Dominik Paukszta

Polymorphism of isotactic polypropylene in presence of additives, in blends and in composites

This article is an overview of our investigations of polymorphism in isotactic polypropylene. We suggest the reason for the formation of different forms is perturbations in the mobility of the chains during crystallization. In this work, we try to prove this hypothesis considering the influence of the presence of small organic compounds or external forces, like an electric field, on the process of crystallization. We also analyzed the formation of the polymorphic forms in polypropylene blends and in composites with natural fibers. It was found that in the composites with natural fibers the hexagonal form arises when the fibers are in motion in relation to the polymeric matrix.

Flammability of Composites Based on Polypropylene and Flax Fibers

Abstract Biodegradability and interesting physical and mechanical properties of polypropylene (PP)/cellulose composites are the essential motive for undertaking fundamental studies of various properties of such materials. An addition of lignocellulosic particles to polymers results in a change in properties of the product obtained which is a resultant of properties of lignocellulosic material and those of polymer and depends on the proportion of both materials. It is also reflected in the flammability characteristics of the composites. In this study we have analyzed flammability of PP composites with long flax fibers obtained by compressing. The amounts of natural fibers were 12.5%, 20%, 30% and 40%. The thickness of the investigated samples was 5 mm. The samples were tested in accordance with ISO 5660 (Cone Calorimeter) at heat flux of 35 kW/m2. Heat release rate (HRR) and mass loss rate (MLR) curves show that thermal decomposition and combustion of the mentioned samples occur in a different way. When flax fiber content was 12.5%, a reduction in maximum heat released (HRR peak) by about 35% was observed. However, time to sustained ignition of composites was shorter than that of PP. The characteristics of the composite are closer to those of lignocellulosic material. The addition of 12.5% fibers resulted in an increase in fire retardancy of the composite compared to polypropylene alone. The addition of fibers in the amount exceeding 20% made the composite material characteristics similar to those of lignocellulosic materials.

The Influence of Processing and the Polymorphism of Lignocellulosic Fillers on the Structure and Properties of Composite Materials—A Review

Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards of green technology, has increased from 0.36 million tons in 2007 to 2.33 million tons in 2012. It is predicted that by 2020 their production will reach 3.45 million tons. Production of biocomposites with lignocellulosic components poses many problems that should be addressed. This paper is a review of the lignocellulosic materials currently used as polymer fillers. First, the many factors determining the macroscopic properties of such composites are described, with particular attention paid to the poor interphase adhesion between the polymer matrix and a lignocellulosic filler and to the effects of cellulose occurrence in polymorphic varieties. The phenomenon of cellulose polymorphism is very important from the point of view of controlling the nucleation abilities of the lignocellulosic filler and hence the mechanical properties of composites. Macroscopic properties of green composites depend also on the parameters of processing which determine the magnitude and range of shearing forces. The influence of shearing forces appearing upon processing the supermolecular structure of the polymer matrix is also discussed. An important problem from the viewpoint of ecology is the possibility of composite recycling which should be taken into account at the design stage. The methods for recycling of the composites made of thermoplastic polymers filled with renewable lignocellulosic materials are presented and discussed. This paper is a review prepared on the basis of currently available literature which describes the many aspects of the problems related to the possibility of using lignocellulosic components for production of composites with polymers.

The sol–gel approach as a method of synthesis of xMgO·ySiO2 powder with defined physicochemical properties including crystalline structure

The physicochemical properties of synthetic powders depend strongly on the method of their preparation. The present work concerns the use of the sol–gel method to prepare xMgO·ySiO2 powders with defined physicochemical and structural properties. An important objective was to determine how the basic process parameters (including the type and concentration of the reactants) influence the physicochemical properties of the resulting material. To obtain a synthetic powders, organic precursors of magnesium (magnesium ethoxide), and silicon (tetraethoxysilane) were used. Selected products were subjected to calcination to identify the crystalline structure of the powders and to determine the impact of the proposed method of preparation on this parameter. This aspect of the research will significantly improve the range of application of the manufactured products. The powders obtained by the proposed method were thoroughly analyzed in terms of chemical composition, crystalline structure, morphology and nature of dispersion, parameters of porous structure, and thermal as well as electrokinetic properties. The sol–gel process proved very effective in the synthesis of highly active powders, as evidenced by the very high values obtained for the products’ surface area. It was also confirmed that the physicochemical parameters are strongly dependent on the mass ratio of the reactants and on the method of final treatment of the precipitates.

Mechanical Properties of Lignocellulosic/Polypropylene Composites

This article discusses the mechanical properties of different composites based on pine, oak wood, rapeseed straw and isotactic polypropylene. The surface of the filler was modified with acetic anhydride to enhance the compatibility between hydrophilic lignocellulosic components and hydrophobic polypropylene matrice. After treatment, mixtures of PP with 30% of the natural components were extruded and injection molded. Tensile strength of composites was not improved by the rapeseed straw chemical modification. However, chemical treatment was successful in improving the strength of the wood in the PP matrice. The results concerning mechanical properties of composites, their aesthetic quality and possibility of their application in various fields indicate an opportunity of production of polypropylene/lignocellulosic composites. Moreover, rapeseed straw so far have been considered as waste materials in plastics industry.

Polypropylene (PP) Composites Reinforced with Stinging Nettle (Utrica dioica L.) Fiber

Composites obtained from polypropylene (PP) and nettle fibers were manufactured by an extrusion method. The samples for mechanical and structural testing (by Wide Angle X-ray Scattering (WAXS) and Differential Scanning Callorymetry (DSC) methods) were obtained by an injection molding method. The tests showed that PP composites reinforced with nettle fiber show satisfactory properties and confirmed usefulness of nettle fibers as a reinforcement material. It was found that nettle fiber shows strong properties nucleating the growth of crystalline structures in the PP matrix. In addition, the presence of hexagonal forms in PP matrix was found in the samples obtained by injection molding.

Structure of polypropylene/polycarbonate blends crystallized under pressure☆

Abstract An analysis has been carried out of the crystalline structure of a blend consisting of amorphous polycarbonate and semicrystalline isotactic polypropylene (PP) crystallized under pressure. Structure investigations were carried out by means of wide-angle X-ray scattering. The amount of particular phases as well as the degree of crystallinity have been analysed. It was found that during pressure crystallization, as well as the monoclinic α-modification, the triclinic γ-form of PP also occurs, which disappears after recrystallization in non-pressure conditions. The crystallinity of PP in the blends is independent of the composition of the polymeric mixture.

TiO2‐SiO2 inorganic barrier composites: from synthesis to application

Purpose – The purpose of this paper is to report on a method of synthesis of TiO2‐SiO2 oxide composites characterised by spherically shaped particles with sizes in the micrometric ranges, which can be applied as a new generation of textile/TiO2‐SiO2 composites with barrier properties against UV radiation. Synthesis and characterisation of TiO2‐SiO2 oxide composites with a high degree of dispersion were performed, and their influence on the barrier properties of textile fabrics was investigated.Design/methodology/approach – The precipitation was performed with the use of solutions of titanium sulphate and sodium silicate as the precipitating agent, which are cheap alternatives to organic precursors of Ti and Si. The reaction was conducted in an emulsion system, where cyclohexane was used as the organic phase and non‐ionic surfactants NP3 and NP6 as emulsifiers were applied.Findings – The direction of substrate supply, concentration of the reagents and their ratio and other conditions of precipitation proce...

Crystallisation of polypropylene matrix in composites filled with wooden parts of rapeseed straw

Nucleation ability of native and modified rapeseed straw during the polypropylene crystallization from the melt was investigated by the DSC method. Composites were made from isotactic polypropylene and lignocellulosic material using extrusion and injection moulding techniques. They were obtained using polypropylenes differing with respect to melt flow rates and different varieties of rapeseed straw. Chemical modification was carried out in two stages: through mercerisation and treatment with acetic acid anhydride. In the course of investigations, it was found that both native and modified rapeseed straw acted as an active nucleant of polypropylene crystallisation characterised by low values of MFR indices. It was found that for polypropylenes with high MFR values, the values of crystallization temperatures and crystallization half-time in composites were identical when compared with non-filled polymers. The investigations demonstrated that there were insignificant differences among composites containing straw from different varieties of rapeseed. The analysis of crystallization temperatures confirmed that rapeseed straw modification failed to change this parameter of the crystallization process. A similar tendency was observed in the case of changes of the half-time crystallization process. Moreover, the analysis of the crystallization temperature and crystallization half-time showed that the presence in composites of lignified rapeseed straw particles played an important role in the crystallization conditions.

Morphology and molecular organisation of liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) deposited on a solid substrate

Liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) forms characteristic dendritic or flower-like structures at room temperature when it is deposited on a hydrophilic glass substrate using the zone-casting technique. It was found that such unique structures were not possible to be created simply by recrystallisation of this dye from a liquid-crystalline columnar phase. On the basis of the observations using a confocal microscope and the study of wide angle X-ray scattering (WAXS) as well as the analysis of the absorption and fluorescence spectra, some conclusions, concerning the molecular organisation in the dendritic structure, are drawn. Based on the research, one can assume that the dendrites are formed by columnar molecular aggregates with the column axes parallel to the substrate. Such an organisation of the molecules can be interesting from the point of view of organic electronics.