Search Results (19)

In this paper, thermal and mechanical properties of ablative thermal protective material (TPM) as inhibitors for a free-standing propellant grain based on phenolic resin (PR) and acrylonitrile butadiene rubber (NBR) were investigated. NBR elastomerized PR composite, reinforced with chopped carbon fibers (CFs) (PR/NBR/CF), was prepared by homogenization of 90 parts by weight (PBW) PR in 100 PBW NBR (28 wt.% of acrylonitrile content). PR/NBR/CF composite was blended in two-roller open and closed mixers and in a twin-screw extruder. Carbon black, aluminum(III)-oxide, and fumed silica were added as promoters of thermal and mechanical properties of PR/NBR/CF. The structural analysis was studied using Fourier transform infrared spectroscopy (FT-IR). Thermal properties of the prepared PR/NBR/CF composite inhibitor were studied by ablation and firing tests, while a morphological analysis of the char layer formed after the ablation test was conducted via scanning electron microscopy (SEM). A low erosion rate of 2.00 × 10⁻⁴ m·s⁻¹ and high tensile strength and elongation at break of 6.7 MPa and 419.92%, respectively, indicate that the developed materials can be applied as a thermal insulation/inhibitor of free-standing rocket propellant grains. Bond strength between PR/NBR/CF composite and aluminized composite rocket propellant (ACRP), determined via a standard peel test, showed higher adhesion forces between the PR/NBR/CF composite and the ACRP compared to the cohesion between the ACRP molecular chains. Full article

Background/Objectives: This study tested a method for evaluating the internal fit of indirect resin-based composite (RBC) restorations, as well as the influence of different combinations of impression and die materials on the reproducibility of the topography of teeth prepared for indirect RBC restoration. Methods: Bovine incisors received flattened and cavitated areas at the cervical and middle thirds of the buccal surface, respectively. The samples were randomly assigned to two groups according to the material used for impression taking (n = 5): irreversible hydrocolloid and polyvinyl siloxane (PVS). Die replicas were obtained with Type IV gypsum or elastomeric material. RBC restorations were fabricated through an indirect technique (test) and a direct-indirect technique as the control. The internal fit of restorations was assessed by measuring the cementation line thickness with a digital caliper (simulated cementation protocol with ultra-light PVS) and validated using scanning electron microscopy (SEM). Surface topography (Sa, Sq, and Sz) was analyzed via optical profilometry, and wettability was assessed through the water contact angle method. The data were analyzed using t-test, ANOVA, and Pearson correlation tests (α = 5%). Results: The simulated cementation resulted in internal gap values positively correlated to the values from SEM (R² = 0.958; p = 0.0102). The internal gap of restorations was not significantly correlated with the discrepancies between the topography of the die and tooth substrate (p ≥ 0.067). The combination of irreversible hydrocolloid and gypsum resulted in restorations with the lowest cementation line thickness, although in terms of roughness, this combination was the only one that resulted in significant differences from the control (p ≤ 0.028). The internal mean gap values of restorations were significantly correlated to the cumulative wettability difference of materials used during impression taking, fabrication of die replica, and restoration build-up (R² = 0.981; p = 0.003). Conclusions: The reproducibility of topographical characteristics of the tooth in the die replica did not affect the internal adaptation of indirect RBC restorations, whereas surface wettability of materials presented a more relevant effect on the overall gap formation. The simulated cementation technique tested in the study shows potential as a simpler, cost-effective, and non-destructive method for evaluating the adaptation of indirect RBC restorations. Full article

Tissue engineering is an emerging field within biomedicine, related to developing functional substitutes for damaged tissues or organs. Despite significant advancements, the development of effective engineering tissue constructs remains challenging, particularly when replicating elastic stretchability, which plays a critical role in many tissues. Therefore, the development of tough, elastomeric scaffolds that mimic the complex elasticity of native tissues, such as the myocardium, heart valves, and blood vessels, is of particular interest. This study aims to evaluate a flexible printable material (Formlabs’ Elastic 50A Resin V2) to develop porous 3D scaffolds using additive manufacturing stereolithography (SLA). The elastomeric samples were tested in relation to their swelling behaviour, mechanical properties, and exposure to low temperatures. Additionally, the effects of print orientation, water immersion, and exposure to low temperatures on surface roughness and porosity were investigated to determine the best conditions to enhance scaffold performance in biomedical applications. The results demonstrated that samples printed at 0°, immersed in water, and exposed to low temperature (−80 °C) showed a more uniform microporosity, which could improve the adhesion and growth of cells on the scaffold. This research highlights a practical and economical approach to enhancing elastomeric scaffolds, paving the way for improved outcomes in tissue engineering applications. Full article

Photocurable materials offer a rapid transition from a liquid to a solid state, and have recently received great interest in the medical field. However, while dental resins are very popular, only a few materials have been developed for soft tissue repair. This study aims to synthesize a difunctional methacrylate monomer using a dibutyltin dilaurate which is suitable for the photocuring of soft materials. These soft materials were compared with PhotoBioCure^® (Szczecin, Poland) material with a similar molecular weight, of Mn ~7000 g/mol on average. Infrared spectroscopy was used to monitor the two-step synthesis catalyzed with dibutyltin dilaurate, while spectroscopic and chromatographic methods were used to determine the chemical structure and molecular weight of the monomers. Photopolymerization kinetics under varying light intensities were explored in a nitrogen atmosphere for representative difunctional monomers. The mechanical testing of the resulting elastomeric films confirmed tensile strength and modulus values consistent with soft tissue parameters in the range of 3–4 MPa. The 3D printability of the macromonomers was also assessed. Additionally, cytotoxicity assessments using cultured cells showed a high cell viability (97%) for all new materials. Overall, we demonstrate that difunctional methacrylate monomers converted to flexible solids during photopolymerization show great potential for biomedical applications. Full article

The fast progress of 3D printing technology has resulted in the creation of innovative materials, such as elastic resins, broadening the field of applications in various sectors. This paper investigates the effect of printing parameters on the strength and elongation of the final part, as well as optimizing elastic resin 3D printing processes using the Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) analyses. In this analysis, the printing parameters post-curing time, exposure time, aging conditions, rotation direction, rest time after lift, photoinitiator effect, and aging time are considered criteria. The report finishes with recommendations for the most effective parameter settings for the best sample elongation (ε) and tensile strength (E). Full article

Rapid prototyping has produced accessible manufacturing methods that offer faster and more cost-effective ways to develop microscale systems for cellular testing. Commercial 3D printers are now increasingly adapted for soft lithography, where elastomers are used in tandem with 3D-printed substrates to produce in vitro cell assays. Newfound abilities to prototype cellular systems have begun to expand fundamental bioengineering research in the visual system to complement tissue engineering studies reliant upon complex microtechnology. This project used 3D printing to develop elastomeric devices that examined the responses of retinal cells to flow. Our experiments fabricated molds for elastomers using metal milling, resin stereolithography, and fused deposition modeling via plastic 3D printing. The systems were connected to flow pumps to simulate different flow conditions and examined phenotypic responses of endothelial and neural cells significant to neurovascular barriers of the retina. The results indicated that microdevices produced using 3D-printed methods demonstrated differences in cell survival and morphology in response to external flow that are significant to barrier tissue function. Modern 3D printing technology shows great potential for the rapid production and testing of retinal cell responses that will contribute to both our understanding of fundamental cell response and the development of new therapies. Future studies will incorporate varied flow stimuli as well as different extracellular matrices and expanded subsets of retinal cells. Full article

Ethylene–vinyl acetate copolymer (EVA), a crucial elastomeric resin, finds extensive application in the footwear industry. Conventional chemical foaming agents, including azodicarbonamide and 4,4′-oxybis(benzenesulfonyl hydrazide), have been identified as environmentally problematic. Hence, this study explores the potential of physical foaming of EVA using supercritical nitrogen as a sustainable alternative, garnering considerable interest in both academia and industry. The EVA formulations and processing parameters were optimized and EVA foams with densities between 0.15 and 0.25 g/cm³ were produced. Key findings demonstrate that physical foaming not only reduces environmental impact but also enhances product quality by a uniform cell structure with small cell size (50–100 μm), a wide foaming temperature window (120–180 °C), and lower energy consumption. The research further elucidates the mechanisms of cell nucleation and growth within the crosslinked EVA network, highlighting the critical role of blowing agent dispersion and localized crosslinking around nucleated cells in defining the foam’s cellular morphology. These findings offer valuable insights for producing EVA foams with a more controllable cellular structure, utilizing physical foaming techniques. Full article

Ablative composites serve as sacrificial materials, protecting underlying materials from high-temperature environments by endothermic reactions. These materials undergo various phenomena, including thermal degradation, pyrolysis, gas generation, char formation, erosion, gas flow, and different modes of heat transfer (such as conduction, convection, and radiation), all stemming from these endothermic reactions. These phenomena synergize to form a protective layer over the underlying materials. Carbon, with its superb mechanical properties and various available forms, is highlighted, alongside phenolics known for good adhesion and fabric ability and elastomers valued for flexibility and resilience. This study focuses on recent advancements in carbon-and-phenolic and carbon-and-elastomeric composites, considering factors such as erosion speed; high-temperature resistance; tensile, bending, and compressive strength; fiber–matrix interaction; and char formation. Various authors’ calculations regarding the percentage reduction in linear ablation rate (LAR) and mass ablation rate (MAR) are discussed. These analyses inform potential advancements in the field of carbon/phenolic and carbon/elastomeric ablative composites. Full article

Advancements in industrial machinery and manufacturing equipment require more reliable and efficient polymer tribo-systems which operate in conditions associated with increasing machine speeds and a lack of cooling oil. The goal of the current research is to improve the tribological properties of elastomeric composites by adding a solid lubricant filler in the form of ultrafine polytetrafluoroethylene (PTFE) with the chemical formula [C₂F₄]_n and recycled polytetrafluoroethylene (r-PTFE) powders. PTFE waste is recycled mechanically by abrasion. The elastomeric composites are prepared by mixing a nitrile butadiene rubber with a phenol-formaldehyde resin and PTFE powders in an extruder followed by rolling. The deformation-strength and tribological tests of r-PTFE elastomeric composites are conducted in comparison with the ultrafine PTFE composites. The latter is based on products of waste fluoropolymer processing using a radiation method. The deformation-strength test shows that the introduction of ultrafine PTFE and r-PTFE powder to the composite leads to a decrease in strength and elongation at break, which is associated with the poor compatibility of additives and the elastomeric matrix. The friction test indicates a decrease in the coefficient of friction of the composite material. It is determined that the 15 wt.% filler added in the elastomeric matrix leads to a reduction in the wear rate by 20%. The results obtained show the possibility of using ultrafine PTFE powder and r-PTFE for creating elastomeric composites with increased tribological properties. These research results are beneficial for rubber products used in many industries, mainly in mechanical engineering. Full article

A series of epoxy vitrimers (EVs) with enhanced glass transition temperatures (T_gs) were synthesized by curing epoxy resin E51 with different ratios of phthalic anhydride and sebacic acid as curing agents, and 1,5,7-triazabicyclic [4.4.0] dece-5-ene as a transesterification catalyst, and their curing dynamics, rheological properties, mechanical properties, and thermal stability were comprehensively investigated. By adjusting the molar ratio of the anhydride to the carboxylic acid in the curing agent, the T_gs of the EVs increased from 79 to 143 °C with the increase in the anhydride content. In particular, the material EV-5.5 with a high usable T_g of 98 °C could undergo stress relaxation through the transesterification reaction when exposed to high temperatures (160 to 200 °C), and the correlation between the relaxation time and temperature follows the Arrhenius equation. Moreover, EV-5.5 exhibited elastomeric behavior, where brittle fractures occurred before yielding, which demonstrated a tensile strength of 52 MPa. EV-5.5 also exhibited good thermal stability with a decomposition temperature (T_d5) of 322 °C. This study introduces new possibilities for practical applications of thermoset epoxy resins under special environmental conditions. Full article

This work deals with developing a self-healing resin designed for aeronautical and aerospace applications. The bifunctional epoxy precursor was suitably functionalized to enhance its toughness to realize good compatibilization with a rubber phase dispersed in the hosting epoxy resin. Subsequently, the resulting mixture was loaded with healing molecules. The effect of the temperature on the epoxy precursor’s functionalization process was deeply studied. Fourier trans-former infrared (FT-IR) spectroscopy and dynamic mechanical analyses (DMA) evidenced that the highest temperature (160 °C) allows for obtaining a bigger amount of rubber phase bonded to the matrix. Elastomeric domains of dimensions lower than 500–600 nanometers were found well distributed in the matrix. Self-healing efficiency evaluated with the tapered double cantilever beam (TDCB) method evidenced a healing efficiency for the system functionalized at 160 °C higher than 69% for all the explored fillers. The highest value was detected for the sample with DBA, for which 88% was found. The healing efficiency of the same sample functionalized at 120 °C was found to decrease to the value of 52%. These results evidence the relevant role of the amount and distribution of rubber domains into the resin for improving the resin’s dynamic properties. The adopted strategy allows for optimizing the self-healing performance. Full article

Microfluidics is a rapidly advancing technology with expansive applications but has been restricted by slow, laborious fabrication techniques for polydimethylsiloxane (PDMS)-based devices. Currently, 3D printing promises to address this challenge with high-resolution commercial systems but is limited by a lack of material advances in generating high-fidelity parts with micron-scale features. To overcome this limitation, a low-viscosity, photopolymerizable PDMS resin was formulated with a methacrylate-PDMS copolymer, methacrylate-PDMS telechelic polymer, photoabsorber, Sudan I, photosensitizer, 2-isopropylthioxanthone, and a photoinitiator, 2,4,6-trimethyl benzoyl diphenylphosphine oxide. The performance of this resin was validated on a digital light processing (DLP) 3D printer, an Asiga MAX X27 UV. Resin resolution, part fidelity, mechanical properties, gas permeability, optical transparency, and biocompatibility were investigated. This resin produced resolved, unobstructed channels as small as 38.4 (±5.0) µm tall and membranes as thin as 30.9 (±0.5) µm. The printed material had an elongation at break of 58.6% ± 18.8%, Young’s modulus of 0.30 ± 0.04 MPa, and was highly permeable to O₂ (596 Barrers) and CO₂ (3071 Barrers). Following the ethanol extraction of the unreacted components, this material demonstrated optical clarity and transparency (>80% transmission) and viability as a substrate for in vitro tissue culture. This paper presents a high-resolution, PDMS 3D-printing resin for the facile fabrication of microfluidic and biomedical devices. Full article

This in vitro study was designed to investigate whether conventionally produced casts and printed casts for prosthodontic purposes show comparable full-arch accuracy; a ceramic reference cast with inlay and crown preparations was fabricated. Ten gypsum casts were fabricated from conventional silicone elastomeric impressions. Ten digital impressions [IOS] of the reference cast were obtained by an intraoral scanner to fabricate 3D-printed resin casts. The ceramic reference cast, the gypsum, and the printed casts were digitized by an industrial structured light scanner (ILS) and provided as stl files. To evaluate absolute mean trueness values, the digitized gypsum casts [CON], digitized printed casts [PRINT], and [IOS] were superimposed with the digitized ceramic reference cast [REF]. Additionally, each [IOS] scan was compared with its corresponding [PRINT]. The precision was calculated for [CON], [IOS], and [PRINT]. The Mann–Whitney U test for independent samples and the Wilcoxon test for connected samples were performed (p ≤ 0.05). As absolute mean deviation trueness values were obtained: 69 ± 24 µm for [REF]-[CON], 33 ± 4 µm for [REF]-[PRINT], and 19 ± 3 µm for [REF]-[IOS]. The superimposition [IOS]-[PRINT] revealed 38 ± 6 µm. The precision was 74 ± 22 µm for [CON], 32 ± 10 µm for [PRINT], and 15 ± 4 µm for [IOS]. With respect to the workflow, the trueness values of [REF]-[CON] and [REF]-[PRINT] differed significantly. Within the digital workflow, [REF]-[PRINT], [REF]-[IOS], and [IOS]-[PRINT], all values differed significantly. Within the limitations of the study, digital impression and printed cast fabrication were more accurate and reproducible than the conventional workflow. Full article

For the design of stretchable and flexible high-performing materials, the reinforcement of elastomeric grades plays a crucial role. State-of-the-art fillers such as carbon black benefit from a high reinforcement but often negatively affect the processing and mixing properties of rubber compounds. To overcome this drawback, the synergistic properties of hybrid in situ filler systems are studied for EPDM compounds comprising a phenol novolac resin and ionic coagents such as zinc (meth)acrylates (ZD(M)A. With the help of a combined novolac/ZD(M)A system, the compounds could be tailored in a unique way towards higher toughness and enhanced cross-link density. Further, the fracture surface of the EPDM–novolac compounds was analyzed by scanning electron microscopy, revealing a significant change of the morphology from rough and disordered to smooth and homogenous for samples with coagents. In addition, the results clearly showed that the introduction of ionic coagents is able to compensate shares of carbon black filler in the EPDM compound. The toughening of samples with zinc (meth)acrylates is attributed to the synergistic formation of an interpenetrating polymer-filler network by simultaneous covalent and ionic cross-linking. Full article

The European steel industry produces about 70 million tons/year of steel by the electric arc furnace (EAF). The slag consists of about 15% by weight of the produced steel, thus from the perspective of the circular economy, it has a high potential as a co-product. This research aims to assess an innovative reuse of EAF slag as filler in different polymer matrixes: thermoplastic (polypropylene), thermosetting (epoxy resin), elastomeric (nitrile butadiene rubber), and recycled end of life rubber tire. A comparison between neat polymer and polymer filled with a certain amount of EAF slag has been carried out by tensile (or flexural), compression, and hardness tests. Experimental results show that slag as a filler increases the composites’ hardness and elastic modulus at the expense of toughness. For a safe reuse of the slag, the leaching of hazardous elements must comply with current legislation. It was found that, although the used EAF slag releases small amounts of Cr, Mo, and V, incorporating it into a polymer matrix reduces the leaching. The EAF slag particles distribution has been observed by scanning electron microscopy (SEM) images. The obtained results show good technical feasibility of this innovative slag application so that it could pave the way to a new industrial symbiosis between dissimilar sectors, bringing economic and environmental benefits. Full article