Octamethyl-POSS−HDPE nanocomposites were prepared by the melt mixing route. The rheological and viscoelastic behavior of HDPE−octamethyl-POSS nanocomposites was investigated with a strain-controlled rheometer and dynamic mechanical analysis (DMA). The rheological results show that while at lower filler concentration (0.25−0.5 wt %) POSS particles act as lubricant and reduce the complex viscosity of the nanocomposites, at higher concentrations, viscosity increases. POSS remains miscible in HDPE at lower concentrations and lower temperatures used in the study; however it starts aggregating at higher concentrations and higher temperatures. The presence of POSS particles causes gelation in HDPE matrix at concentrations higher than 5 wt % possibly due to the segregated particle−particle interaction. The storage modulus shows an increase at lower POSS concentrations but decreases at higher POSS concentrations. The α-transition temperatures shift to higher values at low POSS concentrations and is attributed to r...

Rheological and Viscoelastic Behavior of HDPE/Octamethyl-POSS Nanocomposites

In contrast to other types of segmented multiblock thermoplastic elastomers, simple ABA block copolymers represent a class of well-defined nanostructured materials. Due to the inherent block lengths built in during the polymerization, the microdomain structure of block copolymers exhibits a size scale of typically 10−100 nm. The ability to control the individual chemistry of each block as well as the size and the shape of the domains in a block copolymer affords enormous advantages to tailor physical properties. By globally orienting the microdomains, a well-defined initial morphological state aids greatly in the interpretation and modeling of mechanical deformation and allows for exploitation of the inherent anisotropy of the cylindrical and lamellar structures. Several types of orientation techniques are reviewed. Experiments investigating structure−mechanical properties in styrene−diene triblock copolymers with spherical, cylindrical, and lamellar morphologies are discussed, with emphasis on the clarif...

Impact of Morphological Orientation in Determining Mechanical Properties in Triblock Copolymer Systems

Dynamic mechanical and thermal analysis of aligned vapor grown carbon-nanofibers (VGCNFs)-reinforced high-density polyethylene (HDPE) was performed. High-shear mixing was used to disperse and distribute the nanofibers. Extensional flow was used to obtain anisotropic nanoreinforced composite tapes. Dynamic mechanical analysis showed dual increase of storage modulus and loss modulus with different draw ratios. The modulus and complex viscosities of the drawn samples converged to that of pure PE at high temperatures, indicating that in the melt, the behavior is dominated by the semicrystalline matrix. Additionally, an increase in thermal stability was observed for the composites compared to PE matrix. Differential scanning calorimetry analysis showed that the inclusion of nanofibers hindered the structure evolution of PE upon drawing.

Dynamic mechanical and thermal analysis of aligned vapor grown carbon nanofiber reinforced polyethylene

The effects of extrusion processing temperature on the rheological, dynamic mechanical analysis and tensile properties of kenaf fiber/high-density polyethylene (HDPE) composites were investigated for low and high processing temperatures. The rheological data showed that the complex viscosity, storage and loss modulus were higher with high processing temperature. Complex viscosities of pure HDPE and 3.4 wt% composite with zero shear viscosity of ⩽2340 Pa s were shown to exhibit Newtonian behavior while composites of 8.5 and 17.5 wt% with zero shear viscosity ⩾30,970 Pa s displayed non-Newtonian behavior. The Han plots revealed the sensitivity of rheological properties with changes in processing temperature. An increase in storage and loss modulus and a decrease in mechanical loss factor were observed for 17.5 wt% composites at high processing temperature and not observed at low processing temperature. Processing at high temperature was found to improve the tensile modulus of composites but displayed diminished properties when processed at low processing temperature especially at high fiber content. At both low and high processing temperatures, the tensile strength and strain of the composite decreased with increased content of the fiber.

Effects of extrusion temperature on the rheological, dynamic mechanical and tensile properties of kenaf fiber/HDPE composites

The mechanical properties of the double gyroid (DG) cubic phase in glassy−rubbery block copolymer systems are examined. The stress−strain properties of an isoprene-rich polystyrene/polyisoprene/polystyrene (SIS) triblock and a polystyrene/polyisoprene (SI) starblock DG, both comprised of two separate interpenetrating glassy networks embedded in rubbery matrices, are compared to those of the sphere, cylinder, and lamellar morphologies. This 3-dimensionally interpenetrating periodic nanocomposite is found to have superior properties over those of its classical counterparts, attributable to the morphology rather than to the volume fraction of the glassy component, the architecture of the molecule, or the molecular weight. The DG is the only polygranular/isotropic thermoplastic elastomer morphology which exhibits necking and drawing and which requires considerably higher stresses for deformation up to 200% strain than any of the three classical microdomain morphologies. The deformation behavior of the DG is f...

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Mechanical Properties and Deformation Behavior of the Double Gyroid Phase in Unoriented Thermoplastic Elastomers

Influence de la densite, masse moleculaire, ramification et histoire thermique sur le comportement dynamomecanique

Virgil V. Vickroy

Papers

Dynamic mechanical relaxations in polyethylene