Synthesis of PMMA‐PTHF‐PMMA and PMMA‐PTHF‐PST linear and star block copolymers

Combination of cationic, redox free radical, and thermal free radical polymerizations was performed to obtain linear and star polytetramethylene oxide (poly‐THF)‐polymethyl methacrylate (PMMA)/polystyrene (PSt) multiblock copolymers. Cationic polymerization of THF was initiated by the mixture of AgSbF₆ and bis(4,4′ bromo‐methyl benzoyl) peroxide (BBP) or bis (3,5,3′,5′ dibromomethyl benzoyl) peroxide (BDBP) at 20°C to obtain linear and star poly‐THF initiators with M_w varying from 7,500 to 59,000 Da. Poly‐THF samples with hydroxyl ends were used in the methyl methacrylate (MMA) polymerization in the presence of Ce(IV) salt at 40°C to obtain poly(THF‐b‐MMA) block copolymers containing the peroxide group in the middle. Poly(MMA‐b‐THF) linear and star block copolymers having the peroxide group in the chain were used in the polymerization of methyl methacrylate (MMA) and styrene (St) at 80°C to obtain PMMA‐b‐PTHF‐b‐PMMA and PMMA‐b‐PTHF‐b‐PSt linear and star multiblock copolymers. Polymers obtained were characterizated by GPC, FT‐IR, DSC, TGA, ¹H‐NMR, and ¹³C‐NMR techniques and the fractional precipitation method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 219–226, 2004     

Comparison of different 2D image analysis measurement techniques for the shape of talc particles produced by different media milling

Talc, which is an extremely versatile industrial mineral, has found increasing number of uses in various industries such as paint, paper, plastic, ceramic and cosmetic. As it is well known, the particle shape is one of the main properties affecting the behavior and properties of mineral particles, especially for the bubble-particle attachment in flotation.In this study, shape characteristics of talc particles produced by laboratory ball and rod mills were determined by automated image analysis using Malvern Morphologi® G3 instrument. The results were compared by previous studies on the same samples that used other shape characterization techniques namely Scanning Electron Microscope (SEM) ( [Yekeler et al., 2004] and [Hi?y?lmaz et al., 2004]) and Clemex image analysis system (Ulusoy, 2008). About 10,058 particles for ball milled product and 7086 particles for rod milled product were measured for the shape analysis by the Malvern Morphologi® G3 instrument. They were expressed in terms of Aspect ratio, HS Circularity and Elongation and compared by applying t-test using the software Statistical Package for Social Science (SPSS) with a 0.05 significance level. t-Test revealed that, the difference between the image data group for different mill products are significant with a 95% confidence level.Although lower sample population was used for the SEM and Clemex analysis techniques than for the new technique Malvern Morphologi® G3, there is a clear difference in the particle shape obtained by different grinding methods for the talc mineral used. The determined shape property depends on the measurement technique applied. However, the results are in good agreement with each other by this study. i.e., more elongated talc particles were obtained by rod mill product.     

Implementation of SPC Techniques in the PVC Pipe Industry

ABSTRACT

This paper provides a case history on the implementation of SPC techniques in the PVC pipe industry. The difficulties, complexity of the process environment and the methods followed to reduce the dispersion are discussed. Results of two years' joint effort of academia and industry and the meaning of this research for future production are presented.     

Zinc Recovery From Lead–Zinc–Copper Complex Ores by Using Column Flotation

Pb–Zn–Cu complex ore from Bal?kesir–?vrindi district have been concentrated by GESOM A.?. using a selective mechanical flotation technique. Ore feeds containing 3.23% Pb, 0.52% Cu, and 2.71% Zn were concentrated by six stages of cleaning and four stages of scavenging. The final zinc concentrate which contains 2.13% Pb, 1.14% Cu, and 52.77% Zn were produced with 61.38% Zn recovery. In this study, the effects of air rate, bubble diameter, gas holdup, and superficial air rate on the column flotation performance were investigated. In order to obtain best results, operation parameters were optimized. Besides, the number of cleaning and scavenging stages of zinc circuit was reduced by using column flotation instead of mechanical flotation. Hence, higher grade zinc concentrates with higher recovery were obtained. Using three stages of cleaning and three stages of scavenging, the zinc concentrate having 58.81% Zn was produced with a recovery of 74.21% indicating an improvement in final zinc concentrate. This achievement of column flotation method was recommended as an alternative method for the zinc circuit to the plant mentioned above, since it will reduce the operating costs.     

Cellular architecture and its relationship with mechanical properties in expanded extrudates containing apple pomace

Cereal-based puffed foods can deliver significant amounts of fruit and vegetable fiber, however a major hurdle is the accompanying decrease in expansion and poor textural properties. The objective of this work was to develop a comprehensive understanding of the operative rheology, processing conditions, cellular architecture, macrostructure and mechanical properties of high fiber, starch-based expanded matrices produced using extrusion. The combination of phase transition analysis and non-invasive X-ray microtomography provided a unique analytical approach for this purpose. A lab-scale twin screw extruder was used for processing directly expanded products from corn flour and apple pomace blends containing up to 22.5% total dietary fiber. Different levels of pomace (0-28%) and in-barrel processing moisture (17.5-25%) resulted in extrudates with a wide range of microstructures (average cell size 0.05-3.43 mm, wall thickness 0.12-0.34 mm and void fraction 0.53-0.76). Structural anisotropy biased towards radial expansion was observed in foams without pomace, whereas cellular isotropy, higher cell number density and greater longitudinal expansion were favored in the presence of pomace. A conceptual model for foaming and collapse was developed based on flow temperature of blends (123.7-167.6 °C), specific mechanical energy, and anticipated changes in visco-elasticity and extensibility of the high-fiber melt. Cell size was significantly correlated to average crushing force (r = − 0.69), crispness work (r = − 0.69) and number of spatial ruptures (r = 0.74). Microstructure data in combination with standard theory for brittle foams was employed to understand mechanical properties of extrudates under compression.     

Sponge-like chitosan-based nanostructured antibacterial material as a topical hemostat

In this study, chitosan/alginic acid/zinc oxide (CHI/AA/ZnO) nanostructured hydrogel sponges were fabricated by incorporating ZnO nanoparticles (<100 nm) into polymer matrix to develop a new potential biomaterial for hemorrhage control. For this purpose, the crosslinked CHI/AA/ZnO nanostructured sponges were synthesized by freeze-drying technique. Genipin was used as a crosslinker. The prepared chitosan-based sponges were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy—energy-dispersive spectroscopy analysis. The effects of ZnO content on the physicochemical characteristics of sponge-like nanostructured hydrogels were evaluated by swelling ratio in two different pH values. Physical immobilization of dexamethasone as a model drug in hydrogel matrix resulted sustained release of drug more than 3 days. Antibacterial activity of hydrogel sponges was assessed against Staphylococcus aureus. The cytotoxicity and hemostatic efficacy of crosslinked CHI/AA/ZnO sponge like-nanostructured hydrogels was evaluated in vitro and in vivo, respectively. The results of this study demonstrated that the prepared CHI/AA/ZnO nanostructured sponge had the potential to be an antibacterial topical hemostat. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47522.     

Monolithic voltage conversion in low-voltage CMOS technologies

A high-to-low switching DC-DC converter that operates at input voltages up to two times as high as the maximum voltage permitted in a low-voltage CMOS technology is proposed in this paper. The proposed circuit technique is based on a cascode bridge that maintains the steady-state voltage differences among the terminals of all of the transistors within a range imposed by a specific low-voltage CMOS technology. An efficiency of 87.8% is achieved for 3.6-0.9 V conversion assuming a 0.18 μm CMOS technology. The DC-DC converter operates at a switching frequency of 97 MHz while supplying a DC current of 250 mA to the load.     

Biomethane production kinetics of rumen pretreated lignocellulosic wastes

Clean Technologies and Environmental Policy - Bioenergy production from lignocellulosic biomass is challenging due to its complex structure. Therefore, a pretreatment is required before methane...