Composites of blends of starch with ethylene vinyl alcohol copolymer (SEVA‐C) filled with 10, 30 and 50% by weight (wt.) of hydroxyapatite (HA–the major inorganic constituent of human bone) were produced by twin‐screw extrusion (TSE) compounding. These composites were molded into tensile test bars using two molding techniques: (i) conventional injection molding and (ii) shear controlled orientation in injection molding (SCORIM). The bars produced were mechanically characterized by means of tensile testing and dynamical mechanical analysis (DMA). The structure of the moldings was assessed by wide‐angle X‐ray diffraction (WAXD) and the failure surfaces of the moldings analyzed by scanning electron microscopy (SEM). The enhancement of stiffness observed with HA reinforcement results partially from the stiffening effect of the blend associated with the decrease in plasticizer content during the compounding stage. SCORIM was able to further increase the stiffness of SEVA‐C/HA composites, allowing a maximum improvement of 12% for 30% wt. HA as compared to conventional molding. DMA results showed that the reinforcement of SEVA‐C causes the broadening of the relaxation peak of the polymer, suggesting a structural change within the starch fraction that may be related with thermal degradation of the polymer. The addition of HA particles reduces the preferred orientation exhibited by the SEVA‐C matrix, which is believed to limit the maximum mechanical performance that can be attained. Nevertheless, composites based on a biodegradable matrix with modulus above 7 GPa (in the bounds of the lower limit for human cortical bone) could be successfully produced. 相似文献
The recyclability of a fiber-reinforced poly(butylene terephthalate) (PET) composite has been studied. After treatment with a suitable silane, processed regrind composites are successfully recycled, with mechanical properties as good as a comparable, commercial composite. The three processing techniques investigated are injection molding, extrusion compression molding and compression molding. As expected, processing technique and processing parameters are important in determining the mechanical properties of the molded regrind. Our results show that injection- and extrusion-compression-molded regrind composites have good fiber bundle dispersion and fiber alignment, resulting in tensile properties better than the compression-molded samples. On the other hand, compression-molded samples, which show random fiber orientation and low fiber bundle dispersion, have lower tensile properties, but better impact strength than injection- and extrusioncompression-molded composites. 相似文献
The transcrystal plays an important role in the enhancement of mechanical and thermal performances for polymer/glass fiber composites. Shear has been found to be a very effective way for the formation of transcrystal. Our purpose of this study was to explore the possibility to obtain the transcrystal in real processing such as injection molding. We will report our recent efforts on exploring the development of microstructure of polypropylene (PP)/glass fiber composite from skin to core in the injection-molded bars obtained by so-called dynamic packing injection molding which imposed oscillatory shear on the melt during solidification stage. A clear-cut shear-facilitated transcrystallization of PP on glass fibers was observed in the injection-molding bar for the first time. We suggested that shear could facilitate the transcrystalline growth through significantly improving the fiber orientation and the interfacial adhesion between fiber and matrix. 相似文献
The potential of using exfoliated graphite nanoplatelets, xGnPTM, as a reinforcement that can produce multifunctional polymer composites was explored. xGnP-polypropylene (PP) composites fabricated by melt mixing using a twin-screw extruder followed by injection molding were investigated for their thermal, viscoelastic and barrier properties as a function of xGnP concentration and aspect ratio. These properties of the xGnP-PP composites were compared to the properties of composites made with PAN-based carbon fibers, VGCF, carbon black and nanoclay. Results indicate that when oriented properly, the xGnP will not only stiffen the composite but also reduce the coefficient of thermal expansion in two directions rather than in one as in the case of aligned fiber composites. Furthermore, the large aspect ratio of xGnP, even at low loadings, increases the oxygen barrier of PP at least as effectively as the commonly used nanoclays and finally, addition of xGnP significantly enhances the thermal conductivity of the polymer matrix. 相似文献
The lifespan and the performance of flexible electronic devices and components are affected by the large accumulation of heat, and this problem must be addressed by thermally conductive polymer composite films. Therefore, the need for the development of high thermal conductivity nanocomposites has a strong role in various applications. In this article, the effect of different particle reinforcements such as single and hybrid form, coated and uncoated particles, and chemically treated particles on the thermal conductivity of various polymers are reviewed and the mechanism behind the improvement of the required properties are discussed. Furthermore, the role of manufacturing processes such as injection molding, compression molding, and 3D printing techniques in the production of high thermal conductivity polymer composites is detailed. Finally, the potential for future research is discussed, which can help researchers to work on the thermal properties enhancement for polymeric materials. 相似文献
A new experimental method is presented for quantifying impact damage and estimating the remaining fatigue lifetime of impact damaged polymer matrix composite materials. The procedure is demonstrated using composites of glass fiber reinforced polyurethane produced by injection molding and structural reaction injection molding. Thermoelastic stress analysis (TSA) was used to quantify the stress concentration associated with impact‐damage in test samples of each composite. Following impact and TSA imaging, the samples were fatigued to failure over a range of stress amplitudes. The TSA‐derived stress concentration factors were used to determine a modified stress amplitude that collapsed the impact‐fatigue data onto a master stress‐life curve. This approach provides a quantitative measure of impact damage and a practical methodology for estimating the residual fatigue lifetime of impact; damaged composites. 相似文献
Composite samples consisting of ferromagnetic asymmetric particles incorporated into a polyolefin binder were injection molded using custom designed molds which produced preferential fiber orientations. The relative magnetic permeability values of the composites were measured as a function of the filler volume fraction, injection rate, gate diameter, temperature, aspect ratio of the fibers, and fiber orientation. Fiber orientation was affected by the molding conditions and controlled the relative magnetic permeability of the composites. The degree of fiber orientation was significantly affected by the size of the opening (gate) to the mold, or by the mold geometry going from an edge-gated cylindrical to a center-gated disk cavity. Relative permeability values of the composites were observed to increase when the fiber orientation and the applied field were parallel to one another. For instance, highly aligned composite samples exhibited up to 30% greater relative permeability values compared to those samples which exhibit fiber orientation distributions approaching a random distribution. To our knowledge this is the first study that provides data linking the fiber orientation distribution functions of ferromagnetic asymmetric particles to the relative magnetic permeability values of injection molded composites. 相似文献
Summary: In order to achieve better mechanical properties, most work on polymer/fiber composites has been focused on the importance of the chemistry used to modify the surface of the fibers and improving the adhesion between the fiber and the matrix using coupling agents. Our purpose in this study was to determine the effect of shear on the fiber orientation and interfacial adhesion in poly(propylene)/glass fiber composites via dynamic packing injection molding (DPIM), in which the melt is first injected into the mold and then forced to move repeatedly in a chamber by two pistons that move reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part. SEM, TGA, FT‐IR, AFM and mechanical testing were used to characterize the samples obtained. The majority of fibers are aligned parallel to the flow direction along the sample thickness, even at the core, in contrast to the products obtained via conventional injection molding where the orientation of fibers is observed only at the skin. More importantly, we found that shear could enhance not only the fiber orientation, but also the interfacial adhesion between the fibers and the matrix, particularly for samples with higher fiber contents, resulting in an obvious increase in tensile strength and the onset degradation temperature. A possible transcrystallization was evidenced by AFM investigations of the dynamic packing injection molded samples, which is worth further study.
SEM micrographs representing the glass fiber after PP in the composites was extracted (GF30, dynamic sample). 相似文献