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ABSTRACT:The present study deals with the effects of natural fibers on thermal and mechanical properties of natural fiber polypropylene composites using dynamic mechanical analysis. Composites of polypropylene and various natural fibers including kenaf fibers, wood flour, rice hulls, and newsprint fibers were prepared at 25 and 50% (by weight) fiber content levels. One and two percent maleic anhydride grafted polypropylene was also used as the compatibilizer for composites containing 25 and 50% fibers, respectively. Specimens for dynamic mechanical analysis tests were cut out of injection-molded samples and were tested over a temperature range of Ϫ60 to ϩ120°C. Frequency of the oscillations was fixed at 1 Hz and the strain amplitude was 0.1%, which was well within the linear viscoelastic region. The heating rate was 2°C/min for all temperature scan tests. Storage modulus (EЈ), loss modulus (EЉ), and mechanical loss factor (tan ␦) were collected during the test and were plotted versus temperature. An increase in storage and loss moduli and a decrease in the mechanical loss factor were observed for all composites indicating more elastic behavior of the composites as compared with the pure PP. Changes in phase transition temperatures were monitored and possible causes were discussed. Results indicated that glass transition was slightly shifted to lower temperatures in composites. ␣ transition temperature was higher in the case of composites and its intensity was higher as well.

We show that mucociliary membranes of animal epithelia can create fluid-mechanical microenvironments for the active recruitment of the specific microbiome of the host. In terrestrial vertebrates, these tissues are typically colonized by complex consortia and are inaccessible to observation. Such tissues can be directly examined in aquatic animals, providing valuable opportunities for the analysis of mucociliary activity in relation to bacteria recruitment. Using the squid-vibrio model system, we provide a characterization of the initial engagement of microbial symbionts along ciliated tissues. Specifically, we developed an empirical and theoretical framework to conduct a census of ciliated cell types, create structural maps, and resolve the spatiotemporal flow dynamics. Our multiscale analyses revealed two distinct, highly organized populations of cilia on the host tissues. An array of long cilia (∼25 µm) with metachronal beat creates a flow that focuses bacteria-sized particles, at the exclusion of larger particles, into sheltered zones; there, a field of randomly beating short cilia (∼10 µm) mixes the local fluid environment, which contains host biochemical signals known to prime symbionts for colonization. This cilia-mediated process represents a previously unrecognized mechanism for symbiont recruitment. Each mucociliary surface that recruits a microbiome such as the case described here is likely to have system-specific features. However, all mucociliary surfaces are subject to the same physical and biological constraints that are imposed by the fluid environment and the evolutionary conserved structure of cilia. As such, our study promises to provide insight into universal mechanisms that drive the recruitment of symbiotic partners.cilia | microfluidics | host-bacterial symbiosis | biological fluid mechanics, biofiltration M any eukaryotic cells feature motile cilia, microtubulebased surface actuators that sense and propel the extracellular fluidic environment (1-3). Whereas cilia and cilia-like structures that sort and capture bacteria or particles are common and well-characterized features of aquatic organisms (4-7), in terrestrial animals such as mammals, the internal location of ciliated surfaces has made them difficult to study. A central challenge in internal ciliated mucus membranes, such as those lining the fallopian tube, the Eustachian tube, and the respiratory system (8), is to reconcile the effective clearance of toxic molecules and undesirable microbes with selective engagement of beneficial symbionts. For example, on airway epithelia, the coordinated beat of motile cilia creates a horizontal flow across their tips (9-12), which clears mucus, microorganisms, and debris (Fig. 1A). Disruption of this mucociliary clearance can lead to chronic infection of the airways (13). However, this simple model is incomplete; ciliated airway epithelia not only serve a clearance function, but also provide a habitat and a gateway for coevolved symbionts that play an essential role in the development of the host...

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ABSTRACT:The time-temperature superposition principle was applied to the viscoelastic properties of a kenaffiber/high-density polyethylene (HDPE) composite, and its validity was tested. With a composite of 50% kenaf fibers, 48% HDPE, and 2% compatibilizer, frequency scans from a dynamic mechanical analyzer were performed in the range of 0.1-10 Hz at five different temperatures. Twelve-minute creep tests were also performed at the same temperatures. Creep data were modeled with a simple two-parameter power-law model. Frequency isotherms were shifted horizontally and vertically along the frequency axis, and master curves were constructed. The resulting master curves were compared with an extrapolated creep model and a 24-h creep test. The results indicated that the composite material was thermorheologically complex, and a single horizontal shift was not adequate to predict the long-term performance of the material. This information will be useful for the eventual development of an engineering methodology for creep necessary for the design of structural building products from these composites.