Search results for "polymers"
showing 10 items of 3567 documents
Effect of alkyl derivatization of gellan gum during the fabrication of electrospun membranes
2021
Electrospun nanofibers based on polysaccharides represent a consolidated approach in Tissue Engineering and Regenerative Medicine (TERM) and nanomedicine as a drug delivery system (DDS). In this work, two chemical derivatives of a low molecular weight gellan gum (96.7 kDa) with aliphatic pendant tails were processed by electrospinning technique into non-woven nanofibrous mats. In order to generate spinnable blends, it was necessary to associate poly vinyl alcohol (PVA). The relationships between the physicochemical properties and the processability via electrospinning technique of gellan gum alkyl derivatives (GG-C8 and GG-C12 having a degree of alkyl chain derivatization of 17 mol % and 1…
Structure–property relationship and controlled drug release from multiphasic electrospun carvacrol-embedded polylactic acid/polyethylene glycol and p…
2018
Electrospinning technologies gained considerable interest over the last decade. In this study, it is proposed a systematic study of polylactic acid/polyethylene glycol (PLA/PEG) and polylactic acid/polyethylene oxide (PLA/PEO) electrospun blends at different concentrations. The effect of blend composition and PEG molecular weight on the morphological and mechanical properties of the mats was evaluated. Furthermore, the kinetic release of carvacrol as model drug in phosphate buffer saline at 37℃ was studied and the data were then fitted using an exponential model. The scanning electron microscopy revealed that the morphology of the mats was strongly dependent on the relative ratio PLA:PEG, …
Model of delamination propagation in brittle-matrix composites under cyclic loading
2001
A model of interlaminar fatigue crack growth based on damage accumulation ahead of the crack is proposed. Linear cumulative assumption is used for damage estimation, and a quadratic failure criterion is applied for complex interlaminar loading. Model parameters are determined from mode I and mode II fatigue tests, and used to predict mixed-mode delamination propagation rate. Comparison of theoretical prediction with mixed-mode test results for different brittle graphite FRP at several mode- and load ratios show reasonable agreement.
Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechani…
2012
[EN] This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystalli…
Mechanical properties of pultruded glass fiber reinforced plastic after freeze–thaw cycling
2012
The use of pultruded fiber-reinforced plastics in civil infrastructure requires the long-term prediction of their mechanical properties, which should be based on understanding and estimating the processes in the structure under action of aggressive environmental factors: humidity and freeze–thaw cycles. This article reports on results of short-term exposure to severe freeze–thaw cycling in the temperature range from –30°C to 20°C of polyester-based glass fiber reinforced plastic both dry and wet. The effect of freeze–thaw cycling of flat specimens cut from I-beam pultruded profile was estimated by use of three-point-bending tests and dilatometric investigation in the temperature range from…
Thermodesorption of LB-multilayers of metal stearates
1991
Thermodesorption of stearate multilayers containing different metal ions was investigated by Interference-enhanced Reflection (IeR) and Nomarsky microscopy. Heating of samples in air leads to desorption of stearyl chains and to formation of metal oxide clusters. A new approach to build controlled structures was made by preparing a surface with neighbouring hydrophobic and hydrophilic areas. It is shown that arranging inorganic particles in a predetermined way is possible.
Size effects in micro- and nanoscale indentation
2006
Abstract The indentation size effect (ISE) has been studied in single crystals, polycrystals and amorphous solids using the Vickers microhardness test. The ISE is clearly present in single crystals but is absent in fine-grained polycrystals. A size-dependent hardness for amorphous solids is observed only in the sub-micrometre surface layer. The behaviour of the ISE in single crystals for micro- and nanoindentation is compared. Estimates of the surface hardness are made by the extrapolation of the experimental hardness–indentation depth curves. The extrapolated hardness in the surface region reaches values corresponding to the theoretical shear strength. The results confirm the multifarious …
Effect of processing temperature and mixing time on the properties of PP/GnP nanocomposites
2020
Abstract During processing of molten polymers the thermal and mechanical stress acting on the melt in presence of oxygen can induce degradation with a modification of the chemical structure of the polymers. This picture can become even more relevant if the melt is a multiphasic polymer system. In this last case, the effects of the degradation depend also on the presence of a second phase and on the interactions between the two phases. In this work, the effect of the processing conditions, temperature and time, have been considered in order to investigate the thermo-mechanical and thermo-oxidative degradation of nanocomposites made by polypropylene and different contents of graphene nanoplat…
Degradation and Recycling of Films Based on Biodegradable Polymers: A Short Review
2019
The environmental performance of biodegradable materials has attracted attention from the academic and the industrial research over the recent years. Currently, degradation behavior and possible recyclability features, as well as actual recycling paths of such systems, are crucial to give them both durability and eco-sustainability. This paper presents a review of the degradation behaviour of biodegradable polymers and related composites, with particular concern for multi-layer films. The processing of biodegradable polymeric films and the manufacturing and properties of multilayer films based on biodegradable polymers will be discussed. The results and data collected show that: poly-lactic…
Smart hydrogels for novel optical functions
2007
Nanocomposites of inherently conductive polyaniline (PANT) within a highly hydrophilic polyvinyl alcohol (PVA) based hydrogel have been produced by coupling a conventional dispersion chemical oxidative polymerization to a subsequent high energy irradiation step, in order to convert the polymer stabilizing the aqueous dispersion, namely the PVA, into a highly water swollen hydrogel incorporating the PANT particles. The incorporation of the electroactive and "pH-sensitive" polymer into a transparent and highly permeable hydrogel matrix has been pursued as a route to the development of a novel class of potentially biocompatible, smart hydrogels that can respond to changes of the surrounding en…