Determination of differences in free and bound water contents of beef muscle by DSC under various freezing conditions

The differences in bound water content of beef semimembranous muscle samples obtained from previously chilled (24 h at +4°C) middle-aged beef carcasses were determined by the use of DSC. Initially, samples obtained from fresh, unprocessed meat were frozen at –40, –50 or –65°C to determine their melting peaks for freezable water (free water) content with the use of DSC. The samples were then subjected to an environment with an ambient temperature of –30, –35, –40 or –45°C, with no air circulation, or with an air circulation speed of 2 m s^–1, until a thermal core temperature of –18°C was attained; this was followed by thawing the samples until a thermal core temperature of 0°C was reached. This process was followed by subjecting the samples to the ambient temperatures mentioned above, to accomplish complete freezing and thawing of the samples, with DSC, and thereby determination of the freezable water contents, which were then used to determine the peaks of melting. The calculated peak areas were divided by the latent heat of melting for pure water, to determine the freezable water contents of the samples. The percentage freezable water content of each sample was determined by dividing its freezable water content by its total water content; and the bound water content of each sample was determined by subtracting the percentage free water content from the total. In view of the fact that the free water content of a sample is completely in the frozen phase at temperatures of –40°C and below, the calculations of free and bound water contents of the samples were based on the averages of values obtained at three different temperatures.     

Studies of the heat of vaporization of water associated with cellulose fibers characterized by thermal analysis

The heat of vaporization (H _vap) of water associated with cellulose fibers versus moisture ratio was determined using modulated differential scanning calorimetry. A steep increase in the H _vap for decreasing moisture ratio was observed at low moisture ratios (0.0–0.3 g/g), indicating a higher energy required to evaporate water interacting with the cellulose. The water molecules with elevated H _vap correspond to non-freezing bound water. This may be attributed to (a) energy to break mono and/or multilayer sorption and (b) energy to overcome capillary forces. For polypropylene and glass fibers, H _vap was constant versus moisture ratio, in agreement with no non-freezing bound water existing in these systems. It is suggested that non-freezing bound water could be used as an indicator of H _vap, and vice versa, at low moisture ratios.     

The behaviour of water molecules associated with structural changes in negatively charged phosphatidyl-glycerol assemblies as studied by DSC

Variation of the thermotropic behaviour of both lipid assemblies and associated water molecules with an increase in water content was investigated for negatively charged phosphatidyl-glycerol (PG)-water system up to 90 wt.% water by DSC. The number of water molecules existing in interbilayer regions of the present gel phase was estimated from a deconvolution analysis of ice-melting DSC curves. On the basis of a result of the calorimetric analysis, a water-distribution diagram was constructed over the water content range from 0 to 90 wt.%. The diagram presented a continuous incorporation of interlamellar water up to 90 wt.% water, related to unilamellar-vesicle forming properties of charged lipids. Furthermore, similarly to a result for neutral lipid systems previously reported by us, the present diagram also showed the existence of a specific water content region (i.e., pre-region) where a structural change of planar to curved bilayers for multilamellar structures proceeds with the aid of bulk-like water before finally reaching unilamellar vesicles.     

Characterization of water in polysaccharide hydrogels by DSC

Water molecules in hydrogels were classified into three categories according to phase transition behavior; non-freezing, freezing bound and free water. Melting, crystallization, and glass transition of water in hydrogels reflected the state of the water interacting with polysaccharides. Freezing bound water formed metastable ice by slow cooling and formed amorphous ice by quenching. From the isothermal crystallization measurement, nucleation rate and crystal growth rate were obtained. The crystal growth rate of freezing bound water was about ten times slower than that of free water. The DSC characterization of water in hydrogels was summarized.

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Zusammenfassung In übereinstimmung mit dem Phasenum wandlungsverhalten werden Wassermoleküle in Hydrogelen in drei Kategorien eingestuft; nicht gefrierendes, gefrierendes gebundenes und freies Wasser. Das Schmelzen, die Kristallisation und die Glasumwandlung von Wasser in Hydrogen wiederspiegeln den Zustand von Wasser, welches in Wechselwirkung mit Polysacchariden tritt. Gefrierendes gebundenes Wasser bildet metastabiles Eis durch langsames Abkühlen und amorphes Eis durch Abschrecken. Anhand isothermer Kristallisationsmessungen wurden Keimbildungsgeschwindigkeit und Kristallwachstumsgeschwindigkeit erhalten. Die Kristallwachstumsgeschwindigkeit von gefrierendem gebundenem Wasser liegt zehnmal niedriger als die von freiem Wasser.

     

Antibacterial ultrafiltration membrane with silver nanoparticle impregnation by interfacial polymerization for ballast water

Interfacial polymerization technology was employed to immobilize silver (Ag) nanoparticles on the surface of commercial polyethersulfone (PES) membrane to develop antibacterial and antifouling ultrafiltration membrane. Ag nanoparticles were prepared from the reduction of silver nitrate (AgNO₃) by sodium borohydride in the presence of polyethyleneimine (PEI) as the stabilizer. The encapsulated Ag nanoparticles in the PEI solution were embedded into the PEI membrane when trimesoyl chloride solution was used to crosslink the PEI solution with the PES membrane, forming Ag-polyamide (PA) networks through the interfacial polymerization reaction. Experimental results showed that the membrane prepared with 50 mmol/L of AgNO₃ and 20 mmol/L of PEI had the optimized antibacterial effect against Escherichia coli. Bacterial concentration and species were also investigated. Exiguobacterium aestuarii and Staphylococcus aureus which are gram-positive bacteria, needed significantly more time for the Ag-PA/PES membrane to kill the bacteria completely when compared to E.coli and Vibrio coralliilyticus which are gram-negative bacteria. This study showed that Ag nanoparticles impregnated in membrane surfaces were 100% effective in killing various types of marine bacteria and bacteria in the seawater collected off Sentosa Island in Singapore. These membranes exhibit excellent antibacterial and antifouling properties which can be used to kill bacteria in ballast water and seawater.     

DSC analysis of the state of water in surfactant-based microstructures

A review is made about the different kinds of water in surfactant-based microstructures (liquid crystals, microemulsions and micelles) and their study by DSC.     

Determination of freezable water content of beef semimembranous muscle DSC study

The freezable water contents of samples obtained from previously chilled semimembranous muscle of middle-aged beef carcasses after a 24 h cooling period a room at in 5±1C were determined by differential scanning calorimetry (DSC) at –5, –10, –15, –20, –30, –40, –50 and –65C. This was accomplished by freezing the samples at the above-mentioned temperatures, followed by thawing to 35C, and measuring the melting peaks of freezable water. The areas of these peaks were determined by using the peak integration method programs through a computer linked to the DSC, and they were then used to determine the latent heat of melting (H _m) in kJ kg^–1 at each freezing temperature. The resultant latent heat of melting per sample was divided by the latent heat for pure water to determine the amount of freezable water present in these samples. This amount of freezable water was divided by the total water content of the meat sample to determine the percentage of freezable water in the sample. The percentage of freezable water was subtracted from 100 to determine the percentage of bound water present in the sample.     

Study of the influence of water absorption on different epoxy-diamine systems by DSC

The diffusive, calorimetric and thermal degradation behavior of different epoxy-amine systems was investigated during water sorption at different temperatures (23, 40 and 70°C). Experimental results showed that the water absorption at these temperatures fitted well to Fick’s law. Influence of water immersion during different periods of time on the glass transition temperatures was studied by differential scanning calorimetry. Thermal degradation of saturated samples was studied by thermogravimetric analysis. Dependence on the selected curing cycle was also checked.     

Analysis of the Dynamic Crystallisation of Isotactic Polypropylene/α-Nucleating Agent Systems by DSC

The nucleation efficiency of dibenzylidene sorbitol, methyldibenzylidene sorbitol and 1,2,3,4-bis- (3,4-dimethylbenzylidene) sorbitol in the crystallisation of the monoclinic phase of isotactic polypropylene has been evaluated by differential scanning calorimetry as a function of cooling rate and nucleation agent concentration. In order to analyse the nucleation activity of the additives, the self-nucleation process of the pure polypropylene has also been studied by thermal techniques. A large increment in the crystallisation temperatures has been obtained even for the lowest additive concentration, and the nucleating efficiencies are of the highest observed for α-nucleating agents in isotactic polypropylene. This revised version was published online in August 2006 with corrections to the Cover Date.     

Technological quality determination of pharmaceutical disintegrant by DSC cooling and DSC photovisual

A number of disintegrants are available on the market. They improve tablets’ disintegration. The objective of this work is the comparison of the technological quality parameters of disintegrants using different analytical techniques. Three batches of disintegrants and their binary mixtures (water:disintegrants) were investigated. Cooling experiments were used from –30 up to 200°C. The data obtained showed calorimetric differences between the samples. In the binary mixtures water showed different crystallization behaviour from the one found in the literature. According to the results DSC technique helped the quality control of different disintegrants.     

Grafting of regenerated cellulose membrane by surface‐initiated atom transfer radical polymerization and its pH‐resposive behavior

Regenerated cellulose (RC) membranes which have pH modulated permeability have been prepared by anchoring the hydroxyl groups on the membrane surface with 2‐bromoisobutyryl bromide, followed by grafting with acrylic acid (AA) using atom transfer radical polymerization (ATRP). The obtained membranes were analyzed by X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared attenuated total reflection spectrometer (ATR‐FTIR), scanning electron microscopy (SEM), TGA and the results showed that AA had been grafted onto the membrane surfaces successfully. Then the pH modulated permeability properties were tested by water flux measurement. All results show that the pH modulated permeability properties of a RC membrane can be obtained by surface‐initiated ATRP. Copyright © 2010 John Wiley & Sons, Ltd.     

Detection of multiple nanophases by DSC

Polymer molecules have contour lengths which may exceed the dimension of microphases. Especially in semicrystalline samples a single molecule may traverse several phase areas, giving rise to structures in the nanometer region. While microphases have properties that are dominated by surface effects, nanometer-size domains are dominated by interaction between opposing surfaces. Calorimetry can identify such size effects by shifts in the phase-transition temperatures and shapes, as well as changes in heat capacity. Specially restrictive phase structures exist in drawn fibers and in mesophase structures of polymers with alternating rigid and flexible segments. On several samples shifts in glass and melting temperatures will be documented. The proof of rigid amorphous sections at crystal interfaces will be given by comparison with structure analyses by X-ray diffraction and detection of motion by solid state NMR. Finally, it will be pointed out that nanophases need special attention if they are to be studied by thermal analysis since traditional ‘phase’ properties may not exist.     

Structural analysis of water adsorbed in silica gel

The melting point, T _f of water in a pore decreases as the surface area to pore volume ratio of the pore decreases. Analysis of water absorbed in the pores of silica gels using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) shows that the thickness of the bound, non-freezing water layer adjacent to the pore surface increases as its temperature increases, but that it is independent of the surface silanol concentration, [Si_sOH]. In contrast, the thickness decreases as the cylindrical pore radius r _H decreases. Thus, the increase in the bound water thickness from 0.45 nm for gels with r _H =1.2 nm to 1.2 nm for gels with r _H =7.5 nm is due to the increase from –53°C to –7°C of the temperature (e.g., the melting point T _f ) at which the bound water thickness was measured, and not due to the increase in t _H or the decrease in [Si_sOH]. The T _f of bulk water measured in a DSC was –0.3°C. The boiling point T _v of bulk water measured in a DSC was 81.3°C. T _v increased to 94°C in 7.5 nm pores and to 109°C K in 1.2 nm pores.     

Fabrication of cellulose triacetate/graphene oxide porous membrane

Cellulose triacetate (AC)/graphene oxide (GO) porous membranes were successfully fabricated by combining ultrasonication and phase inversion method. The structures and morphologies of the resultant composite membranes were investigated by X‐ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy, respectively. Microscopic and X‐ray diffraction measurements revealed that GO sheets were uniformly dispersed within the AC matrix. The pore size and structure were modulated by changing GO concentration from 0.25 to 1 wt%. Membrane thermal properties were also studied. Among all tested membranes, the most favorable GO amount was 1 wt%, giving Td_3% of 274°C, which represents a 22°C enhancement compared with AC. Conversely, the membranes showed improved barrier properties against water and ethanol. The decrease of both ethanol and water fluxes was assigned to the stabilization of composite membrane structure, as a result of GO progressive addition. Bovine serum albumin rejection assay indicated an increasing from 78% in the case of CA membrane to 99% in the case of CA/GO 1 wt% of the rejection degree after 90 min. Copyright © 2015 John Wiley & Sons, Ltd.     

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),¹³C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2495–2501, 1997     

On the determination of the melting point of semicrystalline polymer by DSC

This is a study for criteria to judge the melting point of semi-crystalline polymers from the DSC endotherm for polymer melting. Beyond standard indium DSC melting results an evaluation has been made on a series of polyethylenes for which crystal sizes were measured and predicted from Raman LAM analysis. The results confirm the conclusion of Prof. Wunderlich that the DSC content of melting is the proper basis of reporting melting points.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthday     

Effect of a bioactive curcumin derivative on DPPC membrane: A DSC and Raman spectroscopy study

Interactions of dimethoxycurcumin (1) a lipophilic bioactive curcumin derivative with dipalmitoyl phosphatidylcholine (DPPC) were investigated. The thermodynamic changes caused by (1) and its location into DPPC lipid bilayers were monitored by differential scanning calorimetry and Raman spectroscopy. The results reveal that (1) influences the thermotropic properties of DPPC lipid membrane causing abolition of the pretransition and broadening of the phase-transition profile and slightly decreases the T_m at increasing concentrations. The Raman height intensity ratios of the peaks I_2935/2880, I_2844/2880 and I_1090/1130 are representative of the interaction of (1) with the alkyl chains and furnish information about the ratio between disorder and order that exists in the conformation of the alkyl chain. The intensity changes of the peak at 715 cm⁻¹ indicates interaction between the choline head group and (1). The Raman spectroscopy results are in agreement with the thermal analysis results. Biologically active lipophilic molecules such as (1) should be studied in terms of their interaction with lipid bilayers prior to the development of advanced lipid carrier systems such as liposomes. The results of these studies provide information on the membrane integrity and physicochemical properties that are essential for the rational design lipidic drug delivery systems.     

Structural change of water by gelation of curdlan suspension

Phase transition of water restrained by curdlan suspension annealed at a temperature from 20 to 110°C was investigated by differential scanning calorimetry (DSC). The melting temperature of water restrained by annealed curdlan discontinuously decreased at around 60°C, while the amount of bound water calculated from enthalpy of melting increased at 60°C, regardless of water content. Using a highly sensitive DSC, curdlan suspension with various concentrations was studied. It was found that an endothermic transition was observed at ca. 58°C in a wide range of concentrations. The transition observed at 60°C is thermo-reversible and both temperature and transition enthalpy are constant even after gel formation. Well equilibrated suspension at a temperature lower than 60°C formed no gel.