Reduced Graphene Oxide Loading Research Articles

In Situ Bioprocessing of Bacterial Cellulose with Graphene: Percolation Network Formation, Kinetic Analysis with Physicochemical and Structural Properties Assessment.

The understanding of microbial growth dynamics during in situ fermentation and production of bacterial cellulose (BC) with impressive properties mimicking artificial nacre, suitable for commodity applications remains fundamentally challenging. Fabrication of BC/graphene films through a single step in situ fermentation with improved properties provides a sustainable replacement to the conventional chemical-based modification using toxic compounds. This work reports the effect of reduced graphene oxide (RGO) on in situ fermentation kinetics and demonstrates the formation of percolated-network in BC/RGO nanostructures. The evaluation of kinetic parameters shows that the specific growth rate reaches optimal values at 3 wt % RGO loadings, with mixed growth associated BC production behavior. The two-dimensional graphene sheets uniformly dispersed into a three-dimensional matrix of BC nanofibers via hydrogen-bonded interactions along with in situ reductions of RGO sheets, as confirmed from spectroscopic studies. This study also demonstrates the presence of percolated network-like structures between BC fibers and RGO platelets, which resulted in the formation of nanostructures with exceptional mechanical robustness and electrical conductivity. The physicochemical and structural properties of fabricated BC/RGO films were found to significantly depend upon the RGO compositions as well as fermentation conditions. We envision that the proposed ecofriendly and scalable technology for the formation of BC/RGO films with excellent inherent properties and performance will attract great interest for its prospective applications in flexible electronics.

Valorization of sugarcane straw to produce highly conductive bacterial cellulose / graphene nanocomposite films through in situ fermentation: Kinetic analysis and property evaluation

Abstract Bacterial cellulose based nanocomposites have found a growing interest in recent decades due to their impressive inherent characteristics with potential applications in diverse sectors. However, there remain several challenges due to increased production cost, lower yield, and sustainability or biocompatibility issues after chemical-based modifications. This study demonstrates the fabrication of bacterial cellulose-reduced graphene oxide films via in-situ fermentation approach using abundantly available agricultural waste (sugarcane straw) as a feedstock. The presence of reduced graphene oxide at different concentrations in culture media, significantly altered the fermentation kinetics, as evident from kinetic parameter and yield coefficients. Higher yields of bacterial cellulose-reduced graphene oxide nanocomposites, with presence of strongly integrated network-like structures between bacterial cellulose nanofibers and reduced graphene oxide nanosheets were observed at 2 wt % reduced graphene oxide loadings. Formation of such percolated networks was confirmed from improved mechanical properties and enhanced electrical conductivity, through both experimental and modeling investigations. The proposed in-situ fermentation technique to produce highly conductive bacterial cellulose-reduced graphene oxide films provides an alternative approach to meet the growing demands of biomass-derived renewable and sustainable biomaterials with commercial significance.

Synthesis of nitrogen-doped reduced graphene oxide loading with Au-Ag bimetallic nanoparticles for electrochemical detection of daunorubicin

Nitrogen-doped reduced graphene oxide loading with Au-Ag bimetallic nanoparticles (NG-Au-Ag) was synthesized by a facile two-step strategy. The successful formation of NG-Au-Ag nanocomposites were confirmed by transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis. Furthermore, NG-Au-Ag nanocomposites were modified onto the electrode surface for the voltammetric detection of daunorubicin (DNR). The results showed that the NG-Au-Ag modified electrode expressed high electrocatalytic activity toward the redox of DNR, allowed detection of DNR with wide linear range (0.01 μg mL−1 to 15 μg mL−1) and low detection limit (3 ng mL−1). The modified electrode also exhibited satisfactory performance for the detection of DNR in human serum samples.

Polyamide 6/reduced graphene oxide nano-composites prepared via reactive melt processing: formation of crystalline/network structure and electrically conductive properties

In this work, polyamide 6 (PA6)/reduced graphene oxide (RGO)- toluene-2,4-diisocyanate (TDI) composites were fabricated by reactive melt processing, and effect of formation of crystalline/network structure on electrically conductive properties of the composites was studied. The molecular bridge effect of exfoliated RGO-TDI resulted in the homogeneous dispersion of RGO in PA6 matrix. Crystallization analysis shows that RGO facilitated the crystallization of PA6 matrix mainly via accelerating the generation of crystal nucleus, reaching maximum of Xc and minimum of crystal grain size upon RGO level of 1.66 vol.%, which confirmed the formation of most perfect crystalline structure. According to the dynamic rheological analysis, both frequency-independence of G’ and sharply reduce phase angle at low-frequency region with RGO loading level of 1.66 vol.% indicate the transition from liquid-like to solid-like rheological behavior, where terminal to non-terminal transition as well as Cole-Cole arc and rapidly increasing entanglement density confirm the formation of percolation network structure with RGO as a crosslinking center. Corresponding to the analysis above, the electrical conductivity of the nano-composites increased rapidly to the equilibrium value, resulting from the formation of perfect conductive network at RGO loading level of 1.66 vol.%, which was confirmed by TEM analysis.

Enhanced Anti-ablation and Alkali Corrosion Resistance of Graphene Oxide Modified Urea-Melamine-Phenol Formaldehyde Composites Reinforced by R-Glass Fiber

Graphene oxide (GO) modified urea-melamine-phenol formaldehyde resin (UMPF) was reinforced by R-glass fiber woven. GO was reduced by UMPF to reduced graphene oxide (RGO). Transmission electron microscopy (TEM), atomic force microscope (AFM), and scanning electron microscopy (SEM) were used to analyze the morphology and dispersibility of RGO in UMPF. Compared with the pure R-glass fiber woven reinforced urea-melamine-phenol formaldehyde resin (RFW-UMPF), the thermal conductivity and carbon residual value (CRV) of R-glass fiber woven reinforced GO modified urea-melamine-phenol formaldehyde resin (RFW-GO/UMPF) (0.8 wt% RGO) at 800 °C were increased by 6.3% and 20%, respectively. Anti-ablation researches revealed that with 0.8 wt% RGO loading, the linear ablation rate (LAR) and mass ablation rate (MAR) of RFW-GO/UMPF deceased by 25.6% and 12.6%, respectively. Moreover, the enhancement mechanism of RGO on anti-ablation properties and alkali corrosion resistance (ACR) performances were systematically discussed.

Effect of Separate Zinc, Copper and Graphene Oxides Nanofillers on Electrical Properties of PVA Based Composite Strips

Light weight, flexible and easily processable polymeric nanocomposites possessing either high or low dielectric permittivity is in demand for high density capacitors and in microelectronics, respectively. The present study was designed to investigate the effect of separate zinc oxide (ZnO), copper oxide (CuO), graphene oxide (GO) and reduced graphene oxide (RGO) nanofillers on the electrical properties of poly(vinyl alcohol) (PVA) based composite strips. Herein, a simple solution casting technique has been adopted to fabricate composite strips at different nanofillers loadings. The electrical properties of composite strips were evaluated using a frequency response analyzer. There was observed a rise in dielectric constant ( $$ \varepsilon^{\prime } $$ ), dielectric loss ( $$ \varepsilon^{\prime \prime } $$ ) and AC conductivity (σac) of separate ZnO and GO nanofillers loaded PVA strips; whereas a decrease in the said parameters was observed on loading with separate CuO and RGO nanofillers in the PVA based composite strips. The frequency response analysis showed a prominent effect of applied frequency and nanofiller contents on the electrical properties of composite strips. There was observed a significant decrease in $$ \varepsilon^{\prime } $$ and $$ \varepsilon^{\prime \prime } $$ on just 0.004 wt.% RGO loading in the PVA based composite strips. Such efficient nanocomposites might be suitable for their use in microelectronics and microwave applications at above the 1 MHz range.

Reduced Graphene Oxide–TiO2 Nanotube Composite: Comprehensive Study for Gas-Sensing Applications

Graphene oxide (GO) and reduced graphene oxide (RGO) have unique properties that can revolutionize the performances of functional devices. Graphene-based materials can be coupled with metal oxide nanomaterials for gas-sensing applications. In this work, we report the synthesis and gas-sensing properties of a composite material based on RGO-loaded TiO2 nanotubes. To properly tune the reduction of GO to RGO, we adopted a gas-phase process that can be applied in situ on each gas sensor device, allowing one to track the process effects through sensor conductance. We systematically investigated the gas-response dependence from the RGO loading and its reduction, showing the occurrence of an optimal RGO concentration arising from the interplay of these two parameters. Hence, these two factors should be considered in parallel to functionalize the metal oxide materials with GO for the fabrication of chemical sensor devices.

Study of dielectric relaxation behavior of composites of Poly (vinyl alchohol) (PVA) and Reduced graphene oxide (RGO)

The composite films of Poly (vinyl alcohol) (PVA) and Reduced graphene oxide (RGO) with 1 wt%, 1.5 wt% and 2 wt% loading of RGO using solution mixing have been prepared via evaporative casting technique. For this purpose, RGO has been chemically synthesized using modified Hummer's method and characterized using UV–Visible absorption, Fourier Transform Infrared (FTIR) spectroscopy and Transmission electron Microscopy (TEM). Further, the chemical interaction of PVA chains with RGO has been revealed using FTIR spectroscopy. The variation in dielectric parameter (εʹ and εʹʹ) with frequency has been studied at different temperatures (320 K–400 K) in order to epitomize the dielectric relaxation behavior in the prepared composite films. The values of εʹ and εʹʹ have been found to increase with rise in temperature and loading of RGO. The almost linear variation in ac conductivity (ϭac) with frequency at each studied temperature suggests the observation of universal power law in these composites. However, the slope of these curves was found to decrease with rise in temperature suggesting the Correlated Barrier Hopping (CBH) model as charge transport mechanism in these composites. The non-symmetric shape of electric modulus (M″) variation indicate the existence of non-Debye type of relaxation. The relaxation time (τ) determined from M″ variation with frequency is found to be decreased with rise in temperature. This elucidates the transition of long range to short range mobility of charge carriers with rise in temperature. Further, as an effect of increase in RGO concentration in composites, increase in τ has been found depicting their use in energy storage applications where materials with longer discharging time are required.

Enhancing the Mechanical and Electrical Properties of Poly(Vinyl Chloride)-Based Conductive Nanocomposites by Zinc Oxide Nanorods

A simple approach to decorate multi-walled carbon nanotube (MWCNT)–reduced graphene oxide (RGO) hybrid nanoparticles with zinc oxide (ZnO) nanorods is developed to improve the electrical and mechanical properties of poly(vinyl chloride) (PVC)/MWCNT–RGO composites. The ZnO nanorods act as “joint” in three-dimensional (3D) MWCNT–RGO networks and the hybrid particles strongly interact with PVC chains via p-π stacking, hydrogen bonds, and electrostatic interactions, which we confirmed by scanning electron microscopy (SEM) and Raman analysis. By introducing the ZnO nanorods, the RGO–ZnO–MWCNT hybrid particles increased 160% in capacitance compared with MWCNT–RGO hybrids. Moreover, the addition of RGO–ZnO–MWCNT to PVC resulted in the mechanical properties of PVC being enhanced by 30.8% for tensile strength and 60.9% for Young’s modulus at the loadings of 2.0 weight percent (wt.%) and 1.0 wt.%, respectively. Meanwhile, the electrical conductivity of PVC increased by 11 orders of magnitude, from 1 × 10−15 S/m to 1 × 10−4 S/m for MWCNT–ZnO–RGO loading at 5.0 wt.%.

Synthesis and Characterization of Reduced Graphene Oxide Reinforced Polymer Matrix Composite

Graphene and its derivatives, owing to their superior properties have been being used as reinforcement to improve the properties of polymer matrix. In this work, the influence of Reduced Graphene Oxide (RGO) on the properties of Poly Vinyl Alcohol (PVA) has been studied. RGO was synthesized from graphite powder starting with synthesis of Graphene Oxide (GO) by Modified Hummer’s Method followed by the reduction of GO with Hydrazine Hydrate. Synthesized RGO was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). PVA composites with different RGO loading were fabricated by simple solution mixing method. The fabricated composites were characterized by Optical Microscopy, XRD, UV-Visible Spectroscopy, Thermo Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Shore hardness test. The reports from those tests have ensured that after incorporating RGO in PVA matrix, band gap energy was decreased, crystallinity and shore hardness were increased and thermal stability was improved up to a certain level of RGO loading.

Interface design of graphene/copper composites by matrix alloying with titanium

The attainment of intimate and strong interface is critical for promoting the load transfer ability and strength of graphene/metal composites. Herein, we reported an interface design strategy by matrix-alloying with Ti for in-situ interfacial carbide formation in reduced graphene oxide (RGO)/CuTi composites. It was demonstrated that both Ti8C5 nanolayers and Ti8C5 nanoparticles were in-situ formed at the local interface of RGO/CuTi composite, which played a “rivet” role in enhancing the interfacial bonding between the RGO and CuTi matrix. At 1.5vol% RGO loading, compared to RGO/Cu composite without alloying, the RGO/CuTi composite exhibited a higher enhancement in tensile strength (57.7% vs. 37.5%) and a lower reduction in coefficient of thermal expansion (−10.9% vs. −3.9%). The formed interfacial Ti8C5 nanolayers and Ti8C5 nanoparticles were proposed to originate from the amorphous carbon nanolayers and amorphous carbon nanoparticles on the surface of RGO, respectively. This study provides new insights into the interface design and carbide formation mechanism of advanced graphene/Cu composites with enhanced mechanical/thermal properties.

Plasticized PVC graphene nanocomposites: Morphology, mechanical, and dynamic mechanical properties

Improving the properties of polyvinyl chloride matrix by the incorporation of carbonaceous filler by melt mixing is an unusual thought in the polymer research. Here we incorporated reduced graphene oxide (RGO) as a filler into plasticized polyvinyl chloride (PPVC) matrix by melt mixing, an eco‐friendly method. The effect of addition of filler in the morphology of the PPVC nanocomposites was analyzed by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Raman spectroscopy. The mechanical response of the nanocomposites to an applied stress was studied. A 50% improvement in mechanical properties was obtained at a low filler loading. A decrease in elongation was observed at higher RGO loading. The dynamic mechanical analysis (DMA) of the nanocomposites indicated an increase in glass transition temperature of the PVC up on the addition of RGO. This has confirmed the confinement of PVC chains at the graphene surface. As a result, the storage modulus of the nanocomposites showed an increase up on the addition of the nanofiller. Theoretical values of the storage modulus were calculated using various theoretical equations. The effectiveness of filler on the storage modulus is estimated and is found to be consistent with the results obtained experimentally. POLYM. ENG. SCI., 58:E104–E113, 2018. © 2017 Society of Plastics Engineers

Ultrasound–assisted synthesis and characterization of polymethyl methacrylate/reduced graphene oxide nanocomposites

This article reports ultrasound–assisted synthesis of polymethyl methacrylate (PMMA)/reduced graphene oxide (RGO) nanocomposites by in situ emulsion polymerization coupled with in situ reduction of graphene oxide. The thermal degradation kinetics of the nanocomposites was also assessed with Criado and Coats‐Redfern methods. Intense microconvection generated by ultrasound and cavitation results in uniform dispersion of RGO in the polymer matrix, which imparts markedly higher physical properties to resulting nanocomposites at low (≤1.0 wt %) RGO loadings, as compared to nanocomposites synthesized with mechanical stirring. Some important properties of the PMMA/RGO nanocomposites synthesized with sonication (with various RGO loadings) are: glass transition temperature (0.4 wt %) = 124.5°C, tensile strength (0.4 wt %) = 40.4 MPa, electrical conductivity (1.0 wt %) = 2 × 10−7 S/cm, electromagnetic interference shielding effectiveness (1.0 wt %) = 3.3 dB. Predominant thermal degradation mechanism of nanocomposites (1.0 wt % RGO) is 1D diffusion with activation energy of 111.3 kJ/mol. © 2017 American Institute of Chemical Engineers AIChE J, 64: 673–687, 2018

Investigation of Mechanical Properties of Graphene and Reduced Graphene Oxide Reinforced Epoxy Matrix Composites

Abstract Graphene has generated great excitement in the scientific community due its unique mechanical and electronic properties, and also the availability of bulk quantities of graphene as both colloidal dispersion and powder. With the development of relatively high yield and defect-free synthesis methods, this exciting material is ready for practical application in the preparation of polymer nanocomposites. Here, we reported on the mechanical performances of epoxy nanocomposites which have been reinforced with exfoliated graphene nano platelet (GNP) and reduced graphene oxide (RGO) at a loading of 0 to 0.5 wt. %. A soft molding method was used for the preparation of epoxy nanocomposites. The reinforcing effects of GNP and RGO on epoxy resin were examined by tensile testing and dynamic mechanical analysis (DMA). The morphology of the epoxy/GO and epoxy/RGO nanocomposites were investigated using a scanning electron microscope (SEM). A significant improvement on mechanical properties of epoxy/GO and epoxy/RGO nanocomposites was observed at low GNP and RGO loading. Contrary to the literature, the ultimate tensile strength values have mainly decreased, although the Young’s modulus has improved. Dynamic mechanical analysis has shown that with the addition of both GNP and RGO, storage modulus was significantly enhanced at 40 °C. The loss factor was almost not affected by both RGO and GNP loading. SEM investigation of the fractured surface indicates that GNP and RGO fillers are dispersed uniformly in the epoxy matrix.

Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites.

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young’s modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.

Preparation and characterization of graphene‐agar and graphene oxide‐agar composites

ABSTRACTBiodegradable counterparts of petro plastics for packaging applications are highly desired due to environmental considerations. Agar can be a potential material due to its availability and biodegradability. However, moderate mechanical strength and thermal stability, in addition to poor resistance against water, needs to be addressed before agar can be commercially implemented as packaging material. As a step toward this objective, graphene oxide (GO) and reduced GO (RGO) were incorporated in agar and were solution casted in the form of films. The tensile strength was increased by 118.4% and 69.4% at 2% GO and 2% RGO loading, respectively. Higher interfacial bonding between GO and agar compared to that of RGO and agar was attributed for the observed mechanical properties. Resistance to swelling and hydrophobicity (contact angle) of the composite were improved as well when compared to pure agar. The tensile strength and the contact angle values were however, decreased after the addition of 2% GO and 2% RGO. The morphological investigation showed that the formation of pores at higher concentration of reinforcement was the contributing factor for the decrease in tensile strength. No significant change in thermal properties was observed. The transmittance value was reduced to 0% after the incorporation of GO and RGO. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45085.

Manipulating microstructures and electrical properties of carbon fiber/reduced graphene oxide/nickel composite textiles with electrochemical deposition techniques

Since graphene and their composites play significant roles in the catalysts, energy storage, electronics and other fields, where electron transport is highly critical, here, we introduce reduced graphene oxide (RGO) interfaces in the carbon fiber (CF) networks for preparing a novel lightweight carbon fiber/reduced graphene oxide/nickel (CF-RGO-Ni) composite textile. Upon the charaterizations on the microscopic morphologies, electrical and magnetic properties, and density, the presence of RGO nanosheets and nickel nanoparticles would substantially influence the related physical properties in the resulting composite textiles. Furthermore, the key parameters, including RGO loading, deposition time, current density and annealing temperature of carbon matrices, have been studied to understand their effects on the electrochemical deposition of nickel nanoparticles. Implication of the results suggests that the RGO interface is a unique medium for essentially promoting the electrochemical deposition kinetics and active sites for growing nickel nanoparticles, which indicates a universal approach for preparing advanced lightweight composites with the presence of graphene naonstructures.

High capacity supercapacitor material based on reduced graphene oxide loading mesoporpus murdochite-type Ni6MnO8 nanospheres

Mesoporous materials often deliver a series of attractive properties for low-cost and environmentally-friendly energy storage/conversion technologies. Based on this, we prepared mesoporous murdochite-type Ni6MnO8 nanospheres (NMN) with a uniform morphology by using a template route. Then as-prepared NMN were loaded uniformly on reduced graphene oxide (RGO) sheets via electrostatic interaction to fabricate RGO-NMN composite (RGO-NMN), which combines the advantages of both RGO such as double-layer capacity and NMN such as high pseudocapacitity. By the aid of a nanosized mesoporous silica template, NMN and RGO-NMN display a large specific surface areas and concentrated pore diameter distribution. The large surface area and abundant pores can provide a promising route for easy access of electrolyte in energy storage electrodes and favor the availability of Faradic reaction in electroactive sites greatly. Indeed, following electrochemical analysis uncovered a remarkable value of specific capacitance (862.5Fg−1 and 498.3Fg−1 at 0.5Ag−1 for RGO-NMN and NMN) and a predominant long-term stability with slight decays less than 10% after 9000 cycling test in both NMN and RGO-NMN electrodes.

Advanced nanostructured photocatalysts based on reduced graphene oxide-flower-like Bi2WO6 composites for an augmented simulated solar photoactivity activity

A simple hydrothermal process was proposed to prepare the flower-like Bi2WO6 architectures, and the as-synthesized Bi2WO6 photocatalysts were further processed with the prepared graphene oxide (GO) to form novel reduced graphene oxide (RGO)/Bi2WO6 composites. The nano-materials were characterized with the help of XRD, XPS, SEM, FTIR, UV-DRS, PL techniques to investigate their morphological, physical, optical, and photochemical properties. Photocatalytic performances of the pure flower-like Bi2WO6 architectures and RGO/Bi2WO6 composites were compared and evaluated through the degradation of ciprofloxacin hydrochloride (Cipro HCl) wastewater under the simulated visible light. It was found that the RGO/Bi2WO6 composites displayed enhanced visible light-driven photocatalytic activities. It might be that the RGO loading not only effectively suppressed the electron–hole recombination, but also increased the light absorption ability. The effects of operating condition involved in the photocatalytic process were further examined, and the cycle-stability experiment demonstrated that as-obtained 2% RGO/Bi2WO6 photocatalysts had good photocatalytic repeatability.

(Invited) How Beneficial Is Reduced Graphene Oxide (RGO) for Long-Term Photo Generated Charge Transport in Inorganic Oxide - Rgo Nanocomposites? a Case Study of Bismuth Titnate - Rgo Films?

This work begins with a summary of the role of reduced graphene oxide (RGO) in promoting the photoactivity of oxides and chalcogenides. Initial indicators suggest that RGO is a good material for promoting charge speration over short time scales. However the story over long term illumination is different. This presentation delineates the results of a systematic analysis of the photoelectrochemical (PEC) and optical responses of RGO combined with a representative multimetal oxide – bismuth titanate (BTO) on films. We investigated the role of RGO as a promoter of charge separation and transport, by suppressing recombination loss of carriers in BTO. The micro-structure of the BTO/RGO composite observed using transmission, scanning electron, and atomic force microscopy, revealed a well-integrated, and highly porous morphology compared to pristine BTO film. The integration of BTO with RGO resulted in a ~ 7 fold increase in photocurrent density with an optimal RGO loading of 2 wt%. The performance of the BTO/RGO interface was further examined to obtain critical insights on: (i) how the electrolyte influences the stability of the BTO/RGO composite and (ii) what interactions prevail at the BTO/RGO interface, under long-term illumination to impact the RGO stability. This work assumes immediate significance because implementation of RGO as a charge transport agent in oxidative systems is heavily researched currently. Unless a mechanism to protect RGO is determined, its long-term stability, especially under oxidative conditions of any form, has to be thoroughly investigated on a case-to-case basis to ensure composite longevity.