Rheology homopolymer

A comparison is made between a 3.5 melt flow conventional polypropylene homopolymer (Profax 6523) and a 7.0 melt flow, high-melt-strength, foamable PP homopolymer in extensional flow. The importance of extensional or elongational viscosity in the foam process is demonstrated and the way in which the rheological differences permit the production of low-density foam on tandem extrusion equipment is shown. 6 refs. 

Star-branched block and homopolymers are of interest both from a theoretical and practical viewpoint. Studies on the melt rheology have shown the viscosity to be independent of the extent of branching, yet dependent upon the arm molecular weight (6, T, ... 

Effect of addition of homopolymer, salt or conventional surfactants The effect of addition of PEO and PPO homopolymers on the gel formation of Pluronic F127 (defined in Fig. 4.3) in aqueous solution has been studied by Malm-sten and Lindman (1993). The structure, studied via SANS, and rheology of neat F127 solutions in the concentration range 10-20% has been probed by Prud homme et al. (1996). Addition of PEO can reduce the gel region and/or eliminate it at sufficiently high PEO concentration. The amount of PEO required to melt the gel depends on the copolymer concentration and decreases with... 

Cohen andTorradas (1984) investigated blends of a 1,2-PB-1,4-PB diblock with 1,2-PB or 1,4-PB with molecular weight equal to that of the corresponding block in the diblock. It was shown using rheology and SAXS that addition of the 1,2-PB homopolymer led to microphase separation, whereas the neat diblock formed... 

Fig. 6.22 Phase diagram for blends of PE and PEP homopolymers (A/j, - 392 and 409 respectively) with a PE-PEP diblock (iVc = 1925) (Bates et al. 1995). Open and filled circles denote experimental phase transitions between ordered and disordered states measured by SANS and rheology respectively. Phase boundaries obtained from self-consistent field calculations are shown as solid lines. The diamond indicates the Lifshitz point (LP), below which an unbinding transition (UT) separates lamellar and two-phase regions in mean field theory.

The dependence of the experimentally observed ODT on the ordering temperature (final quenching temperature) was shown recently by rheology measurements on SI3 and SI low molecular weight samples [91]. This dependence resembles the dependence of the melting temperature in semicrystalline homopolymers on the crystallization temperature. The existence of an equilibrium transition temperature (Todt°) was demonstrated and a procedure, analogous to the known Hofmann-Weeks plot for crystalline polymers, was proposed as a means to calculate Todt°. The phenomenon was attributed to the fact that grains when produced at different temperatures have different sizes. 

Recently we have conducted rheological experiments wherein the end-tethered PCL nanocomposites were blended with pure PCL homopolymer. Rheological behavior, particularly the terminal zone slopes, obtained for 5% and 10% (obtained by blending equal weight fractions of PCL homopolymer with a 10 weight % PCL and 20 weight % PCL respectively) were found to be similar to those obtained from the as-prepared nanocomposites. 

Several recent studies demonstrate convincingly the possibilities for adjusting the rheology of colloidal dispersions through the incorporation of polymer. Here we briefly review the effects of grafted polymer, adsorbing homopolymer, and nonadsorbing polymer. The literature abounds with other and more complicated phenomena. 

Polyethylene is a man-made homopolymer. Its chemical synthesis is well understood. It is a random walk polymer with little secondary or tertiary structure. A batch can largely be characterised by its molecular weight distribution, and its rheology can be related to these parameters by developed rules of polymer behaviour. The action of specific chemicals as plasticisers can be used to modulate these bulk properties in a predictable way, allowing the nature and characterisation of its glass to fluid transition to be predicted. 

High density (HDPE), 52 Irregularities, 52 Linear low density (LLDPE), 52 Low density (LDPE), 52 Molecular weight, 52 Melt flow index, 53 Melting temperature, 51 Moisture absorption, 51 Polymeric forms, 52 Resistance to chemicals, 52 Resistance to oxidation, 52 Shrinkage, 54 Unsaturations, 54 a-transition, 51 P-transition, 51 y-transition, 51 Polyisocyanate, 79 Polylactic acid, 79, 91 Polymer alloys, 48 Polymer processing additives, 646 Polymer rheology, 619 Polymeric forms, 52 Polyphase PlOO, 451 polypropylene (PP), 2, 11 Polypropylene homopolymer, 70... 

Blends of atactic poly(methyl methacrylate) with poly(ethylene glycol), PMMA/PEG, were reported miscible [Colby, 1989]. Their rheology, PMMA/PEG = 50/50 and 80/20 at T = 160-210°C, was studied in a dynamic shear field [Booij and Palmen, 1992]. By contrast with homopolymers, the blends did not follow the time-temperature superposition. The deviation was particularly large at low temperatures. The reason for the deviation is most likely based on the different temperamre dependence of the relaxation functions. The authors concluded that in miscible blends, the temperature dependence of the relaxation times of individual macromolecules depends on composition. This leads to different degrees of mutual entanglement and hence the rubber plateau moduli. 

The linear viscoelastic behavior of the pure polymer and blends has already been described quantitatively by using models of molecular dynamics based on the reptation concept [12]. To describe the rheological behavior of the copolymers in this study, we have selected and extended the analytical approach of Be-nallal et al. [13], who describe the relaxation function G(t) of Hnear homopolymer melts as the sum of four independent relaxation processes [Eq. (1)]. Each term describes the relaxation domains extending from the lowest frequencies (Gc(t)) to the highest frequencies (Ghf( )), and is well defined for homopolymers in Ref [13]. 

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