Search results for "PLASTICS"

An electron diffraction study of deposited docosanoic acid monolayers

1991

Docosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L2 and L2' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.

The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

2009

An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000◦C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100–200 μm thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1–2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting struct…

X-ray scattering studies of fatty acid films on water and on Cdcl2 solutions

1991

X-ray diffraction methods for Langmuir films on the surface of water are briefly presented, together with recent results for docosanoic acid monolayers on pure water and for eicosanoic acid monolayers on an ionic subphase.

Isotactic polypropylene solidification under pressure and high cooling rates. A master curve approach

2000

Solidification in industrial processes very often involves flow fields, high thermal gradients and high pressures: the development of a model able to describe the polymer behavior becomes complex. Recently a new equipment has been developed and improved to study the crystallization of polymers when quenched under pressure. An experimental apparatus based on a modified, special injection moulding machine has been employed. Polymer samples can be cooled at a known cooling rate up to 100 °C/s and under a constant pressure up to 40 MPa. Density, Micro Hardness (MH), Wide angle X-ray diffraction (WAXD), and annealing measurements were then used to characterize the obtained sample morphology. Res…

2020

Epoxy resin plays a key role in composite matrices and DGEBA is the major precursor used. With the aim of favouring the use of bio resources, epoxy resins can be prepared from lignin. In particular, diglycidyl ether of isoeugenol derivatives are good candidates for the replacement of DGEBA. This article presents an effective and eco-friendly way to prepare epoxy resin derived from isoeugenol (BioIgenox), making its upscale possible. BioIgenox has been totally characterized by NMR, FTIR, MS and elemental analyses. Curing of BioIgenox and camphoric anhydride with varying epoxide function/anhydride molar ratios has allowed determining an optimum ratio near 1/0.9 based on DMA and DSC analyses a…

Synthesis of hydrophilic polymers in supercritical carbon dioxide in the presence of a siloxane-based macromonomer surfactant: Heterogeneous polymeri…

2003

Batch free radical polymerization of 1-vinyl-2-pyrrolidone (VP) in super- critical carbon dioxide (scCO2) was studied in the presence of a reactive polysiloxane surfactant (PDMS-mMA). Phase behavior investigation showed that when the initial concentration of the surface active macromonomer was higher than 2.5% w/w with respect to the monomer, the reaction mixture, in the absence of efficient stirring, was initially opaque to the visible light, and it slowly turned to an orange tint. Polymeriza- tion experiments carried out with surfactant concentration higher than the aforemen- tioned value proceeded with a fast kinetics, and led to the formation of spherical nanoparticles with almost quant…

Dispersion Polymerization of Vinylidene Fluoride in Supercritical Carbon Dioxide

2006

The dispersion polymerization of vinylidene fluoride in supercritical carbon dioxide is investigated using two ammonium carboxylate perfluoropolyether stabilizers of different molecular weights. Under suitable operating conditions a polymer made of well-dispersed spherical particles has been obtained up to relatively high conversion. The experimental data of polymerization rate and molecular weight distribution are in good agreement with the predictions of a model previously developed. Such an agreement supports the conclusion that the polymerization kinetics is dominated by the interphase transport of the active radicals between the continuous phase and the polymer particles.

Copolymerization of vinylidene fluoride and acrylic acid in supercritical carbon dioxide

2009

The free-radical copolymerization of vinylidene fluoride (VDF) and acrylic acid (AA) was carried out in supercritical carbon dioxide using both precipitation and dispersion techniques in the presence of an ammonium carboxylate perfluoropolyether compound. Formation of a copolymer was confirmed by variable contact time CP MAS NMR spectroscopy. Macromolecular matrices were significantly enriched in AA with respect to the initial feed composition and we found that the nonfluorinated monomer has a much higher reactivity ratio with respect to VDF. The cumulative concentration, crystallinity, and water affinity of the synthesized copolymers could be modified changing the initial feed composition,…

Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: Experimental Analysis of the Reaction Loci

2010

Free radical copolymerization reactions of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were carried out in supercritical carbon dioxide at T=50 °C. When ammonium carboxylate perfluoropolyether surfactants were used, the formation of polymer particles was observed provided that HFP mole fraction in the feed was not larger than 0.30. Under these conditions, the effect of the total interphase area of the polymer phase, Ap, on the product propertieswas investigated by comparing experiments with largely different amounts of stabilizer, i.e., ranging from precipitation (smaller Ap) to dispersion (larger Ap) polymerization systems. We found that the copolymer molecular weight distribut…

Dispersion polymerization of vinyl monomers in supercritical carbon dioxide in the presence of drug molecules: A one-pot route for the preparation of…

2008

The polymerization of 1-vinyl-2-pyrrolidone in supercritical carbon di- oxide in the presence of ibuprofen as a model drug was investigated as a new one-pot process for the preparation of polymer-based drug delivery systems (DDSs). The com- posites were prepared at 65 � C and P ¼ 31-42 MPa by changing the initial con- centration of the drug and the concentration of a crosslinking agent and that of a hydrophobic comonomer. The effects of these parameters on the performances of the polymerization and on the in vitro release kinetics of ibuprofen were studied. In all the experiments, part of the drug was entrapped inside the polymer particles and dissolved more slowly with respect to the pure …