All issues / Volume 10 (2016) / Issue 5 (May)
This is an editorial article. It has no abstract.
This paper deals with the influence of an incubation medium pH on the hydrolytic degradation of a novel thermosensitive biodegradable triblock copolymer based on hydrophilic poly(ethylene glycol) and hydrophobic copolymer poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA), consequently modified at α,ω-ends with itaconic acid (ITA) resulting in α,ω-itaconyl(PLGA-PEG-PLGA). Itaconic acid, obtained from renewable resources, delivers a reactive double bond and carboxylic functional group to the end of PLGA-PEG-PLGA copolymer: this is important for a reaction with biologically active substances. The suitability of the sample degradation was assessed depending on whether the copolymer formed a gel at 37 °C. Two reversible physical sol-gel-sol transitions from a sol (liquid phase) to a gel (solid phase) and back to a sol (suspension) were verified using the tube inverting method. The hydrolytical degradation was evaluated at a physiological temperature (37 °C) in the presence of phosphate solutions, at a pH of either 4.2 or 7.4 by monitoring the decrease of the number average molecular weight of copolymers by GPC. Moreover, the degradation kinetics was confirmed by the HPLC/DAD method, where the increasing amount of final degradation products (lactic and glycolic acids) was detected. The study demonstrated that the carboxylic groups modified copolymer (ITA/PLGA–PEG– PLGA/ITA) is more susceptible to hydrolytical degradation than the unmodified copolymer within first days of degradation at pH 7.4.
Tribological performance of the materials greatly depends on the temperature of the contacting zones and surfaces and hence on the heat conducting behaviour of the materials. Heat conduction of polymers is, however, greatly affected even by a very narrow (few tens of nm) modified layer formed on the surface after subjecting the polymer to plasma treatment. In this article the heat flow inhibiting properties of plasma modified surface layers were investigated on polyethylene terephthalate (PET) and polyamide-6 (PA6) engineering polymers. Nitrogen Plasma Immersion Ion Implantation gave rise to compositional and structural changes of the polymers in a depth of 110 nm. It was found that even this thin layer exhibited significant heat flow inhibiting effect. The modified layer considerably decreased the thermal conductivity coefficient of the treated polymer and resulted in a reduced heat transmission for PET and PA6 by 33 and 28%, respectively. This new information supports and is in accordance with the former tribological results about extra friction heat generation experienced under NPIII surface layer of PA6 and PET during dry sliding.
The study deals with the modification of mechanical properties of poly (!-caprolactone) (PCL)/poly(lactic acid) (PLA) system using the microfibrillar composite (MFC) concept. As the in-situ formation of PLA fibrils by melt drawing was impossible due to flow instability during extrusion, the system was modified by adding halloysite nanotubes (HNT) using different mixing protocols. The resulting favourable effect on the rheological parameters of the components allowed successful melt drawing. Consequently, PLA fibrils formation combined with the reinforcement of components by HNT and increased PLA crystallinity lead to a biocompatible and biodegradable material with good performance suitable for a broad range of applications. The best results, comparable with analogous MFC modified with layered silicate (oMMT), have been achieved at a relatively low content of HNT of 3%, in spite of its lower reinforcing ability in a single nanocomposite. This indicates that modifying MFC by HNT, including fibrils and interface parameters, is more complex in comparison with the undrawn system.
This study investigates the effects of nano carboxylic acrylonitrile butadiene rubber (CNBR-NP) and nano acrylonitrile butadiene rubber (NBR-NP) on the interlaminar shear strength and fracture toughness of carbon fibre reinforced polymer composites (CFRP) with dicyandiamide-cured epoxy matrix. The results show that nano-size dispersion of rubber significantly improved the Mode I delamination fracture toughness (GIC) of the CFRP by 250% and its Mode II delamination fracture toughness (GIIC) by 80% with the addition of 20 phr of CNBR-NP. For the NBR-NP system, the GIC and GIIC delamination fracture toughness of the CFRP were increased by 200 and 80% respectively with the addition of 20 phr (parts per hundred rubber) of nano rubber to the matrix. Scanning electron microscopy (SEM) images of the fracture surface revealed that the toughening was mainly achieved by debonding of the nano rubber, crack path deflection and fibre bridging.
The insoluble (macrogel) and soluble fractions of 11 commercial natural rubber (NR) samples (Technically specified rubber) were separated. Nitrogen titrations and lipid extractions enabled a quantitative assessment of the proteins and extractable lipids in each fraction. Swelling was measured in tetrahydrofuran in order to evaluate the crosslink density (Mc–1) of each macrogel. While the soluble fraction had a high lipid concentration, the majority of non-isoprene compounds of the macrogel were found to be proteins, which accounted for 4.6 to 50.8% (w/w) of the macrogel. Indeed, the macrogels contained less than 0.5% (w/w) extractable lipids. However, our results showed that the soluble fraction contained large quantities of proteins (16–66% of the nitrogen content of the raw NR sample), probably structuring microaggregates. An exponential correlation (R2 > 0.96) was found between the crosslink density and the protein concentration of macrogel, suggesting that proteins are involved in the majority of crosslinks in macrogel.
In this work, a hydrophobic surface of lignocellulosic jute fabric was achieved via the laccase-mediated grafting of octadecylamine (OA) on lignin moieties of jute aiming to improve the interfacial compatibility with the hydrophobic polypropylene (PP) resins in the fiber-reinforced composites. Firstly, the surface and total elemental compositions of the modified jute fabrics were investigated by X-ray photoelectron spectroscopy (XPS) and elemental analysis, respectively. The increases in the surface C/O ratio and total nitrogen content of jute fabrics after the laccase/OA treatment indicated that OA molecules were successfully grafted onto the jute surface mediated by laccase. The grafting percentage of OA on jute fabrics was 0.96%. The surface hydrophobicity of jute fabrics with static contact angle of 112.5°, advancing angle of 116.4° and receding angle of 42.7° supported the presence of nonpolar alkyl chains on the jute surface after the laccase-mediated OA-grafting. The tensile strength, tensile modulus as well as the elongation at break of the hydrophobized jute/PP composites were increased. The fracture surface of the composites became neat and the jute fibers on the section surface were surrounded by PP resins closely, which suggested better interfacial adhesion between the jute reinforcement and the PP resin.
In this study, electrospun polycaprolactone (PCL) fibers are plasma-treated and chemically conjugated with cholesteryl succinyl silane (CSS). In addition to Raman spectroscopy, an immobilization study of DiO as a fluorescent probe of lipid membranes provides evidence supporting the CSS coating of plasma-treated PCL fibers. Further, anti-CD20 antibodies are used as a model protein to evaluate the potential of lipid-mediated protein immobilization as a mechanism to functionalize the CSS-PCL fiber scaffolds. Upon anti-CD20 functionalization, the CSS-PCL fiber scaffolds capture Granta-22 cells 2.4 times more than the PCL control does, although the two fiber scaffolds immobilize a comparable amount of anti-CD20. Taken together, results from the present study demonstrate that the CSS coating and CSS-mediated antibody immobilization offers an appealing strategy to functionalize electrospun synthetic polymer fibers and confer cell-specific functions on the fiber scaffolds, which can be mechanically robust but often lack biological functions.