxy resin (EPIKOTE TM resin 8... more Effects of carboxyl functionalized MWCNTs on the cure behavior of epoxy resin (EPIKOTE TM resin 862 and EPICURE TM curing agent W) were investigated by using differential scanning calorimeter in dynamic scan mode. Results indicated that nanotubes could initiate cure reaction at lower temperature while only 0.1 wt% samples were able to suppress the peak temperature (T p ) consistently regardless of different heating rate due to their higher reaction rate, other two batches (0.2 wt% and 0.3 wt% CNT) showed hardly any change in T p compared to neat samples. Furthermore, addition of small amount (0.1 wt%) of CNTs significantly reduced the activation energy of the system but further addition elevated that due to their retarding effect. Also, a correlation was established between the dispersion state of CNTs in epoxy and total heat of reaction (ΔH) where lower ΔH was considered as an indication of better interfacial interaction of CNTs with matrix and hence, better dispersion. The difference in curing behavior of three different CNT percentages was discussed in terms of their steric hindrance and state of dispersion in the matrix.

Optics and Laser Technology, 2014

This research was aimed to use ball milling method to extract cellulose nanofibers (CNFs) from ... more This research was aimed to use ball milling method to extract cellulose nanofibers (CNFs) from a
bio-waste (i.e. wheat straw), and also to use the extracted cellulose nanofibers as reinforcing materials in polyvinyl
alcohol (PVA) thin film. To study the effect of cellulose nanofibers (CNFs) on mechanical and thermal properties of
polyvinyl alcohol (PVA) nano-composite films, thin film nano-composites were loaded with different loading of
cellulose nanofibers (CNFs) by weight percent (i.e. 1,3,5 and 7% loading). As a result of the research, we found that
the tensile and thermal properties of PVA thin composite increased up to 5% loading of cellulose nanofibers
(CNFs). In contrast, the tensile as well as thermal properties of PVA nano -composite film degraded because of poor
dispersion and agglomeration of CNFs

The objective of this work was to find out the compositional characteristics of wheat straw in te... more The objective of this work was to find out the compositional characteristics of wheat straw in
terms of cellulose and lignin contents and assess the suitability of wheat straw for isolation of
cellulose microfibrils. The fractionation process includes formic acid/peroxyformic acid
treatment, bleaching and ball milling of bleached cellulose. 39.10 % Cellulose, 20.40 % lignin
and 25.02 % of other compounds were extracted. Extracted cellulose was characterized using
Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), and
thermogravimetric analysis (TGA). Morphological and thermal analyses studies showed that the
extracted microfibrils had reduced length and diameter and showed good thermal stability
suitable for various advanced nano technological applications.

The prime objective of this study was to fabricate epoxy polymer composite modified with graphene... more The prime objective of this study was to fabricate epoxy polymer composite modified
with graphene nanoplatelets (GP) and montmorillonite nanoclay (MMT) binary filler materials.
Different loading percentages of individual and binary nanofillers were incorporated into an epoxy
matrix system to investigate the synergistic effect of nanofillers on composites properties. Dynamic
mechanical analysis (DMA) and three point bend test were carried out to investigate the viscoelastic
and flexural properties of neat epoxy and nanofillers reinforced nanocomposites. Incorporation of 3
wt. % of MMT and 0.1 wt. % of GP resulted in better flexure strength, modulus and storage
modulus although there is no significance change in glass transition temperature (Tg).

Journal of Materials Research and Technology, 2015

Journal of Nanoscience, 2013

Diglycidyl ether of Bisphenol A (DGEBA) based SC-15 epoxy resin was modified with three different... more Diglycidyl ether of Bisphenol A (DGEBA) based SC-15 epoxy resin was modified with three different commercially available montmorillonite (MMT) nanoclay: Nanomer I.28E and Cloisite 10A and 30B. Cure behavior of nanocomposites was studied using a variety of techniques. Primary focus of this study was to investigate influence of different surface modifications of MMT nanoclay on rheological properties and cure behavior of SC-15 epoxy resin. By adding MMT to SC-15 epoxy resin, chemistry of the epoxy is altered leading to changes in rheological properties and ultimately enthalpy and activation energy of reactions. Addition of Nanomer I.28E delayed gelation, while Cloisite 10A and 30B accelerated gelation, regardless of the curing temperature. Activation energy of reaction was lower with the addition of Nanomer I.28E and Cloisite 10A and higher for Cloisite 30B compared to neat SC-15 epoxy composite.

Polymer Degradation and Stability, 2014

ABSTRACT Effects of UV radiation and associated elevated temperature on properties of polymeric c... more ABSTRACT Effects of UV radiation and associated elevated temperature on properties of polymeric composites have been well documented, limiting the scope of their usage in outdoor applications. In order to improve on this limitation, current study focused on incorporating nanoparticles into epoxy polymer composites and delay onset of deleterious effects of UV radiation by partially curing these samples. Samples were fabricated and cured to 80% conversion (partially cured) based on isothermal cure kinetic studies. Influence of 1, 2 and 3 wt. % loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the study revealed that for optimization of modified epoxy composite properties a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Fabricated samples infused with 1, 2 and 3 wt. % montmorillonite nanoclay were exposed to 2500 h of continuous UV radiation, where effects of UV radiation on viscoelastic and thermal properties were evaluated and compared with identical set of fabricated samples using manufacturers’ recommended cycle (fully cured). Addition of nanoclay increased the viscoelastic properties, and at the end of the study, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fully cured samples degraded over the same period. Samples cured to 80% showed delayed UV radiation degradation effects.

Journal of Materials Research and Technology, 2014

ABSTRACT The primary focus of this study was to evaluate the effects of different montmorillonite... more ABSTRACT The primary focus of this study was to evaluate the effects of different montmorillonite nanoclays (MMT) on the thermal stability and degradation of epoxy composites exposed to UV radiation and elevated temperatures. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin, SC15 was reinforced with three different montmorillonite nanoclays, Nanomer� I.28E, Cloisite� 10A and Cloisite� 30B. Thermal properties of modified DGEBA nanocomposites were characterized. Subsequently, neat and nanocomposites were subjected to 500 h of UV radiation and characterized to determine the effects of various nanoclays on the degradation. Addition of nanoclays increased the thermal properties compared to the unmodified composite and better retention of material properties after exposure to UV radiation. Viscoelastic properties increased with addition of nanoclays in both unexposed and UV radiation exposed samples.

Mechanics of Advanced Materials and Structures, 2014

ABSTRACT Effects of ultraviolet (UV) radiation on mechanical and thermal properties of carbon fib... more ABSTRACT Effects of ultraviolet (UV) radiation on mechanical and thermal properties of carbon fiber-reinforced polymer composites (CFRC) were investigated in this study. Composites samples used for this study were fabricated using an SC-15 resin system modified with 1, 2, and 3 wt% loading of montmorillonite nanoclay (MMT; NanomerR_ 1.28E) and 8 harness satin weave carbon fiber reinforcements. Fabricated samples were UV conditioned using QUV/SE, an accelerated weathering chamber. Mechanical properties were characterized through quasi-static and dynamic compression, and flexural tests. Viscoelastic properties were determined through dynamic mechanical analysis (DMA). Results show an increase in mechanical properties up to 56% for 2 wt% samples at room temperature, and an overall decrease in mechanical properties after conditioning. Viscoelastic properties, such as glass transition temperature (Tg), increased with nanoclay content for room temperature. However, 2 and 3 wt% samples showed a decrease in Tg after conditioning, while an increase was observed in the case of neat and 1 wt% samples. On the other hand, storage modulus showed an increase in both conditioned and unconditioned samples with increasing nanoclay content up to 2 wt% and a decrease for 3 wt%.

ABSTRACT Compressive and flexural properties of carbon fiber reinforced composites (CFRC) infused... more ABSTRACT Compressive and flexural properties of carbon fiber reinforced composites (CFRC) infused with montmorillonite nanoclay exposed to UV radiation and condensation was examined in this study. Nanoclay contents in samples used in this study were 0 (control), 1, 2 and 3 wt%. Samples were exposed to 15 days UV radiation and condensation using QUV/SE accelerated weathering system. Compressive properties were characterized using quasi-static and dynamic loadings before and after exposure. Flexural properties were also characterized through three point bending test according to ASTM standards. Compressive and flexural properties were monitored every 5 days of exposure in each conditioning. UV exposed samples with nanoclay showed a different trend after 5 days compared to neat samples, showing an increase in strength and modulus after 10 days of exposure. Samples exposed to condensation did not follow any specific pattern, although there was a decrease in mechanical properties in all samples.

With the depletion of petrochemical resources, the increase in greenhouse gases emission, and shr... more With the depletion of petrochemical resources, the increase in greenhouse gases emission, and shrinking landfill capacity, the manufacture, use, and disposal of synthetic composites is at an all-time high. This does not lead to any form of sustainable use of composites, let alone allow for growth of the use and supporting industry. Many researchers and industry partners understand the need for sustainable composites and have renewed the research and funding for such progress. One of the particular areas is the expansion into nitroxide mediated polymerization due to the reduction in uncontrolled exothermic reactions during the curing process of thick components. This allows larger and thicker natural composites to be fabricated with a lower cure temperature. The research has expanded from initial work involving the polymerization using a nitroxyl mixed with a conventional initiator like dibenzoyl peroxide [2, p. 422] to chain end functionalization [3], through the development of well...

The objective of this work was to investigate the mitigating effects of montmorillonite nanoclay ... more The objective of this work was to investigate the mitigating effects of montmorillonite nanoclay (MMT) if any, on the properties of carbon fiber reinforced composites (CFRC) infused with different weight percentages of MMT and exposed to UV radiation and condensation. Composites used in this study were control and with 1-3 wt. % of nanoclay. Samples were exposed to 15 days of continuous UV radiation and condensation using QUV/SE accelerated weathering system. Mechanical and thermal properties were characterized by compression tests, thermo-gravimetric analysis (TGA) and dynamic mechanical analyses (DMA) according to ASTM standards. Surface morphology of exposed samples was characterized through Scanning electron microscopy (SEM). These properties were characterized every 120 hours of exposure. Samples exposed to condensation did not follow any specific pattern, although there was a decrease in mechanical properties in all samples.

The objective of this work is to investigate the effect of formic acid, peroxyformic acid and hyd... more The objective of this work is to investigate the effect of formic acid, peroxyformic acid and hydrogen peroxide bleaching on morphology, crystallinity and thermal stability of kenaf fiber as a source of cellulose, and assess the suitability of kenaf fiber for isolation of cellulose nanofibers by acid hydrolysis treatment followed by ultrasonication. Characterization of kenaf fiber after each step of chemical treatments was done using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Extracted cellulose nanofibers had diameters in the nanometer range and showed significant increase in crystallinity, but a decrease in thermal stability.

Open Journal of Composite Materials, 2013

Effects of carboxyl functionalized MWCNTs on the cure behavior of epoxy resin (EPIKOTE TM resin 8... more Effects of carboxyl functionalized MWCNTs on the cure behavior of epoxy resin (EPIKOTE TM resin 862 and EPICURE TM curing agent W) were investigated by using differential scanning calorimeter in dynamic scan mode. Results indicated that nanotubes could initiate cure reaction at lower temperature while only 0.1 wt% samples were able to suppress the peak temperature (T p ) consistently regardless of different heating rate due to their higher reaction rate, other two batches (0.2 wt% and 0.3 wt% CNT) showed hardly any change in T p compared to neat samples. Furthermore, addition of small amount (0.1 wt%) of CNTs significantly reduced the activation energy of the system but further addition elevated that due to their retarding effect. Also, a correlation was established between the dispersion state of CNTs in epoxy and total heat of reaction (ΔH) where lower ΔH was considered as an indication of better interfacial interaction of CNTs with matrix and hence, better dispersion. The difference in curing behavior of three different CNT percentages was discussed in terms of their steric hindrance and state of dispersion in the matrix.

Optics and Laser Technology, 2014

This research was aimed to use ball milling method to extract cellulose nanofibers (CNFs) from ... more This research was aimed to use ball milling method to extract cellulose nanofibers (CNFs) from a
bio-waste (i.e. wheat straw), and also to use the extracted cellulose nanofibers as reinforcing materials in polyvinyl
alcohol (PVA) thin film. To study the effect of cellulose nanofibers (CNFs) on mechanical and thermal properties of
polyvinyl alcohol (PVA) nano-composite films, thin film nano-composites were loaded with different loading of
cellulose nanofibers (CNFs) by weight percent (i.e. 1,3,5 and 7% loading). As a result of the research, we found that
the tensile and thermal properties of PVA thin composite increased up to 5% loading of cellulose nanofibers
(CNFs). In contrast, the tensile as well as thermal properties of PVA nano -composite film degraded because of poor
dispersion and agglomeration of CNFs

The objective of this work was to find out the compositional characteristics of wheat straw in te... more The objective of this work was to find out the compositional characteristics of wheat straw in
terms of cellulose and lignin contents and assess the suitability of wheat straw for isolation of
cellulose microfibrils. The fractionation process includes formic acid/peroxyformic acid
treatment, bleaching and ball milling of bleached cellulose. 39.10 % Cellulose, 20.40 % lignin
and 25.02 % of other compounds were extracted. Extracted cellulose was characterized using
Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), and
thermogravimetric analysis (TGA). Morphological and thermal analyses studies showed that the
extracted microfibrils had reduced length and diameter and showed good thermal stability
suitable for various advanced nano technological applications.

The prime objective of this study was to fabricate epoxy polymer composite modified with graphene... more The prime objective of this study was to fabricate epoxy polymer composite modified
with graphene nanoplatelets (GP) and montmorillonite nanoclay (MMT) binary filler materials.
Different loading percentages of individual and binary nanofillers were incorporated into an epoxy
matrix system to investigate the synergistic effect of nanofillers on composites properties. Dynamic
mechanical analysis (DMA) and three point bend test were carried out to investigate the viscoelastic
and flexural properties of neat epoxy and nanofillers reinforced nanocomposites. Incorporation of 3
wt. % of MMT and 0.1 wt. % of GP resulted in better flexure strength, modulus and storage
modulus although there is no significance change in glass transition temperature (Tg).

Journal of Materials Research and Technology, 2015

Journal of Nanoscience, 2013

Diglycidyl ether of Bisphenol A (DGEBA) based SC-15 epoxy resin was modified with three different... more Diglycidyl ether of Bisphenol A (DGEBA) based SC-15 epoxy resin was modified with three different commercially available montmorillonite (MMT) nanoclay: Nanomer I.28E and Cloisite 10A and 30B. Cure behavior of nanocomposites was studied using a variety of techniques. Primary focus of this study was to investigate influence of different surface modifications of MMT nanoclay on rheological properties and cure behavior of SC-15 epoxy resin. By adding MMT to SC-15 epoxy resin, chemistry of the epoxy is altered leading to changes in rheological properties and ultimately enthalpy and activation energy of reactions. Addition of Nanomer I.28E delayed gelation, while Cloisite 10A and 30B accelerated gelation, regardless of the curing temperature. Activation energy of reaction was lower with the addition of Nanomer I.28E and Cloisite 10A and higher for Cloisite 30B compared to neat SC-15 epoxy composite.

Polymer Degradation and Stability, 2014

ABSTRACT Effects of UV radiation and associated elevated temperature on properties of polymeric c... more ABSTRACT Effects of UV radiation and associated elevated temperature on properties of polymeric composites have been well documented, limiting the scope of their usage in outdoor applications. In order to improve on this limitation, current study focused on incorporating nanoparticles into epoxy polymer composites and delay onset of deleterious effects of UV radiation by partially curing these samples. Samples were fabricated and cured to 80% conversion (partially cured) based on isothermal cure kinetic studies. Influence of 1, 2 and 3 wt. % loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the study revealed that for optimization of modified epoxy composite properties a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Fabricated samples infused with 1, 2 and 3 wt. % montmorillonite nanoclay were exposed to 2500 h of continuous UV radiation, where effects of UV radiation on viscoelastic and thermal properties were evaluated and compared with identical set of fabricated samples using manufacturers’ recommended cycle (fully cured). Addition of nanoclay increased the viscoelastic properties, and at the end of the study, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fully cured samples degraded over the same period. Samples cured to 80% showed delayed UV radiation degradation effects.

Journal of Materials Research and Technology, 2014

ABSTRACT The primary focus of this study was to evaluate the effects of different montmorillonite... more ABSTRACT The primary focus of this study was to evaluate the effects of different montmorillonite nanoclays (MMT) on the thermal stability and degradation of epoxy composites exposed to UV radiation and elevated temperatures. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin, SC15 was reinforced with three different montmorillonite nanoclays, Nanomer� I.28E, Cloisite� 10A and Cloisite� 30B. Thermal properties of modified DGEBA nanocomposites were characterized. Subsequently, neat and nanocomposites were subjected to 500 h of UV radiation and characterized to determine the effects of various nanoclays on the degradation. Addition of nanoclays increased the thermal properties compared to the unmodified composite and better retention of material properties after exposure to UV radiation. Viscoelastic properties increased with addition of nanoclays in both unexposed and UV radiation exposed samples.

Mechanics of Advanced Materials and Structures, 2014

ABSTRACT Effects of ultraviolet (UV) radiation on mechanical and thermal properties of carbon fib... more ABSTRACT Effects of ultraviolet (UV) radiation on mechanical and thermal properties of carbon fiber-reinforced polymer composites (CFRC) were investigated in this study. Composites samples used for this study were fabricated using an SC-15 resin system modified with 1, 2, and 3 wt% loading of montmorillonite nanoclay (MMT; NanomerR_ 1.28E) and 8 harness satin weave carbon fiber reinforcements. Fabricated samples were UV conditioned using QUV/SE, an accelerated weathering chamber. Mechanical properties were characterized through quasi-static and dynamic compression, and flexural tests. Viscoelastic properties were determined through dynamic mechanical analysis (DMA). Results show an increase in mechanical properties up to 56% for 2 wt% samples at room temperature, and an overall decrease in mechanical properties after conditioning. Viscoelastic properties, such as glass transition temperature (Tg), increased with nanoclay content for room temperature. However, 2 and 3 wt% samples showed a decrease in Tg after conditioning, while an increase was observed in the case of neat and 1 wt% samples. On the other hand, storage modulus showed an increase in both conditioned and unconditioned samples with increasing nanoclay content up to 2 wt% and a decrease for 3 wt%.

ABSTRACT Compressive and flexural properties of carbon fiber reinforced composites (CFRC) infused... more ABSTRACT Compressive and flexural properties of carbon fiber reinforced composites (CFRC) infused with montmorillonite nanoclay exposed to UV radiation and condensation was examined in this study. Nanoclay contents in samples used in this study were 0 (control), 1, 2 and 3 wt%. Samples were exposed to 15 days UV radiation and condensation using QUV/SE accelerated weathering system. Compressive properties were characterized using quasi-static and dynamic loadings before and after exposure. Flexural properties were also characterized through three point bending test according to ASTM standards. Compressive and flexural properties were monitored every 5 days of exposure in each conditioning. UV exposed samples with nanoclay showed a different trend after 5 days compared to neat samples, showing an increase in strength and modulus after 10 days of exposure. Samples exposed to condensation did not follow any specific pattern, although there was a decrease in mechanical properties in all samples.