Band 32, Heft 2

Chitin is one of the most abundant biopolymers, but due to its high crystallinity, it is completely insoluble in most organic and inorganic solvents. Chitin is soluble only in solvents that can destroy intersheet and intrasheet H-bonds, and many of these solvents are toxic, corrosive, nondegradable, or mutagenic. Because of these drawbacks, there is a search for more environmentally friendly solvents for chitin. It has been shown that ionic liquids (ILs) can dissolve chitin at elevated temperatures (80°–110°C) or with application of microwave irradiation. The highest solubility of chitin in an IL was about 20% (1-ethyl-3-methylimidazolium acetate), whereas chitin was shown to be insoluble in 1-allyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium formate. Dissolved chitin can be regenerated by mixing with water or methanol, where the polymer precipitates from the solution. X-ray diffraction patterns of native polymer and precipitates have been compared and only small changes in crystallinity have been observed. In addition, Fourier transform infrared spectra remained similar for both forms of chitin, native and regenerated. Presented data hold great promise for the improvement of the chemistry of chitin and open new routes for chemical and enzymatic modifications of this polymer.

The diversified properties of polyurethane (PUR) foam plastics result from differences in the receipts applied during their preparation. The preparation of rigid polyurethane-polyisocyanurate foams (PUR-PIR) with application of different amounts of polyvinyl chloride (PVC) s-70 as a filler is described in this study. It was found that application of PVC s-70 has an effect on the prolongation of processing parameters, i.e., start time and, to a greater extent, expansion and gelation times. Moreover, it was found that introduction of filler into the foam composition causes a reduction in the capacity of the foam to absorb water; however, a distinct change in the amount of closed cells in comparison with standard foam was not observed. A favorable effect of filler on brittleness and flammability of PUR-PIR foams (significant reduction) as well as on compressive strength and softening point (a significant increase in these values) was observed.

Models to predict the evolution of the morphology of immiscible liquid-liquid systems and of solid agglomerates dispersion in single-screw extruders were adapted to compute global distributive and dispersive mixing indices. Using these indices, the direct assessment of the mixing ability of a given screw or a comparison of distinct screws becomes readily available. In the case of liquid-liquid systems, the degree of distributive mixing is computed from the extent of deformation of the individual drops, whereas the degree of dispersive mixing is determined by the reduction in drop size. For solid-liquid systems, distributive mixing is quantified by a normalized Shannon entropy, whereas dispersive mixing is defined from the extent of size reduction. The effect of material properties, operating conditions, and geometry of the screw and die is investigated. Finally, the indices are used to determine ( via optimization) the operating conditions and the screw geometry that maximize the mixing efficiency.

The application of the extrusion embossing process is a fast and cost-effective way to produce large-scale films with structured surfaces. In principle, microscopic and macroscopic surface structures can be manufactured this way. Particularly for the fabrication of microscopic structures, the reproduction accuracy can be remarkably improved by applying variothermal heating concepts for the embossing roll. In this article, two possible heating concepts are investigated: one laser-based and another using an inductor. The generated temperature profile along the circumference of the embossing roll is studied, taking the material of the embossing roll as well as different processing parameters into account. Both external heating systems (laser vs. inductor) are tested and compared. Furthermore, the improvement of the accuracy of the replicated microstructures is examined.

Well-defined poly(styrene-co-butyl acrylate) nanocomposite latexes were synthesized via reverse atom transfer radical polymerization (RATRP) in miniemulsion. Successful RATRP was carried out by using a hydrophobic ligand of 4,4’-dinonyl-2,2’-bipyridine (dNbpy) and a cationic surfactant of cetyltrimethylammonium bromide (CTAB). Dynamic light scattering (DLS) results show that droplets and particles with sizes in the range of about 170 nm were formed. Overall, conversion and molecular weight evaluation were performed by using gravimetry and size exclusion chromatography (SEC), respectively. Increasing nanoclay loading resulted in an increase in the conversion and molecular weight of the nanocomposites. However, polydispersity index (PDI) values increased by adding nanoclay content. Thermal stability of all the nanocomposites improved in comparison with the neat copolymer, according to the thermogravimetric analysis (TGA) results. Differential scanning calorimetry (DSC) results showed that the glass transition temperature (T g ) increased by increasing nanoclay content. Scanning electron microscopy (SEM) images of the nanocomposite with 1 wt% of nanoclay showed a monodisperse distribution of spherical particles, with sizes in the range of approximately 170 nm, as confirmed by the DLS data. Similarly, transmission electron microscopy (TEM) images show that clay layers are delaminated and well dispersed in the matrix of nanocomposite with 1 wt% clay content.

The properties of microcellular polylactic acid (PLA)/organic modified montmorillonite (OMMT) clays and PLA/sericite powder (SP) nanocomposites were investigated and compared in terms of thermal property, rheological property, particles dispersability, and cell microstructure. The batch-foaming process uses carbon dioxide as the physical blowing agent. According to the transmission electron microscopy and X-ray diffraction characterization, fillers (i.e., OMMT and SP) have good dispersions in PLA matrices. The thermal and rheological properties of solid PLA composites are demonstrated by differential scanning calorimetry and capillary rheometer, respectively. The microcellular morphology of fractured cross-sectional surfaces is characterized by scanning electron microscope. The batch-foamed PLA composites have more uniform cells in comparison with foamed pure PLA parts due to the mineral particles.

Hibiscus sabdariffa stem fiber has 73.9% cellulose, high mechanical strength and is found in abundance throughout the world. Hibiscus sabdariffa graft copolymers were synthesized, characterized by FTIR, XRD, TGA, DTA, and SEM techniques, and evaluated for physicochemical changes in properties such as moisture absorption, chemical resistance against 1 n NaOH and 1 n HCl. These graft copolymers were reinforced in phenol-formaldehyde polymer matrix to form biocomposites that were characterized by advanced techniques and evaluated for physicochemicothermal resistance. The mechanical strength was accessed on the basis of hardness, flexural strength, Young modulus, and stress at the limit of proportionality, which was found to be high. These novel materials could have numerous scientific and industrial application to pave the way for development of technology.

Coir fibers were modified with ethyleneglycol dimethacrylate (EGDMA)+MeOH solutions under thermal curing method at different temperatures (50°C–90°C) and curing times (30–70 min). Monomer concentration, curing temperature, and curing time were optimized in terms of grafting and mechanical properties, and 50% EGDMA, 70°C and 50 min curing time, respectively, registered better performance. Coir fibers were pretreated with ultraviolet radiation at different doses, soaked in optimized solution, and cured under optimum conditions. These fibers showed improved properties than EGDMA-treated fibers. Water uptake and simulated weathering test of untreated and treated fibers were studied.

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