Search results for "Crystallin"

Polymeric scaffolds based on blends of poly-l-lactic acid (PLLA) with poly-d-l- lactic acid (PLA) prepared via thermally induced phase separation (TI…

2012

Porous scaffolds based on blends of high crystalline Poly-L-lactic acid (PLLA) with low crystalline poly-D-L-lactic acid (PLA) were prepared via Ther- mally Induced Phase Separation (TIPS), with the aim of exploring the possibility to control the degradation behaviour of the PLA-based scaffold, simultaneously pre- serving the morphological characteristics required for tissue engineering applica- tions. Porous foams with different PLLA/PLA weight ratios (from 95/5 to 60/40) were produced and characterised in terms of pore size, porosity, and thermal properties. The scaffolds present an open porosity, with average pore sizes ranging from 30 to 70 lm. Results showed that, when dealing with a P…

No-Flow Temperature in Injection Molding Simulation

2010

Most injection molding simulation packages use the no-flow temperature (NFT) as a means of determining whether the polymer flows or is solid. The NFT is not well defined, and a standard method for measuring it does not exist. A sensitivity analysis of the filling stage has been carried out with two different packages [VISI Flow (Vero Software Limited, Gloucestershire, UK) and Moldflow (Autodesk, Inc., San Rafael, CA)] to estimate the influence of the NFT on the main processing parameters. The NFT has a large influence on the thickness of the frozen layer, but it does not appreciably affect the filling pressure. Because the NFT affects the frozen layer, an effect on the estimation of shrinka…

Small angle scattering study of the structure of isotactic polypropylene-hydrogenated oligo(cyclopentadiene) blends

1996

Abstract Blends of isotactic polypropylene ( i PP) and hydrogenated oligo cyclopentadiene (HOCP) have been studied by means of small angle X-ray scattering in the temperature range 70–160°C. The structure of blends containing less than 25% HOCP is very similar to the one of plain i PP, i.e. lamellae whose thickness increases by increasing the temperature. Blends containing more than 25% HOCP are characterized by two kinds of lamellae formed by layers of i PP and amorphous material rich in i PP and in HOCP, respectively. The crystallizable i PP present in both phases crystallizes from the melt, in analogy to what happens in HDPE/HOCP blends and in agreement with the values of the crystallini…

Sustainable nanocomposites based on halloysite nanotubes and pectin/polyethylene glycol blend

2013

Abstract This study was focused on the preparation and characterization of biofilms based on pectin/polyethylene glycol 20000 (PEG) blend and halloysite nanotubes (HNTs). The obtained blends loaded with a natural nanoclay are proposed as sustainable alternative to the polymers produced from non-renewable resources such as fossil fuels. Properties of technological interest have been monitored and they were correlated to the structural features of the nanocomposites. It turned out that the wettability of the films can be tuned by changing the composition and the distribution of HNTs into the material as well as the surface roughness. The tensile properties of the blend are enhanced by the pre…

Shear and nonisothermal elongational characterization of a liquid crystalline polymer

1989

A commercial liquid crystalline polymer (LCP) sample was characterized both in shear and in nonisothermal elongational flow over a wide range of temperatures (240–350°C). The LCP sample employed was a copolyesteramide of 2,6 hydroxynaphthoic acid, terephthalic acid, and aminophenol manufactured by Celanese and commercially known as Vectra B950. The viscosity decreases dramatically at temperatures above the crystal-nematic transition of the polymer. At lower temperatures, the extrusion of the sample is mainly due to plastic flow. Die-swell values are very small and contraction of the extrudate is also revealed, but the sample shows high elasticity. The polymer is not spinnable at very low te…

Nonisothermal elongational behavior of blends with liquid crystalline polymers

1994

Measurements of melt strength and breaking stretching ratio of several blends of thermoplastic polymers with liquid crystalline polymers are presented. The melt strength behavior depends not only on the viscosity of the blends but also on the temperature dependence of the viscosity. In particular, even if the viscosities of the blends are, at the extrusion temperature, lower than that of the thermoplastic matrices, the melt strength can be larger than that of the pure thermoplastics if its viscosity-temperature curve exceeds that of the matrices far from the solidification temperature. This behavior allows one to spin or film blow these blends despite the low viscosity.

Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene

2011

Abstract Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in th…

1985

Structures, properties and miscibility behaviour of liquid crystalline polycatenar tetrone derivatives

1995

Abstract The tetrones represent an interesting new mesogenic building block. The results of this study show that they can be incorporated into a variety of mesophases. A smectic phase was observed in the polycatenar compound with four terminal chains as expected. The phase exhibits a tilted structure (Sc phase) to prevent void formation. The compound with six pendant chains forms a columnar phase. In spite of their structural similarity, the tetrones studied tended not to be completely miscible. However, complete miscibility with a semi-discoid phenylhydrazone was observed. When this hydrazone, which forms a columnar ‘Dho phase’, was mixed with tetrone which forms a columnar ‘Dhd phase’ a c…

Influence of“controlled processing conditions” on the solidification of iPP, PET and PA6

2002

In this work reliable experimental data for three semicrystalline polymers (iPP, PA6, PET) crystallised under pressure and high cooling rates are supplied. These results were achieved on the basis of a model experiment where drastic controlled solidification conditions are applied. The final objective was to quantify the effect of two typical operating conditions (pressure and cooling rate) on the final properties and morphology of the obtained product. The influence of processing conditions on some macroscopically relevant properties, such as density and micro hardness is stressed, together with the influence of processing conditions on the product morphology, investigated by means of Wide…