Mikro- és makromechanikai deformációs folyamatok vizsgálata töltőanyagot tartalmazó műanyagokban = Investigation of micro- and macromechanical deformation processes in particulate filled polymers

Természetes szálakat tartalmazó PP kompozitokban vizsgáltuk a polimer mátrix jellemzőinek a hatását a kompozitban lejátszódó deformációs folyamatokra és megállapítottuk, hogy a határfelületek elválása a domináló mechanizmus amennyiben a komponensek közötti kölcsönhatás gyenge, ezzel szemben a mátrix nyírási folyása és/vagy a természetes szálak tördelődése játszódik le a erős adhézió esetén. Ezzel szemben kis szemcseméret esetén elsősorban a határfelületek elválása játszódik le erős és gyenge adhézió mellett is. Bizonyítottuk, hogy a töltőanyagok saját szilárdsága nagymértékben behatárolja azok erősítő hatását. PLA/lignocellulóz szálakból készített kompozitok vizsgálatával igazoltuk, hogy a kompozitok tönkremenetele során elsősorban a szálak tördelődése játszódik le. Ez pedig nagymértékben befolyásolja az erősítő hatást. A viszonylag erős adhézió eredményeként a kompozitok szilárdságának növelése a töltőanyagok saját szilárdságának növelésével érhető el PP/CaCO3 és PP/üveggyöngy kompozitokon végzett akusztikus emissziós és pásztázó elektronmikroszkópiás vizsgálatok segítségével kidolgoztunk egy eljárást, melynek segítségével a határfelületi kölcsönhatások erősségének becslése abban az esetben is elvégezhető, ha nem másodrendű kölcsönhatások eredményezik a komponensek közötti adhéziót. | Polypropylene composites were prepared from different PP matrices, and natural fibers to study the effect of matrix characteristics on deformation and failure. The results proved that the dominating deformations may change with matrix properties. Debonding is the dominating process when the adhesion of the components is poor, while matrix yielding and/or fiber fracture dominate when adhesion is improved by the introduction of a functionalized polymer. In the case of small fiber diameter debonding the dominating deformation process both for poor and good adhesion. The inherent strength of the reinforcement can be limiting factor in the improvement of composite strength. Results obtained on PLA/lignocellulosic fiber composites proved that during the failure of the composites fiber fracture occurs, and this determine the reinforcement of the composites. Because of the strong adhesion further improvement in composite strength is possible only through the increase of the inherent strength of wood particles. According to the results of acoustic emission measurements of PP/Glass beads and PP/CaCO3 composites an approach was proposed for the quantitative determination of adhesion strength in composites, in which adhesion is created by other mechanisms than secondary interactions. The results obtained showed that the use of functionalized polymer and other surface treatments in this composites resulted in adhesion strength one order of magnitude larger than without the coupling agent

Improving interfacial adhesion in pla/wood biocomposites

Two reactive coupling agents, N,N-(1,3-phenylene dimaleiimide) (BMI) and 1,1-(methylenedi-4,1-phenylene)bismaleimide (DBMI) were used to improve interfacial adhesion in PLA/wood composites. First the effect of the coupling agents was established in a series of experiments in which the amount of coupling agent changed at constant wood content, and then the effect of coupling was determined at various wood loadings (0-60 vol%). Composites were homogenized in an internal mixer and compression molded to plates. Tensile properties were determined and micromechanical deformations were studied by acoustic emission measurements. The two compounds improved the properties of the composites. Stiffness, strength and deformability increased simultaneously supplying sufficient proof for coupling. Because of the flexibility of the molecule, DBMI is a more efficient coupling agent in the studied composites than BMI. However, the effect of coupling is small, because only a few very large particles debond under the effect of external load. Smaller particles adhere strongly to the matrix even without coupling proving that interfacial adhesion is strong in PLA/wood composites

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

hermoplastic 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

FACTORS DETERMINING THE PERFORMANCE OF THERMOPLASTIC POLYMER/WOOD COMPOSITES; THE LIMITING ROLE OF FIBER FRACTURE

Thermoplastic polymer/lignocellulosic fiber composites were prepared with a considerable range matrices and fibers in an internal mixer. Tensile properties were determined on bars cut from compression molded plates. Local deformation processes initiated around the fibers were followed by acoustic emission testing supported by electron and polarization optical microscopy. The analysis of results proved that micromechanical deformation pro-cesses initiated by the fibers determine the performance of the composites. Debonding usually leads to the decrease of composite strength, but decreasing strength is not always associated with poor adhesion and debonding. The direction of property change with in-creasing wood content depends on component properties and interfacial adhesion. Good interfacial adhesion often results in the fracture of the fibers. Depending on their size and aspect ratio fibers may fracture parallel or perpendicular to their axis. At good adhesion the maximum strength achieved for a particular polymer/wood pair depends on the inher-ent strength of the fibers, which is larger for perpendicular than parallel fracture. Inherent fiber strength effective in a composite depends also on particle size, larger particles fail at smaller stress, because of the larger number of possible flaws in them. A very close corre-lation exists between the initiation stress of the dominating local deformation process and composite strength proving that these processes lead to the failure of the composite and determine its performance

Competitive interactions, structure and properties in polymer/layered silicate nanocomposites

Thermoplastic polymer/layered silicate composites were prepared from the same organophilized montmorillonite (OMMT) and four different matrices, polypropylene (PP), the blend of PP and a maleated polymer (MAPP), poly(lactic acid) (PLA) and polyamide (PA) in order to study the effect of their chemical structure and interactions on composite structure and properties. The components were homogenized by extrusion and then specimens were injection molded, which were then characterized by a variety of methods. The results showed that competitive interactions among silicate layers and between the silicate and the polymer determine the extent of exfoliation, and structure. The morphology of the composites is complicated, exfoliation is never complete, besides individual silicate layers, the composite can contain a silicate network, stacks of silicate platelets and larger particles in various amounts. Several local deformation processes can take place around the structural entities as well as in the matrix. Fracture and debonding are the main particle related processes, while cavitation takes place in the polymer, at least in PA and PLA. The macroscopic properties of layered silicate composites are determined by the extent of exfoliation and interfacial adhesion that decreases upon organophilization. Increased reinforcement and improved composite properties can be achieved only by the proper control of all interactions prevailing in the composite

Wood fiber reinforced multicomponent, multiphase PP composites : Structure, properties, failure mechanism

Polypropylene (PP) was reinforced with wood flour and impact modified with elastomers to increase stiffness and impact resistance simultaneously. Elastomer was added in 0, 5, 10 and 20 wt%, while wood content changed from 0 to 60 wt% in 10 wt% steps. Structure and adhesion were controlled by the addition of functionalized (maleated) polymers. Composites were homogenized in a twin-screw extruder and then injection molded to tensile bars. The results showed that composite structure is determined by the relative strength of adhesion and shear forces prevailing during processing. Structure can be controlled by the application of function-al polymers within limits. Although embedding is favored by thermodynamics and further promoted by coupling, deencapsulation occurs at the large shear stresses of injection molding even in the presence of a functionalized elastomer. Composite properties depend on composition, increasing elastomer content results in decreasing stiffness and strength. Model calculations showed that the elastomer does not contribute to load bearing, average stress in the matrix increases with increasing elastomer content. Local stresses and adhesion define the initiation of deformation processes around wood particles, which start at the same stress irrespectively of elastomer content. Local processes determine the mechanism of failure and composite strength independently of their mechanism

A keményítő módosítása – A faliszt hatása a termoplasztikus keményítő mechanikai és funkcionális tulajdonságaira.

Jelen cikkünkben a termoplasztikus keményítő (TPS) létrehozásának és módosításának lehetőségeit foglaljuk össze, különös tekintettel a faliszttel erősített kompozitokra. 36 m/m% glicerinnel lágyított keményítő felhasználásával állítottunk elő TPS/faliszt kompozitokat. A komponenseket gyorskeverőben homogenizáltuk, extrudáltuk, majd fröccsöntéssel készítettünk próbatesteket. Meghatároztuk a kompozitok mechanikai jellemzőit, szerkezetét, vízfelvételét és méretváltozását a faliszttartalom függvényében, amelyet 0 és 40 v/v% között változtattunk 7 lépésben. A TPS faliszttel való társítása több szempontból igen előnyös. A merevség és szilárdság nő a töltőanyag-tartalommal, különösen nagy szálhossz esetén. Mindez részben a mátrix gyenge tulajdonságaira, részben pedig az erős szemcse-mátrix adhézióra vezethető vissza. Ez utóbbi a vártnál is nagyobb csökkenést eredményez a kompozitok vízfelvételében, ezzel együtt a víztartalom még 40 v/v% faliszttartalomnál is jelentős marad. A fröccsöntött TPS próbatestek zsugorodása rendkívül nagymértékű, és a méretváltozás igen hosszú idő alatt játszódik le. Mindez már 15-20 v/v% töltőanyag hozzáadásával kiküszöbölhető, a faliszt tehát eredményesen javítja a kompozitok mérettartósságát

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