Search results for "Crystallin"

The use of the indentation test for studying the solidification behaviour of different semicrystalline polymers during injection moulding

2005

Summary: An in-line method for monitoring the solid-ificationprocess during injection molding of semicrystallinepolymers (demonstrated previously in J. Appl. Polym. Sci.2003, 89, 3713) is based on a simple device, where anadditional ejector pin is pushed on the injection molded partatdifferenttimesduringthesolidificationphase.The‘inden-tation depth profile’, i.e., residual deformation as a functionoftime,wasobtainedandallowedtodeterminetheevolutionof the solidification front in the mold as a function of thecooling time. The present work shows the reliability andthe powerfulness of the aforementioned method for a largevariety of different semicrystalline polymers (PET, PBT,polyamide-6 PA6, isota…

Viscoelastic recovery behavior following Atomic Force Microscope nanoindentation of semi-crystalline poly(ethylene)

2007

The residual imprint left behind by the AFM nanoindentation of polymers has been seldom studied in the past. In this work, the evolution of indentations at room temperature performed on a semicrystalline poly- (ethylene) in a broad range of experimental conditions is presented. The study shows that the recovery after 24 h is substantial, although not complete. Moreover, the dynamics of the recovery process is not seen to depend on the magnitude of the applied load for the nanoindentation, but instead on the rate of the indentation used. This points out that viscoelastic processes are minimized when performing fast nanoindentations, while at low loading rates there seems to be a residual vis…

The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

2003

In a previous work a master-curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro-hardness, crystallinity) by supe…

Improvement of biphasic polymerization by application of binary ionic liquid mixture

2013

Abstract The mixture of two ionic liquids, 1- n -butyl-3-methylimidazolium and 1-(2-phenylethyl)-3-methylimidazolium chloroaluminates, [C 4 -mim][AlCl 4 ] and [PhC 2 -mim][AlCl 4 ], were applied as a medium to immobilize the Cp 2 TiCl 2 titanocene catalyst for biphasic ionic liquid/hexane ethylene polymerization. The system makes possible to perform the reaction at lower temperatures, below the melting temperature of the aralkyl ionic liquid. A better separation of the ionic liquid phase was observed and an easier mass transfer of the polymer product from the ionic liquid to the hexane phase was obtained. The polyethylene reveals bimodal distribution of molecular weight. It is characterized…

1982

Synthesis and properties of polymers with unusual structure

1985

This lecture summarize some recent results of our current research. The first part describes the homopolymerization and copolymerization of a monocyclic and two bicyclic unsaturated acetals. In this way polyacetals with 1,4-cis-butadiene units and cyclohexene units respectively are obtained. Secondly, the N-substitution of polyamides is described. By N-metalation and subsequent alkylation comb-like polyamides are available. Longer branches cause a side-chain crystallinity. The anionic “grafting-from” technique forms irregular branched polyamides. By termination reaction between living ends of poly(2-isopropenylnaphthalene) and suitable electrophiles new macromonomers are available. The last…

Copolymers with ordered chemical structure

1984

Copolymers with well defined sequences can be obtained for instance by ring-opening polymerization of selected acetals. In this way regular copolymers of formaldehyde and ethylenoxide of the following structure are available2. In the same way some other copolymers with formaldehyde units were obtained. Of special interest are unsaturated polyacetales; for instance3 They can be modified by chemical reactions, for instance by hydrogenation, addition of bromine, iodine isocyanate or epoxidation. Recently a bicyclic unsaturated cycloacetal was prepared and polymerized4 Branched copolymers with a definite number of uniform sidechains are prepared by N-alkylation of polyamides5 The dependence of …

1983

Resultats preliminaires sur les polysiloxanes discotiques avec des cycles triphenylene pentasubstitue fixes au squelette par des liaisons flexibles

Thermal Analysis, Mechanical and Rheological Behaviour of Melt Manufactured Polyethylene/Liquid Crystal Polymer Blends

2011

Modification of properties of conventional thermoplastics with thermotropic liquid crystal polymers, from one hand, allows decrease their viscosities, substantially facilitating processing conditions, and, from another hand, allows increase their exploitation properties. Orientation of the labile structure of liquid crystal polymer in extrusion or injection moulding causes specific reinforcement (so-called self-reinforcement) to occur in the blends containing liquid crystal polymer. Up to now the effect of self-reinforcement is mostly investigated in the blends, containing considerable amount of liquid crystal polymer. In this research the effect of minor amounts of liquid crystalline co-po…

ChemInform Abstract: Continuous Hydrothermal Synthesis of Nanometric BaZrO3in Supercritical Water.

2008

Abstract Nanocrystalline barium zirconate (BaZrO 3 ) was synthesized using a hydrothermal synthesis process working in supercritical conditions and in a continuous way. By this method, we succeeded in the continuous and rapid production of nanopowders. As a preliminary work three barium precursors have been investigated: barium hydroxide (Ba(OH) 2 ), barium acetate (Ba(CH 3 COO) 2 ) and barium nitrate (Ba(NO 3 ) 2 ). Two of them (Ba(CH 3 COO) 2 and Ba(NO 3 ) 2 ) led to the pure perovskite phase. Then an experimental design has been conducted in order to determine the influence of the experimental parameters on the crystallinity and the grain size of the final product.