Two kinds of retted Canadian linseed flax fibers, dew‐retted (F1) and enzyme‐retted flax fibers (F2) were characterized in detail for their applications in composites, such as retting degree, thermal stability, tensile strength, and interfacial behavior in polypropylene (PP) matrix. It's clear from Scanning Electron Micrograph that the aspect ratio of F2 was much higher than that of F1 in the light of their separated elementary fibers in most cases. Instead, the elementary fibers of F1 remained tightly bundled into technical fiber wrapping with more non‐cellulose portions. This reflected its lower retting degree and resulted in its lower thermal stability. Single fiber tensile test and single fiber pull‐out test were used to evaluate the fiber tensile properties and fiber/PP interfacial shear strength, respectively. Better retting degree and fewer damages on F2 endowed F2 better tensile property. Consequently, higher aspect ratio, retting degree, and tensile strength proved F2 to be a kind of better reinforcing material than F1 for composites. POLYM. ENG. SCI., 2012. 2011 published by Society of Plastics Engineers 相似文献
Thermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.
SEM picture of the fracture surface of a composite with UD flax reinforcement. 相似文献
Abstract Natural fibers are potentially a high‐performance non‐abrasive reinforcing fiber source. In this study, pulp fibers [including bleached Kraft pulp (BKP) and thermomechanical pulp (TMP)], hemp, flax, and wood flour were used for reinforcing in polypropylene (PP) composite. The results show that pulp fibers, in particular, TMP‐reinforced PP has the highest tensile strength, possibly because pulp fibers were subjected to less severe shortening during compounding, compared to hemp and flax fiber bundles. Maleic‐anhydride grafted PP (MAPP) with high maleic anhydride groups and high molecular weight was more effective in improving strength properties of PP composite as a compatiblizer. Coupled with 10% glass fiber, 40% TMP reinforced PP had a tensile strength of 70 MPa and a specific tensile strength comparable to glass fiber reinforced PP. Thermomechanical pulp was more effective in reinforcing than BKP. X‐ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to aid in the analysis. Polypropylene with high impact strength was also used in compounding to improve the low‐impact strength prevalent in natural fiber‐reinforced PP from injection molding. 相似文献
This research investigates the physical and mechanical properties of hybrid composites made of epoxy reinforced by kenaf and flax natural fibers to investigate the hybridization influences of the composites. Pure and hybrid composites were fabricated using bi-directional kenaf and flax fabrics at different stacking sequences utilizing the vacuum-assisted resin infusion method. The pure and hybrid composites' physical properties, such as density, fiber volume fraction (FVF), water absorption capacity, and dimensional stability, were measured. The tests of tensile, flexural, interlaminar shear and fracture toughness (Mode II) were examined to determine the mechanical properties. The results revealed that density remained unchanged for the hybrid compared to pure kenaf/epoxy composites. The tensile, flexural, and interlaminar shear performance of flax/epoxy composite is improved by an increment of kenaf FVF in hybrid composites. The stacking sequence significantly affected the mechanical properties of hybrid composites. The highest tensile strength (59.8 MPa) was obtained for FK2 (alternative sequence of flax and kenaf fibers). However, FK3 (flax fiber located on the outer surfaces) had the highest interlaminar shear strength (12.5 MPa) and fracture toughness (3302.3 J/m2) among all tested hybrid composites. The highest water resistance was achieved for FK5 with the lowest thickness swelling. 相似文献
In the present study, the prefailure damage processes of a series of short glass fiber/mica/epoxy composites under three-point bending were elucidated using acoustic emission (AE) coupled with in situ scanning electron microscopy (SEM) observations. This study consisted of a detailed investigation of the damage tolerance of composite systems that had constant inorganic content of 75% by weight with a varying ratio of glass fibers to mica. The flexural strength was found to increase from 11 to 21 ksi as the glass fiber content increased (mica content decreased), while the flexural modulus decreased from 5.0 to 2.5 Msi. By monitoring the AE during flexural deformation of the glass fiber-to-mica ratio composites, it was determined that low amplitude (0–42 db) AE events, which occurred throughout the deformation process, were caused by matrix cracking, whereas the high-amplitude (43–100 db) AE events, which occurred just prior to failure, were caused by a fiber-related mechanism. In situ SEM observations of the composites during flexural deformation allowed a correlation between the AE and the damage mechanisms as a function of strain. In the all-mica composite, microcracking initiated in the linear region at preexisting flaws, on the order of 10 μm, located at the mica interface. These microcracks grew along the mica contours over the majority of the deformation process, emitting low-amplitude events, until final fracture occurred at relatively low strains. In the glass fiber-containing composites, microcracking initiated in the linear region at preexisting flaws and voids, on the order of 10 μm. These microcracks grew slowly, emitting low-amplitude events, as the strain increased, but were prevented from causing failure at low strains because of the toughening effect of the glass fibers. At sufficiently high strains, however, fiber breakage and fiber pull-out occurred that corresponded to the high-amplitude events detected by the AE. At strains just prior to failure, catastrophic crack growth occurred, producing a rapid increase in both low-and high-amplitude events, causing ultimate failure. 相似文献
The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber‐matrix interface. In contrast, melamine‐formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber‐matrix interface. This suggests that the fiber‐matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements. 相似文献