Jana Mikešová

Thickening of butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid latices with an HEUR associative thickener

Thickening of acrylate copolymer latices containing various amount of 2-hydroxyethyl methacrylate (HEMA) by commercial associative thickener SER-AD FX 1070 (CONDEA Servo BV), based on hydrophobic ethoxylated urethane (HEUR), showed that the thickening efficiency decreases with the HEMA content in the latex copolymer. The strongest increase in viscosity occurred in the latex without HEMA comonomer suggesting formation of the network space structure due to the bridging of the latex particles by adsorption of hydrophobic ends of the thickener. When HEMA was incorporated into the latex copolymers, the particle surface became more hydrophilic and the association of the thickener was more significant. In this case thickening was much lower and was only a result of the hydrodynamic interaction between swollen latex particles and the thickener macromolecules or their aggregates (clusters, micelles).

Phase structure evolution during mixing and processing of poly(lactic acid)/polycaprolactone (PLA/PCL) blends

The morphology of quenched and compression molded samples of poly(lactic acid)/polycaprolactone (PLA/PCL) blend prepared by melt mixing was carefully characterized by the method reflecting eventual nonuniformity of the blend structure and/or broad particle size distribution. Determined number and volume average droplet radii for quenched samples were compared with theory, assuming that flow field in a mixing chamber can be substituted by the shear flow with effective shear rate. An increase in droplet radii during compression molding was compared with theory of the coalescence in quiescent state. Using the concept of effective shear flow to describe mixing leads to a strong disagreement between theory and experiment for the critical droplet radius of its breakup, and for the coalescence efficiency. The theory of coalescence in quiescent state provides fair description of an increase in the number average droplet radius during compression molding, but totally fails at prediction of an increase in the volume average droplet radius.

Coalescence during annealing of quiescent immiscible polymer blends

Abstract Coalescence during annealing of quiescent immiscible polymer blends, containing polypropylene (PP) matrix and different amount of ethylene-propylene copolymer (EPR) as dispersed phase, was studied. Comparison of experimental results with available coalescence theories revealed that changes in the phase structure after 20 min annealing can be precisely estimated using the approximate theory of coalescence induced by van der Waals forces and considering drainage of the matrix film between spherical droplets. All results evidenced growth of the EPR droplet size with the annealing time and temperature; increase in the content of dispersed phase contributed to higher growth rate of the dispersed phase, more pronounced at the coalescence origin. Anisometry of the EPR droplets and droplet shape relaxation were perceived, both interfering the course of coalescence. Enhanced elasticity of examined blends at low frequencies and positive deviation of the complex viscosity from the linear mixing rules was observed.

Impact of Dose-Rate on Rheology, Structure and Wear of Irradiated UHMWPE

Ultrahigh molecular weight polyethylene (UHMWPE) is used as a bearing material in total joint replacements (TJR). UHMWPE for TJR is usually modified by irradiation and thermal treatment to increase wear resistance. We modified UHMWPE in three ways, differing in radiation dose-rate and/or atmosphere during irradiation. Rheological properties before and after irradiation were determined by means of oscillatory shear measurements. Structural changes were followed by X-ray diffraction, infrared spectroscopy, electron spin resonance, and solubility measurements. Wear resistance of selected samples was obtained by the pin-on-disk method. Rheological properties changed sensitively with modification conditions including radiation dose rate. Moreover, rheological results correlated well with both crosslinking extent and wear resistance. Finally, it was demonstrated that the optimal radiation dose, i.e. the dose leading to maximum crosslinking density and wear resistance, was different for each of the three modification procedures.

The effect of (2-hydroxypropyl)-β-cyclodextrin on rheology of hydrophobically end-capped poly(ethylene glycol) aqueous solutions

(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].

Thermoplastic starch composites with TiO2 particles: Preparation, morphology, rheology and mechanical properties

Composites of thermoplastic starch (TPS) with titanium dioxide particles (mTiO2; average size 0.1μm) with very homogeneous matrix and well-dispersed filler were prepared by a two-step method, including solution casting (SC) followed by melt mixing (MM). Light and scanning electron microscopy confirmed that only the two-step procedure (SC+MM) resulted in ideally homogeneous TPS/mTiO2 systems. The composites prepared by single-step MM contained non-plasticized starch granules and the composites prepared by single-step SC suffered from mTiO2 agglomeration. Dynamic mechanical measurements showed an increase modulus with increasing filler concentration. In TPS containing 3wt.% of mTiO2 the stiffness was enhanced by >40%. Further experiments revealed that the recommended addition of chitosan or the exchange of mTiO2 for anisometric titanate nanotubes with high aspect ratio did not improve the properties of the composites.