Intercalated and exfoliated polystyrene/nano‐clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using CO2 as the foaming agent in an extrusion foaming process. The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of 200°C, the addition of a small amount (i.e., 5 wt%) of intercalated nano‐clay greatly reduces cell size from 25.3 to 11.1 μm and increases cell density from 2.7 × 107 to 2.8 × 108 cells/cm3. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 × 109 cells/cm3) and smallest cell size (4.9 μm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams. 相似文献
Wood-fiber composites make use of cellulose fibers as a reinforcing filler in the polymer matrix and are known to have a lower material cost and a higher stiffness than neat polymers. However, the lower material cost and enhanced stiffness of wood-fiber composites are achieved at the expense of other properties such as the ductility and impact strength. Since microcellular plastics exhibit a higher impact strength, higher toughness, and increased fatigue life compared to unfoamed plastics, microcellular foaming of wood-fiber composites will improve the mechanical properties of the composites and therefore increase the usefulness of the materials. In this paper, microcellular foamed PVC/wood-fiber composites with unique cell morphology and material composition are characterized. Microcellular structures are produced in PVC/wood-fiber composites by first saturating the composite samples with CO2 under high pressure followed by rapidly decreasing the solubility of gas in the samples. The void fraction of the microcellular foamed PVC/wood-fiber composites is controlled by tailoring the composition of materials and the foaming process parameters. The results indicate that tensile and impact properties of microcellular foamed PVC/wood-fiber composites are most sensitive to changes in the cell morphology and the surface modification of fibers. 相似文献
The effects of process variables on the microcellular structure and crystallization of foamed polypropylene (PP) with supercritical CO2 as the foaming agent were investigated in this article. The cell size increased and the cell density reduced with increased foaming temperature. Differently, both the cell diameter and cell density increased as saturation pressure increased. DSC curves showed that the melting peak was broadened when supercritical CO2 foaming PP. Furthermore, the width at half-height of the melting peak increased, the melting peak moved to higher temperature, and the melting point and crystallinity enhanced as the foaming temperature lowered and the saturation pressure enhanced. 相似文献
Wood fiber reinforced polymer composites represent a relatively small but rapidly growing material class, extensively applied in interior building applications and in the automotive industry. The polymer‐wood fiber composites utilize fibers as reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the materials cost and mechanical properties such as stiffness and strength. Wood fiber reinforced polymer composites are microcellularly processed to create a new class of materials with unique properties. Most manufacturers are evaluating new alternatives of foamed composites that are lighter and more like wood. Foamed wood composites accept screws and nails like wood, more so than their non‐foamed counterparts. They have other advantages such as better surface definition and sharper contours and corners than non‐foamed profiles, which are created by the internal pressure of foaming. This paper represents a review on microcellular wood fiber reinforced polymer composites obtained by different processes (batch, injection molding, extrusion, and compression molding process) and includes an overview of foaming agents (physical and chemical) and the foaming of wood fiber‐polymer composites (changes in phase morphology, formation of polymer‐gas solution, cell nucleation, and cell growth control).
In this research, the effects of the materials and the processing conditions on the cell morphology of foamed PVC/wood-fiber composites were studied with a view to establishing their process-structure relationships. Each step of microcellular PVC/wood-fiber composites processing is addressed, including the surface treatment of the wood-fiber, mixing of polymer and wood-fiber, manufacture of the composites, the saturation of the composites with gas, microcellular foaming of the composites, and characterization of the cell morphology. The cellular morphologies of the foamed PVC/wood-fiber composites are a strong function of the content of plasticizer and the surface treatment of wood-fiber as well as the gas saturation and foaming conditions. 相似文献
In this article, PA6/poly(tetrafluoroethylene) (PTFE) composites were prepared by internal mixer with high rotor speed. The existence of PTFE nano-fibrillation network structure was observed by scanning electron microscopy (SEM) analysis. The effect of PTFE on crystallization and rheological behavior of PA6 was evaluated. The result showed that the PTFE fibrils improved the crystallization properties of PA6 and do not change the crystal structure. The PTFE effectively enhanced the melt strength of PA6 by fibrillation. The PA6/PTFE composites were then foamed assisted by supercritical CO2. The PTFE was used as cell nucleating agent, crystal nucleating agent and melt strength enhancement agent in the foaming process. Finally, the microcellular PA6 foams were successfully obtained with the cell density higher than 109 cells/cm3, the cell size of ca. 14 μm and the volume expansion ratio of 16. 相似文献