Dispersion of nano-clay at higher levels into polypropylene with carbon dioxide in the presence of maleated polypropylene

The use of supercritical carbon dioxide (scCO₂) has proven to be beneficial for surface modified montmorillonite (MMT) nano-clay dispersion up to 6.6 wt% in a polypropylene (PP) matrix and lead to improved material mechanical properties in our earlier research. Our further modifications of the processing procedure including a sequential mixing technique successfully extended the technique to PP composites with as much as 10 wt% of clays and continuously increasing mechanical properties. In order to obtain additional enhancements of the composite properties at this clay level, polypropylene grafted with maleic anhydride (PP-g-MA) is included in this work. The results from the studies of the mechanical properties, rheological properties, and transmission electron microscopy (TEM) show that PP-g-MA is greatly beneficial in generating an exfoliated nano-clay morphology. Greater enhancements in the mechanical properties and nano-clay dispersion in the polymer matrix are observed when PP-g-MA is combined with the scCO₂ and sequential mixing techniques. The PP-g-MA based nano-clay composites have a high degree of exfoliated structure even with the addition of up to approximately 10 wt% nano-clay when using this technique, with mechanical properties such as yield strength and Young's modulus being increased by as much as 12 and 88%, respectively, relative to the polymer matrix. It is believed that the modulus reported here is the highest reported in the literature for conventional PP's.     

Using supercritical carbon dioxide in preparing carbon nanotube nanocomposite: Improved dispersion and mechanical properties

Improvements in carbon nanotube (CNT) dispersion and subsequent mechanical properties of CNT/poly(phenylsulfone) (PPSF) composites were obtained by applying the supercritical CO₂ (scCO₂)‐aided melt‐blending technique that has been used in our laboratory for nanoclay/polymer composite preparation. The preparation process relied on rapid expansion of the CNTs followed by melt blending using a single‐screw extruder. Scanning electronic microscopy results revealed that the CNTs exposed to scCO₂ at certain pressures, temperatures, exposure time, and depressurization rates have a more dispersed structure. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂‐expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/PPSF composites prepared with scCO₂‐aided melt blending and conventional melt blending showed similar tensile strength and elongation at break. The Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt% CNT, but the scCO₂‐aided melt‐blending method provided continuous improvements in Young's modulus up to the addition of 7 wt% CNT. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of bone morphogenetic protein 2 (BMP2) on oestradiol and inhibin A production by sheep granulosa cells, and localization of BMP receptors in the ovary by immunohistochemistry

The bone morphogenetic proteins (BMPs) have been implicated in the paracrine regulation of ovarian follicular development. In this study, we investigated the expression of the BMP receptors (BMPRs) in sheep ovaries by immunohistochemistry and the effect of BMP2, a natural ligand for these receptors, on granulosa cells cultured in vitro. Ovaries from cyclic ewes were fixed, embedded in paraffin wax and cut into sections. The sections were rehydrated, submitted to microwave antigen retrieval and treated with polyclonal antibodies against BMPR1A, BMPR1B and BMPR2. Strong immunostaining for all three receptors was observed in the granulosa cell layer of follicles from the primary to late antral stages of development. Staining was also present in the oocyte, corpus luteum, ovarian surface epithelium and, to a lesser extent, the theca layer of antral follicles. For functional studies, granulosa cells were obtained from immature follicles 1-3 mm in diameter. The cells were cultured for 6 days in serum-free medium containing 1 ng oFSH-20 ml(-1) in the presence of 0, 3, 10 or 30 ng ml(-1) human recombinant BMP2. The medium was replaced every 2 days and oestradiol and inhibin A concentrations were measured in the spent medium. In the absence of BMP2, oestradiol and inhibin A production increased as the granulosa cells differentiated in vitro. The addition of the highest dose of BMP2 enhanced oestradiol production (P < 0.05) without affecting the proliferation of the cells. It is concluded that BMP receptors are present in sheep ovaries and that BMPs may have a role in the differentiation of granulosa cells by enhancing the action of FSH.     

Infants with autism: an investigation of empathy, pretend play, joint attention, and imitation

Systematic studies of infants with autism have not been previously carried out. Taking advantage of a new prospective screening instrument for autism in infancy (S. Baron-Cohen et al., 1996), the present study found that, compared with developmentally delayed and normally developing children, 20-month-old children with autism were specifically impaired on some aspects of empathy, joint attention, and imitation. Infants with autism failed to use social gaze in the empathy and joint attention tasks. Both the infants with autism and the infants with developmental delay demonstrated functional play, but very few participants in either group produced spontaneous pretend play. In the developmental delay group, but not the autism group, pretend play was shown following prompting. The implications of these findings for developmental accounts of autism and for the early diagnosis of the disorder are discussed.     

In situ composites based on blends of a polyetherimide and thermotropic liquid crystalline polymers subjected to shearfree deformations

The effects of shearfree elongational flows on the morphology and mechanical properties of blends of a polyetherimide (PEI) with thermotropic liquid crystalline polymers (TLCP) have been investigated. Extruded sheets and injection molded plaques of PEI/Vectra A and PEI/HX1000 blends, with a TLCP concentration of ≤30 wt%, were subjected to uniaxial elongation, planar and biaxial deformations at 240°C, above the glass transition temperature of the PEI, and at 265°C, which is below the melting point of the TLCPs. Experimental results revealed that each particular mode of shearfree deformation had a distinct effect on the morphology and properties of the blends. For instance, TLCP droplets were deformed into elongated fibrils by application of uniaxial elongation, deformed into elongated ribbon-like structures after planar deformation, and deformed into a disc-like shape by application of equibiaxial flow. Regarding mechanical properties, it was observed that the tensile modulus and strength of molded plaques of PEI/HX1000 80/20 wt% increased to about twice their initial values (from 5.13 to 10.40 GPa and from 105 to 198 MPa, respectively) after a strain of 0.75 was applied in a direction parallel to the initial direction of the TLCP fibers. In addition, samples exhibiting equal values of flow and transverse direction tensile modulus of ∼5.0 GPa were obtained when molded plaques of PEI/HX1000 80/20 wt% were subjected to planar stretching in a direction transverse to the initial direction of the fibers. Thus, by subjecting injection molded plaques to planar stretching, it was possible to obtain a sample exhibiting balanced flow and transverse direction mechanical properties and, consequently, reduced anisotropy.     

Separation of a thermotropic liquid crystalline polymer from polypropylene composites

This work is concerned with determining how to effectively recycle wholly thermoplastic composites comprised of a polypropylene (PP) matrix reinforced with a thermotropic liquid crystalline polymer (TLCP). A novel reclamation process was developed in which the TLCP could be recovered from the PP matrix. Reactive extrusion was used to reduce the molecular weight of the PP (Montell 6523) and to facilitate phase separation. The melt was then extruded into a heated mineral oil bath, which separated the TLCP (DuPont HX8000) from the matrix by dissolving the PP. It was found that greater than 70 wt% of the TLCP could be reclaimed from the PP matrix at a purity of greater than 96 wt%. In order to determine the ability to reuse the reclaimed HX8000, injection molded in situ composites were generated and their mechanical properties were determined. When the neat HX8000 component was partially replaced with reclaimed HX8000, the injection molded TLCP/PP composites showed no discernible difference in mechanical properties.     

Wholly thermoplastic composites from woven preforms based on nylon-11 fibers reinforced in situ with a hydroquinone-based liquid crystalline polyester

This work concerns a novel means to generate wholly thermoplastic composites based on low-melting thermoplastics reinforced with high-melting thermotropic liquid crystalline polymers (TLCPs). A novel dual extrusion process was employed to generate nylon-11 fibers that are reinforced with continuous fibrils of a hydroquinone-based liquid crystalline polyester (DuPont TLCP, HX8000). These composite fibers display tensile properties significantly higher than those predicted by composite theory. These fibers were subsequently woven into a fabric, which in turn serves as a composite preform. Several layers of the fabric preform were stacked and consolidated to yield a composite plaque. The consolidation was carried out at temperatures just high enough for nylon-11 to melt, but well below the melting temperature of HX8000. Fabric preform composites based on the composite fibers with ∼35 wt% HX8000 gave modulus values close to five and one half times that of nylon-11, and strength values approximately two and one half times that of nylon-11. The tensile and flexural properties of these composites are superior to continuous glass-fiber reinforced composites at comparable loadings on a volume basis. Moreover, as the reinforcing fibrils are already encapsulated by the matrix, fiber wetting and fabric impregnation issues that are critical in the fabrication of continuous glass and carbon fiber composites are eliminated.     

Prediction of fiber orientation in the injection molding of long fiber suspensions

The properties of long glass fiber reinforced parts are highly dependent on the fiber orientation generated during processing. In this research, the orientation of concentrated long glass fibers generated during the filling stage of a center‐gated disk (CGD) mold was simulated. The orientation of the fibers was calculated using both the Folgar‐Tucker model and a recently developed semiflexible Bead‐Rod model. Rheologically consistent model parameters were used in these simulations, as determined from a previously proposed method, using a sliding plate rheometer and newly modified stress theory. The predicted CGD orientations were compared with experimentally measured values obtained from the parts. Both models performed very well when using model parameters consistent with the independent rheological study, and the results provide encouragement for the proposed method. Comparatively, the Folgar‐Tucker model provided slightly better orientation predictions up to 20% of the fill radius, but above 20% the Bead‐Rod model predicted better values of the orientation in both the radial and circumferential directions. The Folgar‐Tucker model, however, provided better orientation values perpendicular to the flow direction. Lastly, both models only qualitatively represented the orientation above 70% of the fill radius where frontal flow effects were suspected to be non‐negligible. The uniqueness of this research rests on a method for obtaining model parameters needed to predict fiber orientation which are independent of the experiments being simulated and a method for handling long semiflexible fiber suspensions. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers