Rubber seed shell (RSS) was modified by grafting treatment using glycidyl methacrylate (GMA) at various concentrations. The RSS was then used to reinforce high-density polyethylene (HDPE). The ...effects of modification on the mechanical, water absorption, and thermal properties of the RSS/HDPE composites were studied using a mechanical testing instrument, weighing method, Vicat softening temperature (VST) testing, thermogravimetry, and dynamic mechanical analysis. The results showed that the GMA grafting produced an improvement in the flexural and tensile properties of the composites. The water absorption rate of the composites also had an obvious decrease. While a slight increase in VST was found, the various concentrations of GMA showed no improvement in VST. GMA modification also could elevate the thermal stability of the composites at the initial decomposition stage. The optimum grafting concentration of GMA (2.5%) led to the lowest thermal weight loss (37.07% and 26.56%) during the first and second decomposition stages. The E’ values of the composites had a significant increase with the addition of GMA. There were two peaks of tan δ for the untreated samples, but the modified samples exhibited a shift in the transition peak at higher temperatures; moreover, the second peak disappeared.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Cellulose nanofibers (CNFs) with nanoscale dimension, high aspect ratio, and easily modified surface chemistry show great potential as novel rheological and filtration modifiers in bentonite ...water-based drilling fluids (BT-WDFs). However, CNFs would suffer from poor redispersibility in an aqueous suspension if they were fully dried for transportation, storage, and field application. Herein, we report a simple, versatile, and scalable strategy to prepare water-redispersible CNFs through compounding them with a water-soluble, commercially available drilling fluid additive, polyanionic cellulose (PAC), and subsequent drying. The results revealed that the water redispersibility of CNF/PAC hybrids was dependent on the PAC’s viscosity (i.e., low viscosity, LV; or regular viscosity, R) as well as drying method (i.e., oven drying, OD; or freeze-drying, FD). Among the obtained CNF/PAC hybrids, the CNF/PAC-R material prepared by FD exhibited optimal water redispersibility due to the enhanced suspending capacity of CNF suspension and the minimized capillary force. As a consequence, the CNF/PAC-R hybrids prepared by FD improved the rheological and filtration performance of BT-WDFs more pronouncedly than others, which could lead to better fluid carrying capacity for drilling cuttings and wellbore stability. The PAC acted not only as water-dispersible agents for CNFs but also as additives for modifying the rheological and filtration properties of BT-WDFs. PAC-coated cellulose nanofibers can be used as water-redispersible dry additive for drilling fluids with enhanced fluid performance.
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•1920 h of longest UV irradiation on superhydrophobic scrimber achieved firstly.•Hierarchical structure of Cu7Cl4(OH)10·H2O could improve UV resistance of scrimber.•Superior ...self-healing and reversible properties was obtained on modified scrimber.
Blackberry inspired superhydrophobic poplar scrimber with superstrong ultra-violet (UV) resistance, self-healing and reversible functional superhydrophobicity was fabricated via in-situ growth of Cu7Cl4(OH)10·H2O nano particles in the absence of low surface-free energy materials. Superhydrophobic poplar scrimber exhibited the best ultraviolet resistance over 1920 h of UV-irradiation at 340 nm, which could be the protection ascribed to UV light absorption by the hierarchical structure of Cu7Cl4(OH)10·H2O. More importantly, superhydrophobicity was reversed by a simply drying process under humid conditions. The results provider a novel strategy for preparing a simple, multifunctional, and reversibly superhydrophobic wood-based engineering material.
Amino resin is widely used in the preparation of wood-based panel adhesives due to its excellent performance and low cost. However, it has drawbacks such as poor water resistance and formaldehyde ...emission. In this study, we developed a new formaldehyde-free amino resin, glyoxal-monomethylolurea-tannin (GUT), which was synthesized from glyoxal, monomethylolurea, and tannin. The influence of tannin on the physical and mechanical properties of GUT plywood was assessed. The results indicated that the plywood made with GUT adhesive met the type III plywood requirements in accordance with the Chinese national standard GB/T 17657–2013, without the use of expensive melamine or phenolic.The wet shear strength in boiling water reached 0.85 ± 0.08 MPa, exceeding the national standard for exterior plywood use (≥ 0.70 MPa). The optimum hot-pressing time was 1 min per millimeter, the hot-pressing temperature was 180 degrees Celsius, the hot-pressing pressure was 1.6 MPa, and the dosage film was 200 g per square meter. The chemical structure of the resin and the adhesion mechanisms involved were analyzed and characterized using nuclear magnetic resonance (13C NMR), liquid chromatography-mass spectrometry (LC-MS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Curing properties were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The findings indicated that GU reacted with tannin to form macromolecules, which reduced its curing temperature and enhanced the crystallinity of cured glyoxal-monomethylolurea (GU) resin. The increase in crystallinity could contribute to the improvement of mechanical characteristics and water resistance in glyoxal-monomethylolurea (GU) resins, primarily attributed to the presence of tannins.
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•Developed a new formaldehyde-free amino resin named glyoxal-monomethylolurea-tannin (GUT) from glyoxal, monomethylolurea, and tannin.•Produced plywood using GUT glue suitable for outdoor environments and meeting the Type III plywood requirement of Chinese national standard GB/T 17657-2013.•Achieved a wet shear strength in boiling water of 0.85 ± 0.08 MPa, surpassing the China National Standard for exterior use of plywood (≥ 0.70 MPa).•Optimal Parameters for Production:•Hot-press temperature: 180 ℃•Hot-press pressure: 1.6 MPa•Dosage film: 200 g/m2.
The objective of this study was to investigate the manufacture process and basic properties of particleboard using foamable polyurethane adhesive. The foaming and curing behaviors of the polyurethane ...adhesive were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The PressMAN hot-pressure monitoring system was used to obtain the internal temperature and gas pressure in the mat during the hot-pressing process. The effects of the hot-pressing temperature, time and mat structure on the physical and mechanical properties of lightweight particleboard were investigated to optimize the process parameters. Results showed that the peak foaming and curing temperatures of the polyurethane adhesive were around 75 °C and 95 °C, respectively. The core layer temperature of the particleboard reached the required temperature for foaming and curing when hot pressing. The lightweight particleboard that was hot-pressed at 180 °C for 5 min had a density of 0.5 g/cm
3
. At a mass ratio of the surface layer to the core layer of 1:3, the lightweight particleboard exhibited a good vertical density profile, as well as excellent mechanical properties. This study demonstrates that lightweight particleboard can be successfully fabricated using foamable polyurethane adhesive without free formaldehyde release.
Filament fused fabrication (FFF) is an extrusion-based 3D printing technology for manufacturing thermoplastic components. One major obstacle facing 3D printed thermoplastic material is the reduced ...crystallinity resulting from a fast quench when material exiting the 3D printer hot nozzle solidifies quickly at the low-temperature platform, leading to weak mechanical performance. Here, we report an accelerated annealing strategy with the assistance of microwave heating, aiming to enhance crystallinity and mechanical performance of FFF 3D printed polylactic acid (PLA) composite. We selected naturally abundant cellulose fibers as precursors for producing carbonized cellulose nanofibers (CCNFs), and compounded CCNFs with PLA to produce bi-component filament for 3D printing final composite. After being irradiated with microwave, the embedded CCNFs in composite selectively absorbed microwave energy and generated heat. Subsequently, the localized heat transferred to the adjacent PLA regions, triggering amorphous PLA chains to repack and convert to new crystallites. In this work, annealing conditions, including heating method (i.e., oven annealing vs. microwave annealing), time (0–120 min), and temperature (80 vs. 120 °C), were systematically studied to understand the relevant effects on the resulting parameters including composite crystallinity and tensile strength. Microwave annealing method was also compared with conventional oven annealing method and results shows that microwave annealing significantly reduced the required annealing time to reach the maximum crystallinity and tensile strength. Notably, microwave annealing performed below cold crystallization temperature was exceptionally suitable to develop an optimized crystallinity and tensile strength for 3D printed PLA composite.
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Influences of secondary hot-pressing overlaying process on properties of fiberboard Xu Xinwu, Nanjing Forestry University, Nanjing (China), College of Wood Science and Technology; Tang Zhengjie, Nanjing Forestry University, Nanjing (China), College of Wood Science and Technology; Zhou Kun, Nanjing Forestry University, Nanjing (China), College of Wood Science and Technology
Xi bei nong lin ke ji da xue xue bao.Zi ran ke xue ban,
Dec. 2011, Letnik:
39, Številka:
12
Journal Article
通过模拟热压贴面工艺，揭示高密度纤维板(HDF)基材在二次热压过程中性能的变化。控制HDF基材的二次热压工艺条件(热压温度分别为160，180，200和220 ℃；热压压力为1 MPa；热压时间分别设定为30，45和60 s)，研究热压对HDF板材的厚度、内结合强度(IB)、静曲强度(MOR)、弹性模量(MOE)及24 ...h吸水厚度膨胀率(TS)的影响。根据HDF板材的显微结构，提出了板材中纤维排列的“叠层”和“‘品’字”模型，并结合上述试验，对板材性能变化进行阐释。经历二次热压后，由于HDF板材受到压缩、内部胶接点受到破坏，板的厚度显著减小(最高压缩率达到8.39%)；热压温度越高、时间越长，板材IB、MOR和MOE的降低和TS值的上升越明显。二次热压工艺对HDF基材性能具有显著影响，建议热压温度不高于180 ℃、热压压力约1 MPa、热压时间小于30 s。
This study was conducted to disclose the change of HDF properties during secondary hotpressing. Hot-pressing conditions were designed, i.e., temperature (160, 180, 200 and 220 ℃), pressure (1 MPa), and time (30, 45, and 60 s), to find out the possible changes of HDF properties, including inner bond strength (IB), bending strength (MOR) and modulus (MOE), and thickness swelling (TS). To explain the above changes, two models of fiber orientation in HDF matrix, i.e., a layering model and a triangle-shaped model, were created, in accordance with the microscopic structure of HDF board. HDF boards through hot-pressing were evidently comp
OBJECTIVE： To assess the effectiveness and safety of acupuncture therapy for angina pectoris. METHODS： Randomized controlled trials （RCTs） concerned with acupuncture treatment of angina pectoris were ...identified by searching Academic Source Premier, MEDLINE, Science Citation Index Expanded, and three Chinese databases （China biol- ogy medicine database, China national knowledge infrastructure, and VlP database for Chinese techni- cal periodicals）. The valid data were extracted in ac- cordance with our inclusion and exclusion criteria. The main outcomes of the included studies were synthesized using Revman 5.1. RESULTS： Twenty-one articles on 16 individual studies were included and evaluated as having high or moderate risk of bias according to the stan- dards of the Cochrane Collaboration. Meta-analysis indicated that acupuncture combined with conven- tional drugs （ACCD） was superior to conventional drugs alone in reducing the incidence of acute myocardial infarction （AMI） 0R=0.18, 95%CI （0.04,0.84）, P=0.03. Moreover, ACCD was superior to con- ventional drugs in the relief of angina symptoms 0R=4.23, 95%C/（2.73, 6..56）, P〈0.00001, and im- provement of electrocardiography （ECG） 0R=2.61, 95%C/（1.83, 3.73）, P〈0.00001. Acupuncture by it- self was also superior to conventional drugs for angi- na symptoms 0R=3.59, 95%C/（1.76, 7.92）, P=0.0004 and ECG improvement 0R=3.07, 95%C/（1.54, 6.10）, P=0.001. ACCD was superior to conventional drugs in shortening the time to onset of angina relief WMD=-1.40, 95% CI （-1.65, -1.15）, P〈 0.00001. However, the time to onset was signifi- cantly longer for acupuncture treatment than for conventional treatment alone WMD=2A3, 95%O （1.63, 3.23）, P〈0.000 01. CONCLUSION： ACCD reduced the occurrence of AMI, and both acupuncture and ACCD relieved an- gina symptoms and improved ECG. However, com- pared with conventional treatment, acupuncture showed a longer delay before its onset of action. This indicates that acupuncture is not suitable for emergency treatment of heart attack. Owing to the poor quality of the current evidence, the findings of this systematic review need to be verified by more RCTs to enhance statistical power.
Coronavirus disease 2019 (COVID-19) is a highly contagious infectious disease. Similar to H7N9 infection, pneumonia and cytokine storm are typical clinical manifestations of COVID-19. Our previous ...studies found that H7N9 patients had intestinal dysbiosis. However, the relationship between the gut microbiome and COVID-19 has not been determined. This study recruited a cohort of 57 patients with either general (n = 20), severe (n = 19), or critical (n = 18) disease. The objective of this study was to investigate changes in the abundance of ten predominant intestinal bacterial groups in COVID-19 patients using quantitative polymerase chain reaction (q-PCR), and to establish a correlation between these bacterial groups and clinical indicators of pneumonia in these patients. The results indicated that dysbiosis occurred in COVID-19 patients and changes in the gut microbial community were associated with disease severity and hematological parameters. The abundance of butyrate-producing bacteria, such as Faecalibacterium prausnitzii, Clostridium butyricum, Clostridium leptum, and Eubacterium rectale, decreased significantly, and this shift in bacterial community may help discriminate critical patients from general and severe patients. Moreover, the number of common opportunistic pathogens Enterococcus (Ec) and Enterobacteriaceae (E) increased, especially in critically ill patients with poor prognosis. The results suggest that these bacterial groups can serve as diagnostic biomarkers for COVID-19, and that the Ec/E ratio can be used to predict death in critically ill patients.
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