Search results for "plastic"
showing 10 items of 7296 documents
Rheological and mechanical properties of biodegradable nanocomposites
2018
Polymer nanocomposites have gained huge interest over the last decade. However, traditional thermoplastic nanocomposites do not match the rising concern about environmental issues. Therefore, during the last years, the search for biodegradable polymer nanocomposites is gaining importance. Most of biobased (i.e. based on biodegradable/bioderived polymer matrices) nanocomposites have poly(lactic acid), PLA, as matrix. However, it is of clear interest to take into account also different biobased polymer matrices, such as MaterBi. In this work, we prepared bionanocomposites containing MaterBi or a PLA-based polymer matrix, with two different kinds of nanofillers (organomodified clay and nanosiz…
Structural modifications in an irradiated ethylene-vinyl alcohol copolymer
1982
Extraction experiments and calorimetric measurements have been performed, on a commercial ethylene-vinyl alcohol copolymer irradiated in the dose range 0–20 Mrad.
Photodegradation of polyglycidol in aqueous solutions exposed to UV irradiation
2011
The photodegradation of polyglycidol in aqueous solution with UV wavelength of 254 nm was investigated. The experiments were carried out in air at a constant temperature and the photodegradation of polyglycidol (PGl) was compared to that of poly(ethylene oxide) (PEO), the most widely studied polyether. Size exclusion chromatography with multiangle light scattering detection (SEC-MALLS) was used to measure the changes in the molar masses and molar mass dispersities of polymers during degradation. The molar mass of PGl decreased dramatically during the first period of UV irradiation and then gradually approached a limiting value of 17,000 g/mol, regardless of the initial polymer concentration…
Effect of carboxymethyl cellulose concentration on rheological behavior of milk and aqueous systems. A creep and recovery study
2009
Carboxymethyl cellulose (CMC) is an anionic polysaccharide used mainly as stabilizer and thickener agent. The purpose of this study was to investigate the effect of CMC concentration on viscoelasticity of dairy and aqueous model systems through the analysis of creep and recovery tests. The viscoelastic properties of different concentrations of CMC (0.75, 1.00, 1.25, and 1.50% w/w) in two milk systems (skimmed milk and whole milk) were compared with those of the same concentration of biopolymer in aqueous solution. Creep curves were fitted to a six parameter mechanical model (Burger + Kelvin-Voigt), whereas an empirical equation was used for recovery. The creep and recovery properties of sam…
Photoswitchable Smectic Liquid-Crystalline Elastomers
2005
We succeeded in the synthesis of azo side chain containing polysioxanes with broad smectic C* and A phases. In these polymers the phase transition temperatures can be shifted reversibly by up to 17°C by irradiation with UV (cis) or VIS (trans) light. Thin films of these polymers in the smectie phase (both on substrates and as free-standing films) orient perfectly in a homeotropic manner. As a consequence, the aze chromophores do no longer absorb during a perpendicular illumination with light (dichroism). It is thus possible to crosslink these films photochemically to prepare photoswitchable smectic LC elastomers.
Amino-functional polyethers: versatile, stimuli-responsive polymers
2020
Due to the increasing demand for “smart” materials and systems e.g. for actuators, microvalves, but also for drug delivery, electrooptical devices and many other applications, multi-stimuli responsive materials such as amino-functional polymers are attracting increasing attention in recent years. The hydrophilic character and excellent biocompatibility of the polyether backbone, in combination with multi-stimuli responsive amine moieties, offer intriguing opportunities for a wide range of applications, such as bioconjugation, stimuli-responsive drug delivery and surface modification. Furthermore, the controlled introduction of amino-functionalities at the polyether backbone via copolymeriza…
Einfluss des polymerrückgrats auf eigenschaften von thermoplastischen elastomeren
1992
4-Urazoyl benzoic acid groups were statistically attached to various hydrocarbon elastomers, polar elastomers and partially crystalline polymers via a polymer-analogous reaction. DSC, FTIR, stress-strain experiments and dynamic-mechanical analysis were used to analyse whether these systems, analogous to functionalized polybutadienes, would form ordered supra-molecular structures of the polar side-groups that would lead to a thermoreversible crosslinking. While the structure formation is suppressed for elastomers with a large cross-sectional area of the chain (e.g. butyl rubber) or polar side-groups, (e.g. polychloroprene), the mechanical propertie can be controlled by balancing supermolecul…
Determination of χ from liquid-liquid phase data in ternary polymer systems (solvent/polymer/polymer) with hydrogen bonding
2008
Two different models accounting for the dependences of χ and g interaction parameters on both temperature and composition have been applied to different ternary polymer systems (TPS) solvent(1)/polymer(2)/polymer(3). The ana- lyzed TPS have consisted on ten different polymer mixtures in chloroform as common solvent that can specifically interact via hydrogen bond. Experimental ternary phase diagrams determined by liquid chromatography were taken from literature. The application of the two models to the experimental data have served to obtain χij and gij interaction parameters for all the binary ij (ij = 12, 13, 23) interactions established between the three components of the system, with si…
Detection of the liquid ? liquid demixing by differential scanning calorimetry
1983
From theoretical considerations it is concluded that the demixing temperatures of moderately concentrated polymer solutions should manifest themselves in a change of the slope of the corresponding DSC trace; the effects are expected to suffice for detection by means of the commercially available dual furnace instrument DSC-2C from Perkin-Elmer.
Controlled Synthesis of Reactive Polymeric Architectures Using 5-Norbornene-2-carboxylic Acid Pentafluorophenyl Ester
2007
Exo-5-norbornene-2-carboxylic acid pentafluorophenyl ester was synthesized from 5-norbornene-2-carboxylic acid and polymerized by ring-opening metathesis polymerization. The obtained polymers were soluble polymeric active esters that could be used for the preparation of multifunctional polymers. The molecular weight of the polymers was controlled by variation of the monomer to initiator ratio. The precursor polymers reacted quantitatively with primary and secondary amines. Time resolved FT-IR studies at different temperatures of the polymer analogous reactions were performed and rate constants were determined.