Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin-screw extruder. The effect of molecular weight of PP-MA (maleic anhydride-modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP-MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP-MA330k/clay, a well-dispersed two-component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP-MA330k/clay, an intercalated three-component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content.
Fluorescence decay and polarization of dansyl-labeled poly(methacrylic acid) (PMA) and poly-(acrylic acid) (PAA) have been studied as a function of pH. The decay measurements have shown that, at low pH, PMA chains form highly compact hydrophobic clusters, which are joined by short extended polymer chains. During the transition from the compact to the expanded form, the size of the clusters decreases up to a limit, beyond which the clusters disintegrate completely to an expanded polymer chain. The effect of PMA molar mass and ionic strength on this process was investigated.
The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs) in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA), the cationic surfactant cetyltrimethylammonium bromide (CTAB), and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT–DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity.
Poultry feathers make up for as much as 8.5% of chicken weight and represent a considerable amount of almost pure keratin waste which is not being adequately utilized at the present time. The present study dealt with the processing of poultry feathers through a two-stage alkaline-enzymatic hydrolysis. In the first stage, feathers were mixed with a 0.1 or 0.3% KOH water solution in a 1 : 50 ratio and were incubated at 70°C for 24 h. After adjusting pH to 9, the effects examined in the second processing stage on the amount of degraded feathers were those of proteolytic enzyme additions (1-5%), time (4-8 h) and temperature (50-70°C). Processing feathers in 0.3% KOH and hydrolysing for 8 h in the second stage at 70°C with a 5% dose of enzyme (relative to dry feathers weight) produced approx. 91% degradation. Keratin hydrolysate is distinct for its high nitrogen content and reasonable inorganic solids level. Two-stage technology of alkaline-enzymatic hydrolysing of poultry feathers in an environment of 0.3% KOH achieves high efficiency under quite mild reaction conditions (temperature not exceeding 70°C with pH in a mildly alkaline region), and is feasible from an economic viewpoint. Keratin hydrolysate can find particular application in packaging technology (films, foils and encapsulates).
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