Search results for "Plastics"

Statistical Mechanics of Polymers: New Developments - International Workshop

2007

Rheological Behaviour, Mechanical Properties and Processability of Biodegradable Polymer Systems for Film Blowing

2017

Films for agricultural or packaging applications are typically made of low density polyethylene (LDPE). They are produced through the film blowing process, which requires the use of polymers with suitable rheological properties. Furthermore, the short shelf-life which is often related to many packed products leads to huge amounts of plastic-based wastes. This suggests the use of biodegradable and/or compostable polymers in replacement for traditional ones. To this regard, only few data exist on the rheological properties of biodegradable polymers undergoing film blowing processing. In this work, a detailed investigation on the rheological, mechanical and processability behaviour of some bio…

Rheological Behavior Under Shear and Non-Isothermal Elongational Flow of Biodegradable Polymers for Foam Extrusion

2013

The production of many items, in particular for food packaging applications, is based on foam extrusion and thermoforming. These operations require the use of polymers which can grant some specific rheological properties, both under shear and elongational flow. In this work, the behavior of some biodegradable polymers [Mater-Bi® and poly(lactic acid)] under shear and non-isothermal elongational flow was investigated and compared with a traditional, non-biodegradable polymer, in order to assess their suitability for industrial-scale foam extrusion and thermoforming. The rheological characterization evidenced the differences between the different biodegradable polymers and the reference polys…

Organocatalytic synthesis of new telechelic polycarbonates and study of their chemical reactivity

2015

Abstract A two-step versatile process for telechelic polycarbonates synthesis is described. 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) was used as thermolabile precursor of N-heterocyclic carbene (NHC) organocatalyst. In a first step, synthesized branched fatty diols or commercially available linear diols were reacted with an excess of dimethylcarbonate (DMC) to afford oligocarbonates with methylcarbonate end-groups. Then, the methylcarbonate groups were reacted with hydroxyl groups of 9-decen-1-ol, 4-hexyn-1-ol and 4-hydroxybenzene ethanol leading to telechelic oligomers with alkene, alkyne and phenol functionalities. Reactivity of these end-groups towards polymerization was …

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…

Titanium isodicyclopentadienide hemimetallocenes for ethylene/styrene copolymerization

2004

Abstract The syndiotactic polymerization of styrene with exo-[(η5-isodiCp)TiCl3] 1/methylalumoxane (MAO; isodiCp=isodicyclopentadienyl) was studied as well as the ethylene/styrene copolymerization with exo-[{η5:η1(N)-isodiCp(SiMe2Nt-Bu)}TiCl2] 2/MAO. These two catalytic systems are stable during polymerization. The half-sandwich titanocene 1 exhibits good syndiospecificity and average activity. The bridged half-sandwich amino complex 2 was found to incorporate styrene into polymer chains at 70 °C. Activity results decrease with increasing styrene concentrations.

Biphasic ethylene polymerisation using ionic liquid over a titanocene catalyst activated by an alkyl aluminium compound

2007

Abstract 1-n-Butyl-3-methylimidazolium tetrachloroaluminate ([BMIM]+[AlCl4]−) was applied to biphasic ionic liquid/hexane ethylene polymerisation as a medium of the Cp2TiCl2 titanocene catalyst activated by alkylaluminium compounds (MAO, AlEt2Cl, AlEt3). The best results were obtained using AlEt2Cl. The results show that catalyst recycling, higher ethylene pressure, and greater Al/Ti molar ratio along with a greater volume of the ionic liquid phase enhance catalyst activity. The polyethylene gathered from the hexane phase is characterised primarily by its high purity. Its physical properties remain polyethylene obtained over a heterogeneous metallocene catalyst. Thus, biphasic ionic liquid …

Vinylic polymerization of norbornene by Pd(II)-catalysis in the presence of ethylene

1997

Pd(II) catalysts with nitrilo ligands and BF4− counter ions give the best results in vinylic polymerization of norbornene. Absolute molecular weight determination of polynorbornene (PN) by means of light scattering and the three-dimensional shape of PN were also investigated. By correlation of molecular weights Mw with intrinsic viscosity (Staudinger-index) [η], yield a close to 0.5 exponent for the Mark-Houwink equation with solvents chlorobenzene and cyclohexane at 25°C expected for polymer molecules with confined conformation. The vinylic polymerization of norbornene with [(CH3CN)4Pd][BF4]2 (I) in nitromethane in the presence of ethylene results in PN with narrow molecular weight distrib…

Synthesis of low density poly(ethylene) using nickel iminophosphonamide complexes

2007

Ethylene polymerization using a catalyst derived from the reaction of the phosphorane (Me3Si)2NP(NSiMe3)2 (1) with either Ni(COD)2 or bis(π-allyl)Ni complexes affords branched poly(ethylene) (PE) of variable MW (103−106) depending on conditions. The branched PE of high MW is semicrystalline with Tm < 100 °C. High field 13C NMR spectra reveal the presence of methyl branches (ca. 10−15 per 1000 C atoms), branches longer than six C atoms (15−20 per 1000 C atoms) and trace levels of ethyl, propyl, n-butyl, and sec-butyl branches (total <2 per 1000 C atoms). The branching distribution changes modestly in response to changes in ethylene pressure in a manner consistent with a chain-walking mechani…

Correlation between processability and properties of a high density polyethylene by a rheological approach

2002

The thermal-oxidative and thermal-mechanical stability of high density polyethylene (chromium based catalyst technology) was examined at many different temperatures using a rheological approach. The changes in molecular structure, which take place during processing, have been studied using a Clextral co-rotating twin-screw extruder in comparison with dynamic measurements performed with a rotational rheometer under definite conditions of temperature, strain and frequency and in presence of air. In order to evaluate the degradation response, an investigation of elastic modulus G' as a function of frequency ω on the residual sample after ageing has been carried out. The molecular weight increa…