Study of nanofiber scaffolds of PAA,PAA/CS,and PAA/ALG for its potential use in biotechnological applications

In recent times, electrospun nanofibers have been widely studied from several biotechnological approaches; in this work, poly(acrylic acid) (PAA) solutions mixed with chitosan and alginate were electrospun and characterized to determine the behavior of these fibers when used in combination with bacteria, different samples were incubated with the bacterial strains: Streptomyces spp., Micromonospora spp., and Escherichia coli and a OD600 test was performed. The formation of nanofibers via electrospinning and the physicochemical properties of the obtained fibers were evaluated. Results showed that the presence of chitosan enhanced the thermal stability of PAA, since PAA/alginate fibers lost 5% of their mass at 41°C, whereas PAA/chitosan lost this amount at around 125°C. The fibers demonstrated suitable characteristics to be used as a bacteria bioreactor.     

Static fatigue of Hi-Nicalon™-S fiber at elevated temperature in air,steam, and silicic acid-saturated steam

A facility for testing SiC fiber tows in static fatigue and creep at elevated temperatures in air and steam was developed. Static fatigue of Hi-Nicalon™-S fibers was investigated at 800°C-1100°C at applied stresses between 115 and 1250 MPa in air, in Si(OH)₄(g)-saturated steam, and in unsaturated steam. Fibers tested in Si(OH)₄(g)-saturated steam and in air had silica scales throughout the test sections, but those tested in unsaturated steam did not develop scales near the steam injection point. Fiber lifetimes in static fatigue were shortest in unsaturated steam, intermediate in Si(OH)₄(g)-saturated steam, and longest in air. Failure strains did not exceed 0.3%. Steady-state strain rates and static fatigue lifetimes are modelled empirically by the Monkman-Grant relationship. Failure mechanisms are discussed.     

SiOC modified carbon-bonded carbon fiber composite with SiC nanowires enhanced interfibrous junctions

Carbon-bonded carbon fiber (CBCF) composites are promising lightweight and high efficient thermal insulators to be applied in aerospace area, but their practical applications are usually restricted by the low mechanical performance and poor oxidation resistance. To overcome these drawbacks, many efforts have been made in the fabrication of ceramic coated CBCF composites. However, the densities of these modified composites are usually very high, which would result in the reduction in their thermal insulation performance. Herein, we prepared a CBCF composite with SiC nanowires enhanced interfibrous junctions and SiOC ceramic coated carbon fibers (SiCNWs-SiOC-CBCF). Similar to CBCF, the SiCNWs-SiOC-CBCF exhibits a low density of 0.35 g/cm³ and an anisotropic and highly porous architecture. The SiCNWs-SiOC-CBCF possesses a compressive strength of 3.8 MPa and a compression modulus of 195.7 MPa in the X (or Y) direction, ~26.7% and 150% higher than those of CBCF respectively. It can also suffer from an isothermal treatment in air at 900°C for 120 minutes. The combination of these properties makes the SiCNWs-SiOC-CBCF a good candidate for thermal insulator to be applied in extreme conditions.     

Effect of processing conditions on wood and glass fiber length attrition during twin screw composite compounding

In this study, we compare the effect of twin-screw extrusion processing on the attrition of wood fibers (WFs) with glass fiber. The effects of process variables and screw design on fiber length were investigated by performing a range of dead-stop experiments where the extruder was stopped, opened-up, and compound removed from the screw elements. Fibers, chemically extracted from the polypropylene matrix, were analyzed for length and width using a commercial fiber analyzer. It was found that WF length attrition and composite properties were less affected by screw design and twin-screw processing conditions (feed rate and screw speed) than glass fiber. Length weighted fiber length and X50 length (a measure used in particle size analysis) were equally correlated with process conditions and composite performance for both fiber types. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48551.     

人造金刚石填充聚酰亚胺树脂基复合材料防刺性能

为研究树脂材料的防刺性能及防刺机制,利用手糊成型与热压法成型制备了手糊分层结构和均布结构层2种结构的人造金刚石填充聚酰亚胺树脂基复合树脂片,并探讨了人造金刚石粒径、填充体积分数对树脂片防刺性能的影响。研究结果表明:经过人造金刚石填充的聚酰亚胺树脂片的防刺性能得到提高,并且均布结构层分层复合结构的树脂片的防刺性能更好;随着人造金刚石粒径的减小,树脂片防刺性能出现先减小后增加的趋势,故防刺机制基本在于碰撞概率与树脂基的防挡;比较防刺力和消耗功发现,不同填充体积分数的单层防刺树脂片的防刺性能随人造金刚石填充体积分数的增加而逐渐降低,该趋势的成因在于复合树脂片的脆化与破坏;在颗粒等效粒径为300 μm、体积分数为10%时,其防刺性能最好。     

Effect of water aging on the mechanical properties of flax fiber/bio-based resin composites

Present work investigates the effect of hydrothermal aging of flax fiber-reinforced bio-based epoxy resin laminates on the mechanical and thermomechanical properties of the composites. Three different types of bio-based resins were used. Plates reinforced with eight layers plain weave flax fibers of 150 g/m², manufactured using Resin Transfer Molding (RTM), compression molding or autoclave technique depends on type of the resin. One dimensional Fickian behavior shows a good fitting to the experimental data derived from weight measurements. The water uptake at the equilibrium state in the case of 60 °C temperature was slightly greater than that at 40 °C. The mechanical properties after hydrothermal aging show a significant reduction and do not return to their initial values even after the drying process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48787.     

Intermolecular interaction of thermoresponsive poly-2-isopropyl-2-oxazoline in solutions and interpolymer complex with fiber-forming polyethylene oxide

The cross-linked poly-2-isopropyl-2-oxazolines (PiPrOx) differing in cross-linker content have been synthesized and characterized by light scattering, chromatography, and rheometry. The dramatic influence of the cross-linker content on solubility and uni- or bimodality was observed. For the first time, the interpolymer complex of cross-linked PiPrOx with polyethylene oxide is manufactured in fibrous form by the electrospinning method. The role of intermolecular hydrogen bonds in the structure and properties of electrospun fibers (EF) was studied by infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. It was established that these interactions allow to obtain a uniform fibrous membrane. At the same time, hydrogen bonding is responsible for the self-organization of PiPrOx in water.     

Effect of a Small Amount of Synthetic Fiber on Performance of Biocarbon-Filled Nylon-Based Hybrid Biocomposites

Advanced hybrid biocomposites are engineered from nylon 6, waste wood biosourced carbon (biocarbon) with a low content of synthetic fiber for lightweight auto-parts uses. The novel engineering process through direct injection molding of only 2 wt% synthetic fibers in the form of masterbatch with 20 wt% biocarbon, results outstanding performance of the resulting nylon biocomposites. Such uniquely developed biocomposites show tensile strength of 105 MPa and tensile modulus of 5.14 GPa with a remarkable heat deflection temperature (HDT) of 206 °C. The direct injection molding of synthetic fiber retains the length ≈3 times higher as compared to traditional extrusion and injection molding; resulting greater degree of entanglement and composite reinforcement effectiveness in the hybrid biocomposites. Highly dimensionally stable nylon 6 biocomposites with a very low coefficient of linear thermal expansion results through reinforcing ability of the sustainable biocarbon and small amount of synthetic fiber.     

Preparation and properties of high-strength-high-modulus polyimide cords/natural rubber composites

High-strength-high-modulus polyimide (PI) cords reinforced natural rubber (NR) composites are prepared, and the PI cords are treated with resorcinol-formaldehyde-latex (RFL) adhesive to enhance the interfacial adhesion with NR matrix. The influence of RFL adhesive variables, such as the ratio of R/F and RF/L, on the adhesion between PI cords and NR is investigated. Furthermore, sorbitol glycidyl ether (SGE) and caprolactam blocked methylene diisocyanate (CBI) are adhered to the surface of the PI cords through a dip-coating procedure to introduce epoxy and NCO groups and graft with more RFL adhesive. The H pull-out force of SGE/CBI-RFL treated PI cords/NR composites reaches as high as 193.9 N, which is 580% higher than that of untreated PI ones. Additionally, the SGE/CBI-RFL treated PI cords/NR composites exhibit superior adhesion, aging, and fatigue resistance together with better mechanical properties as compared with SGE/CBI-RFL treated poly(para-phenylene terephtalamide) (PPTA) cords/NR composites.     

Fine-diameter Si–B–C–N ceramic fibers enabled by polyborosilazanes with N–methyl pendant group

Given the superior thermal stability and electromagnetic features, continuous Si–B–(C)–N ceramic fibers have displayed great potential to fulfill the increasing demand for the high-temperature structural and functional materials. Manufacture of such ceramic fibers depends heavily upon the design of processable polymer precursors. Herein, a class of polyborosilazanes (PBSZs) with high spinnability were created through a facile one-pot synthesis. The trade-off between spinnability and ceramic yield of PBSZs was overcome by using heptamethyldisilazane and hexamethyldisilazane as the co-condensing agents to polymerize silicon and boron chloride monomers. The optimal PBSZs can fabricate continuous Si–B–C–N fibers with homogeneous diameter of 7.9 ± 0.5 μm and high ceramic yield of 80 wt%. Experimental characterization and quantum chemical computation revealed the mechanistic pictures of the impact of pendant groups on the polycondensation, melt spinning, and pyrolyzing process. These insights improve our understanding of spinnable pre-ceramic polymers for exploiting high-performance nitride ceramic fibers.