Search results for "Gradation"

Control of end-of-life oxygen-containing groups accumulation in biopolyesters through introduction of crosslinked polysaccharide particles

2021

The formulation of bio-based materials with good performance in service and controlled end-of-life is imperative for an effective circular economy. In this work, an innovative approach to induce and control the end-of-life of biodegradable polyesters through introduction of crosslinked polysaccharide particles is proposed. Chitosan (Ch) has been subjected to ionotropically crosslinking and then added to polylactic acid (PLA) at different amounts (1.0–4.0%w) by melt mixing. All obtained results suggest that the addition of crosslinked Ch (cCh) particles does not modify significantly the investigated biopolyester properties. Specifically, the thermal analysis of the composites reveals that th…

Photooxidation and Stabilization of Photooxidized Polyethylene and of its Monopolymer Blends

2003

The increasing use of products from recycled polymers, or from blends with recycled polymers exposed to the outdoors, implies the need for good weathering resistance. This is particularly important when the recycled material comes, in turn, from products exposed during their lifetime to the sun. In this case the presence of C=O groups in the macromolecular chains strongly increases the photooxidative degradation kinetics of these secondary materials. In this work the change of the photooxidative degradation of blends of virgin and photooxidized polyethylene was evaluated as a function of the C=O content present in the material. As expected, the presence of the C=O groups strongly increases …

Influence of hydrogen peroxide on the kinetics of phenol photodegradation in aqueous titanium dioxide dispersion

1990

Abstract The influence of hydrogen peroxide on the phenol photodegradation rate under near UV radiation was investigated in homogeneous and heterogeneous systems: the heterogeneous systems were aqueous dispersions of titanium dioxide (anatase). The hydrogen peroxide photodecomposition reaction was also investigated for all the systems used. The highest rate of phenol photodegradation was observed in the heterogeneous system for the contemporary presence of hydrogen peroxide and oxygen. The rate equations for phenol photodegradation and hydrogen peroxide photodecomposition for both systems were obtained. A mechanistic model able to explain the main experimental results is also proposed.

Influence of operational variables on the photodegradation kinetics of Monuron in aqueous titanium dioxide dispersions

1994

The degradation of Monuron [N′—(4-chlorophenyl)—N, N dimethyl urea] in aqueous TiO 2 dispersions irradiated in the near-UV region has been investigated using a Pyrex batch photoreactor. The influence on the degradation kinetics of pH, initial Monuron concentration and catalyst concentration has been studied. The mineralization of the pollutant was also investigated. Measurements of photon absorbed flows allowed to determine the quantum yield values; they were found to increase by increasing the initial pH of the dispersion.

Photocatalytic oxidation of acetonitrile in aqueous suspension of titanium dioxide irradiated by sunlight

2004

The photocatalytic oxidation of acetonitrile (CH3CN) was carried out in aqueous suspensions of polycrystalline TiO2 P25 Degussa irradiated by sunlight. A plug flow photoreactor in a total recycle loop was used for carrying out reactivity experiments in which the concentrations of acetonitrile, of its intermediate oxidation products and of not-purgeable organic carbon (NPOC) were monitored. The influence of the presence of strong oxidant species (H2O2, S2O82−, ClO−) on the process rate was studied. The dependence of acetonitrile photo-oxidation rate on the substrate concentration and on the catalyst amount was also investigated. The photodegradation rate of substrate and NPOC followed first …

Untersuchungen zum oxidativen Abbau nativer Cellulose, 2. Einfluß der Alkalibehandlung auf die Viskositäts-Molekulargewichts-Beziehungen

1974

Um die Kinetik des oxidativen Abbaus nativer Cellulose viskosimetrisch verfolgen zu konnen, mussen neue [η]-M-Eichbeziehungen aufgestellt werden, da die Behandlung der Cellulose mit konzentriertem Alkali den Staudingerindex [η] erniedrigt, ohne das Molekulargewicht M zu verandern. Es wurden zwei Reihen oxidativ abgebauter, verschieden lange mit Alkali vorbehandelter Cellulosen hergestellt und an diesen die Konstanten der Kuhn-Mark-Houwink-Gleichung fur die Cellulosenitrate in Aceton und die Cellulosen in Cuoxam (Cu(NH3)4(OH)2) durch Vergleich mit Lichtstreuungsmessungen bestimmt. For kinetic studies of cellulose degradation by molecular oxygen it is necessary to establish new [η]-M-relation…

Strukturuntersuchung von polyestern durch direkten abbau im massenspektrometer, 1. Polyester der terephthalsäure

1976

Die Abbaureaktionen von Poly(athylenterephthalat) (1a), Poly(tetradeuteroathylenterephthalat) (1b), Poly(trimethylenterephthalat) (1c) und Poly(tetramethylenterephthalat) (1d) im Massenspektrometer wurden untersucht. Hierzu wurden die Polymeren direkt in der Ionenquelle des Massenspektrometers pyrolysiert und die entstehenden thermischen Bruchstucke durch Elektronenstos ionisiert und fragmentiert. Die thermisch- und elektronenstosinduzierten Abbaureaktionen lassen sich nebeneinander nachweisen. Die untersuchten polymeren Terephthalate 1a–d folgen in beiden Abbauschritten den gleichen Mechanismen und konnen anhand ihrer Pyrolyse-Massenspektren unterschieden werden. The degradation reactions …

Recycling of heterogeneous plastics wastes. II—The role of modifier agents

1993

Abstract Recycling of mixed plastics waste, mainly composed of PEs, PET and PVC has been carried out by blending with recycled polyethylene. Although the extrusion of these blends has been carried out at high temperatures, the degradation of the PVC was modest due to the short residence times. The mechanical properties of these secondary materials, up to about 30% of mixed plastics waste, are very similar to those of the recycled polyethylene, except for the elongation to break. By adding some modifier agents, the elongation at break and especially the impact strength can be further improved.

Soda-AQ pulping of reed canary grass

2001

Abstract Delignification of reed canary grass (Phalaris arundinacea L.) was carried out by conventional soda-anthraquinone (AQ) pulping under varying conditions selected according to an orthogonal experimental design with four factors (cooking parameters) at three levels each L9 (34). The influence of these four parameters, i.e. effective alkali, EA (12, 15, and 18% on oven dried (o.d.) reed, as NaOH), maximum temperature (145, 155, and 165°C), time to maximum temperature (70, 90, and 110 min), and time at maximum temperature (0, 15, and 30 min) on the pulp properties (yield, kappa number, and viscosity) was studied. Results indicated that, with respect to delignification, EA was the most i…

1976

The thermal degradation of poly(oxycarbonylpentamethylene), (poly-e-caprolactone), (3), was investigated at 220°C and 80 mm Hg under nitrogen. 3 was found to be thermally much more stable than poly(oxycarbonylethylene), (poly-β-propiolactone), (1), although it decomposed faster than poly(oxycarbonyl-1,1-dimethylethylene), (polypivalolactone), (2). The reaction was of the first order with a rate constant of k=6,2.10−4 min−1 and proceeded via a “zipper mechanism” to yield monomeric e-caprolactone. Der thermische Abbau von Poly(oxycarbonylpentamethylen), (Poly-e-caprolacton), (3), wurde bei 220°C im Stickstoffstrom bei 80 mm Hg untersucht. Dabei wurde gefunden, das 3 thermisch wesentlich stabi…