Three different fiber surface treatments were made to study their influences on drop-weight impact fracture resistance and static in-plane fracture toughness of injection-molded short glass fiberreinforced nylon 6 plates. Scanning acoustic microscopy (SAM) was used to study the microscopic deformation and fracture processes in detail. The SAM observation revealed several fundamental and quantitative features such as: (1) three-dimensional shape of the crack front, (2) three-dimensional distribution of fibers, (3) matrix plastic deformation and/or matrix microcracking, and (4) fiber/matrix debonding and pull-out. These microscopic deformation and fracture features revealed some of the toughning mechanisms, which were then correlated with the macroscopic static and impact fracture properties. The excellent ultrasonic contrast between fiber and matrix could be accomplished by a large difference in acoustic impedance. The plastic deformation of matrix was detected by enhanced attenuation of surface waves. Moreover, fiber/matrix debonding and/or matrix microcracking were clearly observed due to the waves reflected at debonded or cracked interfaces.
Epoxy (Ep)-polyethermide (PEI) blends system were employed as a matrix resin for carbon fiber reinforced plastics (CFRP). Microstructure, dynamic mechanical properties and toughness were investigated for bulk and CFRP consisting of Ep and 20wt% PEI blends. Effects of curing reagents and curing temperature were also studied. SEM observation revealed that Ep rich connected globule structure was presented in PEI rich continuous phase, in all the investigated fractured surface of the cured blend. When bulk blend was cured with a particular conditon, microstructure region consisting of PEI rich spherical domains dispersed in Ep rich continuous phase was also present as a mixture in connected-globule structure region. When CFRP was cured with such condition, Ep rich continuous phase localized arround CF. When CFRP was cured with the condition that connected-globule structure was only present, morphology in CFRP matrix was the same as that in the cured bulk blend. From the results of dynamic mechanical measurements, considerable differences between matrix resin and curing conditions were observed for adhesion between CF and matrix, and adhesion decreased by the addition of PEI. Fracture toughness changed depending on curing conditions, and it increased by the addition of PEI.
The effect of surface treatment on the mechanical properties of unidirectional composites using glass/nylon 6 commingled yarn was studied with three kinds of surface treatment. Commingled yarn composites of unidrectional alignment were fabricated by compression with heating in mold. Three-point bending tests were carried out in both longitudinal and transverse directions. Bending properties were discussed in relation to acoustic emission (AE) properties. The fracture surfaces of test pieces in transverse direction were observed by scanning electron microscopy (SEM) to examine the adhesion between fiber and matrix. Longitudinal bending properties were not affected by the kind of surface treatment. The fracture mechanisms, however, were quite different as revealed by AE properties. In the case of transverse bending test, the bending strength was strongly affected by the surface treatment. SEM observation of the fracture surfaces showed that the surface treatment appreciably changed the adhesion between fiber and matrix.
Finishing of glass cloths with methacryl silane formed physisorbed silane which was able to be removed from glass fiber surface by washiag with methanol. The physisorbed silane was found to arise from the oligomerization of silane molecules from the measurement of molecular weight distribution of physisorbed silane by gel permeation chromatography. Such a physisorbed silane was suggested to migrate into vinylester resin in the process of fabrication of glass cloth/resin laminates. In order to examine the effect of physisorbed silane on the mechanical properties and the dynamic viscoelasticity was measured for the laminates and for the resin mixed with oligomeric silane as a model of the interphase component between glass fiber and resin matrix. Glass transition of the laminates and of the resin mixed with the physisorbed silane shifted to higher temperature in proportion to the amount of the physisorbed and the oligomeric silane, respectively. The fracture toughness of resin mixed with oligomeric silane decreased in proportion to the amount of the silane. This result showed that the crosslinking density of the mixture of resin and oligomeric silane increased. In order to confirm such a structural change from molecular viewpoint, the vicinity of glass fibers in resin matrix was measured by microscopic FT-IR. The resulting spectra showed that the physisorbed silane affected the curing of resin near glass fiber. These results suggested that the mechanical properties of the interphase between glass fiber and resin matrix was influenced by the formation of the physisorbed silane.
Effects of surface treatments with coupling agents and a binder on mechanical properties and processabillities were examined for fiber-reinforced polycarbonate produced by injection molding. Moldings with a weldline were used for the evaluation of the mechanical properties. Polycarbonates and glass fibers treated with a series of surface-treatment agents including three types of silane coupling agents and one type of urethane binder were compounded with a twin screw extruder into pellets for injection molding. Dumbbell test bars with or without a weldline were injection-molded and subjected to tensile test. Molecular weight of polycarbonate, average length of glass fibers and bar-flow length of the compounds in an injection mold were measured. The non-weld strengths of the materials, whose fibers were treated with a silane coupling agent and/or a urethane binder, were improved remarkably as compared with that of the untreated material. An amino silane, which was the most effective amongst three types of silanes, improved the non-weld strength up to 40% higher than that of the untreated material. This result was due to the higher strength of the fiber/resin interface and the longer fiber legth maintained during the processing. As the weld strength was not influenced by the fiber length, it depended only on the interface strength. The weld strength of the material treated with the amino silane increased to a value 25% higher than that of untreated one. The effect of the amino silane was attributed to the hydrogen bond between the amino groups and the carbonyl groups, because thermoplastics such as polycarbonate form no strong chemical bonds with the silanes. The urethane binder was not effective for the adhesion with polycarbonate, but promoted the adhesion of the silanes.
The microstructure of bisphenol A polycarbonate (PC) and poly (ethylene terephthalate) (PET) was studied by Fourier transform infrared microspectroscopy. The spectra of the carbonyl stretching bands for PC/PET blends showed two peaks which correspond to those of the respective polymer components, and no other peaks were found in the region due to aromatic esters and aromatic aliphatic carbonates. This result means that the transesterification of PC/PET blends did not take place. The peak intensity ratios, IPC/IPET, of the carbonyl stretching bands changed depending on the depth. It was also found in a surface region that the position of absorption bands of the carbonyl group in PET varied remarkably in the range of about 20% to 50% of the PET weight fraction. These results suggested that the domain structure changed depending on the composition, and the domain size of phase separation is smaller in a surface region than in a bulk region of PC/PET blends.
The effect of the oxidation treatment of carbon black (CB) on its distribution state in the polymer blends was examined by scanning electron microscopy. This treatment lends to a transfer of CB particles from one phase to another of the polymer blend. This exchange of filler rich phase influences the positive temperature coefficient (PTC) property of the polymer blend filled with CB. It was concluded that PTC property of a polymer blend filled with CB is decided by the distribution state of fillers in the polymer blend, the thermal expansion properties of each component and the blend ratio.