Search results for "Crystallinity"

Compatibilization of polyethylene/polyamide 6 blend nanocomposite films

2015

Polymer blends of incompatible components need to undergo compatibilization, in order to give rise to a blend with good physical properties. At the same way, polymer/clay nanocomposites show this problem because of different chemical nature of the polymer matrix and of the clay. Compatibilization is therefore more necessary if an incompatible polymer blend is filled with an organomodified clay in order to give a final material with good properties. In this work, a polyethylene/polyamide 6 blend filled with an organomodified clay has been compatibilized with a maleic anhydride grafted SEBS (styrene-ethylene-butylene-styrene) copolymer and a glicidylmethacrylate-ethylene copolymer. The result…

Microbiological and ageing performance of polyhydroxyalkanoate-based multilayer structures of interest in food packaging

2014

Polyhydroxyalkanoates undergo crystallization during film processing and storage. In this paper, the physico–chemical ageing properties of multilayer structures based on a commercial polyhydroxybutyrate (PHB) and a polyhydroxybutyrate-co-valerate copolymer with 3% valerate content (PHBV3), containing a nanostructured zein interlayer, were analysed. The microbiological safety of the films was also evaluated by monitoring the growth of an inoculum of Listeria monocytogenes over time. Polyethyleneglycol (PEG) was added to PHBV3 films to facilitate handling as the PHBV3 mutlilayer systems (without plasticizer) cracked during film-formation. Crystallinity, thermal, mechanical, barrier and optica…

Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride

1980

Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…

1982

The stress relaxation behaviour after compression yielding of two semicrystalline polymers, a low density polyethylene and an isotactic polypropylene, is investigated. Data taken at several strains, reached with different sample loading rates, are considered. Master curves are obtained by means of dimensionless stress and time measures, similar to those recently adopted for some amorphous polymers. Die Spannungsrelaxation nach Druckbeanspruchung wurde an zwei semikristallinen Polymeren, Polyethylen neidriger Dichte und isotaktischem Polypropylen, untersucht. Die bei unterschiedlichen Deformationen, welche mit unterschiedlichen Beanspruchungsgeschwindigkeiten erreicht wurdern, erhaltenen Erg…

Characterization of monopolymer blend of virgin and recycled polyamide 6

2002

It is a common industrial practice to blend virgin polymer with the same recycled polymer coming from plastic scraps that, in general, has not undergone relevant degradation. In this work, the characteristics of blends of virgin and recycled polyamide have been considered by changing the amount of recycled polymer and the presence of humidity and a stabilizer. Neither dry nor wet stabilized recycled polyamide samples show significant variations of the molecular weight, but the melt Newtonian viscosity of the blends are slightly different from that predicted by an additive rule, despite the same chemical nature of the two components. This holds true even more for the humid unstabilized sampl…

The effect of macromolecular architecture of ethylene copolymers with multi-alkenylsilsesquioxane on morphological, rheological and dynamic mechanica…

2021

Abstract The influence of the degree and the way of incorporation of multi-alkenylsilsesquioxane into the polymer chain on morphological, rheological and dynamic mechanical parameters were determined. It was found that POSS incorporated into the polymer chain was located outside the crystalline structure of lamella in amorphous phase. The incorporation of POSS-6-2 as a pendant group resulted in significant increase of separation of macromolecules. The key factor in rheological and dynamic mechanical behavior of copolymers turned out to be the way of POSS incorporation into the polymer chain. The incorporation of POSS into the polymer chain as a pendant group resulted in decreased relaxation…

Nanoscale mechanical characterization of polymers by AFM nanoindentations: Critical approach to the elastic characterization

2006

AFM nanoindentations show a dependence of penetration, i.e., the relative motion between the sample and the tip (indenter), on material elastic properties when using the same load. This elationship becomes visible by using of samples being homogeneous down to the scale of nanoindentation. They were prepared from materials covering a broad range of mechanical behavior: from rubbery networks to glassy and semicrystalline polymers. The elastic modulus can be obtained applying Sneddon’s elastic contact mechanics approach. To do this, some calibrations and instrumental features have to be measured accurately. All the polymers tested show that the contact between the tip and the sample is dominat…

Analysis of the intensities of the longitudinal acoustic vibrations inn-alkanes and polyethylene

1980

Simple theoretical considerations indicate, that the integral intensity of the „longitudinal acoustic modes” (LAM) in the Raman spectrum ofn-alkanes should be independent of the chain length. The experiment in fact confirms this expectation. Using this property it becomes possible for polyethylene samples, to derive from the measured LAM-intensity the mass fraction of all-turns sequences contributing to this band. For solution crystallized samples this fraction coincides with the crystallinity, whereas in melt crystallized samples it generally turns out as smaller. The observed difference is likely to be due to the occurrence of local conformational defects (kinks, chain torsions) which int…

Functional templates for hybrid materials with orthogonal functionality.

2009

We demonstrate an integrated approach to prepare a nanostructured, multifunctional material with mutually exclusive, orthogonal properties. The hybrid material was obtained within a single step via self-assembly in solution. It consists of TiO(2) as a functional metal oxide and an amphiphilic block copolymer, poly(ethylene oxide)-b-poly(triphenylamine) (PEO-PTPA). Within the materials' synthesis, the block copolymer not only acts as a templating agent but also adds an electronic functionality to the resulting hybrid material. During the synthesis, a variety of self-assembled morphologies, ranging from spheres to wires, can be created. The obtained morphology depends on the weight fraction o…

Crystallization kinetics of LDPE/Ny6 blends

1988

The crystallization behaviour of low density polyethylene/nylon 6 blends has been investigated as a function of the composition. The melting points of the polymers are almost uninfluenced by the presence of the other homopolymers except for blends with a nylon content of 75–90%. Blends with 10% nylon content do not exhibit the crystallization peak during the cooling step probably because of the low concentration and high viscosity of the low density polyethylene matrix. The crystallinity degree of the polyethylene is independent of the composition, while some variations are shown by the polyamide. Finally the rate of nucleation is strongly affected by the composition, in particular for the …