Hasil untuk "Polymers and polymer manufacture"

Vinicius Duarte Machado, Michele Karoline Lima-Tenório, Ernandes Taveira Tenório-Neto

Richard K. Cross, Ruairidh Cox, Sarah L. Roberts et al.

Abstract Moss presents an excellent candidate for biomonitoring the atmospheric deposition of microplastics across wide spatial scales and to monitor trends over time due to its relative ease of sampling compared to alternative approaches such as conventional wet and dry deposition atmospheric sampling. Evaluation of representative sampling and processing procedures must be performed to ensure that quantification of microplastics in moss maintains integrity to the original sample. Using data from a sampling campaign of 52 locations across United Kingdom, we explore these key considerations and aspects of study design, to evaluate the potential use of moss as a bio-monitor for microplastic atmospheric deposition. A method for the isolation of microplastics from moss biomass using flow displacement and filtration is optimised for the extraction of microplastics approximately > 25 μm in size, appropriate for quantification by vibrational spectroscopy methods such as µ-FTIR. The approach is then applied to samples from six major genus of moss, common to the United Kingdom, across 52 natural or semi-natural landscapes. The survey design and analysis methodology are evaluated against quality assurance and control criteria, whilst the findings are critically discussed in light of relevant literature. This study represents the first survey of the extent of microplastic contamination of mosses across the United Kingdom, investigating correlations between location characteristics and microplastic polymer diversity and abundance. It shows near ubiquitous contamination of mosses with microplastics, irrespective of their location across the United Kingdom, and indicates that a diffuse atmospheric source may play a role in this widespread contamination of moss.

Mao Hongda, Zou Hua, Liu Wei et al.

Electromagnetic interference (EMI) shielding rubber effectively fills gaps in electronic devices to prevent electromagnetic (EM) leakage. However, research on the potential application of EMI shielding rubber in the field of space is limited. This study explores the optimal amount of silver-coated aluminum powder (SCA) in SCA/ methyl vinyl silicone rubber (MVQ) composites to balance the electrical and mechanical properties of EMI shielding rubber. The EMI shielding effectiveness (SE) of 41.8 vol% SCA/MVQ composite exceeded 90 dB in the frequency range between 100 and 1,200 MHz with a compression set of only 14%. To address the outgassing characteristics of silicone rubber in a vacuum environment, both pre-heating and post-heating treatments for reducing rubber volatility are explored, proving that silicone rubber followed by 4 h of post-heating treatment at 200°C, is an appropriate solution to reduce silicone rubber volatility, leading to the SCA/MVQ composite with a total mass loss of only 0.2%, and a collected volatile condensable material of only 0.02%. In addition, high reliability is crucial for EMI shielding materials. SCA/MVQ composite exhibits excellent adaptability to vacuum temperature cycles, with the EMI SE maintained at 90 dB after cycles. At room temperature, after 30 days of storage, the EMI SE of the composite remains at 90 dB. These findings indicate that SCA/MVQ composites exhibit broad potential applications in the field of EM sealing for aerospace electronic devices.

Md. Nur Uddin, Md. Tanvir Hossain, Nadim Mahmud et al.

Abstract Nanoclays, a specific type of nanomaterial, have emerged as versatile and dynamic materials, with tremendous potential for advanced functional applications. Despite publishing a large number of research articles, there are relatively few review articles on this topic. This comprehensive review delves into the most widely used nanoclays and explores the diverse range of applications in different fields, such as aerospace, automobile, construction, biomedical, food packaging, and polymer composites. With their ability to enhance the performance of materials and products, nanoclays have become a highly desired material in various industries. The challenges associated with nanoclays like complex properties, difficulty in developing new synthesis methods, and challenges in investigating long‐term durability and stability have been summarized. The future research directions with the exciting possibilities to develop future innovative materials have been highlighted at the end of the article. Highlights This review provides an extensive examination of the most widely used nanoclays, detailing their properties, types, and limitations. A summary of publication trends over the last 15 years, based on Scopus data up to 2024, indicates growing interest and research output in nanoclays. Applications of nanoclays span across aerospace, automobile, construction, biomedical, food packaging, and polymer composites, showcasing their versatility. Key challenges discussed include complex properties, difficulties in new synthesis methods, and issues in long‐term durability and stability. Future research directions highlight the potential for developing innovative materials using nanoclays.

Mariana Cristiana Iacob, Diana Popescu, Contantin Stochioiu et al.

The primary objective of this study was to investigate the compressive behavior of 3D-printed specimens made of a thermoplastic polyurethane filament, specifically colorFabb varioShore TPU, which incorporates a foaming agent. The foaming technology makes it possible to manipulate 3D prints' properties by adjusting process parameters that affect the level of expansion, such as printing temperature, printing speed or flow ratio. This capability opens new possibilities for 3D-printed personalized foot orthotics or for static comfort-oriented applications by tailoring the stiffness of the print based on the application requirements. Since infill density and infill pattern also affect the compressive characteristics of 3D prints, this research took these two parameters into account as independent variables, alongside the printing temperature. Thus, the specimens with printing temperatures set at 190 °C, 220 °C, and 240 °C, gyroid and honeycomb patterns, and infill variations from 10 % to 35 % in 5 % increments were experimentally investigated in compression testing. The evaluation was conducted to determine the influence of these factors on the stiffness of prints at 10 % and 20 % strains, in accordance with established standard. The findings had an important practical value as they provide data for adjusting the variable stiffness based on peak plantar pressure measurement data when developing tailored foot orthoses (insoles), which was the second objective of the research. The most influential factor affecting the compressive strength was the printing temperature, followed by infill density and pattern type. The difference in compression modulus between 10 % and 20 % strains did not exhibit statistical significance. Moreover, the main effects plots indicated minimal variations in compression modulus effects at 220 °C and 240 °C, whereas an important difference was observed at 190 °C printing temperature, which was confirmed by scanning electron microscopy investigations showing foamed layers at 220 °C and unfoamed layers at 190 °C. Furthermore, interaction plots revealed no significant interaction effect among the studied variables. Additionally, a comparison of samples’ sizes and densities before and two months after testing indicated no observable modifications When applied to custom orthotics (five pairs of insoles were customized and tested), the experimental findings documented variations in the reduction and distribution of peak plantar pressure based on the infill variability.

Guo Dongjun, Zhu Zhisong, Yuan Jie

To obtain better airflow field characteristics of melt-blowing and acquire slender melt-blowing fiber, a new die with multi-channel of melt-blowing airflow was designed. The airflow field under the spinneret hole of the melt-blowing die was simulated and analyzed using computational fluid dynamics method, and distribution rules of the ordinary die and the new die on the airflow field along the spinning centerline were compared and discussed. The melt-blowing fiber diameter distribution for the ordinary die and the new die was numerically calculated using a stretching model of the melt-blowing fiber. In contrast with an ordinary die, the new melt-blowing die enhances the average speed in main stretching zone by 89.8% and increases the peak speed by 50.4%. The higher airflow temperature of new die improves the softening degree and melting fluidity of the polymer. Meanwhile, the smaller turbulence intensity and the reverse speed of the new die make airflow more stable and reduce disturbance and adhesion of the fiber, and a larger pressure difference and a peak pressure can accelerate the refinement and attenuation of the fiber. The new melt-blowing die with airflow multi-channel is conducive to extension, which is a better choice in the manufacturing process of nonwoven melt-blowing fibers.

Yimin Wu, Ling Zhang, Fudong Ma et al.

A new type of carbazole-based blue-emitting dendritic conjugated polymer, poly[(9,9-dioctyl)-2,7-fluorene-co-4,4’,4”-triphenylamine-co-9-(4-(9H-carbazol-9-yl)butyl)-3,6-carbazole](P), was successfully synthesized by Suzuki coupling reaction. Chemical structures of monomers and polymer were verified by FI-IR and 1HNMR characterizations. We found that polymer showed a special selectivity and high sensitivity for I−. With the addition of I−, the fluorescent polymer solution was obviously quenched. The polymer showed a special detection effect on I−. However, the fluorescent polymer was obviously restored when Hg2+ was added to the P/I− system due to the large complexation between I− and Hg2+. The anti-interference experiments of probe P/I− showed that other background cations have a slight influence on detecting Hg2+, and the calculated detection limit of Hg2+ reached 9.7 × 10−8 M, which could be a potential application for a two-channel cyclic detection of I− and Hg2+. Additionally, it was found that the theoretical values were in agreement with the experimental data.

Alexandra Aulova, Alen Oseli, Marko Bek

High-performance polymer composites are used in demanding applications in civil and aerospace engineering. Often, structures made from such composites are monitored using structural health monitoring systems. This investigation aims to use a multilayer perceptron neural network to model polymer response to a non-standard excitation under different temperature conditions. Model could be implemented into health monitoring systems. Specifically, the neural network was used to model PEEK material's creep behavior under constant shear stress rate excitation at different temperatures. Optimal neural network topology, the effect of the amount of training data and its distribution in a temperature range on prediction quality were investigated.The results showed that based on the proposed optimization criterion, a properly trained neural network can predict polymeric material behavior within the experimental error. The neural network also enabled good prediction at temperatures where stress-strain behavior was not experimentally determined.

Erik J. Price, James Covello, Rajib Paul et al.

Abstract Tannic acid (TA) has gained increased attention in recent years for its application in fire safety due to its natural abundance and char‐forming ability. In this paper, TA‐based composites were developed and evaluated against control composites containing pentaerythritol (PER), a common intumescent char‐forming agent. Individual component analysis was performed to provide a fundamental material understanding, followed by compounding in epoxy resin with other intumescent ingredients for intumescent testing (especially compared against PER control). In all TA systems, time to failure was elongated from seconds or minutes to over 15 min (up to 27 min). Quantitative analysis followed using cone calorimetry. TA composites displayed lower peak heat release values (211 vs. 108 kW/m2), lower total heat release values (37.2 vs. 24.4 MJ/m2), and lower fire growth rates (2.43 vs. 1.27 kW/m2s−1) relative to PER composites. X‐ray photoelectron spectroscopy analysis revealed that TA char is more carbonaceous, containing 54.71 at% C (relative to only 39.63 at% C in PER char). This work presents TA‐containing composites that offer superior fire protection as compared to previous reports using TA composites and hence offer significant advancement in fire protection related and packaging industries.

saina akbari, Majid Peyravi

Hypothesis: Despite the wide application of nanofiltration (NF) membranes in forward osmosis (FO) process, one of the most important challenges of this process is the internal concentration polarization (ICP) phenomenon. Different methods have been investigated to reduce the effect of this undesirable phenomenon and it is suggested that one of these methods is loading of hydrophilic nanoparticles in the membrane structure. In this study, SiO2/ZIF-8 nanoparticles were used to improve the structure and performance of polyethersulfone membranes (PES) in FO process.Methods: At first, polyethersulfone membrane was synthesized by phase inversion method. In the next step, ZIF-8 and SiO2/ZIF-8 nanoparticles as filler were synthesized at room temperature. Thin film composite membranes were prepared by the interfacial polymerization (IP) of two reactive organic (TMC) and aqueous (MPD) monomers. Finally, the produced membranes and nanocomposite were characterized by contact angle, FTIR spectroscopy, X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and porosity measurements. Also, the performance of all membranes composed of at least two different components was investigated using reverse and forward osmosisi processes.Finding: The outcomes demonstrated that the presence of a small amount of SiO2/ZIF-8 nanoparticle in the membrane led to an increase in the membrane hydrophilicity and porosity, and also improved the water flux and rejection of the FO. The water flux of TFN FO membrane was reported to increase remarkably from 15.23 to 25.13 L/m2.h when 10 mM NaCl and 2 M NaCl salt were utilized as feed solution (FS) and draw solution (DS), respectively. The improvement in FO water flux was ascribed to the lower S parameter of modified PES sublayer and the reduction of internal concentration polarization (ICP).

Pengfei Cao, Hai Fang, Weiqing Liu et al.

A composite wrapping system for main cable protection of suspension bridges was designed by using prepreg fiber-reinforced composites and nitrile rubber. The circumferential expansion performance of the system was tested, and the curves of circumferential bearing capacity and radial displacement of the components were obtained. Failure modes of each group of components were compared and analyzed. The results show that most of the components are vertically fractured at the lap transition. The increase of the number of prepreg layers contributed the most to the circumferential bearing capacity of components, with a growth rate of 65.31%~109.01%. The increase of rubber belt layers had the most significant effect on the radial displacement of the components, with a growth rate of 7.06%~23.5%. In the initial stage of the test, the strain of each part of the component was smaller due to the compaction by the loading device, and the strain value of the component was generally linearly increased during the loading process, during which the strain of the overlap was the smallest. The calculated cross-sectional temperature deformation of the main cable is in good agreement with the experimental data. The application of the rubber belt increases the deformation of the main cable; therefore, the protection system for the main cable could have more deformation redundancy and delay the arrival of the ultimate strain of the outer prepreg wrap.

Wenjie Zou, Zichuan Fang, Zhijun Zhang et al.

The adsorption of polymers affects the cost and oil recovery in oil reservoir exploitation and the flocculation effect in the treatment of oil sand tailings. The adhesion and adsorption of a hydrophobically modified polyacrylamide (HMPAM), i.e., P(AM-NaAA-C16DMAAC), on silica and asphaltene were investigated using surface force measurements, thermodynamic analysis and quartz crystal microbalance with dissipation (QCM-D) measurement. Our study indicates that HMPAM polymer has strong interaction with both silica and asphaltene. The adhesion force of HMPAM on silica was stronger than that on asphaltene surface. Consistently, the adsorption of HMPAM was also greater on silica surface, with a more rigid layer formed on the surface. For HMPAM/silica system, the attractive interaction and the strong adhesion are mainly driven by the hydrogen bonding and electrostatic interaction. For HMPAM/asphaltene system, it is mainly due to hydrophobic interaction between the long hydrocarbon chains of HMPAM and asphaltene. Furthermore, continuous adsorption of HMPAM was detected and multiple layers formed on both silica and asphaltene surfaces, which can be attributed to the hydrophobic chains of HMPAM polymers. This work has illustrated the interaction mechanism of HMPAM polymer on hydrophilic silica and hydrophobic asphaltene surfaces, which provide insight into the industrial applications of hydrophobically modified polymer.

Takashi Kato, Takuya Matsumoto, Chizuru Hongo et al.

Cellulose nanofibers are green nanomaterials because of their biodegradability and sustainability, they are also attractive structural materials because of their high mechanical performance. For further expansion of their application and acquisition of their reliability, mechanical reinforcement and functionalization of cellulose nanofiber materials are required. In this work, we focused on the mechanical properties and thermal conductivities of composites of cellulose nanofibers and a nanodiamond (ND). Compared with graphene oxides, which are conventional two-dimensional nanocarbon fillers in aqueous media, natural diamond possesses a much larger modulus. It also has the highest thermal conductivity among all the elemental substances. The ND possesses hydrophilic oxygen functional groups at the surface, following a high dispersion in aqueous media and the rigid diamond structure at the core. In this work, the ND resulted in an increased mechanical reinforcement and enhancement of the thermal conductivity of the cellulose nanofiber, while keeping the high visible light transmittance originating from the latter. In particular, 2,2,6,6-tetramethylpiperidine 1-oxyl-oxidized cellulose nanofibers were reinforced more effectively than quaternary ammonium cellulose nanofibers because of the stronger interaction with the ND and higher dispersibility of the ND. Accordingly, it was proved that the cellulose nanofiber/ND composite was a promising high-strength and high-thermal-conductive material.

Leticia Pereira, Maria Marques

Ethylene-norbornene copolymers were synthesized with a homogeneous catalyst system based on bis(imino) pyridine iron with the addition of diethyl zinc (DEZ) as alkyd transfer agent to promote immortal copolymerization. The addition of DEZ did not influence the catalytic activity in copolymerization with 7.5 mmol of norbornene (NB), but in the reactions with 70 mmol, the comonomer promoted an increase of activity. We observed by thermal analysis that the norbornene inserted in the chains promoted an increase in thermal stability of the synthesized material with higher amounts of comonomer, since the temperature of initial degradation was much higher for these copolymers compared to polyethylene. In addition, for the copolymers with 7.5 mmol of norbornene, the DEZ served as alkyd transfer agent, as shown by the gel permeation chromatography analysis, leading to a decrease in both molar mass and polydispersity. The UV-Vis spectra showed that the diethyl zinc did not change the catalytically active center, but only acted as an alkyd transfer agent.

Nikesh B. Samarth, Prakash A. Mahanwar

The free chlorine present in water which is used as a disinfectant is reported to reduce the life of the polymeric material. The objective of this work is to study the influence of chlorine concentration on low-density polyethylene (LDPE) and blends of LDPE with ethylene butene copolymer (EBC) and ethylene propylene diene terpolymer (EPDM). The LDPE blend with EBC and EPDM were tested with water containing 50, 500, and 5000 ppm chlorine under static condition for 500 h at 25 and 80 °C. It has been seen that at 5000 ppm chlorine concentration, the mechanical properties of LDPE, LDPE/EBC blend, and LDPE/EPDM blend changed drastically and a significant reduction in the elongation at break was found for LDPE, LDPE/EBC, and LDPE/EPDM blend. LDPE/EPDM shows stable modulus value for 5000 ppm as 80 °C. Chemical changes in the aged sample were studied by Fourier transform infrared spectroscopy (FTIR) where an increase in the O–H and C=O peaks were observed. The thermal characteristics of LDPE, LDPE/EBC blend, and LDPE/EPDM blends were investigated using DSC and TGA which shows that the melting temperature and crystalline melt temperature remains unchanged while percent crystallinity increases slightly. Scanning electron microscope showed that there was the formation of microcracks and cavities on the fracture surface of LDPE, LDPE/EBC blend, and LDPE/EPDM blend after exposure to a higher concentration of chlorine indicative of degradation. Furthermore, the Chlorine resistance of LDPE/EPDM blend at 5000 ppm chlorine concentration is much higher than that of pristine LDPE.

Mohammad Hassan Moeini, Mohammad Hossein Navid Famili, Kayvan Forooraghi et al.

Microcellular thermoplastic polyurethane foams are examined as absorbing materials in the X-band (8.2-12.4 GHz) frequency range by means of experiment. In this work, we aim to establish relationships between foam morphology including cell size and air volume fraction and electromagnetic properties including absorption, transmission and reflection quality. Nanocomposites based on thermoplastic polyurethane containing carbon black were prepared by coagulation method. In this procedure 15 wt% carbon black-containing nanocomposite was converted to microcellular foams using batch foaming process and supercritical carbon dioxide as physical foaming agent. The morphology of the foams was evaluated by scanning electron microscopy. S-parameters of the samples were measured by a vector network analyzer (VNA) and the effect of morphological parameters such as cell size and air volume fraction on the absorbing properties was investigated. We also established structure/properties relationships which were essential for further optimizations of the materials used in the construction of radar absorbing composites. Foaming reduced the percolation threshold of the nanocomposites due to the reduction in the average distance between nanoparticles. Foaming and dielectric constant reduction dropped the reflection percentage significantly. The increase in air volume fraction in the foam increased absorption per its weight, because of multiple scattering in composite media. The sensitivity of electromagnetic wave toward the variation of cell size is strongly weaker than that toward the variation of air volume fraction. Electromagnetic properties of the microcellular foams deviated a little from effective medium theories (EMTs). Air volume fraction of the cells was a function of cell size and smaller cells showed higher absorption.

آتوسا سامانیان, محمد میرجلیلی

با توجه ‌به پیشرفت روزافزون علم مواد، که موجب افزایش و بهبود خواص و کاربرد‌های آن‌ها می‌شود، لازم است به‌طور دقیق‌تر به بررسی مواد پرکننده دندانی پرداخته شود. پرکردن دندان‌ها موضوع فراگیری در دندان‌پزشکی است که افزون بر حفظ و توسعه سلامت و استحکام دندان‌ها، در حفظ زیبایی ظاهری نیز بسیار اهمیت دارد. در مقاله پیش رو، پس از معرفی کامپوزیت‌های چندعاملی و اجزای آن‌ها، به بررسی سه ماتریس پلیمری، واکنش پلیمرشدن و برخی خواص فیزیکی آن‌ها پرداخته می‌شود. نتایج به‌دست آمده نشان می‌دهد، مواد پرکننده پلیمری با گذشت 50 سال از معرفی به بازار و در اثر پیشرفت‌های روزافزون و سازنده، هم از نظر ظاهری و هم خواص فیزیکی و شیمیایی، می‌تواند به جایگزین مناسبی برای آمالگام، دوست آشنا و قدیمی دندان‌پزشکان، تبدیل شود. در این پژوهش، در کنار معرفی چند ماتریس رزینی، از جمله مونومرهای متاکریلات، متاکریلات با انقباض کم و سیلوران، به پرکننده‌ها و عوامل جفت‌کننده آن‌ها اشاره می‌شود.

فاطمه مولایی

امروزه نسبت زیادی از دارایی های شرکت ها نامشهود است. مدیران و حسابداران در تعیین ارزش دارایی های شرکت ها دچار مشکلاتی می شوند که در گذشته به ندرت وجود داشت. اکثر روش شناسی های موجود برای اندازه گیری و قیمت گذاری دارایی های نامشهود و سرمایه فکری، از درون پژوهش در حوزه های اقتصاد، مدیریت، حسابداری، مهندسی و غیره برخاسته است. نتیجه این فرایندها دستی ابی به برخی چارچوب ها و الگوهای سنجش است که برای توسعه توانمندی های بخش اقتصاد و سنجش دارایی های فکری قابل استفاده اند. تاکنون روش ها و رو کیردهای متنوعی برای قیمت گذاری دانش فنی و فناوری ارائه شده است. برخی از این روش ها کمتر مبتنی بر محاسبات ریاضی اند و به روش های کیفی موسوم هستند. برخی نیز بر پایه محاسبات ریاضی نسبتاً پیچیده ای هستند. در این مقاله، مطالعه ای درباره روش های مرسوم قیمت گذاری و نقاط ضعف و قوت هر کی از این روش ها انجام شده است.

S.S. Madaeni, M. A., S. Pour et al.

H. Mahdavi, S.M. Taghizadeh, H. Mivehchi et al.