Role of anionic and nonionic surfactants on the control of particle size and latex colloidal stability in the seeded emulsion polymerization of butyl methacrylate

The evolution of the main colloidal parameters in the seeded starved‐feed semi‐continuous emulsion polymerization of butyl methacrylate (BMA) was investigated, with the main purpose of assessing the effectiveness of the semi‐empirical relationship S = K · S_S · ΔA/A_S as a tool to define the surfactant/monomer feed ratio (∝ K) best suited to achieve a target particle size. In particular, the effect of the type and amount of surfactant [i.e., anionic, sodium dodecyl sulfate (SDS), or nonionic, Brij 58P] added during the semi‐continuous stage was considered. Coagulum formation was never observed under the adopted experimental conditions. To detect the occurrence of secondary nucleation or particle aggregation, or both, the particle size and number of particles, the surface tension and the particle surface coverage ratio were correlated. The best results were obtained with SDS and 0.8 ≤ K ≤ 3. In fact, under the selected experimental conditions, only with SDS did the number of particles remain nearly constant throughout the polymerization at the value defined by the seed latex; the particle size distribution was highly monodisperse, and the final particle diameter closely matched the calculated one (～ 120 nm). The above semi‐empirical relationship based on the adjustable parameter K was validated by running test polymerizations aimed at lattices with well‐defined particle size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3083–3094, 2006     

Deformation Bands in Ceria-Stabilized Tetragonal Zirconia/Alumina : II, Stress-Induced Aging at Room Temperature

A stress-induced aging phenomenon is observed to occur at room temperature in deformation bands introduced into a 8.5 mol% ceria-stabilized tetragonal zirconia/alumina (CeTZP/A1₂O₃) composite by flexural loading. The aging occurs with time after unloading and in laboratory air. Over a period of 100 days, the concentration of monoclinic zirconia within a deformation band increases and, in addition, the wedge-shaped deformation band grows with time. Accompanying these two changes are an increase in the tensile stress in the remaining tetragonal zirconia within the deformation band and a consequential increase in the overall compressive stress within the band. The average value of the monoclinic concentration within the deformation band is found to increase parabolically with time, suggesting the mechanism responsible for the observed aging is diffusion limited. Away from the deformation bands, no aging is observed to occur, suggesting aging is stress dependent. Although a water-vapor-mediated mechanism cannot be ruled out, it is proposed that the observed aging is in fact due to a tensile stress assisted chemical reduction of Ce⁴⁺ to Ce³⁺ whose rate is controlled by the indiffusion of oxygen vacancies driven by the tensile stress gradient. It is further proposed that the deformation band grows with time, since the region ahead of the band is under tension and hence subject to an enhanced rate of reduction     

Quality analysis of scalable video coding on unstable transmissions

This paper presents a study of quality on scalable video sequences coded using the scalable extension of the H.264 standard (SVC). A group of experiments was performed to measure, primarily, the effects that transmission instability has in the quality of the videos and the relationship among three scalability methods (spatial, temporal and quality) in terms of quality. A set of experiments was performed to measure the subjective quality using the ACR-HRR methodology and recommendations from ITU-R Rec. BT.500 and ITU-T Rec. P.910. The results show that the amount of instability is not as important as just the presence of instability, that video quality can be deteriorated due to instability and that temporal scalability usually produces videos with worse quality than spatial and quality scalabilities.     

Expanding the application field of post‐consumer poly(ethylene terephthalate) through structural modification by reactive blending

With the aim of up‐grading the material properties of post‐consumer PET, making them suitable for extrusion of thermoformable thick sheets, a series of polyepoxy chain extenders have been comparatively evaluated as melt viscosity modifiers for a toughened compatibilized blend containing up to 80 wt % of bottle‐grade post‐consumer recycled poly(ethylene terephtalate) (r‐PET). Combinations of a commercial modifier with pentaerythritol were also successfully employed to cause simultaneous hyperbranching and controlled chain scission, thereby modifying the melt rheology of the material without excessively increasing the molecular weight, as highlighted by common technological melt viscosity measurements such as online torque and off‐line melt flow rate (MFR). Since the high melt fluidity of PET plays a critical role on its flame resistance, the combined effect of chain extenders and halogen‐free phosphorated additives on the fire resistance of the modified toughened blends was also investigated. Preliminary results indicate that the chemical reactions among polymer and additives must be taken into careful account to prevent unfavorable effects on the ultimate melt rheology and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40881.     

Residual Stresses in Alumina/Zirconia Composites: Effect of Cooling Rate and Grain Size

Alumina/zirconia composites with various compositions at the zirconia-rich part of the phase diagram have been prepared with various grain sizes of the starting alumina powders. After firing under identical conditions, the pellets have been cooled systematically, changing the cooling rates from 0.5 to 8000 K/min. Subsequently, the residual stresses in alumina have been determined by monitoring the frequency shifts of the R ₂ luminescence line of alumina (14 430 cm⁻¹). The data indicate that the stress in alumina is compressive in all cases, with increasing absolute values of the stress with decreasing alumina content. Within the same composition, the residual stress as a function of the cooling rate presents a minimum for values between 10 and 100 K/min, with no clear dependence on the alumina or zirconia grain size. An interpretation of the experimental data in terms of a Coble-type diffusional relaxation applies for intermediate cooling rates (from 10 to 800 K/min), but it fails to account for the large stresses at low cooling rates. The width of the stress distribution is narrow (∼150 MPa) and constant for all compositions and grain sizes at low cooling rates, but it increases for cooling rates >10 K/min, depending on the grain size but not on the composition. For fast cooling rates, a correlation is found when reporting the average width of the stress distribution as function of the average sintered grain-size distribution of alumina. Overall, zirconia grain size seems to influence the average stress, whereas alumina grain size determines the stress distribution.     

Load—strength simulation of a mechanical design

The load—strength theory is used to simulate the movements of a mechanical mechanism consisting of a lever and a spring. The purpose of the mechanism is automatically to select the correct speed for a turntable depending on the size (weight) of the record. The procedure for the computation is given in detail.     

Mechanical reliability,how do we advance?

The development of theory and practice for electronic and mechanical reliability is described, and mechanical reliability is seen to be lagging in practice. Theory and practice are described for a project from conception to market feedback for mechanical as well as for electronic reliability. It is noted that for each phase theoretical and practical methods exist for mechanical as well as for electronic reliability analysis. Activities are listed which can strengthen mechanical reliability theory and practice.     

Sorption of Pyrene to Two Estonian Soils

Two typical Estonian soils, Brown pseudopodzolic and Rendzina, were used for sorption studies with pyrene. The soil samples were subjected to a variety of chemical and physical tests. The specific surface area reached 3.05 m² g^?1 for Rendzina, and 0.87 m² g^?1 for Brown pseudopodzolic soil. The Rendzina type of soil was characterized also by a high organic matter content (22.9%) compared with the Brown pseudopodzolic soil (6.64%). A batch technique was used to perform all adsorption studies. K_oc values 2.7 × 10⁴ mg g^?1 for Rendzina and 4.5 × 10⁴ mg g^?1 for Brown pseudopodzolic were obtained. The results suggets that pyrene sorption behaviour could be in some instances mainly influenced by the composition of organic compounds in the soil, not so much by the overall organic matter content. Also the mineral part of the soil can have a impact to pyrene sorption through Ca-binded humic substances.