EFFECTS OF PREPARATION METHODS ON THE STRUCTURE AND MECHANICAL PROPERTIES OF WET CONDITIONED STARCH/MONTMORILLONITE NANOCOMPOSITE FILMS

TPS/Na-montmorillonite nanocomposite films were prepared by solution and melt blending. Clay content changed between 0 and 25 wt% based on the amount of dry starch. Structure, tensile properties, and water content of wet conditioned films were determined as a function of clay content. Intercalated structure and VH-type crystallinity of starch were found for all the nanocomposites independently of clay and plasticizer content or preparation method, but at larger than 10 wt% clay content nanocomposites prepared by melt intercalation contained aggregated particles as well. In spite of the incomplete exfoliation clay reinforces TPS considerably. Preparation method has a strong influence on mechanical properties of wet conditioned films. Mechanical properties of the conditioned samples prepared by solution homogenization are much better than those of nanocomposites prepared by melt blending. Water, which was either adsorbed or bonded in the composites in conditioning or solution mixing process, respectively, has different effect on mechanical properties

Desiccant effect of starch in polylactic acid composites

Polylactic acid (PLA)/starch and PLA/starch-glycerol composites with different glycerol contents were prepared in a wide composition range, in order to study their applicability as packaging materials for dry products. Water uptake was determined at a temperature of 23 °C and different relative humidities. Structure and mechanical properties were also investigated. PLA/ unplasticized starch composites could absorb a considerable amount of water. As a result, they may be adequate as a biodegradable inner container in dry packaging. The absorption capacity of the composites increased significantly with increasing starch content and relative humidity, respectively. Unplasticized starch exhibited not only a desiccant but also a reinforcing effect in PLA, thus both stiffness and strength increased with increasing starch loading. The influence of glycerol content on the water uptake was difficult to reveal due to the migration of glycerol from the bulk to the surface. Furthermore, glycerol weakened the PLA/starch adhesion and softened starch particles

Thermoplastic Starch/Wood Composites: Effect of Processing Technology, Interfacial Interactions and Particle Characteristics

Thermoplastic starch (TPS)/wood composites in a wide composition range were prepared in an internal mixer followed by compression molding. Three types of lignocellulose fibers were used to study the effect of particle and surface characteristics on the processability as well as the mechanical and water absorption properties of the composites. The mechanical properties of these composites were also compared with those of the composites processed by injection molding in an earlier study, and the effect of processing technology on the mechanical properties was also investigated. The processing of TPS/lignocellulose composites in the internal mixer demanded more energy with increasing amount and aspect ratio of the fibers as a result of a network formation. Only a small variation among the dispersion component of the surface tension of the wood samples was found, and almost no difference in the stiffness and strength of the composites prepared in the internal mixer was observed. The results proved that the influence of the processing method on the stiffness and strength of the composites depends strongly on the aspect ratio of the wood particles. Increasing anisotropy results in increasing difference in the mechanical properties of the composites prepared by different methods. The equilibrium water uptake of the fibers and the composites depended especially on the size and, consequently, on the specific surface area of the wood fibers

Interfacial interactions and reinforcement in thermoplastics/zeolite composites

Ten different polymers were selected as possible matrices for zeolite containing desiccant composites in order to prepare functional packaging material. A 5A type zeolite was used as desiccant. Composites containing the zeolite up to 50 vol% were prepared. Interfacial adhesion was estimated by various means including the measurement of surface characteristics, cyclic loading experiments and evaluation of composition dependence of mechanical properties by appropriate models. The results showed that composite properties change in a wide range. The deformability of most composites is small and decreases with increasing zeolite content. Interfacial adhesion between the matrix polymer and the zeolite is not very strong, although quantitative determination is hampered by various factors. Most of the composites fail by debonding, brittle matrices by debonding and/or matrix fracture, while considerable shear yielding has been observed in LDPE composites. Composite properties are determined mainly by matrix characteristics; interfacial adhesion plays only a relatively minor role

Szabályozott méretű, illetve nano részecskékkel társított polimerek előállítása és vizsgálata: adhézió, módosítás, deformációs mechanizmusok = Preparation and study of polymers combined with nanoparticles or fillers of controlled particle size: adhesion, modification, deformation mechanisms

A szerződés által finanszírozott kutatás a heterogén polimer rendszerek szerkezet-tulajdonság összefüggéseinek megállapítására irányult. A munka során több anyagrendszer vizsgálatával és különböző problémák megoldásával foglalkoztunk. A legfontosabb eredményeket ebben a periódusban a nanokompozitok és a természetes szállal erősített anyagok, valamint a heterogén rendszerek mikromechanikai deformációs folyamatainak vizsgálata során értük el. Megállapítottuk, hogy a polimer/rétegszilikát nanokompozitok szerkezete bonyolultabb annál, mint amit az irodalomban állítanak. A kompozitok tartalmaznak eredeti szemcséket, duzzadt szilikát részecskéket, egyedi lemezeket és egy szilikát hálószerkezet is kialakulhat bennünk. Egyszerű reológiai módszer javasoltunk az utóbbi kimutatására és egy korábban kidolgozott modellünk segítségével becsültük az exfoliáció mértékét. A rétegszilikát nanokompozitok és a faliszttel erősített kompozitok mikromechanikai folyamatainak részletes vizsgálata megmutatta, hogy gyakran a részecskék törése korlátozza a tulajdonságok további javítását. A mikromechanikai deformációs folyamatok követése lehetővé tette az egyes folyamatok szétválasztását, így megállapítottuk, hogy a határfelületek elválása és a mátrix plasztikus deformációja egymást követően megy végbe. Munkánkban számos fiatal kutató vesz részt és kutatási eredményeink nagy része a gyakorlatban is hasznosul. | The research financed by this contract focused on the determination of structure-property correlations in heterogeneous polymer systems. Several materials and problems were studied during the years. The most important results have been achieved in the study of polymer/layered silicate nanocomposites and wood flour filled polymers, as well as in the investigation of the micromechanical deformation processes of heterogeneous polymers. We found that the structure of polymer/layered silicate nanocomposites is more complicated than claimed in the literature. The composites contain original particles, swollen silicate stacks, individual platelets, and a silicate network structure may also form in them. We proposed a simple rheological method to detect the formation of the latter, and used our simple model developed earlier for the quantitative estimation of the extent of exfoliation. The detailed study of the micromechanical deformation processes occurring in layered silicate nanocomposites and wood flour filled polymers showed that often the fracture of the particles limits the further improvement of composite properties. We could separate individual micromechanical deformations and found that debonding and the plastic deformation of the matrix are consecutive processes. Several students and young scientists take part in the research and a large part of the results is utilized in practice

Hibrid deszikkáns rendszert tartalmazó funkcionális csomagolóanyagok

Zeolit 4A és CaO felhasználásával, valamint kombinálásával különböző összetételű LDPE/desszikkáns kompozitokat készítettünk és vizsgáltuk azok vízfelvételét. A kompozitok vízfelvételi folyamatai Fick diffúzióval modellezhetők, és a kompozitok vízfelvételi kapacitása, valamint a vízmegkötés sebessége arányos az alkalmazott deszikkánsok, illetve a páratérben jelenlevő víz mennyiségével, és a hibrid kompozitok esetében függ a töltőanyag összetételétől (CaO/zeolit arány). A leggyorsabb és legnagyobb mértékű vízfelvétel a LDPE/CaO kompozitokban mérhető, azonban ezekben a kompozitokban a Ca(OH)2 keletkezése miatt jelentős térfogatnövekedés következik be, ami belső feszültségeket eredményez. A CaO zeolittal történő részleges helyettesítésével a térfogatváltozás mérsékelhető, ami a kompozit egyensúlyi vízfelvételének és nedvességmegkötési sebességének csökkenésével jár. A csomagolás iránti követelményeknek és az adott felhasználási célnak megfelelően kell kiválasztani a hibrid töltőanyag összetételét