Search results for "Chain scission"

Über die Stabilität Von Copolymeren aus 1,3,5-Trioxan mit verschiedenen Lactonen

1976

Der thermische Abbau von Copolymeren aus 1,3,5-Trioxan und den Lactonen β-Propiolacton (3-Propanolid), Pivalolacton (2,2-Dimethyl-3-propanolid) und e-Caprolacton (6-Hexanolid) wurde untersucht. Der langsame und vollstandige Abbau der Copolymeren wird zuruckgefuhrt auf 1 eine statistische acidolytische Kettenspaltung durch Carboxyl-Endgruppen, 2 die Abspaltung von Acrylsaure an den sauren Endgruppen, 3 die statistische Kettenspaltung durch Pyrolyse von Esterbindungen vor allem in Sequenzen aus mehreren β-Propiolactonbausteinen. Die Teilreaktionen (1) und (2) konnen durch Zusatz von Butandiol-Diglycidylather-(1,4-Bis(2,3-epoxypropoxy)butan) oder N-(2-Naphthyl)anilin oder von Epoxiden stark ve…

Recycling of dry and wet polyamide 6

2002

Recycling of polycondensation polymers can give rise to secondary materials with good mechanical properties only if a careful drying is carried out before the melt reprocessing operations. The presence of humidity provokes the hydrolytic chain scission of the macromolecules and the consequent decrease of molecular weight and properties. In this work, the drying step was substituted by the addition of an antioxidant that is able to protect the macromolecules because it is the autioxidant is more prone to hydrolysis, thus removing the water from the melt. The mechanical properties of polyamide 6 reprocessed more times in wet conditions and in the presence of this stabilizer are even better th…

Competition between chain scission and branching formation in the processing of high-density polyethylene: effect of processing parameters and of sta…

2009

Two samples of high-density polyethylene with different molecular weight were processed in a batch mixer and the rheological and structural properties were investigated. In particular, the effect of different processing parameters and the eventual presence of different stabilizers were evaluated. Actually, two reactions may occur during processing: branching/crosslinking or chain scission. The results indicate that when the processing conditions promote a scarce mobility of the macromolecular chains (lower temperatures, lower mixing speed, and higher molecular weight), branching is more favored than chain scission. On increasing the mobility of the chain (higher temperature, higher mixing s…

The antioxidant effect in controlling thermal degradation of a LDPE blow film

2004

It is well known that antioxidants are widely used to prevent thermal degradation of high density and linear low density polyethylene. Antioxidants are not always present in low density polyethylene and only small amounts are usually added to these resins. In this work the effect of an antioxidant system on a low density resin having MFI (190 °C/2.16 kg)=2 g/10′ and density 0.9230 g/cm3 has been studied. Its effect on melt viscosity has been studied by means of a batch mixer and the torque vs time behaviour has been analysed. The results show that a maximum in the torque vs time curve can be seen for the material containing antioxidant. In contrast, the material without antioxidant does not…

Thermodynamically induced shear degradation

1988

The shear degradation of polymers in semiconcentrated solutions is viewed as a function of solvent quality. It is shown that the deterioration of the thermodynamic quality of the solvent leads to a marked flow resistance due to an increasing number of contacts between the chains. This may be probed by viscosimetric measurements as well as by degradation experiments (“thermodynamically induced shear degradation”). For a detailed discussion of this phenomenon the experimental setup for the mechanochemical experiment is outlined first, followed by a survey of the kinetics of chain scission. Finally, experiments mostly obtained on polystyrene in the theta-solvent trans-decalin are discussed. Th…

Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate

1999

Abstract Polyethylene terephthalate (PET), and polyvinyl chloride (PVC), are commonly encountered in plastics stream coming from separate collections of plastic bottles. The presence of PVC in the recycled PET is very dangerous because of the chain scission provoked by the hydrogen chloride evolved from the macromolecules during degradation of PVC. Recycled PET must be free of PVC; contents of PVC as little as 100 ppm can induce degradation and discoloration of the polyester. PET, in its turn, is degraded when the processing is carried out in the presence of water. In previous work, however, the degradation of PET was eliminated and rather an increase of the molecular weight has been measur…

The role of crystalline, mobile amorphous and rigid amorphous fractions in the performance of recycled poly (ethylene terephthalate) (PET)

2012

[EN] The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation of -OH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percen…

Competition between degradation and chain extension during processing of reclaimed poly(ethylene terephthalate)

1998

During processing of poly(ethylene terephthalate) (PET) hydrolytic chain scission, induced by the presence of small amounts of water, is the main cause of degradation. During repeated reprocessing chain scission can also occur because of the presence of other polymeric contaminants like PVC. In order to avoid or to limit hydrolytic chain cleavage adequate drying of PET before melt processing is necessary. Of course this practice is even more recommended when repeated processing steps are used, as for PET recycling. The behavior of recycling PET obtained from post-consumer water bottles when treated in a melt mixer under different conditions has been investigated in order to better understan…

1967

Durch Viskositatsmessungen und spektroskopische Bestimmung des gebildeten Monomeren wird der saurekatalysierte Abbau von Poly-3,4-acrolein verfolgt. Er erfolgt fast ausschlieslich durch Kettenspaltung; eine Depolymerisation tritt nur in untergeordnetem Mase auf. Diese im Vergleich zu anderen polymeren Aldehyden unerwarteten Ergebnisse werden mit dem Auftreten eines durch Resonanz stabilisierten Kettenendes bei der Spaltung erklart. The acid-catalyzed degradation of poly-3,4-acrolein was investigated by viscosity and spectroscopic determination of the monomer formed. The degradation occurs predominantly by chain scission; depolymerization is of minor importance. The results are unexpected in…

The antioxidant effect in controlling thermal degradation of a low density polyethylene blown film

2004

Abstract It is well known that antioxidants are widely used to prevent thermal degradation of high density and linear low density polyethylene. Antioxidants are not always present in low density polyethylene and only small amounts are usually added to these resins. In this work the effect of an antioxidant system on a low density resin having MFI (190 °C/2.16 kg)=2 g/10′ and density 0.9230 g/cm3 has been studied. Its effect on melt viscosity has been studied by means of a batch mixer and the torque vs time behaviour has been analysed. The results show that a maximum in the torque vs time curve can be seen for the material containing antioxidant. In contrast, the material without antioxidant…