The goal of this paper is to discuss the influence of water absorption-desorption cycles on the mechanical properties of natural fiber reinforced plastics. Therefore, epoxy resins with jute wovens as reinforcement with untreated and silane treated fibers were investigated. Silane treatment of fibers led to increased tensile, flexural strength, and Young's modulus of composites with up to 30%. Absorption-desorption cycles of fibers changed the fracture mechanisms of fibers without having significant effects on the tensile strength of the fibers. Light microscopic investigations showed that absorption-desorption cycles of composites led to the debonding of resin from fibers as well as to cracks in the adjacent resin. Because of these mechanisms, tensile strength and Young's modulus decrease, independent of the quality of fiber resin adhesion. For dynamic loadings, storage cycle induces damages, further bringing about a decreased dynamic modulus and an increased progress in damage with increasing load cycles during the first two environmental cycles, being constant afterwards. 相似文献
Summary: By using DSC, 13C CP/MAS NMR and SEM, we studied the physical properties and chemical structure of silk fibers grafted with methacrylamide (MAA). At a given MAA concentration, the inverse of fiber weight gain linearly increased with increasing square root of the initiator concentration, and at a given initiator concentration the fiber weight gain increased with increasing MAA concentration. 13C CP/MAS NMR demonstrated that the primary and secondary structure remained unchanged, regardless of MAA grafting, implying the poor compatibility and the lack of new additional hydrogen bonding between the silk fiber and the MAA graft polymer. The degree of grafting in MAA‐grafted silk fiber (the accurate amount of actually loaded MAA polymer within the fiber matrix) can be evaluated from determination of the ratio of heat capacities calculated from two individual endothermic DSC peaks of silk fibroin and MAA polymer. The major endothermic peaks attributable to thermal degradation of the silk fiber and MAA graft polymer shifted to a higher temperature with increasing fiber weight gain by grafting. These findings are useful for the industrial production of grafted silk fiber with higher thermal stability.
CP/MAS spectra for poly(MAA) grafted silk and control silk fiber. 相似文献
This study analyzes the influence of blend ratio and draw ratio on the fiber properties of blend fibers composed of poly (ethylene terephthalate), or PET, and polypropylene, or PP, (hereafter referred to as PET/PP conjugate fibers). For a comparison, PET and poly (butylene terephthalate), or PBT blends, (hereafter referred to as PET/PBT conjugate fibers) are also investigated. Various blend ratios of fibers are melt spun and drawn in a multistep drawing method. The conjugate fibers are evaluated using tenacity, Young's modulus, wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) tests. The results show that multistep drawing using a lower first-step draw ratio provides a higher tenacity and Young's modulus. Furthermore, when the blend ratio is 75/25 in a PET/PP conjugate fiber and 50/50 in a PET/PBT conjugate fiber, the polymer components undergo a phase inversion phenomenon. A PP sub-micron (10?1 ~ 100 micron) fiber of about 0.0001 ~ 0.00017 tex in fineness, or about 0.4 ~ 0.5 micron in diameter, can be obtained when PET/PP conjugate fiber is treated with a 25% NaOH aqueous solution by weight. However, A PBT sub-micron fiber cannot be achieved using a PET/PBT conjugate fiber. 相似文献
Fused filament fabrication (FFF) has been used to create prototypes and functional parts for various applications using plastic filaments. It has also been extended to the use of continuous fibers for reinforcing thermoplastic polymers. This study aims to optimize the deposition design of a coextruded continuous carbon fiber (CCF) composite filament with a polyethylene terephthalate glycol-modified (PETG) filament. The characterizations on the raw materials revealed that the matrix polymer in CCF composite filament had similar physicochemical properties as PETG, and carbon fibers were homogeneously distributed in CCF filament. The effect of raster orientation and shells number on the mechanical properties of non-reinforced and coextruded CCF-reinforced PETG was investigated. The highest mechanical properties were obtained at a raster orientation of 0° for both reinforced and non-reinforced materials. With the increase of raster orientation, Young's modulus and ultimate tensile strength decreased. The presence of shells improved the tensile strength of non-reinforced PETG. For composite samples printed with unreinforced shells, Young's modulus decreased due to decrease in fibers content, and elongation at break and ultimate tensile strength increased. Tomographic observations showed that the mechanical behavior of printed specimens depended on the anisotropy of porosity in printed specimens. 相似文献
An experimental study was made of single fibers rotating and bending in Couette flow of a Newtonian liquid. A previous result for critical fiber buckling was re-tested and found satisfactory, and the transition between ‘springy’ and ‘snake’ rotation was delineated. The minimum radius, of curvature achieved during rotation in the “snake orbit” regime was measured as a function of fiber aspect ratio, Young's modulus, and fluid shear stress. Two correlations are presented which are constrained to satisfy limiting conditions for very stiff and very flexible fibers. Together with a result from thin rod theory, these correlations may be used to predict breaking conditions for fibers of known Young's modulus and ultimate tensile strength. Predictions are tested in experiments where two types of glass fiber are broken in suspension and found satisfactory. Results show that several reinforcing materials will probably break within the range of conditions covered by our experiments, or in a region which can be treated by extrapolation from our results. 相似文献
The mechanical strength of the poly(vinylidene fluoride) (PVDF) based polymer electrolyte deteriorates with increasing salt content. For a salt concentration of 2 wt% the Young's modulus is 10?5 Pa. The Young's modulus reduces by 60% when the salt concentration increases five‐fold. The decrease in mechanical strength of the polymer electrolyte by the incorporation of the salt is attributed to the intramolecular interaction between the chains of the polymer and the salt. The mechanical strength of the polymer electrolyte was also analyzed for different plasticizer content. The plasticizer used was ethylene carbonate (EC). The Young's modulus of the plasticized polymer electrolyte decreased with increased in EC content, but the elongation of the material and the energy at break increased with EC content, showing increased flexibility. 相似文献
To maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double-coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double-coated optical fibers to minimize the thermally induced coating's delamination is also discussed. 相似文献
A series of 2-hydroxyethylmethacrylate (HEMA)/methacrylamide (MAA)-grafted silk fibers obtained in various comonomer compositions was prepared and their structural characteristics were studied by X-ray diffractometry, differential scanning calorimetry, and scanning electron microscopy. HEMA/MAA-grafted silk fibers with a graft yield of about 60% obtained in a HEMA/MAA mixture system containing 20% of HEMA and 80% of MAA on a weight basis showed endothermic peaks at 280 and 420°C (shoulder form), which are attributed to the thermal decomposition of the MAA and HEMA polymers, respectively, in addition to the thermal decomposition peak of the silk fibroin fiber which appeared at 323°C. These DSC results suggest that the HEMA/MAA-grafted silk fiber showed a low compatibility in the relation between the silk fibroin molecules and HEMA and/or MAA polymers. The crystalline structure of the HEMA/MAA-grafted silk fiber remained unchanged regardless of the HEMA/MAA grafting ratio even when the graft yield value reached 120%. 相似文献
This paper deals with the effect of processing conditions on the mechanical properties of composite material made from newsprint and polystyrene. A masterbatch compound with weight ratio of 50:50 (polystyrene/fiber) was prepared using a Brabender intensive type mixer. Composites with various percentage of fiber, e.g., 40, 30, 20, and 10% of fiber were obtained by adding the measured amount of polymer to the masterbatch followed by another mixing period of time. Test samples were compression molded into shoulder-shaped test specimens, using a steam-heated press, and, kept in room conditioning at 23°C and 50% of relative humidity for a week 48 h prior to testing. The Young's modulus and the strength at break were evaluated, and the averages of six measurements were reported. Test results showed that newsprint loading level has a significant impact on mechanical performance of the resulting composites. Tensile strength increased at first linearly with newsprint content, then reached asymptote at higher level of newsprint content 40% or more. As the Young's modulus is concerned, there is a linear relationship between tensile Young's modulus and fiber concentration as proposed by the various models in the literature. 相似文献