43 research outputs found
Mikro- és makromechanikai deformációs folyamatok vizsgálata töltőanyagot tartalmazó műanyagokban = Investigation of micro- and macromechanical deformation processes in particulate filled polymers
TermĂ©szetes szálakat tartalmazĂł PP kompozitokban vizsgáltuk a polimer mátrix jellemzĹ‘inek a hatását a kompozitban lejátszĂłdĂł deformáciĂłs folyamatokra Ă©s megállapĂtottuk, hogy a határfelĂĽletek elválása a dominálĂł mechanizmus amennyiben a komponensek közötti kölcsönhatás gyenge, ezzel szemben a mátrix nyĂrási folyása Ă©s/vagy a termĂ©szetes szálak tördelĹ‘dĂ©se játszĂłdik le a erĹ‘s adhĂ©ziĂł esetĂ©n. Ezzel szemben kis szemcsemĂ©ret esetĂ©n elsĹ‘sorban a határfelĂĽletek elválása játszĂłdik le erĹ‘s Ă©s gyenge adhĂ©ziĂł mellett is. BizonyĂtottuk, hogy a töltĹ‘anyagok saját szilárdsága nagymĂ©rtĂ©kben behatárolja azok erĹ‘sĂtĹ‘ hatását. PLA/lignocellulĂłz szálakbĂłl kĂ©szĂtett kompozitok vizsgálatával igazoltuk, hogy a kompozitok tönkremenetele során elsĹ‘sorban a szálak tördelĹ‘dĂ©se játszĂłdik le. Ez pedig nagymĂ©rtĂ©kben befolyásolja az erĹ‘sĂtĹ‘ hatást. A viszonylag erĹ‘s adhĂ©ziĂł eredmĂ©nyekĂ©nt a kompozitok szilárdságának növelĂ©se a töltĹ‘anyagok saját szilárdságának növelĂ©sĂ©vel Ă©rhetĹ‘ el PP/CaCO3 Ă©s PP/ĂĽveggyöngy kompozitokon vĂ©gzett akusztikus emissziĂłs Ă©s pásztázĂł elektronmikroszkĂłpiás vizsgálatok segĂtsĂ©gĂ©vel kidolgoztunk egy eljárást, melynek segĂtsĂ©gĂ©vel a határfelĂĽleti kölcsönhatások erĹ‘ssĂ©gĂ©nek becslĂ©se abban az esetben is elvĂ©gezhetĹ‘, ha nem másodrendű kölcsönhatások eredmĂ©nyezik a komponensek közötti adhĂ©ziĂłt. | 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
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 kemĂ©nyĂtĹ‘ mĂłdosĂtása – A faliszt hatása a termoplasztikus kemĂ©nyĂtĹ‘ mechanikai Ă©s funkcionális tulajdonságaira.
Jelen cikkĂĽnkben a termoplasztikus kemĂ©nyĂtĹ‘ (TPS) lĂ©trehozásának Ă©s mĂłdosĂtásának lehetĹ‘sĂ©geit foglaljuk össze, kĂĽlönös tekintettel a faliszttel erĹ‘sĂtett kompozitokra. 36 m/m% glicerinnel lágyĂtott kemĂ©nyĂtĹ‘ felhasználásával állĂtottunk elĹ‘ TPS/faliszt kompozitokat. A komponenseket gyorskeverĹ‘ben homogenizáltuk, extrudáltuk, majd fröccsöntĂ©ssel kĂ©szĂtettĂĽnk prĂłbatesteket. Meghatároztuk a kompozitok mechanikai jellemzĹ‘it, szerkezetĂ©t, vĂzfelvĂ©telĂ©t Ă©s mĂ©retváltozását a faliszttartalom fĂĽggvĂ©nyĂ©ben, amelyet 0 Ă©s 40 v/v% között változtattunk 7 lĂ©pĂ©sben. A TPS faliszttel valĂł társĂtása több szempontbĂłl igen elĹ‘nyös. A merevsĂ©g Ă©s szilárdság nĹ‘ a töltĹ‘anyag-tartalommal, kĂĽlönösen nagy szálhossz esetĂ©n. Mindez rĂ©szben a mátrix gyenge tulajdonságaira, rĂ©szben pedig az erĹ‘s szemcse-mátrix adhĂ©ziĂłra vezethetĹ‘ vissza. Ez utĂłbbi a vártnál is nagyobb csökkenĂ©st eredmĂ©nyez a kompozitok vĂzfelvĂ©telĂ©ben, ezzel egyĂĽtt a vĂztartalom mĂ©g 40 v/v% faliszttartalomnál is jelentĹ‘s marad. A fröccsöntött TPS prĂłbatestek zsugorodása rendkĂvĂĽl nagymĂ©rtĂ©kű, Ă©s a mĂ©retváltozás igen hosszĂş idĹ‘ alatt játszĂłdik le. Mindez már 15-20 v/v% töltĹ‘anyag hozzáadásával kikĂĽszöbölhetĹ‘, a faliszt tehát eredmĂ©nyesen javĂtja a kompozitok mĂ©rettartĂłsságát
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