DMS Content Research Articles

Crystallization behavior and mechanical properties of high open porosity dolomite hollow microspheres filled hybrid geopolymer foams

A novel kind of hybrid geopolymer cellular composite foam (DM/KGP) with multi-scale pores was produced by adding dolomite hollow microspheres into geopolymeric matrix via hydrogen peroxide. Effects of the dolomite type, foaming agent (H2O2) and microsphere content, high-temperature treatment on the microstructure, pore structure and mechanical properties of final foams were investigated. The DM/KGPs were composed of amorphous phase. The total and open porosity of samples reached ~88.8 vol% and 82.1 vol%, respectively. Compression strength of the foams decreased with increasing the content of H2O2, while it had the diametric increase when the DMs content increased. After high-temperature treatment, DM/KGPs were converted to DMs/leucite ceramic foams, which also showed good strength (4.49 MPa) and high open porosity (77.0 vol%). This fresh geopolymer foams could have great potential in membrane supports, catalysis and filtration applications.

Influence of Top Pressure on the Flavor and Sensorial Characteristics of Lager Beer

The top pressure of CO2 has been studied in the brewing industry as a method for improving the quality of beer. This study focused on the influence of top pressure on the flavor of lager beers by measuring different physicochemical and flavor parameters during primary fermentation and maturation. Sensorial analyses were also conducted to reveal the relationship between the instrumental data and the sensory results. Based on a detailed evaluation of the parameters and multivariate data analysis, it was demonstrated that the top pressure influenced the sensorial characteristics of lager beer by balancing the flavor in lager beers. The flavor quality was improved by altering the relative contents of the volatile compounds produced and improving the organoleptic properties of beer. On the other hand, the increased CO2 pressure slightly reduced the rate of fermentation, but its effects on the acetaldehyde and DMS content were minimal. A study on consumer preferences was also carried out to determine the possible impact of top pressure and wort gravity on the flavor quality of beers and market preferences. The maturation characteristics appeared to be improved by using a top pressure of 1.5 bar for 8°P and 0.5 bar for 12°P.

Optimalizace stanovení obsahu dimethylsulfidu v mladině a pivu

Sulphur compounds present in barley, malt and beer are mostly non-volatile substances (amino acids, proteins, inorganic sulphates) from which volatile sensory active substances can be produced under certain conditions. The presence of these substances in beer can adversely affect its organoleptic properties. Dimethyl sulfi de (DMS) is one of the most studied volatile sulphur compounds in beer; therefore a suitable analytical method for monitoring DMS content is necessary. The static headspace method coupled to gas chromatography with fl ame photometric detector (HS-GC-FPD) used for the determination of DMS content in wort and beer was optimized and validated. Optimal yield of HS extraction was achieved after 30 minutes at 50 °C. DMS contents moved from 9.6 to 59.6 μg.l-1 in the analysed worts, from 6.1 to 34.9 μg.l-1 in beers.

Synthesis of hydrophilic copolyesters and the characterization of their moisture-related cooling properties

A series of copolyesters (Co-PETs) containing poly(ethylene glycol) (PEG), 5-sodiumsulfodimethyl isophthalate (DMS), and dimethyl isophthalate (DMI) were synthesized via the conventional two-step melt-polycondensation method. The synthesized Co-PETs were characterized by 1H-NMR spectroscopy, FT-IR spectroscopy, differential scanning calorimeter (DSC), and thermogravimetric analyzer (TGA). The DSC results showed that the melting temperature (T m) and the heats of fusion (ΔH m) of Co-PETs decreased with increasing the DMS content in Co-PET, while the inclusion of PEG did not affect their thermal properties significantly. The water absorption and the water contact angle of the Co-PET films were found to be significantly affected by the DMS content rather than PEG content. The moisture-related cooling properties of the fabric samples made of Co-PET 5 as well as PET were evaluated by using liquid moisture management tester (MMT) and Q max measurements. The MMT and Q max results indicated that Co-PET 5 fabric containing DMS 1.0 mol% and PEG 10.0 wt% in Co-PET seemed to be a good candidate for the fabric having durable cooling effects.

Synthesis and surface properties of polydimethylsiloxane-based block copolymers: poly[dimethylsiloxane-block- (ethyl methacrylate)] and poly[dimethylsiloxane-block-(hydroxyethyl methacrylate)

A polydimethylsiloxane (PDMS) macroazoinitiator was synthesized from bis(hydroxyalkyl)-terminated PDMS and 4,4′-azobis-4-cyanopentanoic acid by a condensation reaction. The bifunctional macroinitiator was used for the block copolymerization of ethyl methacrylate (EMA) and 2-(trimethylsilyloxy)ethyl methacrylate (TMSHEMA) monomers. The poly(DMS-block-EMA) and poly(DMS-block-TMSHEMA) copolymers thus obtained were characterized using Fourier transform infrared and 1H NMR spectroscopy and differential scanning calorimetry. After the deprotection of trimethylsilyl groups, poly(DMS-block-HEMA) and poly(DMS-block-EMA) copolymer film surfaces were analysed using scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of the PDMS concentration in the copolymers on both air and glass sides of films were examined. The PDMS segments oriented and moved to the glass side in poly(DMS-block-EMA) copolymer film while orientation to the air side became evident with increasing DMS content in poly(DMS-block-HEMA) copolymer film. The block copolymerization technique described here is a versatile and economic method and is also applicable to a wide range of monomers. The copolymers obtained have phase-separated morphologies and the effects of DMS segments on copolymer film surfaces are different at the glass and air sides. Copyright © 2010 Society of Chemical Industry

Effect of Physical Structure of Matrix Copolyester on the Conductivity of Polypyrrole/Copolyester Composite Films

The effect of physical structure of matrix copolyester on the electrical conductivity of polypyrrole/copolyester composite films was investigated. The composite films were prepared by polymerizing pyrrole through vapor phase absorption onto the anion-containing copolyester films prepared from copolyester/phenol-TCE/FeCl 3 mixture. The conductivity of polypyrrole/copolyester composite films increased with the DMS content up to 10 mol%. However, it decreased with DMS content when DMS content was greater than 10 mol%. This phenomenon was interpreted according to the physical structure of the copolyester. From the observed and calculated T g data, we found that after 10 mol% inhomogeneous distribution of DMS groups became serious, which suggested that many DMS groups gathered together. This micro-phase separation will lengthen the average distance between DMS units which can act as reaction sites for pyrrole polymerization and consequently reduce the electrical conductivity of the PPy composite film. These phenomenon may be one of the important reasons for the conductivity variation in this composite system.

Removal of dilute volatile organic compounds in water through graft copolymer membranes consisting of poly(alkylmethacrylate) and poly(dimethylsiloxane) by pervaporation and their membrane morphology

Removal of volatile organic compounds (VOCs) such as benzene and chloroform in aqueous benzene and chloroform solutions through the poly(methylmethacrylate)-poly(dimethylsiloxane) (PMMA- g-PDMS), poly(ethylmethacrylate)-PDMS (PEMA- g-PDMS), and poly( n-butylmethacrylate)-PDMS (PBMA- g-PDMS) graft copolymer membranes was investigated by pervaporation. When aqueous solutions of dilute VOCs were permeated through the PMMA- g-PDMS and PEMA- g-PDMS membranes, these membranes showed a benzene- and chloroform-permselectivity. Permeation and separation characteristics of the PMMA- g-PDMS and PEMA- g-PDMS membranes changed drastically at a DMS content of about 40 and 70 mol%, respectively. Permeation rate and VOC-permselectivity of the PBMA- g-PDMS membrane, however, increased gradually with increasing DMS content, unlike those of the PMMA- g-PDMS and PEMA- g-PDMS membranes. Furthermore, the transmission electron microscope observations revealed that the PMMA- g-PDMS and PEMA- g-PDMS membranes had microphase separations consisting of a PDMS phase and a poly(alkylmethacrylate) phase, but the PBMA- g-PDMS membrane was homogeneous. The permeability and permselectivity for aqueous VOCs solutions through their graft copolymer membranes in pervaporation are discussed in detail from the viewpoint of their membrane structure, and permselectivity was analyzed by the solution–diffusion theory.

Relationship between fractal microphase separation and permselectivity of block copolymer membranes containing poly(dimethylsiloxane)

Relationship between fractal microphase separation and permselectivity of block copolymer membranes containing poly(dimethylsiloxane)

Annealing Effect of Microphase-Separated Membranes Containing Poly(dimethylsiloxane) on Their Permselectivity for Aqueous Ethanol Solutions

The annealing effects of block and graft copolymer membranes consisting of ethanol-permselective poly(dimethylsiloxane) (PDMS) plus water-permselective poly(methyl methacrylate) (PMMA) on their permselectivity for an aqueous ethanol solution in pervaporation were investigated in terms of their microphase separation. The ethanol-permselectivity of the block copolymer membranes was strongly influenced by the annealing, but that of the graft copolymer membranes was not. The original block copolymer membranes changed from water- to ethanol-permselectivity at a DMS content of 55 mol %, but the annealed block copolymer membranes changed at a DMS content of 37 mol %. Transmission electron micrography demonstrated that the annealing of the block copolymer membranes with a DMS content between 37 and 55 mol % resulted in dramatic changes in the morphology of their microphase separation. However, the annealing of the graft copolymer membranes had very little effect on the morphology of their microphase separation, which was quite different from the morphology of the block copolymer membranes. The analysis using a combined model consisting of parallel and series models revealed that a continuous PDMS phase in the direction of the membrane thickness is readily formed by the annealing of the block copolymer membranes. As a result, the continuity of the PDMS phase in the microphase separation governed the ethanol-permselectivity of these membranes for an aqueous ethanol solution. This report concludes that the morphological design of microphase-separated membranes, which can be achieved by membrane annealing, is very important in controlling their permeability and permselectivity.

Inactivation of MXR1 abolishes formation of dimethyl sulfide from dimethyl sulfoxide in Saccharomyces cerevisiae.

Dimethyl sulfide (DMS) is a sulfur compound of importance for the organoleptic properties of beer, especially some lager beers. Synthesis of DMS during beer production occurs partly during wort production and partly during fermentation. Methionine sulfoxide reductases are the enzymes responsible for reduction of oxidized cellular methionines. These enzymes have been suggested to be able to reduce dimethyl sulfoxide (DMSO) as well, with DMS as the product. A gene for an enzymatic activity leading to methionine sulfoxide reduction in Saccharomyces yeast was recently identified. We confirmed that the Saccharomyces cerevisiae open reading frame YER042w appears to encode a methionine sulfoxide reductase, and propose the name MXR1 for the gene. We found that Mxr1p catalyzes reduction of DMSO to DMS and that an mxr1 disruption mutant cannot reduce DMSO to DMS. Mutant strains appear to have unchanged fitness under several laboratory conditions, and in this paper I hypothesize that disruption of MXR1 in brewing yeasts would neutralize the contribution of the yeast to the DMS content in beer.

Morphological Effects of Microphase Separation on the Permselectivity for Aqueous Ethanol Solutions of Block and Graft Copolymer Membranes Containing Poly(dimethylsiloxane)

The permselectivity of block copolymer membranes consisting of ethanol-permselective poly(dimethylsiloxane) (PDMS) plus water-permselective poly(methyl methacrylate) (PMMA) was compared to the permselectivity of graft copolymer membranes for the separation of an aqueous ethanol solution. This paper focuses on the difference in molecular architecture between the block and graft copolymers and relates microphase separation in these membranes to their permeability and permselectivity for an aqueous ethanol solution in pervaporation. With increasing DMS content, the block copolymer membranes changed from water- to ethanol-permselective at a DMS content of 55 mol %. As reported in a previous paper, however, the graft copolymer membranes showed a dramatic change in the permselectivity at a DMS content of 35 mol %. Transmission electron micrography demonstrated that both membranes had distinct microphase separation consisting of PDMS and PMMA phases and that the morphology was quite different between the block and graft copolymer membranes. The morphological changes in these membranes were investigated by image processing of the micrographs and analysis using a combined model consisting of both parallel and series models. These investigations revealed that the percolation transition of the PDMS phase in the block and graft copolymer membranes takes place at a DMS content of about 55 and 35 mol %, respectively. This suggests that the continuity of the PDMS phase in the microphase separation strongly influences the ethanol permselectivity of these membranes for an aqueous ethanol solution. This report concludes that the design of the molecular architecture in multicomponent polymer membranes is very important in controlling membrane characteristics which are governed by microphase separation.

Electrical Conductivity of Anion-Containing Copolyesters and Polypyrrole Composite Films

The effect of ionic groups in copolyesters on the electrical conductivity of polypyrrole/copoly -ester composite films was investigated. The composite films were prepared by polymerizing pyrrole through vapor phase absorption onto the copolyester films that contained FeCl3. The conductivity of polypyrrole/copolyester composite films increased with the DMS content up to 10 mol%. However, it decreased with DMS content when DMS content was greater than 10 mol%. This phenomenon was thought to be due to the inhomogeous distribution of DMS in the copolyesters. The ionic group was found to enhance the stability of composite films.

Effect of polymer blending on the electrical conductivity of polypyrrole/copolyester composite films

The effect of polymer blending on the electrical conductivity of polypyrrole/copolyester composite film was investigated. Copolyesters containing sodium sulfonate group with various main chain structures were synthesized and blended with PET. The average anionic group contents in the blend samples were controlled to be 3.5 and 6. mol%. The polypyrrole composite films were prepared by polymerization of pyrrole through vapor phase absorption onto the copolyester-PET blend films which contained FeCl 3 . The conductivity of the blend samples containing 3.5 mol% of DMS was greater than that of the copolyester of the same DMS content when the pyrrole vapor exposure time was longer than 30 min. The blends of 6. mol% of DMS showed higher conductivity than the copolyesters of the same DMS amount even when the exposure time was short. The high electrical conductivity of the blend samples was thought to be due to the phase separation between PET and copolyesters in amorphous region.

Effect of copolyester structure on the conductivity of polypyrrole/copolyester composite films

The effect of ionic group content and main chain structure of copolyesters on the electrical conductivity of polypyrrole/copolyester composite films was investigated. The composite films were prepared by polymerizing pyrrole through vapor phase absorption onto the copolyester films that contained FeCl3. The conductivity of polypyrrole/copolyester composite films increased with the DMS content and reached its maximum when the DMS content reached about 10 mol%. The conductivity increased dramatically when DMS content was more than 5 mol% that was considered as the critical composition for polypyrrole continuity. The conductivity increased with the EG content at the same DMT/DMI ratio and showed maximum when DMT:DMI ratio was 1:1.

Microphase Separation in Graft Copolymer Membranes with Pendant Oligodimethylsiloxanes and Their Permselectivity for Aqueous Ethanol Solutions

Graft copolymer membranes consisting of both ethanol- and water-permselective components for the separation of aqueous ethanol solutions were prepared by the copolymerization of an oligodimethylsiloxane (DMS) macromonomer with methyl methacrylate (MMA). This paper describes the relationship between microphase separation in MMA-g-DMS membranes and their permselectivity for aqueous ethanol solutions by pervaporation. The MMA-g-DMS membranes changed drastically from water to ethanol permselective according to the DMS content. Using a transmission electron microscope, appreciable microphase separation was observed in the MMA-g-DMS membranes. The change in the permselectivity of the MMA-g-DMS membranes could be explained by morphological changes in the microphase separation, based on Maxwell's model and a combined model consisting of both parallel and series models. Furthermore, image processing of the transmission electron micrographs enabled us to reveal the percolation transition of the DMS phase at a DMS content of about 40 mol %. These results suggest that the continuity of DMS phases in the microphase separation of MMA-g-DMS membranes directly affects their permselectivity for aqueous ethanol solutions.

Thermal and mechanical properties of [formula omitted] block copolymer

Several kinds of tetramethyl-p- silphenylenesiloxane dimethylsiloxane (TMPS/DMS) block copolymers having various compositions and segment lengths were synthesized by the polycondensation of p-bis(dimethylhydroxysilyl)benzene and silanol-terminated DMS oligomers of different degrees of polymerization, which were 19, 43, 300, 380 and 540 DMS monomer units. The compositions ranged from TMPS/DMS wt% ratio of 100/0 to 24/76. For these copolymers, differential scanning calorimetry was carried out to determine the melting temperatures, the heat of fusion and the crystallinities. The melting temperatures and the crystallinities of the block copolymers were found to decrease as DMS contents were increased from 11 to 76 wt% and as DMS segment lengths were decreased from 540 to 19. The crystalline parts of TMPS segment would be increased according to the long TMPS sequences which were obtained from the copolymerizations by using DMS oligomers with high degrees of polymerization such as 300, 380 and 540. The stress-strain behaviour and the dynamic mechanical behaviour were also investigated for these copolymers. The tensile strength was decreased and the percentage elongation was increased with increasing DMS content and segment length. In the case of the copolymers for which the DMS contents remained constant at 26 wt%, two major transitions were observed at around −120° and −10°C for the copolymers having DMS block sizes of 300, 380 and 540. But for the copolymers having those of 19 and 43 the two transitions merged together at −50°C. The relaxations at −120°C corresponding to the glass transition of DMS component and those at −10°C are due to the amorphous TMPS phase which is separated from the DMS phase owing to the longer sequence length. The relaxation observed around −50°C is due to the shorter sequence length of TMPS in the main chain plus the presence of more flexible DMS component. It may be suggested that the long sequence length causes large domains of hard and soft phases which consist of TMPS and DMS blocks respectively.

Synthesis of [formula omitted] triblock copolymer by employing living anionic polymerization

Dimethylsiloxane-tetramethyl- p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D 3). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D 3 initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D 3 by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D 3 to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×10 4 to 19.4×10 4 and were close to the predicted values calculated from the M ̄ v of the TMPS prepolymer and the amount of D 3 added. In the case of method 2, weight-average molecular weights ranged from 19.5×10 4 to 24.2×10 4. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers.