High Melt Flow Index Research Articles

Dynamic behavior of melt electrospinning of blended polypropylene

Melt electrospinning is a promising process for fiber production without the need for solvents and with potential applications in various fields. In this study, we investigated the dynamic behavior of melt electrospinning under different blending ratios and process conditions. We used high melt flow index polypropylene and low molecular weight polypropylene, which were blended to lower the melt viscosity, and fibers were successfully manufactured through the melt electrospinning process. The effects of blending ratio and applied voltage on jet and drop formation, as well as fiber morphology, were examined. The results showed that blending low-molecular-weight polypropylene significantly influenced the jet and drop areas, leading to fluctuations in jet morphology. The size of the applied high voltage also had a high effect on the fiber diameter. Additionally, the viscosity reduction achieved through blending allowed for continuous jet formation and improved fiber production. These results provide valuable insights into controlling the process parameters and blending ratios in melt electrospinning, enabling the establishment of stable electrospinning conditions and precise control of fiber diameter.

Impact of Runner Size, Gate Size, Polymer Viscosity, and Molding Process on Filling Imbalance in Geometrically Balanced Multi-Cavity Injection Molding.

The injection molding process is one of the most widely used methods for polymer processing in mass production. Three critical factors in this process include the type of polymer, injection molding machines, and processing molds. Polypropylene (PP) is a widely used semi-crystalline polymer due to its favorable flow characteristics, including a high melt flow index and the absence of a need for a mold temperature controller. Additionally, PP exhibits good elongation and toughness, making it suitable for applications such as box hinges. However, its tensile strength is a limitation; thus, glass fiber is added to enhance this property. It is important to note that the incorporation of glass fiber increases the viscosity of PP. Multi-cavity molds are commonly employed to achieve cost-effective and efficient mass production. The filling challenges associated with geometrically balanced layouts are well documented in the literature. These issues arise due to the varying shear rates of the melt in the runner. High shear rate melts lead to high melt temperatures, which decrease melt viscosity and facilitate easier flow. Consequently, this results in an imbalanced filling phenomenon. This study examines the impact of runner size, gate size, polymer viscosity, and molding process on the filling imbalanced problem in multi-cavity injection molds. Tensile bar injection molding was performed using conventional injection molding (CIM) and microcellular injection molding (MIM) techniques. The tensile properties of the imbalanced multi-cavity molds were analyzed. Flow length within the cavity served as an indicator of the filling imbalance. Additionally, computer simulations were conducted to assess the shear rate's effect on the runner's melt temperature. The results indicated that small runner and gate sizes exacerbate the filling imbalance. Conversely, glass fiber-filled polymer composites also contribute to increased filling imbalance. However, foamed polymers can mitigate the filling imbalance phenomenon.

Morphological analysis of mechanically recycled blends of high density polyethylene and polypropylene with strong difference in melt flow index

Polyolefin (PO) blends are difficult to separate due to density and chemical structure similarities. The associated waste treatment in the context of mechanical recycling is therefore complicated by the establishment of multi-phase morphologies that are not yet fully understood. In the present work, a high density polyethylene (HDPE) with a very high melt flow index (MFI) and a polypropylene (PP) with a very low MFI are deliberately mingled to better understand the full spectrum of morphological variations for PO blending. The linkage with the control over injection mold-based mechanical properties such as tensile strength, elasticity modulus, elongation at break, and impact strength is made. This is done supported by the connecting of experimental analyses at different scales, including (i) the molecular scale via size exclusion chromatography and Fourier transform infrared spectroscopy (FTIR), and (ii) the meso-scale via scanning electron and polarized light microscopy as well as differential scanning calorimetry, including a differentiation between the bulk and surface region. Emphasis is both on blends processed once and re-processed either once, twice or three times. For the single processing, it is demonstrated that in most cases a droplet morphology is obtained, with smaller droplets in case HDPE is the minor component and with a dominance of HDPE at the surface even for 60% PP, due to a better HDPE flowability. It is further shown that the scission of PP chains and crosslinking of HDPE chains respectively facilitates and inhibits crystallization, at least if meso-scale -mixing as more evident during re-processing is not taking over. It is also highlighted that the properties of PP can be enhanced by adding up to 10 wt% HDPE, acting as a filler, and that the (ideally) reprocessed blends remain suitable for application.

Ozone-based in-situ reactive extrusion for rapid functionalisation and degradation of low density polyethylene

Improving the hydrophilicity of low density polyethylene (LDPE) expends its use in blends. LDPE melt was rapidly functionalised and degraded by ozone in twin-screw extruder by varying extrusion times from one to seven and temperatures from 160 °C to 240 °C. Abundant oxygen-containing groups, such as carbonyl group (CO) at 1718 cm−1, hydroxyl group (-OH) at 3400 cm−1 and aldehyde group (-CHO) at 1740 cm−1, were generated into ozone treated PE, resulting in improved hydrophilicity. At 200 °C, ozone treated PE exhibited a high melt flow index (21.5 g/10 min) and low complex viscosity modulus due to molecular degradation. Nevertheless, cross-linking occurred at a higher temperature of 240 °C. A higher crystal peak temperature of ozone treated PE at 200 °C was attributed to the introduction of oxygen atoms. The poor thermal stability of ozone treated PE was evidenced by a lower initial decomposition temperature. The oxidation induction time of ozone treated PE at 200 °C declined from 32 min for one extrusion to 12 min for seven extrusions demonstrating a vulnerability of ageing. Increasing the extrusion times gradually enhanced the tensile modulus of the ozone treated PE at 200 °C, while raising the treatment temperature had no effect on the tensile properties. Rapid functionalisation and degradation of LDPE were successfully achieved using ozone in reactive extrusion, thus broadening the applications of ozone treated PE in composites.

Molecular Weight Dependent Ionomer Volume Expansion and Its Effect on the Performance of PEM Fuel Cell Electrodes

Within the past years, proton exchange membrane (PEM) fuel cells have become more and more attractive due to their potential for the transition towards an environmentally friendly hydrogen economy. Especially by reducing the platinum catalyst loading, significant system cost reductions could be achieved, but low Pt loadings still lead to unassigned voltage losses during operation.[1,2] In order to overcome those losses, well-designed catalyst layers with optimized ionomer content and distribution are indispensable. The used perfluorosulfonic acid (PFSA) ionomers for PEM fuel cells are commonly characterized by the chemical structure of the ionomer and the equivalent weight (EW), which strongly affects the proton conductivity.[3,4] Current research focusses on the synthesis of modified ionomers with higher oxygen permeability to reduce mass transport losses, but also investigates the influence of the ionomer’s molecular weight (MW).[1,5,6] A high MW minimizes the water uptake of the ionomer/membrane in liquid water, which is desired for the use in PEM fuel cells to reduce mechanical stress during relative humidity (RH) cycling.[5] The exact MW of an ionomer is not easily accessible, but can be estimated by measuring the melt flow index (MFI), whereas a high MW is commonly reflected by a lower MFI if the ionomer chemistry and EW are the same.Within this study, a 3M ionomer modified to have a high MFI of 156 g/10 min (measured at 265 °C with a mass of 5 kg) is investigated and compared to a 3M standard ionomer with a low MFI of 6 g/10 min. Both PFSA ionomers have the same chemical structure and a similar EW of ~800. The significantly higher MFI of the modified ionomer (i.e., comprising a lower MW) is clearly reflected by a ~2 times higher water uptake compared to the 3M standard ionomer (measured for solution-cast membranes in liquid water at 80 °C). To evaluate the impact of the MFI within the cathode electrode, 5 cm² active area membrane electrode assemblies (MEAs) with these two ionomers at various ionomer/carbon (I/C) mass ratios in the cathode electrode (based on a 40 wt.% Pt/Vulcan catalyst at loadings of 0.11 mgPt/cm²) are manufactured and electrochemically characterized. At sufficiently high I/C ratios and under humid operation (i.e., I/C = 0.90 and 90 % RH), differential flow H2/air polarization curves of the MEAs reveal that the higher liquid water uptake of the 3M high-MFI ionomer can be correlated with a lower cell voltage (see Figure 1). Contrary to the MEAs with the 3M low-MFI standard ionomer, the larger ionomer swelling in MEAs with the 3M high-MFI ionomer reduces the void volume fraction in the electrode structure during operation. Most pronounced at high current densities, where oxygen mass transport plays an important role, the MEAs containing the 3M high-MFI ionomer show a significant voltage loss of ~50 mV at 2.5 A/cm² compared to the MEAs with the 3M low-MFI ionomer. This study demonstrates that the effect of ionomer volume expansion upon changes in the MFI and thus the MW might not be crucial for the MEA performance when using electrodes with a low I/C ratio, but is critical when aiming for electrode compositions with a high ionomer content, in which case a low-MFI (i.e., a high MW) ionomer should be favorable.

Thermoplastic elastomer melt-blown fiber mats for oil spill remediation: Fabrication, oil uptake, and gel formation studies

Melt-blown fibers, featuring porous structures with designed wetting characteristics can provide superior oil/water separation performance. The core objective of this work was to design a material that provides excellent oil/water selectivity for oil spill remediation. For this, the selective oil gelation properties of styrene-ethylene-butylene-styrene (SEBS) and the enhanced surface area provided by melt-blown mats was leveraged to achieve exceptional oil/water selectivity. Nonwoven mats based on SEBS were fabricated with a twin-screw extruder equipped with a custom-engineered melt-blowing die. To address the inherent low melt flow index (MFI) of SEBS, which presents challenges in the melt-blowing process due to decreased stretchability, high MFI polypropylene (PP) was incorporated as a blending additive. Next, the impact of blending polypropylene with SEBS on melt-blowing processability and fiber quality was studied. The inclusion of 10 wt% PP in SEBS considerably enhanced fiber melt-blowing processability, resulting in a more extensive and evenly spread fiber stream. Further analysis of this fiber composition in terms of oil and water interaction revealed superior oil uptake capacity. Moreover, the increased surface area of SEBS-based fibers enhanced their interaction with oil, resulting in the effective formation of a semi-solid gel. Notably, the generated gel established a barrier that successfully limited further oil dispersion even when the material reached its saturation point. This demonstrated a markedly superior oil immobilizing performance in comparison to polypropylene melt-blown fibers.

Mechanical recycling of PLA: Effect of weathering, extrusion cycles, and chain extender

AbstractThis work evaluated the reprocessing of PLA with a high melt flow index (MFI). PLA samples were prepared by extrusion using a chain extender (Joncryl ADR‐4368) and subjected to two additional extrusion cycles with or without exposure to accelerated weathering. The results showed drastic affectations of PLA properties by weathering. The MFI increased from 65 to 137 g/10 min by reprocessing, while reprocessed and weathered samples reached a MFI of 417 g/10 min after three extrusion cycles. The addition of Joncryl prevented PLA degradation (MFI of 170 g/10 min after three extrusion cycles, even when weathering was performed). Additionally, the tensile strengths of weathered samples were substantially decreased (67%) compared to only reprocessed samples (14%). In this sense, PLA mechanical recycling is a good alternative if it is not exposed to harsh weathering conditions, in which case a chain extender is needed to get reasonable properties. Otherwise, reprocessing accelerated the composting of PLA, and the chain extender addition did not limit it.

Synthesis of Ti–Al Bimodal Powder for High Flowability Feedstock by Electrical Explosion of Wires

In this research, Ti–Al bimodal powders were produced by simultaneous electrical explosion of titanium and aluminum wires. The resulting powders were used to prepare powder–polymer feedstocks. Material characterization involving X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and melt flow index (MFI) determination were carried out to characterize bimodal powders obtained and evaluate the influence of the powder composition on the feedstock flowability. The bimodal distribution of particles in powders has been found to be achieved at a current density of 1.2 × 107 A/cm2 (the rate of energy input is 56.5 J/μs). An increase in the current density to 1.6 × 107 A/cm2 leads to a decrease in the content of micron particles and turning into a monomodal particle size distribution. The use of bimodal powders for powder–polymer feedstocks allows to achieve higher MFI values compared with monomodal powders. In addition, the use of electroexplosive synthesis of bimodal powders makes it possible to achieve a homogeneous distribution of micro- and nanoparticles in the feedstock.

Modified cork/SEBS composites for 3D printed elastomers

AbstractThree dimensional (3D) printed elastomers is a challenge which can be overcome using fillers. With that in perspective, cork was chemically modified via a two‐step reaction, aiming to achieve better compatibility with styrene‐ethylene‐butylene‐styrene (SEBS). In the first step, the OH groups of cork surface were grafted with succinic acid, while in the second step the free acid groups were reacted with a polyol to produce ester moieties. Spectroscopy analysis confirmed the occurrence of the chemical reaction which was supported by contact angle (CA) measurements. The unmodified cork presents a CA of 117.7°, while the modified cork presents a CA of 92.4° which is closer to that of SEBS (102.8°), resulting in better compatibility between the modified filler with the matrix. In fact, the enhancement of compatibility between polymer and filler was observed by inspecting the layer‐to‐layer bonding and was confirmed by the mechanical properties of the 3D printed composites, since the modified cork‐based composite presented higher Young modulus, maximum stress and elongation at break when compared to the untreated counterparts. Additionally, the advantage of the chemical treatment was evaluated by analyzing the processability of composites. The modified filler‐based composite, presents lower glass transition temperature (Tg), higher melt flow index (MFI) and higher thermal stability. Overall, in this work, a simple chemical route to modify lignocellulosic biomass and its benefit on the properties of 3D printing objects is discussed. The improved performance and sustainability of the 3D printed objects produced to be used for example in shoe applications was presented.

Number of Times Recycled and Its Effect on the Recyclability, Fluidity and Tensile Properties of Polypropylene Injection Molded Parts

The ease with which modern plastics can be injection molded makes them very suitable for the production of many different products and, today, plastics are often used as substitutes for metal. Polypropylene (PP) is one of the most widely used thermoplastics globally since it is very useful, cost-effective and flexible for molding. However, the amount of harm to the environment caused by plastic waste has become phenomenal and the recycling of plastics has become a serious aspect of environmental protection. PP, as the most commonly used plastic material, was selected for use in this study. It has a melt flow index of 15 g/min and its recyclability, fluidity, and physical properties, as well as manufacturing conditions, were explored in relation to the number of times the material could be recycled (TR). A cavity pressure sensor was used to measure the viscosity index of the recycled plastic after multiple cycles of plasticizing and injection, part molding, scrap-recycling, and crushing. A paperclip-shaped test specimen was used to determine PP fluidity and crystallinity of specimens with different TRs. Tensile tests were used to detect differences in the tensile strength between specimens made from Raw-PP and recycled PP. The results showed that PP that had been recycled several times had a higher melt flow index, material fluidity, melting peak area, crystallinity, crystallization rate, and crystallization temperature. Repeated injection and recycling of the material had reduced the length of the molecular chains and broadened the molecular weight distribution. This improved the fluidity and increased crystallinity. The increase in fluidity made cavity filling easier, reducing the cavity pressure as well as the viscosity index. The results of this study showed that the recycling of the PP could improve the physical properties of the products to a degree and also went some way to further the benefits of a circular economy. The recycling of injection-molded PP material can be added to renewable energy technologies and used in environmental impact assessment.

Study on polyethylene-based carbon fibers obtained by sulfonation under hydrostatic pressure

Polyethylene based carbon fibers were studied using high density polyethylene(HDPE) fibers and linear low density polyethylene(LLDPE) fibers with various melt flow index. The draw ratio of the polyethylene fibers and the sulfonation mechanism were investigated under hydrostatic pressures of 1 and 5 bar in the first time. The influence of the melt flow index of polyethylene and types of polyethylene fibers on the sulfonation reaction was studied. Carbon fibers were prepared through the sulfonation of LLDPE fibers possessing side chains with a high melt flow index. The polyethylene fibers, which exhibited thermoplastic properties and plastic behavior, were cross-linked through the sulfonation process. Their thermal properties and mechanical properties changed to thermoset properties and elastic behavior. Although sulfonation was performed under a hydrostatic pressure of 5 bar, it was difficult to convert the highly oriented polyethylene fibers because of their high crystallinity, but partially oriented polyethylene fibers could be converted to carbon fibers. Therefore, the effect of fiber orientation on fiber crosslinking, which has not been reported in previous literature, has been studied in detail, and a new method of hydrostatic pressure sulfonation has been successful in thermally stabilizing polyethylene fiber. Hydrostatic sulfonation was performed using partially oriented LLDPE fibers with a melt flow index of 20 at 130 °C for 2.5 h under a hydrostatic pressure of 5 bar. The resulting fibers were carbonized under the following conditions: 1000 °C, 5 °C/min, and five minutes. Carbon fibers with a tensile strength of 2.03 GPa, a tensile modulus of 143.63 GPa, and an elongation at break of 1.42% were prepared.

A novel technique for the development of acetabular cup by cold isostatic compaction and sintering of UHMWPE powder with optimized processing parameters

AbstractLife of a metal on ultra‐high molecular weight polyethylene (UHMWPE) total hip replacement is often limited to 10–15 years, due to wear loss and aseptic loosening. Due to its high melt flow index, UHMWPE is typically processed by ram extrusion or compression molding technique, but yet to be processed to the full potential of its mechanical integrity in acetabular shape without any fusion defects or weak bonding. The main objective of the present study is to develop a novel technique to fabricate defect‐free acetabular cups with desired bearing characteristics and surface finish by sintering medical‐grade UHMWPE GUR 1050 powder after its cold isostatic compaction with optimum processing parameters. Sintering kinetics of UHMWPE is studied comprehensively using a thermomechanical analyzer. The influence of compaction pressure, sintering temperature, and sintering duration on sintering kinetics of UHMWPE is explored to realize their optimum. The optimally processed UHMWPE has the relative density of 97% and Vickers hardness of 5.4 with tensile yield strength and elastic modulus of 21.5 and 625 MPa, respectively. The newly developed acetabular cup exhibited inherent plateau‐finished bearing surface with an average surface roughness of <100 nm, having good bearing characteristics and desired dimension.

Environmental Protection with HDPE Geomembranes in Mining Facility Constructions

The present work evaluated two high-density polyethylene (HDPE) geomembranes exhumed from mining facility constructions in Brazil. The MIN sample was exhumed from a pond for water use for the iron ore process after 7.92 years of exposure. The MIN2 sample was exhumed from a spillway channel of a ferronickel tailing dam after 10.08 years of service. The physical evaluations showed high depletion for antioxidants that work in the temperature range of 200 °C. The samples presented brittle tensile behavior and had similar behaviors between stress cracking and tensile. Low tensile elongation values and low-stress crack resistance were noted. The MIN2 sample presented a higher melt flow index (MFI) value and lower stress crack resistance. Thermogravimetric curves (TG) under synthetic air purge gas evaluation showed that both samples presented a similar behavior during the evaluation but had several mass losses. The results showed that exothermic and endothermic events occurred with loss of mass and showed no combustion events in the differential thermal analysis (DTA) curve evaluation. Differential scanning calorimetry (DSC) analysis showed no changes in the samples’ behavior. Thus, the results of tensile, stress cracking, and viscosity properties can demonstrate that changes in polymer structure occurred after field exposures.

Nanocomposites based on polyamide-6 and montmorillonite intercalated with polyvinylpyrrolidone

ABSTRACT The paper deals with the investigation results of nanocomposites based on polyamide-6 (PA6) and montmorillonite (MMT) intercalated by polyvinylpyrrolidone (PVP). Nanocomposites were obtained by mixing in the melt and the formic acid solution. The structure and presence of physical interaction between the nanocomposite components have been established using X-ray diffraction (XRD), differential thermal analysis (DTA), IR spectroscopy, and scanning electron microscopy (SEM). The presence of PVP in the structure of nanocomposites obtained from the solution was confirmed by IR spectroscopic analysis; the presence of layered MMT in the pyrolysis residue of nanocomposites was confirmed by diffractometry. SEM analysis confirmed the presence of layered MMT nanoparticles in the nanocomposite structure. It is shown that polyamide-based nanocomposites with a supramolecular structure different from PA6 are formed by precipitation from a solution; a crystalline composite is formed by mixing the components in the melt. It was found that nanocomposites obtained from the solution have a higher melt flow index (MFI) and lower softening temperature compared to those obtained in the melt. The formation of a homogeneous blend based on PA6/int-MMT nanocomposite with polypropylene (PP) was confirmed and the increase of thermo-physical characteristics of PP was determined.

Use of virgin/recycled polyethylene blends in rotational moulding

Abstract Aiming to further plastics recycling via rotational moulding plastics processing, blends of virgin and recycled polyethylene sourced from post-consumer plastics were developed. Three different kinds of recycled high density polyethylene – from bottles, pipes and mixed household waste – were compounded with virgin medium density polyethylene in an extruder. The ideal amount of recyclate was chosen based upon the impact resistance of different contents (25, 50 and 75%) of recycled plastic with the 50/50 blend found to have the best performance. Compression-moulded and rotationally-moulded samples were analysed through falling dart impact test, flexural test, melt flow rate and differential scanning calorimetry analysis. The impact results of the compression-moulded samples showed an increase in the impact resistance of the blends with a higher melt flow index and lower degree of crystallinity. The rotationally-moulded specimens displayed much lower impact resistance than the pure virgin plastic and a 20–30% reduction in the flexural moduli, which were ascribed to the crystalline structure of the part and issues in the blends’ rotomoulding process. It was concluded that blending virgin and recycled polyethylene for rotational moulding can be an effective way to further plastics recycling inside the Circular Economy context.

Degradación térmica del polipropileno reprocesado en una extrusora de doble husillo co-rotatorio: modelo cinético y relación entre el índice de flujo de fusión y el peso molecular

Thermo-mechanical degradation of polypropylene (PP) during reprocessing causes significant changes in its properties and presents a challenge to recycling. In this study, PP was reprocessed multiple times (1 to 5 cycles, at 240, 260, or 280 °C), and the physical and structural properties of the reprocessed material were evaluated. In comparison to virgin PP, the reprocessed polymer presented a higher carbonyl index, higher melt flow index, lower average molecular weight, and narrower polydispersity. Changes in these parameters became more pronounced as the processing time and temperature increased. Additionally, two different behavior regions were identified, the first one spanning between 240 - 260 °C, and the second one comprising higher temperatures (280 °C). Moreover, a kinetic model that calculates the Mw of PP reprocessed at different temperatures was evaluated. Finally, adjusted parameters for the relationship between MFI and Mw were obtained, and the MFI of reprocessed PP was also calculated.

Microstructure evolution and mechanism of PLA/PVDF hybrid dielectrics fabricated under elongational flow

Polylactide (PLA)/polyvinylidene fluoride (PVDF) hybrid dielectrics with high melt flow index ratio have been prepared by a novel twin-eccentric rotor extruder (TERE). In TERE, the continuous elongational flow, originated from the alternate compression and release, plays a key role during melt blending. Compared to traditional shear flow, it facilitates the dispersion and orientation of the dispersed phase along the elongational direction, forming the fine and anisotropic micromorphology in PLA/PVDF blends. With the change of composition ratio, twice phase transitions and three structure regions are observed, in which the interpenetrating network structure is formed at 60-70 wt% PVDF loading. Based on the coupling effect of elongational flow and material properties, the mechanism of microstructure evolution for PLA/PVDF blends is put forward. In addition, the effective dielectric constant of PLA/PVDF blends is slowly and then rapidly improved in linear with PVDF content increasing. The turning point is the first phase transition due to the formation of new continuous phase of PVDF.

Influence of polymer structure and amount on microstructure and properties of polyethylene-modified asphalt binders

In recent years, the use of polyethylene (PE) for asphalt modification has been gaining increased attention due to the environmental sustainability and cost-saving benefits. To optimize the performance of the PE-asphalt blends, it is necessary to understand the polymer-binder interactions and their impact on the properties of the modified asphalt binder. In this study, low-density polyethylene (LDPE) with low and high melt flow index (MFI), i.e., LDPE4 and LDPE70, were blended with Pen 60-70 asphalt binder in dosages ranging from 1 to 5 wt.%. PE Wax was also added to the binder or the PE-binder blend to enhance dispersion. The dispersion of PE in the binder and the phase stability of the modified binder were investigated by optical microscope. The equivalent diameter of PE domains increased with time and the polymer dosage level. The addition of PE wax improved the polymer dispersity in the LDPE4 blends. The polymer dispersity in LDPE70 blends was good without adding PE Wax, attributed to the higher MFI value (low molecular weight) of LDPE70. In addition, to understand the stability of polymer modified binder, the steady shear viscosity-temperature profile of these binders was studied using a rotational viscometer. The dynamic rheological properties and performance of the PE-binder blends were evaluated using the dynamic shear rheometer. Based on the microstructure, all other rheological and performance properties, it was concluded that the 3% LDPE70 binder has better polymer dispersity, better low and high temperature performance characteristics.

Polymer, Additives, and Processing Effects on N95 Filter Performance.

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.

Grafting Poly(Methyl Methacrylate) (PMMA) from Cork via Atom Transfer Radical Polymerization (ATRP) towards Higher Quality of Three-Dimensional (3D) Printed PMMA/Cork-g-PMMA Materials.

Cork is a unique material and its by-products are attracting an ever-growing interest for preparing new materials in an attempt to extend the outstanding properties of cork toward innovative and high value applications. Yet, the miscibility of cork particles with thermoplastic matrices is not easy due to its low density and surface properties. Here, cork is functionalized with poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP) to yield cork grafted with PMMA chains particles (cork-g-PMMA). Both the ATRP macroinitiator and the cork-g-PMMA obtained are fully characterized by Fourier-transform infrared spectroscopy (FT-IR), 13C cross-polarized magic-angle spinning solid-state nuclear magnetic resonance (13C CP/MAS solid state NMR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The functionalized cork particles are then blended with commercial PMMA to afford cork-g-PMMA/PMMA. To compare, cork also is mixed with PMMA and the ensuing cork/PMMA sample and its morphology, thermal, and mechanical properties are compared with those of cork-g-PMMA/PMMA and commercial PMMA. The cork surface modification via ATRP of the methyl methacrylate (MMA) yields better dispersion in the matrix. Consequently, a blend with enhanced mechanical performance, higher thermal stability, and a higher melt flow index (MFI) is obtained when compared to the blend prepared using unmodified particles. The similarity of the MFI of cork-g-PMMA/PMMA to that of PMMA suggests good printability. Indeed, a three-dimensional (3D) printed specimen is obtained confirming that grafting using ATRP is a promising route for the preparation of high quality 3D printed products.