Melt Viscosity Behavior Research Articles

Anomalous Terminal Shear Viscosity Behavior of Polycarbonate Nanocomposites Containing Grafted Nanosilica Particles.

Viscosity controls an important issue in polymer processing. This paper reports on the terminal viscosity behavior of a polymer melt containing grafted nanosilica particles. The melt viscosity behavior of the nanocomposites was found to depend on the interaction between the polymer matrix and the nanoparticle surface. In the case of polycarbonate (PC) nanocomposites, the viscosity decreases by approximately 25% at concentrations below 0.7 vol% of nanosilica, followed by an increase at higher concentrations. Chemical analysis shows that the decrease in viscosity can be attributed to in situ grafting of PC on the nanosilica surface, leading to a lower entanglement density around the nanoparticle. The thickness of the graft layer was found to be of the order of the tube diameter, with the disentangled zone being approximately equal to the radius of gyration () polymer chain. Furthermore, it is shown that the grafting has an effect on the motion of the PC chains at all timescales. Finally, the viscosity behavior in the PC nanocomposites was found to be independent of the molar mass of PC. The PC data are compared with polystyrene nanocomposites, for which the interaction between the polymer and nanoparticles is absent. The results outlined in this paper can be utilized for applications with low shear processing conditions, e.g., rotomolding, 3D printing, and multilayer co-extrusion.

Comparing inline extrusion viscosity for different operating conditions to offline capillary viscosity measurements

AbstractDegermed, dehulled cornmeal grits were extruded through a self‐heating single screw extruder with inner restrictions. Constant degree of screw fill was tested at 32.5, 35, and 37.5% w.b. moisture content. The screw speeds tested were 100, 200, and 300 rpm. A novel two hole die was used and showed the melt viscosity to decrease with increased screw speed. The inline data was compared to offline capillary rheometer measurements and showed a decrease in melt viscosity. For example, at 35% moisture content and roughly 110°C the melt viscosity decreased by 32% from offline to 100 rpm for a shear rate of 100 s−1. The melt viscosity change suggested that each process transforms the material differently into two different materials which was supported by RVA pasting profiles. The extruder die temperature increased with increased screw speed and decreased with increased moisture content. The melt viscosity behaved nonlinearly with moisture content due to high temperature rise and starch degradation. The flow behavior index increased with increased screw speed. Overall, the novel two hole die showed general trends of the melt viscosity behavior with operating conditions and made comparisons to offline data.Practical ApplicationsThe extrusion process is an efficient process that can produce a wide range of products at various throughputs depending upon operating conditions and extruder design. Originally developed for the plastics industry, extrusion has been applied to food and pharmaceutical applications. This application comes with increased challenges due to heterogeneous materials that consist of biological macromolecules that are Non‐Newtonian in rheological behavior as well as being susceptible to temperature and shear degradation. The product rheological properties are dependent on extruder design and operating conditions. Unfortunately, measuring the viscosity while extruding can be complicated, time consuming, and expensive. Thus, to facilitate the design of effective future extruders, the viscosity behavior must be able to be predicted from an offline method which is more cost and time effective.

Dependence of melt behavior of star polystyrene/POSS composites on the molecular weight of arm chains.

Rheological behavior of three-arm and six-arm star polystyrene (SPS) with a small amount of polyhedral oligosilsesquioxane (POSS) was studied. Both linear oscillatory frequency sweep and steady state shear results of SPS/POSS composites showed the reduction of melt viscosity in the unentangled SPS matrix and the increase of viscosity in the entangled SPS matrix. In particular, when molecular weight of the arm (Ma) of SPS was smaller than the critical molecular weight for entanglement (Mc) of PS, the melt viscosity of SPS/POSS composites with low content of POSS was lower than that of pure SPS. The abnormal phenomenon of reduced melt viscosity in SPS/POSS composites was in coincidence with the melt viscosity behavior of SPS/C60 composites reported in our previous work ( Soft Matter 2013 , 9 , 6282 - 6290 ), although the diameters of two nanoparticles and their interaction with SPS matrix were different. A possible mechanism behind the melt viscosity behavior was discussed. Furthermore, the time-temperature superposition principle (TTS) was applied in SPS and SPS/POSS composites. The Cox-Merz empirical relationship was verified to be valid for SPS/POSS composites when the content of POSS was low (1 wt %).

Melt viscosity behavior of C60 containing star polystyrene composites

The melt viscosity behavior of three-arm and six-arm star polystyrene (SPS)/C60 composites was studied. It was found that the changing trend in the melt viscosity of SPS/C60 composites depended on the molecular weight of the arm chain (Ma) of SPS and the content of C60. When the Ma of SPS was smaller than the critical molecular weight for the entanglement (Mc) of polystyrene (PS), the complex viscosity obtained at 0.05 rad s−1 (η*0.05) of SPS/C60 composites with a low content of C60 was lower than that of pure SPS. When the Ma was larger than the Mc of PS, however, the η*0.05 of the SPS/C60 composites was higher than that of pure SPS. These results were contrary to the previous work on the melt viscosity behavior of linear PS (LPS)/C60 composites (A. Tuteja et al., Macromolecules, 2007, 40, 9427–9434), where the η* at low shear frequencies of LPS/C60 composites was higher than that of pure LPS when the molecular weight (Mw) of LPS was smaller than the Mc of PS, and the η* at low shear frequencies of LPS/C60 was lower than that of pure LPS when the Mw of LPS was larger than the Mc of PS. The possible mechanism behind the melt viscosity behavior of SPS/C60 composites was discussed. It was expected that the topological structure of SPS induced a more heterogeneous dispersion of C60 in the SPS matrix than the dispersion state of C60 in the LPS matrix. When the molecular weight of SPS was different, the contact states between SPS and C60 might also be different, which would make C60 act as a lubricator or barrier, leading to the reduction or increase of the melt viscosity of SPS/C60, respectively.

Synthesis and characterization of A2+ B3-type hyperbranched aromatic polyesters with phenolic end groups

Abstract Hyperbranched (hb) aromatic polyesters with phenolic end groups were synthesized according to the A 2 + B 3 approach both, by solution polymerization and by melt (bulk) polymerization with different monomer ratios (A 2 :B 3 ). The hb polyesters produced from solution polymerization exhibited higher yields, molar masses and glass transition temperature ( T g ) compared to the products prepared in the melt. The resulting hb aromatic polyesters from the A 2 + B 3 approach were also compared with their properties to hb aromatic polymers produced from the well known AB 2 monomer 3,5-bis(trimethylsiloxy)benzoyl chloride. Both types of hb aromatic polyesters possess high T g , high thermal stability and good solubility in common organic solvents. A typical melt viscosity behavior with shear thinning effect was also observed for both. Thus similar polymer properties compared to melt-condensed products were obtained with the A 2 + B 3 approach by solution polycondensation possessing the advantage of easy monomer availability and much milder polymerization conditions (at room temperature in solution) compared to the AB 2 approach.

Synthesis, characterization, and properties of novel fluorine containing aromatic polyamides

AbstractA series of novel fluorine containing aromatic polyamides were synthesized by the direct polycondensation of various fluorine containing aromatic diamines and commercially available 5‐t‐butyl isophthalic acid. These polyamides have good solubility in several organic solvents such as dimethylformamide, N,N‐dimethylacetamide, 1‐Methyl‐2‐pyrrolidone, dimethyl sulfoxide, and tetrahydrofuran. The synthesized polymers exhibited inherent viscosities up to 0.93 dL/g and Mw up to 1,52,000 with PDI of 2.49. The polyamides exhibited good thermal stability up to 489°C for 10% weight loss in nitrogen and high glass transition temperature up to 273°C. Dynamic mechanical analysis showed a very good retention of storage modulus up to the glass transition temperature. The tan δ peak value at 1 Hz was used to calculate the Tg and these values are in good agreement with differential scanning calorimetry data. The polyamide films were flexible with tensile strength up to 72 MPa, elongations at break up to 14%, and modulus of elasticity up to 1.39 GPa depending on the exact repeating unit structure. X‐ray diffraction measurements indicate that these polyamides are semicrystalline. Rheology study showed same trend of melt viscosity behavior with different shear rate for all polymers. Water absorption study indicates the hydrophobic nature of the polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Molecular Ball Bearings: The Unusual Melt Viscosity Behavior of Dendritic Macromolecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular Ball Bearings: The Unusual Melt Viscosity Behavior of Dendritic MacromoleculesCraig J. Hawker, Peter J. Farrington, Michael E. Mackay, Karen L. Wooley, and Jean M. J. FrechetCite this: J. Am. Chem. Soc. 1995, 117, 15, 4409–4410Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/ja00120a028RIGHTS & PERMISSIONSArticle Views744Altmetric-Citations192LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (279 KB) Get e-Alerts Get e-Alerts

Melt viscosity behavior of some engineering thermoplastics

AbstractFrequently, the enhanced elevated‐temperature rigidity of engineering thermoplastics (ETPs) is a consequence of high glass‐transition temperature, and many ETPs contain aromatic ring structures in the backbone chain. These factors can lead to difficulty in melt processing, or fabrication, of parts. Thus, the definition of the melt rheology of such systems is of considerable technological, as well as scientific importance. The investigation reported here first defines the viscosity‐temperature dependence of five ETPs over a relatively narrow range of temperatures appropriate to melt processing in terms of superposition methodology. The five ETPs studied were bisphenol A polycarbonate, polysulfone, the condensation polymer of bisphenol A and mixed iso‐ and terephthalic acids, and two experimental condensation polymers: bisphenol A/isophthalic acid and 1,2 bis(4,4′‐hydroxy phenyl) ethane/isophthalic acid. Viscous flow energies of activation are examined in terms of polymer chain structure. In the second portion of the investigation it is shown that, for the latter two condensation polymers, the molecular weight, temperature, and shear rate dependence of the viscosity may be expressed in terms of a modified Carreau model. The Newtonian limiting low‐shear viscosity dependence on molecular weight and that of the shear rate shift factor (relaxation time) are found to be somewhat greater than that normally observed.

Thermoplastic elastomers

AbstractAn important new class of polymers, the thermoplastic elastomers, was announced by the Shell Chemical Company (U.S.A.) in 1965. These new products may be formed into useful articles by modern rapid thermoplastics processing techniques, such as injection molding, and without any chemical vulcanization step provide most of the useful physical properties of vulcanized rubber. High resilience, high tensile strength, highly reversible elongation, and abrasion resistance are obtained. The thermoplastic elastomers consist of ordered, block copolymers of the general structure A‐B‐A, where A is a thermoplastic block polymer and B is an elastomeric block polymer. Choice of monomers, block length, and the weight fractions of A and B are crucial in achieving elastomeric performance. An example is the polystyrene–polybutadiene–polystyrene block copolymer (S‐B‐S) where the molecular weights of S and B and the weight fraction of S are restricted. A two‐phase system is formed, with the middle‐block phase constituting a continuous three‐dimensional elastomeric network and the dispersed end‐block phase serving as multijunction points for the ends of the middle blocks. These systems, without vulcanization, have rubber‐like properties similar to those of conventional rubber vulcanizates but flow as thermoplastics at temperatures above the glass transition of the end block. The behavior is fully temperature reversible. Melt viscosity behavior, measured as a function of shear and temperature, is similar to that of conventional thermoplastics. Activation energies obtained at constant shear stress vary with temperature: at high temperatures they are between those of the pure homopolymers and at low temperatures they approach that of the thermoplastic part of the molecule. Melt viscosities, however, are very much higher than those of either homopolymer of the same total molecular weight. An additional energy term is indicated in the flow process which arises from the transfer of the end block from one aggregate to another, in the process being forced to pass through the elastomeric matrix with which it is thermodynamically incompatible. The classical kinetic theory of rubber elasticity can be applied to these polymers, treating the end‐block phase as hard discrete particles which do not contribute to the elastic network For example, equilibrium modulus or swelling measurements are used to calculate the concentration of elastically effective chains or effective crosslink density. The resulting effective elastic chain length (Mc) is thus identified, not with the middle‐block segment length, but with the normal entanglement length. Hence, normal entanglement junctions in the elastomeric matrix behave as strong effective crosslinks because the ends of the middle block are securely anchored in the end‐block aggregates. High tensile strengths, in the absence of reinforcing fillers or crystallization, may be attributed to a highly perfected network (Case theory) or to the inertial masses of the discrete end‐block aggregates (Bueche theory), or to both. The physical properties of the thermoplastic elastomers over a range of temperatures are discussed.