Laminate Surfaces Research Articles

Study of resin coating adhesion on GFRP laminate surfaces after UV degradation

This paper describes research on the effect of UV radiation on the surface of a GFRP (Glass Fiber Reinforced Polymer) laminate in the context of increasing the adhesion between the laminate and polymer resin coatings. GFRP composite samples were prepared using the hand lay-up method. The samples were then exposed to various types of ultraviolet radiation (UVA, UVB, UVC) for 1000 h, with surface roughness measurements every 100 h. The flexural strength of laminates after photoaging was tested, which showed an increase in the strength of aged laminates compared to the reference sample by approximately 5–10 %. Coatings of various thicknesses were applied to the surface of the aged laminates and their adhesion to the substrate material was tested using the mandrel bending method alongside the cross-cut technique. The greatest change in surface roughness was observed on the sample exposed to UVC radiation, where the roughness increased approximately twice in relation to the reference sample. Coating adhesion tests have additionally shown that degradation under the influence of UVC has a positive effect on the adhesion of coatings to the laminate.

Impact of Fiber Buildup Stacking Sequence on Thermo-Mechanical Behaviour of Natural Fiber–Reinforced Anamide Composites

This article focuses on the viscoelastic behaviour of the anamide composites using a dynamic mechanical study developed by hot compression moulding technology at higher temperatures. The frequency range for this analysis is 1 Hz. In the nitrogen atmosphere, thermogravimetry analysis differential scanning calorimetry was used to investigate the thermal stability of composite laminates with various fiber orientations. The findings showed that a glass transition temperature close to 100°C can be achieved at 1 Hz to increase the fiber orientation of the basalt fiber-enhanced anamide compounds. Through the thermo-gravimetric analysis experiments, the excellent thermal stability of composite laminates at temperatures above 600°C was conspicuous. Analysis using the Fourier transform infrared (FTIR) spectroscopy envisioned the surface chemical properties of anamide films at various fiber orientations, and the interaction properties between fiber and matrix were determined. Scanning electron microscopy on composite laminate surfaces proclaimed that the interface relationship between the basalt fiber and the anamide material is superior with FTIR findings being assisted. The findings demonstrate that composite laminates may be a good replacement for high-performance and high-temperature applications since they are thermally extremely robust with great rigidity.

Gas permeability mitigation of cryogenically cycled stitched composites using thin plies

3D through-thickness stitched composites can be used to produce lightweight, unitized structures for cryogenic applications. However, to fully utilize stitched composites for these applications, cryogenic fuel leakage through transverse cracks in these structures must be prevented. In this study, thin plies (cured thickness ≈ 0.032 mm) are incorporated directly into three-dimensional stitched polymer matrix composites (PMCs) to reduce gas permeability and prevent through-thickness cracking. Stitched carbon/epoxy composites ([+45/−45]4s) with standard thickness plies were used as baseline laminates. Thin plies were added to the baseline design to fabricate three different laminates with one thin ply placed on (a) both laminate surfaces, (b) two plies from each laminate surface, and (c) at the laminate midplane. Test coupons were thermally cycled from ambient (23 °C) to cryogenic (−196 °C) temperatures. Gas permeability and ply-level microcrack densities were measured as a function of cryogenic cycles. Results show that both the presence and location of the thin plies impact the gas permeation characteristics of stitched composites. Thin plies were effective in resisting microcrack growth and acted as integral liners to prevent excessive gas flow through the stitched specimens.

Benchmarking for Strain Evaluation in CFRP Laminates Using Computer Vision: Machine Learning versus Deep Learning.

The strengthening of concrete structures with laminates of Carbon-Fiber-Reinforced Polymers (CFRP) is a widely adopted technique. retained The application is more effective if pre-stressed CFRP laminates are adopted. The measurement of the strain level during the pre-stress application usually involves laborious and time-consuming applications of instrumentation. Thus, the development of expedited approaches to accurately measure the pre-stressed application in the laminates represents an important contribution to the field. This paper proposes and benchmarks contact-free architecture for measuring the strain level of CFRP laminate based on computer vision. The main objective is to provide a solution that might be economically feasible, automated, easy to use, and accurate. The architecture is fed by digitally deformed synthetic images, generated based on a low-resolution camera. The adopted methods range from traditional machine learning to deep learning. Furthermore, dropout and cross-validation methods for quantifying traditional machine learning algorithms and neural networks are used to efficiently provide uncertainty estimates. ResNet34 deep learning architecture provided the most accurate results, reaching a root mean square error (RMSE) of 0.057‰ for strain prediction. Finally, it is important to highlight that the architecture presented is contact-free, automatic, cost-effective, and measures directly on the laminate surfaces, which allows them to be widely used in the application of pre-stressed laminates.

Factors influencing environmental sampling recovery of healthcare pathogens from non-porous surfaces with cellulose sponges.

Results from sampling healthcare surfaces for pathogens are difficult to interpret without understanding the factors that influence pathogen detection. We investigated the recovery of four healthcare-associated pathogens from three common surface materials, and how a body fluid simulant (artificial test soil, ATS), deposition method, and contamination levels influence the percent of organisms recovered (%R). Known quantities of carbapenemase-producing KPC+ Klebsiella pneumoniae (KPC), Acinetobacter baumannii, vancomycin-resistant Enterococcus faecalis, and Clostridioides difficile spores (CD) were suspended in Butterfield’s buffer or ATS, deposited on 323cm2 steel, plastic, and laminate surfaces, allowed to dry 1h, then sampled with a cellulose sponge wipe. Bacteria were eluted, cultured, CFU counted and %R determined relative to the inoculum. The %R varied by organism, from <1% (KPC) to almost 60% (CD) and was more dependent upon the organism’s characteristics and presence of ATS than on surface type. KPC persistence as determined by culture also declined by >1 log10 within the 60 min drying time. For all organisms, the %R was significantly greater if suspended in ATS than if suspended in Butterfield’s buffer (p<0.05), and for most organisms the %R was not significantly different when sampled from any of the three surfaces. Organisms deposited in multiple droplets were recovered at equal or higher %R than if spread evenly on the surface. This work assists in interpreting data collected while investigating a healthcare infection outbreak or while conducting infection intervention studies.

Essential Oil Disinfectant Efficacy Against SARS-CoV-2 Microbial Surrogates.

Reports of COVID-19 cases potentially attributed to fomite transmission led to the extensive use of various disinfectants to control viral spread. Alternative disinfectants, such as essential oils, have emerged as a potential antimicrobial. Four essential oil blends were tested on three different surfaces inoculated with a coronavirus surrogate, bacteriophage Phi 6, and a bacterial indicator, Staphylococcus aureus. Log10 concentration reductions were analyzed using GraphPad Prism software. Data collected in this study show that the application of dilute essential oil disinfectants using a spray delivery device is an effective way to reduce concentrations of bacterial and viral microorganisms on ceramic, stainless steel, and laminate surfaces. Surrogate viruses were reduced up to 6 log10 PFU and bacterial were reduced up to 4 log10 CFU. Although surfaces are no longer considered a high risk fomite for COVID-19 transmission, the disinfection of microorganisms on surfaces remains an important consideration for high touch areas in hospitals, waiting rooms, etc. The application of spray disinfectants, based on essential oil blends, provides a rapid and effective means to reduce microbial contamination on high-touched surfaces.

782. A Comparison of Four Different Sampling Methods Used to Recover Contamination from Environmental Surfaces

Abstract Background We hypothesized that sampling tools with the largest surface area would be the most efficient at recovering bacteria. To test this hypothesis, we evaluated four different sampling methods to see which was most effective at recovering bacteria from common environmental surfaces. Methods At UNC Medical Center, a 951 bed academic facility, we tested four collection methods: swabs, RODAC (replicate organism detection and counting) plates, Sponge Sticks with manual extraction and Sponge Sticks using extraction with the Seward Stomacher. Laminate and stainless steel surfaces (100 cm²) were used for testing. Known quantities of Staphylococcus aureus (SA) and Klebsiella pneumoniae (KP) were applied across the test surfaces, then allowed to dry prior to sampling. Swab samples were collected by rubbing a moistened swab over the test surface, followed by a dry swab. Both swab tips were broken into a tube of saline and mixed. An aliquot of each was inoculated to agar plates. Each RODAC agar plate was pressed onto a test surface. Sponge Stick samples were collected by rubbing a pre-moistened sponge over the test surface. Each sponge head was ejected into a bag containing saline. For manual agitation, each bag was kneaded by hand for 1 minute. For Stomacher method, bags were processed for 1 minute. The contents of each bag were poured into tubes, then centrifuged. The supernatant was removed from each tube. An aliquot of each was inoculated to agar plates. Plates were incubated at 35°C, then colonies were counted for each plate. Results Comparative recovery rates across surfaces, organism types and sampling methods are shown in the table. Conclusion Organism type, not sampling method, appeared to the most important factor in bacterial recovery. Recovery of SA was significantly higher than KP, likely because it was able to better withstand manipulation and the physical stress of drying on test surfaces. The sampling tool appeared to have the second largest impact. RODAC yielded the highest recovery, followed by swabs, then sponges. Knowing the variable recovery based on method, surface and organism is important for meaningful interpretation of environmental surveillance conducted during outbreak investigations or quality assurance monitoring. Disclosures William Rutala, MS, MPH, PhD, PDI (Professional Disposibles International) (Consultant) David J. Weber, MD, MPH, PDI (Consultant)

Production of Self-Cleaning Laminate Surfaces with Antimicrobial Effect

Production of Self-Cleaning Laminate Surfaces with Antimicrobial Effect

Thermo-responsive and shape-morphing CF/GF composite skin: Full-field experimental measurement, theoretical prediction, and finite element analysis

Shape morphing is an attractive functionality for fibre reinforced composites. Shape morphing composites can adopt various shapes and undergo different shape morphologies in response to a set of external stimuli. One of the approaches to attain shape morphing materials is through fabrication of multi-layered and asymmetric composites where morphing stems from structural anisotropy. In this work, asymmetric hybrid carbon fibre/glass fibre/epoxy composites are manufactured in which a mismatch in the coefficient of thermal expansion between carbon and glass fibre layers and different fibre directions at each layer resulted in a thermo-responsive morphing behaviour. The full-field displacement of laminate surfaces at the temperature range of −30 °C to 60 °C are monitored using digital image correlation technique. Classical laminate theory and Timoshenko bimetallic strip formula are coupled with experimental observations to predict the radius of curvature for laminates at different temperatures. Furthermore, finite element analyses are performed to uncover the stress state in the laminates and identify the contributing mechanisms. This study contributes to the state of the art by elaborating on the relations between morphing performance with stiffness and thermal expansion of anisotropic fibre reinforced laminates and their connections to the microstructure.

Towards intelligent CFRP composite machining: Surface analysis methods and statistical data analysis of machined fibre laminate surfaces

Many carbon fibre reinforced polymer composite parts need to be edged trimmed before use to ensure both geometry and mechanical performance of the part edge matches the design intent. Measurement and control of machining induced surface damage of composite material is key to ensuring the part retains its strength and fatigue properties. Typically, the overall surface roughness of the machined face is taken to be an indicator of the amount of damage to the surface, and it is important that the measurement and prediction of surface roughness is completed reliably. It is known that the surface damage is heavily dependent on the fibre orientation of the composite and cutting tool edge condition. This research has developed a new ply-by-ply surface roughness measurement methods using optical focus variation surface analysis and image segmentation for calculating areal surface roughness parameters of a machined carbon fibre composite laminate. Machining experiments have been completed using a polycrystalline diamond edge trimming tool at increasing levels of cutting edge radius. Optical surface measurement and µ-CT scanning have been used to assess machining induced surface and sub-surface defects on individual fibre orientations. Statistical analysis has been used to assess the significance of machining parameters on Sa (arithmetic mean height of area) and Sv (areal magnitude of maximum valley depth) areal roughness parameters, on both overall roughness and ply-by-ply fibre orientations. Empirical models have been developed to predict surface roughness parameters using statistical methods. It has been shown that cutting edge degradation, fibre orientation and feed rate will significantly affect the cutting mechanism, machining induced surface defects and surface roughness parameters.

Effectiveness of Copper-Impregnated Solid Surfaces on Lowering Microbial Bio-Burden Levels in an Acute Care Hospital

Microbial bio-burden on high-touch surfaces in patient rooms may lead to acquisition of health care-associated infections in acute care hospitals. This study examined the effect of a novel copper-impregnated solid material (16%-20% copper oxide in a polymer-based resin) on bacterial contamination on high-touch surfaces in patient rooms in an acute care hospital. Five high-touch surfaces were sampled for aerobic bacterial colonies (ABCs) 3 times per day over a 3-day period in 16 rooms with copper installed and 16 rooms with standard noncopper laminate installed on high-touch surfaces. A Bayesian multilevel negative binomial regression model was used to compare ABC plate counts from copper-impregnated surfaces with standard hospital laminate surfaces. The mean and median (interquartile range [IQR]) ABC counts from copper-impregnated surfaces were 25.5 and 11 (4-27), and for standard hospital laminate surfaces they were 60.5 and 29 (10-74.3). The negative binomial regression model-estimated incidence rate for ABC counts on plates taken from copper-impregnated surfaces was 0.40 (0.21-0.70) times the incidence rate of ABC counts on plates taken from standard hospital laminate surfaces. Copper-impregnated solid surfaces may reduce the level of microbial contamination on high-touch surfaces in patient rooms in the acute care environment, as our study demonstrated a decline in microbial bio-burden on samples taken from copper-impregnated compared with standard hospital laminate high-touch surfaces.

Is visual motivation for cleaning surfaces in the kitchen consistent with a hygienically clean environment?

Cleaning is a method at the disposal of domestic cooks for curtailing the dispersal of foodborne pathogens in the process of preparing food. The observation of visible dirt/soil ‘in the wrong place’ operates as one of the stimuli for action. This paper makes a transdisciplinary contribution to understandings of cleaning as a practice for ensuring safety in the kitchen, and it is mainly focused on the (in)visibility of soil or dirt. The social science research included analysis of a consumer survey in 10 European countries where 9966 respondents were asked about motivations for cleaning in the kitchen. This paper draws also on three microbiological tests. First, Portuguese (n = 7) and Norwegian (6) consumers evaluated the visible cleanliness of 10 surface areas in their kitchens, directly and through the visible residue and total bacterial numbers accumulated on a white cotton swab after swabbing the surface areas. Secondly, 15 Norwegian consumers tested if they could visually detect different types of food soils, as these dried on kitchen surfaces. Finally, the survival of Campylobacter and Salmonella in the same soil types was tested under lab conditions as the soil dried out. Cleaning food preparation surfaces “after food preparation” (73%), “before preparing food” (53%) and “when they are dirty” (43%) were the three most common self-reported behaviours. Routine was the most common motivation to clean, but this was age dependent. There was low correlation between visual detection of dirt/soil and bacterial enumeration. Visual detection of soils was dependent on type and concentration of food soils and material of the surface; the soils were more easily detected on laminate surfaces than plastic and wood. Campylobacter died rapidly, while Salmonella survived for at least one week in food soils drying on a countertop laminate surface. Presence of food soils in concentrations that can be detected visually, protected Salmonella against drying. In conclusion, selecting materials where soil/dirt can easily be detected visually in the kitchen surfaces, may motivate consumers to clean and will reduce risk, but establishing a habit to clean surfaces soon after food preparation is also important from a food safety perspective.

Survival and inactivation of Salmonella enterica serovar Typhimurium on food contact surfaces during log, stationary and long-term stationary phases

One of the most important transmission routes of foodborne pathogens is through contaminated food contact surfaces. In this study, we investigated the survival and inactivation of Salmonella enterica serovar Typhimurium on frequently used food contact surfaces in household settings, including plastic cutting board (CB), formica laminate (LA), and stainless steel (SS) surfaces. S. Typhimurium at log (6 h), stationary (24 h), or long-term stationary (LTS) (14 days) phases were evaluated. Results showed that, at medium and high microbial loads, LTS phase cells had significantly higher survivor population compared to log and stationary phase cells at 24 h after inoculation (p < 0.05). Disinfection study showed that LTS phase cells were very resilient to sodium hypochlorite when the initial microbial load was high with disinfection efficacy ranging from 26 to 35%. Scanning electron microscopy of these surfaces at 24 h after inoculation with a high microbial load revealed an early biofilm structure.

Beetle‐Inspired Assembly of Heterostructured Lamellar Membranes with Polymer Cluster–Patterned Surface for Enhanced Molecular Permeation

Abstract2D lamellar membranes hold great promise in efficient molecular separations of liquid and gas mixtures. However, the simultaneous realization of high permeation and precise sieving (i.e., overcoming the permeation–rejection tradeoff) of membranes poses a great challenge. Inspired by the structures and functions of the beetle's back, the heterostructured lamellar membranes fabricated through facile and controllable electrostatic atomization method are reported. Particularly, hydrophobic polymer clusters are patterned on hydrophilic laminate (graphene oxide) surfaces to realize the hydrophilic/hydrophobic heterostructure. It shows that the fast dissolution for nonpolar solvents is achieved by the strong affinity polymer clusters, and the ultralow‐barrier diffusion is achieved by the weak affinity laminate channels. Therefore, the permeance is remarkably enhanced (over 7 times for nonpolar solvents), while fully retaining membrane rejection. In contrast, hydrophilic clusters are patterned on hydrophobic laminate (reduced graphene oxide) surfaces and exhibit similar behaviors toward polar solvents. Furthermore, the lamellar membrane displays highly ordered layer‐by‐layer stacking, affording precise molecular rejection. Besides, the lamellar membrane acquires lower thermodynamic energy and hence superior stability under ultrasonic and strong acid or alkali environments, manifesting great potential for long‐term practical operation.

Effects of release media on the fusion bonding of carbon/PEEK laminates

Carbon fibre reinforced thermoplastic composite laminates have been press-consolidated using various release media. The potential contamination of the laminate’s surface by the release media and its effect on the performance of the joint after fusion bonding was studied. Before bonding, the physical and chemical state of the bonding surfaces were analysed by measurement the surface energy and roughness. The laminate surfaces chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). Subsequently, the laminates were fusion bonded through an autoclave cycle. The mechanical performance of the joints was characterized by mode-I fracture toughness and short beam strength tests. The surface of some of the composite laminates were found to contain high concentration of the release medium residues after consolidation. This contamination showed a significant effect on the mechanical performance of fusion bonded joints. It was demonstrated that the performance of the joint can be regained by employing a simple cleaning method.

An experimental investigation into multi-functional Z-pinned composite laminates

This paper investigates the feasibility of monitoring progressive delamination growth in Z-pinned composite laminates via the measurement of through-thickness electrical resistance. This novel health monitoring technique is based on connecting Z-pins both in series and in parallel by means of arrays of electrodes arranged on the laminate surfaces. This creates a multi-functional (through-thickness reinforcing and sensing) laminated structure. Experimental results on double-cantilever beam coupons demonstrate that the entire Mode I bridging response of Z-pins can be monitored, from the arrival of the delamination front to the complete pull-out of the through-thickness reinforcement. Hence the extent of delamination can be inferred from the through-thickness resistance. This is proved for both conductive (carbon fibre-reinforced) and non-conductive (glass fibre-reinforced) laminates. The premature Z-pin failure during progressive pull-out corresponds to an abrupt increase of through-thickness electrical resistance. The delamination sensing/suppression method presented in this paper can be readily applied to Z-pinned composites at structural level.

The persistence of illicit drug smoke residues and their recovery from common household surfaces.

Third-hand smoke is the residue remaining on surfaces during smoking events. It is composed of particles and vapours that form upon heating. The phrase 'third-hand smoke' is primarily used to describe nicotine and other chemicals from cigarettes, but any residues formed from the smoking of various substances could be classified similarly. There has been an increasing body of research on third-hand smoke from cigarettes in the last decade, but little has been done in regards to understanding the persistence of particles and vapours from illicit drugs. In this work, small samples of cocaine and methamphetamine were volatilized to produce an illicit drug smoke that was collected onto various surface materials and left exposed to ambient conditions over 672 h (four weeks). Chemical analyses by electrospray ionization-mass spectrometry of residues on silicon, plastic, laminate, and artificial leather surfaces indicated a rapid decrease in recovery of the parent molecule, with varied formation of decomposition products over the first 168 h of exposure. Measurable amounts of the parent molecule were still present after 672 h, exhibiting a strong persistence of these drugs on various household materials. This is important in a forensic science context, as third-hand smoke residues could provide a viable source of trace evidence previously not utilized. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Identification and quantitation of processing parameters controlling the surface quality of carbon fibre-reinforced composites

The paper investigates the effect of essential manufacturing parameters on the surface quality of uncoated carbon fibre-reinforced composites used as car body panels with visible surfaces (Class A properties). A series of carbon fibre-reinforced composites laminates were prepared by the resin transfer moulding technique varying the fibre volume content (30 to 60 %), reinforcement material (woven fabrics vs. unidirectional fibre reinforcements), curing temperatures (40℃ to 120℃), additives (SiO2 nanoparticles as matrix fillers) and using a surface finish applied as an in-mould coating. Laminate surfaces were characterised by roughness analysis (white-light interferometry) and wave-scan measurement to quantify the influence of the different manufacturing parameters on the surface quality. Especially, the used resins were intensively characterised concerning thermal properties and total resin shrinkage. These results correlate very well with the performed analysis of surface roughness. It is found that the fibre print through effect is significantly reduced by realising low total resin shrinkage and an even distribution of resin and fibres at the surface. Thus, using of unidirectional fibre reinforcement (no weft or sewing threads; very fine filaments), low curing temperatures (slow curing processes) and an in-mould coating are most successful for reduction of fibre print through effect and getting surface similar to Class A properties. In addition, the surface quality is quite positively affected by the application of nanoparticles and also strongly controlled by roughness of tooling.

Investigation of the Persistence of Nerve Agent Degradation Analytes on Surfaces through Wipe Sampling and Detection with Ultrahigh Performance Liquid Chromatography-Tandem Mass Spectrometry

The persistence of chemical warfare nerve agent degradation analytes on surfaces is important, from indicating the presence of nerve agent on a surface to guiding environmental restoration of a site after a release. Persistence was investigated for several chemical warfare nerve agent degradation analytes on indoor surfaces and presents an approach for wipe sampling of surfaces, followed by wipe extraction and liquid chromatography-tandem mass spectrometry detection. Commercially available wipe materials were investigated to determine optimal wipe recoveries. Tested surfaces included porous/permeable (vinyl tile, painted drywall, and wood) and largely nonporous/impermeable (laminate, galvanized steel, and glass) surfaces. Wipe extracts were analyzed by ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). UPLC provides a separation of targeted degradation analytes in addition to being nearly four times faster than high-performance liquid chromatography, allowing for greater throughput after a large-scale contamination incident and subsequent remediation events. Percent recoveries from nonporous/impermeable surfaces were 60-103% for isopropyl methylphosphonate (IMPA), GB degradate; 61-91% for ethyl methylphosphonate (EMPA), VX degradate; and 60-98% for pinacolyl methylphosphonate (PMPA), GD degradate. Recovery efficiencies for methyl phosphonate (MPA), nerve agent degradate, and ethylhydrogen dimethylphosphonate (EHDMAP), GA degradate, were lower, perhaps due to matrix effects. Diisopropyl methylphosphonate, GB impurity, was not recovered from surfaces. The resulting detection limits for wipe extracts were 0.065 ng/cm(2) for IMPA, 0.079 ng/cm(2) for MPA, 0.040 ng/cm(2) for EMPA, 0.078 ng/cm(2) for EHDMAP, and 0.013 ng/cm(2) for PMPA. The data indicate that laboratories may hold wipe samples for up to 30 days prior to analysis. Target analytes were observed to persist on surfaces for at least 6 weeks.

The Surface Finish of Thermally Aged Carbon Fibre Reinforced Composites Using E-glass as a Surface Barrier

This work investigated the effect of woven E-glass mass (25 g/m2, 50 g/m2, 85 g/m2, 135 g/m2) on the painted surface finish of various thermoset (EPIKOTETM RIM935, EPIKOTETM 04434, Ultratec LpTM ES300, Ultratec LpTM SPV6035) carbon fibre composite laminates, before and after aging at 95 °C for 168 h. The as-moulded laminate surfaces were evaluated using surface profilometry techniques and the painted and aged surfaces were evaluated using a wave-scan distinctness of image (DOI) instrument. It was found that the 25 g/m2 E-glass surface layer assisted with reducing the roughness of the as-moulded surfaces and the long-term waviness of the painted surfaces due to the increase in resin-richness at the surface. The EPIKOTETM 04434 resin system that contained diglycidyl ether of bisphenol F (DGEBF) epoxy had the least change in long-term waviness with thermal aging due to the rigid fluorene-based backbone in comparison to the diglycidyl ether of bisphenol A (DGEBA) systems.