Structural properties and mechanical behavior of injection molded composites of polypropylene and sisal fiber

Composites based on isotactic polypropylene (PP) and sisal fiber (SF) were prepared by melt mixing and injection molding. The melt mixing characteristics, thermal properties, morphology, crystalline structure, and mechanical behavior of the PP/SF composites were systematically investigated. The results show that the PP/SF composites can be melt mixed and injection molded under similar conditions as the PP homo‐polymer. For the composites with low sisal fiber content, the fibers act as sites for the nucleation of PP spherulites, and accelerate the crystallization rate and enhance the degree of crystallinity of PP. On the other hand, when the sisal fiber content is high, the fibers hinder the molecular chain motion of PP, and retard the crystallization. The inclusion of sisal fiber induces the formation of β‐form PP crystals in the PP/SF composites and produces little change in the inter‐planar spacing corresponding to the various diffraction peaks of PP. The apparent crystal size as indicated by the several diffraction peaks such as L_(110)α, L_(040)α, L_(130)α and L_(300)β of the α and β‐form crystals tend to increase in the PP/SF composites considerably. These results lead to the increase in the melting temperature of PP. Moreover, the stiffness of the PP/SF composites is improved by the addition of sisal fibers, but their tensile strength decreases because of the poor interfacial bonding. The PP/SF composites are toughened by the sisal fibers due to the formation of β‐form PP crystals and the pull‐out of sisal fibers from the PP matrix, both factors retard crack growth.     

Effects of glass bead content and surface treatment on viscoelasticity of filled polypropylene/elastomer hybrid composites

The dynamic mechanical properties of A‐glass bead filled polypropylene (PP)/ethylene–propylene–diene monomers polymer (EPDM) ternary composites have been measured over a temperature range from −80 °C to 100 °C and at a fixed frequency of 1 Hz, using a dynamic mechanical analyser (DMA), to identify the effects of the filler content and its surface treatment with a silane coupling agent on the dynamic viscoelastic behaviour. The results show that the storage modulus (E′_c) and loss modulus (E ″_c) of these composites with 10% volume fraction of EPDM at 25 °C increase non‐linearly with increasing volume fraction of glass beads (ϕ_g). At the same test conditions, the E′_c value of the PP/EPDM filled with pretreated glass beads is higher than that of the uncoated glass bead filled PP/EPDM system, especially at higher ϕ_g, while the difference in E ″_c between both systems is very small. The mechanical damping for the former decreases with increasing ϕ_g, but the opposite is true for the latter. The glass transition temperature of these composites varies irregularly with ϕ_g. The dynamic complex viscosity increases nonlinearly with an increase of ϕ_g. In addition, the interfacial structure between the matrix and inclusions has been observed by means of a scanning electron microscope. © 1999 Society of Chemical Industry     

Mechanical and thermal behavior of polycarbonate composites reinforced with aluminum borate whiskers

Inorganic aluminum borate (Al₁₈B₄O₃₃) whisker was employed in this study to reinforce polycarbonate (PC). The composites were prepared in a single-screw extruder, followed by injection molding. The whiskers were pretreated with tetrabutyl orthotitanate prior to compounding. The tensile, dynamic mechanical, impact, and thermal properties of the composites were studied. Tensile results showed that the modulus of PC–Al₁₈B₄O₃₃ composites increased markedly with increasing whisker content. However, the tensile stress of the composite decreased slightly with the addition of 5 wt % whisker; thereafter, it increased slowly with increasing whisker content. Differential thermal analysis and thermogravimetric measurements showed that the glass transition temperature (T_g) and 5% weight loss temperature (T_−5%) of the composite shift rapidly to lower temperature regimes with the addition of Al₁₈B₄O₃₃ whiskers up to 10 wt %. Thereafter, the T_g and T_−5% of PC–Al₁₈B₄O₃₃ composites tended to decrease slowly with increasing whisker content. The mechanical and thermal properties of PC–Al₁₈B₄O₃₃ composites were compared with those of PC–potassium titanate (K₂Ti₆O₁₃) whisker composites. The reinforcing effect of Al₁₈B₄O₃₃ and K₂Ti₆O₁₃ whiskers on PC was discussed and contrasted. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2247–2253, 1999     

Mechanical and thermal properties of poly(acrylonitrile–butadiene–styrene) copolymer reinforced with potassium titanate whiskers

Potassium titanate (K₂Ti₆O₁₃) whisker treated with tetrabutyl orthotitanate was used to improve the mechanical and thermal properties of the poly(acrylonitrile–butadiene–styrene) (ABS) copolymer. The composites were prepared in a twin‐screw extruder followed by injection molding. Static tensile measurements showed that both the modulus and breaking stress of ABS/K₂Ti₆O₁₃ composites increase considerably with increasing whisker content; the strain at break of ABS was almost unaffected by the incorporation of a whisker content up to 15 wt %. Izod impact tests indicated that the composites showed a decrease in the impact strength with increasing whiskers content. Thermogravimetric analysis showed that the K₂Ti₆O₁₃ whisker additions have little effect on the thermooxidative stability of ABS. Scanning electron microscopic observations revealed that the whiskers were aligned along the melt‐flow direction in the thin surface layer, whereas the whiskers were oriented randomly as well as perpendicular to the injection direction in the thick core region of the composites. The Tsai–Halpin equation was used to evaluate the moduli of the ABS/K₂Ti₆O₁₃ composites. The theoretical calculations generally correlated well with the experiment data by assuming K₂Ti₆O₁₃ whiskers to have an aspect ratio of 12. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2985–2991, 1999     

Properties of ternary in situ polycarbonate/polybutylene terephthalate/liquid crystalline polymer composites

Ternary in situ polycarbonate (PC)/polybutylene terephthalate (PBT)/liquid crystalline polymer (LCP) composites were prepared by injection molding. The liquid crystalline polymer used was a versatile Vectra A950. The matrix of composite was composed of PC/PBT 60/40 by weight. A solid epoxy resin (bisphenol type‐A) was used as a compatibilizer for the composites. Dynamic mechanical analysis (DMA) showed that epoxy resin was effective to improve the compatibility between PC and PBT, and between PC/PBT and LCP, respectively. Tensile tests revealed that the stiffness of composites shows little change with the LCP content up to 10 wt %. Above this concentration, the stiffness tended to increase with increasing LCP content. Furthermore, the tensile strengths appeared to increase with increasing LCP content, and their values were close to those predicted from the rule of mixtures. Scanning electron microscopic examination showed that LCP ribbons and short fibrils were developed in the composites containing LCP content ≤10 wt %. However, fine and elongated fibrils were formed in the skin and core sections of the composites when the LCP content reached 25 wt % and above. Thermogravimetric analysis indicated that the thermooxidative stability of the PC/PBT 60/40 blend tended to improve with increasing LCP content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1827–1835, 1999     

Spark Plasma Sintered Hydroxyapatite/Multiwalled Carbon Nanotube Composites With Preferred Crystal Orientation

Hydroxyapatite (HA) and its nanocomposites reinforced with low loading levels of multiwalled carbon nanotubes (MWNTs) are prepared by spark plasma sintering process. The structure, morphology, and hardness of sintered HA and MWNT/HA nanocomposites are characterized by means of X‐ray diffraction (XRD), scanning electron microscopy and nanoindentation techniques. XRD results show that the orientation of crystallographic planes of sintered HA are highly related to the applied pressure direction. The perpendicular section of sintered MWNT/HA nanocomposites shows predominantly oriented HA a‐and b‐planes while the parallel section displays a dominant c‐plane orientation. The hardness of MWNT/HA nanocomposites improves considerably with increasing MWNT content.     

Hydrothermal synthesis and biocompatibility of hydroxyapatite nanorods

A facile micelle precursor having cyclohexane/ethanol/cetyl trimethyl ammonium bromide/aqueous phase was treated hydrothermally to form nanohydroxyapatite. The synthesized products were characterized by means of X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the synthesized products display the crystalline structure and vibration modes of hydroxyapatite. Transmission electron micrograph revealed that nanohydroxyapatite exhibits elongated rod morphology with large aspect ratios. Nanohydroxyapatite prepared from a surfactant of 1.25 millimole showed good thermal stability at 1000 degrees C on the basis of thermogravimetric analysis. Simulated body fluid immersion test indicated that an apatite layer can be readily deposited on the nanohydroxyapatite surface demonstrating its good bio-resorbability.     

The formation of β‐polypropylene crystals in a compatibilized blend of isotactic polypropylene and polyamide‐6

Compatibilized polypropylene (PP)/polyamide (PA6) blends with and without β nucleating agent (β‐NA) are prepared, and are designated as Blend‐0.3 and Blend‐0, respectively. The melting and crystallization characteristic of the blends crystallized under different cooling rates and different crystallization temperatures are studied. It is observed that high β‐PP content can be developed in Blend‐0.3 only at slow cooling rates (<5°C/min), whereas high α‐PP content is formed at fast cooling rates. Isothermal crystallization analysis of Blend‐0 indicates that PA6 is an effective NA for α‐PP in the lower temperature range, whereas the α‐nucleating effect disappears in the higher temperature range. Blend‐0.3 can, therefore, be viewed as a system containing both α‐ and β‐NAs, simultaneously. PA6 is competing with β‐NA in inducing PP crystallization. Under the normal injection of Blend‐0.3, the melt will be cooled through the higher temperature that favors the effectiveness of β‐NA rapidly because of the faster cooling rate. However, the α‐nucleation effect from PA6 predominate at the lower temperature. This explains the difficulty in obtaining high β‐PP content in Blend‐0.3 from injection molding. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Corrosion Protection of In Situ Al-Based Composite by Cerium Conversion Treatment

Cerium conversion films were deposited on the surface of in situ aluminum-based composite in solutions containing different cerium chloride (CeCl₃) and hydrogen peroxide (H₂O₂) concentrations at 30 °C. The morphology and composition of conversion films deposited in various solutions were investigated using scanning electron microscopy, energy dispersive x-ray analysis, and x-ray photoelectron spectroscopy (XPS). SEM observations revealed that only patches of film can be deposited on the composite surface when immersed in solutions with low CeCl₃ and H₂O₂ concentrations. However, entire composite surface was covered with a compact film when immersed in a solution containing 10 g/L CeCl₃ and 100 mL/L H₂O₂. XPS results indicated that cerium was incorporated as Ce⁴⁺ species in the hydrated oxide film. The formation of such hydrated conversion film on the composite resulted in low anodic current density and more noble pitting potential when exposed to 3.5% NaCl solution.     

Ternary polymer composites: PA6,6/maleated SEBS/glass beads

Polyamide 6,6 (PA6,6)/maleated styrene–hydrogenated butadiene–styrene (SEBS) blends filled with up to 20% spherical glass beads (GBs) were prepared by extrusion and subsequent injection molding. Tensile and impact tests were used to examine the effect of GB additions on the mechanical behavior of PA6,6/SEBS–g–MA 80/20 blend. Tensile measurements showed that the GB additions improve the stiffness of the PA6,6/SEBS–g–MA 80/20 blend but had little effect on its tensile ductility. The impact test revealed that the impact strength of PA6,6/SEBS–g–MA 80/20 blend tends to decrease with increasing GB content. Therefore, the GB additions were beneficial to maintain a stiffness-to-toughness balance of the PA6,6/SEBS–g–MA 80/20 blend. Finally, the correlation between the experimental tensile stiffness and strength with various theoretical models is discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3231–3237, 2001