Search results for "polymers"

Role of thermal history on quiescent cold crystallization of PET

2002

8 pags., 9 figs.

SAXS/WAXS study of the annealing process in quenched samples of isotactic poly(propylene)

1999

The structural rearrangement in samples of quenched isotactic poly(propylene) (iPP) submitted to different annealing treatments has been studied using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) at the synchrotron radiation source of DESY, Hamburg. From a quantitative analysis of the WAXS profiles the values of the α-monoclinic, mesomorphic, and amorphous mass fractions coexisting in the material were determined. It is demonstrated that the SAXS patterns were characterized by two different long-period values that are attributed to α- and mesomorphic periodicity, respectively. The related α- and mesomorphic volume phase fractions, calculated from the analysis of the SAXS …

Synthesis and properties of model - micronetworks

1989

Microgels are small network particles with overall dimensions in the 100nm-region. Some experiments concerning the behaviour of cross-linked matter can be more easily performed using the molecular nature of μ-gels. In this publication, the synthesis and characterization by light and neutron scattering and dynamic-mechanical shear experiments of two different types of μ-gels are presented.

Dynamics of Structure Formation in Model Membranes and in Adsorbed Layers

1991

Unconventional and new ways to prepare ultrathin films with defined lateral distribution of components are described. These methods make use of two different principles: (1) Films with two coexisting phases are prepared and an active component preferentially partitions into one of the phases. Domain formation and interdomain distance largely depend on the kinetics of nucleation and growth and can thus be controlled. This is demonstrated by fluorescence microscopy with monolayers on water surfaces as well as with monolayers formed by co-adsorption of a fatty acid and a dye on silicon. (2) The support is structured by conventional techniques, in our case by photolithography. Adsorption or des…

Accelerated laboratory weathering of polypropylene composites filled with synthetic silicon-based compounds

2019

Abstract Non-functionalized and n-alkyl functionalized polyhedral oligomeric silsesquioxanes (POSS), siloxane-silsesquioxane resins and the sol-gel silicas were for the first time examined as possible UV-stabilizers and/or antioxidants in polypropylene (PP). The obtained composites were subjected to the accelerated laboratory weathering tests. The influence of the weathering conditions on the structure and properties of the PP materials was evaluated on the basis of the results from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) studies. It was found that weathering resistance of the PP materials was strongly de…

The Unique Versatility of the Double Metal Cyanide (DMC) Catalyst: Introducing Siloxane Segments to Polypropylene Oxide by Ring-Opening Copolymerizat…

2020

The combination of hydrophobic polydimethylsiloxane (PDMS) blocks with hydrophilic polyether segments plays a key role for silicone surfactants. Capitalizing on the double metal cyanide (DMC) catalyst, the direct (i.e., statistical) copolymerization of cyclic siloxanes and epoxides is shown to be feasible. The solvent-free one-pot copolymerization of hexamethylcyclotrisiloxane and propylene oxide results in the formation of gradient propylene oxide (PPO)-PDMS copolymers. Copolymers with up to 46% siloxane content with low dispersities (Ð < 1.2) are obtained in the molecular weight range of 2100-2900 g mol-1 . The polymerization kinetics are investigated by pressure monitoring and in situ 1 …

Recycling of heterogeneous plastics wastes: I—Blends with low-density polyethylene

1992

Abstract Heterogeneous plastics wastes are usually recycled by means of ad hoc designed equipment which, in a single step, produces objects with large dimensions and poor mechanical properties. In this preliminary work, the possibility of preparing blends of plastics waste and low-density polyethylene is investigated. These ‘secondary’ materials (with plastics waste content up to 50%) show mechanical properties similar, except for the elongation at break, to those of the virgin polyethylene. The addition of moderate amounts of calcium carbonate does not significantly reduce the properties of these materials.

2019

In this study, the structural behavior of small-scale wood beams externally strengthened with various fiber strengthened polymer (FRP) composites (i.e., flax FRP (FFRP), basalt FRP (BFRP), E-glass FRP (“E” stands for electrical resistance, GFRP) and their hybrid FRP composites (HFRP) with different fiber configurations) were investigated. FRP strengthened wood specimens were tested under bending and the effects of different fiber materials, thicknesses and the layer arrangements of the FRP on the flexural behavior of strengthened wood beams were discussed. The beams strengthened with flax FRP showed a higher flexural loading capacity in comparison to the beams with basalt FRP. Flax FRP prov…

Energy Consumption for the Desalination of Salt Water Using Polyelectrolyte Hydrogels as the Separation Agent

2017

The energy consumption for a novel desalination approach using charged hydrogels under externally applied pressure is experimentally measured and calculated. The salt separation is based on a partial rejection of mobile salt ions caused by the fixed charges inside the polyelectrolyte network. Self-synthesized and commercial poly(acrylic acid) hydrogels are used to study the desalination performance in reference to sodium chloride solutions within the concentration range of 0.1–35 g L−1. The influence of various synthetic parameters, such as the degree of crosslinking (DC) and the size and shape of the particles, is investigated. Furthermore, the effect of process parameters including the am…

Determination of highly porous plastic foam structural characteristics by processing light microscopy images data

2013

Mathematical modelling of physical and mechanical properties of plastic foam as well as numerous practical applications requires knowledge of foam structural characteristics. A necessity exists to determine the characteristics of the spatial structure of inhomogeneous materials comprising inclusions of other material, e.g., polyurethane foam without destructing the material and analysis of each element. A methodology is elaborated for preparing highly porous plastic foam specimens and investigation of foam strut-like structure with light microscopy (LM) by taking images in three mutually perpendicular planes. A mathematical model is developed for highly porous plastic foam for the determina…