Polymer Powder Research Articles

From trash to treasure in additive manufacturing: Recycling of polymer powders by acid catalyzed hydrolysis

From trash to treasure in additive manufacturing: Recycling of polymer powders by acid catalyzed hydrolysis

ИССЛЕДОВАНИЕ ФОРМИРОВАНИЯ ДЕМПФИРУЮЩИХ ПОКРЫТИЙ ИЗ ПОЛИМЕРОВ И МЕТАЛЛОВ

The processes of obtaining damping polymeric coatings (gas-flame spraying of powders) and composite metal coatings (deformation cladding with a flexible tool) are studied. It is established that coatings applied by the gas-flame method with thermoplastic polymer powders provide a sufficiently high damping efficiency, while the best dissipative characteristics are provided when sprayed with polyethylene terephthalate powder. The maximum adhesion strength (10.5–10.7 MPa) for normal separation of coatings applied with polyethylene terephthalate powder is achieved when using a combustible mixture with a propane/air ratio of 1:26 and subsequent cooling at a rate of no more than 3 deg/s. Based on the results of tribotechnical tests, the composition of sintered bronze-graphite was selected for applying noise-absorbing coatings by the deformation cladding method. The study of the influence of regime parameters of the cladding process on the thickness and continuity of the formed coating layer of bronze-graphite showed that the ratio of the linear speed of movement of the workpiece and the linear speed of rotation of the brush should be within 0.23–0.27, the interference value N — in the range of 0.8–1.5 mm with the number of passes n = 8–12. The microhardness of the clad layer was H0,049 = 1,700 MPa, which exceeded the microhardness of the donor material by 25 %.

Three-Dimensional Printable Flexible Piezoelectric Composites with Energy Harvesting Features.

The purpose of this work was to obtain an elastic composite material from polymer powders (polyurethane and polypropylene) with the addition of BaTiO3 until 35% with tailored dielectric and piezoelectric features. The filament extruded from the composite material was very elastic but had good features to be used for 3D printing applications. It was technically demonstrated that the 3D thermal deposition of composite filament with 35% BaTiO3 was a convenient process for achieving tailored architectures to be used as devices with functionality as piezoelectric sensors. Finally, the functionality of such 3D printable flexible piezoelectric devices with energy harvesting features was demonstrated, which can be used in various biomedical devices (as wearable electronics or intelligent prosthesis), generating enough energy to make such devices completely autonomous only by exploiting body movements at variable low frequencies.

Controllable preparation of semiconducting polymer microspheres and their application in the photocatalytic degradation of tetracycline antibiotics

The side effects of antibiotics on humans and ambient environment have aroused huge attention from related researchers. In this article, the performances and mechanism of photodegradation of tetracycline (TC) were examined by employing semiconducting polymer microspheres obtained with an emulsion-solvent-evaporation approach. Under the excitation of visible-light, as-prepared semiconducting polymer microspheres show outstanding photocatalytic ability and excellent stability for TC-derived antibiotics. Compared with corresponding semiconducting polymer powders, the adsorption and photocatalytic rates of TC by polymer-based microspheres increased by 8.07 and 6.79 times, respectively. These performance improvements in photodegradation are mainly ascribed to the larger specific surface area and longer conjugation length of as-prepared spherical structure. Characterization of electron spin resonance demonstrates that the primary active species functioning for efficient photodegradations of TC are superoxide radical, hydrogen peroxide, and hole. These results indicated that semiconducting polymer microspheres can serve as efficient photocatalysts for removing destructive TC-derived antibiotics from wastewaters.

DESTRUCTION OF POLYMERCEMENT PLASTER COATING DURING OPERATION OF WALL STRUCTURE

The disadvantage of limesand, limecement and cementlime plaster mortars is the intensive formation of cracks during hardening and operation, which leads to rapid destruction of the plaster coating, its detachment from the masonry, which causes increased humidity and loss of heat through it, as well as reducing the service life of the wall structure.The main reason for this is choosing the components of the mixture and their quantity without taking into account the processes occurring during curing of the coating and its "work" as part of the wall structure during operation.To solve the problem, the wall structure should be considered as a system that includes a plaster coating associated with the masonry through the contact area. The composition of the soluble mixture must be prescribed taking into account the processes occurring during its hardening and operation of the wall structure, the stresses that occur in it. It is necessary to choose the components of the mixture and their quantity, so as to ensure the reduction of stresses in the plaster coating and its contact zone with the masonry, to values, less than destructive. This will increase the service life of the coating and wall construction.Since the properties of polymercement plaster mortar are determined by its composition and structure, to achieve these goals, the possibility of managing them by purposeful selection of components of the soluble mixture was analyzed. For this purpose, redispersible polymer powders (RPP), polymer fiber, cellulose esters, and a fine filler with a low modulus of elasticity were used.Studies have shown that their use has changed the nature of the destruction, reduced the number of cracks formed during the hardening of the plaster mortar, slowed down their development and increased the service life of plaster mortar and the wall structure.

Aqueous cannabidiol β-cyclodextrin complexed polymeric micelle nasal spray to attenuate in vitro and ex vivo SARS-CoV-2-induced cytokine storms

Cannabidiol (CBD) has a number of biological effects by acting on the cannabinoid receptors CB1 and CB2. CBD may be involved in anti-inflammatory processes via CB1 and CB2 receptors, resulting in a decrease of pro-inflammatory cytokines. However, CBD's poor aqueous solubility is a major issue in pharmaceutical applications. The aim of the present study was to develop and evaluate a CBD nasal spray solution. A water-soluble CBD was prepared by complexation with β-cyclodextrin (β-CD) at a stoichiometric ratio of 1:1 and forming polymeric micelles using poloxamer 407. The mixture was then lyophilized and characterized using FT-IR, DSC, and TGA. CBD-β-CD complex-polymeric micelles were formulated for nasal spray drug delivery. The physicochemical properties of the CBD-β-CD complex-polymeric micelle nasal spray solution (CBD-β-CDPM-NS) were assessed. The results showed that the CBD content in the CBD-β-CD complex polymeric micelle powder was 102.1 ± 0.5% labeled claim. The CBD-β-CDPM-NS was a clear colorless isotonic solution. The particle size, zeta potential, pH value, and viscosity were 111.9 ± 0.7 nm, 0.8 ± 0.1 mV, 6.02 ± 0.02, and 12.04 ± 2.64 cP, respectively. This formulation was stable over six months at ambient temperature. The CBD from CBD-β-CDPM-NS rapidly released to 100% within 1 min. Ex vivo permeation studies of CBD-β-CDPM-NS through porcine nasal mucosa revealed a permeation rate of 4.8 μg/cm2/min, which indicated that CBD was effective in penetrating nasal epithelial cells. CBD-β-CDPM-NS was tested for its efficacy and safety in terms of cytokine production from nasal immune cells and toxicity to nasal epithelial cells. The CBD-β-CDPM-NS was not toxic to nasal epithelial at the concentration of CBD equivalent to 3.125–50 μg/mL. When the formulation was subjected to bioactivity testing against monocyte-like macrophage cells, it proved that the CBD-β-CDPM-NS has the potential to inhibit inflammatory cytokines. CBD-β-CDPM-NS demonstrated the formulation's ability to reduce the cytokine produced by S-RBD stimulation in ex vivo porcine nasal mucosa in both preventative and therapeutic modes.

Research and Development on Cold-Sprayed MAX Phase Coatings

Cold spraying is an attractive solid-state processing technique in which micron-sized solid particles are accelerated towards a substrate at high velocities and relatively low temperatures to produce a coating through deformation and bonding mechanisms. Metal, ceramic, and polymer powders can be deposited to form functional coatings via cold spraying. MAX phase coatings deposited via cold spraying exhibit several advantages over thermal spraying, avoiding tensile residual stresses, oxidation, undesirable chemical reactions and phase decomposition. This paper presents a review of recent progress on the cold-sprayed MAX phase coatings. Factors influencing the formation of coatings are summarized and discussions on the corresponding bonding mechanisms are provided. Current limitations and future investigations in cold-sprayed MAX coatings are also listed to facilitate the industrial application of MAX phase coatings.

Recyclability of tannin-furanic foams

Tannin-furanic foams are biogenic, lightweight material comprising of up 95% renewable resources. Replacing 5 to 30% of the tannin powder in the formulation for new foam with finely grinded, recycled tannin-furanic polymer powder was investigated. While 5% and 10% of recycled material did not have a significant influence on the mechanical properties (bending strength, modulus of elasticity, tensile strength and compression resistance) a slight decrease is observed for 15 to 25% replacement, but within these groups, results are not significantly different. An overall decrease of 30% for mechanical properties was observed for foams made with 15% to 25% recycled material. The addition of 30% recycling material in the production of tannin foams is not feasible, as the foaming process is disturbed.

Dimensional accuracy and impact resistance of 3D printed clay reinforced with scrap polymer powder

PurposeThe purpose of this paper is to give an insight into relevant aspects of 3D printing of clay paste enhanced with scrap polymer powder which have not been investigated by previous studies. Specifically, the geometrical features of the deposited lines, dimensional accuracy of benchmarks and mechanical properties of printed parts are investigated.Design/methodology/approachFirstly, the 3D printer is used to deposit lines of the paste under various combinations of material composition and process parameters. 3D scanning is used to measure their dimensional and geometrical errors. The results are elaborated through statistics to highlight the role of material and processing conditions. Then, four benchmark parts are printed using materials with different percentages of polymer powder. The parts are scanned after each step of the post-processing to quantify the effects of printing, drying and melting on dimensional accuracy. Finally, drop weight tests are carried out to investigate the impact resistance of specimens with different powder contents.FindingsIt is found that the quality of deposition varies with the printing speed, nozzle acceleration and material composition. Also, significant differences are observed at the ends of the lines. Materials with 10 Wt.% and 40 Wt.% of powder exhibit relevant shape variations due to the separation of phases. Accuracy analyses show significant deformations of parts at the green state due to material weight. This effect is more pronounced for higher powder contents. On the other hand, the polymer reduces shrinkage during drying. Furthermore, the impact test results showed that the polymer caused a large increase in impact resistance as compared to pure clay. Nonetheless, a decrease is observed for 40 Wt.% due to the higher amount of porosities.Research limitations/implicationsThe results of this study advance the knowledge on the 3D printing of clay paste reinforced with a scrap polymer powder. This offers a new opportunity to reuse leftover powders from powder bed fusion processes. The findings presented here are expected to foster the adoption of this technique reducing the amount of waste powder disposed of by additive manufacturing companies.Originality/valueThis study offers some important insights into the relations between process conditions and the geometry of the deposited lines. This is of practical relevance to toolpath planning. The dimensional analyses allow for understanding the role of each post-processing step on the dimensional error. Also, the comparison with previous findings highlights the role of part dimensions. The present research explores, for the first time, the impact resistance of parts produced by this technology. The observed enhancement of this property with respect to pure clay may open new opportunities for the application of this manufacturing process.

Geometric Accuracy of Components Manufactured by SLS Technology Regarding the Orientation of the Model during 3D Printing

Selective Laser Sintering (SLS) or sintering of polymer powders is one of the most well-known additive technologies for printing 3D components. The properties of individual polymer powder materials have a significant impact on the quality of the manufactured part. Potential deformation and shrinkage can occur during printing if a significant number of parts are piled on top of one another or are oriented incorrectly, accumulating thermal energy in certain areas. The aforementioned research focuses on an experimental study to investigate the impact of the distribution and orientation of printing samples in the build chamber on the accuracy of dimensions and the surface roughness of PA12 prints. The aim of the study was to examine the impact of model settings during production as well as the effect of individual factors on the properties of manufactured parts, with a focus on ensuring that heat rises evenly from each print without accumulating.

Powders of rGO-coated polyamide with special electrical properties for SLS 3D printing

Developing new polymer composites with special properties for 3D printing is one of the most attractive tasks. In our study, we have developed new polymer powders based on rGO-coated polyamide suitable for Selective Laser Sintering (SLS) printing. The obtained materials were characterized using optical microscopy, UV-Vis spectroscopy, scanning electron microscopy and dielectric spectroscopy. The size distribution of the powder particles, the angle of rest after an avalanche, the compactibility (Hausner ratio), the optical properties (absorption and transmission) of the powder monolayer, and the electrical conductivity of the obtained materials have been studied. It has been shown that the developed powders are suitable for the use in the framework of the SLS method, and can be applied to remove static electricity, as well as in reflective screens for electromagnetic radiation.

再乳化型粉末樹脂を用いたポリマーセメントモルタルの収縮特性および圧縮特性

In this study, we investigated the shrinkage and compressive properties of polymer-modified mortars using redispersible polymer powders in the range of the P/C of 10% or less at the W/C of 35% and the S/C of 1.0. As a result, Autogenous shrinkage strain after deforming of polymer-modified mortars using acrylic redispersible polymer powders was almost the same regardless of the P/C. The acrylic redispersible polymer powders affected the drying shrinkage component of polymer-modified mortars. Drying shrinkage strain of polymer-modified mortars increased with increasing the P/C. Mass loss of polymer-modified mortars varied depending on the redispersible polymer powders used and its quantity. Compressive strength and Young's modulus of polymer-modified mortars tended to decrease with increasing the P/C. The effect of redispersible polymer powders on the compressive strength and Young's modulus of polymer-modified mortars was not so large. Poisson's ratio of polymer-modified mortars using acrylic redispersible polymer powders was about 0.2 regardless of the P/C.

Development of a novel rapid repairing agent for concrete based on GFRP waste powder/GGBS geopolymer mortars

The use of waste glass fiber-reinforced polymer (GFRP) powder as a binding agent in the synthesis of geopolymers offers an eco-friendly solution for managing GFRP waste. The aluminosilicate present in GFRP powder can be activated by an alkaline solution to produce a sustainable geopolymer. In this study, a novel rapid repairing material was developed from partially-replaced ground granulated blast furnace slag (GGBS) by GFRP waste powder as precursors in geopolymer mortar (GM). The effect of GFRP powder replacement and mix proportions on the fresh and hardened properties of GMs were evaluated. It was found that an increase in GFRP powder replacement led to an increase in the setting time and a decrease in workability. The highest 28-day compressive strength was obtained at a 20% replacement of GGBS with GFRP powder. At this optimal mixture, the GMs achieved a compressive strength of 15.2 MPa after 6 h and 35.7 MPa after 1 day. Results from the slant shear test revealed that the failure pattern of the GM-repaired concrete samples changed from interface failure to monolithic failure and explosive spalling in the concrete substrate (CS), when the test duration increased from 3-days to 7-days and 28-days, respectively. This was attributed to the formation of a compact interfacial zone with prolonged testing duration, leading to increased bond strength. The developed GMs demonstrate a short setting time, excellent flowability, high early mechanical strength and superior bond properties, and thus can be applied as rapid concrete repair materials or as protective coatings for concrete in corrosive environments.

Photosensing of chain polarity and visualization of latent fingerprints by amine-functionalized polymer nanoparticles containing oxazolidine

Here, the photoluminescent amphiphilic nanoparticles were synthesized by doping of the hydroxylated oxazolidine derivative as a highly fluorescent organic chromophore to the surface of functionalized copolymer nanoparticles containing amine groups. Prepared amphiphilic copolymer nanoparticles have variable particle sizes in the range of 58–1320 nm with various spherical morphologies depending on the concentration of 2-(dimethylamino)ethyl methacrylate (DMAEMA). Investigation of optical properties for constructed photoluminescent amphiphilic nanoparticles indicated photoinduced electron transfer (PET) phenomenon between tertiary amine groups of DMAEMA and oxazolidine molecules. The photoluminescent polymer powder samples were used for printing of encrypted information on cellulose papers by powder dusting method. Printed quick responsive (QR) codes have fluorescent emission in various colors with maximum resolution, intensity, and brightness under UV-light irradiation of 365 nm. In addition, the visualization of fingerprints by powder dusting and fluorescence imaging under UV-light irradiation (365 nm) was carried out by using photoluminescent polymer powders. The fingerprints are detectable by photoluminescent nanomaterials in a rapid and accessible manner, and all three levels of identification for fingerprint ridge patterns are achievable. Therefore, developed photoluminescent nanomaterials can offer authoritative evidence for the encryption of information, and also recognize the individual identity in a short time and with the least facilities.

Experimental Investigation on Friction Behavior of Selective Laser Sintering Processed Parts.

Selective laser sintering (SLS) is a powder bed fusion additive manufacturing process that uses polymer powders to produce functional parts directly from digital 3D models. SLS supports small- to medium-batch fabrication of customized products for various end-use applications. These parts can be used as tooling to support conventional manufacturing and inspection where mechanical and tribological behaviors are important. This article evaluates the friction behavior of parts fabricated by SLS polyamide (PA12) and glass bead-filled polyamide (PA-GF) materials. Pin-on-Disk tribometer was used to characterize the behavior in dry sliding conditions with part build orientation, load, and speed as factors. Taguchi's approach and analysis of variance are used to quantify the influence of these factors on the friction coefficient. Both materials show reduction in friction coefficient with the increase in load; on the other hand, an increase in speed affects adversely. However, the influence of part orientation is comparatively lesser than the other two factors considered in this study. The debris, pin, and disk wear surfaces were examined to learn wear mechanisms. It is observed that surface porosity resulting from the fabrication process plays a significant role in friction behavior. The glass beads in PA-GF material function as reinforcement against load and influences the friction behavior. Low friction and wear characteristics make both materials as a prospective contender for tooling application.

Flowability of polymer powders at elevated temperatures for additive manufacturing

The flowability and spreadability of three different polymer powders for selective laser sintering were investigated by analysing the powder at different temperatures. These measurements were performed using both the Revolution Powder Analyzer and the Schulze Ring Shear Tester. The latter device was modified with a self-developed heating system to allow testing at temperatures up to 170 °C. Overall, the results of both tests showed that the powders' flowability decreases as the temperature increases, with the largest decrease observed near the materials' melting point. Afterwards, recoating tests were conducted on an EOS P395 machine, which utilized a self-built AI monitoring system to detect and evaluate the severity of defects in the powder bed. The tests revealed that the number and severity of defects also increases with temperature. When approaching the sintering window, the number and severity of defects greatly decreases, and the powder bed becomes stronger and more resistant to defects.

Enabling Long-Lived Polymeric Room Temperature Phosphorescence Material in Abominable Solvent.

Long-lived polymeric room temperature phosphorescence (RTP) materials have drawn more attention due to their convenient preparation process and equally efficient phosphorescence performance in recent years. As the polymer matrix is sensitive to air and humidity, some non-covalent interactions in the matrix are easily decomposed in water or air, which means that it is difficult for this material to be stored stably for a long time in the atmospheric environment or under harsh conditions. In this work, polymer powder mBPipQ contains aromatic and piperidine rings that are designed and synthesized successfully. Then the polymer is uniformly dispersed into epoxy resin matrix to form long-lived polymeric RTP material with efficient afterglow properties. The stiff backbone structure of mBPip and dense molecular arrangement of epoxy resin provide a rigid environment to stabilize triplet excitons, the RTP performance is greatly enhanced. The lifetime of mBPipQ in epoxy resin is 2 times higher than that of small molecule chromophore in that one. Interestingly, after soaking in strong acid or alkali solution for 10 days, the material can still emit stable and efficient long-lived phosphorescence. It is thanks to the hard matrix after full curing, which can provide a protective layer to prevent external quenchers from interfering with phosphorescence emission. Utilizing the efficient phosphorescence emission and excellent abominable-solvent resistance of this RTP material, multilevel information encryption has been successfully demonstrated. This work broadens the application scope of polymeric RTP materials in harsh environments and provides a new idea for achieving efficient RTP emission.

Solventless Drug Pelletization and Polymer Coating Techniques for Pharmaceutical Manufacturing

This paper described a review of solventless drug pelletization and polymer coating techniques using a mechanical powder processor as well as conventional processors including a high shear granulator and a V-shaped blender. Mechanical powder processing of drug crystals provided pellets comprising drug alone and the pelletization was due to inherent adhesiveness of drug powder as well as mechanically-induced dehydration or amorphization of drug crystals. Mechanical powder coating of polymethacrylates and ethylcellulose was achieved using freeze dried powder comprising colloidal polymer particles. High shear mixing of drug crystals and cellulose spheres provided drug-layered pellets by ball-milling actions of the spheres in the granulator. V-shaped blending of uncoated tablets and colloidal polymer powder resulted in the coating of the tablets with broken polymer particles. These techniques include only simple mixing processes and need no solvents, thereby contributing to the reduction of the environment impacts and costs in pharmaceutical manufacturing.

Workplace Exposure Measurements of Emission from Industrial 3D Printing.

Particle and gaseous contaminants from industrial scale additive manufacturing (AM) machines were studied in three different work environments. Workplaces utilized powder bed fusion, material extrusion, and binder jetting techniques with metal and polymer powders, polymer filaments, and gypsum powder, respectively. The AM processes were studied from operator's point of view to identify exposure events and possible safety risks. Total number of particle concentrations were measured in the range of 10 nm to 300 nm from operator's breathing zone using portable devices and in the range of 2.5 nm to 10 µm from close vicinity of the AM machines using stationary measurement devices. Gas-phase compounds were measured with photoionization, electrochemical sensors, and an active air sampling method which were eventually followed by laboratory analyses. The duration of the measurements varied from 3 to 5 days during which the manufacturing processes were practically continuous. We identified several work phases in which an operator can potentially be exposed by inhalation (pulmonary exposure) to airborne emissions. A skin exposure was also identified as a potential risk factor based on the observations made on work tasks related to the AM process. The results confirmed that nanosized particles were present in the breathing air of the workspace when the ventilation of the AM machine was inadequate. Metal powders were not measured from the workstation air thanks to the closed system and suitable risk control procedures. Still, handling of metal powders and AM materials that can act as skin irritants such as epoxy resins were found to pose a potential risk for workers. This emphasizes the importance of appropriate control measures for ventilation and material handling that should be addressed in AM operations and environment.

Combined Effect of End-of-Life Rubber and a Hydrophobic Polymer on Coastal Saturated Sand: A Multiaspect Investigation

Nowadays, mass production of tires and construction operations adjacent to saturated soils have become a concern for engineers. The present study aimed to explore the potential of the combined effect of a waterproof polymer and rubber powder, confining pressure, and cyclic stress ratio on the static and dynamic properties of sand-rubber-polymer mixtures using a scanning electron microscope (SEM), attenuated total reflectance (ATR) analysis, unconfined compressive strength (UCS), and cyclic triaxial tests. The findings indicated that with the inclusion of 4% rubber, rough polymer chains are extended due to creating C─ CH3 bonds, uniform distribution of rubber particles between rigid materials, and interlocking rubbers in hydrocarbon chains. These chains increase adhesion with sand particles and prevent rubber flexibility, increasing UCS and shear modulus. In contrast, with the inclusion of 8% rubber, due to several mechanisms, including poor adhesion between particles because of the high surface area of the mixture and low polymer content (i.e., 2%), the dominance of weak rubber–polymer and rubber–rubber bonds over polymer–polymer and sand–polymer bonds, emerging free rubber particles (free CH2 groups), and creating the aromatic and double bond structures due to the nature of rubber flexibility, the trend is reversed.