SPE Library

This study systematically investigated the efficiency of ultrasonic treatment on dispersion of different fillers in polypropylene (PP). PP/graphene nanoplatelets (GNP), PP/carbon nanotube (CNT) and PP/carbon black (CB) were prepared using twin screw extrusion without and with ultrasonic treatment. The ultrasonic power consumption varied with filler concentration exhibiting different trends in these composites: the power consumption increased with concentration for PP/GNP and decreased with concentration for PP/CNT, but for PP/CB, it only slightly increased at high concentration. The difference is related to the bubble concentration in the polymer composites. The efficiency of ultrasonic treatment was verified by rheological, electrical and morphological studies. The morphological study showed that CB exhibited the best dispersion in PP which is followed by CNT, whereas GNP showed the worst dispersion. However, the rheological and electrical percolation threshold from low to high was successively shown in PP/CNT, PP/CB and PP/GNP composites. For PP/CNT and PP/CB composites the storage modulus and complex viscosity at low frequency were increased by the ultrasonic treatment. However, PP/GNP did not show obvious change with ultrasonic treatment. The ultrasonically treated PP/1wt%CNT at an amplitude of 13 um dropped 8 order of magnitudes in electrical resistivity compared with the untreated sample, while PP/5wt%CB dropped 4 orders of magnitudes and PP/5wt%GNP only dropped 2 order of magnitudes. Morphological studies show that the agglomerates and agglomerates area ratio were decreased with ultrasonic treatment for PP/CNT and PP/CB composites, but not for PP/GNP composites. An ultrasonic mechanism is proposed based on the experimental data.

Nylon 6/OMMT/elastomer composite was first prepared by molten compound method and then how its rheological properties, mechanical properties, micro morphology and the shape of fracture surface vary with elastomer content was investigated. The results indicate: With the increase of elastomer content, impact strength increases significantly, tensile strength, flexural strength and modulus decline and elongation at break declines first but then increases?the SEM images of fracture surface go well along with the results of impact tests, and critical matrix thickness for the composite materials of brittle ductile transition layer is 0.14?m. With the increase of elastomer content, the apparent viscosity increases first but then declines, non-Newtonian index declines and the activation energy declines first but then increases. So adding elastomer makes it possible for Nylon 6/OMMT/elastomer composite to flow steadily in a wide temperature range under a constant shear stresses and makes the composite easy to fabricate.

This study presents the rheological and thermal behavior of mineral reinforced Poly(lactic acid)/Poly(methyl methacrylate) (PLA/PMMA) blends prepared by melt processing. In particular, combinations of amorphous or semi-crystalline PLA with high or low viscosity PMMA were used to prepare the blends. The effect of the addition of three commercial minerals, clay, calcium carbonate and quartz, was investigated. The glass transition, crystallization and melting of these blends were examined by differential scanning calorimetry. The blend rheology was investigated by small amplitude oscillatory shear rheology. Miscibility was inferred from the shift in glass transition temperature. A single glass transition temperature was observed for all blends indicating initial miscibility of the PMMA/ PLA blends over the entire composition range. This observation was reinforced by the fact that the mixtures remained transparent. It was however possible to induce a phase separation when placing the blends in conditions that favored PLA crystallization. The ability of PLA to crystallize was strongly restricted by the presence of the amorphous PMMA fraction but remained possible in selected conditions. All binary blends showed a typical viscoelastic behavior with a Newtonian plateau at low frequency range. However, the filled blends showed an increase in viscosity at low frequency typical of materials exhibiting a yield stress.

When applied to shear flow, Maxwell-type constitutive models typically over-predict shear thinning. For many known models such as the Leonov model, the slope of the viscosity vs. shear rate plot in log-log scales converges to -1 at high shear rate. This is not realistic for polymer melts and concentrated solutions. In this work, rotational retardation is introduced to the evolution equation so that rotational ‘softening’ can be better controlled in rotational flow such as shear flow. The new evolution equation involves a new parameter n to control the affine advection of rotation so as to adjust the degree of shear thinning or thickening. In combination with finite stretch, a five-parameter nonlinear viscoelastic fluid model is proposed. The resulting constitutive model is suitable to describe the deformation of polymer coils and demonstrates excellent data fitting capability to realistic rheological data for both shear and extension.

This research is concerned with creating an antibacterial wound dressing material by introducing naturally-derived chitosan into thermoplastic polyurethane (TPU) matrix. Chitosan is a promising filler to improve the antibacterial properties of wound dressing materials including TPU. A combination of chitosan with cellulose nano-crystals (CNCs) can help meeting the mechanical design requirements of wound dressing applications. TPU nanocomposites modified with CNCs were prepared by using an optimized solution casting method. Morphological analysis carried out through scanning electron microscopy (SEM) showed that CNCs are well distributed within the matrix up to a filler amount of 2wt%. Thermal analyses indicated that the incorporation of nanofillers leads to significant changes in the glass transition temperature and melting behavior characteristic of the hard segments. Rheological analyses performed on molten TPU incorporating CNCs indicated that the presence of the filler favors shear-thinning behavior.
TPU films containing a combination of CNCs and chitosan were made through a solvent exchange method and solution casting. Current investigations are focused on the characterization of the mechanical properties, water absorption behavior and water-responsive mechanically adaptive properties of the hybrid TPU-CNC-chitosan composites.

Conventional polyamides with high relative viscosity called “high RV polyamides” or “high RV nylons” are prepared typically by a few large nylon-6 producers with solid state polymerization (SSP) process, which is time consuming and energy intensive and hence expensive. Such polyamides are linear molecules as are high RV polyamides produced by compounding with chain extenders with ?-? functional groups. However ZeMac® alternating copolymers of ethylene and maleic anhydride, which are unique with hundreds of pendant functional groups, can be compounded with low RV polyamides to form high RV polyamides which have a branched structure, confirmed by shear thinning rheology. The paper will cover this and performance and cost advantages of such branched polyamides over conventional SSP and linear polyamides for several high performance applications.

The novel ‘viscosity-cure’ shift factor is used to model the rheological and stress relaxation behavior of epoxy resin during the curing process.

Beta-form polypropylene can be produced through the introduction of a branching molecular architecture and by conducting crystallization under shear and rapid cooling conditions.

A new approach, which combines the eXtended Pom-Pom finite element model and an arbitrary Lagrangian-Eulerian technique, is used to simulate stress levels at different points in a molded part.

Cellulose nanocrystals are used to fabricate novel biodegradable nanocomposites that exhibit reduced oxygen permeability, as well as improved tensile and rheological characteristics.

An in-depth study of polylactide nanocomposite molecular characteristics demonstrates that selecting appropriate organoclays for each polylactide grade is a key issue.

A new approach, based on angle measurements in simple unidirectional tests, reduces the time, samples, and costs required for determination of material parameters such as textile permeability.

Increasing carbonyl iron powder filler content affects polyurethane matrix reactions and causes the loss factor of the composites to decrease.

Increasing short-chain branching length by even just a few carbon atoms reduces extrudate distortion.

The behavior of pristine and functionalized particles within polypropylene was investigated with the use of a prototype small-scale mixer.

A new relaxation model has been developed to predict the level of shrinkage that occurs during continuous annealing processes.

A new approach makes it possible to estimate all ASTM-standard flow rates and flow-rate ratios from a single run of small-amplitude oscillatory shear testing.

Time-temperature superposition principles successfully forecast behavior under long-term loading.

Preparing natural rubber/clay nanocomposites by a drying rather than acid coagulation method improves the thermal resistance, tensile strength, and modulus of the rubber vulcanizates.