Band 35, Heft 4

A chitosan-based hydrogel network was crosslinked with genipin; the crosslinked and uncrosslinked hydrogels were prepared and studied. Uniformly distributed silver cluster particles (AgCPs) were prepared using these hydrogel networks as a carrier via in situ reduction of silver nitrate (AgNO 3 ) in the presence of sodium borohydride (NaBH 4 ) as a reducing agent; UV irradiation reduction was also done. Fourier transform infrared (FTIR) spectroscopy studies of the hydrogels gave results on the decree of crosslinking and some indication on the presence of the AgCPs. The spectrophotometric analysis indicated the presence of AgCPs, as a peak appeared around 400 nm. The microscopy analysis gave images of the presence of AgCPs and their size; it showed that the crosslinked hydrogels have uniformly distributed AgCPs and as the crosslinking increased, the AgCPs size decreased. The studies on the increasing concentration of AgNO 3 solution gave an increase AgCPs size; the maximum size of AgCPs clusters was ∼0.2 micron in uncrosslinked chitosan. It was demonstrated, by using Escherichia coli ( E. coli ) bacterium, that the AgCPs hydrogel can be effectively employed as antibacterial material.

Liquid core capsules have been widely used in various biotechnological applications. The capsules could be formed by the simple extrusion dripping method. However, the method requires strict control of several process variables in order to form spherical capsules. The aim of this study was to systematically investigate the influence of process variables of the method on the capsule size and shape. The results showed that the capsules diameter was decreased when the concentration of alginate solution was increased. The capsule diameter was increased when the gelation time and dripping tip diameter were increased. The membrane thickness of the capsules was significantly increased by the concentration of calcium chloride, gelation time and dripping tip diameter. However, the concentration of alginate gave the opposite trend on the membrane thickness of the capsules. As a recommendation, uniform and spherical alginate liquid core capsules could be formed when concentration of calcium chloride was >10 g/l, the concentration of alginate solution was >5 g/l and <20 g/l, gelation solution height in between 1.7 cm and 3.2 cm, and stirring rate of the gelation bath was in the range of 400–500 rpm.

This work ascertains the effect of the degree of hydrolysis of polyvinyl alcohol under extended interaction with 2-hydroxypropanoic acid (lactic acid). Systems based on three different types of polyvinyl alcohol matrices (of hydrolysis degree 80, 88 and 98 mol%) and lactic acid were characterized according to their physicochemical, mechanical and thermal properties. An agar diffusion test and the dilution and spread plate technique were conducted to facilitate antibacterial activity to counteract Staphylococcus aureus and Escherichia coli. A mathematical model was applied to the experimental data to estimate the antibacterial efficacy of the resultant flexible films.

Multi-functional trisilanol phenyl (TSPH) and trisilanol isobutyl (TSIB) polyhedral oligomeric silsesquioxane (POSS) have been used in the formulation of advanced polystyrene (PS)-zinc oxide (ZnO) nanocomposites. The neat matrix and PS/ZnO-based nanocomposites have been characterized through rheological, morphological, mechanical, and dynamic thermo-mechanical analysis. Both TSPH and TSIB are able to improve the dispersion of ZnO into the polystyrene matrix; furthermore, adding TSIB leads to better results because it facilitates better solubility into the PS matrix and interaction/reaction with the ZnO nanopowder. Finally, the optical properties and photo-oxidative resistance of the nanocomposite films have been evaluated. The POSS molecules synergistically interact with ZnO nanopowder in the protection of PS matrix against photo-oxidative process. The nanocomposite films containing both ZnO and POSS molecules, particularly TSIB, exhibit better UV-shielding properties than the PS/ZnO one, without loss of optical transparency.

The correlation between the behavior of a polyvinylidene fluoride (PVDF) membrane toward protein binding at different physicochemical environments was investigated. The PVDF membrane was first fabricated and characterized to understand its morphological, polymorph and intrinsic characteristics. The results confirmed that the membrane had a microporous, symmetric structure and high hydrophobicity and electronegativity. The membrane was further tested under different physicochemical environments by modifying the type of protein and pH medium used. The results showed that different proteins and pH values contribute to different membrane-protein binding mechanisms. Overall, the results of PVDF membrane-protein binding were satisfactory and demonstrated the ability of the membrane to capture various proteins or reagents.

Polyamide 11 (PA 11)/polyamide 12 (PA 12) blends with and without liquid polybutadiene (LB) containing isocyanate end groups (LBD) were prepared in the Brabender plastograph. The rubber was added in order to increase the impact strength of the polyamides. Tensile strength and elongation at the upper yield point and hardness were also measured. Thermal properties were determined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Fourier transform infrared (FTIR) spectroscopy was used to determine functional groups of polyamides and to reveal possible reactions between the polyamides and LBD. Intrinsic viscosity, measured by an Ubbelohde viscometer, was used to calculate molar mass. The LB has been found as a useful modifier of impact strength.

Poly allyl diglycol carbonate (PADC) has been irradiated by ArF(UV)-laser light (wavelength 193 nm) at different fluences and pulse numbers in order to investigate the photo degradation of chemical molecular structure. The photo-induced chemical reactions and photo-degradation mechanism at the irradiated polymer surface have been clarified by ultraviolet-visible (UV-Vis) spectrum and FTIR spectrum analyses. Optical and surface modifications of irradiated samples have been studied by refractive index and water contact angle measurements. Using the UV-Vis spectra, Urbach’s energy ( Eu ), indirect and direct band gaps energy ( Eg ) of unirradiated and UV-laser irradiated samples were determined. The UV-Vis and FTIR spectra analysis show that photo degradation and photo oxidation of polymer caused free-radical generation. In the presence of air, free-radical generation induced by UV-laser light followed by bond scission and cross-linking process will finally produce new products. New product generation can be affected on chemical and optical properties of irradiated samples. The irradiated PADC at various fluences in the range of medium to high demonstrate improvement of refractive index, and this is highly important in plastic lens technology. The obtained results reveal that chemical modification could affect track parameters when PADC is used as a nuclear track detector.

Polyamide 6 (PA6) matrix composites were prepared by incorporating multiwalled carbon nanotubes (MWCNTs) or by co-incorporating MWCNTs and carbon black (CB) of different contents. The thermal, mechanical and tribological properties of the composites were investigated using thermogravimetric analysis, nano-indentation, ball-on-disc micro-tribological test and micro-scratch test. It was found that a proper carbon filler content in the composites promoted the thermal stability of the composites, but an excessive loading of carbon fillers degraded the thermal stability of the composites. Although the hardness of the composites decreased with increased carbon filler content, the composites filled with mixed MWCNTs and CB had a higher load bearing capacity than the ones without CB. The tribological results indicated that the increased carbon filler content apparently lowered the friction coefficient of the composites due to the lubricating effect of the carbon fillers. It was also observed that the friction coefficients of the PA6-MWCNT-CB composites were consistently higher than those of the PA6-MWCNT composites due to the lower wear resistance of the PA6-MWCNT-CB composites. The scratch resistance of the composites decreased with increased carbon filler content due to the reduced cohesive strength of the composites.

This article describes the laboratory tests necessary to identify the mechanical properties of the polyvinylidene fluoride (PVDF)-coated fabrics named Precontraint 1202S and Precontraint 1302S. First, a short survey of the literature concerning the description of coated woven fabrics is presented. Second, the material parameters for PVDF-coated fabrics are specified on the basis of biaxial tensile tests. A comparison of the 1:1 biaxial and the uniaxial tensile tests results is also given. Additionally, biaxial cyclic tests were performed to observe the change of immediate mechanical properties under cyclic load. The article is aimed as an introduction to a comprehensive investigation of the mechanical properties of coated fabrics.

The processing, characterization, and wear response of a new class of natural fiber ( Luffa cylindrica ) hybrid composite are described. Composite laminates were fabricated by using the hand lay-up technique. Composites were made with a total of four piles by varying the number and position of glass layers so as to obtain different stacking sequences. The erosion rates of the composites were evaluated by varying the impingement angle, particle speed, and dose of the impinging particles. An experimental plan based on the Taguchi technique was used to achieve the erosion in a controlled way. The study reveals that the impact velocity is the most significant factor influencing the erosion rate of the hybrid composite.

Poly(lactic acid) (PLA), used as a matrix, was mixed with wood fibers, coffee grounds, fertilizer and a foaming agent to develop an ecofriendly material to be used in horticulture. For this application materials should have mechanical properties similar to PLA, increased biodegradability and a lower price than currently used materials. The new materials were prepared by melt processing in an internal mixer at 190°C and were characterized by several techniques. The mechanical properties of the biocomposites, measured by flexural tests, were similar to neat PLA, even with a reduction of 40 wt% of polymer. Biodegradation assessment by composting tests in an aerobic environment demonstrated that the green materials exhibited higher biodegradability than PLA. Biocomposites containing wood fibers and fertilizer were revealed to be the most suitable for horticulture application, as these can combine mechanical properties, biodegradability and fertilizer release. Moreover, this green material has two main advantages: it can be prepared using materials from natural resources, and it does not generate any residue after use.