Search results for "Crystallization"
showing 10 items of 774 documents
Crystallization and melting of fractions of branched polyethylene
1983
Effects of the molecular weight on the crystallization behaviour of branched polyethylene become observable if isothermal crystallization is studied at temperatures near to the melting end. Crystallinities decrease with decreasing molecular weight. Thicknesses of lamellae grown during isothermal crystallization are independent of the molecular weight. They depend only on temperature. Compared to the effect of the branches polydispersity gives only a minor contribution to the broadening of the crystallization and melting range of low density polyethylene.
Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide-block-dimethylsi…
2004
The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane-b-ethylene oxide) (COP) and tetrahy- dronaphthalene (THN) was investigated. The crystallization kinetics was studied iso- thermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to h…
Capillary Imbibition, Crystallization, and Local Dynamics of Hyperbranched Poly(ethylene oxide) Confined to Nanoporous Alumina
2017
The crystallization and dynamics of hyperbranched poly(ethylene oxide) (hbPEO), obtained from the direct random copolymerization of EO and glycidol (PEO-co-PG), are studied both in bulk and within nanoporous alumina (AAO). Copolymerization decreases the degree of crystallinity and lowers the crystallization and melting temperatures as compared to linear PEO. The dynamics of capillary imbibition within AAO followed the t1/2 prediction but is slower than predicted by the classical Lucas–Washburn equation. The most prominent effect of confinement is the change in nucleation mechanism—from heterogeneous nucleation in bulk to homogeneous nucleation inside AAO. The homogeneous nucleation temperat…
ESTIMATION OF INJECTION PRESSURE DURING MOLD FILLING.
1982
Dimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified, The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.
On the packing–holding flow in the injection molding of thermoplastic polymers
1988
Injection molding tests were performed on a Ny66 resin. Data of mass entering the mold during the packing–holding stage as a function of filling flow rate and holding time are presented. The experimental results are discussed on the basis of a simple model of the packing–holding stage. Only a small part of density increase due to crystallization seams to be compensated by the packing–holding extra flow.
Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechani…
2012
[EN] This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystalli…
Ellipsoidal core-shell cylindrical microphases in PS-b -PB-b -PCL triblock copolymers with a crystallizable matrix
1997
Polystyrene-block-polybutadiene-block-poly(e-caprolactone) SBC triblock copolymers with a PCL matrix exhibit microphase separation into three different phases within the spherulitic superstructures. Mixing of the PS-block can occur upon melting of the PCL-block if the molecular weight is low enough. Even though the crystallization takes place well below the PS-glass transition, a deformation of the amorphous microphases into ellipsoidal core-shell cylindrical microdomains is observed by TEM. These copolymers have mechanical properties which are dominated by the PCL (Poly(e-caprolactone)) matrix with an influence of the amorphous blocks.
Thermal behavior and spherulitic superstructures of SBC triblock copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ɛ-c…
1996
The dynamic crystallization and the melting behavior of polystyrene-block-poly(e-caprolactone) (PS-b-PCL, short notation SC), polybutadiene-block-poly(e-caprolactone) (PB-b-PCL, BC) and polystyrene-block-polybutadiene-block-poly(e-caprolactone) (PS-b-PB-b-PCL, SBC) have been studied using differential scanning calorimetry. The copolymers with high molecular weight exhibit microphase separation into microphases consisting of polystyrene, polybutadiene and poly(e-caprolactone) and partial crystallization of the corresponding PCL block. The crystallization occurs at temperatures below the PS glass transition. Depending on the block copolymer composition, crystallization takes place through a c…
Investigation on the Properties and on the Photo-Oxidation Behaviour of Polypropylene/Fumed Silica Nanocomposites
2021
This work investigates the effects of very small amounts of fumed silica on the morphology and on the rheological and mechanical behaviour of polypropylene nanocomposites and on their photo-oxidation behaviour. Polypropylene nanocomposites were prepared using a twin-screw corotating extruder with 0, 1 and 2 wt/wt% of SiO2. Morphological, mechanical, thermomechanical and rheological properties were examined. It was found that the viscosity of the matrix is reduced by the presence of the silica nanoparticles, suggesting a poor adhesion between the two phases and probably some lubricating effect. On the contrary, the mechanical and, in particular, the thermomechanical properties of the matrix …
Aging of Nanosized ZnO Modified Polyoxymethylene Blends with Ethylene–octene Copolymer
2015
The influence of ethylene–octene copolymer and zinc oxide (ZnO) on structure and tensile stress–strain behavior of polyoxymethylene were investigated before and after ultraviolet weathering. Addition of ZnO considerably improved stress–strain characteristics of the ultraviolet-irradiation impaired composites. Crystallinities of ultraviolet-irradiated composites were affected by numerous competitive processes, including suppression of crystallization in the presence of multiple components in the system, nucleation induced by nanofiller, secondary crystallization and amorphization because of the chain scissions of the macromolecules. Addition of ZnO considerably improved stability of the comp…