Sławomir Borysiak

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.

Influence of chemical modification of wood on the crystallisation of polypropylene

The mechanical properties of wood/polypropylene composites depend strongly on interfacial adhesion between components. However, the application of chemical modification to improve compatibility can influence the supermolecular structure of polypropylene matrix. The experimental material comprised two most common Polish timber species pine wood (Pinus silvestris L.) as a softwood species and beech wood (Fagus silvatica L.) as a hardwood species. The size of wood sawdust ranged from 0.5 to 1.0xa0mm. Three different types of wood/PP mixture were prepared: (1) PP – untreated wood, (2) PP – NaOH treated wood and (3) PP – esterified wood with maleic anhydride. In this work, the kinetic parameters of crystallization of PP by differential scanning calorimetry were investigated. It is interesting that crystallisation of PP depends on the kind of wood. The chemical treatment of wood caused changes of crystal conversion and half crystallisation time of polypropylene matrix.ZusammenfassungDie mechanischen Eigenschaften von Holz/Polypropylen-Verbundwerkstoffen hängen in grossem Masse von der Oberflächenhaftung zweier Materialien ab. Eine chemische Modifikation zur Verbesserung der Kompatibilität kann jedoch die supermolekulare Struktur der Polypropylenmatrix beeinflussen. Die Untersuchungen wurden an zwei weit verbreiteten polnischen Holzarten, dem Kiefernholz (Pinus silvestris L.) als Beispiel für ein Nadelholz und dem Buchenholz (Fagus silvatica L.) als Beispiel für ein Laubholz, durchgeführt. Die Abmessungen der Sägemehlpartikeln lag zwischen 0,5 und 1.0xa0mm. Es wurden drei verschiedene Holz/Polypropylen-Mischungen hergestellt: (1) PP – unbehandeltes Holz, (2) PP – mit NaOH behandeltes Holz und (3) PP – mit Maleinsäureanhydrid verestertes Holz. In dieser Studie wurden die kinetischen Werte einer Kristallisation von Polypropylen mittels Differenzialrasterkalorimetrie untersucht. Es zeigte sich, dass die Kristallisation von Polypropylen von der Holzart abhängig ist. Die chemische Behandlung von Holz führte zu Veränderungen bei der Kristallumwandlung und der Halbwertzeit der Kristallisation der Polypropylenmatrix.

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.

Influence of wood mercerization on the crystallization of polypropylene in wood/PP composites

Mercerization process is very significant because the alkali treatment facilitates reactivity of lignocellulosic fillers, thus allowing better response to chemical modification. In the present study, the effect of mercerization of pine wood on the nucleation ability of polypropylene was investigated by means of differential scanning calorimetry. We discovered that for the composites with wood containing cellulose II, the decrease in the crystal conversion of the polymer matrix and increase in the half-time of crystallization values are significant. It can be concluded that the amount of cellulose II formed upon alkalization of lignocellulosic fillers determines their nucleation ability. To evaluate the transcrystalline effects caused by various woods, which were untreated or treated with sodium hydroxide, the polarized optical microscopy was also performed. The nucleation of polypropylene on the surface of wood was investigated by induction time measurement. It was found that surfaces of the unmodified wood generate epitaxial nucleation, whereas the mercerized wood generates nonepitaxial nucleation. The differences in the type of nucleation suggest that the effectiveness of formation of transcrystalline structures depends on the contribution of cellulose I and cellulose II. Moreover, the presence of epitaxy is not necessary for the appearance of transcrystalline structures. The results showed that the transcrystalline structures appeared in each system, even with wood containing significant contribution of cellulose II. The only difference noted was the change in the nucleation abilities of the wood surface. Results of this study imply the necessity of quantitative determination of the contributions of cellulose I and cellulose II, whose presence determine the type of nucleation and nucleation ability of the filler surface.

Supermolecular structure and nucleation ability of polylactide-based composites with silica/lignin hybrid fillers

In this paper, amorphous silica Syloid 244 and kraft lignin were mechanically coupled. Four hybrid materials containing silica and lignin in ratios 1:1, 2:1, 5:1 and 20:1 were prepared. As reference samples for hybrid fillers pristine silica and lignin were used. Particle size determination and microscopic observations were applied to determine dispersive and morphological properties of hybrid fillers. Fourier transform infrared spectroscopy confirmed the effective preparation of silica/lignin hybrid materials. The parameters of porous structure of examined hybrid filler were determined using the multipoint Brunauer–Emmett–Teller method and Barrett–Joyner–Halenda algorithm. Composite samples of polylactide (PLA) containing 2.5xa0% (w/w) of hybrid filler were extruded. Optical microscopy, wide-angle X-ray scattering and differential scanning calorimetry were applied to specify the supermolecular structure of functional PLA/hybrid composites and analyze the crystallization parameters as well as the phase transformation in PLA matrix. Silica/lignin hybrid material was found to be a filler capable of an effective crystal nucleation. The nucleating ability of silica/lignin hybrid filler in PLA matrix is related to porous properties of filler and its composition.

The thermo-oxidative stability and flammability of wood/polypropylene composites

The main aim of the study was to evaluate the thermo-oxidative stability and flammability of wood/polypropylene composites. The composites were obtained by extrusion and compression moulding with chemical modification of wood in order to improve adhesion. The composites were characterised by differential scanning calorimetry and cone calorimetry, providing such parameters as the oxidation induction time and a few parameters describing flammability, e.g. time to ignition, heat release rate, mass loss rate, heat of combustion, specific extinction area and emission of toxic gases. The results illustrate a considerable effect of the presence of wood and chemical modifications of lignocellulosic filler on the thermo-oxidative stability and character of combustion of the composites studied. The information provided in the paper contributes towards the correct choice of chemical modification of wood that would improve mechanical properties of the composites and towards getting composite materials of target thermo-oxidative stability and flammability.

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.

Influence of cellulose polymorphs on the polypropylene crystallization

Results of the hitherto research work on alkalisation of lignocellulosic materials have been much divergent. In view of the above, the subject of this study is mercerization of cellulose from pine wood. This choice of the subject permitted observation of transformation of cellulose I to cellulose II with no participation of other components of lignocellulosic materials. According to X-ray results, during mercerization the isolated cellulose was easily (completely) transformed into cellulose II variety, while the pine wood was converted more slowly to cellulose II polymorphs. Therefore, it could be concluded that the presence of lignin and hemicelluloses in wood prevented the transformation from cellulose I to II. The main objective of this research was to establish the effect of cellulose varieties on the nucleation ability of different fillers by using differential scanning calorimetry (DSC) and polarizing microscopy. The nucleating effect of the fillers occurs only in the presence of cellulose I variety. In contrast, the presence of cellulose II variety seems to practically eliminate the nucleating effect of the fillers. Moreover, nucleation of the mercerized wood (mixture of cellulose I and II) can be also observed, but this effect is not strong. It should be emphasised that as yet no correlation has been reported between the quantitative composition of cellulose polymorphic forms (appearing not only in wood, but in cellulose isolated from wood as well) and the nucleation ability of lignocellulosic fillers.

Nucleation ability of advanced functional silica/lignin hybrid fillers in polypropylene composites

Novel advanced functional silica/lignin hybrid fillers were synthesized for the purpose of their application in composites with polypropylene. The use of lignin for the production of hybrid fillers is justified due to the advantages such as reduction in cost of products, improvement in biodegradability as well as antioxidant and antimicrobial properties. The study encompasses an analysis of the dispersive and morphological properties of the hybrid fillers, and investigations of phase transitions and the supermolecular structure of the composites by means of differential scanning calorimetry, polarized light microscopy, and X-ray diffractometry. The nucleation activity of the hybrid fillers was found to be strongly correlated with the chemical composition of the fillers, and their dispersive properties and porous structure characteristics. Furthermore, the particle size and area surface of the hybrid fillers play an important role in the development of polymorphic varieties of the polypropylene matrix. The study also discusses the mechanism of the formation of the β-PP variety and the transcrystalline structure in the context of the nucleation ability of the hybrid fillers. The investigations are very significant because they address the impact of the actual physicochemical parameters of the hybrid fillers on the nucleation ability and structure of composite materials.

Influence of the pulling of embedded natural fibers on the crystal structure of polypropylene matrix

The formation of hexagonal modification (β) of isotactic polypropylene (iPP) matrix, induced by motion of embedded natural fibers (NF) has been investigated by WAXS method. Untreated and chemically modified flax as well as hemp fibers were used as NF. The motion temperature of NF was found to strongly influence the content of hexagonal modification. If the temperature of motion of NF is lower, then the amount of β-iPP significantly increases. The content of β-iPP also depends on the rate of motion of NF; however, the chemical modification of NF surface reduces the content of this form.