Volume 39, Issue 8 -

Natural polymers are being investigated with renewed exuberance as they have a tremendous unexploited potential. During the past few decades, much interest has developed in the biopolymer-based materials due to their biodegradable, nontoxic, biocompatible and non-allergic nature. Chitosan (CS) is the second most abundant naturally occurring amino polysaccharide after cellulose and is extracted from the shells of sea crustaceans. The primary amine group in CS is responsible for its various properties and it is derived from the deacetylated form of chitin. Its biocompatible, nontoxic, biodegradable and antimicrobial properties have led to significant research towards biomedical applications, such as tissue engineering, wound healing, drug delivery, obesity treatment, etc. This review summarizes the present work done by researchers in prospects of CS and its numerous applications in the biomedical field.

Polystyrene-based wood plastic composites (WPCs) containing ammonium polyphosphate (APP) and iron (Fe) powder were prepared in this work by solution blending with the aid of an alternating magnetic field. The mechanical, electrical, thermal and fire performances of the WPCs were analyzed through mechanical testing, thermogravimetry and CONE calorimeter. The addition of Fe powder decreased the tensile strength and increased the impact strength. The APP promoted the formation of sufficient char on the material’s surface and enhanced the flame retardant properties. Furthermore, an alternating magnetic field was used to align the Fe powders. After the magnetic treatment, the electrical conductivity and thermal properties were found to increase considerably compared with those without treatment. The Agari model presented the most reasonable prediction of thermal conductivity as a function of Fe content among three classical thermal conduction models. According to the morphological observations, the iron particles in the composites tended to rearrange along the direction of the magnetic field after treatment, resulting in the enhancement of both thermal and electrical conductivities. The prepared WPCs in this study exhibited good flame retardant properties together with the acceptable mechanical properties of the composites.

Testing of the correlation between physical properties of natural resins such as microhardness, density and UV-excited fluorescence emission with their age, geological conditions, botanical and geographical origin and chemical structure was performed. These physical parameters, especially microhardness, are the result of resins fossilization processes like cross-linking and polymerizations of compounds present in the fossils. In addition, hardening of the resins may be also an effect of miscellaneous chemical processes induced by various environmental, biological and geological conditions. The principal component analysis found that the correlation of microhardness, density and fluorescence intensity with the resin age is quite low. The results suggest that variability of physical properties is caused by geographic location and locally occurring geological conditions. The physical properties of natural resins are most strongly correlated with chemical structure and geographic location. The resins with higher microhardness values come from marine environment depositions. The same trend was observed for resins affected by volcanic activity. Moreover, high fluorescence intensity was also observed for resins affected by above mentioned geological conditions. However, the density values of tested resins revealed the lowest correlation with their age, botanical source and geological history.

In this study, the effect of paraffin (PR) and copper (Cu) incorporation in polycarbonate (PC) was investigated using differential scanning calorimetry (DSC). The effect of PR incorporation in PC was investigated using thermogravimetric analysis (TGA). The effect of thermal treatments on thermophysical properties was studied in PC/PR and PC/Cu composites by using the hot-disk method and a periodic method (DICO). Specimens were heated at 160°C (T g  + 15°C), then two different cooling methods were employed: furnace cooling (annealing) and water cooling (quenching) at 0°C and 35°C. The DSC results showed that a solid-liquid transition occurred in all PR formulations, as well as showed the plasticizing role of the PR additive. Thermal stability decreased with the addition of PR. Thermal conductivities (λ) increased with increasing Cu content and decreased with PR additive content, and the annealed samples showed a higher thermal conductivity (λ) than quenched ones. Meanwhile, a small difference between the thermal conductivity of the DICO samples and the hot-disk samples was noticed.

In this work, a novel hydrophilic reactive polyurethane (HRPU) material and HRPU-based composite materials were prepared and used as chemical anti-water erodibility materials for Pisha sandstone. The compressive strength, surface hardness, penetrability and water contact angle were investigated. The results showed that the deformation rate of Pisha sandstone sprayed with HRPU/ethylene-vinyl acetate (EVA) material was approximately 15%, significantly larger than that of other Pisha sandstone samples, while the compressive strength was significantly improved, providing a good penetrability to form a hydrophobic consolidation layer, locking the water in soil. Meanwhile, the micro-morphology of Pisha sandstone was observed by scanning electron microscopy (SEM) images and the water retaining ability of HRPU/EVA material was discussed in detail. The results showed that the water content of Pisha sandstone sprayed with HRPU/EVA material could reach more than 20%, even after 16 h, which presented an excellent water retaining ability. In addition, the anti-water erodibility of Pisha sandstone with HRPU/EVA was improved to prevent soil and water loss, and provide some feasibility for growing plants. Therefore, it could provide a new material and idea to protect the Pisha sandstone area and other erosion areas.

In this study we have prepared flexible gelatin/sericin/clay blend films for packaging applications of hygiene products. Gelatin/sericin (3:1, 1:1 and 1:3 w/w ratios) films were prepared using glutaraldehyde as a crosslinking agent and glycerol as a plasticizer by the solution casting method. The concentrations of gelatin and sericin were optimized on the basis of their mechanical properties. Closite 30B and copper-modified montmorillonite clay (with concentration of 1–5%) were incorporated into the optimized gelatin/sericin blend films in order to improve the mechanical and antimicrobial properties. The water vapor transmission rate of the film samples was also studied. The soil burial test showed very good biodegradability of the blends films. The antimicrobial testing revealed efficient activity of these blend films against Gram-positive ( Staphylococcus aureus ) and Gram-negative ( Escherichia coli ) bacteria. Hence, on the basis of the above-mentioned properties, these films can be considered as promising candidates for packaging of hygiene maintenance products.

Polymer-based nanofibers are good candidates for medical textiles due to their excellent properties including high surface area, breathability and flexibility. Doping polymer nanofibers with different nanoparticles enhances their existing properties. In this study, electrospun polyamide 6,6 (PA6,6) composite nanofibers containing ZnO nanoparticles (<50 nm) in different amounts (1%, 3% and 5%) were first produced by electrospinning technique; then, these nanofibers were coated with sol-gel ZnO solution (0.5 m ) via dip coating method at 1000, 3000 and 5000 μm/s speeds. The sol-gel coating process increased the breaking strength of nanofiber mats, while the incorporation of ZnO nanoparticles into the polymer nanofibers reduced. Compared to pure PA6,6 nanofiber mats, the ZnO sol-gel coated samples and doped nanofibers had lower reflectance values. In addition, the reflection values decreased as the additive and coating speed increased.

Composites based on commercial thermoplastic polyurethane resin (PU) with three different types of carbon nanotubes (CNT), in 0.5% concentration, were prepared and applied on an AA 7075 aluminum surface. CNT unfunctionalized, CNT functionalized with carboxylic groups, and CNT functionalized with amine groups were tested. The composites were evaluated by optical microscopy, adhesion, impact strength, salt spray, and electrical conductivity. In addition, a wave-guide technique between 8.2 and 12.3 GHz was used to measure the electromagnetic properties of the composites. The results showed that the CNT functionalized with amine group (NH 2 ) presented a good interaction of the PU resin, thus forming a level and uniform film. The analyses of adhesion, direct impact, and salt spray showed that all samples presented excellent performance. Although the samples presented a low electromagnetic performance, an emerging potential for electromagnetic shielding was noticed.

The purpose of this work was to study the causes of the formation of nonlinear and spin modes in the process of frontal polymerization (FP). The latter is an autowave process of the propagation of polymerization heat waves, and is a nontraditional method for the synthesis of various polymers and polymeric composites. Monomers of metal-complexes of acrylamide with and without additions of inert and nano-fillers were chosen as objects of study. Research data on dilatometric analysis, as well as on kinetics and macrokinetics of the polymerization processes of the monomers in frontal mode are presented. On the basis of the results obtained, a conclusion was drawn on the stability loss and transition boundary from a stationary mode to nonstationary one during FP. It was shown that, during the polymerization processes, shrinkage of the resulting polymer composites occurs, commensurate with the phase of the heat wave oscillations, which disturbs the propagating heat waves from layer to layer and violates the stationarity of the process. This, in turn, results in the formation of spin-like rings and a nonstationary mode of FP.

Regardless of colouration for functional or aesthetic purposes, technical polymer parts, like gears, require consistent properties. However, there is a lack of research into the effect of colourants on the tribomechanical properties of gears. Therefore, the effects of two pigments, titanium dioxide (white) and chrome antimony titanium oxide (yellow), and three delivery methods, masterbatch, liquid colour and direct compounding, on part morphology, dimensions, tribological and mechanical performance of injection-moulded polyoxymethylene (POM) spur gears are investigated in this paper. The white pigment accelerates the crystallisation of POM, causing fine and highly-crystalline morphological structures and smaller dimensions. However, the yellow pigment decelerates crystallisation, resulting in a coarser morphology with highly crystalline core material and bigger parts. Furthermore, the delivery method affects only the tribomechanical properties. Using a masterbatch decreases loads at break and increases deflection at break, since the carrier material acts as an impact modifier and a weak spot. The liquid colour decreases wear due to lubricating properties, whereas the pure pigments increases abrasion, especially in combination with a coarse microstructure. However, the effects of carrier systems and changes in morphology are always superimposed. Considering the performance and tolerance of technical components, colourants have to be carefully selected to ensure beneficial properties.