SPE Library

A continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High density polyethylene (HDPE) and isotactic polypropylene (PP) were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured.Rheological properties morphology and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics.

The work deals with the influence of content of the untreated wood flour filler (natural pine wood) on rheological behavior of blends with poly(1-butene) matrix. Therefore the blends with 5, 10, 15, 20, 30 and 50 % of wood flour were prepared in microcompounder. The rheological behavior was studied in oscillatory shear regime. Cole-Cole plot was used for determination of differences in molecular weight and distribution. It was found that low content of the wood flour acts as a lubricant agent and decreases zero shear viscosity. On the contrary, increasing content of the wood flour has an opposite effect.

Polypropylene/clay nanocomposite was compounded by a twin-screw extruder. Rheological property development of samples collected from four different positions along the extruder and microstructure of the endobtained samples was investigated. Flow field parameters including shear rate and residence time profiles were simulated. Then the shear strain was calculated. The relationship between the shear strain and microstructure of nanocomposite was analyzed based on rheological analysis. Results showed that dispersion of clay in polymer matrix can be reflected by the shear strain generated by the flow along the extruder.

The presence of water can dramatically lower the melting point of polyacrylonitrile (PAN) homo- or copolymers and make it possible to melt-spin high acrylonitrile (AN) content PAN fibers. However, the behavior of PAN-water melt has not been adequately investigated and the rheology data for PAN-water melt is not available in literature. We developed pressurized capillary rheometer and used it in PAN/Vinyl Acetate (VA)-H2O viscosity measurement successfully. The shear viscosity at 195?øC decreases as water content increases from 17 wt-% to 23 wt-%. The rheology of PAN-water melt can be useful in characterizing the melt and spinning PAN precursor fibers.

Ultrasonic extrusion of polyethylene naphthalate (PEN), LCP and their blends was studied. Rheological, morphological, thermal and mechanical properties of the samples were investigated. Viscosity of PEN decreased with ultrasonic treatment, while that of the blends decreased at an amplitude of 10 ?¬m. Viscosity of LCP was unaffected by ultrasound. Blends treated at an amplitude of 10 ?¬m had larger LCP particles in moldings, leading to reduced mechanical properties in the blends. The results indicated that ultrasound had the predominant effect of degrading the PEN matrix and hindering LCP fibrillation in the blends, thereby masking possible compatibilization effects introduced by ultrasound.

PEN, PET, and their 50/50 blend were ultrasonically extruded at various amplitudes.Rheological, thermal, mechanical, morphological and spectroscopic characterizations of the untreated and ultrasonically treated samples were carried out. Fast homopolymerization during extrusion of PET was foundto occur at an ultrasonic amplitude of 7.5 ?¬m. In contrast,degradation of PEN was observed with ultrasonic treatment. Ultrasonic treatment at short residence time led to the enhancement of transesterification reaction in the PEN/PET blend, indicating that more copolymerization occurred during ultrasonic treatment.

By incorporating special low glass transition inorganic tin fluorophosphates glass (Pglass) into polyamide 6, the latter exhibits unprecedented non-Einstein-like viscosity decrease in the liquid state and an increase in Young's modulus in the solid state. This behavior makes the hybrid Pglass/polymer solid material stronger yet easier to process in the liquid state. The linear rheological behavior is discussed in terms of the hybrid components rheology. The results should beneficially impact our ability to prepare lower viscosity, highly filled polymers using already existing polymer processing methods, making the simple strategy potentially widely applicable in a number of applications such as barrier resistant thin films and flame-retardant polymer composites.

The thermally expandable microcapsule is a new type of blowing agent for polymer foaming. It has a core and shell structure. A low boiling point hydrocarbon liquid is encapsulated by the shell of acrylonitrile co-polymer. Mixing the microcapsules with the thermoplastic polymer and letting them thermally expand in the polymer can foam the polymer. In this study we developed a new microcapsule so that it can be used at high operating temperatures over 200 oC for foaming polypropylene (PP) by injection molding and extrusion. We investigated the effect of viscoelasticity of the shell polymer on the expandability of the microcapsule as well as on the surface appearance. The visual observation of batch foaming the rheological measurement and the experiments of foam injection molding and extrusion elucidated the existence of the optimal degree of cross-linking of the shell polymer that could realize the superior expandability and appearance at PP foam injection molding and extrusion.

The thermally expandable microcapsule is a new type of blowing agent for polymer foaming. It has a core and shell structure. A low boiling point hydrocarbon liquid is encapsulated by the shell of acrylonitrile co-polymer. Mixing the microcapsules with the thermoplastic polymer and letting them thermally expand in the polymer can foam the polymer. In this study, we developed a new microcapsule so that it can be used at high operating temperatures over 200 oC for foaming polypropylene (PP) by injection molding and extrusion. We investigated the effect of viscoelasticity of the shell polymer on the expandability of the microcapsule as well as on the surface appearance. The visual observation of batch foaming, the rheological measurement and the experiments of foam injection molding and extrusion elucidated the existence of the optimal degree of cross-linking of the shell polymer that could realize the superior expandability and appearance at PP foam injection molding and extrusion.

Supercritical carbon dioxide has advantages of high solubility to the polymer and recovering easily by depressurizing, and it is expected to be use as a plasticizing agent. In this work, we studied on the effect of scCO2 on rheological properties of plastomer layered silicate nanocomposites. A rotational viscometer has been adapted to measure the viscosity of polymer under high temperature and pressure conditions. The rheological properties of Plastomer nanocomposites was performed at experimental conditions of various temperature and pressure. We observed that viscosity of polymer was dramatically reduced by CO2 addition.

Manufacturing of extruded polystyrene (XPS) foam insulation boards is currently based on weak ozone depleting gases. Mixtures of blowing agents are actually seen as one of the most promising solutions to ozonedepleting substances phase-out. This paper investigates various blowing agent formulations based on mixtures of hydrofluorocarbons HFC-134a (1,1,1,2-tetrafluoroethane) and HFC-32 (difluoromethane). The study focuses on the rheological (plasticization) and degassing (solubility) behaviors of the formulations, as measured on-line during foam extrusion. Rules of mixing for such blends of HFCs are proposed based on the relative contribution of each component to the overall processing behavior.

Thermoplastics urethanes (TPU) offer broad property range, processing flexibility, and biocompatibility for medical applications. We have undertaken a thermal and rheological study on thermal transitions which influence physical characteristics and oxidative degradation. In addition, possible effects from hydrolytic degradation with long term exposure to alcoholic solvents are sought. Techniques used include Thermal analysis and oxidative induction time (OIT) by differential scanning calorimetry (DSC), and melt rheology. It was found, for selected but not the majority of TPUs, OIT onsets were difficult to obtain. However, melt rheology, with proper sample conditioning, was capable in quantifying the hydrolytic molecular weight degradation process.h

Incorporation of multi wall carbon nanotube (CNT) into the thermotropic liquid crystal polymer matrix (TLCP) obtained high performance polymer nanocomposites. For fabrication of high performance polymer nanocomposites, major challenge is to improve the dispersion of CNT in the TLCP matrix and the interfacial adhesion between CNT and the TLCP matrix. In this study, Multi-wall carbon nanotube (MWCNT) reinforced TLCP nanocomposites were prepared by a melt compounding using twin-screw extruder. The CNT was functionalized with chemical surface modification to introduce carboxyl groups onto the surfaces of CNT for uniform dispersion and induce excellent interfacial adhesion. The rheological, mechanical, morphological, and thermal properties of TLCP/CNT nanocomposites were investigated.

An in situ structuring rheometer (ISSR) has been developed that allows simultaneous controlled formation of structure in polymer blends and composites and measurements of rheological properties. Multi-layer, interpenetrating, and platelet polymer blend morphologies are examples of structure types producible. Networks among solid particles and dispersions can also be formed.The ISSR is modular for installation into existing rheometer platforms. In situ structuring in the melt occurs by chaotic advection which recursively stretches and folds melt domains. Characteristic structure sizes in the melt can reduce to nano-scales so the ISSR also has application to nanocomposites.

The rheological properties for the binary blends composed of a linear polyethylene and a branched polyethylene (LDPE) are studied. It is found that some blends show enhanced oscillatory shear moduli than the individual pure components, suggesting that the relaxation mechanism with long characteristic time is generated in a molten state. Further, they show higher zero-shear viscosities. The drawdown force, defined as the force needed for the extension of a polymer melt from a capillary rheometer, is also evaluated to comprehend the rheological information under the elongational flows and found to be quite sensitive to the anomalous behavior. Furthermore, it is found that the blends show marked flow instability, because they have longer relaxation time than the pure components.

Using solid-state shear pulverization (SSSP) to process poly(ethylene terephthalate) (PET) without addition of chemical agents, we demonstrate that linear PET can be transformed into lightly branched PET, with resulting improvements in physical and mechanical properties. Rheological characterization demonstrates an increase in the melt viscosity of the pulverized PET while intrinsic viscosity characterization yields data consistent with no increase in linear chain length. These results indicate that branching occurs in situ during SSSP via mechanochemistry involving the production of polymeric radicals that result from low levels of chain scission accompanying SSSP. A hypothetical mechanism for this mechanochemical transformation is discussed. The lightly branched PET resulting from SSSP yields a dramatic increase in the crystallization rate of the PET, improving its processability. The ability to increase the melt viscosity of PET by SSSP may contribute to sustainable engineering of PET; a long-standing issue with recycling PET for high-value applications is the fact that melt processingof PET results in reduction of molecular weight and thereby melt viscosity, making the recycled material often unusable for the original application for which it was made.

Although plastic dental brackets are available on the market, they are all made out of plastic materials with poor mechanical properties. This project sought to develop plastic dental brackets with better mechanical properties than the metallic ones in order to enlarge the aesthetic treatment market. The project started by selecting the material, PSU from BASF, and then focused on prototype production by direct micro milling in order to check the design and mechanical properties experimentally. Once the design was tuned, rheological simulation took place to be produced by microinjection. A first micro mould was produced to check microinjection feasibility. The remaining micro moulds were produced and the first production series obtained. The product was patented and launched on the market.

This study aims to investigate possible correlation between thermo-mechanical properties and percolation threshold in carbon filled polypropylene nanocomposites. The goal is to identify an indirect way to determine the percolation threshold without the need to measure the electrical conductivity of a plethora of specimens which is a cumbersome task. The percolation threshold is the basic required feedback of all the existing theoretical models that describe the electrical conductivity of composites materials and are used as design tools. Polypropylene is used as the polymer and exfoliated graphite nanoplatelets, carbon black and vapor grown carbon fibers are used as fillers. Electrical conductivity and rheological properties of PNCs are characterized as a function of fillerƒ??s concentration. The need of accurately determining the percolation threshold is demonstrated by comparing the electrical conductivity data to the predictions of the modified Mamunya model for all three systems studied.

A single screw extruder having ultrasonic barrel attachment was used to manufacture polyetheretherketone (PEEK) - multi walled carbon nanotubes (MWNT) nanocomposites with enhanced dispersion of carbon nanotubes (CNTs) in polymer matrix. The effect of ultrasonic amplitude and CNTs loading on die pressure, electrical conductivity, rheological, morphological and mechanical properties of PEEK filled with 1-10 wt% MWNT was studied. The die pressure was observed to decrease with the increase of ultrasonic amplitude and increased with the increase of CNTs loading. The electrical percolation threshold was found to be between 1 and 2 wt% loading of CNTs.

A continuous, commercially viable method for the dispersion of multi walled carbon nanotubes (MWNTs) in polymer matrices using an ultrasonically assisted twin screw extruder has been studied. The effects of ultrasound on die pressure, power consumption, rheological, morphological, mechanical and electrical properties in PETI-330 nanocomposites filled with 0-5 wt. % MWNTs have been evaluated. Ultrasonically treated nanocomposites show increased viscosity with a slight improvement in mechanical properties at various loadings and ultrasonic treatment. An electrical percolation of less than 0.5 wt. % was observed.