Search

In polymer composites, the fiber–matrix interface is primarily influenced by the surface treatment of the fibers and polymer morphology. Previous studies have investigated the effect of surface tre...

Abstract The COVID-19 pandemic triggered a surge in demand for N95 or equivalent respirators that the global supply chain was unable to satisfy. This shortage in critical equipment has inspired research that addresses the immediate problems and has accelerated the development of the next-generation filtration media and respirators. This article provides a brief review of the most recent work with regard to face respirators and filtration media. We discuss filtration efficiency of the widely utilized cloth masks. Next, the sterilization of and reuse of existing N95 respirators to extend the existing stockpile is discussed. To expand near-term supplies, optimization of current manufacturing methods, such as melt-blown processes and electrospinning, has been explored. Future manufacturing methods have been investigated to address long-term supply shortages. Novel materials with antiviral and sterilizable properties with the ability for multiple reuses have been developed and will contribute to the development of the next generation of longer lasting multi-use N95 respirators. Finally, additively manufactured respirators are reviewed, which enable a rapidly deployable source of reusable respirators that can use any filtration fabric. Graphic abstract

Epoxy-sized textile-grade polyacrylonitrile (PAN) carbon fiber (TCF) with 450 K filaments (CFTF, ORNL) was reinforced in the polycarbonate (PC) matrix using a compression molding technique. The epo...

In this work, we consider low-cost carbon fiber produced with a textile-grade precursor. The objective of the study is to investigate textile-grade carbon-fiber-reinforced-polypropylene composites (TCF-PP) from compounded pellets for mechanical and thermal characterization. Four sets of pellets with 1%, 5%, 10%, and 15% reinforcement were manufactured using textile-grade carbon fiber (TCF) and polypropylene (PP) by twin-screw compounding. The addition of TCFs through gravimetric feeder directly in the extruder resulted in lower fiber content; however, side feeder has shown good potential. The pellets were further processed in extrusion compression molding to manufacture plaques. An increase in fiber loading has a negligible effect on fiber attrition as fiber length distribution variation between 1% and 15% reinforced pellets was very small. The addition of TCFs in PP showed a significant improvement in mechanical properties. The tensile strength and modulus of the composite were 26% and 161%, respectively, improved by the addition of 10 wt% TCF. Similar results were observed in the flexure test. However, the impact properties were reduced by 25.54% by the addition of 15% TCF.

Inline inspection of carbon fiber tow is desired to enable rapid feedback to key fabrication process parameters. The tow is delicate in that it necessitates wireless techniques to remotely probe the tow properties to avoid damage during production. In this article, we investigate the use of software defined radios (SDRs) to measure microwave signal attenuation through the tow. Carbon fiber samples that have undergone different process conditions are measured with the system, and measurements exhibit over 10 dB in variation based on the process conditions. These measurements are correlated against results from conventional physical analysis. The developed system and measurement technique show promise as a method to wirelessly inspect carbon fiber tow using SDR.

The current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) pandemic has highlighted the need for personal protective equipment, specifically filtering facepiece respirators like N95 masks While it is common knowledge that polypropylene (PP) is the industry standard material for filtration media, trial and error is often required to identify suitable commercial precursors for filtration media production This work aims to identify differences between several commercial grades of PP and demonstrate the development of N95 filtration media with the intent that the industry partners can pivot and help address N95 shortages Three commercial grades of high melt flow index PP were melt blown at Oak Ridge National Laboratory and broadly characterized by several methods including differential scanning calorimetry (DSC), X-ray diffraction (XRD), and neutron scattering Despite the apparent similarities (high melt flow and isotacticity) between PP feedstocks, the application of corona charging and charge enhancing additives improve each material to widely varying degrees From the analysis performed here, the most differentiating factor appears to be related to crystallization of the polymer and the resulting electret formation Materials with higher crystallization onset temperatures, slower crystallization rates, and larger number of crystallites form a stronger electret and are more effective at filtration © XXXX American Chemical Society

Until recently, glass fiber composites (GFRP) were the preferred choice to prepare wind turbine blades due to their low cost compared to their counterpart carbon fiber composites (CFRP). However, to harvest the maximum wind energy, ever larger wind turbine blades are being manufactured. To support such a large structure carbon fiber composites CFRP have become the integral part of load bearing structures in the blade. In this work, we are proposing to utilize the low cost carbon fiber (LCCF), manufactured at Carbon Fiber Technology Facility (CFTF) of Oak Ridge National Laboratory (ORNL) as not only the cost effective alternative to the currently used carbon fiber (CF) but also as the lightning strike protection of the wind turbine blades. A textile-grade precursor was used to prepare LCCF. Wind turbines often get hit by lightning strikes due to their operating locations. LCCF can provide structural integrity to these gigantic structures and mitigate the effect of lightning strike on them by effectively dissipating the current. Two composite panels made of LCCF were tested against artificial lightning strikes of 100 kA and 200 kA (component A of lightning

Polymer composites are used in numerous industries due to their high specific strength and high specific stiffness. Composites have markedly different properties than both the reinforcement and the matrix. Of the several factors that govern the final properties of the composite, the interface is an important factor that influences the stress transfer between the fiber and matrix. The present study is an effort to characterize and model the fiber-matrix interface in polymer matrix composites. Finite element models were developed to study the interfacial behavior during pull-out of a single fiber in continuous fiber-reinforced polymer composites. A three-dimensional (3D) unit-cell cohesive damage model (CDM) for the fiber/matrix interface debonding was employed to investigate the effect of interface/sizing coverage on the fiber. Furthermore, a two-dimensional (2D) axisymmetric model was used to (a) analyze the sensitivity of interface stiffness, interface strength, friction coefficient, and fiber length via a parametric study; and (b) study the shear stress distribution across the fiber-interface-matrix zone. It was determined that the force required to debond a single fiber from the matrix is three times higher if there is adequate distribution of the sizing on the fiber. The parametric study indicated that cohesive strength was the most influential factor in debonding. Moreover, the stress distribution model showed the debonding mechanism of the interface. It was observed that the interface debonded first from the matrix and remained in contact with the fiber even when the fiber was completely pulled out.

In this work, large-scale multimaterial preforms produced by additive manufacturing (AM) underwent compression molding (CM) to produce high-performance thermoplastic composites reinforced with short carbon fibers. AM and CM techniques were integrated to control the fiber orientation (microstructure) and to reduce void content for the improved mechanical performance of the composite. The new integrated manufacturing technique is termed “additive manufacturing-compression molding” (AM-CM). For the present study, the most common materials were used for large-scale printing, i.e., acrylonitrile butadiene styrene (ABS), carbon fiber (CF)–filled ABS (CF/ABS) and glass fiber (GF)–filled ABS (GF/ABS). Three different manufacturing processes; (a) AM (b) extrusion compression molding (ECM), and (c) AM-CM were used to prepare four different panel configurations: (1) neat ABS, (2) CF/ABS, (3) overmold (CF/ABS over neat ABS), and (4) sandwich (neat ABS between two CF/ABS layers). The mechanical properties (tensile and flexural strength and modulus, and Izod impact energy) of samples prepared via all three manufacturing processes were compared. X-ray microcomputer tomography was employed to evaluate the fiber orientation distribution and the volumetric porosity content. The preform maintained high fiber alignment (≈ 82% of fibers within the range of 0–20° in the deposition direction), and the volumetric porosity was reduced by 50% from 3.79% to 1.91% after compression. The alignment of long pores along the deposition direction was also observed. The mechanical properties are discussed with correlation to the fiber alignment and void content in the samples. CF/ABS samples prepared by AM-CM showed significant improvement of 11.15%, 35.27%, 28.6%, and 74.3% in the tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively, when compared with samples prepared by ECM. Unique aspects of this study are the demonstration of large-scale multimaterial AM and the use of multimaterials as preforms to make high-performance composites.

Short carbon fiber reinforced thermoplastic composites (S-CFRTP) are currently used in interior parts of aircraft such as electronic circuitry and assemblies, and their usage in aircraft's exterior is also being studied. A lightning strike study on S-CFRTPs is presented in this paper. High performance thermoplastics such as a polyphenylene sulfide (PPS) reinforced with 50% weight (wt.) short carbon fiber (CF), a polyphenyl sulfone (PPSU) reinforced with 25 % wt. Short CF and a acrylonitrile butadiene styrene (ABS) with 20 % wt. short CF were tested against artificial lightning strikes. All samples were prepared using an extrusion compression molding (ECM) technique. A modified component A (100 kA) of lightning waveform, as defined by SAE ARP 5412-B, was applied. High speed imaging, thermography, scanning electron microscopy (SEM) and ultrasonic non-destructive evaluation were performed to understand the effect of lightning strikes on the thermoplastic panels. The results show that electrical conductivity of the composite, thermal stability of the polymers, and CF orientation significantly affected the damage from artificial lightning strikes. PPS composite had the highest resilience against lightning strike damage, retaining 95% and 89% residual flexural strength and modulus, respectively. CF exfoliation due to internal arcing was observed in the carbon fiber-reinforced ABS polymer (CF-ABS) composite. CF exfoliation damage has been reported for the first time.

Carbon fiber reinforced polymer composites are highly desirable for automotive and wind energy applications due to advantages associated with weight reduction, high stiffness and strength, durability, and recyclability. The high cost of carbon fiber has been a limiting factor in its widespread adoption in non-aerospace applications. A low cost (estimated

Laser flash analysis (LFA), an unsteady-state technique originally developed for measuring the thermal diffusivity of homogenous materials, was used to estimate the thermal conductivity of carbon fibers consolidated in an epoxy matrix to form axially aligned unidirectional composites. Experimental studies were conducted for P-25 and K-1100 mesophase pitch-based carbon fibers whose conductivity values bracket almost two orders of magnitude (∼10 and 1000 W/m·K). Experimentally determined fiber thermal conductivity values were generally consistent with those cited in the literature after appropriate corrections were applied to account for the extremely high conductivity (low thermal resistance) of highly graphitic fibers, relative to the graphite coating. Finite element analysis was used to simulate heat flow patterns that may occur in a uniaxial fiber–polymer composite due to the large differences in the thermal conductivities of carbon fibers and polymer matrices. Simulations reveal that fiber thermal conductivity is accurately determined from composite response for high volume fraction of fibers (≥0.6) regardless of fiber conductivity, or for lower conductivity fibers (10–100 W/m·K) regardless of volume fractions. However, for composites containing high thermal conductivity fibers (100–1000 W/m·K) at low volume fractions (≤0.2), fiber thermal conductivity may not be accurately determined due to transverse heat flow within the graphite layers that channel heat through the highly conductive fiber. Thus, under certain conditions, heat flow paths deviate from the one-dimensional heat flow assumption inherent to laser flash analysis and rule-of-mixtures.

Cure kinetics and decomposition behaviour of a two part epoxy resin system, Epon 862, reinforced with 1 wt.% unmodified, oxidized (MWCNT-COOH) and fluorinated (MWCNT-F) multi-walled carbon nanotubes have been studied through dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) at different conversion levels. Functionalized MWCNTs have disturbed the curing/decomposition behaviour, crosslink density, and the interactions between individual phases in the composite systems thus altering cure kinetics parameters like degree of conversion, activation energy, rate of reaction, enthalpy change, percentage conversion, which were determined using Arrhenius theory.

The effects of various functionalized multi-walled carbon nanotubes (MWCNTs) on morphological, thermal, and mechanical properties of an epoxy based nanocomposite system were investigated. Chemical functionalization of MWCNT by oxidation (MWCNT-COOH) and direct-fluorination (MWCNT-F) were confirmed by FTIR, Raman spectroscopy, and TGA. Utilizing in situ polymerization, 1 wt% loading of MWCNT was used to prepare epoxy-based nanocomposites. Compared to the neat epoxy system, nanocomposites prepared with MWCNT-COOH showed 25.5% increase in ultimate flexural strength and 54.8% increase in flexural modulus. A decrease in strength was observed for the MWCNT-F nanocomposites. The premature degradation was attributed to a presumable catalyzation by hydrofluoric acid, HF, which evolved from the MWCNT-F during the curing process. However, only the MWCNT-F nanocomposites showed 22% increase in thermal properties (Tg). All nanophased systems showed increase in storage modulus.

The processing-structure–property relationships of multiwalled carbon nanotubes (MWNTs)/epoxy nanocomposites processed with a magnetic field have been studied. Samples were prepared by dispersing the nanotube in the epoxy and curing under an applied magnetic field. The nanocomposite morphology was characterized with Raman spectroscopy and wide angle X-ray scattering, and correlated with thermo-mechanical properties. The modulus parallel to the alignment direction, as measured by dynamic mechanical analysis, showed significant anisotropy, with a 72% increase over the neat resin, and a 24% increase over the sample tested perpendicular to the alignment direction. A modest enhancement in the coefficient of thermal expansion (CTE) parallel to the alignment direction was also observed. These enhancements were achieved even though the nanotubes were not fully aligned, as determined by Raman spectroscopy. The partial nanotube alignment is attributed to resin a gel time that is faster than the nanotube orientation dynamics. Thermal conductivity results are also presented.

The effect of the organoclay nanoparticles on the rheology and development of the morphology and properties for epoxy/organoclay nanocomposites has been studied. The interlayer spacing increases with the temperature of cure resulting in intercalated morphologies with varying degrees of interlayer expansion, depending on the cure temperature used. Rheological studies of the curing process indicate that intergallery diffusion before curing is essential for exfoliation, before the morphology is frozen in by gelation and vitrification. The maximum increase in modulus was observed for the 2 wt% clay loading. Viscoelastic behavior and mechanical properties of the cured samples were correlated with the morphological and rheological study.

Effects of various functionalized multi-walled carbon nanotubes (MWCNT) on cure kinetics and flexural properties of an epoxy based nanocomposite system were investigated. Chemical functionalization of MWCNT by oxidation (MWCNT-COOH), direct-fluorination (MWCNT-F) was confirmed by FTIR, and Raman spectroscopy. One weight percentage loading of MWCNT was used to prepare epoxy-based nanocomposites through in-situ polymerization. Curing kinetics showed that MWCNT-COOH and MWCNT-F would catalyze the curing process altering activation energy, enthalpy of reaction, and reaction rate. Compared to neat resin, nanocomposites fabricated with MWCNT-COOH and MWCNT-F showed a 48%, and 33% increases in flexural strengths, and 55% and 16% increases in flexural moduli, respectively. SEM analysis of the fracture surface of the composites confirmed an improvement in dispersion.