Chemical Pretreatments Affecting Drying Characteristics of Chilli (cv. Huarou Yon)

One- (70°C) and two-temperature regimes (70 and 50°C) were used to dry chilli (Capsicum annuum cv. Huarou Yon) using a laboratory tray dryer compared to conventional sun drying. A pretreatment was done by soaking chilli in antibrowning solutions before drying. It was found that the drying rate of chilli soaked in chemical solutions was increased and the drying period of chilli was decreased. Page's model was found to fit well with the experiment for one- and two-temperature drying using least squares analysis. The highest value of the coefficient of determination (R² > 0.99), the lowest value of standard error of estimation (SEE < 0.00031), and the lowest value of the mean relative deviation (P < 10%) were obtained. The effective moisture diffusivities of chilli drying at 70°C and two-stage drying were between 6.01–7.22 × 10^?10 m²/s and 3.16–3.89 × 10^?10 m²/s, respectively. In contrast, the lowest value of effective moisture diffusivity of chilli was obtained by the conventional sun-drying method (0.597 × 10^?10 m²/s). The highest value of moisture diffusivity was observed for chilli soaked in sodium metabisulfite (NaMS) mixed with CaCl₂ solution for both one- and two-temperature regimes. The color of chilli was improved by using chemical pretreatments, in particular, chilli soaked in NaMS mixed with CaCl₂ solution.     

Improvement of interfacial adhesion of poly(m‐phenylene isophthalamide) short fiber–thermoplastic elastomer (SEBS) composites by N‐alkylation on fiber surface

A composite of short‐fiber, poly(m‐phenylene isophthalamide), and thermoplastic elastomer styrene (ethylene–butylene) styrene (SEBS), was investigated. The fiber surface was modified by N‐alkylation (heptylation and dodecylation) to improve their compatibility with a less polar SEBS matrix. Observation of fiber‐surface morphology by SEM revealed surface roughness after N‐alkylation. Nearly complete coating of the polymer matrix on the fiber was observed on a fractured surface of the composite, which is evidence for the improvement of fiber–matrix adhesion. It was found that the modulus of the composites grew with increasing fiber loading to approximately the same extent for both unmodified and modified fiber composites. Tensile strength of the modified fiber composites was found to improve significantly over that of the unmodified fiber composite. This suggests that the presence of the alkyl group on the fiber surface is responsible for an improvement of interfacial adhesion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2414–2422, 1999     

Effect of compatibilizers on mechanical properties and morphology of in-situ composite film of thermotropic liquid crystalline polymer/polypropylene

An in-situ composite film of a thermotropic liquid crystalline polymer (LC3000)/polypropylene (TLCP/PP) was produced using the extrusion cast film technique. The compatibilizing effect of thermoplastic elastomers, styrene-ethylene butylene-styrene (SEBS), maleic anhydride grafted SEBS (MA-SEBS), and maleic anhydride grafted polypropylene (MA-PP) on the mechanical properties and morphology of the TLCP/PP composite films was investigated. It was found that SEBS provided a higher value of tensile modulus than MA-SEBS, which in turn was higher than MA-PP, despite the expected stronger interaction between the MA chain and TLCP. The observation of the morphology under optical and scanning electron microscopes suggested that all three compatibilizers helped improve the dispersion of the TLCP fibers and increased the fiber aspect ratio to a different extent. The fractured surface of the specimens showed more fiber breakage than pull-out when a compatibilizer was added, which suggested the improvement of interfacial adhesion. The surface roughness of fibers with an added elastomeric compatibilizermay also provide mechanical interlocking at the interface. It is suggested that the increase in the viscosity ratio of TLCP/PP due to the added elastomeric compatibilizer, SEBS and MA-SEBS, compared with the thermoplastic compatibilizer, MA-PP, is more effective in improving the composite mechanical properties.     

Bridged double percolation in conductive polymer composites: an electrical conductivity, morphology and mechanical property study

Conductive polymer composites are ubiquitous in technological applications and constitute an ongoing topic of tremendous commercial interest. Strategies developed to improve the level of electrical conductivity achieved at a given filler concentration have relied on double-percolated networks induced by immiscible polymer blends, as well as mixtures of fillers in a single polymer matrix, to enhance interparticle connectivity. In this work, we combine these two strategies by examining quaternary composites consisting of high-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE), graphite (G) and carbon fiber (CF). On the basis of our previous findings, we examine the electrical conductivity, morphology, thermal signature and mechanical properties of HDPE/UHMWPE/G systems that show evidence of double percolation. Upon addition of CF, tremendous increases in conductivity are realized. The mechanism by which this increase occurs is termed bridged double percolation to reflect the role of CF in spanning non-conductive regions and enhancing the continuity of conductive pathways. At CF concentrations above the percolation threshold concentration, addition of G promotes increases in conductivity and dynamic storage modulus in which the conductivity increases exponentially with increasing modulus.     

Correlated electrical conductivity and mechanical property analysis of high-density polyethylene filled with graphite and carbon fiber

The development of conductive polymer composites remains an important endeavor in light of growing energy concerns. In the present work, graphite (G), carbon fiber (CF) and G/CF mixtures are added to high-density polyethylene (HDPE) to discern if mixed fillers afford appreciable advantages over single fillers. The effects of filler type and composition on electrical conductivity, composite morphology and mechanical properties have been examined and correlated to establish structure-property relationships. The threshold loading levels required for G and CF to achieve measurable conductivity in HDPE have been identified. Addition of CF to HDPE/G composites is found to increase the conductivity relative to that of HDPE/G composites at the same filler concentration. This observed increase depends on CF length and becomes more pronounced at and beyond the threshold loading of the HDPE/G composite. Scanning electron microscopy is employed to elucidate the morphology of these multicomponent composites, whereas dynamic mechanical analysis reveals that filler concentration, composition and CF length impact both the magnitude and temperature dependence of the dynamic storage modulus.